Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P35237 (thrombin inhibitor)
 2,012 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombin is a multifunctional serine proteinase that plays a key role in coagulation while exhibiting several other key cellular bioregulatory functions. The X-ray crystal structure of human alpha-thrombin was determined in its complex with the specific thrombin inhibitor D-Phe-Pro-Arg chloromethylketone (PPACK) using Patterson search methods and a search model derived from trypsinlike proteinases of known spatial structure (Bode, W., Mayr, I., Baumann, U., Huber, R., Stone, S.R., & Hofsteenge, J., 1989, EMBO J. 8, 3467-3475). The crystallographic refinement of the PPACK-thrombin model has now been completed at an R value of 0.156 (8 to 1.92 A); in particular, the amino- and the carboxy-termini of the thrombin A-chain are now defined and all side-chain atoms localized; only proline 37 was found to be in a cis-peptidyl conformation. The thrombin B-chain exhibits the characteristic polypeptide fold of trypsinlike serine proteinases; 195 residues occupy topologically equivalent positions with residues in bovine trypsin and 190 with those in bovine chymotrypsin with a root-mean-square (r.m.s.) deviation of 0.8 A for their alpha-carbon atoms. Most of the inserted residues constitute novel surface loops. A chymotrypsinogen numbering is suggested for thrombin based on the topological equivalences. The thrombin A-chain is arranged in a boomeranglike shape against the B-chain globule opposite to the active site; it resembles somewhat the propeptide of chymotrypsin(ogen) and is similarly not involved in substrate and inhibitor binding. Thrombin possesses an exceptionally large proportion of charged residues. The negatively and positively charged residues are not distributed uniformly over the whole molecule, but are clustered to form a sandwichlike electrostatic potential; in particular, two extended patches of mainly positively charged residues occur close to the carboxy-terminal B-chain helix (forming the presumed heparin-binding site) and on the surface of loop segment 70-80 (the fibrin[ogen] secondary binding exosite), respectively; the negatively charged residues are more clustered in the ringlike region between both poles, particularly around the active site. Several of the charged residues are involved in salt bridges; most are on the surface, but 10 charged protein groups form completely buried salt bridges and clusters. These electrostatic interactions play a particularly important role in the intrachain stabilization of the A-chain, in the coherence between the A- and the B-chain, and in the surface structure of the fibrin(ogen) secondary binding exosite (loop segment 67-80).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The refined 1.9-A X-ray crystal structure of D-Phe-Pro-Arg chloromethylketone-inhibited human alpha-thrombin: structure analysis, overall structure, electrostatic properties, detailed active-site geometry, and structure-function relationships. 130 49

In contrast to thrombin the fibrinogen coagulant effect of the thrombin-like enzyme batroxobin in vitro and in vivo is not inhibited by the specific thrombin inhibitor hirudin. The haemostyptic effect of batroxobin has been studied in rats after bleeding had been induced by corresponding hirudin dosages. Dependent on batroxobin concentration bleeding time was shortened by local application of batroxobin containing solutions. Strong bleeding induced by i.v. injection of 5 mg r-hirudin/kg was stopped almost immediately when a batroxobin concentration of 40 BU/ml was used. Thrombin was less active to stop bleeding after r-hirudin administration than batroxobin.
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PMID:Haemostyptic effects of batroxobin with regard to hirudin treatment. 134 Oct 58

The effect of thrombin on mesangial cell function was investigated. Thrombin caused a dose-dependent increase in [3H] thymidine incorporation (EC50 = 0.36 +/- 0.09 U/ml), intracellular calcium [(Ca++)i] mobilization (EC50 = 1.9 +/- 0.5 U/ml) and prostaglandin E2 (PGE2) production (EC50 = 0.25 +/- 0.02 U/ml) in rat glomerular mesangial cells. These effects were blocked by the thrombin inhibitor, hirudin (KB = 10.4 +/- 0.2 nM). The role of (Ca++)i mobilization and arachidonate metabolism in thrombin-stimulated proliferation was tested by the addition of the calcium channel blocker, nifedipine, and the cyclooxygenase inhibitor, indomethacin, to mesangial cell cultures. Indomethacin, at doses that completely inhibited the thrombin-mediated production of PGE2, had no significant effect on proliferation. The Ca++ channel blocker, nifedipine, inhibited both PGE2 production and [3H] thymidine incorporation in a dose-dependent fashion, but only at concentrations considered nonspecific. In addition to its effects on PGE2, thymidine incorporation and Ca++ mobilization, thrombin caused mesangial cell contraction as determined by a substrate distortion technique. This effect was not inhibited by indomethacin. These results indicate that thrombin can alter mesangial cell function in vitro.
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PMID:Effect of thrombin on proliferation, contraction and prostaglandin production of rat glomerular mesangial cells in culture. 140 2

We have studied the cellular mechanism responsible for induction of preproendothelin (preproET)-1 mRNA and release of ET-1 by thrombin in cultured bovine endothelial cells (ECs). Thrombin induced an immediate and dose-dependent formation of inositol-1,4,5-trisphosphate (IP3) with a concomitant increase in intracellular Ca2+ concentration ([Ca2+]i). The thrombin-induced ET-1 release was abolished either by a phospholipase C inhibitor, a protein kinase C (PKC) inhibitor, or an intracellular Ca(2+)-chelator, whereas a Ca(2+)-channel antagonist was ineffective. A selective thrombin inhibitor (argatroban) decreased IP3 formation and the increase in [Ca2+]i and ET-1 release stimulated by thrombin. Northern blot analysis revealed that thrombin-induced expression of preproET-1 mRNA was inhibited completely by a PKC inhibitor and partially by argatroban. These data suggest that thrombin is involved in the mechanism of preproET-1 mRNA expression and subsequent ET-1 release, possibly through activation PKC and mobilization of intracellular Ca2+ resulting from the receptor-mediated phosphoinositide breakdown in ECs.
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PMID:Cellular mechanism of thrombin on endothelin-1 biosynthesis and release in bovine endothelial cell. 147 6

Thrombin at concentrations as low as 20 pM (0.002 U ml-1) was found to stimulate inositol phosphate levels in cultured human non-pigmented ciliary epithelial cells. Several other proteases, including trypsin and plasmin, had little or no effect, of several protease inhibitors tested, only those with specificity for thrombin blocked the effect. Studies with active site-blocked thrombin suggested that the esterolytic active site of thrombin is required for inositol phosphate stimulation, while gamma-thrombin, which has reduced binding affinity to fibrinogen also showed reduced effectiveness in stimulating inositol phosphates. In the presence of 10 mM LiCl, thrombin stimulated inositol monophosphate, inositol bisphosphate and inositol trisphosphate formation, with a prolonged rise of the first and transient early rises in the latter two species. Thrombin also elevated intracellular Ca2+ levels as measured with the fluorescent calcium probe, indo-1-AM. This elevation could be blocked by prior addition to cells of the thrombin inhibitor, hirudin, and was dependent upon extracellular Ca2+ for the maintenance of an elevated level in the presence of thrombin. Incorporation of thymidine into DNA in confluent cultures was also stimulated by thrombin, with a four-fold increase in incorporation at 35 hr in thrombin-treated cells compared to controls. The half-maximal concentration for this process was 0.25 U ml-1. Pretreatment with 100 ng ml-1 pertussis toxin greatly reduced the thrombin effect, which is consistent with a role for a G-protein in stimulation of DNA synthesis by thrombin.
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PMID:Thrombin stimulates inositol phosphate formation, intracellular calcium fluxes and DNA synthesis in cultured fetal human non-pigmented ciliary epithelial cells. 148 37

Myocardial ischemia inhibits endothelium-dependent relaxation stimulated by the coagulant peptide, thrombin. To investigate whether activation of endogenous thrombin contributed to this reduction in relaxant sensitivity, the effects of pretreatment of dogs with the coumarin anticoagulant, brodifacoum, were studied. Experiments were performed in both normal coronary vasculature and coronary vasculature exposed to 90 min of myocardial ischemia, with or without 60 min of subsequent reperfusion. Ischemia was induced in the left anterior descending artery (LAD); nonischemic vessels from the left circumflex (LCX) artery of the same animals were used as control. Thrombin caused dose-dependent relaxation in isolated LCX preconstricted with prostaglandin F2 alpha (Emax of 89.1 +/- 2.33%). Relaxation was reduced by 90 min of ischemia (Emax of 27.5 +/- 8.0%; p less than 0.05), and further reduced after subsequent reperfusion (Emax of 8.7 +/- 8.7%). However, maximum relaxations to acetylcholine, calcimycin, and isoproterenol were unchanged after ischemia (Emax greater than 90% in all groups). Brodifacoum had no effect on thrombin-induced relaxation in control vessels (Emax of 83.0 +/- 3.5%), or on relaxation in response to acetylcholine, calcimycin, or isoproterenol (Emax greater than 90%). In contrast, brodifacoum markedly reduced thrombin-induced relaxation after ischemia (Emax of 3.3 +/- 3.3%; p less than 0.05) yet significantly preserved the relaxant response to thrombin after ischemia and reperfusion (Emax of 36.6 +/- 4.3%). Infusion of the thrombin inhibitor, D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK), during ischemia and reperfusion also preserved in part the relaxant response induced by thrombin (Emax of 30.0 +/- 5.1%; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Inhibition of thrombin-induced endothelium-dependent relaxation after coronary ischemia in the dog: possible role of the coagulation cascade. 171 94

Pharmacological profiling of recombinant hirudin (r-hirudin) has shown that this selective tight-binding thrombin inhibitor is a potent, well-tolerated anticoagulant. Clinical pharmacological studies were performed in human volunteers after single and repeated doses of 0.1-0.5 mg/kg. Generally, administration of r-hirudin was tolerated without side effects. Thrombin time and partial thromboplastin time were prolonged dependent on the r-hirudin level in plasma. Platelet counts, fibrinogen level and fibrinolytic system remained unchanged. Bleeding time was not prolonged. On intravenous injection, r-hirudin was rapidly distributed into the extracellular space and eliminated, with a dose-dependent half-life of 1-2 h (first-order kinetics). After subcutaneous administration, the rH level in blood reached plateau values within 60-120 min. The high recovery of unchanged r-hirudin in the urine identified renal excretion as the predominant route of r-hirudin clearance.
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PMID:Clinical pharmacology of recombinant hirudin. 189 88

Several laboratory methods are available to measure the anticoagulant activity of recombinant hirudin (r-hirudin), a potent thrombin inhibitor. These assays include clot-based, amidolytic, immunologic and physicochemical techniques. Although r-hirudin, like heparin, is an effective anticoagulant, the mechanism of action of the two agents is different. Thus it is not surprising that the global tests, such as the prothrombin time (PT), partial thromboplastin time (APTT) and the Heptest (Haemachem, Inc., St. Louis, Mo., USA), do not show adequate responses to r-hirudin. In the range of 0.5-10.0 microgram/ml, where full anticoagulation is achieved, as determined by animal models of thrombosis, these assays show little to no prolongation of the time to clot. In order to find a more suitable assay system, modifications of the above assays were evaluated. The diluted APTT and diluted Heptest showed linear concentration-dependent responses to lower levels of r-hirudin with an enhanced sensitivity than that of the classical assays. On the other hand, the diluted thrombin time was too sensitive. Whole-blood clotting assays, ACT and thrombelastograph, effectively measured r-hirudin levels up to 25 micrograms/ml. The amidolytic anti-factor IIa assay, specific for evaluating direct thrombin inhibition, was very effective particularly when modified to decrease the sample:thrombin ratio. This assay may be useful in quality control since it is biochemically defined, and reagents are easily standardized. The relevance of the results of the anti-IIa assay to clinical conditions, however, remains to be determined. Thrombin generation assays have limited value in monitoring the anticoagulant effect of r-hirudin since the effect of thrombin inhibition by r-hirudin on coagulation feedback mechanisms, and thus the effect on thrombin generation, appears to be minimal. Immunologic methods such as ELISA and RIA are under development, but they may only be useful for the direct quantitation of absolute levels of r-hirudin and not for monitoring the clinical anticoagulant action. Furthermore, these assays are only sensitive to sub-microgram/ml levels. Therefore, thrombin-based clotting and amidolytic assays may at present be the best choice for evaluating the functional, clinical antithrombotic effects of r-hirudin.
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PMID:Laboratory assays for the evaluation of recombinant hirudin. 130 Oct 38

The efficacy and specificity of a novel synthetic thrombin inhibitor, DuP 714, on thrombin-induced elevation of cytoplasmic calcium, fibrinogen binding and aggregation in human platelets were examined. Thrombin (0.5 U/ml) stimulated an increase in [125I]fibrinogen binding in gel-filtered platelets which was blocked by DuP 714 with an IC50 value of 2 nM. Thrombin (1 U/ml)-induced elevation of intracellular [Ca2+]i was also blocked by DuP 714 with an IC50 value of 67 nM. A much higher concentration of thrombin (25 U/ml) was used to stimulate aggregation with heparinized platelet-rich plasma. Under these conditions, micromolar concentrations of DuP 714 were needed to inhibit thrombin. In all of these preparations, DuP 714 at concentrations as high as 10(-5) M had no intrinsic effects and did not affect the responses induced by arachidonate, ADP, collagen, epinephrine, vasopressin and serotonin. These data indicate that DuP 714 is a potent and specific thrombin inhibitor capable of arresting the actions of thrombin on human fibrin formation and platelet aggregation and secretion. It may serve as a potential antithrombotic agent for various forms of thrombotic disorders.
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PMID:Inhibition of the thrombin-platelet reactions by DuP 714. 193 Jan 90

Esterolytically inactive diisopropyl fluorophosphate-conjugated thrombin (DIP-alpha-thrombin) stimulated 3H-thymidine incorporation and proliferation of growth-arrested vascular smooth muscle cells (SMCs), similar to native alpha-thrombin. Half-maximal mitogenic response of SMCs was obtained at 1 nM thrombin and was specifically blocked by the leech-derived, high-affinity thrombin inhibitor, hirudin. Native thrombin and a variety of thrombin species that were chemically modified to alter thrombin procoagulant or esterolytic functions were found to induce 3H-thymidine incorporation to a similar extent. Exposure of SMCs to DIP-alpha-thrombin caused a rapid and transient expression of the c-fos protooncogene, determined by Northern blot analysis. These results indicate that thrombin is a potent mitogen for SMCs through a distinct non-enzymatic domain. Binding of 125I-alpha-thrombin to SMC cultures revealed an apparent dissociation constant of 6 nM and an estimated 5.4 x 10(5) binding sites per cell. This binding was inhibited to the same extent by native thrombin and by its nonenzymatic form, DIP-alpha-thrombin. Moreover, the chemotactic fragment of thrombin (CB67-129), which failed to elicit a mitogenic response, competed for 125I-alpha-thrombin binding to SMCs. Cross-linking analysis of 125I-alpha-thrombin to SMCs revealed a specific cell-surface binding site 55 kDa in size. Finally, thrombin immobilized to a naturally produced extracellular matrix retained potent mitogenic activity toward SMCs. These observations lend support to the possibility that in vivo, subendothelial basement membranes sequester thrombin (as well as other bioactive molecules), which may stimulate localized and persistent growth of arterial SMCs. Thrombin may thus be involved directly in progression of atherosclerotic plaque formation.
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PMID:Thrombin immobilized to extracellular matrix is a potent mitogen for vascular smooth muscle cells: nonenzymatic mode of action. 196 93


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