Urinary bladder carcinogenic potential of 4,4'-methylenebis(2-chloroaniline) in humanized-liver mice.

Occupational exposure to 4,4'-methylenebis(2-chloroaniline) (MOCA) has been linked to an increased risk of bladder cancer among employees in Japanese plants, indicating its significance as a risk factor for urinary bladder cancer. To investigate the role of MOCA metabolism in bladder carcinogenesis, we administered MOCA to non-humanized (F1-TKm30 mice) and humanized-liver mice for 4 and 28 wk. We compared MOCA-induced changes in metabolic enzyme expression, metabolite formation, and effects on the urinary bladder epithelium in the 2 models. At week 4, MOCA exposure induced simple hyperplasia, cell proliferation, and DNA damage in the urothelium of the humanized-liver mice, whereas in the non-humanized mice, these effects were not observed. Notably, the concentration of 4-amino-4'-hydroxylamino-3,3'-dichlorodiphenylmethane (N-OH-MOCA) in the urine of humanized-liver mice was more than 10 times higher than that in non-humanized mice at the 4-wk mark. Additionally, we observed distinct differences in the expression of cytochrome P450 isoforms between the 2 models. Although no bladder tumors were detected after 28 wk of treatment in either group, these findings suggest that N-OH-MOCA significantly contributes to the carcinogenic potential of MOCA in humans.