Mutagenicity, unscheduled DNA synthesis, and metabolism of 1-nitropyrene in the human hepatoma cell line HepG2.

The cell line HepG2 is derived from a well differentiated human hepatoblastoma, which retains many of the morphological characteristics of liver parenchymal cells. These cells at passages greater than 95 were found to metabolically activate carcinogens to genotoxic metabolites. The addition of 6.8 microM 1-methyl-3-nitro-1-nitrosoguanidine, 5.3 microM 4-nitroquinoline-N-oxide, and 4-20.3 microM 1-nitropyrene resulted in the induction of mutations at the HGPRT locus as determined by 6-thioguanine resistance. This is the first description of the induction of mutations in these cells. Additionally, unscheduled DNA synthesis in the presence of 4 mM hydroxyurea was increased by 9% with 5.3 microM 4-nitroquinoline-N-oxide, 57% with 13.6 microM 1-methyl-3-nitro-1-nitrosoguanidine, and 300% with 8.2 microM 1-nitropyrene. High performance liquid chromatographic analysis of metabolites formed following incubation of HepG2 with either [3H]-1-nitropyrene or [14C]benzo(a)pyrene demonstrate the occurrence of arene oxidation as well as nitroreduction.