The ω-3 epoxide of eicosapentaenoic acid inhibits endothelial cell proliferation by p38 MAP kinase activation and cyclin D1/CDK4 down-regulation

BACKGROUND AND PURPOSE Dietary intake of omega-3 polyunsaturated fatty acids (omega-3 PUFAs) like eicosapentaenoic acid (EPA) decreases cancer risk, while arachidonic acid and other omega-6 PUFAs increase risk, but the underlying mechanisms are unclear. Cytochrome P450 (CYP)-derived epoxides contribute to enhanced tumourigenesis due to omega-6 PUFA intake. Thus, omega-6 arachidonic acid epoxides (EETs) inhibit apoptosis and stimulate proliferation by up-regulating cyclin D1 expression in cells. The present study evaluated the corresponding omega-3 PUFA epoxides and assessed their role in the regulation of cell proliferation. EXPERIMENTAL APPROACH Four chemically stable EPA epoxides (formed at the 8,9-, 11,12-, 14,15- and 17,18-olefinic bonds) were synthesized and tested against growth-related signalling pathways in brain microvascular endothelial bEND.3 cells. Cell cycle distribution was determined by flow cytometry and cyclin gene expression by immunoblotting and real-time PCR. The role of the p38 mitogen-activated protein (MAP) kinase in cyclin D1 dysregulation was assessed using specific inhibitors and dominant-negative expression plasmids. KEY RESULTS The omega-3 17,18-epoxide of EPA decreased cell proliferation, interrupted the cell cycle in S-phase and down-regulated the cyclin D1/cyclin-dependent kinase (CDK)-4 complex, whereas the 8,9-, 11,12- and 14,15-epoxides were either inactive or enhanced proliferation. Cyclin D1 down-regulation by 17,18-epoxy-EPA was mediated by activation of the growth-suppressing p38 MAP kinase, but the alternate EPA-epoxides were inactive. CONCLUSIONS AND IMPLICATIONS The present findings suggest that the epoxide formed by CYP enzymes at the omega-3 olefinic bond may contribute to the beneficial effects of omega-3 PUFA by down-regulating cyclin D1 and suppressing cell proliferation.