Induction of hepatic DNA single strand breaks in rats by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Protective effects of coenzyme Q10 and resveratrol on oxidative stress induced by various dioxins on transheterozigot larvae of Drosophila melanogaster

Dioxin and dioxin-like compounds are known as a class of highly toxic and persistent environmental contaminants threatening human and animal health. In the present study, the protective effects of Coenzyme Q10 (CoQ10) and Resveratrol (RSV) against 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, 1,2,3,7,8,9-HxCDD, and 1,2,3,4,6,7,8,9-OCDD induced acute toxicity and measurement of oxidative stress were studied. Lethal doses of these chemicals were determined. Transheterozigot larvae of Drosophila melanogaster were treated using either dioxins (10 × 10-7 μg mL-1) or dioxins + CoQ10 (10 × 10-7 μg mL-1 + 150 μg mL-1) and dioxins + RSV (10 × 10-7 μg mL-1 + 100 μM). After dioxin treatment, antioxidant combination therapy with dioxins and CoQ10 or dioxins and RSV resulted in indicators of acute toxicity including a decrease in total oxidant status as compared to dioxins alone (p < 0.05). The combination treatment also produced a significant increase in total antioxidant status as compared to dioxins only (p < 0.05). Results indicate a potential role of dioxins for oxidative stress with acute toxicity and the protective performance of CoQ10 and RSV in the overall toxicity of dioxins including measuring oxidative stress.

Specific Caleosin/Peroxygenase and Lipoxygenase Activities Are Tissue-Differentially Expressed in Date Palm (Phoenix dactylifera L.) Seedlings and Are Further Induced Following Exposure to the Toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin

Two caleosin/peroxygenase isoforms from date palm, Phoenix dactylifera L., PdCLO2 and PdCLO4, were characterized with respect to their tissue expression, subcellular localization, and oxylipin pathway substrate specificities in developing seedlings. Both PdCLO2 and PdCLO4 had peroxygenase activities that peaked at the mid-stage (radicle length of 2.5 cm) of seedling growth and were associated with the lipid droplet (LD) and microsomal fractions. Recombinant PdCLO2 and PdCLO4 proteins heterologously expressed in yeast cells were localized in both LD and microsomal fractions. Each of the purified recombinant proteins exhibited peroxygenase activity but they were catalytically distinct with respect to their specificity and product formation from fatty acid epoxide and hydroxide substrates. We recently showed that date palm CLO genes were upregulated following exposure to the potent toxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Hanano et al., 2016), and we show here that transcripts of 9- and 13-lipoxygenase (LOX) genes were also induced by TCDD exposure. At the enzyme level, 9-LOX and 13-LOX activities were present in a range of seedling tissues and responded differently to TCDD exposure, as did the 9- and 13-fatty acid hydroperoxide reductase activities. This demonstrates that at least two branches of the oxylipin pathway are involved in responses to the environmental organic toxin, TCDD in date palm.

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.

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.

DNA strand length and EROD activity in relation to two screening measures of genotoxic exposure in Great Lakes herring gulls

We collected tissues from herring gulls (Larus argentatus) nesting within and outside of the Great Lakes basin. Genotoxin exposure was assessed as fluorescent aromatic compounds (FACs) in bile and SOS Chromotest-inducing activity in muscle extracts. We determined whether these exposures were associated with decreased erythrocyte DNA strand length and/or induction of hepatic ethoxyresorufin-O-deethylase (EROD) activity. FACs were detected in all bile samples. Most muscle extracts produced a positive or marginal SOS response in the presence of S9. SOS induction potentials were strongly associated with dietary trophic level. The median molecular length of DNA isolated from erythrocytes for 14 of 17 adult and 10 of 11 prefledgling collections was reduced compared to the modal class for their respective age group suggesting widespread DNA damage. DNA damage was greatest in gulls from Saginaw Bay, Lake Huron. Median EROD activity in both adults and prefledglings from remote locations was significantly lower than that of gulls from the lower Great Lakes and was not associated with concentrations of benzo[a]pyrene (B[a]P)-like FACs. Our results indicate Great Lakes herring gulls were exposed to genotoxins and Ah-receptor activating agents in biologically significant concentrations in the early 1990s. These agents appear to be persistent bioaccumulative compounds and/or their metabolites.

The modulatory effects of ellagic acid and vitamin E succinate on TCDD-induced oxidative stress in different brain regions of rats after subchronic exposure

The effects of ellagic acid (EA) and vitamin E succinate (VES) on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced oxidative stress in different brain regions of rats have been studied after subchronic exposure to the compounds. TCDD was administered to groups of rats at a dose of 46 ng/kg/day for 90 days. EA and VES were administered to groups of rats, either separately or simultaneously with TCDD, every other day for 90 days. At the end of the treatment period, animals were sacrificed and brains were dissected to cerebral cortex (Cc), hippocampus (H), cerebellum (C), and brain stem (Bs), and were assayed for production of superoxide anion (SA), lipid peroxidation (LP), and DNA single-strand breaks (SSBs). While TCDD administration to rats resulted in significant production of SA, LP, and DNA SSBs in Cc and H, simultaneous administration of VES or EA with the xenobiotics resulted in significant protection against those effects. The results also indicate that VES provided a better protyection against TCDD-induced effects in brains when compared with EA.

Response of anti-oxidant enzymes mRNA in the neonatal rat liver exposed to 1,2,3,4-tetrachlorodibenzo-p-dioxin via lactation

BACKGROUND

The aim of this study was to assess the response to dioxin-induced oxidative stress in neonates via lactation in the model we have described previously.

METHODS

Maternal rats were treated with a single dose of 50 or 100 micro mol/kg 1,2,3,4-tetrachlorodibenzo-p-dioxin (TCDD) on the first day postpartum (day 1). Messenger RNA levels of the key anti-oxidant enzymes (AOE), phospholipid hydroperoxide-glutathione peroxidase (PH-GPx), cellular-glutathione peroxidase (cell-GPx), copper-zinc superoxide dismutase (CuZn SOD), manganese superoxide dismutase (Mn SOD) and catalase (CAT) in the neonatal and maternal livers were determined by a competitive reverse transcription- polymerase chain reaction method.

RESULTS

Lactational transfer of 1,2,3,4-TCDD induced an inhibition of PH-GPx and cell-GPx mRNA in the neonatal liver on day 2 to 68 (P < 0.01) and 62% (P < 0.05) of the control at 100 micro mol/kg, respectively. Both GPx mRNA returned to control levels on day 6 and thereafter increased to levels higher than the controls on day 10. In the dam rat, 10 days after the treatment, no remarkable change of PH-GPx or cell-GPx mRNA was observed. Copper-zinc superoxide dismutase and CAT mRNA of neonates on day 2 were also suppressed at 100 micro mol/kg and then slightly increased on day 10. However, Mn SOD mRNA was not suppressed, but increased to a 2.1-fold level of the control (P < 0.05) on day 10 with 100 micro mol/kg 1,2,3,4-TCDD.

CONCLUSION

Quantitative analysis of AOE mRNA showed that PH-GPx and cell-GPx mRNA, as well as CuZn SOD and CAT mRNA in the neonatal liver were suppressed for a short period of time by 1,2,3,4-TCDD exposure via lactation. Dioxin induced oxidative stress by lactational transfer may alter pretranslation regulation of protective AOE in neonates.

Induction of oxidative stress in the tissues of rats after chronic exposure to TCDD, 2,3,4,7,8-pentachlorodibenzofuran, and 3,3',4,4',5-pentachlorobiphenyl

The abilities of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB126), and mixtures of these xenobiotics (toxic equivalents, TEQs) to induce oxidative stress in hepatic and brain tissues of rats have been investigated after chronic (30 wk) exposure to these congeners. TCDD, PeCDF, PCB126, and TEQs were administered daily to groups of rats at doses that corresponded to their toxic equivalency factors (TEFs), and the biomarkers of oxidative stress, including the production of superoxide anion, lipid peroxidation, and DNA single-strand breaks (SSBs), were determined in hepatic and brain tissues at the end of the exposure period. The three chemicals caused similar dose-dependent increases in the production of superoxide anion, lipid peroxidation, and DNA SSBs, which plateaued at certain dose ranges, followed by secondary increases at the higher dose levels. Similar effects were also produced by the TEQs; however, the dose-dependent increases in the biomarkers of oxidative stress were continuous and never achieved plateau levels. Except for PCB126, where statistical analyses revealed greater productions of superoxide anion and lipid peroxidation in brain tissues as compared with hepatic tissues, no significant differences were revealed between the two tissues in response to the other xenobiotics or the TEQs. Nonsignificant differences were also revealed when comparing the effects induced by the TEQs with those induced by the individual chemicals.

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on oxidative enzymes in adipocytes and liver

Reactive oxygen species are produced in response to environmental toxins, and previous studies have suggested that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) damages a number of target organs through the generation of oxygen free radicals and oxidative stress. Upon exposure, TCDD becomes concentrated in adipose tissue, and adversely affects many organs, including liver. This study examined whether oxidative stress was induced in adipocytes and liver that were exposed to TCDD. 3T3-F442A adipocyte cultures were treated with TCDD (5-200 nM) for up to 72 h, and the activity and mRNA levels of superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px) in adipocyte cell lysates were measured. The addition of 50 nM TCDD induced a two-fold increase in SOD activity after 48 h (P<0.05). In contrast, TCDD had no significant effect on the activity of catalase or GSH-Px in the adipocytes, and the increase in SOD activity was not accompanied by a change in SOD mRNA levels. To assess the effects of TCDD on oxidative stress enzymes in vivo, male Sprague-Dawley rats were injected weekly for 8 weeks with 30 ng/kg TCDD. In addition, the rats were fed either a low-fat complex-carbohydrate (LFCC) diet, or a high fat sucrose diet (HFS). The HFS diet has previously been shown to induce mild obesity and insulin resistance, without inducing diabetes. SOD, catalase, and GSH-Px activities were measured in the liver and adipose tissue of these rats. TCDD injection resulted in a 52% decrease in catalase activity in the adipose tissue of HFS rats (P<0.05). In contrast, SOD and GSH-Px activities were not altered in adipose tissue of TCDD-injected rats. In liver, however, there were significant decreases in GSH-Px activity in response to TCDD. This effect of TCDD was observed in both the LFCC and HFS dietary groups. In addition, GSH-Px activity in the HFS rats was significantly decreased when compared to GSH-Px activity in LFCC rats, in both TCDD-treated and control groups, suggesting that TCDD and a high fat diet may combine to exacerbate oxidative stress. Thus, TCDD induces complex changes in enzymes of oxidative stress in both adipocytes and liver. In adipocytes, these changes occurred post-transcriptionally, as there were no changes in mRNA levels. In addition, a high fat diet per se also resulted in a decrease in GSH-Px activity in liver.

Production of superoxide anion, lipid peroxidation and DNA damage in the hepatic and brain tissues of rats after subchronic exposure to mixtures of TCDD and its congeners

In this study the induction of oxidative stress in the hepatic and brain tissues of rats after subchronic exposure to various mixtures of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and two of its congeners, namely 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 3,3',4,4',5-pentachlorobiphenyl (PCB 126) was investigated. Four mixtures of TCDD and its congeners, corresponding to 10, 22, 46 and 100 ng of toxic equivalence (TEQ) kg(-1) day(-1), were administered to groups of rats for 13 weeks. The animals were sacrificed at the end of the exposure period and the biomarkers of oxidative stress, including the production of superoxide anion, lipid peroxidation and DNA single-strand breaks (SSBs), were determined in the hepatic and brain tissues. All mixtures caused dose-dependent increases in the production of superoxide anion, lipid peroxidation and DNA SSBs in both tissues, with significantly higher damage in the hepatic compared with the brain tissues. The 22 ng TEQ dose level (TEQ = 22) contains TCDD, PeCDF and PCB 126 at levels that correspond to 7.3, 14.5 and 73.3 ng kg(-1) day(-1), respectively, and it produced effects that correspond to ca. 50% of the maximal production of superoxide anion, lipid peroxidation and DNA SSBs in the hepatic and brain tissues of those animals. Relative to the doses that are required to produce 50% of the maximal production of the biomarkers of oxidative stress by the individual congeners in hepatic and brain tissues of rats, the concentrations of the congeners in TEQ = 22 did result in significant interactivity, probably in the form of additive effects in the hepatic but not in brain tissues.

The relative abilities of TCDD and its congeners to induce oxidative stress in the hepatic and brain tissues of rats after subchronic exposure

The abilities of single doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to induce oxidative stress in hepatic and some extra-hepatic tissues of animals, are well documented. In this study we have investigated the induction of oxidative stress in hepatic and brain tissues of rats after subchronic (13 weeks) exposure to TCDD and two of its congeners, namely 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 3,3',4,4',5-pentachlorobiphenyl (PCB126). TCDD, PeCDF and PCB126 were administered daily to groups of rats at various doses, for 13 weeks, and biomarkers of oxidative stress, including the production of superoxide anion, lipid peroxidation and DNA-single strand breaks (SSBs), were determined in the hepatic and brain tissues at the end of the exposure period. The three congeners caused dose-dependent increases in the production of superoxide anion, lipid proxidation and DNA-SSBs, with maximal effects achieved at doses ranging between 10-100, 20-92, and 300-550 ng/kg per day for TCDD, PeCDF and PCB126, respectively. The doses that produce 50% of maximal responses by each of the xenobiotics in the hepatic and brain tissues were found to be within the ranges of 7-34, 13-32, and 137-400 ng/kg per day for TCDD, PeCDF and PCB126, respectively. The results of the study suggest that subchronic exposures to TCDD, PeCDF and PCB126 induce significant oxidative damage in the hepatic and brain tissues of rats, with more damage observed in the brain as compared to the hepatic tissues. Also, as inducers of oxidative stress in the hepatic and brain tissues, TCDD is the most potent among the three congeners and PCB126 being the least potent.

Changes in the hepatic glutathione peroxidase redox system produced by coplanar polychlorinated biphenyls in Ah-responsive and -less-responsive strains of mice: mechanism and implications for toxicity

The alteration in hepatic glutathione peroxidase (GPx) produced by polychlorinated biphenyls (PCBs) was studied in vivo in aryl hydrocarbon (Ah)-responsive C57BL and -less-responsive DBA strains of mice. 3,3',4,4',5-Pentachlorobiphenyl (PCB 126), one of the high-affinity ligands for the Ah receptor, significantly reduced Se-dependent GPx activity in C57BL mice, but not in DBA mice. A reduction in activity in C57BL mice was also observed following treatment with a high dose of 3,3',4,4'-tetrachlorobiphenyl with lesser affinity for the Ah receptor than PCB 126, but not by 2,2',5,5'-tetrachlorobiphenyl, a low-affinity ligand. To assess the effects on GPx in the liver, the content of reduced glutathione (GSH), an obligate co-factor for GPx, and the activity of two enzymes, γ-glutamyl transpeptidase (γ-GTP) and glutathione reductase (GR), which play a role in supplying GSH were determined after PCB treatment. The results showed that although the hepatic activity of γ-GTP and GR was affected differently by PCB 126, the content of GSH was slightly increased rather than reduced in both strains of mice. The activity of non-Se-dependent GPx, which is due to the catalysis by some isozymes of glutathione S-transferase (GST), was significantly increased only in C57BL mice by PCB 126 treatment. Immunoblot analysis demonstrated that the induction of the class θ GST, which is a potent reducer of peroxides (Hiratsuka et al., 1995. Biochem. Biophys. Res. Commun. 212, 743) reflects the enhancement of the above activity. These results suggest that (i) the PCB-induced reduction in Se-dependent GPx activity is mediated by a mechanism involving the Ah receptor; and (ii) a concomitant increase in the class θ GST partially rescues the Ah-responsive mice from coplanar PCB-induced oxidative stress.

TCDD, endrin and lindane induced oxidative stress in fetal and placental tissues of C57BL/6J and DBA/2J mice

The abilities of TCDD, endrin and lindane to induce oxidative stress in fetal and placental tissues have been studied after the oral administration of these xenobiotics to pregnant C57BL/6J and DBA/2J mice. Production of superoxide anion, lipid peroxidation and DNA-single strand breaks (SSB) was determined in live fetal and placental tissues 48 hr after administration of single teratogenic doses of the compounds on day 12 of gestation. Oxidative stress and its biomarkers were also determined in livers of day 18 fetuses after administration on day 12 of gestation. TCDD given at doses of 30 and 60 micrograms/kg body weight to the C57BL/6J and DBA/2J mice, respectively, produced increases of 1.3-2.7-fold in superoxide anion production, 1.6-1.9-fold in lipid peroxidation and 2.1-4.4-fold in DNA-SSB. Endrin, given at a dose of 4.5 mg/kg body weight to C57BL/6J and DBA/2J mice, produced increases of 1.3-2.8-fold in superoxide production, 1.4-1.8-fold in lipid peroxidation and 1.4-4.7-fold in DNA-SSB. Lindane when given at a dose of 30 mg/kg body weight to C57BL/6J and DBA/2J mice produced increases of 1.6-3.0-fold in superoxide production, 1.3-2.1-fold in lipid peroxidation and 1.4-5.0-fold in DNA-SSB. The results suggest that superoxide production, lipid peroxidation and DNA-SSB in fetal and placental tissues may participate in the fetotoxic effects of TCDD and other polyhalogenated cyclic hydrocarbons, and that TCDD-induced oxidative damage in fetal and placental tissues is mediated at least in part by the Ah-receptor. The results also indicate that TCDD as an inducer of oxidative tissue damage in the embryos and placentas is approximately 150 and 1000 times more potent than endrin and lindane, respectively, in C57BL/6J mice, and 75 and 500 times more potent than endrin and lindane, respectively, in the DBA/2J mouse strain.

Evidence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced tissue damage in fetal and placental tissues and changes in amniotic fluid lipid metabolites of pregnant CF1 mice

Pregnant CF1 mice were given 30 micrograms 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg or the vehicle as a single i.p. dose on day 12 of gestation and killed 48 h later. Increases in DNA elution rate constants (single strand breaks) in fetal and placental nuclei of 1.8- and 2.3-fold, respectively, were observed. Increases in lipid peroxidation (thiobarbituric acid reactive substances) in placental and fetal tissues of 1.9- and 1.5-fold, respectively, were also observed. TCDD administration produced increases in the amniotic fluid levels of the lipid metabolites malondialdehyde (MDA), formaldehyde (FA), acetaldehyde (ACT), and acetone (ACON) of 2.5-, 1.6-, 1.4-, and 1.6-fold, respectively relative to control animals. The results suggest that reactive oxygen species may participate in the teratogenic effects of TCDD.

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.

Alterations of hepatic acetyl-CoA carboxylase by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on acetyl-CoA carboxylase (ACC) activity and synthesis was examined. Male Wistar rats received a single i.p. injection of TCDD (53 micrograms/kg), and nine days later body weight, liver weight, hepatic lipid, ACC activity and mass were determined and compared to pair-fed controls. Body weights of TCDD-treated animals decreased, while liver weights increased resulting in an increase in liver to body weight ratios. ACC activity was decreased by 65%, however sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western analysis using a biotin specific probe revealed that ACC protein levels were not appreciably changed. In addition, there was a large increase in exogenous lipid material in TCDD-treated livers as determined by osmium tetroxide staining. These data suggest that the decrease in ACC activity may be due to direct inhibition of the enzyme by negative allosteric interactions with free fatty acids released from adipose tissue that subsequently accumulate in liver.

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.

Desferrioxamine-induced alterations in hepatic iron distribution, DNA damage and lipid peroxidation in control and 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated rats

Desferrioxamine (DFX), an iron chelator, has been used to inhibit in vitro redox cycling of the transition iron irons that may interfere with free-radical formation, and is used clinically to treat conditions associated with iron overload. The effect of DFX on hepatic iron distribution has not been examined. Therefore, we have examined the effect of DFX on iron content and distribution, lipid peroxidation and DNA single-strand breaks in liver. Since 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) enhances hepatic lipid peroxidation and induces DNA damage, the ability of DFX to modulate these effects was also examined. Female Sprague-Dawley rats received 200 mg DFX kg-1 i.p. every 12 h for 10 days and 50 micrograms TCDD kg-1 p.o. on Day 4 as a single dose. All animals were killed 7 days after TCDD administration. The results demonstrate that DFX alone did not decrease hepatic iron content, but enhanced the iron distribution in mitochondria, microsomes and nuclei. A 10-day administration of DFX resulted in enhanced hepatic lipid peroxidation and DNA single-strand breaks, consistent with the alterations in iron distribution. TCDD administration produced large increases in lipid peroxidation in microsomes, nuclei and whole-liver homogenates, as well as enhanced DNA damage. However, the marked increases in lipid peroxidation produced by TCDD were attenuated by DFX, while the DNA damaging effects of TCDD and DFX were additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative stress induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is one of the most potent toxins and tumor promoters known to man. It is prototypical of many halogenated polycyclic hydrocarbons that occur as environmental contaminants. Pathologic lesions produced by these compounds are mediated by an intracellular receptor protein called the TCDD (Ah) receptor which functions as a trans-acting effector of gene expression. However, the ultimate posttranslational pathways and mechanisms involved in the expression of the toxic manifestations of TCDD have received little attention and remain unclear, yet constitute an important segment in our understanding of the overall mechanism of action of TCDD. Recent studies have demonstrated that an oxidative stress occurs in various tissues of TCDD-treated animals. Evidence indicating production of an oxidative stress by TCDD in rodents is reviewed and includes:enhanced in vitro and in vivo hepatic and extrahepatic lipid peroxidation; increased hepatic and macrophage DNA damage; increased urinary excretion of malondialdehyde; decreased hepatic membrane fluidity; increased production of superoxide anion by peritoneal macrophage; and decreased glutathione, nonprotein sulfhydryl, and NADPH contents in liver. The potential role of reactive oxygen species in tumor promotion by TCDD is discussed. Possible sources and mechanisms of production of reactive oxygen species in response to TCDD are considered in light of current information. Evidence demonstrating the involvement of iron in TCDD-induced formation of reactive oxygen species and DNA damage is reviewed. Oxidative damage may contribute to many of the toxic responses produced by TCDD and its bioisosteres, and may be common to most of the tissue-damaging effects.

Comparative effects of pair-feeding and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on various biochemical parameters in female rats

Hypophagia is a common characteristic of the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and may be responsible for some of the toxic manifestations. Pair-feeding has been used in control animals to compensate for the hypophagia, but relatively few studies have assessed biochemical changes associated with pair-feeding versus weight loss induced by TCDD. Rats were treated with TCDD and killed 7 days post-treatment while pair-fed animals received an amount of diet equivalent to TCDD-treated partner animals. Ad libitum-fed rats were also used. No correlations were seen in altered calcium and iron homeostasis between pair-feeding and TCDD administration relative to ad libitum-fed animals. Pair-feeding resulted in greater alterations than TCDD administration in the subcellular distribution of iron in mitochondria, microsomes and cytosol. Pair-feeding also resulted in greater accumulation of calcium in mitochondria and microsomes in pair-fed as compared to TCDD-treated animals. Greater lipid peroxidation was observed in whole liver and nuclei of rats receiving TCDD relative to pair-fed animals. A significantly greater incidence of DNA single strand breaks occurred in hepatic nuclei of TCDD-treated animals as compared to pair-fed and ad libitum-fed animals. Significantly greater inhibition of hepatic glutathione peroxidase activity and thymic involution were observed in TCDD treated animals as compared to the pair-fed group. Although some similarities existed between TCDD-treated animals and pair-fed rats, the overall biochemical changes which were observed following TCDD administration cannot be attributed to weight loss associated with hypophagia.

The further development of a mammalian DNA alkaline unwinding bioassay with potential application to hazard identification for contaminants from environmental samples

Recently, we have detailed a DNA alkaline unwinding assay (DAUA) that can be used to rapidly measure chemically induced strand breaks in mammalian cells (Daniel et al., 1985). In this paper we present further development of this assay, including: (1) studies on the relationship between DNA adducts and DNA strand breaks; (2) evaluation of the role of cytotoxicity in DNA strand breaks; and (3) application of the DAUA to cell preparations from the liver of mice dosed with methylating agents. The level of DNA adducts produced in human CCRF-CEM cells by treatment with benzo(a)pyrene diol-epoxide (BPDE), N-acetoxy-2-acetyl aminofluorene (AAAF), and various methylating agents was linear with concentration over several orders of magnitude. Likewise, the level of strand breaks increased with the concentration over the same dose range. The strand breaks/adduct ratio ranged from 0.05 for the methyl adducts to 0.001 for the BPDE adducts. Using these values and the inherent sensitivity of the DAUA (circa 100 to 1000 breaks/cell), (Daniel et al., 1985), the ability of the assay to detect DNA damage induced by various classes of chemical carcinogens can be calculated. The DAUA appears to be useful for assessing the relative potency of various environmental genotoxic effects on mammalian cells. In addition, it can be conducted on cells isolated from target organs of whole animals.

Factors influencing the induction of DNA single strand breaks in rats by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The ability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to induce lipid peroxidation and DNA damage in rat hepatic nuclei was investigated. In addition, the role of iron in hepatic DNA damage was examined. Female Sprague-Dawley rats were treated with a single dose of 25--100 micrograms TCDD/kg orally, and sacrificed 3-14 days after treatment. Liver nuclei were isolated, and DNA single strand breaks (DNA-SSB) and lipid peroxidation were determined. Lipid peroxidation was assessed by measuring the content and production of thiobarbituric acid reactive substances (TBARS) while DNA-SSB were determined by the alkaline elution technique. The results demonstrate that TCDD dose and time-dependent increases in hepatic nuclear TBARS content and production occur in conjunction with an increase in DNA-SSB. The administration of the dithiolthione antioxidant oltipraz (30 mg/kg/day for 10 days) resulted in a significant decrease (47%) in the incidence of TCDD-induced DNA-SSB. Clofibrate administration (100 mg/kg/day for 12 days) and pair feeding had no effect on TCDD-induced DNA-SSB. The incubation of hepatic microsomes and mitochondria from TCDD-treated rats with nuclei from untreated animals for one hr at 37 degrees C resulted in enhanced DNA damage which was abolished by the addition of 0.10 mM desferrioxamine (DFX). Incubation with cytosol had no significant effect. Incubation of 0.10 mM Fe2+ or Fe3+ with isolated hepatic nuclei from untreated rats produced significant increases in DNA-SSB, which were abolished by the addition of 0.10 mM DFX to the incubation medium. TCDD may produce an increased bioavailability of iron which leads to enhanced DNA single strand breaks and lipid peroxidation in hepatic nuclei.

Carcinogenicity of iron in conjunction with a chlorinated environmental chemical, hexachlorobenzene, in C57BL/10ScSn mice

Pre-loading of C57BL/10ScSn mice with iron greatly sensitizes them to the induction of hepatic porphyria caused by hexachlorobenzene (HCB) (Smith and Francis, 1983). HCB will also cause liver tumours in experimental animals. Elevated liver iron stores are implicated in the development of some human liver cancers. To determine whether iron overload will potentiate the hepatocarcinogenicity of HCB, male C57BL/10ScSn mice received a single dose of iron-dextran complex or the dextran carrier and were then fed HCB in the diet (0.01%) for up to 18 months. A very clear potentiation by iron of liver tumour incidence occurred. Of the mice which received HCB, but no iron, for 12 months a low incidence of liver hyperplastic nodules was observed, whereas preadministration of iron increased the incidence. After 18 months, all surviving mice initially given iron followed by HCB developed advanced hepatic nodules and 90% had hepatocellular carcinomas. No tumours were seen in animals that only received HCB. Nodules were not seen in iron-dosed mice receiving control diet, but another novel observation was that these animals developed porphyria by 6 months. Although iron enhanced tumour formation in the presence of HCB, the foci, nodules and carcinomas formed all excluded iron. Preliminary studies with the DBA/2 strain suggested that these mice were considerably less susceptible to potentiation by iron.