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ADP-mediated Platelet Activation (ADP-mediat + platelet_activation)
Selected AbstractsThe active metabolite of prasugrel inhibits adenosine diphosphate- and collagen-stimulated platelet procoagulant activitiesJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2008A. L. FRELINGER III Summary.,Background:,Prasugrel is a novel antiplatelet prodrug of the same thienopyridine class as clopidogrel and ticlopidine. Metabolism of prasugrel generates the active metabolite R-138727, an antagonist of the platelet P2Y12 adenosine diphosphate (ADP) receptor, leading to inhibition of ADP-mediated platelet activation and aggregation. ADP also enhances the platelet response to collagen, and these two agonists contribute to the generation of platelet procoagulant activity. We therefore examined whether R-138727 inhibits ADP- and collagen-triggered platelet procoagulant activities.Methods and results:,As shown by whole blood flow cytometry, R-138727 inhibited surface phosphatidylserine expression on ADP plus collagen-stimulated platelets and tissue factor (TF) expression on ADP-, collagen-, and ADP plus collagen-stimulated monocyte,platelet aggregates. R-138727 reduced monocyte,platelet aggregate formation, thereby further inhibiting TF expression. ADP, collagen, and ADP plus collagen accelerated the kinetics of thrombin generation in recalcified whole blood and R-138727 significantly inhibited this acceleration. Clot strength in a modified thromboelastograph system was also inhibited by R-138727 (IC50 0.7 ± 0.1 ,m). Conclusions:,In addition to its previously known inhibitory effects on platelet activation and aggregation, the active metabolite of prasugrel, R-138727, inhibits platelet procoagulant activity in whole blood (as determined by phosphatidylserine expression on platelets and TF expression on monocyte,platelet aggregates), resulting in the functional consequences of delayed thrombin generation and impaired clot development. [source] Lipid rafts are required in G,i signaling downstream of the P2Y12 receptor during ADP-mediated platelet activationJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 5 2005T. M. QUINTON Summary., ADP is important in propagating hemostasis upon its secretion from activated platelets in response to other agonists. Lipid rafts are microdomains within the plasma membrane that are rich in cholesterol and sphingolipids, and have been implicated in the stimulatory mechanisms of platelet agonists. We sought to determine the importance of lipid rafts in ADP-mediated platelet activation via the G protein-coupled P2Y1 and P2Y12 receptors using lipid raft disruption by cholesterol depletion with methyl- , -cyclodextrin. Stimulation of cholesterol-depleted platelets with ADP resulted in a reduction in the extent of aggregation but no difference in the extent of shape change or intracellular calcium release. Furthermore, repletion of cholesterol to previously depleted membranes restored ADP-mediated platelet aggregation. In addition, P2Y12-mediated inhibition of cAMP formation was significantly decreased upon cholesterol depletion from platelets. Stimulation of cholesterol-depleted platelets with agonists that depend upon G,i activation for full activation displayed significant loss of aggregation and secretion, but showed restoration when simultaneously stimulated with the G,z -coupled agonist epinephrine. Finally, G,i preferentially localizes to lipid rafts as determined by sucrose density centrifugation. We conclude that G,i signaling downstream of P2Y12 activation, but not G,q or G,z signaling downstream of P2Y1 or ,2A activation, respectively, has a requirement for lipid rafts that is necessary for its function in ADP-mediated platelet activation. [source] Optimizing Antiplatelet Therapy in Coronary InterventionsCLINICAL CARDIOLOGY, Issue S6 2000S. B. King III M.D. Abstract Percutaneous coronary intervention has had a dramatic impact on the current practice of cardiology. One of its important limitations, however, is the potential for producing unfavorable outcomes such as acute coronary closure following angioplasty or atherectomy or subacute thrombosis following stent implantation. These complications may lead to death, myocardial infarction, or the need for urgent bypass surgery. One mechanism underlying these clinical events is platelet-mediated thrombosis due to arterial trauma. Therapeutically, platelet activation by thromboxane and adenosine diphosphate (ADP), as well as platelet aggregation by glycoprotein IIb/IIIa (GPIIb/IIIa) receptors, has been inhibited with various pharmacologic agents. c7E3 (abciximab), a monoclonal antibody directed against GPIIb/IIIa, has been shown to have potent effects on reducing both acute and subacute complications. Other parenteral GPIIb/IIIa inhibitors, including peptide and small nonpepude molecules, have also been found to be clinically effective. Oral versions of similar drugs are currently being evaluated, but several have resulted in disappointing efficacy and safety profiles and have failed to show advantages over aspirin. With all antiplatelet agents, in particular GPIIb/IIIa receptor inhibitors, bleeding and vascular complications must be addressed. Inhibition of thromboxane-induced platelet activation with aspirin has been standard therapy for angioplasty and in the global management of vascular disease. Newer agents that block ADP-mediated platelet activation, the thienopyridines, have been found to be synergistic to aspirin in their effects on the complications of coronary intervention. Ticlopidine and, more recently, clopidogrel, in conjunction with aspirin, have become standard therapies for preventing subacute thrombosis after stent implantation. Large-scale clinical trials are ongoing to optimize their use in combination with GPIIb/IIIa inhibitors. [source] | ||||||||||