The 15-lipoxygenase-derived Oxylipins 15-HETrE And 15-HETE Inhibit Platelet Activation In Part Through Activation Of PPARs

Cardiovascular disease is the leading cause of mortality in the US annually. The underlying cause of mortality in cardiovascular disease is the formation of platelet-rich clots that occlude blood vessels due to aberrant platelet activation. While antiplatelet therapeutic intervention has significantly reduced the risk of an occlusive thrombotic event, many patients remain at risk for a myocardial infarction or stroke. The antiplatelet and antithrombotic effects of omega-6 polyunsaturated fatty acids are primarily attributed to its metabolism to bioactive metabolites by oxygenases such as lipoxygenases (LOX). LOXs are a group of lipid-peroxidizing enzymes named according to the specific position where they add an oxygen to arachidonic acid: 5-LOX, 12-LOX, and 15-LOX. Previous studies from our group have demonstrated that dihomo-γ-linolenic acid and arachidonic acid regulate platelet function through their respective 12-LOX-derived oxylipins, 12(S)-hydroxyeicosatrienoic (12-HETrE) and 12(S)-hydroxyeicosatetraenoic acid (12-HETE). While the expression of 15-LOX in platelets is controversial, platelets have demonstrated the ability to generate the 15-LOX-derived bioactive metabolites. In this study we sought to elucidate the mechanistic effects of 15(S)-hydroxyeicosatrienoic acid (15-HETrE) and 15(S)-hydroxyeicosatetraenoic (15-HETE) on platelet reactivity. Washed human platelets were treated with 15-HETrE or 15-HETE and platelet aggregation, integrin αIIbβ3 activation, calcium mobilization, and granule secretion were quantified. Both 15-HETrE and 15-HETE were shown to inhibit platelet aggregation mediated by collagen. In comparison to vehicle-treated platelets, treatment with 15-HETrE or 15-HETE inhibited agonist-induced intracellular signalling events, including PKC activation, calcium mobilization, and granule secretion. Surprisingly, while 15-HETrE was shown to inhibit platelets through a signalling cascade involving the activation of PPARβ, 15-HETE’s inhibitory effect was shown to involve the activation of PPARα and the inhibition of 12-HETE production. A better understanding of the effects of 15-LOX oxylipins in platelets could lead to the identification of novel antiplatelet therapies.