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 (pH(e)) of 7.8, 7.0, 6.5, 6.0 and 5.5) for 6, 24 and 48 h. In most incubations (pH(e) 7.0-6.5), the pH in the medium returned to the physiological pH 7.8 after 48 h, but at the lowest pH (pH(e) <6.0), this recovery was incomplete. Similar changes were observed for the intracellular pH (pH(i)). 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 (pH(e) 7.8) for both cell lines. Cytochrome P450 (CYP1A1/CYP1B1) expression and its activity (ethoxyresorufin-O-deethylase activity) were repressed at low pH(e) after 6 and 24 h, but were significantly higher at t = 48 h. In addition, a DNA repair assay showed that the incision activity was similar to 80% inhibited for 6 h at low pH(e) and 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 pH(e). After 48 h, higher B[a]P-DNA adduct levels and gamma-H2AX foci were observed at low pH samples than at pH(e) 7.8. 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.
Original language | English |
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Pages (from-to) | 2425-2441 |
Number of pages | 17 |
Journal | Archives of Toxicology |
Volume | 91 |
Issue number | 6 |
DOIs | |
Publication status | Published - Jun 2017 |
Keywords
- Acidic pH
- Benzo[a]pyrene
- Cytochrome P450 (CYP1A1)
- DNA damage
- NER
- NUCLEOTIDE EXCISION-REPAIR
- OXIDATIVE STRESS
- COMET ASSAY
- EPITHELIAL-CELLS
- INTRACELLULAR PH
- ADDUCT FORMATION
- CULTURED-CELLS
- II CELLS
- HYPOXIA
- EXPRESSION