Effects Of TCDD Research Articles

TCDD induced lipid accumulation by impairment of autophagic flux in THP-1 macrophages.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental and food contaminant generated as a byproduct of various industrial activities. It is found in a lot of foods, especially in dairy products, eggs, fish, and meat. Autophagy is a highly conserved cellular degradation and cycling process, which plays an important role in lipid metabolism. This study aimed to explore the effects of TCDD on autophagic flux and lipid metabolism in THP-1 macrophages. The data showed that TCDD promoted the accumulation of autophagosomes in THP-1 macrophages, and subsequent findings revealed that this autophagosome accumulation was caused by the inhibition of autophagic flux by testing the expression of LC3II, p62 levels, and mRFP-GFP-LC3. Further, we found that TCDD treatment significantly increased the amount of triglyceride (TG) and total cholesterol (TC) in THP-1 macrophages. Meanwhile, pretreatment with autophagy activator (rapamycin, Rapa) efficiently relieved TCDD-induced lipid accumulation. On the contrary, pretreatment with autophagy inhibitor (Chloroquine, CQ) promoted TCDD-induced lipid accumulation. In the experiment of co-localization of LC3 and lipid droplets, the co-localization of LC3 and lipid droplets increased after TCDD induction. These results indicated that TCDD promoted lipid accumulation in THP-1 macrophages by inhibiting autophagic flux. Our findings revealed new insights into the toxicity mechanisms of TCDD.

Organ-specific effects on glycolysis by the dioxin-activated aryl hydrocarbon receptor.

Activation of the aryl hydrocarbon receptor (AHR) by the environmental toxin dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) causes diverse toxicities, including thymus atrophy and hepatosteatosis. The mechanisms by which AHR activation by TCDD leads to these toxicities are not fully understood. Here we studied the effects of TCDD on a major energy pathway, glycolysis, using the chick embryo close to hatching, a well-established model for studying dioxin toxicity. We showed that 24 hr of TCDD treatment causes changes in glycolysis in both thymus and liver. In thymus glands, TCDD decreased mRNAs for glycolytic genes and glucose transporters, glycolytic indices and levels of IL7 mRNA, phosphorylated AKT (pAKT) and HIF1A, stimulators of glycolysis and promoters of survival and proliferation of thymic lymphocytes. In contrast, in liver, TCDD increased mRNA levels for glycolytic genes and glucose transporters, glycolytic endpoints and pAKT levels. Similarly, increases by TCDD in mRNA levels for glycolytic genes and glucose transporters in human primary hepatocytes showed that effects in chick embryo liver pertain also to human cells. Treatment with the glycolytic inhibitor 2-deoxy-d-glucose exacerbated the effects on thymus atrophy by TCDD, supporting a role for decreased glycolysis in thymus atrophy by TCDD, but did not prevent hepatosteatosis. NAD+ precursors abolished TCDD effects on glycolytic endpoints in both thymus and liver. In summary, we report here that dioxin disrupts glycolysis mediated energy metabolism in both thymus and liver, and that it does so in opposite ways, decreasing it in the thymus and increasing it in the liver. Further, the findings support NAD+ boosting as a strategy against metabolic effects of environmental pollutants such as dioxins.

From Suppressor T cells to Regulatory T cells: How the Journey That Began with the Discovery of the Toxic Effects of TCDD Led to Better Understanding of the Role of AhR in Immunoregulation.

Aryl hydrocarbon receptor (AhR) was identified in the early 1970s as a receptor for the ubiquitous environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), which is a member of halogenated aromatic hydrocarbons (HAHs). TCDD was found to be highly toxic to the immune system, causing thymic involution and suppression of a variety of T and B cell responses. The fact that environmental chemicals cause immunosuppression led to the emergence of a new field, immunotoxicology. While studies carried out in early 1980s demonstrated that TCDD induces suppressor T cells that attenuate the immune response to antigens, further studies on these cells were abandoned due to a lack of specific markers to identify such cells. Thus, it was not until 2001 when FoxP3 was identified as a master regulator of Regulatory T cells (Tregs) that the effect of AhR activation on immunoregulation was rekindled. The more recent research on AhR has led to the emergence of AhR as not only an environmental sensor but also as a key regulator of immune response, especially the differentiation of Tregs vs. Th17 cells, by a variety of endogenous, microbial, dietary, and environmental ligands. This review not only discusses how the role of AhR emerged from it being an environmental sensor to become a key immunoregulator, but also confers the identification of new AhR ligands, which are providing novel insights into the mechanisms of Treg vs. Th17 differentiation. Lastly, we discuss how AhR ligands can trigger epigenetic pathways, which may provide new opportunities to regulate inflammation and treat autoimmune diseases.

Female mice exposed to low doses of dioxin during pregnancy and lactation have increased susceptibility to diet-induced obesity and diabetes

ObjectiveExposure to persistent organic pollutants is consistently associated with increased diabetes risk in humans. We investigated the short- and long-term impact of transient low-dose dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) exposure during pregnancy and lactation on glucose homeostasis and beta cell function in female mice, including their response to a metabolic stressor later in life. MethodsFemale mice were injected with either corn oil (CO; vehicle control) or 20 ng/kg/d TCDD 2x/week throughout mating, pregnancy and lactation, and then tracked for 6–10 weeks after chemical exposure stopped. A subset of CO- and TCDD-exposed dams was then transferred to a 45% high-fat diet (HFD) or remained on a standard chow diet for an additional 11 weeks to assess the long-term effects of TCDD on adaptability to a metabolic stressor. To summarize, female mice were transiently exposed to TCDD and then subsequently tracked beyond when TCDD had been excreted to identify lasting metabolic effects of TCDD exposure. ResultsTCDD-exposed dams were hypoglycemic at birth but otherwise had normal glucose homeostasis during and post-TCDD exposure. However, TCDD-exposed dams on a chow diet were modestly heavier than controls starting 5 weeks after the last TCDD injection, and their weight gain accelerated after transitioning to a HFD. TCDD-exposed dams also had an accelerated onset of hyperglycemia, impaired glucose-induced plasma insulin levels, reduced islet size, increased MAFA-ve beta cells, and increased proinsulin accumulation following HFD feeding compared to controls. Overall, our study demonstrates that low-dose TCDD exposure during pregnancy has minimal effects on metabolism during the period of active exposure, but has detrimental long-term effects on metabolic adaptability to HFD feeding. ConclusionsOur study suggests that transient low-dose TCDD exposure in female mice impairs metabolic adaptability to HFD feeding, demonstrating that dioxin exposure may be a contributing factor to obesity and diabetes pathogenesis in females.

An aryl hydrocarbon receptor agonist suppresses the growth of human umbilical vein endothelial cells in vitro: Potent effect with polyunsaturated fatty acids.

Human umbilical vein endothelial cells (HUVECs) are a pivotal component of the hematopoietic microenvironment linked to the modulation of the immune response, inflammation and carcinogenesis. HUVEC expresses the aryl hydrocarbon receptor (AHR), which regulates gene expression by binding to the xenobiotic-responsive element. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent agonist for AHR signalling. Treatment with TCDD (0.1-100nmol/L) was found to suppress the proliferation and to stimulate the death of HUVEC. TCDD's effects were abolished by culturing with CH223191, an inhibitor of AHR signalling. Mechanistically, TCDD treatment increased the protein levels of cell growth suppressors, including p53, Rb, p21 and regucalcin, and caspase-3 implicated in apoptotic cell death, and decreased the levels of Stat3, mitogen-activated protein kinase (MAPK/Erk1/2) and phospho-MAPK/Erk1/2. Treatment with polyunsaturated fatty acids (PUFAs), including docosahexaenoic acid, eicosapentaenoic acid and arachidonic acid, suppressed the proliferation and stimulated the death of HUVEC in vitro, and decreased the levels of Stat3, MAPK/Erk1/2 and phospho-MAPK/Erk1/2 and increased caspase-3. Notably, the effects of TCDD in suppressing proliferation and stimulating death of HUVEC were modulated by coculturing with PUFAs. These effects were reversed by treatment with CH223191, an inhibitor of AHR. Treatment with both TCDD and PUFAs collaboratively enhanced the levels of AHR, CYP1A1, p53, p21, Rb and regucalcin. Moreover, TCDD suppressed migration with wound healing of HUVEC. Notably, the combination of TCDD and PUFAs revealed potent suppressive effects on angiogenesis of HUVEC, potentially related to disorders of the stromal microenvironment.

A prolonged exposure of human lung carcinoma epithelial cells to benzo[a]pyrene induces p21-dependent epithelial-to-mesenchymal transition (EMT)-like phenotype

Deciphering the role of the aryl hydrocarbon receptor (AhR) in lung cancer cells may help us to better understand the role of toxic AhR ligands in lung carcinogenesis, including cancer progression. We employed human lung carcinoma A549 cells to investigate their fate after continuous two-week exposure to model AhR agonists, genotoxic benzo[a]pyrene (BaP; 1 μM) and non-genotoxic 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 10 nM). While TCDD increased proliferative rate of A549 cells, exposure to BaP decreased cell proliferation and induced epithelial-to-mesenchymal transition (EMT)-like phenotype, which was associated with enhanced cell migration, invasion, and altered cell morphology. Although TCDD also suppressed expression of E-cadherin and activated some genes linked to EMT, it did not induce the EMT-like phenotype. The results of transcriptomic analysis, and the opposite effects of BaP and TCDD on cell proliferation, indicated that a delay in cell cycle progression, together with a slight increase of senescence (when coupled with AhR activation), favors the induction of EMT-like phenotype. The shift towards EMT-like phenotype observed after simultaneous treatment with TCDD and mitomycin C (an inhibitor of cell proliferation) confirmed the hypothesis. Since BaP decreased cell proliferative rate via induction of p21 expression, we generated the A549 cell model with reduced p21 expression and exposed it to BaP for two weeks. The p21 knockdown suppressed the BaP-mediated EMT-like phenotype in A549 cells, thus confirming that a delayed cell cycle progression, together with p21-dependent induction of senescence-related chemokine CCL2, may contribute to induction of EMT-like cell phenotype in lung cells exposed to genotoxic AhR ligands.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) dysregulates hepatic one carbon metabolism during the progression of steatosis to steatohepatitis with fibrosis in mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a persistent environmental contaminant, induces steatosis that can progress to steatohepatitis with fibrosis, pathologies that parallel stages in the development of non-alcoholic fatty liver disease (NAFLD). Coincidently, one carbon metabolism (OCM) gene expression and metabolites are often altered during NAFLD progression. In this study, the time- and dose-dependent effects of TCDD were examined on hepatic OCM in mice. Despite AhR ChIP-seq enrichment at 2 h, OCM gene expression was not changed within 72 h following a bolus dose of TCDD. Dose-dependent repression of methionine adenosyltransferase 1A (Mat1a), adenosylhomocysteinase (Achy) and betaine-homocysteine S-methyltransferase (Bhmt) mRNA and protein levels following repeated treatments were greater at 28 days compared to 8 days. Accordingly, levels of methionine, betaine, and homocysteic acid were dose-dependently increased, while S-adenosylmethionine, S-adenosylhomocysteine, and cystathionine exhibited non-monotonic dose-dependent responses consistent with regulation by OCM intermediates and repression of glycine N-methyltransferase (Gnmt). However, the dose-dependent effects on SAM-dependent metabolism of polyamines and creatine could not be directly attributed to alterations in SAM levels. Collectively, these results demonstrate persistent AhR activation disrupts hepatic OCM metabolism at the transcript, protein and metabolite levels within context of TCDD-elicited progression of steatosis to steatohepatitis with fibrosis.

The Protective Effect of Xanthohumol on the Content of Selected Elements in the Bone Tissue for Exposed Japanese Quails to TCDD.

Dioxins (including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are highly toxic and persistent chemicals widely distributed in the environment in trace amounts, and are side products of industrial and chemical processes. Exposure to dioxins leads to multiorgan morphological and functional abnormalities, including within the bone tissue, disrupting its microarchitecture and mechanical properties. Xanthohumol (XN) is a chemical compound classified as a prenylated flavonoid, distinguished by multidirectional biological action. The aim of the study is to assess whether xanthohumol, as a substance with strong antioxidant and anti-inflammatory properties, has the ability to eliminate the negative effects of TCDD on bone tissue. The experiment was conducted on adult Japanese quails. Two different doses of TCDD and xanthohumol were administered to birds. After euthanasia of animals, the research material in the form of cranial vault and hind limb bone was collected, and their mineral compositions of calcium, phosphorus, magnesium, zinc, and iron concentrations were determined using atomic emission spectrometry in an acetylene-air flame method. Our results indicate that the administration of TCDD at a low dose causes more dynamic changes in the concentration of elements in bone, in comparison to a higher dose of dioxin. Results show also that higher doses of the XN cause the linear increase in the concentration of phosphorus and iron in the bone of the hind limb, and calcium in the bones of the cranial vault. In conclusion, our experiment shows that the use of TCDD and XN in Japanese quails together in various doses influences the content of phosphorus, magnesium, zinc, and iron in the research material.

Environmentally Available Very Low Doses of a Dioxin (2,3, 7,8 TCDD) Affects to Membrane Bound Ion Dependent ATPases in Mice Brain

The present communication reports very low doses of environmentally available TCDD exposed for sub acute exposure duration affects to membrane bound ATPases enzymes in mice brain. Healthy female Swiss albino mice with the same body weight of about 25-30g were considered for the experimental purposes after acclimatization for a period of 2-3 days prior to the experiment. The animals were grouped before the experiments and kept under standard conditions. The experiments were conducted according to the ethical norms approved by the CPCSEA (Letter: CP6EA/CH/RF/ACK-2003, 29-07-2003). Animals were provided with rodent diet (Keval Sales Corporation, India) and water ad libitum.Different groups of mice were received different concentrations of TCDD (0.004 mg/kg bw and 0.04 mg/kg bw) for 2, 4 and 6 days of exposure durations. Control group of mice were received corn oil as a vehicle. Two hypotheses viz., (a) invivo exposure of environmentally available low concentrations of TCDD provokes both dose and subacute exposure duration dependent effects to membrane bound ATPases system, and (b) TCDD possibly has an indirect effect on membrane bound ATPases system, were tested in this study. The results suggested predominant exposure duration dependent effects on the membrane bound ion dependent ATPases studied. The observed results were indicative of a possible indirect effect of TCDD occurred by complex chain of reactions exhibited by cell when exposed to TCDD. In conclusion of present study being a lipophilic toxic, TCDD affects to ion channels by affecting different physiological reaction. TCDD may not be affecting directly to membrane bound ion channels.

In vivo profiling of 2,3,7,8-tetrachlorodibenzo-p-dioxin–induced estrogenic/anti-estrogenic effects in female estrogen-responsive reporter transgenic mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), commonly referred to simply as “dioxin”, is a persistent environmental pollutant. Because of its high environmental persistence and biological accumulation, humans and animals are often exposed to TCDD. Therefore, the harmful effects on humans and animals is a major concern. Although studies have elucidated the adverse estrogenic and anti-estrogenic effects of TCDD, it is unclear in which tissues TCDD exerts these effects in vivo. To investigate the estrogen-related effects of TCDD in various tissues, we generated an improved estrogen-responsive reporter transgenic mouse in which the luciferase gene luc2 is expressed in response to estrogenic signals. Using these mice, we clarified that TCDD inhibits estrogenic signaling in liver and kidney but enhances estrogenic signaling in the pituitary gland in the same individual. Expression of aryl hydrocarbon receptor, aryl hydrocarbon receptor nuclear translocator, and estrogen receptor alpha mRNA was detected in liver, kidney, and pituitary gland, suggesting that the effects of TCDD on estrogenic signaling in these organs is independent of the expression pattern of these receptors. Thus, our results indicate that TCDD exerts both estrogenic and anti-estrogenic tissue-specific effects within the same individual.

2,3,7,8-Tetrachlorodibenzo-p-dioxin Promotes Proliferation of Astrocyte Cells via the Akt/STAT3/Cyclin D1 Pathway

ObjectiveThe compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a persistent organic pollutant, is harmful to the nervous system, but its effects on the brain are still unclear. This study aimed to investigate the effects of TCDD on astrocytes proliferation and underlying molecular mechanism. MethodsThe cell proliferation was measured by EdU-based proliferation assay and PI staining by flow cytometry. Protein expression levels were detected by Western blotting. Immunofluorescence, cytoplasmic and nuclear fractions separation were used to assess the distribution of signal transducer and activator of transcription 3 (STAT3). ResultsC6 cells treated with 10 and 50 nmol/L TCDD for 24 h showed significant promotion of the proliferation of. The exposure to TCDD resulted in the upregulation in the expression levels of phosphorylated protein kinase B (p-Akt), phosphorylated STAT3, and cyclin D1 in a dose- and time-dependent manner. The inhibition of Akt expression with LY294002 or STAT3 expression with AG490 abolished the TCDD-induced cyclin D1 upregulation and cell proliferation. Furthermore, LY294002 suppressed the activation of STAT3. Finally, TCDD promoted the translocation of STAT3 from the cytoplasm to the nucleus, and LY294002 treatment blocked this effect. ConclusionTCDD exposure promotes the proliferation of astrocyte cells via the Akt/STAT3/cyclin D1 pathway, leading to astrogliosis.

Abstract 2604: Constitutive activation of the human aryl hydrocarbon receptor in mice promotes hepatocarcinogenesis independent of its coactivator Gadd45b

Abstract 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), or dioxin, is a potent liver cancer promoter through its sustained activation of the aryl hydrocarbon receptor (Ahr) in rodents. However, the carcinogenic effect of TCDD and AHR in humans has been controversial. It has been suggested that the inter-species difference in the carcinogenic activity of AhR is largely due to different ligand affinity in that TCDD has a 10-fold lower affinity for the human AHR compared to the mouse Ahr. It remains unclear whether the activation of human AHR is sufficient to promote hepatocellular carcinogenesis. The goal of this study is to clarify whether activation of human AHR can promote hepatocarcinogenesis. Here we reported the oncogenic activity of human AHR in promoting hepatocellular carcinogenesis. Constitutive activation of the human AHR in transgenic mice was as efficient as its mouse counterpart in promoting diethylnitrosamine (DEN)-initiated hepatocellular carcinogenesis. The growth arrest and DNA damage-inducible gene 45 β (Gadd45b), a signaling molecule inducible by external stress and UV irradiation, is highly induced upon AHR activation. Further analysis revealed that Gadd45b is a novel AHR target gene and a transcriptional coactivator of AHR. Interestingly, ablation of Gadd45b in mice did not abolish the tumor promoting effects of the human AHR. Collectively, our findings suggested that constitutive activation of human AHR was sufficient to promote hepatocarcinogenesis. Note: This abstract was not presented at the meeting. Citation Format: Peipei Lu, Xinran Cai, Zihui Fang, Wen Xie. Constitutive activation of the human aryl hydrocarbon receptor in mice promotes hepatocarcinogenesis independent of its coactivator Gadd45b [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2604.

2,3,7,8-Tetrachlorodibenzo-p-dioxin Induces Vascular Dysfunction That is Dependent on Perivascular Adipose and Cytochrome P4501A1 Expression.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is associated with hypertension in humans and animals, and studies suggest that cytochrome P4501A1 (Cyp1a1) induction and vascular dysfunction may contribute. We investigated the role of perivascular adipose tissue (PVAT) and Cyp1a1 in TCDD-induced vascular dysfunction. Cyp1a1 wild-type (WT) and knockout (KO) male mice were fed a dough pill containing 1,4-p-dioxane (TCDD vehicle control) on days 0 and 7, or 1000ng/kg TCDD on day 0 and 250ng/kg TCDD on day 7. mRNA expression of Cyp1a1 was assessed on days 3, 7, and 14, and of Cyp1b1, 1a2, angiotensinogen, and phosphodiesterase 5a on day 14. Dose-dependent vasoconstriction to a thromboxane A2 mimetic (U46619), and vasorelaxation to acetylcholine and a nitric oxide donor (S-nitroso-N-acetyl-DL-penicillamine, SNAP), were investigated in the aorta with and without PVAT. Cyp1a1 and 1a2 mRNA was induced in aorta of WT mice only with PVAT, and Cyp1a1 induction was sustained through day 14. TCDD significantly enhanced constriction to U46619 in WT mice and inhibited relaxation to both acetylcholine and SNAP, but only in the presence of PVAT. The effects of TCDD on U46619 constriction and SNAP relaxation were not observed in Cyp1a1 KO mice. Finally, in aorta + PVAT of WT mice TCDD significantly induced expression of angiotensinogen and phosphodiesterase 5a both of which could contribute to the TCDD-induced vascular dysfunction. These data establish PVAT as a TCDD target which is critically involved in mediating vascular dysfunction. TCDD enhances vasoconstriction via the thromboxane/prostanoid (TP) receptor and inhibits vasorelaxation via nitric oxide (NO) signaling. This TCDD-induced vascular dysfunction requires perivascular adipose (PVAT) and cytochrome P4501a1 (CYP1a1) induction.

AhR ligands differentially affect thymus and peripheral lymphoid organs by targeting T cells and their functions leading to pro- or anti-inflammatory responses

Abstract TCDD, FICZ, and Resveratrol (RES) are potent ligands of aryl hydrocarbon receptor (AhR). TCDD is well known to cause thymic atrophy but the effects of FICZ and RES have not been studied to date. In the current study, we investigated the effect of AhR ligands in vivo. We chose these AhR ligands for their different origin-TCDD, an environmental contaminant, FICZ, endogenously generated, and RES, found in plant products. To this end, C57BL/6 mice were treated with vehicle (corn oil) or TCDD (10 μg/kg bw) or FICZ (10 μg/kg bw) or RES (100 mg/kg bw) by oral gavage. Three days post treatment, thymi and spleens were harvested and stained with fluorochrome-labelled Abs against various T cell surface markers and analyzed by flow cytometry. We observed significant effect of TCDD on decreasing thymic weight and thymic cellularity, when compared to vehicle. FICZ, on the other hand, had no significant effect on thymus. RES, however, significantly caused increase in thymic weight as well as thymic cellularity. Upon analysis of various T cell populations in the thymus, TCDD caused significant downregulation of almost all the markers (CD3, CD4, CD8, CD25, CD44, and αβTCR) whereas, FICZ and RES had moderate effects on thymic T cell subpopulations. Upon analysis of spleen, all the three AhR ligands had mixed effects. We observed significant effect of TCDD and RES in generation of Tregs, when compared to vehicle. FICZ, on the other hand, suppressed Tregs but significantly increased Th17 cells. Together, our studies suggest that although TCDD, FICZ, and RES are AhR ligands, they had different effects on both thymus and spleen. TCDD and RES had role in inducing immune suppression by generating more Tregs, whereas, FICZ had a role in inflammation by generating more Th17 cells.

2,3,7,8-Tetrachloodibenzo-p-dioxin affects the differentiation of CD4 helper T cell

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener of dioxins, is a persistent and ubiquitous environmental contaminant. Although the immunotoxic effects of TCDD have been reported, the mechanisms underlying these effects are still unclear. In this study, we have determined the toxic effects of TCDD on thymocytes and splenic T cells with in vitro cell culture systems. Magnetically isolated mouse splenic Th cells, Treg cells and the mixed spleen lymphocytes (SLC) were cultured and treated with TCDD and the differentiation of CD4 Th cells was determined by flow cytometery. Our results showed that different concentrations of TCDD caused immunotoxic effects through different toxicological mechanisms in both the purified mouse splenic Th cells and the mixed SLC. The low dose exposure to TCDD triggered regulatory effects in the immune system, while the high dose TCDD exposure resulted in severe immune toxicity. Notably, a decline of Treg subset was observed, suggesting an imbalanced immune regulation by TCDD treatment, as well as a possible decrease of TCDD’s indirect effects on bystander immune cells. Our CD4 Th subset co-culture experiments showed that TCDD-induced pathobiology depended on immune cell balance, suggesting that cytokine-induced microenvironments further modulated toxic effects associated with TCDD exposure.

The Investigation of Protective Effect of Quercetin in Rats Exposed to Oxidative Stress by 2,3,7,8-Tetrachlorodibenzo- p -Dioxin

In this study, 28 Wistar Albino male rats were randomly divided into four equal groups. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was intraperitoneally administered at the dose of 2 μg/kg/week, quercetin was administered at the dose of 20 mg/kg/day by gavages, and quercetin+TCDD were intraperitoneally administered at the doses of 20 mg/kg/day and 2 μg/kg/week, respectively. All applications were performed for 8 weeks. At the end of the eighth week, the rats were sacrificed and their heart and vascular tissues were taken for biochemical analysis (reduced glutathione (GSH), glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD) and thiobarbituric acid reactive substance (TBARS) levels) by spectrophotometric method. As a result of the study, TCDD significantly decreased antioxidant activities and increased lipid peroxidation in rats. In contrast, quercetin significantly prevented the toxic effects of TCDD via increasing SOD, CAT, GSH and GSH-Px levels but decreased the formation of TBARS. Therefore, it can be suggested that quercetin has the potential for treatment against the toxicity caused by TCDD or other environmental contaminants and can decrease the risk of mortality due to cardiovascular diseases, especially in humans.

2,3,7,8-Tetrachlorodibenzo-p-dioxin and TGFβ3-Mediated Mouse Embryonic Palatal Mesenchymal Cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental teratogenic effector for cleft palate. Transforming growth factor 3 (TGF-β3) is an essential growth factor for palatogenesis. The objective of this study is to clarify the effects of TCDD and TGF-β3 in mouse embryonic palatal mesenchymal (MEPM) cells. The effects of 10 nM TCDD, 10 ng/mL TGF-β3, or a combination of 10 nM TCDD and 10 ng/mL TGF-β3 on MEPM cells were revealed by cell and biological methods. With the increase in TCDD (0.5-10 nM), the expression of TGF-β3 increased, but at TCDD concentrations greater than 10 nM, the expression of TGF-β3 reduced. The viabilities of MEPM cells decreased in the 10 nM TCDD-treated group. But the viabilities increased in the 10 ng/mL TGF-β3-treated group, and the viabilities were intermediate in the group treated with a combination of 10 nM TCDD and 10 ng/mL TGF-β3. This phenomenon was the same as that of the motilities. In addition, we found that the expression of p-Smad2, p-Smad3,and Smad7 were increased by TCDD, TGF-β3, combination of TCDD and TGF-β3, but the expression of Smad4 were decreased by TCDD, TGF-β3, combination of TCDD and TGF-β3. These data revealed that TCDD and TGF-β3 interacted and affected MEPM cells.

Screening white-rot fungi for bioremediation potential of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Ligninolytic fungi contain a number of representative strains consisting of mainly white-rot fungi (WRF) that produce lignin-modifying enzymes (LME) such as laccases and manganese peroxidases. Lignin-modifying enzymes are multipurpose enzymes which have potential for application in various fields such as, for example, bioremediation and biomass conversion. Because of the non-specific nature of these enzymes, they are also capable of biodegradation and removal of xenobiotic pollutants. In this study we used a tiered screening process where we screened over 70 Vietnamese WRF fungal isolates for LME activity and subsequently for the ability to breakdown the dioxin TCDD. After the initial screening we selected four fungal strains, which belong to the order of Polyporales, which excreted high laccase enzyme levels. The most active fungus being isolate FMD21, a species of Rigidoporus, which was isolated from a forest in the South of Vietnam and which produced both laccase and manganese peroxidase. In the optimized PDSRb medium, FMD21 laccase levels reaced activities of 238800 U/L after 10 days while MnP activity showed the highest activity at day 4 of aproximately 40 U/L. 2,3,7,8-TCDD, which is the most toxic dioxin congener, is a persistent organic pollutant of which few organisms are known that break it down. After the final screening, FMD21 was the only fungus capable of degrading TCDD and was able to reach a breakdown percentage of 73% after 28 days culture with a start concentration of 0.5 pg TEQ/μL TCDD. Co-cultivation experiments of up to three fungi were performed to test for a synergistic breakdown effect of TCDD but such an effect was not observed. FMD21 is a fungus that shows a potential to be used as a bioremediation agent to clean up dioxin contamination in the environment.

Genetic background and window of exposure contribute to thyroid dysfunction promoted by low-dose exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin in mice

Genetic and environmental factors contribute to thyroid diseases. Although still debated, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is thought to induce thyroid dysfunction in humans and rodents. The data here reported point out the contribution of the exposure window and genetic background in mediating the low-dose TCDD effects on thyroid. Indeed, early (from E0.5 to PND30) and low-dose (0,001 μg/kg/day) TCDD exposure reduced the circulating fT4 and altered the expression of thyroid specific transcripts. The role of genetic components was estimated monitoring the same markers in Pax8+/− and Nkx2-1+/− mice, susceptible to thyroid dysfunction, exposed to 0, 1 μg/kg/day TCDD from E15.5 to PND60. Haploinsufficiency of either Pax8 or Nkx2-1 genes exacerbated the effects of the exposure impairing the thyroid enriched mRNAs in sex dependent manner. Such effect was mediated by mechanisms involving the Nkx2-1/p53/p65/IĸBα pathway in vitro and in vivo. Foetal exposure to TCDD impaired both thyroid function and genes expression while thyroid development and differentiation did not appear significantly affected. In mouse, stronger effects were related to earlier exposure or specific genetic background such as either Pax8 or Nkx2-1 haploinsufficiency, both associated to hypothyroidism in humans. Furthermore, our data underline that long exposure time are needed to model in vitro and in vivo results.

Retinoic acid co-treatment aggravates severity of dioxin-induced skin lesions in hairless mice via induction of inflammatory response

Exposure to toxic halogenated polyaromatic hydrocarbons, of which 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most potent, induces diverse skin pathologies in humans, including chloracne, hyperkeratosis, hamartomas, etc. While the toxic effects of TCDD have been extensively studied, effective approaches to their treatment are still lacking. Retinoids are commonly used in therapy of acneiform skin diseases. In vitro, retinoids elicit antagonistic effects on keratinocyte differentiation and proliferation, as compared to TCDD, suggesting their potential in treatment of TCDD-induced skin lesions. Nevertheless, the modulation of TCDD activity in skin by retinoids in vivo was never reported. We have used N-TERT keratinocyte cell line and hairless (hr) mice to determine if retinoic acid (RA) can lessen or reverse TCDD-induced effects in vitro and in vivo. RA co-treatment suppressed TCDD-induced changes in the expression of differentiation-associated genes and N-TERT keratinocyte viability in vitro. However, in hairless mice (in vivo), RA/TCDD co-treatment produced more severe effects, than treatment with either of the two compounds individually. RA/TCDD co-application to mouse skin strongly stimulated keratinocyte proliferation, resulting in dramatic epidermal hyperplasia. It has also led to massive immune cell infiltration into the dermis, and increased mRNA expression of inflammation markers, including IL1β, IL6 and S100A7. Thus, retinoids not only appeared ineffective in treatment of TCDD-induced skin lesions in hairless mice, but also resulted in their exaggeration. These in vivo results question previous cell culture-based claims that RA may reduce TCDD-induced skin effects and caution against the reliance on in vitro data in TCDD toxicology research.