Evaluation of Genotoxicity of 3-Amino-, 3-Acetylamino- and 3-Nitrobenzanthrone Using the Ames/Salmonella Assay and the Comet Assay

3-Nitrobenzanthrone (3-NBA) is an extremely potent direct-acting bacterial mutagen that has been detected in diesel exhaust particles, airborne particles and so forth. Recently, 3-aminobenzanthrone (3-ABA) and 3-acetylaminobenzanthrone (3-AABA) were identified as metabolites of 3-NBA in mammalian cells. In this study, to clarify the genotoxicity of 3-ABA, 3-AABA and 3-NBA in vitro and in vivo, the mutagenicity and DNA-damaging activity of these chemicals were investigated by the Ames assay and by alkaline single gel electrophoresis (Comet assay), respectively. 3-ABA and 3-AABA were mutagenic toward four Salmonella typhimurium strains, i.e. TA98, TA100, YG1024 and YG1029, in the presence of a mammalian metabolic system (S9 mix). Both chemicals showed the highest mutagenicity toward YG1024, and induced 2180000 revertants/nmol of 3-ABA and 131000 revertants/nmol of 3-AABA. 3-NBA also showed mutagenicity toward these four strains with and without S9 mix, but the potencies of 3-NBA in these strains were decreased by the addition of S9 mix. In the presence of S9 mix, the mutagenic activities of 3-NBA in four strains were comparable to or lower than those on 3-ABA. 3-ABA, 3-AABA and 3-NBA produced statistically significant DNA damage, which was detected by an increase in the DNA tail moment, in vivo 3 hr after intraperitoneal injection at 160 mg/kg body weight. 3-ABA, 3-AABA and 3-NBA induced significant DNA damage in the liver, kidney, spleen and lung, spleen only, and liver, kidney, lung and bone marrow, respectively. At a lower dose (40 mg/kg), 3-NBA produced significant DNA damage in the lung. These results indicate that 3-ABA, 3-AABA and 3-NBA are not only mutagenic in vitro in bacteria but also genotoxic in vivo in mouse.