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:3.4.21.6 (thromboplastin)
13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Intravenous administration of thrombin inhibitors, such as hirudin, has been shown to decrease the frequency of coronary artery reocclusion after thrombolysis. However, recent findings in large clinical trials in patients with unstable angina and myocardial infarction have failed to demonstrate a sustained antithrombotic effect after cessation of drug treatment. These findings indicate a need for a prolonged antithrombotic regimen, preferably an orally active thrombin inhibitor. To test the hypothesis that a regimen consisting of oral thrombin inhibitor will delay or prevent the formation of occlusive clot, anesthetized dogs were given saline (n = 9) or a single dose of a novel active site low-molecular-weight thrombin inhibitor melagatran by nasogastric tube (1.5 mg/kg, n = 6; 2.5 mg/kg, n = 6), and 15 min later, a potent thrombogenic stimulus in the form of anodal current (100 microA) was applied to the intimal surface of the narrowed left anterior descending coronary artery (LAD). All saline-treated dogs developed stable thrombus, indicated by zero flow at 34 +/- 7 min after initiation of direct current. On the other hand, one of the six dogs given high-dose melagatran did not develop thrombotic occlusion of the LAD during the entire 4 h of observation. Mean time to occlusive thrombus formation in 11 other dogs was prolonged 4-5 times as compared with that in the saline-treated dogs (p < 0.001). Spontaneous thrombolysis was observed in three of 11 dogs after initial clot formation. Overall, the coronary artery was patent for 68% (low dose) and 75% (high dose) of the observation period in melagatran-treated dogs (vs. 14% of observation period in saline-treated dogs). Peak plasma concentration was 0.87 +/- 0.22 microM in dogs given low-dose and 1.38 +/- 0.30 microM in dogs given high-dose melagatran. The activated partial thromboplastin time (aPTT) increased 1.5-fold at peak plasma concentration of melagatran. These observations imply (a) thrombin generation plays a critical role in thrombus formation in narrowed coronary arteries, (b) oral melagatran prevents or delays thrombus formation, whereas the aPTT is only modestly prolonged, and (c) the thrombus formed in the presence of melagatran is prone to spontaneous lysis in this canine model of coronary thrombosis.
...
PMID:Melagatran, an oral active-site inhibitor of thrombin, prevents or delays formation of electrically induced occlusive thrombus in the canine coronary artery. 951 77

The importance of thrombin in arterial and venous thrombosis renders thrombin inhibition an important therapeutic target. Identification of novel inhibitors requires an appropriate animal model. We modified a previously reported rat arterial thrombosis model to allow simultaneous assessment of the arterial and venous antithrombotic efficacies of heparin, hirudin, hirulog, a novel thrombin inhibitor H-(N-Me-D-Phe)-Pro-L-trans-4-aminocyclohexyl-Gly-[CO-CO]-NHCH3+ ++ (L-370,518) and the factor Xa inhibitor tick anticoagulant peptide in rabbits. Thrombosis was induced through application of 70% ferric chloride to the femoral artery and jugular vein. Incidence of occlusion, thrombus weight, aPTT and plasma inhibitor concentrations were determined. Heparin was efficacious in preventing arterial and venous occlusive thrombosis but at a dose that profoundly elevated aPTT. On a molar dosing basis, the approximate order of potency of the thrombin and factor Xa inhibitors was similar in artery and vein: hirudin>tick anticoagulant peptide>hirulog> or =L-370,518. Data suggested that compounds tended to be more potent in preventing venous thrombosis than arterial. This thrombin-dependent model is an economical and efficient approach to arterial and venous antithrombotic efficacy screening that eliminates variabilities encountered when multiple model/multiple animal strategies are employed.
...
PMID:Assessment of thrombin inhibitor efficacy in a novel rabbit model of simultaneous arterial and venous thrombosis. 953 Oct 58

The signaling pathway initiated by factor Xa on vascular endothelial cells was investigated. Factor Xa stimulated a 5- to 10-fold increased release of nitric oxide (NO) in a dose-dependent reaction (0.1-2.5 microG/ml) unaffected by the thrombin inhibitor hirudin but abolished by active site inhibitors, tick anticoagulant peptide, or Glu-Gly-Arg-chloromethyl ketone. In contrast, the homologous clotting protease factor IXa or another endothelial cell ligand, fibrinogen, was ineffective. A factor Xa inter-epidermal growth factor synthetic peptide L (83)FTRKL(88) (G) blocking ligand binding to effector cell protease receptor-1 inhibited NO release by factor Xa in a dose-dependent manner, whereas a control scrambled peptide KFTGRLL was ineffective. Catalytically active factor Xa induced hypotension in rats and vasorelaxation in the isolated rat mesentery, which was blocked by the NO synthase inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) but not by D-NAME. Factor Xa/NO signaling also produced a dose-dependent endothelial cell release of interleukin 6 (range 0.55-3.1 ng/ml) in a reaction inhibited by L-NAME and by the inter-epidermal growth factor peptide Leu(83)-Leu(88) but unaffected by hirudin. Maximal induction of interleukin 6 mRNA required a brief, 30-min stimulation with factor Xa, unaffected by subsequent addition of tissue factor pathway inhibitor. These data suggest that factor Xa-induced NO release modulates endothelial cell-dependent vasorelaxation and cytokine gene expression. This pathway requiring factor Xa binding to effector cell protease receptor-1 and a secondary step of ligand-dependent proteolysis may preserve an anti-thrombotic phenotype of endothelium but also trigger acute phase responses during activation of coagulation in vivo.
...
PMID:Hypotension and inflammatory cytokine gene expression triggered by factor Xa-nitric oxide signaling. 953 8

This study was designed to identify functionally important factor IX (FIX) residues. Using recombinant techniques and cell culture, we produced a mutant FIX with arginine at 338 changed to alanine (R338A-FIX). This molecule had approximately 3 times greater clotting activity than that of wild type FIX (wt-FIX) in the activated partial thromboplastin assay. R338A-FIX reacted normally with a panel of three FIX specific monoclonal antibodies and migrated on sodium dodecyl sulfate-polyacrylamide gels indistinguishably from wt-FIX. Using functional assays, we determined that R338A-FIXa's Kd for factor VIIIa (FVIIIa) was similar to that of wt-FIXa. Our kinetic analysis, using factor X as substrate, indicated that the mutation's major effects were a 3-fold increase in kcat and a 2-fold decrease in Km both manifested only in the presence of FVIIIa. R338A-FIXa's increased catalytic efficiency did not result from ablation of a thrombin sensitive site, reported to occur at arginine 338, since in our assays the thrombin inhibitor, hirudin, had no effect on activity of either wt-FIXa or R338A-FIXa. R338A-FIXa and wt-FIXa had equal activity, with or without FVIIIa, toward the synthetic substrate, methylsulfonyl-D-cyclohexylglycyl-arginine-p-nitroanilide. Interestingly, R338A-FIXa had reduced affinity for heparin. Therefore, we propose that R338A-FIXa's increased activity is not due to an allosteric effect on the active site, but that the Arg-338 residue is part of an exosite that binds both factor X and the mucopolysaccharide, heparin.
...
PMID:Changing residue 338 in human factor IX from arginine to alanine causes an increase in catalytic activity. 957 52

We have previously identified and characterized a potent and specific thrombin inhibitor, isolated from Bothrops jararaca, named bothrojaracin. Bothrojaracin interacts with the two positively charged recognition sites of thrombin referred to as exosite 1 and exosite 2, whereas it does not interact with the thrombin active site. Consequently, bothrojaracin inhibits thrombin-induced fibrinogen to fibrin conversion and platelet activation, without inhibition of thrombin-catalyzed cleavage of small synthetic substrates. In the present study, we show that bothrojaracin exerts an anticoagulant effect in plasma, illustrated by the prolongation of the aPTT. Using purified proteins, we observed that the anticoagulant effect of bothrojaracin was not only due to the inhibition of fibrinogen to fibrin conversion, but in addition to the inhibition of factor V activation by thrombin. Bothrojaracin decreased the rate of thrombin-catalyzed proteolysis of factor V and concurrently the generation of factor Va cofactor activity measured in a prothrombinase assay. We compared the effect of bothrojaracin with that of ligands binding specifically exosite 1 (hirudin C-terminal peptide SH54-65) or exosite 2 (heparin, prothrombin fragment 2). SH54-65 delayed thrombin catalyzed factor V activation whereas heparin or prothrombin fragment 2 did not. The thrombin derivatives beta- and gamma-thrombin, which are defective in their exosite 1, but present with a normally exposed exosite 2, had a reduced capacity to activate factor V, which was not further impaired by the exosite 2 ligands, bothrojaracin, heparin or prothrombin fragment 2. Altogether, our results provide further insight into the anticoagulant effect of bothrojaracin showing that it is a potent inhibitor of the feedback activation of factor V by thrombin, and thus of the up-regulation of its own production by thrombin. Inhibition of thrombin-catalyzed factor V activation by bothrojaracin is mainly mediated through the interaction of the inhibitor with thrombin exosite 1, whereas contribution of the interaction with exosite 2 does not appear to play a direct role in factor V recognition by thrombin.
...
PMID:Inhibition of thrombin-catalyzed factor V activation by bothrojaracin. 965 41

A coagulation inhibitor was identified and isolated from the salivary glands of a malarial vector mosquito, Anopheles stephensi. The salivary gland extract prolonged activated partial thromboplastin time (APTT) and prothrombin time (PT) in assays with human plasma. The inhibition assay of the factors in the coagulation cascade by using synthetic chromogenic substrates showed that the anticoagulant in the mosquito salivary glands is a thrombin inhibitor, but not an inhibitor of factor Xa. The anticoagulant was purified to homogeneity from the mosquito thorax which contains the salivary glands by means of a combination of thrombin affinity and anion exchange chromatography. All of the anticoagulant activity was recovered from the fraction bound to the thrombin affinity column and no activity was detected in the unbound fraction. This result indicated that the thrombin inhibitor is the sole anticoagulant in the salivary glands of A. stephensi. This also suggested a noncovalent, reversible interaction between thrombin and its inhibitor. Size exclusion chromatography and SDS-PAGE estimated the molecular weight of the inhibitor as 45 kDa.
...
PMID:Purification and characterization of a thrombin inhibitor from the salivary glands of a malarial vector mosquito, Anopheles stephensi. 968 55

Anticoagulant therapy has changed dramatically during the past two years. Low molecular weight heparin has substantially replaced unfractionated heparin as the parenteral anticoagulant of choice. The use of warfarin has substantially increased, especially for prevention of stroke in the setting of atrial fibrillation. It has become clear that warfarin cannot be administered effectively in an unmonitored fixed-dose fashion. The parenteral direct thrombin inhibitor desirudin was shown to be efficacious in the prevention of deep vein thrombosis in man. Small thrombin and factor Xa inhibitors with in vivo oral anticoagulant activity have been identified.
...
PMID:Cardiovascular chemotherapy: anticoagulants. 973 18

The small molecule direct thrombin inhibitor L-374,087 was characterized across species in an in vitro activated partial thromboplastin clotting time (aPTT) assay and in vivo in rhesus monkey and dog thrombosis models. In vitro in rhesus, dog, and human plasma, L-374,087 concentrations eliciting 2-fold increases in aPTT were 0.25, 1.9, and 0.28 microM, respectively. In anesthetized rhesus monkeys, 300 microgram/kg bolus plus 12 microgram/kg/min and 300 microgram/kg bolus plus 30 microgram/kg/min L-374,087 i.v. infusions significantly reduced jugular vein thrombus extension, with both regimens limiting venous thrombus extension to 2-fold that of baseline thrombus mass compared with a 5-fold extension observed in the vehicle control group. Antithrombotic efficacy in the rhesus with the lower-dose regimen was achieved with 2.3- to 2.4-fold increases in aPTT and prothrombin time. In a conscious instrumented dog model of electrolytic vessel injury, the oral administration of two 10 mg/kg L-374,087 doses 12 h apart significantly reduced jugular vein thrombus mass, reduced the incidence of and delayed time to occlusive coronary artery thrombosis, and significantly reduced coronary artery thrombus mass and ensuing posterolateral myocardial infarct size. Antithrombotic efficacy in the dog was achieved with 1.6- to 2.0-fold increases in aPTT at 1 to 6 h after oral dosing with L-374,087. These results indicate significant antithrombotic efficacy against both venous and coronary arterial thrombosis with L-374,087 with only moderate elevations in aPTT or prothrombin time. The oral efficacy of L-374,087 characterizes this compound as a prototype for the further development of orally active direct thrombin inhibitors.
...
PMID:Antithrombotic efficacy of thrombin inhibitor L-374,087: intravenous activity in a primate model of venous thrombus extension and oral activity in a canine model of primary venous and coronary artery thrombosis. 1008 43

The objective of this study was to determine whether a thrombin inhibitor (PPACK) and a factor Xa inhibitor (GGACK) either alone or in combination can anticoagulate whole blood without biasing the analysis of several critical care analytes. Whole blood clot time was used to assess anticoagulant efficacy. The analytical biases mediated by the anticoagulants on glucose, urea, creatinine, electrolytes, amylase, lactate dehydrogenase, creatine kinase, ionized calcium and pH were assessed. The protease inhibitor mixture (100 micrommol/l PPACK + 500 micromol/l GGACK) was more a potent anticoagulant than the individual agents at the same concentrations. Both PPACK and GGACK, alone and in combination, reduced the activity of creatine kinase and amylase by 3-10% while the remaining critical care analytes were less affected. In conclusion, PPACK and GGACK mixtures can effectively anticoagulate whole blood, but the mixtures exert pre-analytical influences that limit the analytical versatility of these novel plasma-matrices.
...
PMID:Evaluation of the thrombin inhibitor D-phenylalanyl-L-prolyl-L-arginine chloromethylketone (PPACK) with the factor Xa inhibitor 1,5-dansyl-L-glutamyl-L-glycyl-L-arginine chloromethylketone (GGACK) as anticoagulants for critical care clinical chemistry specimens. 1009 May 27

Forty-eight patients with acute proximal deep vein thrombosis (DVT) were randomised to intravenous infusions for 4 to 6 days with melagatran, a novel synthetic low molecular weight thrombin inhibitor, or unfractionated heparin adjusted by the activated partial thromboplastin time (APTT). The aim of the study was to investigate the pharmacokinetics, pharmacodynamics and the safety of melagatran therapy at three different doses. Steady-state plasma concentrations were rapidly achieved and maintained throughout the infusion period. The mean plasma concentrations in the low, medium and high dose groups were 0.17, 0.31 and 0.53 micromol/l, respectively. The prolongation of APTT was stable during the melagatran infusions and correlated to the plasma concentration. Phlebographically verified regression of thrombus size measured as decrease in Marder score was seen after 4 to 6 days in 8 of 12 patients, 6 of 12 patients and 5 of 11 patients in the low, medium and high dose groups of melagatran and in 5 of the heparin-treated patients. In the low dose group with melagatran, thrombus extension was seen in one patient. At the dose levels studied, melagatran was well tolerated with no clinically significant bleeding problems, suggesting that melagatran could safely be given to patients suffering from DVT.
...
PMID:Pharmacokinetics and pharmacodynamics of melagatran, a novel synthetic LMW thrombin inhibitor, in patients with acute DVT. 1010 60


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---