The synergistic effect of sodium chlorite and bromochloroacetic acid on BrO3(-)-induced renal cell death.

Bromate (BrO(3)(-)) is a drinking water disinfection by-product (DBP) that induces renal cell death via DNA damage-dependent and -independent mechanisms. Drinking water contains other DBPs in addition to BrO(3)(-). We tested the effect of two of these, sodium chlorite (NaClO(2)) and bromochloroacetic acid (BCAA), on BrO(3)(-) cytotoxicity in normal rat kidney (NRK) cells. NaClO(2) and BCAA alone induced cytotoxicity at concentrations of over 20ppm, while BrO(3)(-) was only moderately cytotoxic at concentrations of 200ppm. Combining BrO(3)(-) with NaClO(2) or BCAA alone enhanced cytotoxicity 1.5-4 fold. Exposing cells to all three compounds induced synergistic-like increases in cytotoxicity. This effect did not correlate to increases in reactive oxygen species (ROS), even though all three compounds induced ROS formation alone. NaClO(2), but not BCAA, increased BrO(3)(-)-mediated DNA damage as measured by 8-hydroxydeoxyguanosine (8-OHdG) staining. In addition, NaClO(2), but not BCAA, decreased BrO(3)(-)-induced G2/M cell cycle arrest. Both compounds increased apoptosis in the presence of BrO(3)(-) as assessed by annexin V, PI, and DAPI staining. This is in contrast to BrO(3)(-) treatment alone, which induced necrosis. Immunoblot analysis showed that both NaClO(2) and BCAA increased p38 activation; however, consistent with 8-OHdG staining, only NaClO(2) increased BrO(3)(-)-induced histone H2AX phosphorylation, a marker of DNA damage. In contrast, BCAA, but not NaClO(2), increased BrO(3)(-)-induced phosphorylation of p53. These data support the novel finding that mixtures of DBPs increase BrO(3)(-)-induced renal cell death by DNA-dependent and -independent mechanisms, and could alter how the risk of these DBPs towards humans is assessed.