title: Competing roles of cytochrome P450 1A1/1B1 and aldo-keto reductase 1A1 in the metabolic activation of (+/-)-7,8-dihydroxy-7,8-dihydro-benzo[a]pyrene in human bronchoalveolar cell extracts.
abstract: (+/-)-7,8-Dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol), a proximate carcinogen derived from benzo[a]pyrene (BP) requires further metabolic activation to exert its carcinogenic effects. Two principal pathways have been implicated, and these involve either the formation of (+/-)-trans-7,8-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) catalyzed by P450 1A1/P450 1B1 (NADPH-dependent monoxygenases) or the formation of benzo[a]pyrene-7,8-dione (BP-7,8-dione) catalyzed by human aldo-keto reductases AKR1A1 and AKR1C1-AKR1C4 [NAD(P)(H)-dependent oxidoreductases]. The relative contributions of the two pathways to PAH activation are unknown. In this study, BP-7,8-diol metabolism was studied in human bronchoalveolar H358 cell extracts. Parental H358 cells do not constitutively express P450 1A1/P450 1B1 or AKRs but were manipulated by induction with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to express P450 1A1/P450 1B1 or by stable transfection to express AKR1A1 (aldehyde reductase). TCDD induction of AKR1A1 transfectants provided a cell line that expressed both pathways. Extracts derived from parental H358 cells plus TCDD (P450 induction) produced electrophilic anti-BPDE, which hydrolyzed to benzo[a]pyrene tetrahydrotetrols (BP-tetrols), extracts derived from AKR1A1-transfected cells (AKR1A1 expression) produced reactive and redox-active BP-7,8-dione, which was trapped in situ as its mono(thioether) conjugate, and extracts derived from AKR1A1 transfectants plus TCDD (coexpression of P450 1A1/P450 1B1 and AKR1A1) produced both anti-BPDE and BP-7,8-dione. The competing activation of BP-7,8-diol by P450 1A1/P450 1B1 and AKR1A1 was studied with varied NADPH:NAD+ ratios. The system with a relatively higher concentration of NADPH favored formation of anti-BPDE via P450 1A1/P450 1B1, while the system with the higher concentration of NAD+ favored formation of BP-7,8-dione via AKR1A1. Under conditions that mimic the cellular redox state, 10 microM NADPH and 1 mM NAD+, equal amounts of BP-tetrols and BP-7,8-dione were formed. This suggests that P450 1A1/P450 1B1 and AKR1A1 play competing roles in the metabolic activation of BP-7,8-diol and that the dominant pathway of BP-7,8-diol activation depends on the redox state of the cells. These model systems provide a cellular context in which the dominant DNA adducts/lesions formed by either pathway may be compared.
authors.affiliation: Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6084, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Jiang
authors.forename: Yu-Min
authors.initials: YM
authors.lastname: Shen
authors.forename: Amy M
authors.initials: AM
authors.lastname: Quinn
authors.forename: Trevor M
authors.initials: TM
authors.lastname: Penning
mesh_terms: D000429:Alcohol Oxidoreductases / Q000187:drug effects / Q000378:metabolism*; D001189:Aryl Hydrocarbon Hydroxylases / Q000187:drug effects / Q000378:metabolism*; D001564:Benzo(a)pyrene / Q000031:analogs & derivatives* / Q000378:metabolism*; D001667:Binding, Competitive; D001711:Biotransformation; D002384:Catalysis; D002457:Cell Extracts / Q000737:chemistry; D002460:Cell Line; D019363:Cytochrome P-450 CYP1A1 / Q000187:drug effects / Q000378:metabolism*; D065633:Cytochrome P-450 CYP1B1; D004247:DNA / Q000378:metabolism; D018736:DNA Adducts / Q000378:metabolism; D006801:Humans; D008168:Lung / Q000737:chemistry / Q000166:cytology / Q000187:drug effects; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D013997:Time Factors
chemical_list: D002457:Cell Extracts; D018736:DNA Adducts; D000072317:Polychlorinated Dibenzodioxins; D001564:Benzo(a)pyrene; D004247:DNA; D000429:Alcohol Oxidoreductases; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1