Toxicity and DNA damage induced by 1-nitropyrene and its derivatives in Chinese hamster lung fibroblasts

1-Nitropyrene and its chemically synthesised derivatives were investigated for their cytotoxicity and ability to induce DNA-strand breaks in Chinese hamster lung fibroblasts. Both 1-nitrosopyrene (0.25-60 micrograms/ml) and 1-aminopyrene (0.25-25 micrograms/ml) were cytotoxic, and induced the formation of DNA lesions, which were measured as DNA single-strand breaks after sedimentation in alkaline sucrose-density gradients. Higher doses of 1-aminopyrene (25-60 micrograms/ml) inhibited the formation of DNA single-strand breaks. 1-Nitropyrene was not toxic (0.25-60 micrograms/ml) and induced low levels of detectable DNA strand breaks, whilst N-acetyl-1-aminopyrene was inactive. The post-mitochondrial supernatant fraction of Aroclor-induced rat-liver containing 4 mM NADPH (S9 mix) did not promote the activation of 1-nitropyrene. In fact DNA strand breaks induced by either 1-nitropyrene or 1-nitrosopyrene was abolished in the presence of S9 mix. The 1-nitropyrene reduced intermediate, N-hydroxy-1-aminopyrene was synthesised by the reduction of 1-nitrosopyrene with ascorbic acid. In the presence of ascorbic acid, 1-nitrosopyrene caused a 5-fold increase in the number of DNA single-strand breaks when compared to cells treated with 1-nitrosopyrene alone. The results are discussed in terms of the metabolic activation of 1-nitropyrene and 1-aminopyrene in Chinese hamster lung cells.

The clastogenic activity of dinitropyrenes in a rat-liver epithelial cell line

The ability of 1,6-dinitropyrene and 1,8-dinitropyrene to induce chromosome aberrations has been examined in a rat epithelial cell line (RL4). Both compounds were found to be potent clastogenic agents in these cells, inducing predominantly chromatid type abberations. The number of aberrant metaphases was dose-related up to 1.25 micrograms/ml, after which the response showed a plateau at a frequency of around 60%. The number of chromatid gaps per 100 cells also increased linearly with concentration from 3.5 in the control cultures up to 117 with 1,6-DNP (1.25 micrograms/ml) and 98 with 1,8-DNP (2.5 micrograms/ml), indicating that the induction of chromatid gaps was a valid and sensitive measure of chromosome damage in this cell line. The fact that a positive result as obtained in RL4 cells implies that these cells contain enzyme systems which are capable of converting dinitropyrenes to a mutagenic form.