Do Antioxidant Enzymes and Glutathione Play Roles in the Induction of Hepatic Oxidative Stress in Mice upon Subchronic Exposure to Mixtures of Dichloroacetate and Trichloroacetate?

Dichloroacetate (DCA) and trichloroacetate (TCA) are water chlorination byproducts, and their mixtures were previously found to induce additive to greater than additive effects on hepatic oxidative stress (OS) induction in mice after subchronic exposure. To investigate the roles of antioxidant enzymes and glutathione (GSH) in those effects, livers of B6C3F1 mice treated by gavage with 7.5, 15, or 30 mg DCA/kg/day, 12.5, 25, or 50 mg TCA/kg/day, and mixtures (Mix I, Mix II and Mix III) at DCA:TCA ratios corresponding to 7.5:12.5, 15:25 and 25:50 mg/kg/day, respectively, for 13 weeks. Livers were assayed for superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), as well as for GSH levels. In general, DCA suppressed SOD and GSH-Px activities and GSH levels but caused no changes in CAT activity; TCA increased SOD and CAT activities, suppressed GSH-Px activity, but did not change GSH levels; mixtures of DCA and TCA increased SOD and CAT activities and suppressed GSH-Px activity and GSH levels. In conclusion, antioxidant enzymes contribute to DCA-, TCA- and mixtures-induced OS, but not to changes from additive to greater than additive effects produced by different mixture compositions of the compounds. GSH on the hand may contribute to these changes.

The effects of mixtures of dichloroacetate and trichloroacetate on induction of oxidative stress in livers of mice after subchronic exposure.

Dichloroacetate (DCA) and trichloroacetate (TCA) are drinking-water chlorination by-products previously found to induce oxidative stress (OS) in hepatic tissues of B6C3F1 male mice. To assess the effects of mixtures of the compounds on OS, groups of male B6C3F1 mice were treated daily by gavage with DCA at doses of 7.5, 15, or 30 mg/kg/d, TCA at doses of 12.5, 25, or 50 mg/kg/d, and 3 mixtures of DCA and TCA (Mix I, Mix II, and Mix III), for 13 wk. The concentrations of the compounds in Mix I, Mix II, and Mix III corresponded to those producing approximately 15, 25, and 35%, respectively, of maximal induction of OS by individual compounds. Livers were assayed for production of superoxide anion (SA), lipid peroxidation (LP), and DNA single-strand breaks (SSB). DCA, TCA, and the mixtures produced dose-dependent increases in the three tested biomarkers. Mix I and II effects on the three biomarkers, and Mix III effect on SA production were found to be additive, while Mix III effects on LP and DNA-SSB were shown to be greater than additive. Induction of OS in livers of B6C3F1 mice after subchronic exposure to DCA and TCA was previously suggested as an important mechanism in chronic hepatotoxicity/hepatocarcinogenicity induced by these compounds. Hence, there may be rise in exposure risk to these compounds as these agents coexist in drinking water.

The induction of phagocytic activation by mixtures of the water chlorination by-products, dichloroacetate- and trichloroacetate, in mice after subchronic exposure.

In this study, groups of B6C3F1 male mice were treated with dichloroacetate (DCA), trichloroacetate (TCA), and mixtures of the compounds (Mix I, II, and III) daily by gavage, for 13 weeks. The tested doses were 7.5, 15, and 30 mg DCA/kg/day and 12.5, 25, and 50 mg TCA/kg/day. The DCA: TCA ratios in Mix I, II, and III were 7.5:12.5, 15:25, and 30:50 mg/kg/day, respectively. Peritoneal lavage cells were collected at the end of the treatment period and assayed for the biomarkers of phagocytic activation, including superoxide anion and tumor necrosis factor-alpha production, and myeloperoxidase activity. The mixtures produced nonlinear effects on the biomarkers of phagocytic activation, with Mix I and II effects were found to be additive, but Mix III effects were found to be less than additive.

The effects of a low vitamin E diet on dichloroacetate- and trichloroacetate-induced oxidative stress in the livers of mice.

Groups of mice were fed either a standard (Std) diet or a diet not supplemented with vitamin E (Low-E) and were divided into three subgroups that were treated subchronically by gavage, with water (control), dichloroacetate (DCA), or trichloroacetate (TCA). The livers of the animals were assayed for various biomarkers of oxidative stress (OS), antioxidant enzyme activities, and total glutathione (GSH). In general, livers from the low-E diet group expressed lower levels of biomarkers of OS associated with greater increases in various antioxidant enzymes activities and GSH when compared with the corresponding treatments in the Std diet group. These results suggest that vitamin E supplementation to the diet, while essential to maintain certain body functions, can compromise the effectiveness of the hepatic antioxidant enzymes and GSH resulting in an increase in DCA- and TCA-induced OS and a possible increase in the compounds-induced hepatotoxic/hepatocarcinogenic effects in mice.

Dichloroacetate- and Trichloroacetate-Induced Modulation of Superoxide Dismutase, Catalase, and Glutathione Peroxidase Activities and Glutathione Level in the livers of Mice after Subacute and Subchronic exposure.

Dichloroacetate (DCA) and trichloroacetate (TCA) were previously found to induce various levels of oxidative stress in the hepatic tissues of mice after subacute and subchronic exposure. The cells are known to have several protective mechansims against production of oxidative stress by different xenobiotics. To assess the roles of the antioxidant enzymes and glutathione (GSH) in DCA- and TCA-induced oxidative stress, groups of B6C3F1 mice were administered either DCA or TCA at doses of 7.7, 77, 154 and 410 mg/kg/day, by gavage for 4 weeks (4-W) and 13 weeks (13-W), and superoxide dismutase (SOD) catalase (CAT) and glutathione peroxidase (GSH-Px) activities, as well as GSH were determined in the hepatic tissues. DCA at doses ranging between 7.7-410, and 7.7-77 mg/kg/day, given for 4-W and 13-W, respectively, resulted in either suppression or no change in SOD, CAT and GSH-Px activities, but doses of 154-410 mg DCA/kg/day administered for 13-W were found to result in significant induction of the three enzyme activities. TCA administration on the other hand, resulted in increases in SOD and CAT activities, and suppression of GSH-Px activity in both periods. Except for the DCA doses of 77-154 mg/kg/day administered for 13-W that resulted in significant reduction in GSH levels, all other DCA, as well as TCA treatments produced no changes in GSH. Since these enzymes are involved in the detoxification of the reactive oxygen species (ROS), superoxide anion (SA) and H(2)O(2), it is concluded that SA is the main contributor to DCA-induced oxidative stress while both ROS contribute to that of TCA. The increases in the enzyme activities associated with 154-410 mg DCA/kg/day in the 13-W period suggest their role as protective mechanisms contributing to the survival of cells modified in response to those treatments.

The induction of tumor necrosis factor-alpha, superoxide anion, myeloperoxidase, and superoxide dismutase in the peritoneal lavage cells of mice after prolonged exposure to dichloroacetate and trichloroacetate.

The induction of phagocytic activation in response to prolonged treatment with different doses of dichloroacetate (DCA) and trichloroacetate (TCA) has been investigated in mice. Groups of B6C3F1 male mice were administered 7.7, 77, 154, and 410 mg of DCA or TCA/kg/day, postorally, for 4- and 13-weeks. Peritoneal lavage cells (PLCs) were isolated and assayed for the different biomarkers of phagocytic activation, including superoxide anion (SA), tumor necrosis factor-alpha (TNF-alpha), and myeloperoxidase (MPO). In addition, the role of superoxide dismutase (SOD) in the SA production was also assessed. DCA and TCA produced significant and dose-dependent increases in SA and TNF-alpha production and in MPO activity, but the increases in response to the high doses of the compounds (>77 mg/kg/day) in the 13-week treatment period were less significant than those produced in the 4-week treatment period. Also, dose-dependent increases in SOD activity were observed in both periods of treatments. In general, the results demonstrate significant induction of the biomarkers of phagocytic activation by doses of DCA and TCA that were previously shown to be noncarcinogenic, with significantly greater increases observed at the earlier period of exposure, as compared with later period. These findings may argue against the contribution of those mechanisms to the hepatotoxicity/hepatocarcinogenicity of the compounds and suggest them to be early adaptive/ protective mechanisms against their long-term effects.

Dichloroacetate- and trichloroacetate-induced oxidative stress in the hepatic tissues of mice after long-term exposure.

Dichoroacetate (DCA) and trichloroacetate (TCA) were found to be hepatotoxic and hepatocarcinogenic in rodents. To investigate the role of oxidative stress in the long-term hepatotoxicity of the compounds, groups of mice were administered 7.7, 77, 154 and 410 mg kg(-1) per day, of either DCA or TCA, by gavage, for 4 weeks (4-W) and 13 weeks (13-W), and superoxide anion (SA), lipid peroxidation (LP) and DNA-single strand breaks (SSBs) were determined in the hepatic tissues. Significant increases in all of the biomarkers were observed in response to the tested doses of both compounds in the two test periods, with significantly greater increases observed in the 13-W, as compared with the 4-W, period. Hepatomegaly was only observed with a DCA dose of 410 mg kg(-1) per day in the 13-W treatment period, and that was associated with significant declines in the biomarkers, when compared with the immediately lower dose. With the exception of LP production in the 13-W treatment period that was similarly induced by the two compounds, the DCA-induced increases in all of the biomarkers were significantly greater than those of TCA. Since those biomarkers were significantly induced by the compounds' doses that were shown to be carcinogenic but at earlier periods than those demonstrating hepatotoxicity/haptocarcinogencity, they can be considered as initial events that may lead to later production of those long-term effects. The results also suggest LP to be a more significant contributing mechanism than SA and DNA damage to the long-term hepatotoxicity of TCA.