N²-ethyldeoxyguanosine as a potential biomarker for assessing effects of alcohol consumption on DNA

Head and neck cancers are causally related to alcohol consumption, but the underlying mechanisms are unclear. Ethanol is metabolized to acetaldehyde, an experimental carcinogen. Quantitation of the major DNA adduct of acetaldehyde, N²-ethylidenedeoxyguanosine, in human tissues could help to elucidate the mechanism of alcohol carcinogenicity. We applied a quantitative method for the analysis of this adduct, measured as the NaBH₃CN reduction product N²-ethyldeoxyguanosine (N²-ethyl-dGuo) by liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring, on DNA (0.04 ± 0.03 mg) isolated from blood collected from control subjects recruited from two studies conducted in different areas of Europe between 1999 and 2005. The group selected from the first study (n = 127) included alcohol drinkers and abstainers while the group from the second study (n = 50) included only heavy drinkers. N ²-ethyl-dGuo was detected in all DNA samples. After adjusting for potential confounders, in the first study, drinkers showed a higher level of N²-ethyld-Guo (5,270 ± 8,770 fmol/Mmol dGuo) compared with nondrinkers (2,690 ± 3040 fmol/Mmol dGuo; P = 0.04). A significant trend according to dose was observed in both studies (P = 0.02 and 0.04, respectively). Taking into account the amount of alcohol consumption, adduct levels were higher in younger compared with older subjects (P = 0.01), whereas no differences were observed comparing men with women. These results show the feasibility of quantifying N²-ethyl-dGuo in small-volume blood samples and are consistent with the hypothesis that ethanol contributes to carcinogenesis through DNA adducts formation.