Redox Cycling in the Metabolism of the Environmental Pollutant and Suspected Human Carcinogen o-Anisidine by Rat and Rabbit Hepatic Microsomes

• Published in: Chemical research in toxicology Vol. 21; no. 8; pp. 1610 - 1621
• Main Authors: Naiman, Karel, Dračínská, Helena, Martínková, Markéta, Šulc, Miroslav, Dračínský, Martin, Kejíková, Lucie, Hodek, Petr, Hudeček, Jirí, Liberda, Jirí, Schmeiser, Heinz H, Frei, Eva, Stiborová, Marie
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.08.2008
• Subjects: Aniline Compounds - metabolism; Animals; Carcinogens, Environmental - metabolism; Chromatography, High Pressure Liquid; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System - metabolism; Inactivation, Metabolic; Microsomes, Liver - enzymology; Microsomes, Liver - metabolism; Oxidation-Reduction; Rabbits; Rats; Spectrometry, Mass, Electrospray Ionization; Tandem Mass Spectrometry
• ISSN: 0893-228X; 1520-5010
• DOI: 10.1021/tx8001127

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.