title: Redox cycling in the metabolism of the environmental pollutant and suspected human carcinogen o-anisidine by rat and rabbit hepatic microsomes.
abstract: We investigated the ability of hepatic microsomes from rat and rabbit to metabolize 2-methoxyaniline (o-anisidine), an industrial and environmental pollutant and a bladder carcinogen for rodents. Using HPLC combined with electrospray tandem mass spectrometry, we determined that o-anisidine is oxidized by microsomes of both species to N-(2-methoxyphenyl)hydroxylamine, o-aminophenol, and one additional metabolite, the exact structure of which has not been identified as yet. N-(2-Methoxyphenyl)hydroxylamine is either further oxidized to 2-methoxynitrosobenzene (o-nitrosoanisole) or reduced to parental o-anisidine, which can be oxidized again to produce o-aminophenol. To define the role of microsomal cytochromes P450 (P450) in o-anisidine metabolism, we investigated the modulation of this metabolism by specific inducers and selective inhibitors of these enzymes. The results of the studies suggest that o-anisidine is a promiscuous substrate of P450s of rat and rabbit liver; because P450s of 1A, 2B, 2E, and 3A subfamilies metabolize o-anisidine in hepatic microsomes of both studied species. Using purified enzymes of rat and rabbit (P450s 1A1, 1A2, 2B2, 2B4, 2E1, 2C3, 3A1, and 3A6), reconstituted with NADPH:P450 reductase, the ability of P450s 1A1, 1A2, 2B2, 2B4, 2E1, and 3A6 to metabolize o-anisidine was confirmed. In the reconstituted P450 system, rabbit P450 2E1 was the most efficient enzyme metabolizing o-anisidine. The data demonstrate the participation of different rat and rabbit P450s in o-anisidine metabolism and indicate that both experimental animal species might serve as suitable models to mimic the fate of o-anisidine in human.
authors.affiliation: Department of Biochemistry, Faculty of Science, Charles University, AlbertoV 2030, 128 40 Prague 2, Czech Republic.
authors.forename: Karel
authors.initials: K
authors.lastname: Naiman
authors.forename: Helena
authors.initials: H
authors.lastname: Dracínská
authors.forename: Markéta
authors.initials: M
authors.lastname: Martínková
authors.forename: Miroslav
authors.initials: M
authors.lastname: Sulc
authors.forename: Martin
authors.initials: M
authors.lastname: Dracínský
authors.forename: Lucie
authors.initials: L
authors.lastname: Kejíková
authors.forename: Petr
authors.initials: P
authors.lastname: Hodek
authors.forename: Jirí
authors.initials: J
authors.lastname: Hudecek
authors.forename: Jirí
authors.initials: J
authors.lastname: Liberda
authors.forename: Heinz H
authors.initials: HH
authors.lastname: Schmeiser
authors.forename: Eva
authors.initials: E
authors.lastname: Frei
authors.forename: Marie
authors.initials: M
authors.lastname: Stiborová
mesh_terms: D000814:Aniline Compounds / Q000378:metabolism*; D000818:Animals; D002274:Carcinogens, Environmental / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D008658:Inactivation, Metabolic; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D011817:Rabbits; D051381:Rats; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
chemical_list: D000814:Aniline Compounds; D002274:Carcinogens, Environmental; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; C003898:2-anisidine