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The Water Disinfectant Byproduct Dibromoacetonitrile Induces Apoptosis in Rat Intestinal Epithelial Cells: Possible Role of Redox Imbalance

Chemically induced oxidative stress poses cytotoxic effects on intestinal epithelial cells that may trigger various forms of injuries in intestinal mucosa. Haloacetonitriles, including dibromoacetonitrile (DBAN, a drinking water contaminant and direct acting mutagen and carcinogen), are known to induce GI disorders. Earlier, we showed that dichloroacetonitrile (DBAN analog) alters glutathione status and increases reactive oxygen species in murine macrophage cell line. Therefore, the present study was undertaken to understand the role of redox imbalance and apoptosis in DBAN-induced GI disorders using rat intestinal epithelial (RIE) cells. Cultured confluent monolayers of RIE cells were continuously exposed to DBAN at 50 to 400 ppb (0.6 to 4.4 μM). After 24, 48, and 72 h of the exposure, oxidative stress and apoptosis were determined. At higher exposure regimens (100 to 400 ppb), a concentration- and time-dependent increase in glutathione disulfide levels (1.5 to 4-fold and 1.6 to 5-fold, p < 0.05) was noticed at 48 and 72 h, respectively, as compared to control. Severe depletion of reduced glutathione was also observed at 72 h after DBAN treatment. DBAN-induced oxidative stress was demonstrated at all concentrations by increased malondialdehyde (MDA) levels (1.3 to 3- and 1.8 to 4-fold, p < 0.05) at 48 and 72 h after treatment, respectively. Increase (1.3 to 2-fold, p < 0.05) in 8-hydroxy-2-deoxyguanosine (8OHdG) levels was observed at 48 h after treatment with 100–400 ppb DBAN. At 72 h these levels were 1.7 to 3- fold higher in DBAN-treated RIE cells as compared to control. DBAN-induced apoptosis, evaluated using TUNEL assay and differential staining techniques, indicates an increase in nuclear damage along with various apoptotic features using epifluorescence or light microscopy. The results of the present study suggest that DBAN-induced redox imbalance could lead to apoptosis and overall oxidative stress in RIE cells.