Reduction of genotoxic effects of the carcinogen N-methyl-N′-nitro-N-nitrosoguanidine by dietary lignin in mammalian cells cultured in vitro

In the present study the protective effect of several lignin polymers against the genotoxic effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was tested in hamster lung V79 cells and human colon Caco-2 cells. Preculturing of cells with sublethal, nongenotoxic concentrations of the lignins A, B, and C (50,mug/ml) was found to decrease significantly the level of DNA strand breaks in both hamster and human cells treated with MNNG. Lignin A also reduced MNNG-induced gene mutations in V79 cells. As in addition to alkyl lesions MNNG gives rise to hydroxyl free radicals (OH) and nitrogen-centered free radicals (M), we tried to determine whether antimutagenicity of lignin A was connected only with the well-known ability of lignin to bind MNNG molecules or also with its antioxidative effects. The use of the modified comet assay technique proved that pre-culturing of hamster V79 cells with lignin A resulted in a significant decrease of the level of DNA strand breaks originating from oxidized DNA bases. Therefore, we suggest that the antimutagenic effect of lignin A against MNNG is associated with both adsorptive and antioxidative action. This study also showed that the presence of lignin A neither helped to renew DNA replication nor influenced the kinetics of DNA rejoining in MNNG-treated V79 cells.