Pomolic acid, triterpenoid isolated from Licania pittieri, as competitive antagonist of ADP-induced aggregation of human platelets

Pomolic acid (PA), triterpenoid isolated from Licania pittieri, has previously shown a potent ability to inhibit adenosine diphosphate (ADP)- and epinephrine-induced human platelet aggregation. To investigate whether PA could be an antagonist of ADP-activated receptors of human platelets (P2Y(1) and P2Y(12)), pharmacological studies were conducted to examining its ability to modulate the platelet shape change induced by a selective P2Y(1) receptor agonist MRS2365 and also the nature of its possible interaction with ADP receptors by analyzing the characteristics of log concentration-response curves of ADP constructed in the absence and in the presence of fixed concentrations of PA, using in vitro platelet aggregation assays. PA did not interfere with the activation of P2Y(1) receptor by MRS2365 to induce platelet shape change and displayed a competitive antagonism of ADP-induced platelet aggregation, which most probably involves competition for a single binding site in platelets. The estimated equilibrium dissociate constant (K(b)) of PA as ADP receptor antagonist was 15.4±0.06nM. Together, these findings give indirect evidence for the idea that PA could be a potent competitive antagonist of P2Y(12) receptor, and open the possibility to consider it as new member of the non-nucleotide generation of antiplatelet drugs.