Single-cell gel electrophoresis assays with human-derived hepatoma (Hep G2) cells

The purpose of the present study was the development of a protocol for detecting chemically-induced DNA damage, using the alkaline single-cell gel electrophoresis (SCGE) assay with human-derived, metabolically competent hepatoma (Hep G2) cells. Previous studies indicated that Hep G2 cells have retained the activities of certain phase I and phase II enzymes and reflect the metabolism of genotoxins in mammals better than other in vitro models which require addition of exogenous activation mixtures. The optimal trypsin concentration for the removal of the cells from the plates were found to be 0.1%. Dimethylsulfoxide, at concentrations up to 2%, was an appropriate solvent for water-insoluble compounds. To determine the optimal exposure periods for mutagen treatment, the time kinetics of comet formation was investigated with genotoxic chemicals representing various classes of promutagens namely benzo[a]pyrene (B[a]P), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), and N-nitrosodimethylamine (NDMA) and with N-nitrosomethylurea (NMU). All compounds caused a statistically significant induction in DNA damage. With the promutagens, comet formation increased gradually as a function of the exposure duration, and reached maximum values between 20-24 h. With NMU, comet induction maximized already after a short exposure (1 h) and remained at a constant level for up to 24 h. Based on these results, the Hep G2/SCGE assay appears to be a suitable approach for investigating DNA damaging potential of chemicals. Further experiments with IQ and B[a]P showed that the assays are highly reproducible. Comparisons of the present results with those from earlier experiments in which other endpoints (induction of sister chromatid exchanges, micronuclei and chromosomal aberrations) were measured in Hep G2 cells, indicated that the sensitivity of the SCGE assays is more or less identical. Since the SCGE assay is less time consuming than other genotoxicity assays we anticipate that it might be a suitable approach to investigate DNA damaging effects of chemicals in the human-derived, metabolically competent cell line.