title: Importance of CYP1A1 and CYP1B1 in bioactivation of benzo[a]pyrene in human lung cell lines.
abstract: Polycyclic aromatic hydrocarbons are ubiquitous environmental pollutants classified as carcinogens in humans and rodents. The cytochromes P4501A1 and 1B1 have both shown capacity to carry out bioactivation of the prototype PAH, benzo[a]pyrene (B[a]P) to its ultimate carcinogenic B[a]P-diol-epoxide-I-1 form. The part played by each enzyme in human lung cells, however, has not been clarified. To get further insight into their individual role in the metabolic activation of B[a]P, RNA-interference was used to down-regulate CYP1A1 and/or CYP1B1 gene expression in the human lung cell lines BEP2D and NCIH2009. Fluorescence-HPLC analysis revealed that formation of B[a]P-tetrol-I-1 (hydrolyzed form of the corresponding diol-epoxide) was dependent primarily on CYP1A1. In cells without down-regulation of CYP1A1, the B[a]P-tetrol-I-1 was the major tested isomer formed. In contrast, the B[a]P-cis- and trans-7,8-dihydrodiol isomers were readily formed in cells expressing high levels of either CYP-gene. Simultaneous down-regulation of CYP1A1 and CYP1B1 mRNA resulted in low levels of metabolites overall. Residual unmetabolized B[a]P levels followed the expression of CYP1A1 in an inverse manner. In conclusion, these results indicate a major role of CYP1A1 in the bioactivation of B[a]P to carcinogenic B[a]P-diol-epoxides and in overall metabolism of B[a]P in human lung cell lines. In contrast, both CYP1A1 and CYP1B1 contribute significantly to the formation of the B[a]P-cis- and trans-7,8-dihydrodiol isomers.
authors.affiliation: Department of Chemical and Biological Working Environment, National Institute of Occupational Health, Oslo, Norway.
authors.forename: Heidi
authors.initials: H
authors.lastname: Uppstad
authors.forename: Steinar
authors.initials: S
authors.lastname: Øvrebø
authors.forename: Aage
authors.initials: A
authors.lastname: Haugen
authors.forename: Steen
authors.initials: S
authors.lastname: Mollerup
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism*; D001564:Benzo(a)pyrene / Q000031:analogs & derivatives / Q000378:metabolism / Q000633:toxicity*; D002460:Cell Line; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism*; D065633:Cytochrome P-450 CYP1B1; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D008168:Lung / Q000201:enzymology / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism
chemical_list: D034741:RNA, Small Interfering; D001564:Benzo(a)pyrene; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1