A Sensitive Hepatocytemediated Assay for the Metabolism of Nitrosamines to Mutagens for Mammalian Cells1

A sensitive cell-mediated assay has been developed for testing mutagenesis in Chinese hamster V79 cells by carcino genic nitrosamines. Mutations were characterized by resist ance to ouabain and 6-thioguanine. Since V79 cells do not metabolize nitrosamines, mutagenesis in the V79 cells was tested in the presence of primary hepatocytes capable of metabolizing nitrosamines. The hepatocytes were isolated after collagenase and hyaluronidase digestion of liver slices. All seven liver carcinogens of the nine tested nitrosamines ex hibited a mutagenic response in this cell-mediated assay. The potent liver carcinogens nitrosodimethylamine, nitrosodieth ylamine, nitrosoethylmethylamine, and nitrosodipropylamine could be detected with doses as low as 1 @M. The noncarcin ogenic nitrosodiphenylamine was not mutagenic. Nitrosome thoxymethylamine was the only nitrosamine that exhibited mu tagenic activity in the absence of hepatocytes, and this activity was diminished in the presence of hepatocytes. It is suggested that the use of hepatocytes prepared by the slicing method for carcinogen metabolism and mutable V79 cells offers a highly sensitive assay for determining the mutagenic potential of carcinogenic nitrosamines and probably of other classes of hazardous chemicals occurring in the environment.