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Residual platelet ADP reactivity after clopidogrel treatment is dependent on activation of both the unblocked P2Y(1) and the P2Y (12) receptor and is correlated with protein expression of P2Y (12).

ABSTRACT: Two ADP receptors have been identified on human platelets: P2Y(1) and P2Y(12). The P2Y(12) receptor blocker clopidogrel is widely used to reduce the risks in acute coronary syndromes, but, currently, there is no P2Y(1) blocker in clinical use. Evidence for variable responses to clopidogrel has been described in several reports. The mechanistic explanation for this phenomenon is not fully understood. The aim of this study was to examine mechanisms responsible for variability of 2MeS-ADP, a stable ADP analogue, induced platelet reactivity in clopidogrel-treated patients. Platelet reactivity was assessed by flow cytometry measurements of P-selectin (CD62P) and activated GpIIb/IIIa complex (PAC-1). Residual 2MeS-ADP activation via the P2Y(12) and P2Y(1) receptors was determined by co-incubation with the selective antagonists AR-C69931 and MRS2179 in vitro. P2Y(1) and P2Y(12) receptor expression on both RNA and protein level were determined, as well as the P2Y(12) H1 or H2 haplotypes. Our data suggest that the residual platelet activation of 2MeS-ADP after clopidogrel treatment is partly due to an inadequate antagonistic effect of clopidogrel on the P2Y(12) receptor and partly due to activation of the P2Y(1) receptor, which is unaffected by clopidogrel. Moreover, a correlation between increased P2Y(12) protein expression on platelets and decreased response to clopidogrel was noticed, r(2)=0.43 (P<0.05). No correlation was found between P2Y(12) mRNA levels and clopidogrel resistance, indicating post-transcriptional mechanisms. To achieve additional ADP inhibition in platelets, antagonists directed at the P2Y(1) receptor could be more promising than the development of more potent P2Y(12) receptor antagonists.

SUBMITTER: Braun OO

PROVIDER: S-EPMC2096644 | biostudies-other | 2007 Jun

REPOSITORIES: biostudies-other

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Project description:Background: Platelet-derived microvesicles (PMVs), shed from platelet surface membranes, constitute the majority of circulating microvesicles and have been implicated in procoagulant, pro-inflammatory and pro-atherosclerotic effects. Our aim was to compare plasma PMVs numbers in relation to platelet reactivity during dual antiplatelet therapy (DAPT) with various P2Y12 adenosine diphosphate (ADP) receptor antagonists. Methods: In pre-discharge men treated with DAPT for an acute coronary syndrome, plasma PMVs were quantified by flow cytometry on the basis of CD62P (P-selectin) and CD42 (glycoprotein Ib) positivity, putative indices of PMVs release from activated and all platelets, respectively. ADP-induced platelet aggregation was measured by multiple-electrode aggregometry. Results: Clinical characteristics were similar in patients on clopidogrel (n=16), prasugrel (n=10) and ticagrelor (n=12). Platelet reactivity was comparably reduced on ticagrelor or prasugrel versus clopidogrel (p<0.01). Compared to clopidogrel-treated patients, CD42+/CD62P+ PMVs counts were 3-4-fold lower in subjects receiving ticagrelor (p=0.001) or prasugrel (p<0.05), while CD42+ PMVs were significantly reduced on ticagrelor (by about 6-fold, p<0.001), but not prasugrel (p=0.3). CD42+/CD62P+ PMVs numbers correlated positively to the ADP-induced aggregation on clopidogrel (p<0.01) or prasugrel (p<0.05), which was absent in ticagrelor users (p=0.8). CD42+ PMVs counts were unrelated to platelet reactivity (p>0.5). Conclusions: Higher antiplatelet potency of prasugrel and ticagrelor versus clopidogrel is associated with decreased plasma CD42+/CD62P+ PMVs numbers. However, in contrast to thienopyridines, the association of reduced CD42+/CD62P+ PMVs counts with ticagrelor use appears independent of its anti-aggregatory effect. Despite similar platelet-inhibitory activity of ticagrelor and prasugrel, only the treatment with ticagrelor seems associated with lower total PMVs release. Our preliminary findings may suggest a novel pleiotropic effect of ticagrelor extending beyond pure anti-aggregatory properties of the drug.

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Residual platelet ADP reactivity after clopidogrel treatment is dependent on activation of both the unblocked P2Y(1) and the P2Y (12) receptor and is correlated with protein expression of P2Y (12).

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