Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During the aerobic conversion of xanthine to uric acid by xanthine oxidase, superoxide anion and hydrogen peroxide are produced along with the hydroxyl radical. Our studies demonstrate that washed human platelets incubated with xanthine and xanthine oxidase aggregated and released [14C]serotonin. Aggregation and release were dependent on the duration of exposure to xanthine oxidase as well as the concentration of enzyme. Both reactions were inhibited by the superoxide scavenger enzyme superoxide dismutase but not by catalase, or the free radical scavenger mannitol, suggesting that they were induced by superoxide anion. Superoxide-dependent release was inhibited by prior incubation of platelets with 1 mM EDTA, 1 micronM prostaglandin E1, or 1 mM dibutyryl cyclic AMP, but was unaffected by 1 mM acetylsalicylic acid or 1 micronM indomethacin. After prolonged incubation with xanthine and xanthine oxidase there was also efflux of up to 15% of intraplatelet 51Cr, a cytosol marker. This leakage was prevented by the addition of catalase to the media but not by superoxide dismutase. Incubation with xanthine and xanthine oxidase did not produce malonyldialdehyde, the three-carbon fatty acid fragment produced during prostaglandin endoperoxide synthesis and lipid peroxidation. Prior exposure of platelets to low fluxes of superoxide anion lowered the threshold for release by subsequent addition of thrombin, suggesting a synergistic effect. We conclude that superoxide-dependent aggregation and release may be a physiologically important method to modulate hemostatic reactions particularly in areas of inflammation or vessel injury which could have high local concentrations of superoxide anion.
...
PMID:Enhancement of platelet function by superoxide anion. 19 66

Carrageenan or thrombin-induced aggregation of plasma-free rabbit platelets was inhibited by calcium and magnesium chelating agents, by N-ethylmaleimide and by drugs that increase the intra-cellular cyclic AMP content. Inhibitors of prostaglandin (PG) synthetase were only partially active, and had to be present in the platelet suspension to inhibit aggregation. Inhibition of PG synthetase, as evaluated by bioassay and by AA-induced platelet aggregation, was not reduced when inhibitors were washed from platelets. The phospholipase A2 inhibitors bromophenacyl bromide and mepacrine, the chymotrypsin inhibitor tosylphenylalaninechloromethylketone, catalase and dithiothreitol also inhibited aggregation, whereas inhibitors of trypsin failed to do so. Incubation of rabbit platelet-rich plasma with carrageenan was followed by generation of PG-like and of rabbit aorta contracting activities. Generation of these activities was inhibited by drugs effective against aggregation, and also by non-steroidal anti-inflammatory drugs. Aggregation of rabbit platelets by carrageenan and by thrombin does not appear to be dependent upon activation of PG synthetase, although PG-like substances are formed during aggregation.
...
PMID:Involvement of mediators in the interaction of platelets and carrageenan. 41 34

The structure and functions of platelets from a patient in whom albinism and hemorrhagic diathesis were associated have been investigated. Electron microscope studies showed a large reduction in the number of dense bodies and this was confirmed by an examination of fluorescent platelets loaded with mepacrine. The rare dense bodies were much bigger than normally observed; their density was diminished and was localized in a peripheral ring. Other platelet constituents were found to be normal. Platelet peroxidase activity was normal in the canaliculi of the dense tubular system; catalase-positive granules were also present. Serotonin uptake by the patient's platelets was much decreased and reserpine, a potent inhibitor of serotonin accumulation by normal human platelets, did not further decrease this incorporation. The uptake of free 14 C-arachidonic acid by the platelets was greatly diminished, as was its thrombin-induced liberation from phosphatidyl-choline and phosphatidyl inositol. Moreover, platelet phospholipase A1 activity was much reduced and phospholipase A2 activity was undetectable.
...
PMID:Studies on a new variant of the Hermansky-Pudlak syndrome: qualitative, ultrastructural, and functional abnormalities of the platelet-dense bodies associated with a phospholipase A defect. 71 98

The production of hydrogen peroxide was measured by following the oxidation of dichlorofluorescein (DCFH) entrapped into platelets. Resting platelets produced nanomolar quantities of DCF, which was proportional to the concentration of platelets and was steady during 1 h of incubation. A significant increase of basal DCF fluorescence was induced by stimuli namely thrombin, arachidonic acid, the Ca2+ ionophore A23187 and PMA. The effect of agonists has been also measured in the presence of 3-amino-1,2,4-triazole (AT) or N-ethylmaleimide (NEM), inhibitors of catalase and glutathione peroxidase, respectively. A further significant enhancement of DCF produced in stimulated platelets was detected only in the presence of NEM. A correlation was found between the increase in DCF and externally added hydrogen peroxide or the oxidizing species formed by xanthine oxidase plus acetaldehyde. The yield was not affected by superoxide dismutase and was higher in the presence of AT or NEM. A cooperative effect in the presence of both inhibitors was shown. Glutathione peroxidase plus glutathione diminished the level of DCF to basal levels.
...
PMID:Generation of hydrogen peroxide in resting and activated platelets. 162 82

Human blood platelets produce oxidant species when stimulated by collagen and thrombin. The oxidative burst of platelets has been studied by cytofluorimetry taking advantage of the fluorogenic dye DCFH2-DA, which is taken up and deacetylated by platelets and then oxidized to the fluorescent derivative DCF. The oxidation of DCFH2 is induced by stimulation with collagen but not with thrombin and inhibited by external catalase. Catalase also inhibited the aggregation induced by collagen, but not that induced by thrombin. Aspirin and indomethacin inhibited the formation of the fluorochrome only when platelets were stimulated by thrombin. Externally added H2O2 increased the cytoplasmic calcium content as probed by the fluorescence of Indo-1. The present data suggest that collagen induces the production of H2O2, which in turn may stimulate the aggregation of platelets through a calcium mobilization. Instead the stimulation by thrombin does not require the intermediacy of H2O2.
...
PMID:Hydrogen peroxide is an intermediate in the platelet activation cascade triggered by collagen, but not by thrombin. 189 57

Superoxide dismutase (SOD) triggers activation of human platelets exposed to subthreshold concentrations of arachidonic acid and collagen. The subthreshold concentrations used are not able to activate platelets but "prime" platelets to be activated by SOD. The addition of SOD to arachidonic acid-or collagen-primed platelets induced aggregation, thromboxane A2 production, and release of [3H]serotonin. Superoxide dismutase does not have any effect on resting platelets and ADP-, thrombin-, calcium ionophore A23187-, PAF-, or U46619-stimulated platelets. Furthermore, superoxide dismutase-dependent platelet activation is fully prevented by catalase and/or aspirin, suggesting a role for H2O2 and the involvement of the cyclooxygenase pathway of arachidonic acid in such activation.
...
PMID:Superoxide dismutase triggers activation of "primed" platelets. 191 Mar 14

We have shown that platelet-activating factor (PAF) primes neutrophil (PMN) responses and enhances their ability to damage endothelial cells. Furthermore, thrombin-stimulated endothelial cells which produce PAF can augment and prime PMN superoxide production, elastase release and adhesion to endothelium. We wondered whether these marginated neutrophils (PMN) themselves, or their release products, might feedback and further amplify endothelial cell activation. To measure cellular activation, we assessed changes in endothelial cell intracellular calcium [( Ca2+]i) in endothelial monolayers loaded with Fura-2, and PAF production by [3H]acetate incorporation into phospholipid. Resting PMNs induced no change in [Ca2+]i, while N-formyl-L-methionine-L-leucyl-L-phenylalanine stimulated PMN and their lysosomal products caused a 25% increase in endothelial cell calcium. Sonicates of PMN produced a much larger increase in [Ca2+]i than activated PMN; the effect of PMN sonicates could in part be reduced by the serine protease inhibitor, alpha 1 antitrypsin. In contrast, purified neutrophil elastase did not alter endothelial cell [Ca2+]i. Despite hydrogen peroxide's ability to increase [Ca2+]i, catalase failed to inhibit the PMN-induced rise in [Ca2+]i. Since polyanionic heparin inhibited the PMN sonicate rise in calcium, a cationic protein released by PMN was thought to be responsible. The cationic primary granule enzyme, cathepsin G, duplicates the rise in [Ca2+]i seen with PMN sonicates. Furthermore, PAF production increased threefold in response to neutrophil sonicates. Thus, during inflammation, when coagulation and inflammatory cells are activated the endothelium responds by priming PMNs and promoting margination.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Endothelial cell platelet-activating factor primes neutrophil responses: amplification of endothelial activation by neutrophil products. 196 17

Lytic H2O2-induced injury to human umbilical vein endothelial cells provides a model for endothelial cell damage in diverse states including acute respiratory distress and septic shock. Endothelial cell lysis is an extreme result of inflammatory cell activation. Functional alterations such as responsiveness to endothelial cell agonists and eicosanoid production might be impaired by exposure to inflammatory cell products including H2O2. Soluble mediators such as thrombin or histamine cause endothelial cell activation via a signal transduction mechanism that hydrolyzes phosphatidylinositol 4,5-bisphosphate (IP), liberating inositol trisphosphate (IP3). Accordingly, pretreatment of endothelial cells with H2O2 blocked the subsequent production of IP3 in response to thrombin and histamine. H2O2 inhibition of IP3 was time- and concentration-dependent. The endothelial cells were viable by trypan blue dye exclusion and chromium release. H2O2 inhibition of signaling was completely prevented by catalase. Iron-dependent oxidant radical formation appears critical because deferoxamine (10(-4) mol/L) pretreatment of endothelial cells prevented H2O2 inhibition of IP hydrolysis. Prostacyclin and platelet activating factor production in response to thrombin have been linked to IP hydrolysis. Pretreatment of endothelial cells with H2O2 reduced prostacyclin and platelet-activating factor production by thrombin by at least 50%. It appears H2O2 can induce defects in signaling pathways with sequelae (decreased prostacyclin and platelet-activating factor) short of endothelial cell death. The possible consequences of H2O2 interaction with endothelial cells is reviewed with the aim of presenting a hypothesis to integrate these various observations.
...
PMID:Hydrogen peroxide alters signal transduction in human endothelial cells. 198 9

The metabolic and functional responses of human polymorphonuclear cells (PMNs) to thrombin-activated platelet supernatants were studied. The incubation of PMNs with supernatants from stimulated platelets (SPS) caused a 50% decrease in both killing of Staphylococcus aureus and luminol-enhanced chemiluminescence (CL) by PMNs stimulated by opsonized-zymosan (OZ), Concanavalin A (Con A), or calcium ionophore A23187. The levels of PMN intracellular fluorescence measured by flow cytometry, using the fluorochrome dichlorofluorescein diacetate (DCF-DA), were considerably less in the presence of SPS than in resting platelet supernatants (RPS). No influence of platelet supernatant on O2 consumption and O2- generation by OZ-activated PMNs was observed. The incubation of PMNs with SPS caused a significant increase in the rate of chemotaxis and aggregation elicited by Con A, OZ, and phorbol myristate acetate (PMA). The supernatant from resting platelets did not show any of the above-reported effects. Platelets previously degranulated by thrombin were unable to inhibit CL when activated with agonists. Studies on the differential release of the granules by platelets showed that the CL-quenching activity paralleled the discharge of lysosomal content. The release of myeloperoxidase (MPO) from PMNs elicited by OZ was reduced in the presence of SPS. The platelet supernatant did not affect the MPO activity if PMNs were lysed with Triton X-100. The leakage of lactate dehydrogenase (LDH) from platelets was less than 3%, and no catalase or superoxide dismutase was released. This activity withstood lyophilization, but was destroyed by 10 min heating at 100 degrees C or by treatment with proteolytic enzymes.
...
PMID:Stimulated platelets release factor(s) affecting the in vitro response of human polymorphonuclear cells. 211 64

Human umbilical vein endothelial cells subjected to 24 h of anoxia followed by reoxygenation released less prostacyclin (PGI2) in response to thrombin, calcium ionophore A23187, or arachidonic acid. This was associated with a substantial increase in stimulated platelet adherence. Increased lactate dehydrogenase and 51Cr release occurred after 1 h of reoxygenation, but the high rate of release did not persist during the subsequent 23 h of reoxygenation. The changes in platelet adherence and PGI2 release partially resolved over 24 h. PGI2 formation from prostaglandin H2 was not reduced, suggesting that cyclooxygenase activity, but not prostacyclin synthase, is affected by reoxygenation. A decrease in arachidonic acid release from cellular lipids also occurred. The reduction in cyclooxygenase activity, but not arachidonic acid release, was prevented by the presence of ibuprofen during reoxygenation. Addition of catalase or superoxide dismutase during reoxygenation increased PGI2 release but did not completely overcome the reduction relative to control cultures. These findings suggest that the increase in platelet adherence during reoxygenation may be mediated in part by a change in cyclooxygenase activity. This is only partly overcome by extracellular oxygen species scavengers but is prevented by the presence of a reversible cyclooxygenase inhibitor during reoxygenation.
...
PMID:Reduced prostacyclin formation after reoxygenation of anoxic endothelium. 212 35


1 2 3 4 5 6 Next >>

---