Bromobenzene (BB) is known to pose a serious threat to human health. We previously demonstrated that BB showed chronotoxicity, that is, daily fluctuations in the severity of hepatotoxicity induced in mice. Although BB showed mild nephrotoxicity, a daily fluctuation was not observed in this toxicity. This might be attributed to the fact that BB-induced chronotoxicity is observed only in the liver and not in the kidneys and that the damage caused by BB is prominent in the liver, masking the daily fluctuation in nephrotoxicity. To confirm these two possibilities, we examined the daily fluctuations in nephrotoxicity due to BB intermediate metabolites that target the kidneys: 3-bromophenol, bromohydroquinone, and 4-bromocatechol. Mice were injected with 3-bromophenol, bromohydroquinone, or 4-bromocatechol intraperitoneally at six different time points in a day (zeitgeber time (ZT): ZT2, ZT6, ZT10, ZT14, ZT18, or ZT22). Mortality was monitored for 7 d post-injection. Mice were more sensitive to the acute toxicity of these metabolites around at ZT14 (dark-phase) exposure than around at ZT2 (light-phase) exposure. Furthermore, mice administered with a non-lethal dose of 4-bromocatechol showed significant increases in the levels of plasma blood urea nitrogen and renal malondialdehyde at ZT14 exposure. Moreover, glutathione peroxidase-4, a ferroptosis indicator, was attenuated at ZT14 exposure. These results indicate the toxicity of BB metabolites was higher during the dark-phase exposure, and demonstrate the reason why the diurnal variation of nephrotoxicity by BB was not observed in our previous report is that renal damage was masked due to severe hepatic damage.
Keywords: bromobenzene; chronotoxicity; circadian rhythm; diurnal variation; kidney.