In vitro genoprotective and genotoxic effect of nicotine on human leukocytes evaluated by the comet assay

The comet assay was used to measure the DNA damage induced in vitro by nicotine in human leukocytes as the extent of DNA migration in the comet head area, tail length, percent DNA in the tail, and Olive tail moment. Samples of whole blood were collected and blood cells were challenged with acute doses of 0.1, 1 and 10 µM of (-)-nicotine for 60 minutes. We found that nicotine treatment had dose-dependent effects on the level of DNA damage. At 1 and 10 µM of nicotine, both Olive tail moment and percent DNA in the tail significantly increased (p < 0.001), compared to the control. In the presence of 10 µM of nicotine, the shortest tail length and the smallest head area were detected. At a concentration of 0.1 µM, surprisingly, DNA damage detected by the comet assay was lower than in the control, which was proved by the observed significantly (p < 0.001) lower Olive tail moment and percent DNA in the tail as well as larger head area. The results suggest that nicotine, at a reasonably low concentration (0.1 µM), comparable to those found in the blood of habitual smokers, may have a protective effect, whereas higher doses of nicotine (1 and 10 µM) are genotoxic. The possible participation of reactive oxygen species in the DNA-damaging potential of nicotine is discussed.