Induction of oxidative stress and TNF- α secretion by Dichloroacetonitrile, a water disinfectant by-product, as possible mediators of apoptosis or necrosis in a murine macrophage cell line (RAW)

Abstract

The water disinfectant by-product dichloroacetonitrile (DCAN) is a direct-acting mutagen and induces DNA strand breaks in cultured human lymphoblastic cells. Cellular activation by environmental agents may exert detrimental effects to the cells. Activated macrophages produce reactive oxygen intermediates such as H 2O 2, −OH and O 2. Therefore, the effect of various concentrations of DCAN (100–400 μ m) on the activity macrophage cells (RAW 264.7) was studied. In these cells, DCAN-induced oxidative stress was characterized by the production of reactive oxygen intermediates (ROI). Also, the ratios of intracellular GSH/GSSG was assessed and used as a biomarker for oxidative stress. The secretion of TNF- α was assessed since macrophages are known to secrete TNF- α as a result of cellular oxidative stress. Electrophoretic detection of DNA degradation and light microscopy was utilized for the characterization of DCAN-induced apoptosis. Lactate dehydrogenase (LDH) leakage and trypan blue exclusion were used as markers of cellular necrosis. Following exposure to DCAN (200 μ m and 400 μ m), intracellular GSSG was increased (2.5-fold of control, P<0.05). DCAN activation of RAW cells was detected by elevated levels of intracellular ROI (1.9–2.5-fold than control, P<0.05) and increased secretion of TNF- α (4.5 fold–than control, P <0.05). Elecrophoresis of genomic DNA of treated cells indicated a dose-dependent increase in degradation of genomic DNA. Morphological studies also indicated that exposure of RAW cells to 100 μ m or 200 μ m DCAN incites apoptic cell death. At higher concentrations (400 μ m), however, significant ( P<0.05) increase in LDH leakage and decrease in cell viability (55% of control) indicative of cellular necrosis, were observed. These studies indicate that DCAN induces dose-dependent apoptosis or necrosis in RAW cells that could be due to the disturbance in intracellular redox status and initiation of ROI-mediated oxidative mechanisms of cellular damage.