Ticagrelor inhibits human platelet aggregation via adenosine in addition to P2Y12 antagonism

BackgroundTicagrelor, a P2Y(12) antagonist, is an antiplatelet agent approved for the treatment of acute coronary syndromes; it also inhibits adenosine uptake by erythrocytes and other cells. ObjectiveTo test whether ticagrelor inhibits platelet aggregation (PA) in whole blood (WB) by increasing the extracellular levels of adenosine, which inhibits PA via the A(2A) receptor. MethodsCollagen-induced PA was measured in WB or platelet-rich plasma (PRP) from 50 healthy subjects and two patients with inherited P2Y(12) deficiency, in presence/absence of adenosine concentrations that by themselves marginally affected PA in WB, and ZM241385 (A(2A) antagonist). The effects of ticagrelor, the active metabolite of prasugrel (PAM) (P2Y(12) antagonist), and dipyridamole (adenosine uptake inhibitor) on PA and on adenosine clearance in WB were compared. ResultsFor PA in WB, adenosine contributed to drug-induced inhibition of PA; the adenosine contribution was similar for dipyridamole and ticagrelor but was significantly greater for ticagrelor than for PAM (P<0.01). For PA in PRP (no adenosine uptake by erythrocytes), adenosine contributed to inhibition of PA in the presence/absence of all tested drugs. ZM241385 reversed the inhibition by adenosine in WB and PRP. Similar results were obtained with WB and PRP from P2Y(12)-deficient patients. Adenosine (7.1mol L-1) added to WB, was detectable for 0.5min in the presence of vehicle or PAM, for 3-6min in the presence of ticagrelor, and for >60min in the presence of dipyridamole. ConclusionThis study provides the first evidence of an additional antiplatelet mechanism by ticagrelor, mediated by the induced increase of adenosine levels.