Platelet activation and antiplatelet therapy in patients with ischemic stroke

In patients with ischemic stroke, findings of platelet activation are frequent in platelet function tests. They include increases in plasma levels of beta-thromboglobulin and platelet factor 4, shortening of platelet survival and increasing of platelet lysis, enhancing of shear-induced platelet aggregation (SIPA), and increasing of reticulated platelets as well as platelet fibrinogen binding (PFB) and P-selectin expression (PSE). Aspirin can reduce vascular events including stroke, myocardial infarction and vascular death in high-risk patients with occlusive vascular disease. Aspirin's effect on vascular events is J-shaped, which appeared to be related to the effects on platelet aggregation and release reaction as well as prostaglandin synthesis. Thienopyridines can reduce vascular events even more than aspirin. SIPA was inhibited by thienopyridines but not by aspirin. Combination of aspirin and dipyridamole has an additive effect on preventing subsequent stroke. Aspirin enhanced an inhibitory effect of dipyridamole on SIPA in whole blood. PFB and PSE were not inhibited by aspirin but were partially inhibited by ticlopidine, and markedly inhibited by aspirin plus ticlopidine. Glycoprotein (GP) IIb/IIIa, inhibitors can block the final common pathway of platelet aggregation. However, PSE and platelet-derived microparticle formation induced by shear stress were never inhibited at lower concentrations and were rather enhanced at higher concentrations of GP IIb/IIIa inhibitors. These results might be related to the fact that many oral GP IIb/IIIa inhibitors fail to show efficacy in patients with acute coronary syndrome. (C) 2003 Elsevier Science B.V. All rights reserved.