Detection of DNA adducts in human oral tissue: correlation of adduct levels with tobacco smoking and differential enhancement of adducts using the butanol extraction and nuclease P1 versions of 32P postlabeling.

Samples of clinically normal oral tissue were obtained from patients undergoing surgery for intraoral squamous cell carcinoma. DNA was extracted from samples obtained from 20 tobacco smokers, four exsmokers, and nine nonsmokers and analyzed for the presence of aromatic DNA adducts using two distinct modifications of the 32P postlabeling assay. 32P postlabeling following butanol extraction enhancement revealed a much wider range and substantially higher levels of DNA adducts than obtained following nuclease P1 enrichment. Adduct levels in smokers, exsmokers, and nonsmokers were 1133 +/- 354, 785 +/- 251, and 660 +/- 317 amol/microgram of DNA (+/- SD), respectively. The elevation of adduct levels in smokers compared with either nonsmokers or non- and exsmokers combined is statistically significant (P < 0.005). These observations are consistent with epidemiological evidence linking tobacco smoking with oral cancer. The differential enhancement of DNA adducts with the two 32P postlabeling protocols indicate that aromatic amines and nitroaromatics may be important sources of the DNA adducts detected in human oral tissue.