Induction of DNA damage by N-nitrosodiethylamine in rat hepatoma cells: correlation with cytochrome P450-mediated aldrin epoxidase activity.

The genotoxic potency of the hepatocarcinogen N-nitrosodiethylamine (NDEA) was tested in various Reuber hepatoma cell lines, which differ in their expression of differentiated liver specific functions including hepatic cytochrome P450 forms, and in rat hepatocytes, with the aim of characterizing the enzymes involved in activation. DNA single-strand breaks assessed by alkaline elution served as an indicator of genetic damage. Aldrin epoxidase activity was used as a marker for various hepatic cytochrome P450 forms. The poorly differentiated cell lines RH35 and H4IIEC3/T were apparently not affected by NDEA; moderate effects were observed in the well-differentiated lines H4IIEC3/G- and 2sFou, and major effects in two other well-differentiated lines, Fao and C2Rev7, and in hepatocytes. The degree of DNA damage in the cell lines correlated positively with the expression of aldrin epoxidase. Furthermore, DNA damage induced by N-nitrosodimethylamine (NDMA) was determined in C2Rev7 cells and in rat hepatocytes in order to assess a possible involvement of the NDMA-metabolizing cytochrome P45oIIE1 in the activation of NDEA by comparing the genotoxic potencies of the two compounds. NDMA was distinctly less effective than NDEA in C2Rev7 cells at all concentrations tested. In hepatocytes, NDMA induced more DNA damage than NDEA at low concentrations, but was slightly less active at high concentrations. The results suggest that NDEA is preferentially metabolized to genotoxic products by one or several cytochrome P450 forms different from P450IIE1.