Thyroxine-binding globulin, peripheral deiodinase activity, and thyroid autoantibody status in association of phthalates and phenolic compounds with thyroid hormones in adult population

Association between multipollutant exposure and thyroid hormones in elderly people: A cross-sectional study in China

Environmental chemicals have been indicated to cause disruption of thyroid homeostasis in human populations. However, previous studies mostly focused on single group of chemicals. Herein, we investigate the independent and combined effects of multiple pollutants on thyroid homeostasis, including thyroid-stimulating hormone (TSH), total and free thyroxine (tT4 and fT4) and total and free triiodothyronine (tT3 and fT3) in elderly people. These environmental pollutants (n = 144) are from ten categories, including phenols, parabens, perfluoroalkyl substances (PFASs), polychlorinated biphenyls (PCBs), phthalate esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), synthetic pyrethroids (SPs), herbicides, and metals. Few studies have evaluated the health risks of these 144 chemicals, especially their joint effects. In single-pollutant evaluations, multiple linear regression (MLR) models were used to estimate the independent associations between multiple exposures and thyroid biomarkers. In multi-pollutant evaluations, elastic net regression and Bayesian kernel machine regression (BKMR) models were used to estimate the combined associations. The MLR models showed that 41 chemicals were significantly related to THs levels. BKMR models revealed the most important chemical groups: metals for TSH, PAHs, SPs and PCBs for tT4, herbicides and SPs for tT3. This study will contribute to the understanding of multipollutant exposure and help prioritize specific chemical groups related to thyroid hormone disruption.

Exploring the mechanism of interaction between TBG and halogenated thiophenols: Insights from fluorescence analysis and molecular simulation

Thyroxine-binding globulin (TBG) plays a vital role in regulating metabolism, growth, organ differentiation, and energy homeostasis, exerting significant effects in various key metabolic pathways. Halogenated thiophenols (HTPs) exhibit high toxicity and harmfulness to organisms, and numerous studies have demonstrated their thyroid-disrupting effects. To understand the mechanism of action of HTPs on TBG, a combination of competitive binding experiments, multiple fluorescence spectroscopy techniques, molecular docking, and molecular simulations was employed to investigate the binding mechanism and identify the binding site. The competition binding assay between HTPs and ANS confirmed the competition of HTPs with thyroid hormone T4 for the active site of TBG, resulting in changes in the TBG microenvironment upon the binding of HTPs to the active site. Key amino acid residues involved in the binding process of HTPs and TBG were further investigated through residue energy decomposition. The distribution of high-energy contributing residues was determined. Analysis of root-mean-square deviation (RMSD) demonstrated the stability of the HTPs-TBG complex. These findings confirm the toxic mechanism of HTPs in thyroid disruption, providing a fundamental reference for accurately assessing the ecological risk of pollutants and human health. Providing mechanistic insights into how HTPS causes thyroid diseases.

Relationship between bisphenol A and autoimmune thyroid disease in women of childbearing age

Background

Autoimmune thyroid disease (AITD) is the main cause of hypothyroidism in women of childbearing age. Bisphenol A (BPA) is an environmental factor affecting AITD. This study aims to investigate relationship between BPA and AITD in women of childbearing age, thereby contributing novel evidence for the prevention of hypothyroidism in this specific demographic.

Methods

A total of 155 women of childbearing age were enrolled in this study, including the euthyroid group comprised 60 women with euthyroidism and thyroid autoantibodies negativity and the AITD group consisted of 95 women with euthyroidism and at least one thyroid autoantibody positivity. The general information, thyroid function, thyroid autoantibodies, and thyroid ultrasound results of the two groups of women of childbearing age were recorded. Urinary BPA and urinary BPA/creatinine were detected. The difference of BPA levels between the two groups was compared. logistic regression was used to analyze the correlation between BPA and AITD.

Results

The proportion of multiparous and serum thyroid stimulating hormone levels were significantly higher in the AITD group compared to the euthyroid group. Logistic regression analysis revealed that BPA levels did not exhibit a statistically significant association with AITD. Spearman correlation analysis revealed a statistically significant correlation between BPA and urinary iodine levels (r=0.30, P < 0.05), as well as a correlation between urinary BPA and free tetraiodothyronine (FT4) levels (r=0.29, P < 0.05).

Conclusion

This study revealed a correlation between urinary BPA levels and FT4 levels. However, it did not establish a relationship between BPA and AITD in women of childbearing age.

Correlation between systemic inflammatory response index and thyroid function: 2009-2012 NHANES results

Aims

This study investigates the relationship between the Systemic Inflammatory Response Index (SIRI) and thyroid function.

Methods

Utilizing data from the National Health and Nutrition Examination Survey (NHANES) 2009-2012, we excluded participants lacking SIRI or thyroid function data, those under 20 years, and pregnant individuals. SIRI was determined using blood samples. We conducted weighted multivariate regression and subgroup analyses to discern the independent relationship between SIRI and thyroid function.

Results

The study included 1,641 subjects, with an average age of 47.26±16.77 years, including 48.65% males and 51.35% females. The population was divided into three SIRI-based groups (Q1-Q3). Q3, compared to Q1, exhibited higher age-at-onset, greater male prevalence, and increased levels of FT3, FT4, TT4, leukocytes, and triglycerides. This group also showed a higher incidence of diabetes, hypertension, and smoking. Notably, Q1 had lower LDL and HDL levels. SIRI maintained a positive association with FT4 (β = 0.01, 95% CI = 0.00-0.03, P for trend = 0.0071), TT4 (β = 0.20, 95% CI = 0.10, 0.31, P for trend=0.0001), and TPOAb (β = 8.0, 95% CI = 1.77-14.30, P for trend = 0.0120), indicating that each quartile increase in SIRI corresponded to a 0.01 ng/dL increase in FT4, a 0.2 g/dL increase in TT4, and an 8.03 IU/mL rise in TPOAb. The subgroup analysis suggested the SIRI-thyroid function correlation was influenced by hypertension.

Conclusion

Inflammation may impact the development and progression of thyroid function disorders. Proactive anti-inflammatory treatment might mitigate thyroid abnormalities.

Sex-specific association of exposure to a mixture of phenols, parabens, and phthalates with thyroid hormone and antibody levels in US adolescents and adults

Individuals are exposed to multiple phenols, parabens, and phthalates simultaneously since they are important endocrine-disrupting compounds (EDCs) and share common exposure pathways. It is necessary to assess the effects of the co-exposure of these EDCs on thyroid hormones (THs). In this study, data included 704 adolescents and 2911 adults from the 2007-2012 National Health and Nutrition Examination Survey (NHANES). Serum THs measured total triiodothyronine (T3), total thyroxine (T4), free forms of T3 (FT3) and T4 (FT4), thyroid-stimulating hormone (TSH), thyroglobulin (Tg), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb). And 16 EDCs (3 phenols, 2 parabens, and 11 phthalates) were measured from urine. The relationship between single EDCs and single THs was analyzed using generalized linear regression. And results showed that several EDCs were positively associated with serum T3 and FT3 levels in boys but negatively associated with serum T4 and FT4 levels in girls. And in adults, five EDCs were negatively associated with T3, T4, or FT4. The effects of co-exposure to 16 EDCs on THs were calculated using Bayesian kernel machine regression and quantile-based g-computational modeling, confirmed that co-exposure was related to the increase of T3 in adolescents and the decrease of T4 in both adolescents and adults. Besides, nonlinear and linear relationships were identified between co-exposure and the risk of positive TPOAb and TgAb in girls and adult females, respectively. In conclusion, phenols, parabens, and phthalates as a mixture might interfere the concentrations of THs and thyroid autoantibodies, and the interfering effect varies significantly by sex as well as by age. Further prospective research is warranted to investigate the causal effects and underlying mechanisms of co-exposure on thyroid dysfunction.

Associations of Urinary Phthalate Metabolites with Thyroid Function and the Mediated Role of Cytokines: A Panel Study of Healthy Children

Evidence on joint association of a phthalate mixture with thyroid function among children and its underlying mechanism is largely unknown. We aimed to explore the associations of 10 urinary phthalate metabolites (mPAEs), either as individuals or as a mixture, with thyroid function indicators [free thyroxine, free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH)] in 144 children aged 4-12 years with up to 3 repeated visits across 3 seasons. Significant and positive associations were observed for mono-(2-ethylhexyl) phthalate (MEHP), mono-iso-butyl phthalate (MiBP), and mono-n-butyl phthalate (MnBP) with TSH, as well as monobenzyl phthalate (MBzP) with FT3 in dose-response manners. The relationship between MEHP and TSH remained robust in multiple-phthalate models. Bayesian kernel machine regression (BKMR) models revealed overall linear associations of the 10 mPAE mixture with higher TSH and FT3 levels, and MEHP and MBzP were major contributors. Meanwhile, MEHP, MiBP, and MnBP were linked to the elevation of multiple cytokines including CCL 27, CCL3, CXCL1, and IL-16. Among them, IL-16 mediated the relationships of MEHP and MiBP with TSH, and the mediated proportions were 24.16% and 24.27%, respectively. Our findings suggested that mPAEs dominated by MEHP were dose-responsively associated with elevated TSH among healthy children and mediated by IL-16.

Association of exposure to perfluoroalkyl substances (PFAS) and phthalates with thyroid hormones in adolescents from HBM4EU aligned studies

BACKGROUND

Perfluoroalkyl substances (PFAS) and phthalates are synthetic chemicals widely used in various types of consumer products. There is epidemiological and experimental evidence that PFAS and phthalates may alter thyroid hormone levels; however, studies in children and adolescents are limited.

AIM

To investigate the association of exposure to PFAS and phthalate with serum levels of thyroid hormones in European adolescents.

METHODS

A cross-sectional study was conducted in 406 female and 327 male adolescents (14-17 years) from Belgium, Slovakia, and Spain participating in the Aligned Studies of the HBM4EU Project (FLEHS IV, PCB cohort, and BEA, respectively). Concentrations of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorononanoic acid (PFNA), free thyroxine (FT4), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH) were measured in sera from study participants, and urinary metabolites of six phthalates (DEP, DiBP, DnBP, BBzP, DEHP, and DiNP) and the non-phthalate plasticizer DINCH® were quantified in spot urine samples. Associations were assessed with linear regression and g-computational models for mixtures. Effect modification by sex was examined.

RESULTS

In females, serum PFOA and the PFAS mixture concentrations were associated with lower FT4 and higher FT3 levels; MEP and the sums of DEHP, DiNP, and DINCH® metabolites (∑DEHP, ∑DiNP, and ∑DINCH) were associated with higher FT4; ∑DEHP with lower FT3; and the phthalate/DINCH® metabolite mixture with higher FT4 and lower FT3. In males, PFOA was associated with lower FT4 and the PFAS mixture with higher TSH levels and lower FT4/TSH ratio; MEP and ∑DiNP were associated with higher FT4; and MBzP, ∑DEHP, and the phthalate/DINCH® metabolite mixture with lower TSH and higher FT4/TSH. PFOA, mono-(2-ethyl-5-hydroxyhexyl) phthalate (OH-MEHP), mono-(2-ethyl-5-oxohexyl) phthalate (oxo-MEHP), and monocarboxyoctyl phthalate (MCOP) made the greatest contribution to the mixture effect.

CONCLUSIONS

Results suggest that exposure to PFAS and phthalates is associated with sex-specific differences in thyroid hormone levels in adolescents.

Environmental Endocrinology: Parabens Hazardous Effects on Hypothalamic-Pituitary-Thyroid Axis

Parabens are classified as endocrine-disrupting chemicals (EDCs) capable of interfering with the normal functioning of the thyroid, affecting the proper regulation of the biosynthesis of thyroid hormones (THs), which is controlled by the hypothalamic-pituitary-thyroid axis (HPT). Given the crucial role of these hormones in health and the growing evidence of diseases related to thyroid dysfunction, this review looks at the effects of paraben exposure on the thyroid. In this study, we considered research carried out in vitro and in vivo and epidemiological studies published between 1951 and 2023, which demonstrated an association between exposure to parabens and dysfunctions of the HPT axis. In humans, exposure to parabens increases thyroid-stimulating hormone (TSH) levels, while exposure decreases TSH levels in rodents. The effects on THs levels are also poorly described, as well as peripheral metabolism. Regardless, recent studies have shown different actions between different subtypes of parabens on the HPT axis, which allows us to speculate that the mechanism of action of these parabens is different. Furthermore, studies of exposure to parabens are more evident in women than in men. Therefore, future studies are needed to clarify the effects of exposure to parabens and their mechanisms of action on this axis.

The relationship between dietary inflammatory index values and thyroid function in the US adult population: An analysis of the NHANES 2007-2012 cohort

OBJECTIVE

Researchers have developed the Dietary Inflammatory Index (DII) as a tool to quantify the inflammatory potential of a given diet. Higher DII scores indicated a more proinflammatory diet. While inflammation is known to have a strong impact on thyroid function, the precise nature of the association between DII scores and thyroid function has yet to be clarified. This study was conducted with the goal of exploring this relationship in a representative population of adults from the United States.

METHODS

For this study, we used data from the National Health and Nutrition Examination Survey (NHANES). Standardized questionnaires were used to collect demographic and dietary data from the participants, and laboratory tests were used to collect data on the participants' thyroid parameters and other relevant data. Linear regression models and smoothed curve fitting were used to assess the relationship between DII scores and thyroid function, with weighted data analyses and subgroup analyses being conducted as appropriate.

RESULTS

In total, 7712 subjects were recruited from the NHANES 2007-2012 cohort. Their weighted mean age was 44.87 (0.47) years, mean DII score was 1.41 (0.05). Mean FT3 was 3.20 (0.01) pg/mL and mean TT4 was 7.81 (0.03) µg/dL. In adjusted analyses, higher DII values were related to increases in FT3 (β = .007; p = .027) and TT4 (β = .050; p = .005) levels. Subgroup analyses showed a negative correlation between FT3 levels and DII scores in a population with high urinary iodine concentrations.

CONCLUSION

These data indicate that the consumption of a more proinflammatory diet, as evidenced by elevated DII scores, is correlated with significant increases in FT3 and TT4 levels. However, for people with high urinary iodine concentrations, a more proinflammatory diet was associated with lower FT3 levels. Additional research will be vital to clarify the mechanistic basis for these findings.

Cross-species applicability of an adverse outcome pathway network for thyroid hormone system disruption

Thyroid hormone system disrupting compounds are considered potential threats for human and environmental health. Multiple adverse outcome pathways (AOPs) for thyroid hormone system disruption (THSD) are being developed in different taxa. Combining these AOPs results in a cross-species AOP network for THSD which may provide an evidence-based foundation for extrapolating THSD data across vertebrate species and bridging the gap between human and environmental health. This review aimed to advance the description of the taxonomic domain of applicability (tDOA) in the network to improve its utility for cross-species extrapolation. We focused on the molecular initiating events (MIEs) and adverse outcomes (AOs) and evaluated both their plausible domain of applicability (taxa they are likely applicable to) and empirical domain of applicability (where evidence for applicability to various taxa exists) in a THSD context. The evaluation showed that all MIEs in the AOP network are applicable to mammals. With some exceptions, there was evidence of structural conservation across vertebrate taxa and especially for fish and amphibians, and to a lesser extent for birds, empirical evidence was found. Current evidence supports the applicability of impaired neurodevelopment, neurosensory development (eg, vision) and reproduction across vertebrate taxa. The results of this tDOA evaluation are summarized in a conceptual AOP network that helps prioritize (parts of) AOPs for a more detailed evaluation. In conclusion, this review advances the tDOA description of an existing THSD AOP network and serves as a catalog summarizing plausible and empirical evidence on which future cross-species AOP development and tDOA assessment could build.

Endocrine-disrupting chemicals and autoimmune diseases

Endocrine-disrupting chemicals (EDCs) widely exist in people's production and life which have great potential to damage human and animal health. Over the past few decades, growing attention has been paid to the impact of EDCs on human health, as well as immune system. So far, researchers have proved that EDCs (such as bisphenol A (BPA), phthalate, tetrachlorodibenzodioxin (TCDD), etc.) affect human immune function and promotes the occurrence and development of autoimmune diseases (ADs). Therefore, in order to better understand how EDCs affect ADs, we summarized the current knowledge about the impact of EDCs on ADs, and elaborated the potential mechanism of the impact of EDCs on ADs in this review.

Association between bisphenol A exposure and thyroid dysfunction in adults: a systematic review and meta-analysis

The occurrence of thyroid dysfunction is affected by environmental factors, and BPA is a ubiquitous environmental pollutant with the potential to cause thyroid dysfunction. However, the limited epidemiological evidence shows an inconsistent association between BPA exposure and thyroid dysfunction. Therefore, the literature on the impact of BPA on thyroid was sorted and analyzed to study the relationship between BPA and adult thyroid function. The studies published on or before 23rd May 2022 from PubMed, Web of Science, and Scopus were collected analyzing the association between BPA exposure and the levels of thyroid hormones. The methodological quality of each study was assessed, the sensitivity analysis and subgroup analysis based on study population and gender were also performed, and publication bias was evaluated. A total of 2969 literature studies were retrieved. Based on inclusion and exclusion criteria, eleven studies were included. Our results showed that BPA concentration was negatively correlated with FT4 and TSH in males. Pooled correlation coefficients between BPA and FT4/TSH were -0.027 (95%CI = -0.030∼-0.024) and -0.058 (95%CI = -0.111∼-0.004). BPA concentration was positively correlated with FT4 in females, and the pooled correlation coefficient was 0.006 (95%CI = 0.003-0.008). The effects of BPA on thyroid hormone levels were significantly different between males and females. BPA may significantly decrease the levels of FT4 and TSH in males but increase the levels of FT4 in females. Considering the high heterogeneity among studies and the limited investigations into subgroups, the relationship between BPA exposure and thyroid dysfunction needs to be further investigated.

Maternal paraben exposure and intra-pair thyroid-stimulating hormone difference in twin neonates

Thyroid hormones are essential for fetal growth and neurodevelopment. The recent frequent use of parabens has raised concerns about their endocrine-disrupting potential. However, the effects of maternal paraben exposure on neonatal thyroid hormone levels are still largely unknown. In our study, a co-twin control design was employed to analyze the relationships between maternal paraben exposure and neonatal thyroid-stimulating hormone (TSH) difference. We collected information from 252 mother-twin pairs from a twin birth cohort in Wuhan, China. Concentrations of six parabens were measured in maternal urine samples collected at < 16, 16-28, and > 28 weeks of gestation. Data of neonatal TSH levels were retrieved from medical records. Multiple informant models were applied to explore the time-specific relationships between paraben exposure and intra-twin TSH difference and to determine the susceptible window of exposure. We found that maternal urinary methyl paraben (MeP) during early pregnancy was positively associated with intra-twin TSH difference (%change = 5.96 %; 95 % confidant interval (CI): 0.04 %, 12.2 %). However, no significant differences were observed for exposure to ethyl paraben (EtP) and propyl paraben (PrP), and the associations between parabens and intra-twin TSH difference did not differ materially across pregnancy. Further, a stratified analysis based on twin zygosity and chorionicity and sex types indicated that the positive association between early pregnancy MeP exposure and intra-twin TSH difference was significant in monochorionic diamniotic (MCDA) twins of female-female fetuses and dichorionic diamniotic (DCDA) twins of opposite-sex. The prospective twin study provides first evidence that MeP exposure in early pregnancy was associated with an increased TSH difference in twin neonates, especially in female fetuses.

Integrated toxicity assessment of DEHP and DBP toward aquatic ecosystem based on multiple trophic model assays

To comprehensively understand the toxic risks of phthalates to aquatic ecosystems, we examined the acute toxicity of di-(2-ethylhexyl) phthalate (DEHP) and di-butyl phthalate (DBP) on multiple trophic models, including algae (Chlorella vulgaris), Daphnia magna and fish (Danio rerio, Pseudorasbora parva). Thus, a 15-day zebrafish exposure was conducted to trace the dynamic changes of phthalate-induced toxic effects. Among the four species, D. magna exhibited the strongest sensitivity to both DEHP and DBP, followed by D. rerio and P. parva. C. vulgaris exhibited the lowest sensitivity to phthalates. The sub-chronic zebrafish assay demonstrated that 1000 μg/L DBP induced significant mortality at 15 days post-exposure (dpe), and DEHP exhibited no lethality at the tested concentrations (10-5000 μg/L). Zebrafish hepatic SOD activity and sod transcription levels were inhibited by DBP from 3 dpe, which was accompanied by increased malondialdehyde level, while zebrafish exposed to DEHP exhibited less oxidative damage. Both DEHP and DBP induced time-dependent alterations on Ache activity in zebrafish brains, thus indicating the potential neurotoxicity toward aquatic organisms. Additionally, 1000 μg/L and higher concentration of DBP caused hepatic DNA damage in zebrafish from 7 dpe. These results provide a better understanding of the health risks of phthalate to water environment.

Spatiotemporal variation of childhood hyperthyroidism: a 10-year nationwide study

OBJECTIVE

Childhood hyperthyroidism is mostly caused by Graves' disease, a rare autoimmune disease in children. Epidemiological data are scarce and the variability of within-region incidence is unknown. We aimed to provide the first description of temporal trends in pediatric hyperthyroidism in France and to explore spatial trends, with a view to identifying possible environmental triggers.

DESIGN AND METHODS

We performed an observational population-based study on data collected from the National Health Data System, covering the 2008-2017 period and the whole of France. We identified patients with an indicator reflecting incident cases of treated hyperthyroidism, in children aged 6 months-17.9 years, localized at the scale of the département (equivalent to a county) of residence. We performed descriptive analyses of incidence rate by sex, age, and year, and used a spatiotemporal model for estimation at département level.

RESULTS

We identified 4734 incident cases: 3787 girls (80%) and 947 boys (20%). The crude incidence rate was 3.35 (95% CI: 3.26; 3.45) per 100 000 person-years over the study period. We estimated the increase in incidence between 2008 and 2017 at 30.1% (19.0%; 42.3%). Annual incidence rate increased linearly over the 10-year period in both girls and boys, rising similarly in all age groups and in all départements. The spatial model highlighted marked heterogeneity in the risk of childhood hyperthyroidism across France.

CONCLUSION

The trend toward increasing incidence observed may reflect changes in genetic and environmental interactions, and the marked spatial heterogeneity may reflect localized ethnic or environmental factors worthy of further investigation.

Associations between phthalate exposure and thyroid function in pregnant women during the first trimester

Phthalates are a class of environmental endocrine disruptors. Previous studies have demonstrated that phthalate exposure can affect thyroid function; however, limited studies have assessed the associations between phthalate exposure and thyroid function, especially thyroid autoimmunity in pregnant women during the first trimester. We recruited participants from a cohort of pregnant women in Beijing, China, and collected urine samples to measure ten phthalate metabolites, serum samples to measure free thyroxine (FT₄), thyroid-stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb) during the first trimester. We included 325 pregnant women without thyroid diseases or dysfunction in this study. Associations between phthalate metabolites and thyroid function parameters were assessed with the Bayesian kernel machine regression (BKMR) model, multiple linear regression model, and restricted cubic spline. In the BKMR model analysis, compared to the 50th percentile, total urinary phthalate metabolites levels were negatively associated with serum TPOAb levels when phthalate metabolites were at or below the 40th percentile. Stratifying by body mass index, total urinary phthalate metabolites levels were negatively associated with serum TPOAb levels in normal weight women when phthalate metabolites were at or below the 45th percentile. However, total urinary phthalate metabolites levels were positively associated with serum TPOAb levels in underweight women when phthalate metabolites were at or below the 30th percentile. In restricted cubic spline analysis, L-shaped nonlinear associations of mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), di-(2-ethylhexyl) phthalate (ΣDEHP), and inverted S-shaped nonlinear association of mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) with TPOAb were observed. In conclusion, our findings suggest that phthalate exposure may affect thyroid autoimmunity in underweight pregnant women during early pregnancy, and the potential effects of phthalate exposure on thyroid autoimmunity may be nonlinear.

Nongenomic effects and mechanistic study of butyl benzyl phthalate-induced thyroid disruption: Based on integrated in vitro, in silico assays and proteome analysis

Based on in vitro and in silico assays as well as proteome analysis, this study explored the nongenomic mechanism for butyl benzyl phthalate (BBP)-induced thyroid disruption. Molecular docking simulations showed that BBP could dock into the Arg-Gly-Asp (RGD) domain of integrin α_vβ₃ and form hydrogen bonds with a docking energy of -35.80 kcal/mol. This chemical enhanced rat pituitary tumor cell (GH3) proliferation and exhibited thyroid hormone-disrupting effects at 5-10 μmol/L. Meanwhile, BBP upregulated β₃ gene expression and activated the downstream mitogen-activated protein kinase (MAPK) pathway in GH3 cells. Interestingly, GH3 cell proliferation was attenuated by integrin α_vβ₃ inhibitor (RGD peptide) or ERK1/2 inhibitor (PD98059), suggesting that the disruptions might be partly attributed to its interaction with integrin α_vβ₃ and activation of MAPK. Furthermore, quantitative proteomic analysis of zebrafish embryos exposed to BBP at an environmentally relevant concentration of 0.3 μmol/L revealed that BBP perturbed proteins and pathways related to cell communication (e.g., integrin binding) and signal transduction (e.g., MAPK signaling pathway). Taken together, our results supported that the biological effects of BBP-activated integrin α_vβ₃ mediated by the nongenomic pathway play an important role in its thyroid disruption. CAPSULE: The nongenomic pathway plays a vital role in the thyroid disruption-inducing actions of BBP.

Urinary phthalate metabolites in pregnant women: occurrences, related factors, and association with maternal hormones

In this study, we aimed to evaluate phthalate metabolite levels in pregnant women, to explore the factors influencing exposure, and to assess phthalate metabolite levels in relation to thyroid hormone synthesis. We recruited 463 pregnant women and collected urine, blood, and questionnaire data at participant's first prenatal examination. Ten phthalate metabolites were analyzed: mono-isobutyl phthalate (MiBP); mono-methyl phthalate (MMP); mono-ethyl phthalate (MEP); mono-n-butyl phthalate (MnBP); mono-n-octyl phthalate (MOP); mono-benzyl phthalate (MBzP); and the metabolite of di-2-ethylhexyl phthalate (DEHP), which were mono (2-ethylhexyl) phthalate, mono-(2-ethyl-5-oxohexyl) phthalate, and mono-(2-ethyl-5-carboxypentyl) phthalate. Multivariable generalized estimating equation models and linear mixed models were used to predict urinary biomarker concentrations and to assess the associations between phthalate exposure and thyroid hormones. Positive associations were found between phthalate metabolites and lower education (MEP and MOP), living near the road (MEP, MnBP, and ∑DEHP), and consuming more puffed food (MEP and MBzP). In addition, MnBP (percent change [%△] = 4.25; 95% confidence interval [CI] = 0.32, 8.18) and ∑DEHP (%△ = 5.12; 95% CI = 1.25, 8.99) were positively associated with thyroid-stimulating hormones, although MEP and MnBP were inversely associated with free thyroxine and total triiodothyronine. Our findings suggest that certain habits and behaviors were predictive of the positive presence of phthalate metabolites and that certain phthalate esters are associated with altered thyroid hormone levels.

Association of phthalate exposure with thyroid function during pregnancy

BACKGROUND

The extent of thyroid disruptive effects of phthalates during pregnancy remains unclear.

AIM

To investigate the association of maternal urinary phthalates with markers of the thyroid system during early pregnancy.

METHODS

Urinary concentrations of phthalate metabolites and serum concentrations of thyroid stimulating hormone (TSH), free and total thyroxine (FT4 and TT4) and free and total triiodothyronine (FT3 and TT3) were measured in pregnant women in early pregnancy in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy study (2007-ongoing), a population-based prospective cohort.

RESULTS

In the 1,996 included women, higher di-ethyl-hexyl phthalate (DEHP) metabolites were associated with a lower FT4 (β [SE] for the molar sum: -0.13 [0.06], P = 0.03) and a higher TSH/FT4 ratio (0.003 [0.001], P = 0.03). Higher concentrations of di-iso-nonyl phthalate (DINP) metabolites were associated with a lower TT4 (β [SE] for the molar sum: 0.93 [0.44], P = 0.03) as well as with lower TT4/FT4 and TT4/TT3 ratios. Higher metabolites of both dibutyl and butyl-benzyl phthalate (DBP and BBzP) were associated with lower T4/T3 ratio (free and total) and higher FT4/TT4 and FT3/TT3 ratios. A higher diisononyl cyclohexane dicarboxylate (DINCH) metabolite concentration was associated with a higher TT3.

CONCLUSIONS

These results translate results from experimental studies suggesting that exposure to phthalates may interfere with the thyroid system during pregnancy. This is also true for compounds that have been introduced to replace known disruptive phthalates. Further experimental studies should take into account the human evidence to better investigate the potential underlying mechanisms of thyroid disruption by phthalates.

The Association between the Dietary Inflammatory Index and Thyroid Function in U.S. Adult Males

Thyroid function has a close link with inflammation. However, it is still unknown whether the dietary inflammatory potential is associated with thyroid function. We aimed to assess the relationship among them using the data from the National Health and Nutrition Examination Survey (NHANES). This study was a cross-sectional study, where weighted multivariable linear regression, subgroup analyses, and interaction terms were employed. Thyroid function was assessed by eight indexes, including total and free T4 and T3, Tg, TgAb, TPOAb, and TSH. A total of 2346 male participants aged ≥20 years with an average age of 50.74 ± 17.68 years were enrolled. The mean DII score among participants was −0.46 ± 1.73, ranging from −4.12 to 4.41, and mean total thyroxine (T4) was 7.61 ± 1.51 μg/dL. We found a positive association between DII and total T4 (β = 0.07; p = 0.0044). Using subgroup analysis, this association became stronger in both the iodine-deficient and obese group (iodine-deficient group: β = 0.15, p < 0.0001; obese group: β = 0.14, p < 0.0001). In conclusion, men adhering to a more pro-inflammatory diet appeared to have higher total T4 levels. However, these hormone variations were still within the normal clinical range and more well-designed studies are still needed to validate the causal relationship between DII and thyroid function.

Thyroid hormone system disrupting chemicals

The thyroid hormone system is a main target of endocrine disruptor compounds (EDC) at all levels of its intricately fine-tuned feedback regulation, synthesis, distribution, metabolism and action of the 'prohormone' thyroxine and its active metabolites. Apart from classical antithyroid effects of EDC on the gland, the majority of known and suspected effects occurs at the pre-receptor control of T3 ligand availability to T3 receptors exerting ligand modulated thyroid hormone action. Tissue-, organ- and cell-specific expression and function of thyroid hormone transporters, deiodinases, metabolizing enzymes and T3-receptor forms, all integral components of the system, may mediate adverse EDC effects. Established evidence from nutritional, pharmacological and molecular genetic studies clearly support the functional, biological, and clinical relevance of these targets. Iodine-containing thyroid hormones and the organization of this system are highly conserved during evolution from primitive aquatic life forms, amphibia, birds throughout all vertebrates including humans. Mechanistic studies from various animal experimental models strongly support cause-effect relationships upon EDC exposure, hazards and adverse effects of EDC across various species. Retrospective case-control, cohort and population studies linking EDC exposure with epidemiological data on thyroid hormone-related (dys-)functions provide clear evidence that human development, especially of the fetal and neonatal brain, growth, differentiation and metabolic processes in adult and aging humans are at risk for adverse EDC effects. Considering that more than half of the world population still lives on inadequate iodine supply, the additional ubiquitous exposure to EDC and their mixtures is an additional threat for the essential thyroid hormone system, the health of the human population and their future progenies, animal life forms and our global environment.

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.

Association of exposure to polycyclic aromatic hydrocarbons and heavy metals with thyroid hormones in general adult population and potential mechanisms

Air pollution and fuel emissions are the common sources of human exposure to polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Several studies have suggested potential associations between PAHs/heavy metals and thyroid hormones, however, reports have been inconsistent. In this study, we employed a subpopulation of the adults (n = 1254) who participated in the Korean National Environmental Health Survey 2015-2017, and investigated the association of PAHs and major heavy metals with thyroid hormones, and explored the underlying mechanisms of thyroid disruption. Four PAH metabolites and three heavy metals of lead (Pb), mercury (Hg), and cadmium (Cd) were measured either in urine or in total blood. In addition, thyroid hormones (T3 and T4), TSH, thyroxine-binding globulin (TBG), and thyroid autoantibodies were measured, and peripheral deiodinase activity (G_D) and thyroid's secretory capacity (G_T) were calculated. Urinary Hg was negatively associated with total T3 in both males and females, while it was positively associated with total T4 among females only. Urinary Hg was related to decreased G_D and increased G_T in both sexes. In contrast, urinary Cd was positively associated with total T3 and G_D in both male and female populations. Urinary Cd also showed a positive association with thyroid autoantibodies, but only in males. A multi-factor model considering co-exposure to multiple chemicals also resulted in similar associations. Among the measured PAH metabolites, only urinary 1-hydroxypyrene showed a negative association with total T3 in males. However, this association was marginal, and disappeared in a multi-chemical model. The present observations are suggestive that exposures to Hg and Cd might disrupt thyroid hormones, possibly through an alteration of deiodinase activity. Association of PAH exposure with thyroid hormone appears to be insignificant.

Association of Phthalate Exposure with Thyroid Function and Thyroid Homeostasis Parameters in Type 2 Diabetes

AIMS

Phthalates, which are recognized environmental endocrine-disrupting chemicals, are associated with thyroid hormone disruption. We aimed to evaluate the relationship of phthalate metabolites with thyroid function and thyroid homeostasis parameters in type 2 diabetes and to explore whether thyroid autoimmunity status and metformin, the most common antidiabetic drug, may influence such associations.

METHODS

Concurrent urine and blood samples were collected from 639 participants with type 2 diabetes in the METAL (Environmental Pollutant Exposure and Metabolic Diseases in Shanghai) study. We measured urinary concentrations of thirteen phthalate metabolites along with serum levels of thyroid-stimulating hormone (TSH), total T₄ and T₃, free T₄ (FT₄) and T₃ (FT₃), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb). Four parameters of thyroid homeostasis, including the sum activity of step-up deiodinases (SPINA-GD), thyroid secretory capacity (SPINA-GT), Jostel's TSH index (TSHI), and thyrotroph thyroid hormone resistance index (TTSI), were also calculated.

RESULTS

Among all participants, after full adjustment, multivariable regression analysis showed that some urine phthalate metabolites were negatively associated with TSH, TSHI, and TTSI levels and positively associated with FT₃, T₃, SPINA-G_D, and SPINA-G_T levels. None of the urine phthalate metabolites exhibited a significant association with thyroid autoimmunity. The associations of phthalate metabolites with thyroid function and thyroid homeostasis parameters differed based on thyroid autoantibody and metformin treatment status.

CONCLUSIONS

Urinary phthalate metabolites may be associated with thyroid function and thyroid homeostasis parameters among participants with type 2 diabetes. Furthermore, our present study suggested that thyroid autoantibody status and metformin treatment status are potential mediators of such associations.

Urinary phthalate metabolites are associated with biomarkers of DNA damage and lipid peroxidation in pregnant women - Tainan Birth Cohort Study (TBCS)

Phthalate exposure and oxidative stress have been linked to adverse reproductive outcomes in experimental studies, whereas no clear line has been drawn for human, especially in pregnant women. This study explored relationships between urinary phthalate metabolites and biomarkers of lipid peroxidation and oxidative and nitrosative DNA damage. Measurements from 97 Taiwanese pregnant women were taken at three different times during second and third trimesters. Five oxidative/nitrosative stress biomarkers - 8-hydroxy-2'-deoxyguanosine (8-OHdG), 8-nitroguanine (8-NO₂Gua), 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA), 8-isoprostaglandin F_2α (8-isoPF_2α), and malondialdehyde (MDA), and 11 phthalate metabolites were measured in urine samples. Linear regressions in each visit and linear mixed-model regressions were fitted to estimate percent changes in oxidative/nitrosative stress biomarkers resulting from inter-tertile increase of phthalate metabolite level and the cumulative concentrations of di (2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate. The highest urine concentrations of phthalate metabolites and the greatest number of significant positive associations between phthalate metabolites and oxidative/nitrosative stress biomarkers were observed in the third visit and in repeated measurements analysis, respectively. Of the biomarkers related to DNA damage, 8-OHdG (25.4% inter-tertile increase for mono-iso-butyl phthalate) was more sensitive to phthalate exposure than 8-NO2Gua. Among the biomarkers of lipid peroxidation, HNE-MA (61.2% inter-tertile increase for sum of DEHP metabolites) was more sensitive than 8-isoPF_2α and MDA. Our findings support the hypothesis that pregnant phthalate exposure increases the oxidative stress biomarkers of DNA damage and lipid peroxidation. Future research may elucidate the mediating roles of oxidative/nitrosative stress biomarkers in the link between phthalate exposure and adverse reproductive outcomes.