Anti-thrombotic action of clopidogrel and PIA1/A2 polymorphism of β3 integrin in patients with coronary artery disease not being treated with aspirin

Individual variability in response to clopidogrel is known but its mechanism is poorly understood.We examined the relationship between glycoprotein Ilia polymorphism Pl(A1/A1) and anti-thrombotic actions of clopidogrel. Clopidogrel (75 mg/d; 2 weeks) was administered to 48 normolipemic patients with coronary artery disease. Bleeding time,thrombin generation at the site of microvascular injury, platelet function under high shear, using PFA-100 with ADP cartridge, and platelet surface activation markers (P-selectin and fibrinogen binding sites on GPIIb/IIIa complex detected by PAC-I antibody), were studied both before and after clopidogrel treatment. Both unstimulated and low-dose (0.02 mu M and 1 mu M) in vitroADP-stimulated platelets were examined. GP Ilia polymorphism was assessed by polymerase chain reaction and restriction fragment length polymorphism analysis. We identified 32 Pl(A1/A1) homozygotes, 15 Pl(A1/A2) heterozygotes and one Pl(A2/A2) homozygote. Clopidogrel significantly prolonged bleeding time in all subjects, but this effect was greater in Pl(A2) carriers (p < 0.01). Furthermore, clopidogrel only depressed thrombin generation at the site of microvascular injury (p < 0.01) in Pl(A2) patients and prolonged closure time measured in vitro by PFA-100 (p < 0.05).At baseline spontaneous expression of PAC-1 and P-selectin was higher in Pl(A2) subjects as compared to Pl(A1) homozygotes (p < 0.05 for both antigens). Clopidogrel lowered the expression of both markers affecting more Pl(A2) carriers, so that the difference in binding PAC-1 antibody between platelets from Pl(A1) and Pl(A2) carriers disappeared, while the difference in P-selectin expression slightly diminished. Anti-thrombotic effects of clopidogrel are more pronounced in CAD patients carrying the pl(A2) allele than in Pl(A1) homozygotes.