Ethanol and acetaldehyde enhance benzo[a]pyrene-DNA adduct formation in human mammary epithelial cells

A positive association between alcohol intake and breast cancer risk has been found in many epidemiological studies, yet the biological basis for this association is incompletely understood. The present experiments were designed to determine the chronic effect of physiologically relevant concentrations of ethanol (5–25 mM) and acetaldehyde (0.5–5.0 μM) on benzo[a]pyrene (B[a]P)–DNA adduct formation in the non-neoplastic human mammary epithelial cell line, MCF-10F. We tentatively identified the major adduct formed as the anti-dihydrodiol epoxide of B[a]P bound to deoxyguanosine (dGuo). For these studies, cells were treated with ethanol or acetaldehyde for 6 days before exposure to B[a]P at 0.02 or 0.08 μg/ml. Cells incubated with B[a]P at 0.08 μg/ml for 12 h after 6 days' exposure to 15 and 25 mM ethanol exhibited 1.3- and 2.2-fold increases in B[a]P–DNA adduct formation, respectively. MCF-10F cells treated with B[a]P at 0.02 μg/ml for 12 h after 6 days' exposure to acetaldehyde at 0.5–5.0 μM concentrations exhibited increases in adduct formation from 3.4- to 4.8-fold compared with controls. For cells incubated with 0.08 μg/ml B[a]P after 6 days' exposure to 2.5 and 5.0 μM acetaldehyde, adduct levels increased 1.4- and 1.7-fold, respectively, compared with controls. Treatment of cells with ethanol did not affect the activity of cytochrome P450 1A (ethoxyresorufin O-deethylase), whereas the protein expression of glutathione S-transferase and NAD(P)H-quinone oxidoreductase (GSTP1-1 and QR), as judged by immunoblotting, decreased significantly after ethanol exposure. These studies indicate that ethanol and acetaldehyde treatment of the non-neoplastic human mammary epithelial cell line MCF-10F before addition of the environmental carcinogen B[a]P can lead to increased formation of the anti-BP-dihydrodiol epoxide–dGuo adduct. The influence of ethanol appears to be due, in part, to a decrease in protein expression of the phase II detoxification enzyme GSTP1-1. Thus, this report provides evidence for a biological mechanism whereby alcohol consumption may increase the risk of breast cancer in women.