H4IIEC3 rat hepatoma cells activate N-nitrosodimethylamine but are resistant to the genotoxic products

Abstract

Exposure of the differentiated rat hepatoma cells H4IIEC3 (H4) or several of their subclones to 20 mM N-nitrosodimethylamine (NDMA) did not significantly increase the number of 6-thioguanine (TG)-resistant cells or of micronuclei. Similar results were obtained with H4 cells pretreated with isopropanol, an inducer of the NDMA-metabolizing cytochrome P450 form. However, when H4 cells were co-cultured with V79 Chinese hamster cells, which are incapable of activating NDMA, exposure to the nitrosamine (5-40 mM) caused a concentration-dependent increase in the frequency of TG-resistant V79 cells; pretreatment of H4 cells with 0.5% isopropanol nearly doubled the magnitude of this response. When freshly isolated rat hepatocytes were used as the activation system in co-cultures with either H4 cells or V79 cells, NDMA induced up to 20 times more TG-resistant mutants in V79 cells than in H4 cells. The results indicate that H4 hepatoma cells are capable of metabolizing NDMA to genotoxic products but can protect themselves, presumably by repairing the potentially mutagenic DNA lesions.