O-6-METHYLGUANINE-DNA ADDUCTS IN RAT LYMPHOCYTES AFTER IN-VIVO EXPOSURE TO N-NITROSODIMETHYLAMINE (NDMA)

A non-invasive approach in immunopathological risk assessment was appl ied for analysis of the in vivo formation of DNA adducts. DNA methylat ion was studied in peripheral blood lymphocytes (PBLs) collected from Sprague - Dawley rats exposed to a single dose (75 mg/kg b.w.) of N-ni trosodimethylamine (NDMA). Three different techniques were applied for characterization and quantification of DNA adducts: (i) colloidal gol d ultraimmunocytochemical localization of O-6-methylguanosine (O-6-meG ) - DNA adducts, using affinity-purified, polyclonal antibody directed against O-6-meG, (ii) quantitative assay using enzyme-linked immunoso rbent assay (ELISA), amplified by the avidin-biotin (AB) system, and ( iii) highperformance liquid chromatography (HPLC). The O-6-meG-immunor eactive sites in PBLs seem to be concentrated in the nucleus. However, significant immunolabelling was also noted in the cytoplasm of the in vivo NDMA-exposed PBLs. Control preparations showed no specific gold immunolabelling. The O-6-meG - DNA adduct formation in PBLs and hepato cytes, at 2 - 24 h following the exposure to NDMA, was analogous for b oth types of cells. The data showed high correlation for the ELISA and HPLC analytical methods. The data suggest an efficient O-6-metG-DNA r epair mechanism in lymphocytes, possibly analogous to the enzymatic re pair of DNA adducts in liver cells.