title: N-hydroxylation of 4-aminobiphenyl by CYP2E1 produces oxidative stress in a mouse model of chemically induced liver cancer.
abstract: 4-Aminobiphenyl (ABP) is a trace component of cigarette smoke and hair dyes, a suspected human carcinogen and a potent rodent liver carcinogen. Postnatal exposure of mice to ABP results in a higher incidence of liver tumors in males than in females, paralleling the sex difference in human liver cancer incidence. A traditional model of ABP tumorigenesis involves initial CYP1A2-mediated N-hydroxylation, which eventually leads to production of mutagenic ABP-DNA adducts that initiate tumor growth. However, several studies have found no correlation between sex or CYP1A2 function and the DNA-damaging, mutagenic, or tumorigenic effects of ABP. Oxidative stress may be an important etiological factor for liver cancer, and it has also been linked to ABP exposure. The goals of this study were to identify novel enzyme(s) that contribute to ABP N-oxidation, and to investigate a potential role for oxidative stress in ABP liver tumorigenicity. Isozyme-selective inhibition experiments using liver microsomes from wild-type and genetically modified mice identified CYP2E1 as a major ABP N-hydroxylating enzyme. The N-hydroxylation of ABP by transiently expressed CYP2E1 produced oxidative stress in cultured mouse hepatoma cells. In vivo postnatal exposure of mice to a tumorigenic dose of ABP also produced oxidative stress in male wild-type mice, but not in male Cyp2e1(-/-) mice or in female mice. However, a stronger NRF2-associated antioxidant response was observed in females. Our results identify CYP2E1 as a novel ABP-N-oxidizing enzyme, and suggest that sex differences in CYP2E1-dependent oxidative stress and antioxidant responses to ABP may contribute to the observed sex difference in tumor incidence.
authors.affiliation: *Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada M5S 1A8 and Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada M5S 3M2.
authors.forename: Shuang
authors.initials: S
authors.lastname: Wang
authors.affiliation: *Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada M5S 1A8 and Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada M5S 3M2.
authors.forename: Kim S
authors.initials: KS
authors.lastname: Sugamori
authors.affiliation: *Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada M5S 1A8 and Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada M5S 3M2.
authors.forename: Aveline
authors.initials: A
authors.lastname: Tung
authors.affiliation: *Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada M5S 1A8 and Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada M5S 3M2.
authors.forename: J Peter
authors.initials: JP
authors.lastname: McPherson
authors.affiliation: *Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada M5S 1A8 and Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada M5S 3M2 *Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada M5S 1A8 and Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada M5S 3M2 denis.grant@utoronto.ca.
authors.forename: Denis M
authors.initials: DM
authors.lastname: Grant
mesh_terms: D000611:Aminobiphenyl Compounds / Q000494:pharmacology*; D000818:Animals; D002273:Carcinogens / Q000633:toxicity; D045744:Cell Line, Tumor; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism*; D004195:Disease Models, Animal; D005260:Female; D006900:Hydroxylation; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000378:metabolism*; D008297:Male; D051379:Mice; D008862:Microsomes, Liver / Q000201:enzymology; D018384:Oxidative Stress / Q000187:drug effects*
chemical_list: D000611:Aminobiphenyl Compounds; D002273:Carcinogens; C006757:4-biphenylamine; D019392:Cytochrome P-450 CYP2E1
keywords: 4-aminobiphenyl; NRF2; bioactivation; liver tumorigenesis; oxidative stress