Selective activation of the prostaglandin E2 receptor subtype EP2 or EP4 leads to inhibition of platelet aggregation

The effect of selective activation of platelet prostaglandin (PG) E-2 receptor subtype EP2 or EP4 on platelet aggregation remains to be determined. In platelets prepared from wild-type mice (WT platelets), high concentrations of PGE(2) inhibited platelet aggregation induced by U-46619, a thromboxane receptor agonist. However, there was no significant change in the inhibitory effect of PGE(2) on platelets lacking EP2 (EP2-/- platelets) and EP4 (EP4-/- platelets) compared with the inhibitory effect on WT platelets. On the other hand, AE1-259 and AE1-329, agonists for EP2 and EP4, respectively, potently inhibited U-46619-induced aggregation with respective IC50 values of 590 +/- 14 and 100 +/- 4.9 nM in WT platelets, while the inhibition was significantly blunted in EP2-/- and EP4-/- platelets. In human platelets, AE1-259 and AE1-329 inhibited U-46619-induced aggregation with respective IC50 values of 640 +/- 16 and 2.3 +/- 0.3 nM. Notably, the inhibitory potency of AE1-329 in human platelets was much higher than that in murine platelets, while such a difference was not observed in the inhibitory potency of AE1-259. AE1-329 also inhibited adenosine diphosphate-induced platelet aggregation, and the inhibition was almost completely blocked by AE3-208, an EP4 antagonist. In addition, AE1-329 increased intracellular cAMP concentrations in a concentration- and EP4-dependent manner in human platelets. These results indicate that selective activation of EP2 or EP4 can inhibit platelet aggregation and that EP4 agonists are particularly promising as novel anti-platelet agents.