Chemical contamination and the thyroid

Ultrahigh-Performance Fiber-Supported Iron-Based Ionic Liquid for Synthesizing 3,4-Dihydropyrimidin-2-(1H)-ones in a Cleaner Manner

Herein, a fiber-supported iron-based ionic liquid as a type of fibrous catalyst has been developed for the synthesis of bioactive 3,4-dihydropyrimidin-2-(1H)-ones (DHPMs) via three-component Biginelli reactions in a cleaner manner. The described fibrous catalyst was obtained from the commercially available polyetheretherketone (PEEK) fiber by postfunctionalization processes and was characterized and analyzed in detail by means of diversified technologies. Furthermore, the fiber-supported iron-based ionic liquids could mediate the classical three-component Biginelli reactions to proceed smoothly to gain a variety of substituted DHPMs with yields of up to 99%. The superior catalytic activities of the fibrous catalyst were ascribed to the quasi-homogeneous medium by ionic liquids generated in the surface layer of the PEEK fiber, which could afford an appropriate reaction zone and could further be available for the aggregation of substrates to facilitate the three-component reaction. Notably, the fibrous catalyst is available for recycling over 10 runs just by a pair of tweezers, and the operational procedure was capable of enlarging the catalytic system to the gram-scale without any performance degradation, which provided a cleaner manner to take advantage of the iron-based catalyst in organic synthesis with potential industrialization prospects.

In silico bioavailability triggers applied to direct and indirect thyroid hormone disruptors

Among endocrine disruption, interference with the thyroid hormone (TH) regulation is of increasing concern. Respective compounds encode through their structural features both the potential for TH disruption, and the bioavailability mitigating the toxicological effect. The aim of this study is to provide a substructure-based screening-level QSAR (quantitative structure-activity relationship) that discriminates bioavailable TH disruptors from not bioavailable counterparts, covering both direct and indirect (retinoid- and AhR-mediated) modes of action. The QSAR has been derived from literature data for 1642 compounds, and takes into account Lipinski's rule-of-five and the brain/blood partition coefficient Kbrain/blood. For its validation, an external test set of 145 substances has been used. For 1787 compounds meeting the model application domain, the model yields only one false negative. The discussion addresses the mechanistic meaning of the bioavailability triggers molecular weight, H-bond donor and acceptor, hydrophobicity (log Kow), and the physicochemical properties underlying log Kbrain/blood. The model may serve as bioavailability-screening step within a decision support system for the predictive assessment of chemicals regarding their potential to disrupt thyroid hormone function in a direct or indirect manner.

Human exposure to a mixture of endocrine disruptors and serum levels of thyroid hormones: A cross-sectional study

Exposure to endocrine disruptors (EDCs) could disrupt thyroid hormone homeostasis. However, human epidemiological studies reported inconsistent observations, and scarce information on the effect of a mixture of chemicals. The aim of the present study was to examine the associations of multiple chemicals with thyroid hormones among adults from China. We measured serum levels of thyroid hormones and urinary levels of 11 EDCs, including six phthalate metabolites, bisphenol A (BPA), bisphenol F (BPF), bisphenol S (BPS), perchlorate, and thiocyanate among 177 healthy adults without occupational exposure. Associations of multiple urinary analytes with serum thyroid hormones were examined by performing general linear regression analysis and bayesian kernal machine regression analysis. These EDCs were detected in almost all samples. After adjusting for various covariates, we observed only BPF significantly associated with total thyroxin (TT4) (β=-0.27, 95% confidence interval (CI) [-0.41, -0.14]), total triiodothyronine (TT3) (β=-0.02 95% CI [-0.03, -0.01]), free T4 (fT4) (β=-0.02, 95% CI [-0.03, -0.01]), and free T3 (fT3) (β=-0.04, 95% CI [-0.07, -0.01]), and mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) and monoethyl phthalate (MEP) positively associated with TT4 (β=0.24, 95% CI [0.01, 0.48]) and fT4 (β=0.02, 95% CI [0.01, 0.04]), respectively. Moreover, we observed significant dose-response relationships between TT4 and the mixture of 11 EDCs, and BPF was the main contributor to the mixture effect, suggesting the priority of potential effect of BPF on disrupting thyroid function under a real scenario of human exposure to multiple EDCs. Our findings supported the hypothesis that human exposure to low levels of EDCs could alter thyroid hormones homeostasis among non-occupational healthy adults.

Associations between repeated measurements of urinary polycyclic aromatic hydrocarbon metabolites and thyroid hormones among reproductive-aged men

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs) have been shown to disrupt thyroid function in toxicological studies, but epidemiological evidence is inconsistent. Furthermore, little is known on potential effects of mixtures of PAHs.

OBJECTIVE

This study aimed to examine the associations of exposure to PAHs as individual chemicals and mixtures with thyroid hormones.

METHODS

We included 378 men from a Reproductive Medicine Center in Wuhan, China. Ten monohydroxylated PAH (OH-PAH) metabolites in repeated urine specimens collected at two-time points and three thyroid hormones [thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3)] in one serum sample were measured. Multivariable linear regression models were applied to assess the associations between individual OH-PAH metabolites and thyroid hormones, and the associations with mixtures of OH-PAH metabolites were assessed by Bayesian kernel machine regression (BKMR) models.

RESULTS

Multivariable linear regression models showed inverse associations between urinary 1-OHNa and TSH, between urinary 1-OHPh and 9-OHPh and FT3, as well as between urinary 2-OHPh, 3-OHPh, 9-OHPh and ∑OHPh and FT4, regardless of these individual OH-PAH metabolites modeled as continuous or tertile variables (e.g., -21.57 % in TSH; 95 % CI: -35.33 %, -4.88 % for the third vs first tertiles of 1-OHNa; p for trend = 0.014). BKMR models showed negative overall effects of all urinary OH-PAH metabolite mixtures on TSH, FT3, and FT4, and 1-OHNa, 9-OHPh, and 2-OHPh as the most important contributors, respectively, with linear inverse exposure-response associations when holding other OH-PAH metabolites at their median concentrations.

CONCLUSION

Urinary OH-PAH metabolites as individual chemicals and mixtures were adversely associated with thyroid hormones among reproductive-aged men.

Endocrine adverse effects of mono(2-ethylhexyl) phthalate and monobutyl phthalate in male pubertal rats

Considering that research of adverse effects of mono(2-ethylhexyl) phthalate (MEHP) and monobutyl phthalate (MBP), two key metabolites of the most common phthalates used as plasticisers in various daily-life products, has been scattered and limited, the aim of our study was to provide a more comprehensive analysis by focusing on major organ systems, including blood, liver, kidney, and pancreas in 66 male pubertal rats randomised into eleven groups of six. The animals were receiving either metabolite at doses of 25, 50, 100, 200, or 400 mg/kg bw a day by gavage for 28 days. The control group was receiving corn oil. At the end of the experiment, blood samples were collected for biochemical, haematological, and immunological analyses. Samples of kidney, liver, and pancreas were dissected for histopathological analyses. Exposure to either compound resulted in increased liver and decreased pancreas weight, especially at the highest doses. Exposed rats had increased ALT, AST, glucose, and triglyceride levels and decreased total protein and albumin levels. Both compounds increased MCV and decreased haemoglobin levels compared to control. Although they also lowered the insulin level, exposed rats had negative islet cell and insulin antibodies, same as control. Treatment-related histopathological changes included sinusoidal degeneration in the liver, glomerular degeneration in the kidney, and degeneration of pancreatic islets. Our findings document toxic outcomes of MEHP and MBP on endocrine organs in male pubertal rats but also suggest the need for additional studies to better understand the mechanisms behind adverse effects in chronic exposure.

South American National Contributions to Knowledge of the Effects of Endocrine Disrupting Chemicals in Wild Animals: Current and Future Directions

Human pressure due to industrial and agricultural development has resulted in a biodiversity crisis. Environmental pollution is one of its drivers, including contamination of wildlife by chemicals emitted into the air, soil, and water. Chemicals released into the environment, even at low concentrations, may pose a negative effect on organisms. These chemicals might modify the synthesis, metabolism, and mode of action of hormones. This can lead to failures in reproduction, growth, and development of organisms potentially impacting their fitness. In this review, we focused on assessing the current knowledge on concentrations and possible effects of endocrine disruptor chemicals (metals, persistent organic pollutants, and others) in studies performed in South America, with findings at reproductive and thyroid levels. Our literature search revealed that most studies have focused on measuring the concentrations of compounds that act as endocrine disruptors in animals at the systemic level. However, few studies have evaluated the effects at a reproductive level, while information at thyroid disorders is scarce. Most studies have been conducted in fish by researchers from Brazil, Argentina, Chile, and Colombia. Comparison of results across studies is difficult due to the lack of standardization of units in the reported data. Future studies should prioritize research on emergent contaminants, evaluate effects on native species and the use of current available methods such as the OMICs. Additionally, there is a primary focus on organisms related to aquatic environments, and those inhabiting terrestrial environments are scarce or nonexistent. Finally, we highlight a lack of funding at a national level in the reviewed topic that may influence the observed low scientific productivity in several countries, which is often negatively associated with their percentage of protected areas.

Iodine as a potential endocrine disruptor-a role of oxidative stress

PURPOSE

Iodine is an essential micronutrient required for thyroid hormone biosynthesis. However, overtreatment with iodine can unfavorably affect thyroid physiology. The aim of this review is to present the evidence that iodine-when in excess-can interfere with thyroid hormone synthesis and, therefore, can act as a potential endocrine-disrupting chemical (EDC), and that this action, as well as other abnormalities in the thyroid, occurs-at least partially-via oxidative stress.

METHODS

We reviewed published studies on iodine as a potential EDC, with particular emphasis on the phenomenon of oxidative stress.

RESULTS

This paper summarizes current knowledge on iodine excess in the context of its properties as an EDC and its effects on oxidative processes.

CONCLUSION

Iodine does fulfill the criteria of an EDC because it is an exogenous chemical that interferes-when in excess-with thyroid hormone synthesis. However, this statement cannot change general rules regarding iodine supply, which means that iodine deficiency should be still eliminated worldwide and, at the same time, iodine excess should be avoided. Universal awareness that iodine is a potential EDC would make consumers more careful regarding their diet and what they supplement in tablets, and-what is of great importance-it would make caregivers choose iodine-containing medications (or other chemicals) more prudently. It should be stressed that compared to iodine deficiency, iodine in excess (acting either as a potential EDC or via other mechanisms) is much less harmful in such a sense that it affects only a small percentage of sensitive individuals, whereas the former affects whole populations; therefore, it causes endemic consequences.

Network Toxicology Guided Mechanism Study on the Association between Thyroid Function and Exposures to Polychlorinated Biphenyls Mixture

Polychlorinated biphenyls (PCBs) are persistent and highly toxic pollutants, which can accumulate in organisms and produce toxic effects, especially damaging the function of thyroid hormones. So far, the molecular mechanism of PCBs mixture and their metabolites interfering with thyroid hormones has not been studied thoroughly except for individual compounds. In this study, PubMed, Web of Science, and STITCH databases were used to search PCBs and their corresponding target proteins. The intersection of PCBs and thyroid hormone dysfunction target proteins was obtained from GeneCards. The “compounds-targets-pathways” network was constructed by Cytoscape software. And KEGG and Go analyses were performed for key targets. Finally, molecular docking was used to verify the binding effect. Four major active components, five key targets, and 10 kernel pathways were successfully screened by constructing the network. Functional enrichment analysis showed that the interference was mediated by cancer, proteoglycans, PI3K-Akt, thyroid hormone, and FoxO signaling pathways. The molecular docking results showed that the binding energies were less than -5 kcal·mol-1. PCBs and their metabolites may act on the key targets of MAPK3, MAPK1, RXRA, PIK3R1, and TP53. The toxic effect of sulfated and methyl sulfone PCBs is greater. The method of screening targets based on the simultaneous action of multiple PCBs can provide a reference for other research. The targets were not found in previous metabolite toxicity studies. It also provides a bridge for the toxic effects and experimental research of PCBs and their metabolites in the future.

Short-Term Exposure Effects of the Environmental Endocrine Disruptor Benzo(a)Pyrene on Thyroid Axis Function in Zebrafish

Benzo(a)Pyrene (BaP) is one of the most widespread polycyclic aromatic hydrocarbons (PAHs) with endocrine disrupting properties and carcinogenic effects. In the present study, we tested the effect of BaP on thyroid development and function, using zebrafish as a model system. Zebrafish embryos were treated with 50 nM BaP from 2.5 to 72 h post fertilization (hpf) and compared to 1.2% DMSO controls. The expression profiles of markers of thyroid primordium specification, thyroid hormone (TH) synthesis, hypothalamus-pituitary-thyroid (HPT) axis, TH transport and metabolism, and TH action were analyzed in pools of treated and control embryos at different developmental stages. BaP treatment did not affect early markers of thyroid differentiation but resulted in a significant decrease of markers of TH synthesis (tg and nis) likely secondary to defective expression of the central stimulatory hormones of thyroid axis (trh, tshba) and of TH metabolism (dio2). Consequently, immunofluorescence of BaP treated larvae showed a low number of follicles immunoreactive to T4. In conclusion, our results revealed that the short-term exposure to BaP significantly affects thyroid function in zebrafish, but the primary toxic effects would be exerted at the hypothalamic-pituitary level thus creating a model of central hypothyroidism.

Perchlorate, nitrate, and thiocyanate: Environmental relevant NIS-inhibitors pollutants and their impact on thyroid function and human health

Thyroid disruptors are found in food, atmosphere, soil, and water. These contaminants interfere with the thyroid function through the impairment of thyroid hormone synthesis, plasma transport, peripheral metabolism, transport into the target cells, and thyroid hormone action. It is well known that iodide uptake mediated by the sodium-iodide symporter (NIS) is the first limiting step involved in thyroid hormones production. Therefore, it has been described that several thyroid disruptors interfere with the thyroid function through the regulation of NIS expression and/or activity. Perchlorate, nitrate, and thiocyanate competitively inhibit the NIS-mediated iodide uptake. These contaminants are mainly found in food, water and in the smoke of cigarettes. Although the impact of the human exposure to these anions is highly controversial, some studies indicated their deleterious effects in the thyroid function, especially in individuals living in iodine deficient areas. Considering the critical role of thyroid function and the production of thyroid hormones for growth, metabolism, and development, this review summarizes the impact of the exposure to these NIS-inhibitors on thyroid function and their consequences for human health.

Effects of chronic exposure to nonylphenol at environmental concentration on thyroid function and thyroid hyperplasia disease in male rats

The aim of this work was to determine whether chronic exposure to nonylphenol (NP), a representative substance of environmental endocrine disruptors (EEDs), at environmental concentration would have toxic effects on thyroid function and thyroid hyperplasia disease. Two hundred SPF Sprague-Dawley rats were divided into five groups (n = 40 per group): blank control group (corn oil), low-dose NP exposure group (0.4 mg/kg/d), medium-dose NP exposure group (4 mg/kg/d), high-dose NP exposure group (40 mg/kg/d), and estradiol control group (E₂: 30 μg/kg/d). The rats were treated by gavage for 34 weeks, which were sampled twice (17 weeks and 34 weeks respectively). NP accumulation in the thyroid tissue (F = 52.93, P < 0.001) and serum (F = 5.54, P = 0.00) continuously increased in a significant dose-effect relationship. After NP exposure, the serum FT3 levels exhibited a dose-dependent increasing trend (F = 4.68, P = 0.01), while the serum FT4 level showed an opposite trend (F = 3.93, P= 0.01). Compared with the control group, hyperechoic areas (i.e., calcification points) were observed in the high-dose group. Follicular epithelial stratification was extremely severe, the monolayer cubic epithelial cells became flat, and the area of single follicles was even smaller in the high-dose group. In the high-dose NP group, there were numerous mitochondria that were severely swollen. The rough endoplasmic reticulum was abundant, with obvious expansion and vesiculation. The relative expression of ERα (F = 5.29, P = 0.00), ERβ (F = 10.17, P = 0.00), TRα (F = 7.71, P = 0.00), TRβ (F = 3.52.17, P = 0.02) and HMGB1 (F = 10.16, P = 0.01) proteins in the thyroid tissue in each NP exposure group was increased compared with the control group, and the relative expression of proteins increased if the exposure time was prolonged under the same exposure dose. Chronic exposure to NP at environmental concentration could have toxic effects on thyroid function, and induce thyroid hyperplasia disease in male rats.

Mediation effects of thyroid function in the associations between phthalate exposure and glucose metabolism in adults

The mediating influence of thyroid function on the association of phthalate exposure with glucose metabolism, including insulin resistance, remains unclear. We explored the mediating influence of thyroid hormone levels on the phthalate exposure-insulin resistance association. This cross-sectional study of 217 Taiwanese adults assessed insulin resistance (Homeostatic Model Assessment for Insulin Resistance, HOMA-IR scores) and the levels of 11 urinary phthalate metabolites and 5 thyroid hormones. Multiple regression models were used to analyze the associations among serum thyroid hormone levels, urinary phthalate metabolite levels, and HOMA-IR scores. The mediation analysis assessed the influence of thyroid function on the phthalate exposure-HOMA-IR association. Our data indicated urinary mono-ethylhexyl phthalate (MEHP) levels was negatively associated with free thyroxine (T₄) (β = -0.018; 95% confidence interval [CI]: -0.031, -0.005) and positively associated with HOMA-IR scores (β = 0.051, 95% CI: 0.012, 0.090). The study also revealed urinary mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) levels was negatively associated with free T₄ (β = -0.036, 95% CI: -0.056, -0.017) and HOMA-IR (β = 0.070, 95% CI: 0.013, 0.126). Free T₄ and HOMA-IR had a negative association (β = -0.757, 95% CI: -1.122, -0.392). In the mediation analysis, free T₄ mediated 24% and 35% of the associations of urinary MEHP and MEOHP with HOMA-IR, respectively. Our findings revealed the mediating role of thyroid function in the phthalate exposure-glucose metabolism association in adults.

Cross-species physiological interactions of endocrine disrupting chemicals with the circadian clock

Endocrine disrupting chemicals (EDCs) are endocrine-active chemical pollutants that disrupt reproductive, neuroendocrine, cardiovascular and metabolic health across species. The circadian clock is a transcriptional oscillator responsible for entraining 24-hour rhythms of physiology, behavior and metabolism. Extensive bidirectional cross talk exists between circadian and endocrine systems and circadian rhythmicity is present at all levels of endocrine control, from synthesis and release of hormones, to sensitivity of target tissues to hormone action. In mammals, a range of hormones directly alter clock gene expression and circadian physiology via nuclear receptor (NR) binding and subsequent genomic action, modulating physiological processes such as nutrient and energy metabolism, stress response, reproductive physiology and circadian behavioral rhythms. The potential for EDCs to perturb circadian clocks or circadian-driven physiology is not well characterized. For this reason, we explore evidence for parallel endocrine and circadian disruption following EDC exposure across species. In the reviewed studies, EDCs dysregulated core clock and circadian rhythm network gene expression in brain and peripheral organs, and altered circadian reproductive, behavioral and metabolic rhythms. Circadian impacts occurred in parallel to endocrine and metabolic alterations such as impaired fertility and dysregulated metabolic and energetic homeostasis. Further research is warranted to understand the nature of interaction between circadian and endocrine systems in mediating physiological effects of EDC exposure at environmental levels.

The Association of Myo-Inositol and Selenium Contrasts Cadmium-Induced Thyroid C Cell Hyperplasia and Hypertrophy in Mice

Previous studies have demonstrated that, in addition to inducing structural changes in thyroid follicles, cadmium (Cd) increased the number of C cells. We examined the effects of myo-inositol (MI), seleno-L-methionine (Se), MI + Se, and resveratrol on C cells of mice exposed to cadmium chloride (Cd Cl2), as no data are currently available on the possible protective effects of these molecules. In contrast, we have previously shown this protective effect against CdCl2 on the thyroid follicles of mice. Ninety-eight C57 BL/6J adult male mice were divided into 14 groups of seven mice each: (i) 0.9% NaCl (vehicle; 1 ml/kg/day i.p.); (ii) Se (0.2 mg/kg/day per os); (iii) Se (0.4 mg/kg/day per os); (iv) MI (360 mg/kg/day per os); (v) Se (0.2 mg/kg/day) + MI; (vi) Se (0.4 mg/kg/day) + MI; (vii) resveratrol (20 mg/kg); (viii) CdCl2 (2 mg/kg/day i.p.) + vehicle; (ix) CdCl2 + Se (0.2 mg/kg/day); (x) CdCl2 + Se (0.4 mg/kg/day); (xi) CdCl2 + MI; (xii) CdCl2 + Se (0.2 mg/kg/day) + MI; (xiii) CdCl2 + Se (0.4 mg/kg/day) + MI; (xiv) CdCl2 + resveratrol (20 mg/kg). After 14 days, thyroids were processed for histological, immunohistochemical, and morphometric evaluation. Compared to vehicle, Cd significantly decreased follicle mean diameter, increased CT-positive cells number, area and cytoplasmic density, and caused the disappearance of TUNEL-positive C cells, namely, the disappearance of C cells undergoing apoptosis. Se at either 0.2 or 0.4 mg/kg/day failed to significantly increase follicular mean diameter, mildly decreased CT-positive cells number, area and cytoplasmic density, and was ineffective on TUNEL-positive C cells. Instead, MI alone increased significantly follicular mean diameter and TUNEL-positive cells number, and decreased significantly CT-positive cells number, area and cytoplasmic density. MI + Se 0.2 mg/kg/day or MI + Se 0.4 mg/kg/day administration improved all five indices more markedly. Indeed, follicular mean diameter and TUNEL-positive cells number increased significantly, while CT-positive cells number, area and cytoplasmic density decreased significantly. Thus, all five indices overlapped those observed in vehicle-treated mice. Resveratrol improved significantly all the considered parameters, with a magnitude comparable to that of MI alone. In conclusion, the association Myo + Se is effective in protecting the mouse thyroid from the Cd-induced hyperplasia and hypertrophy of C cells. This benefit adds to that exerted by Myo + Se on thyrocytes and testis.

Proteomic Profiles of Thyroid Gland and Gene Expression of the Hypothalamic-Pituitary-Thyroid Axis Are Modulated by Exposure to AgNPs during Prepubertal Rat Stages

Silver nanoparticles (AgNPs) have potent antimicrobial activity and, for this reason, are incorporated into a variety of products, raising concern about their potential risks and impacts on human health and the environment. The developmental period is highly dependent on thyroid hormones (THs), and puberty is a sensitive period, where changes in the hormonal environment may have permanent effects. We evaluated the hypothalamic-pituitary (HP)-thyroid axis after exposure to low doses of AgNPs using a validated protocol to assess pubertal development and thyroid function in immature male rats. For stimulatory events of the HP-thyroid axis, we observed an increase in the expression of Trh mRNA and serum triiodothyronine. Negative feedback reduced the hypothalamic expression of Dio2 mRNA and increased the expression of Thra1, Thra2, and Thrb2 mRNAs. In the pituitary, there was a reduced expression of Mct-8 mRNA and Dio2 mRNA. For peripheral T3-target tissues, a reduced expression of Mct-8 mRNA was observed in the heart and liver. An increased expression of Dio3 mRNA was observed in the heart and liver, and an increased expression of Thrb2 mRNA was observed in the liver. The quantitative proteomic profile of the thyroid gland indicated a reduction in cytoskeletal proteins (Cap1, Cav1, Lasp1, Marcks, and Tpm4; 1.875 μg AgNP/kg) and a reduction in the profile of chaperones (Hsp90aa1, Hsp90ab1, Hspa8, Hspa9, P4hb) and proteins that participate in the N-glycosylation process (Ddost, Rpn1 and Rpn2) (15 μg AgNP/kg). Exposure to low doses of AgNPs during the window of puberty development affects the regulation of the HP-thyroid axis with further consequences in thyroid gland physiology.

Low Doses of Methylmercury Induce the Proliferation of Thyroid Cells In Vitro Through Modulation of ERK Pathway

Exposure to environmental endocrine disruptors has been associated with an increased frequency of thyroid pathology. In this study, we evaluated the effects of various concentrations of methylmercury (MeHg) on immortalized, non-tumorigenic thyroid cells (Nthy-ori-3-1). Exposure to MeHg at 2.5 and 5 µM for 24 h caused a reduction in cell viability with a decrease of the cell population in sub-G0 phase, as detected by MTT and flow cytometry. Conversely, MeHg at the lower concentration of 0.1 µM increased the cell viability with a rise of G2/M phase. An immunoblot analysis showed higher expression levels of phospho-ERK and not of phospho-Akt. Further enhancement of the cell growth rate was observed after a prolonged exposure of the cells up to 18 days to MeHg 0.1 µM. The present findings demonstrate the toxicity of high concentrations of MeHg on thyroid cells, while showing that treatment with lower doses of Hg, as may occur after prolonged exposure to this environmental contaminant, exerts a promoting effect on thyroid cell proliferation, by acting on the ERK-mediated pro-oncogenic signal transduction pathway.

Exposure to Bisphenol A Analogs and the Thyroid Function and Volume in Women of Reproductive Age-Cross-Sectional Study

Bisphenols (BPs) are commonly known plastifiers that are widely used in industry. The knowledge about the impact of BPs on thyroid function is scarce. Proper thyroid functioning is especially important for women of reproductive age, as hypothyroidism affects fertility, pregnancy outcomes and the offspring. There are no studies analyzing the influence of BPs on thyroid function and volume in non-pregnant young women. The aim of this cross-sectional study was to evaluate the relationship between bisphenol A and its 10 analogs (BPS, BPC, BPE, BPF, BPG, BPM, BPP, BPZ, BPFL, and BPBP) on thyroid function and volume in women of reproductive age. Inclusion criteria were: female sex, age 18-40 years. Exclusion criteria were history of any thyroid disease, pharmacotherapy influencing thyroid function, pregnancy or puerperium, and diagnosis of autoimmune thyroid disease during this study. Venous blood was drawn for measurement of thyrotropin (TSH), free thyroxine, thyroid peroxidase antibodies, thyroglobulin antibodies, BPs. Urine samples were analyzed for: ioduria and BPs. Ultrasound examination of thyroid gland was performed. One hundred eighty participants were included into the study. A negative correlation was found between urine BPC and the thyroid volume (R = -0.258; p = 0.0005). Patients with detected urine BPC presented smaller thyroid glands than those with not-detected urine BPC (p = 0.0008). A positive correlation was found between TSH and urine BPC (R = 0.228; p = 0.002). Patients with detected urine BPC presented higher concentrations of TSH versus those with not-detected urine BPC (p = 0.003). There were no relationships between any of serum BPs as well as the other urine BPs and thyroid function and its volume. The only BP that demonstrated the relationship between thyroid function and its volume was BPC, probably because of its chemical structure that most resembles thyroxine. Exposure to this BP may result in the development of hypothyroidism that could have a negative impact on pregnancy and the offspring.

Developmental Thyroid Hormone Insufficiency Induces a Cortical Brain Malformation and Learning Impairments: A Cross-Fostering Study

Thyroid hormones (THs) are essential for brain development, but few rodent models exist that link TH inefficiency to apical neurodevelopmental endpoints. We have previously described a structural anomaly, a heterotopia, in the brains of rats treated in utero with propylthiouracil (PTU). However, how the timing of an exposure relates to this birth defect is unknown. This study seeks to understand how various temporal treatments of the mother relates to TH insufficiency and adverse neurodevelopment of the offspring. Pregnant rats were exposed to PTU (0 or 3 ppm) through the drinking water from gestational day 6 until postnatal day (PN) 14. On PN2 a subset of pups was cross-fostered to a dam of the opposite treatment, to create 4 conditions: pups exposed to PTU prenatally, postnatally, during both periods, or not at all (control). Both PTU and TH concentrations were characterized in the mother and offspring over time, to capture the dynamics of a developmental xenobiotic exposure. Brains of offspring were examined for heterotopia presence and severity, and adult littermates were assessed for memory impairments. Heterotopia were observed under conditions of prenatal exposure, and its severity increased in animals in the most prolonged exposure group. This malformation was also permanent, but not sex biased. In contrast, behavioral impairments were limited to males, and only in animals exposed to PTU during both the gestational and postnatal periods. This suggests a distinct TH-dependent etiology for both phenotypes, and illustrates how timing of hypothyroxinemia can induce abnormal brain structure and function.

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

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

Association of in utero exposure to organochlorine pesticides with thyroid hormone levels in cord blood of newborns

Organochlorine pesticides (OCPs) had been widely used in agriculture and disease prevention from the 1940s-1960s. Currently, OCPs are raising global concerns due to their associated prevalent contamination and adverse health effects, such as endocrine disruption. Several epidemiological studies have explored the underlying association of OCPs on thyroid hormone (TH) status in adults and newborns, but the results of studies performed on newborns are often inconclusive. This exploratory study was conducted with the purpose of assessing the potential association of the prenatal exposure to OCPs with the concentrations of TH in the cord blood of newborns from China. Cord blood and information on demographic characteristics were collected from 115 newborns between November 2013 and June 2014. The exposure levels of 17 OCPs were measured with a gas chromatography/mass spectrometry, and TH levels including free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) were detected using electrochemiluminescence immunoassay methods. After adjusting for confounding factors (the age of pregnant mothers, education level, monthly household income, parity, and sex of the newborns), we found marginally significant inverse associations of cord plasma measurements of ∑hexachlorcyclohexanes (∑HCHs), 1,1-dichloro-2,2-di(4-chlorophenyl)ethylene (ρ,ρ'-DDE) and methoxychlor with FT4 levels, but not with FT3 and TSH levels. Moreover, higher cord plasma levels of aldrin, dieldrin, ∑dichlorodiphenyltrichloroethanes (∑DDTs), ∑Drins, and ∑OCPs were found to be related to the increase in cord plasma TSH levels after the adjustment for confounders. The results of this exploratory study indicate that in utero exposure to certain OCPs may affect TH status in newborns, and therefore, pose potential effects on early human development. Further research, with larger sample sizes, should be conducted to confirm these findings.

Thyroid Disrupting Chemicals

Endocrine disruptor compounds are exogenous agents able to interfere with a gland function, exerting their action across different functional passages, from the synthesis to the metabolism and binding to receptors of the hormone produced. Several issues, such as different levels and time of exposure and different action across different ages as well as gender, make the study of endocrine disruptors still a challenge. The thyroid is very sensitive to the action of disruptors, and considering the importance of a correct thyroid function for physical and cognitive functioning, addressing this topic should be considered a priority. In this review, we examined the most recent studies, many of them concentrating on maternal and child exposure, conducted to assess the impact of industrial chemicals which showed an influence on thyroid function. So far, the number of studies conducted on that topic is not sufficient to provide solid conclusions and lead to homogeneous guidelines. The lack of uniformity is certainly due to differences in areas and populations examined, the different conditions of exposures and the remarkable inter-subject variability. Nonetheless, the European Commission for Health and Food Safety is implementing recommendations to ensure that substances identified as endocrine disruptors will be withdrawn from the market.

Increased risk for hypothyroidism after anticholinesterase pesticide poisoning: a nationwide population-based study

PURPOSE

Previous animal studies have reported that acute anticholinesterase pesticide (organophosphate and carbamate) poisoning may affect thyroid hormones. However, there is no human study investigating the association between hypothyroidism and anticholinesterase pesticide poisoning, and therefore, we conducted a retrospective nationwide population-based cohort study to delineate this issue.

METHODS

We identified 10,372 anticholinesterase pesticide poisoning subjects and matched 31,116 non-anticholinesterase pesticide poisoning subjects between 2003 and 2012 from the Nationwide Poisoning Database and the Longitudinal Health Insurance Database 2000, respectively, in a 1:3 ratio by index date, age, and sex for this study. We compared the cumulative incidence of hypothyroidism between the two cohorts by following up until 2013. Independent predictors for hypothyroidism were also investigated.

RESULTS

In total, 75 (0.72%) anticholinesterase pesticide poisoning subjects and 184 (0.59%) non-anticholinesterase pesticide poisoning subjects were diagnosed with hypothyroidism during the follow-up. Cox proportional hazard regression analysis showed that anticholinesterase pesticide poisoning subjects had higher risk for hypothyroidism than did non-anticholinesterase pesticide poisoning subjects (adjusted hazard ratio: 1.47, 95% confidence interval: 1.11-1.95) after adjusting for age, sex, hypertension, malignancy, liver disease, renal disease, atrial fibrillation or flutter, thyroiditis, goiter, other endocrine disorders, and mental disorder. Stratified analysis showed that anticholinesterase pesticide poisoning subjects had higher risk for hypothyroidism than did non-anticholinesterase pesticide poisoning subjects in terms of the age subgroup of 40-64 years, female sex, past history of goiter, follow-up of <1 month, and anticholinesterase pesticide poisoning subjects without atropine treatment (incidence rate ratio [IRR]: 1.66, 95% confidence interval: 1.20-2.30). Female sex, malignancy, renal disease, thyroiditis, goiter, mental disorder, and anticholinesterase pesticide poisoning without atropine treatment were independent predictors for hypothyroidism.

CONCLUSIONS

Anticholinesterase pesticide poisoning is associated with increased risk for hypothyroidism. Early evaluation of thyroid function in anticholinesterase pesticide poisoning subjects is suggested, especially in subjects without atropine treatment, aged 40-64 years, female sex, and past history of goiter.

The influence of phthalates and bisphenol A on the obesity development and glucose metabolism disorders

The prevalence of obesity and type 2 diabetes mellitus epidemics presents a great health problem worldwide. Beside the changes in diet and decreased physical activity, there is growing interest in endocrine disrupting chemicals that may have effects on these conditions. Among them, the role of certain phthalates and bisphenol A is confirmed. We have summarized the existing literature on this issue including cross-sectional, follow up epidemiological studies and in vivo and in vitro studies. Most data support the effects of bisphenol A and some phthalates, such as di-2-ethyl-hexyl phthalate, diethyl phthalate, dibuthyl phthalate, dimethyl phthalate, dibenzyl phthalate, diisononyl phthalate and others on the development obesity and type 2 diabetes mellitus. These endocrine disrupting chemicals interfere with different cell signaling pathways involved in weight and glucose homeostasis. Since the data are rather inconsistent, there is a need for new, well-designed prospective studies.

Cancer incidence among capacitor manufacturing workers exposed to polychlorinated biphenyls

BACKGROUND

We evaluated cancer incidence in a cohort of polychlorinated biphenyl (PCB) exposed workers.

METHODS

Incident cancers, identified using state registries, were compared to those in a national population using standardized incidence ratios. Trends in prostate cancer incidence with cumulative PCB exposure were evaluated using standardized rate ratios and Cox regression models. For selected sites, cumulative PCB exposure was compared between aggressive (fatal/distant stage) and localized/regional cancers.

RESULTS

We identified 3,371 invasive first primary cancer diagnoses among 21,317 eligible workers through 2007. Overall relative incidence was reduced. Elevations were only observed for respiratory cancers and among women, urinary organ cancers. Among men, prostate cancer incidence was reduced and not associated with cumulative PCB exposure although median exposures were significantly higher for aggressive compared to localized/regional prostate cancers.

CONCLUSION

Previously observed associations between cumulative PCB exposure and prostate cancer mortality were not confirmed in this analysis; prostate cancer stage at diagnosis may explain the discrepancy. Am. J. Ind. Med. 60:198-207, 2017. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Relative developmental toxicity of short-chain chlorinated paraffins in Zebrafish (Danio rerio) embryos

Short-chain chlorinated paraffins (SCCPs) are ubiquitous in the environment and might cause adverse environmental and human health effects. Little is known about the relative toxicity of different SCCP compounds especially during development. The objective of this study was to characterize and compare effects of seven SCCP groups at environmentally relevant levels, using a zebrafish (Danio rerio) model. Observations on malformation, survival rates at 96 h post fertilization (hpf), and hatching rates at 72 hpf indicated that the C_10- groups (C₁₀H₁₈Cl₄, 1,2,5,6,9,10-C₁₀H₁₆Cl₆ and C₁₀H₁₅Cl₇) were more toxic than the C_12- groups (C₁₂H₂₂Cl₄, C₁₂H₁₉Cl₇ and 1,1,1,3,10,12,12,12-C₁₂H₁₈Cl₈) and Cereclor 63L. The C_10- groups were also more potent than C_12- groups and Cereclor 63L in decreasing thyroid hormone levels. Among the three compounds within the C_10- group, the compounds with less chlorine content had stronger effects on sub-lethal malformations but less effects on triiodothyronine (T3) and tetraiodothyronine (T4). Only C₁₀H₁₈Cl₄ significantly decreased the mRNA expression of tyr, ttr, dio2 and dio3 at a dose-dependent manner suggesting that the specific mode of actions differ with different congeners. The mechanisms of disruption of thyroid status by different SCCPs could be different. C₁₀H₁₈Cl₄ might inhibit T3 production through the inhibition effect on dio2. These results indicate that SCCP exposure could alter gene expression in the hypothalamic-pituitary-thyroid (HPT) axis and thyroid hormone levels. The mechanisms of disruption of thyroid status by different SCCPs could be different. Our results on the relative developmental toxicities of SCCPs will be useful to reach a better understanding of SCCP toxicity supporting environmental risk evaluation and regulation and used as a guidance for environmental monitoring of SCCPs in the future.

Advances in TRH signaling

The activity of the hypothalamus-pituitary-thyroid axis (HPT) is coordinated by hypophysiotropic thyrotropin releasing hormone (TRH) neurons present in the paraventricular nucleus of the hypothalamus. Hypophysiotropic TRH neurons act as energy sensors. TRH controls the synthesis and release of thyrotropin, which activates the synthesis and secretion of thyroid hormones; in target tissues, transporters and deiodinases control their local availability. Thyroid hormones regulate many functions, including energy homeostasis. This review discusses recent evidence that covers several aspects of TRH role in HPT axis regulation. Knowledge about the mechanisms of TRH signaling has steadily increased. New transcription factors engaged in TRH gene expression have been identified, and advances made on how they interact with signaling pathways and define the dynamics of TRH neurons response to acute and/or long-term influences. Albeit yet incomplete, the relationship of TRH neurons activity with positive energy balance has emerged. The importance of tanycytes as a central relay for the feedback control of the axis, as well as for HPT responses to alterations in energy balance, and other stimuli has been reinforced. Finally, some studies have started to shed light on the interference of prenatal and postnatal stress and nutrition on HPT axis programing, which have confirmed the axis susceptibility to early insults.

Assessment of synergistic thyroid disrupting effects of a mixture of EDCs in ovariectomized rats using factorial analysis and dose addition

Endocrine disrupting chemicals (EDCs) have been implicated in a broad spectrum of health problems related to reproduction, thyroid function, neurodevelopment, and metabolism. In many cases, EDCs in the environment are at extremely low concentrations which rarely induce health problems alone, however, a mixture of these EDCs may interact and induce potential additive and synergistic effects. Many mixture studies on EDCs were conducted in terms of high doses with the direct effect addition method, which didn't comply with the dose-response relationship of toxicants in the "S" or "U" shaped curves. In the present study, the thyroid disrupting effects of a mixture of three EDCs, propylthiouracil (PTU), polychlorinated biphenyls (PCBs), and ammonium perchlorate (AP), were measured in an ovariectomized rat model. Sixty female SD rats were ovariectomized bilaterally and randomly assigned to ovariectomization (OVX) control, PTU + PCBs, PTU + AP, PCBs + AP and PTU + PCBs + AP groups treated with doses at lowest observed adverse effect levels (LOAELs) or benchmark dose lower limits (BMDLs) obtained from our previous dose-response relationship studies. OVX control animals were treated with vehicle control while all other animals were treated with different combinations of EDCs by gavage for 8 days. The body weight change, serum total thyroxine (tT₄), triiodothyroxine (tT₃), the thyroid/body weight ratio, and thyroid histopathological endpoints were measured and analyzed using factorial analysis and dose addition. All EDC treated groups showed a marked change compared to vehicle control in serum tT₄, the thyroid/body weight ratio, and the thyroid epithelium/colloid ratio. Both factorial analysis and dose addition analysis showed a synergistic effect on thyroid function by PTU, PCBs and AP together, but the modes of interaction varied when either two were mixed at LOAELs. To conclude, a mixture of PTU, PCBs, and AP mainly acted synergistically on thyroid function and induced a significant health effect.

Environmental Contaminants and Pancreatic Beta-Cells

Despite health policies as well as clinical and research efforts, diabetes prevalence is still rising around the world. A multitude of causes have been suggested for this increase, mostly related to familial background, the occidental diet which is rich in fat/carbohydrates, and sedentary life style. Type 2 diabetes involves malfunctions of the primary pancreatic beta-cells, usually attributed to local damage; however, it can be associated with other stressful environmental agents, such as chemical contaminants from food, plastic and air, among others. Indeed, exposure to these chemical agents during perinatal and adolescent life can increase the risk of developing cardiometabolic diseases later in life. This review explores data showing which environmental chemical agents may produce injury in beta-cells and further impair the insulinotropic process of type 2 diabetes. Additionally, it points the need to also consider unusual causes of metabolic diseases, such as environmental contaminants.

Identifying reference chemicals for thyroid bioactivity screening

Reference chemicals were selected based on thyroid bioactivity in 'Tier 1' screening assays used by the U.S. EPA's Endocrine Disruptor Screening Program. Active reference chemicals had significant effects on thyroid-responsive endpoints in the amphibian metamorphosis assay, and the male and female pubertal rat assays. In the absence of thyroid weight or histopathological effects, additional published studies providing mechanistic data on thyroid activity were required for active chemicals. Inactive reference chemicals had no significant effects on thyroid-responsive endpoints in Tier 1 assays, or in amphibian or rodent studies from several online databases. The 34 reference chemicals (29 active and five inactive) will be useful for performance-based validation of alternative, high throughput screening assays for thyroid bioactivity.

Assessing the potential impact on the thyroid axis of environmentally relevant food constituents/contaminants in humans

Occurrence and mode of action of potentially relevant goitrogens in human nutrition and their mode of action (MOA) are reviewed, with special focus on the anionic iodine uptake inhibitors perchlorate (PER), thiocyanate (SCN) and nitrate (NO3). Epidemiological studies suggest persistent halogenated organic contaminants and phthalates as well as certain antimicrobials to deserve increased attention. This also applies to natural goitrogens, including polyphenols and glucosinolates, food constituents with limited data density concerning human exposure. Glucosinolates present in animal feed are presumed to contribute to SCN transfer into milk and milk products. PER, SCN and NO3 are well-investigated environmental goitrogens in terms of MOA and relative potency. There is compelling evidence from biomarker monitoring that the exposure to the goitrogens SCN and NO3 via human nutrition exceeds that of PER by orders of magnitude. The day-to-day variation in dietary intake of these substances (and of iodide) is concluded to entail corresponding variations in thyroidal iodide uptake, not considered as adverse to health or toxicologically relevant. Such normal variability of nutritional goitrogen uptake provides an obvious explanation for the variability in radioactive iodine uptake (RAIU) measurements observed in healthy individuals. Based on available data, a 20 % change in the thyroidal uptake of iodide is derived as threshold value for a biologically meaningful change induced by perchlorate and other goitrogens with the same MOA. We propose this value to be used as the critical effect size or benchmark response in benchmark dose analysis of human RAIU data. The resulting BMDL20 is 0.0165 mg/kg bw/day or 16.5 μg/kg bw/day. Applying a factor of 4, to allow for inter-human differences in toxicokinetics, leads to a TDI for perchlorate of 4 μg/kg bw/day.

Ultrasensitive Bisphenol A Field-Effect Transistor Sensor Using an Aptamer-Modified Multichannel Carbon Nanofiber Transducer

Bisphenol A (BPA) is a known endocrine-disrupting compound (EDC) that has a structure similar to that of the hormone estrogen. Even low concentrations of BPA are able to bind estrogen receptors, thereby inducing severe diseases such as reproductive disorders, chronic diseases, and various types of cancer. Despite such serious effects, the use of BPA remains widespread. Therefore, monitoring of both dietary and nondietary exposure to BPA is important for human healthcare. Herein, we present a field-effect transistor (FET) sensor using aptamer-modified multichannel carbon nanofibers (MCNFs) to detect BPA. The MCNFs are fabricated via single-nozzle electrospinning of two immiscible polymer solutions followed by thermal treatment in an inert atmosphere. The MCNFs are then oxidized using a solution of HNO3 and H2SO4 to introduce carboxyl groups on the surface of the fibers. The carboxyl-functionalized MCNFs (CMCNFs) are immobilized on an amine-functionalized electrode substrate by forming a covalent bond, and amine-functionalized BPA-binding aptamers are modified in the same manner on the CMCNFs. The resulting FET sensors exhibit a high sensitivity, as well as specificity toward BPA at an unprecedentedly low concentration of 1 fM. Furthermore, these sensors are stable and could be reused for repeated assays.

Toxic chemicals and thyroid function: hard facts and lateral thinking

Increasing quantities of evidence-based data incriminate a large number of environmental pollutants for toxic effects on the thyroid. Among the many chemical contaminants, halogenated organochlorines and pesticides variably affect the hypothalamic-pituitary-thyroid axis and disrupt thyroid function. PCBs and their metabolites and PBDEs bind to thyroid transport proteins, such as transthyretin, displace thyroxine, and disrupt thyroid function. Meanwhile, at the molecular level, PCB congeners may activate phosphorylation of Akt, p-Akt, and forkhead box O3a (FoxO3a) protein resulting in inhibition of the natrium/iodide symporter. Given therefore the growing concern developing around these multiple toxic chemicals today invading numerous environments and their long-term deleterious effects not only on the thyroid but also on general health, we strongly advocate their strict regulation and, moreover, their gradual reduction. A good degree of "lateral thinking", we feel, will lead to a use of chemicals that will enhance life while concurrently carefully protecting the environment.