Oxygenation of arachidonic acid by hepatic monooxygenases. Isolation and metabolism of four epoxide intermediates

Abstract

[3H]Arachidonic (eicosatetraenoic) acid was incubated with rabbit liver microsomes, NADPH, and 1 mM 1,2-epoxy-3,3,3-trichloropropane, an epoxide hydrolase inhibitor, for 15 min at 37 degrees C. The metabolites were separated by reverse phase high performance liquid chromatography and two epoxides, 11(12)oxido-5,8,14-eicosatrienoic acid and 14(15)oxido-5,8,11-eicosatrienoic acid, were identified by gas chromatography-mass spectrometry. Hepatic cytochromes P-450 purified from rabbits and rats treated with phenobarbital metabolized arachidonic acid to these two epoxides, as well as 5(6)oxido-8,11,14-eicosatrienoic acid and 8(9)oxido-5,11,14-eicosatrienoic acid and the corresponding vic-diols as the major products. Cytochromes P-450 purified from rabbits and rats treated with beta-naphthoflavone mainly formed (omega-1)- and omega-hydroxylated arachidonic acids, while the four epoxides and the vic-diols were formed in small amounts. Synthetic [14C]14(15)oxido-, 11(12) oxido-, 8(9)oxido-, and 5(6)oxidoeicosatrienoic acid were enzymatically converted to vic-diols by hepatic and renal cortical microsomal and cytosolic fractions and by purified liver microsomal epoxide hydrolase. Liver microsomes oxygenated the epoxides to many polar products in the presence of NADPH. All eight trihydroxy acids, formed by omega- or (omega-1)-hydroxylation of the four vic-diols, four vic-diol dicarboxylic acids, and other metabolites were identified by gas chromatography-mass spectrometry.