title: Hydroxylation of 5 alpha-androstane-3 beta,17 beta-diol by rat prostate microsomes: potent inhibition by imidazole-type antimycotic drugs and lack of inhibition by steroid 5 alpha-reductase inhibitors.
abstract: 5 alpha-Dihydrotestosterone, the principal androgen mediating prostate growth and function in the rat, is formed from testosterone by steroid 5 alpha-reductase. The inactivation of 5 alpha-dihydrotestosterone involves reversible reduction to 5 alpha-androstane-3 beta,17 beta-diol by 3 beta-hydroxysteroid oxidoreductase followed by 6 alpha-, 7 alpha-, or 7 beta-hydroxylation. 5 alpha-Androstane-3 beta,17 beta-diol hydroxylation represents the ultimate inactivation step of dihydrotestosterone in rat prostate and is apparently catalyzed by a single, high-affinity (Km approximately 0.5 microM) microsomal cytochrome P450 enzyme. The present studies were designed to determine if 5 alpha-androstane-3 beta,17 beta-diol hydroxylation by rat prostate microsomes is inhibited by agents that are known inhibitors of androgen-metabolizing enzymes. Inhibitors of steroid 5 alpha-reductase (4-azasteroid analogs; 10 microM) or inhibitors of 3 beta-hydroxysteroid oxidoreductase (trilostane, azastene, and cyanoketone; 10 microM) had no appreciable effect on the 6 alpha-, 7 alpha-, or 7 beta-hydroxylation of 5 alpha-androstane-3 beta,17 beta-diol (10 microM) by rat prostate microsomes. Imidazole-type antimycotic drugs (ketoconazole, clotrimazole, and miconazole; 0.1-10 microM) all markedly inhibited 5 alpha-androstane-3 beta,17 beta-diol hydroxylation in a concentration-dependent manner, whereas triazole-type antimycotic drugs (fluconazole and itraconazole; 0.1-10 microM) had no inhibitory effect. The rank order of inhibitory potency of the imidazole-type antimycotic drugs was miconazole greater than clotrimazole greater than ketoconazole. In the case of clotrimazole, the inhibition was shown to be competitive in nature, with a Ki of 0.03 microM. The imidazole-type antimycotic drugs inhibited all three pathways of 5 alpha-androstane-3 beta,17 beta-diol hydroxylation to the same extent, which provides further evidence that, in rat prostate microsomes, a single cytochrome P450 enzyme catalyzes the 6 alpha-, 7 alpha-, and 7 beta-hydroxylation of 5 alpha-androstane-3 beta,17 beta-diol. These studies demonstrate that certain imidazole-type compounds are potent, competitive inhibitors of 5 alpha-androstane-3 beta,17 beta-diol hydroxylation by rat prostate microsomes, which is consistent with the effect of these antimycotic drugs on cytochrome P450 enzymes involved in the metabolism of other androgens and steroids.
authors.affiliation: Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City 66160-7417.
authors.forename: B
authors.initials: B
authors.lastname: Gemzik
authors.forename: A
authors.initials: A
authors.lastname: Parkinson
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors; D058891:5-alpha Reductase Inhibitors; D015113:Androstane-3,17-diol / Q000378:metabolism*; D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology*; D001667:Binding, Competitive; D003022:Clotrimazole / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors; D006900:Hydroxylation; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D011467:Prostate / Q000201:enzymology* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D014230:Triazoles / Q000494:pharmacology
chemical_list: D058891:5-alpha Reductase Inhibitors; D000935:Antifungal Agents; D065607:Cytochrome P-450 Enzyme Inhibitors; D007093:Imidazoles; D014230:Triazoles; D015113:Androstane-3,17-diol; D015096:3-Hydroxysteroid Dehydrogenases; D003022:Clotrimazole