Pathways of epoxyeicosatrienoic acid metabolism in endothelial cells - Implications for the vascular effects of soluble epoxide hydrolase inhibition

Epoxyeicosatrienoic acids (EETs) are products of cytochrome P-450 epoxygena se that possess important vasodilating and anti-inflammatory properties. EE Ts are converted to the corresponding dihydroxyeicosatrienoic acid (DHET) b y soluble epoxide hydrolase (sEH) in mammalian tissues, and inhibition of s EH has been proposed as a novel approach for the treatment of hypertension, We observed that sEH is present in porcine coronary endothelial cells (PCE C), and we found that low concentrations of N,N'-dicyclohexylurea (DCU), a selective sEH inhibitor, have profound effects on EET metabolism in PCEC cu ltures. Treatment with 3 muM DCU reduced cellular conversion of 14,15-EET t o 14,15-DHET by 3-fold after 4 h of incubation, with a concomitant increase in the formation of the novel beta -oxidation products 10,11-epoxy-16:2 an d 8,9-epoxy-14:1, DCU also markedly enhanced the incorporation of 14,18-EET and its metabolites into PCEC lipids. The most abundant product in DCU tre ated cells was 16,17-epoxy-22:3, the elongation product of 14,15-EET, Anoth er novel metabolite, 14,15-epoxy-20:2, was present in DCU-treated cells. DC U also caused a 4-fold increase in release of 14,15-EET when the cells were stimulated with a calcium ionophore, Furthermore, DCU decreased the conver sion of [H-3]11,12-EET to 11,12-DHET, increased 11,12-EET retention in PCEC lipids, and produced an accumulation of the partial S-oxidation product 7, 8-epoxy-16:2 in the medium. These findings suggest that in addition to bein g metabolized by sEH, EETs are substrates for beta -oxidation and chain elo ngation in endothelial cells and that there is considerable interaction amo ng the three pathways. The modulation of EET metabolism by DCU provides nov el insight into the mechanisms by which pharmacological or molecular inhibi tion of sEH effectively treats hypertension.