No association between N7-methyldeoxyguanosine and 8-oxodeoxyguanosine levels in human lymphocyte DNA

To examine associations between two different classes of DNA damage that can occur through endogenous processes or exogenous exposures such as smoking, N7-methyldeoxyguanosine (N7-MedG) and 8-oxodeoxyguanosine (8-oxodG) levels were measured in lymphocyte DNA from 22 bronchoscopy patients. 8-OxodG and N7-MedG was detected in 100% and 91% of samples, respectively with 8-oxodG levels being approx 20 times higher (mean 8.39 ± 3.57 8-oxodG/106dG versus 0.41 ± 0.33 N7-MedG/106 dG) which provides an indication of the relative importance of the agents that induce oxidative DNA damage or alkylation damage. The sources of these genotoxic lesions remain to be established but N7-MedG and 8-oxodG levels were not correlated (r2 < 0.01) suggesting that there is no association between alkylating agent and reactive oxygen species exposure, their metabolism and/or the DNA repair processes that can remove this DNA damage.