Induction of oxidative stress in brain tissues of mice after subchronic exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The ability of single doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to induce oxidative stress in hepatic and some extrahepatic tissues of animals is well documented. However, no previous study has examined the ability of TCDD to induce oxidative stress and tissue damage in brain in vivo. In this study the ability of TCDD to induce oxidative stress in brain tissues of mice was studied after subchronic exposures. Groups of female B6C3F1 mice were treated orally with TCDD (0, 0.45, 1.5, 15, and 150 ng/kg/day) for 13 weeks, 5 days/week. The animals were euthanized 3 days after the last treatment and brain tissues were collected. Biomarkers of oxidative stress including production of superoxide anion, lipid peroxidation, and DNA-single-strand breaks (SSB) were determined. TCDD treatment resulted in significant and dose-dependent increases in the production of superoxide anion as assessed by reduction of cytochrome c. Significant increases were also observed in lipid peroxidation and DNA-SSB in those tissues, as assessed by the presence of thiobarbituric acid-reactive substances and the alkaline elution technique, respectively. These results clearly indicate that subchronic exposure to low doses of TCDD can induce oxidative tissue damage in brain tissues which may at least in part play a role in the effects of TCDD on the central nervous system.

Modulation of TCDD-induced fetotoxicity and oxidative stress in embryonic and placental tissues of C57BL/6J mice by vitamin E succinate and ellagic acid.

The ability of vitamin E succinate and ellagic acid to modulate 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced developmental toxicity and oxidative damage in embryonic/fetal and placental tissues was studied in C57BL/6J mice. Vitamin E succinate (100 mg/kg per day) and ellagic acid(6 mg/kg per day) were administered by gavage to groups of pregnant mice on days 10, 11 and 12 of gestation and 40 mg vitamin E succinate/kg or 3 mg ellagic acid/kg on day 13 of gestation. A number of animals from the vitamin E succinate and ellagic acid treated groups also received 30 microg TCDD/kg on day 12 of gestation, 2 h prior to vitamin E succinate or ellagic acid treatment. Groups of treated animals were terminated on day 14 of gestation, and the biomarkers of oxidative stress, including superoxide anion production and the induction of lipid peroxidation and DNA-single strand breaks (SSB), were determined in whole embryonic and placental tissues homogenates. Groups of treated animals were also killed on day 18 of gestation for investigation of the fetotoxic and teratogenic effects as well as effects on the placentae. Vitamin E succinate and ellagic acid significantly decreased TCDD-induced fetal growth retardation fetal death and placental weight reduction, with no significant ameliorating effects on TCDD-induced malformations including cleft palate and hydronephrosis. Vitamin E succinate treatment resulted in decreases of 77-88%, 70-87%, and 21-47% in the production of superoxide anion, lipid peroxidation and DNA-SSB, respectively, in embryonic and placental tissues, while ellagic acid caused 47-98%, 79-93%, and 37-53% decreases, respectively, in these parameters. These results indicate that TCDD-induced fetal death and fetal and placental weight reductions in C57BL/6J mice may be due to oxidative damage induced by TCDD, and ellagic acid and vitamin E succinate provide protection against those effects. Ellagic acid provided better protection than vitamin E succinate against TCDD-induced fetal growth retardation and increases in lipid peroxidation in embryonic and placental tissues.

Protective effects of antioxidants against uraemia-induced lipid peroxidation and glutathione depletion in humans.

The effects of uraemias and antioxidant therapy for 40 days with vitamin A, vitamin C and vitamin E on blood and erythrocyte sulfhydryl (glutathione, GSH) content and on erythrocyte glutathione-S transferase (GST), glutathione reductase (GSR) and glutathione peroxidase activities were studied in six uraemic patients maintained on haemodialysis. In addition, the effect of antioxidant therapy on erythrocyte lipid peroxidation was determined, and erythrocyte haemoglobin content was measured. Uraemic patients in dialysis exhibited significant decreases in blood and erythrocyte GSH content as well as significant decreases in the activities of GST, GSR and GSH-peroxidase relative to control subjects. Furthermore, the uraemic patients had elevated erythrocyte malondialdehyde levels. Blood and erythrocyte GSH content from uraemic patients was significantly elevated after 20 days of antioxidant treatment and remained elevated thereafter throughout the remaining 20 days of the study (130% and 173%, respectively). Antioxidant therapy also produced significant increases in GSR and GSH-peroxidase activities after 20 days of treatment which remained relatively constant thereafter. No significant change in GST activity was observed. Erythrocyte malondialdehyde levels, as an index of oxidative tissue damage, exhibited a significant decrease (70%) in the patients after 40 days of antioxidant therapy. A gradual increase in erythrocyte haemoglobin content was observed following treatment of the uraemic subjects (45% at day 40). The results suggest that antioxidant therapy may protect against oxidative stress associated with uraemia.

Oxidative stress induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin is mediated by the aryl hydrocarbon (Ah) receptor complex.

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and its bioisosteres involves binding to a specific TCDD (Aryl hydrocarbon (Ah)) receptor, interaction of this complex with chromatin, and the ultimate production of a pleiotropic response. The mechanism whereby toxic effects are produced following interaction of TCDD with the receptor complex is not known. Oxidative stress (OS) may play an important role in expression of the toxic manifestations of TCDD. TCDD has been shown to produce a dose- and time-dependent increase in superoxide anion from peritoneal lavage cells (PLC) (primarily macrophage). Therefore, to determine if TCDD-induced production of superoxide anion by PLC is mediated through the Ah receptor, congenic mice were used which differ at the Ah locus. One day after the administration of 5, 25, 50 or 125 micrograms TCDD/kg p.o. as a single dose, 1.4-, 1.7-, 4.3- and 3.5-fold increases, respectively, occurred in superoxide anion production by PLC from the TCDD-responsive C57BL/6J (bb) mice relative to control cells. However, only 125 micrograms TCDD/kg produced a significant increase in superoxide anion formation with PLC from the non-responsive C57BL/6J (dd) strain of mice (1.7-fold increase). The role of the Ah receptor was further evaluated by utilizing the TCDD-resistant DBA/2 strain of mice, two TCDD congeners and in vitro studies. The combined results indicate that TCDD produces an oxidative stress in mice as measured by production of superoxide anion, and this effect is controlled in part by the Ah receptor complex.

Stimulation of NADPH-dependent reactive oxygen species formation and DNA damage by 2,3,7,8-tetrachlorodibenzo-p-dioxin in rat peritoneal lavage cells.

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD] and its congeners involves binding to a specific TCDD [Ah] receptor, interaction of this complex with chromatin, and the ultimate production of pleiotropic responses. The mechanism whereby these effects are produced following interaction of TCDD with the receptor complex is not known. Oxidative stress following the production of reactive oxygen species (ROS) may play an important role in the toxic manifestations of TCDD. Thus, the dose and time-dependent effects of TCDD on the production of superoxide anion by peritoneal lavage cells (primarily macrophages) from rats were examined. A maximum increase in superoxide anion production occurred on day 1 after treatment in rats with 50 and 125 micrograms TCDD/kg. At 6 h after a single dose of 125 micrograms TCDD/kg, a 2.4-fold increase in superoxide anion production was observed in peritoneal lavage cells from rats. A single dose of 5 micrograms TCDD/kg had no effect on superoxide anion production by peritoneal lavage cells. A significant increase in DNA single strand breaks within peritoneal lavage cells occurred at 12 h after the oral administration of 50 micrograms TCDD/kg, and a maximum increase in DNA single strand breaks was observed on days 3-5 after treatment. No DNA damage was detected at a dose of 5 micrograms TCDD/kg. No difference was observed with respect to dose and time in the composition of the peritoneal lavage cells. The results clearly indicate that the oral administration of TCDD activates peritoneal lavage cells in rats, and that the activation precedes the formation of DNA single strand breaks.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of anti-TNF-alpha antibody and dexamethasone on TCDD-induced oxidative stress in mice.

Recent studies have implicated tumor necrosis factor alpha (TNF-alpha) in the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Since TNF-alpha sensitizes and activates phagocytic cells to agents that induce them to release reactive oxygen species, TNF-alpha may act as an amplifying loop in TCDD-induced oxidative stress (OS). Therefore, the effects of anti-TNF-alpha antibody (40 micrograms/mouse) and dexamethasone (2 mg/kg) treatment on TCDD-induced OS as measured by DNA single-strand breaks (SSB) in hepatic nuclei, lipid peroxidation in hepatic mitochondria and microsomes, and activation of peritoneal lavage cells (PLC) in C57BL/6J mice were studied. One day after treatment with 125 micrograms TCDD/kg, anti-TNF-alpha resulted in 70, 27, 33 and 21% decreases in DNA-SSB, mitochondrial and microsomal lipid peroxidation and PLC activation, respectively, relative to TCDD-treated mice. Dexamethasone produced 8, 32, 35 and 9% decreases in DNA-SSB, mitochondrial and microsomal lipid peroxidation and PLC activation, respectively, in TCDD-treated animals. The combination of anti-TNF-alpha and dexamethasone resulted in 67, 55, 61 and 25% decreases in the above parameters of OS, respectively. The results suggest that TNF-alpha release may play a role in sensitizing and activating phagocytic cells following treatment with TCDD, contributing to the overall OS of animals following exposure to TCDD.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced oxidative stress in female rats.

Oxidative stress may play a role in the toxic manifestations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Therefore, the time-dependent effects of 100 micrograms TCDD/kg on various indices of oxidative stress including lipid peroxidation. DNA damage, membrane fluidity, calcium homeostasis, nonprotein sulfhydryl content, and NADPH content of hepatic subcellular fractions of female rats were followed for 12 days. Increases in lipid peroxidation of 400-500% occurred in mitochondrial and microsomal membranes and nuclei, with maximum increases occurring 5-6 days post-treatment. Decreases in the nonprotein sulfhydryl content of mitochondrial and microsomal fractions of approximately 80% were observed by Day 12 posttreatment. Membrane fluidity gradually decreased following administration of TCDD, with decreases of 30-40% being observed in mitochondria, microsomes, and plasma membranes. A sharp increase in the incidence of hepatic nuclear DNA single strand breaks was observed 3 days after treatment with an increase of approximately 600% by Day 9. Following the administration of TCDD, increases of 70-80% occurred in the calcium content of mitochondria and microsomes. An 18% increase in cytosolic calcium was present 12 days after the administration of TCDD. Cytosol and mitochondria both exhibited an initial increase in NADPH content following administration of TCDD, but by Day 12 both had decreased to approximately two-thirds of control values. The results clearly demonstrate that TCDD administration induces an oxidative stress in rat liver. The most pronounced effects were observed in membrane lipid peroxidation and DNA damage with gradual changes being observed in calcium and nonprotein sulfhydryl contents and membrane fluidity.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced decrease in the fluidity of rat liver membranes.

1. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCCD)-induced lipid peroxidation has previously been demonstrated by assessing the hepatic content of thiobarbituric acid reactive substances (TBARS) as well as the NADPH-dependent microsomal formation of TBARS as well as the NADPH-dependent microsomal formation of TBARS using malondialdehyde as the standard. 2. Changes in membrane fluidity as a result of lipid peroxidation may occur. Therefore the dose- and time-dependent effects of TCDD on lipid peroxidation in mitochondrial, microsomal, and plasma membranes, and changes in membrane fluidity in these subcellular fractions, were examined. Animals were treated with either 50 or 100 micrograms TCDD/kg orally, and killed 3, 6, or 9 days post-treatment. 3. Time-dependent increases occurred in TBARS content and formation following TCDD administration for all three membranes. Similar results were observed after 50 and 100 micrograms TCDD/kg. 4. Following TCDD administration, fluorescence polarization measurements as determined by the fluorescence polarization (r) and anisotropy parameter (a.p.) values demonstrated significant decreases in membrane fluidity in all membrane fractions, indicative of membrane structural alterations. 5. Excellent inverse correlations between lipid peroxidation and membrane fluidity were observed. Thus, decreased membrane fluidity and increased membrane damage may contribute to the toxic manifestations of TCDD as a consequence of an oxidative stress.