Kinetics of DNA adduct formation in the oral cavity after drinking alcohol

Abstract

Background: Alcohol consumption is one of the top 10 risks for the worldwide burden of disease and an established cause of head and neck cancer, as well as cancer at other sites. Acetaldehyde, the major metabolite of ethanol, reacts with DNA to produce adducts, which are critical in the carcinogenic process and can serve as biomarkers of exposure and, possibly, of disease risk. Acetaldehyde associated with alcohol consumption is considered "carcinogenic to humans." We have previously developed the technology to quantify acetaldehyde-DNA adducts in human tissues, but there are no studies in the literature defining the formation and removal of acetaldehyde-DNA adducts in people who consumed alcohol.

Methods: We investigated levels of N(2)-ethylidene-dGuo, the major DNA adduct of acetaldehyde, in DNA from human oral cells at several time points after consumption of increasing alcohol doses. Ten healthy nonsmokers were dosed once a week for three weeks. Mouthwash samples were collected before and at several time points after the dose. N(2)-Ethylidene-dGuo was measured as its NaBH(3)CN reduction product N(2)-ethyl-dGuo by liquid chromatography-electrospray-tandem mass spectrometry.

Results: N(2)-ethylidene-dGuo levels increased as much as 100-fold from baseline within 4 hours after each dose for all subjects and in a dose-responsive manner (P = 0.001).

Conclusion: These results show an effect of alcohol on oral cell DNA adduct formation, strongly supporting the key role of acetaldehyde in head and neck cancer caused by alcohol drinking.

Impact: Our results provide some of the first conclusive evidence linking exposure to a lifestyle carcinogen and kinetics of DNA adduct formation in humans.

Figure 1. Summary of the mean levels of N²-ethyl-dGuo at various intervals before and after the three doses

The graph summarizes the mean levels of N²-ethyl-dGuo (fmol/μmol dGuo) measured in the oral cell DNA of the 10 subjects at the time-points analyzed in the study. The first time-point reported on the left (B00) refers to the orientation meeting, 1 week before consumption of the first dose. This time-point represents the point at which participants began to abstain from consuming any alcoholic beverage other than the dose administered for the study. The next time-point (BD1) refers to the baseline level detected 1 week later, 1 h before consumption of the first dose (d1, lowest). Subsequently, the graph shows the levels of N²-ethyl-dGuo measured at the various time-points considered after each dose (2h – 120h). The DNA adduct levels were measured at the same time-points before and after exposure to the next 2 doses (d2, intermediate, and d3, highest). The baseline time points measured 1h before the dose (BD1, BD2 and BD3) are seven days apart. Values are means and standard errors.