Association of brominated proteins and changes in protein expression in the rat kidney with subcarcinogenic to carcinogenic doses of bromate

The water disinfection byproduct bromate (BrO₃⁻) produces cytotoxic and carcinogenic effects in rat kidneys. Our previous studies demonstrated that BrO₃⁻ caused sex-dependent differences in renal gene and protein expression in rats and the elimination of brominated organic carbon in their urine. The present study examined changes in renal cell apoptosis and protein expression in male and female F344 rats treated with BrO₃⁻ and associated these changes with accumulation of 3-bromotyrosine (3-BT)-modified proteins. Rats were treated with 0, 11.5, 46 and 308 mg/L BrO₃⁻ in drinking water for 28 days and renal sections were prepared and examined for apoptosis (TUNEL-staining), 8-oxo-deoxyguanosine (8-oxoG), 3-BT, osteopontin, Kim-1, clusterin, and p-21 expression. TUNEL-staining in renal proximal tubules increased in a dose-related manner beginning at 11.5 mg BrO₃⁻/L in female rats and 46 mg/L in males. Increased 8-oxoG staining was observed at doses as low as 46 mg/L. Osteopontin expression also increased in a dose-related manner after treatment with 46 mg/L, in males only. In contrast, Kim-1 expression increased in a dose-related manner in both sexes, although to a greater extent in females at the highest dose. Clusterin and p21 expression also increased in a dose-related manner in both sexes. The expression of 3-BT-modified proteins only increased in male rats, following a pattern previously reported for accumulation of α-2_u-globulin. Increases in apoptosis in renal proximal tubules of male and female rats at the lowest doses suggest a common mode of action for renal carcinogenesis for the two sexes that is independent of α-2_u-globulin nephropathy.