Exposure level to cigarette tar or nicotine is associated with leukocyte DNA damage in male Japanese smokers

We investigated the number of cigarettes smoked daily, years of smoking, cigarette pack-years, levels of daily exposure to cigarette tar (LECT, mg/day) or nicotine (LECN, mg/day) in 53 male Japanese smokers using a questionnaire and measured each participant's baseline leukocyte DNA damage using the alkaline comet assay. The results showed that the baseline value of peripheral leukocyte DNA strand breaks was significantly associated with LECT (P < 0.05), LECN (P < 0.05), years of smoking or cigarette pack-years (P < 0.05) but not with the number of cigarettes smoked per day. Stepwise multiple regression analyses of factors including age, occupation, years of employment, alcohol drinking behaviour, physical activity, nutritional balance and cigarette smoking parameters showed that LECT was a positively significant predictor (Partial r = 0.0005, P < 0.05) of the comet tail moment. In consideration of the high correlation between LECT and LECN (Ytar = 12.53 Xnicotine −7.23, r = 0.995, P < 0.0001), these results suggest that levels of exposure to cigarette tar or nicotine (mg/day) would be a sensitive parameter in appreciation of genotoxicity of cigarette smoking in these male Japanese smokers.