title: Interstrain differences in the expression and activity of Cyp2a5 in the mouse liver.
abstract: BACKGROUND
  Cytochrome P450 2A5 (Cyp2a5), a mouse enzyme orthologous of human CYP2A6, catalyzes a number of toxicologically important reactions, including the metabolism of nicotine, aflatoxin B1, and several other xeno- and endobiotics. Cyp2a5 expression is complex and not yet fully understood. We investigated inter-strain differences in the activity and mRNA expression of hepatic Cyp2a5. Cyp1a1/2 and Cyp2b9/10 activities were evaluated for comparative purposes. Data on the interstrain differences in the expression and activity of Cyp2a5 are important to select a suitable mouse model for studying CYP2A6-mediated metabolism.
  
  
  RESULTS
  Activity of Cyp2a5 (coumarin 7-hydroxylase) was highest in DBA-2 and DBA-1, intermediate in B6D2F1 (hybrid) and low in the remaining strains (C57BL/6, C57BL/10, CBA, BALB/cAn, SW). Contrasting with the activity, background levels of Cyp2a4/5 mRNA did not differ between high- and low-activity murine strains. Phenobarbital (PB, 80 mg/kg body weight/day × 3 days, i.p.) increased Cyp2a5, Cyp1a1/2 (ethoxyresorufin-O-deethylase) and Cyp2b9/10 (bezyloxyresorufin-O-debenzylase) activities while only Cyp2a5 was enhanced by pyrazole (PYR, 100 mg/kg body weight/day × 3 days, i.p.). Inductions of Cyp2a5 activity by PYR and PB were accompanied by increases of Cyp2a4/5 mRNA. PYR and PB did not upregulate heme oxygenase-1 (hmox-1) mRNA expression in any strain, a finding that is apparently at odds with the notion that Cyp2a5 and hmox-1 inductions are coordinated events.
  
  
  CONCLUSIONS
  Since background levels of Cyp2a4/5 gene transcripts of high-activity strains did not differ from those of low-activity mice, distinct constitutive activities did not result from different transcription rates and/or mRNA half-lives. Results therefore suggested that interstrain differences in constitutive activity of Cyp2a5 possibly arise from distinct translation efficiencies, protein half-lives and/or enzyme kinetics toward the substrate. Data from this study indicated that all tested strains are suitable models for studying toxicants that are substrates for human CYP2A6; DBA-2, DBA-1 and the hybrid B62DF1, however, have the advantage of presenting high constitutive activities of Cyp2a5.
authors.affiliation: Laboratory of Environmental Toxicology, Department of Biological Sciences, National School of Public Health, Oswaldo Cruz Foundation, FIOCRUZ, Av. Brasil 4036, Rio de Janeiro, RJ, 21040-361, Brazil.
authors.forename: Katia S
authors.initials: KS
authors.lastname: Poça
authors.affiliation: Laboratory of Environmental Toxicology, Department of Biological Sciences, National School of Public Health, Oswaldo Cruz Foundation, FIOCRUZ, Av. Brasil 4036, Rio de Janeiro, RJ, 21040-361, Brazil.
authors.forename: Thiago E M
authors.initials: TE
authors.lastname: Parente
authors.affiliation: Laboratory of Environmental Toxicology, Department of Biological Sciences, National School of Public Health, Oswaldo Cruz Foundation, FIOCRUZ, Av. Brasil 4036, Rio de Janeiro, RJ, 21040-361, Brazil.
authors.forename: Lucas F
authors.initials: LF
authors.lastname: Chagas
authors.affiliation: Laboratory of Environmental Toxicology, Department of Biological Sciences, National School of Public Health, Oswaldo Cruz Foundation, FIOCRUZ, Av. Brasil 4036, Rio de Janeiro, RJ, 21040-361, Brazil.
authors.forename: Bruna S
authors.initials: BS
authors.lastname: Leal
authors.affiliation: Laboratory of Environmental Toxicology, Department of Biological Sciences, National School of Public Health, Oswaldo Cruz Foundation, FIOCRUZ, Av. Brasil 4036, Rio de Janeiro, RJ, 21040-361, Brazil.
authors.forename: Hellen S
authors.initials: HS
authors.lastname: Leal
authors.affiliation: Laboratory of Environmental Toxicology, Department of Biological Sciences, National School of Public Health, Oswaldo Cruz Foundation, FIOCRUZ, Av. Brasil 4036, Rio de Janeiro, RJ, 21040-361, Brazil.
authors.forename: Francisco J R
authors.initials: FJ
authors.lastname: Paumgartten
authors.affiliation: Laboratory of Environmental Toxicology, Department of Biological Sciences, National School of Public Health, Oswaldo Cruz Foundation, FIOCRUZ, Av. Brasil 4036, Rio de Janeiro, RJ, 21040-361, Brazil. ana.oliveira@ensp.fiocruz.br.
authors.forename: Ana C A X
authors.initials: AC
authors.lastname: De-Oliveira
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2 / Q000378:metabolism*; D005260:Female; D051379:Mice; D013045:Species Specificity
chemical_list: D001189:Aryl Hydrocarbon Hydroxylases; C585520:Cyp2a5 protein, mouse; D000072467:Cytochrome P450 Family 2
keywords: Coumarin 7-hydroxylase; Cyp2a4; Cyp2a5; Heme oxygenase; Liver toxicity