Heterocyclic aromatic amines induce DNA strand breaks and cell transformation

Heterocyclic aromatic amines (HAAs), formed during the cooking of foods, are known to induce tumours in rodent bioassays acid may thus contribute to human cancer risk. We tested six HAAs in a morphological transformation assay and in three in vitro genotoxicity assays. The morphological transforming abilities of HAAs were tested, in the presence of rat-liver S9, in the C3H/M2 fibroblast cell line. Concentration levels of 50 mu M 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (8-MeIQx), 100 mu M 2-amino-3,4,8-trimethylimidazo-[4,5-f]quinoxaline (4,8-DiMeIQx), 50 mu M 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 100 mu M 2-amino-3-methyl-9H-pyrido[2,3-b]indole (A alpha C), 100 mu M 2-amino-3methyl-9H-pyrido[2,3-b]indole (MeA alpha C) and 15 mu M 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) induced maximum transformation potencies of 5.5, 6.6, 6.3, 5.2, 7.3 and 9.2 transformed foci per 10(4) surviving cells, respectively. Bacterial mutagenic activity was determined in the presence of rat-liver S9 using the Salmonella typhimurium reverse-mutation assay employing strain YG1019. Mutagenic potencies of 3800 revertants (revs)lng with 8-MeIQx, 2900 revs/ng with 4,8-DiMeIQx, 3480 revs/ng with IQ, 1.6 revs/ng with AaC, 2.9 revs/ng with MeAaC and 5 revs/ng with PhIP were observed. Clastogenic activity in vitro was analysed by the micronucleus assay in metabolically competent MCL-5 cells. Dose-dependent induction of micronuclei was observed for all HAAs tested with 1-5.4 % of cells containing micronuclei at 10 ng/ml, Micronucleus induction was in the order 4,8-DiMeIQx > 8-MeIQx > IQ > MeA alpha C > PhIP > AaC, DNA strand-breaking activity in MCL-5 cells was measured by the alkaline single cell-gel (comet) assay. The lowest effect doses for significant increases (P less than or equal to 0.0007, Mann-Whitney test) in comet tail length (mu m) were 45.5 mu g/ml (200 mu M) for PhIP, 90.9 mu g/ml (410-510 mu M) for 4,8-DiMeIQx, IQ, MeA alpha C and A alpha C, and 454.5 mu g/ml (2130 mu M) for 8-MeIQx, It is not yet clear which of these assays most accurately reflects the genotoxic potential to humans of compounds of this class of environmental carcinogens.