DETECTION OF EXOCYCLIC 1,N-2-PROPANODEOXYGUANOSINE ADDUCTS AS COMMON DNA LESIONS IN RODENTS AND HUMANS

Exocyclic adducts are unique DNA modifications resulting from binding at two sites of bases that normally are involved in hydrogen-bonding f or maintaining the double-helical structure of DNA. These adducts have been shown to be formed in rodents upon exposure to carcinogens. Usin g a sensitive P-32-postlabeling method combined with high performance liquid chromatography, we obtained evidence that 1,N-2-propanodeoxygua nosine adducts of acrolein (AdG) and crotonaldehyde (CdG) are present in the liver DNA of humans and rodents without carcinogen treatment. T he identities of these adducts were verified by cochromatography with the synthetic adduct standards. Further proof of identities was obtain ed by conversion mediated by nuclease P1 of the labeled AdG and CdG 3' ,5'-bisphosphates to their corresponding 5'-monophosphates. This treat ment converted the in vivo adducts into products that again cochromato graphed in a characteristic pattern with the synthetic 5'-monophosphat es of AdG and CdG. Using this assay, we also demonstrated the in vivo stereoselective formation of one of the AdG isomers. The estimated tot al levels of modification were 1.0-1.7, 0.2-1.0, and 0.3-2.0 adducts i n 10(6) guanine bases in the liver DNA of mice, rats, and humans, resp ectively. The detection of these adducts in relatively high levels wit hout carcinogen treatment suggests that the endogenous factors such as lipid peroxidation may be important for their formation. This study p rovides evidence for the presence of acrolein- and crotonaldehyde-deri ved exocyclic adducts as common lesions in the liver DNA of rodents an d humans.