Bisphenol A interferes with thyroid specific gene expression

Bisphenol A alters retinal morphology, visually guided behavior, and thyroid hormone levels in zebrafish larvae

Bisphenols are industrial chemicals that are produced in large quantities and have been detected in all parts of the environment as well as in a multitude of different organisms including humans and fish. Several bisphenols, such as bisphenol A (BPA) and bisphenol F, have been shown to disrupt endocrine systems thereby affecting development and reproduction. While numerous studies investigated the effect of bisphenols on estrogen signaling, their impact on the thyroid hormone system (THS), which is vital for neurodevelopment including sensory development, has been explored to a lesser extent. The present work selected BPA as a representative for structurally similar bisphenols and assessed its impact on the THS as well as sensory development and function in zebrafish. To this end, zebrafish were exposed to BPA until up to 8 days post fertilization (dpf) and thyroid hormone levels, eye morphology, and sensory-mediated behaviors were analyzed. Zebrafish larvae exposed to BPA showed altered retinal layering, decreased motility across varying light conditions, and a loss of responsiveness to red light. Furthermore, whole-body levels of the thyroid hormones thyroxine (T4) and 3,5-diiodothyronine (3,5-T2) were significantly decreased in 5 dpf zebrafish. Taken together, BPA disrupted THS homeostasis and compromised visual development and function, which is pivotal for the survival of fish larvae. This work underlines the necessity for ongoing research on BPA and its numerous substitutes, particularly concerning their effects on the THS and neurodevelopment, to ensure a high level of protection for the environment and human health.

IL-10-TG/TPO-T4 axis, the target of bis (2-ethylhexyl) tetrabromophthalate on thyroid function imbalance

Bis (2-ethylhexyl) tetrabromophthalate (TBPH) is a new type of brominated flame retardant. Some studies suggest that TBPH exposure may be associated with thyroid damage. However, there is a paucity of research on the authentic exposure-related effects and molecular mechanisms in animals or cells. In this study, we used male Sprague-Dawley (SD) rats and the Nthy ori3-1 cell line (the human thyroid follicular epithelial cell) to explore the potential effects of TBPH (5, 50, 500 mg/kg and 1, 10, 100 nM) on the thyroid. The genes and their proteins of cytokines and thyroid-specific proteins, thyroglobulin (TG), thyroid peroxidase (TPO), and sodium iodide cotransporter (NIS) were examined to investigate the possible mechanisms. At the end of the experiment, it was found that 50 and 500 mg/kg TBPH could increase the levels of total thyroxine (TT4) and free thyroxine (FT4) significantly. The messenger RNAs (mRNAs) of Tg, Tpo, Interleukin-6 (Il6), and Interleukin-10 (Il10) in the thyroid tissues from the rats treated with 500 mg/kg were enhanced clearly. Meanwhile, the mRNAs of TG, TPO, IL6, and IL10 were elevated in Nthy ori3-1 cells treated with 100 nM TBPH as well. The mRNAs of TG and TPO were elevated after the knockdown of IL6. To our surprise, after the knockdown of IL10 or the treatment of anti-IL-10-receptor (anti-IL-10-R) antibody, the mRNAs of TG and TPO were significantly reduced, and the effects of TBPH were diminished. In conclusion, our results suggested that the IL-10-IL-10R-TG/TPO-T4 axis is one important target of TBPH in the thyroid.

Bisphenol analogues induce thyroid dysfunction via the disruption of the thyroid hormone synthesis pathway

Bisphenol analogues are widely used in industrial and daily-use consumer products having imperfect thyroid hormones (THs) structures. Widespread exposure interferes with thyroid-related health outcomes in human. The mechanisms of disruption on TH synthesis and subsequent thyroid dysfunction by different bisphenol analogues remain unclear. Here, we evaluated bisphenol-induced thyroid endocrine disruption in C57BL/6 mice at doses of 0.002, 0.02, 2, and 20 mg/kg body weight/day (BW/d) for five consecutive weeks. Administration of 20 mg/kg BW/d bisphenol S (BPS) and 2 mg/kg BW/d tetrabromobisphenol S (TBBPS) significantly increased serum thyrotropin (TSH) levels to 1.21-fold and 1.20-fold of control group, respectively, indicating that bisphenols induced thyroid dysfunction in mice. Height of the thyroid follicle epithelium significantly increased to 1.27-, 1.24-, 1.26-, and 1.36-fold compared to control group with BPA, BPS, TBBPA, and TBBPS at 20 mg/kg BW/d, respectively, indicating impairment of the thyroid gland structure, and TBBPS showed potent effect. Exposure to bisphenol analogues of 0.02 mg/kg BW/d downregulated the protein expression levels of thyrotropin receptor, the sodium/iodide symporter, thyroperoxidase. The TH-dependent effects were further determined using the T-Screen assay at 10-11 M to 10-5 M concentrations. Bisphenol analogues significantly decreased TH-dependent GH3 cell proliferation, indicating the antagonistic activity of bisphenol analogues. The gene responsible for THs synthesis of thyrotropin releasing hormone receptor and TSH were upregulated, but downregulation of thyroid receptor β was observed. Our results suggest that bisphenol analogues distinctly induce thyroid dysfunction via TH synthesis, implying adverse effect of bisphenol analogues on TH homeostasis and subsequent physiological processes.

Assessment of five typical environmental endocrine disruptors and thyroid cancer risk: a meta-analysis

Introduction

There are conflicting reports on the association between environmental endocrine disruptors (EEDs) and thyroid cancer. This meta-analysis aimed to elucidate the relationship between EEDs and thyroid cancer.

Methods

We searched for epidemiological studies on EEDs and thyroid cancer published in PubMed and Web of Science up to December 2022. We then screened the articles that could extract data on EEDs concentration levels in both thyroid cancer patients and healthy controls. We excluded articles that could not calculate effect sizes, focused on other thyroid diseases, or lacked controls. Standardized mean difference (SMD) was calculated to analyze the association between EEDs and thyroid cancer. We measured the heterogeneity among the included studies using I2, assessed publication bias by Egger's and Begg's test, and evaluated article quality using the Newcastle-Ottawa Quality Score (NOS). In the end, fifteen eligible case-control studies were included.

Results

Our comprehensive analysis revealed that polychlorinated biphenyls (PCBs) were negatively associated with thyroid cancer{ SMD = -0.03, 95% confidence interval (CI) = (-0.05, -0.00), P = 0.03}, while polybrominated diphenyl ethers (PBDEs), phthalates (PAEs), and heavy metals were positively associated with thyroid cancer{PBDEs: SMD = 0.14, 95%CI = (0.04, 0.23), P = 0.007; PAEs: SMD = 0.30, 95%CI = (0.02, 0.58), P = 0.04; heavy metals: SMD = 0.21, 95%CI = (0.11, 0.32), P < 0.001}. We did not find a statistically significant relationship between bisphenol A (BPA) and thyroid cancer. Most of the included studies did not show publication bias, except for those on PCBs.

Discussion

Our results indicate that exposure to certain EEDs, such as PBDEs, PAEs, and heavy metals, increases the risk of thyroid cancer. However, further large-scale epidemiological studies and mechanism studies are needed to verify these potential relationships and understand the underlying biological mechanisms.

Screening for chemicals with thyroid hormone-disrupting effects using zebrafish embryo

Thyroid disruption is an increasingly recognized issue in the use and development of chemicals and new drugs, especially to help toxicologist to complement the reproductive and developmental toxicology information of chemicals. Still, adequate assessment methods are scarce and often suffer a trade-off between physiological relevance and labor- and cost-intensive assays. Here, we present a tiered approach for a medium-throughput screening of chemicals to identify their thyroid disrupting potential in zebrafish embryos as a New Approach Methodology (NAM). After identifying the maximum tolerated concentrations, we exposed zebrafish larvae to sub-adverse effect levels of the reference compounds benzophenone-2, bisphenol A, phenylthiourea, potassium perchlorate, propylthiouracil, and phloroglucinol to exclude any systemic toxicity. Applying the transgenic zebrafish line that carries a gene for the red fluorescence protein (Tg(tg:mCherry)) under the thyroglobulin promoter, we could identify the thyroid disrupting effects of the chemicals by a time and cost-effective image analysis measuring the fluorescence levels in the thyroid glands. Our observations could be confirmed by altered expression patterns of genes involved in the hypothalamus-pituitary-thyroid (HPT) axis. Finally, to anchor the observed thyroid disruption, we determined some changes in the Thyroid hormone levels of triiodothyronine (T3) and Thyroxine (T4) using a newly developed liquid chromatography mass spectrometric (LCMS) method. The presented approach carries the potential to extend the toolbox for legislative authorities and chemical producers for the assessment of thyroid-specific endocrine disruption and to overcome current challenges in the evaluation of endocrine disruptors.

Association of urinary bisphenols with thyroid function in the general population: a cross-sectional study of an industrial park in China

Bisphenols (BPs) are potential thyroid disruptors that are widely used in many consumer products, leading to their widespread exposure in the general population. Current cross-sectional and case-control studies have found associations between exposure to BPs and serum thyroid function, but the results were contradictory. The objectives of this study are to describe demographic characteristics, BP exposure levels, and thyroid function measurements in potentially exposed and control districts and to investigate the association of urinary BPs with thyroid function. Data were collected from a general population aged 3-79 years (N = 281) recruited by the Zhejiang Human Biomonitoring Program (ZJHBP). The concentrations of 10 kinds of BPs in urine and serum free triiodothyronine (FT3), total triiodothyronine (TT3), free thyroxine (FT4), total thyroxine (TT4), thyroid-stimulating hormone (TSH), thyroglobulin (Tg), thyroglobulin antibodies (TgAb), thyroid peroxidase antibodies (TPOAb), and thyrotropin receptor antibody (TRAb) in serum were measured. Multiple linear regression and weighted quantile sum (WQS) regression were used to estimate the relationship between single and mixed exposure of BPs and thyroid function. Bisphenol A (BPA), bisphenol S (BPS), and bisphenol P (BPP) were detected, respectively, in 82.73%, 94.24%, and 55.40% of the population in the exposed area and 81.69%, 61.27%, and 43.66% of the population in the control area. Among adult females, serum TT3 was negatively associated with urinary BPA (β = -0.033, 95% CI = -0.071, -0.008, P = 0.021). Among minor females, FT4 and Tg levels were negatively associated with the urinary BPA (β = -0.026, 95% CI = -0.051, -0.002, P = 0.032 for FT4; β = -0.129, 95% CI = -0.248, -0.009, P = 0.035 for Tg), and TPOAb was positively associated with urinary BPA (β = 0.104, 95% CI = 0.006, 0.203, P = 0.039). In WQS models, BPs mixture was positively associated with FT3 (βWQS = 0.022, 95% CI = 0.002, 0.042) and TT3 (βWQS = 0.033, 95% CI = 0.004, 0.062), and negatively associated with FT4 (βWQS = -0.024, 95% CI = -0.044, 0.004). We found widespread exposure to BPA, BPS, and BPP in the general population of Zhejiang province and found an association between BPA and thyroid hormones. This association is gender- and age-dependent and needs to be confirmed in further studies.

Chronic Exposure to Chlorpyrifos Damages Thyroid Activity and Imbalances Hepatic Thyroid Hormones Signaling and Glucose Metabolism: Dependency of T3-FOXO1 Axis by Hyperglycemia

Early life exposure to Endocrine Disruptor Chemicals (EDCs), such as the organophosphate pesticide Chlorpyrifos (CPF), affects the thyroid activity and dependent process, including the glucose metabolism. The damage of thyroid hormones (THs) as a mechanism of action of CPF is underestimated because the studies rarely consider that TH levels and signaling are customized peripherally. Here, we investigated the impairment of metabolism/signaling of THs and lipid/glucose metabolism in the livers of 6-month-old mice, developmentally and lifelong exposed to 0.1, 1, and 10 mg/kg/die CPF (F1) and their offspring similarly exposed (F2), analyzing the levels of transcripts of the enzymes involved in the metabolism of T3 (Dio1), lipids (Fasn, Acc1), and glucose (G6pase, Pck1). Both processes were altered only in F2 males, affected by hypothyroidism and by a systemic hyperglycemia linked to the activation of gluconeogenesis in mice exposed to 1 and 10 mg/kg/die CPF. Interestingly, we observed an increase in active FOXO1 protein due to a decrease in AKT phosphorylation, despite insulin signaling activation. Experiments in vitro revealed that chronic exposure to CPF affected glucose metabolism via the direct modulation of FOXO1 activity and T3 levels in hepatic cells. In conclusion, we described different sex and intergenerational effects of CPF exposure on the hepatic homeostasis of THs, their signaling, and, finally, glucose metabolism. The data points to FOXO1-T3-glucose signaling as a target of CPF in liver.

Endocrine disrupting chemicals: effects on pituitary, thyroid and adrenal glands

BACKGROUND

In recent years, scientific research has increasingly focused on Endocrine Disrupting Chemicals (EDCs) and demonstrated their relevant role in the functional impairment of endocrine glands. This induced regulatory authorities to ban some of these compounds and to carefully investigate others in order to prevent EDCs-related conditions. As a result, we witnessed a growing awareness and interest on this topic.

AIMS

This paper aims to summarize current evidence regarding the detrimental effects of EDCs on pivotal endocrine glands like pituitary, thyroid and adrenal ones. Particularly, we directed our attention on the known and the hypothesized mechanisms of endocrine dysfunction brought by EDCs. We also gave a glimpse on recent findings from pioneering studies that could in the future shed a light on the pathophysiology of well-known, but poorly understood, endocrine diseases like hormone-producing adenomas.

CONCLUSIONS

Although intriguing, studies on endocrine dysfunctions brought by EDCs are challenging, in particular when investigating long-term effects of EDCs on humans. However, undoubtedly, it represents a new intriguing field of science research.

Association between phenols and thyroid hormones: The role of iodothyronine deiodinase genes

Previous literature on prenatal phenol exposure and thyroid hormone (TH) alteration is conflicting, and the possible mechanisms of action involved remain unclear. We aimed to examine the association between prenatal phenol exposure and levels of maternal and neonatal THs, as well as the possible role of iodothyronine deiodinase (DIO) gene polymorphisms in this relation. We studied 387 Spanish mother-neonate pairs with measurements of maternal phenols, total triiodothyronine (TT3) and free thyroxine (FT4), maternal and neonatal thyroid-stimulating hormone (TSH), and maternal genotypes for single nucleotide polymorphisms in the DIO1(rs2235544) and DIO2(rs12885300) genes. We implemented multivariate linear and weighted quantile sum (WQS) regressions to examine the association between phenols and THs (including sex-stratified models for neonatal TSH) and investigated effect modification of genotypes in the maternal phenol-TH associations. In single exposure models, we found negative associations between maternal triclosan (TCS) and neonatal TSH (% change [95%CI]: -2.95 [-5.70, -0.11], per twofold phenol increase) - stronger for girls - and less clearly for maternal ethylparaben (EPB) and TSH (-2.27 [-4.55, 0.07]). In phenol mixture models, we found no association with THs. In the genetic interaction models, we found some evidence of effect modification of DIO gene polymorphisms with stronger negative associations between methylparaben (MPB), propylparaben (PPB), butylparaben (BPB) and TT3 as well as bisphenol A (BPA) and FT4 for DIO1(rs2235544)-CC. Stronger inverse associations for genotypes DIO2(rs12885300)-CC and DIO2(rs12885300)-CT and positive ones for DIO2(rs12885300)-TT were also reported for BPA and FT4. In conclusion, we found some evidence of an association between phenols and TSH during pregnancy and at birth in single exposure models, the latter being stronger for girls. Since no association was observed between maternal levels of phenols and TT3 or FT4, the possible role of the genetic background in these associations warrants further investigation.

Stable magnetic CoZn/N-doped polyhedron with self-generating carbon nanotubes for highly efficient removal of bisphenols from complex wastewaters

Bisphenols have extensively been found in various environmental matrices and caused public concerns due to their endocrine-disrupting potential. Herein, we developed a ZIF-67@ZIF-8-derived CoZn/nitrogen-doped carbon (CoZn/NC) as a robust adsorbent for bisphenols in wastewaters. The self-generating carbon nanotubes and the open metal sites provided sufficient adsorption sites. The Co component endowed the derivative with strong magnetism facilitating its separation from water. CoZn/NC exhibited exceeding water stability in pH 3 - 12 solution and withstood water up to 15 days. The great applicability of CoZn/NC was validated with 16 real wastewaters from different sources (recoveries exceeding 97.9%). Fast adsorption kinetics were observed with removal efficiencies above 96.5% within 1 min. The adsorption isotherms were well fitted with the Langmuir model, with adsorption capacities of 222, 200, 193, and 321 mg g^-1 for bisphenol A, bisphenol F, bisphenol S, and bisphenol AF, respectively. Variations in external conditions, including pH 3 - 9, humic acid (50 mg L^-1), and NaCl (0.1 mol L^-1), had negligible impacts on the adsorption process. The characterizations and density functional theory computation demonstrated that electrostatic, hydrophobic, π - π, and cation- π interactions are the driving forces in this system. The as-prepared CoZn/NC exhibits great promise in real wastewater treatment.

Harbours as unique environmental sites of multiple anthropogenic stressors on fish hormonal systems

Fish development and acclimation to environmental conditions are strongly mediated by the hormonal endocrine system. In environments contaminated by anthropogenic stressors, hormonal pathway alterations can be detrimental for growth, survival, fitness, and at a larger scale for population maintenance. In the context of increasingly contaminated marine environments worldwide, numerous laboratory studies have confirmed the effect of one or a combination of pollutants on fish hormonal systems. However, this has not been confirmed in situ. In this review, we explore the body of knowledge related to the influence of anthropogenic stressors disrupting fish endocrine systems, recent advances (focusing on thyroid hormones and stress hormones such as cortisol), and potential research perspectives. Through this review, we highlight how harbours can be used as "in situ laboratories" given the variety of anthropogenic stressors (such as plastic, chemical, sound, light pollution, and invasive species) that can be simultaneously investigated in harbours over long periods of time.

Factors influencing the levothyroxine dose in the hormone replacement therapy of primary hypothyroidism in adults

Levothyroxine (LT4) is a safe, effective means of hormone replacement therapy for hypothyroidism. Here, we review the pharmaceutical, pathophysiological and behavioural factors influencing the absorption, distribution, metabolism and excretion of LT4. Any factor that alters the state of the epithelium in the stomach or small intestine will reduce and/or slow absorption of LT4; these include ulcerative colitis, coeliac disease, bariatric surgery, Helicobacter pylori infection, food intolerance, gastritis, mineral supplements, dietary fibre, resins, and various drugs. Once in the circulation, LT4 is almost fully bound to plasma proteins. Although free T4 (FT4) and liothyronine concentrations are extensively buffered, it is possible that drug- or disorder-induced changes in plasma proteins levels can modify free hormone levels. The data on the clinical significance of genetic variants in deiodinase genes are contradictory, and wide-scale genotyping of hypothyroid patients is not currently justified. We developed a decision tree for the physician faced with an abnormally high thyroid-stimulating hormone (TSH) level in a patient reporting adequate compliance with the recommended LT4 dose. The physician should review medications, the medical history and the serum FT4 level and check for acute adrenal insufficiency, heterophilic anti-TSH antibodies, antibodies against gastric and intestinal components (gastric parietal cells, endomysium, and tissue transglutaminase 2), and Helicobacter pylori infection. The next step is an LT4 pharmacodynamic absorption test; poor LT4 absorption should prompt a consultation with a gastroenterologist and (depending on the findings) an increase in the LT4 dose level. An in-depth etiological investigation can reveal visceral disorders and, especially, digestive tract disorders.

Concentrations of bisphenols, parabens, and benzophenones in human breast milk: A systematic review and meta-analysis

BACKGROUND

Breast milk is the main source of nutrition for infants but may be responsible for their exposure to environmental chemicals, including endocrine-disrupting chemicals.

AIM

To review available evidence on the presence and concentrations of bisphenols, parabens (PBs), and benzophenones (BPs) in human milk and to explore factors related to exposure levels.

METHODS

A systematic review was carried out using Medline, Web of Science, and Scopus databases, conducting a comprehensive search of peer-reviewed original articles published during the period 2000-2020, including epidemiological and methodological studies. Inclusion criteria were met by 50 studies, which were compiled by calculating weighted detection frequencies and arithmetic mean concentrations of the chemicals. Their risk of bias was assessed using the ROBINS-I checklist.

RESULTS

Among the 50 reviewed studies, concentrations of bisphenols were assessed by 37 (74.0%), PBs by 21 (42.0%), and BPs by 10 (20.0%). Weighted detection frequencies were 63.6% for bisphenol-A (BPA), 27.9-63.4% for PBs, and 39.5% for benzophenone-3 (BP-3). Weighted mean concentrations were 1.4 ng/mL for BPA, 0.2-14.2 ng/mL for PBs, and 24.4 ng/mL for BP-3. Mean concentrations ranged among studies from 0.1 to 3.9 ng/mL for BPA, 0.1 to 1063.6 ng/mL for PBs, and 0.5 to 72.4 ng/mL for BP-3. The highest concentrations of BPA and PBs were reported in samples from Asia (versus America and Europe). Higher BPA and lower methyl-paraben concentrations were observed in samples collected after 2010. Elevated concentrations of these chemicals were associated with socio-demographic and lifestyle factors in eight studies (16.0%). Two epidemiological studies showed moderate/serious risk of bias.

CONCLUSIONS

This systematic review contributes the first overview of the widespread presence and concentrations of bisphenols, PBs, and BPs in human breast milk, revealing geographical and temporal variations. The methodological heterogeneity of published studies underscores the need for well-conducted studies to assess the magnitude of exposure to these chemicals from human milk.

[Rapid determination of bisphenols in surface water by modified QuEChERS-ultra performance liquid chromatography-tandem mass spectrometry]

Chromatography combined with mass spectrometry is the most commonly used detection technology, and it offers the advantages of high sensitivity and high selectivity. However, the contents of bisphenols (BPs) in water samples are at the ng/L level. Even if the BPs contents are determined by mass spectrometry, the samples must be pretreated and enriched. A quick, easy, inexpensive, effective, rugged, and safe technique (QuEChERS) can offer advantages such as cost effectiveness and time efficiency. The application of QuEChERS is currently extended to the analysis of contaminants in food and water samples. In this work, QuEChERS coupled with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was proposed for the determination of eight BPs in surface water. Method optimization was carried out in terms of process efficiency (PE), which included the matrix effect (ME) and extraction recovery (RE). First, the water samples were extracted with 10 mL ethyl acetate and cleaned with 50 mg primary secondary amine (PSA) and 50 mg graphitized carbon black (GCB). Then, the organic layer was collected and evaporated to dryness under nitrogen flow (40 ℃). Finally, the extracts were redissolved in 0.5 mL of a methanol-water (1∶1, v/v) mixture and subjected to UPLC-MS/MS analysis. Chromatographic separation was accomplished on a Waters ACQUITY UPLC BEH C18 column (100 mm×2.1 mm, 1.7 μm) with gradient elution. Methanol and 0.1 mmol/L ammonium bicarbonate aqueous solution were used as the mobile phases. The eight BPs were analyzed by MS/MS with negative electrospray ionization (ESI-) and in the multiple reaction monitoring (MRM) mode. The matrix matching external standard method was used for quantitative determination. The eight compounds could be analyzed within 8 min. Under the optimized conditions, the calibration curves showed good linearities for the eight BPs, and the coefficients of determination (R2) were greater than 0.9990. The limits of detection (LODs, S/N=3) and limits of quantification (LOQs, S/N=10) were in the ranges of 0.1-2.3 ng/L and 0.3-6.1 ng/L, respectively. The average recoveries of the eight BPs in river water samples were 78.8%-116.6%, and the corresponding relative standard deviations (RSDs) were 1.8%-9.0% (n=6). This method was applied to the analysis of BPs pollution in Guangyuan section of Jialing river and its tributaries, and widespread pollution was confirmed. The detection rate of BPA was 100% with a content of 6.15-90.03 ng/L, and the detection rate of BPS was 91%, with the contents being in the range not detected (nd) to 4.63 ng/L. The method established in this study allowed for the rapid enrichment and purification of the eight BPs in water. With its advantages of simplicity, rapidness, high sensitivity, and low cost, the method can be used for the rapid determination of trace BPs in surface water such as lake water and river water.

Effects of bisphenol A on pancreas and thyroid gland of young and adult female Sprague Dawlеy rats

Bisphenol A (BPA), a chemical involved in formation of plastic vessels, is one of the most widespread endocrine disrupting chemicals. The study was designed to investigate the effect of BPA on pancreas and thyroid gland of young and adult female Sprague Dawley rats. The rats were exposed to 330 mg/kg BPA orally every other day for 12 weeks; control rats were exposed orally to ethyl alcohol and corn oil. Samples were collected at 4, 8 and 12 weeks for hormonal, biochemical assays and histopathological examination. The insulin hormone in exposed young rats was decreased, but its level in adult ones was increased; the biochemical assay for blood sugar level showed a significant increase in young rats and decrease in adult ones. T3 hormone was increased in treated young and adult rats; T4 hormone was increased in treated adults, while calcium level was decreased in treated adult rats. The histopathological findings of pancreas revealed vacuolation in its endocrine parts in young rats, while in adult ones there was intralobular fatty infiltration - a typical picture of diabetes. The thyroid gland in treated young female rats showed increased cellularity of parafollicular cells; moreover there was parafollicular haemorrhage, and in adult ones - desquamation in lining epithelium of follicular cells. In conclusion, exposure of young and adult female rats to BPA resulted in changes in the pancreatic and thyroid gland cells manifested by morphological, hormonal and biochemical parameters.

The Impact of Bisphenol A on Thyroid Function in Neonates and Children: A Systematic Review of the Literature

Background: Bisphenol A (BPA) is an endocrine-disrupting chemical widely used in plastic products that may have an adverse effect on several physiologic functions in children. The aim of this systematic review is to summarize the current knowledge of the impact of BPA concentrations on thyroid function in neonates, children, and adolescents. Methods: A systematic search of Medline, Scopus, Clinical Trials.gov, Cochrane Central Register of Controlled Trials CENTRAL, and Google Scholar databases according to PRISMA guidelines was performed. Only case–control, cross-sectional, and cohort studies that assessed the relationship between Bisphenol A and thyroid function in neonates and children aged <18 years were included. Initially, 102 articles were assessed, which were restricted to 73 articles after exclusion of duplicates. A total of 73 articles were assessed by two independent researchers based on the title/abstract and the predetermined inclusion and exclusion criteria. According to the eligibility criteria, 18 full-text articles were selected for further assessment. Finally, 12 full-text articles were included in the present systematic review. Results: The presented studies offer data that suggest a negative correlation of BPA concentrations with TSH in children, a gender-specific manner of action, and a potential effect on proper neurodevelopment. However, the results are inconclusive with respect to specific thyroid hormone concentrations and the effect on thyroid autoimmunity. Conclusion: The potential negative effect of BPA in the developing thyroid gland of children that may affect proper neurodevelopment, suggesting the need to focus future research on designing studies that elucidate the underlying mechanisms and the effects of BPA in thyroid function in early life.

In vivo and in vitro transcriptomics meta-analyses reveal that BPA may affect TGF-beta signaling regardless of the toxicology system employed

Bisphenol A (BPA) is a high-production-volume monomer for the manufacture of a wide variety of polycarbonate plastics and resins. Evidence suggests BPA can induce carcinogenesis, reproductive toxicity, abnormal inflammatory or immune response, and developmental disorders of the brain or nervous system. However, whether BPA affects the very same basic molecular processes in all the in vivo and in vitro systems employed to exert its molecular mechanisms of toxicity remains to be clarified. In this study, we collected multi-source global transcriptomics datasets for BPA-exposed organisms and cells, and evaluated the adverse effects of BPA by using data integration and gene functional enrichment analyses. We found that BPA may affect basic cellular processes, such as cell growth, survival, proliferation, differentiation, and apoptosis, independent of species and specific in vivo or in vitro systems. Mechanistically, BPA could regulate cell-extra cellular matrix interactions via challenging TGF-beta signaling pathways. Furthermore, we compared our in vitro BPA-dependent mouse embryoid body (EB) global differentiation transcriptomics with all the other datasets. We verified the EB-based toxicological system could recapitulate several in vivo and other in vitro findings very efficiently, and in a less time- and resource-consuming fashion. Taken together, this study emphasizes the utility of meta-analyses to understand common molecular mechanisms of toxicity of synthetic chemicals.

Neurodevelopmental impact of the offspring by thyroid hormone system-disrupting environmental chemicals during pregnancy

Everyday use chemicals have been demonstrated to be endocrine disruptors. Since normal thyroid function during pregnancy is transcendental for the neurodevelopment of the offspring, knowledge of endocrine disrupting chemicals (EDC) is of main importance. The aim of our study is to recognize and describe EDC actions in pregnant women and focus on neurodevelopmental processes that can lead to neurotransmitter imbalance and cognitive impairment, and the possible clinical outcomes in the newborn and child. We searched PubMed databases for animal studies and clinical trials evaluating chemicals recognized as thyroid disruptors -perchlorate, phthalates, bisphenol A-, as well as chemicals with potential thyroid disruption activity -parabens, pesticides and persistent organic pollutants, on thyroid hormones (THs) levels and their bioavailability during pregnancy, and the outcome in newborns, infants and children. We also exhibit evidence from worldwide cohort studies to this regard. The publications reviewed show: 1) known endocrine disruptors have an association with hormonal thyroid levels, where an effect of increase or decrease in TH concentrations has been reported depending on the chemical exposed 2) associations between TH, EDCs and neurocognitive disorders have been addressed, such as ADHD, though no conclusive impact on potential related disorders as autism has been established, 3) perchlorate has demonstrated effects on thyroid levels on iodine uptake. In conclusion, detrimental risks and long-term consequences after in-utero exposure to EDCs are being reported in several cohort studies and further research must be conducted to establish a well-known cause-effect association.

Characterization of Estrogenic Activity and Site-Specific Accumulation of Bisphenol-A in Epididymal Fat Pad: Interfering Effects on the Endocannabinoid System and Temporal Progression of Germ Cells

The objective of this work has been to characterize the estrogenic activity of bisphenol-A (BPA) and the adverse effects on the endocannabinoid system (ECS) in modulating germ cell progression. Male offspring exposed to BPA during the foetal-perinatal period at doses below the no-observed-adverse-effect-level were used to investigate the exposure effects in adulthood. Results showed that BPA accumulates specifically in epididymal fat rather than in abdominal fat and targets testicular expression of 3β-hydroxysteroid dehydrogenase and cytochrome P450 aromatase, thus promoting sustained increase of estrogens and a decrease of testosterone. The exposure to BPA affects the expression levels of some ECS components, namely type-1 (CB1) and type-2 cannabinoid (CB2) receptor and monoacylglycerol-lipase (MAGL). Furthermore, it affects the temporal progression of germ cells reported to be responsive to ECS and promotes epithelial germ cell exfoliation. In particular, it increases the germ cell content (i.e., spermatogonia while reducing spermatocytes and spermatids), accelerates progression of spermatocytes and spermatids, promotes epithelial detachment of round and condensed spermatids and interferes with expression of cell–cell junction genes (i.e., zonula occcludens protein-1, vimentin and β-catenin). Altogether, our study provides evidence that early exposure to BPA produces in adulthood sustained and site-specific BPA accumulation in epididymal fat, becoming a risk factor for the reproductive endocrine pathways associated to ECS.

Associations Between Thyroid Hormone Levels and Urinary Concentrations of Bisphenol A, F, and S in 6-Year-old Children in Korea

OBJECTIVES

Bisphenol A (BPA) is used in the electrical, mechanical, medical, and food industries. Previous studies have suggested that BPA is an endocrine disruptor. Regulation of BPA has led to increased use of bisphenol F (BPF) and bisphenol S (BPS). However, few studies have investigated the associations of BPF and BPS with thyroid dysfunction in children. Our study investigated the associations of prenatal BPA and early childhood BPA, BPF, and BPS exposure with thyroid function in 6-year-old children.

METHODS

Prenatal BPA concentrations were measured during the second trimester of pregnancy in an established prospective birth cohort. We measured urinary BPA, BPF, and BPS concentrations and thyroid hormone levels (thyroid-stimulating hormone, total T3, and free T4) in 6-year-old children (n=574). We examined the associations between urinary bisphenol concentrations and percentage change of thyroid hormone concentrations using multivariate linear regression. We also compared thyroid hormone levels by dividing the cohort according to BPA, BPF, and BPS concentrations.

RESULTS

The associations between prenatal BPA and total T3 levels were statistically significant in all models, except for girls when using a crude model. The associations between urinary BPA and BPS concentrations and levels of all thyroid hormones were not statistically significant. However, we observed that lower free T4 levels (-1.94%; 95% confidence interval, -3.82 to -0.03) were associated with higher urinary BPF concentrations in girls only.

CONCLUSIONS

Our findings identified significant associations between prenatal BPA exposure and total T3 levels in all children and between BPF exposure and free T4 levels in girls only.

Endocrine Disrupting Chemicals and Thyroid Cancer: An Overview

Endocrine disruptive chemicals (EDC) are known to alter thyroid function and have been associated with increased risk of certain cancers. The present study aims to provide a comprehensive overview of available studies on the association between EDC exposure and thyroid cancer. Relevant studies were identified via a literature search in the National Library of Medicine and National Institutes of Health PubMed as well as a review of reference lists of all retrieved articles and of previously published relevant reviews. Overall, the current literature suggests that exposure to certain congeners of flame retardants, polychlorinated biphenyls (PCBs), and phthalates as well as certain pesticides may potentially be associated with an increased risk of thyroid cancer. However, future research is urgently needed to evaluate the different EDCs and their potential carcinogenic effect on the thyroid gland in humans as most EDCs have been studied sporadically and results are not consistent.

Bisphenols alter thermal responses and performance in zebrafish (Danio rerio)

Plastic pollutants are novel environmental stressors that are now persistent components of natural ecosystems. Endocrine disrupting chemicals such as bisphenols that leach out of plastics can modify physiological responses of animals by interfering with hormone signalling. Here, we tested whether three commonly produced bisphenols, bisphenol A (BPA), bisphenol F (BPF) and bisphenol S (BPS), impair thermal acclimation of swimming performance and metabolic enzyme [citrate synthase (CS) and lactate dehydrogenase (LDH)] activities in adult zebrafish (Danio rerio). We found that exposure to 30-μg l-1 BPF and BPS, but not BPA, reduced swimming performance, and no interactions between bisphenol exposure and acclimation (3 weeks to 18°C and 28°C) or acute test (18°C and 28°C) temperatures were found. BPA interacted with acclimation and acute test temperatures to determine CS activity, an indicator of mitochondrial density and aerobic metabolic capacity. BPS reduced CS activity and an interaction (at a one-tailed significance) between acclimation temperature and BPF exposure determined CS activity. LDH activity reflects anaerobic ATP production capacity, and BPA and BPF altered the effects of thermal acclimation and acute test temperatures on LDH activity. Our data show that all bisphenols we tested at ecologically relevant concentrations can disrupt the thermal responses of fish. BPS and BPF are used as environmentally safer alternatives to BPA, but our data show that these bisphenols are also of concern, particularly in thermally variable environments.

Association of urinary bisphenols during pregnancy with maternal, cord blood and childhood thyroid function

BACKGROUND

Most pregnant women are exposed to bisphenols, a group of chemicals that can interfere with various components of the thyroid system.

OBJECTIVES

To investigate the association of maternal urinary bisphenol concentrations during pregnancy with maternal, newborn and early childhood thyroid function.

METHODS

This study was embedded in Generation R, a prospective, population-based birth cohort (Rotterdam, the Netherlands). Maternal urine samples were analyzed for eight bisphenols at early (<18), mid (18-25) and late (>25 weeks) pregnancy. Maternal serum thyroid stimulating hormone (TSH), free thyroxine (FT4) and total thyroxine (TT4) were measured in early pregnancy and child TSH and FT4 were measured in cord blood and childhood.

RESULTS

The final study population comprised 1,267 mothers, 853 newborns and 882 children. Of the eight bisphenols measured, only bisphenol A (BPA) was detected in >50% of samples at all three time-points and bisphenol S (BPS) at the first time-point. There was no association of BPA or the bisphenol molar sum with maternal thyroid function. Higher BPS concentrations were associated with a higher maternal TT4 (β [95% CI] per 1 (natural-log) unit increase: 0.97 [0.03 to 1.91]) but there was no association with TSH or FT4. Furthermore, higher BPS was associated with an attenuation of the association between maternal FT4 and TSH (P_interaction = 0.001). There was no association of early or mid-pregnancy BPA or early pregnancy BPS with cord blood or childhood TSH and FT4. A higher late pregnancy maternal BPA exposure was associated with a higher TSH in female newborns (P_interaction = 0.06) and a higher FT4 during childhood in males (P_interaction = 0.08).

DISCUSSION

Our findings show that exposure to bisphenols may interfere with the thyroid system during pregnancy. Furthermore, the potential developmental toxicity of exposure to bisphenols during pregnancy could affect the thyroid system in the offspring in a sex-specific manner.

Association of placental concentrations of phenolic endocrine disrupting chemicals with cognitive functioning in preschool children from the Environment and Childhood (INMA) Project

Developmental exposure to bisphenol A (BPA) and other phenolic endocrine disrupting chemicals (EDCs) may affect child neurodevelopment, but data on the effects of prenatal exposure to phenols on cognitive function remain sparse. Our aim was to examine the association of placental concentrations of several phenolic EDCs, including BPA, parabens (PBs), and benzophenones (BzPs), with cognitive development in preschool children from the Environment and Childhood (INMA) Project in Spain. Concentrations of BPA, four PBs (methylparaben [MePB], ethylparaben [EtPB], propylparaben [PrPB], and butylparaben [BuPB]), and six BzPs (BzP-1, BzP-2, BzP-3, BzP-6, BzP-8, and 4-hydroxybenzophenone [4-OH-BzP]) were measured in 490 placenta samples randomly selected from five INMA cohorts collected between 2000 and 2008. Neuropsychological assessment of cognitive and motor function was performed with the McCarthy Scales of Children's Abilities (MSCA) at the age of 4-5 years. Associations were assessed in a sub-sample of 191 mother-child pairs using linear and logistic regression models adjusted for confounding factors. PB compounds were detected in more than 71% of placentas, BPA in 62%, 4-OH-BzP in 50%, and the remaining BzPs in <9% of the samples. Because of the low detection frequency of BzP compounds, only 4-OH-BzP was included in the exposure-outcome analyses. After adjustment for confounders, BPA was associated with greater odds of scoring lower (below the 20th percentile) in the verbal (third vs. first exposure tertile: odds ratio [OR] = 2.78, 95% confidence interval [CI] = 1.00; 5.81, p-trend = 0.05) and gross motor (detected vs. undetected: OR = 1.75, 95%CI = 1.06; 9.29) areas, and these associations were only significant for boys. Regarding PB compounds, PrPB was associated with lower scores in memory (detected vs. undetected: β = -4.96, 95%CI = -9.54; -0.31), span memory (OR = 2.50, 95%CI = 0.95; 6.92 and 2.71, 95%CI = 0.97; 6.64, respectively for second and third tertiles, p-trend = 0.03), and motor function (β = -5.15, 95%CI = -9.26; -0.01 for third vs. first exposure tertile, p-trend = 0.04). EtPB and total PBs concentrations in the second tertile were also associated with poorer visual function of posterior cortex and worse quantitative performance, respectively, but linear trends were not statistically significant. The associations of BPA and PrPB with poorer verbal, memory, and motor skills are novel observations that warrant further attention. Larger prospective studies are required to confirm whether prenatal exposure to BPA and other phenolic EDCs is associated with impaired cognitive development.

Effect of the plastic pollutant bisphenol A on the biology of aquatic organisms: A meta-analysis

Plastic pollution is a global environmental concern. In particular, the endocrine-disrupting chemical bisphenol A (BPA) is nearly ubiquitous in aquatic environments globally, and it continues to be produced and released into the environment in large quantities. BPA disrupts hormone signalling and can thereby have far-reaching physiological and ecological consequences. However, it is not clear whether BPA has consistent effects across biological traits and phylogenetic groups. Hence, the aim of this study was to establish the current state of knowledge of the effect of BPA in aquatic organisms. We show that overall BPA exposure affected aquatic organisms negatively. It increased abnormalities, altered behaviour and had negative effects on the cardiovascular system, development, growth and survival. Early life stages were the most sensitive to BPA exposure in invertebrates and vertebrates, and invertebrates and amphibians seem to be particularly affected. These data provide a context for management efforts in the face of increasing plastic pollution. However, data availability is highly biased with respect to taxonomic groups and traits studies, and in the geographical distribution of sample collection. The latter is the case for both measurements of the biological responses and assessing pollution levels in water ways. Future research effort should be directed towards biological systems, such as studying endocrine disruption directly, and geographical areas (particularly in Africa and Asia) which we identify to be currently undersampled.

Bisphenols as Environmental Triggers of Thyroid Dysfunction: Clues and Evidence

Bisphenols (BPs), and especially bisphenol A (BPA), are known endocrine disruptors (EDCs), capable of interfering with estrogen and androgen activities, as well as being suspected of other health outcomes. Given the crucial role of thyroid hormones and the increasing incidence of thyroid carcinoma in the last few decades, this review analyzes the effects of BPS on the thyroid, considering original research in vitro, in vivo, and in humans published from January 2000 to October 2019. Both in vitro and in vivo studies reported the ability of BPs to disrupt thyroid function through multiple mechanisms. The antagonism with thyroid receptors (TRs), which affects TR-mediated transcriptional activity, the direct action of BPs on gene expression at the thyroid and the pituitary level, the competitive binding with thyroid transport proteins, and the induction of toxicity in several cell lines are likely the main mechanisms leading to thyroid dysfunction. In humans, results are more contradictory, though some evidence suggests the potential of BPs in increasing the risk of thyroid nodules. A standardized methodology in toxicological studies and prospective epidemiological studies with individual exposure assessments are warranted to evaluate the pathophysiology resulting in the damage and to establish the temporal relationship between markers of exposure and long-term effects.

Ginger extract ameliorates bisphenol A (BPA)-induced disruption in thyroid hormones synthesis and metabolism: Involvement of Nrf-2/HO-1 pathway

Environmental exposure to BPA is alarming because of the potential health threats for example those concerning the thyroid glands which may show signs of oxidative stress. This original study aimed to investigate the possible antioxidant protective effects of ginger extract (GE) against BPA-induced thyroid injury in male rats, focusing on its effect on Nrf-2/HO-1 signaling and thyroid hormone synthesis regulating genes. The cascade of events in thyroid injury induced by chronic exposure to BPA (200 mg/kg b.w/day for 35 days) involved a preliminary overproduction of ROS followed by significant (p ≤ 0.05) depletion of reduced glutathione (GSH) levels and superoxide dismutase (SOD) activity as well as significant increases of malondialdehyde (MDA) contents, myeloperoxidase (MPO) activity and inducible nitric oxide synthase (iNOS) gene expression. These actions consequently down-regulate the Nrf-2/HO-I signaling which eventually resulting in the DNA fragmentation within the thyroid tissues. Moreover, BPA administration caused a reduction of thyroid iodide uptake evidenced by significant inhibitions (p ≤ 0.05) of sodium-iodide symporter (NIS), thyroid peroxidase (TPO) and thyroid-stimulating hormone receptor (TSHR) mRNA expressions within the thyroid glands. A subsequent significant decreased serum levels of T3 and T4 accompanied by a significantly increased serum TSH level were also detected. These findings were confirmed by the severe pathological changes detected in the thyroid tissue of BPA treated rats. These biochemical and histological alterations were significantly alleviated with ginger administration (250 mg/kg b.w/day for 35 days) plus BPA. In conclusion, ginger extract is a potent antioxidant that can effectively protect against BPA-induced thyroid oxidative damage by activating the Nrf-2/HO-1 gene expressions and enhancing the thyroid hormones synthesis. This is the first study to show the contribution of Nrf-2/HO-1 pathway to the protective effect of ginger extract against BPA-induced thyroid oxidative damage and thyroid hormonal disruption.

Fetal-Perinatal Exposure to Bisphenol-A Affects Quality of Spermatozoa in Adulthood Mouse

Bisphenol-A (BPA) is considered an endocrine disruptor with estrogenic activity. It is described as an environment-polluting industrial chemical whose adverse effects on the male reproductive system depend on the period of exposure (i.e., fetal, prepubertal, or adult life). We exposed male mice to BPA during the fetal-perinatal period (from 10 days post coitum to 31 days post partum) and investigated the impact of this early-life exposure on gamete health in adulthood animals at 78 days of age. Both in control and BPA-exposed mice, viability and motility of spermatozoa, as well as sperm motility acquisition and chromatin condensation of spermatozoa, have been evaluated. Results reveal harmful effect of BPA on viability and motility of sperm cells as well as on chromatin condensation status during epididymal maturation of spermatozoa. In particular, BPA exposure interferes with biochemical mechanism useful to stabilize sperm chromatin condensation, as it interferes with oxidation of thiol groups associated to chromatin.

Bisphenol A and Phthalates Exhibit Similar Toxicogenomics and Health Effects

Bisphenol A and phthalates are most frequently detected organic pollutants found in our surroundings because of their regular use as plasticizers in daily use polymeric products. BPA is used in manufacturing baby feeding bottles, water pipes, canned food linings, and food packaging materials. Phthalates are used in polyvinyl chloride products including clothing, toys, medical devices, and food packaging. These chemicals are not bound to the matrix and leach out into the surroundings on slight change in the environment, like alteration in pH, temperature, and pressure. Humans are continuously exposed to these chemicals through skin contact, inhalation, or ingestion when the leachates enter food, drinks, air, water, or soil. The Comparative Toxicogenomics Database (CTD) revealed that Bisphenol A has 1932 interactions with genes/proteins and few frequently used phthalates (DEHP, MEHP, DBP, BBP, and MBP) showed 484 gene/protein interactions. Similar toxicogenomics and adverse effects of Bisphenol A and phthalates on human health are attributed to their 89 common interacting genes/proteins.

Bisphenols as a Legacy Pollutant, and Their Effects on Organ Vulnerability

Bisphenols are widely used in the synthesis of polycarbonate plastics, epoxy resins, and thermal paper, which are used in manufacturing items of daily use. Packaged foods and drinks are the main sources of exposure to bisphenols. These chemicals affect humans and animals by disrupting the estrogen, androgen, progesterone, thyroid, and aryl hydrocarbon receptor functions. Bisphenols exert numerous harmful effects because of their interaction with receptors, reactive oxygen species (ROS) formation, lipid peroxidation, mitochondrial dysfunction, and cell signal alterations. Both cohort and case-control studies have determined an association between bisphenol exposure and increased risk of cardiovascular diseases, neurological disorders, reproductive abnormalities, obesity, and diabetes. Prenatal exposure to bisphenols results in developmental disorders in animals. These chemicals also affect the immune cells and play a significant role in initiating the inflammatory response. Exposure to bisphenols exhibit age, gender, and dose-dependent effects. Even at low concentrations, bisphenols exert toxicity, and hence deserve a critical assessment of their uses. Since bisphenols have a global influence on human health, the need to discover the underlying pathways involved in all disease conditions is essential. Furthermore, it is important to promote the use of alternatives for bisphenols, thereby restricting their uses.

Neonatal Screening for Congenital Hypothyroidism: What Can We Learn From Discordant Twins?

CONTEXT

Newborn screening program for congenital hypothyroidism (CH) adopting rescreening in at-risk neonates.

OBJECTIVES

To estimate the concordance rate for CH in twin pairs discordant at the first screening; to verify whether long-term follow-up of healthy cotwins belonging to CH discordant pairs may be useful to diagnose thyroid hypofunction during development; to evaluate the importance of genetic and environmental influences on liability to permanent and transient CH.

DESIGN AND PATIENTS

Forty-seven screening discordant twin pairs were investigated. Proband was defined as the twin in the pair with a positive test at the first screening and a confirmed diagnosis of CH.

RESULTS

Seven screening discordant twin pairs became concordant for CH within the first month of life (pairwise concordance of 14.9%) because seven screening negative cotwins showed high TSH values when retested. During long-term follow-up (range, 3 to 21 years), hypothyroidism was diagnosed in two monozygotic screening negative cotwins at the age of 9 months and 12 years, respectively. Furthermore, the twin analysis showed that 95% of liability to transient CH was explained by genetic factors and 5% by environmental (unshared) factors, whereas 64% of phenotypic variance of permanent CH was explained by common environmental factors (shared during the fetal life) and 36% by unshared environmental factors.

CONCLUSIONS

This study showed that the introduction of rescreening permits the diagnosis of CH in a greater number of twins. It also showed the importance of long-term follow-up in both twins in the pair, and the role of nongenetic factors in the etiology of permanent CH.

Association of urinary bisphenols and triclosan with thyroid function during early pregnancy

BACKGROUND

Bisphenols and triclosan are considered as potential thyroid disruptors. While mild alterations in maternal thyroid function can result in adverse pregnancy and child developmental outcomes, there is still uncertainty whether bisphenols or triclosan can interfere with thyroid function during pregnancy.

OBJECTIVES

We aimed to investigate the association of urinary bisphenol A (BPA), bisphenol S (BPS), bisphenol F (BPF) and triclosan with early pregnancy thyroid function.

METHODS

This study was embedded in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy study (SELMA), a population-based prospective pregnancy cohort. In total, 1996 participants were included in the current study. Maternal urinary concentrations of three bisphenols and triclosan, collected at median (95% range) 10 (6-14) weeks of pregnancy as well as serum concentrations of thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), total thyroxine (TT4), and total triiodothyronine (TT3) were measured.

RESULTS

Higher BPA levels were associated with lower TT4 concentrations (non-monotonic, P = 0.03), a lower FT4/FT3 ratio (β [SE] -0.02 [0.01], P = 0.03) and a lower TT4/TT3 ratio (β [SE] -0.73 [0.27], P = 0.008). Higher BPF levels were associated with a higher FT3 (β [SE] 0.01 [0.007], P = 0.04). There were no associations between other bisphenols or triclosan and absolute TSH, (F)T4 or (F)T3 concentrations. The association of BPA with thyroid function differed with gestational age. The negative association of BPA with FT4/FT3 and TT4/TT3 ratios was only apparent in early but not late gestation (P for interaction: 0.003, 0.008, respectively).

CONCLUSION

These human data during pregnancy substantiate experimental findings suggesting that BPA could potentially affect thyroid function and deiodinase activities in early gestation.

Bisphenols and Thyroid Hormone

In recent decades, attention has been directed toward the effects of bisphenol A (BPA) on human health. BPA has estrogenic activity and is regarded as a representative endocrine disruptor. In addition, mounting evidence indicates that BPA can disrupt thyroid hormone and its action. This review examined human epidemiological studies to investigate the association between BPA exposure and thyroid hormone levels, and analyzed in vivo and in vitro experiments to identify the causal relationship and its mechanism of action. BPA is involved in thyroid hormone action not only as a thyroid hormone receptor antagonist, but also through several other mechanisms. Since the use of bisphenols other than BPA has recently increased, we also reviewed the effects of other bisphenols on thyroid hormone action.

Evaluating Chemicals for Thyroid Disruption: Opportunities and Challenges with in Vitro Testing and Adverse Outcome Pathway Approaches

BACKGROUND

Extensive clinical and experimental research documents the potential for chemical disruption of thyroid hormone (TH) signaling through multiple molecular targets. Perturbation of TH signaling can lead to abnormal brain development, cognitive impairments, and other adverse outcomes in humans and wildlife. To increase chemical safety screening efficiency and reduce vertebrate animal testing, in vitro assays that identify chemical interactions with molecular targets of the thyroid system have been developed and implemented.

OBJECTIVES

We present an adverse outcome pathway (AOP) network to link data derived from in vitro assays that measure chemical interactions with thyroid molecular targets to downstream events and adverse outcomes traditionally derived from in vivo testing. We examine the role of new in vitro technologies, in the context of the AOP network, in facilitating consideration of several important regulatory and biological challenges in characterizing chemicals that exert effects through a thyroid mechanism.

DISCUSSION

There is a substantial body of knowledge describing chemical effects on molecular and physiological regulation of TH signaling and associated adverse outcomes. Until recently, few alternative nonanimal assays were available to interrogate chemical effects on TH signaling. With the development of these new tools, screening large libraries of chemicals for interactions with molecular targets of the thyroid is now possible. Measuring early chemical interactions with targets in the thyroid pathway provides a means of linking adverse outcomes, which may be influenced by many biological processes, to a thyroid mechanism. However, the use of in vitro assays beyond chemical screening is complicated by continuing limits in our knowledge of TH signaling in important life stages and tissues, such as during fetal brain development. Nonetheless, the thyroid AOP network provides an ideal tool for defining causal linkages of a chemical exerting thyroid-dependent effects and identifying research needs to quantify these effects in support of regulatory decision making. https://doi.org/10.1289/EHP5297.

CLARITY-BPA: Bisphenol A or Propylthiouracil on Thyroid Function and Effects in the Developing Male and Female Rat Brain

The CLARITY-BPA experiment, a large collaboration between the National Institute of Environmental Health Sciences, the National Toxicology Program, and the US Food and Drug Administration, is designed to test the effects of bisphenol A (BPA) on a variety of endocrine systems and end points. The specific aim of this subproject was to test the effect of BPA exposure on thyroid functions and thyroid hormone action in the developing brain. Timed-pregnant National Center for Toxicological Research Sprague-Dawley rats (strain code 23) were dosed by gavage with vehicle control (0.3% carboxymethylcellulose) or one of five doses of BPA [2.5, 25, 250, 2500, or 25,000 µg/kg body weight (bw) per day] or ethinyl estradiol (EE) at 0.05 or 0.50 µg/kg bw/d (n = 8 for each group) beginning on gestational day 6. Beginning on postnatal day (PND) 1 (day of birth is PND 0), the pups were directly gavaged with the same dose of vehicle, BPA, or EE. We also obtained a group of animals treated with 3 ppm propylthiouracil in the drinking water and an equal number of concordant controls. Neither BPA nor EE affected serum thyroid hormones or thyroid hormone‒sensitive end points in the developing brain at PND 15. In contrast, propylthiouracil (PTU) reduced serum T4 to the expected degree (80% reduction) and elevated serum TSH. Few effects of PTU were observed in the male brain and none in the female brain. As a result, it is difficult to interpret the negative effects of BPA on the thyroid in this rat strain because the thyroid system appears to respond differently from that of other rat strains.

Multidisciplinary haematology as prognostic device in environmental and xenobiotic stress-induced response in fish

The variations of haematological parameters hematocrit, hemoglobin concentration, leukocyte and erythrocyte count have been used as pollution and physiological indicators of organic dysfunction in both environmental and aquaculture studies. These parameters are commonly applied as prognostic and diagnostic tools in fish health status. However, there are both extrinsic and intrinsic factors to consider when performing a blood test, because a major limitation for field researchers is that the "rules" for animal or human haematology do not always apply to wildlife. The main objective of this review is to show how some environmental and xenobiotic factors are capable to modulating the haematic cells. Visualizing the strengths and limitations of a haematological analysis in the health assessment of wild and culture fish. Finally, we point out the importance of the use of mitochondrial activities as part of haematological evaluations associated to environment or aquaculture stress.

Bisphenol A exposure and risk of thyroid nodules in Chinese women: A case-control study

BACKGROUND

Thyroid nodules (TNs) are highly prevalent worldwide and have a pattern of female predominance. Bisphenol A (BPA) is an endocrine disruptor that can lead to adverse effects in human health. However, epidemiologic studies revealing the association between BPA exposure and TNs are limited and the results are inconsistent. We aimed to examine the association between urinary BPA and TNs in women who are more susceptible to TNs.

METHODS

We conducted a case-control study with 1416 women aged 18 years or older (705 cases, 711 controls). All participants underwent thyroid ultrasonography. Urinary total BPA (free and conjugated) concentration was quantified using the HPLC-MS/MS. We analyzed the association between urinary BPA concentration and the risk of TNs using crude and multivariable logistic regression models. Participants were further stratified into thyroid autoantibody positive group (at least one positive) and thyroid autoantibody negative group (both negative) according to the thyroglobulin antibody (TGAb) and thyroid peroxidase antibody (TPOAb) levels, and restricted cubic spline regression was also applied to determine the possible nonlinear relationship between urinary BPA and TNs.

RESULTS

Compared with women in the first quartile, the odds of TNs was 72% (adjusted OR = 1.72, 95% CI: 1.25 to 2.35) higher for those in the second quartile, 54% (adjusted OR = 1.54, 95% CI: 1.12 to 2.12) higher for those in the third quartile, and 108% (adjusted OR = 2.08, 95% CI: 1.50 to 2.90) higher for those in the fourth quartile after adjusting for age, BMI, education, HDL-C, LDL-C, triglyceride, total cholesterol, urinary iodine, TGAb and TPOAb. When the study population was stratified into thyroid autoantibody positive group and thyroid autoantibody negative group, we found that only in the positive group, the association was significant in model 1 (crude OR = 2.80; 95% CI = 1.90 to 4.12), model 2 (adjusted OR = 2.84; 95% CI = 1.91 to 4.22), model 3 (adjusted OR = 4.01; 95% CI = 2.57 to 6.27) and model 4 (adjusted OR = 3.71; 95% CI = 2.36 to 5.83). Multivariable-adjusted restricted cubic spline analysis demonstrated a similar result that in the thyroid autoantibody positive group, the association between urinary BPA and TNs risk was near linear (P-overall <0.001; P-non-linear = 0.054).

CONCLUSION

In Chinese women, higher urinary BPA concentration was associated with increased risk of TNs only in those with positive thyroid autoantibodies. Moreover, this association was near linear, indicating that any rise in BPA exposure was associated with elevated TNs risk.

Comparison of thyroid hormone disruption potentials by bisphenols A, S, F, and Z in embryo-larval zebrafish

Several structural analogues of bisphenol A (BPA), e.g., bisphenol F (BPF), bisphenol S (BPS), and bisphenol Z (BPZ), have been used as its substitutes in many applications and consequently detected in the environment, and human specimen such as urine and serum. While BPA has been frequently reported for thyroid hormone disruption in both experimental and epidemiological studies, less is known for the BPA analogues. In the present study, thyroid hormone disrupting effects of BPF, BPS and BPZ, were investigated, and compared with those of BPA, using embryo-larval zebrafish (Danio rerio). At 120 hpf, significant increases in T3 and/or T4 were observed in the larval fish following exposure to BPA, BPF, or BPS. Moreover, transcriptional changes of the genes related to thyroid development (hhex and tg), thyroid hormone transport (ttr) and metabolism (ugt1ab) were observed as well. Thyroid hormone (T4) disruption by BPF was observed even at the concentration (2.0 mg/L) lower than the effective concentration determined for BPA (>2.0 mg/L). Delayed hatching was observed by all tested bisphenols. Our results clearly show that these BPA analogues can disrupt thyroid function of the larval fish, and their thyroid hormone disruption potencies could be even greater than that of BPA. The concentrations which disrupt thyroid function of the larval fish were orders of magnitude higher than those occurring in the ambient environment. However, thyroid hormone disruption by longer term exposure and its consequences in the fish population, deserve further investigation.

Parental co-exposure to bisphenol A and nano-TiO2 causes thyroid endocrine disruption and developmental neurotoxicity in zebrafish offspring

The coexistence of organic toxicants and nanoparticles in the environment influences pollutant bioavailability and toxicity. Using chronic co-exposure to an adult zebrafish model, this study investigated the transfer kinetics and transgenerational effects of bisphenol A (BPA) and titanium dioxide nanoparticles (n-TiO₂) exposure in F1 offspring. When single and combined exposure to BPA (0, 2, and 20 μg/L) and n-TiO₂ (100 μg/L) were compared, combined exposure was found to reciprocally facilitate bioaccumulation in adult fish while enhancing maternal transfer to offspring. Thyroid endocrine disruption and developmental neurotoxicity were observed in larval offspring by parental exposure to BPA alone or in combination with n-TiO₂. Exposure to 20 μg/L BPA significantly decreased the thyroxine (T4) concentration in adult plasma, leading to less transfer into the eggs. The presence of 20 μg/L BPA with n-TiO₂ further decreased the level of T4 compared to BPA exposure alone. Additionally, offspring larvae derived from exposed parents exhibited lethargic swimming behavior. Overall, this study examined the interactions of BPA and n-TiO₂ with regard to their bioaccumulation, maternal transfer, and developmental effects, which highlighted that co-exposure dynamics are important and need to be considered for accurate environmental risk assessment.

A Toxicogenomic Approach Reveals a Novel Gene Regulatory Network Active in In Vitro and In Vivo Models of Thyroid Carcinogenesis

Epidemiological and experimental studies emphasize the link between environmental chemicals exposure and thyroid cancer. However, this association is strongly debated and the mechanisms of action of environmental thyroid carcinogens still need to be identified. The analysis of in vitro transcriptomic data developed to investigate the effects of chlorpyrifos on immortalized thyrocytes highlighted the impaired expression of genes involved in endodermal carcinogenesis. This endodermal carcinogenic gene-network (ECGN, including Zfp36l2, Dmbt1, Ddit4), was validated in cellular and mouse models of thyroid carcinogenesis, characterized by the constitutive activation of the mitogen-activated protein kinase (MAPK) pathway and in immortalized thyrocytes exposed to tetrachlorodibenzo-p-dioxin (TCDD) and chlorpyrifos (CPF). The mRNA levels of Zfp36l2, Dmbt1 and Ddit4 were increased in models characterized by MAPK activation or following TCDD exposure, whereas they were inhibited by CPF exposure. Overall, the ECGN transcripts identify a novel gene-regulatory network associated with thyroid carcinogenesis promoted by genetic mutation or by environmental carcinogens. The latter have opposite effects on the modulation of the ECGN transcripts according to their mechanisms of action in promoting carcinogenesis. Therefore, the analyses of ECGN might be helpful in discriminating compounds that promote cellular survival associated or not to proliferation of thyrocytes.

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.

Acute exposure of zebrafish embryo (Danio rerio) to flutolanil reveals its developmental mechanism of toxicity via disrupting the thyroid system and metabolism

Flutolanil, an amide fungicide, had been detected frequently in aquatic environments; it is thus potentially a great risk to aquatic organisms and human health. Therefore, we investigated the developmental toxicity and the potential mechanism of thyroid endocrine disruption induced by flutolanil based on ¹H NMR metabolomics analysis using a zebrafish model. Hatching of zebrafish embryo exposed to flutolanil was inhibited at 72 hpf (hour post-fertilization) and survival and body length at 96 hpf. In addition, increased teratogenic effects on embryos were observed, including pericardial edema, spine deformation, and tail malformation. Furthermore, flutolanil induced slower heartbeat and larger pericardial area in the treated groups than control group. Transcription levels of TRH, TSHR, TPO, Dio1, TRα, and UGT1ab were significantly altered after flutolanil exposure. Metabolomics analysis further indicated that flutolanil induced alterations of energy, amino acids, nucleotide, lipids, and fatty acid metabolism. Our study also indicated that flutolanil exposure led to alterations of endogenous metabolites, which induced the thyroid endocrine disruption in zebrafish. Ultimately, embryonic developmental toxicity was caused by flutolanil.

Nutritional and Environmental Factors in Thyroid Carcinogenesis

Several epidemiological studies suggest an increased incidence of thyroid carcinoma (TC) in recent years, especially for the papillary histotype (PTC), suggesting that specific carcinogens might promote molecular abnormalities that are typical of PTC. The increased incidence is probably attributed to more intensive and sensitive diagnostic procedures, even if recent data suggest that various toxic elements could explain the phenomenon. Ionizing radiation exposure represents the most accepted risk factor for differentiated thyroid cancer that includes both the follicular and papillary histotypes. In this review, we examined the other environmental carcinogens that play a role in TC, such as eating habits, living in volcanic areas, and xenobiotic elements. Among eating habits, iodine intake represents one of the more discussed elements, because its deficiency is associated with follicular thyroid carcinomas (FTCs), while its progressive increment seems to be responsible for PTC. The gas, ash, and lava emissions of volcanoes are composed of various toxic compounds that pollute ground water, vegetables, and animals, contaminating humans via the food chain. Finally, the risk of developing PTC has also been associated with exposure of the population to xenobiotics in the environment or in the home. Their carcinogenic effects are probably caused by their accumulation, but additional studies are necessary to better understand the mechanisms of action.

Thyroid Hormone-Disrupting Potentials of Major Benzophenones in Two Cell Lines (GH3 and FRTL-5) and Embryo-Larval Zebrafish

Benzophenones (BPs) have been widely used in personal care products (PCPs) such as UV protectants. Sex endocrine-disrupting effects have been documented for some BPs, but, significant knowledge gaps are present for their thyroid-disrupting effects. To investigate the thyroid-disrupting potential of BPs, a rat pituitary (GH3) and thyroid follicle (FRTL-5) cell line were employed on six BPs, i.e., benzophenone (BP), benzophenone-1 (BP-1), benzophenone-2 (BP-2), benzophenone-3 (BP-3), benzophenone-4 (BP-4), and benzophenone-8 (BP-8). Subsequently, zebrafish ( Danio rerio) embryo exposure was conducted for three potent BPs that were identified based on the transcriptional changes observed in the cells. In GH3 cells, all BPs except BP-4 down-regulated the Tshβ, Trhr, and Trβ genes. In addition, some BPs significantly up-regulated the Nis and Tg genes while down-regulating the Tpo gene in FRTL-5 cells. In zebrafish embryo assay conducted for BP-1, BP-3, and BP-8, significant decreases in whole-body T4 and T3 level were observed at 6 day postfertilization (dpf). The up-regulation of the dio1 and ugt1ab genes in the fish suggests that decreased thyroid hormones are caused by changing metabolism of the hormones. Our results show that these frequently used BPs can alter thyroid hormone balances by influencing the central regulation and metabolism of the hormones.

Thyroid Function Disruptors: from nature to chemicals

The modern concept of thyroid disruptors includes man-made chemicals and bioactive compounds from food that interfere with any aspect of the hypothalamus-pituitary-thyroid axis, thyroid hormone biosynthesis and secretion, blood and transmembrane transport, metabolism and local action of thyroid hormones. This review highlights relevant disruptors that effect populations through their diet: directly from food itself (fish oil and polyunsaturated fatty acids, pepper, coffee, cinnamon and resveratrol/grapes), through vegetable cultivation (pesticides) and from containers for food storage and cooking (bisphenol A, phthalates and polybrominated diphenyl ethers). Due to the vital role of thyroid hormones during every stage of life, we review effects from the gestational period through to adulthood, including evidence from in vitro studies, rodent models, human trials and epidemiological studies.

Current Knowledge on Endocrine Disrupting Chemicals (EDCs) from Animal Biology to Humans, from Pregnancy to Adulthood: Highlights from a National Italian Meeting

Wildlife has often presented and suggested the effects of endocrine disrupting chemicals (EDCs). Animal studies have given us an important opportunity to understand the mechanisms of action of many chemicals on the endocrine system and on neurodevelopment and behaviour, and to evaluate the effects of doses, time and duration of exposure. Although results are sometimes conflicting because of confounding factors, epidemiological studies in humans suggest effects of EDCs on prenatal growth, thyroid function, glucose metabolism and obesity, puberty, fertility, and on carcinogenesis mainly through epigenetic mechanisms. This manuscript reviews the reports of a multidisciplinary national meeting on this topic.

Oleuropein and hydroxytyrosol protect rats' pups against bisphenol A induced hypothyroidism

Bisphenol A (BPA) can disturb the endocrine system and the organs that respond to endocrine signals in organisms, indirectly exposed during prenatal and/or early postnatal life. The present study was designed to assess the protective effect of phenolic compounds from olive leaves against BPA induced thyroid dysfunction and growth perturbation in young rats during lactation. The BPA disrupting effect on thyroid function was investigated by measuring changes in plasma levels of thyroid hormones. Free triiodothyronine (FT3) and thyroxine (FT4) were decreased in young rats breast-fed from mothers treated with bisphenol A. This effect was associated with an increase in the plasma level of thyroid-stimulating hormone (TSH). The histological and immunohistochemical study of the thyroid gland revealed a disturbance in morphological structure and thyroid cells function. Thyroid dysfunction led to a disruption in the skeletal bone growth of young rats. In fact, the infrared microspectroscopic analysis and histological examination of femoral bone showed significant changes in their histoarchitecture associated with a perturbation in the mechanism of bone tissue mineralization. The administration of oleuropein or hydroxytyrosol in BPA treated lactating mothers improved the thyroid cells function by enhancing thyroid hormone levels. Moreover, these phenolics increased the body growth characterized by an amelioration in the structure and the microstructure of femoral bone tissue. HPLC analysis of rats-breast milk indicated the presence of oleuropein and hydroxytyrosol, which could contribute to the protective effect against bisphenol A induced hypothyroidism in pups rats.

Sub-lethal effects of herbicides penoxsulam, imazamox, fluridone and glyphosate on Delta Smelt (Hypomesus transpacificus)

Concerns regarding non-target toxicity of new herbicides used to control invasive aquatic weeds in the San Francisco Estuary led us to compare sub-lethal toxicity of four herbicides (penoxsulam, imazamox, fluridone, and glyphosate) on an endangered fish species Delta Smelt (Hypomesus transpacificus). We measured 17β-estradiol (E2) and glutathione (GSH) concentrations in liver, and acetylcholinesterase (AChE) activity in brain of female and male fish after 6 h of exposure to each of the four herbicides. Our results indicate that fluridone and glyphosate disrupted the E2 concentration and decreased glutathione concentration in liver, whereas penoxsulam, imazamox, and fluridone inhibited brain AChE activity. E2 concentrations were significantly increased in female and male fish exposed to 0.21 μM of fluridone and in male fish exposed to 0.46, 4.2, and 5300 μM of glyphosate. GSH concentrations decreased in males exposed to fluridone at 2.8 μM and higher, and glyphosate at 4.2 μM. AChE activity was significantly inhibited in both sexes exposed to penoxsulam, imazamox, and fluridone, and more pronounced inhibition was observed in females. The present study demonstrates the potential detrimental effects of these commonly used herbicides on Delta Smelt.

Thyroid hormone- and estrogen receptor interactions with natural ligands and endocrine disruptors in the cerebellum

Although the effects of phytoestrogens on brain function is widely unknown, they are often regarded as "natural" and thus as harmless. However, the effects of phytoestrogens or environmental pollutants on brain function is underestimated. Estrogen (17beta-estradiol, E2) and thyroid hormones (THs) play pivotal roles in brain development. In the mature brain, these hormones regulate metabolism on cellular and organismal levels. Thus, E2 and THs do not only regulate the energy metabolism of the entire organism, but simultaneously also regulate important homeostatic parameters of neurons and glia in the CNS. It is, therefore, obvious that the mechanisms through which these hormones exert their effects are pleiotropic and include both intra- and intercellular actions. These hormonal mechanisms are versatile, and the experimental investigation of simultaneous hormone-induced mechanisms is technically challenging. In addition, the normal physiological settings of metabolic parameters depend on a plethora of interactions of the steroid hormones. In this review, we discuss conceptual and experimental aspects of the gonadal and thyroid hormones as they relate to in vitro models of the cerebellum.

A frequent oligogenic involvement in congenital hypothyroidism

Congenital hypothyroidism (CH), the most frequent form of preventable mental retardation, is predicted to have a relevant genetic origin. However, CH is frequently reported to be sporadic and candidate gene variations were found in <10% of the investigated patients. Here, we characterize the involvement of 11 candidate genes through a systematic Next Generation Sequencing (NGS) analysis. The NGS was performed in 177 unrelated CH patients (94 gland-in-situ; 83 dysgenesis) and in 3,538 control subjects. Non-synonymous or splicing rare variants (MAF < 0.01) were accepted, and their functional impact was predicted by a comprehensive bioinformatic approach and co-segregation studies. The frequency of variations in cases and controls was extended to 18 CH-unrelated genes. At least one rare variant was accepted in 103/177 patients. Monogenic recessive forms of the disease were found in five cases, but oligogenic involvement was detected in 39 patients. The 167 variations were found to affect all genes independently of the CH phenotype. These findings were replicated in an independent cohort of additional 145 CH cases. When compared to 3,538 controls, the CH population was significantly enriched with disrupting variants in the candidate genes (P = 5.5 × 10-7), but not with rare variations in CH-unrelated genes. Co-segregation studies of the hypothyroid phenotype with multiple gene variants in several pedigrees confirmed the potential oligogenic origin of CH. The systematic NGS approach reveals the frequent combination of rare variations in morphogenetic or functional candidate genes in CH patients independently of phenotype. The oligogenic origin represents a suitable explanation for the frequent sporadic CH occurrence.