Effects of acetylenic epoxygenase inhibitors on recombinant cytochrome p450s.

Arachidonate epoxidation, which mediates important biological functions in several tissues, is catalyzed by specific cytochrome P450 (P450) enzymes. Two fatty acid derivatives [2-(2-propynyloxy)-benzenehexanoic acid (PPOH) and N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide (MS-PPOH)] are used as general, mechanism-based P450 epoxygenase inactivators, but the effects of these drugs on nearly all P450 isoforms are unknown. Here, the activity of these compounds on nine human and three rat recombinant P450s was studied. As expected, PPOH inhibited five known epoxygenases [CYP2B1, 2B6, 2C6, 2C9, and 2C11 (IC(50) = 23-161 μM)] but had little or no activity on P450s typically not considered to be epoxygenases (CYP1A1, 1A2, 1B1, 2A6, 2D6, and 2E1). PPOH was only a very weak inhibitor (IC(50) = ∼300 μM) of CYP2C19, an important human expoxygenase. An unexpected finding was that MS-PPOH (a metabolically stable congener of PPOH) potently inhibited only two P450 epoxygenases (2C9 and 2C11, IC(50) = 11-16 μM) and showed considerably lower activity (IC(50) = >90 μM) on all other P450s tested, including three epoxygenases (CYP2B1, 2B6, and 2C19). In addition, PPOH and MS-PPOH displayed time- and NADPH-dependent inhibition of CYP2C9 and other epoxygenases. These results support the putative mechanism of action of PPOH and MS-PPOH on recombinant P450s and (with one exception) confirm a general epoxygenase inhibitory profile for PPOH. However, the heterogeneity of inhibitory potencies for MS-PPOH on these enzymes suggests caution in the use of this drug as a general epoxygenase inhibitor. These results will facilitate the judicious use of PPOH and MS-PPOH for epoxygenase research.