title: Oxidative detoxication of carcinogenic 2-nitroanisole by human, rat and rabbit cytochrome P450.
abstract: OBJECTIVE
  The detoxifying metabolism of a potent rodent carcinogen, 2-nitroanisole (2-NA) by human, rabbit and rat cytochromes P450 (P450) was investigated. Comparison between P450s of experimental animals and humans is essential for the extrapolation of animal carcinogenicity data to the human situation and to assess health risk.
  
  
  METHODS
  HPLC with UV detection was employed for the separation and characterization of 2-NA metabolites formed by hepatic microsomes, human recombinant P450s and purified rat and rabbit P450s.
  
  
  RESULTS
  An O-demethylated metabolite of 2-NA, 2-nitrophenol (2-NP), and two oxidation products of this metabolite [2,5-dihydroxynitrobenzene (2,5-DNB) and 2,6-dihydroxynitrobenzene (2,6-DNB)] were generated by microsomes and P450s from the species investigated, but at different levels. All the metabolites are detoxication products. 2-NP is the major metabolite generated by rabbit and rat microsomes, but 2,5-DNB is the predominant product in human microsomes. Using human recombinant P450s and purified rodent P450s, we found that human P450 2E1, 1A1 and 2B6 as well as orthologous animal P450s were the most efficient enzymes oxidizing 2-NA to 2-NP, while P450 2E1 and 1A1 were the most effective in the formation of 2,5-DNB and 2,6-DNB. In human hepatic microsomes, 2-NA was oxidized mainly by P4502E1. 2-NA and its reductive metabolite o-anisidine induced rat hepatic and renal P450 1A1/2 and NAD(P)H:quinone oxidoreductase (NQO1), thus modifying their own detoxication and/or activation pathways.
  
  
  CONCLUSIONS
  The data demonstrated the participation of orthologous P450s in 2-NA oxidation by all species and indicated that the rat and rabbit might serve as suitable models to mimic 2-NA oxidation in man.
authors.affiliation: Department of Biochemistry, Faculty of Science, Charles University, Prague, Czech Republic.
authors.forename: Helena
authors.initials: H
authors.lastname: Dracínska
authors.forename: Markéta
authors.initials: M
authors.lastname: Miksanová
authors.forename: Martina
authors.initials: M
authors.lastname: Svobodová
authors.forename: Stanislav
authors.initials: S
authors.lastname: Smrcek
authors.forename: Eva
authors.initials: E
authors.lastname: Frei
authors.forename: Heinz H
authors.initials: HH
authors.lastname: Schmeiser
authors.forename: Marie
authors.initials: M
authors.lastname: Stiborová
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D000840:Anisoles / Q000493:pharmacokinetics*; D002273:Carcinogens / Q000493:pharmacokinetics; D002648:Child; D002675:Child, Preschool; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D050216:Metabolic Detoxication, Phase I; D008862:Microsomes, Liver / Q000378:metabolism; D008875:Middle Aged; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000814:Aniline Compounds; D000840:Anisoles; D002273:Carcinogens; D003577:Cytochrome P-450 Enzyme System; D016660:NAD(P)H Dehydrogenase (Quinone); C447479:NQO1 protein, human; C003898:2-anisidine; C005328:2-nitroanisole