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

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

Thrombin activity has been implicated as a mechanism for failed reperfusion and reocclusion following thrombolysis. Aggregating platelets provide a phospholipid surface on which prothrombin is cleaved to form thrombin. We examined markers of thrombin generation and activity in patients enrolled in a randomized, placebo-controlled, dose escalating trial of the platelet glycoprotein IIb-IIIa inhibitor eptifibatide (Integrilintrade mark) administered concomitantly with tissue plasminogen activator for the treatment of myocardial infarction. Measurements were obtained at baseline, at 90 minutes, and at 6, 12, and 24 hours after starting therapy. Eptifibatide inhibited platelet aggregation in response to 20 microM ADP. Levels of fibrinopeptide A (FPA), thrombin-antithrombin complexes (TAT), and prothrombin fragment 1.2 (F1.2) were not lower in patients treated with eptifibatide than in the control group. In the course of dose escalation, two groups of patients received the same 135 microg/kg bolus of eptifibatide, one with and one without a heparin bolus. FPA levels were dramatically lower in the heparin-treated patients. Levels of FPA, TAT, and F1.2 were not higher in patients with than in those without recurrent ischemia, or in patients without than in those with Thrombolysis in Myocardial Infarction (TIMI) grade 3 angiographic flow at 90 minutes. These data suggest that thrombin generation and activity persist following thrombolysis, despite inhibition of platelet aggregation, and that treatment with inhibitors of thrombin activity may be required even when glycoprotein IIb-IIIa inhibitors are used.
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PMID:Inhibition of platelet aggregation with a glycoprotein IIb-IIIa antagonist does not prevent thrombin generation in patients undergoing thrombolysis for acute myocardial infarction. 1059 Jan 83

Several platelet inhibitors were examined in a tissue factor (TF)-initiated model of whole blood coagulation. In vitro coagulation of human blood from normal donors was initiated by 25 pM TF while contact pathway coagulation was suppressed using corn trypsin inhibitor. Products of the reaction were analyzed by immunoassay. Preactivation of platelets with the thrombin receptor activation peptide did not influence significantly the clotting time or thrombin-antithrombin III complex (TAT) formation. Addition of prostaglandin E(1) (5 microM) caused a significant delay in clotting (10.0 minutes) versus control (4.3 minutes). The prolonged clotting time is correlated with delays in platelet activation, formation of TAT, and fibrinopeptide A (FPA) release. In blood from subjects receiving acetylsalicylic acid (ASA or aspirin), none of the measured products of coagulation were significantly affected. Similarly, no significant effect was observed when 5 microM dipyridamole (Persantine) was added to the blood. Antagonists of the platelet integrin receptor glycoprotein (gp) IIb/IIIa had intermediate effects on the reaction. A 1- to 2-minute delay in clot time and FPA formation was observed with addition of the antibodies 7E3 and Reopro (abciximab) (10 microg/mL), accompanied by a 40% to 70% reduction in the maximal rate of TAT formation and delay in platelet activation. The cyclic heptapetide, Integrilin (eptifibatide), at 5 microM concentration slightly prolonged clot time and significantly attenuated the maximum rate of TAT formation. The disruption of the gpIIb/IIIa-ligand interaction not only affects platelet aggregation, but also decreases the rate of TF-initiated thrombin generation in whole blood, demonstrating a potent antithrombotic effect superimposed on the antiaggregation characteristics.
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PMID:Antiplatelet agents in tissue factor-induced blood coagulation. 1129 May 93

Platelets play an important role in the pathophysiology of acute myocardial infarction, unstable angina, and ischemic stroke. The expression of the glycoprotein IIb/IIIa (alphaIIb/beta3 integrin) receptor on the surface of activated platelets constitutes the common pathway for platelet aggregation. Glycoprotein IIb/IIIa has low affinity for its soluble ligands (fibrinogen and von Willebrand factor) in resting platelets. In the setting of vascular injury, platelet activation occurs after binding of the glycoprotein Ib-IX-V receptor to von Willebrand factor in the extracellular matrix (at high shear rate) and binding of soluble agonists to specific platelet membrane receptors. The ensuing inside-out signaling increases several-fold the affinity and avidity of alphaIIb/beta3 for its ligands. High affinity ligand binding to alphaIIb/beta3 triggers outside-in signaling, causing microskeletal contraction and platelet retraction. The signaling pathways for inside-out and outside-in signaling are incompletely understood. Glycoprotein IIb/IIIa antagonists were developed under the premise that these agents would abrogate platelet aggregation while preserving platelet monolayer deposition at sites of injury. A number of parenteral and oral agents have been developed and evaluated in clinical trials. Three of them are approved in the United States and other countries: abciximab (ReoPro; the Fab fragment of a chimeric human-mouse antibody), eptifibatide (Integrelin; a cyclic heptapeptide), and tirofiban (Aggrastat; a tyrosine-derived nonpeptide molecule). The greatest clinical impact of these parenteral agents (used in conjunction with aspirin and heparin) has been in the prevention of ischemic complications after percutaneous coronary intervention. In contrast, oral agents have yielded disappointing results in the secondary prevention of acute coronary syndromes, and none of them are approved at present. Eptifibatide and tirofiban are specific for alphaIIb/beta3, whereas abciximab also exhibits cross-reactivity with the alphavbeta3 and alphaMbeta2 integrins. Although alphaIIb/beta3 is unique to platelets and megakaryocytes, alphavbeta3 is more widely distributed and mediates several functions, including endothelial cell migration, monocyte adhesion, angiogenesis, and inhibition of apoptosis. alphaMbeta2 mediates leukocyte-platelet interactions. In the percutaneous coronary intervention trials, abciximab has been more efficacious than the other parenteral agents, perhaps because of cross-reactivity with these other integrins, the pharmacodynamic profile of abciximab, or other effects. Other documented effects of abciximab include acute dethrombosis, reduction of thrombin generation, and improved flow in the coronary microcirculation after percutaneous coronary intervention. Abciximab is presently under evaluation in the treatment of acute ischemic stroke. Promising data have been obtained in experimental models of tumor angiogenesis and sickle cell anemia.
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PMID:Platelet glycoprotein IIb/IIIa antagonists: lessons learned from clinical trials and future directions. 1200 56

Aim of our study was to investigate effects of eptifibatide and anticoagulants on platelet aggregation and thrombin generation under low and high coagulant challenge in tissue factor-activated platelet rich plasma using a model allowing simultaneous determination of the time course of platelet aggregation and thrombin generation. Eptifibatide exerted a dose-dependent anti-aggregating effect under both high and significantly stronger under low coagulant challenge. Combination of eptifibatide and anticoagulants resulted in significant additive prolongation of the lag phase until the onset of platelet aggregation, more pronounced under low coagulant challenge. Under high, but not under low coagulant challenge combination of eptifibatide and anticoagulants had a significant synergistic inhibitory effect on platelet aggregation. Under low coagulant challenge combination of eptifibatide with LMWH, but not with UH, or rH, resulted in significantly reduced thrombin potential, F 1+2 generation, and FXa formation compared to measurements in the absence of eptifibatide. We demonstrate a synergistic effect of eptifibatide and anticoagulants on platelet aggregation inhibition and an additional inhibitory effect of LMWH and eptifibatide on thrombin generation. Our results support the notion that combination of eptifibatide and anticoagulants might be beneficial in atherosclerotic disease to palliate the thrombogenic potency of ruptured atherosclerotic plaques.
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PMID:Combined effects of eptifibatide and anticoagulants: differences between LMWH and UH or rH in thrombin generation inhibition but not in platelet aggregation inhibition. 1252 53

Irrespective of their mechanism of action, anticoagulants reduce the formation and action of thrombin. Thus they interfere with a final step in coagulation. Among platelet inhibitors only the GPIIb/IIIa antagonists inhibit the common pathway of aggregation, namely the formation of platelet-to-platelet bridges which are mediated by fibrinogen or von Willebrand factor. In contrast, acetylsalicylic acid (ASA), NSAIDs, clopidogrel (Plavix) or ticlopidine (Tyklid) inhibit platelet activation by abrogating the formation or action of a secondary platelet agonist, namely of thromboxane A(2) or ADP. They do not block platelet aggregation which is directly induced by thrombin. Therefore, ASA, clopidogrel, or ticlopidine are not associated with a significant risk of bleeding as long as other factors such as an extensive thrombocytopenia or anticoagulation are not involved. Therefore, in contrast to anticoagulants, therapeutic drug monitoring is not necessary with ASA, clopidogrel, nor ticlopidine. On the other hand, ASA has even to be applied at a dosage that almost completely inhibits thromboxane synthesis in order to act on platelet aggregation at all. Among the GPIIb/IIIa-antagonists only parenteral drugs have been approved for therapeutic use, e. g. abciximab (ReoPro), eptifibatide (Integrilin), and tirofiban (Aggrastat). Clinical studies revealed an increased risk of bleeding without a sufficient therapeutic benefit of oral GPIIb/IIIa antagonists. GPIIb/IIIa antagonists may induce thrombocytopenia that is attributed to an out-side-in signalling or immunological phenomena. A test system (Ultegra, Accumetrics) is available for a therapeutic drug monitoring of GPIIb/IIIa antagonists. However, estimation of the bleeding risk always requires an evaluation of all factors influencing the haemostatic system, especially when heparin or other inhibitors are applied additionally.
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PMID:[Platelet aggregation disorders]. 1460 82

The aim of our study was to investigate the combined in vitro effects of melagatran and eptifibatide on platelet aggregation and thrombin generation under low and high coagulant challenge in tissue-factor-activated, platelet-rich plasma. Increasing amounts of melagatran dose-dependently decreased prothrombin fragment 1.2 and activated factor X values, and dose-dependently prolonged the lag phase until the onset of platelet aggregation. Eptifibatide exerted a dose-dependent anti-aggregating effect under both high and low coagulant challenge. The combination of melagatran and eptifibatide resulted in significant additive prolongation of the lag phase until the onset of platelet aggregation, which was more pronounced under low coagulant challenge. Under low, but not under high, coagulant challenge, the combination of melagatran and eptifibatide had a significant additive inhibitory effect on platelet aggregation. No additive effects on decreasing prothrombin fragment 1.2 and activated factor X values were observed with combined administration of the drugs. The present study demonstrates the additive effect of melagatran and eptifibatide on platelet aggregation inhibition and on prolongation of the lag phase until the onset of platelet aggregation.
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PMID:Combined effects of melagatran and eptifibatide on platelet aggregation inhibition but not thrombin generation inhibition. 1509 Oct

Integrin beta(3) is polymorphic at residue 33 (Leu(33) or Pro(33)), and the Pro(33)-positive platelets display enhanced aggregation, P-selectin secretion, and shorter bleeding times. Because outside-in signaling is critical for platelet function, we hypothesized that the Pro(33) variant provides a more efficient signaling than the Leu(33) isoform. When compared with Pro(33)-negative platelets, Pro(33)-positive platelets demonstrated significantly greater serine/threonine phosphorylation of extracellular signal-regulated kinase (ERK2) and myosin light chain (MLC) but not cytoplasmic phospholipase A2 upon thrombin-induced aggregation. Tyrosine phosphorylation of integrin beta(3) and the adaptor protein Shc was no different in the fibrinogen-engaged platelets from both genotypes. The addition of Integrilin (alpha(IIb)beta(3)-fibrinogen blocker) or okadaic acid (serine/threonine phosphatase inhibitor) dramatically enhanced ERK2 and MLC phosphorylation in the Pro(33)-negative platelets when compared with Pro(33)-positive platelets, suggesting that integrin engagement during platelet aggregation activates serine/threonine phosphatases. The phosphatase activity of myosin phosphatase (MP) that dephosphorylates MLC is inactivated by phosphorylation of the myosin binding subunit of MP at Thr(696), and aggregating Pro(33)-positive platelets exhibited an increased Thr(696) phosphorylation of MP. These studies highlight a role for the dephosphorylation events via the serine/threonine phosphatases during the integrin outside-in signaling mechanism, and the Leu(33) --> Pro polymorphism regulates this process. Furthermore, these findings support a mechanism whereby the reported enhanced alpha granule secretion in the Pro(33)-positive platelets could be mediated by an increased phosphorylation of MLC, which in turn is caused by an increased phosphorylation and subsequent inactivation of myosin phosphatase.
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PMID:The Pro33 isoform of integrin beta3 enhances outside-in signaling in human platelets by regulating the activation of serine/threonine phosphatases. 1582 39

An acute inflammatory response occurs following percutaneous coronary and peripheral vascular interventions (PVI), partly mediated by platelet activation. Glycoprotein (GP) IIb-IIIa inhibitors might partially attenuate this inflammation rise in the coronary patient, but data in patients undergoing PVI are lacking. In the Integrilin Reduces Inflammation in Peripheral Vascular Interventions trial (INFLAME), we hypothesized that eptifibatide reduces the acute inflammatory responses following PVI. This is a single-center, randomized, open-label study of intravenous eptifibatide (180 micro/kg bolus x 2, 10 minutes apart, then 2 micro/kg/min infusion over 18 hours) and low-dose unfractionated heparin (60 Units per kg, target activated clotting time (ACT) 200-250 sec) [LDH+I group; n = 21] versus high-dose unfractionated heparin alone (100 Units per kg, target ACT 300-400 sec) [HDH group; n = 21] in patients undergoing iliac and infrainguinal interventions. The primary endpoints of the study were markers of inflammation (soluble CD-40L [sCD-40L], high-sensitivity C-reactive protein [hs-CRP] and interleukin-6 [IL-6]), thrombin generation (Fragment 1.2 [F1.2]), and fibrinogen measured at baseline and postrandomization. Markers were assayed at baseline, postdilatation at 30 minutes, 2 hours, 18 hours, 48 hours and 7 days. Mean platelet inhibition with eptifibatide was 98% (range 92-100%) using the Accumetrics Rapid Platelet Function Assay at 10 minutes after final bolus. After adjusting for baseline values, the mean +/- SE difference in sCD-40L (loge scale), hs-CRP and F1.2 between the LDH+I group and the HDH was not significant. Fibrinogen had significantly higher mean levels at 7 days for the LDH+I group (541.19 mg/dL versus 472.26 mg/dL; p-value = 0.024). IL-6 was more detectable in the LDH+I group compared to the HDH following intervention. We conclude that LDH+I combination did not reduce acute inflammatory responses as compared to HDH in patients undergoing peripheral vascular interventions.
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PMID:Eptifibatide in peripheral vascular interventions: results of the Integrilin Reduces Inflammation in Peripheral Vascular Interventions (INFLAME) trial. 1639 77

The current study systematically evaluates the in vitro effect of eptifibatide, a GPIIb/IIIa blocker, on various responses of porcine platelets evoked by principal physiological stimulators. Eptifibatide at concentrations up to 40 mg/mL did not affect the calcium signal produced by thrombin, partly reduced the procoagulant response evoked by collagen, and strongly inhibited (IC50 approximately 11 mg/mL) adhesion of these cells to fibrinogen coated surfaces. Eptifibatide in a concentration-dependent manner reduced ADP, collagen, and thrombin-induced platelet aggregation (IC50 = 16-27 mg/mL), dense granule secretion (IC50 = 22-31 mg/mL) and lysosome secretion (IC50 = 25-50 mg/mL). Substantial (up to 30-40%) collagen or thrombin-evoked platelet aggregation still occurred at high (52 mg/mL) eptifibatide concentrations. Direct comparison of the susceptibility of platelet aggregation and dense granule secretion to the inhibitory action of eptifibatide indicates that aggregation is appreciably more sensitive than secretion. Eptifibatide (8 mg/mL) added together with a low (70 ng/mL) concentration of bivalirudin (a direct thrombin inhibitor) effectively (approximately 90%) reduced platelet aggregation induced by thrombin (0.2 U/mL). Based on these results, eptifibatide is not expected to reduce efficiently thrombus formation initiated by rapid local production of large amounts of thrombin. One practical consequence of our in vitro studies is the suggestion that the anti-thrombotic efficacy of eptifibatide, especially in preventing acute thrombotic events, may be largely improved by its combination with direct thrombin inhibitors.
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PMID:The in vitro effect of eptifibatide, a glycoprotein IIb/IIIa antagonist, on various responses of porcine blood platelets. 1964 23

Thromboembolic disorders are one of the disorders for which we are still on the look out for a safe and efficient drug. Despite the widespread use of antithrombotic drugs for the prevention and treatment of arterial and venous thrombosis, thromboembolic diseases continue to be a major cause of death and disability worldwide. This shows our inefficiency in searching efficacious and safe antithrombotic drugs. We have reached the basic mechanism of thrombus formation and by interrupting various steps of this mechanism, we can prevent as well as treat thromboembolic disorders. In continuation of Aspirin, now, we are using Clopidogrel, Ticlopidine and GpIIb/IIIa inhibitors (Abciximab, Tirofiban and Eptifibatide). Warfarin is an old antithrombotic drug which is still being used; but due to various side effects and drug interactions, we are bound to use newer drugs. Newer antiplatelet drugs include Prasugrel, Ticagrelor and Cangrelor, whereas newer thrombin inhibitors are Ximelgatran and Dabigatran. Apixaban is also a newer entry in this category as factor Xa inhibitor. Idrabiotaparinux is an indirect inhibitor of Xa as it accelerates the activity of antithrombin. Moreover, researches and trials for better and safe drugs are ongoing.
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PMID:Newer antithrombotic drugs. 2157 50


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