Sample records for ligand release mechanism

  1. Investigations of Takeout proteins' ligand binding and release mechanism using molecular dynamics simulation. (United States)

    Zhang, Huijing; Yu, Hui; Zhao, Xi; Liu, Xiaoguang; Feng, Xianli; Huang, Xuri


    Takeout (To) proteins exist in a diverse range of insect species. They are involved in many important processes of insect physiology and behaviors. As the ligand carriers, To proteins can transport the small molecule to the target tissues. However, ligand release mechanism of To proteins is unclear so far. In this contribution, the process and pathway of the ligand binding and release are revealed by conventional molecular dynamics simulation, steered molecular dynamics simulation and umbrella sampling methods. Our results show that the α4-side of the protein is the unique gate for the ligand binding and release. The structural analysis confirms that the internal cavity of the protein has high rigidity, which is in accordance with the recent experimental results. By using the potential of mean force calculations in combination with residue cross correlation calculation, we concluded that the binding between the ligand and To proteins is a process of conformational selection. Furthermore, the conformational changes of To proteins and the hydrophobic interactions both are the key factors for ligand binding and release.

  2. Mode switching is the major mechanism of ligand regulation of InsP3 receptor calcium release channels. (United States)

    Ionescu, Lucian; White, Carl; Cheung, King-Ho; Shuai, Jianwei; Parker, Ian; Pearson, John E; Foskett, J Kevin; Mak, Don-On Daniel


    The inositol 1,4,5-trisphosphate (InsP(3)) receptor (InsP(3)R) plays a critical role in generation of complex Ca(2+) signals in many cell types. In patch clamp recordings of isolated nuclei from insect Sf9 cells, InsP(3)R channels were consistently detected with regulation by cytoplasmic InsP(3) and free Ca(2+) concentrations ([Ca(2+)](i)) very similar to that observed for vertebrate InsP(3)R. Long channel activity durations of the Sf9-InsP(3)R have now enabled identification of a novel aspect of InsP(3)R gating: modal gating. Using a novel algorithm to analyze channel modal gating kinetics, InsP(3)R gating can be separated into three distinct modes: a low activity mode, a fast kinetic mode, and a burst mode with channel open probability (P(o)) within each mode of 0.007 +/- 0.002, 0.24 +/- 0.03, and 0.85 +/- 0.02, respectively. Channels reside in each mode for long periods (tens of opening and closing events), and transitions between modes can be discerned with high resolution (within two channel opening and closing events). Remarkably, regulation of channel gating by [Ca(2+)](i) and [InsP(3)] does not substantially alter channel P(o) within a mode. Instead, [Ca(2+)](i) and [InsP(3)] affect overall channel P(o) primarily by changing the relative probability of the channel being in each mode, especially the high and low P(o) modes. This novel observation therefore reveals modal switching as the major mechanism of physiological regulation of InsP(3)R channel activity, with implications for the kinetics of Ca(2+) release events in cells.


    Michelson, C.


    An electromagnetic release mechanism is offered that may be used, for example, for supporting a safety rod for a nuclear reactor. The release mechanism is designed to have a large excess holding force and a rapid, uniform, and dependable release. The fast release is accomplished by providing the electromagnet with slotttd polts separated by an insulating potting resin, and by constructing the poles with a ferro-nickel alloy. The combination of these two features materially reduces the eddy current power density whenever the magnetic field changes during a release operation. In addition to these features, the design of the armature is such as to provide ready entrance of fluid into any void that might tend to form during release of the armature. This also improves the release time for the mechanism. The large holding force for the mechanism is accomplished by providing a small, selected, uniform air gap between the inner pole piece and the armature.

  4. Miniature Release Mechanism Project (United States)

    National Aeronautics and Space Administration — The objective is to design, build and functionally test a miniature release mechanism for CubeSats and other small satellites. The WFF 6U satellite structure will be...

  5. Mechanisms of HSP72 release

    Indian Academy of Sciences (India)

    Alexzander Asea


    Currently two mechanisms are recognized by which heat shock proteins (HSP) are released from cells; a passive release mechanism, including necrotic cell death, severe blunt trauma, surgery and following infection with lytic viruses, and an active release mechanism which involves the non classical protein release pathway. HSPs are released both as free HSP and within exosomes. This review covers recent findings on the mechanism by which stress induces the release of HSP72 into the circulation and the biological significance of circulating HSP72 to host defense against disease.

  6. Ligand binding mechanics of maltose binding protein. (United States)

    Bertz, Morten; Rief, Matthias


    In the past decade, single-molecule force spectroscopy has provided new insights into the key interactions stabilizing folded proteins. A few recent studies probing the effects of ligand binding on mechanical protein stability have come to quite different conclusions. While some proteins seem to be stabilized considerably by a bound ligand, others appear to be unaffected. Since force acts as a vector in space, it is conceivable that mechanical stabilization by ligand binding is dependent on the direction of force application. In this study, we vary the direction of the force to investigate the effect of ligand binding on the stability of maltose binding protein (MBP). MBP consists of two lobes connected by a hinge region that move from an open to a closed conformation when the ligand maltose binds. Previous mechanical experiments, where load was applied to the N and C termini, have demonstrated that MBP is built up of four building blocks (unfoldons) that sequentially detach from the folded structure. In this study, we design the pulling direction so that force application moves the two MBP lobes apart along the hinge axis. Mechanical unfolding in this geometry proceeds via an intermediate state whose boundaries coincide with previously reported MBP unfoldons. We find that in contrast to N-C-terminal pulling experiments, the mechanical stability of MBP is increased by ligand binding when load is applied to the two lobes and force breaks the protein-ligand interactions directly. Contour length measurements indicate that MBP is forced into an open conformation before unfolding even if ligand is bound. Using mutagenesis experiments, we demonstrate that the mechanical stabilization effect is due to only a few key interactions of the protein with its ligand. This work illustrates how varying the direction of the applied force allows revealing important details about the ligand binding mechanics of a large protein.

  7. Heat release mechanism of energetics

    Energy Technology Data Exchange (ETDEWEB)

    Kubota, N. [Third Research Center, Technical Research and development Institute (Japan)


    Determination of the heat release mechanism of energetic materials is a major subject of combustion study. In order to elucidate the combustion process of various types of energetic materials a generalized combustion wave structure was proposed and the heat release process was discussed. The heat release process was significantly different between the physical structures of the materials: homogeneous and heterogeneous materials. The thermal structure of an azide polymer was evaluated to demonstrate the heat release mechanism. (author) 6 refs.

  8. Notch Ligand Endocytosis Generates Mechanical Pulling Force Dependent on Dynamin, Epsins and Actin (United States)

    Meloty-Kapella, Laurence; Shergill, Bhupinder; Kuon, Jane; Botvinick, Elliot; Weinmaster, Gerry


    SUMMARY Notch signaling induced by cell surface ligands is critical to development and maintenance of many eukaryotic organisms. Notch and its ligands are integral membrane proteins that facilitate direct cell-cell interactions to activate Notch proteolysis and release the intracellular domain that directs Notch-specific cellular responses. Genetic studies suggest Notch ligands require endocytosis, ubiquitylation and epsin endocytic adaptors to activate signaling, yet the exact role ligand endocytosis serves remains unresolved. Here we characterize a molecularly distinct mode of clathrin-mediated endocytosis requiring ligand ubiquitylation, epsins and actin for ligand cells to activate signaling in Notch cells. Using a cell-bead optical tweezers system, we obtained evidence for cell-mediated mechanical force dependent on this distinct mode of ligand endocytosis. We propose mechanical pulling force produced by endocytosis of Notch-bound ligand drives conformational changes in Notch that permit activating proteolysis. PMID:22658936

  9. Mechanics, thermodynamics, and kinetics of ligand binding to biopolymers. (United States)

    Jarillo, Javier; Morín, José A; Beltrán-Heredia, Elena; Villaluenga, Juan P G; Ibarra, Borja; Cao, Francisco J


    Ligands binding to polymers regulate polymer functions by changing their physical and chemical properties. This ligand regulation plays a key role in many biological processes. We propose here a model to explain the mechanical, thermodynamic, and kinetic properties of the process of binding of small ligands to long biopolymers. These properties can now be measured at the single molecule level using force spectroscopy techniques. Our model performs an effective decomposition of the ligand-polymer system on its covered and uncovered regions, showing that the elastic properties of the ligand-polymer depend explicitly on the ligand coverage of the polymer (i.e., the fraction of the polymer covered by the ligand). The equilibrium coverage that minimizes the free energy of the ligand-polymer system is computed as a function of the applied force. We show how ligands tune the mechanical properties of a polymer, in particular its length and stiffness, in a force dependent manner. In addition, it is shown how ligand binding can be regulated applying mechanical tension on the polymer. Moreover, the binding kinetics study shows that, in the case where the ligand binds and organizes the polymer in different modes, the binding process can present transient shortening or lengthening of the polymer, caused by changes in the relative coverage by the different ligand modes. Our model will be useful to understand ligand-binding regulation of biological processes, such as the metabolism of nucleic acid. In particular, this model allows estimating the coverage fraction and the ligand mode characteristics from the force extension curves of a ligand-polymer system.

  10. The ligand binding domain controls glucocorticoid receptor dynamics independent of ligand release. (United States)

    Meijsing, Sebastiaan H; Elbi, Cem; Luecke, Hans F; Hager, Gordon L; Yamamoto, Keith R


    Ligand binding to the glucocorticoid receptor (GR) results in receptor binding to glucocorticoid response elements (GREs) and the formation of transcriptional regulatory complexes. Equally important, these complexes are continuously disassembled, with active processes driving GR off GREs. We found that co-chaperone p23-dependent disruption of GR-driven transcription depended on the ligand binding domain (LBD). Next, we examined the importance of the LBD and of ligand dissociation in GR-GRE dissociation in living cells. We showed in fluorescence recovery after photobleaching studies that dissociation of GR from GREs is faster in the absence of the LBD. Furthermore, GR interaction with a target promoter revealed ligand-specific exchange rates. However, using covalently binding ligands, we demonstrated that ligand dissociation is not required for receptor dissociation from GREs. Overall, these studies showed that activities impinging on the LBD regulate GR exchange with GREs but that the dissociation of GR from GREs is independent from ligand dissociation.

  11. Shape-Memory-Alloy Release Mechanism (United States)

    Mckinnis, Darin


    Release-nut mechanism activated by electric current applied to shape-memory alloy. Separates attached objects quickly by remote control. Does not create hazard or cause damage. Shape-memory release-nut mechanism unaffected by moisture or vacuum. Requires sustained current lasting 5 seconds or longer, and insensitive to electromagnetic interference. Mechanism can be reused.

  12. Ligand-based reduction of CO2 and release of CO on iron(II). (United States)

    Thammavongsy, Zachary; Seda, Takele; Zakharov, Lev N; Kaminsky, Werner; Gilbertson, John D


    A synthetic cycle for the CO(2)-to-CO conversion (with subsequent release of CO) based on iron(II), a redox-active pydridinediimine ligand (PDI), and an O-atom acceptor is reported. This conversion is a passive-type ligand-based reduction, where the electrons for the CO(2) conversion are supplied by the reduced PDI ligand and the ferrous state of the iron is conserved.

  13. Neutrophil Integrins and Matrix Ligands and NET Release

    Directory of Open Access Journals (Sweden)

    Jonathan S. Reichner


    Full Text Available Neutrophils are motile and responsive to tissue injury and infection. As neutrophils emigrate from the bloodstream and migrate towards a site of affliction, they encounter the tissue extracellular matrix (ECM and thereby engage integrins. Our laboratory studies the neutrophilic response to the fungal pathogen Candida albicans either in the filamentous state of the microbe or to the purified pathogen-associated molecular pattern, β-glucan. We have gained an appreciation for the role of integrins in regulating the neutrophil anti-Candida response and how the presence or absence of ECM can drive experimental outcome. The β2 integrin CR3 (Complement Receptor 3; αMβ2; Mac-1; CD11b/CD18 plays an important role in fungal recognition by its ability to bind β-glucan at a unique lectin-like domain. The presence of ECM differentially regulates essential neutrophil anti-fungal functions including chemotaxis, respiratory burst, homotypic aggregation, and the release of neutrophil extracellular traps (NETosis. We have shown that NET release to C. albicans hyphae or immobilized β-glucan occurs rapidly and without the requirement for respiratory burst on ECM. This is in contrast to the more frequently reported mechanisms of NETosis to other pathogens without the context of ECM which occur after a prolonged lag period and require respiratory burst. As expected for an ECM-dependent phenotype, NETosis and other neutrophil functions are dependent on specific β1 integrins. The focus of this review is the role of ECM ligation by neutrophil integrins as it pertains to host defense functions with an emphasis on lessons we have learned studying the anti-Candida response of human neutrophils.

  14. Insights into Protein–Ligand Interactions: Mechanisms, Models, and Methods

    Directory of Open Access Journals (Sweden)

    Xing Du


    Full Text Available Molecular recognition, which is the process of biological macromolecules interacting with each other or various small molecules with a high specificity and affinity to form a specific complex, constitutes the basis of all processes in living organisms. Proteins, an important class of biological macromolecules, realize their functions through binding to themselves or other molecules. A detailed understanding of the protein–ligand interactions is therefore central to understanding biology at the molecular level. Moreover, knowledge of the mechanisms responsible for the protein-ligand recognition and binding will also facilitate the discovery, design, and development of drugs. In the present review, first, the physicochemical mechanisms underlying protein–ligand binding, including the binding kinetics, thermodynamic concepts and relationships, and binding driving forces, are introduced and rationalized. Next, three currently existing protein-ligand binding models—the “lock-and-key”, “induced fit”, and “conformational selection”—are described and their underlying thermodynamic mechanisms are discussed. Finally, the methods available for investigating protein–ligand binding affinity, including experimental and theoretical/computational approaches, are introduced, and their advantages, disadvantages, and challenges are discussed.

  15. Mechanisms of Methane Release From Lake Sediments


    Shiba, Jacob


    Methane is a powerful greenhouse gas that can be produced in bottom sediments of lakes and reservoirs and released through ebullition and other properties. Many studies have quantified ebullition rates, however, the detailed mechanisms remain incompletely understood. This study was undertaken to better understand, through in situ and laboratory measurements, the mechanisms of gas ebullition from lake sediment. Four sites on Lake Elsinore, CA with different properties were evaluated through th...

  16. Drug release mechanisms of compressed lipid implants. (United States)

    Kreye, F; Siepmann, F; Siepmann, J


    The aim of this study was to elucidate the mass transport mechanisms controlling drug release from compressed lipid implants. The latter steadily gain in importance as parenteral controlled release dosage forms, especially for acid-labile drugs. A variety of lipid powders were blended with theophylline and propranolol hydrochloride as sparingly and freely water-soluble model drugs. Cylindrical implants were prepared by direct compression and thoroughly characterized before and after exposure to phosphate buffer pH 7.4. Based on the experimental results, an appropriate mathematical theory was identified in order to quantitatively describe the resulting drug release patterns. Importantly, broad release spectra and release periods ranging from 1 d to several weeks could easily be achieved by varying the type of lipid, irrespective of the type of drug. Interestingly, diffusion with constant diffusivities was found to be the dominant mass transport mechanism, if the amount of water within the implant was sufficient to dissolve all of the drug. In these cases an analytical solution of Fick's second law could successfully describe the experimentally measured theophylline and propranolol hydrochloride release profiles, even if varying formulation and processing parameters, e.g. the type of lipid, initial drug loading, drug particles size as well as compression force and time. However, based on the available data it was not possible to distinguish between drug diffusion control and water diffusion control. The obtained new knowledge can nevertheless significantly help facilitating the optimization of this type of advanced drug delivery systems, in particular if long release periods are targeted, which require time consuming experimental trials.

  17. The Formyl Peptide Receptors: Diversity of Ligands and Mechanism for Recognition

    Directory of Open Access Journals (Sweden)

    Hui-Qiong He


    Full Text Available The formyl peptide receptors (FPRs are G protein-coupled receptors that transduce chemotactic signals in phagocytes and mediate host-defense as well as inflammatory responses including cell adhesion, directed migration, granule release and superoxide production. In recent years, the cellular distribution and biological functions of FPRs have expanded to include additional roles in homeostasis of organ functions and modulation of inflammation. In a prototype, FPRs recognize peptides containing N-formylated methionine such as those produced in bacteria and mitochondria, thereby serving as pattern recognition receptors. The repertoire of FPR ligands, however, has expanded rapidly to include not only N-formyl peptides from microbes but also non-formyl peptides of microbial and host origins, synthetic small molecules and an eicosanoid. How these chemically diverse ligands are recognized by the three human FPRs (FPR1, FPR2 and FPR3 and their murine equivalents is largely unclear. In the absence of crystal structures for the FPRs, site-directed mutagenesis, computer-aided ligand docking and structural simulation have led to the identification of amino acids within FPR1 and FPR2 that interact with several formyl peptides. This review article summarizes the progress made in the understanding of FPR ligand diversity as well as ligand recognition mechanisms used by these receptors.

  18. The Formyl Peptide Receptors: Diversity of Ligands and Mechanism for Recognition. (United States)

    He, Hui-Qiong; Ye, Richard D


    The formyl peptide receptors (FPRs) are G protein-coupled receptors that transduce chemotactic signals in phagocytes and mediate host-defense as well as inflammatory responses including cell adhesion, directed migration, granule release and superoxide production. In recent years, the cellular distribution and biological functions of FPRs have expanded to include additional roles in homeostasis of organ functions and modulation of inflammation. In a prototype, FPRs recognize peptides containing N-formylated methionine such as those produced in bacteria and mitochondria, thereby serving as pattern recognition receptors. The repertoire of FPR ligands, however, has expanded rapidly to include not only N-formyl peptides from microbes but also non-formyl peptides of microbial and host origins, synthetic small molecules and an eicosanoid. How these chemically diverse ligands are recognized by the three human FPRs (FPR1, FPR2 and FPR3) and their murine equivalents is largely unclear. In the absence of crystal structures for the FPRs, site-directed mutagenesis, computer-aided ligand docking and structural simulation have led to the identification of amino acids within FPR1 and FPR2 that interact with several formyl peptides. This review article summarizes the progress made in the understanding of FPR ligand diversity as well as ligand recognition mechanisms used by these receptors.

  19. A statistical mechanics handbook for protein-ligand binding simulation. (United States)

    Rocchia, Walter; Bonella, Sara


    In this work, the fundamental elements of statistical mechanics underlying the simulation of the protein-ligand binding process, such as statistical ensembles and the concept of microscopic estimators of macroscopic observables and free energy, are summarized in a self consistent fashion. Particular attention is then devoted to the introduction of some mathematical tools that are used in atomistic simulations aimed at estimating binding affinities and free energy profiles, and to the illustration of the origins of the difficulties encountered in this endeavor.

  20. FORTE antenna element and release mechanism design

    Energy Technology Data Exchange (ETDEWEB)

    Rohweller, D.J. [Astro Aerospace Corp., Carpinteria, CA (United States); Butler, T.Af. [Los Alamos National Lab., NM (United States)


    The Fast On-Orbit Recording of Transient Events (FORTE) satellite being built by Los Alamos National Laboratory (LANL) and Sandia National Laboratories (SNL) has as its most prominent feature a large deployable (11 m by 5 m) log periodic antenna to monitor emissions from electrical storms on the Earth. This paper describes the antenna and the design for the long elements and explains the dynamics of their deployment and the damping system employed. It also describes the unique paraffin-actuated reusable tie-down and release mechanism employed in the system.

  1. PDB ligand conformational energies calculated quantum-mechanically. (United States)

    Sitzmann, Markus; Weidlich, Iwona E; Filippov, Igor V; Liao, Chenzhong; Peach, Megan L; Ihlenfeldt, Wolf-Dietrich; Karki, Rajeshri G; Borodina, Yulia V; Cachau, Raul E; Nicklaus, Marc C


    We present here a greatly updated version of an earlier study on the conformational energies of protein-ligand complexes in the Protein Data Bank (PDB) [Nicklaus et al. Bioorg. Med. Chem. 1995, 3, 411-428], with the goal of improving on all possible aspects such as number and selection of ligand instances, energy calculations performed, and additional analyses conducted. Starting from about 357,000 ligand instances deposited in the 2008 version of the Ligand Expo database of the experimental 3D coordinates of all small-molecule instances in the PDB, we created a "high-quality" subset of ligand instances by various filtering steps including application of crystallographic quality criteria and structural unambiguousness. Submission of 640 Gaussian 03 jobs yielded a set of about 415 successfully concluded runs. We used a stepwise optimization of internal degrees of freedom at the DFT level of theory with the B3LYP/6-31G(d) basis set and a single-point energy calculation at B3LYP/6-311++G(3df,2p) after each round of (partial) optimization to separate energy changes due to bond length stretches vs bond angle changes vs torsion changes. Even for the most "conservative" choice of all the possible conformational energies-the energy difference between the conformation in which all internal degrees of freedom except torsions have been optimized and the fully optimized conformer-significant energy values were found. The range of 0 to ~25 kcal/mol was populated quite evenly and independently of the crystallographic resolution. A smaller number of "outliers" of yet higher energies were seen only at resolutions above 1.3 Å. The energies showed some correlation with molecular size and flexibility but not with crystallographic quality metrics such as the Cruickshank diffraction-component precision index (DPI) and R(free)-R, or with the ligand instance-specific metrics such as occupancy-weighted B-factor (OWAB), real-space R factor (RSR), and real-space correlation coefficient

  2. PGE2/EP3/SRC signaling induces EGFR nuclear translocation and growth through EGFR ligands release in lung adenocarcinoma cells (United States)

    Bazzani, Lorenzo; Donnini, Sandra; Finetti, Federica; Christofori, Gerhard; Ziche, Marina


    Prostaglandin E2 (PGE2) interacts with tyrosine kinases receptor signaling in both tumor and stromal cells supporting tumor progression. Here we demonstrate that in non-small cell lung carcinoma (NSCLC) cells, A549 and GLC82, PGE2 promotes nuclear translocation of epidermal growth factor receptor (nEGFR), affects gene expression and induces cell growth. Indeed, cyclin D1, COX-2, iNOS and c-Myc mRNA levels are upregulated following PGE2 treatment. The nuclear localization sequence (NLS) of EGFR as well as its tyrosine kinase activity are required for the effect of PGE2 on nEGFR and downstream signaling activities. PGE2 binds its bona fide receptor EP3 which by activating SRC family kinases, induces ADAMs activation which, in turn, releases EGFR-ligands from the cell membrane and promotes nEGFR. Amphiregulin (AREG) and Epiregulin (EREG) appear to be involved in nEGFR promoted by the PGE2/EP3-SRC axis. Pharmacological inhibition or silencing of the PGE2/EP3/SRC-ADAMs signaling axis or EGFR ligands i.e. AREG and EREG expression abolishes nEGFR induced by PGE2. In conclusion, PGE2 induces NSCLC cell proliferation by EP3 receptor, SRC-ADAMs activation, EGFR ligands shedding and finally, phosphorylation and nEGFR. Since nuclear EGFR is a hallmark of cancer aggressiveness, our findings reveal a novel mechanism for the contribution of PGE2 to tumor progression. PMID:28415726

  3. Identifying Carbohydrate Ligands of a Norovirus P Particle using a Catch and Release Electrospray Ionization Mass Spectrometry Assay (United States)

    Han, Ling; Kitova, Elena N.; Tan, Ming; Jiang, Xi; Klassen, John S.


    Noroviruses (NoVs), the major cause of epidemic acute gastroenteritis, recognize human histo-blood group antigens (HBGAs), which are present as free oligosaccharides in bodily fluid or glycolipids and glycoproteins on the surfaces of cells. The subviral P particle formed by the protruding (P) domain of the NoV capsid protein serves as a useful model for the study NoV-HBGA interactions. Here, we demonstrate the application of a catch-and-release electrospray ionization mass spectrometry (CaR-ESI-MS) assay for screening carbohydrate libraries against the P particle to rapidly identify NoV ligands and potential inhibitors. Carbohydrate libraries of 50 and 146 compounds, which included 18 and 24 analogs of HBGA receptors, respectively, were screened against the P particle of VA387, a member of the predominant GII.4 NoVs. Deprotonated ions corresponding to the P particle bound to carbohydrates were isolated and subjected to collision-induced dissociation to release the ligands in their deprotonated forms. The released ligands were identified by ion mobility separation followed by mass analysis. All 13 and 16 HBGA ligands with intrinsic affinities >500 M-1 were identified in the 50 and the 146 compound libraries, respectively. Furthermore, screening revealed interactions with a series of oligosaccharides with structures found in the cell wall of mycobacteria and human milk. The affinities of these newly discovered ligands are comparable to those of the HBGA receptors, as estimated from the relative abundance of released ligand ions.

  4. Regulation mechanisms of the FLT3-ligand after irradiation; Mecanismes de regulation du FLT3-ligand apres irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Prat-Lepesant, M


    The hematopoietic compartment is one of the most severely damaged after chemotherapy, radiotherapy or accidental irradiations. Whatever its origin, the resulting damage to the bone marrow remains difficult to evaluate. Thus, it would be of great interest to get a biological indicator of residual hematopoiesis in order to adapt the treatment to each clinical situation. Recent results indicated that the plasma Flt3 ligand concentration was increased in patients suffering from either acquired or induced aplasia, suggesting that Flt3 ligand might be useful as a biological indicator of bone marrow status. We thus followed in a mouse model as well as in several clinical situations the variations in plasma Flt3 ligand concentration, after either homogeneous or heterogeneous irradiations. These variations were correlated to the number of hematopoietic progenitors and to other parameters such as duration and depth of pancytopenia. The results indicated that the concentration of Flt3 ligand in the blood reflects the bone marrow status, and that the follow-up of plasma Flt3 ligand concentration could give predictive information about the bone marrow function and the duration and severity of pancytopenia and thrombocytopenia. Nevertheless, the clinical use of Flt3 ligand as a biological indicator of bone marrow damage require the knowledge of the mechanisms regulating the variations in plasma Flt3 ligand concentration. We thus developed a study in the mouse model. The results indicated that the variations in plasma Flt3 ligand variations were not solely due to a balance between its production by lymphoid cells and its consumption by hematopoietic cells. Moreover, we showed that T lymphocytes are not the main regulator of plasma Flt3 ligand concentration as previously suggested, and that other cell types, possibly including bone marrow stromal cells, might be strongly implicated. These results also suggest that the Flt3 ligand is a main systemic regulator of hematopoiesis

  5. Light-Controlled Release and Uptake of Zinc Ions in Solution by a Photochromic Terthiazole-Based Ligand. (United States)

    Guérin, Juliette; Léaustic, Anne; Berthet, Jérôme; Métivier, Rémi; Guillot, Régis; Delbaere, Stéphanie; Nakatani, Keitaro; Yu, Pei


    We have synthesized and fully characterized a photochromic zinc complex with a terphenylthiazole-based ligand with a salen-like cavity. The solution stability of the complex was found to be greatly dependent on the state of the photochromic ligand and an interesting photo-triggered release and uptake of zinc ions was found as well as monitored by its fluorescence. The contrasting stability difference of the zinc complex between its two isomeric states was rationalized by DFT calculations.

  6. Nitroavidin as a ligand for the surface capture and release of biotinylated proteins. (United States)

    Bolivar, Jowell G; Soper, Steven A; McCarley, Robin L


    Discussed here is the preparation, detailed purification, and evaluation of nitroavidin as a ligand for surface capture and release of biotinylated proteins. Avidin from chicken egg white was nitrated using dilute tetranitromethane solutions. UV-vis spectroscopy was used to show decreased binding of the biotin analogue, 2-(4'-hydroxyazobenzene)benzoic acid, HABA, to nitroavidin compared to binding of HABA to native avidin. From enzyme-linked immunosorbent assay (ELISA)-based assays of the modified avidin, it was found that there are approximately three tyrosine residues converted to nitrotyrosine out of the total four tyrosine residues in the protein tetramer. For the first time, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to demonstrate the point of nitration in nitroavidin as that of the tyrosine associated with the binding of biotin (Y33). From surface plasmon resonance spectroscopy (SPR) experiments, it is shown that biotin has less binding propensity to immobilized nitroavidin (K(D) = 4.4 +/- 1.9 x 10(-6) M) than immobilized avidin (K(D) < or = 10(-11) M). Importantly, the use of pH 10 carbonate buffer as eluent resulted in facile release of bound biotin from the nitroavidin-functionalized surfaces, allowing for readily regenerated biotin capture surfaces (reversible binding surfaces). These outcomes are important for the development of protein concentration methods directed at isolation of select proteins from a large population using gentle target protein isolation/release conditions.

  7. Mechanisms of renin release from juxtaglomerular cells

    DEFF Research Database (Denmark)

    Skøtt, O; Salomonsson, Max; Sellerup Persson, Anja;


    In microdissected, nonperfused afferent arterioles changes in intravascular pressure did not affect renin secretion. On the contrary, renin release from isolated afferent arterioles perfused in a free-flow system has been reported to be sensitive to simultaneous changes in luminal pressure and flow....... Hence local blood flow may be involved in the baroreceptor control of renin release. If flow is sensed, the sensor is likely to be located near the endothelial cell layer, where ion channels have been shown to be influenced by variations in shear stress....

  8. Force spectroscopy studies on protein-ligand interactions: a single protein mechanics perspective. (United States)

    Hu, Xiaotang; Li, Hongbin


    Protein-ligand interactions are ubiquitous and play important roles in almost every biological process. The direct elucidation of the thermodynamic, structural and functional consequences of protein-ligand interactions is thus of critical importance to decipher the mechanism underlying these biological processes. A toolbox containing a variety of powerful techniques has been developed to quantitatively study protein-ligand interactions in vitro as well as in living systems. The development of atomic force microscopy-based single molecule force spectroscopy techniques has expanded this toolbox and made it possible to directly probe the mechanical consequence of ligand binding on proteins. Many recent experiments have revealed how ligand binding affects the mechanical stability and mechanical unfolding dynamics of proteins, and provided mechanistic understanding on these effects. The enhancement effect of mechanical stability by ligand binding has been used to help tune the mechanical stability of proteins in a rational manner and develop novel functional binding assays for protein-ligand interactions. Single molecule force spectroscopy studies have started to shed new lights on the structural and functional consequence of ligand binding on proteins that bear force under their biological settings. Copyright © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  9. Factors controlling alkalisalt deposition in recovery boiler- release mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    McKeough, P.; Kylloenen, H.; Kurkela, M. [VTT Energy, Espoo (Finland). Process Technology Group


    As part of a cooperative effort to develop a model to describe the behaviour of inorganic compounds in kraft recovery boilers, an experimental investigation of the release of sulphur during black liquor pyrolysis has been undertaken. Previous to these studies, the mechanisms of sulphur release and the reasons for the observed effects of process conditions on sulphur release were very poorly understood. On the basis of the experimental results, the main reactions leading to sulphur release have been elucidated with a fair degree of certainty. Logical explanations for the variations of sulphur release with temperature and with liquor solids content have been proposed. The influence of pressure has been investigated in order to gain insights into the effects of mass transfer on the sulphur-release rate. In the near future, the research will be aimed at generating the kinetic data necessary for modelling the release of sulphur in the recovery furnace. (author)

  10. Nonequilibrium thermodynamics of fuel cells: Heat release mechanisms and voltage

    Energy Technology Data Exchange (ETDEWEB)

    Wilemski, G.


    Nonequilibrium thermodynamics is used to analyze the spatial distribution of heat release mechanisms occurring in fuel cells operating under load in nonisothermal steady states. Novel contributions to heat release in the bulk electrolyte are found which are analogous to Peltier and Thomson effects in metallic conductors. Expresions for the heat release at individual electrodes are presented. An equation for the voltage of these cells is also derived.

  11. Fabrication of hybrid nanocomposite scaffolds by incorporating ligand-free hydroxyapatite nanoparticles into biodegradable polymer scaffolds and release studies

    Directory of Open Access Journals (Sweden)

    Balazs Farkas


    Full Text Available We report on the optical fabrication approach of preparing free-standing composite thin films of hydroxyapatite (HA and biodegradable polymers by combining pulsed laser ablation in liquid and mask-projection excimer laser stereolithography (MPExSL. Ligand-free HA nanoparticles were prepared by ultrafast laser ablation of a HA target in a solvent, and then the nanoparticles were dispersed into the liquid polymer resin prior to the photocuring process using MPExSL. The resin is poly(propylene fumarate (PPF, a photo-polymerizable, biodegradable material. The polymer is blended with diethyl fumarate in 7:3 w/w to adjust the resin viscosity. The evaluation of the structural and mechanical properties of the fabricated hybrid thin film was performed by means of SEM and nanoindentation, respectively, while the chemical and degradation studies were conducted through thermogravimetric analysis, and FTIR. The photocuring efficiency was found to be dependent on the nanoparticle concentration. The MPExSL process yielded PPF thin films with a stable and homogenous dispersion of the embedded HA nanoparticles. Here, it was not possible to tune the stiffness and hardness of the scaffolds by varying the laser parameters, although this was observed for regular PPF scaffolds. Finally, the gradual release of the hydroxyapatite nanoparticles over thin film biodegradation is reported.

  12. Novel mechanisms of growth hormone regulation: growth hormone-releasing peptides and ghrelin

    Directory of Open Access Journals (Sweden)

    A.-M.J. Lengyel


    Full Text Available Growth hormone secretion is classically modulated by two hypothalamic hormones, growth hormone-releasing hormone and somatostatin. A third pathway was proposed in the last decade, which involves the growth hormone secretagogues. Ghrelin is a novel acylated peptide which is produced mainly by the stomach. It is also synthesized in the hypothalamus and is present in several other tissues. This endogenous growth hormone secretagogue was discovered by reverse pharmacology when a group of synthetic growth hormone-releasing compounds was initially produced, leading to the isolation of an orphan receptor and, finally, to its endogenous ligand. Ghrelin binds to an active receptor to increase growth hormone release and food intake. It is still not known how hypothalamic and circulating ghrelin is involved in the control of growth hormone release. Endogenous ghrelin might act to amplify the basic pattern of growth hormone secretion, optimizing somatotroph responsiveness to growth hormone-releasing hormone. It may activate multiple interdependent intracellular pathways at the somatotroph, involving protein kinase C, protein kinase A and extracellular calcium systems. However, since ghrelin has a greater ability to release growth hormone in vivo, its main site of action is the hypothalamus. In the current review we summarize the available data on the: a discovery of this peptide, b mechanisms of action of growth hormone secretagogues and ghrelin and possible physiological role on growth hormone modulation, and c regulation of growth hormone release in man after intravenous administration of these peptides.

  13. Guar gum, xanthan gum, and HPMC can define release mechanisms and sustain release of propranolol hydrochloride. (United States)

    Mughal, Muhammad Akhlaq; Iqbal, Zafar; Neau, Steven Henry


    The objectives were to characterize propranolol hydrochloride-loaded matrix tablets using guar gum, xanthan gum, and hydroxypropylmethylcellulose (HPMC) as rate-retarding polymers. Tablets were prepared by wet granulation using these polymers alone and in combination, and physical properties of the granules and tablets were studied. Drug release was evaluated in simulated gastric and intestinal media. Rugged tablets with appropriate physical properties were obtained. Empirical and semi-empirical models were fit to release data to elucidate release mechanisms. Guar gum alone was unable to control drug release until a 1:3 drug/gum ratio, where the release pattern matched a Higuchi profile. Matrix tablets incorporating HPMC provided near zero-order release over 12 h and erosion was a contributing mechanism. Combinations of HPMC with guar or xanthan gum resulted in a Higuchi release profile, revealing the dominance of the high viscosity gel formed by HPMC. As the single rate-retarding polymer, xanthan gum retarded release over 24 h and the Higuchi model best fit the data. When mixed with guar gum, at 10% or 20% xanthan levels, xanthan gum was unable to control release. However, tablets containing 30% guar gum and 30% xanthan gum behaved as if xanthan gum was the sole rate-retarding gum and drug was released by Fickian diffusion. Release profiles from certain tablets match 12-h literature profiles and the 24-h profile of Inderal(®) LA. The results confirm that guar gum, xanthan gum, and HPMC can be used for the successful preparation of sustained release oral propranolol hydrochoride tablets.

  14. Shape memory-based actuators and release mechanisms therefrom (United States)

    Vaidyanathan, Rajan (Inventor); Snyder, Daniel W. (Inventor); Schoenwald, David K. (Inventor); Lam, Nhin S. (Inventor); Watson, Daniel S. (Inventor); Krishnan, Vinu B. (Inventor); Noebe, Ronald D. (Inventor)


    SM-based actuators (110) and release mechanisms (100) therefrom and systems (500) including one or more release mechanisms (100). The actuators (110) comprise a SM member (118) and a deformable member (140) mechanically coupled to the SM member (118) which deforms upon a shape change of the SM member triggered by a phase transition of the SM member. A retaining element (160) is mechanically coupled to the deformable member (140), wherein the retaining element (160) moves upon the shape change. Release mechanism (100) include an actuator, a rotatable mechanism (120) including at least one restraining feature (178) for restraining rotational movement of the retaining element (160) before the shape change, and at least one spring (315) that provides at least one locked spring-loaded position when the retaining element is in the restraining feature and at least one released position that is reached when the retaining element is in a position beyond the restraining feature (178). The rotatable mechanism (120) includes at least one load-bearing protrusion (310). A hitch (400) is for mechanically coupling to the load, wherein the hitch is supported on the load bearing protrusion (310) when the rotatable mechanism is in the locked spring-loaded position.

  15. Upflow bioreactor with septum and pressure release mechanism (United States)

    Hansen, Conly L.; Hansen, Carl S.; Pack, Kevin; Milligan, John; Benefiel, Bradley C.; Tolman, C. Wayne; Tolman, Kenneth W.


    An upflow bioreactor includes a vessel having an inlet and an outlet configured for upflow operation. A septum is positioned within the vessel and defines a lower chamber and an upper chamber. The septum includes an aperture that provides fluid communication between the upper chamber and lower chamber. The bioreactor also includes means for releasing pressure buildup in the lower chamber. In one configuration, the septum includes a releasable portion having an open position and a closed position. The releasable portion is configured to move to the open position in response to pressure buildup in the lower chamber. In the open position fluid communication between the lower chamber and the upper chamber is increased. Alternatively the lower chamber can include a pressure release line that is selectively actuated by pressure buildup. The pressure release mechanism can prevent the bioreactor from plugging and/or prevent catastrophic damage to the bioreactor caused by high pressures.

  16. Long-Range Conformational Response of a PDZ Domain to Ligand Binding and Release: A Molecular Dynamics Study. (United States)

    Lu, Cheng; Knecht, Volker; Stock, Gerhard


    The binding of a ligand to a protein may induce long-range structural or dynamical changes in the biomacromolecule even at sites physically well separated from the binding pocket. A system for which such behavior has been widely discussed is the PDZ2 domain of human tyrosine phosphatase 1E. Here, we present results from equilibrium trajectories of the PDZ2 domain in the free and ligand-bound state, as well as nonequilibrium simulations of the relaxation of PDZ2 after removal of its peptide ligand. The study reveals changes in inter-residue contacts, backbone dihedral angles, and C(α) positions upon ligand release. Our findings show a long-range conformational response of the PDZ2 domain to ligand release in the form of a collective shift of the secondary structure elements α2, β2, β3, α1-β4, and the C terminal loop relative to the rest of the protein away from the N-terminus, and a shift of the loops β2-β3 and β1-β2 in the opposite direction. The shifts lead to conformational changes in the backbone, especially in the β2-β3 loop but also in the β5-α2 and the α2-β6 loop, and are accompanied by changes of inter-residue contacts mainly within the β2-β3 loop as well as between the α2 helix and other segments. The residues showing substantial changes of inter-residue contacts, backbone conformations, or C(α) positions are considered "key residues" for the long-range conformational response of PDZ2. By comparing these residues with various sets of residues highlighted by previous studies of PDZ2, we investigate the statistical correlation of the various approaches. Interestingly, we find a considerable correlation of our findings with several works considering structural changes but no significant correlations with approaches considering energy flow or networks based on inter-residue energies.

  17. Identification of calcium-modulating cyclophilin ligand as a human host restriction to HIV-1 release overcome by Vpu (United States)

    Varthakavi, Vasundhara; Heimann-Nichols, Ellen; Smith, Rita M; Sun, Yuehui; Bram, Richard J; Ali, Showkat; Rose, Jeremy; Ding, Lingmei; Spearman, Paul


    The HIV-1 Vpu protein is required for efficient viral release from human cells. For HIV-2, the envelope (Env) protein replaces the role of Vpu. Both Vpu and HIV-2 Env enhance virus release by counteracting an innate host-cell block within human cells that is absent in African green monkey (AGM) cells. Here we identify calcium-modulating cyclophilin ligand (CAML) as a Vpu-interacting host factor that restricts HIV-1 release. Expression of human CAML (encoded by CAMLG) in AGM cells conferred a strong restriction of virus release that was reversed by Vpu and HIV-2 Env, suggesting that CAML is the mechanistic link between these two viral regulators. Depletion of CAML in human cells eliminated the need for Vpu in enhancing HIV-1 and murine leukemia virus release. These results point to CAML as a Vpu-sensitive host restriction factor that inhibits HIV release from human cells. The ability of CAML to inhibit virus release should illuminate new therapeutic strategies against HIV. PMID:18500349

  18. Desensitization mechanism in prokaryotic ligand-gated ion channel. (United States)

    Velisetty, Phanindra; Chakrapani, Sudha


    Crystal structures of Gloeobacter violaceus ligand-gated ion channel (GLIC), a proton-gated prokaryotic homologue of pentameric ligand-gated ion channel (LGIC) from G. violaceus, have provided high-resolution models of the channel architecture and its role in selective ion conduction and drug binding. However, it is still unclear which functional states of the LGIC gating scheme these crystal structures represent. Much of this uncertainty arises from a lack of thorough understanding of the functional properties of these prokaryotic channels. To elucidate the molecular events that constitute gating, we have carried out an extensive characterization of GLIC function and dynamics in reconstituted proteoliposomes by patch clamp measurements and EPR spectroscopy. We find that GLIC channels show rapid activation upon jumps to acidic pH followed by a time-dependent loss of conductance because of desensitization. GLIC desensitization is strongly coupled to activation and is modulated by voltage, permeant ions, pore-blocking drugs, and membrane cholesterol. Many of these properties are parallel to functions observed in members of eukaryotic LGIC. Conformational changes in loop C, measured by site-directed spin labeling and EPR spectroscopy, reveal immobilization during desensitization analogous to changes in LGIC and acetylcholine binding protein. Together, our studies suggest conservation of mechanistic aspects of desensitization among LGICs of prokaryotic and eukaryotic origin.

  19. Physics-based scoring of protein-ligand interactions: explicit polarizability, quantum mechanics and free energies. (United States)

    Bryce, Richard A


    The ability to accurately predict the interaction of a ligand with its receptor is a key limitation in computer-aided drug design approaches such as virtual screening and de novo design. In this article, we examine current strategies for a physics-based approach to scoring of protein-ligand affinity, as well as outlining recent developments in force fields and quantum chemical techniques. We also consider advances in the development and application of simulation-based free energy methods to study protein-ligand interactions. Fuelled by recent advances in computational algorithms and hardware, there is the opportunity for increased integration of physics-based scoring approaches at earlier stages in computationally guided drug discovery. Specifically, we envisage increased use of implicit solvent models and simulation-based scoring methods as tools for computing the affinities of large virtual ligand libraries. Approaches based on end point simulations and reference potentials allow the application of more advanced potential energy functions to prediction of protein-ligand binding affinities. Comprehensive evaluation of polarizable force fields and quantum mechanical (QM)/molecular mechanical and QM methods in scoring of protein-ligand interactions is required, particularly in their ability to address challenging targets such as metalloproteins and other proteins that make highly polar interactions. Finally, we anticipate increasingly quantitative free energy perturbation and thermodynamic integration methods that are practical for optimization of hits obtained from screened ligand libraries.

  20. Theoretical Modeling of Mechanical Behavior and Release Properties of Microcapsules

    NARCIS (Netherlands)

    Sagis, L.M.C.


    Microcapsules in food often have a shell with a complex microstructure; the mechanical and structural properties of these shells affect the response of the capsules to deforming forces and the release kinetics of encapsulated components. In this chapter we will discuss a number of models which are t

  1. Solid lipid nanoparticles (SLN) for controlled drug delivery--drug release and release mechanism. (United States)

    zur Mühlen, A; Schwarz, C; Mehnert, W


    Solid lipid nanoparticles (SLN) are particulate systems for parenteral drug administration with mean particle diameters ranging from 50 up to 1000 nm. The model drugs tetracaine, etomidate and prednisolone were incorporated (1, 5 and 10%) to study the drug load, effect of drug incorporation on the structure of the lipid matrix and the release profiles and mechanism. SLN were produced by high pressure homogenization of aqueous surfactant solutions containing the drug-loaded lipids in the melted or in the solid state (500/1500 bar, 3/10 cycles). In case of tetracaine and etomidate, high drug loadings up to 10% could be achieved when using Compritol 888 ATO and Dynasan 112 as matrix material. The melting behavior of the drug loaded particles revealed that little or no interactions between drug and lipid occurred. A burst drug release (100% release < 1 min) was observed with tetracaine and etomidate SLN, which was attributed to the large surface area of the nanoparticles and drug enrichment in the outer shell of the particles. In contrast, prednisolone loaded SLN showed a distinctly prolonged release over a monitored period of 5 weeks. Depending on the chemical nature of the lipid matrix, 83.8 and 37.1% drug were released (cholesterol and compritol, respectively). These results demonstrate the principle suitability of SLN as a prolonged release formulation for lipophilic drugs.

  2. Regulated ADAM17-dependent EGF family ligand release by substrate-selecting signaling pathways. (United States)

    Dang, Michelle; Armbruster, Nicole; Miller, Miles A; Cermeno, Efrain; Hartmann, Monika; Bell, George W; Root, David E; Lauffenburger, Douglas A; Lodish, Harvey F; Herrlich, Andreas


    Ectodomain cleavage of cell-surface proteins by A disintegrin and metalloproteinases (ADAMs) is highly regulated, and its dysregulation has been linked to many diseases. ADAM10 and ADAM17 cleave most disease-relevant substrates. Broad-spectrum metalloprotease inhibitors have failed clinically, and targeting the cleavage of a specific substrate has remained impossible. It is therefore necessary to identify signaling intermediates that determine substrate specificity of cleavage. We show here that phorbol ester or angiotensin II-induced proteolytic release of EGF family members may not require a significant increase in ADAM17 protease activity. Rather, inducers activate a signaling pathway using PKC-α and the PKC-regulated protein phosphatase 1 inhibitor 14D that is required for ADAM17 cleavage of TGF-α, heparin-binding EGF, and amphiregulin. A second pathway involving PKC-δ is required for neuregulin (NRG) cleavage, and, indeed, PKC-δ phosphorylation of serine 286 in the NRG cytosolic domain is essential for induced NRG cleavage. Thus, signaling-mediated substrate selection is clearly distinct from regulation of enzyme activity, an important mechanism that offers itself for application in disease.

  3. DMPD: Anti-inflammatory actions of PPAR ligands: new insights on cellular andmolecular mechanisms. [Dynamic Macrophage Pathway CSML Database

    Lifescience Database Archive (English)

    Full Text Available 17981503 Anti-inflammatory actions of PPAR ligands: new insights on cellular andmol...) (.html) (.csml) Show Anti-inflammatory actions of PPAR ligands: new insights on cellular andmolecular mech...anisms. PubmedID 17981503 Title Anti-inflammatory actions of PPAR ligands: new in

  4. Urokinase plasminogen activator cleaves its cell surface receptor releasing the ligand-binding domain

    DEFF Research Database (Denmark)

    Høyer-Hansen, G; Rønne, E; Solberg, H


    -domain form, uPAR(2+3), lacking ligand-binding domain 1. Trypsin treatment showed that both variants are present on the outside of the cells. Addition to the culture medium of an anticatalytic monoclonal antibody to uPA inhibited the formation of the uPAR(2+3), indicating that uPA is involved in its...

  5. Symmetric allosteric mechanism of hexameric Escherichia coli arginine repressor exploits competition between L-arginine ligands and resident arginine residues.

    Directory of Open Access Journals (Sweden)

    Rebecca Strawn


    Full Text Available An elegantly simple and probably ancient molecular mechanism of allostery is described for the Escherichia coli arginine repressor ArgR, the master feedback regulator of transcription in L-arginine metabolism. Molecular dynamics simulations with ArgRC, the hexameric domain that binds L-arginine with negative cooperativity, reveal that conserved arginine and aspartate residues in each ligand-binding pocket promote rotational oscillation of apoArgRC trimers by engagement and release of hydrogen-bonded salt bridges. Binding of exogenous L-arginine displaces resident arginine residues and arrests oscillation, shifting the equilibrium quaternary ensemble and promoting motions that maintain the configurational entropy of the system. A single L-arg ligand is necessary and sufficient to arrest oscillation, and enables formation of a cooperative hydrogen-bond network at the subunit interface. The results are used to construct a free-energy reaction coordinate that accounts for the negative cooperativity and distinctive thermodynamic signature of L-arginine binding detected by calorimetry. The symmetry of the hexamer is maintained as each ligand binds, despite the conceptual asymmetry of partially-liganded states. The results thus offer the first opportunity to describe in structural and thermodynamic terms the symmetric relaxed state predicted by the concerted allostery model of Monod, Wyman, and Changeux, revealing that this state is achieved by exploiting the dynamics of the assembly and the distributed nature of its cohesive free energy. The ArgR example reveals that symmetry can be maintained even when binding sites fill sequentially due to negative cooperativity, which was not anticipated by the Monod, Wyman, and Changeux model. The molecular mechanism identified here neither specifies nor requires a pathway for transmission of the allosteric signal through the protein, and it suggests the possibility that binding of free amino acids was an early

  6. Comparison of molecular mechanics, semi-empirical quantum mechanical, and density functional theory methods for scoring protein-ligand interactions. (United States)

    Yilmazer, Nusret Duygu; Korth, Martin


    Correctly ranking protein-ligand interactions with respect to overall free energy of binding is a grand challenge for virtual drug design. Here we compare the performance of various quantum chemical approaches for tackling this so-called "scoring" problem. Relying on systematically generated benchmark sets of large protein/ligand model complexes based on the PDBbind database, we show that the performance depends first of all on the general level of theory. Comparing classical molecular mechanics (MM), semiempirical quantum mechanical (SQM), and density functional theory (DFT) based methods, we find that enhanced SQM approaches perform very similar to DFT methods and substantially different from MM potentials.

  7. Mechanisms of fluoride release in sediments of Argentina's central region. (United States)

    Borgnino, L; Garcia, M G; Bia, G; Stupar, Y V; Le Coustumer, Ph; Depetris, P J


    We analyze the sources and mechanisms that control the release of fluoride from sediments collected from two types of aquatic reservoirs in the central region of Argentina: 1) mountainous rivers draining crystalline rocks from the Sierras Pampeanas ranges, and 2) shallow aquifers in loessic sediments. The assessment was performed on the basis of experimental work and the study of chemical and mineralogical characteristics of sediments in contact with F-rich waters of the studied region. The chemical and mineralogical compositions of sediments were analyzed by ICP/OES, DRX, and SEM-EDS. Batch experiments were conducted to evaluate the kinetics of fluoride release under variable pH and ionic composition of the solution. The enhanced release of fluoride at more acidic pH, the inhibition of release in Ca-rich solutions and the positive significant linear trends between Ca(2+) and fluoride concentrations suggest that the dissolution of a Ca/F-bearing phase (like fluorapatite) strongly controls the dynamics of fluoride in the early stages of water-sediment interaction, particularly under acidic conditions. Calculations revealed that the dissolution of an amount of FAp equivalent to that estimated in the studied sediments may widely account for the values measured in the leaching experiments at pH6, whatever the dominant cation in the solution. Under such conditions, dissolution of FAp (present as coatings onto glass surfaces or as detritic grains) is likely the major primary source of fluorine in the studied sediments. Contribution from biotite may be also considered as a source in fluvial sediments. When adequate surfaces are present the released anions may partially be scavenged from the solution by adsorption at acidic pH. Increasing alkalinity in the aquatic reservoirs may then release the adsorbed fluoride through desorption or through competition with other anionic species. Comparing both mechanisms, dissolution predominates at lower pH while desorption is the main

  8. Mechanism of controlled release kinetics from medical devices

    Directory of Open Access Journals (Sweden)

    A. Raval


    Full Text Available Utilization of biodegradable polymers for controlled drug delivery has gained immense attention in the pharmaceutical and medical device industry to administer various drugs, proteins and other bio-molecules both systematically and locally to cure several diseases. The efficacy and toxicity of this local therapeutics depends upon drug release kinetics, which will further decide drug deposition, distribution, and retention at the target site. Drug Eluting Stent (DES presently possesses clinical importance as an alternative to Coronary Artery Bypass Grafting due to the ease of the procedure and comparable safety and efficacy. Many models have been developed to describe the drug delivery from polymeric carriers based on the different mechanisms which control the release phenomenon from DES. Advanced characterization techniques facilitate an understanding of the complexities behind design and related drug release behavior of drug eluting stents, which aids in the development of improved future drug eluting systems. This review discusses different drug release mechanisms, engineering principles, mathematical models and current trends that are proposed for drug-polymer coated medical devices such as cardiovascular stents and different analytical methods currently utilized to probe diverse characteristics of drug eluting devices.

  9. New Ru(II) Complex for Dual Activity: Photoinduced Ligand Release and (1)O2 Production. (United States)

    Loftus, Lauren M; White, Jessica K; Albani, Bryan A; Kohler, Lars; Kodanko, Jeremy J; Thummel, Randolph P; Dunbar, Kim R; Turro, Claudia


    The new complex [Ru(pydppn)(biq)(py)](2+) (1) undergoes both py photodissociation in CH3CN with Φ500 =0.0070(4) and (1)O2 production with ΦΔ =0.75(7) in CH3 OH from a long-lived (3) ππ* state centered on the pydppn ligand (pydppn=3-(pyrid-2-yl)benzo[i]dipyrido[3,2-a:2',3'-c]phenazine; biq = 2,2'-biquinoline; py=pyridine). This represents an order of magnitude decrease in the Φ500 compared to the previously reported model compound [Ru(tpy)(biq)(py)](2+) (3) (tpy=2,2':6',2''-terpyridine) that undergoes only ligand exchange. The effect on the quantum yields by the addition of a second deactivation pathway through the low-lying (3) ππ* state necessary for dual reactivity was investigated using ultrafast and nanosecond transient absorption spectroscopy, revealing a significantly shorter (3) MLCT lifetime in 1 relative to that of the model complex 3. Due to the structural similarities between the two compounds, the lower values of Φ500 and ΦΔ compared to that of [Ru(pydppn)(bpy)(py)](2+) (2) (bpy=2,2'-bipyridine) are attributed to a competitive excited state population between the (3) LF states involved in ligand dissociation and the long-lived (3) ππ* state in 1. Complex 1 represents a model compound for dual activity that may be applied to photochemotherapy.

  10. Quantum mechanical calculation of nanomaterial-ligand interaction energies by molecular fractionation with conjugated caps method (United States)

    Zhang, Dawei


    Molecular fractionation with conjugate caps (MFCC) method is introduced for the efficient estimation of quantum mechanical (QM) interaction energies between nanomaterial (carbon nanotube, fullerene, and graphene surface) and ligand (charged and neutral). In the calculations, nanomaterials are partitioned into small fragments and conjugated caps that are properly capped, and the interaction energies can be obtained through the summation of QM calculations of the fragments from which the contribution of the conjugated caps is removed. All the calculations were performed by density functional theory (DFT) and dispersion contributions for the attractive interactions were investigated by dispersion corrected DFT method. The predicted interaction energies by MFCC at each computational level are found to give excellent agreement with full system (FS) calculations with the mean energy deviation just a fractional kcal/mol. The accurate determination of nanomaterial-ligand interaction energies by MFCC suggests that it is an effective method for performing QM calculations on nanomaterial-ligand systems.

  11. Quantum mechanical calculation of nanomaterial-ligand interaction energies by molecular fractionation with conjugated caps method (United States)

    Zhang, Dawei


    Molecular fractionation with conjugate caps (MFCC) method is introduced for the efficient estimation of quantum mechanical (QM) interaction energies between nanomaterial (carbon nanotube, fullerene, and graphene surface) and ligand (charged and neutral). In the calculations, nanomaterials are partitioned into small fragments and conjugated caps that are properly capped, and the interaction energies can be obtained through the summation of QM calculations of the fragments from which the contribution of the conjugated caps is removed. All the calculations were performed by density functional theory (DFT) and dispersion contributions for the attractive interactions were investigated by dispersion corrected DFT method. The predicted interaction energies by MFCC at each computational level are found to give excellent agreement with full system (FS) calculations with the mean energy deviation just a fractional kcal/mol. The accurate determination of nanomaterial-ligand interaction energies by MFCC suggests that it is an effective method for performing QM calculations on nanomaterial-ligand systems. PMID:28300179

  12. Frequency-Dependent Modulation of Dopamine Release by Nicotine and Dopamine D1 Receptor Ligands: An In Vitro Fast Cyclic Voltammetry Study in Rat Striatum. (United States)

    Goutier, W; Lowry, J P; McCreary, A C; O'Connor, J J


    Nicotine is a highly addictive drug and exerts this effect partially through the modulation of dopamine release and increasing extracellular dopamine in regions such as the brain reward systems. Nicotine acts in these regions on nicotinic acetylcholine receptors. The effect of nicotine on the frequency dependent modulation of dopamine release is well established and the purpose of this study was to investigate whether dopamine D1 receptor (D1R) ligands have an influence on this. Using fast cyclic voltammetry and rat corticostriatal slices, we show that D1R ligands are able to modulate the effect of nicotine on dopamine release. Nicotine (500 nM) induced a decrease in dopamine efflux at low frequency (single pulse or five pulses at 10 Hz) and an increase at high frequency (100 Hz) electrical field stimulation. The D1R agonist SKF-38393, whilst having no effect on dopamine release on its own or on the effect of nicotine upon multiple pulse evoked dopamine release, did significantly prevent and reverse the effect of nicotine on single pulse dopamine release. Interestingly similar results were obtained with the D1R antagonist SCH-23390. In this study we have demonstrated that the modulation of dopamine release by nicotine can be altered by D1R ligands, but only when evoked by single pulse stimulation, and are likely working via cholinergic interneuron driven dopamine release.

  13. STARD6 on steroids: solution structure, multiple timescale backbone dynamics and ligand binding mechanism (United States)

    Létourneau, Danny; Bédard, Mikaël; Cabana, Jérôme; Lefebvre, Andrée; Lehoux, Jean-Guy; Lavigne, Pierre


    START domain proteins are conserved α/β helix-grip fold that play a role in the non-vesicular and intracellular transport of lipids and sterols. The mechanism and conformational changes permitting the entry of the ligand into their buried binding sites is not well understood. Moreover, their functions and the identification of cognate ligands is still an active area of research. Here, we report the solution structure of STARD6 and the characterization of its backbone dynamics on multiple time-scales through 15N spin-relaxation and amide exchange studies. We reveal for the first time the presence of concerted fluctuations in the Ω1 loop and the C-terminal helix on the microsecond-millisecond time-scale that allows for the opening of the binding site and ligand entry. We also report that STARD6 binds specifically testosterone. Our work represents a milestone for the study of ligand binding mechanism by other START domains and the elucidation of the biological function of STARD6.

  14. Retention and release mechanisms of deuterium implanted into beryllium (United States)

    Oberkofler, M.; Reinelt, M.; Linsmeier, Ch.


    The fraction of deuterium (D) that is retained upon irradiation of beryllium (Be) as well as the temperatures at which implanted D is released are of importance for the international fusion experiment ITER, where Be will be used as an armor material. The influence of single parameters on retention and release is investigated in laboratory experiments performed under well defined conditions with the aim to identify dominant underlying mechanisms and thus be able to predict the behavior of the Be wall in ITER. Recent progress in the quantification of retained fractions and release temperatures as well as in the understanding of the governing mechanisms is presented. The retained fraction upon implantation of D at 1 keV into Be(1 1 2¯ 0) to fluences far below the saturation threshold of 10 21 m -2 is almost 95%, the remaining 5% being attributed to reflection at the surface. At these low fluences, no dependence of the retained fractions on implantation energy is observed. At fluences of the order of 10 21 m -2 and higher, saturation of the irradiated material affects the retention, leading to lower retained fractions. Furthermore, at these fluences the retained fractions decrease with decreasing implantation energies. Differences in the retained fractions from implanted Be(1 1 2¯ 0) and polycrystalline Be are explained by anisotropic diffusion of interstitials during implantation, leading to an amount of surviving D-trap complexes that depends on surface-orientation. Temperature-programmed desorption (TPD) spectra are recorded after implantation of fluences of the order of 10 19 m -2 at various energies and simulated by means of a newly developed code based on coupled reaction-diffusion systems (CRDS). The asymmetric shape of the TPD peaks is reproduced by introducing a local D accumulation process into the model.

  15. [Mechanisms of neurotransmitter release facilitation in strontium solutions]. (United States)

    Mukhamed'iarov, M A; Kochunova, Iu O; Telina, E N; Zefirov, A L


    Mechanisms of neurotransmitter release facilitation were studied using electrophysiological recording of end-plate currents (EPC) and nerve ending (NE) responses after substitution of extracellular Ca ions with Sr ions at the frog neuromuscular junction. The solutions with 0.5 mM concentration of Ca ions (calcium solution) or 1 mM concentration of Sr ions (strontium solution) were used where baseline neurotransmitter release (at low-frequency stimulation) is equal. Decay of paired-pulse facilitation of EPC at calcium solutions with increase of interpulse interval from 5 to 500 ms was well described by three-exponential function consisting of early, first and second components. Facilitation at strontium solutions was significantly diminished due mainly to decrease of early and first components. At the same time, EPC facilitation with rhythmic stimulation (10 or 50 imp/s) at strontium solutions was significantly increased. Also more pronounced decrease of NE response 3rd phase, reflecting potassium currents was detected under rhythmic stimulation of 50 imp/s at strontium solutions comparing to calcium solutions. It was concluded that facilitation sites underlying first and early components had lower affinity to Sr ions than to Ca ions. The enhancement of frequency facilitation at strontium solutions is mediated by two mechanisms: more pronounced broadening of NE action potential and increase of bivalent cation influx due to feebly marked activation of Ca(2+)-dependent potassium current by Sr ions, and slower dynamics of Sr(2+) removal from NE axoplasm comparing to Ca(2+).

  16. Effects of ligand binding on the mechanical properties of ankyrin repeat protein gankyrin.

    Directory of Open Access Journals (Sweden)

    Giovanni Settanni

    Full Text Available Ankyrin repeat proteins are elastic materials that unfold and refold sequentially, repeat by repeat, under force. Herein we use atomistic molecular dynamics to compare the mechanical properties of the 7-ankyrin-repeat oncoprotein Gankyrin in isolation and in complex with its binding partner S6-C. We show that the bound S6-C greatly increases the resistance of Gankyrin to mechanical stress. The effect is specific to those repeats of Gankyrin directly in contact with S6-C, and the mechanical 'hot spots' of the interaction map to the same repeats as the thermodynamic hot spots. A consequence of stepwise nature of unfolding and the localized nature of ligand binding is that it impacts on all aspects of the protein's mechanical behavior, including the order of repeat unfolding, the diversity of unfolding pathways accessed, the nature of partially unfolded intermediates, the forces required and the work transferred to the system to unfold the whole protein and its parts. Stepwise unfolding thus provides the means to buffer repeat proteins and their binding partners from mechanical stress in the cell. Our results illustrate how ligand binding can control the mechanical response of proteins. The data also point to a cellular mechano-switching mechanism whereby binding between two partner macromolecules is regulated by mechanical stress.

  17. Wnt Ligands Differentially Regulate Toxicity and Translocation of Graphene Oxide through Different Mechanisms in Caenorhabditis elegans (United States)

    Zhi, Lingtong; Ren, Mingxia; Qu, Man; Zhang, Hanyu; Wang, Dayong


    In this study, we investigated the possible involvement of Wnt signals in the control of graphene oxide (GO) toxicity using the in vivo assay system of Caenorhabditis elegans. In nematodes, the Wnt ligands, CWN-1, CWN-2, and LIN-44, were found to be involved in the control of GO toxicity. Mutation of cwn-1 or lin-44 gene induced a resistant property to GO toxicity and resulted in the decreased accumulation of GO in the body of nematodes, whereas mutation of cwn-2 gene induces a susceptible property to GO toxicity and an enhanced accumulation of GO in the body of nematodes. Genetic interaction assays demonstrated that mutation of cwn-1 or lin-44 was able to suppress the susceptibility to GO toxicity shown in the cwn-2 mutants. Loss-of-function mutations in all three of these Wnt ligand genes resulted in the resistance of nematodes to GO toxicity. Moreover, the Wnt ligands might differentially regulate the toxicity and translocation of GO through different mechanisms. These findings could be important in understanding the function of Wnt signals in the regulation of toxicity from environmental nanomaterials.

  18. Molecular mechanism of ligand recognition by NR3 subtype glutamate receptors

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Yongneng; Harrison, Chris B.; Freddolino, Peter L.; Schulten, Klaus; Mayer, Mark L. (UIUC); (NIH)


    NR3 subtype glutamate receptors have a unique developmental expression profile, but are the least well-characterized members of the NMDA receptor gene family, which have key roles in synaptic plasticity and brain development. Using ligand binding assays, crystallographic analysis, and all atom MD simulations, we investigate mechanisms underlying the binding by NR3A and NR3B of glycine and D-serine, which are candidate neurotransmitters for NMDA receptors containing NR3 subunits. The ligand binding domains of both NR3 subunits adopt a similar extent of domain closure as found in the corresponding NR1 complexes, but have a unique loop 1 structure distinct from that in all other glutamate receptor ion channels. Within their ligand binding pockets, NR3A and NR3B have strikingly different hydrogen bonding networks and solvent structures from those found in NR1, and fail to undergo a conformational rearrangement observed in NR1 upon binding the partial agonist ACPC. MD simulations revealed numerous interdomain contacts, which stabilize the agonist-bound closed-cleft conformation, and a novel twisting motion for the loop 1 helix that is unique in NR3 subunits.

  19. Towards full Quantum-Mechanics-based Protein-Ligand Binding Affinities. (United States)

    Ehrlich, Stephan; Göller, Andreas H; Grimme, Stefan


    Computational methods play a key role in modern drug design in the pharmaceutical industry but are mostly based on force fields, which are limited in accuracy when describing non-classical binding effects, proton transfer, or metal coordination. Here, we propose a general fully quantum mechanical (QM) scheme for the computation of protein-ligand affinities. It works on a single protein cutout (of about 1000 atoms) and evaluates all contributions (interaction energy, solvation, thermostatistical) to absolute binding free energy on the highest feasible QM level. The methodology is tested on two different protein targets: activated serine protease factor X (FXa) and tyrosine-protein kinase 2 (TYK2). We demonstrate that the geometry of the model systems can be efficiently energy-minimized by using general purpose graphics processing units, resulting in structures that are close to the co-crystallized protein-ligand structures. Our best calculations at a hybrid DFT level (PBEh-3c composite method) for the FXa ligand set result in an overall mean absolute deviation as low as 2.1 kcal mol(-1) . Though very encouraging, an analysis of outliers indicates that the structure optimization level, conformational sampling, and solvation treatment require further improvement.

  20. Structures of pattern recognition receptors reveal molecular mechanisms of autoinhibition, ligand recognition and oligomerization. (United States)

    Chuenchor, Watchalee; Jin, Tengchuan; Ravilious, Geoffrey; Xiao, T Sam


    Pattern recognition receptors (PRRs) are essential sentinels for pathogens or tissue damage and integral components of the innate immune system. Recent structural studies have provided unprecedented insights into the molecular mechanisms of ligand recognition and signal transduction by several PRR families at distinct subcellular compartments. Here we highlight some of the recent discoveries and summarize the common themes that are emerging from these exciting studies. Better mechanistic understanding of the structure and function of the PRRs will improve future prospects of therapeutic targeting of these important innate immune receptors.

  1. Source regions and water release mechanisms of Martian Valley Networks (United States)

    Jaumann, R.; Reiss, D.; Sander, T.; Gwinner, K.; Roatsch, T.; Matz, K.-D.; Hauber, E.; Mertens, V.; Hoffmann, H.; Neukum, G.; HRSC Co-Investigator Team

    Martian valley networks have been cited as the best evidence that Mars maintained flow of liquid water across the surface. Although internal structures associated with a fluvial origin within valleys like inner channels, terraces, slip-off and undercut slopes are extremely rare on Mars (Carr and Malin, 2000) such features can be identified in high-resolution imagery (e.g. Malin and Edgett, 2001; Jaumann et al., 2005). However, besides internal features the source regions are an important indicator for the flow processes in Martian valleys because they define the drainage area and thus constrain the amount of available water for eroding the valley network. Furthermore, the morphology of the source regions and their topographic characteristics provide information about the origin of the water. On Mars valley networks are thought to be formed by retreating erosion where the water is supplied from the sub-surface. However, the mechanisms that are responsible for the release of ground water are poorly understood. The three dimensional highly resolved data of the High Resolution Stereo Camera (HRSC) on the Mars Express Mission (Neukum et al., 2004) allow the detailed examination of valley network source regions. A valley network in the western Lybia Montes region valley between 1.4°N to 3.5°N and 81.6°E to 82.5°E originates at a highland mountain region and drains down to Isidis Planitia over a distance of 400 km. Most of its distance the valley exhibits an interior channel that allows to constraint discharge and erosion budgets (Jaumann, et al., 2005). The valley was formed in the Noachian/Hesperian between 3.7 and 3.3 billion years. However, discharge and erosion budgets restrict the erosion time to a few million years in total, indicating single events rather than continuous flow over long periods. The source region of the valley is covered by a series of lava flows. Even the upstream part of the valley is covered by lava flows that cover the interior channel

  2. Design of protein-ligand binding based on the molecular-mechanics energy model. (United States)

    Boas, F Edward; Harbury, Pehr B


    While the molecular-mechanics field has standardized on a few potential energy functions, computational protein design efforts are based on potentials that are unique to individual laboratories. Here we show that a standard molecular-mechanics potential energy function without any modifications can be used to engineer protein-ligand binding. A molecular-mechanics potential is used to reconstruct the coordinates of various binding sites with an average root-mean-square error of 0.61 A and to reproduce known ligand-induced side-chain conformational shifts. Within a series of 34 mutants, the calculation can always distinguish between weak (K(d)>1 mM) and tight (K(d)mechanics potential is used to redesign a ribose-binding site. Out of a search space of 2 x 10(12) sequences, the calculation selects a point mutant of the native protein as the top solution (experimental K(d)=17 microM) and the native protein as the second best solution (experimental K(d)=210 nM). The quality of the predictions depends on the accuracy of the generalized Born electrostatics model, treatment of protonation equilibria, high-resolution rotamer sampling, a final local energy minimization step, and explicit modeling of the bound, unbound, and unfolded states. The application of unmodified molecular-mechanics potentials to protein design links two fields in a mutually beneficial way. Design provides a new avenue for testing molecular-mechanics energy functions, and future improvements in these energy functions will presumably lead to more accurate design results.

  3. Application of the quantum mechanical IEF/PCM-MST hydrophobic descriptors to selectivity in ligand binding. (United States)

    Ginex, Tiziana; Muñoz-Muriedas, Jordi; Herrero, Enric; Gibert, Enric; Cozzini, Pietro; Luque, F Javier


    We have recently reported the development and validation of quantum mechanical (QM)-based hydrophobic descriptors derived from the parametrized IEF/PCM-MST continuum solvation model for 3D-QSAR studies within the framework of the Hydrophobic Pharmacophore (HyPhar) method. In this study we explore the applicability of these descriptors to the analysis of selectivity fields. To this end, we have examined a series of 88 compounds with inhibitory activities against thrombin, trypsin and factor Xa, and the HyPhar results have been compared with 3D-QSAR models reported in the literature. The quantitative models obtained by combining the electrostatic and non-electrostatic components of the octanol/water partition coefficient yield results that compare well with the predictive potential of standard CoMFA and CoMSIA techniques. The results also highlight the potential of HyPhar descriptors to discriminate the selectivity of the compounds against thrombin, trypsin, and factor Xa. Moreover, the graphical representation of the hydrophobic maps provides a direct linkage with the pattern of interactions found in crystallographic structures. Overall, the results support the usefulness of the QM/MST-based hydrophobic descriptors as a complementary approach for disclosing structure-activity relationships in drug design and for gaining insight into the molecular determinants of ligand selectivity. Graphical Abstract Quantum Mechanical continuum solvation calculations performed with the IEF/PCM-MST method are used to derived atomic hydrophobic descriptors, which are then used to discriminate the selectivity of ligands against thrombin, trypsin and factor Xa. The descriptors provide complementary view to standard 3D-QSAR analysis, leading to a more comprehensive understanding of ligand recognition.

  4. Molecular mechanics approach for design and conformational studies of macrocyclic ligands

    Energy Technology Data Exchange (ETDEWEB)

    Rohini,; Akbar, Rifat; Kanungo, B. K., E-mail: [Department of Chemistry, Sant Longowal Institute of Engineering & Technology, Longowal-148106 (India)


    Computational Chemistry has revolutionized way of viewing molecules at the quantum mechanical scale by allowing simulating various chemical scenarios that are not possible to study in a laboratory. The remarkable applications of computational chemistry have promoted to design and test of the effectiveness of various methods for searching the conformational space of highly flexible molecules. In this context, we conducted a series of optimization and conformational searches on macrocyclic based ligands, 9N3Me5Ox, (1,4,7-tris(5-methyl-8-hydroxyquinoline)-1,4,7-triazacyclononane) and 12N3Me5Ox, (1,5,9-tris(5-methyl-8-hydroxyquinoline)-1,5,9-triazacyclododecane) and studied their selectivity and coordination behavior with some lanthanide metal ions in molecular mechanics and semiempirical methods. The methods include both systematic and random conformational searches for dihedral angles, torsion angles and Cartesian coordinates. Structural studies were carried out by using geometry optimization, coordination scans and electronic properties were evaluated. The results clearly show that chair-boat conformational isomer of 9N3Me5Ox ligand is more stable due to lower eclipsing ethane interaction and form stronger adduct complexes with lanthanide metal ion. This is because of the fact that, in a central unit of 9N3 of the ligand form six endo type bonds out of nine. The rest of bonds have trans conformation. In contrast, for the adduct of 12N3Me5Ox, two C-C bonds have on eclipsed conformation, and others have synclinal and antiperiplanar confirmations. The distortion of the two eclipsed conformations may affect the yields and the stability of the complexes.

  5. Recent Progress in Treating Protein-Ligand Interactions with Quantum-Mechanical Methods. (United States)

    Yilmazer, Nusret Duygu; Korth, Martin


    We review the first successes and failures of a "new wave" of quantum chemistry-based approaches to the treatment of protein/ligand interactions. These approaches share the use of "enhanced", dispersion (D), and/or hydrogen-bond (H) corrected density functional theory (DFT) or semi-empirical quantum mechanical (SQM) methods, in combination with ensemble weighting techniques of some form to capture entropic effects. Benchmark and model system calculations in comparison to high-level theoretical as well as experimental references have shown that both DFT-D (dispersion-corrected density functional theory) and SQM-DH (dispersion and hydrogen bond-corrected semi-empirical quantum mechanical) perform much more accurately than older DFT and SQM approaches and also standard docking methods. In addition, DFT-D might soon become and SQM-DH already is fast enough to compute a large number of binding modes of comparably large protein/ligand complexes, thus allowing for a more accurate assessment of entropic effects.

  6. Recent Progress in Treating Protein–Ligand Interactions with Quantum-Mechanical Methods

    Directory of Open Access Journals (Sweden)

    Nusret Duygu Yilmazer


    Full Text Available We review the first successes and failures of a “new wave” of quantum chemistry-based approaches to the treatment of protein/ligand interactions. These approaches share the use of “enhanced”, dispersion (D, and/or hydrogen-bond (H corrected density functional theory (DFT or semi-empirical quantum mechanical (SQM methods, in combination with ensemble weighting techniques of some form to capture entropic effects. Benchmark and model system calculations in comparison to high-level theoretical as well as experimental references have shown that both DFT-D (dispersion-corrected density functional theory and SQM-DH (dispersion and hydrogen bond-corrected semi-empirical quantum mechanical perform much more accurately than older DFT and SQM approaches and also standard docking methods. In addition, DFT-D might soon become and SQM-DH already is fast enough to compute a large number of binding modes of comparably large protein/ligand complexes, thus allowing for a more accurate assessment of entropic effects.

  7. Kinetics and Mechanism of Metal Retention/Release in Geochemical Processes in Soil - Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Robert W.


    Effective, remediation of soils contaminated with heavy metals requires a better understanding of the mechanisms by which the metals are retained/released in soils over a long period of time. Studies on reaction of Cr(VI) with iron-rich clays indicated that structural iron (II) in these surfaces is capable of reducing chromate to chromium (III). We found that iron (II) either found naturally or produced by treatment of clay with sodium dithionite, effectively reduced Cr (VI) to Cr (III). Thus, in situ remediation of chromium combines reduction of Cr (VI) to Cr (III) and immobilization of chromium on mineral surfaces. During this study, lead sorption on a kaolin surface was found to be a rapid and a pH dependant process in which lead sorption significantly increased with the amount of phosphate on the clay surface. This study verifies that methylmercury cation remains intact when it binds to humic acids, forming a monodentate complex with some sub-population of humic thiol ligands .

  8. Release mechanisms behind polysaccharides-based famotidine controlled release matrix tablets. (United States)

    Elmowafy, Enas M; Awad, Gehanne A S; Mansour, Samar; El-Shamy, Abd El-Hamid A


    Polysaccharides, which have been explored to possess gelling properties and a wide margin of safety, were used to formulate single-unit floating matrix tablets by a direct compression technique. This work has the aim to allow continuous slow release of famotidine above its site of absorption. The floating approach was achieved by the use of the low density polypropylene foam powder. Polysaccharides (kappa-carrageenan, gellan gum, xyloglucan, and pectin) and blends of polysaccharides (kappa-carrageenan and gellan gum) and cellulose ethers (hydroxypropylmethyl cellulose, hydroxypropylcellulose, sodium carboxymethyl cellulose) were tried to modulate the release characteristics. The prepared floating tablets were evaluated for their floating behavior, matrix integrity, swelling studies, in vitro drug release studies, and kinetic analysis of the release data. The differential scanning calorimetry and Fourier transform infrared spectroscopy studies revealed that changing the polymer matrix system by formulation of polymers blends resulted in formation of molecular interactions which may have implications on drug release characteristics. This was obvious from the retardation in drug release and change in its mechanistics.

  9. Targeted delivery of RNAi therapeutics with endogenous and exogenous ligand-based mechanisms. (United States)

    Akinc, Akin; Querbes, William; De, Soma; Qin, June; Frank-Kamenetsky, Maria; Jayaprakash, K Narayanannair; Jayaraman, Muthusamy; Rajeev, Kallanthottathil G; Cantley, William L; Dorkin, J Robert; Butler, James S; Qin, Liuliang; Racie, Timothy; Sprague, Andrew; Fava, Eugenio; Zeigerer, Anja; Hope, Michael J; Zerial, Marino; Sah, Dinah W Y; Fitzgerald, Kevin; Tracy, Mark A; Manoharan, Muthiah; Koteliansky, Victor; Fougerolles, Antonin de; Maier, Martin A


    Lipid nanoparticles (LNPs) have proven to be highly efficient carriers of short-interfering RNAs (siRNAs) to hepatocytes in vivo; however, the precise mechanism by which this efficient delivery occurs has yet to be elucidated. We found that apolipoprotein E (apoE), which plays a major role in the clearance and hepatocellular uptake of physiological lipoproteins, also acts as an endogenous targeting ligand for ionizable LNPs (iLNPs), but not cationic LNPs (cLNPs). The role of apoE was investigated using both in vitro studies employing recombinant apoE and in vivo studies in wild-type and apoE(-/-) mice. Receptor dependence was explored in vitro and in vivo using low-density lipoprotein receptor (LDLR(-/-))-deficient mice. As an alternative to endogenous apoE-based targeting, we developed a targeting approach using an exogenous ligand containing a multivalent N-acetylgalactosamine (GalNAc)-cluster, which binds with high affinity to the asialoglycoprotein receptor (ASGPR) expressed on hepatocytes. Both apoE-based endogenous and GalNAc-based exogenous targeting appear to be highly effective strategies for the delivery of iLNPs to liver.

  10. Transfer of the human NKG2D ligands UL16 binding proteins (ULBP) 1-3 is related to lytic granule release and leads to ligand retransfer and killing of ULBP-recipient natural killer cells. (United States)

    López-Cobo, Sheila; Romera-Cárdenas, Gema; García-Cuesta, Eva M; Reyburn, Hugh T; Valés-Gómez, Mar


    After immune interactions, membrane fragments can be transferred between cells. This fast transfer of molecules is transient and shows selectivity for certain proteins; however, the constraints underlying acquisition of a protein are unknown. To characterize the mechanism and functional consequences of this process in natural killer (NK) cells, we have compared the transfer of different NKG2D ligands. We show that human NKG2D ligands can be acquired by NK cells with different efficiencies. The main findings are that NKG2D ligand transfer is related to immune activation and receptor-ligand interaction and that NK cells acquire these proteins during interactions with target cells that lead to degranulation. Our results further demonstrate that NK cells that have acquired NKG2D ligands can stimulate activation of autologous NK cells. Surprisingly, NK cells can also re-transfer the acquired molecule to autologous effector cells during this immune recognition that leads to their death. These data demonstrate that transfer of molecules occurs as a consequence of immune recognition and imply that this process might play a role in homeostatic tuning-down of the immune response or be used as marker of interaction. © 2015 John Wiley & Sons Ltd.

  11. Internalization mechanisms of the epidermal growth factor receptor after activation with different ligands

    DEFF Research Database (Denmark)

    Henriksen, Lasse; Grandal, Michael Vibo; Knudsen, Stine Louise Jeppe


    fully inhibits EGFR degradation after all ligands tested. Furthermore, inhibition of dynamin function blocked EGFR internalization after stimulation with all ligands. Knocking out a number of clathrin-independent dynamin-dependent pathways of internalization had no effect on the ligand...

  12. Factors controlling alkali salt deposition in recovery boilers. Release mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    McKeough, P.; Kurkela, M.; Kylloenen, H.; Tapola, E. [VTT Energy, Espoo (Finland). Process Technology Group


    The research was part of an ongoing cooperative research effort aimed at developing a model to describe the behaviour of inorganic compounds in kraft recovery boilers. During 1996 experimental investigations of sulphur release were continued. Experiments at elevated pressures and employing larger particle sizes were performed in order to gain information about mass transfer effects. The first experiments yielding data on the rates of the sulphur-release reactions were performed. This data will be used as the basis of a drop model for sulphur release being developed in cooperation with another research group. The other part of the work during 1996 explored the possibility of using chemical equilibrium calculations to predict the release of sodium, potassium and chlorine in the recovery furnace. The approach is essentially different from that employed in earlier studies in that the effects of fume formation are taken into account. So far, the predictions of the chemical equilibrium release model have, in no way, conflicted with field measurements. (orig.)

  13. Epidermal growth factor (EGF) ligand release by substrate-specific a disintegrin and metalloproteases (ADAMs) involves different protein kinase C (PKC) isoenzymes depending on the stimulus. (United States)

    Dang, Michelle; Dubbin, Karen; D'Aiello, Antonio; Hartmann, Monika; Lodish, Harvey; Herrlich, Andreas


    The dysregulation of EGF family ligand cleavage has severe consequences for the developing as well as the adult organism. Therefore, their production is highly regulated. The limiting step is the ectodomain cleavage of membrane-bound precursors by one of several a disintegrin and metalloprotease (ADAM) metalloproteases, and understanding the regulation of cleavage is an important goal of current research. We have previously reported that in mouse lung epithelial cells, the pro-EGF ligands TGFα, neuregulin 1β (NRG), and heparin-binding EGF are differentially cleaved depending on the cleavage stimulus (Herrlich, A., Klinman, E., Fu, J., Sadegh, C., and Lodish, H. (2008) FASEB J.). In this study in mouse embryonic fibroblasts that lack different ADAMs, we show that induced cleavage of EGF ligands can involve the same substrate-specific metalloprotease but does require different stimulus-dependent signaling pathways. Cleavage was stimulated by phorbol ester (12-O-tetradecanoylphorbol-13-acetate (TPA), a mimic of diacylglycerol and PKC activator), hypertonic stress, lysophosphatidic acid (LPA)-induced G protein-coupled receptor activation, or by ionomycin-induced intracellular calcium release. Although ADAMs showed substrate preference (ADAM17, TGFα and heparin-binding EGF; and ADAM9, NRG), substrate cleavage differed substantially with the stimulus, and cleavage of the same substrate depended on the presence of different, sometimes multiple, PKC isoforms. For instance, classical PKC was required for TPA-induced but not hypertonic stress-induced cleavage of all EGF family ligands. Inhibition of PKCζ enhanced NRG release upon TPA stimulation, but it blocked NRG release in response to hypertonic stress. Our results suggest a model in which substantial regulation of ectodomain cleavage occurs not only on the metalloprotease level but also on the level of the substrate or of a third protein.

  14. Mechanism of electron transfer reaction of ternary dipicolinatochromium(III) complex involving oxalate as secondary ligand

    Indian Academy of Sciences (India)

    Hassan Amroun Ewais; Iqbal Mohamed Ibrhium Ismail


    Mechanism of electron transfer reaction of ternary Mechanism of the oxidation of [CrIII(DPA)(OX)(H2O)]− (DPA = dipicolinate and OX = oxalate) by periodate in aqueous acidic medium has been studied spectrophotometrically over the pH range of 4.45-5.57 at different temperatures. The reaction is first order with respect to both [IO$^{−}_{4}$] and the complex concentration, and it obeys the following rate law: $$d[{\\text Cr}^{\\text{VI}}]/dt = k_6K_4K_6[{\\text IO}^−_4][{\\text{Cr}}^{\\text{III}}]_{\\text{T}}/\\{([H^+] + K_4) + (K_5[H+] + K_6K_4)[{\\text{IO}}^{−}_{4}]\\}.$$ The rate of the reaction increases with increasing pH due to the deprotonation equilibria of the complex. The experimental rate law is consistent with a mechanism in which the deprotonated form [CrIII(DPA)(OX)(OH)]2− is more reactive than the conjugated acid. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO$^{−}_{4}$ to chromium(III). Thermodynamic activation parameters were calculated using the transition state theory equation.dipicolinatochromium(III) complex involving oxalate as secondary ligand

  15. Iron complexes of tetramine ligands catalyse allylic hydroxyamination via a nitroso-ene mechanism. (United States)

    Porter, David; Poon, Belinda M-L; Rutledge, Peter J


    Iron(II) complexes of the tetradentate amines tris(2-pyridylmethyl)amine (TPA) and N,N'-bis(2-pyridylmethyl)-N,N'-dimethylethane-1,2-diamine (BPMEN) are established catalysts of C-O bond formation, oxidising hydrocarbon substrates via hydroxylation, epoxidation and dihydroxylation pathways. Herein we report the capacity of these catalysts to promote C-N bond formation, via allylic amination of alkenes. The combination of N-Boc-hydroxylamine with either FeTPA (1 mol %) or FeBPMEN (10 mol %) converts cyclohexene to the allylic hydroxylamine (tert-butyl cyclohex-2-en-1-yl(hydroxy)carbamate) in moderate yields. Spectroscopic studies and trapping experiments suggest the reaction proceeds via a nitroso-ene mechanism, with involvement of a free N-Boc-nitroso intermediate. Asymmetric induction is not observed using the chiral tetramine ligand (+)-(2R,2'R)-1,1'-bis(2-pyridylmethyl)-2,2'-bipyrrolidine ((R,R')-PDP).

  16. The mechanism of protein release from triglyceride microspheres. (United States)

    Zaky, A; Elbakry, A; Ehmer, A; Breunig, M; Goepferich, A


    The purpose of this study was to reveal factors that have an impact on the protein release kinetics from triglyceride microspheres prepared by spray congealing. We investigated the effect of protein particle size, morphology and distribution on protein release from microspheres by confocal laser scanning microscopy (CLSM)(.) The microspheres were loaded with three types of model particles made of FITC-labeled bovine serum albumin: freeze dried protein, spherical particles obtained by precipitation in the presence of PEG and micronized material. Investigation by light microscopy and laser light diffraction revealed that the freeze dried material consisted mainly of app. 29 μm elongated shaped particles. The precipitated BSA consisted mainly of 9.0 μm diameter spherically shaped particles while the micronized protein prepared by jet milling consisted of 4.9 μm sized rounded particles of high uniformity. Microspheres were embedded into a cold-curing resin and cut with a microtome. Subsequent investigation by CLSM revealed major differences of distribution of the polydisperse protein particles inside the microsphere sections depending on the type of BSA that was used. Particles of micronized and precipitated protein were distributed almost throughout the microsphere cross section. The protein distribution had a marked impact on the release kinetics in phosphate buffer. Large protein particles led to a considerably faster release than small ones. By staining the release medium we demonstrated that in all three cases there was a strong correlation between protein release and buffer intrusion. Copyright © 2010 Elsevier B.V. All rights reserved.

  17. Macula densa sensing and signaling mechanisms of renin release. (United States)

    Peti-Peterdi, János; Harris, Raymond C


    Macula densa cells in the distal nephron, according to the classic paradigm, are salt sensors that generate paracrine chemical signals in the juxtaglomerular apparatus to control vital kidney functions, including renal blood flow, glomerular filtration, and renin release. Renin is the rate-limiting step in the activation of the renin-angiotensin system, a key modulator of body fluid homeostasis. Here, we discuss recent advances in understanding macula densa sensing and suggest these cells, in addition to salt, also sense various chemical and metabolic signals in the tubular environment that directly trigger renin release.

  18. Optimization of release locations for small self-stress large stiffness flexure mechanisms

    NARCIS (Netherlands)

    Brouwer, D.M.; Boer, S.E.; Meijaard, J.P.; Aarts, R.G.K.M.


    In overconstrained mechanisms inherent alignment errors cause self-stress. The level of stress can be reduced by inserting flexure releases making the mechanism exactly constrained. The location and orientation of releases can be optimized for a combination of minimum self-stress and maximum stiffne

  19. Insights on Structural Characteristics and Ligand Binding Mechanisms of CDK2

    Directory of Open Access Journals (Sweden)

    Yan Li


    Full Text Available Cyclin-dependent kinase 2 (CDK2 is a crucial regulator of the eukaryotic cell cycle. However it is well established that monomeric CDK2 lacks regulatory activity, which needs to be aroused by its positive regulators, cyclins E and A, or be phosphorylated on the catalytic segment. Interestingly, these activation steps bring some dynamic changes on the 3D-structure of the kinase, especially the activation segment. Until now, in the monomeric CDK2 structure, three binding sites have been reported, including the adenosine triphosphate (ATP binding site (Site I and two non-competitive binding sites (Site II and III. In addition, when the kinase is subjected to the cyclin binding process, the resulting structural changes give rise to a variation of the ATP binding site, thus generating an allosteric binding site (Site IV. All the four sites are demonstrated as being targeted by corresponding inhibitors, as is illustrated by the allosteric binding one which is targeted by inhibitor ANS (fluorophore 8-anilino-1-naphthalene sulfonate. In the present work, the binding mechanisms and their fluctuations during the activation process attract our attention. Therefore, we carry out corresponding studies on the structural characterization of CDK2, which are expected to facilitate the understanding of the molecular mechanisms of kinase proteins. Besides, the binding mechanisms of CDK2 with its relevant inhibitors, as well as the changes of binding mechanisms following conformational variations of CDK2, are summarized and compared. The summary of the conformational characteristics and ligand binding mechanisms of CDK2 in the present work will improve our understanding of the molecular mechanisms regulating the bioactivities of CDK2.

  20. Insights on Structural Characteristics and Ligand Binding Mechanisms of CDK2 (United States)

    Li, Yan; Zhang, Jingxiao; Gao, Weimin; Zhang, Lilei; Pan, Yanqiu; Zhang, Shuwei; Wang, Yonghua


    Cyclin-dependent kinase 2 (CDK2) is a crucial regulator of the eukaryotic cell cycle. However it is well established that monomeric CDK2 lacks regulatory activity, which needs to be aroused by its positive regulators, cyclins E and A, or be phosphorylated on the catalytic segment. Interestingly, these activation steps bring some dynamic changes on the 3D-structure of the kinase, especially the activation segment. Until now, in the monomeric CDK2 structure, three binding sites have been reported, including the adenosine triphosphate (ATP) binding site (Site I) and two non-competitive binding sites (Site II and III). In addition, when the kinase is subjected to the cyclin binding process, the resulting structural changes give rise to a variation of the ATP binding site, thus generating an allosteric binding site (Site IV). All the four sites are demonstrated as being targeted by corresponding inhibitors, as is illustrated by the allosteric binding one which is targeted by inhibitor ANS (fluorophore 8-anilino-1-naphthalene sulfonate). In the present work, the binding mechanisms and their fluctuations during the activation process attract our attention. Therefore, we carry out corresponding studies on the structural characterization of CDK2, which are expected to facilitate the understanding of the molecular mechanisms of kinase proteins. Besides, the binding mechanisms of CDK2 with its relevant inhibitors, as well as the changes of binding mechanisms following conformational variations of CDK2, are summarized and compared. The summary of the conformational characteristics and ligand binding mechanisms of CDK2 in the present work will improve our understanding of the molecular mechanisms regulating the bioactivities of CDK2. PMID:25918937

  1. Investigation of Performances and Mechanism of Fluoride Removal by Fe(Ⅲ)-Loaded Ligand Exchange Cotton Cellulose Adsorbent

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ya-ping; LI Xiu-yan; LIU Lu; CHEN Fu-hua


    Novel adsorbent, Fe( Ⅲ )-loaded ligand exchange cotton cellulose adsorbent [Fe(Ⅲ)LECCA], was used to investigate the adsorption performances and mechanism of fluoride removal from aqueous solutions. The adsorbent was found to adsorb fluoride rapidly and effectively. The fluoride removal was influenced by pH. Adsorption mode followed first-order reaction at different temperature, theapparent adsorption maximal integer coordination ratio of fluoride with Fe (Ⅲ)LECCA was 3: 1. The ligand exchange mechanism of adsorption was elucidated through chemical methods and IR spectral analysis.

  2. Effects of ligand binding on the mechanical stability of protein GB1 studied by steered molecular dynamics simulation. (United States)

    Su, Ji-Guo; Zhao, Shu-Xin; Wang, Xiao-Feng; Li, Chun-Hua; Li, Jing-Yuan


    Regulation of the mechanical properties of proteins plays an important role in many biological processes, and sheds light on the design of biomaterials comprised of protein. At present, strategies to regulate protein mechanical stability focus mainly on direct modulation of the force-bearing region of the protein. Interestingly, the mechanical stability of GB1 can be significantly enhanced by the binding of Fc fragments of human IgG antibody, where the binding site is distant from the force-bearing region of the protein. The mechanism of this long-range allosteric control of protein mechanics is still elusive. In this work, the impact of ligand binding on the mechanical stability of GB1 was investigated using steered molecular dynamics simulation, and a mechanism underlying the enhanced protein mechanical stability is proposed. We found that the external force causes deformation of both force-bearing region and ligand binding site. In other words, there is a long-range coupling between these two regions. The binding of ligand restricts the distortion of the binding site and reduces the deformation of the force-bearing region through a long-range allosteric communication, which thus improves the overall mechanical stability of the protein. The simulation results are very consistent with previous experimental observations. Our studies thus provide atomic-level insights into the mechanical unfolding process of GB1, and explain the impact of ligand binding on the mechanical properties of the protein through long-range allosteric regulation, which should facilitate effective modulation of protein mechanical properties.

  3. Identification of metal species by ESI-MS/MS through release of free metals from the corresponding metal-ligand complexes. (United States)

    Tsednee, Munkhtsetseg; Huang, Yu-Chen; Chen, Yet-Ran; Yeh, Kuo-Chen


    Electrospray ionization-mass spectrometry (ESI-MS) is used to analyze metal species in a variety of samples. Here, we describe an application for identifying metal species by tandem mass spectrometry (ESI-MS/MS) with the release of free metals from the corresponding metal-ligand complexes. The MS/MS data were used to elucidate the possible fragmentation pathways of different metal-deoxymugineic acid (-DMA) and metal-nicotianamine (-NA) complexes and select the product ions with highest abundance that may be useful for quantitative multiple reaction monitoring. This method can be used for identifying different metal-ligand complexes, especially for metal species whose mass spectra peaks are clustered close together. Different metal-DMA/NA complexes were simultaneously identified under different physiological pH conditions with this method. We further demonstrated the application of the technique for different plant samples and with different MS instruments.

  4. Macula Densa Sensing and Signaling Mechanisms of Renin Release


    Peti-Peterdi, János; Raymond C Harris


    Macula densa cells in the distal nephron, according to the classic paradigm, are salt sensors that generate paracrine chemical signals in the juxtaglomerular apparatus to control vital kidney functions, including renal blood flow, glomerular filtration, and renin release. Renin is the rate-limiting step in the activation of the renin-angiotensin system, a key modulator of body fluid homeostasis. Here, we discuss recent advances in understanding macula densa sensing and suggest these cells, in...

  5. Human beta-defensin-2 and -3 enhance pro-inflammatory cytokine expression induced by TLR ligands via ATP-release in a P2X7R dependent manner. (United States)

    Wanke, Daniela; Mauch-Mücke, Katrin; Holler, Ernst; Hehlgans, Thomas


    Our previous results indicate that HBD2 and HBD3 are chemotactic for a broad spectrum of leukocytes in a CCR6- and CCR2-dependent manner. In this study we report that pre-stimulation of primary human macrophages or THP-1 cells with HBD2 or HBD3 results in a synergistic, enhanced expression of pro-inflammatory cytokines and chemokines induced by TLR ligand re-stimulation. Experiments using specific inhibitors of the ATP-gated channel receptor P2X7 or its functional ligand ATP, suggest that the enhanced expression of pro-inflammatory cytokines and chemokines seems to be mediated by P2X7R. Furthermore, our data provide evidence that beta-defensins do not directly interact with P2X7R but rather induce the release of intracellular ATP. Interference with ATP release abrogated the synergistic effect mediated by HBD2 and HBD3 pre-stimulation in THP-1 cells. However, extracellular ATP alone seems not to be sufficient to elicit the enhanced synergistic effect on cytokine and chemokine expression observed by pre-stimulation of primary human macrophages or THP-1 cells with HBD2 or HBD3. Collectively, our findings provide new insights into the molecular mechanisms how HBD2 and HBD3 interact with cells of myeloid origin and demonstrate their immuno-modulating functions during innate immune responses.

  6. Identification of metal species by ESI-MS/MS through release of free metals from the corresponding metal-ligand complexes


    Munkhtsetseg Tsednee; Yu-Chen Huang; Yet-Ran Chen; Kuo-Chen Yeh


    Electrospray ionization-mass spectrometry (ESI-MS) is used to analyze metal species in a variety of samples. Here, we describe an application for identifying metal species by tandem mass spectrometry (ESI-MS/MS) with the release of free metals from the corresponding metal–ligand complexes. The MS/MS data were used to elucidate the possible fragmentation pathways of different metal–deoxymugineic acid (–DMA) and metal–nicotianamine (–NA) complexes and select the product ions with highest abunda...

  7. A Herpesviral induction of RAE-1 NKG2D ligand expression occurs through release of HDAC mediated repression. (United States)

    Greene, Trever T; Tokuyama, Maria; Knudsen, Giselle M; Kunz, Michele; Lin, James; Greninger, Alexander L; DeFilippis, Victor R; DeRisi, Joseph L; Raulet, David H; Coscoy, Laurent


    Natural Killer (NK) cells are essential for control of viral infection and cancer. NK cells express NKG2D, an activating receptor that directly recognizes NKG2D ligands. These are expressed at low level on healthy cells, but are induced by stresses like infection and transformation. The physiological events that drive NKG2D ligand expression during infection are still poorly understood. We observed that the mouse cytomegalovirus encoded protein m18 is necessary and sufficient to drive expression of the RAE-1 family of NKG2D ligands. We demonstrate that RAE-1 is transcriptionally repressed by histone deacetylase inhibitor 3 (HDAC3) in healthy cells, and m18 relieves this repression by directly interacting with Casein Kinase II and preventing it from activating HDAC3. Accordingly, we found that HDAC inhibiting proteins from human herpesviruses induce human NKG2D ligand ULBP-1. Thus our findings indicate that virally mediated HDAC inhibition can act as a signal for the host to activate NK-cell recognition.

  8. On the Denaturation Mechanisms of the Ligand Binding Domain of Thyroid Hormone Receptors

    NARCIS (Netherlands)

    Martínez, Leandro; Telles de Souza, P C; Garcia, Wanius; Batista, Fernanda A H; Portugal, Rodrigo V; Nascimento, Alessandro S; Nakahira, Marcel; Lima, Luis M T R; Polikarpov, Igor; Skaf, Munir S


    The ligand binding domain (LBD) of nuclear hormone receptors adopts a very compact, mostly alpha-helical structure that binds specific ligands with very high affinity. We use circular dichroism spectroscopy and high-temperature molecular dynamics Simulations to investigate unfolding of the LBDs of t

  9. On the denaturation mechanisms of the ligand binding domain of thyroid hormone receptors

    NARCIS (Netherlands)

    Martínez, Leandro; Souza, Paulo C T; Garcia, Wanius; Batista, Fernanda A H; Portugal, Rodrigo V; Nascimento, Alessandro S; Nakahira, Marcel; Lima, Luis M T R; Polikarpov, Igor; Skaf, Munir S


    The ligand binding domain (LBD) of nuclear hormone receptors adopts a very compact, mostly alpha-helical structure that binds specific ligands with very high affinity. We use circular dichroism spectroscopy and high-temperature molecular dynamics simulations to investigate unfolding of the LBDs of t

  10. On the Denaturation Mechanisms of the Ligand Binding Domain of Thyroid Hormone Receptors

    NARCIS (Netherlands)

    Martínez, Leandro; Telles de Souza, P C; Garcia, Wanius; Batista, Fernanda A H; Portugal, Rodrigo V; Nascimento, Alessandro S; Nakahira, Marcel; Lima, Luis M T R; Polikarpov, Igor; Skaf, Munir S


    The ligand binding domain (LBD) of nuclear hormone receptors adopts a very compact, mostly alpha-helical structure that binds specific ligands with very high affinity. We use circular dichroism spectroscopy and high-temperature molecular dynamics Simulations to investigate unfolding of the LBDs of t

  11. Hemolysis is a primary ATP-release mechanism in human erythrocytes (United States)

    Sikora, Jacek; Orlov, Sergei N.; Furuya, Kishio


    The hypothesis that regulated ATP release from red blood cells (RBCs) contributes to nitric oxide-dependent control of local blood flow has sparked much interest in underlying release mechanisms. Several stimuli, including shear stress and hypoxia, have been found to induce significant RBC ATP release attributed to activation of ATP-conducting channels. In the present study, we first evaluated different experimental approaches investigating stimulated RBC ATP release and quantifying hemolysis. We then measured ATP and free hemoglobin in each and every RBC supernatant sample to directly assess the contribution of hemolysis to ATP release. Hypotonic shock, shear stress, and hypoxia, but not cyclic adenosine monophosphate agonists, significantly enhanced ATP release. It tightly correlated, however, with free hemoglobin in RBC supernatants, indicating that lysis was responsible for most, if not all, ATP release. Luminescence ATP imaging combined with simultaneous infrared cell imaging showed that ATP was released exclusively from lysing cells with no contribution from intact cells. In summary, with all stimuli tested, we found no evidence of regulated ATP release from intact RBCs other than by cell lysis. Such a release mechanism might be physiologically relevant in vivo, eg, during exercise and hypoxia where intravascular hemolysis, predominantly of senescent cells, is augmented. PMID:25097178

  12. Notch inhibition by the ligand DELTA-LIKE 3 defines the mechanism of abnormal vertebral segmentation in spondylocostal dysostosis. (United States)

    Chapman, Gavin; Sparrow, Duncan B; Kremmer, Elisabeth; Dunwoodie, Sally L


    Mutations in the DELTA-LIKE 3 (DLL3) gene cause the congenital abnormal vertebral segmentation syndrome, spondylocostal dysostosis (SCD). DLL3 is a divergent member of the DSL family of Notch ligands that does not activate signalling in adjacent cells, but instead inhibits signalling when expressed in the same cell as the Notch receptor. Targeted deletion of Dll3 in the mouse causes a developmental defect in somite segmentation, and consequently vertebral formation is severely disrupted, closely resembling human SCD. In contrast to the canonical Notch signalling pathway, very little is known about the mechanism of cis-inhibition by DSL ligands. Here, we report that Dll3 is not presented on the surface of presomitic mesoderm (PSM) cells in vivo, but instead interacts with Notch1 in the late endocytic compartment. This suggests for the first time a mechanism for Dll3-mediated cis-inhibition of Notch signalling, with Dll3 targeting newly synthesized Notch1 for lysosomal degradation prior to post-translational processing and cell surface presentation of the receptor. An inhibitory role for Dll3 in vivo is further supported by the juxtaposition of Dll3 protein and Notch1 signalling in the PSM. Defining a mechanism for cis-inhibition of Notch signalling by Dll3 not only contributes greatly to our understanding of this ligand's function during the formation of the vertebral column, but also provides a paradigm for understanding how other ligands of Notch cis-inhibit signalling.

  13. A computational study of the protein-ligand interactions in CDK2 inhibitors: using quantum mechanics/molecular mechanics interaction energy as a predictor of the biological activity. (United States)

    Alzate-Morales, Jans H; Contreras, Renato; Soriano, Alejandro; Tuñon, Iñaki; Silla, Estanislao


    We report a combined quantum mechanics/molecular mechanics (QM/MM) study to determine the protein-ligand interaction energy between CDK2 (cyclin-dependent kinase 2) and five inhibitors with the N(2)-substituted 6-cyclohexyl-methoxy-purine scaffold. The computational results in this work show that the QM/MM interaction energy is strongly correlated to the biological activity and can be used as a predictor, at least within a family of substrates. A detailed analysis of the protein-ligand structures obtained from molecular dynamics simulations shows specific interactions within the active site that, in some cases, have not been reported before to our knowledge. The computed interaction energy gauges the strength of protein-ligand interactions. Finally, energy decomposition and multiple regression analyses were performed to check the contribution of the electrostatic and van der Waals energies to the total interaction energy and to show the capabilities of the computational model to identify new potent inhibitors.

  14. Action and mechanism of Fas and Fas ligand in immune escape of gallbladder carcinoma (United States)

    Xu, Li-Ning; Zou, Sheng-Quan; Wang, Jian-Ming


    AIM: To study the role of Fas and Fas ligand (FasL) in biological behaviors of gallbladder carcinoma, and their correlated action and mechanism in tumor escape. METHODS: Streptavidin-biotin-peroxidase immunohisto-chemistry technique was used to study the expression of Fas and FasL protein in 26 gallbladder carcinoma tissues, 18 gallbladder adenoma tissues, 3 gallbladder dysplasia tissues and 20 chronic cholecystitis tissues. Apoptosis of the infiltrating lymphocytes in these tissues was studied by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) method. Expression of both proteins and apoptosis of the tumor infiltrating lymphocytes in cancer tissues of primary foci was compared with clinicopathological features of gallbladder carcinoma. RESULTS: The positive rates of Fas were not significantly different among carcinoma, adenoma, dysplasia and chronic cholecystitis. The positive rate of FasL in carcinoma was significantly higher than that in chronic cholecystitis (χ2 = 4.89, P0.05). Apoptosis of infiltrating lymphocytes was not discovered in adenoma and chronic cholecystitis. CONCLUSION: FasL expressed in gallbladder carcinoma cells permits tumor cells to escape from immune surveillance of organism by inducing apoptosis in infiltrating lymphocytes of carcinoma tissues. Up-regulation of FasL expression plays an important role in invasive depth, histological classification and metastasis of gallbladder carcinoma. PMID:15968727

  15. Reprogramming the mechanism of action of chlorambucil by coupling to a G-quadruplex ligand. (United States)

    Di Antonio, Marco; McLuckie, Keith I E; Balasubramanian, Shankar


    The nitrogen mustard Chlorambucil (Chl) generates covalent adducts with double-helical DNA and inhibits cell proliferation. Among these adducts, interstrand cross-links (ICLs) are the most toxic, as they stall replication by generating DNA double strand breaks (DSBs). Conversely, intrastrand cross-links generated by Chl are efficiently repaired by a dedicated Nucleotide Excision Repair (NER) enzyme. We synthesized a novel cross-linking agent that combines Chl with the G-quadruplex (G4) ligand PDS (PDS-Chl). We demonstrated that PDS-Chl alkylates G4 structures at low μM concentrations, without reactivity toward double- or single-stranded DNA. Since intramolecular G4s arise from a single DNA strand, we reasoned that preferential alkylation of such structures might prevent the generation of ICLs, while favoring intrastrand cross-links. We observed that PDS-Chl selectively impairs growth in cells genetically deficient in NER, but did not show any sensitivity to the repair gene BRCA2, involved in double-stranded break repair. Our findings suggest that G4 targeting of this clinically important alkylating agent alters the overall mechanism of action. These insights may inspire new opportunities for intervention in diseases specifically characterized by genetic impairment of NER, such as skin and testicular cancers.

  16. Iron complexes of tetramine ligands catalyse allylic hydroxyamination via a nitroso–ene mechanism

    Directory of Open Access Journals (Sweden)

    David Porter


    Full Text Available Iron(II complexes of the tetradentate amines tris(2-pyridylmethylamine (TPA and N,N′-bis(2-pyridylmethyl-N,N′-dimethylethane-1,2-diamine (BPMEN are established catalysts of C–O bond formation, oxidising hydrocarbon substrates via hydroxylation, epoxidation and dihydroxylation pathways. Herein we report the capacity of these catalysts to promote C–N bond formation, via allylic amination of alkenes. The combination of N-Boc-hydroxylamine with either FeTPA (1 mol % or FeBPMEN (10 mol % converts cyclohexene to the allylic hydroxylamine (tert-butyl cyclohex-2-en-1-yl(hydroxycarbamate in moderate yields. Spectroscopic studies and trapping experiments suggest the reaction proceeds via a nitroso–ene mechanism, with involvement of a free N-Boc-nitroso intermediate. Asymmetric induction is not observed using the chiral tetramine ligand (+-(2R,2′R-1,1′-bis(2-pyridylmethyl-2,2′-bipyrrolidine ((R,R′-PDP.

  17. Modeling comodulation masking release using an equalization cancellation mechanism

    DEFF Research Database (Denmark)

    Piechowiak, Tobias; Ewert, Stephan; Dau, Torsten

    of the study investigates the relation between CMR and envelope-based binaural masking level differences (BMLD), using narrowband noise maskers and classical across-channel configurations (like N0Spi, N0Sm). In the second part, a model is presented that explicitly simulates CMR whereby the EC mechanism...

  18. Modeling comodulation masking release using an equalization cancellation mechanism

    DEFF Research Database (Denmark)

    Piechowiak, Tobias; Ewert, Stephan; Dau, Torsten

    of the study investigates the relation between CMR and envelope-based binaural masking level differences (BMLD), using narrowband noise maskers and classical across-channel configurations (like N0Spi, N0Sm). In the second part, a model is presented that explicitly simulates CMR whereby the EC mechanism...

  19. Complexation- and ligand-induced metal release from 316L particles: importance of particle size and crystallographic structure. (United States)

    Hedberg, Yolanda; Hedberg, Jonas; Liu, Yi; Wallinder, Inger Odnevall


    Iron, chromium, nickel, and manganese released from gas-atomized AISI 316L stainless steel powders (sized 316L particles immersed in ALF. Iron was mainly released, while manganese was preferentially released as a consequence of the reduction of manganese oxide on the surface. These processes resulted in highly complexing media in a partial oxidation of trivalent chromium to hexavalent chromium on the surface. The extent of metal release was partially controlled by surface properties (e.g., availability of elements on the surface and structure of the outermost surface) and partially by the complexation capacity of the different metals with the complexing agents of the different media. In general, compared to the coarse powder (<45 μm), the fine (<4 μm) powder displayed significantly higher released amounts of metals per surface area, increased with increased solution complexation capacity, while less amounts of metals were released into non-complexing solutions. Due to the ferritic structure of lower solubility for nickel of the fine powder, more nickel was released into all solutions compared with the coarser powder.

  20. New insights into the mechanisms whereby low molecular weight CCR5 ligands inhibit HIV-1 infection. (United States)

    Garcia-Perez, Javier; Rueda, Patricia; Staropoli, Isabelle; Kellenberger, Esther; Alcami, Jose; Arenzana-Seisdedos, Fernando; Lagane, Bernard


    CC chemokine receptor 5 (CCR5) is a G-protein-coupled receptor for the chemokines CCL3, -4, and -5 and a coreceptor for entry of R5-tropic strains of human immunodeficiency virus type 1 (HIV-1) into CD4(+) T-cells. We investigated the mechanisms whereby nonpeptidic, low molecular weight CCR5 ligands block HIV-1 entry and infection. Displacement binding assays and dissociation kinetics demonstrated that two of these molecules, i.e. TAK779 and maraviroc (MVC), inhibit CCL3 and the HIV-1 envelope glycoprotein gp120 binding to CCR5 by a noncompetitive and allosteric mechanism, supporting the view that they bind to regions of CCR5 distinct from the gp120- and CCL3-binding sites. We observed that TAK779 and MVC are full and weak inverse agonists for CCR5, respectively, indicating that they stabilize distinct CCR5 conformations with impaired abilities to activate G-proteins. Dissociation of [(125)I]CCL3 from CCR5 was accelerated by TAK779, to a lesser extent by MVC, and by GTP analogs, suggesting that inverse agonism contributes to allosteric inhibition of the chemokine binding to CCR5. TAK779 and MVC also promote dissociation of [(35)S]gp120 from CCR5 with an efficiency that correlates with their ability to act as inverse agonists. Displacement experiments revealed that affinities of MVC and TAK779 for the [(35)S]gp120-binding receptors are in the same range (IC(50) ∼6.4 versus 22 nm), although we found that MVC is 100-fold more potent than TAK779 for inhibiting HIV infection. This suggests that allosteric CCR5 inhibitors not only act by blocking gp120 binding but also alter distinct steps of CCR5 usage in the course of HIV infection.

  1. Examination of Mechanisms Responsible for Organic Dust-related Diseases: Mediator Release induced by Microorgansims. A review

    DEFF Research Database (Denmark)

    Norn, Svend; Clementsen, Paul; Kristensen, K.S.;


    Farmakologi, org. dust-related diseases, bacteria, pathogenic mechanisms, mediator release, entoxins - fungal spores......Farmakologi, org. dust-related diseases, bacteria, pathogenic mechanisms, mediator release, entoxins - fungal spores...

  2. A Single Mutation in a Tunnel to the Active Site Changes the Mechanism and Kinetics of Product Release in Haloalkane Dehalogenase LinB* (United States)

    Biedermannová, Lada; Prokop, Zbyněk; Gora, Artur; Chovancová, Eva; Kovács, Mihály; Damborský, Jiří; Wade, Rebecca C.


    Many enzymes have buried active sites. The properties of the tunnels connecting the active site with bulk solvent affect ligand binding and unbinding and also the catalytic properties. Here, we investigate ligand passage in the haloalkane dehalogenase enzyme LinB and the effect of replacing leucine by a bulky tryptophan at a tunnel-lining position. Transient kinetic experiments show that the mutation significantly slows down the rate of product release. Moreover, the mechanism of bromide ion release is changed from a one-step process in the wild type enzyme to a two-step process in the mutant. The rate constant of bromide ion release corresponds to the overall steady-state turnover rate constant, suggesting that product release became the rate-limiting step of catalysis in the mutant. We explain the experimental findings by investigating the molecular details of the process computationally. Analysis of trajectories from molecular dynamics simulations with a tunnel detection software reveals differences in the tunnels available for ligand egress. Corresponding differences are seen in simulations of product egress using a specialized enhanced sampling technique. The differences in the free energy barriers for egress of a bromide ion obtained using potential of mean force calculations are in good agreement with the differences in rates obtained from the transient kinetic experiments. Interactions of the bromide ion with the introduced tryptophan are shown to affect the free energy barrier for its passage. The study demonstrates how the mechanism of an enzymatic catalytic cycle and reaction kinetics can be engineered by modification of protein tunnels. PMID:22745119

  3. Physicochemical characterization of liposomes after ultrasound exposure - mechanisms of drug release

    DEFF Research Database (Denmark)

    Evjen, Tove J; Hupfeld, Stefan; Barnert, Sabine


    Ultrasound is investigated as a novel drug delivery tool within cancer therapy. Non-thermal ultrasound treatment of solid tumours post i.v.-injection of drug-carrying liposomes may induce local drug release from the carrier followed by enhanced intracellular drug uptake. Recently, ultrasound......-mediated drug release of liposomes (sonosensitivity) was shown to strongly depend on liposome membrane composition. In the current study the ultrasound-mediated drug release mechanism of liposomes was investigated. The results showed that differences in ultrasound drug release kinetics obtained for different...... liposomal compositions were caused by distinctive release mechanisms of the carriers. Two types of liposomes composed of 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) and hydrogenated soy L-α-phosphatidylcholine (HSPC) as main lipids, respectively, were recently shown to vary in sonosensitivity...

  4. Charting the mechanism and reactivity of zirconium oxalate with hydroxamate ligands using density functional theory: implications in new chelate design. (United States)

    Holland, Jason P; Vasdev, Neil


    The reaction of [(89)Zr(C2O4)4](4-) with the tris-hydroxamate ligand desferrioxamine B (DFO) provides the basis of radiolabelling biological vectors such as antibodies and proteins with the radionuclide (89)Zr for positron emission tomography imaging. In this work, density functional theory methods were used to investigate the mechanism of reaction from [Zr(C2O4)4](4-) to Zr(MeAHA)4 by ligand substitution with N-methyl acetohydroxamate (MeAHA). Calculations were performed under simulated basic and acidic conditions. Ligand substitution under basic conditions was found to be thermodynamically feasible with an overall calculated change in solvation free energy, ΔGsol = -97 kJ mol(-1) using the B3LYP/DGDZVP methodology and a water continuum solvation model. In contrast, an acid-mediated mechanism of ligand substitution was found to be thermodynamically non-feasible. Molecular orbital analysis provides a rationale for the difference in thermodynamic stability between [Zr(C2O4)4](4-) and Zr(MeAHA)4. Overall, the DFT calculations are consistent with observed experimental (89)Zr-radiolabelling reactions and suggest that computational methods may prove useful in designing novel chelates for increasing the thermodynamic and kinetic stability of (89)Zr-complexes in vivo.

  5. Tonic control of kisspeptin release in prepubertal monkeys: implications to the mechanism of puberty onset. (United States)

    Kurian, Joseph R; Keen, Kim L; Guerriero, Kathryn A; Terasawa, Ei


    Previously we have shown that a reduction in γ-amino butyric acid (GABA) inhibition is critical for the mechanism initiating puberty onset because chronic infusion of the GABA(A) receptor antagonist, bicuculline, significantly increased GnRH release and accelerated the timing of menarche and first ovulation in female rhesus monkeys. Because previous studies in our laboratory indicate that in prepubertal female monkeys, kisspeptin release in the medial basal hypothalamus is low, whereas kisspeptin-10 can stimulate GnRH release, we hypothesized that a low level of kisspeptin release prior to puberty onset is due to tonic GABA inhibition. To test this hypothesis we examined the effects of bicuculline infusion on kisspeptin release using a microdialysis method. We found that bicuculline at 1 μM dramatically stimulates kisspeptin release in the medial basal hypothalamus of prepubertal monkeys but had little effect on kisspeptin release in midpubertal monkeys. We further examined whether bicuculline-induced GnRH release is blocked by the presence of the kisspeptin antagonist, peptide 234. We found that inhibition of kisspeptin signaling blocked the bicuculline-induced stimulation of GnRH release, suggesting that kisspeptin neurons may relay inhibitory GABA signals to GnRH neurons. This implies that a reduction in tonic GABA inhibition of GnRH release is, at least in part, mediated through kisspeptin neurons.

  6. Gonadotropin-releasing hormone stimulates prolactin release from lactotrophs in photoperiodic species through a gonadotropin-independent mechanism. (United States)

    Henderson, Helen L; Hodson, David J; Gregory, Susan J; Townsend, Julie; Tortonese, Domingo J


    Previous studies have provided evidence for a paracrine interaction between pituitary gonadotrophs and lactotrophs. Here, we show that GnRH is able to stimulate prolactin (PRL) release in ovine primary pituitary cultures. This effect was observed during the breeding season (BS), but not during the nonbreeding season (NBS), and was abolished by the application of bromocriptine, a specific dopamine agonist. Interestingly, GnRH gained the ability to stimulate PRL release in NBS cultures following treatment with bromocriptine. In contrast, thyrotropin-releasing hormone, a potent secretagogue of PRL, stimulated PRL release during both the BS and NBS and significantly enhanced the PRL response to GnRH during the BS. These results provide evidence for a photoperiodically modulated functional interaction between the GnRH/gonadotropic and prolactin axes in the pituitary gland of a short day breeder. Moreover, the stimulation of PRL release by GnRH was shown not to be mediated by the gonadotropins, since immunocytochemical, Western blotting, and PCR studies failed to detect pituitary LH or FSH receptor protein and mRNA expressions. Similarly, no gonadotropin receptor expression was observed in the pituitary gland of the horse, a long day breeder. In contrast, S100 protein, a marker of folliculostellate cells, which are known to participate in paracrine mechanisms within this tissue, was detected throughout the pituitaries of both these seasonal breeders. Therefore, an alternative gonadotroph secretory product, a direct effect of GnRH on the lactotroph, or another cell type, such as the folliculostellate cell, may be involved in the PRL response to GnRH in these species.

  7. Internalization mechanisms of the epidermal growth factor receptor after activation with different ligands.

    Directory of Open Access Journals (Sweden)

    Lasse Henriksen

    Full Text Available The epidermal growth factor receptor (EGFR regulates normal growth and differentiation, but dysregulation of the receptor or one of the EGFR ligands is involved in the pathogenesis of many cancers. There are eight ligands for EGFR, however most of the research into trafficking of the receptor after ligand activation focuses on the effect of epidermal growth factor (EGF and transforming growth factor-α (TGF-α. For a long time it was believed that clathrin-mediated endocytosis was the major pathway for internalization of the receptor, but recent work suggests that different pathways exist. Here we show that clathrin ablation completely inhibits internalization of EGF- and TGF-α-stimulated receptor, however the inhibition of receptor internalization in cells treated with heparin-binding EGF-like growth factor (HB-EGF or betacellulin (BTC was only partial. In contrast, clathrin knockdown fully inhibits EGFR degradation after all ligands tested. Furthermore, inhibition of dynamin function blocked EGFR internalization after stimulation with all ligands. Knocking out a number of clathrin-independent dynamin-dependent pathways of internalization had no effect on the ligand-induced endocytosis of the EGFR. We suggest that EGF and TGF-α lead to EGFR endocytosis mainly via the clathrin-mediated pathway. Furthermore, we suggest that HB-EGF and BTC also lead to EGFR endocytosis via a clathrin-mediated pathway, but can additionally use an unidentified internalization pathway or better recruit the small amount of clathrin remaining after clathrin knockdown.

  8. A fast and powerful release mechanism based on pulse heating of shape memory wires (United States)

    Malka, Yoav; Shilo, Doron


    This article presents a novel actuator and a new concept for a release mechanism that are especially useful in applications that require fast motion of large masses over long distances. The actuator is based on ultra-fast pulse heating of NiTi wires, which provide a unique combination of large work per volume, short response time and enhanced energy efficiency. The release mechanism utilizes the fast and powerful actuator to form conditions in which the latch (safety pin) moves faster than the deployed device. As a result, the contact between these two masses is disconnected and the resulting friction forces are decreased to approximately zero. The actuator and release mechanism address the two major drawbacks of conventional shape memory alloy (SMA) actuators: slow actuation time and low energy efficiency. Using a dedicated setup, the experimental results validate the disconnection between the masses and map the effects of several variables on the performance of the actuator and release mechanism. In particular, we map the energetic efficiency and find the optimal operating conditions for a successful release using a minimal amount of input energy. At the optimal conditions, the actuator response time and the consumed input energy are smaller by an order of magnitude with respect to performances of previous SMA-based release mechanisms with comparable requirements.

  9. Study of catalase adsorption on two mixed-mode ligands and the mechanism involved therein. (United States)

    Shiva Ranjini, S; Vijayalakshmi, M A


    Mixed-mode chromatography sorbents n-hexylamine HyperCel™ (HEA) and phenylpropylamine HyperCel™ (PPA) were evaluated for the study of adsorption of catalase from two different sources. Various parameters such as buffer composition, ionic strength and pH were investigated to study the mechanism of interaction of commercially available pre-purified catalase from Bovine liver, purified catalase from black gram (Vigna mungo) and crude extract of black gram containing catalase with these mixed-mode ligands. A simple and economical screening protocol for identifying optimal buffer conditions for adsorption and desorption of catalase was established with micro volumes of the sorbent in batch mode. With HEA HyperCel, it was observed that pre-purified catalase from both bovine liver and black gram was completely retained at pH 7.0, irrespective of the presence or absence of NaCl in the adsorption buffer, whereas the catalase from crude extract of black gram was completely retained only in the presence of 0.2 M salt in the adsorption buffer. The elution of catalase from both the sources was accomplished by lowering the pH to 4.5 in absence of salt. In case of PPA HyperCel, catalase from both the sources was very strongly adsorbed under different buffer conditions studied, and elution did not yield a significant catalase activity. From the screening experiments, it could be concluded that the interaction of catalase with HEA HyperCel could be dominated by hydrophobic forces with minor contributions from ionic interaction and with PPA HyperCel, it could be a combination of different non-covalent interactions acting on different loci on the surface of the protein.

  10. Small Molecule Inhibition of the TNF Family Cytokine CD40 Ligand Through a Subunit Fracture Mechanism

    Energy Technology Data Exchange (ETDEWEB)

    L Silvian; J Friedman; K Strauch; T Cachero; E Day; F Qian; B Cunningham; A Fung; L Sun; et al.


    BIO8898 is one of several synthetic organic molecules that have recently been reported to inhibit receptor binding and function of the constitutively trimeric tumor necrosis factor (TNF) family cytokine CD40 ligand (CD40L, aka CD154). Small molecule inhibitors of protein-protein interfaces are relatively rare, and their discovery is often very challenging. Therefore, to understand how BIO8898 achieves this feat, we characterized its mechanism of action using biochemical assays and X-ray crystallography. BIO8898 inhibited soluble CD40L binding to CD40-Ig with a potency of IC{sub 50} = 25 {mu}M and inhibited CD40L-dependent apoptosis in a cellular assay. A co-crystal structure of BIO8898 with CD40L revealed that one inhibitor molecule binds per protein trimer. Surprisingly, the compound binds not at the surface of the protein but by intercalating deeply between two subunits of the homotrimeric cytokine, disrupting a constitutive protein-protein interface and breaking the protein's 3-fold symmetry. The compound forms several hydrogen bonds with the protein, within an otherwise hydrophobic binding pocket. In addition to the translational splitting of the trimer, binding of BIO8898 was accompanied by additional local and longer-range conformational perturbations of the protein, both in the core and in a surface loop. Binding of BIO8898 is reversible, and the resulting complex is stable and does not lead to detectable dissociation of the protein trimer. Our results suggest that a set of core aromatic residues that are conserved across a subset of TNF family cytokines might represent a generic hot-spot for the induced-fit binding of trimer-disrupting small molecules.

  11. Multifunctionality and mechanism of ligand binding in a mosquito antiinflammatory protein

    Energy Technology Data Exchange (ETDEWEB)

    Calvo, Eric; Mans, Ben J.; Ribeiro, José M.C.; Andersen, John F.; (NIH)


    The mosquito D7 salivary proteins are encoded by a multigene family related to the arthropod odorant-binding protein (OBP) superfamily. Forms having either one or two OBP domains are found in mosquito saliva. Four single-domain and one two-domain D7 proteins from Anopheles gambiae and Aedes aegypti (AeD7), respectively, were shown to bind biogenic amines with high affinity and with a stoichiometry of one ligand per protein molecule. Sequence comparisons indicated that only the C-terminal domain of AeD7 is homologous to the single-domain proteins from A. gambiae, suggesting that the N-terminal domain may bind a different class of ligands. Here, we describe the 3D structure of AeD7 and examine the ligand-binding characteristics of the N- and C-terminal domains. Isothermal titration calorimetry and ligand complex crystal structures show that the N-terminal domain binds cysteinyl leukotrienes (cysLTs) with high affinities (50-60 nM) whereas the C-terminal domain binds biogenic amines. The lipid chain of the cysLT binds in a hydrophobic pocket of the N-terminal domain, whereas binding of norepinephrine leads to an ordering of the C-terminal portion of the C-terminal domain into an alpha-helix that, along with rotations of Arg-176 and Glu-268 side chains, acts to bury the bound ligand.

  12. Mechanism of selective VEGF-A binding by neuropilin-1 reveals a basis for specific ligand inhibition.

    Directory of Open Access Journals (Sweden)

    Matthew W Parker

    Full Text Available Neuropilin (Nrp receptors function as essential cell surface receptors for the Vascular Endothelial Growth Factor (VEGF family of proangiogenic cytokines and the semaphorin 3 (Sema3 family of axon guidance molecules. There are two Nrp homologues, Nrp1 and Nrp2, which bind to both overlapping and distinct members of the VEGF and Sema3 family of molecules. Nrp1 specifically binds the VEGF-A(164/5 isoform, which is essential for developmental angiogenesis. We demonstrate that VEGF-A specific binding is governed by Nrp1 residues in the b1 coagulation factor domain surrounding the invariant Nrp C-terminal arginine binding pocket. Further, we show that Sema3F does not display the Nrp-specific binding to the b1 domain seen with VEGF-A. Engineered soluble Nrp receptor fragments that selectively sequester ligands from the active signaling complex are an attractive modality for selectively blocking the angiogenic and chemorepulsive functions of Nrp ligands. Utilizing the information on Nrp ligand binding specificity, we demonstrate Nrp constructs that specifically sequester Sema3 in the presence of VEGF-A. This establishes that unique mechanisms are used by Nrp receptors to mediate specific ligand binding and that these differences can be exploited to engineer soluble Nrp receptors with specificity for Sema3.

  13. Soluble ligands for the NKG2D receptor are released during endometriosis and correlate with disease severity.

    Directory of Open Access Journals (Sweden)

    Iñaki González-Foruria

    Full Text Available Endometriosis is a benign gynaecological disease. Abundant bulk of evidence suggests that patients with endometriosis have an immunity dysfunction that enables ectopic endometrial cells to implant and proliferate. Previous studies show that natural killer cells have a pivotal role in the immune control of endometriosis.This is a prospective laboratory study conducted in a tertiary-care university hospital between January 2011 and April 2013. We investigated non-pregnant, younger than 42-year-old patients (n= 202 during surgery for benign gynaecological conditions. After complete surgical exploration of the abdominopelvic cavity, 121 women with histologically proven endometriosis and 81 endometriosis-free controls women were enrolled. Patients with endometriosis were classified according to a surgical classification in three different types of endometriosis: superficial peritoneal endometriosis (SUP, ovarian endometrioma (OMA and deep infiltrating endometriosis (DIE. Peritoneal fluid samples were obtained from all study participants during the surgery in order to detect soluble NKG2D ligands (MICA, MICB and ULBP-2. When samples with undetectable peritoneal fluid levels of MICA, MICB and ULBP-2 were excluded, MICA ratio levels were significantly higher in endometriosis patients than in controls (median, 1.1 pg/mg; range, 0.1-143.5 versus median, 0.6 pg/mg; range, 0.1-3.5; p=0.003. In a similar manner peritoneal fluid MICB levels were also increased in endometriosis-affected patients compared with disease-free women (median, 4.6 pg/mg; range, 1.2-4702 versus median, 3.4 pg/mg; range, 0.7-20.1; p=0.001. According to the surgical classification, peritoneal fluid soluble MICA, MICB and ULBP-2 ratio levels were significantly increased in DIE as compared to controls (p=0.015, p=0.003 and p=0.045 respectively. MICA ratio levels also correlated with dysmenorrhea (r=0.232; p=0.029, total rAFS score (r=0.221; p=0.031 and adhesions rAFS score (r=0.221; p=0

  14. In Pursuit of Fully Flexible Protein-Ligand Docking: Modeling the Bilateral Mechanism of Binding. (United States)

    Henzler, Angela M; Rarey, Matthias


    Modern structure-based drug design aims at accounting for the intrinsic flexibility of therapeutic relevant targets. Over the last few years a considerable amount of docking approaches that encounter this challenging problem has emerged. Here we provide the readership with an overview of established methods for fully flexible protein-ligand docking and current developments in the field. All methods are based on one of two fundamental models which describe the dynamic behavior of proteins upon ligand binding. Methods for ensemble docking (ED) model the protein conformational change before the ligand is placed, whereas induced-fit docking (IFD) optimizes the protein structure afterwards. A third category of docking approaches is formed by recent approaches that follow both concepts. This categorization allows to comprehensively discover strengths and weaknesses of the individual processes and to extract information for their applicability in real world docking scenarios.

  15. Dielectric study on membrane adsorption and release:Relaxation mechanism and diffusion dynamics

    Institute of Scientific and Technical Information of China (English)

    LI YuHong; ZHAO KongShuang; HAN Ying


    Dielectric monitoring of the adsorption or release process of salicylic acid (SA) by chitosan membrane shows that the dielectric spectra of the chitosan membrane/SA solution systems change regularly in the adsorption or release process. By analyzing the regularity, a new mechanism for the relaxations is proposed. The concentration polarization layer (CPL) caused by SA adsorption or release is confirmed to be essential for the dielectric relaxations. The changes of the spectra with time are explained by account of the relationship between CPL properties and dielectric strength. Based on this relaxation mechanism, a theoretical method can be established to calculate dynamical parameters of inner structure of the adsorption or release systems from their dielectric spectra. Therefore, dielectric spec-troscopy is demonstrated to be a promising method for estimating interfacial distribution of ionic sub-stances and their binding to membrane in a non-invasive way.

  16. Dielectric study on membrane adsorption and release: Relaxation mechanism and diffusion dynamics

    Institute of Scientific and Technical Information of China (English)


    Dielectric monitoring of the adsorption or release process of salicylic acid (SA) by chitosan membrane shows that the dielectric spectra of the chitosan membrane/ SA solution systems change regularly in the adsorption or release process. By analyzing the regularity, a new mechanism for the relaxations is proposed. The concentration polarization layer (CPL) caused by SA adsorption or release is confirmed to be essential for the dielectric relaxations. The changes of the spectra with time are explained by account of the relationship between CPL properties and dielectric strength. Based on this relaxation mechanism, a theoretical method can be established to calculate dynamical parameters of inner structure of the adsorption or release systems from their dielectric spectra. Therefore, dielectric spec- troscopy is demonstrated to be a promising method for estimating interfacial distribution of ionic sub- stances and their binding to membrane in a non-invasive way.

  17. The stress response to surgery: release mechanisms and the modifying effect of pain relief

    DEFF Research Database (Denmark)

    Kehlet, H


    This short review updates information on the release mechanisms of the systemic response to surgical injury and the modifying effect of pain relief. Initiation of the response is primarily due to afferent nerve impulses combined with release of humoral substances (such as prostaglandins, kinins...... in releasing the classical endocrine catabolic response, while humoral factors are important for the hyperthermic response, changes in coagulation and fibrinolysis immunofunction, and capillary permeability. The modifying effect of pain relief on the surgical stress response is dependent upon the technique...... on the stress response. In summary, pain alleviation itself may not necessarily lead to an important modification of the stress response, and a combined approach with inhibition of the neural and humoral release mechanisms is necessary for a pronounced inhibition or prevention of the response to surgical injury....

  18. Mechanical stretch induces MMP-2 release and activation in lung endothelium: role of EMMPRIN. (United States)

    Haseneen, Nadia A; Vaday, Gayle G; Zucker, Stanley; Foda, Hussein D


    High-volume mechanical ventilation leads to ventilator-induced lung injury. This type of lung injury is accompanied by an increased release and activation of matrix metalloproteinases (MMPs). To investigate the mechanism leading to the increased MMP release, we systematically studied the effect of mechanical stretch on human microvascular endothelial cells isolated from the lung. We exposed cells grown on collagen 1 BioFlex plates to sinusoidal cyclic stretch at 0.5 Hz using the Flexercell system with 17-18% elongation of cells. After 4 days of cell stretching, conditioned media and cell lysate were collected and analyzed by gelatin, casein, and reverse zymograms as well as Western blotting. RT-PCR of mRNA extracted from stretched cells was performed. Our results show that 1) cyclic stretch led to increased release and activation of MMP-2 and MMP-1; 2) the activation of MMP-2 was accompanied by an increase in membrane type-1 MMP (MT1-MMP) and inhibited by a hydroxamic acid-derived inhibitor of MMPs (Prinomastat, AG3340); and 3) the MMP-2 release and activation were preceded by an increase in production of extracellular MMP inducer (EMMPRIN). These results suggest that cyclic mechanical stretch leads to MMP-2 activation through an MT1-MMP mechanism. EMMPRIN may play an important role in the release and activation of MMPs during lung injury.

  19. Polymer excipients enable sustained drug release in low pH from mechanically strong inorganic geopolymers. (United States)

    Jämstorp, Erik; Yarra, Tejaswi; Cai, Bing; Engqvist, Håkan; Bredenberg, Susanne; Strømme, Maria


    Improving acid resistance, while maintaining the excellent mechanical stability is crucial in the development of a sustained and safe oral geopolymer dosage form for highly potent opioids. In the present work, commercially available Methacrylic acid-ethyl acrylate copolymer, Polyethylene-glycol (PEG) and Alginate polymer excipients were included in dissolved or powder form in geopolymer pellets to improve the release properties of Zolpidem, herein acting as a model drug for the highly potent opioid Fentanyl. Scanning electron microscopy, compression strength tests and drug release experiments, in gastric pH 1 and intestinal pH 6.8 conditions, were performed. The polymer excipients, with an exception for PEG, reduced the drug release rate in pH 1 due to their ability to keep the pellets in shape, in combination with the introduction of an insoluble excipient, and thereby maintain a barrier towards drug diffusion and release. Neither geopolymer compression strength nor the release in pH 6.8 was considerably impaired by the incorporation of the polymer excipients. The geopolymer/polymer composites combine high mechanical strength and good release properties under both gastric and intestinal pH conditions, and are therefore promising oral dosage forms for sustained release of highly potent opioids.

  20. Kinetics, Ca2+ dependence, and biophysical properties of integrin-mediated mechanical modulation of transmitter release from frog motor nerve terminals (United States)

    Chen, B. M.; Grinnell, A. D.


    Neurotransmitter release from frog motor nerve terminals is strongly modulated by change in muscle length. Over the physiological range, there is an approximately 10% increase in spontaneous and evoked release per 1% muscle stretch. Because many muscle fibers do not receive suprathreshold synaptic inputs at rest length, this stretch-induced enhancement of release constitutes a strong peripheral amplifier of the spinal stretch reflex. The stretch modulation of release is inhibited by peptides that block integrin binding of natural ligands. The modulation varies linearly with length, with a delay of no more than approximately 1-2 msec and is maintained constant at the new length. Moreover, the stretch modulation persists in a zero Ca2+ Ringer and, hence, is not dependent on Ca2+ influx through stretch activated channels. Eliminating transmembrane Ca2+ gradients and buffering intraterminal Ca2+ to approximately normal resting levels does not eliminate the modulation, suggesting that it is not the result of release of Ca2+ from internal stores. Finally, changes in temperature have no detectable effect on the kinetics of stretch-induced changes in endplate potential (EPP) amplitude or miniature EPP (mEPP) frequency. We conclude, therefore, that stretch does not act via second messenger pathways or a chemical modification of molecules involved in the release pathway. Instead, there is direct mechanical modulation of release. We postulate that tension on integrins in the presynaptic membrane is transduced mechanically into changes in the position or conformation of one or more molecules involved in neurotransmitter release, altering sensitivity to Ca2+ or the equilibrium for a critical reaction leading to vesicle fusion.

  1. Stabilization of coordinatively unsaturated Ir4 clusters with bulky ligands: a comparative study of chemical and mechanical effects. (United States)

    Okrut, Alexander; Gazit, Oz; de Silva, Namal; Nichiporuk, Rita; Solovyov, Andrew; Katz, Alexander


    The synthesis and characterization of new cluster compounds represented by the series Ir(4)(CO)(12-x)L(x) (L = tert-butyl-calix[4]-arene(OPr)(3)(OCH(2)PPh(2)); x = 2 and 3) is reported using ESI mass spectrometry, NMR spectroscopy, IR spectroscopy and single-crystal X-ray diffraction. Thermally driven decarbonylation of the cluster compound series represented by x = 1-3 according to the formula above is followed via FTIR and NMR spectroscopies, and dynamic light scattering in toluene solution. The propensity of these clusters to decarbonylate in solution is shown to be directly correlated with number density of adsorbed calixarene phosphine ligands and controlled via Pauli repulsion between metal d and CO 5σ orbitals. The tendency for cluster aggregation unintuitively follows a trend that is exactly opposite to the cluster's propensity to decarbonylate. No cluster aggregation is observed for clusters consisting of x = 3, even after extensive decarbonylation via loss of all bridging CO ligands and coordinative unsaturation. Some of the CO lost during thermal treatment via decarbonylation can be rebound to the coordinatively unsaturated cluster consisting of x = 3. In contrast, the clusters consisting of x = 1 and x = 2 both aggregate into large nanoparticles when treated under identical conditions. Clusters in which the calixarene phosphine ligand is replaced with a sterically less demanding PPh(2)Me ligand 6 lead to significantly less coordinative unsaturation upon thermal treatment. Altogether, these data support a mechanical model of accessibility in coordinatively unsaturated metal clusters in solution, which hinges on having at least three sterically bulky organic ligands per Ir(4) core.

  2. Action and mechanism of Fas and Fas ligand in immune escape of gallbladder carcinoma

    Institute of Scientific and Technical Information of China (English)

    Li-Ning Xu; Sheng-Quan Zou; Jian-Ming Wang


    AIM: To study the role of Fas and Fas ligand (FasL) in biological behaviors of gallbladder carcinoma, and their correlated action and mechanism in tumor escape.METHODS: Streptavidin-biotin-peroxidase immunohistochemistry technique was used to study the expression of Fas and FasL protein in 26 gallbladder carcinoma tissues,18 gallbladder adenoma tissues, 3 gallbladder dysplasia tissues and 20 chronic cholecystitis tissues. Apoptosis of the infiltrating lymphocytes in these tissues was studied by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) method. Expression of both proteins and apoptosis of the tumor infiltrating lymphocytes in cancer tissues of primary foci was compared with clinicopathological features of gallbladder carcinoma.RESULTS: The positive rates of Fas were not significantly different among carcinoma, adenoma, dysplasia and chronic cholecystitis. The positive rate of FasL in carcinoma was significantly higher than that in chronic cholecystitis (x2 = 4.89, P<0.05). The apoptotic index (AI) in carcinoma was significantly higher than that in adenoma (t'= 4.19, P<0.01) and chronic cholecystitis (t'= 8.06, P<0.01). The AI was significantly lower in well-differentiated carcinoma and Nevin Ⅰ-Ⅲ carcinoma than that in poorly-differentiated carcinoma (t'= 2.63, P<0.05) and Nevin Ⅳ-Ⅴ carcinoma(t'= 3.33, P<0.01). The confidence interval (CI) ofinfiltrating lymphocytes in adenoma, chronic cholecystitis, well-differentiated carcinoma and Nevin Ⅰ-Ⅲ carcinoma wasvery significantly lower than that in carcinoma (t' = 6.99,P<0.01), adenoma (t' = 3.66, P<0.01), poorly-differentiated carcinoma (t' = 5.31, P<0.01) and Nevin Ⅳ-Ⅴ carcinoma(t' = 3.76, P<0.01), respectively. The CI of apoptosis of infiltrating lymphocytes in well-differentiated carcinoma was significantly lower than that in poorly-differentiated carcinoma (t = 2.52, P<0.05), and was not significantly lower in Nevin Ⅰ-Ⅲ carcinoma than

  3. Molecular Dynamics Simulations Reveal the Mechanisms of Allosteric Activation of Hsp90 by Designed Ligands. (United States)

    Vettoretti, Gerolamo; Moroni, Elisabetta; Sattin, Sara; Tao, Jiahui; Agard, David A; Bernardi, Anna; Colombo, Giorgio


    Controlling biochemical pathways through chemically designed modulators may provide novel opportunities to develop therapeutic drugs and chemical tools. The underlying challenge is to design new molecular entities able to act as allosteric chemical switches that selectively turn on/off functions by modulating the conformational dynamics of their target protein. We examine the origins of the stimulation of ATPase and closure kinetics in the molecular chaperone Hsp90 by allosteric modulators through atomistic molecular dynamics (MD) simulations and analysis of protein-ligand interactions. In particular, we focus on the cross-talk between allosteric ligands and protein conformations and its effect on the dynamic properties of the chaperone's active state. We examine the impact of different allosteric modulators on the stability, structural and internal dynamics properties of Hsp90 closed state. A critical aspect of this study is the development of a quantitative model that correlates Hsp90 activation to the presence of a certain compound, making use of information on the dynamic adaptation of protein conformations to the presence of the ligand, which allows to capture conformational states relevant in the activation process. We discuss the implications of considering the conformational dialogue between allosteric ligands and protein conformations for the design of new functional modulators.

  4. The Influence of Ligand Valency on Aggregation Mechanisms for Inhibiting Bacterial Toxins

    NARCIS (Netherlands)

    Sisu, C.; Baron, A.J.; Branderhorst, H.M.; Connell, S.D.; Weijers, C.A.G.M.; Vries, de R.; Hayes, E.D.; Pukin, A.V.; Gilbert, M.; Pieters, R.J.; Zuilhof, H.; Visser, G.M.; Turnbull, W.B.


    Divalent and tetravalent analogues of ganglioside GM1 are potent inhibitors of cholera toxin and Escherichia coli heat-labile toxin. However, they show little increase in inherent affinity when compared to the corresponding monovalent carbohydrate ligand. Analytical ultracentrifugation and dynamic

  5. Converging ligand-binding free energies obtained with free-energy perturbations at the quantum mechanical level. (United States)

    Olsson, Martin A; Söderhjelm, Pär; Ryde, Ulf


    In this article, the convergence of quantum mechanical (QM) free-energy simulations based on molecular dynamics simulations at the molecular mechanics (MM) level has been investigated. We have estimated relative free energies for the binding of nine cyclic carboxylate ligands to the octa-acid deep-cavity host, including the host, the ligand, and all water molecules within 4.5 Å of the ligand in the QM calculations (158-224 atoms). We use single-step exponential averaging (ssEA) and the non-Boltzmann Bennett acceptance ratio (NBB) methods to estimate QM/MM free energy with the semi-empirical PM6-DH2X method, both based on interaction energies. We show that ssEA with cumulant expansion gives a better convergence and uses half as many QM calculations as NBB, although the two methods give consistent results. With 720,000 QM calculations per transformation, QM/MM free-energy estimates with a precision of 1 kJ/mol can be obtained for all eight relative energies with ssEA, showing that this approach can be used to calculate converged QM/MM binding free energies for realistic systems and large QM partitions. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

  6. Evidence for a new mechanism behind HIFU-triggered release from liposomes. (United States)

    Oerlemans, Chris; Deckers, Roel; Storm, Gert; Hennink, Wim E; Nijsen, J Frank W


    A promising approach for local drug delivery is high-intensity focused ultrasound (HIFU)-triggered release of drugs from stimuli-responsive nanoparticles such as liposomes. The aim of this study was to investigate whether another release mechanism is involved with HIFU-triggered release from liposomes beside cavitation and temperature. Furthermore, it was studied whether this new release mechanism allows the release of lipophilic compounds. Therefore, both a lipophilic (Nile red) and a hydrophilic (fluorescein) compound were loaded into thermosensitive (TSL) or non-thermosensitive liposomes (NTSL) and the liposomes were subjected both to continuous wave (CW)- and pulsed wave (PW)-HIFU. The mean liposome size varied from 97 to 139 nm with a polydispersity index (PDI)≤0.06 for the different formulations. The Tm of the phospholipid bilayer of the TSL was around 42°C. Approximately 80% of fluorescein was released within 15 min from TSL at temperatures≥42°C. In contrast, no fluorescein release from NTSL and NR release from both TSL and NTSL was observed at temperatures up to 60 °C. CW-HIFU exposure of TSL resulted in rapid temperature elevation up to 52°C and subsequently almost quantitative fluorescein release. Fluorescein release from NTSL was also substantial (~64% after 16 min at 20 W). Surprisingly, CW-HIFU exposure (20W for 16 min) resulted in the release of NR from TSL (~66% of the loaded amount), and this was even higher from NTSL (~78%). PW-HIFU exposure did not result in temperatures above the Tm of TSL. However, nearly 85% of fluorescein was released from TSL after 32 min at 20W of PW-HIFU exposure, whereas the release from NTSL was around 27%. Interestingly, NR release from NTSL was~30% after 2 min PW-HIFU exposure and increased to~70% after 32 min. Furthermore, addition of microbubbles to the liposomes prior to PW-HIFU exposure did not result in more release, which suggests that cavitation can be excluded as the main mechanism responsible for the

  7. Study of the release mechanism of Terminalia chebula extract from nanoporous silica gel. (United States)

    Chakraborty, Suparna; Mitra, Manoj Kumar; Chaudhuri, Mahua Ghosh; Sa, Biswanath; Das, Satadal; Dey, Rajib


    Sol/gel-derived silica gel was prepared at room temperature from tetraethyl orthosilicate precursor. The extracts of Terminalia chebula (Haritoki) were entrapped into the porous silica gel. Fourier transform infrared analysis revealed the proper adsorption of herbal values in the nanopores of the silica gel. Porosity was estimated by transmission electron microscope studies. The release kinetics of the extract in both 0.1 N HCl, pH 1.2, and Phosphate-buffer saline (PBS), pH 7.2, were determined using UV-Vis spectroscopy. Different dissolution models were applied to release data in order to evaluate the release mechanisms and kinetics. Biphasic release patterns were found in every formulation for both the buffer systems. The kinetics followed a zero-order equation for first 4 h and a Higuchi expression in a subsequent timeline in the case of 0.1 N HCl. In the case of PBS, the formulations showed best linearity with a first-order equation followed by Higuchi's model. The sustained release of the extract predominantly followed diffusion and super case II transport mechanism. The release value was always above the minimum inhibitory concentration.

  8. Mechanism of preventing coal and gas compression disseminated values outburst with stress pre-released hydraulically

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Zhong-fei; Yu, Qi-xiang [Jiangsu University, Zhenjiang (China). Center of Safety Engineering


    Based on the conditions of coal and gas outburst, the action mechanism for preventing coal and gas compression disseminated values outburst with stress pre-released hydraulically was analyzed. The accuracy of this mechanism was validated by measuring the gas emission before and after pre-releasing stress hydraulically, measuring the rupture failure by the electromagnetic radiation technique and the correlative practical datum. The results show that the electromagnetic radiation intensity and pulse count are increscent when taking the measure of stress pre-released hydraulically, which is propitious to prevent the coal and gas outburst. The action mechanism consists of three aspects: 1) Pre-releasing gas and increasing tangential stress and disseminated values friction resistance; 2) Pre-releaseing the radial effective geostress on high-tension side and reducing the radial stress difference of disseminated values chop motion for enhancing coal displacement; 3) Making the disseminated values and adjacent coal and rock felting by flooding water and increasing the disseminated values' friction resistance coefficients. 9 refs., 2 figs.

  9. The influence of ligand valency on aggregation mechanisms for inhibiting bacterial toxins. (United States)

    Sisu, Cristina; Baron, Andrew J; Branderhorst, Hilbert M; Connell, Simon D; Weijers, Carel A G M; de Vries, Renko; Hayes, Edward D; Pukin, Aliaksei V; Gilbert, Michel; Pieters, Roland J; Zuilhof, Han; Visser, Gerben M; Turnbull, W Bruce


    Divalent and tetravalent analogues of ganglioside GM1 are potent inhibitors of cholera toxin and Escherichia coli heat-labile toxin. However, they show little increase in inherent affinity when compared to the corresponding monovalent carbohydrate ligand. Analytical ultracentrifugation and dynamic light scattering have been used to demonstrate that the multivalent inhibitors induce protein aggregation and the formation of space-filling networks. This aggregation process appears to arise when using ligands that do not match the valency of the protein receptor. While it is generally accepted that multivalency is an effective strategy for increasing the activity of inhibitors, here we show that the valency of the inhibitor also has a dramatic effect on the kinetics of aggregation and the stability of intermediate protein complexes. Structural studies employing atomic force microscopy have revealed that a divalent inhibitor induces head-to-head dimerization of the protein toxin en route to higher aggregates.

  10. Double Variational Binding—(SMILES Conformational Analysis by Docking Mechanisms for Anti-HIV Pyrimidine Ligands

    Directory of Open Access Journals (Sweden)

    Mihai V. Putz


    Full Text Available Variational quantitative binding–conformational analysis for a series of anti-HIV pyrimidine-based ligands is advanced at the individual molecular level. This was achieved by employing ligand-receptor docking algorithms for each molecule in the 1,3-disubstituted uracil derivative series that was studied. Such computational algorithms were employed for analyzing both genuine molecular cases and their simplified molecular input line entry system (SMILES transformations, which were created via the controlled breaking of chemical bonds, so as to generate the longest SMILES molecular chain (LoSMoC and Branching SMILES (BraS conformations. The study identified the most active anti-HIV molecules, and analyzed their special and relevant bonding fragments (chemical alerts, and the recorded energetic and geometric docking results (i.e., binding and affinity energies, and the surface area and volume of bonding, respectively. Clear computational evidence was also produced concerning the ligand-receptor pocket binding efficacies of the LoSMoc and BraS conformation types, thus confirming their earlier presence (as suggested by variational quantitative structure-activity relationship, variational-QSAR as active intermediates for the molecule-to-cell transduction process.

  11. Double Variational Binding—(SMILES) Conformational Analysis by Docking Mechanisms for Anti-HIV Pyrimidine Ligands (United States)

    Putz, Mihai V.; Dudaș, Nicoleta A.; Isvoran, Adriana


    Variational quantitative binding–conformational analysis for a series of anti-HIV pyrimidine-based ligands is advanced at the individual molecular level. This was achieved by employing ligand-receptor docking algorithms for each molecule in the 1,3-disubstituted uracil derivative series that was studied. Such computational algorithms were employed for analyzing both genuine molecular cases and their simplified molecular input line entry system (SMILES) transformations, which were created via the controlled breaking of chemical bonds, so as to generate the longest SMILES molecular chain (LoSMoC) and Branching SMILES (BraS) conformations. The study identified the most active anti-HIV molecules, and analyzed their special and relevant bonding fragments (chemical alerts), and the recorded energetic and geometric docking results (i.e., binding and affinity energies, and the surface area and volume of bonding, respectively). Clear computational evidence was also produced concerning the ligand-receptor pocket binding efficacies of the LoSMoc and BraS conformation types, thus confirming their earlier presence (as suggested by variational quantitative structure-activity relationship, variational-QSAR) as active intermediates for the molecule-to-cell transduction process. PMID:26295229

  12. Mechanized azobenzene-functionalized zirconium metal-organic framework for on-command cargo release (United States)

    Meng, Xiangshi; Gui, Bo; Yuan, Daqiang; Zeller, Matthias; Wang, Cheng


    Stimuli-responsive metal-organic frameworks (MOFs) have gained increasing attention recently for their potential applications in many areas. We report the design and synthesis of a water-stable zirconium MOF (Zr-MOF) that bears photoresponsive azobenzene groups. This particular MOF can be used as a reservoir for storage of cargo in water, and the cargo-loaded MOF can be further capped to construct a mechanized MOF through the binding of β-cyclodextrin with the azobenzene stalks on the MOF surface. The resulting mechanized MOF has shown on-command cargo release triggered by ultraviolet irradiation or addition of competitive agents without premature release. This study represents a simple approach to the construction of stimuli-responsive mechanized MOFs, and considering mechanized UiO-68-azo made from biocompatible components, this smart system may provide a unique MOF platform for on-command drug delivery in the future. PMID:27493996

  13. Inhibitory Effect of Clopidogrel on Release of Soluble CD40 Ligand by ADP-activated Platelet in Patients With Non-ST-segment elevation Acute Coronary Syndromes

    Institute of Scientific and Technical Information of China (English)

    Wei Wei; Chufan Luo; Zhimin Du


    Objectives To investigate the inhibitory effect of clopidogrel on release of soluble CD40 ligand (sCD40L) by ADP-activated platelet in patients with non-ST-segment elevation acute coronary syndromes(NSTEACS).Methods Forty-two patients with NSTEACS were treated with clopidogrel for 6~8 days.In order to obtain platelet rich plasma (PRP) samples,the venous blood was drawn before and after treatment,respectively.The platelets were activated by adenosine diphosphate (ADP),thus releasing sCD4OL,sCD40L levels were determined by enzyme-linked immunosorbent assay (ELISA) at different time of the reaction.Results Plasma sCD40L concentration before treatment was (0.199±0.155 ) ng/mL,and (0.190±0.176) ng/mL after treatment (P>0.05).Before treatment the PRP sCD40L level at 20-minute of platelet activation was (4.34±2.51 )ng/mL,and decreased to (2.79±1.93 ) ng/mL after treatment (P<0.001).The corresponding level at 40-minute of platelet activation was (5.29±3.13 ) ng/mL before treatment and (2.87±1.59 ) ng/mL after treatment(P<0.001 ).Conclusions Short-term clopidogrel administration might inhibit the release of sCD40L by ADP-activated platelet in patients with NSTEACS,suggesting that,in addition to its antiplatelet potency,clopidogrel may still have an anti-inflammatory effect.

  14. The α7 nicotinic acetylcholine receptor ligands methyllycaconitine, NS6740 and GTS-21 reduce lipopolysaccharide-induced TNF-α release from microglia

    DEFF Research Database (Denmark)

    Thomsen, Morten S; Mikkelsen, Jens D


    The anti-inflammatory properties of, particularly the α7, nicotinic acetylcholine receptors (nAChRs) in the peripheral immune system are well documented. There are also reports of anti-inflammatory actions of nicotine in the CNS, but it is unclear, whether this is due to activation or inhibition...... of nAChRs. Here we investigate the mechanisms behind α7 nAChR-mediated modulation of TNF-α release. We show that α7 nAChR agonists or positive allosteric modulators do not affect LPS-induced release of the pro-inflammatory cytokine TNF-α from cultured microglia. This suggests that classical activation...... of, i.e. ion-flux through, the α7 nAChR does not reduce TNF-α release from activated microglia. Contrarily, the α7 nAChR antagonist methyllycaconitine and the weak (...

  15. Rates and mechanisms of radioactive release and retention inside a waste disposal canister - in Can Processes

    Energy Technology Data Exchange (ETDEWEB)

    Oversby, V.M. (ed.) [and others


    the system that will not be present under long term disposal conditions. A simulation of long-term conditions can be done using uranium dioxide that contains a short-lived isotope of uranium, but this will not include the effects of fission product and higher actinide elements on the behaviour of the spent fuel. We designed a project that had as its objective to improve the scientific understanding of the processes that control release of radioactive species from spent fuel inside a disposal canister and the chemical changes in those species that might limit release of radioactivity from the canister. If the mechanisms that control dissolution of the fuel matrix, including self-irradiation effects, can be clarified, a more realistic assessment of the long-term behaviour of spent fuel under disposal conditions can be made. By removing uncertainties concerning waste form performance, a better assessment of the individual and collective role of the engineered barriers can be made. To achieve the overall objective of the project, the following scientific and technical objectives were set. 1. Measure the actual rate of matrix dissolution of uranium dioxide under oxidising and reducing conditions. 2. Measure the effect of alpha radiolysis on the dissolution rate of uranium dioxide under oxidising and reducing conditions. 3. Measure the dissolution rate of the matrix material of spent fuel and thereby determine the additional effects of beta and gamma radiation on uranium dioxide dissolution rate under oxidising and reducing conditions. 4. Measure the ability of actively corroding iron to reduce oxidised U(VI) to U(IV) when U is present as the complex ion uranyl carbonate. 5. Measure the rate of reduction of Np(V) species in the presence of actively corroding iron. 6. Calculate the expected equilibrium and steady state concentrations of U under the conditions of the experiments used for meeting objectives 1 through 3 and compare the calculated results with those measured in

  16. A Discussion of SY-101 Crust Gas Retention and Release Mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    SD Rassat; PA Gauglitz; SM Caley; LA Mahoney; DP Mendoza


    The flammable gas hazard in Hanford waste tanks was made an issue by the behavior of double-shell Tank (DST) 241-SY-101 (SY-101). Shortly after SY-101 was filled in 1980, the waste level began rising periodically, due to the generation and retention of gases within the slurry, and then suddenly dropping as the gases were released. An intensive study of the tank's behavior revealed that these episodic releases posed a safety hazard because the released gas was flammable, and, in some cases, the volume of gas released was sufficient to exceed the lower flammability limit (LFL) in the tank headspace (Allemann et al. 1993). A mixer pump was installed in SY-101 in late 1993 to prevent gases from building up in the settled solids layer, and the large episodic gas releases have since ceased (Allemann et al. 1994; Stewart et al. 1994; Brewster et al. 1995). However, the surface level of SY-101 has been increasing since at least 1995, and in recent months the level growth has shown significant and unexpected acceleration. Based on a number of observations and measurements, including data from the void fraction instrument (VFI), we have concluded that the level growth is caused largely by increased gas retention in the floating crust. In September 1998, the crust contained between about 21 and 43% void based on VFI measurements (Stewart et al. 1998). Accordingly, it is important to understand the dominant mechanisms of gas retention, why the gas retention is increasing, and whether the accelerating level increase will continue, diminish or even reverse. It is expected that the retained gas in the crust is flammable, with hydrogen as a major constituent. This gas inventory would pose a flammable gas hazard if it were to release suddenly. In May 1997, the mechanisms of bubble retention and release from crust material were the subject of a workshop. The evaluation of the crust and potential hazards assumed a more typical void of roughly 15% gas. It could be similar to

  17. Insight into the electronic effect of phosphine ligand on Rh catalyzed CO2 hydrogenation by investigating the reaction mechanism. (United States)

    Ni, Shao-Fei; Dang, Li


    Improving the catalytic efficiency of CO2 hydrogenation is a big challenge in catalysed CO2 recycling and H2 conservation. The detailed mechanism of [Rh(PCH2X(R)CH2P)2](+) (X(R) = CH2, N-CH3, CF2) catalyzed CO2 hydrogenation is studied to obtain insights into the electronic effect of the substituents at diphosphine ligand on the catalytic efficiency. The most favorable reaction mechanism is found to be composed of three steps: (1) oxidative addition of dihydrogen onto the Rh center of the catalyst; (2) the first hydride abstraction by base from the Rh dihydride complexes; (3) the second hydride transfer from the Rh hydride complexes to CO2. It was found that the transition state for the first hydride abstraction from the Rh dihydride complex is the TOF-determining transition state (TDTS) in the most favorable mechanism. The energetic span (δE) of the cycle is suggested related to the thermodynamic hydricity of the Rh dihydride complex. Model catalyst [Rh(PCH2CF2CH2P)2](+) with a strong σ electron withdrawing group on the diphosphine ligand provides higher hydricity in the Rh dihydride complex and lower activation energy when compared with the other two catalysts. Our study shows that it is the σ electron withdrawing ability rather than the electron donating ability that enhances the catalytic efficiency in catalyzed CO2 hydrogenation. This finding will benefit ligand design in transition metal catalysts and lead to more efficient methods for CO2 transformation.

  18. Diastereoselective Addition of α-Metalated Sulfoxides to Imines Revisited: Mechanism, Computational Studies, and the Effect of External Chiral Ligands

    DEFF Research Database (Denmark)

    Pedersen, Brian; Rein, Tobias; Søtofte, Inger


    six-membered "flat chair") was probed by quantum mechanical calculations, which underpinned the idea of using external chiral ligands to enhance the diastereoselectivity of otherwise moderately selective reactions. In this way, the diastereomeric ratio of the product 3a could be raised from (84 : 16......Some new results on asymmetric synthesis via the addition of a-metalated methyl tolyl sulfoxides to imines are presented. Good diastereoselectivity (up to > 98% d.e. for product 3g) can be obtained under conditions of kinetic control (short reaction time, low temperature). The transition state (a...

  19. Dual release and molecular mechanism of bilayered aceclofenac tablet using polymer mixture. (United States)

    Van Nguyen, Hien; Nguyen, Van Hong; Lee, Beom-Jin


    The objectives of the present study were to develop a controlled-release bilayered tablet of aceclofenac (AFN) 200mg with dual release and to gain a mechanistic understanding of the enhanced sustained release capability achieved by utilizing a binary mixture of the sustained release materials. Different formulations of the sustained-release layer were formulated by employing hydroxypropyl methylcellulose (HPMC) and hydroxypropyl cellulose (HPC) as the major retarding polymers. The in vitro dissolution studies of AFN bilayered tablets were carried out in intestinal fluid (pH 6.8 buffer). The mechanism of the synergistic rate-retarding effect of the polymer mixture containing HPC and carbomer was elucidated by the rate of swelling and erosion in intestinal fluid and the molecular interactions in the polymer network. The optimized bilayered tablets had similar in vitro dissolution profiles to the marketed tablet Clanza(®)CR based on the similarity factor (f2) in combination with their satisfactory micromeritic, physicochemical properties, and stability profiles. Drug release from HPMC-based matrix was controlled by non-Fickian transport, while drug release from HPC-based matrix was solely governed by drug diffusion. The swelling and erosion data exhibited a dramatic increase of water uptake and a reduction of weight loss in the polymer mixture-loaded tablet. Fourier transform infrared (FTIR) spectra revealed strong hydrogen bonding between HPC and carbomer in the polymer mixture. Regarding spatial distribution of polymers in the polymer mixture-loaded tablet, carbomer was found to be the main component of the gel layer during the first 2h of the hydration process, which was responsible for retarding drug release at initial stage. This process was then followed by a gradual transition of HPC from the glassy core to the gel layer for further increasing gel strength. Copyright © 2016 Elsevier B.V. All rights reserved.

  20. Coatings of Eudragit® RL and L-55 Blends: Investigations on the Drug Release Mechanism. (United States)

    Wulff, Robert; Leopold, Claudia S


    In a previous study, generally lower drug release rates from RL:L55 blend coated pellets in neutral/basic release media than in acidic release media were reported. The aim of this study was to obtain information on the drug release mechanism of solid dosage forms coated with blends of Eudragit® RL (RL) and Eudragit® L-55 (L55). Swelling experiments with free films were analyzed spectroscopically and gravimetrically to identify the physicochemical cause for this release behavior. With Raman spectroscopy, the swelling of copolymer films could be monitored. IR spectroscopic investigations on RL:L55 blends immersed in media at pH 6.8 confirmed the formation of interpolyelectrolyte complexes (IPECs) that were not detectable after swelling in hydrochloric acid pH 1.2. Further investigations revealed that these IPECs decreased the extent of ion exchange between the quaternary ammonium groups of RL and the swelling media. This is presumably the reason for the previously reported decreased drug permeability of RL:L55 coatings in neutral/basic media as ion exchange is the determining factor in drug release from RL coated dosage forms. Gravimetric erosion studies confirmed that L55 was not leached out of the film blends during swelling in phosphate buffer pH 6.8. In contrast to all other investigated films, the 4:1 (RL:L55) blend showed an extensive swelling within 24 h at pH 6.8 which explains the reported sigmoidal release behavior of 4:1 blend coated pellets. These results help to understand the release behavior of RL:L55 blend coated solid dosage forms.

  1. Dipicolinic Acid Release by Germinating Clostridium difficile Spores Occurs through a Mechanosensing Mechanism (United States)

    Francis, Michael B.


    ABSTRACT Classically, dormant endospores are defined by their resistance properties, particularly their resistance to heat. Much of the heat resistance is due to the large amount of dipicolinic acid (DPA) stored within the spore core. During spore germination, DPA is released and allows for rehydration of the otherwise-dehydrated core. In Bacillus subtilis, 7 proteins are encoded by the spoVA operon and are important for DPA release. These proteins receive a signal from the activated germinant receptor and release DPA. This DPA activates the cortex lytic enzyme CwlJ, and cortex degradation begins. In Clostridium difficile, spore germination is initiated in response to certain bile acids and amino acids. These bile acids interact with the CspC germinant receptor, which then transfers the signal to the CspB protease. Activated CspB cleaves the cortex lytic enzyme, pro-SleC, to its active form. Subsequently, DPA is released from the core. C. difficile encodes orthologues of spoVAC, spoVAD, and spoVAE. Of these, the B. subtilis SpoVAC protein was shown to be capable of mechanosensing. Because cortex degradation precedes DPA release during C. difficile spore germination (opposite of what occurs in B. subtilis), we hypothesized that cortex degradation would relieve the osmotic constraints placed on the inner spore membrane and permit DPA release. Here, we assayed germination in the presence of osmolytes, and we found that they can delay DPA release from germinating C. difficile spores while still permitting cortex degradation. Together, our results suggest that DPA release during C. difficile spore germination occurs though a mechanosensing mechanism. IMPORTANCE Clostridium difficile is transmitted between hosts in the form of a dormant spore, and germination by C. difficile spores is required to initiate infection, because the toxins that are necessary for disease are not deposited on the spore form. Importantly, the C. difficile spore germination pathway

  2. Mechanized silica nanoparticles based on pillar[5]arenes for on-command cargo release. (United States)

    Sun, Yu-Long; Yang, Ying-Wei; Chen, Dai-Xiong; Wang, Guan; Zhou, Yue; Wang, Chun-Yu; Stoddart, J Fraser


    Mechanized silica nanoparticles, equipped with pillar[5]arene-[2]pseudorotaxane nanovalves, operate in biological media to trap cargos within their nanopores, but release them when the pH is lowered or a competitive binding agent is added. Although cargo size plays an important role in cargo loading, cargo charge-type does not appear to have any significant influence on the amount of cargo loading or its release. These findings open up the possibility of using pillar[n]arene and its derivatives for the formation of robust and dynamic nanosystems that are capable of performing useful functions.

  3. The design and development of a release mechanism for space shuttle life-science experiments (United States)

    Jones, H. M.; Daniell, R. G.


    The design, development, and testing of a release mechanism for use in two life science experiments on the Spacelab 1, 4, and D1 missions is described. The mechanism is a self latching ball lock device actuated by a linear solenoid. An unusual feature is the tapering of the ball lock plunger to give it a near constant breakout force for release under a wide range of loads. The selection of the design, based on the design requirements, is discussed. A number of problems occurred during development and test, including problems caused by human factors that became apparent after initial delivery for crewtraining sessions. These problems and their solutions are described to assist in the design and testing of similar mechanisms.

  4. Product release mechanism and the complete enzyme catalysis cycle in yeast cytosine deaminase (yCD): A computational study. (United States)

    Zhao, Yuan; She, Nai; Zhang, Xin; Wang, Chaojie; Mo, Yirong


    Yeast cytosine deaminase (yCD) is critical in gene-directed enzyme prodrug therapy as it catalyzes the hydrolytic deamination of cytosine. The product (uracil) release process is considered as rate-limiting in the whole enzymatic catalysis and includes the cleavage of the uracil-metal bond and the delivery of free uracil out of the reactive site. Herein extensive combined random acceleration molecular dynamics (RAMD) and molecular dynamics (MD) simulations coupled with the umbrella sampling technique have been performed to study the product transport mechanism. Five channels have been identified, and the thermodynamic and dynamic characterizations for the two most favorable channels have been determined and analyzed. The free energy barrier for the most beneficial pathway is about 13kcal/mol and mainly results from the cleavage of hydrogen bonds between the ligand uracil and surrounding residues Asn51, Glu64, and Asp155. The conjugated rings of Phe114 and Trp152 play gating and guiding roles in the product delivery via π⋯π van der Waals interactions with the product. Finally, the full cycle of the enzymatic catalysis has been determined, making the whole process computationally more precise. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Ca{sup 2+} influx and ATP release mediated by mechanical stretch in human lung fibroblasts

    Energy Technology Data Exchange (ETDEWEB)

    Murata, Naohiko [Department of Respiratory Medicine, Nagoya University Graduate School of Medicine, Nagoya 466-8550 (Japan); Ito, Satoru, E-mail: [Department of Respiratory Medicine, Nagoya University Graduate School of Medicine, Nagoya 466-8550 (Japan); Furuya, Kishio [Mechanobiology Laboratory, Nagoya University Graduate School of Medicine, Nagoya 466-8550 (Japan); Takahara, Norihiro [Department of Respiratory Medicine, Nagoya University Graduate School of Medicine, Nagoya 466-8550 (Japan); Naruse, Keiji [Department of Cardiovascular Physiology, Okayama University Graduate School of Medicine, Okayama 700-8558 (Japan); Aso, Hiromichi; Kondo, Masashi [Department of Respiratory Medicine, Nagoya University Graduate School of Medicine, Nagoya 466-8550 (Japan); Sokabe, Masahiro [Mechanobiology Laboratory, Nagoya University Graduate School of Medicine, Nagoya 466-8550 (Japan); Hasegawa, Yoshinori [Department of Respiratory Medicine, Nagoya University Graduate School of Medicine, Nagoya 466-8550 (Japan)


    Highlights: • Uniaxial stretching activates Ca{sup 2+} signaling in human lung fibroblasts. • Stretch-induced intracellular Ca{sup 2+} elevation is mainly via Ca{sup 2+} influx. • Mechanical strain enhances ATP release from fibroblasts. • Stretch-induced Ca{sup 2+} influx is not mediated by released ATP or actin cytoskeleton. - Abstract: One cause of progressive pulmonary fibrosis is dysregulated wound healing after lung inflammation or damage in patients with idiopathic pulmonary fibrosis and severe acute respiratory distress syndrome. The mechanical forces are considered to regulate pulmonary fibrosis via activation of lung fibroblasts. In this study, the effects of mechanical stretch on the intracellular Ca{sup 2+} concentration ([Ca{sup 2+}]{sub i}) and ATP release were investigated in primary human lung fibroblasts. Uniaxial stretch (10–30% in strain) was applied to fibroblasts cultured in a silicone chamber coated with type I collagen using a stretching apparatus. Following stretching and subsequent unloading, [Ca{sup 2+}]{sub i} transiently increased in a strain-dependent manner. Hypotonic stress, which causes plasma membrane stretching, also transiently increased the [Ca{sup 2+}]{sub i}. The stretch-induced [Ca{sup 2+}]{sub i} elevation was attenuated in Ca{sup 2+}-free solution. In contrast, the increase of [Ca{sup 2+}]{sub i} by a 20% stretch was not inhibited by the inhibitor of stretch-activated channels GsMTx-4, Gd{sup 3+}, ruthenium red, or cytochalasin D. Cyclic stretching induced significant ATP releases from fibroblasts. However, the stretch-induced [Ca{sup 2+}]{sub i} elevation was not inhibited by ATP diphosphohydrolase apyrase or a purinergic receptor antagonist suramin. Taken together, mechanical stretch induces Ca{sup 2+} influx independently of conventional stretch-sensitive ion channels, the actin cytoskeleton, and released ATP.

  6. A selection fit mechanism in BMP receptor IA as a possible source for BMP ligand-receptor promiscuity.

    Directory of Open Access Journals (Sweden)

    Stefan Harth

    Full Text Available BACKGROUND: Members of the TGF-β superfamily are characterized by a highly promiscuous ligand-receptor interaction as is readily apparent from the numeral discrepancy of only seven type I and five type II receptors available for more than 40 ligands. Structural and functional studies have been used to address the question of how specific signals can be deduced from a limited number of receptor combinations and to unravel the molecular mechanisms underlying the protein-protein recognition that allow such limited specificity. PRINCIPAL FINDINGS: In this study we have investigated how an antigen binding antibody fragment (Fab raised against the extracellular domain of the BMP receptor type IA (BMPR-IA recognizes the receptor's BMP-2 binding epitope and thereby neutralizes BMP-2 receptor activation. The crystal structure of the complex of the BMPR-IA ectodomain bound to the Fab AbD1556 revealed that the contact surface of BMPR-IA overlaps extensively with the contact surface for BMP-2 interaction. Although the structural epitopes of BMPR-IA to both binding partners coincides, the structures of BMPR-IA in the two complexes differ significantly. In contrast to the structural differences, alanine-scanning mutagenesis of BMPR-IA showed that the functional determinants for binding to the antibody and BMP-2 are almost identical. CONCLUSIONS: Comparing the structures of BMPR-IA bound to BMP-2 or bound to the Fab AbD1556 with the structure of unbound BMPR-IA shows that binding of BMPR-IA to its interaction partners follows a selection fit mechanism, possibly indicating that the ligand promiscuity of BMPR-IA is inherently encoded by structural adaptability. The functional and structural analysis of the BMPR-IA binding antibody AbD1556 mimicking the BMP-2 binding epitope may thus pave the way for the design of low-molecular weight synthetic receptor binders/inhibitors.

  7. Dimeric Arrangement of the Parathyroid Hormone Receptor and a Structural Mechanism for Ligand-induced Dissociation

    Energy Technology Data Exchange (ETDEWEB)

    Pioszak, Augen A.; Harikumar, Kaleeckal G.; Parker, Naomi R.; Miller, Laurence J.; Xu, H. Eric (Van Andel); (Mayo)


    The parathyroid hormone receptor (PTH1R) is a class B G protein-coupled receptor that is activated by parathyroid hormone (PTH) and PTH-related protein (PTHrP). Little is known about the oligomeric state of the receptor and its regulation by hormone. The crystal structure of the ligand-free PTH1R extracellular domain (ECD) reveals an unexpected dimer in which the C-terminal segment of both ECD protomers forms an {alpha}-helix that mimics PTH/PTHrP by occupying the peptide binding groove of the opposing protomer. ECD-mediated oligomerization of intact PTH1R was confirmed in living cells by bioluminescence and fluorescence resonance energy transfer experiments. As predicted by the structure, PTH binding disrupted receptor oligomerization. A receptor rendered monomeric by mutations in the ECD retained wild-type PTH binding and cAMP signaling ability. Our results are consistent with the hypothesis that PTH1R forms constitutive dimers that are dissociated by ligand binding and that monomeric PTH1R is capable of activating G protein.

  8. A statistical mechanical model for drug release: Investigations on size and porosity dependence (United States)

    Gomes Filho, Márcio Sampaio; Oliveira, Fernando Albuquerque; Barbosa, Marco Aurélio Alves


    A lattice gas model is proposed for investigating the release of drug molecules in capsules covered with semi-permeable membranes. Release patterns in one and two dimensional systems are obtained with Monte Carlo simulations and adjusted to the semi-empirical Weibull distribution function. An analytical solution to the diffusion equation is used to complement and guide simulations in one dimension. Size and porosity dependence analysis was made on the two semi-empirical parameters of the Weibull function, which are related to characteristic time and release mechanism, and our results indicate that a simple scaling law occurs only for systems with almost impermeable membranes, represented in our model by capsules with a single leaking site.

  9. Mechanical, Rheological and Release Behaviors of a Poloxamer 407/ Poloxamer 188/Carbopol 940 Thermosensitive Composite Hydrogel

    Directory of Open Access Journals (Sweden)

    Jianyu Su


    Full Text Available The aims of this study were to prepare a thermosensitive composite hydrogel (TCH by mixing 24% (w/v poloxamer 407 (P407, 16% (w/v poloxamer 188 (P188 and 0.1% (w/v carbopol 940 (C940, and to determine the effect of natural borneol/ (2-hydroxypropyl-β-cyclodextrin (NB/HP-β-CD inclusion complex on the phase transition temperature, mechanical, rheological properties, and release behaviors of the TCH using the tube inversion method, a texture analyzer, a rheometer, and in vitro release , respectively. The results showed that as the concentration of NB/HP-β-CD increased, the phase transition temperature of the TCH was increased from 37.26 to 38.34 °C and the mechanical properties of the TCH showed that the hardness, cohesiveness, strength, and adhesiveness were increased from 0.025 to 0.064 kg, 0.022 to 0.064 kg, 0.110 to 0.307 kg and 0.036 to 0.105 kg, respectively, but the rheological properties of the TCH showed that G′, G′′ and η were decreased from 7,760 to 157.50 Pa, 1,274 to 36.28 Pa and 1,252 to 25.37 Pas, respectively. The in vitro release showed that an increasing NB/HP-β-CD concentration decreased the release rate of NB from the TCH, but the amount of NB released was more than 96% at 60 min, which showed the TCH had good release behavior.

  10. Structural Characterization of Calcium Alginate Matrices by Means of Mechanical and Release Tests

    Directory of Open Access Journals (Sweden)

    Romano Lapasin


    Full Text Available In this paper we have concentrated on the characterization of calcium alginate hydrogels loaded with a model drug (myoglobin by means of a mechanical approach; in addition, release tests of myoglobin from alginate hydrogels were performed. At a fixed temperature, relaxation tests (mechanical study were carried out on matrices constituted by different polymer concentrations. The interpretation of the relaxation behavior of the different matrices was conducted using the generalized Maxwell model; as a result of this investigation it was possible to conclude that for polymer concentrations greater than 0.5 g/ 100 mL the matrices behaved as solid materials. In addition, it was observed that the mechanical properties of the matrices increased with polymer concentration. With regard to the release tests, the diffusion coefficient of myoglobin in the matrix in relation to polymer concentrations was determined. The mechanical and release data where then analyzed by Flory’s theory and by a modified free-volume theory, respectively, to estimate the network mesh size ξ. The comparison between the mesh sizes obtained by the two approaches showed a satisfactory agreement for polymer concentrations greater than 0.5 g/100 mL. It should be noted that the approach proposed here to determine the polymeric network meshes is absolutely general and can be advantageously applied to the characterization of other similar polymeric systems.

  11. Mathematical modelling and computational study of two-dimensional and three-dimensional dynamics of receptor-ligand interactions in signalling response mechanisms. (United States)

    García-Peñarrubia, Pilar; Gálvez, Juan J; Gálvez, Jesús


    Cell signalling processes involve receptor trafficking through highly connected networks of interacting components. The binding of surface receptors to their specific ligands is a key factor for the control and triggering of signalling pathways. But the binding process still presents many enigmas and, by analogy with surface catalytic reactions, two different mechanisms can be conceived: the first mechanism is related to the Eley-Rideal (ER) mechanism, i.e. the bulk-dissolved ligand interacts directly by pure three-dimensional (3D) diffusion with the specific surface receptor; the second mechanism is similar to the Langmuir-Hinshelwood (LH) process, i.e. 3D diffusion of the ligand to the cell surface followed by reversible ligand adsorption and subsequent two-dimensional (2D) surface diffusion to the receptor. A situation where both mechanisms simultaneously contribute to the signalling process could also occur. The aim of this paper is to perform a computational study of the behavior of the signalling response when these different mechanisms for ligand-receptor interactions are integrated into a model for signal transduction and ligand transport. To this end, partial differential equations have been used to develop spatio-temporal models that show trafficking dynamics of ligands, cell surface components, and intracellular signalling molecules through the different domains of the system. The mathematical modeling developed for these mechanisms has been applied to the study of two situations frequently found in cell systems: (a) dependence of the signal response on cell density; and (b) enhancement of the signalling response in a synaptic environment.

  12. Evidence of Kinetic Control of Ligand Binding and Staged Product Release in MurA (enolpyruvyl UDP-GlcNAc synthase)-catalyzed Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Jackson, S.; Zhang, F; Chindemi, P; Junop, M; Berti, P


    MurA (enolpyruvyl UDP-GlcNAc synthase) catalyzes the first committed step in peptidoglycan biosynthesis. In this study, MurA-catalyzed breakdown of its tetrahedral intermediate (THI), with a k{sub cat}/K{sub M} of 520 M{sup -1} s{sup -1}, was far slower than the normal reaction, and 3 x 10{sup 5}-fold slower than the homologous enzyme, AroA, reacting with its THI. This provided kinetic evidence of slow binding and a conformationally constrained active site. The MurA cocrystal structure with UDP-N-acetylmuramic acid (UDP-MurNAc), a potent inhibitor, and phosphite revealed a new 'staged' MurA conformation in which the Arg397 side chain tracked phosphite out of the catalytic site. The closed-to-staged transition involved breaking eight MurA {center_dot} ligand ion pairs, and three intraprotein hydrogen bonds helping hold the active site loop closed. These were replaced with only two MurA {center_dot} UDP-MurNAc ion pairs, two with phosphite, and seven new intraprotein ion pairs or hydrogen bonds. Cys115 appears to have an important role in forming the staged conformation. The staged conformation appears to be one step in a complex choreography of release of the product from MurA.

  13. Effect of mechanical and electrical behavior of gelatin hydrogels on drug release and cell proliferation. (United States)

    Biswal, Dibyajyoti; Anupriya, B; Uvanesh, K; Anis, Arfat; Banerjee, Indranil; Pal, Kunal


    The present study was aimed to explore the effect of the mechanical and the electrical properties of the gelatin hydrogels on the mammalian cell proliferation and drug release properties. FTIR analysis of the hydrogels suggested that gelatin retained its secondary protein structure. A decrease in the diffusion constant of the water molecules was observed with the increase in the gelatin concentration in the hydrogels. The mechanical and the electrical stabilities of the hydrogels were enhanced with the increase in the gelatin content. Stress relaxation and creep studies were modeled using Weichert and Burger׳s models, respectively. The relaxation time (stress relaxation study) did not follow a concentration-dependent relationship and was found to affect the MG-63 cell (human osteoblast) proliferation. The impedance profile of the hydrogels was modeled using a (RQ)Q model. Release of ciprofloxacin from the hydrogels was inversely dependent on the rate of swelling. The release of the drug was not only dependent on the Fickian diffusion but also on the relaxation process of the gelatin chains. The inhomogeneous constant of the constant phase element representing the hydrogel-electrode interface indicated improved cell proliferation rate with a decrease in the inhomogeneous constant. In gist, the rate of cell proliferation could be related to the relaxation time (stress relaxation) and the inhomogeneous constant of the sample-electrode constant phase element (electrical study) properties, whereas, the drug release properties can be related to the bulk resistance of the formulations.

  14. Evidence of the hydrogen release mechanism in bulk MgH2 (United States)

    Nogita, Kazuhiro; Tran, Xuan Q.; Yamamoto, Tomokazu; Tanaka, Eishi; McDonald, Stuart D.; Gourlay, Christopher M.; Yasuda, Kazuhiro; Matsumura, Syo


    Hydrogen has the potential to power much of the modern world with only water as a by-product, but storing hydrogen safely and efficiently in solid form such as magnesium hydride remains a major obstacle. A significant challenge has been the difficulty of proving the hydriding/dehydriding mechanisms and, therefore, the mechanisms have long been the subject of debate. Here we use in situ ultra-high voltage transmission electron microscopy (TEM) to directly verify the mechanisms of the hydride decomposition of bulk MgH2 in Mg-Ni alloys. We find that the hydrogen release mechanism from bulk (2 μm) MgH2 particles is based on the growth of multiple pre-existing Mg crystallites within the MgH2 matrix, present due to the difficulty of fully transforming all Mg during a hydrogenation cycle whereas, in thin samples analogous to nano-powders, dehydriding occurs by a `shrinking core' mechanism.

  15. Ligand-biased regulation of PtdIns(3,4,5)P3-dependent signal transduction in GPCR control of pituitary hormone release. (United States)

    Pemberton, Joshua G; Chang, John P


    Biased signaling describes the selective activation of signal transduction cascades by structurally-related ligands downstream of shared G protein-coupled receptors (GPCRs). Although class I phosphoinositide 3-kinases (PI3Ks) are important components of GPCR-controlled transduction networks, little is known regarding the potential for biased regulation of class I PI3K-dependent signaling. The full compliment of class I PI3K catalytic subunits (p110α, p110β, p110δ and p110γ) first appear in bony fishes and, despite being associated with distinct cellular functions, all class I PI3Ks produce the lipid second-messenger phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3). We have previously shown that two endogenous gonadotropin-releasing hormones (GnRH2 and GnRH3), which both signal through shared Gαq/11-coupled receptors, selectively activate different subsets of class I PI3K isoforms in their control of hormone release from goldfish (Carassius auratus) pituitary cells. Here, we tested the hypothesis that the biased activation of class I PI3K isoforms results in the selective recruitment of PtdIns(3,4,5)P3-sensitive effectors downstream of GnRH-stabilized GPCRs using pharmacological mapping. Our results reveal that distinct PtdIns(3,4,5)P3-sensitive effectors are involved in the differential control of GnRH2- and GnRH3-stimulated, as well as basal, hormone release and implicate the participation of non-canonical PtdIns(3,4,5)P3-sensitive transduction elements. Furthermore, observations using a selective inhibitor of the shared Gβγ-effector interaction surface indicate a role for Gβγ-dependent signaling in the integrated control of pituitary hormone exocytosis. These novel findings add to our understanding of functional selectivity in GPCR signal transduction networks, in general, and reveal the complexity of biased signaling downstream of class I PI3K catalytic activity.

  16. Mechanisms in bradykinin stimulated arachidonate release and synthesis of prostaglandin and platelet activating factor

    Directory of Open Access Journals (Sweden)

    D. Ricupero


    Full Text Available Regulatory mechanisms in bradykinin (BK activated release of arachidonate (ARA and synthesis of prostaglandin (PG and platelet activating factor (PAF were studied in bovine pulmonary artery endothelial cells (BPAEC. A role for GTP binding protein (G-protein in the binding of BK to the cells was determined. Guanosine 5-O- (thiotriphosphate, (GTPτS, lowered the binding affinity for BK and increased the Kd for the binding from 0.45 to 1.99 nM. The Bmax remained unaltered at 2.25 × 10-11 mole. Exposure of the cells to aluminium fluoride also reduced the affinity for BK. Bradykinin-induced release of ARA proved pertussis toxin (PTX sensitive, with a maximum sensitivity at 10 ug/ml PTX. GTPτS at 100 μM increased the release of arachidonate. The effect of GTPτS and BK was additive at suboptimal doses of BK up to 0.5 nM but never exceeded the levels of maximal BK stimulation at 50 nM. PTX also inhibited the release of ARA induced by the calcium ionophore, A23187. Phorbol 12-myristate 13-acetate or more commonly known as tetradecanoyl phorbol acetate (TPA itself had little effect on release by the intact cells. However, at 100 nM it augmented the BK activated release. This was downregulated by overnight exposure to TPA and correlated with down-regulation of protein kinase C (PKC activity. The down-regulation only affected the augmentation of ARA release by TPA but not the original BK activated release. TPA displayed a similar, but more potent amplification of PAF synthesis in response to both BK or the calcium ionophore A23187. These results taken together point to the participation of G-protein in the binding of BK to BPAEC and its activation of ARA release. Possibly two types of G-protein are involved, one associated with the receptor, the other activated by Ca2+ and perhaps associated with phospholipase A2 (PLA2. Our results further suggest that a separate route of activation, probably also PLA2 related, takes place through a PKC catalysed

  17. POE-PEG-POE triblock copolymeric microspheres containing protein. II. Polymer erosion and protein release mechanism. (United States)

    Wan, J P; Yang, Y Y; Chung, T S; Tan, D; Ng, S; Heller, J


    The first paper of this series presented the fabrication and characterization of POE-PEG-POE triblock copolymeric microspheres containing protein. In this paper, we focus on the polymer erosion and the mechanism of protein release. Fourteen-week in vitro behaviors of POE-PEG-POE microspheres loaded with bovine serum albumin (BSA) have been monitored. SEM micrographs reveal that after 14-week incubation in PBS buffer, pH 7.4, 37 degrees C, the polymeric particles remain spherical despite mass loss of almost 90%. On the other hand, molecular weight undergoes a high initial loss of 38% and 44% during the first 2-week incubation for POE-PEG(5%)-POE and POE-PEG(10%)-POE, respectively. Then, it keeps relatively unchanged over 12 weeks. However, POE-PEG(20%)-POE copolymer provides a better compatibility between the POE and PEG blocks. Hydrolysis is homogeneous through the polymer backbone. Thus, its molecular weight remains relatively constant and mass loss shows quite sustained over the 14-week in vitro release. The similar phenomena are observed in the polydispersity index of the degrading copolymers. SDS-PAGE of the encapsulated BSA within the POE-PEG(5%)-POE microspheres displays that the structural integrity of BSA is intact for at least 8 weeks due to a mild environment provided by the copolymer. In addition, XPS and FTIR are utilized to investigate protein behaviors in the degrading microspheres. Protein release from the POE-PEG-POE microspheres shows a biphasic pattern, characterized by an initial stage followed by a non-detectable release. The non-release phase is dominated by either slow polymer degradation or dense microsphere matrix structures. The microsphere formulation is optimized and a sustained protein release over 2 weeks is achieved by using POE-PEG(20%)-POE at a high protein loading.

  18. Human formyl peptide receptor ligand binding domain(s). Studies using an improved mutagenesis/expression vector reveal a novel mechanism for the regulation of receptor occupancy. (United States)

    Perez, H D; Vilander, L; Andrews, W H; Holmes, R


    Recently, we reported the domain requirements for the binding of formyl peptide to its specific receptor. Based on experiments using receptor chimeras, we also postulated an importance for the amino-terminal domain of the receptor in ligand binding (Perez, H. D., Holmes, R., Vilander, L., Adams, R., Manzana, W., Jolley, D., and Andrews, W. H. (1993) J. Biol. Chem. 268, 2292-2295). We have begun to perform a detailed analysis of the regions within the formyl peptide receptor involved in ligand binding. To address the importance of the receptor amino-terminal domain, we substituted (or inserted) hydrophilic sequences within the amino-terminal domain, expressed the receptors, and determined their ability to bind ligand. A stretch of nine amino acids next to the initial methionine was identified as crucial for receptor occupancy. A peptide containing such a sequence specifically completed binding of the ligand to the receptor. Alanine screen mutagenesis of the second extracellular domain also identified amino acids involved in ligand binding as well as a disulfide bond (Cys98 to Cys176) crucial for maintaining the binding pocket. These studies provide evidence for a novel mechanism involved in regulation of receptor occupancy. Binding of the ligand induces conformational changes in the receptor that result in the apposition of the amino-terminal domain over the ligand, providing a lid to the binding pocket.

  19. Mechanics of robust and releasable adhesion in biology: Bottom up designed hierarchical structures of gecko (United States)

    Yao, Haimin; Gao, Huajian


    Gecko and many insects have evolved specialized adhesive tissues with bottom-up designed (from nanoscale and up) hierarchical structures that allow them to maneuver on vertical walls and ceilings. The adhesion mechanisms of gecko must be robust enough to function on unknown rough surfaces and also easily releasable upon animal movement. How does nature design such macroscopic sized robust and releasable adhesion devices? How can an adhesion system designed for robust attachment simultaneously allow easy detachment? These questions have motivated the present investigation on mechanics of robust and releasable adhesion in biology. On the question of robust adhesion, we introduce a fractal gecko hairs model, which assumes self-similar fibrillar structures at multiple hierarchical levels mimicking gecko's spatula ultrastructure, to show that structural hierarchy plays a key role in robust adhesion: it allows the work of adhesion to be exponentially enhanced with each added level of hierarchy. We demonstrate that, barring fiber fracture, the fractal gecko hairs can be designed from nanoscale and up to achieve flaw tolerant adhesion at any length scales. However, consideration of crack-like flaws in the hairs themselves results in an upper size limit for flaw tolerant design. On the question of releasable adhesion, we hypothesize that the asymmetrically aligned seta hairs of gecko form a strongly anisotropic material with adhesion strength strongly varying with the direction of pulling. We use analytical solutions to show that a strongly anisotropic elastic solid indeed exhibits a strongly anisotropic adhesion strength when sticking on a rough surface. Furthermore, we perform finite element calculations to show that the adhesion strength of a strongly anisotropic attachment pad exhibits essentially two levels of adhesion strength depending on the direction of pulling, resulting in an orientation-controlled switch between attachment and detachment. These findings not only

  20. Quantum mechanics/molecular mechanics simulation of the ligand vibrations of the water-oxidizing Mn4CaO5 cluster in photosystem II. (United States)

    Nakamura, Shin; Noguchi, Takumi


    During photosynthesis, the light-driven oxidation of water performed by photosystem II (PSII) provides electrons necessary to fix CO2, in turn supporting life on Earth by liberating molecular oxygen. Recent high-resolution X-ray images of PSII show that the water-oxidizing center (WOC) is composed of an Mn4CaO5 cluster with six carboxylate, one imidazole, and four water ligands. FTIR difference spectroscopy has shown significant structural changes of the WOC during the S-state cycle of water oxidation, especially within carboxylate groups. However, the roles that these carboxylate groups play in water oxidation as well as how they should be properly assigned in spectra are unresolved. In this study, we performed a normal mode analysis of the WOC using the quantum mechanics/molecular mechanics (QM/MM) method to simulate FTIR difference spectra on the S1 to S2 transition in the carboxylate stretching region. By evaluating WOC models with different oxidation and protonation states, we determined that models of high-oxidation states, Mn(III)2Mn(IV)2, satisfactorily reproduced experimental spectra from intact and Ca-depleted PSII compared with low-oxidation models. It is further suggested that the carboxylate groups bridging Ca and Mn ions within this center tune the reactivity of water ligands bound to Ca by shifting charge via their π conjugation.

  1. Combined quantum mechanics/molecular mechanics (QM/MM) simulations for protein-ligand complexes: free energies of binding of water molecules in influenza neuraminidase. (United States)

    Woods, Christopher J; Shaw, Katherine E; Mulholland, Adrian J


    The applicability of combined quantum mechanics/molecular mechanics (QM/MM) methods for the calculation of absolute binding free energies of conserved water molecules in protein/ligand complexes is demonstrated. Here, we apply QM/MM Monte Carlo simulations to investigate binding of water molecules to influenza neuraminidase. We investigate five different complexes, including those with the drugs oseltamivir and peramivir. We investigate water molecules in two different environments, one more hydrophobic and one hydrophilic. We calculate the free-energy change for perturbation of a QM to MM representation of the bound water molecule. The calculations are performed at the BLYP/aVDZ (QM) and TIP4P (MM) levels of theory, which we have previously demonstrated to be consistent with one another for QM/MM modeling. The results show that the QM to MM perturbation is significant in both environments (greater than 1 kcal mol(-1)) and larger in the more hydrophilic site. Comparison with the same perturbation in bulk water shows that this makes a contribution to binding. The results quantify how electronic polarization differences in different environments affect binding affinity and also demonstrate that extensive, converged QM/MM free-energy simulations, with good levels of QM theory, are now practical for protein/ligand complexes.

  2. Numerical research on the mechanism of contaminant release through the porous sediment-overlying water interface

    Institute of Scientific and Technical Information of China (English)

    郑淑君; 曹洋; 郭加宏


    After the pollutant discharged into the river or lake has been reduced, the release of the contaminant from the sediment to the overlying water may cause the river and lake be contaminated again. On the condition that the overlying water flow does not lead to sediment suspension, numerical researches are carried out for the mechanism of contaminant release through the sediment-overlying water interface. The overlying water flow is calculated as turbulence. The sediment is regarded as isotropic homogeneous porous medium, therefore the seepage field in the porous sediment layer is obtained by solving Darcy’s equations. Coupled two dimensional steady flows of the overlying water and the pore water in the sediment are calculated. Based on the flow fields obtained, the unsteady contaminant solute transportation process in the pore water in the sediment and the overlying water is numerically simulated, as the shapes of the sediment-overlying water interface are flat or periodic triangular respectively. Numerical results show that the exchange of the pore water and the overlying water is an important factor which decides the release flux of the contaminant from the sediment to the overlying water. The pressure distribution produced by the overlying water flow along the sediment-overlying water interface, as it is not flat, may induce the seepage of the pore water in the sediment and through the sediment-overlying water interface, which may increase the release flux of the contaminant from the sediment to the overlying water.

  3. Different immunological mechanisms govern protection from experimental stroke in young and older mice with recombinant TCR ligand therapy

    Directory of Open Access Journals (Sweden)



    Full Text Available Stroke is a leading cause of death and disability in the United States. The lack of clinical success in stroke therapies can be attributed, in part, to inadequate basic research on aging rodents. The current study demonstrates that recombinant TCR ligand therapy uses different immunological mechanisms to protect young and older mice from experimental stroke. In young mice, RTL1000 therapy inhibited splenocyte efflux while reducing frequency of T cells and macrophages in the spleen. Older mice treated with RTL1000 exhibited a significant reduction in inflammatory cells in the brain and inhibition of splenic atrophy. Our data suggest age specific differences in immune response to stroke that allow unique targeting of stroke immunotherapies.

  4. Release of hydrogen sulfide during microwave pyrolysis of sewage sludge: Effect of operating parameters and mechanism. (United States)

    Zhang, Jun; Zuo, Wei; Tian, Yu; Yin, Linlin; Gong, Zhenlong; Zhang, Jie


    The effects of sludge characteristics, pyrolysis temperature, heating rate and catalysts on the release of H2S and mechanism of H2S formation during sludge pyrolysis were investigated in a microwave heating reactor (MHR). The evolution of sulfur-containing compounds in the pyrolysis chars obtained at temperature range of 400-800°C was characterized by XPS. For a given temperature, the maximum concentration of H2S appeared at moisture content of 80%. Compared to the influence of heating rate on the H2S yields, pyrolysis temperature and catalyst played a more significant role on the release of H2S during microwave pyrolysis process. The H2S concentration increased with increasing temperature from 400°C to 800°C while decreased with increasing heating rate. Both the Nickel-based catalyst and Dolomite displayed significant desulfurization effect and Ni-based catalyst exhibited the larger desulfurization capability than that of Dolomite. The organic sulfur compounds accounted for about 60% of the total sulfur in the sludge which was the main reason for the formation of H2S. The mechanism analysis indicated that the cleavage reactions of mercaptan and aromatic-S compounds at temperatures below 600°C and the cracking reaction of sulfate above 700°C respectively were responsible for the H2S release during sludge pyrolysis. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Release of exendin-4 is controlled by mechanical action in Gila monsters, Heloderma suspectum. (United States)

    Christel, Carolyn M; Denardo, Dale F


    Exendin-4 is a peptide produced exclusively by the salivary glands of the Gila Monster, Heloderma suspectum. Although exendin-4 is considered a venom component, circulating plasma levels of exendin-4 have been shown to increase in response to feeding. Previous studies using mammals have demonstrated exendin-4 has prolonged plasma glucose-lowering properties. While these findings suggest a possible role of exendin-4 as a metabolic hormone in the Gila Monster, the mechanism controlling its release by the salivary gland has not previously been studied. We investigated possible factors driving exendin-4 release by testing Gila Monsters' response to one of six treatment groups: fed egg, fed juvenile rat, gastric intubation with egg while under anesthesia, olfactory stimulation from egg without ingestion, unfed control, and biting without feeding. These treatments were designed to separately test actions associated with feeding and different food types. We measured plasma exendin-4 levels using an immunoenzymetric assay before and at three time points after each treatment. Exendin-4 levels increased significantly in groups where considerable biting occurred but not in the other treatment groups. These results suggest that exendin-4 is released from the salivary glands in response to mechanical stimulation and not the detection of food either by smell, taste, or distention of the gut. Further study of exendin-4 in its natural organism is needed to elucidate the functional role of exendin-4 as a venom component and/or a metabolic regulator.

  6. Deeper insight into the drug release mechanisms in Eudragit RL-based delivery systems. (United States)

    Glaessl, B; Siepmann, F; Tucker, I; Rades, T; Siepmann, J


    Tartaric acid, metoprolol free base and metoprolol tartrate act as plasticisers for Eudragit RL, in the dry but also in the wet state. Fitting analytical solutions of Fick's second law of diffusion allowed for the determination of the apparent diffusivities of water and of tartaric acid, metoprolol free base and metoprolol tartrate upon exposure of thin films to 0.1M HCl, phosphate buffer pH 7.4 and distilled water. Based on these calculations, it could be shown that water penetration into the systems is predominantly controlled by pure diffusion, irrespective of the type of bulk fluid. Interestingly, the plasticising effect of metoprolol tartrate was much more pronounced than that of tartaric acid, resulting in monotonically increasing diffusion coefficients with increasing initial drug content. In contrast, the plasticising activity of metoprolol free base was very limited in the wet state, due to drug precipitation in aqueous environments. Partially observed film shrinking (after an initial system swelling) could be attributed to the leaching of the plasticising compound into the release medium, resulting in less flexible polymeric networks and squeezing out of water. Also the release of tartaric acid, metoprolol free base and metoprolol tartrate into the investigated bulk fluids was predominantly diffusion controlled. However, the precipitation of the free base in wet films rendered the mass transport mechanisms more complex, at moderate and high initial drug loadings. The obtained new insight into the underlying drug release mechanisms in Eudragit RL networks can help to facilitate the optimisation of this type of dosage forms.

  7. Fas ligand expression in colon cancer: A possible mechanism of tumor immune privilege

    Institute of Scientific and Technical Information of China (English)

    Wei Zhang; Er-Xun Ding; Qiang Wang; Da-Qiao Zhu; Jin He; Yu-Li Li; Yuan-He Wang


    AIM: To detect the expression of Fas ligand (FasL) in colon cancer tissues and cell lines and analyze the function of FasL-expressing colon cancer cells in inducing Fas-sensitive T lymphocyte apoptosis. METHODS: Ninety surgically resected colon cancer tissues and 15 hepatic metastasis specimens were investigatedby immunohistochemical method with normal colon mucosa and colon adenoma as control. The relationship between FasL expression and pathologic features was also analyzed.FasL expression of 4 colon cancer cell lines, SW620, Lovo, LS-174T and SW1116, were detected by Western blotting assay. The function of FasL expressed on colon cancer cells was determined by coculture assay with Jurkat T lymphocytes, the apoptotic rate of which was detectedby flow cytometry assay.RESULTS: Fifty-six (62.22%) cases of all the 90 colon cancer tissues and all (100%) the liver metastasis specimens expressed FasL, significantly higher than normal colon mucosa and colonic adenoma. Higher expression of FasL was found in more advanced stage of colon cancer and in cancer tissues with lymphatic or hepatic metastasis.All the colon cancer cell lines were found to express FasL.After coculture with the SW1116 cells for 24 h with an effector: target ratio 10:1, the rate of apoptosis of Jurkat cells rose from 1.9% to 21.0%.CONCLUSION: The expression of FasL is upregulated in colon cancer and the functionally expressed FasL can induce apoptosis of Fas-expressing T lymphocytes.

  8. Clavulanic acid increases dopamine release in neuronal cells through a mechanism involving enhanced vesicle trafficking (United States)

    Kost, Gina Chun; Selvaraj, Senthil; Lee, Young Bok; Kim, Deog Joong; Ahn, Chang-Ho; Singh, Brij B


    Clavulanic acid is a CNS-modulating compound with exceptional blood-brain barrier permeability and safety profile. Clavulanic acid has been proposed to have anti-depressant activity and is currently entering Phase IIb clinical trials for the treatment of Major Depressive Disorder (MDD). Studies have also shown that clavulanic acid suppresses anxiety and enhances sexual functions in rodent and primate models by a mechanism involving central nervous system (CNS) modulation, although its detailed mechanism of action has yet to be elucidated. To further examine its potential as a CNS modulating agent as well as its mechanism of action, we investigated the effects of clavulanic acid in neuronal cells. Our results indicate that clavulanic acid enhances dopamine release in PC12 and SH-SY5Y cells without affecting dopamine synthesis. Furthermore, using affinity chromatography we were able to identify two proteins, Munc18-1 and Rab4 that potentially bind to clavulanic acid and play a critical role in neurosecretion and the vesicle trafficking process. Consistent with this result, an increase in the translocation of Munc18-1 and Rab4 from the cytoplasm to the plasma membrane was observed in clavulanic acid treated cells. Overall, these data suggest that clavulanic acid enhances dopamine release in a mechanism involving Munc18-1 and Rab4 modulation and warrants further investigation of its therapeutic use in CNS disorders, such as depression. PMID:21964384

  9. Clavulanic acid increases dopamine release in neuronal cells through a mechanism involving enhanced vesicle trafficking. (United States)

    Kost, Gina Chun; Selvaraj, Senthil; Lee, Young Bok; Kim, Deog Joong; Ahn, Chang-Ho; Singh, Brij B


    Clavulanic acid is a CNS-modulating compound with exceptional blood-brain barrier permeability and safety profile. Clavulanic acid has been proposed to have anti-depressant activity and is currently entering Phase IIb clinical trials for the treatment of Major Depressive Disorder (MDD). Studies have also shown that clavulanic acid suppresses anxiety and enhances sexual functions in rodent and primate models by a mechanism involving central nervous system (CNS) modulation, although its detailed mechanism of action has yet to be elucidated. To further examine its potential as a CNS modulating agent as well as its mechanism of action, we investigated the effects of clavulanic acid in neuronal cells. Our results indicate that clavulanic acid enhances dopamine release in PC12 and SH-SY5Y cells without affecting dopamine synthesis. Furthermore, using affinity chromatography we were able to identify two proteins, Munc18-1 and Rab4 that potentially bind to clavulanic acid and play a critical role in neurosecretion and the vesicle trafficking process. Consistent with this result, an increase in the translocation of Munc18-1 and Rab4 from the cytoplasm to the plasma membrane was observed in clavulanic acid treated cells. Overall, these data suggest that clavulanic acid enhances dopamine release in a mechanism involving Munc18-1 and Rab4 modulation and warrants further investigation of its therapeutic use in CNS disorders, such as depression.

  10. Silver nanoparticles embedded in zeolite membranes: release of silver ions and mechanism of antibacterial action

    Directory of Open Access Journals (Sweden)

    Nagy A


    Full Text Available Amber Nagy1, Alistair Harrison2, Supriya Sabbani3, Robert S Munson, Jr2, Prabir K Dutta3, W James Waldman11Department of Pathology, The Ohio State University; 2Center for Microbial Pathogenesis, Research Institute at Nationwide Children's Hospital, 3Department of Chemistry, The Ohio State University, Columbus, OH, USABackground: The focus of this study is on the antibacterial properties of silver nanoparticles embedded within a zeolite membrane (AgNP-ZM.Methods and Results: These membranes were effective in killing Escherichia coli and were bacteriostatic against methicillin-resistant Staphylococcus aureus. E. coli suspended in Luria Bertani (LB broth and isolated from physical contact with the membrane were also killed. Elemental analysis indicated slow release of Ag+ from the AgNP-ZM into the LB broth. The E. coli killing efficiency of AgNP-ZM was found to decrease with repeated use, and this was correlated with decreased release of silver ions with each use of the support. Gene expression microarrays revealed upregulation of several antioxidant genes as well as genes coding for metal transport, metal reduction, and ATPase pumps in response to silver ions released from AgNP-ZM. Gene expression of iron transporters was reduced, and increased expression of ferrochelatase was observed. In addition, upregulation of multiple antibiotic resistance genes was demonstrated. The expression levels of multicopper oxidase, glutaredoxin, and thioredoxin decreased with each support use, reflecting the lower amounts of Ag+ released from the membrane. The antibacterial mechanism of AgNP-ZM is proposed to be related to the exhaustion of antioxidant capacity.Conclusion: These results indicate that AgNP-ZM provide a novel matrix for gradual release of Ag+.Keywords: silver nanoparticles, zeolite, antibacterial agent, oxidative stress

  11. A Lactobacillus rhamnosus GG-derived soluble protein, p40, stimulates ligand release from intestinal epithelial cells to transactivate epidermal growth factor receptor. (United States)

    Yan, Fang; Liu, Liping; Dempsey, Peter J; Tsai, Yu-Hwai; Raines, Elaine W; Wilson, Carole L; Cao, Hailong; Cao, Zheng; Liu, LinShu; Polk, D Brent


    p40, a Lactobacillus rhamnosus GG (LGG)-derived soluble protein, ameliorates intestinal injury and colitis, reduces apoptosis, and preserves barrier function by transactivation of the EGF receptor (EGFR) in intestinal epithelial cells. The aim of this study is to determine the mechanisms by which p40 transactivates the EGFR in intestinal epithelial cells. Here we show that p40-conditioned medium activates EGFR in young adult mouse colon epithelial cells and human colonic epithelial cell line, T84 cells. p40 up-regulates a disintegrin and metalloproteinase domain-containing protein 17 (ADAM17) catalytic activity, and broad spectrum metalloproteinase inhibitors block EGFR transactivation by p40 in these two cell lines. In ADAM17-deficient mouse colonic epithelial (ADAM17(-/-) MCE) cells, p40 transactivation of EGFR is blocked, but can be rescued by re-expression with WT ADAM17. Furthermore, p40 stimulates release of heparin binding (HB)-EGF, but not transforming growth factor (TGF)α or amphiregulin, in young adult mouse colon cells and ADAM17(-/-) MCE cells overexpressing WT ADAM17. Knockdown of HB-EGF expression by siRNA suppresses p40 effects on transactivating EGFR and Akt, preventing apoptosis, and preserving tight junction function. The effects of p40 on HB-EGF release and ADAM17 activation in vivo are examined after administration of p40-containing pectin/zein hydrogel beads to mice. p40 stimulates ADAM17 activity and EGFR activation in colonic epithelial cells and increases HB-EGF levels in blood from WT mice, but not from mice with intestinal epithelial cell-specific ADAM17 deletion. Thus, these data define a mechanism of a probiotic-derived soluble protein in modulating intestinal epithelial cell homeostasis through ADAM17-mediated HB-EGF release, leading to transactivation of EGFR.

  12. Molecular mechanism of hydrophobic charge-induction chromatography: interactions between the immobilized 4-mercaptoethyl-pyridine ligand and IgG. (United States)

    Lin, Dong-Qiang; Tong, Hong-Fei; Wang, Hong-Yin; Shao, Shuang; Yao, Shan-Jing


    Hydrophobic charge-induction chromatography (HCIC) is a novel bioseparation technology, especially for antibody purification. In order to better understand the molecular mechanism of HCIC, the typical ligand of 4-mercaptoethyl-pyridine (MEP) was coupled onto the cellulose matrix, and the binding and departing of IgG were studied with the molecular dynamics simulation. Based on the previous work with free MEP ligand (J. Phys. Chem. B, 116 (4) (2012) 1393-1400), the pocket around TYR319 and LEU309 on the CH2 domain of IgG was selected as the potential binding site for the Fc fragment of IgG (Fc-A), and the complex of matrix-ligand-Fc-A was formed for the molecular simulation. Both single ligand and ligand net were investigated in the present work. It was found that the MEP ligand immobilized on the cellulose matrix could capture the Fc-A at neutral pH during the simulation, and the Fc-A would depart quickly when pH was changed to 4.0. The hydrophobic interactions and hydrogen bonds controlled the binding of Fc-A on the immobilized ligands at neutral pH and the electrostatic repulsion caused the departing of Fc-A at acid condition. For the ligand net, multipoint binding was found, while one ligand dominated the binding of Fc-A and other ligands might enhance the adsorption of protein. In addition, the adsorption isotherm and the isothermal titration calorimetry (ITC) were used to evaluate the molecular interactions. The experimental results indicated that the hydrophobic interaction is the major driving force for the adsorption of IgG on the MEP resin, which was in good agreement with those findings of molecular simulation. The molecular simulation and thermodynamic results verified strongly the molecular mechanism of HCIC--the hydrophobic interactions for binding and the charge-induction repulsion for elution. Better understanding on the molecular interactions would be beneficial to design new HCIC ligands for improving the efficiency of antibody separation

  13. Properties and mechanisms of drug release from matrix tablets containing poly(ethylene oxide) and poly(acrylic acid) as release retardants. (United States)

    Zhang, Feng; Meng, Fan; Lubach, Joseph; Koleng, Joseph; Watson, N A


    The interactions between poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) in aqueous medium at pH 6.8 were investigated in the current study. We have also studied the effect of interpolymer interactions and various formulation variables, including the molecular weight of PEO, the ratio between PEO and PAA, the crystallinity of PEO, and the presence of an acidifying agent, on the release of theophylline from matrix tablets containing both PEO and PAA as release retardants. At pH 6.8, the synergy in solution viscosity between PEO and PAA as the result of ion-dipole interaction was observed in this study. The release of theophylline from the matrix tablets containing physical mixtures of PEO and PAA was found to be a function of dissolution medium pH because of the pH-dependent interactions between these two polymers. Because of the formation of water insoluble interpolymer complex between PEO and PAA in aqueous medium at pH below 4.0, the release of theophylline was independent of PEO molecular weight and was controlled by Fickian diffusion mechanism in 0.01N hydrochloric acid solution. In comparison, the drug release was a function of PEO molecular weight and followed the anomalous transport mechanism in phosphate buffer pH 6.8. The presence of PAA exerted opposite effects on the release of theophylline in phosphate buffer pH 6.8. In one aspect, theophylline release was accelerated because the erosion of PAA was much faster than that of PEO at pH6.8. On the opposite aspect, theophylline release was slowed down because of the formation of insoluble complex inside the gel layer as the result of the acidic microenvironment induced by PAA, and the increase in the viscosity of the gel layer as the result of the synergy between PEO and PAA. These two opposite effects offset each other. As a result, the release of theophylline remained statistically the same even when 75% PEO in the formulation was replaced with PAA. In phosphate buffer pH 6.8, the release of

  14. Method of forming through substrate vias (TSVs) and singulating and releasing die having the TSVs from a mechanical support substrate (United States)

    Okandan, Murat; Nielson, Gregory N


    Accessing a workpiece object in semiconductor processing is disclosed. The workpiece object includes a mechanical support substrate, a release layer over the mechanical support substrate, and an integrated circuit substrate coupled over the release layer. The integrated circuit substrate includes a device layer having semiconductor devices. The method also includes etching through-substrate via (TSV) openings through the integrated circuit substrate that have buried ends at or within the release layer including using the release layer as an etch stop. TSVs are formed by introducing one or more conductive materials into the TSV openings. A die singulation trench is etched at least substantially through the integrated circuit substrate around a perimeter of an integrated circuit die. The integrated circuit die is at least substantially released from the mechanical support substrate.

  15. On the intracellular release mechanism of hydrophobic cargo and its relation to the biodegradation behavior of mesoporous silica nanocarriers. (United States)

    von Haartman, Eva; Lindberg, Desiré; Prabhakar, Neeraj; Rosenholm, Jessica M


    The intracellular release mechanism of hydrophobic molecules from surface-functionalized mesoporous silica nanoparticles was studied in relation to the biodegradation behavior of the nanocarrier, with the purpose of determining the dominant release mechanism for the studied drug delivery system. To be able to follow the real-time intracellular release, a hydrophobic fluorescent dye was used as model drug molecule. The in vitro release of the dye was investigated under varying conditions in terms of pH, polarity, protein and lipid content, presence of hydrophobic structures and ultimately, in live cancer cells. Results of investigating the drug delivery system show that the degradation and drug release mechanisms display a clear interdependency in simple aqueous solvents. In pure aqueous media, the cargo release was primarily dependent on the degradation of the nanocarrier, while in complex media, mimicking intracellular conditions, the physicochemical properties of the cargo molecule itself and its interaction with the carrier and/or surrounding media were found to be the main release-governing factors. Since the material degradation was retarded upon loading with hydrophobic guest molecules, the cargo could be efficiently delivered into live cancer cells and released intracellularly without pronounced premature release under extracellular conditions. From a rational design point of view, pinpointing the interdependency between these two processes can be of paramount importance considering future applications and fundamental understanding of the drug delivery system. Copyright © 2016 Elsevier B.V. All rights reserved.

  16. Mechanism of cleaving DNA through hydrolysis of a novel complex of Mg containing dien ligand

    Institute of Scientific and Technical Information of China (English)


    A series of metal complexes were designed and synthesized and a novel binuclear magnesium complex has been selected, namely [Mg2(dien)Cl(OH2)2]Cl2·H2O (dien=diethylene-triamine), which can cleave the plasmid pBR322 DNA effectively in close to physiological condition without adding any external materials.Through biological and chemical methods, especially the comparative experiments, we find the interaction between the complex and DNA belongs to hydrolytic mechanism.

  17. Nanoparticle Photoresists: Ligand Exchange as a New, Sensitive EUV Patterning Mechanism

    KAUST Repository

    Kryask, Marie


    Hybrid nanoparticle photoresists and their patterning using DUV, EUV, 193 nm lithography and e-beam lithography has been investigated and reported earlier. The nanoparticles have demonstrated very high EUV sensitivity and significant etch resistance compared to other standard photoresists. The current study aims at investigating and establishing the underlying mechanism for dual tone patterning of these nanoparticle photoresist systems. Infrared spectroscopy and UV absorbance studies supported by mass loss and dissolution studies support the current model. © 2013SPST.

  18. Modeling the retention mechanism for high-performance liquid chromatography with a chiral ligand mobile phase and enantioseparation of mandelic acid derivatives. (United States)

    Tong, Shengqiang; Shen, Mangmang; Zhang, Hu; Cheng, Dongping; Yan, Jizhong


    The chromatographic retention mechanism describing relationship between retention factor and concentration of Cu(2+) (l-phenylalanine)2 using chiral ligand mobile phase was investigated and eight mandelic acid derivatives were enantioseparated by chiral ligand exchange chromatography. The relationship between retention factor and concentration of the Cu(2+) (l-phenylalanine)2 complex was proven to be in conformity with chromatographic retention mechanism in which chiral discrimination occurred both in mobile and stationary phase. Different copper(II) salts, chiral ligands, organic modifier, pH of aqueous phase, and conventional temperature on retention behavior were optimized. Eight racemates were successfully enantioseparated on a common reversed-phase column with an optimized mobile phase composed of 6 mmol/L of l-phenylalanine or N,N-dimethyl-l-phenylalanine and 3 mmol/Lof copper(II) acetate or copper(II) sulfate aqueous solution and methanol. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


    Institute of Scientific and Technical Information of China (English)

    BIAN Kejian; LUO Chunqiao; CAO Mengjun


    Copper(Ⅱ) complexes of sericin, chitosan, 6-and 2-aminodeoxystarch were used as catalysts in oxidative coupling of β-naphthol, the effects of conformation of the polymer ligands in these complexes on activities of the catalysts and mechanisms of the reaction were studied. It was found that if the catalysts react with the substrate by mechanism similar to the enzymic catalysis they must be composed of polymer ligands with highly coiled, especially with densely helicoidal,conformations. While catalysts composed of loosely coiled or helicoidal ligands react with the substrate through molecular collision and have relatively lower activities only. Under nitrogen,catalysts from sericin and chitosam reacting with β-naphthol give optically active β-binaphthol,rotating polarized light to right, but the stereoselectivities are rather low.

  20. Inorganic Reactive Sulfur-Nitrogen Species: Intricate Release Mechanisms or Cacophony in Yellow, Blue and Red? (United States)

    Grman, Marian; Nasim, Muhammad Jawad; Leontiev, Roman; Misak, Anton; Jakusova, Veronika; Ondrias, Karol; Jacob, Claus


    Since the heydays of Reactive Sulfur Species (RSS) research during the first decade of the Millennium, numerous sulfur species involved in cellular regulation and signalling have been discovered. Yet despite the general predominance of organic species in organisms, recent years have also seen the emergence of inorganic reactive sulfur species, ranging from inorganic polysulfides (HSx−/Sx2−) to thionitrous acid (HSNO) and nitrosopersulfide (SSNO−). These inorganic species engage in a complex interplay of reactions in vitro and possibly also in vivo. Employing a combination of spectrophotometry and sulfide assays, we have investigated the role of polysulfanes from garlic during the release of nitric oxide (•NO) from S-nitrosoglutathione (GSNO) in the absence and presence of thiol reducing agents. Our studies reveal a distinct enhancement of GSNO decomposition by compounds such as diallyltrisulfane, which is most pronounced in the presence of cysteine and glutathione and presumably proceeds via the initial release of an inorganic mono- or polysulfides, i.e., hydrogen sulfide (H2S) or HSx−, from the organic polysulfane. Albeit being of a preliminary nature, our spectrophotometric data also reveals a complicated underlying mechanism which appears to involve transient species such as SSNO−. Eventually, more in depth studies are required to further explore the underlying chemistry and wider biological and nutritional implications of this interplay between edible garlic compounds, reductive activation, inorganic polysulfides and their interplay with •NO storage and release. PMID:28212297

  1. Inorganic Reactive Sulfur-Nitrogen Species: Intricate Release Mechanisms or Cacophony in Yellow, Blue and Red? (United States)

    Grman, Marian; Nasim, Muhammad Jawad; Leontiev, Roman; Misak, Anton; Jakusova, Veronika; Ondrias, Karol; Jacob, Claus


    Since the heydays of Reactive Sulfur Species (RSS) research during the first decade of the Millennium, numerous sulfur species involved in cellular regulation and signalling have been discovered. Yet despite the general predominance of organic species in organisms, recent years have also seen the emergence of inorganic reactive sulfur species, ranging from inorganic polysulfides (HSx(-)/Sx(2-)) to thionitrous acid (HSNO) and nitrosopersulfide (SSNO(-)). These inorganic species engage in a complex interplay of reactions in vitro and possibly also in vivo. Employing a combination of spectrophotometry and sulfide assays, we have investigated the role of polysulfanes from garlic during the release of nitric oxide ((•)NO) from S-nitrosoglutathione (GSNO) in the absence and presence of thiol reducing agents. Our studies reveal a distinct enhancement of GSNO decomposition by compounds such as diallyltrisulfane, which is most pronounced in the presence of cysteine and glutathione and presumably proceeds via the initial release of an inorganic mono- or polysulfides, i.e., hydrogen sulfide (H₂S) or HSx(-), from the organic polysulfane. Albeit being of a preliminary nature, our spectrophotometric data also reveals a complicated underlying mechanism which appears to involve transient species such as SSNO(-). Eventually, more in depth studies are required to further explore the underlying chemistry and wider biological and nutritional implications of this interplay between edible garlic compounds, reductive activation, inorganic polysulfides and their interplay with (•)NO storage and release.

  2. Inorganic Reactive Sulfur-Nitrogen Species: Intricate Release Mechanisms or Cacophony in Yellow, Blue and Red?

    Directory of Open Access Journals (Sweden)

    Marian Grman


    Full Text Available Since the heydays of Reactive Sulfur Species (RSS research during the first decade of the Millennium, numerous sulfur species involved in cellular regulation and signalling have been discovered. Yet despite the general predominance of organic species in organisms, recent years have also seen the emergence of inorganic reactive sulfur species, ranging from inorganic polysulfides (HSx−/Sx2− to thionitrous acid (HSNO and nitrosopersulfide (SSNO−. These inorganic species engage in a complex interplay of reactions in vitro and possibly also in vivo. Employing a combination of spectrophotometry and sulfide assays, we have investigated the role of polysulfanes from garlic during the release of nitric oxide (•NO from S-nitrosoglutathione (GSNO in the absence and presence of thiol reducing agents. Our studies reveal a distinct enhancement of GSNO decomposition by compounds such as diallyltrisulfane, which is most pronounced in the presence of cysteine and glutathione and presumably proceeds via the initial release of an inorganic mono- or polysulfides, i.e., hydrogen sulfide (H2S or HSx−, from the organic polysulfane. Albeit being of a preliminary nature, our spectrophotometric data also reveals a complicated underlying mechanism which appears to involve transient species such as SSNO−. Eventually, more in depth studies are required to further explore the underlying chemistry and wider biological and nutritional implications of this interplay between edible garlic compounds, reductive activation, inorganic polysulfides and their interplay with •NO storage and release.

  3. Release of dissolved phosphorus from riparian vegetated buffer strips: a field assessment of mechanisms and risks (United States)

    Gruau, Gerard; Gu, Sen; Petitjean, Patrice; Dupas, Rémi; Gascuel-odoux, Chantal; Rumpel, Cornelia


    Riparian vegetated buffer strips (RVBS) have been promoted worldwide as a tool to reduce diffused phosphorus (P) emission from agriculture lands, mainly through their ability to retain particulate P. However, RVBSs are zones of periodic water table fluctuations, which may stimulate the transformation and release of particulate P into mobile dissolved P species. In this study, we evaluated how soil characteristics (P content and P speciation), groundwater dynamics and biogeochemical processes interact together to trigger these transformations and releases, by monitoring over three years molybdate reactive dissolved P (MRDP) and total dissolved P (TDP) concentrations in soil solutions from two RVBSs set in a small agricultural catchment located in Western France, as well as in the stream immediately close of these two RVBSs and at the catchment outlet. Two main mechanisms were evidenced that released dissolved P in the studied RVBSs, each under the control of groundwater dynamics, namely soil rewetting during water table rise after dry periods, and reductive dissolution of soil Fe-(hydr)oxides during prolonged soil water saturation. However, both mechanisms were shown to be strongly temporarily and spatially variable, being dependent on the local topographic slope and the amount and frequency of rainfall. In fact, the third monitored year which was characterized by numerous dry episodes during the winter season resulted in the almost total inhibition of the reductive dissolution release process in the steeper of the two monitored RVBSs. Comparison of sites also revealed strong differences in the size of the mobile P pools as well as in the speciation of the released P, which correlated with differences in the status and speciation of P in soils. Finally, P concentration fluctuations and P speciation variations similar to those observed in RVBS soils were observed in the stream both immediately close to the RVBSs and at the outlet of the catchment, demonstrating the

  4. Isolation of TRPV1 independent mechanisms of spontaneous and asynchronous glutamate release at primary afferent to NTS synapses. (United States)

    Fenwick, Axel J; Wu, Shaw-Wen; Peters, James H


    Cranial visceral afferents contained within the solitary tract (ST) contact second-order neurons in the nucleus of the solitary tract (NTS) and release the excitatory amino acid glutamate via three distinct exocytosis pathways; synchronous, asynchronous, and spontaneous release. The presence of TRPV1 in the central terminals of a majority of ST afferents conveys activity-dependent asynchronous glutamate release and provides a temperature sensitive calcium conductance which largely determines the rate of spontaneous vesicle fusion. TRPV1 is present in unmyelinated C-fiber afferents and these facilitated forms of glutamate release may underlie the relative strength of C-fibers in activating autonomic reflex pathways. However, pharmacological blockade of TRPV1 signaling eliminates only ~50% of the asynchronous profile and attenuates the temperature sensitivity of spontaneous release indicating additional thermosensitive calcium influx pathways may exist which mediate these forms of vesicle release. In the present study we isolate the contribution of TRPV1 independent forms of glutamate release at ST-NTS synapses. We found ST afferent innervation at NTS neurons and synchronous vesicle release from TRPV1 KO mice was not different to control animals; however, only half of TRPV1 KO ST afferents completely lacked asynchronous glutamate release. Further, temperature driven spontaneous rates of vesicle release were not different from 33 to 37°C between control and TRPV1 KO afferents. These findings suggest additional temperature dependent mechanisms controlling asynchronous and thermosensitive spontaneous release at physiological temperatures, possibly mediated by additional thermosensitive TRP channels in primary afferent terminals.

  5. Depolarization by K*O+ and glutamate activates different neurotransmitter release mechanisms in gabaergic neurons: vesicular versus non-vesicular release of gaba

    DEFF Research Database (Denmark)

    Belhage, Bo; Hansen, G.H.; Schousboe, Arne


    Neurotransmitter release, gaba release, membrane transporter, vesicles, intracellular CA*OH, neuron cultures......Neurotransmitter release, gaba release, membrane transporter, vesicles, intracellular CA*OH, neuron cultures...

  6. Modeling signal propagation mechanisms and ligand-based conformational dynamics of the Hsp90 molecular chaperone full-length dimer.

    Directory of Open Access Journals (Sweden)

    Giulia Morra


    Full Text Available Hsp90 is a molecular chaperone essential for protein folding and activation in normal homeostasis and stress response. ATP binding and hydrolysis facilitate Hsp90 conformational changes required for client activation. Hsp90 plays an important role in disease states, particularly in cancer, where chaperoning of the mutated and overexpressed oncoproteins is important for function. Recent studies have illuminated mechanisms related to the chaperone function. However, an atomic resolution view of Hsp90 conformational dynamics, determined by the presence of different binding partners, is critical to define communication pathways between remote residues in different domains intimately affecting the chaperone cycle. Here, we present a computational analysis of signal propagation and long-range communication pathways in Hsp90. We carried out molecular dynamics simulations of the full-length Hsp90 dimer, combined with essential dynamics, correlation analysis, and a signal propagation model. All-atom MD simulations with timescales of 70 ns have been performed for complexes with the natural substrates ATP and ADP and for the unliganded dimer. We elucidate the mechanisms of signal propagation and determine "hot spots" involved in interdomain communication pathways from the nucleotide-binding site to the C-terminal domain interface. A comprehensive computational analysis of the Hsp90 communication pathways and dynamics at atomic resolution has revealed the role of the nucleotide in effecting conformational changes, elucidating the mechanisms of signal propagation. Functionally important residues and secondary structure elements emerge as effective mediators of communication between the nucleotide-binding site and the C-terminal interface. Furthermore, we show that specific interdomain signal propagation pathways may be activated as a function of the ligand. Our results support a "conformational selection model" of the Hsp90 mechanism, whereby the protein may

  7. Molecular Mechanisms of Gonadotropin-Releasing Hormone Signaling: Integrating Cyclic Nucleotides into the Network

    Directory of Open Access Journals (Sweden)

    Craig Alexander McArdle


    Full Text Available Gonadotropin-releasing hormone (GnRH is the primary regulator of mammalian reproductive function in both males and females. It acts via G-protein coupled receptors on gonadotropes to stimulate synthesis and secretion of the gonadotropin hormones luteinizing hormone and follicle-stimulating hormone. These receptors couple primarily via G-proteins of the Gq/11 family, driving activation of phospholipase C and mediating GnRH effects on gonadotropin synthesis and secretion. There is also good evidence that GnRH causes activation of other heterotrimeric G-proteins (Gs and Gi with consequent effects on cyclic AMP production, as well as for effects on the soluble and particulate guanylyl cyclases that generate cGMP. Here we provide an overview of these pathways. We emphasise mechanisms underpinning pulsatile hormone signaling and the possible interplay of GnRH and autocrine or paracrine regulatory mechanisms in control of cyclic nucleotide signaling.

  8. Development of the Orion Crew-Service Module Umbilical Retention and Release Mechanism (United States)

    Delap, Damon C.; Glidden, Joel Micah; Lamoreaux, Christopher


    The Orion CSM umbilical retention and release mechanism supports and protects all of the cross-module commodities between the spacecrafts crew and service modules. These commodities include explosive transfer lines, wiring for power and data, and flexible hoses for ground purge and life support systems. The mechanism employs a single separation interface which is retained with pyrotechnically actuated separation bolts and supports roughly two dozen electrical and fluid connectors. When module separation is commanded, either for nominal on-orbit CONOPS or in the event of an abort, the mechanism must release the separation interface and sever all commodity connections within milliseconds of command receipt. There are a number of unique and novel aspects of the design solution developed by the Orion mechanisms team. The design is highly modular and can easily be adapted to other vehiclesmodules and alternate commodity sets. It will be flight tested during Orions Exploration Flight Test 1 (EFT-1) in 2014, and the Orion team anticipates reuse of the design for all future missions. The design packages fluid, electrical, and ordnance disconnects in a single separation interface. It supports abort separations even in cases where aerodynamic loading prevents the deployment of the umbilical arm. Unlike the Apollo CSM umbilical which was a destructive separation device, the Orion design is resettable and flight units can be tested for separation performance prior to flight.Initial development testing of the mechanisms separation interface resulted in binding failures due to connector misalignments. The separation interface was redesigned with a robust linear guide system, and the connector separation and boom deployment were separated into two discretely sequenced events. These changes addressed the root cause of the binding failure by providing better control of connector alignment. The new design was tuned and validated analytically via Monte Carlo simulation. The

  9. A quality control mechanism linking meiotic success to release of ascospores.

    Directory of Open Access Journals (Sweden)

    Haiyan Guo

    Full Text Available Eukaryotic organisms employ a variety of mechanisms during meiosis to assess and ensure the quality of their gametes. Defects or delays in successful meiotic recombination activate conserved mechanisms to delay the meiotic divisions, but many multicellular eukaryotes also induce cell death programs to eliminate gametes deemed to have failed during meiosis. It is generally thought that yeasts lack such mechanisms. Here, we show that in the fission yeast Schizosaccharomyces pombe, defects in meiotic recombination lead to the activation of a checkpoint that is linked to ascus wall endolysis--the process by which spores are released in response to nutritional cues for subsequent germination. Defects in meiotic recombination are sensed as unrepaired DNA damage through the canonical ATM and ATR DNA damage response kinases, and this information is communicated to the machinery that stimulates ascus wall breakdown. Viability of spores that undergo endolysis spontaneously is significantly higher than that seen upon chemical endolysis, demonstrating that this checkpoint contributes to a selective mechanism for the germination of high quality progeny. These results provide the first evidence for the existence of a checkpoint linking germination to meiosis and suggest that analysis solely based on artificial, enzymatic endolysis bypasses an important quality control mechanism in this organism and potentially other ascomycota, which are models widely used to study meiosis.

  10. X-ray structures of progesterone receptor ligand binding domain in its agonist state reveal differing mechanisms for mixed profiles of 11beta-substituted steroids.

    NARCIS (Netherlands)

    Lusher, S.J.; Raaijmakers, H.C.A.; Vu-Pham, D.; Kazemier, B.; Bosch, R.; McGuire, R.; Azevedo, R.; Hamersma, H.; Dechering, K.; Oubrie, A.; Duin, M. van; Vlieg, J. de


    We present here the x-ray structures of the progesterone receptor (PR) in complex with two mixed profile PR modulators whose functional activity results from two differing molecular mechanisms. The structure of Asoprisnil bound to the agonist state of PR demonstrates the contribution of the ligand t

  11. Deciphering the kinetic binding mechanism of dimeric ligands using a potent plasma-stable dimeric inhibitor of postsynaptic density protein-95 as an example

    DEFF Research Database (Denmark)

    Chi, Celestine N; Bach, Anders; Gottschalk, Marie


    addressed the kinetic mechanism of interaction of such bivalent ligands. We have investigated the binding interaction of a recently identified potent plasma-stable dimeric pentapeptide and PDZ1-2 of postsynaptic density protein-95 (PSD-95) using protein engineering in combination with fluorescence...

  12. Ion Selectivity Mechanism in a Bacterial Pentameric Ligand-Gated Ion Channel

    Energy Technology Data Exchange (ETDEWEB)

    Fritsch, Sebastian M [ORNL; Ivanov, Ivaylo N [ORNL; Wang, Hailong [Mayo Clinic College of Medicine; Cheng, Xiaolin [ORNL


    The proton-gated ion channel from Gloeobacter violaceus (GLIC) is a prokaryotic homolog of the eukaryotic nicotinic acetylcholine receptor (nAChR) that responds to the binding of neurotransmitter acetylcholine and mediates fast signal transmission. Recent emergence of a high resolution crystal structure of GLIC captured in a potentially open state allowed detailed, atomic-level insight into ion conduction and selectivity mechanisms in these channels. Herein, we have examined the barriers to ion conduction and origins of ion selectivity in the GLIC channel by the construction of potential of mean force (PMF) profiles for sodium and chloride ions inside the transmembrane region. Our calculations reveal that the GLIC channel is open for a sodium ion to transport, but presents a ~10 kcal/mol free energy barrier for a chloride ion, which arises primarily from the unfavorable interactions with a ring of negatively charged glutamate residues (E-2 ) at the intracellular end and a ring of hydrophobic residues (I9 ) in the middle of the transmembrane domain. Our collective findings further suggest that the charge selection mechanism can, to a large extent, be attributed to the narrow intracellular end and a ring of glutamate residues in this position their strong negative electrostatics and ability to bind cations. By contrast, E19 at the extracellular entrance only plays a minor role in ion selectivity of GLIC. In addition to electrostatics, both ion hydration and protein dynamics are found to be crucial for ion conduction as well, which explains why a chloride ion experiences a much greater barrier than a sodium ion in the hydrophobic region of the pore.

  13. Structural mechanism of ligand activation in human calcium-sensing receptor

    Energy Technology Data Exchange (ETDEWEB)

    Geng, Yong; Mosyak, Lidia; Kurinov, Igor; Zuo, Hao; Sturchler, Emmanuel; Cheng, Tat Cheung; Subramanyam, Prakash; Brown, Alice P.; Brennan, Sarah C.; Mun, Hee-chang; Bush, Martin; Chen, Yan; Nguyen, Trang X.; Cao, Baohua; Chang, Donald D.; Quick, Matthias; Conigrave, Arthur D.; Colecraft, Henry M.; McDonald, Patricia; Fan, Qing R.


    Human calcium-sensing receptor (CaSR) is a G-protein-coupled receptor (GPCR) that maintains extracellular Ca2+homeostasis through the regulation of parathyroid hormone secretion. It functions as a disulfide-tethered homodimer composed of three main domains, the Venus Flytrap module, cysteine-rich domain, and seven-helix transmembrane region. Here, we present the crystal structures of the entire extracellular domain of CaSR in the resting and active conformations. We provide direct evidence that L-amino acids are agonists of the receptor. In the active structure, L-Trp occupies the orthosteric agonist-binding site at the interdomain cleft and is primarily responsible for inducing extracellular domain closure to initiate receptor activation. Our structures reveal multiple binding sites for Ca2+and PO43-ions. Both ions are crucial for structural integrity of the receptor. While Ca2+ions stabilize the active state, PO43-ions reinforce the inactive conformation. The activation mechanism of CaSR involves the formation of a novel dimer interface between subunits.

  14. Up-regulation of NKG2D ligand ULBP2 by matrine in K562 cells and the underlying molecular mechanisms

    Institute of Scientific and Technical Information of China (English)



    Objective To probe matrine acting on natural killer cell(NK)activating receptor NKG2D ligands expression in CML cell line K562 and its underlying molecular mechanism.Methods The expression of NKG2D ligands(major histocompatibility complex class I chain-related molecule A or B(MICA/B),UL16-binding proteins(ULBP)1,2,and 3 on K562 cells were analyzed before and after treated with matrine by FCM.The cytotoxic sensitivity of K562 to NK cell was detected by FCM after

  15. Modulation of noradrenaline release in rat isolated stomach by prostanoids, but not by histaminergic mechanisms. (United States)

    Racké, K; Berrino, L; Möhlig, A; Jäger, R; Griepenkerl, I; Bräutigam, M; Reimann, A


    Several gastric functions are modulated by the sympathetic nervous system, but local mechanisms involved in the control of noradrenaline release are largely unknown. Overflow of endogenous noradrenaline was studied from isolated rat stomach incubated in Ussing chambers allowing the separate determination of mucosal and serosal overflow. Spontaneous noradrenaline overflow was similar at the mucosal and serosal side, but electrical field stimulation caused a frequency-dependent increase in noradrenaline overflow selectively at the serosal side. Evoked noradrenaline overflow was blocked by tetrodotoxin, not affected by indometacin and markedly enhanced (by about 250%) by yohimbine. In the presence of indometacin and yohimbine, sulprostone (an agonist at EP1/EP3 receptors) and misoprostol (an agonist at EP2/EP3 receptors) reduced the noradrenaline overflow evoked by stimulation at 3 Hz maximally by about 80% (EC50: 6 nmol/l and 11 nmol/l, respectively). The EP1 receptor selective antagonist AH 6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) did not antagonize the inhibition by sulprostone. Noradrenaline overflow evoked by stimulation at 1 Hz and 3 Hz was increased by scopolamine by about 50% and almost completely inhibited by oxotremorine. Neither, histamine nor the H3 receptor selective agonist (R)-alpha-methyl-histamine, nor the H1, H2 and H3 selective receptor antagonists mepyramine, cimetidine and thioperamide significantly affected noradrenaline overflow evoked by stimulation at 1 Hz or 3 Hz. In conclusion, impulse-induced noradrenaline release in the rat stomach is controlled by multiple presynaptic mechanisms involving alpha 2-adrenergic autoreceptors, EP3 prostanoid and muscarine heteroreceptors, whereas histaminergic mechanisms do not appear to be significant.

  16. Ligand-controlled reactivity, selectivity, and mechanism of cationic ruthenium-catalyzed hydrosilylations of alkynes, ketones, and nitriles: a theoretical study. (United States)

    Yang, Yun-Fang; Chung, Lung Wa; Zhang, Xinhao; Houk, K N; Wu, Yun-Dong


    Density functional theory calculations with the M06 functional have been performed on the reactivity, selectivity, and mechanism of hydrosilylations of alkynes, ketones, and nitriles catalyzed by cationic ruthenium complexes [CpRu(L)(MeCN)2](+), with L = P(i)Pr3 or MeCN. The hydrosilylation of alkynes with L = P(i)Pr3 involves an initial silyl migration mechanism to generate the anti-Markovnikov product, in contrast to the Markovnikov product obtained with L = MeCN. The bulky phosphine ligand directs the silyl group to migrate to Cβ of the alkyne. This explains the anti-Markovnikov selectivity of the catalyst with L = P(i)Pr3. By contrast, the silane additions to either ketone or nitrile proceed through an ionic SN2-Si outer-sphere mechanism, in which the substrate attacks the Si center. The P(i)Pr3 ligand facilitates the activation of the Si-H bond to furnish a η(2)-silane complex, whereas a η(1)-silane complex is formed for the MeCN ligand. This property of the phosphine ligand enables the catalytic hydrosilylation of ketones and nitriles in addition to that of alkynes.

  17. Recombinant Escherichia coli GMP reductase: kinetic, catalytic and chemical mechanisms, and thermodynamics of enzyme-ligand binary complex formation. (United States)

    Martinelli, Leonardo Krás Borges; Ducati, Rodrigo Gay; Rosado, Leonardo Astolfi; Breda, Ardala; Selbach, Bruna Pelegrim; Santos, Diógenes Santiago; Basso, Luiz Augusto


    Guanosine monophosphate (GMP) reductase catalyzes the reductive deamination of GMP to inosine monophosphate (IMP). GMP reductase plays an important role in the conversion of nucleoside and nucleotide derivatives of guanine to adenine nucleotides. In addition, as a member of the purine salvage pathway, it also participates in the reutilization of free intracellular bases. Here we present cloning, expression and purification of Escherichia coli guaC-encoded GMP reductase to determine its kinetic mechanism, as well as chemical and thermodynamic features of this reaction. Initial velocity studies and isothermal titration calorimetry demonstrated that GMP reductase follows an ordered bi-bi kinetic mechanism, in which GMP binds first to the enzyme followed by NADPH binding, and NADP(+) dissociates first followed by IMP release. The isothermal titration calorimetry also showed that GMP and IMP binding are thermodynamically favorable processes. The pH-rate profiles showed groups with apparent pK values of 6.6 and 9.6 involved in catalysis, and pK values of 7.1 and 8.6 important to GMP binding, and a pK value of 6.2 important for NADPH binding. Primary deuterium kinetic isotope effects demonstrated that hydride transfer contributes to the rate-limiting step, whereas solvent kinetic isotope effects arise from a single protonic site that plays a modest role in catalysis. Multiple isotope effects suggest that protonation and hydride transfer steps take place in the same transition state, lending support to a concerted mechanism. Pre-steady-state kinetic data suggest that product release does not contribute to the rate-limiting step of the reaction catalyzed by E. coli GMP reductase.

  18. A Change in the Ion Selectivity of Ligand-Gated Ion Channels Provides a Mechanism to Switch Behavior.

    Directory of Open Access Journals (Sweden)

    Jennifer K Pirri

    Full Text Available Behavioral output of neural networks depends on a delicate balance between excitatory and inhibitory synaptic connections. However, it is not known whether network formation and stability is constrained by the sign of synaptic connections between neurons within the network. Here we show that switching the sign of a synapse within a neural circuit can reverse the behavioral output. The inhibitory tyramine-gated chloride channel, LGC-55, induces head relaxation and inhibits forward locomotion during the Caenorhabditis elegans escape response. We switched the ion selectivity of an inhibitory LGC-55 anion channel to an excitatory LGC-55 cation channel. The engineered cation channel is properly trafficked in the native neural circuit and results in behavioral responses that are opposite to those produced by activation of the LGC-55 anion channel. Our findings indicate that switches in ion selectivity of ligand-gated ion channels (LGICs do not affect network connectivity or stability and may provide an evolutionary and a synthetic mechanism to change behavior.

  19. On the reaction mechanism of the complete intermolecular O2 transfer between mononuclear nickel and manganese complexes with macrocyclic ligands. (United States)

    Zapata-Rivera, Jhon; Caballol, Rosa; Calzado, Carmen J; Liakos, Dimitrios G; Neese, Frank


    The recently described intermolecular O2 transfer between the side-on Ni-O2 complex [(12-TMC)Ni-O2](+) and the manganese complex [(14-TMC)Mn](2+), where 12-TMC and 14-TMC are 12- and 14-membered macrocyclic ligands, 12-TMC=1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane and 14-TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, is studied by means of DFT methods. B3LYP calculations including long-range corrections and solvent effects are performed to elucidate the mechanism. The potential energy surfaces (PESs) compatible with different electronic states of the reactants have been analyzed. The calculations confirm a two-step reaction, with a first rate-determining bimolecular step and predict the exothermic character of the global process. The relative stability of the products and the reverse barrier are in line with the fact that no reverse reaction is experimentally observed. An intermediate with a μ-η(1):η(1)-O2 coordination and two transition states are identified on the triplet PES, slightly below the corresponding stationary points of the quintet PES, suggesting an intersystem crossing before the first transition state. The calculated activation parameters and the relative energies of the two transition sates and the products are in very good agreement with the experimental data. The calculations suggest that a superoxide anion is transferred during the reaction.

  20. Molecular Mechanisms That Underlie the Dynamic Adaptation of Innate Monocyte Memory to Varying Stimulant Strength of TLR Ligands. (United States)

    Yuan, Ruoxi; Geng, Shuo; Li, Liwu


    In adaptation to rising stimulant strength, innate monocytes can be dynamically programed to preferentially express either pro- or anti-inflammatory mediators. Such dynamic innate adaptation or programing may bear profound relevance in host health and disease. However, molecular mechanisms that govern innate adaptation to varying strength of stimulants are not well understood. Using lipopolysaccharide (LPS), the model stimulant of toll-like-receptor 4 (TLR4), we reported that the expressions of pro-inflammatory mediators are preferentially sustained in monocytes adapted by lower doses of LPS, and suppressed/tolerized in monocytes adapted by higher doses of LPS. Mechanistically, monocytes adapted by super-low dose LPS exhibited higher levels of transcription factor, interferon regulatory factor 5 (IRF5), and reduced levels of transcriptional modulator B lymphocyte-induced maturation protein-1 (Blimp-1). Intriguingly, the inflammatory monocyte adaptation by super-low dose LPS is dependent upon TRAM/TRIF but not MyD88. Similar to LPS, we also observed biphasic inflammatory adaptation and tolerance in monocytes challenged with varying dosages of TLR7 agonist. In sharp contrast, rising doses of TLR3 agonist preferentially caused inflammatory adaptation without inducing tolerance. At the molecular level, the differential regulation of IRF5 and Blimp-1 coincides with unique monocyte adaptation dynamics by TLR4/7 and TLR3 agonists. Our study provides novel clue toward the understanding of monocyte adaptation and memory toward distinct TLR ligands.

  1. Halogenation processes of secondary organic aerosol and implications on halogen release mechanisms

    Directory of Open Access Journals (Sweden)

    J. Ofner


    Full Text Available Reactive halogen species (RHS, such as X·, X2 and HOX containing X = chlorine and/or bromine, are released by various sources like photo-activated sea-salt aerosol or from salt pans, and salt lakes. Despite many studies of RHS reactions, the potential of RHS reacting with secondary organic aerosol (SOA and organic aerosol derived from biomass-burning (BBOA has been neglected. Such reactions can constitute sources of gaseous organohalogen compounds or halogenated organic matter in the tropospheric boundary layer and can influence physicochemical properties of atmospheric aerosols.

    Model SOA from α-pinene, catechol, and guaiacol was used to study heterogeneous interactions with RHS. Particles were exposed to molecular chlorine and bromine in an aerosol smog-chamber in the presence of UV/VIS irradiation and to RHS, released from simulated natural halogen sources like salt pans. Subsequently, the aerosol was characterized in detail using a variety of physicochemical and spectroscopic methods. Fundamental features were correlated with heterogeneous halogenation, which results in new functional groups (FTIR spectroscopy, changes UV/VIS absorption, chemical composition (ultrahigh resolution mass spectroscopy (ICR-FT/MS, or aerosol size distribution. However, the halogen release mechanisms were also found to be affected by the presence of organic aerosol. Those interaction processes, changing chemical and physical properties of the aerosol are likely to influence e.g. the ability of the aerosol to act as cloud condensation nuclei, its potential to adsorb other gases with low-volatility, or its contribution to radiative forcing and ultimately the Earth's radiation balance.

  2. An investigation of effects of modification processes on physical properties and mechanism of drug release for sustaining drug release from modified rice. (United States)

    Ngo, Vuong Duy; Luu, Thinh Duc; Van Vo, Toi; Tran, Van-Thanh; Duan, Wei; Tran, Phuong Ha-Lien; Tran, Thao Truong-Dinh


    The aim of this study was to investigate the effect of modification processes on physical properties and explain the mechanism of sustained drug release from modified rice (MR). Various types of Vietnamese rice were introduced in the study as the matrices of sustained release dosage form. Rice was thermally modified in water for a determined temperature at different times with a simple process. Then tablets containing MR and isradipine, the model drug, were prepared to investigate the capability of sustained drug release. Scanning electron microscopy (SEM) was used to determine different morphologies between MR formulations. Flow property of MR was analyzed by Hausner ratio and Carr's indices. The dissolution rate and swelling/erosion behaviors of tablets were evaluated at pH 1.2 and pH6.8 at 37±0.5°C. The matrix tablet containing MR showed a sustained release as compared to the control. The SEM analyses and swelling/erosion studies indicated that the morphology as well as swelling/erosion rate of MR were modulated by modification time, drying method and incubation. It was found that the modification process was crucial because it could highly affect the granule morphologies and hence, leading to the change of flowability and swelling/erosion capacity for sustained release of drug.

  3. Mechanism of drug release from silica-gelatin aerogel-Relationship between matrix structure and release kinetics. (United States)

    Veres, Péter; Kéri, Mónika; Bányai, István; Lázár, István; Fábián, István; Domingo, Concepción; Kalmár, József


    Specific features of a silica-gelatin aerogel (3 wt.% gelatin content) in relation to drug delivery has been studied. It was confirmed that the release of both ibuprofen (IBU) and ketoprofen (KET) is about tenfold faster from loaded silica-gelatin aerogel than from pure silica aerogel, although the two matrices are structurally very similar. The main goal of the study was to understand the mechanistic background of the striking difference between the delivery properties of these closely related porous materials. Hydrated and dispersed silica-gelatin aerogel has been characterized by NMR cryoporometry, diffusiometry and relaxometry. The pore structure of the silica aerogel remains intact when it disintegrates in water. In contrast, dispersed silica-gelatin aerogel develops a strong hydration sphere, which reshapes the pore walls and deforms the pore structure. The drug release kinetics was studied on a few minutes time scale with 1s time resolution. Simultaneous evaluation of all relevant kinetic and structural information confirmed that strong hydration of the silica-gelatin skeleton facilitates the rapid desorption and dissolution of the drugs from the loaded aerogel. Such a driving force is not operative in pure silica aerogels.

  4. An alternate mechanism of abortive release marked by the formation of very long abortive transcripts. (United States)

    Chander, Monica; Austin, Karyn M; Aye-Han, Nwe-Nwe; Sircar, Piya; Hsu, Lilian M


    The Esigma70-dependent N25 promoter is rate-limited at promoter escape. Here, RNA polymerase repeatedly initiates and aborts transcription, giving rise to a ladder of short RNAs 2-11 nucleotides long. Certain mutations in the initial transcribed sequence (ITS) of N25 lengthen the abortive initiation program, resulting in the release of very long abortive transcripts (VLATs) 16-19 nucleotides long. This phenomenon is completely dependent on sequences within the first 20 bases of the ITS since altering sequences downstream of +20 has no effect on their formation. VLAT formation also requires strong interactions between RNA polymerase and the promoter. Mutations that change the -35 and -10 hexamers and the intervening 17 base pair spacer away from consensus decrease the probability of aborting at positions +16 to +19. An unusual characteristic of the VLATs is their undiminished levels in the presence of GreB, which rescues abortive RNAs (mechanism distinct from backtracking, which we propose entails polymerase molecules hyper forward translocating during the promoter escape transition. We discuss how certain features in the ITS, when combined with the N25 promoter, may lead to hyper forward translocation and abortive release at VLAT positions.

  5. Solubility Characteristics and Slow-Release Mechanism of Nitrogen from Organic-Inorganic Compound Coated Urea

    Directory of Open Access Journals (Sweden)

    Hongtao Zou


    Full Text Available A soil incubation method was used to investigate the solubility characteristics and slow-release mechanism of organic-inorganic compound coated urea at temperature of 10, 20, and 30°C. The membrane microstructure with and without incubation was tested via scanning electron microscopy (SEM. Slow release of nitrogen (N from different inorganic minerals was analysed by the activation energy from the nutrient solubility system. The rate of nitrogen solubility increased with temperature increasing. The first-order reaction kinetic equation described the solubility process of coated urea. The rate constant k also increased with temperature increasing. Moreover, the SEM images showed that the microstructure of the coating layer changed into a flocculent structure and the number of tiny pores and holes on the membrane surface increased significantly with temperature increasing, which increased N solubility rate. The Arrhenius equation indicated that activation energy was closely related to k during the solubility process; the activation energy was reduced with k rising, which resulted in N solubility rate increasing. Overall, the N solubility rate of coated urea was affected by temperature.

  6. Novel Alleviation Mechanisms of Aluminum Phytotoxicity via Released Biosilicon from Rice Straw-Derived Biochars (United States)

    Qian, Linbo; Chen, Baoliang; Chen, Mengfang


    Replacing biosilicon and biocarbon in soil via biochar amendment is a novel approach for soil amelioration and pollution remediation. The unique roles of silicon (Si)-rich biochar in aluminum (Al) phytotoxicity alleviation have not been discovered. In this study, the alleviation of Al phytotoxicity to wheat plants (root tips cell death) by biochars fabricated from rice straw pyrolyzed at 400 and 700 °C (RS400 and RS700) and the feedstock (RS100) were studied using a slurry system containing typical acidic soils for a 15-day exposure experiment. The distributions of Al and Si in the slurry solution, soil and plant root tissue were monitored by staining methods, chemical extractions and SEM-EDS observations. We found that the biological sourced silicon in biochars served dual roles in Al phytotoxicity alleviation in acidic soil slurry. On one hand, the Si particles reduced the amount of soil exchangeable Al and prevented the migration of Al to the plant. More importantly, the Si released from biochars synchronously absorbed by the plants and coordinated with Al to form Al-Si compounds in the epidermis of wheat roots, which is a new mechanism for Al phytotoxicity alleviation in acidic soil slurry by biochar amendment. In addition, the steady release of Si from the rice straw-derived biochars was a sustainable Si source for aluminosilicate reconstruction in acidic soil.

  7. Divergent kleisin subunits of cohesin specify mechanisms to tether and release meiotic chromosomes. (United States)

    Severson, Aaron F; Meyer, Barbara J


    We show that multiple, functionally specialized cohesin complexes mediate the establishment and two-step release of sister chromatid cohesion that underlies the production of haploid gametes. In C. elegans, the kleisin subunits REC-8 and COH-3/4 differ between meiotic cohesins and endow them with distinctive properties that specify how cohesins load onto chromosomes and then trigger and release cohesion. Unlike REC-8 cohesin, COH-3/4 cohesin becomes cohesive through a replication-independent mechanism initiated by the DNA double-stranded breaks that induce crossover recombination. Thus, break-induced cohesion also tethers replicated meiotic chromosomes. Later, recombination stimulates separase-independent removal of REC-8 and COH-3/4 cohesins from reciprocal chromosomal territories flanking the crossover site. This region-specific removal likely underlies the two-step separation of homologs and sisters. Unexpectedly, COH-3/4 performs cohesion-independent functions in synaptonemal complex assembly. This new model for cohesin function diverges from that established in yeast but likely applies directly to plants and mammals, which utilize similar meiotic kleisins.

  8. A Spring-loaded Release Mechanism Regulates Domain Movement and Catalysis in Phosphoglycerate Kinase* (United States)

    Zerrad, Louiza; Merli, Angelo; Schröder, Gunnar F.; Varga, Andrea; Gráczer, Éva; Pernot, Petra; Round, Adam; Vas, Mária; Bowler, Matthew W.


    Phosphoglycerate kinase (PGK) is the enzyme responsible for the first ATP-generating step of glycolysis and has been implicated extensively in oncogenesis and its development. Solution small angle x-ray scattering (SAXS) data, in combination with crystal structures of the enzyme in complex with substrate and product analogues, reveal a new conformation for the resting state of the enzyme and demonstrate the role of substrate binding in the preparation of the enzyme for domain closure. Comparison of the x-ray scattering curves of the enzyme in different states with crystal structures has allowed the complete reaction cycle to be resolved both structurally and temporally. The enzyme appears to spend most of its time in a fully open conformation with short periods of closure and catalysis, thereby allowing the rapid diffusion of substrates and products in and out of the binding sites. Analysis of the open apoenzyme structure, defined through deformable elastic network refinement against the SAXS data, suggests that interactions in a mostly buried hydrophobic region may favor the open conformation. This patch is exposed on domain closure, making the open conformation more thermodynamically stable. Ionic interactions act to maintain the closed conformation to allow catalysis. The short time PGK spends in the closed conformation and its strong tendency to rest in an open conformation imply a spring-loaded release mechanism to regulate domain movement, catalysis, and efficient product release. PMID:21349853


    Energy Technology Data Exchange (ETDEWEB)

    Weberg, Micah J. [PhD Candidate in Space Science, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2134A Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States); Lepri, Susan T. [Associate Professor, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2429 Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States); Zurbuchen, Thomas H., E-mail:, E-mail:, E-mail: [Professor, Space Science and Aerospace Engineering, Associate Dean for Entrepreneurship Senior Counselor of Entrepreneurship Education, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2431 Space Research Building, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA. (United States)


    The elemental abundances of heavy ions (masses larger than He) in the solar wind provide information about physical processes occurring in the corona. Additionally, the charge state distributions of these heavy ions are sensitive to the temperature profiles of their respective source regions in the corona. Heavy ion dropouts are a relatively new class of solar wind events identified by both elemental and ionic charge state distributions. We have shown that their origins lie in large, closed coronal loops where processes such as gravitational settling dominate and can cause a mass-dependent fractionation pattern. In this study we consider and attempt to answer three fundamental questions concerning heavy ion dropouts: (1) 'where are the source loops located in the large-scale corona?'; (2) 'how does the interplay between coronal processes influence the end elemental abundances?'; and (3) 'what are the most probable release mechanisms'? We begin by analyzing the temporal and spatial variability of heavy ion dropouts and their correlation with heliospheric plasma and magnetic structures. Next we investigate the ordering of the elements inside dropouts with respect to mass, ionic charge state, and first ionization potential. Finally, we discuss these results in the context of the prevailing solar wind theories and the processes they posit that may be responsible for the release of coronal plasma into interplanetary space.

  10. Sustained release of doxorubicin from zeolite-magnetite nanocomposites prepared by mechanical activation. (United States)

    Arruebo, Manuel; Fernández-Pacheco, Rodrigo; Irusta, Silvia; Arbiol, Jordi; Ibarra, M Ricardo; Santamaría, Jesús


    Nanocomposites consisting of magnetite and FAU zeolite with a high surface area and adsorption capacity have been prepared by mechanical activation using high-energy milling at room temperature. FTIR results, as well as HRTEM, EFTEM, and XPS measurements, show that the resulting magnetic nanoparticles are covered by a thin aluminosilicate coating. A saturation magnetization as high as 16 emu g(-1) and 94.2 Oe of coercivity were observed for the obtained composites. The main advantages of this synthesis procedure are (i) simplicity of the preparation procedure, (ii) prevention of agglomeration of the magnetite nanoparticles to a large extent, and (iii) absence of free magnetite outside the zeolitic matrix. In addition, in vitro experiments revealed that the nanoparticles prepared were able to store and release substantial amounts of doxorubicin. In view of these advantages, these magnetic nanoparticles can be considered as potential candidates for drug-delivery applications.

  11. Release of chromosomes from the nuclear envelope: a universal mechanism for eukaryotic mitosis? (United States)

    Kanoh, Junko


    Multiple domains of chromosomes are associated with the nuclear envelope (NE) in interphase. The association between chromosomes and the NE is involved in a variety of chromosomal reactions, such as gene expression and DNA repair. However, efficient chromosome movements are required for the fidelity of chromosome segregation in mitosis. Most higher eukaryotes perform open mitosis, in which the NE is broken down, enabling chromosomes to be released from the NE as well as spindle microtubules to access to kinetochores. By contrast, lower eukaryotes, such as Schizosaccharomyces pombe, perform closed mitosis, during which NE breakdown does not occur. In S. pombe, telomeres are tethered to the NE in interphase. Phosphorylation of the telomere-binding protein Rap1 at M phase promotes transient dissociation of telomeres from the NE, facilitating the faithful chromosome segregation. These findings imply a common mechanism for genome stability via the dissociation of chromosomes from the NE in eukaryotic mitosis.

  12. An electromagnetism-like mechanism for the single machine total stepwise tardiness problem with release dates (United States)

    Tseng, Chao-Tang; Chen, Kuan-Han


    In recent years, a new type of tardiness cost, called stepwise tardiness, has received attention. To the authors' knowledge, only a few studies have investigated this type of tardiness in the scheduling problem. This study considered the single machine total stepwise tardiness problem with release dates, which is strongly NP hard. Because of the essential complexity of the problem, heuristics were first developed to quickly generate initial solutions. Subsequently, a new electromagnetism-like mechanism (EM), which is a novel metaheuristic, was proposed to improve the solution quality. The new EM includes a natural encoding scheme, a new distance measure between solutions, and effective attraction and repulsion operators. Comparisons with a current EM and other metaheuristics were performed to verify the proposed EM. The computational results show that the proposed EM exhibits good performance for the considered problem.

  13. Ligand fitting with CCP4 (United States)


    Crystal structures of protein–ligand complexes are often used to infer biology and inform structure-based drug discovery. Hence, it is important to build accurate, reliable models of ligands that give confidence in the interpretation of the respective protein–ligand complex. This paper discusses key stages in the ligand-fitting process, including ligand binding-site identification, ligand description and conformer generation, ligand fitting, refinement and subsequent validation. The CCP4 suite contains a number of software tools that facilitate this task: AceDRG for the creation of ligand descriptions and conformers, Lidia and JLigand for two-dimensional and three-dimensional ligand editing and visual analysis, Coot for density interpretation, ligand fitting, analysis and validation, and REFMAC5 for macromolecular refinement. In addition to recent advancements in automatic carbohydrate building in Coot (LO/Carb) and ligand-validation tools (FLEV), the release of the CCP4i2 GUI provides an integrated solution that streamlines the ligand-fitting workflow, seamlessly passing results from one program to the next. The ligand-fitting process is illustrated using instructive practical examples, including problematic cases such as post-translational modifications, highlighting the need for careful analysis and rigorous validation. PMID:28177312

  14. Neurons respond directly to mechanical deformation with pannexin-mediated ATP release and autostimulation of P2X7 receptors. (United States)

    Xia, Jingsheng; Lim, Jason C; Lu, Wennan; Beckel, Jonathan M; Macarak, Edward J; Laties, Alan M; Mitchell, Claire H


    Mechanical deformation produces complex effects on neuronal systems, some of which can lead to dysfunction and neuronal death. While astrocytes are known to respond to mechanical forces, it is not clear whether neurons can also respond directly. We examined mechanosensitive ATP release and the physiological response to this release in isolated retinal ganglion cells. Purified ganglion cells released ATP upon swelling. Release was blocked by carbenoxolone, probenecid or peptide (10)panx, implicating pannexin channels as conduits. Mechanical stretch of retinal ganglion cells also triggered a pannexin-dependent ATP release. Whole cell patch clamp recording demonstrated that mild swelling induced the activation of an Ohmic cation current with linear kinetics. The current was inhibited by removal of extracellular ATP with apyrase, by inhibition of the P2X(7) receptor with A438079, zinc, or AZ 10606120, and by pannexin blockers carbenoxolone and probenecid. Probenecid also inhibited the regulatory volume decrease observed after swelling isolated neurons. Together, these observations indicate mechanical strain triggers ATP release directly from retinal ganglion cells and that this released ATP autostimulates P2X(7) receptors. Since extracellular ATP levels in the retina increase with elevated intraocular pressure, and stimulation of P2X(7) receptors on retinal ganglion cells can be lethal, this autocrine response may impact ganglion cells in glaucoma. It remains to be determined whether the autocrine stimulation of purinergic receptors is a general response to a mechanical deformation in neurons, or whether preventing ATP release through pannexin channels and blocking activation of the P2X(7) receptor, is neuroprotective for stretched neurons.

  15. An investigation of effects of modification processes on physical properties and mechanism of drug release for sustaining drug release from modified rice

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, Vuong Duy; Luu, Thinh Duc; Van Vo, Toi [Pharmaceutical Engineering Laboratory, Biomedical Engineering Department, International University, Vietnam National University, Ho Chi Minh City (Viet Nam); Tran, Van-Thanh [Faculty of Pharmacy, University of Medicine and Pharmacy, Ho Chi Minh City (Viet Nam); Duan, Wei [School of Medicine, Deakin University, Pigdons Road, Waurn Ponds, Victoria (Australia); Tran, Phuong Ha-Lien, E-mail: [School of Medicine, Deakin University, Pigdons Road, Waurn Ponds, Victoria (Australia); Tran, Thao Truong-Dinh, E-mail: [Pharmaceutical Engineering Laboratory, Biomedical Engineering Department, International University, Vietnam National University, Ho Chi Minh City (Viet Nam)


    The aim of this study was to investigate the effect of modification processes on physical properties and explain the mechanism of sustained drug release from modified rice (MR). Various types of Vietnamese rice were introduced in the study as the matrices of sustained release dosage form. Rice was thermally modified in water for a determined temperature at different times with a simple process. Then tablets containing MR and isradipine, the model drug, were prepared to investigate the capability of sustained drug release. Scanning electron microscopy (SEM) was used to determine different morphologies between MR formulations. Flow property of MR was analyzed by Hausner ratio and Carr's indices. The dissolution rate and swelling/erosion behaviors of tablets were evaluated at pH 1.2 and pH 6.8 at 37 ± 0.5 °C. The matrix tablet containing MR showed a sustained release as compared to the control. The SEM analyses and swelling/erosion studies indicated that the morphology as well as swelling/erosion rate of MR were modulated by modification time, drying method and incubation. It was found that the modification process was crucial because it could highly affect the granule morphologies and hence, leading to the change of flowability and swelling/erosion capacity for sustained release of drug. - Highlights: • Modification process affected granule morphologies and flowability of modified rice. • Modification process affected swelling/erosion capacity for drug sustained release. • Freeze-drying could decrease the erosion as well as increase the swelling rate.

  16. A Functional Selectivity Mechanism at the Serotonin-2A GPCR Involves Ligand-Dependent Conformations of Intracellular Loop 2


    Perez-Aguilar, Jose Manuel; Shan, Jufang; Michael V LeVine; Khelashvili, George; Weinstein, Harel


    With recent progress in determination of G protein-coupled receptor (GPCR) structure with crystallography, a variety of other experimental approaches (e.g., NMR spectroscopy, fluorescent-based assays, mass spectrometry techniques) are also being used to characterize state-specific and ligand-specific conformational states. MD simulations offer a powerful complementary approach to elucidate the dynamic features associated with ligand-specific GPCR conformations. To shed light on the conformati...

  17. Mechanism of oxygen releasing of copper ferrite in the formation of the corresponding oxygen-deficient compound

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ping; YU Bo; ZHANG Lei


    Copper ferrite is a promising material for hydrogen production through thermochemical water splitting. In this work, the cation distribution of copper ferrite and the corresponding oxygen-deficient compound of spinel structure was analyzed based on the crystal structural chemistry theory. The mechanism of oxygen releasing of CuO, Fe2O3, CuFe2O4 and metal (M=Ni, Mn or Zn) doped copper ferrite in the proc-ess of temperature rising was investigated by differential thermal analysis-thermogravimetry (DTA-TG). By combining the theoretical analysis with experimental results, the mechanism of oxygen releasing of copper ferrite is proposed, which is different from that of other ferrites. For copper ferrite, the oxygen releasing caused by Cu(Ⅱ)→Cu(I) plays a predominant role, while for other ferrites, the oxygen releas-ing resulting from Fe(ⅡI)→Fe(Ⅱ) is dominant.

  18. Mechanism of oxygen releasing of copper ferrite in the formation of the corresponding oxygen-deficient compound

    Institute of Scientific and Technical Information of China (English)


    Copper ferrite is a promising material for hydrogen production through thermochemical water splitting.In this work,the cation distribution of copper ferrite and the corresponding oxygen-deficient compound of spinel structure was analyzed based on the crystal structural chemistry theory.The mechanism of oxygen releasing of CuO,Fe2O3,CuFe2O4 and metal(M=Ni,Mn or Zn) doped copper ferrite in the proc-ess of temperature rising was investigated by differential thermal analysis-thermogravimetry(DTA-TG).By combining the theoretical analysis with experimental results,the mechanism of oxygen releasing of copper ferrite is proposed,which is different from that of other ferrites.For copper ferrite,the oxygen releasing caused by Cu(Ⅱ)→Cu(Ⅰ) plays a predominant role,while for other ferrites,the oxygen releas-ing resulting from Fe(Ⅲ)→Fe(Ⅱ) is dominant.

  19. Signaling Mechanisms in the Nitric Oxide Donor- and Amphetamine-Induced Dopamine Release in Mesencephalic Primary Cultured Neurons. (United States)

    Salum, Cristiane; Schmidt, Fanny; Michel, Patrick P; Del-Bel, Elaine; Raisman-Vozari, Rita


    Previous research has shown that nitric oxide (NO) synthase inhibitors prevent rodents' sensorimotor gating impairments induced by dopamine releasing drugs, such as amphetamine (Amph) and methylphenidate. The mechanisms of this effect have not been entirely understood. In the present work, we investigated some possible mechanisms by which the NO donor, NOC-12 (3-ethyl-3-(ethylaminoethyl)-1-hydroxy-2-oxo-1-triazene), influence spontaneous and Amph-induced dopamine release, using rat mesencephalic primary cultured neurons preparations. Our results showed that NOC-12 increased dopamine release in a concentration-dependent manner and potentiated the Amph-induced one. Dopamine release induced by NOC-12 was disrupted by N-acetyl-L-cystein (NAC-a free radical scavenger) and MK-801, a NMDA (N-methyl-D-aspartate) non-competitive antagonist, and was concentration dependently affected by oxadiazolo[4,3]quinoxalin-1-one, an inhibitor of the soluble guanylate cyclase (sGC). In contrast, dopamine released by Amph was facilitated by NAC and by MK-801 and not affected by nifedipine (a L-type-Ca(+2) channel blocker), which enhanced NOC-12-induced dopamine release. The present work demonstrates that DA release induced by NOC-12 is partially dependent on sGC and on NMDA activation, and is modulated by L-type Ca(+2) channel and the antioxidant NAC. This mechanism differs from the Amph-induced one, which appears not to depend on L-type Ca(+2) channel and seems to be facilitated by NMDA channel blocking and by NAC. These results suggest that Amph and NOC-12 induce dopamine release through complementary pathways, which may explain the potentiation of Amph-induced dopamine release by NOC-12. These findings contribute to understand the involvement of NO in dopamine-related neuropsychiatric and neurodegenerative diseases.

  20. Mechanisms and origins of switchable chemoselectivity of Ni-catalyzed C(aryl)-O and C(acyl)-O activation of aryl esters with phosphine ligands. (United States)

    Hong, Xin; Liang, Yong; Houk, K N


    Many experiments have shown that nickel with monodentate phosphine ligands favors the C(aryl)-O activation over the C(acyl)-O activation for aryl esters. However, Itami and co-workers recently discovered that nickel with bidentate phosphine ligands can selectively activate the C(acyl)-O bond of aryl esters of aromatic carboxylic acids. The chemoselectivity with bidentate phosphine ligands can be switched back to C(aryl)-O activation when aryl pivalates are employed. To understand the mechanisms and origins of this switchable chemoselectivity, density functional theory (DFT) calculations have been conducted. For aryl esters, nickel with bidentate phosphine ligands cleaves C(acyl)-O and C(aryl)-O bonds via three-centered transition states. The C(acyl)-O activation is more favorable due to the lower bond dissociation energy (BDE) of C(acyl)-O bond, which translates into a lower transition-state distortion energy. However, when monodentate phosphine ligands are used, a vacant coordination site on nickel creates an extra Ni-O bond in the five-centered C(aryl)-O cleavage transition state. The additional interaction energy between the catalyst and substrate makes C(aryl)-O activation favorable. In the case of aryl pivalates, nickel with bidentate phosphine ligands still favors the C(acyl)-O activation over the C(aryl)-O activation at the cleavage step. However, the subsequent decarbonylation generates a very unstable tBu-Ni(II) intermediate, and this unfavorable step greatly increases the overall barrier for generating the C(acyl)-O activation products. Instead, the subsequent C-H activation of azoles and C-C coupling in the C(aryl)-O activation pathway are much easier, leading to the observed C(aryl)-O activation products.

  1. Mechanisms of Prolonged Presynaptic Ca2+ Signaling and Glutamate Release Induced by TRPV1 Activation in Rat Sensory Neurons



    TRPV1-mediated release of neuroactive peptides and neurotransmitters from the peripheral and central terminals of primary sensory neurons can critically contribute to nociceptive processing at the periphery and in the CNS. However, the mechanisms that link TRPV1 activation with Ca2+ signaling at the release sites and neurosecretion are poorly understood. Here we demonstrate that a brief stimulation of the receptor using either capsaicin or the endogenous TRPV1 agonist N-arachidonoyl-dopamine ...

  2. Heparin-mimetic polyurethane hydrogels with anticoagulant, tunable mechanical property and controllable drug releasing behavior. (United States)

    Chen, Yuan; Wang, Rui; Wang, Yonghui; Zhao, Weifeng; Sun, Shudong; Zhao, Changsheng


    In the present study, novel heparin-mimetic polyurethane hydrogels were prepared by introducing chemical crosslinked sulfated konjac glucomannan (SKGM). Scanning electron microscopy (SEM) results indicated that the introduction of SKGM and the increase of the molecular weight of diol segments could enlarge the pore sizes of the hydrogels. The swelling behavior corresponded with the SEM results, and the hydrogels could absorb more water after the modification. The modification also led to an improvement in the mechanical property. Meanwhile, the SKGM and the modified polyurethane hydrogels showed excellent hemocompatibility. The thromboplastin time of SKGM could reach up to 182.9s. Gentamycin sulfate (GS) was used as a model drug to be loaded into the hydrogels, and the loading amount was increased ca. 50% after the introduction of SKGM, thus resulting in high bactericidal efficiency. The results indicated that the introduction of SKGM and the alternation in the diol's molecular weight bestowed polyurethane hydrogels with promising properties of integrated blood-compatibility, mechanical properties and drug loading-releasing behavior. Therefore, the heparin-mimetic multifunctional polyurethane hydrogels have great potential to be used in biomedical applications. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. Thermo Vacuum and Vibration Tests on a Shape Memory Alloy (SMA) Actuated Release Mechanism for Microsatellite (United States)

    Gardi, R.


    Seen the efforts to find alternative actuation systems to the pyrotechnic devices, our department is developing and testing release mechanisms, for microsatellites, actuated by Shape Memory Alloy (SMA) wires. Following up increasing interest on SMA actuated mechanisms, the author has been developing, in the last few years, a mechanism of which a prototype version has been presented in the last IAF congress. The present work describes the test phase of the mechanism, aimed at proving the capability of the parts of withstanding the severe space environmental conditions. The mechanism task is to open a steel rope loop, replacing a pyrotechnic guillotine. It is activated by three SMA wires that, shrinking, pull a sleeve and separate the two parts of the mechanism where the extremities of the rope are fixed. In the paper, after a short review of the past design and realization activities, we describe the tests conducted and their results. After the room condition tests, the mechanism has been set up for thermo-vacuum tests. In high vacuum condition, 10-10 bar, we validate the thermodynamic model for the SMA alloy. In room condition, free convection around the wires subtracts a large amount of the energy provided to the wires due to Joule effect, and then we have been obliged to actuate the mechanism with a power greater than that needed in vacuum, providing a constant current of 5 Amperes. In the thermo-vacuum chamber of the University we can simulate space environment and we can power the mechanism exactly with the current (3A) that will be actually employed during the mission. Moreover, the environmental control of the chamber allowed us to test the real capability of the mechanism, and of the SMA wires, to operate correctly at different temperatures. Inside the chamber a set of lamps irradiate energy toward the mechanism and heat it, simulating the solar and albedo radiation. Cooling the internal surface of the chamber with liquid nitrogen, we can simulate the

  4. Insights into the swelling process and drug release mechanisms from cross-linked pectin/high amylose starch matrices

    Directory of Open Access Journals (Sweden)

    Fernanda M. Carbinatto


    Full Text Available Cross-linked pectin/high amylose mixtures were evaluated as a new excipient for matrix tablets formulations, since the mixing of polymers and cross-linking reaction represent rational tools to reach materials with modulated and specific properties that meet specific therapeutic needs. Objective: In this work the influence of polymer ratio and cross-linking process on the swelling and the mechanism driving the drug release from swellable matrix tablets prepared with this excipient was investigated. Methods: Cross-linked samples were characterized by their micromeritic properties (size and shape, density, angle of repose and flow rate and liquid uptake ability. Matrix tablets were evaluated according their physical properties and the drug release rates and mechanisms were also investigated. Results: Cross-linked samples demonstrated size homogeneity and irregular shape, with liquid uptake ability insensible to pH. Cross-linking process of samples allowed the control of drug release rates and the drug release mechanism was influenced by both polymer ratio and cross-linking process. The drug release of samples with minor proportion of pectin was driven by an anomalous transport and the increase of the pectin proportion contributed to the erosion of the matrix. Conclusion: The cross-linked mixtures of high amylose and pectin showed a suitable excipient for slowing the drug release rates.

  5. Induction of tryptase and histmine release from human colon mast cells by IgE dependent or independent mechanisms

    Institute of Scientific and Technical Information of China (English)

    Shao-Heng He; Hua Xie; Yong-Song He


    AIM: To investigate the tryptase and histamine release ability of human colon mast cells upon IgE dependent or independent activation and the potential mechanisms.METHODS: Enzymatically dispersed cells from human colons were challenged with anti-IgE or calcium ionophore A23187, and the cell supernatants after challenge were collected. Both concentration dependent and time course studies with anti-IgE or calcium ionophore A23187 were performed. Tryptase release was determined with a sandwich ELISA procedure and histamine release was measured usina a glass fibre-based fluorometric assay.RESULTS: Both anti-IgE and calcium ionophore were able to induce dose dependent release of histamine from colon mast cells with up to approximately 60% and 25% net histamine release being achieved with 1 μg/mL calcium ionophore and 10 μg/mL anti-IgE, respectively. Dose dependent release of tryptase was also observed with up to approximately 19 ng/mL and 21 ng/mL release of tryptase being achieved with 10 μg/mL anti-IgE and 1 μg/mL calcium ionophore, respectively. Time course study revealed that both tryptase and histamine release from colon mast cells stimulated by anti-IgE initiated within 10 sec and reached their maximum release at 6 min following challenge. Pretreatment of cells with metabolic inhibitors abolished the actions of anti-IgE as well as calcium ionophore. Tryptase and histamine release, particularly that induced by calcium ionophore was inhibited by pretreatment of cells with pertussis toxin.CONCLUSION: Both anti-IgE and calcium ionophore are able to induce significant release of tryptase and histamine from colon mast cells, indicating that this cell type is likely to contribute to the pathogenesis of colitis and other mast cell associated intestinal diseases.

  6. Expression of Fas ligand by human gastric adenocarcinomas: a potential mechanism of immune escape in stomach cancer.

    LENUS (Irish Health Repository)

    Bennett, M W


    BACKGROUND: Despite being immunogenic, gastric cancers overcome antitumour immune responses by mechanisms that have yet to be fully elucidated. Fas ligand (FasL) is a molecule that induces Fas receptor mediated apoptosis of activated immunocytes, thereby mediating normal immune downregulatory roles including immune response termination, tolerance acquisition, and immune privilege. Colon cancer cell lines have previously been shown to express FasL and kill lymphoid cells by Fas mediated apoptosis in vitro. Many diverse tumours have since been found to express FasL suggesting that a "Fas counterattack" against antitumour immune effector cells may contribute to tumour immune escape. AIM: To ascertain if human gastric tumours express FasL in vivo, as a potential mediator of immune escape in stomach cancer. SPECIMENS: Thirty paraffin wax embedded human gastric adenocarcinomas. METHODS: FasL protein was detected in gastric tumours using immunohistochemistry; FasL mRNA was detected in the tumours using in situ hybridisation. Cell death was detected in situ in tumour infiltrating lymphocytes using terminal deoxynucleotidyl transferase mediated dUTP nick end labelling (TUNEL). RESULTS: Prevalent expression of FasL was detected in all 30 resected gastric adenocarcinomas examined. In the tumours, FasL protein and mRNA were co-localised to neoplastic gastric epithelial cells, confirming expression by the tumour cells. FasL expression was independent of tumour stage, suggesting that it may be expressed throughout gastric cancer progression. TUNEL staining disclosed a high level of cell death among lymphocytes infiltrating FasL positive areas of tumour. CONCLUSIONS: Human gastric adenocarcinomas express the immune downregulatory molecule, FasL. The results suggest that FasL is a prevalent mediator of immune privilege in stomach cancer.

  7. Characterization of drug release and diffusion mechanism through hydroxyethylmethacrylate/methacrylic acid pH-sensitive hydrogel. (United States)

    Varshosaz, Jaleh; Hajian, Mahmood


    Hydroxyethylmethacrylate/methacrylic acid copolymer cross-linked with ethylenglycol dimethacrylate was prepared by a bulk free radical polymerization method. The permeability studies of this pH-sensitive hydrogel to drugs with different water solubilities showed a water-content dependent diffusion or pore mechanism for ephedrine HCl (water-soluble model drug), whereas, a partition or solute-diffusion mechanism for indomethacin (a water-insoluble drug) was seen. Data analysis of release tests, according to the swelling interface number and Peppas equation for ephedrine HCl in pH 7.4, showed a biexponential model kinetic, whereas in pH 1.2 a swelling-controlled mechanism was seen. Indomethacin was released by an anomalous or non-Fickian release kinetics.

  8. World Stress Map Release 2005 - Stress orientations from single focal mechanisms at plate boundaries (United States)

    Heidbach, O.; Barth, A.; Müller, B.; Reinecker, J.; Sperner, B.; Tingay, M.


    The World Stress Map (WSM) is a global compilation of data about recent tectonic stresses from a wide range of indicators (e.g. focal mechanisms, borehole breakouts). It is a valuable tool for the solution of numerous of technological and scientific problems. The orientation of the stress field, for instance, is a primary control on subsurface fluid flow and thus WSM data can be used to improve petroleum production or the efficiency of geothermal power stations. In scientific context, information on the stress state is essential for seismic hazard assessment. The WSM database release 2005 contains more than 14,000 data sets all classified according to a unified quality ranking. Thus, the comparability of data from different types of measurement is guaranteed. The database as well as guidelines and software for plotting stress maps are available free of charge from our website Users can create their own stress map including their own stress data almost instantly with the CASMO (Create A Stress Map Online) web tool. Alternatively, users can download the software CASMI (Create A Stress Map Interactively) free of charge and produce their own stress maps. In the WSM 2005 release we refined the definition of so-called Possible Plate Boundary Events (PBE) for stress data from single focal mechanisms (FMS) considering that the orientations of these earthquakes might be rather controlled by the geometry of the plate boundary than by the stress field orientation. In general, it is assumed that numerous randomly oriented faults are present in the crust, so that earthquakes occur on faults optimally oriented relative to the regional stress field. In such a setting the principal axes of the moment tensor (P, B, T) provide good approximations for the principal stress orientations (σ_1, σ2, σ3). However, plate boundaries show a different mechanical behavior. They are characterized by faults with preferred orientations and presumably include major

  9. Kinetics and mechanism of the ligand substitution reaction of di--hydroxobis(bipyridyl)dipalladium(II) ion with diethyldithiocarbamate anion in aqueous solution

    Indian Academy of Sciences (India)

    Subhasis Mallick; Biplab K Bera; Subala Mondal; Parnajyoti Karmakar; Arup Mandal; Alak K Ghosh


    The kinetics of the interaction between diethyldithiocarbamate (Et2DTC) and the title complex has been studied spectrophotometrically in aqueous medium as a function of nucleophile concentration, temperature and pH at constant ionic strength. The reaction is a two-step process in which the first step is liganddependent, but the second step is ligand-independent and is assigned to ring closure. The rate and activation parameters, conductivity studies and IR data were used to deduce a plausible mechanism.

  10. Kinetics and mechanism of interaction of some bioactive ligands with cis-diaqua(cis-1,2-diaminocyclohexane)platinum(II) in aqueous medium

    Indian Academy of Sciences (India)

    P Karmakar; S Ray; S Mallick; B K Bera; A Mandal; S Mondal; A K Ghosh


    The substitution reaction of cis-[Pt(cis-dach)(H2O)2]2+ (where `dach’ is cis-1,2-diaminocyclohexane) with 2-thiouracil (S, N), 1,2-cyclohexanedionedioxime (N, N) and acetylacetone (O, O) were studied in aqueous solution in 0.10 M NaClO4 under pseudo-first order conditions as a functions of concentration, pH and temperature using UV-Vis spectrophotometry. The substitution reaction proceeds via rapid outer sphere association complex formation, followed by two slow consecutive steps. The first of these involves ligand-assisted deaquation, while second involves chelation as the second aqua ligand is displaced. The association equilibrium constant (KE) for the outer sphere complex formation has been evaluated together with rate constants for the two subsequent steps. The rate constants increase with increasing ligand concentration and the evaluated activation parameters for all reactions suggest an associative substitution mechanism for both the aqua ligand substitution processes. The product of the reaction has been characterized by IR, NMR and ESI-MS spectral analysis; which throws more light on the mechanistic behaviour of platinum(II) antitumour complexes.

  11. Fabrication of drug eluting implants: study of drug release mechanism from titanium dioxide nanotubes (United States)

    Hamlekhan, Azhang; Sinha-Ray, Suman; Takoudis, Christos; Mathew, Mathew T.; Sukotjo, Cortino; Yarin, Alexander L.; Shokuhfar, Tolou


    Formation of titanium dioxide nanotubes (TNTs) on a titanium surface holds great potential for promoting desirable cellular response. However, prolongation of drug release from these nano-reservoirs remains to be a challenge. In our previous work TNTs were successfully loaded with a drug. In this study the effect of TNTs dimensions on prolongation of drug release is quantified aiming at the introduction of a simple novel technique which overcomes complications of previously introduced methods. Different groups of TNTs with different lengths and diameters are fabricated. Samples are loaded with a model drug and rate of drug release over time is monitored. The relation of the drug release rate to the TNT dimensions (diameter, length, aspect ratio and volume) is established. The results show that an increase in any of these parameters increases the duration of the release process. However, the strongest parameter affecting the drug release is the aspect ratio. In fact, TNTs with higher aspect ratios release drug slower. It is revealed that drug release from TNT is a diffusion-limited process. Assuming that diffusion of drug in (Phosphate-Buffered Saline) PBS follows one-dimensional Fick’s law, the theoretical predictions for drug release profile is compatible with our experimental data for release from a single TNT.

  12. Mechanism of histamine release from rat mast cells induced by the ionophore A23187: effects of calcium and temperature

    DEFF Research Database (Denmark)

    Johansen, Torben


    1 The mechanism of histamine release from a pure population of rat mast cells induced by the lipid soluble antibiotic, A23187, has been studied and compared with data for anaphylactic histamine release reported in the literature. 2 Histamine release induced by A23187 in the presence of calcium 10......(-3) mol/l was completed in 10 minutes. By preincubation of the mast cells with A23187 for 10 min in the absence of calcium the histamine release induced by calcium, 10(-3) mol/l or 5 x 10(-3) mol/l, was completed in 90 s and 45 s, respectively. 3 A23187-induced histamine release was maximal with calcium...... 10(-3) mol/l when the cells were incubated at 33 to 39 degrees C for 10 minutes. 4 The cellular mechanism, which was stimulated by A23187 and calcium for the release of histamine, was irreversibly inactivated by incubation at 45 degrees C. 5 An inhibition of energy metabolism was excluded...

  13. Mechanisms of peptide YY release induced by an intraduodenal meal in rats: neural regulation by proximal gut. (United States)

    Fu-Cheng, X; Anini, Y; Chariot, J; Castex, N; Galmiche, J P; Rozé, C


    Peptide YY (PYY) release in anaesthetized rats was studied during the 2 h following the intraduodenal administration of a semi-liquid meal of 21 kJ. Surgical and pharmacological manipulations were performed in order to analyse the mechanisms of PYY release. Postprandial PYY release was suppressed or strongly decreased by caecocolonectomy, truncal vagotomy, tetrodotoxin, hexamethonium, sensory denervation by perivagal capsaicin, and by the NO-synthase inhibitor L-N-arginine methyl ester, while atropine, adrenergic blockers, antagonists of type-A or type-B cholecystokinin (CCK) receptors or bombesin receptors had no effect. Comparing the digestive transit of the semi-liquid meal with the amount of PYY contained in the small bowel wall showed that nutrients had not reached the area rich in cells containing PYY by 30 min, the time at which there was a large PYY release in plasma. By 120 min, the meal front had travelled 72% of the small intestine length, just beginning to reach the PYY-rich part of the ileum. We conclude that the main postprandial PYY release studied in this model comes from ileal and colonic L-cells indirectly stimulated through a neural mechanism originating in the proximal gut and involving sensory vagal fibres, nicotinic synapses and NO release, while CCK and bombesin do not seem to be physiologically involved.

  14. Two gonadotropin-releasing hormone receptor subtypes with distinct ligand selectivity and differential distribution in brain and pituitary in the goldfish (Carassius auratus)


    Illing, Nicola; Troskie, Brigitte E.; Nahorniak, Carol S.; Janet P Hapgood; Peter, Richard E.; Millar, Robert P.


    In the goldfish (Carassius auratus) the two endogenous forms of gonadotropin-releasing hormone (GnRH), namely chicken GnRH II ([His5,Trp7,Tyr8]GnRH) and salmon GnRH ([Trp7,Leu8]GnRH), stimulate the release of both gonadotropins and growth hormone from the pituitary. This control is thought to occur by means of the stimulation of distinct GnRH receptors. These receptors can be distinguished on the basis of differential gonadotropin and growth hormone releasing activities of naturally occurring...

  15. Matrix formation in sustained release tablets: possible mechanism of dose dumping. (United States)

    Krajacic, Aleksandra; Tucker, Ian G


    Conditions under which poly(ethyl acrylate, methyl methacrylate) 2:1 (poly(EA-MMA), Eudragit NE) forms a stable matrix were investigated in tablets with diclofenac sodium (DS) as an active substance. DS was granulated with the aqueous polymer dispersion. Granules and/or tablets were cured under various temperature and humidity conditions. A six position rotating disk (200 rpm) apparatus was used for the release studies conducted in 37 degrees C acid then phosphate buffer (0.4 M) pH 6.8 or buffer only as the dissolution media. Morphological characteristics of the tablet surface were observed under SEM. Changes in tablet structure upon curing were evaluated through changes in tablet mechanical characteristics. Modulus of rupture, Young's modulus, AUC, AUC(max), where AUC=AUC(max), were determined by the three-point bending test. Some poorly cured tablets dose-dumped when placed directly into buffer but not if first placed in acid and then buffer. A higher content of polymer in the matrix, led to formation of a stronger polymer network upon higher curing temperature and/or longer curing duration, whereas relative humidity had a minor effect.

  16. Release of copper-amended particles from micronized copper-pressure-treated wood during mechanical abrasion


    Civardi, Chiara; Schlagenhauf, Lukas; Kaiser, Jean-Pierre; Hirsch, Cordula; Mucchino, Claudio; Wichser, Adrian; Wick, Peter; Schwarze, Francis W. M. R.


    Background We investigated the particles released due to abrasion of wood surfaces pressure-treated with micronized copper azole (MCA) wood preservative and we gathered preliminary data on its in vitro cytotoxicity for lung cells. The data were compared with particles released after abrasion of untreated, water (0% MCA)-pressure-treated, chromated copper (CC)-pressure-treated wood, and varnished wood. Size, morphology, and composition of the released particles were analyzed. Results Our resul...

  17. The pH effect of solvent in silanization on fluoride released and mechanical properties of heat-cured acrylic resin containing fluoride-releasing filler. (United States)

    Nakornchai, Natha; Arksornnukit, Mansuang; Kamonkhantikul, Krid; Takahashi, Hidekazu


    This study aimed to evaluate the effect of an acidic-adjusted pH of solvent in silanization on the amount of fluoride released and mechanical properties of heat-cured acrylic resin containing a silanized fluoride-releasing filler. The experimental groups were divided into 4 groups; non-silanized, acidic-adjusted pH, non-adjusted pH, and no filler as control. For fluoride measurement, each specimen was placed in deionized water which was changed every day for 7 days, every week for 7 weeks and measured. The flexural strength and flexural modulus were evaluated after aging for 48 h, 1, and 2 months. Two-way ANOVA indicated significant differences among groups, storage times, and its interaction in fluoride measurement and flexural modulus. For flexural strength, there was significant difference only among groups. Acidic-adjusted pH of solvent in silanization enhanced the amount of fluoride released from acrylic resin, while non-adjusted pH of solvent exhibited better flexural strength of acrylic resin.

  18. Solid lipid particles for oral delivery of peptide and protein drugs I - Elucidating the release mechanism of lysozyme during lipolysis

    DEFF Research Database (Denmark)

    Christophersen, Philip Carsten B; Zhang, L.; Yang, M


    The mechanism of protein release from solid lipid particles was investigated by a new lipolysis model in a biorelevant medium containing both bile salts and phospholipids. Lysozyme, a model protein, was formulated into solid lipid particles using four different types of lipids, two triglycerides...... with different chain-length of fatty acyl groups i.e. trimyristin (TG14) and tristearin (TG18), and two lipid blends dominated by diglycerides and monoglycerides, respectively. The release of lysozyme from the solid lipid particles and the lipid hydrolysis process were assessed in the lipolysis model, while...... the drug release mechanism from solid lipid particles and can potentially be used in rational selection of lipid excipients for oral delivery of peptide/protein drugs....

  19. Considerations for conducting incubations to study the mechanisms of As release in reducing groundwater aquifers

    Energy Technology Data Exchange (ETDEWEB)

    Radloff, Kathleen A. [Department of Earth and Environmental Engineering, Columbia University, New York, NY 10027 (United States)], E-mail:; Manning, Anya R.; Mailloux, Brian [Barnard College, Columbia University, New York, NY 10027 (United States); Zheng Yan [Queens College, City University of New York, Flushing, NY 11367 (United States); Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964 (United States); Moshiur Rahman, M.; Rezaul Huq, M.; Ahmed, Kazi M. [Department of Geology, University of Dhaka, Dhaka (Bangladesh); Geen, Alexander van [Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964 (United States)


    Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orange-colored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1x or (4) 10x the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment. Using gamma irradiation as an abiotic control, shallow grey sediment and groundwater from 3 closely spaced locations along a gradient of dissolved As concentrations (60-130-210 {mu}g/L) in Bangladesh were incubated for 8 months with and without organic C addition (0.9 and 0.6 mM of acetate and lactate). Unexpectedly, levels of dissolved As (64 {+-} 68, 92 {+-} 70, 217 {+-} 68 {mu}g/L) and P-extractable As (0.7 {+-} 0.2, 2.1 {+-} 0.5 and 2.0 {+-} 0.3 mg/kg) at each location were highly variable over the duration of the experiment and prevented the detection of the relatively small levels of As release that were anticipated. Maintenance of an adsorptive equilibrium

  20. [Preparation and release mechanism of gestodene reservoir-type intravaginal rings]. (United States)

    Li, Chun-Xiao; Wang, Yan-Kun; Ning, Mei-Ying


    This study taking gestodene (GEST) as a model, investigated the factors affecting reservoir-type intravaginal ring (IVR)'s drug release. This paper reported a gestodene intravaginal ring of reservoir design, comprising a gestodene silicone elastomer core encased in a non-medicated silicone sheath, separately manufactured by reaction injection moulding at 80 degrees C and heating vulcanization at 130 degrees C is reported. The test investigated the factors affecting drug release through a single variable method, taking the drug release rates of 21 days as standards. When changing the thickness of the controlling sheath outside, the ratio of the first day of drug release and mean daily release (MDR), named the relatively burst effect, is closing to 1 with the thickness of controlling sheath increasing, while the 1.25 mm sheath corresponding to 1.04 controlled the burst release effectively; a positive correlation (r = 0.992 2) existed between the average drug release (Q/t) and drug loading (A) within a certain range. The C6-165 controlling sheath with high solubility of GEST is easier to achieve controlled release of the drug; GEST crystalline power is more effective to implement controlled release of drugs among difficent states of the drug. A 1/4 fractional segment core gives a relatively burst effect of 1.76, while the 1/1 and 1/2 are 1.93 and 1.87 separately, at the same drug loading, concluding that use of a fractional segment core would allow development of a suitable GEST reservoir IVR. In summary, GEST reservoir-type IVR could be adjusted by the thickness of controlling sheath, the loading of drug, the material properties of controlling sheath, the dispersion state of drug, the additive composition and structure of intravaginal ring, to control the drug release behavior and achieve the desired drug release rate.

  1. Pharmacological analysis for mechanisms of GPI-80 release from tumour necrosis factor-alpha-stimulated human neutrophils. (United States)

    Nitto, Takeaki; Araki, Yoshihiko; Takeda, Yuji; Sendo, Fujiro


    1 GPI-80, a glycosylphosphatidylinositol (GPI)-anchored protein initially identified on human neutrophils, plays a role(s) in the regulation of beta2 integrin function. Previous studies have shown that GPI-80 is sublocated in secretory vesicles. It is also found in soluble form in the synovial fluid of rheumatoid arthritis patients, and in the culture supernatant of formyl-methionyl-leucyl-phenylalanine-stimulated neutrophils. To understand the behaviour of GPI-80 under conditions of stimulation, we investigated the effects of tumour necrosis factor (TNF)-alpha on its expression and release. We also probed the mechanism of its release with various pharmacologic tools. 2 TNF-alpha induced the release of GPI-80 from human neutrophils in a concentration- and time-dependent manner (in the range of 1-100 u ml(-1) and 30-120 min, respectively), but did not affect surface GPI-80 levels. 3 Cytochalasin B, genistein, and SB203580 but not PD98059 inhibited TNF-alpha-stimulated GPI-80 release and neutrophil adherence at the same concentration. In addition, TNF-alpha-induced GPI-80 release was inhibited by blocking monoclonal antibodies specific to components of Mac-1 (CD11b and CD18). 4 Antioxidants (pyrrolidine dithiocarbamate and N-acetyl-L-cysteine) inhibited GPI-80 release by TNF-alpha stimulation, but superoxide dismutase did not. Antioxidants but not superoxide dismutase reduced an intracellular oxidation state. 5 These findings indicate that TNF-alpha-stimulated GPI-80 release from human neutrophils depends upon adherence via beta2 integrins. They also suggest that cytochalasin B, genistein, and SB203580 inhibit GPI-80 release by suppressing signals for cell adherence, rather than by a direct effect on its secretion. Finally, we suggest that GPI-80 release involves an intracellular change in a redox state.

  2. Effects of Biowastes Released by Mechanically Damaged Muscle Cells on the Propagation of Deep Tissue Injury: A Multiphysics Study. (United States)

    Yao, Yifei; Da Ong, Lucas Xian; Li, Xiaotong; Wan, Kinlun; Mak, Arthur F T


    Deep tissue injuries occur in muscle tissues around bony prominences under mechanical loading leading to severe pressure ulcers. Tissue compression can potentially compromise lymphatic transport and cause accumulation of metabolic biowastes, which may cause further cell damage under continuous mechanical loading. In this study, we hypothesized that biowastes released by mechanically damaged muscle cells could be toxic to the surrounding muscle cells and could compromise the capability of the surrounding muscle cells to withstand further mechanical loadings. In vitro, we applied prolonged low compressive stress (PLCS) and short-term high compressive stress to myoblasts to cause cell damage and collected the biowastes released by the damaged cells under the respective loading scenarios. In silico, we used COMSOL to simulate the compressive stress distribution and the diffusion of biowastes in a semi-3D buttock finite element model. In vitro results showed that biowastes collected from cells damaged under PLCS were more toxic and could compromise the capability of normal myoblasts to resist compressive damage. In silico results showed that higher biowastes diffusion coefficient, higher biowastes release rate, lower biowastes tolerance threshold and earlier timeline of releasing biowastes would cause faster propagation of tissue damage. This study highlighted the importance of biowastes in the development of deep tissue injury to clinical pressure ulcers under prolonged skeletal compression.

  3. Real-time imaging of ATP release induced by mechanical stretch in human airway smooth muscle cells. (United States)

    Takahara, Norihiro; Ito, Satoru; Furuya, Kishio; Naruse, Keiji; Aso, Hiromichi; Kondo, Masashi; Sokabe, Masahiro; Hasegawa, Yoshinori


    Airway smooth muscle (ASM) cells within the airway walls are continually exposed to mechanical stimuli, and exhibit various functions in response to these mechanical stresses. ATP acts as an extracellular mediator in the airway. Moreover, extracellular ATP is considered to play an important role in the pathophysiology of asthma and chronic obstructive pulmonary disease. However, it is not known whether ASM cells are cellular sources of ATP secretion in the airway. We therefore investigated whether mechanical stretch induces ATP release from ASM cells. Mechanical stretch was applied to primary human ASM cells cultured on a silicone chamber coated with type I collagen using a stretching apparatus. Concentrations of ATP in cell culture supernatants measured by luciferin-luciferase bioluminescence were significantly elevated by cyclic stretch (12 and 20% strain). We further visualized the stretch-induced ATP release from the cells in real time using a luminescence imaging system, while acquiring differential interference contrast cell images with infrared optics. Immediately after a single uniaxial stretch for 1 second, strong ATP signals were produced by a certain population of cells and spread to surrounding spaces. The cyclic stretch-induced ATP release was significantly reduced by inhibitors of Ca(2+)-dependent vesicular exocytosis, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester, monensin, N-ethylmaleimide, and bafilomycin. In contrast, the stretch-induced ATP release was not inhibited by a hemichannel blocker, carbenoxolone, or blockade of transient receptor potential vanilloid 4 by short interfering RNA transfection or ruthenium red. These findings reveal a novel property of ASM cells: mechanically induced ATP release may be a cellular source of ATP in the airway.

  4. Mechanical properties and total hydroxycinnamic derivative release of starch/glycerol/Melissa officinalis extract films

    Directory of Open Access Journals (Sweden)

    Letícia Mello Rechia


    Full Text Available The aim of this study was to investigate the mechanical properties of starch/glycerol/Melissa officinalis, a topical drug delivery system for labial herpes treatment. Four films were prepared with different concentrations of starch, glycerol, and Melissa officinalis extract. The results revealed that increasing the glycerol concentration in the film reduced elasticity modulus and tensile strength, exhibiting a plasticizing effect. The increase in free volume resulted in increased release of hydroxycinnamic derivatives expressed as rosmarinic acid.O objetivo deste trabalho foi estudar as propriedades mecânicas e o mecanismo de liberação de um sistema tópico de liberação prolongada para o tratamento do Herpes labial a partir de filmes de amido/glicerol/extrato de Melissa officinalis, planta com comprovada atividade antiviral. Foram obtidos quatro filmes poliméricos com diferentes concentrações de amido, glicerol e extrato de Melissa officinalis os quais foram caracterizados mecanicamente e determinado o perfil de liberação de derivados hidroxicinâmicos. Os resultados demonstraram que o aumento da concentração de glicerol no filme produz uma redução no módulo de elasticidade e na tensão de deformação como conseqüência do efeito plastificante. O aumento no volume livre do polímero resultou em aumento da liberação dos derivados hidroxicinâmicos expressos como ácido rosmarínico.

  5. Strong-Sludge Gas Retention and Release Mechanisms in Clay Simulants

    Energy Technology Data Exchange (ETDEWEB)

    Gauglitz, Phillip A.; Buchmiller, William C.; Probert, Samuel G.; Owen, Antionette T.; Brockman, Fred J.


    The Hanford Site has 28 double-shell tanks (DSTs) and 149 single-shell tanks (SSTs) containing radioactive wastes that are complex mixes of radioactive and chemical products. The mission of the Department of Energy's River Protection Project is to retrieve and treat the Hanford tank waste for disposal and close the tank farms. A key aspect of the mission is to retrieve and transfer waste from the SSTs, which are at greater risk for leaking, into DSTs for interim storage until the waste is transferred to and treated in the Waste Treatment and Immobilization Plant. There is, however, limited space in the existing DSTs to accept waste transfers from the SSTs, and approaches to overcoming the limited DST space will benefit the overall mission. The purpose of this study is to summarize and analyze the key previous experiment that forms the basis for the relaxed controls and to summarize progress and results on new experiments focused on understanding the conditions that result in low gas retention. The previous large-scale test used about 50 m3 of sediment, which would be unwieldy for doing multiple parametric experiments. Accordingly, experiments began with smaller-scale tests to determine whether the desired mechanisms can be studied without the difficulty of conducting very large experiments. The most significant results from the current experiments are that progressively lower gas retention occurs in tests with progressively deeper sediment layers and that the method of gas generation also affects the maximum retention. Based on the results of this study, it is plausible that relatively low gas retention could occur in sufficiently deep tank waste in DSTs. The current studies and previous work, however, have not explored how gas retention and release will behave when two or more layers with different properties are present.

  6. Drug release-modulating mechanism of hydrophilic hydroxypropylmethylcellulose matrix tablets: distribution of atoms and carrier and texture analysis. (United States)

    Park, Jun-Bom; Lim, Jisung; Kang, Chin-Yang; Lee, Beom-Jin


    Although release profiles of drug from hydrophilic matrices have been well recognized, the visual distribution of hydroxypropylmethylcellulose (HPMC) and atoms inside of internal structures of hydrophilic HPMC matrices has not been characterized. In this paper, drug release mechanism from HPMC matrix tablet was investigated based on the release behaviors of HPMC, physical properties of gelled HPMC tablet and atomic distributions of formulation components using diverse instruments. A matrix tablet consisting of hydroxypropyl methylcellulose (HPMC 6, 4,000 and 100,000 mPa·s), chlorpheniramine maleate (CPM) as a model and fumed silicon dioxide (Aerosil(®) 200) was prepared via direct compression. The distribution of atoms and HPMC imaging were characterized using scanning electron microscope (SEM)/ energy-dispersive X-ray spectroscopy (EDX), and near-infrared (NIR) analysis, respectively as a function of time. A texture analyzer was also used to characterize the thickness and maintenance of gel layer of HPMC matrix tablet. The HPMC matrix tablets showed Higuchi release kinetics with no lag time against the square root of time. High viscosity grades of HPMC gave retarded release rate because of the greater swelling and gel thickness as characterized by texture analyzer. According to the NIR imaging, low-viscosity-grade HPMC (6 mPa·s) quickly leached out onto the surface of the tablet, while the high-viscosity-grade HPMC (4000 mPa·s) formed much thicker gel layer around the tablet and maintained longer via slow erosion, resulting in retarded drug release. The atomic distribution of the drug (chlorine, carbon, oxygen), HPMC (carbon, oxygen) and silicon dioxide (silica, oxygen) and NIR imaging of HPMC corresponded with the dissolution behaviors of drug as a function of time. The use of imaging and texture analyses could be applicable to explain the release- modulating mechanism of hydrophilic HPMC matrix tablets.

  7. Influence of Different Polymer Types on the Overall Release Mechanism in Hydrophilic Matrix Tablets

    Directory of Open Access Journals (Sweden)

    Bengt Wittgren


    Full Text Available The effect of three different types of polymer chain structures on the polymer release from hydrophilic matrix tablets was investigated by comparing a synthetic semi-crystalline linear polymer (PEO, a branched amorphous polysaccharide (dextran and an amorphous substituted cellulose derivative (HPMC. The polymer release rates for tablets containing mixtures of high and low molecular weight grades in different ratios were determined by using a modified USP II method and a SEC-RI chromatography system. The results showed that independent of polymer type: (i plots of the release versus time had similar shapes, (ii the release of long and short polymer chains was equal and no fractionation occurred during the release and (iii the release rate could be related to the average intrinsic viscosity of the polymer mixtures. This confirms the hypothesis that the release rate can be related to a constant viscosity on the surface of the hydrophilic matrix tablet and that it is valid for all the investigated polymers.

  8. Mechanisms, pools, and sites of spontaneous vesicle release at synapses of rod and cone photoreceptors. (United States)

    Cork, Karlene M; Van Hook, Matthew J; Thoreson, Wallace B


    Photoreceptors have depolarized resting potentials that stimulate calcium-dependent release continuously from a large vesicle pool but neurons can also release vesicles without stimulation. We characterized the Ca(2+) dependence, vesicle pools, and release sites involved in spontaneous release at photoreceptor ribbon synapses. In whole-cell recordings from light-adapted horizontal cells (HCs) of tiger salamander retina, we detected miniature excitatory post-synaptic currents (mEPSCs) when no stimulation was applied to promote exocytosis. Blocking Ca(2+) influx by lowering extracellular Ca(2+) , by application of Cd(2+) and other agents reduced the frequency of mEPSCs but did not eliminate them, indicating that mEPSCs can occur independently of Ca(2+) . We also measured release presynaptically from rods and cones by examining quantal glutamate transporter anion currents. Presynaptic quantal event frequency was reduced by Cd(2+) or by increased intracellular Ca(2+) buffering in rods, but not in cones, that were voltage clamped at -70 mV. By inhibiting the vesicle cycle with bafilomycin, we found the frequency of mEPSCs declined more rapidly than the amplitude of evoked excitatory post-synaptic currents (EPSCs) suggesting a possible separation between vesicle pools in evoked and spontaneous exocytosis. We mapped sites of Ca(2+) -independent release using total internal reflectance fluorescence (TIRF) microscopy to visualize fusion of individual vesicles loaded with dextran-conjugated pHrodo. Spontaneous release in rods occurred more frequently at non-ribbon sites than evoked release events. The function of Ca(2+) -independent spontaneous release at continuously active photoreceptor synapses remains unclear, but the low frequency of spontaneous quanta limits their impact on noise.

  9. Note: A SMA wire actuated extremely long-lifetime release actuator using two ball-lock mechanisms (United States)

    Huang, Dawei; Yan, Xiaojun; Zhang, Xiaoyong; Bai, Haibo; Wang, Xian; Liu, Ying


    A shape memory alloy (SMA)-wire actuated release actuator with an extremely long lifetime was designed and validated. To ensure the ability of repeated actuation, two stages of ball-lock mechanisms were adopted to reduce the load in the SMA wire. In addition, a length-increasing design of the SMA wire was employed. Validation tests, including function tests, vibration tests, shock tests, and thermal vacuum tests were conducted on prototypes. According to the test results, the actuator can release a maximum preload of 15 kN and has a lifetime of more than 693 cycles. Furthermore, the actuator can function well, even under severe thermal and vibration environments.

  10. Note: A SMA wire actuated extremely long-lifetime release actuator using two ball-lock mechanisms. (United States)

    Huang, Dawei; Yan, Xiaojun; Zhang, Xiaoyong; Bai, Haibo; Wang, Xian; Liu, Ying


    A shape memory alloy (SMA)-wire actuated release actuator with an extremely long lifetime was designed and validated. To ensure the ability of repeated actuation, two stages of ball-lock mechanisms were adopted to reduce the load in the SMA wire. In addition, a length-increasing design of the SMA wire was employed. Validation tests, including function tests, vibration tests, shock tests, and thermal vacuum tests were conducted on prototypes. According to the test results, the actuator can release a maximum preload of 15 kN and has a lifetime of more than 693 cycles. Furthermore, the actuator can function well, even under severe thermal and vibration environments.

  11. A concerted mechanism for opening the GDP binding pocket and release of the nucleotide in hetero-trimeric G-proteins. (United States)

    Louet, Maxime; Perahia, David; Martinez, Jean; Floquet, Nicolas


    G-protein hetero-trimers play a fundamental role in cell function. Their dynamic behavior at the atomic level remains to be understood. We have studied the Gi hetero-trimer through a combination of molecular dynamics simulations and normal mode analyses. We showed that these big proteins could undergo large-amplitude conformational changes, without any energy penalty and with an intrinsic dynamics centered on their GDP binding pocket. Among the computed collective motions, one of the modes (mode 17) was particularly able to significantly open both the base and the phosphate sides of the GDP binding pocket. This mode describing mainly a motion between the Ras-like and the helical domains of G(α) was in close agreement with some available X-ray data and with many other biochemical/biophysical observations including the kink of helix α5. The use of a new protocol, which allows extraction of the GDP ligand along the computed normal modes, supported that the exit of GDP was largely coupled to an opening motion along mode 17. We propose for the first time a "concerted mechanism" model in which the opening of the GDP pocket and the kink of the α5 helix occur concomitantly and favor GDP release from G(αβγ) complexes. This model is discussed in the context of the G-protein-coupled receptor/G-protein interaction close to the cell membrane. Copyright © 2011 Elsevier Ltd. All rights reserved.

  12. [Research advances on controlled-release mechanisms of nutrients in coated fertilizers]. (United States)

    Zhang, Haijun; Wu, Zhijie; Liang, Wenju; Xie, Hongtu


    Using encapsulation techniques to coat easily soluble fertilizers is an important way to improve fertilizer use efficiency while reduce environmental hazards. Based on a wide range of literature collection on coated fertilizer research, the theories, processes, and characters of nutrient controlled-release from coated fertilizer were discussed, and the factors affecting nutrient controlled-release and the mathematical simulations on it were reviewed. The main tendencies related to this research in China were also put forward.

  13. Mechanisms of diphylline release from dual-solute loaded poly(vinyl alcohol) matrices

    Energy Technology Data Exchange (ETDEWEB)

    Hasimi, Albana; Papadokostaki, Kyriaki G.; Sanopoulou, Merope, E-mail:


    The release kinetics of the model hydrophilic drug, diphylline (DPL), from physically crosslinked poly(vinyl alcohol) (PVA) matrices, is studied in relation to the drug load and the presence of a second solute incorporated in the matrix. The second solute, a gadolinium (III) complex (Gd-DTPA), is a commonly used MRI contrast agent. The water uptake kinetics by the glassy PVA matrix was found to deviate from t{sup 1/2} law and to occur on time scales comparable to those of diphylline release. The corresponding rate of diphylline release was found to be substantially stabilized as compared to a purely diffusion-controlled release process, in line with theoretical predictions under conditions of relaxation-controlled water uptake kinetics. The release rate of DPL was found (i) to increase with increasing DPL load and (ii) for a particular DPL load, to increase in the presence of Gd-DTPA, incorporated in the matrix. The results were interpreted on the basis of the diphylline-induced plasticization of the polymer (evidenced by the depression of T{sub g}) and of the excess hydration of the matrix at high solute loads. The latter effect was found to be additive in the case of dual-solute loaded matrices. - Highlights: • Diphylline (DPL) release rate from PVA matrices increases with increasing DPL load • The effect is partly correlated with the acceleration of water uptake by the plasticized matrix • Release rate of DPL increases if a second solute is also incorporated in the matrix • An additive effect of the two solutes on excess hydration of the matrix is mainly responsible • Relevant theoretical calculations on release kinetics are presented.

  14. A GTPase chimera illustrates an uncoupled nucleotide affinity and release rate, Providing insight into the activation mechanism

    DEFF Research Database (Denmark)

    Guilfoyle, Amy P.; Deshpande, Chandrika N.; Font Sadurni, Josep;


    The release of GDP from GTPases signals the initiation of a GTPase cycle, where the association of GTP triggers conformational changes promoting binding of downstream effector molecules. Studies have implicated the nucleotide-binding G5 loop to be involved in the GDP release mechanism. For example......, biophysical studies on both the eukaryotic Gα proteins and the GTPase domain (NFeoB) of prokaryotic FeoB proteins have revealed conformational changes in the G5 loop that accompany nucleotide binding and release. However, it is unclear whether this conformational change in the G5 loop is a prerequisite...... GTPase activity at a similar level to wild-type NFeoB, and structural analyses of the nucleotide-free and GDP-bound proteins show that the G5 loop adopts conformations analogous to that of the human nucleotide-bound Giα1 protein in both states. Interestingly, isothermal titration calorimetry and stopped...

  15. Agonists and Antagonists of TGF-β Family Ligands. (United States)

    Chang, Chenbei


    The discovery of the transforming growth factor β (TGF-β) family ligands and the realization that their bioactivities need to be tightly controlled temporally and spatially led to intensive research that has identified a multitude of extracellular modulators of TGF-β family ligands, uncovered their functions in developmental and pathophysiological processes, defined the mechanisms of their activities, and explored potential modulator-based therapeutic applications in treating human diseases. These studies revealed a diverse repertoire of extracellular and membrane-associated molecules that are capable of modulating TGF-β family signals via control of ligand availability, processing, ligand-receptor interaction, and receptor activation. These molecules include not only soluble ligand-binding proteins that were conventionally considered as agonists and antagonists of TGF-β family of growth factors, but also extracellular matrix (ECM) proteins and proteoglycans that can serve as "sink" and control storage and release of both the TGF-β family ligands and their regulators. This extensive network of soluble and ECM modulators helps to ensure dynamic and cell-specific control of TGF-β family signals. This article reviews our knowledge of extracellular modulation of TGF-β growth factors by diverse proteins and their molecular mechanisms to regulate TGF-β family signaling.

  16. Microstructure, mechanical property and metal release of As-SLM CoCrW alloy under different solution treatment conditions. (United States)

    Lu, Yanjin; Wu, Songquan; Gan, Yiliang; Zhang, Shuyuan; Guo, Sai; Lin, Junjie; Lin, Jinxin


    In the study, the microstructure, mechanical property and metal release behavior of selective laser melted CoCrW alloys under different solution treatment conditions were systemically investigated to assess their potential use in orthopedic implants. The effects of the solution treatment on the microstructure, mechanical properties and metal release were systematically studied by OM, SEM, XRD, tensile test, and ICP-AES, respectively. The XRD indicated that during the solution treatment the alloy underwent the transformation of γ-fcc to ε-hcp phase; the ε-hcp phase nearly dominated in the alloy when treated at 1200°C following the water quenching; the results from OM, SEM showed that the microstructural change was occurred under different solution treatments; solution at 1150°C with furnace cooling contributed to the formation of larger precipitates at the grain boundary regions, while the size and number of the precipitates was decreased as heated above 1100°C with the water quenching; moreover, the diamond-like structure was invisible at higher solution temperature over 1150°C following water quenching; compared with the furnace cooling, the alloy quenched by water showed excellent mechanical properties and low amount of metal release; as the alloy heated at 1200°C, the mechanical properties of the alloy reached their optimum combination at UTS=1113.6MPa, 0.2%YS=639.5MPa, and E%=20.1%, whilst showed the lower total quantity of metal release. It is suggested that a proper solution treatment is an efficient strategy for improving the mechanical properties and corrosion resistance of As-SLM CoCrW alloy that show acceptable tensile ductility.

  17. Expression of toll-like receptors by human muscle cells in vitro and in vivo: TLR3 is highly expressed in inflammatory and HIV myopathies, mediates IL-8 release and up-regulation of NKG2D-ligands. (United States)

    Schreiner, Bettina; Voss, Joachim; Wischhusen, Jörg; Dombrowski, Yvonne; Steinle, Alexander; Lochmüller, Hanns; Dalakas, Marinos; Melms, Arthur; Wiendl, Heinz


    The particular microenvironment of the skeletal muscle can be the site of complex immune reactions. Toll-like receptors (TLRs) mediate inflammatory stimuli from pathogens and endogenous danger signals and link the innate and adaptive immune system. We investigated innate immune responses in human muscle. Analyzing TLR1-9 mRNA in cultured myoblasts and rhabdomyosarcoma cells, we found constitutive expression of TLR3. The TLR3 ligand Poly (I:C), a synthetic analog of dsRNA, and IFN-gamma increased TLR3 levels. TLR3 was mainly localized intracellularly and regulated at the protein level. Poly (I:C) challenge 1) activated nuclear factor-kappaB (NF-kappaB), 2) increased IL-8 release, and 3) up-regulated NKG2D ligands and NK-cell-mediated lysis of muscle cells. We examined muscle biopsy specimens of 6 HIV patients with inclusion body myositis/polymyositis (IBM/PM), 7 cases of sporadic IBM and 9 nonmyopathic controls for TLR3 expression. TLR3 mRNA levels were elevated in biopsy specimens from patients with IBM and HIV-myopathies. Muscle fibers in inflammatory myopathies expressed TLR3 in close proximity of infiltrating mononuclear cells. Taken together, our study suggests an important role of TLR3 in the immunobiology of muscle, and has substantial implications for the understanding of the pathogenesis of inflammatory myopathies or therapeutic interventions like vaccinations or gene transfer.


    Directory of Open Access Journals (Sweden)

    Seyed Mohsen Latifi


    Full Text Available Ca ion release from bioactive biomaterials could play an important role in their bioactivity and osteoconductivity properties. In order to improve hydroxyapatite (HA dissolution rate, in situ apatite-silica nanocomposite powders with various silica contents were synthesized via sol-gel method and mechanisms controlling the Ca ion release from them were investigated. Obtained powders were characterized by X-ray diffraction (XRD and transmission electron spectroscopy (TEM techniques, acid dissolution test, and spectroscopy by atomic absorption spectrometer (AAS. Results indicated the possible incorporation of (SiO44- into the HA structure and tendency of amorphous silica to cover the surface of HA particles. However, 20 wt. % silica was the lowest amount that fully covered HA particles. All of the nanocomposite powders showed more Ca ion release compared with pure HA, and HA - 10 wt. % silica had the highest Ca ion release. The crystallinity, the crystallite size, and the content of HA, along with the integrity, thickness, and ion diffusion possibility through the amorphous silica layer on the surface of HA, were factors that varied due to changes in the silica content and were affected the Ca ion release from nanocomposite powders.

  19. Evaluation of Antidiabetic Effects of the Traditional Medicinal Plant Gynostemma pentaphyllum and the Possible Mechanisms of Insulin Release (United States)

    Lokman, Ezarul Faradianna; Gu, Harvest F.; Wan Mohamud, Wan Nazaimoon; Östenson, Claes-Göran


    Aims. To evaluate the antidiabetic effects of Gynostemma pentaphyllum (GP) in Goto-Kakizaki (GK) rat, an animal model of type 2 diabetes, and to investigate the mechanisms of insulin release. Methods. Oral glucose tolerance test was performed and plasma insulin levels were measured. Results. An oral treatment with GP (0.3 g/kg of body weight daily) for two weeks in GK rats improved glucose tolerance versus placebo group (P < 0.01). Plasma insulin levels were significantly increased in the GP-treated group. The insulin release from GP-treated GK rats was 1.9-fold higher as compared to the control group (P < 0.001). GP stimulated insulin release in isolated GK rat islets at high glucose. Opening of ATP-sensitive potassium (K-ATP) channels by diazoxide and inhibition of calcium channels by nifedipine significantly decreased insulin response to GP. Furthermore, the protein kinase A (PKA) inhibitor H89 decreased the insulin response to GP (P < 0.05). In addition, GP-induced insulin secretion was decreased after preincubation of GK islets with pertussis toxin to inhibit exocytotic Ge proteins (P < 0.05). Conclusion. The antidiabetic effect of GP is associated with the stimulation of insulin release from the islets. GP-induced insulin release is partly mediated via K-ATP and L-type Ca2+ channels, the PKA system and also dependent on pertussis toxin sensitive Ge-protein. PMID:26199630

  20. Evaluation of Antidiabetic Effects of the Traditional Medicinal Plant Gynostemma pentaphyllum and the Possible Mechanisms of Insulin Release

    Directory of Open Access Journals (Sweden)

    Ezarul Faradianna Lokman


    Full Text Available Aims. To evaluate the antidiabetic effects of Gynostemma pentaphyllum (GP in Goto-Kakizaki (GK rat, an animal model of type 2 diabetes, and to investigate the mechanisms of insulin release. Methods. Oral glucose tolerance test was performed and plasma insulin levels were measured. Results. An oral treatment with GP (0.3 g/kg of body weight daily for two weeks in GK rats improved glucose tolerance versus placebo group (P<0.01. Plasma insulin levels were significantly increased in the GP-treated group. The insulin release from GP-treated GK rats was 1.9-fold higher as compared to the control group (P<0.001. GP stimulated insulin release in isolated GK rat islets at high glucose. Opening of ATP-sensitive potassium (K-ATP channels by diazoxide and inhibition of calcium channels by nifedipine significantly decreased insulin response to GP. Furthermore, the protein kinase A (PKA inhibitor H89 decreased the insulin response to GP (P<0.05. In addition, GP-induced insulin secretion was decreased after preincubation of GK islets with pertussis toxin to inhibit exocytotic Ge proteins (P<0.05. Conclusion. The antidiabetic effect of GP is associated with the stimulation of insulin release from the islets. GP-induced insulin release is partly mediated via K-ATP and L-type Ca2+ channels, the PKA system and also dependent on pertussis toxin sensitive Ge-protein.

  1. Anaerobic phosphate release from activated sludge with enhanced biological phosphorus removal. A possible mechanism of intracellular pH control

    Energy Technology Data Exchange (ETDEWEB)

    Bond, P.L.; Keller, J.; Blackall, L.L. [Univ. of Queensland, Brisbane (Australia)


    The biochemical mechanisms of the wastewater treatment process known as enhanced biological phosphorus removal (EBPR) are presently described in a metabolic model. The authors investigated details of the EBPR model to determine the nature of the anaerobic phosphate release and how this may be metabolically associated with polyhydroxyalkanoate (PHA) formation. Iodoacetate, an inhibitor of glycolysis, was found to inhibit the anaerobic formation of PHA and phosphate release, supporting the pathways proposed in the EBPR metabolic model. In the metabolic model, it is proposed that polyphosphate degradation provides energy for the microorganisms in anaerobic regions of these treatment systems. Other investigations have shown that anaerobic phosphate release depends on the extracellular pH. The authors observed that when the intracellular pH of EBPR sludge was raised, substantial anaerobic phosphate release was caused without volatile fatty acid (VFA) uptake. Acidification of the sludge inhibited anaerobic phosphate release even in the presence of VFA. from these observations, the authors postulate that an additional possible role of anaerobic polyphosphate degradation in EBPR is for intracellular pH control. Intracellular pH control may be a metabolic feature of EBPR, not previously considered, that could have some use in the control and optimization of EBPR.

  2. Distinct Dasatinib-Induced Mechanisms of Apoptotic Response and Exosome Release in Imatinib-Resistant Human Chronic Myeloid Leukemia Cells

    Directory of Open Access Journals (Sweden)

    Juan Liu


    Full Text Available Although dasatinib is effective in most imatinib mesylate (IMT-resistant chronic myeloid leukemia (CML patients, the underlying mechanism of its effectiveness in eliminating imatinib-resistant cells is only partially understood. This study investigated the effects of dasatinib on signaling mechanisms driving-resistance in imatinib-resistant CML cell line K562 (K562RIMT. Compared with K562 control cells, exsomal release, the phosphoinositide 3-kinase (PI3K/protein kinase B (Akt/ mammalian target of rapamycin (mTOR signaling and autophagic activity were increased significantly in K562RIMT cells and mTOR-independent beclin-1/Vps34 signaling was shown to be involved in exosomal release in these cells. We found that Notch1 activation-mediated reduction of phosphatase and tensin homolog (PTEN was responsible for the increased Akt/mTOR activities in K562RIMT cells and treatment with Notch1 γ-secretase inhibitor prevented activation of Akt/mTOR. In addition, suppression of mTOR activity by rapamycin decreased the level of activity of p70S6K, induced upregulation of p53 and caspase 3, and led to increase of apoptosis in K562RIMT cells. Inhibition of autophagy by spautin-1 or beclin-1 knockdown decreased exosomal release, but did not affect apoptosis in K562RIMT cells. In summary, in K562RIMT cells dasatinib promoted apoptosis through downregulation of Akt/mTOR activities, while preventing exosomal release and inhibiting autophagy by downregulating expression of beclin-1 and Vps34. Our findings reveal distinct dasatinib-induced mechanisms of apoptotic response and exosomal release in imatinib-resistant CML cells.

  3. Nanoporous anodic titanium dioxide layers as potential drug delivery systems: Drug release kinetics and mechanism. (United States)

    Jarosz, Magdalena; Pawlik, Anna; Szuwarzyński, Michał; Jaskuła, Marian; Sulka, Grzegorz D


    Nanoporous anodic titanium dioxide (ATO) layers on Ti foil were prepared via a three step anodization process in an electrolyte based on an ethylene glycol solution with fluoride ions. Some of the ATO samples were heat-treated in order to achieve two different crystallographic structures - anatase (400°C) and a mixture of anatase and rutile (600°C). The structural and morphological characterizations of ATO layers were performed using a field emission scanning electron microscope (SEM). The hydrophilicity of ATO layers was determined with contact angle measurements using distilled water. Ibuprofen and gentamicin were loaded effectively inside the ATO nanopores. Afterwards, an in vitro drug release was conducted for 24h under a static and dynamic flow conditions in a phosphate buffer solution at 37°C. The drug concentrations were determined using UV-Vis spectrophotometry. The absorbance of ibuprofen was measured directly at 222nm, whether gentamicin was determined as a complex with silver nanoparticles (Ag NPs) at 394nm. Both compounds exhibited long term release profiles, despite the ATO structure. A new release model, based on the desorption of the drug from the ATO top surface followed by the desorption and diffusion of the drug from the nanopores, was derived. The proposed release model was fitted to the experimental drug release profiles, and kinetic parameters were calculated.

  4. Lack of the specific influence of histamine and histamine H1, H2 and H3 receptor ligands on the serotonin uptake and release in rat blood platelets. (United States)

    Pawlak, D; Malinowska, B; Wollny, T; Godlewski, G; Buczko, W


    This work was designed to investigate the influence of histamine, and H1 receptor agonist 2-(2-thiazolyl)ethylamine, H2 receptor agonist dimaprit and H3 receptor agonist R-(-)-alpha-methylhistamine on the serotonin uptake and release in rat blood platelets. Histamine and R-(-)-alpha-methylhistamine (up to 1 mmol/l), 2-(2-thiazolyl)ethylamine (up to 10 mumol/l) and dimaprit (up to 1 mumol/l) failed to affect the serotonin uptake. The concentration-dependent inhibitory effects of higher concentrations of 2-(2-thiazolyl)ethylamine and dimaprit (up to 1 mmol/l) were not diminished by the H1 receptor antagonist dimetindene and the H2 receptor antagonist ranitidine (1 and 100 mumol/l each), respectively. Histamine, 2-(2-thiazolyl)ethylamine, dimaprit and R-(-)-alpha-methylhistamine (up to 10 mumol/l) did not change the serotonin release from rat blood platelets. Our results demonstrate that histamine and histamine H1, H2 and H3 receptor agonists do not affect in a specific manner the serotonin uptake and release in rat blood platelets.

  5. Anthocyanin Incorporated Dental Copolymer: Bacterial Growth Inhibition, Mechanical Properties, and Compound Release Rates and Stability by 1H NMR

    Directory of Open Access Journals (Sweden)

    Halyna Hrynash


    Full Text Available Objective. To evaluate bacterial growth inhibition, mechanical properties, and compound release rate and stability of copolymers incorporated with anthocyanin (ACY; Vaccinium macrocarpon. Methods. Resin samples were prepared (Bis-GMA/TEGDMA at 70/30 mol% and incorporated with 2 w/w% of either ACY or chlorhexidine (CHX, except for the control group. Samples were individually immersed in a bacterial culture (Streptococcus mutans for 24 h. Cell viability (n=3 was assessed by counting the number of colony forming units on replica agar plates. Flexural strength (FS and elastic modulus (E were tested on a universal testing machine (n=8. Compound release and chemical stability were evaluated by UV spectrophotometry and 1H NMR (n=3. Data were analyzed by one-way ANOVA and Tukey’s test (α = 0.05. Results. Both compounds inhibited S. mutans growth, with CHX being most effective (P<0.05. Control resin had the lowest FS and E values, followed by ACY and CHX, with statistical difference between control and CHX groups for both mechanical properties (P<0.05. The 24 h compound release rates were ACY: 1.33 μg/mL and CHX: 1.92 μg/mL. 1H NMR spectra suggests that both compounds remained stable after being released in water. Conclusion. The present findings indicate that anthocyanins might be used as a natural antibacterial agent in resin based materials.

  6. Effect of chloride on Ca2+ release from the sarcoplasmic reticulum of mechanically skinned skeletal muscle fibres. (United States)

    Coonan, J R; Lamb, G D


    The effect of intracellular Cl- on Ca2+ release in mechanically skinned fibres of rat extensor digitorum longus (EDL) and toad iliofibularis muscles was examined under physiological conditions of myoplasmic [Mg2+] and [ATP] and sarcoplasmic reticulum (SR) Ca2+ loading. Both in rat and toad fibres, the presence of 20 mM Cl- in the myoplasm increased Ca2+ leakage from the SR at pCa (i.e. -log10 [Ca2+]) 6.7, but not at pCa 8. Ca2+ uptake was not significantly affected by the presence of Cl-. This Ca2+-dependent effect of Cl- on Ca2+ leakage was most likely due to a direct action on the ryanodine receptor/Ca2+ release channel, and could influence channel sensitivity and the resting [Ca2+] in muscle fibres in vivo. In contrast to this effect, acute addition of 20 mM Cl- to the myoplasm caused a 40-50% reduction in Ca2+ release in response to a low caffeine concentration both in toad and rat fibres. One possible explanation for this latter effect is that the addition of Cl- induces a potential across the SR (lumen negative) which might reduce Ca2+ release via several different mechanisms.

  7. A Rat Model of Full Thickness Thermal Injury Characterized by Thermal Hyperalgesia, Mechanical Allodynia, Pronociceptive Peptide Release and Tramadol Analgesia (United States)


    hyperalgesia, mechanical allodynia, pronociceptive peptide release and tramadol analgesia 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT...therapeutic tramadol combines opioid receptor activation and 5HT/NE reuptake inhibition [9 11]. Both preclinical and clinical research has reported that... tramadol reduces acute, postoperative, neuropathic and cancer pain [9,10,12 14] and may have a lower propensity to induce addiction [15] with little to

  8. Identification and mechanism of 10-carbon fatty acid as modulating ligand of peroxisome proliferator-activated receptors. (United States)

    Malapaka, Raghu R V; Khoo, Sokkean; Zhang, Jifeng; Choi, Jang H; Zhou, X Edward; Xu, Yong; Gong, Yinhan; Li, Jun; Yong, Eu-Leong; Chalmers, Michael J; Chang, Lin; Resau, James H; Griffin, Patrick R; Chen, Y Eugene; Xu, H Eric


    Peroxisome proliferator-activated receptors (PPARα, -β/δ, and -γ) are a subfamily of nuclear receptors that plays key roles in glucose and lipid metabolism. PPARγ is the molecular target of the thiazolidinedione class of antidiabetic drugs that has many side effects. PPARγ is also activated by long chain unsaturated or oxidized/nitrated fatty acids, but its relationship with the medium chain fatty acids remains unclear even though the medium chain triglyceride oils have been used to control weight gain and glycemic index. Here, we show that decanoic acid (DA), a 10-carbon fatty acid and a major component of medium chain triglyceride oils, is a direct ligand of PPARγ. DA binds and partially activates PPARγ without leading to adipogenesis. Crystal structure reveals that DA occupies a novel binding site and only partially stabilizes the AF-2 helix. DA also binds weakly to PPARα and PPARβ/δ. Treatments with DA and its triglyceride form improve glucose sensitivity and lipid profiles without weight gain in diabetic mice. Together, these results suggest that DA is a modulating ligand for PPARs, and the structure can aid in designing better and safer PPARγ-based drugs.

  9. Therapeutic ion-releasing bioactive glass ionomer cements with improved mechanical strength and radiopacity (United States)

    Fuchs, Maximilian; Gentleman, Eileen; Shahid, Saroash; Hill, Robert; Brauer, Delia


    Bioactive glasses (BG) are used to regenerate bone, as they degrade and release therapeutic ions. Glass ionomer cements (GIC) are used in dentistry, can be delivered by injection and set in situ by a reaction between an acid-degradable glass and a polymeric acid. Our aim was to combine the advantages of BG and GIC, and we investigated the use of alkali-free BG (SiO2-CaO-CaF2-MgO) with 0 to 50% of calcium replaced by strontium, as the beneficial effects of strontium on bone formation are well documented. When mixing BG and poly(vinyl phosphonic-co-acrylic acid), ions were released fast (up to 90% within 15 minutes at pH 1), which resulted in GIC setting, as followed by infrared spectroscopy. GIC mixed well and set to hard cements (compressive strength up to 35 MPa), staying hard when in contact with aqueous solution. This is in contrast to GIC prepared with poly(acrylic acid), which were shown previously to become soft in contact with water. Strontium release from GIC increased linearly with strontium for calcium substitution, allowing for tailoring of strontium release depending on clinical requirements. Furthermore, strontium substitution increased GIC radiopacity. GIC passed ISO10993 cytotoxicity test, making them promising candidates for use as injectable bone cements.

  10. The mechanism of gastrin release in cysteamine-induced duodenal ulcer

    DEFF Research Database (Denmark)

    Poulsen, Steen Seier


    a rise in serum gastrin from 29 +/- 5 pg/ml to a maximum of 203 +/- 62 pg/ml after 3 h in unoperated rats, whereas no rise was seen in vagotomized or antrectomized rats. The beta-adrenergic blocking agent propranolol strongly inhibited cysteamine-induced gastrin release, whereas atropine dependent...

  11. Factor VII-activating protease: Mechanism and regulation of nucleosome release from dead cells

    NARCIS (Netherlands)

    F. Stephan


    Cell death is indispensable for tissue homeostasis and is a fundamental principle of inflammation and lymphocyte generation. Rapid removal and destruction of cellular corpses is critical and insufficient removal may lead to the release of cellular content into the environment. These immunogenic "hos

  12. Mutagenesis of the aspartic acid ligands in human serum transferrin: lobe-lobe interaction and conformation as revealed by antibody, receptor-binding and iron-release studies. (United States)

    Mason, A; He, Q Y; Tam, B; MacGillivray, R A; Woodworth, R


    Recombinant non-glycosylated human serum transferrin and mutants in which the liganding aspartic acid (D) in one or both lobes was changed to a serine residue (S) were produced in a mammalian cell system and purified from the tissue culture media. Significant downfield shifts of 20, 30, and 45 nm in the absorption maxima were found for the D63S-hTF, D392S-hTF and the double mutant, D63S/D392S-hTF when compared to wild-type hTF. A monoclonal antibody to a sequential epitope in the C-lobe of hTF reported affinity differences between the apo- and iron-forms of each mutant and the control. Cell-binding studies performed under the same buffer conditions used for the antibody work clearly showed that the mutated lobe(s) had an open cleft. It is not clear whether the receptor itself may play a role in promoting the open conformation or whether the iron remains in the cleft. PMID:9461487

  13. Mechanism of Cooperativity and Nonlinear Release Kinetics in Multivalent Dendrimer-Atropine Complexes. (United States)

    Mukherjee, Jhindan; Wong, Pamela T; Tang, Shengzhuang; Gam, Kristina; Coulter, Alexa; Baker, James R; Choi, Seok Ki


    Despite extensive studies on drug delivery using multivalent complexation systems, the biophysical basis for release kinetics remains poorly defined. The present study addresses this aspect involved in the complexation of a fifth generation poly(amidoamine) (PAMAM) dendrimer with atropine, an essential antidote used for treating organophosphate poisoning. First, we designed (1)H NMR titration studies for determining the molecular basis of the drug complexation with a glutarate-modified anionic dendrimer. These provide evidence pointing to a combination of electrostatic and hydrophobic interactions as the driving forces for dendrimer complexation with the alkaloid drug molecule. Second, using LC-MS/MS spectrometry, we determined the dissociation constants (KD) at steady state and also measured the drug release kinetics of atropine complexes with four negatively charged dendrimer types. Each of these dendrimers has a high payload capacity for up to ∼ 100 atropine molecules. However, the affinity of the atropine to the carrier was highly dependent on the drug to dendrimer ratio. Thus, a complex made at a lower loading ratio (≤ 0.1) displayed greater atropine affinity (KD ≈ μM) than other complexes prepared at higher ratios (>10), which showed only mM affinity. This negative cooperative variation in affinity is tightly associated with the nonlinear release kinetics observed for each complex in which drug release occurs more slowly at the later time phase at a lower loading ratio. In summary, the present study provides novel insights on the cooperativity as the mechanistic basis for nonlinear release kinetics observed in multivalent carrier systems.

  14. Review: Regulatory mechanisms of gonadotropin-inhibitory hormone (GnIH synthesis and release in photoperiodic animals

    Directory of Open Access Journals (Sweden)

    Kazuyoshi eTsutsui


    Full Text Available Gonadotropin-inhibitory hormone (GnIH is a novel hypothalamic neuropeptide that was discovered in quail as an inhibitory factor for gonadotropin release. GnIH inhibits gonadotropin synthesis and release in birds through actions on gonadotropin-releasing hormone (GnRH neurons and gonadotropes, mediated via the GnIH receptor (GnIH-R, GPR147. Subsequently, GnIH was identified in mammals and other vertebrates. As in birds, mammalian GnIH inhibits gonadotropin secretion, indicating a conserved role for this neuropeptide in the control of the hypothalamic-pituitary-gonadal (HPG axis across species. Identification of the regulatory mechanisms governing GnIH expression and release is important in understanding the physiological role of the GnIH system. A nocturnal hormone, melatonin, appears to act directly on GnIH neurons through its receptor to induce expression and release of GnIH in quail, a photoperiodic bird. Recently, a similar, but opposite, action of melatonin on the inhibition of expression of mammalian GnIH was shown in hamsters and sheep, photoperiodic mammals. These results in photoperiodic animals demonstrate that GnIH expression is photoperiodically modulated via a melatonin-dependent process. Recent findings indicate that GnIH may be a mediator of stress-induced reproductive disruption in birds and mammals, pointing to a broad role for this neuropeptide in assessing physiological state and modifying reproductive effort accordingly. This paper summarizes the advances made in our knowledge regarding the regulation of GnIH synthesis and release in photoperiodic birds and mammals. This paper also discusses the neuroendocrine integration of environmental signals, such as photoperiods and stress, and internal signals, such as GnIH, melatonin and glucocorticoids, to control avian and mammalian reproduction.

  15. Modulation of fast synaptic transmission by presynaptic ligand-gated cation channels. (United States)

    Khakh, B S; Henderson, G


    There is now considerable evidence demonstrating that ligand-gated cation channels (i.e., P2X, nicotinic, kainate, NMDA, AMPA and 5-HT(3) receptors), in addition to mediating fast excitatory neurotransmission, may be located presynaptically on nerve terminals in the peripheral and central nervous systems where they function to modulate neurotransmitter release. This modulation can be facilitation, inhibition or both. In this article, we first outline the multiple mechanisms by which activation of presynaptic ligand-gated cation channels can modulate spontaneous and evoked neurotransmitter release, before reviewing in detail published electrophysiological studies of presynaptic P2X, nicotinic, kainate, NMDA, AMPA and 5-HT(3) receptors.

  16. Nanocarriers for DNA Vaccines: Co-Delivery of TLR-9 and NLR-2 Ligands Leads to Synergistic Enhancement of Proinflammatory Cytokine Release

    Directory of Open Access Journals (Sweden)

    Johanna Poecheim


    Full Text Available Adjuvants enhance immunogenicity of vaccines through either targeted antigen delivery or stimulation of immune receptors. Three cationic nanoparticle formulations were evaluated for their potential as carriers for a DNA vaccine, and muramyl dipeptide (MDP as immunostimulatory agent, to induce and increase immunogenicity of Mycobacterium tuberculosis antigen encoding plasmid DNA (pDNA. The formulations included (1 trimethyl chitosan (TMC nanoparticles, (2 a squalene-in-water nanoemulsion, and (3 a mineral oil-in-water nanoemulsion. The adjuvant effect of the pDNA-nanocomplexes was evaluated by serum antibody analysis in immunized mice. All three carriers display a strong adjuvant effect, however, only TMC nanoparticles were capable to bias immune responses towards Th1. pDNA naturally contains immunostimulatory unmethylated CpG motifs that are recognized by Toll-like receptor 9 (TLR-9. In mechanistic in vitro studies, activation of TLR-9 and the ability to enhance immunogenicity by simultaneously targeting TLR-9 and NOD-like receptor 2 (NLR-2 was determined by proinflammatory cytokine release in RAW264.7 macrophages. pDNA in combination with MDP was shown to significantly increase proinflammatory cytokine release in a synergistic manner, dependent on NLR-2 activation. In summary, novel pDNA-Ag85A loaded nanoparticle formulations, which induce antigen specific immune responses in mice were developed, taking advantage of the synergistic combinations of TLR and NLR agonists to increase the adjuvanticity of the carriers used.

  17. Structure and Genome Release Mechanism of the Human Cardiovirus Saffold Virus 3. (United States)

    Mullapudi, Edukondalu; Nováček, Jiří; Pálková, Lenka; Kulich, Pavel; Lindberg, A Michael; van Kuppeveld, Frank J M; Plevka, Pavel


    In order to initiate an infection, viruses need to deliver their genomes into cells. This involves uncoating the genome and transporting it to the cytoplasm. The process of genome delivery is not well understood for nonenveloped viruses. We address this gap in our current knowledge by studying the uncoating of the nonenveloped human cardiovirus Saffold virus 3 (SAFV-3) of the family Picornaviridae SAFVs cause diseases ranging from gastrointestinal disorders to meningitis. We present a structure of a native SAFV-3 virion determined to 2.5 Å by X-ray crystallography and an 11-Å-resolution cryo-electron microscopy reconstruction of an "altered" particle that is primed for genome release. The altered particles are expanded relative to the native virus and contain pores in the capsid that might serve as channels for the release of VP4 subunits, N termini of VP1, and the RNA genome. Unlike in the related enteroviruses, pores in SAFV-3 are located roughly between the icosahedral 3- and 5-fold axes at an interface formed by two VP1 and one VP3 subunit. Furthermore, in native conditions many cardioviruses contain a disulfide bond formed by cysteines that are separated by just one residue. The disulfide bond is located in a surface loop of VP3. We determined the structure of the SAFV-3 virion in which the disulfide bonds are reduced. Disruption of the bond had minimal effect on the structure of the loop, but it increased the stability and decreased the infectivity of the virus. Therefore, compounds specifically disrupting or binding to the disulfide bond might limit SAFV infection. A capsid assembled from viral proteins protects the virus genome during transmission from one cell to another. However, when a virus enters a cell the virus genome has to be released from the capsid in order to initiate infection. This process is not well understood for nonenveloped viruses. We address this gap in our current knowledge by studying the genome release of Human Saffold virus 3

  18. Pituitary Adenylate cyclase-activating polypeptide orchestrates neuronal regulation of the astrocytic glutamate-releasing mechanism system xc (.). (United States)

    Kong, Linghai; Albano, Rebecca; Madayag, Aric; Raddatz, Nicholas; Mantsch, John R; Choi, SuJean; Lobner, Doug; Baker, David A


    Glutamate signaling is achieved by an elaborate network involving neurons and astrocytes. Hence, it is critical to better understand how neurons and astrocytes interact to coordinate the cellular regulation of glutamate signaling. In these studies, we used rat cortical cell cultures to examine whether neurons or releasable neuronal factors were capable of regulating system xc (-) (Sxc), a glutamate-releasing mechanism that is expressed primarily by astrocytes and has been shown to regulate synaptic transmission. We found that astrocytes cultured with neurons or exposed to neuronal-conditioned media displayed significantly higher levels of Sxc activity. Next, we demonstrated that the pituitary adenylate cyclase-activating polypeptide (PACAP) may be a neuronal factor capable of regulating astrocytes. In support, we found that PACAP expression was restricted to neurons, and that PACAP receptors were expressed in astrocytes. Interestingly, blockade of PACAP receptors in cultures comprised of astrocytes and neurons significantly decreased Sxc activity to the level observed in purified astrocytes, whereas application of PACAP to purified astrocytes increased Sxc activity to the level observed in cultures comprised of neurons and astrocytes. Collectively, these data reveal that neurons coordinate the actions of glutamate-related mechanisms expressed by astrocytes, such as Sxc, a process that likely involves PACAP. A critical gap in modeling excitatory signaling is how distinct components of the glutamate system expressed by neurons and astrocytes are coordinated. In these studies, we found that system xc (-) (Sxc), a glutamate release mechanism expressed by astrocytes, is regulated by releasable neuronal factors including PACAP. This represents a novel form of neuron-astrocyte communication, and highlights the possibility that pathological changes involving astrocytic Sxc may stem from altered neuronal activity.

  19. The study on the interaction between Tb(III) and ligand in Tb-acetylsalicylic acid complex and fluorescence mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Wu Wenru; Rong Yuzhi; Zhao Bo [Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Environmental Science, Nanjing Normal University, Nanjing, 210097 (China); Sun Peipei, E-mail: [Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Environmental Science, Nanjing Normal University, Nanjing, 210097 (China); Huang Xiaohua, E-mail: [Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Environmental Science, Nanjing Normal University, Nanjing, 210097 (China)


    In this paper, a luminescent complex of terbium-acetylsalicylic acid (Tb-ASA) was studied for the first time using combination of the quantum chemical calculation, fluorescence spectroscopic method and X-ray photoelectron spectroscopy (XPS). The results from the quantum chemical calculation indicated that it is possible for the energy-transfer from ASA to Tb (III); Fluorescence spectroscopy demonstrated that there is an intramolecular energy-transfer from ASA to Tb with the efficiency (III) of about 87.9% under an excitation at 308 nm. The XPS indicated that the coordinate covalent bond between Tb and O existed in the complex of Tb-ASA leads to the effective energy transfer from ASA to Tb (III) because the energy transfer rate may be improved with reducing the distance between the ligand and Tb (III). The results will have important values for the studies of this type of complexes.

  20. Dendronized Mesoporous Silica Nanoparticles Provide an Internal Endosomal Escape Mechanism for Successful Cytosolic Drug Release

    CERN Document Server

    Weiss, Veronika; Torrano, Adriano A; Strobel, Claudia; Mackowiak, Stephan A; Gatzenmeier, Tim; Hilger, Ingrid; Braeuchle, Christoph; Bein, Thomas


    Mesoporous silica nanoparticles (MSNs) attract increasing interest in the field of gene and drug delivery due to their versatile features as a multifunctional drug delivery platform. Here, we describe poly(amidoamine) (PAMAM) dendron-functionalized MSNs that fulfill key prerequisites for a controllable intracellular drug release. In addition to high loading capacity, they offer 1) low cytotoxicity, showing no impact on the metabolism of endothelial cells, 2) specific cancer cell targeting due to receptor-mediated cell uptake, 3) a redox-driven cleavage of disulfide bridges allowing for stimuli-responsive cargo release, and most importantly, 4) a specific internal trigger based on the high buffering capacity of PAMAM dendrons to provide endosomal escape.

  1. Mechanical compression release device in steel bracing system for retrofitting RC frames

    Institute of Scientific and Technical Information of China (English)

    H. Ghaffarzadeh; M.R. Maheri


    The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can release the compressive force in the bracing members is developed, and its performance is evaluated. For comparison, four steel braced RC frames were constructed and tested under reverse cyclic loads. Two of them had different amounts of bracing and the other two had the same amount of bracing but incorporated different type of device, called compression release device, which is developed and described in this paper. It can be concluded from the test results that the newly developed device can effectively be used in steel braced systems to prevent buckling failure of the bracing members. Therefore, the device enhances the ductility of brace-framed systems by allowing an adequate capacity for energy dissipation.

  2. Strontium and cesium release mechanisms during unsaturated flow through waste-weathered Hanford sediments

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Hyun-Shik; Um, Wooyong; Rod, Kenton A.; Serne, R. Jeffrey; Thompson, Aaron; Perdrial, Nicolas; Steefel, Carl I.; Chorover, Jon


    Leaching behavior of Sr and Cs in the vadose zone of Hanford site (WA, USA) was studied with laboratory-weathered sediments mimicking realistic conditions beneath the leaking radioactive waste storage tanks. Unsaturated column leaching experiments were conducted using background Hanford pore water focused on first 200 pore volumes. The weathered sediments were prepared by 6 months reaction with a synthetic Hanford tank waste leachate containing Sr and Cs (10-5 and 10-3 molal representative of LO- and HI-sediment, respectively) as surrogates for 90Sr and 137Cs. The mineral composition of the weathered sediments showed that zeolite (chabazite-type) and feldspathoid (sodalite-type) were the major byproducts but different contents depending on the weathering conditions. Reactive transport modeling indicated that Cs leaching was controlled by ion-exchange, while Sr release was affected primarily by dissolution of the secondary minerals. The later release of K, Al, and Si from the HI-column indicated the additional dissolution of a more crystalline mineral (cancrinite-type). A two-site ion-exchange model successfully simulated the Cs release from the LO-column. However, a three-site ion-exchange model was needed for the HI-column. The study implied that the weathering conditions greatly impact the speciation of the secondary minerals and leaching behavior of sequestrated Sr and Cs.

  3. Release mechanism and kinetic exchange for phosphorus (P) in lake sediment characterized by diffusive gradients in thin films (DGT). (United States)

    Wu, Zhihao; Wang, Shengrui


    Diffusive gradients in thin films (DGT) technique has been newly designed for the identification of formation mechanisms of "internal phosphorus (P)-loading" and the numerical simulation of P exchange at DGT/sediment interface in Lake Dianchi. The primary mechanism was Fe-redox controlled P release from Fe-bound P in sediments, which was revealed by CDGT (P and Fe), total P (Fe) and P (Fe) fractions in NH4Cl and BD phases in sediments and their relationships at sites (N-T). The breakdown of algae biomass in the top layer of sediments at sites (O-T) and the coupled P/Fe/sulfur reactions at two depths at site N played a minor role in P release. The "internal P-loading" was calculated to be 19.23ta(-1), which was 3.0% of the "entering P-loading". At sites (1-9), DGT induced flux in sediments (DIFS) model for P was used to derive curves (i) the resupply parameter (R) against deployment time and (ii) the dissolved/sorbed concentrations against the distance at DGT/sediment interface, the variation characters of which were controlled by kinetics and sediment-P pool. Sulfide microniches in sediments related to P release were evaluated by computer imaging densitometry (CID). DGT-DIFS-CID should be a reliable method to reveal P mobilization in lake sediments.

  4. [Effects of mechanical transplanting of rice with controlled release bulk blending fertilizer on rice yield and soil fertility]. (United States)

    Zhang, Xuan; Ding, Jun-Shan; Liu, Yan-Ling; Gu, Yan; Han, Ke-Feng; Wu, Liang-Huan


    Abstract: A 2-year field experiment with a yellow-clay paddy soil in Zhejiang Province was conducted to study the effects of different planting measures combined with different fertilization practices on rice yield, soil nutrients, microbial biomass C and N and activities of urease, phosphatase, sucrase and hydrogen peroxidase at the maturity stage. Results showed that mechanical transplanting of rice with controlled release bulk blending (BB) fertilizer (BBMT) could achieve a significantly higher mean yield than traditional manual transplanting with traditional fertilizer (TFTM) and direct seeding with controlled release BB fertilizer (BBDS) by 16.3% and 27.0%, respectively. The yield by BBMT was similar to that by traditional manual transplanting with controlled release BB fertilizer (BBTM). Compared with TFTM, BBMT increased the contents of soil total-N, available N, available P and microbial biomass C, and the activities of urease, sucrase and hydrogen peroxidase by 21.5%, 13.6%, 41.2%, 27.1%, 50.0%, 22.5% and 46.2%, respectively. Therefore, BBMT, a simple high-efficiency rice cultivation method with use of a light-weighted mechanical transplanter, should be widely promoted and adopted.

  5. Evaluation of drug delivery profiles in geometric three-layered tablets with various mechanical properties, in vitro-in vivo drug release, and Raman imaging. (United States)

    Choi, Du Hyung; Kim, Ki Hyun; Park, Jun Sang; Jeong, Seong Hoon; Park, Kinam


    Even though various multi-layered tablets have been developed for sustained release formulations, evaluations of mechanical properties during dissolution with drug release and imaging in the tablets have been limited. A novel geometric system consisting of an inner immediate release layer and two extended release barrier layers with swellable hydrophilic polymers was suggested as a once-a-day formulation. To evaluate drug release mechanisms with geometric properties, various mechanical characteristics during swelling were investigated to comprehend the relationship among in vitro drug release, human pharmacokinetics, and geometric characteristics. Imaging of drug movement was also studied in real-time using Raman spectroscopy. Drug delivery in the tablets might be divided into three processes through the geometric properties. When exposed to aqueous environments, the drug in the mid-layer was released until wrapped by the swollen barrier layers. Then, the drug in the mid-layer was mainly delivered to the barrier layers and a small amount of the drug was delivered to the contact region of the swollen barrier layers. Finally, the delivered drug to the barrier layers was consistently released out in response to the characteristics of the polymer of the barrier layers. Using Raman spectroscopy, these processes were confirmed in real-time analysis. Moreover, in vitro drug release profiles and human pharmacokinetics showed consistent results suggesting that drug release might be dependent on the various geometric properties and be modified consistently during the formulation development. © 2013.

  6. A lactobacillus rhamnosus GG-derived soluble protein, p40, stimulates ligand release from intestinal epithelial cells to transactivate epidermal growth factor receptor (United States)

    Protein p40, a Lactobacillus rhamnosus GG (LGG)-derived soluble protein, ameliorates intestinal injury and colitis, reduces apoptosis and preserves barrier function by activation of EGF receptor (EGFR) in intestinal epithelial cells. The aim of this study was to determine the mechanisms by which p40...

  7. Solvolysis mechanisms of RNA phosphodiester analogues promoted by mononuclear zinc(II) complexes: mechanisic determination upon solvent medium and ligand effects. (United States)

    Zhang, Xuepeng; Zhu, Yajie; Gao, Hui; Zhao, Cunyuan


    The solvolysis mechanisms of RNA phosphodiester model 2-(hydroxypropyl)-4-nitrophenyl phosphate (HpPNP) catalyzed by mononuclear zinc(II) complexes are investigated in the paper via a theoretical approach. The general-base-catalyzed (GBC) and specific-base-catalyzed (SBC) mechanisms are thoroughly discussed in the paper, and the calculations indicate a SBC mechanism (also named as the direct nucleophilic attack mechanism) when the cyclization of HpPNP is promoted by the Zn:[12]aneN3 complex ([12]aneN3 = 1,5,9-triazacyclododecane). The ligand effect is considered by involving two different catalysts, and the results show that the increasing size catalyst provides a lower energy barrier and a significant mechanistic preference to the SBC mechanism. The solvent medium effect is also explored, and reduced polarity/dielectric constant solvents, such as light alcohols methanol and ethanol, are more favorable. Ethanol is proven to be a good solvent medium because of its low dielectric constant. The computational results are indicative of concerted pathways. Our theoretical results are consistent with and well interpret the experimental observations and, more importantly, provide practical suggestions on the catalyst design and selection of reaction conditions.

  8. A modified release analysis procedure using advanced froth flotation mechanisms. Technical report, September 1--November 30, 1995

    Energy Technology Data Exchange (ETDEWEB)

    Honaker, R.Q.; Mohanty, M.K. [Southern Illinois Univ., Carbondale, IL (United States). Dept. of Mining Engineering


    The objective of this study is to reinvestigate the release analysis procedure, which is traditionally conducted using a laboratory Denver cell, and to develop a modified process that can be used for all froth flotation technologies. Recent studies have found that the separation performance achieved by multiple stage cleaning and, in some cases, single stage cleaning using column flotation is superior to the performance achieved by the traditional release procedure. These findings are a result of the advanced flotation mechanisms provided by column flotation, which will be incorporated into a modified release analysis procedure developed in this study. A fundamental model of an open column has been developed which incorporates the effects of system hydrodynamics, froth drop-back, selective and non-selective detachment, operating parameters, feed solids content, and feed component flotation kinetics. Simulation results obtained during this reporting period indicate that the ultimate separation that can be achieved by a column flotation process can only be obtained in a single cleaning stage if the detachment mechanism in the froth phase is highly selective, which does not appear to occur in practice based on experimental results. Two to three cleaning stages were found to be required to obtain the ultimate performance if non-selective detachment or kinetic limiting conditions are assumed. this simulated finding agrees well with the experimental results obtained from the multiple stage cleaning of an Illinois No. 5 seam coal using the Packed-Column. Simulated results also indicate that the separation performance achieved by column flotation improves with increasing feed solids content after carrying-capacity limiting conditions are realized. These findings will be utilized in the next reporting period to modify the traditional release analysis procedure.

  9. Effect of Fluoride-Releasing Adhesive Systems on the Mechanical Properties of Eroded Dentin. (United States)

    Guedes, Ana Paula Albuquerque; Moda, Mariana Dias; Suzuki, Thaís Yumi Umeda; Godas, André Gustavo de Lima; Sundfeld, Renato Herman; Briso, André Luiz Fraga; Santos, Paulo Henrique dos


    The aim of the study was to evaluate the effect of erosive pH cycling with solutions that simulate dental erosion on Martens hardness (HMV) and elastic modulus (Eit) of dentin restored with fluoride-releasing adhesive systems. Twenty-seven bovine dentin slabs were restored with three adhesive systems: Adper Single Bond 2 total-etch adhesive system, One Up Bond F and Clearfil SE Protect fluoride-containing self-etching adhesive systems. The restorations were made with Filtek Z250. The HMV and Eit values at distances of 10, 30, 50 and 70 µm from the interface were evaluated using a dynamic ultra microhardness tester before and after immersion in deionized water, citric acid and hydrochloric acid (n=9). Data were submitted to repeated-measures ANOVA and Fisher's PLSD tests (=0.05). After erosive cycling, HMV values of dentin decreased in all groups. For dentin restored with Adper Single Bond 2, the lowest values were found closer to the hybrid layer, while for One Up Bond F and Clearfil SE Protect, the values remained unaltered at all distances. For dentin restored with fluoride-releasing adhesive systems, a decrease in Eit was found, but after 30 µm this difference was not significant. The acid substances were able to alter HMV and Eit of the underlying dentin. For fluoride-releasing adhesives, the greater the distance from bonded interface, the lower the Eit values. The fluoride in One Up Bond F and Clearfil SE Protect was able to protect the underlying dentin closer to the materials. In this way, the fluoride from adhesive systems could have some positive effect in the early stages of erosive lesions.

  10. Forensic mental health clinician's experiences with and assessment of alliance regarding the patient's readiness to be released from mechanical restraint

    DEFF Research Database (Denmark)

    Nielsen, Lea Deichmann; Gildberg, Frederik Alkier; Bech, Per


    One of the main reasons for prolonged duration of mechanical restraint is patient behaviour in relation to the clinician-patient alliance. This article reports on the forensic mental health clinicians experiences of the clinician-patient alliance during mechanical restraint, and their assessment...... of parameters of alliance regarding the patient's readiness to be released from restraint. We used a qualitative, descriptive approach and conducted focus group interviews with nurses, nurse assistants and social and healthcare assistants. The results show that a pre-established personal clinician......-patient alliance formed the basis for entering into, and weighing the quality of, the alliance during mechanical restraint. In consideration of the patient's psychiatric condition, the clinicians observed and assessed two quality parameters for the alliance: 'the patient's insight into or understanding of present...

  11. Hybrid Elastin-like Polypeptide–Polyethylene Glycol (ELP-PEG) Hydrogels with Improved Transparency and Independent Control of Matrix Mechanics and Cell Ligand Density (United States)


    Hydrogels have been developed as extracellular matrix (ECM) mimics both for therapeutic applications and basic biological studies. In particular, elastin-like polypeptide (ELP) hydrogels, which can be tuned to mimic several biochemical and physical characteristics of native ECM, have been constructed to encapsulate various types of cells to create in vitro mimics of in vivo tissues. However, ELP hydrogels become opaque at body temperature because of ELP’s lower critical solution temperature behavior. This opacity obstructs light-based observation of the morphology and behavior of encapsulated cells. In order to improve the transparency of ELP hydrogels for better imaging, we have designed a hybrid ELP-polyethylene glycol (PEG) hydrogel system that rapidly cross-links with tris(hydroxymethyl) phosphine (THP) in aqueous solution via Mannich-type condensation. As expected, addition of the hydrophilic PEG component significantly improves the light transmittance. Coherent anti-Stokes Raman scattering (CARS) microscopy reveals that the hybrid ELP-PEG hydrogels have smaller hydrophobic ELP aggregates at 37 °C. Importantly, this hydrogel platform enables independent tuning of adhesion ligand density and matrix stiffness, which is desirable for studies of cell–matrix interactions. Human fibroblasts encapsulated in these hydrogels show high viability (>98%) after 7 days of culture. High-resolution confocal microscopy of encapsulated fibroblasts reveals that the cells adopt a more spread morphology in response to higher RGD ligand concentrations and softer gel mechanics. PMID:25111283

  12. Preparation and drug release mechanism of CTS-TAX-NP-MSCs drug delivery system. (United States)

    Dai, Tian; Yang, Enyun; Sun, Yongjun; Zhang, Linan; Zhang, Li; Shen, Ning; Li, Shuo; Liu, Lei; Xie, Yinghua; Wu, Shaomei; Gao, Zibin


    Targeting delivery of anticancer agents is a promising field in anticancer therapy. Inherent tumor-tropic and migratory properties of mesenchymal stem cells (MSCs) make them potential vehicles for targeting drug delivery systems for tumors. Although, MSCs have been successfully studied and discussed as a vehicle for cancer gene therapy, they have not yet been studied adequately as a potential vehicle for traditional chemical anticancer drugs. In this study, we have engineered MSCs as a potential targeting delivery vehicle for paclitaxel (TAX)-loaded nanoparticles (NPs). The size, surface charge, starving time of MSCs, incubating time and concentration of NPs could influence the efficiency of NPs uptake. In vitro release of TAX from CTS (chitosan)-TAX-NP-MSCs and the expression of P-glycoprotein demonstrated that release of TAX from MSCs might involve both passive diffusion and active transport. In vitro migration assays indicated that MSCs at passage number 3 have the highest migrating ability. Although, the migration ability of CTS-TAX-NP-MSCs could be inhibited by uptake of CTS-TAX-NPs, this ability could recover 6 days after the internalization.

  13. Snow Slab Release, its Mechanism and Conclusion for the Arrangements of Supporting Structures

    Directory of Open Access Journals (Sweden)

    Bruno Salm


    Full Text Available The paper presents a model of snow slab release based on the concept of the presence of ground-parallel thin super-weak layers. The fact that the same snow type under same state may or may not fracture under a certain stress unless a critical strain-rate and critical fracture-strain is reached highlights the necessity of stress and strain-rate concentrations. Super-weak layer, which cannot or can only insufficiently transmit the shear stress caused by the overlying snow layers, is considered to provide such concentrations. The model establishes that although the existence of weak layers in a snowpack is a necessary condition, yet it is not sufficient for avalanche formation. A minimum length of the super-weak zone is required for the crack to propagate leading to the release of a slab avalanche Critical crack lengths are found to be of the order of 5 m to 10 m. Critical value of crack length has been found to be dependent on slope, thickness and viscosity of the weak layer. The model does not hold good, if the super-weak zone vanishes. The paper finally discusses the arrangement of supporting structures to minimise the development of super-weak zones.

  14. Lanthanide-directed synthesis of luminescent self-assembly supramolecular structures and mechanically bonded systems from acyclic coordinating organic ligands. (United States)

    Barry, Dawn E; Caffrey, David F; Gunnlaugsson, Thorfinnur


    Herein some examples of the use of lanthanide ions (f-metal ions) to direct the synthesis of luminescent self-assembly systems (architectures) will be discussed. This area of lanthanide supramolecular chemistry is fast growing, thanks to the unique physical (magnetic and luminescent) and coordination properties of the lanthanides, which are often transferred to the resulting supermolecule. The emphasis herein will be on systems that are luminescent, and hence, generated by using either visibly emitting ions (such as Eu(III), Tb(III) and Sm(III)) or near infrared emitting ions (like Nd(III), Yb(III) and Er(III)), formed through the use of templating chemistry, by employing structurally simple ligands, possessing oxygen and nitrogen coordinating moieties. As the lanthanides have high coordination requirements, their use often allows for the formation of coordination compounds and supramolecular systems such as bundles, grids, helicates and interlocked molecules that are not synthetically accessible through the use of other commonly used templating ions such as transition metal ions. Hence, the use of the rare-earth metal ions can lead to the formation of unique and stable species in both solution and in the solid state, as well as functional and responsive structures.

  15. Metal release from stainless steel in biological environments: A review. (United States)

    Hedberg, Yolanda S; Odnevall Wallinder, Inger


    Due to its beneficial corrosion resistance, stainless steel is widely used in, e.g., biomedical applications, as surfaces in food contact, and for products intended to come into skin contact. Low levels of metals can be released from the stainless steel surface into solution, even for these highly corrosion resistant alloys. This needs to be considered in risk assessment and management. This review aims to compile the different metal release mechanisms that are relevant for stainless steel when used in different biological settings. These mechanisms include corrosion-induced metal release, dissolution of the surface oxide, friction-induced metal release, and their combinations. The influence of important physicochemical surface properties, different organic species and proteins in solution, and of biofilm formation on corrosion-induced metal release is discussed. Chemical and electrochemical dissolution mechanisms of the surface oxides of stainless steel are presented with a focus on protonation, complexation/ligand-induced dissolution, and reductive dissolution by applying a perspective on surface adsorption of complexing or reducing ligands and proteins. The influence of alloy composition, microstructure, route of manufacture, and surface finish on the metal release process is furthermore discussed as well as the chemical speciation of released metals. Typical metal release patterns are summarized.

  16. Identifying the mechanisms of drug release from amorphous solid dispersions using MRI and ATR-FTIR spectroscopic imaging. (United States)

    Punčochová, Kateřina; Ewing, Andrew V; Gajdošová, Michaela; Sarvašová, Nina; Kazarian, Sergei G; Beránek, Josef; Štěpánek, František


    The dissolution mechanism of a poorly aqueous soluble drug from amorphous solid dispersions was investigated using a combination of two imaging methods: attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic imaging and magnetic resonance imaging (MRI). The rates of elementary processes such as water penetration, polymer swelling, growth and erosion of gel layer, and the diffusion, release and in some cases precipitation of drug were evaluated by image analysis. The results from the imaging methods were compared with drug release profiles obtained by classical dissolution tests. The study was conducted using three polymeric excipients (soluplus, polyvinylpyrrolidone - PVP K30, hydroxypropylmethyl cellulose - HPMC 100M) alone and in combination with a poorly soluble drug, aprepitant. The imaging methods were complementary: ATR-FTIR imaging enabled a qualitative observation of all three components during the dissolution experiments, water, polymer and drug, including identifying structural changes from the amorphous form of drug to the crystalline form. The comparison of quantitative MRI data with drug release profiles enabled the different processes during dissolution to be established and the rate-limiting step to be identified, which - for the drug-polymer combinations investigated in this work - was the drug diffusion through the gel layer rather than water penetration into the tablet.

  17. Release behavior and formation mechanism of polycyclic aromatic hydrocarbons during coal pyrolysis. (United States)

    Gao, Meiqi; Wang, Yulong; Dong, Jie; Li, Fan; Xie, Kechang


    Polycyclic aromatic hydrocarbons (PAHs) are major environmental pollutants. They have attracted considerable attention due to their severe potential carcinogenic, mutagenic and genotoxic effects on human health. In this study, five different rank coals from China were pyrolyzed using pyro-probe CDS 5250 and the release behavior of 16 PAHs under different pyrolysis conditions were studied by Gas Chromatography-Mass Spectrometer (GC-MS). The structural characteristics of the five coals were determined by Cross-Polarization/Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS (13)C NMR) spectroscopy, and then the factors influencing the formation of PAHs during coal pyrolysis were discussed together with the coal structural data. It was shown that the amount of PAHs generated during coal pyrolysis was largely related to coal rank and followed the order of medium metamorphic coal > low metamorphic coal > high metamorphic coal. The amount of total PAHs varied as the temperature was increased from 400 °C to 1200 °C, which showed a trend of first increasing and then decreasing, with the maximum value at 800 °C. Moreover, the species of PAHs released varied with pyrolysis temperatures. When the temperature was lower than 800 °C, the small ring PAHs were the most abundant, while the proportion of heavy rings increased at higher temperature. The results indicate that the formation of PAHs during coal pyrolysis depends on the structure of the coal. The species and amounts of PAHs generated during coal pyrolysis are closely related to the contents of protonated aromatic carbons and bridging ring junction aromatic carbons present in the coal structure.

  18. Effect of thermal and chemical modifications on the mechanical and release properties of paracetamol tablet formulations containing corn, cassava and sweet potato starches as filler-binders

    Directory of Open Access Journals (Sweden)

    Mariam Vbamiunomhene Lawal


    Conclusions: Modification of the experimental starches improved the mechanical and release properties of directly compressed paracetamol tablet formulations. Thus, they can be developed for use as pharmaceutical excipients in specific formulations.

  19. A modified release analysis procedure using advanced froth flotation mechanisms. Final technical report, September 1, 1995--August 31, 1996

    Energy Technology Data Exchange (ETDEWEB)

    Honaker, R.Q.; Mohanty, M.K. [Southern Illinois Univ., Carbondale, IL (United States)


    Recent studies indicate that the optimum separation performances achieved by multiple stage cleaning using various column flotation technologies and single stage cleaning using a Packed-Flotation Column are superior to the performance achieved by the traditional release procedure, especially in terms of pyritic sulfur rejection. This superior performance is believed to be the result of the advanced flotation mechanisms provided by column flotation technologies. Thus, the objective of this study was to develop a suitable process utilizing the advanced froth flotation mechanisms to characterize the true flotation response of a coal sample. This investigation resulted in the development of a modified coal flotation characterization procedure, termed as the Advanced Flotation Washability (AFW) technique. The apparatus used for this procedure is a batch operated Packed-Column device which provides enhanced selectivity due to a plug-flow environment and a deep froth zone. The separation performance achieved by the AFW procedure was found to be superior to those produced by the conventional tree and release procedures for three nominally -100 mesh coal samples and two micronized samples. The largest difference in separation performance was obtained on the basis of product pyritic sulfur content. A comparison conducted between the AFW and the release procedures at an 80% recovery value showed that the AFW technique provided a 19% improvement in the reduction of pyritic sulfur. For an Illinois No. 5 coal sample, this improvement corresponded to a reduction in pyritic sulfur content from 1.38% to 0.70% or a total rejection of 66%. Micronization of the sample improved the pyritic sulfur rejection to 85% while rejecting 92% of the ash-bearing material. In addition, the separation performance provided by the AFW procedure was superior to that obtained from multiple cleaning stages using a continuous Packed-Column under both kinetic and carrying-capacity limiting conditions.

  20. Investigation on Releasing of a Stuck Drill String by Means of a Mechanical Jar

    Directory of Open Access Journals (Sweden)

    Moisyshyn V.


    Full Text Available Purpose. In this article the most important part is dedicated to the research of elimination of accident that is caused by drill string sticking during the process. That is why it is necessary to develop a mathematical model of the mechanic system: travelling system + drill string + mechanical jar + rock, to develop a computer model for numerical calculation of dynamic characteristics of firing gear. The aim is to use the results of the research and to work out recommendations for expediency of jar application. Methods. For description of the drill string we are using synthesis of the wave theory and theory of the local distortions. For mathematical modeling of firing device we are offering the use of the combined method that combines static solutions of the theory of elasticity for contact zone of drill string and method of a plain wave of Saint-Venant. We solved systems of differential equations using the methods of mathematical physics. An algorithm of the numerical decision which mounted in the computing environment were used at simulation of the longitudinal impact to the stuck drill pipe. In this article we designed a wave chart of the equation system of the drill pipe and conducted step-by-step calculation of a collision momentum. We also designed a computer program for numerical modeling of the drill pipe mechanism with firing gear. We also designed a method of calculation of main dynamic characteristics of firing device that will help analyze and prove the performance of the mechanical jar. A wave diagram was built that shows the impact forces and speeds on the boundary surfaces of the sections of the drill string. There were calculated main dynamic characteristic of mechanical the jar. Originality. Authors also developed a dynamic mathematical model that combined elastic vibrations of continual system of loose part drill pipe, impact mechanisms and discrete movements of a given drill pipe. The process of a mechanical jar

  1. Spontaneous Ca2+ release from the sarcoplasmic reticulum limits Ca2+- dependent twitch potentiation in individual cardiac myocytes. A mechanism for maximum inotropy in the myocardium



    We hypothesized that the occurrence of spontaneous Ca2+ release from the sarcoplasmic reticulum (SR), in diastole, might be a mechanism for the saturation of twitch potentiation common to a variety of inotropic perturbations that increase the total cell Ca. We used a videomicroscopic technique in single cardiac myocytes to quantify the amplitude of electrically stimulated twitches and to monitor the occurrence of the mechanical manifestation of spontaneous SR Ca2+ release, i.e., the spontaneo...

  2. Depolarization by K+ and glutamate activates different neurotransmitter release mechanisms in GABAergic neurons: vesicular versus non-vesicular release of GABA

    DEFF Research Database (Denmark)

    Belhage, B; Hansen, Gert Helge; Schousboe, A


    Neurotransmitter release and changes in the concentration of intracellular free calcium ([Ca++]i) were studied in cultured GABAergic cerebral cortical neurons, from mice, upon depolarization with either an unphysiologically high potassium concentration (55 mM) or the physiological excitatory...... neurotransmitter glutamate (100 microM). Both depolarizing stimuli exerted prompt increases in the release of preloaded [3H]GABA as well as in [Ca++]i. However, the basic properties of transmitter release and the increase in [Ca++]i under a variety of conditions were different during stimulation with K...... in nature whereas that induced by the neurotransmitter glutamate is not....

  3. Retention and release mechanisms of tritium loaded in plasma-sprayed tungsten coatings by plasma exposure

    Energy Technology Data Exchange (ETDEWEB)

    Otsuka, T., E-mail: [Kyushu University, Interdisciplinary Graduate School of Engineering and Sciences, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581 (Japan); Tanabe, T. [Kyushu University, Interdisciplinary Graduate School of Engineering and Sciences, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581 (Japan); Tokunaga, K. [Kyushu University, Research Institute for Applied Mechanics, Kasugakoen 6-1, Kasuga-shi, Fukuoka 816-8580 (Japan)


    Depth profiles of tritium (T) loaded by gas and plasma in tungsten (W) coatings on ferritic steels have been examined by using a tritium imaging plate technique and their changes during storage and after annealing have been monitored. The depth profiles of T consisted of 4 components, (I) T trapped at impurities and defects newly introduced in the near surface region of the coating by plasma loading, (II) T trapped at the inner surfaces of the grains and dissolved in the grains resulting in a flat depth profile throughout the whole coating, (III) T dissolved and diffused into the substrate giving a decaying profile, and (IV) T trapped at the backside surface of the substrate. The results support that retention of T is mainly caused by pore diffusion of gaseous T followed by dissolution and trapping in/at each W grain, and dissolution of T into the F82H substrate to allow permeation. Release of T proceeds in an opposite way of retention but each component desorbs independently.

  4. Mechanical assembly of complex, 3D mesostructures from releasable multilayers of advanced materials. (United States)

    Yan, Zheng; Zhang, Fan; Liu, Fei; Han, Mengdi; Ou, Dapeng; Liu, Yuhao; Lin, Qing; Guo, Xuelin; Fu, Haoran; Xie, Zhaoqian; Gao, Mingye; Huang, Yuming; Kim, JungHwan; Qiu, Yitao; Nan, Kewang; Kim, Jeonghyun; Gutruf, Philipp; Luo, Hongying; Zhao, An; Hwang, Keh-Chih; Huang, Yonggang; Zhang, Yihui; Rogers, John A


    Capabilities for assembly of three-dimensional (3D) micro/nanostructures in advanced materials have important implications across a broad range of application areas, reaching nearly every class of microsystem technology. Approaches that rely on the controlled, compressive buckling of 2D precursors are promising because of their demonstrated compatibility with the most sophisticated planar technologies, where materials include inorganic semiconductors, polymers, metals, and various heterogeneous combinations, spanning length scales from submicrometer to centimeter dimensions. We introduce a set of fabrication techniques and design concepts that bypass certain constraints set by the underlying physics and geometrical properties of the assembly processes associated with the original versions of these methods. In particular, the use of releasable, multilayer 2D precursors provides access to complex 3D topologies, including dense architectures with nested layouts, controlled points of entanglement, and other previously unobtainable layouts. Furthermore, the simultaneous, coordinated assembly of additional structures can enhance the structural stability and drive the motion of extended features in these systems. The resulting 3D mesostructures, demonstrated in a diverse set of more than 40 different examples with feature sizes from micrometers to centimeters, offer unique possibilities in device design. A 3D spiral inductor for near-field communication represents an example where these ideas enable enhanced quality (Q) factors and broader working angles compared to those of conventional 2D counterparts.

  5. Mechanical assembly of complex, 3D mesostructures from releasable multilayers of advanced materials (United States)

    Yan, Zheng; Zhang, Fan; Liu, Fei; Han, Mengdi; Ou, Dapeng; Liu, Yuhao; Lin, Qing; Guo, Xuelin; Fu, Haoran; Xie, Zhaoqian; Gao, Mingye; Huang, Yuming; Kim, JungHwan; Qiu, Yitao; Nan, Kewang; Kim, Jeonghyun; Gutruf, Philipp; Luo, Hongying; Zhao, An; Hwang, Keh-Chih; Huang, Yonggang; Zhang, Yihui; Rogers, John A.


    Capabilities for assembly of three-dimensional (3D) micro/nanostructures in advanced materials have important implications across a broad range of application areas, reaching nearly every class of microsystem technology. Approaches that rely on the controlled, compressive buckling of 2D precursors are promising because of their demonstrated compatibility with the most sophisticated planar technologies, where materials include inorganic semiconductors, polymers, metals, and various heterogeneous combinations, spanning length scales from submicrometer to centimeter dimensions. We introduce a set of fabrication techniques and design concepts that bypass certain constraints set by the underlying physics and geometrical properties of the assembly processes associated with the original versions of these methods. In particular, the use of releasable, multilayer 2D precursors provides access to complex 3D topologies, including dense architectures with nested layouts, controlled points of entanglement, and other previously unobtainable layouts. Furthermore, the simultaneous, coordinated assembly of additional structures can enhance the structural stability and drive the motion of extended features in these systems. The resulting 3D mesostructures, demonstrated in a diverse set of more than 40 different examples with feature sizes from micrometers to centimeters, offer unique possibilities in device design. A 3D spiral inductor for near-field communication represents an example where these ideas enable enhanced quality (Q) factors and broader working angles compared to those of conventional 2D counterparts. PMID:27679820

  6. Azole energetic materials: initial mechanisms for the energy release from electronical excited nitropyrazoles. (United States)

    Yuan, Bing; Yu, Zijun; Bernstein, Elliot R


    Decomposition of energetic material 3,4-dinitropyrazole (DNP) and two model molecules 4-nitropyrazole and 1-nitropyrazole is investigated both theoretically and experimentally. The initial decomposition mechanisms for these three nitropyrazoles are explored with complete active space self-consistent field (CASSCF) level. The NO molecule is observed as an initial decomposition product from all three materials subsequent to UV excitation. Observed NO products are rotationally cold (energetic material DNP, NO is produced on the ground state surface, as the S1 decomposition pathway is energetically unavailable. The theoretically predicted mechanism is consistent with the experimental results, as DNP decomposes in a lower electronic state than do the model systems and thus the vibrational energy in the NO product from DNP should be hotter than from the model systems. The observed rotational energy distributions for NO are consistent with the final structures of the respective transition states for each molecule.

  7. Leaching of boron, arsenic and selenium from sedimentary rocks: II. pH dependence, speciation and mechanisms of release

    Energy Technology Data Exchange (ETDEWEB)

    Tabelin, Carlito Baltazar, E-mail: [Laboratory of Soil Environment Engineering, Faculty of Engineering, Hokkaido University, Sapporo (Japan); Hashimoto, Ayaka, E-mail: [DIA Consultants Co. Ltd., Sapporo (Japan); Igarashi, Toshifumi, E-mail: [Laboratory of Groundwater and Mass Transport, Faculty of Engineering, Hokkaido University, Sapporo (Japan); Yoneda, Tetsuro, E-mail: [Laboratory of Soil Environment Engineering, Faculty of Engineering, Hokkaido University, Sapporo (Japan)


    Sedimentary rocks excavated in Japan from road- and railway-tunnel projects contain relatively low concentrations of hazardous trace elements like boron (B), arsenic (As) and selenium (Se). However, these seemingly harmless waste rocks often produced leachates with concentrations of hazardous trace elements that exceeded the environmental standards. In this study, the leaching behaviors and release mechanisms of B, As and Se were evaluated using batch leaching experiments, sequential extraction and geochemical modeling calculations. The results showed that B was mostly partitioned with the residual/crystalline phase that is relatively stable under normal environmental conditions. In contrast, the majority of As and Se were associated with the exchangeable and organics/sulfides phases that are unstable under oxidizing conditions. Dissolution of water-soluble phases controlled the leaching of B, As and Se from these rocks in the short term, but pyrite oxidation, calcite dissolution and adsorption/desorption reactions became more important in the long term. The mobilities of these trace elements were also strongly influenced by the pH of the rock-water system. Although the leaching of Se only increased in the acidic region, those of B and As were enhanced under both acidic and alkaline conditions. Under strongly acidic conditions, the primarily release mechanism of B, As and Se was the dissolution of mineral phases that incorporated and/or adsorbed these elements. Lower concentrations of these trace elements in the circumneutral pH range could be attributed to their strong adsorption onto minerals like Al-/Fe-oxyhydroxides and clays, which are inherently present and/or precipitated in the rock-water system. The leaching of As and B increased under strongly alkaline conditions because of enhanced desorption and pyrite oxidation while that of Se remained minimal due to its adsorption onto Fe-oxyhydroxides and co-precipitation with calcite. - Highlights: • The bulk of

  8. Mechanized azobenzene-functionalized zirconium metal-organic framework for on-command cargo release


    Meng, Xiangshi; Gui, Bo; Yuan, Daqiang; Zeller, Matthias; Wang, Cheng


    Stimuli-responsive metal-organic frameworks (MOFs) have gained increasing attention recently for their potential applications in many areas. We report the design and synthesis of a water-stable zirconium MOF (Zr-MOF) that bears photoresponsive azobenzene groups. This particular MOF can be used as a reservoir for storage of cargo in water, and the cargo-loaded MOF can be further capped to construct a mechanized MOF through the binding of β-cyclodextrin with the azobenzene stalks on the MOF sur...

  9. Data Monitoring Recorder for Mechanical Properties of Release Coil in Circuit Breaker

    Institute of Scientific and Technical Information of China (English)

    XU Jianyuan; YANG Zhuangzhuang; LIN Xiangbin; LI Bin; LIU Yang


    A design of data monitoring recorder is introduced to ensure the stable work of circuit breakers.The recorder is mainly adopted to collect data of different mechanical properties of circuit breakers for real-time online working in power-industrial labs,and to set up a database including both correct information and fault information for assessing and diagnosing power systems.The recorder uses the master-slave detection core design which adopts both digital signal processor (DSP) and peripheral interface controller (PIC).Not-AND (NAND) flash memory is adopted as a mass storage unit,and the designed clock is used to identify the data being accessed.Access to data and communications between the upper computer and the lower computer are achieved through a universal serial bus (USB) communication.Results of an experiment further illustrate the accuracy and reliability of the data obtained by the proposed recorder.

  10. Weight loss, ion release and initial mechanical properties of a binary calcium phosphate glass fibre/PCL composite. (United States)

    Ahmed, I; Parsons, A J; Palmer, G; Knowles, J C; Walker, G S; Rudd, C D


    Composites comprising a biodegradable polymeric matrix and a bioactive filler show considerable promise in the field of regenerative medicine, and could potentially serve as degradable bone fracture fixation devices, depending on the properties obtained. Therefore, glass fibres from a binary calcium phosphate (50P(2)O(5)+50CaO) glass were used to reinforce polycaprolactone, at two different volume fractions (V(f)). As-drawn, non-treated and heat-treated fibres were assessed. Weight loss, ion release and the initial mechanical properties of the fibres and composites produced have been investigated. Single fibre tensile testing revealed a fibre strength of 474MPa and a tensile modulus of 44GPa. Weibull analysis suggested a scale value of 524. The composites yielded flexural strength and modulus of up to 30MPa and 2.5GPa, respectively. These values are comparable with human trabecular bone. An 8% mass loss was seen for the lower V(f) composite, whereas for the two higher V(f) composites an approximate 20% mass loss was observed over the course of the 5week study. A plateau in the degradation profile at 350h indicated that fibre dissolution was complete at this interval. This assertion was further supported via ion release studies. The leaching of fibres from the composite created a porous structure, including continuous channels within the polymer matrix. This offers further scope for tailoring scaffold development, as cells from the surrounding tissue may be induced to migrate into the resulting porous matrix.

  11. Microglial VPAC1R mediates a novel mechanism of neuroimmune-modulation of hippocampal precursor cells via IL-4 release. (United States)

    Nunan, Robert; Sivasathiaseelan, Harri; Khan, Damla; Zaben, Malik; Gray, William


    Neurogenesis, the production of new neurons from neural stem/progenitor cells (NSPCs), occurs throughout adulthood in the dentate gyrus of the hippocampus, where it supports learning and memory. The innate and adaptive immune systems are increasingly recognized as important modulators of hippocampal neurogenesis under both physiological and pathological conditions. However, the mechanisms by which the immune system regulates hippocampal neurogenesis are incompletely understood. In particular, the role of microglia, the brains resident immune cell is complex, as they have been reported to both positively and negatively regulate neurogenesis. Interestingly, neuronal activity can also regulate the function of the immune system. Here, we show that depleting microglia from hippocampal cultures reduces NSPC survival and proliferation. Furthermore, addition of purified hippocampal microglia, or their conditioned media, is trophic and proliferative to NSPCs. VIP, a neuropeptide released by dentate gyrus interneurons, enhances the proliferative and pro-neurogenic effect of microglia via the VPAC1 receptor. This VIP-induced enhancement is mediated by IL-4 release, which directly targets NSPCs. This demonstrates a potential neuro-immuno-neurogenic pathway, disruption of which may have significant implications in conditions where combined cognitive impairments, interneuron loss, and immune system activation occurs, such as temporal lobe epilepsy and Alzheimer's disease.

  12. Crystal structure of the E. coli dipeptidyl carboxypeptidase Dcp: further indication of a ligand-dependent hinge movement mechanism. (United States)

    Comellas-Bigler, M; Lang, R; Bode, W; Maskos, K


    Dcp from Escherichia coli is a 680 residue cytoplasmic peptidase, which shows a strict dipeptidyl carboxypeptidase activity. Although Dcp had been assigned to the angiotensin I-converting enzymes (ACE) due to blockage by typical ACE inhibitors, it is currently grouped into the M3 family of mono zinc peptidases, which also contains the endopeptidases neurolysin and thimet oligopeptidase (TOP). We have cloned, expressed, purified, and crystallized Dcp in the presence of an octapeptide "inhibitor", and have determined its 2.0A crystal structure using MAD methods. The analysis revealed that Dcp consists of two half shell-like subdomains, which enclose an almost closed two-chamber cavity. In this cavity, two dipeptide products presumably generated by Dcp cleavage of the octapeptide bind to the thermolysin-like active site fixed to side-chains, which are provided by both subdomains. In particular, an Arg side-chain backed by a Glu residue, together with two Tyr phenolic groups provide a charged anchor for fixing the C-terminal carboxylate group of the P2' residue of a bound substrate, explaining the strict dipeptidyl carboxypeptidase specificity of Dcp. Tetrapeptidic substrates are fixed only via their main-chain functions from P2 to P2', suggesting a broad residue specificity for Dcp. Both subdomains exhibit very similar chain folds as the equivalent but abducted subdomains of neurolysin and TOP. Therefore, this "product-bound" Dcp structure seems to represent the inhibitor/substrate-bound "closed" form of the M3 peptidases, generated from the free "open" substrate-accessible form by a hinge-bending mechanism. A similar mechanism has recently been demonstrated experimentally for ACE2.

  13. In-situ investigation of the hydrogen release mechanism in bulk Mg2NiH4 (United States)

    Tran, Xuan Quy; McDonald, Stuart D.; Gu, Qinfen; Yamamoto, Tomokazu; Shigematsu, Koji; Aso, Kohei; Tanaka, Eishi; Matsumura, Syo; Nogita, Kazuhiro


    Hydrogen storage is an important aspect to enable the so-called hydrogen economy. Mg-Ni alloys are among the most promising candidates for solid-state hydrogen storage systems yet many questions remain unanswered regarding the hydriding/dehydriding mechanism of the alloys. Mg2NiH4 particularly has received much attention both for its potential as a hydrogen storage medium and also exhibits interesting properties relating to its different polymorphs. Here, the dehydriding mechanism in bulk Mg2NiH4 is investigated using in-situ ultra-high voltage transmission electron microscopy (TEM) combined with Synchrotron powder X-ray diffraction (XRPD) and differential scanning calorimetry (DSC). We find that the hydrogen release is based on a mechanism of nucleation and growth of Mg2NiHx (x∼0-0.3) solid solution grains and is greatly enhanced in the presence of crystal defects occurring as a result of the polymorphic phase transformation. Also importantly, with atomic resolution TEM imaging a high density of stacking faults is identified in the dehydrided Mg2NiHx (x∼0-0.3) lattices.

  14. Cyclo-oxygenase-2 mediated prostaglandin release regulates blood flow in connective tissue during mechanical loading in humans

    DEFF Research Database (Denmark)

    Langberg, H; Boushel, Robert Christopher; Skovgaard, D


    Mechanical loading is known to increase connective tissue blood flow of human tendons and to cause local release of vasodilatory substances. The present study investigated the importance of prostaglandins (PG) formed by cyclo-oxygenase isoforms (COX-1 and 2) for the exercise-related increase...... in blood flow in connective tissue. Healthy individuals (n = 24, age: 23-31 years) underwent 30 min of intermittent, isometric, plantarflexion with both calf muscles either without (n = 6, Control, C) or with blockade of PG formation, either COX-2 specific (n = 10, Celecoxib 2 x 100 mg day-1 for 3 days.......2 +/- 2.0)(P tissue prostaglandin plays an important role for blood flow in peritendinous connective tissue during physical loading in vivo....

  15. The effect of motivation and positive affect on ego depletion: Replenishment versus release mechanism. (United States)

    Zhu, Ze; Li, Jian; Zhang, Bo; Li, Ye; Zhang, Houcan


    In this study, 2 experiments were conducted to investigate whether motivation and positive affect can alleviate ego depletion and to elucidate their possible mechanisms. In Experiment 1, a crossing-out-letter task was adapted to reach an ego depletion state for Chinese participants. Participants were then randomly assigned to the extrinsic motivation group, the positive affect group or the depletion control group. After the experimental treatment, a dumbbell task was used to measure participants' remaining self-regulatory resources. The results showed that participants in the motivation and positive affect groups performed better on the dumbbell task than participants in the depletion control group. Experiment 2 was similar to Experiment 1 except that participants were asked to perform an additional unexpected dumbbell task after a neutral video following the above procedure. The results of Experiment 1 were replicated; however, participants' performance on the additional dumbbell task differed. The positive affect group performed better than the depletion control group, indicating an increase in self-regulatory resources and thus supporting the replenishment effect of positive affect. No significant difference was found between the motivation group and the depletion control group.

  16. Preliminary Study of Strong-Sludge Gas Retention and Release Mechanisms in Clay Simulants

    Energy Technology Data Exchange (ETDEWEB)

    Gauglitz, Phillip A.; Buchmiller, William C.; Probert, Samuel G.; Owen, Antionette T.


    The Hanford Site has 28 double-shell tanks (DSTs) and 149 single-shell tanks (SSTs) containing radioactive wastes that are complex mixes of radioactive and chemical products. The mission of the Department of Energy’s River Protection Project is to retrieve and treat the Hanford tank waste for disposal and close the tank farms. A key aspect of the mission is to retrieve and transfer waste from the SSTs, which are at greater risk for leaking, into DSTs for interim storage until the waste is transferred to and treated in the Waste Treatment and Immobilization Plant. There is, however, limited space in the existing DSTs to accept waste transfers from the SSTs, and approaches to overcoming the limited DST space will benefit the overall mission. The purpose of this study is to summarize and analyze the key previous experiment that forms the basis for the relaxed controls and to summarize initial progress and results on new experiments focused on understanding the conditions that result in low gas retention. The work is ongoing; this report provides a summary of the initial findings. The previous large-scale test used about 50 m3 of sediment, which would be unwieldy for doing multiple parametric experiments. Accordingly, experiments will begin with smaller-scale tests to determine whether the desired mechanisms can be studied without the difficulty of conducting very large experiments.

  17. A modified release analysis procedure using advanced froth flotation mechanisms: Technical report, March 1, 1996-May 31, 1996

    Energy Technology Data Exchange (ETDEWEB)

    Honaker, R.Q., Mohanty, M.K. [Southern Illinois Univ., Department of Mining Engineering, Carbondale, IL (United States)


    Recent studies indicate that the optimum separation performances achieved by multiple stage cleaning using various column flotation technologies and single stage cleaning using a Packed-Flotation Column are superior to the performance achieved by the traditional release procedure, especially in terms of pyritic sulfur rejection. This superior performance is believed to be the result of the advanced flotation mechanisms provided by column flotation technologies. Thus, the objective of this study is to develop a suitable process utilizing the advanced froth flotation mechanisms to characterize the true flotation response of a coal sample. Work in this reporting period concentrated on developing a modified coal flotation characterization procedure, termed as Advanced Flotation Washability (AFW) technique. The new apparatus used for this procedure is essentially a batch operated packed-column device equipped with a controlled wash water system. Several experiments were conducted using the AFW technique on a relatively high sulfur, -100 mesh Illinois No. 5 run-of-mine coal sample collected from a local coal preparation plant. Similar coal characterization experiments were also conducted using the traditional release and tree analysis procedures. The best performance curve generated using the AFW technique was found to be superior to the optimum curve produced by the traditional procedures. For example, at a combustible recovery of 80%, a 19% improvement in the reduction of the pyritic sulfur content was achieved by the AFW method while the ash reduction was also enhanced by 4%. Several tests are on-going to solidify the AFW procedure and verify the above finding by conducting Anova analyses to evaluate the repeatability of the AFW method and the statistical significance of the difference in the performance achieved from the traditional and modified coal characterization procedures.

  18. Junction properties and conduction mechanism of new terbium complexeswith triethylene glycol ligand for potential application in organic electronic device

    Institute of Scientific and Technical Information of China (English)

    N.K.Za’aba1; M.A. Mohd Sarjidan; W.H.Abd. Majid; Eny Kusrini; Muhammad I.Saleh


    Terbium-picrate triethylene glycol (EO3-Tb-Pic) complex was prepared in thin film and single layer device structure of ITO/EO3-Tb-Pic/Al, using spin coating technique. The UV-Vis absorption spectroscopy analysis was performed to evaluate the elec-tronic molecular transition of the complex. The optical band gap, Eg estimated from the Tauc model revealed that EO3-Tb-Pic thin film exhibited a direct transition with Eg of 2.70 eV. The electronic parameters of the ITO/EO3-Tb-Pic/Al device such as the ideality factor n, barrier heightΦb, saturation current Io, and series resistance Rs, were extracted from the conventional lnI-V, Cheung’s func-tions and Norde’s method. It was found that the evaluated parameters calculated from Norde’s and Cheung’s methods were consistent with those calculated from the conventional I-V method. In the double logarithmic I-V plot, three distinct regions based on the slope were identified, and the conduction mechanisms were discussed and explained. The mobility,μvalue was estimated from SCLC re-gion as 2.58×10-7 cm2/(V·s). This newly obtained lanthanide complex may be potentially utilized in electronic devices.

  19. Potentiation of glutamate release caused by delta—methrin and the possible mechanism associated with carbon monoxide pathway and protein kinase C

    Institute of Scientific and Technical Information of China (English)

    AiBM; LiuYG


    The acute neurotoxicity of delta-methrin is thought to be associated with the release of grutamate from synaptosomes in brain.However,the mechanism how delta-methrin enhances the glutamate release has still not been elucidated.Here we report that both carbon monoxide(CO) and the activator of protein kinase C(PKC),similarly to delta-methrin,potentiate the Ca2+-dependent glutamate release from rat cerebral cortical synaptosomes,otherwise,the release of glutamate is inhibited by zinc proporphyrin-9(ZnPP-9) and inhibitors of PKC or of protein kinase G(PKG).In addition,the inhibitors of ZnPP-9 PKC and PKG seem to weaken the enhancement of glutamate releas caused by delta-methrin.So,we conclude that CO signal transduction pathway and PKC mediate the glutamate release from synptosomes by delta-methrin.

  20. Conformational analysis of a polyconjugated protein-binding ligand by joint quantum chemistry and polarizable molecular mechanics. Addressing the issues of anisotropy, conjugation, polarization, and multipole transferability. (United States)

    Goldwaser, Elodie; de Courcy, Benoit; Demange, Luc; Garbay, Christiane; Raynaud, Françoise; Hadj-Slimane, Reda; Piquemal, Jean-Philip; Gresh, Nohad


    We investigate the conformational properties of a potent inhibitor of neuropilin-1, a protein involved in cancer processes and macular degeneration. This inhibitor consists of four aromatic/conjugated fragments: a benzimidazole, a methylbenzene, a carboxythiourea, and a benzene-linker dioxane, and these fragments are all linked together by conjugated bonds. The calculations use the SIBFA polarizable molecular mechanics procedure. Prior to docking simulations, it is essential to ensure that variations in the ligand conformational energy upon rotations around its six main-chain torsional bonds are correctly represented (as compared to high-level ab initio quantum chemistry, QC). This is done in two successive calibration stages and one validation stage. In the latter, the minima identified following independent stepwise variations of each of the six main-chain torsion angles are used as starting points for energy minimization of all the torsion angles simultaneously. Single-point QC calculations of the minimized structures are then done to compare their relative energies ΔE conf to the SIBFA ones. We compare three different methods of deriving the multipoles and polarizabilities of the central, most critical moiety of the inhibitor: carboxythiourea (CTU). The representation that gives the best agreement with QC is the one that includes the effects of the mutual polarization energy E pol between the amide and thioamide moieties. This again highlights the critical role of this contribution. The implications and perspectives of these findings are discussed.

  1. Presynaptic. cap alpha. -adrenoceptors and opiate receptors: inhibition of (/sup 3/H)noradrenaline release from rat cerebral cortex slices by different mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Schoffelmeer, A.N.M.; Mulder, A.H. (Vrije Univ., Amsterdam (Netherlands))


    The inhibitory effects of morphine and Cd/sup 2 +/ on electrically evoked (/sup 3/H)noradrenaline release from superfused brain slices were unaffected when release was enhanced by increasing the pulse duration, while the inhibitory effect of noradrenaline and the enhancing effect of phentolamine were diminished. A similar enhancement of (/sup 3/H)noradrenaline release by 4-aminopyridine reduced the modulatory effects of all drugs examined. Therefore there seem to be different mechanisms for the effect of presynaptic ..cap alpha..-adrenoceptors and opiate receptors on the availability of Ca/sup 2 +/ for the stimulus-secretion coupling process in noradrenergic nerve terminals.


    Directory of Open Access Journals (Sweden)

    Muzaffer Ahmet Karaaslan


    Full Text Available The cell wall of most plant biomass from forest and agricultural resources consists of three major polymers, cellulose, hemicellulose, and lignin. Of these, hemicelluloses have gained increasing attention as sustainable raw materials. In this study, novel pH-sensitive semi-IPN hydrogels based on hemicelluloses and chitosan were prepared using glutaraldehyde as the crosslinking agent. The hemicellulose isolated from aspen was analyzed for sugar content by HPLC, and its molecular weight distribution was determined by high performance size exclusion chromatography. Results revealed that hemicellulose had a broad molecular weight distribution with a fair amount of polymeric units, together with xylose, arabinose, and glucose. The effects of hemicellulose content on mechanical properties and swelling behavior of hydrogels were investigated. The semi-IPNs hydrogel structure was confirmed by FT-IR, X-ray study, and the ninhydrin assay method. X-ray analysis showed that higher hemicellulose contents yielded higher crystallinity. Mechanical properties were mainly dependent on the crosslink density and average molecular weight between crosslinks. Swelling ratios increased with increasing hemicellulose content and were high at low pH values due to repulsion between similarly charged groups. In vitro release study of a model drug showed that these semi-IPN hydrogels could be used for controlled drug delivery into gastric fluid.

  3. Mechanism-Based Tumor-Targeting Drug Delivery System. Validation of Efficient Vitamin Receptor-Mediated Endocytosis and Drug Release

    Energy Technology Data Exchange (ETDEWEB)

    Chen, S.; Wong, S.; Zhao, X.; Chen, J.; Chen, J.; Kuznetsova, L.; Ojima, I.


    An efficient mechanism-based tumor-targeting drug delivery system, based on tumor-specific vitamin-receptor mediated endocytosis, has been developed. The tumor-targeting drug delivery system is a conjugate of a tumor-targeting molecule (biotin: vitamin H or vitamin B-7), a mechanism-based self-immolative linker and a second-generation taxoid (SB-T-1214) as the cytotoxic agent. This conjugate (1) is designed to be (i) specific to the vitamin receptors overexpressed on tumor cell surface and (ii) internalized efficiently through receptor-mediated endocytosis, followed by smooth drug release via glutathione-triggered self-immolation of the linker. In order to monitor and validate the sequence of events hypothesized, i.e., receptor-mediated endocytosis of the conjugate, drug release, and drug-binding to the target protein (microtubules), three fluorescent/fluorogenic molecular probes (2, 3, and 4) were designed and synthesized. The actual occurrence of these processes was unambiguously confirmed by means of confocal fluorescence microscopy (CFM) and flow cytometry using L1210FR leukemia cells, overexpressing biotin receptors. The molecular probe 4, bearing the taxoid linked to fluorescein, was also used to examine the cell specificity (i.e., efficacy of receptor-based cell targeting) for three cell lines, L1210FR (biotin receptors overexpressed), L1210 (biotin receptors not overexpressed), and WI38 (normal human lung fibroblast, biotin receptor negative). As anticipated, the molecular probe 4 exhibited high specificity only to L1210FR. To confirm the direct correlation between the cell-specific drug delivery and anticancer activity of the probe 4, its cytotoxicity against these three cell lines was also examined. The results clearly showed a good correlation between the two methods. In the same manner, excellent cell-specific cytotoxicity of the conjugate 1 (without fluorescein attachment to the taxoid) against the same three cell lines was confirmed. This mechanism

  4. A GTPase chimera illustrates an uncoupled nucleotide affinity and release rate, Providing insight into the activation mechanism

    DEFF Research Database (Denmark)

    Guilfoyle, Amy P.; Deshpande, Chandrika N.; Font Sadurni, Josep


    for GDP release, or, alternatively, the movement is a consequence of release. To gain additional insight into the sequence of events leading to GDP release, we have created a chimeric protein comprised of Escherichia coli NFeoB and the G5 loop from the human Giα1 protein. The protein chimera retains...

  5. Relevance of the ligand exchange rate and mechanism of fac-[(CO)3M(H2O)3]+ (M = Mn, Tc, Re) complexes for new radiopharmaceuticals. (United States)

    Grundler, Pascal V; Helm, Lothar; Alberto, Roger; Merbach, André E


    The water exchange process on fac-[(CO)3Mn(H2O)3]+ and fac-[(CO)3Tc(H2O)3]+ was kinetically investigated by 17O NMR as a function of the acidity, temperature, and pressure. Up to pH 6.3 and 4.4, respectively, the exchange rate is not affected by the acidity, thus demonstrating that the contribution of the monohydroxo species fac-[(CO)3M(OH)(H2O)2] is not significant, which correlates well with a higher pKa for these complexes compared to the homologue fac-[(CO)3Re(H2O)3]+ complex. The water exchange rate K298ex/s(-1) (DeltaHex double dagger/kJ mol(-1); DeltaSex double dagger/J mol(-1) K(-1); DeltaV double dagger/cm3 mol-1) decreases down group 7 from Mn to Tc and Re: 23 (72.5; +24.4; +7.1) > 0.49 (78.3; +11.7; +3.8) > 5.4 x 10(-3) (90.3; +14.5; -). For the Mn complex only, an O exchange on the carbonyl ligand could be measured (K338co = 4.3 x 10(-6) s(-1)), which is several orders of magnitude slower than the water exchange. In the case of the Tc complex, the coupling between 17O (I = 5/2) and 99Tc (I = 9/2) nuclear spins has been observed (1J99Tc,17O = 80 +/- 5 Hz). The substitution of water in fac-[(CO)3M(H2O)3]+ by dimethyl sulfide (DMS) is slightly faster than that by CH3CN: 3 times faster for Mn, 1.5 times faster for Tc, and 1.2 times faster for Re. The pressure dependence behavior is different for Mn and Re. For Mn, the change in volume to reach the transition state is always clearly positive (water exchange, CH3CN, DMS), indicating an Id mechanism. In the case of Re, an Id/Ia changeover is assigned on the basis of reaction profiles with a strong volume maximum for pyrazine and a minimum for DMS as the entering ligand.

  6. Light-cured dimethacrylate-based resins and their composites: comparative study of mechanical strength, water sorption and ion release (United States)

    O’Donnell, J.N.R.; Langhorst, S.E.; Fow, M.D.; Antonucci, J.M.; Skrtic, D.


    This study explored how resin type affects selected physicochemical properties of complex methacrylate copolymers and their amorphous calcium phosphate (ACP)-filled and glass-filled composites. Two series of photo-polymerizable resin matrices were formulated employing 2,2-bis[p-(2’-hydroxy-3’-methacryloxypropoxy)phenyl]propane (Bis-GMA) or an ethoxylated bisphenol A dimethacrylate (EBPADMA) as the base monomer, Unfilled copolymers and composites filled with a mass fraction with 40 %, 35 % and 30 %, respectively, of ACP or the un-silanized glass were assessed for biaxial flexure strength (BFS), water sorption (WS) and mineral ion release upon immersion in HEPES-buffered saline solution for up to six months. Substituting EBPADMA for Bis-GMA significantly reduced the WS while only marginally affected the BFS of both dry and wet copolymers. Independent of the filler level, both dry and wet ACP composites formulated with either BTHM or ETHM resins were mechanically weaker than the corresponding copolymers. The BFS of ACP composite specimens after 1 month in saline did not further decrease with further aqueous exposure. The BFS of glass-filled composites decreased with the increased level of the glass filler and the time of aqueous exposure. After 6 months of immersion, the BFS of glass-filled BTHM and ETHM composites, respectively, remained 58 % and 41 % higher than the BFS of the corresponding ACP composites. Ion release data indicated that a minimum mass fraction of 35 % ACP was required to attain the desired solution supersaturation with respect to hydroxyapatite for both the BTHM and ETHM derived composites. PMID:18607513

  7. Determinants governing ligand specificity of the Vibrio harveyi LuxN quorum-sensing receptor. (United States)

    Ke, Xiaobo; Miller, Laura C; Bassler, Bonnie L


    Quorum sensing is a process of bacterial cell-cell communication that relies on the production, release and receptor-driven detection of extracellular signal molecules called autoinducers. The quorum-sensing bacterium Vibrio harveyi exclusively detects the autoinducer N-((R)-3-hydroxybutanoyl)-L-homoserine lactone (3OH-C4 HSL) via the two-component receptor LuxN. To discover the principles underlying the exquisite selectivity LuxN has for its ligand, we identified LuxN mutants with altered specificity. LuxN uses three mechanisms to verify that the bound molecule is the correct ligand: in the context of the overall ligand-binding site, His210 validates the C3 modification, Leu166 surveys the chain-length and a strong steady-state kinase bias imposes an energetic hurdle for inappropriate ligands to elicit signal transduction. Affinities for the LuxN kinase on and kinase off states underpin whether a ligand will act as an antagonist or an agonist. Mutations that bias LuxN to the agonized, kinase off, state are clustered in a region adjacent to the ligand-binding site, suggesting that this region acts as the switch that triggers signal transduction. Together, our analyses illuminate how a histidine sensor kinase differentiates between ligands and exploits those differences to regulate its signaling activity.

  8. Release Mechanism and Pharmaceutical Care of Oral Sustained/Controlled Release Preparations in Clinical Application%临床常用口服缓控释制剂的释药原理与服用要点

    Institute of Scientific and Technical Information of China (English)

    钱卿; 谢云芬


    缓控释药物在现今临床使用上已日趋广泛,也是药物制剂学研究的热点内容.本文简要地介绍了缓控释制剂的释药原理,并列举了常用的缓控释药品及正确的使用方法,为临床工作者合理应用提供了必要的依据.%With the increasing application in modern clinical therapy, the sustained/controlled release drug delivery systems (DDSs) are the hot spot and main trend of pharmaceutic research. The release characteristics and mechanisms for oral sustained/controlled release preparations are discussed, and those commonly used in the hospitals are introduced in this article. Providing rational administration of the drugs and strengthening pharmaceutical care is critical to ensure their safe and effective application.

  9. Molecular Mechanism of Peroxisome Proliferator-Activated Receptor alpha Activation by WY14643: a New Mode of Ligand Recognition and Receptor Stabilization

    NARCIS (Netherlands)

    Bernardes, Amanda; Telles de Souza, Paulo C; Muniz, João R C; Ricci, Clarisse G; Ayers, Stephen D; Parekh, Nili M; Godoy, André S; Trivella, Daniela B B; Reinach, Peter; Webb, Paul; Skaf, Munir S; Polikarpov, Igor


    Peroxisome proliferator-activated receptors (PPARs) are members of a superfamily of nuclear transcription factors. They are involved in mediating numerous physiological effects in humans, including glucose and lipid metabolism. PPAR alpha ligands effectively treat dyslipidemia and have significant

  10. Riluzole and gabapentinoids activate glutamate transporters to facilitate glutamate-induced glutamate release from cultured astrocytes


    Yoshizumi, Masaru; Eisenach, James C.; Hayashida, Ken-ichiro


    We have recently demonstrated that the glutamate transporter activator riluzole paradoxically enhanced glutamate-induced glutamate release from cultured astrocytes. We further showed that both riluzole and the α2δ subunit ligand gabapentin activated descending inhibition in rats by increasing glutamate receptor signaling in the locus coeruleus and hypothesized that these drugs share common mechanisms to enhance glutamate release from astrocytes. In the present study, we examined the effects o...

  11. Different HPMC viscosity grades as coating agents for an oral time and/or site-controlled delivery system: an investigation into the mechanisms governing drug release. (United States)

    Zema, L; Maroni, A; Foppoli, A; Palugan, L; Sangalli, M E; Gazzaniga, A


    When used as release-controlling coating agents for tableted core-based pulsatile delivery systems, three different hydroxypropyl methylcellulose (HPMC) grades, Methocel E5, E50, and K4M, provided lag phases of varying duration (Methocel K4M > E50 > E5) and a prompt and quantitative model drug release. Dissolution/mechanical erosion, permeability increase and disruption of the hydrated polymeric layer were assumed to participate in the definition of the overall release pattern. Based on these premises, we investigated what process(es) might prevail in the release-controlling mechanism for each HPMC grade. The polymers were evaluated for dissolution and swelling, while the finished systems were concomitantly evaluated for drug release and polymer dissolution. The obtained results indicated likely similarities between Methocel E5 and E50 performances, which we hypothesized to be mainly dissolution/erosion-controlled, and a clearly different behavior for Methocel K4M. This polymer indeed proved to yield higher viscosity and slower dissolving gel layer, which was able to withstand extensive dissolution/erosion for periods that exceeded the observed lag phases. The particular characteristics of swollen Methocel K4M were shown to be associated with possible drug diffusion phenomena, which might impair the prompt and quantitative release phase that is typical of pulsatile delivery.

  12. Differential mechanisms involved in the effect of nicotinic agonists DMPP and lobeline to release [3H]5-HT from rat hippocampal slices. (United States)

    Lendvai, B; Sershen, H; Lajtha, A; Santha, E; Baranyi, M; Vizi, E S


    In the present study we investigated the effect of different nicotinic agonists (dimethylphenyl-piperazinium-iodide (DMPP), (-)nicotine, cytisine, (-)-lobeline, and (-)epibatidine) and antagonists (mecamylamine and dihydro-beta-erythroidine) on the release of [3H]5-HT from hippocampal slices. The nicotinic agonists DMPP and lobeline and electrical field stimulation, released [3H]5-HT from the hippocampus; other nicotinic agonists, such as (-)-nicotine, cytisine, and (-)-epibatidine had no effect. Unlike lobeline-induced release of [3H]5-HT, the effect of DMPP (10 and 40 microM) was antagonized by mecamylamine (20 and 10 microM). The effect of DMPP was [Ca2+]o-independent. In experiments carried out at 7 degrees C, i.e. the membrane carrier proteins are inhibited and the release by lobeline was abolished while the DMPP-induced release of 5-HT was rather potentiated. It is proposed that the effect of DMPP and lobeline, to enhance the release of [3H]5-HT from the hippocampus, was mediated by two different mechanisms. While DMPP-induced 5-HT release can be linked to a non-classical nAChR activation ([Ca2+]o-independence), the effect of lobeline was likely mediated by uptake carriers.

  13. Exosomes are released by bystander cells exposed to radiation-induced biophoton signals: Reconciling the mechanisms mediating the bystander effect. (United States)

    Le, Michelle; Fernandez-Palomo, Cristian; McNeill, Fiona E; Seymour, Colin B; Rainbow, Andrew J; Mothersill, Carmel E


    The objective of our study was to explore a possible molecular mechanism by which ultraviolet (UV) biophotons could elicit bystander responses in reporter cells and resolve the problem of seemingly mutually exclusive mechanisms of a physical UV signal & a soluble factor-mediated bystander signal. The human colon carcinoma cell line, HCT116 p53 +/+, was directly irradiated with 0.5 Gy tritium beta particles to induce ultraviolet biophoton emission. Bystander cells were not directly irradiated but were exposed to the emitted UV biophotons. Medium was subsequently harvested from UV-exposed bystander cells. The exosomes extracted from this medium were incubated with reporter cell populations. These reporter cells were then assayed for clonogenic survival and mitochondrial membrane potential with and without prior treatment of the exosomes with RNase. Clonogenic cell survival was significantly reduced in reporter cells incubated with exosomes extracted from cells exposed to secondarily-emitted UV. These exosomes also induced significant mitochondrial membrane depolarization in receiving reporter cells. Conversely, exosomes extracted from non-UV-exposed cells did not produce bystander effects in reporter cells. The treatment of exosomes with RNase prior to their incubation with reporter cells effectively abolished bystander effects in reporter cells and this suggests a role for RNA in mediating the bystander response elicited by UV biophotons and their produced exosomes. This study supports a role for exosomes released from UV biophoton-exposed bystander cells in eliciting bystander responses and also indicates a reconciliation between the UV-mediated bystander effect and the bystander effect which has been suggested in the literature to be mediated by soluble factors.

  14. Non-invasive insight into the release mechanisms of a poorly soluble drug from amorphous solid dispersions by confocal Raman microscopy. (United States)

    Punčochová, Kateřina; Vukosavljevic, Branko; Hanuš, Jaroslav; Beránek, Josef; Windbergs, Maike; Štěpánek, František


    In this study, we investigated the release mechanism of the poorly water soluble drug aprepitant from different amorphous solid dispersions using confocal Raman microscopy (CRM). Solid dispersions were fabricated based on either Soluplus®, as an amphiphilic copolymer and solubilizer, or on polyvinylpyrrolidone, as a hydrophilic polymer, in order to elucidate the influence of the polymer characteristics on the drug form and dissolution mechanisms. Aprepitant exhibited its amorphous form in both solid dispersions. However, the release differed depending on the polymer. The high complexation effect of Soluplus was shown to be a crucial factor for stabilization of the amorphous drug, resulting in continuous release without any recrystallization of aprepitant. In contrast, solid dispersions based on polyvinylpyrrolidone showed a different mechanism of dissolution; due to the good affinity of PVP and water, the polymer is dissolving fast, leading to phase separation and local recrystallization of the drug. The study highlights the complexity of release processes from solid dispersions and elucidates the influence of the polymer on drug release kinetics.

  15. Acute release of tissue-type plasminogen activator (t-PA) from the endothelium ; regulatory mechanisms and therapeutic target

    NARCIS (Netherlands)

    Schrauwen, Y.; Vries, R.E.M. de; Kooistra, T.; Emeis, J.J.


    The acute release of t-PA was studied in vitro in human endothelial cells from different origin. It proved possible to enhance the amounts of t-PA which can be released by increasing t-PA synthesis, both in vitro, and in vivo in rats. These data suggest the feasibility to induce and (or) enhance acu

  16. Design of sustained release fine particles using two-step mechanical powder processing: particle shape modification of drug crystals and dry particle coating with polymer nanoparticle agglomerate. (United States)

    Kondo, Keita; Ito, Natsuki; Niwa, Toshiyuki; Danjo, Kazumi


    We attempted to prepare sustained release fine particles using a two-step mechanical powder processing method; particle-shape modification and dry particle coating. First, particle shape of bulk drug was modified by mechanical treatment to yield drug crystals suitable for the coating process. Drug crystals became more rounded with increasing rotation speed, which demonstrates that powerful mechanical stress yields spherical drug crystals with narrow size distribution. This process is the result of destruction, granulation and refinement of drug crystals. Second, the modified drug particles and polymer coating powder were mechanically treated to prepare composite particles. Polymer nanoparticle agglomerate obtained by drying poly(meth)acrylate aqueous dispersion was used as a coating powder. The porous nanoparticle agglomerate has superior coating performance, because it is completely deagglomerated under mechanical stress to form fine fragments that act as guest particles. As a result, spherical drug crystals treated with porous agglomerate were effectively coated by poly(meth)acrylate powder, showing sustained release after curing. From these findings, particle-shape modification of drug crystals and dry particle coating with nanoparticle agglomerate using a mechanical powder processor is expected as an innovative technique for preparing controlled-release coated particles having high drug content and size smaller than 100 μm.

  17. Melatonin supplementation decreases prolactin synthesis and release in rat adenohypophysis: correlation with anterior pituitary redox state and circadian clock mechanisms. (United States)

    Jiménez-Ortega, Vanesa; Barquilla, Pilar Cano; Pagano, Eleonora S; Fernández-Mateos, Pilar; Esquifino, Ana I; Cardinali, Daniel P


    In the laboratory rat, a number of physiological parameters display seasonal changes even under constant conditions of temperature, lighting, and food availability. Since there is evidence that prolactin (PRL) is, among the endocrine signals, a major mediator of seasonal adaptations, the authors aimed to examine whether melatonin administration in drinking water resembling in length the exposure to a winter photoperiod could affect accordingly the 24-h pattern of PRL synthesis and release and some of their anterior pituitary redox state and circadian clock modulatory mechanisms. Melatonin (3 µg/mL drinking water) or vehicle was given for 1 mo, and rats were euthanized at six time intervals during a 24-h cycle. High concentrations of melatonin (>2000 pg/mL) were detected in melatonin-treated rats from beginning of scotophase (at 21:00 h) to early photophase (at 09:00 h) as compared with a considerably narrower high-melatonin phase observed in controls. By cosinor analysis, melatonin-treated rats had significantly decreased MESOR (24-h time-series average) values of anterior pituitary PRL gene expression and circulating PRL, with acrophases (peak time) located in the middle of the scotophase, as in the control group. Melatonin treatment disrupted the 24-h pattern of anterior pituitary gene expression of nitric oxide synthase (NOS)-1 and -2, heme oxygenase-1 and -2, glutathione peroxidase, glutathione reductase, Cu/Zn- and Mn-superoxide dismutase, and catalase by shifting their acrophases to early/middle scotophase or amplifying the maxima. Only the inhibitory effect of melatonin on pituitary NOS-2 gene expression correlated temporally with inhibition of PRL production. Gene expression of metallothionein-1 and -3 showed maxima at early/middle photophase after melatonin treatment. The 24-h pattern of anterior pituitary lipid peroxidation did not vary after treatment. In vehicle-treated rats, Clock and Bmal1 expression peaked in the anterior pituitary at middle

  18. Kinetics and mechanism of S-nitrosothiol acid-catalyzed hydrolysis: sulfur activation promotes facile NO+ release. (United States)

    Moran, Ernesto E; Timerghazin, Qadir K; Kwong, Elizabeth; English, Ann M


    The denitrosation of three primary S-nitrosothiols (RSNO; S-nitrosocysteine, S-nitroso-N-acetylcysteine, and S-nitrosoglutathione) and two tertiary RSNOs (S-nitrosopenicillamine and S-nitroso-N-acetylpenicillamine) was investigated in 3.75 M H(2)SO(4) to probe the mechanism of acid-catalyzed RSNO hydrolysis and its dependence on RSNO structure. This reversible reaction was forced to proceed in the denitrosation direction by trapping the nitrosating agent with HN(3). The primary RSNOs exhibited hydrolysis k(obs) values of ∼2 × 10(-4) s(-1), and the tertiary RSNO k(obs) values were an order of magnitude higher. Product analysis by HPLC revealed that the parent thiols (RSHs) were formed in 90-100% yield on 79-99% RSNO denitrosation. Possible hydrolysis mechanisms were studied computationally at the CBS-QB3 level using S-nitrosomethanethiol (MeSNO) as a model RSNO. Consideration of RSNOs as a combination of conventional R-S-N═O, zwitterionic R-S(+)═N-O(-), and RS(-)/NO(+) ion-pair resonance structures was key in understanding the mechanistic details of acid-catalyzed hydrolysis. Protonation of the S-nitroso oxygen or nitrogen activates the sulfur and nucleophilic attack by H(2)O at this atom leads to the formation of the sulfoxide-protonated N-hydroxysulfinamide, MeS(+)(OH)NHOH, with barriers of 19 and 29 kcal/mol, respectively. Proton loss and reprotonation at the nitrogen lead to secondary hydrolysis that produces the sulfinic acid MeS(═O)OH and NH(2)OH. Notably, no low-energy RSNO hydrolysis pathway for HNO release was found in the computational analysis. Protonation of the S-nitroso sulfur gives rise to NO(+) release with a low activation barrier (ΔH(double dagger)(calc) ≈ 6 kcal/mol) and the formation of MeSH in agreement with experiment. The experimental k(obs) can be expressed as K(a)k(1), where K(a) is the acid dissociation constant for protonation of the S-nitroso sulfur and k(1) the pseudo-first-order hydrolysis rate constant. Given the low

  19. Organic nanofibers containing insect pheromone disruptants: a novel technical approach to controlled release dispensers with potential for process mechanization. (United States)

    Hummel, H E; Hein, D F; Breuer, M; Lindner, I; Greiner, A; Wendorff, J H; Hellmann, C; Dersch, R; Kratt, A; Kleeberg, H; Leithold, G


    Beginning fifty years ago, the search for suitable dispensers containing insect pheromones grew with the availability of these synthetic biotechnical tools. Many economic entomologists and application engineers dearly wish they had the "smart, intelligent and ideal dispenser". More or less suitable approximations are available commercially, but none so far meets all demands. Under economic strictures, novel inexpensive systems would be advantageous with release characteristics tailored to the specific life histories of pest insects, the plants considered and the numerous requirements of growers alike. Simultaneously, their field distribution should be mechanizable and be accomplished by one (or very few) application runs. The dispensers should be biodegradable, biocompatible, sustainably applicable, and they should be based on renewable resources. This report presents first results of a novel organic, electrospun nanofiber dispenser with dimensions in the upper nanometer range. Its load of pheromone can be adjusted to be sufficient for 7 weeks of constant disruptive action in vineyards and can be directed against the European Grape Vine Moth Lobesia botrana (Lepidoptera: Tortricidae) which here serves as a readily available model. Mating disruption in L. botrana and the related Eupoecilia ambiguella is a well studied and developed engineering process. Equally, nanofiber production by electrospinning (for a comprehensive review see Greiner and Wendorff, 2007A, B) is well known and already has numerous applications in filtration technology, air conditioning, and medical wound dressing. Our goal was to bring together and successfully mate these (partly incompatible) technologies via technical tricks of a proprietary nature. Even though the lifetime and effectiveness of currently available nanofibers still must be doubled, the rather complicated system of their production and analysis is known well enough to identify the parameters that need future adjustment. Another

  20. Multiple-path dissociation mechanism for mono- and dinuclear tris(hydroxamato)iron(III) complexes with dihydroxamic acid ligands in aqueous solution. (United States)

    Boukhalfa, H; Crumbliss, A L


    Linear synthetic dihydroxamic acids ([CH3N(OH)C=O)]2(CH2)n; H2Ln) with short (n = 2) and long (n = 8) hydrocarbon-connecting chains form mono- and dinuclear complexes with Fe(III) in aqueous solution. At conditions where the formation of Fe2(Ln)3 is favored, complexes with each of the two ligand systems undergo [H+]-induced ligand dissociation processes via multiple sequential and parallel paths, some of which are common and some of which are different for the two ligands. The pH jump induced ligand dissociation proceeds in two major stages (I and II) where each stage is shown to be comprised of multiple components (Ix, where x = 1-3 for L2 and L8, and IIy, where y = 1-3 for L2 and y = 1-4 for L8). A reaction scheme consistent with kinetic and independent ESI-MS data is proposed that includes the tris-chelated complexes (coordinated H2O omitted for clarity) (Fe2(Ln)3, Fe2(L2)2(L2H)2, Fe(LnH)3, Fe(L8)(L8H)), bis-chelated complexes (Fe2(Ln)2(2+), Fe(LnH)2+, Fe(L8)+), and monochelated complexes (Fe(LnH)2+). Analysis of kinetic data for ligand dissociation from Fe2(Ln)(LnH)3+ (n = 2, 4, 6, 8) allows us to estimate the dielectric constant at the reactive dinuclear Fe(III) site. The existence of multiple ligand dissociation paths for the dihydroxamic acid complexes of Fe(III) is a feature that distinguishes these systems from their bidentate monohydroxamic acid and hexadentate trihydroxamic acid counterparts and may be a reason for the biosynthesis of dihydroxamic acid siderophores, despite higher environmental molar concentrations necessary to completely chelate Fe(III).

  1. Mechanism of angiotensin II-induced arachidonic acid metabolite release in aortic smooth muscle cells: involvement of phospholipase D. (United States)

    Shinoda, J; Kozawa, O; Suzuki, A; Watanabe-Tomita, Y; Oiso, Y; Uematsu, T


    In a previous study, we have shown that angiotensin II (Ang II) activates phosphatidylcholine-hydrolyzing phospholipase D due to Ang II-induced Ca2+ influx from extracellular space in subcultured rat aortic smooth muscle cells. In the present study, we have investigated the role of phospholipase D in Ang II-induced arachidonic acid (AA) metabolite release and prostacyclin synthesis in subcultured rat aortic smooth muscle cells. Ang II significantly stimulated AA metabolite release in a concentration-dependent manner in the range between 1 nmol/I and 0.1 mumol/I. D.L.-Propranolol hydrochloride (propranolol), an inhibitor of phosphatidic acid phosphohydrolase, significantly inhibited the Ang II-induced release of AA metabolites. The Ang II-induced AA metabolite release was reduced by chelating extracellular Ca2+ with EGTA. Genistein, an inhibitor of protein tyrosine kinases, significantly suppressed the Ang II-induced AA metabolite release. 1,6-Bis-(cyclohexyloximinocarbonylamino)-hexane (RHC-80267), a potent and selective inhibitor of diacylglycerol lipase, significantly inhibited the Ang II-induced AA metabolite release. Both propranolol and RHC-80267 inhibited the Ang II-induced synthesis of 6-keto-prostaglandin F1 alpha, a stable metabolite of prostacyclin. The synthesis was suppressed by genistein. These results strongly suggest that the AA metabolite release induced by Ang II is mediated, at least in part, through phosphatidylcholine hydrolysis by phospholipase D activation in aortic smooth muscle cells.

  2. Effects of free oxygen radicals on Ca2+ release mechanisms in the sarcoplasmic reticulum of scallop (Pecten jacobaeus) adductor muscle. (United States)

    Burlando, B; Viarengo, A; Pertica, M; Ponzano, E; Orunesu, M


    In vitro oxyradical effects on SR Ca2+ regulation were studied by using a SR-containing cell-free preparation from scallop (Pecten jacobaeus) adductor muscle. Ca2+ variations were fluorimetrically detected after incubation with Fluo-3 in the presence of ATP. Exposure to Fe3+/ascorbate produced dose-dependent Ca2+ release from SR vesicles, eventually leading to massive Ca2+ loss. Exposure to hypoxanthine/xanthine oxidase also caused Ca2+ release but at a much slower rate. Pre-incubations with catalase or with the hydroxyl radical scavenger KMBA led to a significant decrease in the Fe3+/ascorbate-induced Ca2+ release rate and to a delay of massive Ca2+ loss. Pre-incubations with GSH or DTT strongly reduced the Ca2+ release caused by Fe3+/ascorbate and, moreover, they prevented massive Ca2+ loss from SR vesicles. Addition of GSH or DTT after Fe3+/ascorbate promptly reduced the Ca2+ release rate and delayed massive Ca2+ release. Pre-incubation with the SR Ca2+ channel blocker ruthenium red strongly reduced the Ca2+ release caused by Fe3+/ascorbate, and also prevented massive Ca2+ loss. In the presence of ruthenium red, Fe3+/ascorbate treatments followed by Ca2+ addition revealed that Ca2+ uptake inhibition was slower than Ca2+ release. Taken together, data showed that free radicals and, in particular, hydroxyl radicals, affected the scallop SR Ca2+ regulation. This mainly occurred through Ca2+ channel opening, most likely triggered by sulfhydryl oxidation, which eventually led to massive Ca2+ release from SR vesicles. The demonstration of a specific effect of oxyradicals on SR Ca2+ channels is in line with their possible involvement in cell signaling.

  3. Mechanical properties and drug release behavior of PCL/zein coated 45S5 bioactive glass scaffolds for bone tissue engineering application. (United States)

    Fereshteh, Zeinab; Nooeaid, Patcharakamon; Fathi, Mohammadhossein; Bagri, Akbar; Boccaccini, Aldo R


    This article presents data related to the research article entitled "The effect of coating type on mechanical properties and controlled drug release of PCL/zein coated 45S5 bioactive glass scaffolds for bone tissue engineering" [1]. We provide data on mechanical properties, in vitro bioactivity and drug release of bioactive glass (BG) scaffolds coated by poly (ε-caprolactone) (PCL) and zein used as a controlled release device for tetracycline hydrochloride (TCH). By coating the BG scaffolds with PCL or PCL/zein blend the mechanical properties of the scaffolds were substantially improved, i.e., the compressive strength increased from 0.004±0.001 MPa (uncoated BG scaffolds) to 0.15±0.02 MPa (PCL/zein coated BG scaffolds). A dense bone-like apatite layer formed on the surface of PCL/zein coated scaffolds immersed for 14 days in simulated body fluid (SBF). The data describe control of drug release and in vitro degradation behavior of coating by engineering the concentration of zein. Thus, the developed scaffolds exhibit attractive properties for application in bone tissue engineering research.

  4. Mechanical properties and drug release behavior of PCL/zein coated 45S5 bioactive glass scaffolds for bone tissue engineering application

    Directory of Open Access Journals (Sweden)

    Zeinab Fereshteh


    Full Text Available This article presents data related to the research article entitled “The effect of coating type on mechanical properties and controlled drug release of PCL/zein coated 45S5 bioactive glass scaffolds for bone tissue engineering” [1]. We provide data on mechanical properties, in vitro bioactivity and drug release of bioactive glass (BG scaffolds coated by poly (ε-caprolactone (PCL and zein used as a controlled release device for tetracycline hydrochloride (TCH. By coating the BG scaffolds with PCL or PCL/zein blend the mechanical properties of the scaffolds were substantially improved, i.e., the compressive strength increased from 0.004±0.001 MPa (uncoated BG scaffolds to 0.15±0.02 MPa (PCL/zein coated BG scaffolds. A dense bone-like apatite layer formed on the surface of PCL/zein coated scaffolds immersed for 14 days in simulated body fluid (SBF. The data describe control of drug release and in vitro degradation behavior of coating by engineering the concentration of zein. Thus, the developed scaffolds exhibit attractive properties for application in bone tissue engineering research.

  5. The kinetics of the swelling process and the release mechanisms of Coriandrum sativum L. essential oil from chitosan/alginate/inulin microcapsules. (United States)

    Dima, Cristian; Pătraşcu, Livia; Cantaragiu, Alina; Alexe, Petru; Dima, Ştefan


    The encapsulation by spray drying method of coriander essential oil (CEO) in various materials (chitosan, alginate, chitosan/alginate, chitosan/inulin) was studied. The viscoelastic properties of the oil-in-water (O/W) emulsions and the characteristics of CEO-loaded microcapsules like morphology, moisture, wettability, solubility, flowability properties, swelling and release mechanisms were investigated. The chitosan microcapsules had a brain-like structure while the alginate and chitosan/alginate microcapsules are spherical with a smooth surface. The Compressibility Index (CI=29.09-32.25%) and Hausner Ratio (HR=1.38-1.44) values showed that all the microcapsules prepared correspond to the "poor" flowability powders group. The chitosan microcapsules exhibited the maximum release rate at pH 2.5 while the alginate microcapsules exhibited the maximum release rate at pH 6.5. Kinetics and mechanism of CEO release were studied using various mathematical models such as, zero order, first order, Higuchi model and Peppas model. The diffusional exponent (n) values of Peppas equation explains a non Fickian transport mechanism and diffusion or diffusion-swelling controlled process.

  6. Effect of thermal and chemical modifications on the mechanical and release properties of paracetamol tablet formulations containing corn, cassava and sweet potato starches as filler-binders

    Institute of Scientific and Technical Information of China (English)

    Mariam; Vbamiunomhene; Lawal; Michael; Ayodele; Odeniyi; Oludele; Adelanwa; Itiola


    Objective: To investigate the effects of acetylation and pregelatinization of cassava and sweet potato starches on the mechanical and release properties of directly compressed paracetamol tablet formulations in comparison with official corn starch.Methods: The native starches were modified by acetylation and pregelatinization. The tablets were assessed using friability(Fr), crushing strength(Cs), disintegration time(Dt) and dissolution parameters. Results: Starch acetylation produced paracetamol tablets that were stronger and had the best balance of mechanical and disintegration properties, while pregelatinization produced tablets that were more friable but had a better overall strength in relation to disintegration than formulations made from natural starches. Correlations mainly existed between Dt and the dissolution parameters t80, t2 and k1 in the formulations. Conclusions: Modification of the experimental starches improved the mechanical and release properties of directly compressed paracetamol tablet formulations. Thus, they can be developed for use as pharmaceutical excipients in specific formulations.

  7. Effect of thermal and chemical modiifcations on the mechanical and release properties of paracetamol tablet formulations containing corn, cassava and sweet potato starches as ifller-binders

    Institute of Scientific and Technical Information of China (English)

    Mariam Vbamiunomhene Lawal; Michael Ayodele Odeniyi; Oludele Adelanwa Itiola


    Objective:To investigate the effects of acetylation and pregelatinization of cassava and sweet potato starches on the mechanical and release properties of directly compressed paracetamol tablet formulations in comparison with official corn starch. Methods: The native starches were modified by acetylation and pregelatinization. The tablets were assessed using friability (Fr), crushing strength (Cs), disintegration time (Dt) and dissolution parameters. Results: Starch acetylation produced paracetamol tablets that were stronger and had the best balance of mechanical and disintegration properties, while pregelatinization produced tablets that were more friable but had a better overall strength in relation to disintegration than formulations made from natural starches. Correlations mainly existed between Dt and the dissolution parameters t80, t2 and k1 in the formulations. Conclusions:Modification of the experimental starches improved the mechanical and release properties of directly compressed paracetamol tablet formulations. Thus, they can be developed for use as pharmaceutical excipients in specific formulations.

  8. Triggered drug release from dynamic microspheres via a protein conformational change. (United States)

    King, William J; Pytel, Nicholas J; Ng, Kelvin; Murphy, William L


    In this study we formed and characterized dynamic hydrogel microspheres in which a protein conformational change was used to control microsphere volume changes and the release of an encapsulated drug. In particular, a specific biochemical ligand, trifluoperazine, induced calmodulin's nanometer scale conformation change, which translated to a 48.7% microsphere volume decrease. This specific, ligand-induced volume change triggered the release of a model drug, vascular endothelial growth factor (VEGF), at pre-determined times. After release from the microspheres, 85.6 +/- 10.5% of VEGF was in its native conformation. Taken together, these results suggest that protein conformational change could serve as a useful mechanism to control drug release from dynamic hydrogels.

  9. An Order Release Control Mechanism Based on self-Adaptive Neural Fuzzy Inference System and Theory of Constraints

    Directory of Open Access Journals (Sweden)

    Chuandong Zhan


    Full Text Available Order release is the key premise for the semiconductor wafer fabrication system to perform well, which is also one of the paramount significant components in the scheduling strategies. Most order release strategies merely have focused on the workloadbut failed in considering the remarkable influence oncycletime of common orders that is brought by unexpectedrushones.In this paper an on-linemechanismbased on Theory of Constraintsfor lot releaseusingself-Adaptive Neural Fuzzy Inference System modelswas presentedwhich is able to adjust the release rhythmdynamicallyaccording to dynamics of fabs.In our approach, an ANFIS model was established to predict the ratiobetweenhotand common lotsin wafer fabto perform adjustments on the order release schedule in advance.Simulated experimentsbased on the HP24 model were carefully performed and experimental results proved a better performance of common lotsthan original TOC on a large scale, especially when it comes to the situation of disturbance.  

  10. Sleep-wake sensitive mechanisms of adenosine release in the basal forebrain of rodents: an in vitro study.

    Directory of Open Access Journals (Sweden)

    Robert Edward Sims

    Full Text Available Adenosine acting in the basal forebrain is a key mediator of sleep homeostasis. Extracellular adenosine concentrations increase during wakefulness, especially during prolonged wakefulness and lead to increased sleep pressure and subsequent rebound sleep. The release of endogenous adenosine during the sleep-wake cycle has mainly been studied in vivo with microdialysis techniques. The biochemical changes that accompany sleep-wake status may be preserved in vitro. We have therefore used adenosine-sensitive biosensors in slices of the basal forebrain (BFB to study both depolarization-evoked adenosine release and the steady state adenosine tone in rats, mice and hamsters. Adenosine release was evoked by high K(+, AMPA, NMDA and mGlu receptor agonists, but not by other transmitters associated with wakefulness such as orexin, histamine or neurotensin. Evoked and basal adenosine release in the BFB in vitro exhibited three key features: the magnitude of each varied systematically with the diurnal time at which the animal was sacrificed; sleep deprivation prior to sacrifice greatly increased both evoked adenosine release and the basal tone; and the enhancement of evoked adenosine release and basal tone resulting from sleep deprivation was reversed by the inducible nitric oxide synthase (iNOS inhibitor, 1400 W. These data indicate that characteristics of adenosine release recorded in the BFB in vitro reflect those that have been linked in vivo to the homeostatic control of sleep. Our results provide methodologically independent support for a key role for induction of iNOS as a trigger for enhanced adenosine release following sleep deprivation and suggest that this induction may constitute a biochemical memory of this state.

  11. Biochemical Analysis of Pathogenic Ligand-Dependent FGFR2 Mutations Suggests Distinct Pathophysiological Mechanisms for Craniofacial and Limb Abnormalities in Human Skeletal Disorders

    Energy Technology Data Exchange (ETDEWEB)

    Ibrahimi,O.; Zhang, F.; Eliseenkova, A.; Itoh, N.; Linhardt, R.; Mohammadi, M.


    Gain-of-function missense mutations in FGF receptor 2 (FGFR2) are responsible for a variety of craniosynostosis syndromes including Apert syndrome (AS), Pfeiffer syndrome (PS) and Crouzon syndrome (CS). Unlike the majority of FGFR2 mutations, S252W and P253R AS mutations and a D321A PS mutation retain ligand-dependency and are also associated with severe limb pathology. In addition, a recently identified ligand-dependent S252L/A315S double mutation in FGFR2 was shown to cause syndactyly in the absence of craniosynostosis. Here, we analyze the effect of the canonical AS mutations, the D321A PS mutation and the S252L/A315S double mutation on FGFR2 ligand binding affinity and specificity using surface plasmon resonance. Both AS mutations and the D321A PS mutation, but not the S252L/A315S double mutation, increase the binding affinity of FGFR2c to multiple FGFs expressed in the cranial suture. Additionally, all four pathogenic mutations also violate FGFR2c ligand binding specificity and enable this receptor to bind FGF10. Based on our data, we propose that an increase in mutant FGFR2c binding to multiple FGFs results in craniosynostosis, whereas binding of mutant FGFR2c to FGF10 results in severe limb pathology. Structural and biophysical analysis shows that AS mutations in FGFR2b also enhance and violate FGFR2b ligand binding affinity and specificity, respectively. We suggest that elevated AS mutant FGFR2b signaling may account for the dermatological manifestations of AS.


    Directory of Open Access Journals (Sweden)

    S. V. Trofimov


    Full Text Available This article reviews cellulose esters as important excipients in development of dosage forms with sustained release. We have studied modern methods of drug development, based on technological, and physical and chemical properties of excipients to provide a sustained release effect and the mechanism of interaction between active substance and excipients for justification of choice of the optimum prolonging agent in compliance with desirable result. Different cellulose esters were used as model excipients. They were hydroxypropylmethylcellulose (HPMC and hydroxyethylcellulose (HEC. we have studied an effect of molecular weight and hydrophilic properties on dissolution rate of active substance from the tablets with sustained release.

  13. The effect of poly(lactic-co-glycolic acid) (PLGA) coating on the mechanical, biodegradable, bioactive properties and drug release of porous calcium silicate scaffolds. (United States)

    Zhao, Lang; Wu, Chengtie; Lin, Kaili; Chang, Jiang


    Ideal scaffolds for bone tissue engineering require 3D interconnected porous structures, enough mechanical strength for hand of treatment as well as proper bioactivity and biodegradability. Calcium silicate (CaSiO3, CS) scaffolds have been studied for bone tissue engineering application due to their excellent bioactivity. However, the main disadvantages of CS scaffolds are their low mechanical strength and high alkaline ionic products. In this study, sintered CS scaffolds were prepared and coated with poly(lactic-co-glycolic acid) (PLGA), and the effect of PLGA coating on the mechanical, biodegradable, bioactive properties and drug release of porous CS scaffolds were investigated. The results showed that the PLGA-coated CS scaffolds maintained large pore size and high porosity. The compressive strength of PLGA/CS scaffolds was significantly improved compared to pure CS scaffolds, and increased with the increase of intrinsic viscosity and concentration of PLGA. In addition, the PLGA coating neutralized alkaline level resulted from the ionic products of CS scaffolds and reduced the pH value of biological solution during the degradation of scaffolds. It was found that PLGA/CS scaffolds still maintained excellent apatite-mineralization ability in SBF. Furthermore, the PLGA coating effectively inhibited the burst release and maintained a sustained release of drugs from the CS scaffolds. Our results indicate that the PLGA/CS scaffolds have great potential for bone tissue engineering application by the virtue of improved mechanical strength, and excellent bioactivity, degradation as well as drug-delivery property.

  14. In vitro drug release behavior, mechanism and antimicrobial activity of rifampicin loaded low molecular weight PLGA-PEG-PLGA triblock copolymeric nanospheres. (United States)

    Gajendiran, M; Divakar, S; Raaman, N; Balasubramanian, S


    Poly (lactic-co-glycolic acid) (PLGA (92:8)) and a series of PLGA-PEG-PLGA tri block copolymers were synthesized by direct melt polycondensation. The copolymers were characterized by FTIR, and 1HNMR spectroscopic techniques, viscosity, gel permeation chromatography (GPC) and powder x-ray diffraction (XRD). The rifampicin (RIF) loaded polymeric nanospheres (NPs) were prepared by ultrasonication-W/O emulsification technique. The NPs have been characterized by field emission scanning electron microscopy (FESEM), TEM, powder X-ray diffraction (XRD), UVvisible spectroscopy and DLS measurements. The drug loaded triblock copolymeric NPs have five folds higher drug content and drug loading efficiency than that of PLGA microspheres (MPs). The in vitro drug release study shows that the drug loaded NPs showed an initial burst release after that sustained release up to 72 h. All the triblock copolymeric NPs follow anomalous drug diffusion mechanism while the PLGA MPs follow non-Fickian super case-II mechanism up to 12 h. The overall in-vitro release follows second order polynomial kinetics up to 72 h. The antimicrobial activity of the RIF loaded polymer NPs was compared with that of pure RIF and tetracycline (TA). The RIF loaded triblock copolymeric NPs inhibited the bacterial growth more effectively than the pure RIF and TA.

  15. Effect of ligand self-assembly on nanostructure and carrier transport behaviour in CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Li, Kuiying, E-mail:; Xue, Zhenjie


    Adjustment of the nanostructure and carrier behaviour of CdSe quantum dots (QDs) by varying the ligands used during QD synthesis enables the design of specific quantum devices via a self-assembly process of the QD core–shell structure without additional technologies. Surface photovoltaic (SPV) technology supplemented by X-ray diffractometry and infrared absorption spectroscopy were used to probe the characteristics of these QDs. Our study reveals that while CdSe QDs synthesized in the presence of and capped by thioglycolic acid, 3-mercaptopropionic acid, mercaptoethanol or α-thioglycerol ligands display zinc blende nanocrystalline structures, CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures, because different end groups in these ligands induce distinctive nucleation and growth mechanisms. Carboxyl end groups in the ligand served to increase the SPV response of the QDs, when illuminated by hν ≥ E{sub g,nano-CdSe}. Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit photo-generated free charge carrier (FCC) transfer transitions of CdSe QDs illuminated by photon energy of 4.13 to 2.14 eV. The terminal hydroxyl group might better accommodate energy released in the non-radiative de-excitation process of photo-generated FCCs in the ligand's lowest unoccupied molecular orbital in the 300–580 nm wavelength region, when compared with other ligand end groups. - Highlights: • CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures. • Carboxyl end groups in the ligand serve to increase the SPV response of CdSe QDs. • Terminal hydroxyl group in the ligand might accommodate non-radiative de-excitation process in CdSe QDs. • Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit carriers transport of CdSe QDs.

  16. Synthesis and Characterisation of Copper(II Complexes with Tridentate NNO Functionalized Ligand: Density Function Theory Study, DNA Binding Mechanism, Optical Properties, and Biological Application

    Directory of Open Access Journals (Sweden)

    Madhumita Hazra


    Full Text Available The photo physical properties of two mononuclear pentacoordinated copper(II complexes formulated as [Cu(L(Cl(H2O] (1 and [Cu(L(Br(H2O] (2 HL = (1-[(3-methyl-pyridine-2-ylimino-methyl]-naphthalen-2-ol were synthesized and characterized by elemental, physicochemical, and spectroscopic methods. The density function theory calculations are used to investigate the electronic structures and the electronic properties of ligand and complex. The interactions of copper(II complexes towards calf thymus DNA were examined with the help of absorption, viscosity, and fluorescence spectroscopic techniques at pH 7.40. All spectroscopy's result indicates that complexes show good binding activity to calf thymus DNA through groove binding. The optical absorption and fluorescence emission properties of microwires were characterized by fluorescence microscope. From a spectroscopic viewpoint, all compounds strongly emit green light in the solid state. The microscopy investigation suggested that microwires exhibited optical waveguide behaviour which are applicable as fluorescent nanomaterials and can be used as building blocks for miniaturized photonic devices. Antibacterial study reveals that complexes are better antimicrobial agents than free Schiff base due to bacterial cell penetration by chelation. Moreover, the antioxidant study of the ligand and complexes is evaluated by using 1,1-diphenyl-2-picrylhydrazyl (DPPH free-radical assays, which demonstrate that the complexes are of higher antioxidant activity than free ligand.

  17. Mechanical properties and in vitro evaluation of bioactivity and degradation of dexamethasone-releasing poly-D-L-lactide/nano-hydroxyapatite composite scaffolds. (United States)

    Chen, Ling; Tang, Chak Yin; Tsui, Chi Pong; Chen, Da Zhu


    The purpose of this study was to fabricate drug-release nano-composite scaffolds and perform in vitro evaluation of their mechanical properties, bioactivity, biodegradability and drug release behaviors. Porous drug-release poly-d-l-lactide (PDLLA) composite scaffolds filled with different amounts of nano-hydroxyapatite (nano-HAp) were prepared by a technique combining polymer coagulation, cold compression moulding, salt leaching and drug coating. Apatite detected on the scaffolds after exposure to a simulated body fluid showed improvement in bioactivity and the apatite formation ability through the addition of the nano-HAp content in the composites. Nano-HAp incorporation and apatite formation made a positive impact on the mechanical properties of the scaffolds; however, plasticization and degradation of PDLLA had a negative impact. The pH-compensation effect of the composite scaffolds can reduce the risk of chronic inflammation complications. The fabrication method in this study can produce scaffolds with controllable structure, appropriate mechanical properties and degradation rates for cancellous bone repair applications.

  18. X-ray structure of Triatoma virus empty capsid: insights into the mechanism of uncoating and RNA release in dicistroviruses. (United States)

    Sánchez-Eugenia, Rubén; Durana, Aritz; López-Marijuan, Ibai; Marti, Gerardo A; Guérin, Diego M A


    In viruses, uncoating and RNA release are two key steps of successfully infecting a target cell. During these steps, the capsid must undergo the necessary conformational changes to allow RNA egress. Despite their importance, these processes are poorly understood in the family Dicistroviridae. Here, we used X-ray crystallography to solve the atomic structure of a Triatoma virus(TrV) empty particle (Protein Data Bank ID 5L7O), which is the resulting capsid after RNA release. It is observed that the overall shape of the capsid and of the three individual proteins is maintained in comparison with the mature virion. Furthermore, no channels indicative of RNA release are formed in the TrV empty particle. However, the most prominent change in the empty particle when compared with the mature virion is the loss of order in the N-terminal domain of the VP2 protein. In mature virions, the VP2 N-terminal domain of one pentamer is swapped with its twofold related copy in an adjacent pentamer, thereby stabilizing the binding between the pentamers. The loss of these interactions allows us to propose that RNA release may take place through transient flipping-out of pentameric subunits. The lower number of stabilizing interactions between the pentamers and the lack of formation of new holes support this model. This model differs from the currently accepted model for rhinoviruses and enteroviruses, in which genome externalization occurs by extrusion of the RNA through capsid channels.

  19. Mechanisms of Dopamine Release From Rat Striatum and Nucleus Accumbens Slices:The Role of Transporters, Receptors and Membrane Depolarization (United States)


    The release of 5-HT is controlled by autoreceptors of the 5-HT’a and 5- HT’b type , inhibitory heteroreceptors of the GABAB, muscarinic, Ŗ , and D...type , and stimulatory heteroreceptors for somatostatin. Regulation is also afforded by receptors that are acted upon by co-localized

  20. Polyplex Formation Influences Release Mechanism of Mono- and Di-Valent Ions from Phosphorylcholine Group Bearing Hydrogels

    Directory of Open Access Journals (Sweden)

    A. Nolan Wilson


    Full Text Available The release of monovalent potassium and divalent calcium ions from zwitterionic phosphorylcholine containing poly(2-hydroxyethyl methacrylate (pHEMA-based hydrogels was studied and the effects of polymer swelling, ion valence and temperature were investigated. For comparison, ions were loaded during hydrogel formulation or loaded by partitioning following construct synthesis. Using the Koshmeyer-Peppas release model, the apparent diffusion coefficient, Dapp, and diffusional exponents, n, were Dapp (pre-K+ = 2.03 × 10−5, n = 0.4 and Dapp (post-K+ = 1.86 × 10−5, n = 0.33 respectively, indicative of Fickian transport. The Dapp (pre-Ca2+ = 3.90 × 10−6, n = 0.60 and Dapp (post-Ca2+ = 2.85 × 10−6, n = 0.85, respectively, indicative of case II and anomalous transport. Results indicate that divalent cations form cation-polyelectrolyte anion polymer complexes while monovalent ions do not. Temperature dependence of potassium ion release was shown to follow an Arrhenius-type relation with negative apparent activation energy of −19 ± 15 while calcium ion release was temperature independent over the physiologically relevant range (25–45 °C studied. The negative apparent activation energy may be due to temperature dependent polymer swelling. No effect of polymer swelling on the diffusional exponent or rate constant was found suggesting polymer relaxation occurs independent of polymer swelling.

  1. Common Mechanisms Underlying the Proconflict Effects of Corticotropin-Releasing Factor, A Benzodiazepine Inverse Agonist and Electric Foot-Shock

    NARCIS (Netherlands)

    Boer, Sietse F. de; Katz, Jonathan L.; Valentino, Rita J.


    The effects of corticotropin-releasing factor (CRF), a benzodiazepine inverse agonist (methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate; DMCM) and electric foot-shock on rat conflict behavior were characterized and compared. Rats were trained to lever press under a multiple fixed-ratio schedul

  2. Inhibition of ACh release at an Aplysia synapse by neurotoxic phospholipases A2: specific receptors and mechanisms of action. (United States)

    Fossier, P; Lambeau, G; Lazdunski, M; Baux, G


    1. Monochain (OS2) and multichain (taipoxin) neurotoxic phospholipases A2 (PLA2), purified from taipan snake venom, both inhibited ACh release at a concentration of 20 nM (90% inhibition in 2 h) at an identified synapse from buccal ganglion of Aplysia californica. 2. The Na+ current was unchanged upon application of either OS2 or taipoxin. Conversely, presynaptic K+ currents (IA and IK) were increased by taipoxin but not by OS2. In addition, OS2 induced a significant decrease of the presynaptic Ca2+ current (30%) while taipoxin increased this latter current by 20-30%. 3. Bee venom PLA2, another monochain neurotoxic PLA2, also inhibited ACh release while non-toxic enzymatically active PLA2s like OS1 (also purified from taipan snake venom) or porcine pancreatic PLA2 elicited a much weaker inhibition of ACh release, suggesting a specific action of neurotoxic PLA2s versus non-toxic PLA2s on ACh release. 4. Using iodinated OS2, specific high affinity binding sites with molecular masses of 140 and 18 kDa have been identified on Aplysia ganglia. The maximal binding capacities were 55 and 300-400 fmol (mg protein)-1 for membrane preparations from whole and buccal ganglia, respectively. These binding sites are of high affinity for neurotoxic PLA2s (Kd values, 100-800 pM) and of very low affinity for non-toxic PLA2s (Kd values in the micromolar range), thus indicating that these binding sites are presumably involved in the blockade of ACh release by neurotoxic PLA2s. Images Figure 8 Figure 9 PMID:8583413

  3. 平面正方形配合物取代反应的机理和反位效应%Ligand substitution reaction mechanism and trans-effect of square-planar complexes

    Institute of Scientific and Technical Information of China (English)

    于兆文; 张武; 滕洪梅


      平面正方形配合物反位效应的起因已经困惑了人们将近一个世纪。作者根据平面正方形配合物取代反应的缔合机理,考虑了配体取代反应进行过程中配体间的排斥作用,分析了最易形成的中间体和过渡态2的空间构型;揭示了反位效应的起因,提出了一种配体排斥理论,从而比较系统和圆满地解释了平面正方形配合物取代反应的反位效应。%The cause of trans-effect for square planar complexes has puzzled people for nearly a century .Based on the fact that the ligand substitution reactions of square-planar complexes re-act by a SN2 mechanism ,the most preferable configurations for the intermediate and transition state 2 were deduced while the repulsions between the ligands in the reaction pathway were considered .Furthermore ,the causes of trans-effect were revealed ,and a new theory---ligand repulsion theory was proposed to illustrate the trans-effect . It was found that as-proposed theory can be well adopted to independently and systematically explain the trans-effect for all kinds of monodentate ligands .

  4. Soluble CD40 ligand in acute coronary syndromes

    NARCIS (Netherlands)

    C. Heeschen (Christopher); S. Dimmeler (Stefanie); C.W. Hamm (Christian); A.M. Zeiher (Andreas); M.L. Simoons (Maarten); M.J.B.M. van den Brand (Marcel); H. Boersma (Eric)


    textabstractBACKGROUND: CD40 ligand is expressed on platelets and released from them on activation. We investigated the predictive value of soluble CD40 ligand as a marker for clinical outcome and the therapeutic effect of glycoprotein IIb/IIIa receptor inhibition in patients with acute coronary syn

  5. Physicochemical properties and mechanism of drug release from ethyl cellulose matrix tablets prepared by direct compression and hot-melt extrusion. (United States)

    Crowley, Michael M; Schroeder, Britta; Fredersdorf, Anke; Obara, Sakae; Talarico, Mark; Kucera, Shawn; McGinity, James W


    The objective of this research project was to determine the physicochemical properties and investigate the drug release mechanism from ethyl cellulose (EC) matrix tablets prepared by either direct compression or hot-melt extrusion (HME) of binary mixtures of water soluble drug (guaifenesin) and the polymer. Ethyl cellulose was separated into "fine" or "coarse" particle size fractions corresponding to 325-80 and 80-30 mesh particles, respectively. Tablets containing 30% guaifenesin were prepared at 10, 30, or 50 kN compaction forces and extruded at processing temperatures of 80-90 and 90-110 degrees C. The drug dissolution and release kinetics were determined and the tablet pore characteristics, tortuosity, thermal properties and surface morphologies were studied using helium pycnometry, mercury porosimetry, differential scanning calorimetry and scanning electron microscopy. The tortuosity was measured directly by a novel technique that allows for the calculation of diffusion coefficients in three experiments. The Higuchi diffusion model, Percolation Theory and Polymer Free Volume Theory were applied to the dissolution data to explain the release properties of drug from the matrix systems. The release rate was shown to be dependent on the ethyl cellulose particle size, compaction force and extrusion temperature.

  6. Quantification of Locusta diuretic hormone in the central nervous system and corpora cardiaca: influence of age and feeding status, and mechanism of release. (United States)

    Audsley, N; Goldsworthy, G J; Coast, G M


    Locusta-DH is known to have a hormonal function in the control of post-feeding diuresis in the migratory locust. This study has quantified Locusta-DH in tissues from V(th) instar nymphs and adults, and investigated the K+-induced release of the peptide from corpora cardiaca. Locusta-DH is present in thoracic and abdominal ganglia, but the amounts are small (25-200 fmol) compared with brain (approximately 1 pmol) and corpora cardiaca ( > 5 pmol) from 14-day old locusts. About 50% of the immunoreactive material in corpora cardiaca coelutes with Locusta-DH on reversed-phase HPLC. An earlier eluting fraction is also biologically active, suggesting locusts have a second, previously undetected, CRF-related peptide. The amount of peptide stored in corpora cardiaca varies with age and physiological status. Reductions on day 1 of the adult instar and immediately after feeding suggest Locusta-DH controls post-eclosion as well as post-feeding diureses. Locusta-DH is released by a Ca2+-dependent mechanism from corpora cardiaca held in salines containing > or =40 mM K+. This is blocked by verapamil, implicating L-type Ca2+ channels. Release is most rapid shortly after transfer to a high K+ saline, and more peptide is released from glands allowed to recover in normal saline between successive K+ depolarisations.

  7. Microcystin release and Microcystis cell damage mechanism by alum treatment with long-term and large dose as in-lake treatment. (United States)

    Han, Jisun; Jeon, Bong-Seok; Park, Ho-Dong


    Most of our previous studies reported aluminum causes no cell damage or lysis, and no subsequent toxin release in conventional treatment of drinking water or in the laboratory, on the contrary, we investigated the effect of long-term and large-dose alum treatment, because the environmental conditions in lakes and treatment plants are widely different. The microcosm experiments were designed to simulate the effect of adding alum under the similar conditions of common lakes and reservoirs, and the bottle experiments were conducted to examine the budget or dynamics of microcystin after adding alum. In precipitate analyses, we also confirm the release and dynamics of microcystin and the damage mechanisms of Microcystis cells under alum treatment. In microcosms treated with alum alone, the extracellular microcystin-LR (MC-LR) concentration increased to approximately 82% in 7 days. Similar results were obtained in bottle experiments. By plotting the concentration of released microcystin over time, we inferred that the extracellular MC-LR concentration exponentially rose toward an asymptotic maximum. Moreover, in scanning electron microscope images, some cells exhibited torn membranes with miniscule traces of aluminum hydroxide coating. We conclude that alum treatment, particularly at maximum dosage administered over long periods, seriously damages Microcystis cells and induces microcystin release. Therefore, long-term application of large alum doses is not recommended as an in-lake treatment.

  8. Melatonin: functions and ligands. (United States)

    Singh, Mahaveer; Jadhav, Hemant R


    Melatonin is a chronobiotic substance that acts as synchronizer by stabilizing bodily rhythms. Its synthesis occurs in various locations throughout the body, including the pineal gland, skin, lymphocytes and gastrointestinal tract (GIT). Its synthesis and secretion is controlled by light and dark conditions, whereby light decreases and darkness increases its production. Thus, melatonin is also known as the 'hormone of darkness'. Melatonin and analogs that bind to the melatonin receptors are important because of their role in the management of depression, insomnia, epilepsy, Alzheimer's disease (AD), diabetes, obesity, alopecia, migraine, cancer, and immune and cardiac disorders. In this review, we discuss the mechanism of action of melatonin in these disorders, which could aid in the design of novel melatonin receptor ligands.

  9. Crystal Structure of Epiphyas Postvittana Takeout 1 With Bound Ubiquinone Supports a Role As Ligand Carriers for Takeout Proteins in Insects

    Energy Technology Data Exchange (ETDEWEB)

    Hamiaux, C.; Stanley, D.; Greenwood, D.R.; Baker, E.N.; Newcomb, R.D.


    Takeout (To) proteins are found exclusively in insects and have been proposed to have important roles in various aspects of their physiology and behavior. Limited sequence similarity with juvenile hormone-binding proteins (JHBPs), which specifically bind and transport juvenile hormones in Lepidoptera, suggested a role for To proteins in binding hydrophobic ligands. We present the first crystal structure of a To protein, EpTo1 from the light brown apple moth Epiphyas postvittana, solved in-house by the single-wavelength anomalous diffraction technique using sulfur anomalous dispersion, and refined to 1.3 {angstrom} resolution. EpTo1 adopts the unusual {alpha}/{beta}-wrap fold, seen only for JHBP and several mammalian lipid carrier proteins, a scaffold tailored for the binding and/or transport of hydrophobic ligands. EpTo1 has a 45 {angstrom} long, purely hydrophobic, internal tunnel that extends for the full length of the protein and accommodates a bound ligand. The latter was shown by mass spectrometry to be ubiquinone-8 and is probably derived from Escherichia coli. The structure provides the first direct experimental evidence that To proteins are ligand carriers; gives insights into the nature of endogenous ligand(s) of EpTo1; shows, by comparison with JHBP, a basis for different ligand specificities; and suggests a mechanism for the binding/release of ligands.

  10. A novel experimental design method to optimize hydrophilic matrix formulations with drug release profiles and mechanical properties. (United States)

    Choi, Du Hyung; Lim, Jun Yeul; Shin, Sangmun; Choi, Won Jun; Jeong, Seong Hoon; Lee, Sangkil


    To investigate the effects of hydrophilic polymers on the matrix system, an experimental design method was developed to integrate response surface methodology and the time series modeling. Moreover, the relationships among polymers on the matrix system were studied with the evaluation of physical properties including water uptake, mass loss, diffusion, and gelling index. A mixture simplex lattice design was proposed while considering eight input control factors: Polyethylene glycol 6000 (x1 ), polyethylene oxide (PEO) N-10 (x2 ), PEO 301 (x3 ), PEO coagulant (x4 ), PEO 303 (x5 ), hydroxypropyl methylcellulose (HPMC) 100SR (x6 ), HPMC 4000SR (x7 ), and HPMC 10(5) SR (x8 ). With the modeling, optimal formulations were obtained depending on the four types of targets. The optimal formulations showed the four significant factors (x1 , x2 , x3 , and x8 ) and other four input factors (x4 , x5 , x6 , and x7 ) were not significant based on drug release profiles. Moreover, the optimization results were analyzed with estimated values, targets values, absolute biases, and relative biases based on observed times for the drug release rates with four different targets. The result showed that optimal solutions and target values had consistent patterns with small biases. On the basis of the physical properties of the optimal solutions, the type and ratio of the hydrophilic polymer and the relationships between polymers significantly influenced the physical properties of the system and drug release. This experimental design method is very useful in formulating a matrix system with optimal drug release. Moreover, it can distinctly confirm the relationships between excipients and the effects on the system with extensive and intensive evaluations.

  11. Mechanisms involved in ketone body release by rat liver cells: influence of pH and bicarbonate

    Energy Technology Data Exchange (ETDEWEB)

    Fafournoux, P.; Demigne, C.; Remesy, C.


    The aim of the present work is to study the intra- and extracellular concentration gradient of ketone bodies across the hepatic cell membrane, ketone bodies released by liver cells, and the effects of changes in acid-base status on these processes. Ketone bodies appeared to be released by liver cells against a concentration gradient both in vivo and in vitro. In vitro, a decrease in external pH and bicarbonate gradient measured with ( UC)- and (TH)-labelled compounds, and efflux rates. Analysis of the distribution ratio of ketone bodies as a function of pH across the cell membrane indicates that additional factors must be invoked to account for the observed distribution ratios. These data along with measurement of ketone body efflux are consistent with the existence of a system promoting the efflux of ketone bodies from liver cells, which is trans-stimulated by external bicarbonate. In vivo, ketogenesis was also inhibited by acidosis, and slightly enhanced by bicarbonate infusion, although this was not solely due to effects on transfer across the cell membrane. The study indicates that the hepatic release of ketone bodies might be auto-limited by ketoacidosis.

  12. Acute pancreatitis-induced enzyme release and necrosis are attenuated by IL-1 antagonism through an indirect mechanism. (United States)

    Fink, G; Yang, J; Carter, G; Norman, J


    Interleukin-1 beta (IL-1) is a proinflammatory cytokine which is produced within the pancreas during acute pancreatitis reaching levels which are toxic to many cell types. Since antagonism of this cytokine provides dramatic survival benefits during lethal pancreatitis, we hypothesized that IL-1 had direct secretagogue and cytolytic effects within the pancreas. The effect of IL-1 on pancreatic exocrine function and tissue viability was assessed in vivo by blockade of IL-1 with varying doses of IL-1 receptor antagonist (IL-1ra) prior to the induction of either moderate (caerulein-induced) or severe (choline deficient diet-induced) necrotizing pancreatitis. Subsequent in vitro studies were conducted to determine the direct effect of IL-1 on dispersed rat acini prepared through collagenase digestion. Amylase release was measured after a 30-min incubation with varying doses of recombinant IL-1 beta. Viability was determined in the presence of IL-1 via trypan blue exclusion at multiple time points. Blockade of the IL-1 receptor decreased pancreatic amylase release and tissue necrosis in both models of pancreatitis in a dose-dependent fashion (1.0 mg/kg, P = NS; 10 mg/kg, P amylase release and tissue necrosis are significantly attenuated during experimental pancreatitis by IL-1 antagonism. These changes do not appear to be due to the direct action of IL-1 on pancreatic acini and are likely due to more complex interactions between acini and cytokine-producing leukocytes.

  13. Understanding the Selectivity Mechanism of the Human Asialoglycoprotein Receptor (ASGP-R toward Gal- and Man- type Ligands for Predicting Interactions with Exogenous Sugars

    Directory of Open Access Journals (Sweden)

    Emo Chiellini


    Full Text Available A practical approach for addressing the computer simulation of protein-carbohydrate interactions is described here. An articulated computational protocol was setup and validated by checking its ability to predict experimental data, available in theliterature, and concerning the selectivity shown by the Carbohydrate Recognition Domain(CRD of the human asialoglycoprotein receptor (ASGP-R toward Gal-type ligands. Somerequired features responsible for the interactions were identified. Subsequently the sameprotocol was applied to monomer sugar molecules that constitute the building blocks foralginates and ulvans. Such sugar polymers may supply a low-cost source of rare sugars witha potential impact on several industrial applications, from pharmaceutical to fine chemicalindustry. An example of their applicative exploitation could be given by their use indeveloping biomaterial with adhesion properties toward hepatocytes, through interactionwith the ASGP-R. Such a receptor has been already proposed as a target for exogenousmolecules, specifically in the case of hepatocytes, for diagnostic and therapeutic purposes.The DOCK5.2 program was used to search optimal locations of the above ligands of interestinto CRD binding site and to roughly estimate interaction energies. Finally, the binding ∆G oftheoretical protein-ligand complexes was estimated by using the DelPhi program in which thesolvation free energy is accounted for with a continuum solvent model, by solving the Poisson-Boltzmann equation. The structure analysis of the obtained complexes and their ∆G values suggest that one of the sugar monomers of interest shows the desired characteristics.

  14. Release of infectious cells from epidermal ulcers in Ichthyophonus sp.–infected Pacific Herring (Clupea pallasii): Evidence for multiple mechanisms of transmission (United States)

    Hershberger, Paul K.; Gregg, Jacob L.; Kocan, R.M.


    A common clinical sign of ichthyophoniasis in herring and trout is “sandpaper” skin, a roughening of the epidermis characterized by the appearance of small papules, followed by ulceration and sloughing of the epithelium; early investigators hypothesized that these ulcers might be a means of transmitting the parasite, Ichthyophonus sp., without the necessity of ingesting an infected host. We examined the cells associated with the epidermal lesions and confirmed that they were viable Ichthyophonus sp. cells that were readily released from the skin into the mucous layer and ultimately into the aquatic environment. The released cells were infectious when injected into the body cavity of specific-pathogen-free herring. Our hypothesis is that different mechanisms of transmission occur in carnivorous and planktivorous hosts: Planktonic feeders become infected by ingestion of ulcer-derived cells, while carnivores become infected by ingestion of whole infected fish.

  15. Optimization of biodegradable sponges as controlled release drug matrices. I. Effect of moisture level on chitosan sponge mechanical properties. (United States)

    Foda, Nagwa H; El-laithy, Hanan M; Tadros, Mina I


    Cross-linked chitosan sponges as controlled release drug carrier systems were developed. Tramadol hydrochloride, a centrally acting analgesic, was used as a model drug. The sponges were prepared by freeze-drying 1.25% and 2.5% (w/w) high and low M.wt. chitosan solutions, respectively, using glutaraldehyde as a cross-linking agent. The hardness of the prepared sponges was a function of glutaraldehyde concentration and volume where the optimum concentration that offered accepted sponge consistency was 5%. Below or above 5%, very soft or very hard and brittle sponges were obtained, respectively. The determined drug content in the prepared sponges was uniform and did not deviate markedly from the calculated amount. Scanning electron microscopy (SEM) was used to characterize the internal structures of the sponges. The SEM photos revealed that cross-linked high M.wt. chitosan sponges have larger size surface pores that form connections (channels) with the interior of the sponge than cross-linked low M.wt. ones. Moreover, crystals of the incorporated Tramadol hydrochloride were detected on the lamellae and within pores in both chitosan sponges. Differences in pore size and dissolution medium uptake capacity were crucial factors for the more delayed drug release from cross-linked low M.wt. chitosan sponges over high M.wt. ones at pH 7.4. Kinetic analysis of the release data using linear regression followed the Higuchi diffusion model over 12 hours. Setting storage conditions at room temperature under 80-92% relative humidity resulted in soft, elastic, and compressible sponges.

  16. Secreted phospholipase A(2) as a new enzymatic trigger mechanism for localised liposomal drug release and absorption in diseased tissue

    DEFF Research Database (Denmark)

    Davidsen, Jesper; Jørgensen, K.; Andresen, Thomas Lars;


    destabilization and drug release at the same time as the permeability of the target membrane is enhanced. Moreover, the proposed system can be made thermosensitive and offers a rational way for developing smart liposome-based drug delivery systems. This can be achieved by incorporating specific lipid......Polymer-coated liposomes can act as versatile drug-delivery systems due to long vascular circulation time and passive targeting by leaky blood vessels in diseased tissue. We present an experimental model system illustrating a new principle for improved and programmable drug-delivery, which takes...

  17. Mechanical properties, biological activity and protein controlled release by poly(vinyl alcohol)–bioglass/chitosan–collagen composite scaffolds: A bone tissue engineering applications

    Energy Technology Data Exchange (ETDEWEB)

    Pon-On, Weeraphat, E-mail: [Department of Physics, Faculty of Science, Kasetsart University, Bangkok 10900 (Thailand); Charoenphandhu, Narattaphol; Teerapornpuntakit, Jarinthorn; Thongbunchoo, Jirawan; Krishnamra, Nateetip [Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University (Thailand); Department of Physiology, Faculty of Science, Mahidol University (Thailand); Tang, I-Ming [ThEP Center, Commission of Higher Education, 328 Si Ayutthaya Rd. (Thailand); Department of Materials Science, Faculty of Science, Kasetsart University, Bangkok 10900 (Thailand)


    In the present study, composite scaffolds made with different weight ratios (0.5:1, 1:1 and 2:1) of bioactive glass (15Ca:80Si:5P) (BG)/polyvinyl alcohol (PVA) (PVABG) and chitosan (Chi)/collagen (Col) (ChiCol) were prepared by three mechanical freeze–thaw followed by freeze-drying to obtain the porous scaffolds. The mechanical properties and the in vitro biocompatibility of the composite scaffolds to simulated body fluid (SBF) and to rat osteoblast-like UMR-106 cells were investigated. The results from the studies indicated that the porosity and compressive strength were controlled by the weight ratio of PVABG:ChiCol. The highest compressive modulus of the composites made was 214.64 MPa which was for the 1:1 weight ratio PVABG:ChiCol. Mineralization study in SBF showed the formation of apatite crystals on the PVABG:ChiCol surface after 7 days of incubation. In vitro cell availability and proliferation tests confirmed the osteoblast attachment and growth on the PVABG:ChiCol surface. MTT and ALP tests on the 1:1 weight ratio PVABG:ChiCol composite indicated that the UMR-106 cells were viable. Alkaline phosphatase activity was found to increase with increasing culturing time. In addition, we showed the potential of PVABG:ChiCol drug delivery through PBS solution studies. 81.14% of BSA loading had been achieved and controlled release for over four weeks was observed. Our results indicated that the PVABG:ChiCol composites, especially the 1:1 weight ratio composite exhibited significantly improved mechanical, mineral deposition, biological properties and controlled release. This made them potential candidates for bone tissue engineering applications. - Graphical abstract: Mechanical properties, biological activity and protein controlled release by poly(vinyl alcohol)–bioglass/chitosan–collagen composite scaffolds: A bone tissue engineering applications. - Highlights: • Preparation of PVABG:ChiCol hybrid composites and their bioactivities • Mechanical

  18. Study of the inhibition by polymorphonuclear leukocytes of TNF-α release from human mononuclear cells and its mechanism

    Institute of Scientific and Technical Information of China (English)


    @@ The present study was undertaken to investigate the effect of human PMNs on the production of TNF-α by the human peripheral blood mononuclear cells (PBMCs) and to elucidate its tentative mechanism.

  19. Antidepressant-like effects of the cannabinoid receptor ligands in the forced swimming test in mice: mechanism of action and possible interactions with cholinergic system. (United States)

    Kruk-Slomka, Marta; Michalak, Agnieszka; Biala, Grazyna


    The purpose of the experiments was to explore the role of the endocannabinoid system, through cannabinoid (CB) receptor ligands, nicotine and scopolamine, in the depression-related responses using the forced swimming test (FST) in mice. Our results revealed that acute injection of oleamide (10 and 20 mg/kg), a CB1 receptor agonist, caused antidepressant-like effect in the FST, while AM 251 (0.25-3 mg/kg), a CB1 receptor antagonist, did not provoke any effect in this test. Moreover, acute administration of both CB2 receptor agonist, JWH 133 (0.5 and 1 mg/kg) and CB2 receptor antagonist, AM 630 (0.5 mg/kg), exhibited antidepressant action. Antidepressant effects of oleamide and JWH 133 were attenuated by acute injection of both non-effective dose of AM 251, as well as AM 630. Among the all CB compounds used, only the combination of non-effective dose of oleamide (2.5 mg/kg) with non-effective dose of nicotine (0.5 mg/kg) caused an antidepressant effect. However, none of the CB receptor ligands, had influence on the antidepressant effects provoked by nicotine (0.2 mg/kg) injection. In turn, the combination of non-effective dose of oleamide (2.5 mg/kg); JWH (2 mg/kg) or AM 630 (2 mg/kg), but not of AM 251 (0.25 mg/kg), with non-effective dose of scopolamine (0.1 mg/kg), exhibited antidepressant properties. Indeed, all of the CB compounds used, intensified the antidepressant-like effects induced by an acute injection of scopolamine (0.3 mg/kg). Our results provide clear evidence that the endocannabinoid system participates in the depression-related behavior and through interactions with cholinergic system modulate these kind of responses.

  20. Structure of eEF3 and the mechanism of transfer RNA release from the E-site

    DEFF Research Database (Denmark)

    Andersen, Christian Brix Folsted; Becker, T.; Blau, M.


    Elongation factor eEF3 is an ATPase, which, in addition to the two canonical factors eEF1A and eEF2, serves an essential function in the translation cycle of fungi. eEF3 is required for the binding of the aatRNA-eEF1A-GTP ternary complex to the ribosomal A-site and has been suggested to facilitate......-bound form of eEF3 in complex with the post-translocational state 80S ribosome from yeast. eEF3 uses an entirely new factor binding site near the ribosomal E-site, with the chromodomain stabilizing the ribosomal L1 stalk in an open conformation, thus, allowing tRNA release....

  1. Temperature and magnetism bi-responsive molecularly imprinted polymers: Preparation, adsorption mechanism and properties as drug delivery system for sustained release of 5-fluorouracil. (United States)

    Li, Longfei; Chen, Lin; Zhang, Huan; Yang, Yongzhen; Liu, Xuguang; Chen, Yongkang


    Temperature and magnetism bi-responsive molecularly imprinted polymers (TMMIPs) based on Fe3O4-encapsulating carbon nanospheres were prepared by free radical polymerization, and applied to selective adsorption and controlled release of 5-fluorouracil (5-FU) from an aqueous solution. Characterization results show that the as-synthesized TMMIPs have an average diameter of about 150 nm with a typical core-shell structure, and the thickness of the coating layer is approximately 50 nm. TMMIPs also displayed obvious magnetic properties and thermo-sensitivity. The adsorption results show that the prepared TMMIPs exhibit good adsorption capacity (up to 96.53 mg/g at 25 °C) and recognition towards 5-FU. The studies on 5-FU loading and release in vitro suggest that the release rate increases with increasing temperature. Meanwhile, adsorption mechanisms were explored by using a computational analysis to simulate the imprinted site towards 5-FU. The interaction energy between the imprinted site and 5-FU is -112.24 kJ/mol, originating from a hydrogen bond, Van der Waals forces and a hydrophobic interaction between functional groups located on 5-FU and a NIPAM monomer. The electrostatic potential charges and population analysis results suggest that the imprinted site of 5-FU can be introduced on the surface of TMMIPs, confirming their selective adsorption behavior for 5-FU.

  2. Role of the chemically non-innocent ligand in the catalytic formation of hydrogen and carbon dioxide from methanol and water with the metal as the spectator. (United States)

    Li, Haixia; Hall, Michael B


    The catalytic mechanism for the production of H2 and CO2 from CH3OH and H2O by [K(dme)2][Ru(H) (trop2dad)] (K(dme)2.1_exp) was investigated by density functional theory (DFT) calculations. Since the reaction occurs under mild conditions and at reasonable rates, it could be considered an ideal way to use methanol to store hydrogen. The predicted mechanism begins with the dehydrogenation of methanol to formaldehyde through a new ligand-ligand bifunctional mechanism, where two hydrogen atoms of CH3OH eliminate to the ligand's N and C atoms, a mechanism that is more favorable than the previously known mechanisms, β-H elimination, or the metal-ligand bifunctional. The key initiator of this first step is formed by migration of the hydride in 1 from the ruthenium to the meta-carbon atom, which generates 1″ with a frustrated Lewis pair in the ring between N and C. Hydroxide, formed when 1″ cleaves H2O, reacts rapidly with CH2O to give H2C(OH)O(-), which subsequently donates a hydride to 6 to generate HCOOH and 5. HCOOH then protonates 5 to give formate and a neutral complex, 4, with a fully hydrogenated ligand. The hydride of formate transfers to 6, releasing CO2. The fully hydrogenated complex, 4, is first deprotonated by OH(-) to form 5, which then releases hydrogen to regenerate the catalyst, 1″. In this mechanism, which explains the experimental observations, the whole reaction occurs on the chemically non-innocent ligand with the ruthenium atom appearing as a spectator.

  3. Pulse radiolysis studies on the release of cytotoxins from electron affinic anticancer prodrugs following their one-electron reduction

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, R.F.; Ware, D.C.; Denny, W.A.; Lee, H.; Tercel, M.; Wilson, W.R. [Auckland Univ. (New Zealand)


    New approaches to killing chemoresistant and radioresistant hypoxic cells of solid tumours include the selective release of potent cytotoxins from relatively non-toxic prodrugs through reductive metabolism and/or radiolytic reduction. Central to these studies, is an understanding of the mechanism of cytotoxin release and the basis of hypoxia-selectivity, since such information can be used to design compounds of high potency against solid tumours. Pulse radiolysis studies can offer unique insights into these underlying mechanisms in aqueous solution through the determination of thermodynamic one-electron reduction potentials of the prodrugs, rate constants for the formation and spectral charaterization of one-electron reduced prodrugs, the kinetics release of the cytotoxins from one-electron reduced prodrugs and the influence of molecular oxygen on the obligate radical intermediates. A series of different triggers, which are found to vary greatly in the rate constant for release of the effectors upon one-electron reduction of the prodrugs, will be discussed. Release of effector from a prodrug does not solely depend upon the type of trigger but can also be dependent on the type of linker and released effector. For example, whereas fast quantitative release of the mustard effector mechlorethamine is seen from the quaternary nitroimidazole upon one electron reduction, release of N-[2-(dimethylamino)ethyl] acridine-4-carboxamide (DACA), requires a higher level of reduction of the same trigger. Release of cytotoxic ligands from metal complexes requires that the metal centre is reduced. When the metal centre is lower than DACA bound as a ligand, reduction is seen to occur solely on the ligand without release from the metal centre. 1 ref., 1 fig.

  4. Triggered Release from Polymer Capsules

    Energy Technology Data Exchange (ETDEWEB)

    Esser-Kahn, Aaron P. [Univ. of Illinois, Urbana, IL (United States). Beckman Inst. for Advanced Science and Technology and Dept. of Chemistry; Odom, Susan A. [Univ. of Illinois, Urbana, IL (United States). Beckman Inst. for Advanced Science and Technology and Dept. of Chemistry; Sottos, Nancy R. [Univ. of Illinois, Urbana, IL (United States). Beckman Inst. for Advanced Science and Technology and Dept. of Materials Science and Engineering; White, Scott R. [Univ. of Illinois, Urbana, IL (United States). Beckman Inst. for Advanced Science and Technology and Dept. of Aerospace Engineering; Moore, Jeffrey S. [Univ. of Illinois, Urbana, IL (United States). Beckman Inst. for Advanced Science and Technology and Dept. of Chemistry


    Stimuli-responsive capsules are of interest in drug delivery, fragrance release, food preservation, and self-healing materials. Many methods are used to trigger the release of encapsulated contents. Here we highlight mechanisms for the controlled release of encapsulated cargo that utilize chemical reactions occurring in solid polymeric shell walls. Triggering mechanisms responsible for covalent bond cleavage that result in the release of capsule contents include chemical, biological, light, thermal, magnetic, and electrical stimuli. We present methods for encapsulation and release, triggering methods, and mechanisms and conclude with our opinions on interesting obstacles for chemically induced activation with relevance for controlled release.

  5. HIV gp120 inhibits the somatotropic axis: A possible GH-releasing hormone receptor mechanism for the pathogenesis of AIDS wasting (United States)

    Mulroney, Susan E.; McDonnell, Kevin J.; Pert, Candace B.; Ruff, Michael R.; Resch, Zachary; Samson, Willis K.; Lumpkin, Michael D.


    AIDS is often associated with growth retardation in children and wasting in adults. The dissociated envelope protein of the HIV (HIV-1), gp120, can be found in significant concentrations in the parenchyma and cerebrospinal fluid of brains in infected individuals, even in the earliest stages of HIV-1 disease. On the basis of this and the fact that we observed pentapeptide sequence homology between GH-releasing hormone (GHRH) and the V2 receptor-binding region of gp120, we initiated experiments to determine whether gp120 could affect GH secretion and growth in vivo and/or interact with anterior pituitary GHRH receptors in vitro. Although acute IV administration of gp120 in conscious rats had no effect on plasma GH levels, acute administration of gp120 (400 ng) into the brain significantly suppressed pulsatile GH release over a 6-h period compared with saline-injected controls. Furthermore, the putative gp120 antagonist, Peptide T (DAPTA), prevented the suppression of GH by gp120. In support of these in vivo findings, gp120 also significantly (P < 0.05) suppressed GHRH-stimulated GH release in static cultures of dispersed pituitary cells and from cells undergoing perifusion with the peptides. DAPTA prevented the GH suppression by gp120 in both of the pituitary cell paradigms. Furthermore, chronic administration of gp120 into the third ventricle significantly reduced body weight in juvenile rats, compared with saline-injected controls. Thus, gp120 appears to act both at the hypothalamus and pituitary to suppress GH release, and its action at these two locations is associated with a significant loss in body weight in chronically treated young animals. These findings may suggest a specific mechanism for the pathogenesis of wasting in HIV-1 patients that involves blockade of endogenous GHRH receptors by gp120. PMID:9465119

  6. A new offshore transport mechanism for shoreline-released tracer induced by transient rip currents and stratification (United States)

    Kumar, Nirnimesh; Feddersen, Falk


    Offshore transport from the shoreline across the inner shelf of early-stage larvae and pathogens is poorly understood yet is critical for understanding larval fate and dilution of polluted shoreline water. With a novel coupling of a transient rip current (TRC) generating surf zone model and an ocean circulation model, we show that transient rip currents ejected onto a stratified inner shelf induce a new, previously unconsidered offshore transport pathway. For incident waves and stratification typical for Southern California in the fall, this mechanism subducts surf zone-origin tracers and transports them at least 800 m offshore at 1.2 km/d analogous to subduction at ocean fronts. This mechanism requires both TRCs and stratification. As TRCs are ubiquitous and the inner shelf is often stratified, this mechanism may have an important role in exporting early-stage larvae, pathogens, or other tracers onto the shelf.

  7. Novel mechanism for gonadotropin-releasing hormone neuronal migration involving Gas6/Ark signaling to p38 mitogen-activated protein kinase. (United States)

    Allen, Melissa P; Linseman, Daniel A; Udo, Hiroshi; Xu, Mei; Schaack, Jerome B; Varnum, Brian; Kandel, Eric R; Heidenreich, Kim A; Wierman, Margaret E


    Gonadotropin-releasing hormone (GnRH) is the central regulator of the reproductive axis. Normal sexual maturation depends on the migration of GnRH neurons from the olfactory placode to the hypothalamus during development. Previously, we showed restricted expression of the membrane receptor adhesion-related kinase (Ark) in immortalized cell lines derived from migratory but not postmigratory GnRH neurons. In addition, Ark and GnRH transcripts were detected along the GnRH neuron migratory route in the E13 mouse cribriform plate. In the present study, we examined the role of Ark and its ligand, Gas6 (encoded by growth arrest-specific gene 6), in GnRH neuron migration. Gas6 stimulated lamellipodial extension, membrane ruffling, and chemotaxis of immortalized NLT GnRH neuronal cells via the Ark receptor. Gas6/Ark signaling promoted activation of the Rho family GTPase Rac, and adenoviral-mediated expression of dominant negative N17Rac abolished Gas6/Ark-induced actin cytoskeletal reorganization and migration of GnRH neuronal cells. In addition, p38 MAPK was activated downstream of Ark and Rac, and inhibition of p38 MAPK with either SB203580 or adenoviral dominant negative p38alpha also blocked Gas6/Ark-mediated migration. Finally, downstream of Rac and p38 mitogen-activated protein kinase (MAPK), Gas6/Ark signaling promoted activation of MAPK-activated protein kinase 2 and induced phosphorylation of HSP25, a known regulator of cortical actin remodeling. The data are the first to demonstrate a migratory signaling pathway downstream of Ark/Axl family receptors and suggest a previously unidentified role for p38 MAPK in neuronal migration. Furthermore, these studies support a potential role for Ark in the regulation of GnRH neuronal migration.

  8. Contraction-stimulated glucose transport in muscle is controlled by AMPK and mechanical stress but not sarcoplasmatic reticulum Ca2+ release

    Directory of Open Access Journals (Sweden)

    Thomas E. Jensen


    Full Text Available Understanding how muscle contraction orchestrates insulin-independent muscle glucose transport may enable development of hyperglycemia-treating drugs. The prevailing concept implicates Ca2+ as a key feed forward regulator of glucose transport with secondary fine-tuning by metabolic feedback signals through proteins such as AMPK. Here, we demonstrate in incubated mouse muscle that Ca2+ release is neither sufficient nor strictly necessary to increase glucose transport. Rather, the glucose transport response is associated with metabolic feedback signals through AMPK, and mechanical stress-activated signals. Furthermore, artificial stimulation of AMPK combined with passive stretch of muscle is additive and sufficient to elicit the full contraction glucose transport response. These results suggest that ATP-turnover and mechanical stress feedback are sufficient to fully increase glucose transport during muscle contraction, and call for a major reconsideration of the established Ca2+ centric paradigm.

  9. Analysis of long-term mechanical grooming on large-scale test panels coated with an antifouling and a fouling-release coating. (United States)

    Hearin, John; Hunsucker, Kelli Z; Swain, Geoffrey; Stephens, Abraham; Gardner, Harrison; Lieberman, Kody; Harper, Michael


    Long-term grooming tests were conducted on two large-scale test panels, one coated with a fluorosilicone fouling-release (FR) coating, and one coated with a copper based ablative antifouling (AF) coating. Mechanical grooming was performed weekly or bi-weekly using a hand operated, electrically powered, rotating brush tool. The results indicate that weekly grooming was effective at removing loose or heavy biofilm settlement from both coatings, but could not prevent the permanent establishment of low-profile tenacious biofilms. Weekly grooming was very effective at preventing macrofouling establishment on the AF coating. The effectiveness of weekly grooming at preventing macrofouling establishment on the FR coating varied seasonally. The results suggest that frequent mechanical grooming is a viable method to reduce the fouling rating of ships' hulls with minimal impact to the coating. Frequent grooming could offer significant fuel savings while reducing hull cleaning frequencies and dry dock maintenance requirements.

  10. Studies on the Mechanism of Single Basal Application of Controlled-Release Fertilizers for Increasing Yield of Rice (Oryza sativa L.)

    Institute of Scientific and Technical Information of China (English)

    TANG Shuan-hu; YANG Shao-hai; CHEN Jian-sheng; XU Pei-zhi; ZHANG Fa-bao; AI Shao-ying; HUANG Xu


    This paper was to explore the mechanism of single basal application of controlled-release fertilizers for increasing yield of rice (Oryza sativa L.). Pot trials and cylinder trials were carried out from 2002 to 2005 to study the influences of single basal application of 3 controlled-release fertilizers on the changes of soil available N, root development, senescence and lodging resistance at late growth stages. Results showed that at 30 days after fertilization, single basal application of controlled-release fertilizers coated with vegetal-substance (CRF1) and polymer materials (CRF3) increased soil available N to 12.0 and 147.9%, respectively, in comparison to split fertilization of rice-specific fertilizer (RSF1). Treatments of the two CRFs obviously benefited the development of root system, resulting in greater rice root weights with extensive distribution and higher root activity. In addition, the two CRF treatments, in comparison to RSF1, enhanced chlorophyll consents of the flag leaves to 9.5 and 15.5%, and soluble protein up to 89.7 and 108.0% respectively. Application of the two CRFs also made the base of rice stems strong and large, declined the proportion of shoot and root, increased root depth index. Though relatively low K rate, single basal application of the CRF3 coated with NH4MgPO4 could also promote the development of root system, enhance root activity and some physiological functions of flag leaves. Based on these results, it was concluded that major mechanisms for increasing rice yield by single basal application of the CRFs should be attributed to grater soil available N supply, superior development of root systems, better nutrient absorption capacity, slower senescence and enhancement of lodging resistance at late stages.

  11. A rat model of full thickness thermal injury characterized by thermal hyperalgesia, mechanical allodynia, pronociceptive peptide release and tramadol analgesia. (United States)

    Fowler, Marcie; Clifford, John L; Garza, Thomas H; Slater, Terry M; Arizpe, Helen M; Novak, Joseph; Petz, Lawrence N; Loyd, Dayna R


    Opioid-related side effects are problematic for burn patients. Dual mechanism therapeutics targeting opioid and non-opioid mechanisms may have reduced side effects with similar analgesic efficacy. Tramadol combines mu opioid receptor agonism with norepinephrine reuptake inhibition and has been effective in treating some types of pain. The effectiveness of tramadol in treating pain associated with burns is unclear. We hypothesized that tramadol is effective in reducing thermal injury-evoked pain behaviors in a rat model. Rats were anesthetized and a 100°C metal probe was placed on the hindpaw for 30 s to induce a full thickness thermal injury. A subset of rats was perfusion fixed and hindpaw tissue and spinal cord collected for anatomical analysis. Rats received morphine (5 mg/kg; i.p.), tramadol (10-30 mg/kg; i.p.) or vehicle and latency to paw withdrawal from a noxious thermal or non-noxious mechanical stimulus was recorded every 10 min over 70 min and again at 2 h. We report that pain behaviors developed within 48 h and peaked at 1 week; paralleled by enhanced expression of pronociceptive neuropeptides in the spinal cord. Morphine and tramadol significantly attenuated hyperalgesia and allodynia, while not significantly altering motor coordination/sedation. These data indicate dual mechanism therapeutics may be effective for treating pain associated with burns.

  12. Understanding misfit strain releasing mechanisms via molecular dynamics simulations of CdTe growth on {112}zinc-blende CdS (United States)

    Zhou, X. W.; Chavez, J. J.; Almeida, S.; Zubia, D.


    Molecular dynamics simulations have been used to analyse microstructures of CdTe films grown on {112} surfaces of zinc-blende CdS. Interestingly, CdTe films grow in ⟨331⟩ orientations as opposed to ⟨112⟩ epitaxial orientations. At the CdTe-{331}/CdS-{112} interface, however, there exists an axis that is parallel to the ⟨110⟩ orientation of both CdS and CdTe. It is the direction orthogonal to this ⟨110⟩ that becomes different, being ⟨116⟩ for CdTe and ⟨111⟩ for CdS, respectively. Missing CdTe-{110} planes are found along the ⟨110⟩ axis, suggesting that the misfit strain is released by the conventional misfit dislocation mechanism along this axis. In the orthogonal axis, the misfit strain is found to be more effectively released by the new grain orientation mechanism. Our finding is supported by literature experimental observations of the change of growth direction when Cd0.96Zn0.04Te films are deposited on GaAs. Analyses of energetics clearly demonstrate the cause for the formation of the new orientation, and the insights gained from our studies can help understand the grain structures experimentally observed in lattice mismatched systems.

  13. In vivo evaluation of the potential neurotoxicity of aerosols released from mechanical stress of nano-TiO2 additived paints in mice chronically exposed by inhalation (United States)

    Manixay, S.; Delaby, S.; Gaie-Levrel, F.; Wiart, M.; Motzkus, C.; Bencsik, A.


    Engineered Nanomaterials (ENM) provide technical and specific benefits due to their physical-chemical properties at the nanometer scale. For instance, many ENM are used to improve products in the building industry. Nanoscaled titanium dioxide (TiO2) is one of the most used ENM in this industry. Incorporated in different matrix, cement, glass, paints… TiO2 nanoparticles (NPs) provide the final product with anti-UV, air purification and self-cleaning properties, thanks to their photocatalytic activity. However, ageing processes of such products, as photocatalytic paints, during a mechanical stress have been shown to release TiO2 NPs from this matrix associated with sanding dust. Thus, workers who sand painted walls could be exposed to TiO2 NPs through inhalation. As inhalation may lead to a translocation of particulate matter to the brain via olfactory or trigeminal nerves, there is an urgent need for evaluating a potential neurotoxicity. In order to provide new knowledge on this topic, we developed a dedicated experimental set-up using a rodent model exposed via inhalation. The aerosol released from a mechanical stress of photocatalytic paints containing TiO2 NPs was characterized and coupled to an exposition chamber containing group of mice free to move and chronically exposed (2 hours per day for 5 days a week during 8 weeks).

  14. Mechanisms of gas retention and release: Experimental results for Hanford single-shell waste tanks 241-A-101, 241-S-106, and 241-U-103

    Energy Technology Data Exchange (ETDEWEB)

    Rassat, S.D.; Caley, S.M.; Bredt, P.R.; Gauglitz, P.A.; Rinehart, D.E.; Forbes, S.V.


    The 177 underground waste storage tanks at the Hanford Site contain millions of gallons of radioactive waste resulting from the purification of nuclear materials and related processes. Through various mechanisms, flammable gas mixtures of hydrogen, ammonia, methane, and nitrous oxide are generated and retained in significant quantities within the waste in many ({approximately}25) of these tanks. The potential for large releases of retained gas from these wastes creates a flammability hazard. It is a critical component of the effort to understand the flammability hazard and a primary goal of this laboratory investigation to establish an understanding of the mechanisms of gas retention and release in these wastes. The results of bubble retention experimental studies using waste samples from several waste tanks and a variety of waste types support resolution of the Flammable Gas Safety Issue. Gas bubble retention information gained in the pursuit of safe storage will, in turn, benefit future waste operations including salt-well pumping, waste transfers, and sluicing/retrieval.

  15. Insights into the Interaction Mechanism of Ligands with Aβ42 Based on Molecular Dynamics Simulations and Mechanics: Implications of Role of Common Binding Site in Drug Design for Alzheimer's Disease. (United States)

    Kundaikar, Harish S; Degani, Mariam S


    Aggregation of β-amyloid (Aβ) into oligomers and further into fibrils is hypothesized to be a key factor in pathology of Alzheimer's disease (AD). In this study, mapping and docking were used to study the binding of ligands to protofibrils. It was followed by molecular simulations to understand the differences in interactions of known therapeutic agents such as curcumin, fluorescence-based amyloid staining agents such as thioflavin T, and diagnostic agents such as florbetapir (AV45), with Aβ protofibrils. We show that therapeutic agents bind to and distort the protofibrils, thus causing destabilization or prevention of oligomerization, in contrast to diagnostic agents which bind to but do not distort such structures. This has implications in the rational design of ligands, both for diagnostics and therapeutics of AD.

  16. Noxa induces apoptosis in oncogene-expressing cells through catch-and-release mechanism operating between Puma and Mcl-1. (United States)

    Nakajima, Wataru; Tanaka, Nobuyuki


    Tumor suppressor p53 induces apoptosis by transcriptional induction of Noxa and Puma, which encode the proapoptotic BH3-only member of the Bcl-2 family proteins. In the p53-mediated tumor surveillance system, p53 induces apoptosis or replicative senescence in oncogene-expressing cells, resulting in elimination of such cells. In this context, we previously found that Noxa and Puma synergistically induce apoptosis. Here, we found the adenovirus oncogene E1A to induce p53-dependently expression of Puma, but not Noxa. The induced Puma associates with antiapoptotic Bcl-2 protein Mcl-1, accompanied by accumulated Mcl-1 protein on mitochondria. Moreover, E1A also reduces expression of the antiapoptotic Bcl-2 protein Bcl-X(L). In contrast, the DNA-damaging agent adriamycin induces Noxa expression in E1A-expressing cells. Interestingly, Mcl-1 knockdown itself induced apoptosis in E1A-expressing MEFs. Furthermore, Noxa displaced Puma's association with Mcl-1, accompanied by Mcl-1 degradation and apoptosis induction by activating mitochondrial apoptotic executers Bax and Bak. These results suggest that p53-induced apoptosis in oncogene-expressing cells is regulated by differential induction and sequential activation of Noxa and Puma. Accumulated Puma by oncogene enhances susceptibility to apoptosis through "catch" in mitochondria by Mcl-1. Subsequently, in response to DNA-damage, Noxa efficiently induces apoptosis by "release" of Puma from Mcl-1.

  17. Structure of eEF3 and the mechanism of transfer RNA release from the E-site. (United States)

    Andersen, Christian B F; Becker, Thomas; Blau, Michael; Anand, Monika; Halic, Mario; Balar, Bharvi; Mielke, Thorsten; Boesen, Thomas; Pedersen, Jan Skov; Spahn, Christian M T; Kinzy, Terri Goss; Andersen, Gregers R; Beckmann, Roland


    Elongation factor eEF3 is an ATPase that, in addition to the two canonical factors eEF1A and eEF2, serves an essential function in the translation cycle of fungi. eEF3 is required for the binding of the aminoacyl-tRNA-eEF1A-GTP ternary complex to the ribosomal A-site and has been suggested to facilitate the clearance of deacyl-tRNA from the E-site. Here we present the crystal structure of Saccharomyces cerevisiae eEF3, showing that it consists of an amino-terminal HEAT repeat domain, followed by a four-helix bundle and two ABC-type ATPase domains, with a chromodomain inserted in ABC2. Moreover, we present the cryo-electron microscopy structure of the ATP-bound form of eEF3 in complex with the post-translocational-state 80S ribosome from yeast. eEF3 uses an entirely new factor binding site near the ribosomal E-site, with the chromodomain likely to stabilize the ribosomal L1 stalk in an open conformation, thus allowing tRNA release.

  18. Strain-release mechanisms in bimetallic core-shell nanoparticles as revealed by Cs-corrected STEM (United States)

    Bhattarai, Nabraj; Casillas, Gilberto; Ponce, Arturo; Jose-Yacaman, Miguel


    Lattice mismatch in a bimetallic core-shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. Here we report the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd core-shell nanoparticles. Our results show that first Shockley partial dislocations (SPD) combined with stacking faults (SF) appear at the last Pd layer; then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shells growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles. PMID:23457419

  19. Cholinesterases: structure of the active site and mechanism of the effect of cholinergic receptor blockers on the rate of interaction with ligands

    Energy Technology Data Exchange (ETDEWEB)

    Antokhin, A M; Gainullina, E T; Taranchenko, V F [Federal State Agency ' 27 Scientific Centre of Ministry of Defence of the Russian Federation' (Russian Federation); Ryzhikov, S B; Yavaeva, D K [Department of Physics, M.V.Lomonosov Moscow State University (Russian Federation)


    Modern views on the structure of cholinesterase active sites and the mechanism of their interaction with organophosphorus inhibitors are considered. The attention is focused on the mechanism of the effect of cholinergic receptor blockers, acetylcholine antagonists, on the rate of interaction of acetylcholine esterase with organophosphorus inhibitors.

  20. Multiple ligand simultaneous docking: orchestrated dancing of ligands in binding sites of protein. (United States)

    Li, Huameng; Li, Chenglong


    Present docking methodologies simulate only one single ligand at a time during docking process. In reality, the molecular recognition process always involves multiple molecular species. Typical protein-ligand interactions are, for example, substrate and cofactor in catalytic cycle; metal ion coordination together with ligand(s); and ligand binding with water molecules. To simulate the real molecular binding processes, we propose a novel multiple ligand simultaneous docking (MLSD) strategy, which can deal with all the above processes, vastly improving docking sampling and binding free energy scoring. The work also compares two search strategies: Lamarckian genetic algorithm and particle swarm optimization, which have respective advantages depending on the specific systems. The methodology proves robust through systematic testing against several diverse model systems: E. coli purine nucleoside phosphorylase (PNP) complex with two substrates, SHP2NSH2 complex with two peptides and Bcl-xL complex with ABT-737 fragments. In all cases, the final correct docking poses and relative binding free energies were obtained. In PNP case, the simulations also capture the binding intermediates and reveal the binding dynamics during the recognition processes, which are consistent with the proposed enzymatic mechanism. In the other two cases, conventional single-ligand docking fails due to energetic and dynamic coupling among ligands, whereas MLSD results in the correct binding modes. These three cases also represent potential applications in the areas of exploring enzymatic mechanism, interpreting noisy X-ray crystallographic maps, and aiding fragment-based drug design, respectively.

  1. Comparison of Airway Pressure Release Ventilation to Conventional Mechanical Ventilation in the Early Management of Smoke Inhalation Injury in Swine (United States)


    acute respiratory distress syndrome developed ( PaO2 /FIO2 ratio ), plateau pressures were limited to ន cm H2O. Six uninjured pigs received...conventional mechanical ventilation for 48 hrs and served as time controls. Changes in PaO2 /FIO2 ratio, tidal volume, respiratory rate, mean airway pressure...plateau pressure, and hemody- namic variables were recorded. Survival was assessed using Kaplan- Meier analysis. PaO2 /FIO2 ratio was lower in airway

  2. Mechanisms of modulation of cytokine release by human cord blood monocytes exposed to high concentrations of caffeine (United States)

    Chavez-Valdez, Raul; Ahlawat, Rajni; Wills-Karp, Marsha; Gauda, Estelle B.


    Background Serum caffeine concentrations >20µg/mL (100 µM) in infants treated for apnea of prematurity increases TNF-α and decreases IL-10, change that perhaps is linked to co-morbidities. We hypothesize that this pro-inflammatory cytokine profile may be linked to differential binding of caffeine to adenosine receptor subtypes (AR), inhibition of phosphodiesterases (PDEs), and modulation of toll-like receptors (TLR). Methods LPS-activated cord blood monocytes (CBM) from 19 infants were exposed to caffeine (0 to 200 µM) with or without previous exposure to A1R, A3R, or PDE IV antagonists to determine changes in dose-response curves. Cytokines levels (ELISA), intracellular cAMP accumulation (EIA) and TLR gene expression (real time qRT PCR) were measured. Results Caffeine at ≤100µM decreased TNF-α levels (~25%, p=0.01) and cAMP. All caffeine concentrations decreased IL-10 levels (17 to 35%, p<0.01). A1R, A3R and PDE blockades decreased TNF-α (31%, 21%, and 88%, p≤0.01), but not IL-10. Caffeine further decreased TNF-α following A3R and PDE blockades. Caffeine concentrations directly correlated to TLR4 gene expression (r=0.84; p<0.001). Conclusion Neither A3R, nor PDE blockades are involved in caffeine’s modulation of cytokine release by CBM at any concentration. Besides A1R blockade, caffeine’s up-regulation of TLR4 may promote inflammation at high concentrations. PMID:26982450

  3. Presynaptic facilitation of glutamate release in the basolateral amygdala: a mechanism for the anxiogenic and seizurogenic function of GluK1 receptors. (United States)

    Aroniadou-Anderjaska, V; Pidoplichko, V I; Figueiredo, T H; Almeida-Suhett, C P; Prager, E M; Braga, M F M


    Kainate receptors containing the GluK1 subunit (GluK1Rs; previously known as GluR5 kainate receptors) are concentrated in certain brain regions, where they play a prominent role in the regulation of neuronal excitability, by modulating GABAergic and/or glutamatergic synaptic transmission. In the basolateral nucleus of the amygdala (BLA), which plays a central role in anxiety as well as in seizure generation, GluK1Rs modulate GABAergic inhibition via postsynaptic and presynaptic mechanisms. However, the role of these receptors in the regulation of glutamate release, and the net effect of their activation on the excitability of the BLA network are not well understood. Here, we show that in amygdala slices from 35- to 50-day-old rats, the GluK1 agonist (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid (ATPA) (300 nM) increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) and miniature EPSCs (mEPSCs) recorded from BLA principal neurons, and decreased the rate of failures of evoked EPSCs. The GluK1 antagonist (S)-1-(2-amino-2-carboxyethyl)-3-(2-carboxybenzyl) pyrimidine-2,4-dione (UBP302) (25 or 30 μM) decreased the frequency of mEPSCs, reduced evoked field potentials, and increased the "paired-pulse ratio" of the field potential amplitudes. Taken together, these results suggest that GluK1Rs in the rat BLA are present on presynaptic terminals of principal neurons, where they mediate facilitation of glutamate release. In vivo bilateral microinjections of ATPA (250 pmol) into the rat BLA increased anxiety-like behavior in the open field test, while 2 nmol ATPA induced seizures. Similar intra-BLA injections of UBP302 (20 nmol) had anxiolytic effects in the open field and the acoustic startle response tests, without affecting pre-pulse inhibition. These results suggest that although GluK1Rs in the rat BLA facilitate both GABA and glutamate release, the facilitation of glutamate release prevails, and these receptors can have an

  4. The role and molecular mechanism of D-aspartic acid in the release and synthesis of LH and testosterone in humans and rats

    Directory of Open Access Journals (Sweden)

    Ronsini Salvatore


    Full Text Available Abstract Background D-aspartic acid is an amino acid present in neuroendocrine tissues of invertebrates and vertebrates, including rats and humans. Here we investigated the effect of this amino acid on the release of LH and testosterone in the serum of humans and rats. Furthermore, we investigated the role of D-aspartate in the synthesis of LH and testosterone in the pituitary and testes of rats, and the molecular mechanisms by which this amino acid triggers its action. Methods For humans: A group of 23 men were given a daily dose of D-aspartate (DADAVIT® for 12 days, whereas another group of 20 men were given a placebo. For rats: A group of 10 rats drank a solution of either 20 mM D-aspartate or a placebo for 12 days. Then LH and testosterone accumulation was determined in the serum and D-aspartate accumulation in tissues. The effects of D-aspartate on the synthesis of LH and testosterone were gauged on isolated rat pituitary and Leydig cells. Tissues were incubated with D-aspartate, and then the concentration (synthesis of LH and cGMP in the pituitary and of testosterone and cAMP in the Leydig cells was determined. Results In humans and rats, sodium D-aspartate induces an enhancement of LH and testosterone release. In the rat pituitary, sodium D-aspartate increases the release and synthesis of LH through the involvement of cGMP as a second messenger, whereas in rat testis Leydig cells, it increases the synthesis and release of testosterone and cAMP is implicated as second messenger. In the pituitary and in testes D-Asp is synthesized by a D-aspartate racemase which convert L-Asp into D-Asp. The pituitary and testes possesses a high capacity to trapping circulating D-Asp from hexogen or endogen sources. Conclusion D-aspartic acid is a physiological amino acid occurring principally in the pituitary gland and testes and has a role in the regulation of the release and synthesis of LH and testosterone in humans and rats.

  5. MOST: most-similar ligand based approach to target prediction. (United States)

    Huang, Tao; Mi, Hong; Lin, Cheng-Yuan; Zhao, Ling; Zhong, Linda L D; Liu, Feng-Bin; Zhang, Ge; Lu, Ai-Ping; Bian, Zhao-Xiang


    Many computational approaches have been used for target prediction, including machine learning, reverse docking, bioactivity spectra analysis, and chemical similarity searching. Recent studies have suggested that chemical similarity searching may be driven by the most-similar ligand. However, the extent of bioactivity of most-similar ligands has been oversimplified or even neglected in these studies, and this has impaired the prediction power. Here we propose the MOst-Similar ligand-based Target inference approach, namely MOST, which uses fingerprint similarity and explicit bioactivity of the most-similar ligands to predict targets of the query compound. Performance of MOST was evaluated by using combinations of different fingerprint schemes, machine learning methods, and bioactivity representations. In sevenfold cross-validation with a benchmark Ki dataset from CHEMBL release 19 containing 61,937 bioactivity data of 173 human targets, MOST achieved high average prediction accuracy (0.95 for pKi ≥ 5, and 0.87 for pKi ≥ 6). Morgan fingerprint was shown to be slightly better than FP2. Logistic Regression and Random Forest methods performed better than Naïve Bayes. In a temporal validation, the Ki dataset from CHEMBL19 were used to train models and predict the bioactivity of newly deposited ligands in CHEMBL20. MOST also performed well with high accuracy (0.90 for pKi ≥ 5, and 0.76 for pKi ≥ 6), when Logistic Regression and Morgan fingerprint were employed. Furthermore, the p values associated with explicit bioactivity were found be a robust index for removing false positive predictions. Implicit bioactivity did not offer this capability. Finally, p values generated with Logistic Regression, Morgan fingerprint and explicit activity were integrated with a false discovery rate (FDR) control procedure to reduce false positives in multiple-target prediction scenario, and the success of this strategy it was demonstrated with a case of fluanisone

  6. Mechanical properties, biological activity and protein controlled release by poly(vinyl alcohol)-bioglass/chitosan-collagen composite scaffolds: a bone tissue engineering applications. (United States)

    Pon-On, Weeraphat; Charoenphandhu, Narattaphol; Teerapornpuntakit, Jarinthorn; Thongbunchoo, Jirawan; Krishnamra, Nateetip; Tang, I-Ming


    In the present study, composite scaffolds made with different weight ratios (0.5:1, 1:1 and 2:1) of bioactive glass (15Ca:80Si:5P) (BG)/polyvinyl alcohol (PVA) (PVABG) and chitosan (Chi)/collagen (Col) (ChiCol) were prepared by three mechanical freeze-thaw followed by freeze-drying to obtain the porous scaffolds. The mechanical properties and the in vitro biocompatibility of the composite scaffolds to simulated body fluid (SBF) and to rat osteoblast-like UMR-106 cells were investigated. The results from the studies indicated that the porosity and compressive strength were controlled by the weight ratio of PVABG:ChiCol. The highest compressive modulus of the composites made was 214.64 MPa which was for the 1:1 weight ratio PVABG:ChiCol. Mineralization study in SBF showed the formation of apatite crystals on the PVABG:ChiCol surface after 7 days of incubation. In vitro cell availability and proliferation tests confirmed the osteoblast attachment and growth on the PVABG:ChiCol surface. MTT and ALP tests on the 1:1 weight ratio PVABG:ChiCol composite indicated that the UMR-106 cells were viable. Alkaline phosphatase activity was found to increase with increasing culturing time. In addition, we showed the potential of PVABG:ChiCol drug delivery through PBS solution studies. 81.14% of BSA loading had been achieved and controlled release for over four weeks was observed. Our results indicated that the PVABG:ChiCol composites, especially the 1:1 weight ratio composite exhibited significantly improved mechanical, mineral deposition, biological properties and controlled release. This made them potential candidates for bone tissue engineering applications.

  7. Precise investigation of the axial ligand substitution mechanism on a hydrogenphosphato-bridged lantern-type platinum(III) binuclear complex in acidic aqueous solution. (United States)

    Iwatsuki, Satoshi; Mizushima, Chiho; Morimoto, Naoyuki; Muranaka, Shinji; Ishihara, Koji; Matsumoto, Kazuko


    Detailed equilibrium and kinetic studies on axial water ligand substitution reactions of the "lantern-type" platinum(III) binuclear complex, [Pt(2)(mu-HPO(4))(4)(H(2)O)(2)](2)(-), with halide and pseudo-halide ions (X(-) = Cl(-), Br(-), and SCN(-)) were carried out in acidic aqueous solution at 25 degrees C with I = 1.0 M. The diaqua Pt(III) dimer complex is in acid dissociation equilibrium in aqueous solution with -log K(h1) = 2.69 +/- 0.04. The consecutive formation constants of the aquahalo complex () and the dihalo complex () were determined spectrophotometrically to be log = 2.36 +/- 0.01 and log = 1.47 +/- 0.01 for the reaction with Cl(-) and log = 2.90 +/- 0.04 and log = 2.28 +/- 0.01 for the reaction with Br(-), respectively. In the kinetic measurements carried out under the pseudo-first-order conditions with a large excess concentration of halide ion compared to that of Pt(III) dimer (C(X)()- > C(Pt)), all of the reactions proceeded via a one-step first-order reaction, which is a contrast to the consecutive two-step reaction for the amidato-bridged platinum(III) binuclear complexes. The conditional first-order rate constant (k(obs)) depended on C(X)()- as well as the acidity of the solution. From kinetic analyses, the rate-limiting step was determined to be the first substitution process that forms the monohalo species, which is in rapid equilibrium with the dihalo complex. The reaction with 4-penten-1-ol was also kinetically investigated to examine the reactivity of the lantern complex with olefin compounds.

  8. Symmetrical P4 cleavage at cobalt half sandwich complexes [(η5-C5H5)Co(L)] (L = CO, NHC)--a computational case study on the mechanism of symmetrical P4 degradation to P2 ligands. (United States)

    Zarzycki, Bartosz; Bickelhaupt, F Matthias; Radius, Udo


    A full theoretical mechanistic investigation on the symmetrical cleavage of P4 at the active complex fragments [(η(5)-C5H5)Co(L)] (L = CO, (i)Pr2Im; (i)Pr2Im = 1,3-di-iso-propylimidazolin-2-ylidene), which results in the formation of the complex [{(η(5)-C5H5)Co}2(μ,η(2:2)-P2)2] 9, is presented. The overall reaction mechanism is a complex, multistep process. Rate-determining steps of the reaction sequence are two consecutive dissociations of the co-ligands L, which induce the decisive structural rearrangements of the P4 unit. The choice of the co-ligand L ( = CO, (i)Pr2Im) influences the kinetic barrier as well as the energy balance of the overall reaction path significantly. The calculations further reveal a strong influence of the entropic effect on the overall reaction. As a consequence, the energy balance of the overall formation of 9 starting from [(η(5)-C5H5)Co(CO)] precursors is almost thermoneutral and has to overcome high kinetic barriers, whereas the reaction starting from [(η(5)-C5H5)Co((i)Pr2Im)] precursors is exothermic, featuring lower transition barriers with stabilized intermediates. From the direct comparison of both reaction coordinates it seems that the entropic effect of the co-ligands is even stronger than their electronic influence, as for both investigated systems the reactions' energy profiles are almost identical up to intermediate [{(η(5)-C5H5)Co(L)}2(μ,η(2:2)-P4)] 5 (L = CO, (i)Pr2Im). After the formation of 5, the first CO dissociation step renders the reaction endothermic for L = CO, whereas in the case of (i)Pr2Im dissociation the reaction progresses exothermically. Energy decomposition analysis and fragment analysis provide a picture of the bonding mechanisms between the metal complex fragments and P4 in the case of the most significant intermediates and the final product.

  9. Serotonin receptor B may lock the gate of PTTH release/synthesis in the Chinese silk moth, Antheraea pernyi; a diapause initiation/maintenance mechanism?

    Directory of Open Access Journals (Sweden)

    Qiushi Wang

    Full Text Available The release of prothoracicotropic hormone, PTTH, or its blockade is the major endocrine switch regulating the developmental channel either to metamorphosis or to pupal diapause in the Chinese silk moth, Antheraea pernyi. We have cloned cDNAs encoding two types of serotonin receptors (5HTRA and B. 5HTRA-, and 5HTRB-like immunohistochemical reactivities (-ir were colocalized with PTTH-ir in two pairs of neurosecretory cells at the dorsolateral region of the protocerebrum (DL. Therefore, the causal involvement of these receptors was suspected in PTTH release/synthesis. The level of mRNA(5HTRB responded to 10 cycles of long-day activation, falling to 40% of the original level before activation, while that of 5HTRA was not affected by long-day activation. Under LD 16:8 and 12:12, the injection of dsRNA(5HTRB resulted in early diapause termination, whereas that of dsRNA(5HTRA did not affect the rate of diapause termination. The injection of dsRNA(5HTRB induced PTTH accumulation, indicating that 5HTRB binding suppresses PTTH synthesis also. This conclusion was supported pharmacologically; the injection of luzindole, a melatonin receptor antagonist, plus 5th inhibited photoperiodic activation under LD 16:8, while that of 5,7-DHT, induced emergence in a dose dependent fashion under LD 12:12. The results suggest that 5HTRB may lock the PTTH release/synthesis, maintaining diapause. This could also work as diapause induction mechanism.

  10. Ligand modeling and design

    Energy Technology Data Exchange (ETDEWEB)

    Hay, B.P. [Pacific Northwest National Lab., Richland, WA (United States)


    The purpose of this work is to develop and implement a molecular design basis for selecting organic ligands that would be used in the cost-effective removal of specific radionuclides from nuclear waste streams. Organic ligands with metal ion specificity are critical components in the development of solvent extraction and ion exchange processes that are highly selective for targeted radionuclides. The traditional approach to the development of such ligands involves lengthy programs of organic synthesis and testing, which in the absence of reliable methods for screening compounds before synthesis, results in wasted research effort. The author`s approach breaks down and simplifies this costly process with the aid of computer-based molecular modeling techniques. Commercial software for organic molecular modeling is being configured to examine the interactions between organic ligands and metal ions, yielding an inexpensive, commercially or readily available computational tool that can be used to predict the structures and energies of ligand-metal complexes. Users will be able to correlate the large body of existing experimental data on structure, solution binding affinity, and metal ion selectivity to develop structural design criteria. These criteria will provide a basis for selecting ligands that can be implemented in separations technologies through collaboration with other DOE national laboratories and private industry. The initial focus will be to select ether-based ligands that can be applied to the recovery and concentration of the alkali and alkaline earth metal ions including cesium, strontium, and radium.

  11. Crystalline capsules: metal-organic frameworks locked by size-matching ligand bolts. (United States)

    Wang, Hao; Xu, Jian; Zhang, Da-Shuai; Chen, Qiang; Wen, Rong-Mei; Chang, Ze; Bu, Xian-He


    Metal-organic frameworks (MOFs) are shown to be good examples of a new class of crystalline porous materials for guest encapsulation. Since the encapsulation/release of guest molecules in MOF hosts is a reversible process in nature, how to prevent the leaching of guests from the open pores with minimal and nondestructive modifications of the structure is a critical issue. To address this issue, we herein propose a novel strategy of encapsulating guests by introducing size-matching organic ligands as bolts to lock the pores of the MOFs through deliberately anchoring onto the open metal sites in the pores. Our proposed strategy provides a mechanical way to prevent the leaching of guests and thereby has less dependence on the specific chemical environment of the hosts, thus making it applicable for a wide variety of existing MOFs once the size-matching ligands are employed.

  12. Peptidomimetic escape mechanisms arise via genetic diversity in the ligand-binding site of the hepatitis C virus NS3/4A serine protease. (United States)

    Welsch, Christoph; Shimakami, Tetsuro; Hartmann, Christoph; Yang, Yan; Domingues, Francisco S; Lengauer, Thomas; Zeuzem, Stefan; Lemon, Stanley M


    It is a challenge to develop direct-acting antiviral agents that target the nonstructural protein 3/4A protease of hepatitis C virus because resistant variants develop. Ketoamide compounds, designed to mimic the natural protease substrate, have been developed as inhibitors. However, clinical trials have revealed rapid selection of resistant mutants, most of which are considered to be pre-existing variants. We identified residues near the ketoamide-binding site in x-ray structures of the genotype 1a protease, co-crystallized with boceprevir or a telaprevir-like ligand, and then identified variants at these positions in 219 genotype-1 sequences from a public database. We used side-chain modeling to assess the potential effects of these variants on the interaction between ketoamide and the protease, and compared these results with the phenotypic effects on ketoamide resistance, RNA replication capacity, and infectious virus yields in a cell culture model of infection. Thirteen natural binding-site variants with potential for ketoamide resistance were identified at 10 residues in the protease, near the ketoamide binding site. Rotamer analysis of amino acid side-chain conformations indicated that 2 variants (R155K and D168G) could affect binding of telaprevir more than boceprevir. Measurements of antiviral susceptibility in cell-culture studies were consistent with this observation. Four variants (ie, Q41H, I132V, R155K, and D168G) caused low-to-moderate levels of ketoamide resistance; 3 of these were highly fit (Q41H, I132V, and R155K). Using a comprehensive sequence and structure-based analysis, we showed how natural variation in the hepatitis C virus protease nonstructural protein 3/4A sequences might affect susceptibility to first-generation direct-acting antiviral agents. These findings increase our understanding of the molecular basis of ketoamide resistance among naturally existing viral variants. Copyright © 2012 AGA Institute. Published by Elsevier Inc. All

  13. The ligand-receptor-G-protein ternary complex as a GTP-synthase. steady-state proton pumping and dose-response relationships for beta -adrenoceptors. (United States)

    Broadley, K J; Nederkoorn, P H; Timmerman, H; Timms, D; Davies, R H


    Steady-state solutions are developed for the rate of G alpha.GTP production in a synthase model of the ligand-receptor-G-protein ternary complex activated by a ligand-receptor proton pumping mechanism. The effective rate, k(31), defining the proton transfer, phosphorylation and G alpha.GTP release is a controlling rate of the synthase in the presence of a ligand with an efficient mode of signal activation, the ligand-receptor interaction taking place under effectively equilibrium conditions. The composite rate, however, becomes an amplifying factor in any dose-response relationship. The amplification is a triple product of the rate, k(31), the equilibrium constant associated with the activation of the proton signal, K(act)and the fraction of agonist conformer transmitting the signal, f(*). Where the rate of activation of the proton signal becomes critically inefficient, the rate of activation, k(act 1)replaces k(31)K(act). A correlation between beta(1)-adrenergic receptor-stimulated GDP release and adenylate cyclase activation shows that this correlation is not unique to an exchange reaction. Within the initiating Tyr-Arg-Tyr receptor proton shuttle mechanism, the position of Arg(r156) paralleldictates the high-(R(p)) and low-(R(u)) ligand-binding affinities. These states are close to R(*)and R(0)of the equilibrium model (De Lean et al., 1980, J. Biol. Chem.255, 7108-7117). An increased rate of hydrogen ion diffusion into a receptor mutant can give rise to constitutive activity while increased rates of G-protein release and changes in receptor state balance can contribute to the resultant level of action. Constitutive action will arise from a faster rate of G-protein release alone if proton diffusion in the wild-type receptor contributes to a basal level of G-protein activation. Competitive ligand-receptor occupancy for constitutive mutants shows that, where the rate of G-protein activation from the proportion of ligand-occupied receptors is less than the

  14. Thermoresponsive fluconazole gels for topical delivery: rheological and mechanical properties, in vitro drug release and anti-fungal efficacy. (United States)

    Gandra, Sarath C R; Nguyen, Sanko; Nazzal, Sami; Alayoubi, Alaadin; Jung, Rose; Nesamony, Jerry


    The aim of this study was to develop thermosensitive gels using poloxamers for topical delivery of fluconazole (FLZ). Eight different formulations containing 1% FLZ in poloxamer and a particular co-solvent (propylene glycol (PG) or Transcutol-P) of various concentrations were prepared. The gels were characterized for transition temperatures, rheological and mechanical properties. FLZ permeability and antifungal effect of the gels were also evaluated. Except for one formulation, all gels exhibited thermosensitive property, i.e. transformed from Newtonian (liquid-like) behavior at 20 °C to non-Newtonian (gel-like) behavior at 37 °C. Transcutol-P increased the transition temperature of the formulations, while the opposite effect was observed for PG. At 37 °C, formulations with high poloxamer concentrations (17%) resulted in high viscosity, compressibility and hardness. Formulations containing 17% poloxamer and 20% Transcutol-P and 10% PG, respectively, exhibited high adhesiveness. No significant differences in the in vitro antifungal activity of FLZ were observed among the formulations suggesting that the gel vehicles did not influence the biological effect of FLZ. FLZ permeability decreased with increasing poloxamer concentration. Formulations containing 17% poloxamer and 20% Transcutol-P and 10% PG seemed to be promising in situ gelling systems for the topical delivery of FLZ.

  15. Study of molecular mechanisms of pro-apoptotic activity of NCX 4040, a novel nitric oxide-releasing aspirin, in colon cancer cell lines

    Directory of Open Access Journals (Sweden)

    Vannini Ivan


    Full Text Available Abstract Background Despite numerous studies aimed at verifying the antitumor activity of nitric oxide-releasing nonsteroidal antiflammatory drugs (NO-NSAIDs, little is known about the molecular targets responsible for their antineoplastic properties. In the present study, we investigated the mechanisms underlying the cytotoxicity of NCX 4040, a novel NO-aspirin with promising antineoplastic action, in in vitro human colon cancer models. Methods The effect on tumor growth was evaluated in four human colon cancer cell lines (LoVo, LRWZ, WiDr and LoVo Dx by sulforhodamine B assay, oxidative stress by immunohistochemistry, apoptosis by laddering assay, mitochondrial membrane potential (ΔΨm by flow cytometry, and apoptosis- and chemoresistance-related markers by western-blot and real-time method, respectively. Prostaglandin E2 levels were determined by ELISA. Results NCX 4040 produced a higher cytotoxic effect in all the cell lines than that produced by other NO donors tested. In particular, in LoVo and LRWZ cells, NCX 4040 induced a cytocidal effect and apoptosis through p53 and NAG-1 expression, an early ΔΨm collapse, and a sequential release of cytoplasmatic cytochrome c and caspase -9 and -3 active forms. 8-hydroxyguanine lesions, indicative of oxidative stress, were also observed. Conversely, in WiDr line, the drug caused a cytocidal effect, albeit not through apoptosis, and a concomitant increase in COX-2 activity. In LoVo Dx line, characterized by high levels drug resistance and DNA repair-related markers, only a cytostatic effect was observed, again in concomitance with the increase in COX-2 enzyme activity. Conclusion This study highlights the multiplicity of mechanisms involved in sensitivity or resistance to NCX 4040 and could provide useful indications for tailored therapy by identifying potentially drug-responsive tumors.

  16. A poly(glycerol sebacate)-coated mesoporous bioactive glass scaffold with adjustable mechanical strength, degradation rate, controlled-release and cell behavior for bone tissue engineering. (United States)

    Lin, Dan; Yang, Kai; Tang, Wei; Liu, Yutong; Yuan, Yuan; Liu, Changsheng


    Various requirements in the field of tissue engineering have motivated the development of three-dimensional scaffold with adjustable physicochemical properties and biological functions. A series of multiparameter-adjustable mesoporous bioactive glass (MBG) scaffolds with uncrosslinked poly(glycerol sebacate) (PGS) coating was prepared in this article. MBG scaffold was prepared by a modified F127/PU co-templating process and then PGS was coated by a simple adsorption and lyophilization process. Through controlling macropore parameters and PGS coating amount, the mechanical strength, degradation rate, controlled-release and cell behavior of the composite scaffold could be modulated in a wide range. PGS coating successfully endowed MBG scaffold with improved toughness and adjustable mechanical strength covering the bearing range of trabecular bone (2-12MPa). Multilevel degradation rate of the scaffold and controlled-release rate of protein from mesopore could be achieved, with little impact on the protein activity owing to an "ultralow-solvent" coating and "nano-cavity entrapment" immobilization method. In vitro studies indicated that PGS coating promoted cell attachment and proliferation in a dose-dependent manner, without affecting the osteogenic induction capacity of MBG substrate. These results first provide strong evidence that uncrosslinked PGS might also yield extraordinary achievements in traditional MBG scaffold. With the multiparameter adjustability, the composite MBG/PGS scaffolds would have a hopeful prospect in bone tissue engineering. The design considerations and coating method of this study can also be extended to other ceramic-based artificial scaffolds and are expected to provide new thoughts on development of future tissue engineering materials.

  17. Cultured Mesenchymal Stem Cells Stimulate an Immune Response by Providing Immune Cells with Toll-Like Receptor 2 Ligand. (United States)

    Weinstock, Ada; Pevsner-Fischer, Meirav; Porat, Ziv; Selitrennik, Michael; Zipori, Dov


    Mesenchymal stem cells (MSCs) serve as supporting and regulatory cells, by providing tissues with multiple factors and are also known for their immunosuppressive capabilities. Our laboratory had previously shown that MSCs expressed toll-like receptor (TLR) 2 and are activated by its ligand Pam3Cys. TLR2 is an important component of the innate immune system, as it recognizes bacterial lipopeptides, thus priming a pro-inflammatory immune response. This study showed that Pam3Cys attached extensively to cells of both wild-type and TLR2 deficient cultured MSCs, thus, independently of TLR2. The TLR2 independent binding occurred through the adsorption of the palmitoyl moieties of Pam3Cys. It was further showed that Pam3Cys was transferred from cultured MSCs to immune cells. Moreover, Pam3Cys provided to the immune cells induced a pro-inflammatory response in vitro and in vivo. Overall, it is demonstrated herein that a TLR2 ligand bound to MSCs also through a TLR2 independent mechanism. Furthermore, the ligand incorporated by MSCs is subsequently released to stimulate an immune response both in vitro and in vivo. It is thus suggested that during bacterial infection, stromal cells may retain a reservoir of the TLR2 ligands, in a long-term manner, and release them slowly to maintain an immune response.

  18. Insight into the neuroendocrine site and cellular mechanism by which cortisol suppresses pituitary responsiveness to gonadotropin-releasing hormone. (United States)

    Breen, Kellie M; Davis, Tracy L; Doro, Lisa C; Nett, Terry M; Oakley, Amy E; Padmanabhan, Vasantha; Rispoli, Louisa A; Wagenmaker, Elizabeth R; Karsch, Fred J


    Stress-like elevations in plasma glucocorticoids rapidly inhibit pulsatile LH secretion in ovariectomized sheep by reducing pituitary responsiveness to GnRH. This effect can be blocked by a nonspecific antagonist of the type II glucocorticoid receptor (GR) RU486. A series of experiments was conducted to strengthen the evidence for a mediatory role of the type II GR and to investigate the neuroendocrine site and cellular mechanism underlying this inhibitory effect of cortisol. First, we demonstrated that a specific agonist of the type II GR, dexamethasone, mimics the suppressive action of cortisol on pituitary responsiveness to GnRH pulses in ovariectomized ewes. This effect, which became evident within 30 min, documents mediation via the type II GR. We next determined that exposure of cultured ovine pituitary cells to cortisol reduced the LH response to pulse-like delivery of GnRH by 50% within 30 min, indicating a pituitary site of action. Finally, we tested the hypothesis that suppression of pituitary responsiveness to GnRH in ovariectomized ewes is due to reduced tissue concentrations of GnRH receptor. Although cortisol blunted the amplitude of GnRH-induced LH pulses within 1-2 h, the amount of GnRH receptor mRNA or protein was not affected over this time frame. Collectively, these observations provide evidence that cortisol acts via the type II GR within the pituitary gland to elicit a rapid decrease in responsiveness to GnRH, independent of changes in expression of the GnRH receptor.

  19. 生物质热解氯的析出机制研究%Mechanism Study of Chlorine Release During Biomass Pyrolysis

    Institute of Scientific and Technical Information of China (English)

    吴鹏; 余春江; 柏继松; 李廉明; 黄芳


    以稻草为主要研究对象,以含氯生物质模化物为对照,通过管式炉、热重红外联用以及理论计算,对生物质中无机氯的热解析出机制进行探索.管式炉热解试验表明:低温下(200~600℃)稻草和模化物中的KC1可以与活性基团反应而析出HCl;灰成分对低温条件下氯析出的过程可能有催化促进作用;模化物中的氯在高温区(>600℃)主要以气态碱金属氯化物形式析出.TG-FTIR试验表明:稻草热解脱挥发分过程与HCl的析出之间存在直接的关联;管式炉稻草热解过程在较低温度条件下析出的Cl是HCl;在高温区,碱金属氯化物和灰成分SiO2之间未发生显著的化学反应.理论计算表明:生物质中的Cl是以碱金属氯化物形式存在的;碱金属氯化物在高温下(>700℃)主要以蒸汽态进入气相;碱金属氯化物与SiO2的反应在高温下(800~900℃)可以进行.%Taking straw as a study object and a chlorine-based biomass model compound as a reference, the author analyzed the release mechanism of Cl during biomass pyrolysis by tube furnace, thermogravimetric-Fourier transform infrared spectroscopy(TG-FTIR) and theoretical calculation. Tube furnace pyrolysis tests show that KC1 in straw and model compound reacts with organic functional groups and generates HC1 at 200—600℃; straw ash might promote the release of chlorine under low temperature; and chlorine in the model compound releases in the form of gaseous alkali metal chlorides at temperature above 600 ℃. TG-FTIR results show that the release of HC1 relates directly with the release of volatile components; Cl is released in the form of is HC1 at low temperature during the tube furnace pyrolysis tests; chemical reaction between alkali metal chlorides and SiO2 is not significant at high temperature. Theoretical calculations show that Cl of biomass exists in the form of alkali metal chlorides; the alkali metal chlorides would go into gas phase at high

  20. Ligand modeling and design

    Energy Technology Data Exchange (ETDEWEB)

    Hay, B. [Pacific Northwest Lab., Richland, WA (United States)


    The purpose of this work is to develop and implement a molecular design basis for selecting organic ligands that would be used tin applications for the cost-effective removal of specific radionuclides from nuclear waste streams.

  1. The SQM/COSMO filter: reliable native pose identification based on the quantum-mechanical description of protein-ligand interactions and implicit COSMO solvation. (United States)

    Pecina, Adam; Meier, René; Fanfrlík, Jindřich; Lepšík, Martin; Řezáč, Jan; Hobza, Pavel; Baldauf, Carsten


    Current virtual screening tools are fast, but reliable scoring is elusive. Here, we present the 'SQM/COSMO filter', a novel scoring function featuring a quantitative semiempirical quantum mechanical (SQM) description of all types of noncovalent interactions coupled with implicit COSMO solvation. We show unequivocally that it outperforms eight widely used scoring functions. The accuracy and chemical generality of the SQM/COSMO filter make it a perfect tool for late stages of virtual screening.

  2. Dual role of mitochondria in producing melatonin and driving GPCR signaling to block cytochrome c release. (United States)

    Suofu, Yalikun; Li, Wei; Jean-Alphonse, Frédéric G; Jia, Jiaoying; Khattar, Nicolas K; Li, Jiatong; Baranov, Sergei V; Leronni, Daniela; Mihalik, Amanda C; He, Yanqing; Cecon, Erika; Wehbi, Vanessa L; Kim, JinHo; Heath, Brianna E; Baranova, Oxana V; Wang, Xiaomin; Gable, Matthew J; Kretz, Eric S; Di Benedetto, Giulietta; Lezon, Timothy R; Ferrando, Lisa M; Larkin, Timothy M; Sullivan, Mara; Yablonska, Svitlana; Wang, Jingjing; Minnigh, M Beth; Guillaumet, Gérald; Suzenet, Franck; Richardson, R Mark; Poloyac, Samuel M; Stolz, Donna B; Jockers, Ralf; Witt-Enderby, Paula A; Carlisle, Diane L; Vilardaga, Jean-Pierre; Friedlander, Robert M


    G protein-coupled receptors (GPCRs) are classically characterized as cell-surface receptors transmitting extracellular signals into cells. Here we show that central components of a GPCR signaling system comprised of the melatonin type 1 receptor (MT1), its associated G protein, and β-arrestins are on and within neuronal mitochondria. We discovered that the ligand melatonin is exclusively synthesized in the mitochondrial matrix and released by the organelle activating the mitochondrial MT1 signal-transduction pathway inhibiting stress-mediated cytochrome c release and caspase activation. These findings coupled with our observation that mitochondrial MT1 overexpression reduces ischemic brain injury in mice delineate a mitochondrial GPCR mechanism contributing to the neuroprotective action of melatonin. We propose a new term, "automitocrine," analogous to "autocrine" when a similar phenomenon occurs at the cellular level, to describe this unexpected intracellular organelle ligand-receptor pathway that opens a new research avenue investigating mitochondrial GPCR biology.

  3. Characterization of Selectin Ligands on Hematopoietic Stem Cells

    KAUST Repository

    Mahmood, Hanan


    Successful bone marrow (BM) transplantation requires the homing of the transplanted hematopoietic stem/progenitor cells (HSPCs) to their bone marrow niche, where they undergo differentiation to form mature cells that are eventually released into the peripheral blood. However, the survival rate of patients receiving BM transplants is poor since many of the transplanted HSPCs do not make it to their BM niches in the recipient’s body. Since the availability of HSPCs from traditional sources is limited, transplanting more number of HSPCs is not a solution to this problem. This study aims to characterize the adhesion molecules mediating cell migration in order to better understand the adhesion mechanisms of HSCs with the bone marrow endothelium. This will aid in developing future tools to improve the clinical transplantation of HSPCs. This study also aims to understand the factors that influence HSPC proliferation in the bone marrow niche. E-selectin plays an important role in the process of homing; however, its ligands on HSPCs are not well characterized. We used western blotting and immunoprecipitation to show that endomucin is expressed on HSPCs and plays a role in the binding of HSPCs to E-selectin. We also studied the effect of recombinant E-selectin on the expression of a newly characterized E-selectin ligand in our lab, CD34, in HSPCs. This will provide us insight into novel roles for endomucin and E-selectin and help us to understand the factors influencing HSPC migration to BM endothelium.

  4. Ethylene Polymerization Catalyzed by Monocyclopentadienyl Titanium Complex Containing 8-Quinolinolato Ligand and ADF Study on the Formation Mechanism of Active Species

    Institute of Scientific and Technical Information of China (English)

    Jianjun Yi; Xiaoguang Zhao; Han Zhou; Zhenhua Jing


    A monocyclopentadienyl titanium complex containing 8-quinolinolato (QCpTiCl2) was synthesized. Its activities in ethylene polymerization at various Al/Ti molar ratios, different temperatures and activation time were investigated. The activity with a Al/Ti molar ratio of 500 exhibited a maximum of 2.8× 105 g/(mol.h) at 30 ℃. The activation time of QCpTiCl2 with MAO before polymerization also plays a role on the activity. The structural properties of the produced polyethylene (molecular weight, molecular weight distribution and melting point) were discussed. Kinetic behaviors of ethylene polymerization with the QCpTiCl2/MAO system at different Al/Ti molar ratios were studied. For the QCpTiMeCl/MAO system and the CpTiMe2Cl/MAO system, binding energies of the examined intermediates were calculated by quantum-mechanical method based on ADF program, respectively. It is confirmed that the chlorinebridged adduct formed by the reaction of QCpTiMeCl with MAO is thermodynamically steady. In the case of the QCpTiMeCl/MAO system, olefin-separated ion pair (OSIP) mechanism is much favorable than ion-pair dissociation (IPD) mechanism. The experimental result on the CpTiMe2Cl/MAO system showed lower activity for ethylene polymerization than that on the QCpTiMeCl/MAO system, which revealed that the CpTiMe2Cl/MAO system is unfavorable to form active species with ethylene.

  5. Dissection of the molecular mechanism of action of GW5638, a novel estrogen receptor ligand, provides insights into the role of estrogen receptor in bone. (United States)

    Willson, T M; Norris, J D; Wagner, B L; Asplin, I; Baer, P; Brown, H R; Jones, S A; Henke, B; Sauls, H; Wolfe, S; Morris, D C; McDonnell, D P


    The estrogen receptor (ER) mixed agonists tamoxifen and raloxifene have been shown to protect against bone loss in ovariectomized rats. However, the mechanism by which these compounds manifest their activity in bone is unknown. We have used a series of in vitro screens to select for compounds that are mechanistically distinct from tamoxifen and raloxifene in an effort to define the properties of an ER modulator required for bone protection. Using this approach, we identified a novel high affinity ER antagonist, GW5638, which when assayed in vitro functions as an ER antagonist, inhibiting the agonist activity of estrogen, tamoxifen, and raloxifene and reversing the "inverse agonist" activity of the pure antiestrogen ICI182,780. Thus, GW5638 appears to function as an antagonist in these in vitro systems, although in a manner distinct from other known ER modulators. Predictably, therefore, GW5638 alone displays minimal uterotropic activity in ovariectomized rats, but will inhibit the agonist activity of estradiol in this environment. Unexpectedly, however, this compound functions as a full ER agonist in bone and the cardiovascular system. These data suggest that the mechanism by which ER operates in different cells is not identical, and that classical agonist activity is not required for the bone protective activity of ER modulators.

  6. Influence of Citric Acid on the Metal Release of Stainless Steels

    Energy Technology Data Exchange (ETDEWEB)

    Mazinanian, N.; Wallinder, I. Odnevall; Hedberg, Y. S. [KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry, Division of Surface and Corrosion Science, Stockholm (Sweden)


    Knowledge of how metal releases from the stainless steels used in food processing applications and cooking utensils is essential within the framework of human health risk assessment. A new European standard test protocol for testing metal release in food contact materials made from metals and alloys has recently been published by the Council of Europe. The major difference from earlier test protocols is the use of citric acid as the worst-case food simulant. The objectives of this study were to assess the effect of citric acid at acidic, neutral, and alkaline solution pH on the extent of metal release for stainless steel grades AISI 304 and 316, commonly used as food contact materials. Both grades released lower amounts of metals than the specific release limits when they were tested according to test guidelines. The released amounts of metals were assessed by means of graphite furnace atomic absorption spectroscopy, and changes in the outermost surface composition were determined using X-ray photoelectron spectroscopy. The results demonstrate that both the pH and the complexation capacity of the solutions affected the extent of metal release from stainless steel and are discussed from a mechanistic perspective. The outermost surface oxide was significantly enriched in chromium upon exposure to citric acid, indicating rapid passivation by the acid. This study elucidates the effect of several possible mechanisms, including complex ion- and ligand-induced metal release, that govern the process of metal release from stainless steel under passive conditions in solutions that contain citric acid.

  7. CLE Peptides in Plants: Proteolytic Processing,Structure-Activity Relationship, and Ligand-Receptor Interaction

    Institute of Scientific and Technical Information of China (English)

    Xiaoming Gao; Yongfeng Guo


    Ligand-receptor signaling initiated by the CLAVATA3/ENDOSPERM SURROUNDING REGION (CLE) family peptides is critical in regulating cell division and differentiation in meristematic tissues in plants.Biologically active CLE peptides are released from precursor proteins via proteolytic processing.The mature form of CLE ligands consists of 12-13 amino acids with several post-translational modifications.This review summarizes recent progress toward understanding the proteolytic activities that cleave precursor proteins to release CLE peptides,the molecular structure and function of mature CLE ligands,and interactions between CLE ligands and corresponding leucine-rich repeat (LRR) receptor-like kinases (RLKs).

  8. An attempt to increase efficacy of moth mating disruption by co-releasing pheromones with kairomones and to understand possible underlying mechanisms of this technique. (United States)

    Stelinski, Lukasz L; Gut, Larry J; Miller, James R


    Pheromone-based mating disruption is used worldwide for management of the internal fruit feeding codling moth, Cydia pomonella (L.). There has been recent interest in the potential of improving mating disruption of C. pomonella, and potentially other insect species in general, by broadcasting combinations of pheromone and attractive host-plant kairomones. Given that such kairomones are attractive by themselves (often to both sexes), and also enhance male moth response to their pheromone, it is possible that the effects of competitive attraction and potentially other mechanisms of disruption might be increased. Herein, we tested the hypothesis that mating disruption of C. pomonella could be enhanced by co-deploying pheromone with either of two kairomones: (2E, 4Z)-2, 4-decadienoate (pear ester), or (E)-β-farnesene, as compared with various pheromone blend components alone. When deployed individually, each kairomone caused a low level of synthetic lure trap disruption and (E)-β-farnesene also caused disruption of mating as measured by tethering virgin females. However, combined release of either pear ester or (E)-β-farnesene with pheromone within the same dispenser or as a co-deployed dispenser treatment, respectively, did not increase the level of mating disruption as compared with deploying pheromone alone. Disruption efficacy did not decline when reducing the amount of (E,E)-8,10-dodecadien-1-ol (codlemone) in dispensers by fourfold, when combined with pear ester. C. pomonella readily were observed briefly approaching all dispenser types (with and without pheromone) in the field. Exposure of male C. pomonella to pear ester alone in a manner mimicking observed field exposures did not reduce the number of males able to contact a female-mimic pheromone lure in flight tunnel assays. Also, reduction of male moth behavioral response to pheromone was similar after exposure to codlemone alone, and codlemone and pear ester after exposures that mimicked those observed in

  9. Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties (United States)

    Möncke, D.; Kamitsos, E. I.; Palles, D.; Limbach, R.; Winterstein-Beckmann, A.; Honma, T.; Yao, Z.; Rouxel, T.; Wondraczek, L.


    A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn2+ enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb2+ and Bi3+ induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was determined

  10. DNA-histone complexes as ligands amplify cell penetration and nuclear targeting of anti-DNA antibodies via energy-independent mechanisms. (United States)

    Zannikou, Markella; Bellou, Sofia; Eliades, Petros; Hatzioannou, Aikaterini; Mantzaris, Michael D; Carayanniotis, George; Avrameas, Stratis; Lymberi, Peggy


    We have generated three monoclonal cell-penetrating antibodies (CPAbs) from a non-immunized lupus-prone (NZB × NZW)F1 mouse that exhibited high anti-DNA serum titres. These CPAbs are polyreactive because they bind to DNA and other cellular components, and localize mainly in the nucleus of HeLa cells, albeit with a distinct nuclear labelling profile. Herein, we have examined whether DNA-histone complexes (DHC) binding to CPAbs, before cell entry, could modify the cell penetration of CPAbs or their nuclear staining properties. By applying confocal microscopy and image analysis, we found that extracellular binding of purified CPAbs to DHC significantly enhanced their subsequent cell-entry, both in terms of percentages of positively labelled cells and fluorescence intensity (internalized CPAb amount), whereas there was a variable effect on their nuclear staining profile. Internalization of CPAbs, either alone or bound to DHC, remained unaltered after the addition of endocytosis-specific inhibitors at 37° or assay performance at 4°, suggesting the involvement of energy-independent mechanisms in the internalization process. These findings assign to CPAbs a more complex pathogenetic role in systemic lupus erythematosus where both CPAbs and nuclear components are abundant.

  11. Probing ligand-binding modes and binding mechanisms of benzoxazole-based amide inhibitors with soluble epoxide hydrolase by molecular docking and molecular dynamics simulation. (United States)

    Chen, Hang; Zhang, Ying; Li, Liang; Han, Ju-Guang


    Soluble epoxide hydrolase (sEH) has become a new therapeutic target for treating a variety of human diseases. The inhibition of human sEH hydrolase activity was studied by molecular docking and molecular dynamics (MD) simulation techniques. A set of six benzoxazole-based amide inhibitors binding to sEH has been studied through molecular docking, MD simulation, free energy calculations, and energy decomposition analysis. On the basis of molecular mechanics-generalized Born/surface area (MM-GB/SA) computation and normal-mode analysis (NMA), the obtained results indicate that the rank of calculated binding free energies (ΔΔGTOT) of these inhibitors is in excellent agreement with that of experimental bioactivity data (IC50). The correlation coefficient (r(2)) between the predicted ΔΔGTOT and IC50 is 0.88. van der Waals energies are the largest component of the total energies, and the entropy changes play an indispensable role in determining the ΔΔGTOT. Rational binding modes were discussed and determined by the docking results and binding free energies. The free energy decomposition of each residue reveals that the residue Trp334 dominates the most binding free energies among all residues and that the activities for these molecules to the sEH are not decided by hydrogen bonds or a certain residue but by the common effect of multiple side chains in the active site.

  12. CLiBE: a database of computed ligand binding energy for ligand-receptor complexes. (United States)

    Chen, X; Ji, Z L; Zhi, D G; Chen, Y Z


    Consideration of binding competitiveness of a drug candidate against natural ligands and other drugs that bind to the same receptor site may facilitate the rational development of a candidate into a potent drug. A strategy that can be applied to computer-aided drug design is to evaluate ligand-receptor interaction energy or other scoring functions of a designed drug with that of the relevant ligands known to bind to the same binding site. As a tool to facilitate such a strategy, a database of ligand-receptor interaction energy is developed from known ligand-receptor 3D structural entries in the Protein Databank (PDB). The Energy is computed based on a molecular mechanics force field that has been used in the prediction of therapeutic and toxicity targets of drugs. This database also contains information about ligand function and other properties and it can be accessed at The computed energy components may facilitate the probing of the mode of action and other profiles of binding. A number of computed energies of some PDB ligand-receptor complexes in this database are studied and compared to experimental binding affinity. A certain degree of correlation between the computed energy and experimental binding affinity is found, which suggests that the computed energy may be useful in facilitating a qualitative analysis of drug binding competitiveness.

  13. Structural basis for ligand recognition of incretin receptors

    DEFF Research Database (Denmark)

    Underwood, Christina Rye; Parthier, Christoph; Reedtz-Runge, Steffen


    been solved recently by X-ray crystallography. The crystal structures reveal a similar fold of the ECD and a similar mechanism of ligand binding, where the ligand adopts an α-helical conformation. Residues in the C-terminal part of the ligand interact directly with the ECD and hydrophobic interactions...... appear to be the main driving force for ligand binding to the ECD of incretin receptors. Obviously, the-still missing-structures of full-length incretin receptors are required to construct a complete picture of receptor function at the molecular level. However, the progress made recently in structural...

  14. Rac1 regulates the release of Weibel-Palade Bodies in human aortic endothelial cells

    Institute of Scientific and Technical Information of China (English)

    YANG Shui-xiang 杨水祥; YAN Juan 闫娟; Shailesh S. Deshpande; Kaikobad Irani; Charles J. Lowenstein


    Background The release of Weibel-Palade Bodies (WPB) is a form of endothelial cell activation. But the signal transduction pathway leading to WPB release is not yet defined. We hypothesized that small G-protein rac1 and reactive oxygen species (ROS) mediate the ligand induced release of Weibel-Palade Bodies. Methods We tested this hypothesis by using wild-type and mutant adenoviral rac1 expression vectors, and by manipulating the production and destruction of superoxide and hydrogen peroxide in human aortic endothelial cells (HAEC). Results Thrombin (1.0 Unit, 30 min) induced the increase of WPB release by 3.7-fold in HAEC, and that H2O2 (0.1 mmol/L, 30 min) induced by 4.5-fold. These results correlated with thrombin-stimulated activation of rac-GTP binding activity by 3.5-fold, and increase of ROS production by 3.4-fold. The dominant negative adenoviral rac-N17 gene transfer dramatically inhibited the release of WPB by 64.2% (control) and 77.3% (thrombin-stimulation), and decreased ROS production by 65.5% (control) and 83.6% (thrombin-stimulation) compared with non-infected cells, respectively. Anti-oxidants, catalase and N-acetyl-cysteine significantly decreased the release of WPB by 34% and 79% in control cells, and further decreased by 63.6% and 46.7% in rac-N17 transferred cells compared with non-infected cells. We also confirmed that rac1 was located upstream of ROS in the WPB release pathway. Conclusions Small G-protein rac1 medicates ligand-induced release of Weibel-Palade Bodies in human aortic endothelial cells, and the signal pathway of WPB release is a rac1-dependent ROS regulating mechanism.

  15. Landscape of protein-small ligand binding modes. (United States)

    Kasahara, Kota; Kinoshita, Kengo


    Elucidating the mechanisms of specific small-molecule (ligand) recognition by proteins is a long-standing conundrum. While the structures of these molecules, proteins and ligands, have been extensively studied, protein-ligand interactions, or binding modes, have not been comprehensively analyzed. Although methods for assessing similarities of binding site structures have been extensively developed, the methods for the computational treatment of binding modes have not been well established. Here, we developed a computational method for encoding the information about binding modes as graphs, and assessing their similarities. An all-against-all comparison of 20,040 protein-ligand complexes provided the landscape of the protein-ligand binding modes and its relationships with protein- and chemical spaces. While similar proteins in the same SCOP Family tend to bind relatively similar ligands with similar binding modes, the correlation between ligand and binding similarities was not very high (R(2)  = 0.443). We found many pairs with novel relationships, in which two evolutionally distant proteins recognize dissimilar ligands by similar binding modes (757,474 pairs out of 200,790,780 pairs were categorized into this relationship, in our dataset). In addition, there were an abundance of pairs of homologous proteins binding to similar ligands with different binding modes (68,217 pairs). Our results showed that many interesting relationships between protein-ligand complexes are still hidden in the structure database, and our new method for assessing binding mode similarities is effective to find them.

  16. Ligand Exchange Kinetics of Environmentally Relevant Metals

    Energy Technology Data Exchange (ETDEWEB)

    Panasci, Adele Frances [Univ. of California, Davis, CA (United States)


    The interactions of ground water with minerals and contaminants are of broad interest for geochemists but are not well understood. Experiments on the molecular scale can determine reaction parameters (i.e. rates of ligand exchange, activation entropy, activation entropy, and activation volume) that can be used in computations to gain insight into reactions that occur in natural groundwaters. Experiments to determine the rate of isotopic ligand exchange for three environmentally relevant metals, rhodium (Rh), iron (Fe), and neptunium (Np), are described. Many environmental transformations of metals (e.g. reduction) in soil occur at trivalent centers, Fe(III) in particular. Contaminant ions absorb to mineral surfaces via ligand exchange, and the reversal of this reaction can be dangerous, releasing contaminants into the environment. Ferric iron is difficult to study spectroscopically because most of its complexes are paramagnetic and are generally reactive toward ligand exchange; therefore, Rh(III), which is diamagnetic and less reactive, was used to study substitution reactions that are analogous to those that occur on mineral oxide surfaces. Studies on both Np(V) and Np(VI) are important in their own right, as 237Np is a radioactive transuranic element with a half-life of 2 million years.

  17. Stimulatory effect of an algal fucoidan on the release of vascular endothelial tissue-type plasminogen activator as a mechanism of fucoidan-mediated thrombolysis. (United States)

    Min, Soon-Ki; Han, Sung-Mi; Jang, Jae-Seok; Kim, Jong-Ki


    Identifying a pharmacological means for increasing the production of tissue-type plasminogen activator (t-PA) is always desirable to cure impaired production of this enzyme. An algal fucoidan has been shown to exhibit both novel thrombolytic and synergistic stimulatory effects in a mouse thrombosis model. The plasma levels of active t-PA were measured in mouse arterial thrombus models that were treated with various fucoidans to investigate the mechanism of thrombolysis. The mean plasma level of active t-PA after the infusion of fucoidan was 2.136 ± 0.231 ng/ml for nonthrombolytic Fucus fucoidan and 3.917 ± 0.0.529 ng/ml for thrombolytic Undaria fucoidan, which resulted in a 1.56-2.29-fold increase compared with the healthy control group (1.706 ± 0.194 ng/ml) and the untreated thrombus group (2.506 ± 0.301 ng/ml) (P fucoidan has demonstrated to exert a thrombolytic and stimulatory effect via the induction of t-PA release in a dose-dependent manner in an arterial thrombosis model.

  18. In vitro screening of major neurotransmitter systems possibly involved in the mechanism of action of antibodies to S100 protein in released-active form

    Directory of Open Access Journals (Sweden)

    Gorbunov EA


    Full Text Available Evgeniy A Gorbunov, Irina A Ertuzun, Evgeniya V Kachaeva, Sergey A Tarasov, Oleg I EpsteinOOO “NPF “MATERIA MEDICA HOLDING”, Moscow, Russian FederationAbstract: Experimentally and clinically, it was shown that released-active form of antibodies to S100 protein (RAF of Abs to S100 exerts a wide range of pharmacological activities: anxiolytic, antiasthenic, antiaggressive, stress-protective, antihypoxic, antiischemic, neuroprotective, and nootropic. The purpose of this study was to determine the influence of RAF of Abs to S100 on major neurotransmitter systems (serotoninergic, GABAergic, dopaminergic, and on sigma receptors as well which are possibly involved in its mechanism of pharmacological activity. Radioligand binding assays were used for assessment of the drug influence on ligand–receptor interaction. [35S]GTPγS binding assay, cyclic adenosine monophosphate HTRF™, cellular dielectric spectroscopy assays, and assays based on measurement of intracellular concentration of Ca2+ ions were used for assessment of agonist or antagonist properties of the drug toward receptors. RAF of Abs to S100 increased radioligand binding to 5-HT1F, 5-HT2B, 5-HT2Cedited, 5-HT3, and to D3 receptors by 142.0%, 131.9%, 149.3%, 120.7%, and 126.3%, respectively. Also, the drug significantly inhibited specific binding of radioligands to GABAB1A/B2 receptors by 25.8%, and to both native and recombinant human sigma1 receptors by 75.3% and 40.32%, respectively. In the functional assays, it was shown that the drug exerted antagonism at 5-HT1B, D3, and GABAB1A/B2 receptors inhibiting agonist-induced responses by 23.24%, 32.76%, and 30.2%, respectively. On the contrary, the drug exerted an agonist effect at 5-HT1A receptors enhancing receptor functional activity by 28.0%. The pharmacological profiling of RAF of Abs to S100 among 27 receptor provides evidence for drug-related modification of major neurotransmitter systems.Keywords: dopamine agent, released

  19. CB receptor ligands from plants. (United States)

    Woelkart, Karin; Salo-Ahen, Outi M H; Bauer, Rudolf


    Advances in understanding the physiology and pharmacology of the endogenous cannabinoid system have potentiated the interest of cannabinoid receptors as potential therapeutic targets. Cannabinoids have been shown to modulate a variety of immune cell functions and have therapeutic implications on central nervous system (CNS) inflammation, chronic inflammatory conditions such as arthritis, and may be therapeutically useful in treating autoimmune conditions such as multiple sclerosis. Many of these drug effects occur through cannabinoid receptor signalling mechanisms and the modulation of cytokines and other gene products. Further, endocannabinoids have been found to have many physiological and patho-physiological functions, including mood alteration and analgesia, control of energy balance, gut motility, motor and co-ordination activities, as well as alleviation of neurological, psychiatric and eating disorders. Plants offer a wide range of chemical diversity and have been a growing domain in the search for effective cannabinoid ligands. Cannabis sativa L. with the known plant cannabinoid, Delta(9-)tetrahydrocannabinol (THC) and Echinacea species with the cannabinoid (CB) receptor-binding lipophilic alkamides are the best known herbal cannabimimetics. This review focuses on the state of the art in CB ligands from plants, as well their possible therapeutic and immunomodulatory effects.

  20. Systematic study of ligand structures of metal oxide EUV nanoparticle photoresists

    KAUST Repository

    Jiang, Jing


    Ligand stabilized metal oxide nanoparticle resists are promising candidates for EUV lithography due to their high sensitivity for high-resolution patterning and high etching resistance. As ligand exchange is responsible for the patterning mechanism, we systematically studied the influence of ligand structures of metal oxide EUV nanoparticles on their sensitivity and dissolution behavior. ZrO2 nanoparticles were protected with various aromatic ligands with electron withdrawing and electron donating groups. These nanoparticles have lower sensitivity compared to those with aliphatic ligands suggesting the structures of these ligands is more important than their pka on resist sensitivity. The influence of ligand structure was further studied by comparing the nanoparticles’ solubility for a single type ligand to mixtures of ligands. The mixture of nanoparticles showed improved pattern quality. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  1. Towards an interpretation of the mechanism of the actinides(III)/lanthanides(III) separation by synergistic solvent extraction with nitrogen-containing polydendate ligands; Vers une interpretation des mecanismes de la separation actinides(III)/lanthanides(III) par extraction liquide-liquide synergique impliquant des ligands polyazotes

    Energy Technology Data Exchange (ETDEWEB)

    Francois, N. [CEA/VALRHO - site de Marcoule, Dept. de Recherche en Retraitement et en Vitrification, (DRRV), 30 - Marcoule (France); Universite Henri Poincare, 54 - Vandoeuvre-les-Nancy (France)


    In the field of the separation of long-lived radionuclides from the wastes produced by nuclear fuel reprocessing, aromatic nitrogen-containing polydendate ligands are potential candidates for the selective extraction, alone or in synergistic mixture with acidic extractants, of trivalent actinides from trivalent lanthanides. The first part of this work deals with the complexation of trivalent f cations with various nitrogen-containing ligands (poly-pyridine analogues). Time-resolved laser-induced fluorimetry (TRLIF) and UV-visible spectrophotometry were used to determine the nature and evaluate the stability of each complex. Among the ligands studied, the least basic Me-Btp proved to be highly selective towards americium(III) in acidic solution. In the second part, two synergistic systems (nitrogen-containing polydendate ligand and lipophilic carboxylic acid) are studied and compared in regard to the extraction and separation of lanthanides(III) and actinides(III). TRLIF and gamma spectrometry allowed the nature of the extracted complexes and the optimal conditions of efficiency of both systems to be determined. Comparison between these different studies showed that the selectivity of complexation of trivalent f cations by a given nitrogen-containing polydendate ligand could not always be linked to the Am(III)Eu(III) selectivity reached in synergistic extraction. The latter depends on the 'balance' between the acid-basic properties on the one hand, and on the hard-soft characteristics on the other hand, of both components of synergistic system. (author)

  2. pH-controlled quaternary ammonium herbicides capture/release by carboxymethyl-β-cyclodextrin functionalized magnetic adsorbents: Mechanisms and application

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chang; Wang, Peng [Department of Applied Chemistry, China Agricultural University, No. 2 West Yuanmingyuan Road, Beijing 100193 (China); Shen, Zhigang [Zhong Nong Fa Seed Industry Group Co. Ltd, Beijing 600313 (China); Liu, Xueke; Zhou, Zhiqiang [Department of Applied Chemistry, China Agricultural University, No. 2 West Yuanmingyuan Road, Beijing 100193 (China); Liu, Donghui, E-mail: [Department of Applied Chemistry, China Agricultural University, No. 2 West Yuanmingyuan Road, Beijing 100193 (China)


    In our work, the pH-controlled magnetic solid phase extraction for the determination of paraquat and diquat was introduced firstly. Furthermore, to clarify the mechanism of carboxymethyl-β-cyclodextrin functionalized magnetic adsorbents, we studied the pH-responsive supramolecular interaction between carboxymethyl-β-cyclodextrin (CM-β-CD) and paraquat/diquat by ultraviolet–visible (UV–vis) spectroscopy and nuclear magnetic resonance (NMR) experiment, and the energy-minimized structures were also obtained. Then, the functional group CM-β-CD was modified on the surface of magnetic materials to synthesize the adsorbent. The Fourier transform infrared spectrum (FT-IR) results proved the successful modification of CM-β-CD. Thus, this absorbent was applied for the determination of paraquat and diquat in water. Under the optimal condition, limits of detection (LODs) of paraquat and diquat were 0.8 μg L{sup −1} and 0.9 μg L{sup −1}, relative standard deviations (RSD) and recoveries varied 0.7–4.6% and 86.5–106.6%, respectively. Good recoveries (70.2–100.0%) and low RSD (1.7–9.6%) were achieved in analyzing spiked water samples. Furthermore, with the capillary electrophoresis (CE) as the analyser, the whole analytical process did not need the attendance of organic solvents. - Highlights: • The carboxymethyl-β-cyclodextrin functionalized magnetic adsorbents were synthesized. • The adsorbents could capture or release quaternary ammonium herbicides by changing pH. • The adsorbents were applied in the analysis of real water samples. • There is no attendance of organic solvents in the whole analysis process.

  3. Dimeric ligands for GPCRs involved in human reproduction : synthesis and biological evaluation

    NARCIS (Netherlands)

    Bonger, Kimberly Michelle


    Dimeric ligands for G-protein coupled receptors that are involved in human reproduction, namely the gonadotropin releasing hormone receptor, the luteinizing hormone receptor and the follicle-stimulating hormone receptor, were synthesized and biologically evaluated.

  4. LigandRNA: computational predictor of RNA-ligand interactions. (United States)

    Philips, Anna; Milanowska, Kaja; Lach, Grzegorz; Bujnicki, Janusz M


    RNA molecules have recently become attractive as potential drug targets due to the increased awareness of their importance in key biological processes. The increase of the number of experimentally determined RNA 3D structures enabled structure-based searches for small molecules that can specifically bind to defined sites in RNA molecules, thereby blocking or otherwise modulating their function. However, as of yet, computational methods for structure-based docking of small molecule ligands to RNA molecules are not as well established as analogous methods for protein-ligand docking. This motivated us to create LigandRNA, a scoring function for the prediction of RNA-small molecule interactions. Our method employs a grid-based algorithm and a knowledge-based potential derived from ligand-binding sites in the experimentally solved RNA-ligand complexes. As an input, LigandRNA takes an RNA receptor file and a file with ligand poses. As an output, it returns a ranking of the poses according to their score. The predictive power of LigandRNA favorably compares to five other publicly available methods. We found that the combination of LigandRNA and Dock6 into a "meta-predictor" leads to further improvement in the identification of near-native ligand poses. The LigandRNA program is available free of charge as a web server at

  5. Analysis of macromolecules, ligands and macromolecule-ligand complexes (United States)

    Von Dreele, Robert B [Los Alamos, NM


    A method for determining atomic level structures of macromolecule-ligand complexes through high-resolution powder diffraction analysis and a method for providing suitable microcrystalline powder for diffraction analysis are provided. In one embodiment, powder diffraction data is collected from samples of polycrystalline macromolecule and macromolecule-ligand complex and the refined structure of the macromolecule is used as an approximate model for a combined Rietveld and stereochemical restraint refinement of the macromolecule-ligand complex. A difference Fourier map is calculated and the ligand position and points of interaction between the atoms of the macromolecule and the atoms of the ligand can be deduced and visualized. A suitable polycrystalline sample of macromolecule-ligand complex can be produced by physically agitating a mixture of lyophilized macromolecule, ligand and a solvent.

  6. Automated docking of flexible ligands: applications of AutoDock. (United States)

    Goodsell, D S; Morris, G M; Olson, A J


    AutoDock is a suite of C programs used to predict the bound conformations of a small, flexible ligand to a macromolecular target of known structure. The technique combines simulated annealing for conformation searching with a rapid grid-based method of energy evaluation. This paper reviews recent applications of the technique and describes the enhancements included in the current release.

  7. Ligand-Receptor Interactions

    CERN Document Server

    Bongrand, Pierre


    The formation and dissociation of specific noncovalent interactions between a variety of macromolecules play a crucial role in the function of biological systems. During the last few years, three main lines of research led to a dramatic improvement of our understanding of these important phenomena. First, combination of genetic engineering and X ray cristallography made available a simultaneous knowledg of the precise structure and affinity of series or related ligand-receptor systems differing by a few well-defined atoms. Second, improvement of computer power and simulation techniques allowed extended exploration of the interaction of realistic macromolecules. Third, simultaneous development of a variety of techniques based on atomic force microscopy, hydrodynamic flow, biomembrane probes, optical tweezers, magnetic fields or flexible transducers yielded direct experimental information of the behavior of single ligand receptor bonds. At the same time, investigation of well defined cellular models raised the ...

  8. Therapeutic androgen receptor ligands


    Allan, George F.; Sui, Zhihua


    In the past several years, the concept of tissue-selective nuclear receptor ligands has emerged. This concept has come to fruition with estrogens, with the successful marketing of drugs such as raloxifene. The discovery of raloxifene and other selective estrogen receptor modulators (SERMs) has raised the possibility of generating selective compounds for other pathways, including androgens (that is, selective androgen receptor modulators, or SARMs).

  9. Imidazoline receptors ligands

    Directory of Open Access Journals (Sweden)

    Agbaba Danica


    Full Text Available Extensive biochemical and pharmacological studies have determined three different subtypes of imidazoline receptors: I1-imidazoline receptors (I1-IR involved in central inhibition of sympathicus that produce hypotensive effect; I2-imidazoline receptors (I2-IR modulate monoamine oxidase B activity (MAO-B; I3-imidazoline receptors (I3-IR regulate insulin secretion from pancreatic β-cells. Therefore, the I1/I2/I3 imidazoline receptors are selected as new, interesting targets for drug design and discovery. Novel selective I1/I2/I3 agonists and antagonists have been recently developed. In the present review, we provide a brief update to the field of imidazoline research, highlighting some of the chemical diversity and progress made in the 2D-QSAR, 3D-QSAR and quantitative pharmacophore development studies of I1-IR and I2-IR imidazoline receptor ligands. Theoretical studies of I3-IR ligands are not yet performed because of insufficient number of synthesized I3-IR ligands.

  10. SDF-1α-induced dual pairs of E-selectin/ligand mediate endothelial progenitor cell homing to critical ischemia. (United States)

    Liu, Zhao-Jun; Tian, Runxia; Li, Yan; Zhang, Leiming; Shao, Hongwei; Yang, Cuixia; Velazquez, Omaida C


    Homing of endothelial progenitor cells (EPC) to the ischemic tissues is a key event in neovascularization and tissue regeneration. In response to ischemic insult, injured tissues secrete several chemo-cytokines, including stromal cell-derived factor-1α (SDF-1α), which triggers mobilization and homing of bone marrow-derived EPC (BMD-EPC). We previously reported that SDF-1α-induced EPC homing is mediated by a panel of adhesion molecules highly or selectively expressed on the activated endothelium in ischemic tissues, including E-selectin. Elevated E-selectin on wound vasculature serve as docking sites for circulating EPC, which express counterpart E-selectin ligands. Here, we show that SDF-1α presented in wound tissue and released into circulation can act both locally and remotely to induce ischemic tissue endothelium and BMD-EPC to express both E-selectin and its ligands. By performing BM transplantation using E-selectin(-/-) and E-selectin(+/+) mice as the donors and recipients respectively, we demonstrate that upregulated dual E-selectin/ligand pairs reciprocally expressed on ischemic tissue endothelium and BMD-EPC act as double-locks to secure targeted EPC- endothelium interactions by which to facilitate EPC homing and promote neovascularization and tissue repair. These findings describe a novel mechanism for BMD-EPC homing and indicate that dual E-selectin/ligand pairs may be effective targets/tools for therapeutic neovascularization and targeted cell delivery.

  11. Modulation of the release of ( sup 3 H)norepinephrine from the base and body of the rat urinary bladder by endogenous adrenergic and cholinergic mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Somogyi, G.T.; de Groat, W.C. (Univ. of Pittsburgh, PA (USA))


    Modulation of (3H)NE release was studied in rat urinary bladder strips prelabeled with (3H)NE. (3H)NE uptake occurred in strips from the bladder base and body, but was very prominent in the base where the noradrenergic innervation is most dense. Electrical field stimulation markedly increased (3H)NE outflow from the superfused tissue. The quantity of (3H)NE release was approximately equal during three consecutive periods of stimulation. Activation of presynaptic muscarinic receptors by 1.0 microM oxotremorine reduced (3H)NE release to 46% of the control. Atropine (1 microM) blocked the effect of oxotremorine and increased the release to 147% of predrug control levels. Activation of presynaptic alpha-2 adrenoceptors by 1 microM clonidine reduced (3H)NE release to 55% of control. Yohimbine blocked the action of clonidine and increased the release to 148% of control. The release of (3H)NE from the bladder base and body was increased by both 1 microM atropine (to 167% and 174% of control, respectively) and 1 microM yohimbine (to 286% and 425% of control, respectively). Atropine and yohimbine administered in combination had similar facilitatory effects as when administered alone. We conclude that the release of (3H)NE from adrenergic nerve endings in electrically stimulated bladder strips is modulated via endogenous transmitters acting on both muscarinic and alpha-2 adrenergic presynaptic receptors and that the latter provide the most prominent control.

  12. Border cell release

    DEFF Research Database (Denmark)

    Mravec, Jozef


    Plant border cells are specialised cells derived from the root cap with roles in the biomechanics of root growth and in forming a barrier against pathogens. The mechanism of highly localised cell separation which is essential for their release to the environment is little understood. Here I present...

  13. Optogenetic control of ATP release (United States)

    Lewis, Matthew A.; Joshi, Bipin; Gu, Ling; Feranchak, Andrew; Mohanty, Samarendra K.


    Controlled release of ATP can be used for understanding extracellular purinergic signaling. While coarse mechanical forces and hypotonic stimulation have been utilized in the past to initiate ATP release from cells, these methods are neither spatially accurate nor temporally precise. Further, these methods cannot be utilized in a highly effective cell-specific manner. To mitigate the uncertainties regarding cellular-specificity and spatio-temporal release of ATP, we herein demonstrate use of optogenetics for ATP release. ATP release in response to optogenetic stimulation was monitored by Luciferin-Luciferase assay (North American firefly, photinus pyralis) using luminometer as well as mesoscopic bioluminescence imaging. Our result demonstrates repetitive release of ATP subsequent to optogenetic stimulation. It is thus feasible that purinergic signaling can be directly detected via imaging if the stimulus can be confined to single cell or in a spatially-defined group of cells. This study opens up new avenue to interrogate the mechanisms of purinergic signaling.

  14. Bexarotene ligand pharmaceuticals. (United States)

    Hurst, R E


    Bexarotene (LGD-1069), from Ligand, was the first retinoid X receptor (RXR)-selective, antitumor retinoid to enter clinical trials. The company launched the drug for the treatment of cutaneous T-cell lymphoma (CTCL), as Targretin capsules, in the US in January 2000 [359023]. The company filed an NDA for Targretin capsules in June 1999, and for topical gel in December 1999 [329011], [349982] specifically for once-daily oral administration for the treatment of patients with early-stage CTCL who have not tolerated other therapies, patients with refractory or persistent early stage CTCL and patients with refractory advanced stage CTCL. The FDA approved Targretin capsules at the end of December 1999 for once-daily oral treatment of all stages of CTCL in patients refractory to at least one prior systemic therapy, at an initial dose of 300 mg/m2/day. After an NDA was submitted in December 1999 for Targretin gel, the drug received Priority Review status for use as a treatment of cutaneous lesions in patients with stage IA, IB or IIA CTCL [354836]. The FDA issued an approvable letter in June 2000, and granted marketing clearance for CTCL in the same month [370687], [372768], [372769], [373279]. Ligand had received Orphan Drug designation for this indication [329011]. At the request of the FDA, Ligand agreed to carry out certain post-approval phase IV and pharmacokinetic studies [351604]. The company filed an MAA with the EMEA for Targretin Capsules to treat lymphoma in November 1999 [348944]. The NDA for Targretin gel is based on a multicenter phase III trial that was conducted in the US, Canada, Europe and Australia involving 50 patients and a multicenter phase I/II clinical program involving 67 patients. Targretin gel was evaluated for the treatment of patients with early stage CTCL (IA-IIA) who were refractory to, intolerant to, or reached a response plateau for at least 6 months on at least two prior therapies. Efficacy results exceeded the protocol-defined response

  15. CO-releasing molecule (CORM) conjugate systems. (United States)

    Kautz, Anna Christin; Kunz, Peter C; Janiak, Christoph


    The development of CORMs (CO-releasing molecules) as a prodrug for CO administration in living organisms has attracted significant attention. CORMs offer the promising possibility of a safe and controllable release of CO in low amounts triggered by light, ligands, enzymes, etc. For the targeting of specific tissues or diseases and to prevent possible side effects from metals and other residues after CO release, these CORMs are attached to biocompatible systems, like peptides, polymers, nanoparticles, dendrimers, protein cages, non-wovens, tablets, and metal-organic frameworks. We discuss in this review the known CORM carrier conjugates, in short CORM conjugates, with covalently-bound or incorporated CORMs for medicinal and therapeutic applications. Most conjugates are nontoxic, show increasing half-lives of CO release, and make use of the EPR-effect, but still show problems because of a continuous background of CO release and the absence of an on/off-switch for the CO release.

  16. Estrogens Suppress Spinal Endomorphin 2 Release in Female Rats in Phase with the Estrous Cycle (United States)

    Kumar, Arjun; Storman, Emiliya M.; Liu, Nai-Jiang; Gintzler, Alan R.


    Background/Aims Male and female rats differ in their ability to utilize spinal endomorphin 2 (EM2; the predominant mu-opioid receptor ligand in spinal cord) and in the mechanisms that underlie spinal EM2 analgesic responsiveness. We investigated the relevance of spinal estrogen receptors (ERs) to the in vivo regulation of spinal EM2 release. Methods ER antagonists were administered directly to the lumbosacral spinal cord of male and female rats, intrathecal perfusate was collected, and resulting changes in EM2 release were quantified using a plate-based radioimmunoassay. Results Intrathecal application of an antagonist of either estrogen receptor-α (ERα) or the ER GPR30 failed to alter spinal EM2 release. Strikingly, however, the concomitant blockade of ERα and GPR30 enhanced spinal EM2 release. This effect was sexually dimorphic, being absent in males. Furthermore, the magnitude of the enhancement of spinal EM2 release in females was dependent upon estrous cycle stage, suggesting a relationship with circulating levels of 17β-estradiol. The rapid onset of enhanced EM2 release following intrathecal application of ERα/GPR30 antagonists (within 30–40 min) suggests mediation via ERs in the plasma membrane, not the nucleus. Notably, both ovarian and spinally synthesized estrogens are essential for membrane ER regulation of spinal EM2 release. Conclusion These findings underscore the importance of estrogens for the regulation of spinal EM2 activity and, by extension, endogenous spinal EM2 antinoci-ception in females. Components of the spinal estrogenic mechanism(s) that suppress EM2 release could represent novel drug targets for improving utilization of endogenous spinal EM2, and thereby pain management in women. PMID:25925013

  17. The Effect of Ethanol on the Release of Opioids from Oral Prolonged-Release Preparations


    Walden, Malcolm; Nicholls, Fiona A.; Smith, Kevin J.; Tucker, Geoffrey T


    Recent experience has prompted the US FDA to consider whether ethanol ingestion may modify the release characteristics of prolonged-release formulations, where dose dumping may be an issue for patient safety. The influence of ethanol on the in vitro release of opioid drugs from some prolonged-release formulations utilizing different release technologies was examined. Results indicated that the prolonged-release mechanisms remained intact under the testing conditions, although one product show...

  18. Current state of laser synthesis of metal and alloy nanoparticles as ligand-free reference materials for nano-toxicological assays

    Directory of Open Access Journals (Sweden)

    Christoph Rehbock


    Full Text Available Due to the abundance of nanomaterials in medical devices and everyday products, toxicological effects related to nanoparticles released from these materials, e.g., by mechanical wear, are a growing matter of concern. Unfortunately, appropriate nanoparticles required for systematic toxicological evaluation of these materials are still lacking. Here, the ubiquitous presence of surface ligands, remaining from chemical synthesis are a major drawback as these organic residues may cause cross-contaminations in toxicological studies. Nanoparticles synthesized by pulsed laser ablation in liquid are a promising alternative as this synthesis route provides totally ligand-free nanoparticles. The first part of this article reviews recent methods that allow the size control of laser-fabricated nanoparticles, focusing on laser post irradiation, delayed bioconjugation and in situ size quenching by low salinity electrolytes. Subsequent or parallel applications of these methods enable precise tuning of the particle diameters in a regime from 4–400 nm without utilization of any artificial surface ligands. The second paragraph of this article highlights the recent progress concerning the synthesis of composition controlled alloy nanoparticles by laser ablation in liquids. Here, binary and ternary alloy nanoparticles with totally homogeneous elemental distribution could be fabricated and the composition of these particles closely resembled bulk implant material. Finally, the model AuAg was used to systematically evaluate composition related toxicological effects of alloy nanoparticles. Here Ag+ ion release is identified as the most probable mechanism of toxicity when recent toxicological studies with gametes, mammalian cells and bacteria are considered.

  19. Separation of tryptophan enantiomers by ligand-exchange chromatography with novel chiral ionic liquids ligand. (United States)

    Qing, Haiqun; Jiang, Xinyu; Yu, Jingang


    Chiral ionic liquids (CILs) with amino acids as cations have been applied as novel chiral ligands coordinated with Cu(2+) to separate tryptophan enantiomers in ligand exchange chromatography. Four kinds of amino acid ionic liquids, including [L-Pro][CF3COO], [L-Pro][NO3], [L-Pro]2[SO4], and [L-Phe][CF3COO] were successfully synthesized and used for separation of tryptophan enantiomers. To optimize the separation conditions, [L-Pro][CF3COO] was selected as the model ligand. Some factors influencing the efficiency of chiral separation, such as copper ion concentration, CILs concentration, methanol ratio (methanol/H2O, v/v), and pH, were investigated. The obtained optimal separation conditions were as follows: 8.0 mmol/L Cu(OAc)2, 4.0 mmol/L [L-Pro][CF3COO], and 20% (v/v) methanol at pH 3.6. Under the optimum conditions, acceptable enantioseparation of tryptophan enantiomers could be observed with a resolution of 1.89. The results demonstrate the good applicability of CILs with amino acids as cations for chiral separation. Furthermore, a comparative study was also conducted for exploring the mechanism of the CILs as new ligands in ligand exchange chromatography. © 2014 Wiley Periodicals, Inc.

  20. Alternaria-induced release of IL-18 from damaged airway epithelial cells: an NF-κB dependent mechanism of Th2 differentiation?

    Directory of Open Access Journals (Sweden)

    Hiroki Murai

    Full Text Available BACKGROUND: A series of epidemiologic studies have identified the fungus Alternaria as a major risk factor for asthma. The airway epithelium plays a critical role in the pathogenesis of allergic asthma. These reports suggest that activated airway epithelial cells can produce cytokines such as IL-25, TSLP and IL-33 that induce Th2 phenotype. However the epithelium-derived products that mediate the pro-asthma effects of Alternaria are not well characterized. We hypothesized that exposure of the airway epithelium to Alternaria releasing cytokines that can induce Th2 differentiation. METHODOLOGY/PRINCIPAL FINDING: We used ELISA to measure human and mouse cytokines. Alternaria extract (ALT-E induced rapid release of IL-18, but not IL-4, IL-9, IL-13, IL-25, IL-33, or TSLP from cultured normal human bronchial epithelial cells; and in the BAL fluids of naïve mice after challenge with ALT-E. Both microscopic and FACS indicated that this release was associated with necrosis of epithelial cells. ALT-E induced much greater IL-18 release compared to 19 major outdoor allergens. Culture of naïve CD4 cells with rmIL-18 induced Th2 differentiation in the absence of IL-4 and STAT6, and this effect was abrogated by disrupting NF- κB p50 or with a NEMO binding peptide inhibitor. CONCLUSION/SIGNIFICANCE: Rapid and specific release of IL-18 from Alternaria-exposed damaged airway epithelial cells can directly initiate Th2 differentiation of naïve CD4(+ T-cells via a unique NF-κB dependent pathway.

  1. Mechanics

    CERN Document Server

    Hartog, J P Den


    First published over 40 years ago, this work has achieved the status of a classic among introductory texts on mechanics. Den Hartog is known for his lively, discursive and often witty presentations of all the fundamental material of both statics and dynamics (and considerable more advanced material) in new, original ways that provide students with insights into mechanical relationships that other books do not always succeed in conveying. On the other hand, the work is so replete with engineering applications and actual design problems that it is as valuable as a reference to the practicing e

  2. Improved Metathesis Lifetime: Chelating Pyridinyl-Alcoholato Ligands in the Second Generation Grubbs Precatalyst

    Directory of Open Access Journals (Sweden)

    Jean I. du Toit


    Full Text Available Hemilabile ligands can release a free coordination site “on demand” of an incoming nucleophilic substrate while occupying it otherwise. This is believed to increase the thermal stability and activity of catalytic systems and therefore prevent decomposition via free coordination sites. In this investigation chelating pyridinyl-alcoholato ligands were identified as possible hemilabile ligands for incorporation into the second generation Grubbs precatalyst. The O,N-alcoholato ligands with different steric bulk could be successfully incorporated into the precatalysts. The incorporation of the sterically hindered, hemilabile O,N-ligands improved the thermal stability, activity, selectivity and lifetime of these complexes towards the metathesis of 1-octene. A decrease in the activity of the second generation Grubbs precatalyst was additionally observed after incorporating a hemilabile O,N-ligand with two phenyl groups into the system, while increasing their lifetime.

  3. Renin release

    DEFF Research Database (Denmark)

    Schweda, Frank; Friis, Ulla; Wagner, Charlotte;


    The aspartyl-protease renin is the key regulator of the renin-angiotensin-aldosterone system, which is critically involved in salt, volume, and blood pressure homeostasis of the body. Renin is mainly produced and released into circulation by the so-called juxtaglomerular epithelioid cells, located......, salt, and volume overload. In contrast, the events controlling the function of renin-secreting cells at the organ and cellular level are markedly less clear and remain mysterious in certain aspects. The unravelling of these mysteries has led to new and interesting insights into the process of renin...

  4. Hydrolysis mechanisms of trans platinum-based anticancer drug with heterocyclic amine ligands: A comparative DFT study%杂环反铂(Ⅱ)抗癌药物水解反应机理的DFT研究

    Institute of Scientific and Technical Information of China (English)

    李添; 周立新; 李娟


    In this work, the hydrolysis processes of the anticancer drugs trans-[PtCl2 (piperi-dine) ( Am)], Am = 2.-pico]ine( 1), 3-picoline(2) , 4-picoiine(3), trans-[PtCl; (piperidine) ( piper-azine)] (4), trans-[PtCl2 ( piperazme )2 ] (5 ) and trans-[ PtCl2 (iminoether )2 ] (6 ) have been studied using hybrid density functional theory (B3LYP) and iso-electnc focusing polarized con-tinuum model CIEF-PCM) solvation models. The hydrolysis reactions leading to the activated drug form a key step for the reaction with the target DNA. The stationary points on the poten-tial energy surfaces for the first and second hydrolysis steps, proceeding via a general SN2 pathway, were fully optimized and characterized. It is found that the processes of the reactions follow the established theory for ligand substitution in square planar complexes,that is, substi-tution reactions usually occur via Pt-Iigand exchange reactions with a trigonal-bipyramidsl transition stale structure; the geometries of the transition states (TS) agree with the previous related work and all of the reactions are endothermic; the barrier height of the second hydroly-sis is always higher than that of the first step for all the systems. In comparison with previous work on cisplatin, a faster rate of hydrolysis is determined for the reaction. We make a com-parison with previous work on the hydrolysis processes of analogous trans platinum-based anti- cancer drugs. The results provide detailed energy profiles for the mechanism of hydrolysis of 1, 2, 3. 4, 5 and 6, which may assist in understanding the reaction mechanism of the drug with the DNA target and in the design of novel Pt-based anticancer drugs with trans geometries.%用DFT-B3LYP方法和IEF-PCM溶剂化模型研究了反铂抗癌药物trans-[PtCl2(piperidine)(Am)](Am=2-picoline(1).3-picoline(2),4 picoline(3)),trans-[PtCl2(piperidine)(piperazine)](4),trans-[PtCl2(piperazine)2](5)and trans-[PtCl2(iminoether)2](6)的水解过程.水解反应是药物与DNA靶

  5. Database of ligand-induced domain movements in enzymes

    Directory of Open Access Journals (Sweden)

    Hayward Steven


    Full Text Available Abstract Background Conformational change induced by the binding of a substrate or coenzyme is a poorly understood stage in the process of enzyme catalysed reactions. For enzymes that exhibit a domain movement, the conformational change can be clearly characterized and therefore the opportunity exists to gain an understanding of the mechanisms involved. The development of the non-redundant database of protein domain movements contains examples of ligand-induced domain movements in enzymes, but this valuable data has remained unexploited. Description The domain movements in the non-redundant database of protein domain movements are those found by applying the DynDom program to pairs of crystallographic structures contained in Protein Data Bank files. For each pair of structures cross-checking ligands in their Protein Data Bank files with the KEGG-LIGAND database and using methods that search for ligands that contact the enzyme in one conformation but not the other, the non-redundant database of protein domain movements was refined down to a set of 203 enzymes where a domain movement is apparently triggered by the binding of a functional ligand. For these cases, ligand binding information, including hydrogen bonds and salt-bridges between the ligand and specific residues on the enzyme is presented in the context of dynamical information such as the regions that form the dynamic domains, the hinge bending residues, and the hinge axes. Conclusion The presentation at a single website of data on interactions between a ligand and specific residues on the enzyme alongside data on the movement that these interactions induce, should lead to new insights into the mechanisms of these enzymes in particular, and help in trying to understand the general process of ligand-induced domain closure in enzymes. The website can be found at:

  6. Dopamine dysregulation syndrome in Parkinson's disease patients with unsatisfactory switching from immediate to extended release pramipexole: a further clue to incentive sensitization mechanisms? (United States)

    Solla, Paolo; Cannas, Antonino; Corona, Marta; Marrosu, Maria Giovanna; Marrosu, Francesco


    A small proportion of patients with Parkinson's disease (PD), chronically under dopamine replacement therapy, may undergo an addiction-like behavioral disturbance, named dopamine dysregulation syndrome (DDS). This behavioral disorder is characterized by the increase of doses beyond those required for motor control, and its management remains difficult; thus, early recognition and careful monitoring of at-risk individuals are crucial. We report the cases of two PD patients with a previous unsatisfactory switching from an immediate release (IR) to an extended release (ER) pramipexole formulation who developed DDS. PD patients unsatisfactorily switched from an IR to an ER formulation of dopamine agonists should be considered as at-risk individuals for DDS development.

  7. Macrocyclic G-quadruplex ligands

    DEFF Research Database (Denmark)

    Nielsen, M C; Ulven, Trond


    G-quadruplex stabilizing compounds have recently received increased interest due to their potential application as anticancer therapeutics. A significant number of structurally diverse G-quadruplex ligands have been developed. Some of the most potent and selective ligands currently known are macr...