The possible roles of environmental factors and the aryl hydrocarbon receptor in the prevalence of thyroid diseases in Vietnam era veterans

Polyphenol and glucosinolate-derived AhR modulators regulate GPR15 expression on human CD4+ T cells

Diets high in fruit and vegetables are perceived to be beneficial for intestinal homeostasis, in health as well as in the context of inflammatory bowel diseases (IBDs). Recent breakthroughs in the field of immunology have highlighted the importance of the ligand-activated transcription factor aryl hydrocarbon receptor (AhR) as a critical regulator of mucosal immunity, including the intestinal trafficking of CD4+ helper T cells, an immune cell subset implicated in a wide range of homeostatic and pathogenic processes. Specifically, the AhR has been shown to directly regulate the expression of the chemoattractant receptor G Protein-Coupled Receptor 15 (GPR15) on CD4+ T cells. GPR15 is an important gut homing marker whose expression on CD4+ T cells in the peripheral circulation is elevated in patients suffering from ulcerative colitis, raising the possibility that, in this setting, the beneficial effect of a diet rich in fruits and vegetables may be mediated through the modulation of GPR15 expression. To address this, we screened physiologically-relevant polyphenol and glucosinolate metabolites for their ability to affect both AhR activity and GPR15 expression. Our complementary approach and associated findings suggest that polyphenol and glucosinolate metabolites can regulate GPR15 expression on human CD4+ T cells in an AhR-dependent manner.

Human 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure and thyroid cancer risk

Thyroid cancer incidence has been steadily rising since the 1970s and exposure to environmental pollutants, including persistent organic pollutants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other dioxins, has emerged as a potential explanation for this increase. This study aimed to summarize available human studies on the association between TCDD exposure and thyroid cancer. A systematic review of the literature was performed searching the National Library of Medicine and National Institutes of Health PubMed, Embase, and Scopus databases, through January 2022, using the following keywords: "thyroid", "2,3,7,8-tetrachlorodibenzo-p-dioxin", "TCDD", "dioxin", and "Agent Orange". Six studies were included in this review. Three studies evaluated the acute exposure to the chemical factory accident in Seveso, Italy, and found a non-significant increase in the risk of thyroid cancer. Two studies investigating Agent Orange exposure among United States Vietnam War veterans found a significant risk of thyroid cancer following exposure. No association was found in one study evaluating TCDD exposure through herbicides. The current study highlights the limited information on the potential association between TCDD exposure and thyroid cancer and thus the need for future human studies, especially considering the persistent human exposure to dioxins in the environment.

Expanded assessment of xenobiotic associations with antinuclear antibodies in the United States, 1988-2012

BACKGROUND

The prevalence of autoimmunity in the U.S. has increased recently for undetermined reasons. Little is known about associations between autoimmunity and environmental causes.

OBJECTIVES

In a large representative sample of the U.S. population, we expanded our prior exploratory study of how exposures to selected xenobiotics and dioxin-like (DL) mixtures relate to antinuclear antibodies (ANA), the most common biomarker of autoimmunity.

METHODS

We analyzed cross-sectional data on 12,058 participants aged ≥ 12 years from three time periods of the National Health and Nutrition Examination Survey between 1988 and 2012, of whom 14% were ANA-positive. We used lognormal regression models and censored-data methods to estimate ANA associations with xenobiotic concentrations overall and in sex, age, and race/ethnicity subgroups. Our analyses adjusted for potential confounders and appropriately handled concentrations below detection limits.

RESULTS

Observed ANA associations were positive for most DL compounds and nonDL polychlorinated biphenyls (PCBs), negative for most phthalates, and mixed for other xenobiotic classes. After correcting for multiple comparisons, some associations remained statistically significant. In subgroup analyses, the most significant finding was a positive ANA association with N-acetyl-S-(2-hydroxy-3-butenyl)-L-cysteine (MHB2) in males, followed by positive associations with 2,2',3,5'-tetrachlorobiphenyl (PCB 44), 2,2',4,5'-tetrachlorobiphenyl (PCB 49), and 2,2',3,4',5',6-hexachlorobiphenyl (PCB 149) in 12-19 year-olds, and with 3,4,4',5-tetrachlorobiphenyl (PCB 81), 2,2',3,3',4,4',5,5',6-nonachlorobiphenyl (PCB 206), and N-acetyl-S-(phenyl)-L-cysteine (PMA) in Mexican Americans. Negative associations were found with mono-benzyl phthalate (MBzP) in 20-49 year-olds and mono-n-butyl phthalate (MnBP) in 12-19 year-olds. In overall analyses, combining stratum-specific results across race/ethnicity strata revealed a positive ANA association with PCB 81 and a negative ANA association with N-acetyl-S-(2-hydroxyethyl)-L-cysteine (HEMA).

DISCUSSION

This study identified potential associations between ANA and various xenobiotics. Further investigation to confirm these observations and elucidate effects of certain xenobiotics on immune regulation could have important mechanistic, preventive, and treatment implications for a variety of immune-mediated disorders.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced suppression of immunity in THP-1-derived macrophages and the possible mechanisms

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known immunotoxic environmental pollutant. However, most immunotoxicology studies of TCDD were based on the animal models and the inner mechanisms have just focused on a few genes/proteins. In this study, the immune functions of THP-1-derived macrophages was measured with in-vitro bioassays after 24-h exposure of TCDD including environmentally relevant concentrations. RNA-seq and Weighted Gene Co-expression Network Analysis were used to characterize the immunotoxicity molecular mechanisms. Our study is the first report on the TCDD-induced effects of cell adhesion, morphology, and multiple cytokines/chemokines production on THP-1 macrophages. After TCDD treatment, we observed an inhibited cell adherence, probably attributed to the suppressed mRNA levels of adhesion molecules ICAM-1, VCAM-1 and CD11b, and a decrease in cell pseudopodia and expression of F-actin. The inflammatory cytokines TNF-α, IL-10 and other 8 cytokines/chemokines regulating granulocytes/T cells and angiogenesis were disrupted by TCDD. Alternative splicing event was found to be a sensitive target for TCDD. Using WGCNA, we identified 10 hub genes (TNF, SRC, FGF2, PTGS2, CDH2, GNG11, BDNF, WNT5A, CXCR5 and RUNX2) highly relevant to these observed phenotypes, suggesting AhR less important in the effects TCDD have on THP-1 macrophages than in other cells. Our findings broaden the understanding of TCDD immunotoxicity on macrophages and provide new potential targets for clarifying the molecular mechanisms.

Practical Approach To Explore the Effects of Polyphenols on Aryl Hydrocarbon Receptor Regulated Immune Function

The ligand-activated aryl hydrocarbon receptor (AhR) is an important molecular regulator of immune function, whose activity can be modulated by dietary glucosinolate- and tryptophan-derived metabolites. In contrast, the potential use of polyphenols as dietary regulators of AhR-dependent immunity remains unclear. In this perspective, we discuss how cellular metabolism may alter the net effect of polyphenols on AhR, thus potentially reconciling some of the conflicting observations reported in the literature. We further provide a methodological roadmap, across the fields of immunology, metabolomics, and gut microbial ecology, to explore the potential effects of polyphenol-rich diets on AhR-regulated immune function in humans.

Transgenerational disease specific epigenetic sperm biomarkers after ancestral exposure to dioxin

Dioxin was historically one of the most common industrial contaminants with several major industry accidents, as well as governmental actions involving military service, having exposed large numbers of the worldwide population over the past century. Previous rat studies have demonstrated the ability of dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)) exposure to promote the epigenetic transgenerational inheritance of disease susceptibility in subsequent generations. The types of disease previously observed include puberty abnormalities, testis, ovary, kidney, prostate and obesity pathologies. The current study was designed to use an epigenome-wide association study (EWAS) to identify potential sperm DNA methylation biomarkers for specific transgenerational diseases. Therefore, the transgenerational F3 generation dioxin lineage male rats with and without a specific disease were compared to identify differential DNA methylation regions (DMRs) as biomarkers for disease. The genomic features of the disease-specific DMRs were characterized. Observations demonstrate that disease-specific epimutation DMRs exist for the transgenerational dioxin lineage rats that can potentially be used as epigenetic biomarkers for testis, kidney, prostate and obesity diseases. These disease-specific DMRs were associated with genes that have previously been shown to be linked with the specific diseases. This EWAS for transgenerational disease identified potential epigenetic biomarkers and provides the proof of concept of the potential to develop similar biomarkers for humans to diagnose disease susceptibilities and facilitate preventative medicine.

Endocrine disruptors and thyroid autoimmunity

Many papers evaluated the effect of the environmental, or occupational endocrine disruptors (ED), on the thyroid gland, that can lead to thyroid autoimmunity. A higher prevalence of autoimmune thyroid diseases (AITD) was observed in people living in polluted areas near to petrochemical plants, and in petrochemical workers, but also in area contaminated with organochlorine pesticides, or with polychlorinated biphenyls, or near aluminum foundries. The exposure to Hg in chloralkali workers, or in swordfish consumers has been also found to increase AITD prevalence. Vanadium has been shown to increase the inflammatory response of thyrocytes. A beneficial effect of omega-3 fatty acids, and of myo-inositol and selenomethionine have been shown to counteract the appearance of AITD in subjects exposed to environmental or occupational ED. More large studies are needed to investigate the potential roles of ED in the induction of AITD, and of agents or habits that are able to prevent them.

Graves' disease: Epidemiology, genetic and environmental risk factors and viruses

Graves' disease (GD) is the most common cause of hyperthyroidism in developed Countries. It is more common between 30 and 60 years; 5-10 times more frequent in women. The genetic predisposition accounts for 79% of the risk for GD, while environmental factors for 21%. About 70% of genes associated with autoimmune thyroid disorders (AITD) are implicated in T-cell function. Among GD endogenous factors, estrogens, X-inactivation and microchimerism are important. Among environmental risk factors, smoking, iodine excess, selenium and vitamin D deficiency, and the occupational exposure to Agent Orange have been associated with GD. Many studies showed that HCV is associated with thyroid autoimmunity and hypothyroidism, in patients with chronic HCV hepatitis (CHC); a significant link has been shown also between HCV-related mixed cryoglobulinemia and risk for GD. Moreover, IFN-α-treated CHC patients develop GD more frequently. Novel studies are needed about possible risk factors to reduce the occurence of GD in West Countries.

HIGH PREVALENCE OF AGENT ORANGE EXPOSURE AMONG THYROID CANCER PATIENTS IN THE NATIONAL VA HEALTHCARE SYSTEM

OBJECTIVE

Thyroid cancer is the most common endocrine malignancy and the most rapidly increasing cancer in the U.S. Little is known regarding the epidemiology and characteristics of patients with thyroid cancer within the national Veterans Health Administration (VHA) integrated healthcare system. The aim of this study was to further understand the characteristics of thyroid cancer patients in the VHA population, particularly in relation to Agent Orange exposure.

METHODS

This is a descriptive analysis of the VA (Veterans Affairs) Corporate Data Warehouse database from all U.S. VHA healthcare sites from October1, 1999, to December 31, 2013. Information was extracted for all thyroid cancer patients based on International Classification of Diseases-ninth revision diagnosis codes; histologic subtypes of thyroid cancer were not available.

RESULTS

There were 19,592 patients (86% men, 76% white, 58% married, 42% Vietnam-era Veteran) in the VHA system with a diagnosis of thyroid cancer within this 14-year study period. The gender-stratified prevalence rates of thyroid cancer among the Veteran population during the study period were 1:1,114 (women) and 1:1,023 (men), which were lower for women but similar for men, when compared to the U.S. general population in 2011 (1:350 for women and 1:1,219 for men). There was a significantly higher proportion of self-reported Agent Orange exposure among thyroid cancer patients (10.0%), compared to the general VHA population (6.2%) (P<.0001).

CONCLUSION

Thyroid cancer patients, in this sample, have a higher prevalence of self-reported Agent Orange exposure compared to the overall national VA patient population.

ABBREVIATIONS

T4 = thyroxine TCDD = 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin TSH = thyroid-stimulating hormone VA = Veterans Affairs VHA = Veterans Health Administration.

Thyroid nodules and thyroid autoimmunity in the context of environmental pollution

Evidence suggests that in most industrialized countries autoimmune disorders, including chronic lymphocytic thyroiditis, are increasing. This increase parallels the one regarding differentiated thyroid cancer, the increment of which is mainly due to the papillary histotype. A number of studies have pointed to an association between chronic lymphocytic thyroiditis and differentiated thyroid cancer. The upward trend of these two thyroid diseases is sustained by certain environmental factors, such as polluting substances acting as endocrine disrupting chemicals. Herein we will review the experimental and clinical literature that highlights the effects of environmental and occupational exposure to polluting chemicals in the development of autoimmune thyroid disease or differentiated thyroid cancer. Stakeholders, starting from policymarkers, should become more sensitive to the consequences for the thyroid resulting from exposure to EDC. Indeed, the economic burden resulting from such consequences has not been quantified thus far.

A high frequency of circulating th22 and th17 cells in patients with new onset graves' disease

T-helper (Th) 22 and Th17 cells are involved in the pathogenesis of autoimmune diseases. However, their roles in the pathogenesis of Graves'disease (GD) are unclear. This study is aimed at examining the frequency of peripheral blood Th22, Th17, and Th1 cells and the levels of plasma IL-22, IL-17, and IFN-γ in patients with GD. A total of 27 patients with new onset GD and 27 gender- and age-matched healthy controls (HC) were examined for the frequency of peripheral blood Th22, Th17, and IFN-γ cells by flow cytometry. The concentrations of plasma IL-22, IL-17, and IFN-γ were examined by enzyme-linked immunosorbent assay. The levels of serum TSHR antibodies (A-TSHR), free triiodothyronine (FT3), free thyroxine (FT4), and thyroid stimulating hormone (TSH) were examined by radioimmunoassay and chemiluminescent assay, respectively. The levels of serum TSAb were examined by enzyme-linked immunosorbent assay. In comparison with those in the HC, significantly elevated percentages of Th22 and Th17 cells, but not Th1 cells, and increased levels of plasma IL-22 and IL-17, but not IFN-γ, were detected in GD patients (P<0.0001, for both). The percentages of both Th22 and Th17 cells and the levels of plasma IL-22 and IL-17 were correlated positively with the levels of serum TSAb in GD patients (r = 0.7944, P<0.0001; r = 0.8110, P<0.0001; r = 0.7101, p<0.0001; r = 0.7407, p<0.0001, respectively). Th22 and Th17 cells may contribute to the pathogenesis of GD.

Deletion or activation of the aryl hydrocarbon receptor alters adult hippocampal neurogenesis and contextual fear memory

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the toxicity of dioxin and serves multiple developmental roles. In the adult brain, while we now localize AhR mRNA to nestin-expressing neural progenitor cells in the dentate gyrus (DG) of the hippocampus, its function is unknown. This study tested the hypothesis that AhR participates in hippocampal neurogenesis and associated functions. AhR deletion and activation by the potent environmental toxicant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), adversely impacted neurogenesis and cognition. Adult AhR-deficient mice exhibited impaired hippocampal-dependent contextual fear memory while hippocampal-independent memory remained intact. AhR-deficient mice displayed reduced cell birth, decreased cell survival, and diminished neuronal differentiation in the DG. Following TCDD exposure, wild-type mice exhibited impaired hippocampal-dependent contextual memory, decreased cell birth, reduced neuronal differentiation, and fewer mature neurons in the DG. Glial differentiation and apoptosis were not altered in either TCDD-exposed or AhR-deficient mice. Finally, defects observed in TCDD-exposed mice were dependent on AhR, as TCDD had no negative effects in AhR-deficient mice. Our findings suggest that AhR should be further evaluated as a potential transcriptional regulator of hippocampal neurogenesis and function, although other sites of action may also warrant consideration. Moreover, TCDD exposure should be considered as an environmental risk factor that disrupts adult neurogenesis and potentially related memory processes.

Dioxin (TCDD) induces epigenetic transgenerational inheritance of adult onset disease and sperm epimutations

Environmental compounds can promote epigenetic transgenerational inheritance of adult-onset disease in subsequent generations following ancestral exposure during fetal gonadal sex determination. The current study examined the ability of dioxin (2,3,7,8-tetrachlorodibenzo[p]dioxin, TCDD) to promote epigenetic transgenerational inheritance of disease and DNA methylation epimutations in sperm. Gestating F0 generation females were exposed to dioxin during fetal day 8 to 14 and adult-onset disease was evaluated in F1 and F3 generation rats. The incidences of total disease and multiple disease increased in F1 and F3 generations. Prostate disease, ovarian primordial follicle loss and polycystic ovary disease were increased in F1 generation dioxin lineage. Kidney disease in males, pubertal abnormalities in females, ovarian primordial follicle loss and polycystic ovary disease were increased in F3 generation dioxin lineage animals. Analysis of the F3 generation sperm epigenome identified 50 differentially DNA methylated regions (DMR) in gene promoters. These DMR provide potential epigenetic biomarkers for transgenerational disease and ancestral environmental exposures. Observations demonstrate dioxin exposure of a gestating female promotes epigenetic transgenerational inheritance of adult onset disease and sperm epimutations.