Timing influences the impact of aryl hydrocarbon receptor activation on the humoral immune response to respiratory viral infection.

Humoral responses to respiratory viruses, such as influenza viruses, develop over time and are central to protection from repeated infection with the same or similar viruses. Epidemiological and experimental studies have linked exposures to environmental contaminants that bind the aryl hydrocarbon receptor (AHR) with modulated antibody responses to pathogenic microorganisms and common vaccinations. Other studies have prompted investigation into the potential therapeutic applications of compounds that activate AHR. Herein, using two different AHR ligands [2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2-(1H-Indol-3-ylcarbonyl)-4-thiazolecarboxylic acid methyl ester (ITE), to modulate the duration of AHR activity, we show that the humoral response to viral infection is dependent upon the duration and timing of AHR signaling, and that different cellular elements of the response have different sensitivities. When AHR activation was initiated prior to infection with influenza A virus, there was suppression of all measured elements of the humoral response (i.e., the frequency of T follicular helper cells, germinal center B cells, plasma cells, and circulating virus-specific antibody). However, when the timing of AHR activation was adjusted to either early (days -1 to +5 relative to infection) or later (days +5 onwards), then AHR activation affected different aspects of the overall humoral response. These findings highlight the importance of considering the timing of AHR activation in relation to triggering an immune response, particularly when targeting the AHR to manipulate disease processes.

Transcriptomic analysis of AHR wildtype and Knock-out rat livers supports TCDD's role in AHR/ARNT-mediated circadian disruption and hepatotoxicity.

Single, high doses of TCDD in rats are known to cause wasting, a progressive loss of 30 to 50% body weight and death within several weeks. To identify pathway perturbations at or near doses causing wasting, we examined differentially gene expression (DGE) and pathway enrichment in centrilobular (CL) and periportal (PP) regions of female rat livers following 6 dose levels of TCDD - 0, 3, 22, 100, 300, and 1000 ng/kg/day, 5 days/week for 4 weeks. At the higher doses, rats lost weight, had increased liver/body weight ratios and nearly complete cessation of liver cell proliferation, signs consistent with wasting. DGE curves were left shifted for the CL versus the PP regions. Canonical Phase I and Phase II genes were maximally increased at lower doses and remained elevated at all doses. At lower doses, ≤ 22 ng/kg/day in the CL and ≤ 100 ng/kg/day, upregulated genes showed transcription factor (TF) enrichment for AHR and ARNT. At the mid- and high-dose doses, there was a large number of downregulated genes and pathway enrichment for DEGs which showed downregulation of many cellular metabolism processes including those for steroids, fatty acid metabolism, pyruvate metabolism and citric acid cycle. There was significant TF enrichment of the hi-dose downregulated genes for RXR, ESR1, LXR, PPARalpha. At the highest dose, there was also pathway enrichment with upregulated genes for extracellular matrix organization, collagen formation, hemostasis and innate immune system. TCDD demonstrates most of its effects through binding the aryl hydrocarbon receptor (AHR) while the downregulation of metabolism genes at higher TCDD doses is known to be independent of AHR binding to DREs. Based on our results with DEG, we provide a hypothesis for wasting in which high doses of TCDD shift circadian processes away from the resting state, leading to greatly reduced synthesis of steroids and complex lipids needed for cell growth, and producing gene expression signals consistent with an epithelial-to-mesenchymal transition in hepatocytes.

Effect of oxidative stress induced by 2,3,7,8- tetrachlorodibenzo-p-dioxin on DNA damage.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic persistent organic pollutant (POP) that can induce DNA damage within cells. Although oxidative stress is one of the primary mechanisms causing DNA damage, its role in the process of TCDD-induced DNA damage remains unclear. In this study, the TCDD-induced production of reactive oxygen species (ROS) and the occurrence of DNA damage at the AP site were monitored simultaneously. Further investigation revealed that TCDD impaired the activities of superoxide dismutase (SOD) and catalase (CAT), compromising the cellular antioxidant defense system. Consequently, this led to an increase in the production of O2.- and NO, thus inducing DNA damage at the AP site under oxidative stress. Our findings were further substantiated by the upregulation of key genes in the base excision repair (BER) pathway and the absence of DNA AP site damage after inhibiting O2.- and NO. In addition, transcriptome sequencing revealed that TCDD induces DNA damage by upregulating genes associated with oxidative stress in the mitogen-activated protein kinase (MAPK), cyclic adenosine monophosphate (cAMP), and breast cancer pathways. This study provides important insights into the toxicity mechanisms of TCDD.

Impact of dioxins on reproductive health in female mammals.

Extensive research has been conducted to investigate the toxicological impact of dioxins on mammals, revealing profound effects on the female reproductive system in both humans and animals. Dioxin exposure significantly disrupts the intricate functions of the ovary, a pivotal organ responsible for reproductive and endocrine processes. This disruption manifests as infertility, premature ovarian failure, and disturbances in sex steroid hormone levels. Comprehensive studies, encompassing accidental human exposure and experimental animal data, have raised a wealth of information with consistent yet varied conclusion influenced by experimental factors. This review begins by providing an overarching background on the ovary, emphasizing its fundamental role in reproductive health, particularly in ovarian steroidogenesis and hormone receptor regulation. Subsequently, a detailed examination of the Aryl hydrocarbon Receptor (AhR) and its role in governing ovarian function is presented. The review then outlines the sources and toxicity of dioxins, with a specific focus on AhR involvement in mediating reproductive toxicity in mammals. Within this context, the impact of dioxins, notably 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), on Folliculogenesis and Preimplantation embryos is discussed. Furthermore, the review delves into the disruptions of the female hormonal system caused by TCDD and their ramifications in endometriosis. Notably, variations in the effects of TCDD on the female reproductive and hormonal system are highlighted in relation to TCDD dose, animal species, and age. As a forward-looking perspective, questions arise regarding the potential involvement of molecular mechanisms beyond AhR in mediating the female reproductive toxicity of dioxins.

Breast milk-mediated exposure to dioxins and antigen in infancy enhances antigen-specific antibody production capacity in adulthood in mice.

The immune system is sensitive to many chemicals. Among dioxin compounds, 2,3,7,8-tetrachlorodizenzo-p-dioxin (TCDD) is the most toxic environmental pollutant. The effects of perinatal maternal exposure to dioxins may persist into childhood. However, there have been no reports to date on the effects of exposure to dioxins during infancy, when the immune organs are developing. Therefore, we investigated the effects of TCDD and antigen exposure during lactation on immune function, especially antibody production capacity, in adult mice. Beginning the day after delivery, lactating mothers were orally administered TCDD or a mixture of TCDD and ovalbumin (OVA) daily for 4 weeks, until the pups were weaned. At 6 weeks of age, progeny mice were orally administered OVA daily for 10 weeks, while non-progeny mice were orally administered OVA or a mixture of TCDD and OVA daily for 10 weeks. Production of serum OVA-specific IgG was examined weekly. The amount of TCDD transferred from the mother to the progeny via breast milk was determined by measuring TCDD in the gastric contents of the progeny. A trend toward increasing IgA titer was observed in TCDD-treated mice, and production of IgE was observed only in progeny whose mothers were treated with TCDD and OVA. The results suggest that exposure to TCDD and OVA in breast milk can affect immune function in newborns.

The aryl hydrocarbon receptor differentially modulates the expression profile of antibody isotypes in a human B-cell line.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent environmental contaminant and high affinity ligand for the aryl hydrocarbon receptor (AhR). In animal models, AhR activation by TCDD generally inhibits antibody secretion. However, it is less clear if this translates to human antibody production. Using a human Burkitt lymphoma B-cell line (CL-01) that can be stimulated to secrete Ig and undergo class switch recombination to other Ig isotypes, the current study evaluated the effects of AhR activation or antagonism on the human Ig isotypic expression profile with CD40L+IL-4 stimulation. Our results suggest that AhR agonists (TCDD and indirubin) have little to no effect on IgM or IgA secretion, which were also not induced with stimulation. However, AhR activation significantly inhibited stimulation-induced IgG secretion, an effect reversed by the AhR antagonist CH223191. Evaluation of Ig heavy chain (IgH) constant region gene expression (ie Cµ, Cγ1-4, Cα1-2, and Cε that encode for IgM, IgG1-4, IgA1-2, and IgE, respectively) demonstrated differential effects. While Cµ and Cα2 transcripts were unaffected by stimulation or AhR agonists, AhR activation significantly inhibited stimulation-induced Cγ2-4 and Cε mRNA transcripts, which was reversed by AhR antagonism. Notably, AhR antagonism in the absence of exogenous AhR ligands significantly increased IgG and IgA secretion as well as the expression of Cγ2-4 and Cε. These results suggest that modulation of AhR activity differentially alters the IgH isotypic expression profile and antibody secretion that may be partly dependent on cellular stimulation. Since a variety of chemicals from anthropogenic, industrial, pharmaceutical, dietary, and bacterial sources bind the AhR, the ability of environmental exposures to alter AhR activity (i.e. activate or inhibit) may have a direct influence on immune function and antibody-relevant disease conditions.

Potential AhR-independent mechanisms of 2,3,7,8-Tetrachlorodibenzo-p-dioxin inhibition of human glioblastoma A172 cells migration.

The toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is generally believed to be mediated by aryl hydrocarbon receptor (AhR), but some evidence suggests that the effects of TCDD can also be produced through AhR-independent mechanisms. In previous experiments, we found that mainly AhR-dependent mechanism was involved in the migration inhibition of glioblastoma U87 cells by TCDD. Due to the heterogeneity of glioblastomas, not all tumor cells have significant AhR expression. The effects and mechanisms of TCDD on the migration of glioblastomas with low AhR expression are still unclear. We employed a glioblastoma cell line A172 with low AhR expression as a model, using wound healing and Transwell® assay to detect the effect of TCDD on cell migration. We found that TCDD can inhibit the migration of A172 cells without activating AhR signaling pathway. Further, after being pre-treated with AhR antagonist CH223191, the inhibition of TCDD on A172 cells migration was not changed, indicating that the effect of TCDD on A172 cells is not dependent on AhR activation. By transcriptome sequencing analysis, we propose dysregulation of the expression of certain migration-related genes, such as IL6, IL1B, CXCL8, FOS, SYK, and PTGS2 involved in cytokines, MAPK, NF-κB, and IL-17 signaling pathways, as potential AhR-independent mechanisms that mediate the inhibition of TCDD migration in A172 cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin and kynurenine induce Parkin expression in neuroblastoma cells through different signaling pathways mediated by the aryl hydrocarbon receptor.

Parkin regulates protein degradation and mitophagy in dopaminergic neurons. Deficiencies in Parkin expression or function lead to cellular stress, cell degeneration, and the death of dopaminergic neurons, which promotes Parkinson's disease. In contrast, Parkin overexpression promotes neuronal survival. Therefore, the mechanisms of Parkin upregulation are crucial to understand. We describe here the molecular mechanism of AHR-mediated Parkin regulation in human SH-SY5Y neuroblastoma cells. Specifically, we report that the human Parkin gene (PRKN) is transcriptionally upregulated by the aryl hydrocarbon receptor (AHR) through two different selective ligand-dependent pathways. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a stress-inducing AHR ligand, indirectly promotes PRKN transcription by inducing ATF4 expression via TCDD-mediated endoplasmic reticulum (ER) stress. In contrast, kynurenine, a nontoxic AHR agonist, induces PRKN transcription by promoting AHR binding to the PRKN promoter without activating ER stress. Our results demonstrate that AHR activation may be a potential pharmacological pathway to induce human Parkin, but such a strategy must carefully consider the choice of AHR ligand to avoid neurotoxic side effects.

Differential eigengene network analysis reveals benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin consensus regulatory network in human liver cell line HepG2.

Aryl hydrocarbon receptor (AHR) is one of the main mediators of the toxic effects of benzo[a]pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, a vast number of BaP- and TCDD-affected genes may suggest a more complex transcriptional regulatory network driving common adverse effects of these two chemicals. Unlike TCDD, BaP is rapidly metabolized in the liver, yielding products with a questionable ability to bind and activate AHR. In this study, we used transcriptomics data from the BaP- and TCCD-exposed human liver cell line HepG2, and performed differential eigengene network analysis to understand the correlation among genes and to untangle the common regulatory mechanism in the action of BaP and TCDD. The genes were grouped into 11 meta-modules with an overall preservation of 0.72 and were also segregated into three consensus time clusters: 12, 24, and 48 h. The analysis showed that the consensus genes in each time cluster were either directly regulated by the AHR or the AHR-TF interactions. Some TFs form a direct physical interaction with AHR such as ESR1, FOXA1, and E2F1, whereas others, including CTCF, RXRA, FOXO1, CEBPA, CEBPB, and TP53 show an indirect interaction with AHR. The analysis of biological processes (BPs) identified unique and common BPs in BaP and TCDD samples, with DNA damage response detected in all three time points. In summary, we identified a consensus transcriptional regulatory network common for BaP and TCDD consisting of direct AHR targets and AHR-TF targets. This analysis sheds new light on the common mechanism of action of a genotoxic (BaP) and non-genotoxic (TCDD) chemical in liver cells.

Environmentally relevant concentrations of 2,3,7,8-TCDD induced inhibition of multicellular alternative splicing and transcriptional dysregulation.

Alternative splicing (AS), found in approximately 95 % of human genes, significantly amplifies protein diversity and is implicated in disease pathogenesis when dysregulated. However, the precise involvement of AS in the toxic mechanisms induced by TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) remains incompletely elucidated. This study conducted a thorough global AS analysis in six human cell lines following TCDD exposure. Our findings revealed that environmentally relevant concentration (0.1 nM) of TCDD significantly suppressed AS events in all cell types, notably inhibiting diverse splicing events and reducing transcript diversity, potentially attributed to modifications in the splicing patterns of the inhibitory factor family, particularly hnRNP. And we identified 151 genes with substantial AS alterations shared among these cell types, particularly enriched in immune and metabolic pathways. Moreover, TCDD induced cell-specific changes in splicing patterns and transcript levels, with increased sensitivity notably in THP-1 monocyte, potentially linked to aberrant expression of pivotal genes within the spliceosome pathway (DDX5, EFTUD2, PUF60, RBM25, SRSF1, and CRNKL1). This study extends our understanding of disrupted alternative splicing and its relation to the multisystem toxicity of TCDD. It sheds light on how environmental toxins affect post-transcriptional regulatory processes, offering a fresh perspective for toxicology and disease etiology investigations.

Proteomic insight towards key modulating proteins regulated by the aryl hydrocarbon receptor involved in ovarian carcinogenesis and chemoresistance.

Gynecological malignancies pose a severe threat to female lives. Ovarian cancer (OC), the most lethal gynecological malignancy, is clinically presented with chemoresistance and a higher relapse rate. Several studies have highly correlated the incidence of OC to exposure to environmental pollutants, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a process mainly mediated through activating the aryl hydrocarbon receptor (AhR). We have previously reported that exposure of OC cells to TCDD, an AhR activator, significantly modulated the expression of several genes that play roles in stemness and chemoresistance. However, the effect of AhR activation on the whole OC cell proteome aiming at identifying novel druggable targets for both prevention and treatment intervention purposes remains unrevealed. For this purpose, we conducted a comparative proteomic analysis of OC cells A2780 untreated/treated with TCDD for 24 h using a mass spectrometry-based label-free shotgun proteomics approach. The most significantly dysregulated proteins were validated by Western blot analysis. Our results showed that upon AhR activation by TCDD, out of 2598 proteins identified, 795 proteins were upregulated, and 611 were downregulated. STRING interaction analysis and KEGG-Reactome pathway analysis approaches identified several significantly dysregulated proteins that were categorized to be involved in chemoresistance, cancer progression, invasion and metastasis, apoptosis, survival, and prognosis in OC. Importantly, selected dysregulated genes identified by the proteomic study were validated at the protein expression levels by Western blot analysis. In conclusion, this study provides a better understanding of the the cross-talk between AhR and several other molecular signaling pathways and the role and involvement of AhR in ovarian carcinogenesis and chemoresistance. Moreover, the study suggests that AhR is a potential therapeutic target for OC prevention and maintenance. SIGNIFICANCE: To our knowledge, this is the first study that investigates the role and involvement of AhR and its regulated genes in OC by performing a comparative proteomic analysis to identify the critical proteins with a modulated expression upon AhR activation. We found AhR activation to play a tumor-promoting and chemoresistance-inducing role in the pathogenesis of OC. The results of our study help to devise novel therapeutics for better management and prevention and open the doors to finding novel biomarkers for the early detection and prognosis of OC.

Dimethylmonothioarsinic acid (DMMTAV) differentially modulates the expression of AHR-regulated cytochrome P450 1A enzymes in vivo and in vitro.

Dimethylmonothioarsinic acid (DMMTAV), a pentavalent thio-arsenic derivative, has been found in bodily fluids and tissues including urine, liver, kidney homogenates, plasma, and red blood cells. Although DMMTAV is a minor metabolite in humans and animals, its substantial toxicity raises concerns about potential carcinogenic effects. This toxicity could be attributed to arsenicals' ability to regulate cytochrome P450 1 A (CYP1A) enzymes, pivotal in procarcinogen activation or detoxification. The current study investigates DMMTAV's impact on CYP1A1/2 expression, individually and in conjunction with its inducer, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). C57BL/6 mice were intraperitoneally injected with 6 mg/kg DMMTAV, alone or with 15 µg/kg TCDD, for 6 and 24 h. Similarly, Hepa-1c1c7 cells were exposed to DMMTAV (0.5, 1, and 2 µM) with or without 1 nM TCDD for 6 and 24 h. DMMTAV hindered TCDD-induced elevation of Cyp1a1 mRNA, both in vivo (at 6 h) and in vitro, associated with reduced CYP1A regulatory element activation. Interestingly, in C57BL/6 mice, DMMTAV boosted TCDD-induced CYP1A1/2 protein and activity, unlike Hepa-1c1c7 cells where it suppressed both. DMMTAV co-exposure increased TCDD-induced Cyp1a2 mRNA. While Cyp1a1 mRNA stability remained unchanged, DMMTAV negatively affected protein stability, indicated by shortened half-life. Baseline levels of CYP1A1/2 mRNA, protein, and catalytic activities showed no significant alterations in DMMTAV-treated C57BL/6 mice and Hepa-1c1c7 cells. Taken together, these findings indicate, for the first time, that DMMTAV differentially modulates the TCDD-mediated induction of AHR-regulated enzymes in both liver of C57BL/6 mice and murine Hepa-1c1c7 cells suggesting that thio-arsenic pentavalent metabolites are extremely reactive and could play a role in the toxicity of arsenic.

The Aryl Hydrocarbon Receptor Regulates Epidermal Differentiation through Transient Activation of TFAP2A.

The aryl hydrocarbon receptor (AHR) is an evolutionary conserved environmental sensor identified as an indispensable regulator of epithelial homeostasis and barrier organ function. Molecular signaling cascade and target genes upon AHR activation and their contribution to cell and tissue function are however not fully understood. Multiomics analyses using human skin keratinocytes revealed that upon ligand activation, AHR binds open chromatin to induce expression of transcription factors, for example, TFAP2A, as a swift response to environmental stimuli. The terminal differentiation program, including upregulation of barrier genes, FLG and keratins, was mediated by TFAP2A as a secondary response to AHR activation. The role of AHR-TFAP2A axis in controlling keratinocyte terminal differentiation for proper barrier formation was further confirmed using CRISPR/Cas9 in human epidermal equivalents. Overall, the study provides additional insights into the molecular mechanism behind AHR-mediated barrier function and identifies potential targets for the treatment of skin barrier diseases.

Toxicogenomics of the C-C chemokine receptor type 5 (CCR5): Exploring the potential impacts of chemical-CCR5 interactions on inflammation and human health.

This article explores the impact of environmental chemicals on CCR5 expression and related inflammatory responses based on curated data from the Comparative Toxicogenomics Database (CTD). A total of 143 CCR5-interacting chemicals was found, with 229 chemical interactions. Of note, 67 (29.3%) out of 229 interactions resulted in "increased expression" of CCR5 mRNA or CCR5 protein, and 42 (18.3%) chemical interactions resulted in "decreased expression". The top-5 CCR5-interacting chemicals were "Tetrachlorodibenzodioxin", "Lipopolysaccharides", "Benzo(a)pyrene", "Drugs, Chinese Herbal", and "Ethinyl Estradiol". Based on the number of interactions and importance as environmental contaminant, we then focused our analysis on Tetrachlorodibenzodioxin and Benzo(a)pyrene. There is some consistency in the data supporting an increase in CCR5 expression triggered by Tetrachlorodibenzodioxin; although data concerning CCR5-Benzo(a)pyrene interactions is limited. Considering the high linkage disequilibrium between CCR5 and CCR2 genes, we also search for chemicals that interact with both genes, which resulted in 72 interacting chemicals, representing 50.3% of the 143 CCR5-interacting chemicals and 37.5% of the 192 CCR2-interacting chemicals. In conclusion, CTD data showed that environmental contaminants indeed affect CCR5 expression, with a tendency towards increased expression. The interaction of environmental contaminants with other chemokine receptor genes may potentialize their toxic effects on the chemokine system, favoring inflammation.

Boron Compounds Mitigate 2,3,7,8-Tetrachlorodibenzo-p-dioxin-Induced Toxicity in Human Peripheral Blood Mononuclear Cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) stands as one of the most potent halogenated polycyclic hydrocarbons, known to inflict substantial cytotoxic effects on both animal and human tissues. Its widespread presence and recalcitrance make it an environmental and health concern. Efforts are being intensively channeled to uncover strategies that could mitigate the adverse health outcomes associated with TCDD exposure. In the realm of counteractive agents, boron compounds are emerging as potential candidates. These compounds, which have found applications in a spectrum of industries ranging from agriculture to pharmaceutical and cosmetic manufacturing, are known to modulate several cellular processes and enzymatic pathways. However, the dose-response relationships and protective potentials of commercially prevalent boron compounds, such as boric acid (BA), ulexite (UX), and borax (BX), have not been comprehensively studied. In our detailed investigation, when peripheral blood mononuclear cells (PBMCs) were subjected to TCDD exposure, they manifested significant cellular disruptions. This was evidenced by compromised membrane integrity, a marked reduction in antioxidant defense mechanisms, and a surge in the malondialdehyde (MDA) levels, a recognized marker for oxidative stress. On the genomic front, increased 8-OH-dG levels and chromosomal aberration (CA) frequency suggested that TCDD had the potential to cause DNA damage. Notably, our experiments have revealed that boron compounds could act as protective agents against these disruptions. They exhibited a pronounced ability to diminish the cytotoxic, genotoxic, and oxidative stress outcomes instigated by TCDD. Thus, our findings shed light on the promising role of boron compounds. In specific dosages, they may not only counteract the detrimental effects of TCDD but also serve as potential chemopreventive agents, safeguarding the cellular and genomic integrity of PBMCs.

Association of UGT1A1 gene variants, expression levels, and enzyme concentrations with 2,3,7,8-TCDD exposure in individuals exposed to Agent Orange/Dioxin.

Among the congener of dioxin, 2,3,7,8-TCDD is the most toxic, having a serious long-term impact on the environment and human health. UDP-glucuronosyltransferase 1A1 (UGT1A1) plays a crucial role in the detoxification and excretion of endogenous and exogenous lipophilic compounds, primarily in the liver and gastrointestinal tract. This study aimed to investigate the association of UGT1A1 gene polymorphisms, expression levels, and enzyme concentration with Agent Orange/Dioxin exposure. The study included 100 individuals exposed to Agent Orange/Dioxin nearby Da Nang and Bien Hoa airports in Vietnam and 100 healthy controls. UGT1A1 SNP rs10929303, rs1042640 and rs8330 were determined by Sanger sequencing, mRNA expression was quantified by RT-qPCR and plasma UGT1A1 concentrations were measured by ELISA. The results showed that UGT1A1 polymorphisms at SNPs rs10929303, rs1042640 and rs8330 were associated with Agent Orange/Dioxin exposure (OR = 0.55, P = 0.018; OR = 0.55, P = 0.018 and OR = 0.57, P = 0.026, respectively). UGT1A1 mRNA expression levels and enzyme concentration were significantly elevated in individuals exposed to Agent Orange/Dioxin compared to controls (P < 0.0001). Benchmark dose (BMD) analyses showed that chronic exposure to 2,3,7,8-TCDD contamination affects the UGT1A1 mRNA and protein levels. Furthermore, UGT1A1 polymorphisms affected gene expression and enzyme concentrations in individuals exposed to Agent Orange/Dioxin. In conclusion, UGT1A1 gene polymorphisms, UGT1A gene expression levels and UGT1A1 enzyme concentrations were associated with Agent Orange/Dioxin exposure. The metabolism of 2,3,7,8-TCDD may influence UGT1A gene expression and enzyme concentrations.

Transgenerational Transmission of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Effects in Human Granulosa Cells: The Role of MicroRNAs.

Endocrine-disrupting chemicals (EDCs) might contribute to the increase in female-specific cancers in Western countries. 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) is considered the "prototypical toxicant" to study EDCs' effects on reproductive health. Epigenetic regulation by small noncoding RNAs (sncRNAs), such as microRNAs (miRNA), is crucial for controlling cancer development. The aim of this study was to analyze transcriptional activity and sncRNA expression changes in the KGN cell line after acute (3 h) and chronic (72 h) exposure to 10 nM TCDD in order to determine whether sncRNAs' deregulation may contribute to transmitting TCDD effects to the subsequent cell generations (day 9 and day 14 after chronic exposure). Using Affymetrix GeneChip miRNA 4.0 arrays, 109 sncRNAs were found to be differentially expressed (fold change < -2 or >2; p-value < 0.05) between cells exposed or not (control) to TCDD for 3 h and 72 h and on day 9 and day 14 after chronic exposure. Ingenuity Pathway Analysis predicted that following the acute and chronic exposure of KGN cells, sncRNAs linked to cellular development, growth and proliferation were downregulated, and those linked to cancer promotion were upregulated on day 9 and day 14. These results indicated that TCDD-induced sncRNA dysregulation may have transgenerational cancer-promoting effects.

Protective effect of didymin against 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin-induced reproductive toxicity in male rats.

PURPOSE: 2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin (TCDD) is one of the most potent environmental toxicants, which causes oxidative stress and adversely affects the male reproductive system. The current study aimed to evaluate the ameliorative role of didymin (DDM) against TCDD-induced testicular toxicity. METHODS: Forty-eight male Sprague-Dawley rats were divided into four equal groups (n=12). (i) Control group, (ii) TCDD-induced group was provided with 10 µg/kg/day of TCDD, (iii) TCDD + DDM group received 10 µg/kg/day of TCDD and 2 mg/kg/day of DDM, and (iv) DDM-treated group was administered with 2 mg/kg/day of DDM. After 56 days of treatment, biochemical, steroidogenic, hormonal, spermatogenic, apoptotic, and histopathological parameters were estimated. RESULTS: TCDD affected the biochemical profile by reducing the activities of antioxidant enzymes, while increasing the levels of malondialdehyde (MDA) and reactive oxygen species (ROS). Furthermore, it decreased the expressions of steroidogenic enzymes, 3ß-hydroxysteroid dehydrogenase (HSD), 17ß-HSD, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (CYP11A1), and 17α-hydroxylase/17, 20-lyase (CYP17A1), as well as reduced the levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and plasma testosterone. Besides, epididymal sperm count, viability, and motility were decreased, while sperm morphological anomalies were increased. Moreover, TCDD altered the apoptotic profile by up-regulating the expressions of Bax and caspase-3, while downregulated the Bcl-2 expression. Additionally, histopathological damages were prompted due to TCDD administration. However, DDM restored all the TCDD-induced damages owing to its antioxidant, anti-apoptotic, and androgenic potential. CONCLUSION: Our data suggested that DDM might play its role as a therapeutic agent against TCDD-prompted testicular toxicity.

Inhibition of the urea cycle by the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin increases serum ammonia levels in mice.

The aryl hydrocarbon receptor is a ligand-activated transcription factor known for mediating the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. TCDD induces nonalcoholic fatty liver disease (NAFLD)-like pathologies including simple steatosis that can progress to steatohepatitis with fibrosis and bile duct proliferation in male mice. Dose-dependent progression of steatosis to steatohepatitis with fibrosis by TCDD has been associated with metabolic reprogramming, including the disruption of amino acid metabolism. Here, we used targeted metabolomic analysis to reveal dose-dependent changes in the level of ten serum and eleven hepatic amino acids in mice upon treatment with TCDD. Bulk RNA-seq and protein analysis showed TCDD repressed CPS1, OTS, ASS1, ASL, and GLUL, all of which are associated with the urea cycle and glutamine biosynthesis. Urea and glutamine are end products of the detoxification and excretion of ammonia, a toxic byproduct of amino acid catabolism. Furthermore, we found that the catalytic activity of OTC, a rate-limiting step in the urea cycle was also dose dependently repressed. These results are consistent with an increase in circulating ammonia. Collectively, the repression of the urea and glutamate-glutamine cycles increased circulating ammonia levels and the toxicity of TCDD.