Extended-term cultures of human T-lymphocytes and the comet assay: a useful combination when testing for genotoxicity in vitro?

Extended-term cultures of human lymphocytes provide a source of uniform human cells that can be used for several experiments performed over a long time, avoiding the variability arising from taking blood samples for individual experiments. The use of extended-term cultures of human T-lymphocytes in the alkaline single-cell gel electrophoresis assay (comet assay) was evaluated as a test for the potential genotoxicity of chemicals. The DNA-damaging effects of five DNA-reactive mutagens and clastogens (benzo[a]pyrene, cyclophosphamide, formaldehyde, 4-nitroquinoline-N-oxide (4NQO) and N-nitrosopiperidine) was determined and compared with the effects of one non-DNA-reactive mutagen (5-hydroxyurea), and one non-mutagenic agent (ethanol). The alkylating and/or DNA-adduct forming agents N-nitrosopiperidine, cyclophosphamide, 4-nitroquinoline-N-oxide and benzo[a]pyrene increased the DNA migration in a dose-dependent manner. In contrast, the DNA/protein-crosslinking agent formaldehyde decreased the migration of DNA during the electrophoresis. The lowest observed effect levels (LOELs) under the experimental conditions used in the present study, were: 0.0001 mM (4-nitroquinoline-N-oxide without S9), 0.05 mM (benzo[a]pyrene with S9), 0.1mM (formaldehyde without S9), 0.25 mM (cyclophosphamide with S9), and 0.5mM (N-nitrosopiperidine with S9), respectively. The antimetabolite 5-hydroxyurea was also found to increase the tail moment, but only in cells that had been exposed to rather high concentrations (> or =10mM) of the compound. Ethanol did not affect the tail moment, not even in cells that had been exposed to an apparently cytotoxic concentration (500 mM). The results of the present study are in qualitative agreement with those obtained using other cells in the alkaline comet assay and it is therefore concluded that extended-term cultures of human T-lymphocytes and the alkaline version of the single-cell gel electrophoresis assay is a useful combination when testing for the potential genotoxicity of chemicals.