title: Cytochrome-P-450-dependent metabolism of retinoic acid in rat skin microsomes: inhibition by ketoconazole.
abstract: Epidermal microsomes, prepared from neonatal Wistar or Sprague-Dawley rats, show low levels of retinoic acid (RA) metabolism. The specific activities (as fmol/min/mg protein) of epidermal microsomes, using [15-14C]-RA as substrate, are 232 (Wistar rats) and 222 (Sprague-Dawley rats). Topical application of RA (1 mg) on 4-day-old rats induces a 3.3- and 3.9-fold increase in epidermis microsomal RA metabolism. A 4.6- to 8.1-fold increase is observed 24 h after topical application of 3-methylcholanthrene (0.5 mg). By contrast, phenobarbital (1 mg topically) has a much smaller inducing effect. So far the chemical structure of the metabolites has not been identified. The Rf values of two major compounds correspond with those of 4-hydroxy- and 4-ketoretinoic acid, formed after incubation of hamster liver microsomes in the presence of [15-14C]-RA. The RA metabolism in rat epidermal microsomes shows the typical characteristics of a cytochrome-P-450 (P450)-dependent enzyme system, i.e. a requirement for NADPH and oxygen and inhibition by CO and SKF-525A. Ketoconazole and miconazole, imidazole antifungal agents and inhibitors of some fungal and mammalian P450-dependent enzymes, inhibit in vitro RA metabolism by rat epidermal microsomes. 50% inhibition is achieved at 6.5 X 10(-7) and greater than or equal to 10(-5) mol/l, respectively. The triazole antifungal agent, itraconazole, has no effect at concentrations up to 10(-5) mol/l. Topical treatment of 4-day-old Wistar rats with ketoconazole, at doses of 1,5 and 10 mg/kg, 1 h before the application of RA (1 mg/rat) results in a dose-dependent inhibition of RA metabolism by epidermal microsomes, prepared 24 h later. Our data show a P450-dependent RA metabolism in rat epidermal microsomes and suggest that ketoconazole may prove to be effective in maintaining biologically active levels of RA in epidermal cells.
authors.affiliation: Janssen Research Foundation, Beerse, Belgium.
authors.forename: H
authors.initials: H
authors.lastname: Vanden Bossche
authors.forename: G
authors.initials: G
authors.lastname: Willemsens
authors.forename: P A
authors.initials: PA
authors.lastname: Janssen
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D000963:Antimetabolites / Q000494:pharmacology; D001711:Biotransformation; D002248:Carbon Monoxide / Q000494:pharmacology; D006224:Cricetinae; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D066298:In Vitro Techniques; D017964:Itraconazole; D007654:Ketoconazole / Q000031:analogs & derivatives / Q000494:pharmacology*; D008647:Mesocricetus; D008825:Miconazole / Q000494:pharmacology; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012867:Skin / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D014212:Tretinoin / Q000378:metabolism*
chemical_list: D000963:Antimetabolites; D017964:Itraconazole; D014212:Tretinoin; D008825:Miconazole; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System; D007654:Ketoconazole; D010100:Oxygen