P-450-dependent arachidonic acid metabolism in rabbit olfactory microsomes

Microsomes isolated from rabbit olfactory epithelium catalyzed the conversion of arachidonic acid to several metabolites at a rate of 692 +/- 106 pmol/min/nmol P-450. The major metabolite was the omega-hydroxylated metabolite, 20-hydroxyeicosatetraenoic acid, accounting for 57% of the total metabolite produced. A putative omega-1 hydroxylated metabolite was also formed to a lesser extent. Epoxyeicosatrienoic acids were not detected with microsomal incubations, although metabolites corresponding to the dihydroxyeicosatrienoic acids were observed and represented about 20% of the total metabolite produced. The metabolism of arachidonic acid was also studied in a reconstituted system with six purified P-450 isoforms that are known to be expressed in rabbit olfactory mucosa. These included P-450NMa, P-450 2G1 (NMb), P-450 1A2, P-450 2B4, P-450 2E1, P-450 3A6 and a partially purified preparation of P-450 4A isoforms. The P-450 4A forms were the only enzymes to produce significant amounts of the omega-hydroxylated metabolite of arachidonic acid. The other isoforms were either inactive (P-450NMa and P-450 3A6) or produced metabolites other than the 20-hydroxyeicosatetraenoic acid and, thus, cannot account for the majority of the miscrosomal metabolism of arachidonic acid. Immunoblot analysis with goat anti-rat P-450 4A1 identified one major and a second minor protein of the P-450 4A gene family in olfactory microsomes. The same antibody identified two proteins in rabbit renal tissue that were significantly induced by pretreatment with clofibric acid and were present in a partially purified preparation of P-450 4A from rabbit renal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)