Antibodies against 7-Methyldeoxyguanosine: Its Detection in Rat Peripheral Blood Lymphocyte DNA and Potential Applications to Molecular Epidemiology¹

Polyclonal antibodies have been raised against the imidazole ring-open form of 7-methyldeoxyguanosine (7-mdGua). A combined high performance liquid chromatography/immunoassay method has been developed using these antibodies which provides a specific and sensitive way to quantitate 7-mdGua in DNA. Following enzyme hydrolysis and chromatographic purification of 7-mdGua, the adduct is quantitatively converted to the ring-open form and can be measured at levels as low as 0.05 pmol by immunoassay. With 1 mg of DNA a level below 1 adduct per 10⁷ normal deoxynucleosides can be measured. Using DNA modified by radiolabeled carcinogens, a good correlation between 7-mdGua levels, as measured by immunoassay or radioactivity, was obtained. In rats treated with dimethylnitrosamine (0.4 and 1.0 mg/kg), both 7-mdGua and O⁶-methyldeoxyguanosine were detected in peripheral blood lymphocyte DNA. In addition the levels of both adducts at time points up to 48 h posttreatment were very similar to those seen in liver DNA from the same animals. The measurement of 7-mdGua, quantitatively the major methylation adduct, in small cell samples such as lymphocytes has great potential in determining the exposure of humans to environmental methylating agents such as nitrosamines.