| Summary: | Chronic inflammation creates an acidic microenvironment, which may play an important role in cancer development. To investigate how a low pH may change the cellular response to the environmental carcinogen benzo[a]pyrene (B[a]P), we exposed human pulmonary epithelial cells (A549) to non-toxic doses of 1µM B[a]P at various extracellular pH’s (pHe = 7.8, 7.0, 6.5, 6.0 and 5.5) for 6, 24 and 48 hours. In most incubations (pHe 7.0- 6.5), the pH restored to pH 7.8 after 48 hours of exposure. However, at the lowest pH (pHe< 6.0), this recovery was imcomplete and only reached to pH 6.5 at t=48 h. Similar changes were observed for the intracellular pH (pHi). The acidic pH delayed the metabolism of B[a]P and at t=48 h, the concentrations of unmetabolised extracellular B[a]P was 60-fold higher at pHe 5.5 than at normal pH (pHe 7.8). However, the concentration of the pre-mutagenic metabolite B[a]P-7,8-diol was 955-fold increased at pHe 5.5 when compared to exposure to B[a]P at pHe 7.8 at 48 hours. Cytochrome P450 (CYP1A1) expression and its activity (assessed as ethoxyresorufin-O-deethylase (EROD) activity) were initially repressed at low pHe, but then significantly increased at later later time points (48 hours) when compared to normal pHe. In addition, the nucleotide excision repair (NER) capacity, assessed by a modified Comet assay, was ~80% inhibited at pH 5.5 at 6 hours after exposure to B[a]P. However at t=48 h, the NER capacity recovered to 100% of the initial repair activity observed at pHe=7.8. Eventually, 6 times higher B[a]P-DNA adduct levels were observed at low pHe than at pHe 7.8. Overall, our data suggest that acidic pH delayed the metabolism of B[a]P and inhibited DNA repair, which increased B[a]P induced DNA damage.
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