Dioxin: a review of its environmental effects and its aryl hydrocarbon receptor biology

Comprehensive metabolic profiling of dioxin-like compounds exposure in laying hens: Implications for toxicity assessment

The evaluation of toxicity related to polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) is crucial for a comprehensive risk assessment in real-world exposure scenarios. This study employed a controlled feeding experiment to investigate the metabolic effects of dioxin-like compounds (DLCs) on laying hens via feed exposure. Diets enriched with two concentrations (1.17 and 5.13 pg toxic equivalents (TEQ)/g dry weight (dw)) were administered over 14 days, followed by 28 days of clean feed. Metabolomics analyses of blood samples revealed significant metabolic variations between PCDD/Fs and DL-PCBs exposed groups and controls, reflecting the induced metabolic disruption. Distinct changes were observed in sphingosine, palmitoleic acid, linoleate, linolenic acid, taurocholic acid, indole acrylic acid, and dibutyl phthalate levels, implying possible connections between PCDD/Fs and DL-PCBs toxic effects and energy-neuronal imbalances, along with lipid accumulation and anomalous amino acid metabolism, impacting taurine metabolism. Moreover, we identified three differential endogenous metabolites-L-tryptophan, indole-3-acetaldehyde, and indole acrylic acid-as potential ligands for the aryl hydrocarbon receptor (AhR), suggesting their role in mediating PCDD/Fs and DL-PCBs toxicity. This comprehensive investigation provides novel insights into the metabolic alterations induced by PCDD/Fs and DL-PCBs in laying hens, thereby enhancing our ability to assess risks associated with their exposure in human populations.

Effects of microplastic interaction with persistent organic pollutants on the activity of the aryl hydrocarbon and estrogen receptors

Environmental microplastics (MPs) are complex mixtures of plastic polymers and sorbed chemical pollutants with high degrees of heterogeneity, particularly in terms of particle size, morphology and degree of weathering. Currently, limitations exist in sampling sufficient amounts of environmental particles for laboratory studies to assess toxicity endpoints with statistical rigor and to examine chemical pollutant interactions. This study seeks to bridge this gap by investigating environmental plastic particle mimetics and pollutant-polymer interactions by mixing polymer particles with persistent organic pollutants (POPs) at set concentrations over time. Solutions containing combinations of polymers including polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), and polyamide (PA) and POPs including 2,3,7,8 -Tetrachlorodibenzo-p-dioxin (TCDD), bisphenol A (BPA), and atrazine, were stirred for up to 19 weeks and monitored using assays to test for aryl hydrocarbon (AhR) and estrogen receptor (ER) activity which are cell signaling pathways impacted by environmental pollutants. TCDD induced AhR activity decreased over time in the presence of PS in a surface area dependent manner. BPA and atrazine also exhibited AhR antagonist activity in the presence of TCDD. The addition of BPA slowed the loss of activity but atrazine did not, suggesting that polymer chemistry impacts interactions with POPs. We also observed potential differences in TCDD sorption with different plastic polymers and that higher concentrations of PS particles may inhibit BPA-induced estrogen receptor activation. These results emphasize the need for additional understanding of how POPs and polymer chemistry impact their interaction and toxicity.

The Aryl Hydrocarbon Receptor Controls IFNγ-Induced Immune Checkpoints PD-L1 and IDO via the JAK/STAT Pathway in Lung Adenocarcinoma

While immunotherapy has shown efficacy in lung adenocarcinoma (LUAD) patients, many respond only partially or not at all. One limitation in improving outcomes is the lack of a complete understanding of immune checkpoint regulation. Here, we investigated a possible link between an environmental chemical receptor implicated in lung cancer and immune regulation, (the aryl hydrocarbon receptor/AhR), a known but counterintuitive mediator of immunosuppression (IFNγ), and regulation of two immune checkpoints (PD-L1 and IDO). AhR gene-edited LUAD cell lines, a syngeneic LUAD mouse model, bulk- and scRNA sequencing of LUADs and tumor-infiltrating leukocytes were used to map out a signaling pathway leading from IFNγ through the AhR to JAK/STAT, PD-L1, IDO, and tumor-mediated immunosuppression. The data demonstrate that: 1) IFNγ activation of the JAK/STAT pathway leading to PD-L1 and IDO1 upregulation is mediated by the AhR in murine and human LUAD cells, 2) AhR-driven IDO1 induction results in the production of Kynurenine (Kyn), an AhR ligand, which likely mediates an AhR→IDO1→Kyn→AhR amplification loop, 3) transplantation of AhR-knockout LUAD cells results in long-term tumor immunity in most recipients. 4) The 23% of AhR-knockout tumors that do grow do so at a much slower pace than controls and exhibit higher densities of CD8+ T cells expressing markers of immunocompetence, increased activity, and increased cell-cell communication. The data definitively link the AhR to IFNγ-induced JAK/STAT pathway and immune checkpoint-mediated immunosuppression and support the targeting of the AhR in the context of LUAD.

Identifying Universal Fish Biomarker Genes in Response to PCB126 Exposure by Comparative Transcriptomic Analyses

Water pollution remains a major environmental concern, with increased toxic by-products being released into water bodies. Many of these chemical contaminants persist in the environment and bio-accumulate in aquatic organisms. At present, toxicological tests are mostly based on laboratory tests, and effective methods for monitoring wild aquatic environments remain lacking. In the present study, we used a well-characterized toxic chemical, 3,3',4,4',5-polychlorinated biphenyl (PCB126), as an example to try to identify common biomarker genes to be used for predictive toxicity of this toxic substance. First, we used two laboratory fish models, the zebrafish (Danio rerio) and medaka (Oryzias latipes), to expose PCB126 to obtain liver transcriptomic data by RNA-seq. Comparative transcriptomic analyses indicated generally conserved and concerted changes from the two species, thus validating the transcriptomic data for biomarker gene selection. Based on the common up- and downregulated genes in the two species, we selected nine biomarker genes to further test in other fish species. The first validation experiment was carried out using the third fish species, Mozambique tilapia (Oreochromis mossambicus), and essentially, all these biomarker genes were validated for consistent responses with the two laboratory fish models. Finally, to develop universal PCR primers suitable for potentially all teleost fish species, we designed degenerate primers and tested them in the three fish species as well as in another fish species without a genomic sequence available: guppy (Poecilia reticulata). We found all the biomarker genes showed consistent response to PCB126 exposure in at least 50% of the species. Thus, our study provides a promising strategy to identify common biomarker genes to be used for teleost fish analyses. By using degenerate PCR primers and analyzing multiple biomarker genes, it is possible to develop diagnostic PCR arrays to predict water contamination from any wild fish species sampled in different water bodies.

Serum metabolism distribution in individuals exposed to dioxins: A case study of residents near the municipal solid waste incinerators in China

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) have attracted considerable attention owing to their environmental persistence, bioaccumulation, and high toxicity. This study aimed to investigate changes in serum metabolites following exposure to PCDD/Fs and to reveal a novel pathogenesis of PCDD/Fs. Serum samples were collected from 75 residents living near a municipal solid waste incinerator in China to analyse the relationship between PCDD/Fs and serum metabolic components. The serum level in the low-exposure group [19.07 (13.44-23.89) pg-TEQ/L] was significantly lower than that in the high-exposure group [115.60 (52.28-592.65) pg-TEQ/L]. Non-targeted metabolomic studies based on liquid chromatography-high resolution mass spectrometry have been applied to the metabolomic analysis of serum. Thirty-seven metabolites with significant differences among the different groups were identified as biomarkers. Pathway analysis revealed that high dioxin exposure perturbed various biological processes, including glycerol phospholipid metabolism and the interconversion of pentose and glucuronate. The results of a population health survey showed that the serum dioxin concentration in patients with diabetes was significantly higher than that in the control population. These findings suggest that dioxin exposure is associated with several potential adverse health risks, including inflammation, diabetes, and cardiovascular disease, through metabolic changes.

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) induces depression-like phenotype

The etiology of major depressive disorder (MDD) remains poorly understood. Our previous studies suggest a role for the aryl hydrocarbon receptor (AhR) in depression. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a toxic environmental contaminant, with a high AhR binding affinity, and an established benchmark for assessing AhR activity. Therefore, this study examined the effect of TCDD on depression-like behaviors. Female mice were fed standard chow or a high-fat diet (HFD) for 11 weeks, and their weight was recorded. Subsequently, they were tested for baseline sucrose preference and splash test grooming. Then, TCDD (0.1 µg/kg/day) or vehicle was administered orally for 28 days, and mice were examined for their sucrose preference and performances in the splash test, forced swim test (FST), and Morris water maze (MWM) task. TCDD significantly decreased sucrose preference, increased FST immobility time, and decreased groom time in chow-fed mice. HFD itself significantly reduced sucrose preference. However, TCDD significantly increased FST immobility time and decreased groom time in HFD-fed mice. A small decrease in bodyweight was observed only at the fourth week of daily TCDD administration in chow-fed mice, and no significant effects of TCDD on bodyweights were observed in HFD-fed mice. TCDD did not have a significant effect on spatial learning in the MWM. Thus, this study demonstrated that TCDD induces a depression-like state, and the effects were not due to gross lethal toxicity. This study further suggests that more studies should examine a possible role for AhR and AhR-active environmental pollutants in precipitating or worsening MDD.

Kynurenic Acid/AhR Signaling at the Junction of Inflammation and Cardiovascular Diseases

Persistent systemic chronic inflammatory conditions are linked with many pathologies, including cardiovascular diseases (CVDs), a leading cause of death across the globe. Among various risk factors, one of the new possible contributors to CVDs is the metabolism of essential amino acid tryptophan. Proinflammatory signals promote tryptophan metabolism via the kynurenine (KYN) pathway (KP), thereby resulting in the biosynthesis of several immunomodulatory metabolites whose biological effects are associated with the development of symptoms and progression of various inflammatory diseases. Some participants in the KP are agonists of aryl hydrocarbon receptor (AhR), a central player in a signaling pathway that, along with a regulatory influence on the metabolism of environmental xenobiotics, performs a key immunomodulatory function by triggering various cellular mechanisms with the participation of endogenous ligands to alleviate inflammation. An AhR ligand with moderate affinity is the central metabolite of the KP: KYN; one of the subsequent metabolites of KYN-kynurenic acid (KYNA)-is a more potent ligand of AhR. Understanding the role of AhR pathway-related metabolites of the KP that regulate inflammatory factors in cells of the cardiovascular system is interesting and important for achieving effective treatment of CVDs. The purpose of this review was to summarize the results of studies about the participation of the KP metabolite-KYNA-and of the AhR signaling pathway in the regulation of inflammation in pathological conditions of the heart and blood vessels and about the possible interaction of KYNA with AhR signaling in some CVDs.

Occurrence of halogenated organic contaminants in surface sediments of the Yangtze River estuary and its adjacent marine area

Halogenated organic contaminants, such as chlorinated and brominated polycyclic aromatic hydrocarbons (Cl/Br-PAHs), are some of the most important emerging environmental pollutants. However, empirical data on Cl/Br-PAHs in estuarine and marine ecosystems are limited, rendering assessments of Cl/Br-PAH contamination in estuarine and offshore environments uncertain. Here the occurrence, sources, and ecological risks of 7 Cl-PAHs and 18 Br-PAHs were determined in surface sediments of the Yangtze River Estuary (YRE), a highly urbanized and industrialized area, and its adjacent marine area. The concentrations of Cl-PAHs ranged from 4.50 to 18.38 ng g-1 (average 7.19 ng g-1), while those of Br-PAHs ranged from 4.80 to 61.18 ng g-1 (average 14.11 ng g-1). The dominant Cl-PAH and Br-PAH in surface sediment were 9-chlorofluorene (17.79%) and 9-bromofluorene (58.49%), respectively. The distributions and compositions of Cl/Br-PAHs in the surface sediments varied considerably due to complex hydrodynamic and depositional conditions in the YRE and its adjacent marine area, as well as differences in physicochemical properties of different Cl/Br-PAHs. Positive matrix factorization revealed that the primary sources of Cl/Br-PAHs in the study area were e-waste dismantling (33.6%), waste incineration (23.2%), and metal smelting (11.0%). According to the risk quotient, the Cl/Br-PAHs in sediments posed no toxic risk to aquatic organisms.

Inhalation of particulate matter containing environmentally persistent free radicals induces endothelial dysfunction mediated via AhR activation at the air-blood interface

Particulate matter (PM) containing environmentally persistent free radicals (EPFR) is formed by the incomplete combustion of organic wastes, resulting in the chemisorption of pollutants to the surface of PM containing redox-active transition metals. In prior studies in mice, EPFR inhalation impaired endothelium-dependent vasodilation. These findings were associated with aryl hydrocarbon receptor (AhR) activation in the alveolar type-II (AT-II) cells that form the air-blood interface in the lung. We thus hypothesized that AhR activation in AT-II cells promotes the systemic release of mediators that promote endothelium dysfunction peripheral to the lung. To test our hypothesis, we knocked down AhR in AT-II cells of male and female mice and exposed them to 280 µg/m3 EPFR lo (2.7e + 16 radicals/g) or EPFR (5.5e + 17 radicals/g) compared with filtered air for 4 h/day for 1 day or 5 days. AT-II-AhR activation-induced EPFR-mediated endothelial dysfunction, reducing endothelium-dependent vasorelaxation by 59%, and eNOS expression by 50%. It also increased endothelin-1 mRNA levels in the lungs and peptide levels in the plasma in a paracrine fashion, along with soluble vascular cell adhesion molecule-1 and iNOS mRNA expression, possibly via NF-kB activation. Finally, AhR-dependent increases in antioxidant response signaling, coupled to increased levels of 3-nitrotyrosine in the lungs of EPFR-exposed littermate control but not AT-II AhR KO mice suggested that ATII-specific AhR activation promotes oxidative and nitrative stress. Thus, AhR activation at the air-blood interface mediates endothelial dysfunction observed peripheral to the lung, potentially via release of systemic mediators.

Exposure to Environmental Toxins: Potential Implications for Stroke Risk via the Gut- and Lung-Brain Axis

Recent evidence indicates that exposure to environmental toxins, both short-term and long-term, can increase the risk of developing neurological disorders, including neurodegenerative diseases (i.e., Alzheimer's disease and other dementias) and acute brain injury (i.e., stroke). For stroke, the latest systematic analysis revealed that exposure to ambient particulate matter is the second most frequent stroke risk after high blood pressure. However, preclinical and clinical stroke investigations on the deleterious consequences of environmental pollutants are scarce. This review examines recent evidence of how environmental toxins, absorbed along the digestive tract or inhaled through the lungs, affect the host cellular response. We particularly address the consequences of environmental toxins on the immune response and the microbiome at the gut and lung barrier sites. Additionally, this review highlights findings showing the potential contribution of environmental toxins to an increased risk of stroke. A better understanding of the biological mechanisms underlying exposure to environmental toxins has the potential to mitigate stroke risk and other neurological disorders.

Polychlorinated biphenyls exposure and type 2 diabetes: Molecular mechanism that causes insulin resistance and islet damage

Polychlorinated biphenyls (PCBs) are typical persistent organic pollutants that have been associated with type 2 diabetes (T2DM) in cohort studies. This review aims to comprehensively assess the molecular mechanisms of PCBs-induced T2DM. Recent progress has been made in the research of PCBs in liver tissue, adipose tissue, and other tissues. By influencing the function of nuclear receptors, such as the aryl hydrocarbon receptor (AhR), pregnancy X receptor (PXR), and peroxisome proliferator activated receptor γ (PPARγ), as well as the inflammatory response, PCBs disrupt the balance of hepatic glucose and lipid metabolism. This is associated with insulin resistance (IR) in the target organ of insulin. Through androgen receptor (AR), estrogen receptor α/β (ERα/β), and pancreato-duodenal-homeobox gene-1 (PDX-1), PCBs affect the secretion of insulin and increase blood glucose. Thus, this review is a discussion on the relationship between PCBs exposure and the pathogenesis of T2DM. It is hoped to provide basic concepts for diabetes research and disease treatment.

The Role of Endocrine Disruption Chemical-Regulated Aryl Hydrocarbon Receptor Activity in the Pathogenesis of Pancreatic Diseases and Cancer

The aryl hydrocarbon receptor (AHR) serves as a ligand-activated transcription factor crucial for regulating fundamental cellular and molecular processes, such as xenobiotic metabolism, immune responses, and cancer development. Notably, a spectrum of endocrine-disrupting chemicals (EDCs) act as agonists or antagonists of AHR, leading to the dysregulation of pivotal cellular and molecular processes and endocrine system disruption. Accumulating evidence suggests a correlation between EDC exposure and the onset of diverse pancreatic diseases, including diabetes, pancreatitis, and pancreatic cancer. Despite this association, the mechanistic role of AHR as a linchpin molecule in EDC exposure-related pathogenesis of pancreatic diseases and cancer remains unexplored. This review comprehensively examines the involvement of AHR in EDC exposure-mediated regulation of pancreatic pathogenesis, emphasizing AHR as a potential therapeutic target for the pathogenesis of pancreatic diseases and cancer.

Exosomes released by environmental pollutant-stimulated Keratinocytes/PBMCs can trigger psoriatic inflammation in recipient cells via the AhR signaling pathway

Introduction: Exosomes, pivotal in intercellular communication during skin disease pathogenesis, have garnered substantial attention. However, the impact of environmental pollutants, such as benzo[a]pyrene (BaP) and 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD), on exosome release amid inflammatory skin diseases remains unexplored. This study addresses this gap by examining the influence of BaP and TCDD on exosome function, specifically focusing on immune-related pathway alterations in normal recipient keratinocytes and peripheral blood mononuclear cells (PBMCs). Methods: HaCaT cells were treated with exosomes from BaP- or TCDD-treated keratinocytes. Proinflammatory cytokines and chemokines, including TNF-α, IL-1β, IL-6, IL-8, CXCL1, and CXCL5, were assessed. The involvement of the p65NF-κB/p38MAPK/ERK signaling pathway in recipient keratinocytes was investigated. Aryl hydrocarbon receptor (AhR) silencing was employed to elucidate its role in mediating the proinflammatory response induced by exosomes from BaP- or TCDD-treated keratinocytes. Results and discussion: Treatment with exosomes from BaP- or TCDD-treated keratinocytes induced a significant increase in proinflammatory cytokines and chemokines in HaCaT cells. The upregulation implicated the p65NF-κB/p38MAPK/ERK signaling pathway. AhR silencing attenuated this response, suggesting a role for AhR in mediating this response. In PBMCs from healthy controls, exosomes from BaP-stimulated PBMCs of psoriatic patients led to increased expression of proinflammatory cytokines and modulation of Th1/Th17 cell distribution via AhR activation. These findings unveil a novel dimension in the interplay between environmental xenobiotic agents (BaP and TCDD) and exosomal functions. The study establishes their influence on psoriatic inflammatory responses, shedding light on the underlying mechanisms mediated through the AhR signaling pathway in recipient keratinocytes and PBMCs.

Differential effects of pesticides on dioxin receptor signaling and p53 activation

As modern agricultural practices increase their use of chemical pesticides, it is inevitable that we will find a number of these xenobiotics within drinking water supplies and disseminated throughout the food chain. A major problem that arises from this pollution is that the effects of most of these pesticides on cellular mechanisms in general, and how they interact with each other and affect human cells are still poorly understood. In this study we make use of cultured human cancer cells to measure by qRT-PCR how pesticides affect gene expression of stress pathways. Immunoblotting studies were performed to monitor protein expression levels and activation of signaling pathways. We make use of immunofluorescence and microscopy to visualize and quantify DNA damage events in those cells. In the current study, we evaluate the potential of a subset of widely used pesticides to activate the dioxin receptor pathway and affect its crosstalk with estrogen receptor signaling. We quantify the impact of these chemicals on the p53-dependent cellular stress response. We find that, not only can the different pesticides activate the dioxin receptor pathway, most of them have better than additive effects on this pathway when combined at low doses. We also show that different pesticides have the ability to trigger crosstalk events that may generate genotoxic estrogen metabolites. Finally, we show that some, but not all of the tested pesticides can induce a p53-dependent stress response. Taken together our results provide evidence that several xenobiotics found within the environment have the potential to interact together to elicit significant effects on cell systems. Our data warrants caution when the toxicity of substances that are assessed simply for individual chemicals, since important biological effects could be observed only in the presence of other compounds, and that even at very low concentrations.

A review of food contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin and its toxicity associated with metabolic disorders

Dioxins are a group of chemicals not only regarded as highly toxic trace environmental contaminants, but also considered typical contaminants in food. Dioxins spread across the ecosystem after factory manufacture, contaminate the soil and vegetation before either directly or indirectly entering the food chain through meat products, dairy products, and aquatic products. The compound in question poses a challenge for metabolic processes within the human body, due to its intricate mechanism for inducing diseases. Therefore, it presents a significant risk and is largely undisclosed. Dioxins are mainly exposed to humans by water, food, and air, as well as inducing organ failure and metabolic disorders through but not limited to the activation of aryl hydrocarbon receptors (AhR). As a notorious compound in the family of dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exhibits long-term toxic effects on diverse organs, which induces continuous metabolic disorders. This review discussed the mechanisms of TCDD-associated metabolic syndrome. The expression of the cytochrome P450 subfamily transfers TCDD into liver, promotes its accumulation in fat tissue, and affects cholesterol metabolism. This process also alters the glucose tolerance of the human organism, disrupting glucose metabolism. It can also elicit cardiovascular pathogenesis, exacerbate liver fibrosis and neuronal death. The long-term metabolic impact of this effect is found to be sex-related. This review summarized the toxicity of TCDD on the human metabolism system and discussed the plausible correlation between TCDD and five metabolic disorders, which helped offer novel insights for future research and therapeutic interventions for these ailments.

Molecular Modelling of Polychlorinated Dibenzo-p-Dioxins Non-Covalent Interactions with β and γ-Cyclodextrins

Polychlorinated dibenzo-p-dioxins (PCDD) are persistent organic pollutants which result as byproducts in industrial or combustion processes and induce toxicity in both wildlife and humans. In this study, all seven PCDD, tetrachlorinated dibenzo-p-dioxins (TCDD), pentachlorinated dibenzo-p-dioxins (P5CDD), hexachlorinated dibenzo-p-dioxins (H6CDD), heptachlorinated dibenzo-p-dioxins (H7CDD), and octachlorinated dibenzo-p-dioxins (OCDD) were studied in interaction with two cyclodextrins, β-CD and γ-CD, resulting in a total of 40 host-guest complexes. The flexibility of the cyclodextrins was given by the number of glucose units, and the placement of the chlorine groups on the dioxins structure accounted for the different complex formed. Various geometries of interaction obtained by guided docking were studied, and the complexation and binding energy were calculated in the frame of MM+ and OPLS force fields. The results show that the recognition of the PCDD pollutants by the CD may be possible through the formation of PCDD:CD inclusion complexes. This recognition is based on the formation of Coulombic interactions between the chlorine atom of the PCDD and the primary and secondary hydroxyl groups of the CD and van der Waals interaction of the CD hydrophobic cavity with PCDD aromatic structures. Both MM+ and OPLS calculus resulted in close values for the complexation and binding energies. Molecular mechanics calculations offer a proper insight into the molecular recognition process between the PCDD compounds and CD molecules, proved by a good description of the C-H···O bonds formed between the guest and host molecules. It was shown for the first time that CD may efficiently trap PCCDs, opening the way for their tremendous potential use in environmental remediation.

Impact of air pollution on human health in different geographical locations of Nepal

According to a recent survey, Nepal's urban air quality has been classified as one of the worst in the globe. A large portion of the country's population is subjected to health risks caused by air pollution. As Nepal has a wide variation in altitude coupled with socio-cultural and biological diversities, it is important to understand the different health hazards in the different geographical regions - Terai, Hills and Mountains. Constantly increasing physical infrastructures (such as transport vehicles, open burning of plastics and other fuels) are the main reasons for the escalating air pollution in the country. This study aims to critically review the current air pollution status in different geographical locations along with its impacts on public health in the country. It has been revealed that irrespective of geographic location, the air pollutants interfere with different human physiological systems related to respiration as well as cardiovascular, ophthalmic, and gastrointestinal functioning. Further, the research findings highlighting the influence of prolonged exposure of the population to the air pollution leading to the significant number of deaths have been presented. A notable rise in the number of hospitalized patients suffering from illnesses related to above mentioned pollution borne cases has been reported.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induces liver lipid metabolism disorder via the ROS/AMPK/CD36 signaling pathway

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is widely considered as the most toxic and common carcinogen in the world. Exposure to TCDD causes liver lipid metabolism disorder and steatosis. However, the molecular mechanism of TCDD-induced liver lipid accumulation is not completely clear. Here, we found that a 5 μg/kg TCDD exposure for 3 weeks induced hepatocyte lipid deposition, increased CD36 expression, and promoted AMP-activated protein kinase (AMPK) ɑ phosphorylation in the liver of C57BL/6J mice. Furthermore, sulfo-N-succinimidyl oleate, a CD36 inhibiter, blunted TCDD-induced lipid deposition in Huh7 cells, confirming the critical role of CD36 in TCDD-induced hepatic steatosis. In terms of molecular mechanisms, we found that TCDD exposure increased reactive oxygen species (ROS) levels in Huh7 cells, which activated AMPK. Moreover, the activated AMPK upregulated CD36 expression. Therefore, we can see that the increase in CD36 expression induced by TCDD was regulated by ROS/AMPK/CD36 signaling pathway. Our results help to clarify the molecular mechanism of TCDD-induced hepatic steatosis.

PFOS Induces Lipometabolism Change, Immune Defense, and Endocrine Disorders in Black-Spotted Frogs: Application of Transcriptome Profiling

Amphibian population declines are closely linked to increasingly serious environmental pollution. Field investigations revealed that perfluorooctane sulfonic acid (PFOS) distribution was detected in 100% of amphibians. In the present study, global transcriptome sequencing was determined on black-spotted frogs to quantify transcript expression levels and the development of an adverse outcome pathway for PFOS. A total of 1441 differentially expressed genes were identified in the PFOS exposure for 21 d, with 645 being downregulated and 796 upregulated. The gene functions and pathways for lipid metabolism, endocrine system, and immune defense were enriched. An adverse outcome pathway has been proposed, including PPAR (peroxisome proliferator-activated receptors) as the molecular initiating events; followed by changes in lipid metabolism, endocrine system, and immune defense; with an end result of liver damage or even population decline. This research provides molecular insight into the toxicity of PFOS. More research about differentially expressed genes is warranted to further provide the underlying mechanism that is altered as a result of PFOS toxicity in organisms.

Multi-omics responses in tree swallow (Tachycineta bicolor) nestlings from the Maumee Area of Concern, Maumee River, Ohio

A multi-omics approach was utilized to identify altered biological responses and functions, and to prioritize contaminants to assess the risks of chemical mixtures in the Maumee Area of Concern (AOC), Maumee River, OH, USA. The Maumee AOC is designated by the United States Environmental Protection Agency as having significant beneficial use impairments, including degradation of fish and wildlife populations, bird or animal deformities or reproduction problems, and loss of fish and wildlife habitat. Tree swallow (Tachycineta bicolor) nestlings were collected at five sites along the Maumee River, which included wastewater treatment plants (WWTPs) and industrial land-use sites. Polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo p dioxins and furans (PCDD/Fs), and chlorinated pesticide concentrations were elevated in Maumee tree swallows, relative to a remote reference site, Star Lake, WI, USA. Liver tissue was utilized for non-targeted transcriptome and targeted metabolome evaluation. A significantly differentially expressed gene cluster related to a downregulation in cell growth and cell cycle regulation was identified when comparing all Maumee River sites with the reference site. There was an upregulation of lipogenesis genes, such as PPAR signaling (HMGCS2, SLC22A5), biosynthesis of unsaturated fatty acids (FASN, SCD, ELOVL2, and FADS2), and higher lipogenesis related metabolites, such as docosapentaenoic acid (DPA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (AA) at two industrial land-use sites, Ironhead and Maumee, relative to WWTP sites (Perrysburg and SideCut), and the reference site. Toledo Water, in the vicinity of the other two industrial sites and also adjacent to a WWTP, showed a mix of signals between industrial land-use and WWTP land-use. PAHs, oxychlordane, and PBDEs were determined to be the most likely causes of the differentiation in biological responses, including de novo lipogenesis and biosynthesis of unsaturated fatty acids.

Unintentional formation of mixed chloro-bromo diphenyl ethers (PBCDEs), dibenzo-p-dioxins and dibenzofurans (PBCDD/Fs) from pyrolysis of polybrominated diphenyl ethers (PBDEs)

This study presents the comprehensive investigation for formation pathways of chloro-bromo-mixed products from the pyrolysis of polybrominated diphenyl ethers (PBDEs). In the study, a total of 23 PBDEs with bromination levels from mono-to deca-were selected. Each PBDE standard was sealed in the glass vial and then heated under 450 °C in the muffle furnace to simulate the pyrolysis process. The results demonstrated that PBDEs in the glass vials can unintentionally transform into chloro-bromo diphenyl ethers (PBCDEs) and dibenzo-p-dioxin and dibenzofurans (PBCDD/Fs) during the pyrolysis process. Atmosphere pressure gas chromatography (APGC) coupled with high-resolution mass spectrometry (HRMS) was used to identify these pyrolysis products, which demonstrated that all investigated nPBDEs (n represents the number of bromine substituents) can unintentionally transform into Cl₁-(n-1)BDEs, Cl₂-(n-2)BDEs, Cl₁-(n-1)BDFs, and Cl₁-(n-3)BDDs, while some nPBDEs can transform into Cl₁-(n-2)PBDD/Fs during pyrolysis. Experimental phenomena assisted with density functional theory (DFT) calculations reveal that Cl atom can substitute at C-Br rather than C-H, and Cl₁-(n-1)BDEs can be easily generated by Cl atom attacking at C-Br sites with low energy barriers (3.66-11.9 kcal/mol). In addition, nPBDEs with lower bromination levels are more favorable to generate Cl₁-(n-1)BDEs than those with higher bromination levels. Further DFT calculations suggest that PBDEs are preferentially first transformed into Cl₁-(n-1)BDEs, then subsequentially transform into PBCDD/Fs. We believe the results of this study can greatly improve our understanding of the transformation mechanism from PBDEs to cholo-bromo-mixed products in thermal treatment processes and provide new insight into controlling the emission of toxic cholo-bromo-mixed products.

Effect of Chronic Cadmium Exposure on Brain and Liver Transporters and Drug-Metabolizing Enzymes in Male and Female Mice Genetically Predisposed to Alzheimer's Disease

Cadmium (Cd) exposure is associated with increased Alzheimer's disease (AD) risks. The human Apolipoprotein E (ApoE) gene encodes a lipid-transporting protein that is critical for brain functions. Compared with ApoE2 and E3, ApoE4 is associated with increased AD risk. Xenobiotic biotransformation-related genes have been implicated in the pathogenesis of AD. However, little is known about the effects of Cd, ApoE, and sex on drug-processing genes. We investigated the Cd-ApoE interaction on the transcriptomic changes in the brains and livers of ApoE3/ApoE4 transgenic mice. Cd disrupts the transcriptomes of transporter and drug-processing genes in brain and liver in a sex- and ApoE-genotype-specific manner. Proinflammation related genes were enriched in livers of Cd-exposed ApoE4 males, whereas circadian rhythm and lipid metabolism related genes were enriched in livers of Cd-exposed ApoE3 females. In brains, Cd up-regulated the arachidonic acid-metabolizing Cyp2j isoforms only in the brains of ApoE3 mice, whereas the dysregulation of cation transporters was male-specific. In livers, several direct target genes of the major xenobiotic-sensing nuclear receptor pregnane X receptor were uniquely upregulated in Cd-exposed ApoE4 males. There was a female-specific hepatic upregulation of the steroid hormone-metabolizing Cyp2 isoforms and the bile acid synthetic enzyme Cyp7a1 by Cd exposure. The dysregulated liver transporters were mostly involved in intermediary metabolism, with the most significant response observed in ApoE3 females. In conclusion, Cd dysregulated the brain and liver drug-processing genes in a sex- and ApoE-genotype specific manner, and this may serve as a contributing factor for the variance in the susceptibility to Cd neurotoxicity. SIGNIFICANCE STATEMENT: Xenobiotic biotransformation plays an important role in modulating the toxicity of environmental pollutants. The human ApoE4 allele is the strongest genetic risk factor for AD, and cadmium (Cd) is increasingly recognized as an environmental factor of AD. Very little is known regarding the interactions between Cd exposure, sex, and the genes involved in xenobiotic biotransformation in brain and liver. The present study has addressed this critical knowledge gap.

Understanding disposable plastics effects generated from the PCR testing labs during the COVID-19 pandemic

In medical labs, especially in polymerase chain reaction (PCR) testing labs, plastic residues (PCR tubes, pipet tips, falcon tubes, buffer bottles, medical globes, and others) wastes are potential sources of plastic waste. Evidence showed that a single PCR test for COVID-19 diagnosis used 37 g of disposable plastic per sample. Globally, an estimated amount of above 15,000 tons of plastic residue have been generated from the PCRs tests during the COVID-19 pandemic. These plastic residues are mismanaged and dumped with other solid wastes, especially in molecular testing labs (MTLs) from academic institutes such as universities thereby polluting the ecosystem. Plastic wastes from PCR testing labs also contain hazardous chemicals and pathogenic microorganisms. Thus, plastic residues in PCR testing labs are an important add-on source to conventional plastic wastes. In this perspective, research questions on (1) type and characteristics of plastic, (2) quantity of plastic residues as an add-on source to the conventional plastic wastes, (3) prevalence of microplastics generated from PCR testing labs of plastic wastes, (4) handling, disinfection techniques, and management strategies of these plastic residues, (5) PCR test materials as a source of hazardous chemical pollutants, and (6) future environmental pollution threats imposed by genetic material determination were raised. It is suggested that this work will be used as the baseline information in addressing the knowledge gap for improving PCR testing labs plastic waste management, and regulation to control environmental pollution. Understanding these plastics' impacts and risks is crucial for driving predictions and innovative technology processes towards sustainability.

Aryl hydrocarbon receptor-targeted therapy for CD4+ T cell-mediated idiopathic pneumonia syndrome in mice

We previously demonstrated that interferon γ (IFN-γ) derived from donor T cells co-opts the indoleamine 2,3-dioxygenase 1 (IDO1) → aryl hydrocarbon receptor (AHR) axis to suppress idiopathic pneumonia syndrome (IPS). Here we report that the dysregulated expression of AP-1 family genes in Ahr-/- lung epithelial cells exacerbated IPS in allogeneic bone marrow transplantation settings. AHR repressed transcription of Jund by preventing STAT1 from binding to its promoter. As a consequence, decreased interleukin-6 impaired the differentiation of CD4+ T cells toward Th17 cells. IFN-γ- and IDO1-independent induction of Ahr expression indicated that the AHR agonist might be a better therapeutic target for IPS than the IDO1 activator. We developed a novel synthetic AHR agonist (referred to here as PB502) that potently inhibits Jund expression. PB502 was highly effective at inducing AHR activation and ameliorating IPS. Notably, PB502 was by far superior to the endogenous AHR ligand, L-kynurenine, in promoting the differentiation of both mouse and human FoxP3+ regulatory CD4+ T cells. Our results suggest that the IDO1-AHR axis in lung epithelial cells is associated with IPS repression. A specific AHR agonist may exhibit therapeutic activity against inflammatory and autoimmune diseases by promoting regulatory T-cell differentiation.

Effects of 1,3,7-tribromodibenzo-p-dioxin, a natural dioxin on chicken embryos: Comparison with effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Several naturally occurring dioxins, including 1,3,7-tribromodibenzo-p-dioxin (1,3,7-TriBDD), synthesized by red algae, have been detected in the marine environment. As 1,3,7-TriBDD is accumulated in mussels and fish, predators, such as marine birds, are exposed to this congener, similar to anthropogenic dioxins (including 2,3,7,8-tetrachlorodibenzo-p-dioxin TCDD). However, little is known about the impact of 1,3,7-TriBDD exposure on the bird health. To understand the effects of 1,3,7-TriBDD on birds, the phenotypic effects and hepatic transcriptome were investigated in chicken (Gallus gallus) embryos treated with 27 μM (2.9 ng/g egg) and 137 μM (14.4 ng/g egg) 1,3,7-TriBDD. The blood glucose levels in the 1,3,7-TriBDD-treated groups were lower than those in the control group. The transcriptome analysis of 6520 sequences in the 27 and 137 μM 1,3,7-TriBDD-treated groups identified 733 and 596 differentially expressed genes (DEGs). Cytochrome P450 1A4 and 1A5 were also identified as DEGs, suggesting that the aryl hydrocarbon receptor is activated by this congener. Pathway and network analyses with DEGs suggested that 1,3,7-TriBDD may induce carcinogenic effects and metabolic alterations. These results were similar to the effects on TCDD-treated embryos. Nevertheless, the overall transcriptome results suggested that compared with TCDD, 1,3,7-TriBDD has a unique impact on insulin- and peroxisome-signaling pathways in chicken embryos. Differences in altered transcriptome profiles between 1,3,7-TriBDD- and TCDD-treated embryos may lead to different phenotypic effects: less severe effects of 1,3,7-TriBDD and more fatal effects of TCDD. Collectively, these findings warrant the further assessment of the hazard and risk of 1,3,7-TriBDD on marine animals, considering increased exposure due to climate change.

Baicalein ameliorates ulcerative colitis by improving intestinal epithelial barrier via AhR/IL-22 pathway in ILC3s

Ulcerative colitis (UC) is a chronic inflammatory disease of the gastrointestinal tract, which is closely related to gut barrier dysfunction. Emerging evidence shows that interleukin-22 (IL-22) derived from group 3 innate lymphoid cells (ILC3s) confers benefits on intestinal barrier, and IL-22 expression is controlled by aryl hydrocarbon receptor (AhR). Previous studies show that baicalein protects the colon from inflammatory damage. In this study we elucidated the molecular mechanisms underlying the protective effect of baicalein on intestinal barrier function in colitis mice. Mice were administered baicalein (10, 20, 40 mg·kg-1·d-1, i.g.) for 10 days; the mice freely drank 3% dextran sulfate sodium (DSS) on D1-D7 to induce colitis. We showed that baicalein administration simultaneously ameliorated gut inflammation, decreased intestinal permeability, restored tight junctions of colons possibly via promoting AhR/IL-22 pathway. Co-administration of AhR antagonist CH223191 (10 mg/kg, i.p.) partially blocked the therapeutic effects of baicalein in colitis mice, whereas AhR agonist FICZ (1 μg, i.p.) ameliorated symptoms and gut barrier function in colitis mice. In a murine lymphocyte line MNK-3, baicalein (5-20 μM) dose-dependently increased the expression of AhR downstream target protein CYP1A1, and enhanced IL-22 production through facilitating AhR nuclear translocation, these effects were greatly diminished in shAhR-MNK3 cells, suggesting that baicalein induced IL-22 production in AhR-dependent manner. To further clarify that, we constructed an in vitro system consisting of MNK-3 and Caco-2 cells, in which MNK-3 cell supernatant treated with baicalein could decrease FITC-dextran permeability and promoted the expression of tight junction proteins ZO-1 and occluding in Caco-2 cells. In conclusion, this study demonstrates that baicalein ameliorates colitis by improving intestinal epithelial barrier via AhR/IL-22 pathway in ILC3s, thus providing a potential therapy for UC.

The involvement of CYP1A2 in biodegradation of dioxins in pigs

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is one of the most harmful chemicals showing resistance to biodegradation. The majority of TCDD effects is mediated by the aryl hydrocarbon receptor (AhR) pathway. TCDD binding to AhR results in the activation of cytochrome P450 enzymes (CYP1A1, CYP1A2, CYP1B1) involved in dioxin biodegradation. The goal of the study was to explore the potentialrole of CYP1A2 in the metabolism of TCDD. We investigated a molecular structure of CYP1A2 and the binding selectivity and affinity between the pig CYP1A2 and: 1/ DiCDD or TCDD (dioxins differing in toxicity and biodegradability) or 2/ their selected metabolites. pCYP1A2 demonstrated higher affinity towards DiCDD and TCDD than other pCYP1 enzymes. All dioxin-pCYP1A2 complexes were found to be stabilized by hydrophobic interactions. The calculated distances between the heme oxygen and the dioxin carbon nearest to the oxygen, reflecting the hydroxylating potential of CYP1A2, were higher than in other pCYP1 enzymes. The distances between the heme iron and the nearest dioxin carbon exceeded 5 Å, a distance sufficient to allow the metabolites to leave the active site. However, the molecular dynamics simulations revealed that two access channels of CYP1A2 were closed upon binding the majority of the examined dioxins. Moreover, the binding of dioxin metabolites did not promote opening of channel S–an exit for hydroxylated products. It appears that the undesired changes in the behavior of access channels prevail over the hydroxylating potential of CYP1A2 towards TCDD and the favorable distances, ultimately trapping the metabolites at the enzyme’s active site.

Dioxin-like polychlorinated biphenyl 126 (PCB126) disrupts gut microbiota-host metabolic dysfunction in mice via aryl hydrocarbon receptor activation

Exposure to environmental pollutants, including dioxin-like pollutants, can cause numerous health issues. A common exposure route to pollutants is through contaminated foods, and thus the gastrointestinal system and gut microbiota are often exposed to high amounts of pollutants. Multiple studies have focused on the imbalance in intestinal microbiota composition caused by dioxin-like pollutants. Here, we examined the effects of polychlorinated biphenyl 126 (PCB126) on the composition and functions of gut microbes through metagenomic sequencing, and explored the correlations between microflora dysbiosis and aryl hydrocarbon receptor (AHR) signaling. Adult male wild-type and Ahr^-/- mice with a C57BL/6 background were weekly exposed to 50 μg/kg body weight of PCB126 for 8 weeks. Results showed that PCB126 had the opposite effect on gut microbiota composition and diversity in the wild-type and Ahr^-/- mice. Functional prediction found that PCB126 exposure mainly altered carbon metabolism and signal regulatory pathways in wild-type mice but impacted DNA replication and lipopolysaccharide biosynthesis in Ahr^-/- mice. In wild-type mice, PCB126 exposure induced liver injury, decreased serum lipid content, and delayed gastrointestinal motility, which were significantly correlated to several specific bacterial taxa, such as Helicobacter. Following AHR knockout, however, the holistic effects of PCB126 on the host were lessened or abolished. These results suggest that PCB126 may disrupt host metabolism and gut microbiota dynamics via AHR activation. Overall, our findings provide new insight into the complex interactions between host metabolism and gut microbiota, which may contribute to grouped assessment of environmental pollutants in the future.

Dietary intakes of dioxins and polychlorobiphenyls (PCBs) and breast cancer risk in 9 European countries

BACKGROUND

Dioxins and polychlorobiphenyls (PCBs) are persistent organic pollutants that have demonstrated endocrine disrupting properties. Several of these chemicals are carcinogenic and positive associations have been suggested with breast cancer risk. In general population, diet represents the main source of exposure.

METHODS

Associations between dietary intake of 17 dioxins and 35 PCBs and breast cancer were evaluated in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort from nine European countries using multivariable Cox regressions. The present study included 318,607 women (mean ± SD age: 50.7 ± 9.7) with 13,241 incident invasive breast cancers and a median follow-up of 14.9 years (IQR = 13.5-16.4). Dietary intake of dioxins and PCBs was assessed combining EPIC food consumption data with food contamination data provided by the European Food Safety Authority.

RESULTS

Exposure to dioxins, dioxins + Dioxin-Like-PCBs, Dioxin-Like-PCBs (DL-PCBs), and Non-Dioxin-Like-PCBs (NDL-PCBs) estimated from reported dietary intakes were not associated with breast cancer incidence, with the following hazard ratios (HRs) and 95% confidence intervals for an increment of 1 SD: HRdioxins = 1.00 (0.98 to 1.02), HRdioxins+DL-PCB = 1.01 (0.98 to 1.03), HRDL-PCB = 1.01 (0.98 to 1.03), and HRNDL-PCB = 1.01 (0.99 to 1.03). Results remained unchanged when analyzing intakes as quintile groups, as well as when analyses were run separately per country, or separating breast cancer cases based on estrogen receptor status or after further adjustments on main contributing food groups to PCBs and dioxins intake and nutritional factors.

CONCLUSIONS

This large European prospective study does not support the hypothesis of an association between dietary intake of dioxins and PCBs and breast cancer risk.

Aryl Hydrocarbon Receptor-Dependent and -Independent Pathways Mediate Curcumin Anti-Aging Effects

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor whose activity can be modulated by polyphenols, such as curcumin. AhR and curcumin have evolutionarily conserved effects on aging. Here, we investigated whether and how the AhR mediates the anti-aging effects of curcumin across species. Using a combination of in vivo, in vitro, and in silico analyses, we demonstrated that curcumin has AhR-dependent or -independent effects in a context-specific manner. We found that in Caenorhabditis elegans, AhR mediates curcumin-induced lifespan extension, most likely through a ligand-independent inhibitory mechanism related to its antioxidant activity. Curcumin also showed AhR-independent anti-aging activities, such as protection against aggregation-prone proteins and oxidative stress in C. elegans and promotion of the migratory capacity of human primary endothelial cells. These AhR-independent effects are largely mediated by the Nrf2/SKN-1 pathway.

Decabromodiphenyl ether induces ROS-mediated intestinal toxicity through the Keap1-Nrf2 pathway

Polybrominated diphenyl ethers (PBDEs) are widely used brominated flame retardants as commercial products. PBDEs have been demonstrated to induce hepatic, reproductive, neural, and thyroid toxicity effects. This study aimed to clarify the potential intestinal toxicity effects of decabrominated diphenyl ether (PBDE-209) in vivo and in vitro. First, we investigated the change of PBDE-209 on oxidative stress in the intestine of mice. Subsequently, the potential toxicity mechanism of PBDE-209 in vitro was investigated. Caco-2 cells were treated with different concentrations of PBDE-209 (1, 5, and 25 μmol/L) for 24  and 48 h. We determined the cell viability, reactive oxygen species (ROS) level, multiple cellular parameters, and relative mRNA expressions. The results showed that PBDE-209 significantly injured the colon of mice, increased the intestinal levels of malondialdehyde (MDA), and changed the antioxidant enzyme activities. PBDE-209 inhibited the proliferation and induced cytotoxicity of Caco-2 cells. The change in ROS production and mitochondrial membrane potential (MMP) revealed that PBDE-209 caused oxidative stress in Caco-2 cells. The real-time PCR assays revealed that PBDE-209 inhibited the mRNA expression level of antioxidative defense factor, nuclear factor erythroid 2-related factor 2 (Nrf2). Furthermore, the FAS and Cytochrome P450 1A1 (CYP1A1) mRNA expression levels were increased in Caco-2 cells. These results suggested that PBDE-209 exerts intestinal toxicity effects in vivo and in vitro and inhibits the antioxidative defense gene expression in Caco-2 cells. This study provides an opportunity to advance the understanding of toxicity by the persistent environmental pollutant PBDE-209 to the intestine.

Gestational and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin primes cortical microglia to tissue injury

Recent studies have shown that the aryl hydrocarbon receptor (AhR) is expressed in the brain's native immune cells, known as microglia. However, while the impact of exposure to AhR ligands is well studied in the peripheral immune system, the impact of such exposure on immune function in the brain is less well defined. Microglia serve dual roles in providing synaptic and immunological support for neighboring neurons and in mediating responses to environmental stimuli, including exposure to environmental chemicals. Because of their dual roles in regulating physiological and pathological processes, cortical microglia are well positioned to translate toxic stimuli into defects in cortical function via aberrant synaptic and immunological functioning, mediated either through direct microglial AhR activation or in response to AhR activation in neighboring cells. Here, we use gene expression studies, histology, and two-photon in vivo imaging to investigate how developmental exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a high-affinity and persistent AhR agonist, modulates microglial characteristics and function in the intact brain. Whole cortical RT-qPCR analysis and RNA-sequencing of isolated microglia revealed that gestational and lactational TCDD exposure produced subtle, but durable, changes in microglia transcripts. Histological examination and two-photon in vivo imaging revealed that while microglia density, distribution, morphology, and motility were unaffected by TCDD exposure, exposure resulted in microglia that responded more robustly to focal tissue injury. However, this effect was rectified with depletion and repopulation of microglia. These results suggest that gestational and lactational exposure to AhR ligands can result in long-term priming of microglia to produce heightened responses towards tissue injury which can be restored to normal function through microglial repopulation.

Brominated and chlorinated contaminants in food (PCDD/Fs, PCBs, PBDD/Fs PBDEs): Simultaneous determination and occurrence in Italian produce

Validated methodology for the simultaneous determination of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) and polybrominated diphenyl ethers (PBDEs) in foods of animal origin is presented. Method performance indicators were equivalent or better than those required for the control of EU regulated (EU, 2017/644) PCDD/F and PCB congeners in these foods, and for risk assessment through dietary intake. The method uses a high (>90%) proportion of ¹³Carbon-labelled surrogates for internal standardisation combined with high resolution mass spectrometry that allow accurate quantitation, and this was confirmed by multiple successful participations in proficiency testing for PCDD/Fs, PCBs and PBDEs in food. The same validation and method performance requirements as used for PCDD/Fs were followed for PBDD/Fs. The analysis of a range of food samples (eggs, milk, fish, shellfish, pork, beef and poultry), showed the occurrence of all four classes of contaminants at varying concentration ranges. In general, PCBs were the most prominent contaminant, both, in terms of dioxin-like toxicity, as well as in the occurrence of non-dioxin-like congeners, an observation that concurs with those made in other studies on Italian foods. The levels of PCDD/F and PCB occurrence are consistent with a gradual decline in contamination as reported by some other similar studies. Although all the determined contaminants were detected in the sampled foods, there was poor correlation between the occurrences of the brominated and chlorinated contaminants, and between PBDEs and PBDD/Fs, but better associations were observed between the occurrences of the chlorinated contaminants.

TCDD Inhibition of IgG1 Production in Experimental Autoimmune Encephalomyelitis (EAE) and In Vitro

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) is a ligand for the aryl hydrocarbon receptor (AhR). TCDD is well-characterized to produce immunotoxicity, including suppression of antibody production. Previously we showed that TCDD inhibited myelin oligodendrocyte glycoprotein (MOG) peptide-specific IgG and attenuated disease in experimental autoimmune encephalomyelitis (EAE) model in mice. Thus, the purpose of this study was to characterize the effects of TCDD on IgG subclasses in EAE and in vitro and assess effects in B cells derived from various tissues. TCDD modestly suppressed intracellular IgG expression in splenocytes (SPLC), but not bone marrow (BM) or lymph node (LN) cells. To further understand TCDD's effects on IgG, we utilized LPS and LPS + IL-4 in vitro to stimulate IgG3 and IgG1 production, respectively. TCDD preferentially suppressed IgG1+ cell surface expression, especially in SPLC. However, TCDD was able to suppress IgG1 and IgG3 secretion from SPLC and B cells, but not BM cells. Lastly, we revisited the EAE model and determined that TCDD suppressed MOG-specific IgG1 production. Together these data show that the IgG1 subclass of IgG is a sensitive target of suppression by TCDD. Part of the pathophysiology of EAE involves production of pathogenic antibodies that can recruit cytolytic cells to destroy MOG-expressing cells that comprise myelin, so inhibition of IgG1 likely contributes to TCDD's EAE disease attenuation.

PCDD/Fs and Dioxin-like PCBs in Chicken Eggs and Soils in Dong Nai Province, Southern Vietnam: Impacts of Raising Methods and Nearby Pollution Sources

Polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and dioxin-like PCBs (DL-PCBs) were examined in chicken egg and soil samples collected from Dong Nai Province, southern Vietnam. PCDD/F and DL-PCB levels in egg samples ranged from 5.74 to 1320 (median 350) and from 120 to 51,200 (median 1470) pg/g lipid weight (lw), respectively. Toxic equivalents to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TEQ) in egg samples ranged from 0.817 to 245 (median 10.8) pg TEQ/g lw. Higher dioxin levels were found in free-range eggs than non-free-range ones. We found significant correlation between TEQ levels in paired egg and soil samples collected from the Bien Hoa Airbase and some communities adjacent to industrial areas (Spearman's ρ = 0.671; p < 0.05), suggesting the co-occurrence of legacy and current dioxin emission sources in these areas.

Effects of Acute 2,3,7,8-Tetrachlorodibenzo-p-Dioxin Exposure on the Circulating and Cecal Metabolome Profile

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a polyhalogenated planar hydrocarbon belonging to a group of highly toxic and persistent environmental contaminants known as "dioxins". TCDD is an animal teratogen and carcinogen that is well characterized for causing immunosuppression through activation of aryl hydrocarbon receptor (AHR). In this study, we investigated the effect of exposure of mice to an acute dose of TCDD on the metabolic profile within the serum and cecal contents to better define the effects of TCDD on host physiology. Our findings demonstrated that within the circulating metabolome following acute TCDD exposure, there was significant dysregulation in the metabolism of bioactive lipids, amino acids, and carbohydrates when compared with the vehicle (VEH)-treated mice. These widespread changes in metabolite abundance were identified to regulate host immunity via modulating nuclear factor-kappa B (NF-κB) and extracellular signal-regulated protein kinase (ERK1/2) activity and work as biomarkers for a variety of organ injuries and dysfunctions that follow TCDD exposure. Within the cecal content of mice exposed to TCDD, we were able to detect changes in inflammatory markers that regulate NF-κB, markers of injury-related inflammation, and changes in lysine degradation, nicotinamide metabolism, and butanoate metabolism, which collectively suggested an immediate suppression of broad-scale metabolic processes in the gastrointestinal tract. Collectively, these results demonstrate that acute TCDD exposure results in immediate irregularities in the circulating and intestinal metabolome, which likely contribute to TCDD toxicity and can be used as biomarkers for the early detection of individual exposure.

Environmental profile, distributions and potential sources of halogenated polycyclic aromatic hydrocarbons

Halogenated polycyclic aromatic hydrocarbons (HPAHs) are high lipophilic and degradation-resistant, which have been detected in the air, water, sediment and biota. HPAHs tend to have strong adverse effects on animals and humans. Although we have realized HPAHs are emerging contaminants which needs to be paid attention, there is still a lack of their individual commercial standards. This makes it difficult for understanding HPAHs comprehensively. This review is devoted to collect all the results have reported, and give a systemic look of their global distributions, influence factors and sources. Compared with air, studies on other environmental matrices (water and sediment) are more limited. The researches on organisms are fewest. Comparing the studied congeners, there are more studies on ClPAHs than BrPAHs. Human activities contribute mostly to their occurrence. Further, we then also introduce the toxicity and analytical methods to better understand HPAHs. The future research directions are also provided. Through this review, we can conclude there is an urgent need to develop analysis methods and ecologic risk assessment for better exploring HPAHs. Effective methods should be done to control HPAHs. Therefore, this review can provide a good basis for researchers to understand and control global pollution.

Bone toxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the retinoid system: A causality analysis anchored in osteoblast gene expression and mouse data

Dioxin exposures impact on bone quality and osteoblast differentiation, as well as retinoic acid metabolism and signaling. In this study we analyzed associations between increased circulating retinol concentrations and altered bone mineral density in a mouse model following oral exposure to 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD). Additionally, effects of TCDD on differentiation marker genes and genes involved with retinoic acid metabolism were analysed in an osteoblast cell model followed by benchmark dose-response analyses of the gene expression data. Study results show that the increased trabecular and decreased cortical bone mineral density in the mouse model following TCDD exposure are associated with increased circulating retinol concentrations. Also, TCDD disrupted the expression of genes involved in osteoblast differentiation and retinoic acid synthesis, degradation, and nuclear translocation in directions compatible with increasing cellular retinoic acid levels. Further evaluation of the obtained results in relation to previously published data by the use of mode-of-action and weight-of-evidence inspired analytical approaches strengthened the evidence that TCDD-induced bone and retinoid system changes are causally related and compatible with an endocrine disruption mode of action.

Aryl Hydrocarbon Receptor and Its Diverse Ligands and Functions: An Exposome Receptor

The aryl hydrocarbon receptor (AhR) is a transcriptional factor that regulates multiple functions following its activation by a variety of ligands, including xenobiotics, natural products, microbiome metabolites, and endogenous molecules. Because of this diversity, the AhR constitutes an exposome receptor. One of its main functions is to regulate several lines of defense against chemical insults and bacterial infections. Indeed, in addition to its well-established detoxication function, it has several functions at physiological barriers, and it plays a critical role in immunomodulation. The AhR is also involved in the development of several organs and their homeostatic maintenance. Its activity depends on the type of ligand and on the time frame of the receptor activation, which can be either sustained or transient, leading in some cases to opposite modes of regulations as illustrated in the regulation of different cancer pathways. The development of selective modulators and their pharmacological characterization are important areas of research. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Transcriptional profiling of Chinese hamster ovary (CHO) cells exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a man-made chemical compound contaminating the environment. An exposure of organisms to TCDD results in numerous disorders. The main mechanism of TCDD action involves the induction of the aryl hydrocarbon receptor (AhR) pathway followed by the increase in the expression and activity of cytochrome P450 family 1 (CYP1) enzymes. The main aim of the present study was to identify, by means of RNA sequencing, transcripts involved in the mechanism of TCDD action in Chinese hamster ovary (CHO) cells, known to not express CYP1A1 enzyme. The CHO cells were treated with TCDD for 3, 12 or 24 h, and total RNA was isolated and sequenced. Thirty six (p_adjusted < 0.05) or six (p_adjusted < 0.05, log2FC ≥ 1.0/log2FC≤-1.0) differentially expressed genes (DEGs) were identified in TCDD-treated cells depending on the assumed statistical criteria. The dioxin up- and downregulated the expression of genes associated with ovarian follicle functions, development, cardiovascular system, signal transduction, inflammation and carcinogenesis. TCDD did not affect the expression of any of 522 miRNAs which were identified in the cells. The expression of CYP1A1, CYP1A2 and CYP1B1 was demonstrated neither in control nor in TCDD-treated CHO cells, although the respective genes were found in the cell genome. Twenty two other CYP enzymes were identified in CHO cells, however their expression was also not affected by TCDD.

Amino Acid Trp: The Far Out Impacts of Host and Commensal Tryptophan Metabolism

Tryptophan (Trp) is an essential amino acid primarily derived from the diet for use by the host for protein synthesis. The intestinal tract is lined with cells, both host and microbial, that uptake and metabolize Trp to also generate important signaling molecules. Serotonin (5-HT), kynurenine and its downstream metabolites, and to a lesser extent other neurotransmitters are generated by the host to signal onto host receptors and elicit physiological effects. 5-HT production by neurons in the CNS regulates sleep, mood, and appetite; 5-HT production in the intestinal tract by enterochromaffin cells regulates gastric motility and inflammation in the periphery. Kynurenine can signal onto the aryl hydrocarbon receptor (AHR) to elicit pleiotropic responses from several cell types including epithelial and immune cells, or can be further metabolized into bioactive molecules to influence neurodegenerative disease. There is a remarkable amount of cross-talk with the microbiome with regard to tryptophan metabolites as well. The gut microbiome can regulate the production of host tryptophan metabolites and can use dietary or recycled trp to generate bioactive metabolites themselves. Trp derivatives like indole are able to signal onto xenobiotic receptors, including AHR, to elicit tolerogenic effects. Here, we review studies that demonstrate that tryptophan represents a key intra-kingdom signaling molecule.

Twenty-year trends and exposure assessment of polychlorinated dibenzodioxins and dibenzofurans in human serum from the Seoul citizens

This study investigated polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs) in air (n = 108) and human serum (n = 1802) samples collected over 20 years to evaluate the long-term exposure to PCDD/Fs and health effects on the Korean general population. The serum PCDD/F levels were higher in males than in females and were significantly correlated with age, body mass index, and manifestation of diabetes mellitus. From 2000 to 2019, the PCDD/F levels declined by 96% in the air, but only by 36% in the serum, because PCDD/Fs are relatively stable in the human body and are exposed to humans after PCDD/Fs are distributed and migrated in various environmental matrices. The PCDD/F levels in other environmental matrices have also decreased at rates that differed among the matrices due to the different retention times and changes in continuous input of contaminants. As PCDD/Fs migrate from environmental matrices to the human body, the fraction of PCDDs increased whereas that of PCDFs decreased because of their relatively short half-lives. This study provides a concrete evidence that PCDD/F emissions by national regulations can achieve long-term reduction in human exposure. To the best of our knowledge, this is the longest and largest study to evaluate the long-term trends and annual changes of PCDD/Fs in the atmosphere and human serum, simultaneously.

Chloracne: a case series on cutaneous expression of CYP1A1 as diagnostic biomarker

Chloracne, also known as metabolizing acquired dioxin-induced skin hamartomas (MADISH), is a rare disfiguring disease related to dioxin exposure. There is a paucity of literature on the clinical manifestations and pathogenesis of chloracne/MADISH. The aim of this study was to assess the clinical features of this very unusual acneiform eruption and to explore the pathogenesis of the disease. This was a retrospective, observational report study was conducted on five patients belonging to the same nuclear family (father, mother and three children) and a relative (father's brother) living in the same house. Histopathological, immunohistochemical, laboratory and toxicological analyses were performed for all patients. The results suggest that CYP1A1 in human skin is a diagnostic biomarker in chloracne, and was positive for all the patients in our sample. Tetrachlorodibenzo-p-dioxin is the most investigated dioxin responsible for chloracne; however, several other agonists, whether dioxin-like or not, can activate the aryl hydrocarbon receptor. To our knowledge, this Italian case series is the first study to suggest polychlorinated biphenyls as a possible cause of an overstimulation of aryl hydrocarbons causing the consequent acneiform eruption.

AhR Ligands Modulate the Differentiation of Innate Lymphoid Cells and T Helper Cell Subsets That Control the Severity of a Pulmonary Fungal Infection

In agreement with other fungal infections, immunoprotection in pulmonary paracoccidioidomycosis (PCM) is mediated by Th1/Th17 cells whereas disease progression by prevalent Th2/Th9 immunity. Treg cells play a dual role, suppressing immunity but also controlling excessive tissue inflammation. Our recent studies have demonstrated that the enzyme indoleamine 2,3 dioxygenase (IDO) and the transcription factor aryl hydrocarbon receptor (AhR) play an important role in the immunoregulation of PCM. To further evaluate the immunomodulatory activity of AhR in this fungal infection, Paracoccidioides brasiliensis infected mice were treated with two different AhR agonists, L-Kynurenin (L-Kyn) or 6-formylindole [3,2-b] carbazole (FICZ), and one AhR specific antagonist (CH223191). The disease severity and immune response of treated and untreated mice were assessed 96 hours and 2 weeks after infection. Some similar effects on host response were shared by FICZ and L-Kyn, such as the reduced fungal loads, decreased numbers of CD11c+ lung myeloid cells expressing activation markers (IA, CD40, CD80, CD86), and early increased expression of IDO and AhR. In contrast, the AhR antagonist CH223191 induced increased fungal loads, increased number of pulmonary CD11c+ leukocytes expressing activation markers, and a reduction in AhR and IDO production. While FICZ treatment promoted large increases in ILC3, L-Kyn and CH223191 significantly reduced this cell population. Each of these AhR ligands induced a characteristic adaptive immunity. The large expansion of FICZ-induced myeloid, lymphoid, and plasmacytoid dendritic cells (DCs) led to the increased expansion of all CD4+ T cell subpopulations (Th1, Th2, Th17, Th22, and Treg), but with a clear predominance of Th17 and Th22 subsets. On the other hand, L-Kyn, that preferentially activated plasmacytoid DCs, reduced Th1/Th22 development but caused a robust expansion of Treg cells. The AhR antagonist CH223191 induced a preferential expansion of myeloid DCs, reduced the number of Th1, Th22, and Treg cells, but increased Th17 differentiation. In conclusion, the present study showed that the pathogen loads and the immune response in pulmonary PCM can be modulated by AhR ligands. However, further studies are needed to define the possible use of these compounds as adjuvant therapy for this fungal infection.

Role of aryl hydrocarbon receptor (AHR) in overall retinoid metabolism: Response comparisons to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure between wild-type and AHR knockout mice

Young adult wild-type and aryl hydrocarbon receptor knockout (AHRKO) mice of both sexes and the C57BL/6J background were exposed to 10 weekly oral doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; total dose of 200 μg/kg bw) to further characterize the observed impacts of AHR as well as TCDD on the retinoid system. Unexposed AHRKO mice harboured heavier kidneys, lighter livers and lower serum all-trans retinoic acid (ATRA) and retinol (REOH) concentrations than wild-type mice. Results from the present study also point to a role for the murine AHR in the control of circulating REOH and ATRA concentrations. In wild-type mice, TCDD elevated liver weight and reduced thymus weight, and drastically reduced the hepatic concentrations of 9-cis-4-oxo-13,14-dihydro-retinoic acid (CORA) and retinyl palmitate (REPA). In female wild-type mice, TCDD increased the hepatic concentration of ATRA as well as the renal and circulating REOH concentrations. Renal CORA concentrations were substantially diminished in wild-type male mice exclusively following TCDD-exposure, with a similar tendency in serum. In contrast, TCDD did not affect any of these toxicity or retinoid system parameters in AHRKO mice. Finally, a distinct sex difference occurred in kidney concentrations of all the analysed retinoid forms. Together, these results strengthen the evidence of a mandatory role of AHR in TCDD-induced retinoid disruption, and suggest that the previously reported accumulation of several retinoid forms in the liver of AHRKO mice is a line-specific phenomenon. Our data further support participation of AHR in the control of liver and kidney development in mice.

Plastic residues produced with confirmatory testing for COVID-19: Classification, quantification, fate, and impacts on human health

In March 2020, several international organizations started making recommendations regarding the need for prompt coronavirus-based diagnosis in order to prevent its spread among the world's population. The most widely used test for confirmation of COVID-19 is real-time PCR (RT-PCR). This technique uses plastic supplies in its procedures, which are 100% disposable to avoid cross-contamination and biological risks. The scientific community has become increasingly worried because of the environmental impacts associated with the current COVID-19 pandemic, such as medical plastic residues. We classified and estimated the amount of plastic residues generated as a consequence of COVID-19 diagnostic tests and analyzed the relationships of the plastics generated with number of confirmed cases, population size, and gross domestic product in each country. We evidenced that the RT-PCR generates 37.27 g of plastic residues per sample. All patients COVID-19 tested with RT-PCR have generated 15,439.59 tons of plastic residue worldwide, until August 2020. The plastic residues generated by the COVID-19 tests have no relation with size population or gross domestic product of the countries. There is also no relationship between the plastic residues generated by the COVID-19 tests and the confirmed cases. About 97% of the plastic residues from diagnostic tests for coronavirus are incinerated due to their hazardous nature to humans, but toxic chemicals are released into the environment during the process. In the short term, there is a need to reduce plastic waste and improve controls of gas emissions from incineration plants in countries where there is a deficit. In the long term, biodegradable biomedical manufacturing that are free of releasing toxic chemicals when they are incinerated, must be considered.

Bovine Holo-Beta-Lactoglobulin Cross-Protects Against Pollen Allergies in an Innate Manner in BALB/c Mice: Potential Model for the Farm Effect

The lipocalin beta-lactoglobulin (BLG) is a major protein compound in cow's milk, and we detected it in cattle stable dust. BLG may be a novel player in the farm protective effect against atopic sensitization and hayfever. In previous studies, we demonstrated that only the ligand-filled holo-form of BLG prevented sensitization to itself. Here, we investigated whether holo-BLG could, in an innate manner, also protect against allergic sensitization to unrelated birch pollen allergens using a murine model. BALB/c mice were nasally pretreated four times in biweekly intervals with holo-BLG containing quercetin-iron complexes as ligands, with empty apo-BLG, or were sham-treated. Subsequently, mice were intraperitoneally sensitized two times with apo-BLG or with the unrelated birch pollen allergen apo-Bet v 1, adjuvanted with aluminum hydroxide. After subsequent systemic challenge with BLG or Bet v 1, body temperature drop was monitored by anaphylaxis imaging. Specific antibodies in serum and cytokines of BLG- and Bet v 1-stimulated splenocytes were analyzed by ELISA. Additionally, human peripheral blood mononuclear cells of pollen allergic subjects were stimulated with apo- versus holo-BLG before assessment by FACS. Prophylactic treatment with the holo-BLG resulted in protection against allergic sensitization and clinical reactivity also to Bet v 1 in an unspecific manner. Pretreatment with holo-BLG resulted in significantly lower BLG-as well as Bet v 1-specific antibodies and impaired antigen-presentation with significantly lower numbers of CD11c+MHCII+ cells expressing CD86. Pretreatment with holo-BLG also reduced the release of Th2-associated cytokines from Splenocytes in BLG-sensitized mice. Similarly, in vitro stimulation of PBMCs from birch pollen allergic subjects with holo-BLG resulted in a relative decrease of CD3+CD4+ and CD4+CRTh2 cells, but not of CD4+CD25+CD127- Treg cells, compared to apo-BLG stimulation. In conclusion, prophylactic treatment with holo-BLG protected against allergy in an antigen-specific and -unspecific manner by decreasing antigen presentation, specific antibody production and abrogating a Th2-response. Holo-BLG therefore promotes immune resilience against pollen allergens in an innate manner and may thereby contribute to the farm protective effect against atopic sensitization.

Identification of viable TCDD access pathways to human AhR PAS-B ligand binding domain

Unintentionally released in the environment as by-products of industrial activities, dioxins, exemplified by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), represent a primary concern for human health. Exposure to these chemicals is known to produce a broad spectrum of adverse effects, including cancer. The main mechanism of action of TCDD in humans involves binding to the Aryl hydrocarbon Receptor (AhR). Although qualitatively established, TCDD capture by the AhR remains poorly characterized at the molecular level. Starting from a recently developed structural model of the human AhR PAS-B domain, in this work we attempt the identification of viable TCDD access pathways to the human AhR ligand binding domain by means of molecular dynamics. Based on the result of metadynamics simulations, we identify two main regions that may potentially serve as access paths for TCDD. For each path, we characterize the residues closely interacting with TCDD, thereby suggesting a possible mechanism for TCDD capture. Our results are reviewed and discussed in the light of the available information about Human AhR structure and functions.

Environmental behavior and safety of polyhalogenated carbazoles (PHCZs): A review

Polyhalogenated carbazoles (PHCZs) are well-known as emergent environmental contaminants. Given their wide distribution in the environment and structural similarity with dioxins and dioxin-like chemicals (DLCs), the environmental behavior and ecological risks of these chemicals have become the major issue concerned by the governments and scientists. Since the initial report of PHCZ residues in the environment in the 1980s, over 20 PHCZ congeners with different residual levels had been identified in various environmental media all over the world. Nevertheless, researches concerning the toxicological effects of PHCZs are of an urgent need for the relatively lagging study of their ecological risks. Currently, only limited evidence has indicated that PHCZs would pose dioxin-like toxicity, including developmental toxicity, cardiotoxicity, etc; and their toxicological effects were partially consistent with AhR activation. And yet, much remains to be done to fill in the knowledge gaps of their toxicological effects. In this review, the research progresses in environmental behavior and toxicology study of PHCZs were remarked; and the lack of current research, as well as future research prospects, were discussed.