Abstract 1315: Pharmacological Inhibition of Cytosolic Phospholipase A2 Alpha Suppresses Platelet Secretion and Aggregation, and Provides Protection in Rodent Models of Arterial Thrombosis
Cytosolic phospholipase A2α (cPLA2α) mediates the release of arachidonic acid upon cell activation. Metabolites of arachidonic acid, the eicosanoids, are recognized as important modulators of platelet signaling. Inhibitors of the eicosanoid pathway (e.g. aspirin) reduce the formation of thromboxane A2, a labile platelet agonist, resulting in depression of platelet function and thrombus formation, and have proven clinical benefit in reducing morbidity and mortality. We examined the effects of cPLA2α inhibition on platelet function. In vitro, the selective inhibitor PLA-902 blocked platelet dense granule ATP secretion in human whole blood, with inhibition observed down to 0.3ug/ml. Platelet aggregation was studied using the platelet function analyzer (PFA-100®). In whole human blood, maximal prolongation of closure time was seen using 2.5ug/ml compound. Ex vivo analyses of cPLA2α inhibition were studied in mice fed a normal chow diet supplemented with PLA-902 at 3.3mg/g chow for 2 days (yielding ~500ng/mL CMAX). Serum TXB2 levels were decreased to 56% of control in drug-treated animals compared to normal chow animals. Ex vivo platelet aggregation of dosed animals showed a significant increase in the closure time of the PFA-100, compared to control animals (194±49 vs 142±16 sec., p<0.02). Reduced thromboxane levels and impaired platelet function led us to hypothesize that cPLA2α inhibition would yield an anti-thrombotic effect. Two rodent models of acute thrombosis were used with PLA-902, dosed orally at 100mg/kg. PLA-902 treated mice showed a significant reduction in platelet deposition and thrombus formation in a model of laser-induced vessel injury, monitored by intravital microscopy. Similarly, in a ferric chloride model of oxidative endothelial cell injury, PLA-902 dosed rats showed a significant improvement in arterial blood flow, with no vessel occlusion seen during the 30 minute test, unlike the control animals which completely occluded within ~17 minutes. Our data demonstrate that pharmacological inhibition of cPLA2α reduces serum TXB2 levels, inhibits platelet function, and reduces thrombus formation in two rodent models of acute thrombosis, and therefore may be a novel strategy for the prevention of thrombotic events in humans.