PB0864 - TRAP-Induced platelet reactivity is inhibited by omega-3 fatty acid-derived prostaglandin E3 (PGE3).

Background: Thrombin is one of the most important factors that regulates platelet reactivity and coagulation. Clinical trials have consistently shown that omega-3 fatty acid supplementation lowers the risk for cardiovascular mortality and morbidity [7]. Since omega-3 fatty acids are the main precursors of PGE3 in vivo, [13,14,15] it would be relevant to investigate the effects of PGE3 on Thrombin Receptor Activating Peptide (TRAP)-induced platelet reactivity to determine the receptors and possible mechanisms of action of these compounds.

Aims: To investigate whether omega-3 fatty acid-derived PGE3 might inhibit TRAP-induced platelet reactivity, especially in the presence of an Gi-coupled EP3 receptor antagonist, where the effects of PGE3 at the Gs-coupled EP4 receptor would be potentiated.

Methods: Platelet aggregation (by platelet counting) and activation (by P-selectin expression) were measured by flow cytometry in whole blood in response to thrombin-receptor activating peptide (TRAP) and PGE3, in the absence or presence of the EP3 and EP4 receptor antagonists: DG-041 and ONO-AE3-208. Vasodilator-stimulated phosphoprotein (VASP) phosphorylation was determined using a cytometric bead (VASPFix) assay as a measure of cAMP.

Results: PGE3 inhibited TRAP-induced platelet aggregation and activation. This inhibition was enhanced in the presence of an Gi-coupled EP3 receptor antagonist and abolished in the presence of an Gs-coupled EP4 receptor antagonist (Table 1). The effects of PGE3 were directly related to changes in cAMP, assessed by VASP phosphorylation (Table 2).

Conclusion(s): The general effects of PGE3 on human platelet reactivity are the consequence of a balance between promotory and inhibitory effects at receptors that have contrary effects on adenylate cyclase. When the balance is shifted towards a major interaction of PGE3 with EP4 receptor its ability to inhibit platelet function increases. These results indicate a potential mechanism by which omega-3 fatty acids underlie cardioprotective effects.