The active metabolite of prasugrel effectively blocks the platelet P2Y12 receptor and inhibits procoagulant and pro-inflammatory platelet responses

The aim of these studies was to investigate the extent of platelet P2Y₁₂ receptor inhibition by the thienopyridine active metabolite of prasugrel, R-138727. Blood was taken from healthy volunteers and pre-incubated with R-138727 or cangrelor (AR-C66931MX). Platelet aggregation was assessed in platelet rich plasma (PRP) and whole blood (WB). Vasodilator stimulated phosphoprotein (VASP) phosphorylation, platelet procoagulant activity (annexin V binding and microparticle formation) and calcium mobilisation were measured by flow cytometry. Platelet-leukocyte co-aggregate formation and sCD40L release, both pro-inflammatory responses of platelets, were measured by flow cytometry and ELISA, respectively. P2Y₁₂ receptor antagonism was determined using a radioligand binding assay (³³P 2-MeSADP) in resting and stimulated platelets and the effects of clopidogrel administration were also assessed. R-138727 yielded concentration-dependent inhibition of platelet aggregation, VASP phosphorylation inhibition, procoagulant activity and pro-inflammatory responses. In the presence of R-138727 or cangrelor there was increased calcium reuptake following agonist stimulation. R-138727 30 µmol/L and cangrelor 1 µmol/L completely inhibited ³³P 2-MeSADP binding, compared to partial inhibition following clopidogrel administration. Platelet activation and granule secretion did not expose an additional pool of P2Y₁₂ receptors. Prasugrel's active metabolite effectively blocks the P2Y₁₂ receptor with the highest concentrations tested yielding complete inhibition of P2Y₁₂-mediated amplification of several important platelet responses.