Cell replication and unscheduled DNA synthesis (UDS) activity of low molecular weight chlorinated paraffins in the rat liver in vivo.

The rodent carcinogen C12-chlorinated paraffin (C12-CP) has been evaluated for unscheduled DNA synthesis (UDS) activity in the rat liver in vivo. Evidence of cell proliferation was also assessed by measuring cells undergoing semi-conservative DNA activity (S phase). No evidence of UDS was observed at doses up to 2 g/kg at either 2 or 12 h after dosing. Concomitant positive UDS responses were observed for the liver genotoxins N-nitrosodimethylamine, 4-aminobiphenyl, methyl methanesulphonate, 2-acetylaminofluorene, benzidine and 6-dimethylaminophenylazobenzthiazole. A strong positive response was observed in the cell proliferation assay for the test agent and the positive control agents quinoline and 4-acetylaminofluorene. These observations are discussed within the context of the rodent carcinogenicity reported for the same sample of C12-CPs as studied by the US National Toxicology Program.