title: Hypoxia diminishes the detoxification of the environmental mutagen benzo[a]pyrene.
abstract: Hypoxia promotes genetic instability and is therefore an important factor in carcinogenesis. We have previously shown that activation of the hypoxia responsive transcription factor HIFα can enhance the mutagenic phenotype induced by the environmental mutagen benzo[a]pyrene (BaP). To further elucidate the mechanism behind the ability of hypoxia to increase mutagenicity of carcinogens, we examined the activation and detoxification of BaP under hypoxic conditions. To this end, the human lung carcinoma cell line A549 was treated with BaP under 20%, 5% or 0.2% oxygen for 18h and alterations in BaP metabolism were assayed. First, BaP-induced expression of key metabolic enzymes was analysed; expression levels of the activating CYP1A1 and CYP1B1 were increased, while the detoxifying enzymes UGT1A6 and UGT2B7 were significantly reduced by hypoxia. To evaluate whether these changes had an effect on metabolism, levels of BaP and several of its metabolites were determined. Cells under hypoxia have a reduced capacity to metabolise BaP leaving more of the parent molecule intact. Additionally, BaP-7,8-dihydrodiol, the pre-cursor metabolite of the reactive metabolite BaP-7,8-dihydroxy-9,10-epoxide (BPDE), was formed in higher concentrations. Finally, under hypoxia, DNA adducts accumulated over a period of 168 h, whereas adducts were efficiently removed in 20% oxygen conditions. The delayed detoxification kinetics resulted in a 1.5-fold increase in DNA adducts. These data indicate that the metabolism under hypoxic conditions has shifted towards increased activation of BaP instead of detoxification and support the idea that modulation of carcinogen metabolism is an important additional mechanism for the observed HIF1 mediated genetic instability.
authors.affiliation: Department of Toxicology, NUTRIM-School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Marten A
authors.initials: MA
authors.lastname: Schults
authors.affiliation: Department of Toxicology, NUTRIM-School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Sanen
authors.affiliation: Department of Toxicology, NUTRIM-School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Roger W
authors.initials: RW
authors.lastname: Godschalk
authors.affiliation: Department of Radiation Oncology (MAASTRO), GROW-School for Oncology and Developmental Biology, Maastricht University Medical Centre, PO Box 616, 6200 MD Maastricht, The Netherlands and.
authors.forename: Jan
authors.initials: J
authors.lastname: Theys
authors.affiliation: Department of Toxicology, NUTRIM-School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Frederik J
authors.initials: FJ
authors.lastname: van Schooten
authors.affiliation: Department of Toxicology, NUTRIM-School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands, Department of Radiation Oncology, University Medical Center Groningen, PO Box 30001, 9700 RB Groningen, The Netherlands r.k.chiu@umcg.nl.
authors.forename: Roland K
authors.initials: RK
authors.lastname: Chiu
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000378:metabolism; D001564:Benzo(a)pyrene / Q000633:toxicity*; D015687:Cell Hypoxia / Q000187:drug effects; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media / Q000737:chemistry; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D065633:Cytochrome P-450 CYP1B1 / Q000378:metabolism; D018736:DNA Adducts / Q000378:metabolism; D004101:Dihydroxydihydrobenzopyrenes / Q000378:metabolism; D004785:Environmental Pollutants / Q000633:toxicity*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008658:Inactivation, Metabolic / Q000187:drug effects; D007700:Kinetics; D009153:Mutagens / Q000633:toxicity*; D010100:Oxygen / Q000494:pharmacology; D013997:Time Factors
chemical_list: D003470:Culture Media; D018736:DNA Adducts; D004101:Dihydroxydihydrobenzopyrenes; D004785:Environmental Pollutants; D009153:Mutagens; C017228:benzo(a)pyrene 7,8-dihydrodiol; D001564:Benzo(a)pyrene; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; C110655:UDP-glucuronosyltransferase, UGT1A6; C491474:UGT2B7 protein, human; D014453:Glucuronosyltransferase; D010100:Oxygen