Low concentrations of reactive γ-ketoaldehydes prime thromboxane-dependent human platelet aggregation via p38-MAPK activation

Oxidative stress has been strongly implicated in pathological processes. Isoketals are highly reactive γ-ketoaldehydes of the isoprostanes pathway of free radical-induced peroxidation of arachidonic acid that are analogous to cyclooxygenase-derived levuglandins. Because aldehydes, that are much less reactive than isoketals, have been shown to trigger platelet activation, we investigated the effect of one isoketal (E2-IsoK) on platelet aggregation. Isoketal potentiated aggregation and the formation of thromboxane B2 in platelets challenged with collagen at a concentration as low as 1 nM. Moreover, the potentiating effect of 1 nM isoketal on collagen-induced platelet aggregation was prevented by pyridoxamine, an effective scavenger of γ-ketoaldehydes. Furthermore, we provide evidence for the involvement of p38 mitogen-activated protein kinase in isoketal-mediated platelet priming, suggesting that isoketals may act upstream the activation of collagen-induced cytosolic phospholipase A2. Additionally, the incubation of platelets with 1 nM isoketal led to the phosphorylation of cytosolic phospholipase A2. The cytosolic phopholipase A2 inhibitors AACOCF3 and MAFP both fully prevented the increase in isoketal-mediated platelet aggregation challenged with collagen. These results indicate that isoketals could play an important role in platelet hyperfunction observed in pathological states such as atherosclerosis and thrombosis through the activation of the endogenous arachidonic acid cascade.