Evaluation of the single cell gel electrophoresis assay with human hepatoma (Hep G2) cells

Human Hep G2 cells have retained the activities of phase I and phase Il enz ymes which are involved in the metabolism of environmental genotoxins. The present study describes the results of single cell gel electrophoresis (SCG E) assays with a panel of different model compounds with these cells. With genotoxic carcinogens such as aflatoxin B-1 (AFB(1)), benzo(a)pyrene (B(a)P ), nitrosodimethylamine (NDMA) and cyclophosphamide (CP), statistically sig nificant dose dependent induction of DNA migration was measured. With the t wo heterocyclic amines, 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) an d 3-amino-1,4-dimethyl-5H-pyrido[4,3-b)]indole (Trp-P-l), and also with rod ent carcinogens such as safrole, hexamethylphosphoramide (HMPA) and the pyr rolizidine alkaloid isatidine, which give negative results in other in vitr o genotoxicity tests, positive results were obtained in Hep G2/SCGE assays. Nitrosomethylurea (NMU) was the only directly acting compound tested in th e study and was by far (ca. 10(3)-fold) more active than the corresponding nitrosamine. The exposure concentrations required to cause significant effe cts varied over a broad range. The most pronounced effect was seen with AFB (1) (0.008 mu M) followed by HMPA (15 mu M), B(a)P (25 mu M), NMU (100 mu M ), isatidin (500 mu M), CP (900 mu M), IQ (1200 mu M), safrol (4000 mu M), and NDMA (90 x 10(3) mu M). Numbers in parenthesis give the lowest concentr ations, which caused a significant increase of DNA migration. With two comp ounds, namely, the non-carcinogen pyrene and the synthetic hormone tamoxife n (TF), negative results were obtained under all test conditions. These fin dings are in agreement with the results of recent investigations which indi cated that human hepatocytes are unable to convert TF to DNA reactive metab olites, whereas it is activated by rat liver cells and causes DNA adducts i n these cells. Comparisons of the present results with data from earlier ex periments indicate that the Hep G2/SCGE assay enables the detection of geno toxins including compounds which give misleading results in other in vitro genotoxicity tests and appears to be an alternative to tests with primary l iver cells from laboratory animals. (C) 2000 Elsevier Science B.V. All righ ts reserved.