Cyclic 1, N2-propanodeoxyguanosine adducts are formed in vitro in DNA treated with α-acetoxy-N-nitrosopyrrolidine or its metabolite, crotonaldehyde. However, the in vivo formation of these cyclic adducts in DNA has not been demonstrated due to the lack of a sensitive detection method. In this study, a 32P-postlabeling method specific for the detection of 1, N2-propanodeoxyguanosine adducts was developed by using the corresponding 3'-monophosphates as standards. This method was validated by using DNA modified in vitro. It was then applied for the in vivo experiments in which hepatic DNA of rats treated with N-nitosopyrrolidine (NPYR) (total dose, 1.0 mmol) in drinking water or skin DNA of Sencar mice treated topically with crotonaldehyde (1.4 mmol) was isolated and subjected to 32P-postlabeling analysis. 1, N2-Propanodeoxyguanosine adducts were detected in these DNA samples. The minimal levels of adducts from liver DNA and skin DNA detected were estimated to be ∼0.06 and ∼0.24 μmol/mol guanine respectively. Interestingly, a background adduct spot chromatographically indistinguishable from the 1, N2-cyclic adducts was observed in the liver DNA of untreated rats. However, no such background adduct was detected in skin DNA of mice. This method demonstrated for the first time the in vivo formation of the cyclic 1, N2-propanodeoxyguanosine adducts.
Bibliographical noteFunding Information:
We would like to thank Drs M.Y.Wang, P.Foiles, M.Morse and R.Sodum for providing some of the DNA samples used in this study. This work was supported by grants CA-44377 and CA^3159 from the National Cancer Institute. This is paper no. 125 in 'A Study of Chemical Carcinogenesis'.