Genotoxicity of propoxur and its N-nitroso derivative in mammalian cells

N-Nitroso propoxur (NP) can be synthesized from a widely used N-methylcarbamate insecticide, propoxur, in vitro in the laboratory, Because of the extensive use of aerosol propoxur, the adverse effect on cells of respiratory origin is worth elucidating. In this report, two mammalian cell cultures from respiratory tissues [a hamster lung fibroblast, V79, and a primary rat tracheal epithelial cell (RTE)], were used to investigate the genotoxicity of propoxur and NP. NP was more cytotoxic than propoxur, with LC(50)s (20 and six times smaller, respectively in V79 and RTE cells. NP significantly induced sister chromatid exchange (greater than or equal to 0.01 mu g/ml), chromosome aberration (greater than or equal to 2,5 mu g/ml) and hprt gene mutation (greater than or equal to 0.5 mu g/ml) in V79 cells, and cell transformation (greater than or equal to 0,2 mu g/ml) in RTE cells. Results of chromosome aberration and hprt gene mutation indicated that the major pre-mutagenic lesion induced by NP must be the O(6)-methylguanine adduct, which frequently mispairs with thymine and thus gives rise to a GC-->AT transition, Propoxur was not mutagenic to either type of cells, However, it inhibited gap-junctional intercellular communication in V79 cells, which indicates that propoxur could act through some epigenetic mechanisms, such as tumor promotion or cell proliferation, in the multiple process of chemical carcinogenesis.