title: Acidic cellular microenvironment modifies carcinogen-induced DNA damage and repair.
abstract: Chronic inflammation creates an acidic microenvironment, which plays an important role in cancer development. To investigate how low pH changes the cellular response to the carcinogen benzo[a]pyrene (B[a]P), we incubated human pulmonary epithelial cells (A549 and BEAS-2B) with nontoxic doses of B[a]P using culturing media of various pH's (extracellular pH (pHe) of 7.8, 7.0, 6.5, 6.0 and 5.5) for 6, 24 and 48 h. In most incubations (pHe7.0-6.5), the pH in the medium returned to the physiological pH 7.8 after 48 h, but at the lowest pH (pHe< 6.0), this recovery was incomplete. Similar changes were observed for the intracellular pH (pHi). We observed that acidic conditions delayed B[a]P metabolism and at t = 48 h, and the concentration of unmetabolized extracellular B[a]P and B[a]P-7,8-diol was significantly higher in acidic samples than under normal physiological conditions (pHe7.8) for both cell lines. Cytochrome P450 (CYP1A1/CYP1B1) expression and its activity (ethoxyresorufin-O-deethylase activity) were repressed at low pHeafter 6 and 24 h, but were significantly higher at t = 48 h. In addition, a DNA repair assay showed that the incision activity was ~80% inhibited for 6 h at low pHeand concomitant exposure to B[a]P. However, at t = 48 h, the incision activity recovered to more than 100% of the initial activity observed at neutral pHe. After 48 h, higher B[a]P-DNA adduct levels and γ-H2AX foci were observed at low pH samples than at pHe7.8. In conclusion, acidic pH delayed the metabolism of B[a]P and inhibited DNA repair, ultimately leading to increased B[a]P-induced DNA damage.
authors.affiliation: Department of Pharmacology and Toxicology, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University, PO Box 616, 6200 MD, Maastricht, The Netherlands.
authors.forename: Q
authors.initials: Q
authors.lastname: Shi
authors.affiliation: Department of Pharmacology and Toxicology, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University, PO Box 616, 6200 MD, Maastricht, The Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: Maas
authors.affiliation: Department of Pharmacology and Toxicology, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University, PO Box 616, 6200 MD, Maastricht, The Netherlands.
authors.forename: C
authors.initials: C
authors.lastname: Veith
authors.affiliation: Department of Pharmacology and Toxicology, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University, PO Box 616, 6200 MD, Maastricht, The Netherlands.
authors.forename: F J
authors.initials: FJ
authors.lastname: Van Schooten
authors.affiliation: Department of Pharmacology and Toxicology, NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University, PO Box 616, 6200 MD, Maastricht, The Netherlands. R.Godschalk@maastrichtuniversity.nl.
authors.forename: R W
authors.initials: RW
authors.lastname: Godschalk
mesh_terms: D000072283:A549 Cells; D001564:Benzo(a)pyrene / Q000378:metabolism / Q000633:toxicity*; D002273:Carcinogens / Q000378:metabolism / Q000633:toxicity*; D018929:Cell Culture Techniques; D060833:Cellular Microenvironment / Q000187:drug effects*; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D065633:Cytochrome P-450 CYP1B1 / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D006801:Humans; D006863:Hydrogen-Ion Concentration; D053858:Metabolic Networks and Pathways
chemical_list: D002273:Carcinogens; D001564:Benzo(a)pyrene; C569463:CYP1A1 protein, human; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1
keywords: Acidic pH; Benzo[a]pyrene; Cytochrome P450 (CYP1A1); DNA damage; NER