Genotoxicity of 3,6-dinitrobenzo(e)pyrene, a novel mutagen in ambient air and surface soil, in mammalian cells in vitro and in vivo

3,6-Dinitrobenzo[e]pyrene (3,6-DNBeP), newly identified in airborne particles and surface soil, is a potent mutagen in Salmonella typhimurium. The present study investigated the genotoxic potency of 3,6-DNBeP in vitro and in vivo using mammalian cell strains (Chinese hamster CHL/IU and human HepG2) and ICR mice, respectively. In the hprt gene mutation assay using HepG2 cells, the spontaneous mutant frequency was 61.1 per 10 5 clonable cells, which increased to 229 per 10 5 clonable cells after treatment with 1.0 mg/ml (3 mM) 3,6-DNBeP. Notably, in HepG2 cells with increased N-acetyltransferase 2 activity, the mutant frequency increased to 648 per 10 5 clonable cells by treatment of 1.0 mg/ml (3 mM) 3,6-DNBeP. The sister chromatid exchange frequency increased approximately three times the control level in HepG2 cells treated with 3,6-DNBeP at a concentration of 1.0 mg/ml (3 mM). In HepG2 and CHL/IU cells, the frequency of the cells with micronuclei was 0.9 and 1.2%, and the frequencies increased to 2.3 and 7.6% after 1.0 mg/ml (3 mM) 3,6DNBeP-treatment, respectively. The H2AX phosphorylation level increased 8-fold compared with the background level with 1.0 mg/ml (3 mM) 3,6-DNBeP-treatment in HepG2 cells. Moreover, the comet assay showed that 3,6DNBeP produced DNA damage in the cells of liver, kidney, lung and bone marrow in ICR mice 3 h after intraperitoneal injection at 40 mg/kg (0.12 mmol/kg) body weight. These data indicate that 3,6-DNBeP is genotoxic to mammalian cells in vitro and in vivo.