Heterocyclic aromatic amines induce DNA strand breaks and cell transformation

Heterocyclic aromatic amines (HAAs), formed during the cooking of foods, ar e known to induce tumours in rodent bioassays acid may thus contribute to h uman cancer risk. We tested six HAAs in a morphological transformation assa y 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-dimet hylimidazo[4,5-f]quinoxaline (8-MeIQx), 100 mu M 2-amino-3,4,8-trimethylimi dazo-[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 m u 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 fo ci per 10(4) surviving cells, respectively. Bacterial mutagenic activity wa s determined in the presence of rat-liver S9 using the Salmonella typhimuri um reverse-mutation assay employing strain YG1019. Mutagenic potencies of 3 800 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 c ells 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-bre aking activity in MCL-5 cells was measured by the alkaline single cell-gel (comet) assay. The lowest effect doses for significant increases (P less th an 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-DiMeI Qx, IQ, MeA alpha C and A alpha C, and 454.5 mu g/ml (2130 mu M) for 8-MeIQ x, It is not yet clear which of these assays most accurately reflects the g enotoxic potential to humans of compounds of this class of environmental ca rcinogens.