Modulation of iodide uptake by dialkyl phthalate plasticisers in FRTL-5 rat thyroid follicular cells

Associations between Urinary Phthalate Metabolites with BDNF and Behavioral Function among European Children from Five HBM4EU Aligned Studies

Based on toxicological evidence, children's exposure to phthalates may contribute to altered neurodevelopment and abnormal regulation of brain-derived neurotrophic factor (BDNF). We analyzed data from five aligned studies of the Human Biomonitoring for Europe (HBM4EU) project. Ten phthalate metabolites and protein BDNF levels were measured in the urine samples of 1148 children aged 6-12 years from Italy (NACII-IT cohort), Slovakia (PCB-SK cohort), Hungary (InAirQ-HU cohort) and Norway (NEBII-NO). Serum BDNF was also available in 124 Slovenian children (CRP-SLO cohort). Children's total, externalizing and internalizing behavioral problems were assessed using the Child Behavior Checklist at 7 years of age (only available in the NACII-IT cohort). Adjusted linear and negative binomial regression models were fitted, together with weighted quantile sum (WQS) regression models to assess phthalate mixture associations. Results showed that, in boys but not girls of the NACII-IT cohort, each natural-log-unit increase in mono-n-butyl phthalate (MnBP) and Mono(2-ethyl-5-oxohexyl) phthalate (MEOHP) was cross-sectionally associated with higher externalizing problems [incidence rate ratio (IRR): 1.20; 95% CI: 1.02, 1.42 and 1.26; 95% CI: 1.03, 1.55, respectively]. A suggestive mixture association with externalizing problems was also observed per each tertile mixture increase in the whole population (WQS-IRR = 1.15; 95% CI: 0.97, 1.36) and boys (IRR = 1.20; 95% CI: 0.96, 1.49). In NACII-IT, PCB-SK, InAirQ-HU and NEBII-NO cohorts together, urinary phthalate metabolites were strongly associated with higher urinary BDNF levels, with WQS regression confirming a mixture association in the whole population (percent change (PC) = 25.9%; 95% CI: 17.6, 34.7), in girls (PC = 18.6%; 95% CI: 7.92, 30.5) and mainly among boys (PC = 36.0%; 95% CI: 24.3, 48.9). Among CRP-SLO boys, each natural-log-unit increase in ∑DINCH concentration was associated with lower serum BDNF levels (PC: -8.8%; 95% CI: -16.7, -0.3). In the NACII-IT cohort, each natural-log-unit increase in urinary BDNF levels predicted worse internalizing scores among all children (IRR: 1.15; 95% CI: 1.00, 1.32). Results suggest that (1) children's exposure to di-n-butyl phthalate (DnBP) and di(2-ethylhexyl) phthalate (DEHP) metabolites is associated with more externalizing problems in boys, (2) higher exposure to DINCH may associate with lower systemic BDNF levels in boys, (3) higher phthalate exposure is associated with higher urinary BDNF concentrations (although caution is needed since the possibility of a "urine concentration bias" that could also explain these associations in noncausal terms was identified) and (4) higher urinary BDNF concentrations may predict internalizing problems. Given this is the first study to examine the relationship between phthalate metabolite exposure and BDNF biomarkers, future studies are needed to validate the observed associations.

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.

The association between urinary phthalate metabolites and serum thyroid function in US adolescents

The aim was to investigate the association between mixed exposure to phthalates and serum thyroid function among US adolescents. The study used 2007-2008 survey data from the National Health and Nutrition Examination Survey (NHANES). Data on urinary phthalates metabolites and serum thyroid function indicators were collected. The weighted multivariable linear regression models and Bayesian kernel machine regression (BKMR) analyses were used to analyze the relationship between phthalates metabolites and thyroid function. A total of 356 adolescents aged 12-19 years were included in the analysis. Linear regression models showed that mono-(carboxyisoctyl) phthalate (MCOP) was positively correlated with total triiodothyronine (TT3) (β = 0.045, 95% confidence interval [CI] 0.022, 0.068) and thyroid stimulating hormone (TSH) (β = 0.1461, 95% CI 0.059, 0.232), while mono-(carboxyisononyl) phthalate (MCNP) was negatively correlated with TSH (β = - 0.119, 95% CI - 0.196, - 0.042). BKMR analyses showed phthalate metabolites mixtures have significantly positive overall effect on TT3. Exposure to phthalate mixtures might be positively correlated with increased TT3 serum level in US adolescents. The study provided evidence for the association between mixed phthalates exposure and thyroid health in adolescent population.

Associations between exposure to phthalates and subclinical hypothyroidism in pregnant women during early pregnancy: A pilot case-control study in China

Phthalates are environmental endocrine disruptors with thyroid-disrupting properties; however, the association between phthalate exposure and subclinical hypothyroidism (SCH) during pregnancy is unknown. We recruited a study population from a cohort of pregnant women in Beijing, China, and conducted the present pilot case-control study of 42 SCH cases and 84 non-SCH controls matched with age and body mass index (BMI). Serum levels of thyroid peroxidase antibody, free thyroxine (FT₄), thyroid-stimulating hormone (TSH), and urinary levels of ten phthalate metabolites during early pregnancy were measured. Urinary monoethyl phthalate (MEP) levels in SCH cases were observably higher than those in controls (p = 0.01). Conditional logistic regression analysis revealed that mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), MEP, mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and di-(2-ethylhexyl) phthalate (ΣDEHP) were significantly associated with a higher risk of SCH during early pregnancy (adjusted odds ratios = 1.89, 1.42, 1.81, and 1.92, respectively). Concomitantly, multiple linear regression analysis showed that MECPP, MEOHP, and ΣDEHP were positively associated with TSH and FT₄ × TSH in the entire study population. Bayesian kernel machine regression analysis and stratified analysis by BMI revealed upward tendencies in the serum levels of TSH and FT₄ × TSH. In summary, exposure to phthalates, especially DEHP, may be associated with a higher risk of SCH during early pregnancy, and a possible mechanism is the disruption of the hypothalamus-pituitary-thyroid axis.

Bisphenols, but not phthalate esters, modulate gene expression in activated human MAIT cells in vitro

One route of human exposure to environmental chemicals is oral uptake. This is primarily true for chemicals that may leach from food packaging materials, such as bisphenols and phthalate esters. Upon ingestion, these compounds are transported along the intestinal tract, from where they can be taken up into the blood stream or distributed to mucosal sites. At mucosal sites, mucosal immune cells and in the blood stream peripheral immune cells may be exposed to these chemicals potentially modulating immune cell functions. In the present study, we investigated the impact of three common bisphenols and two phthalate esters on mucosal-associated invariant T (MAIT) cells in vitro, a frequent immune cell type in the intestinal mucosae and peripheral blood of humans. All compounds were non-cytotoxic at the chosen concentrations. MAIT cell activation was only slightly affected as seen by flow cytometric analysis. Phthalate esters did not affect MAIT cell gene expression, while bisphenol-exposure induced significant changes. Transcriptional changes occurred in ∼ 25 % of genes for BPA, ∼ 22 % for BPF and ∼ 8 % for BPS. All bisphenols down-modulated expression of CCND2, CCL20, GZMB and IRF4, indicating an effect on MAIT cell effector function. Further, BPA and BPF showed a high overlap in modulated genes involved in cellular stress response, activation signaling and effector function suggesting that BPF may not be safe substitute for BPA.

Plasticizers: negative impacts on the thyroid hormone system

This review aims to understand the impacts of plasticizers on the thyroid system of animals and humans. The thyroid gland is one of the earliest endocrine glands that appear during embryogenesis. The thyroid gland synthesizes thyroid hormones (TH), triiodothyronine (T3), and thyroxine (T4) that are important in the regulation of body homeostasis. TH plays critical roles in regulating different physiological functions, including metabolism, cell growth, circadian rhythm, and nervous system development. Alteration in thyroid function can lead to different medical problems. In recent years, thyroid-related medical problems have increased and this could be due to rising environmental pollutants. Plasticizers are one such group of a pollutant that impacts thyroid function. Plasticizers are man-made chemicals used in a wide range of products, such as children's toys, food packaging items, building materials, medical devices, cosmetics, and ink. The increased use of plasticizers has resulted in their detection in the environment, animals, and humans. Studies indicated that plasticizers could alter thyroid function in both animals and humans at different levels. Several studies demonstrated a positive and/or negative correlation between plasticizers and serum T4 and T3 levels. Plasticizers could also change the expression of various TH-related genes and proteins, including thyroid-stimulating hormone (TSH), thyrotropin-releasing hormone (TRH), and transporters. Histological analyses demonstrated thyroid follicular cell hypertrophy and hyperplasia in response to several plasticizers. In conclusion, plasticizers could disrupt TH homeostasis and the mechanisms of toxicity could be diverse.

Risk of Nonalcoholic Fatty Liver Disease Is Associated with Urinary Phthalate Metabolites Levels in Adults with Subclinical Hypothyroidism: Korean National Environmental Health Survey (KoNEHS) 2012-2014

Nonalcoholic fatty liver disease (NAFLD) is a condition of excess accumulation of fats in the liver. Thyroid dysfunction is commonly observed in adult populations with NAFLD. In subjects with thyroid dysfunction, phthalates, which are chemical compounds widely used to increase the flexibility of various plastic products, may increase the risk of NAFLD prevalence. Therefore, our study aimed to evaluate the relationship between the levels of urinary phthalate metabolites and the risk of NAFLD stratified by the levels of thyroid-stimulating hormone (TSH). Data (n = 2308) were obtained from the Korean National Environmental Health Survey II (2012−2014). Using the hepatic steatosis index, participants were classified into non-NAFLD (<30) and NAFLD (>36) groups. Participants with euthyroidism were defined as 0.45−4.5 mIU/L for serum TSH and normal thyroxine (T4) levels (n = 2125). Subclinical hypothyroidism (SCH) was defined as a higher TSH level (4.5−10 mIU/L) with normal total T4 levels in the serum (n = 183). A multivariate analysis was performed to assess the association of the urinary phthalate concentration with the risk of NAFLD after stratification based on the thyroid hormone levels. The levels of phthalate metabolites in urine were not significantly associated with NAFLD in adults with euthyroidism. However, a significant increased risk of NAFLD in those with SCH was observed in the fourth quartile of mono (2-ethyl-5-hydroxyhexyl) phthalate (odds ratio (OR) 13.59, 95% confidence interval (CI) 12.13−86.44), mono (2-ethyl-5-oxohexyl) phthalate (OR 8.55, 95% CI 1.20−60.53), mono-(2-ethyl-5-carboxypentyl) phthalate (OR 9.06, 95% CI 1.78−45.96), and mono-benzyl phthalate (OR 6.05, 95% CI 1.62−22.54) compared to those of the lowest quartile after being adjusted with covariates. In conclusion, the levels of phthalate metabolites in urine are positively associated with NAFLD in adults with SCH. More experimental studies are needed to clarify the risk of NAFLD caused by phthalate exposure in cases with poor thyroid function.

The associations of urinary DEHP metabolite levels, serum thyroid hormones, and thyroid-related genes among the adolescent students from China: a cross-sectional study

Our study aimed to investigate the associations between DEHP exposure and serum thyroid hormone levels in 347 adolescents and young adults. We measured DEHP metabolites including mono(2-ethylhexyl) phthalate (MEHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-carboxypentyl) phthalate (MECPP), and mono(2-carboxymethyl)hexyl phthalate (MCMHP) in their urine. Total thyroxine (TT4), total triiodothyronine, free triiodothyronine, free thyroxine (FT4), thyroid-stimulating hormone and the mRNA levels of thyroid peroxidase (TPO), thyroglobulin (TG), sodium iodide symporter (NIS), thyroid transcription factor 1 (TTF-1), and paired box gene 8 (PAX-8) in serum were measured. The results of statistical analysis showed that urinary DEHP metabolites were generally negatively associated with TT4 levels in serum. In the males, the FT4 levels showed positive associations with urinary MEHP, MECPP, MCMHP, and ∑DEHP. The mRNA level of TG was significantly positively correlated with the levels of MECPP, MCMHP, and ∑DEHP, while the levels of TTF-1 and PAX-8 mRNA were significantly positively correlated with the levels of DEHP metabolites. Taken together, DEHP may affect the synthesis of TG by altering the normal transcription of TTF-1 and PAX-8, leading to decreased TT4 levels in Chinese adolescents.

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 Impairment of Thyroid Hormones Homeostasis after Short-Term Exposure to Di(2-ethylhexyl)phthalate in Adolescent Male Rats

Di(2-ethylhexyl)phthalate (DEHP) could induce metabolic disorders through interfering with thyroid homeostasis. Therefore, we evaluated the effects of short term to environmental relevant doses of DEHP on thyroid hormones. Four week old Sprague-Dawley (SD) rats were treated with vehicle (corn oil), and DEHP 0.75, 7.5, and 150 mg/kg/day. The rats were treated with once daily by oral gavage and were sacrificed with after 1 week. They were measured body weight and relative thyroid weight, serum thyroid hormones and histological changes of thyroid. There was no difference in body weight between the control and DEHP exposed rats. Relative thyroid weight in DEHP 150 mg/kg/day treated group was significantly lower than control. Serum thyroxine levels was decreased in rats exposed to 0.75 and 150 mg/kg/day DEHP. No histological changes were observed in the thyroid of rats administered DEHP compared to control. Exposure to DEHP at environmental relevant levels, even short-term exposure, can cause hypothyroidism in adolescent rats even the exposure period is relative short.

Associations of serum phthalate metabolites with thyroid hormones in GraMo cohort, Southern Spain

The general population is continuously exposed to phthalates via various consumer products. Epidemiological research relating phthalate exposure to thyroid function during non-developmental periods is limited. This study aimed to investigate the associations between specific serum phthalate metabolites and indicators of thyroid function in adults. We measured 10 serum phthalate metabolites and thyroid hormones - total triiodothyronine (TT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) - in a subsample of 207 adults from the GraMo cohort. This subsample was made up of men and women (in equal proportions) of middle age (49 ± 17 years) and from Southern Spain (province of Granada). Data on age, sex, body mass index, residence area, tobacco use, alcohol consumption and attained education were obtained from a questionnaire. Phthalate metabolites were log-transformed and categorized into tertiles. Cross-sectional associations of each metabolite with thyroid hormones were analyzed using multivariable-adjusted linear regression models. The mixture effect of metabolite phthalates was assessed using weighted quantile sum regression. After multivariable-adjustment, the following phthalate metabolites were significantly associated with TT3 in a dose-response manner: MMP (β = 0.90: 95% confidence interval 0.68,1.12), MEP (β = 0.67: 0.44, 0.90), MiBP (β = 0.49: 0.21, 0.77), MiDP (β = 0.27: 0.03, 0.52), MBzP (β = 0.51: 0.28, 0.73), MEHP (β = -0.59: -0.82, -0.35) and MiNP (β = -0.43: -0.71, -0.14), when comparing highest vs. lowest exposed. The sum of all metabolites was also linked to FT4 levels. No significant associations were observed for TSH except for MiNP. Although phthalate metabolites with different molecular weight showed opposite associations, overall metabolite concentrations seem to associate with increased TT3 and FT4 serum levels. The cross-sectional nature of this analysis limits causal inference.

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.

Novel insights into di‑(2‑ethylhexyl)phthalate activation: Implications for the hypothalamus‑pituitary‑thyroid axis

Di (2‑ethylhexyl) phthalate (DEHP), an environmental pollutant, is widely used as a plasticizer and causes serious pollution in the ecological environment. As previously reported, exposure to DEHP may cause thyroid dysfunction of the hypothalamic‑pituitary‑thyroid (HPT) axis. However, the underlying role of DEHP remains to be elucidated. The present study performed intragastrical administration of DEHP (150, 300 and 600 mg/kg) once a day for 90 consecutive days. DEHP‑stimulated oxidative stress increased the thyroid follicular cavity diameter and caused thyrocyte oedema. Furthermore, DEHP exposure altered mRNA and protein levels. Thus, DEHP may perturb TH homeostasis by affecting biosynthesis, biotransformation, bio‑transportation, receptor levels and metabolism through disruption of the HPT axis and activation of the thyroid‑stimulating hormone (TSH)/TSH receptor signaling pathway. These results identified the formerly unappreciated endocrine‑disrupting activities of phthalates and the molecular mechanisms of DEHP‑induced thyrotoxicity.

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.

SCREENED: A Multistage Model of Thyroid Gland Function for Screening Endocrine-Disrupting Chemicals in a Biologically Sex-Specific Manner

Endocrine disruptors (EDs) are chemicals that contribute to health problems by interfering with the physiological production and target effects of hormones, with proven impacts on a number of endocrine systems including the thyroid gland. Exposure to EDs has also been associated with impairment of the reproductive system and incidence in occurrence of obesity, type 2 diabetes, and cardiovascular diseases during ageing. SCREENED aims at developing in vitro assays based on rodent and human thyroid cells organized in three different three-dimensional (3D) constructs. Due to different levels of anatomical complexity, each of these constructs has the potential to increasingly mimic the structure and function of the native thyroid gland, ultimately achieving relevant features of its 3D organization including: 1) a 3D organoid based on stem cell-derived thyrocytes, 2) a 3D organoid based on a decellularized thyroid lobe stromal matrix repopulated with stem cell-derived thyrocytes, and 3) a bioprinted organoid based on stem cell-derived thyrocytes able to mimic the spatial and geometrical features of a native thyroid gland. These 3D constructs will be hosted in a modular microbioreactor equipped with innovative sensing technology and enabling precise control of cell culture conditions. New superparamagnetic biocompatible and biomimetic particles will be used to produce "magnetic cells" to support precise spatiotemporal homing of the cells in the 3D decellularized and bioprinted constructs. Finally, these 3D constructs will be used to screen the effect of EDs on the thyroid function in a unique biological sex-specific manner. Their performance will be assessed individually, in comparison with each other, and against in vivo studies. The resulting 3D assays are expected to yield responses to low doses of different EDs, with sensitivity and specificity higher than that of classical 2D in vitro assays and animal models. Supporting the "Adverse Outcome Pathway" concept, proteogenomic analysis and biological computational modelling of the underlying mode of action of the tested EDs will be pursued to gain a mechanistic understanding of the chain of events from exposure to adverse toxic effects on thyroid function. For future uptake, SCREENED will engage discussion with relevant stakeholder groups, including regulatory bodies and industry, to ensure that the assays will fit with purposes of ED safety assessment. In this project review, we will briefly discuss the current state of the art in cellular assays of EDs and how our project aims at further advancing the field of cellular assays for EDs interfering with the thyroid gland.

Associations between urine phthalate metabolites and thyroid function in pregnant women and the influence of iodine status

BACKGROUND

Human populations, including susceptible subpopulations such as pregnant women and their fetuses, are continuously exposed to phthalates. Phthalates may affect the thyroid hormone system, causing concern for pregnancy health, birth outcomes and child development. Few studies have investigated the joint effect of phthalates on thyroid function in pregnant women, although they are present as a mixture with highly inter-correlated compounds. Additionally, no studies have investigated if the key nutrient for thyroid health, iodine, modifies these relationships.

METHODS

In this study, we examined the cross-sectional relationships between concentrations of 12 urinary phthalate metabolites and 6 plasma thyroid function biomarkers measured mid-pregnancy (~17 week gestation) in pregnant women (N = 1072), that were selected from a population-based prospective birth cohort, The Norwegian Mother, Father and Child Cohort study (MoBa). We investigated if the phthalate metabolite-thyroid function biomarker associations differed by iodine status by using a validated estimate of habitual dietary iodine intake based on a food frequency questionnaire from the 22nd gestation week. We accounted for the phthalate metabolite mixture by factor analyses, ultimately reducing the exposure into two uncorrelated factors. These factors were used as predictors in multivariable adjusted linear regression models with thyroid function biomarkers as the outcomes.

RESULTS

Factor 1, which included high loadings for mono-iso-butyl phthalate (MiBP), mono-n-butyl phthalate (MnBP), and monobenzyl phthalate (MBzP), was associated with increased total triiodothyronine (TT3) and free T3 index (fT3i). These associations appeared to be driven primarily by women with low iodine intake (<150 µg/day, ~70% of our sample). Iodine intake significantly modified (p-interaction < 0.05) the association of factor 1 with thyroid stimulating hormone (TSH), total thyroxine (TT4) and free T4 index (fT4i), such that only among women in the high iodine intake category (≥150 µg/day, i.e. sufficient) was this factor associated with increased TSH and decreased TT4 and FT4i, respectively. In contrast, factor 2, which included high loadings for di-2-ethylhexyl phthalate metabolites (∑DEHP) and di-iso-nonyl phthalate metabolites (∑DiNP), was associated with a decrease in TT3 and fT3i, which appeared fairly uniform across iodine intake categories.

CONCLUSION

We find that phthalate exposure is associated with thyroid function in mid-pregnancy among Norwegian women, and that iodine intake, which is essential for thyroid health, could influence some of these relationships.

Associations of Phthalates and Phthalate Replacements With CRH and Other Hormones Among Pregnant Women in Puerto Rico

CONTEXT

Phthalates are endocrine-disrupting chemicals that may be associated with adverse birth outcomes. Dysregulation of maternal endocrine homeostasis could be a possible biological pathway between phthalates and birth outcomes.

OBJECTIVE

Examine associations between 19 maternal urinary phthalate or phthalate replacement metabolites and 9 serum hormones measured over two time points during pregnancy.

DESIGN

Longitudinal study conducted in the PROTECT pregnancy cohort.

SETTING

Puerto Rico.

PATIENTS

Six hundred seventy-seven women in the first trimester of pregnancy.

MAIN OUTCOME MEASURES SERUM

CRH, estriol, SHBG, progesterone, TSH, total T3, free T4, total T4, and testosterone.

RESULTS

T3 was significantly associated with most metabolites. CRH was inversely associated with mono carboxyisononyl phthalate [MCNP; percent change (%Δ), -4.08; 95% CI, -7.24, -0.804], mono-3-carboxypropyl phthalate (MCPP; %Δ, -5.25; 95% CI, -8.26, -2.14), mono-2-ethyl-5-carboxypentyl phthalate (MECPP; %Δ, -18.4; 95% CI, -30.4, -4.37), mono-2-ethyl-5-hydroxyhexyl phthalate (MEHHP; %Δ, -13.4; 95% CI, -22.7, -2.92), and mono-2-ethyl-5-oxohexyl phthalate (MEOHP; %Δ, -12.7; 95% CI, -22.2, -2.20). Positive associations were found between numerous phthalate metabolites and free T4, T4, and the T3/T4 ratio. Testosterone was positively associated with mono hydroxybutyl phthalate (MHBP; %Δ, 4.71; 95% CI, 0.27, 9.35) and inversely associated with monoethyl phthalate (MEP; %Δ, -14.5; 95% CI, -24.3, -3.42), and relationships with MCNP and mono carboxyisooctyl phthalate (MCOP) were significantly modified by study visit. Finally, an inverse association was found between mono-2-ethyl-5-hydrohexyl terephthalate (MEHHTP), a terephthalate metabolite, and progesterone at visit 3 only (%Δ, -13.1; 95% CI, -22.3, -2.75).

CONCLUSIONS

These results indicate that exposure to phthalates may differentially impact the maternal endocrine system at different points during pregnancy, and that exposures to phthalate replacement chemicals may be particularly important to consider in future human health studies.

Effects of perinatal di (2-ethylhexyl) phthalate exposure on thyroid function in rat offspring

Di (2-ethylhexyl) phthalate (DEHP) is a commonly used plasticizer in industry and displays the characteristics of an endocrine disruptor. Disorders of the maternal thyroid hormone (TH) during pregnancy can cause adverse effects on the fetus. We investigated the effects and possible mechanism of perinatal DEHP exposure on the thyroid function of pups. Pregnant female Wistar rats were randomly divided into four groups and received doses of DEHP of 0, 30, 300, 750 mg/kg/day by gavage at from gestational day (GD) 0 to postnatal day (PN) 21. The concentration of serum THs and the ultrastructure of thyroid follicular cells in the offspring were examined. Related protein level and gene expression of thyroid proteins in pups were analyzed by western blotting and real-time PCR. We found that DEHP significantly reduced total thyroxine (TT₄) and increased thyroid stimulating hormone (TSH) in pups, while total triiodothyronine (TT₃) showed no change. Thyroid follicular cells ultrastructure was damaged in DEHP exposed pups as viewed by electron microscopy. Furthermore, exposure to DEHP significantly increased protein and mRNA levels of thyroid transcription factor 1 (TTF-1), paired box 8 (PAX8), sodium iodide symporter (NIS) and thyroid peroxidase (TPO) in pups. In addition, levels of deiodinases of pups were also affected. These findings indicated that DEHP can disrupt thyroid function by damaging thyroid follicles and affecting TTF-1, PAX8, NIS, TPO and the deiodinase protein family.

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.

Prenatal and Childhood Exposure to Phthalate Diesters and Thyroid Function in a 9-Year Follow-up Birth Cohort Study: Taiwan Maternal and Infant Cohort Study

BACKGROUND

Phthalates are widely used in industry, personal care products, and medications. Recent studies have suggested that phthalate exposure alters thyroid hormones. However, longitudinal studies concerning the association between phthalate exposure and thyroid function in children are scant. Therefore, we examined the association between pre- and postnatal phthalate exposure and thyroid function in children born in 2000-2001.

METHODS

We studied 181 mother-child pairs in central Taiwan and followed-up the children from 2000 to 2009 at 2, 5, and 8 years old. We measured serum levels of thyroxine (T4), free T4, triiodothyronine (T3), and thyroid-stimulating hormone in children by using radioimmunoassay. We quantified seven phthalate metabolites, representing the five most commonly used phthalates, in maternal and child urine samples by using liquid chromatography-tandem mass spectrometry. The metabolites were monoethylhexyl phthalate (MEHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) derived from di(2-ethylhexyl) phthalate (DEHP), monomethyl phthalate (MMP), monoethyl phthalate (MEP), monobutyl phthalate (MBP), and monobenzyl phthalate (MBzP). We constructed a linear mixed model to examine these associations after adjustments for covariates.

RESULTS

The T4 levels were inversely associated with maternal urinary MEHHP (β = -0.028 [95% confidence interval (CI) = -0.051, -0.006]) and MEOHP (β = -0.027 [-0.050, -0.003]), with similar T3 levels being observed in boys, even when the children exposure levels were considered spontaneously. In the girls, the free T4 levels were inversely associated with levels of maternal urinary MEP (β = -0.042), maternal urinary MBzP (β = -0.050), and children's urinary MEHP (β = -0.027).

CONCLUSIONS

Early life phthalate exposure was associated with decreased thyroid hormone levels in young children.

Longitudinal assessment of prenatal phthalate exposure on serum and cord thyroid hormones homeostasis during pregnancy - Tainan birth cohort study (TBCS)

An increasing number of studies have revealed that phthalate exposure alters thyroid hormone homeostasis in the general population, but there is insufficient evidence of the effect of longitudinal maternal phthalate exposure on maternal and fetal thyroid hormones during pregnancy. We longitudinally assessed the effect of prenatal phthalate exposure in pregnant women on umbilical cord and maternal thyroid hormones at three trimesters during pregnancy. We recruited 98 pregnant women and collected urine and blood samples at three trimesters in an obstetrics clinic in Southern Taiwan from 2013 to 2014. We analyzed the concentrations of 11 urinary phthalate metabolites, including monoethylhexyl phthalate, mono-(2-ethyl-5-oxo-hexyl) phthalate (MEOHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate, mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), mono-n-butyl phthalate, monoisobutyl phthalate (MiBP), monoethyl phthalate (MEP), using online liquid chromatography-tandem mass spectrometry. The cord and maternal serum levels of thyroxine (T₄), free T₄, triiodothyronine (T₃), thyroid-stimulating hormone (TSH), and thyroxine-binding globulin were measured using an electrochemiluminescence immunoassay. A mixed-model analysis was utilized to assess the effect of longitudinal phthalate exposure on thyroid hormones and adjusted for significant covariates. We found that urinary MiBP (β=-0.065, 95% confidence interval (CI): -0.124, -0.005), and MEOHP (β=-0.083, 95% CI: -0.157, -0.009) were significantly negatively associated with serum TSH. Urinary MECPP was inversely related to serum T₃ (β=-0.027, 95% CI: -0.047, -0.006). Urinary MEP (β=0.014, 95% CI: -0.001, 0.028) and MiBP (β=0.033, 95% CI: 0.018, 0.049) were positively related to free T₄. We found that cord serum T₃ (β=0.067, 95% CI: 0.003, 0.131) and free T₄ (β=0.031, 95% CI: 0.001, 0.062) levels had significant positive associations with maternal ΣDBPm levels at the second trimester. We concluded that different phthalates exposure windows during gestation may alter cord and serum thyroid hormone homoeostasis.

Roles and potential mechanisms of selenium in countering thyrotoxicity of DEHP

Di-(2-ethylhexyl) phthalate (DEHP) as a ubiquitous environmental contaminant could disturb thyroid hormone (TH) homeostasis. Selenium as an essential trace element has protective effects on thyroids. To verify roles of selenium in countering thyrotoxicity of DEHP and elucidate potential mechanisms, Sprague-Dawley rats and Nthy-ori 3-1 cells were treated with DEHP or/and selenomethionine (SeMet). Results showed that selenium supplementation elevated plasma free thyroxine (FT4) that was decreased by DEHP, and free triiodothyronine (FT3) and thyroid stimulating hormone (TSH) levels were also partially recovered. DEHP-caused histopathologic changes were ameliorated after selenium supplementation, as indicated by recovered thyroid follicular epithelial cell numbers and cavity diameters. DEHP disrupted the redox equilibrium, causing depletions of SOD, GPx1, GPx3, and TxnRd, and accumulations of MDA. Nevertheless, selenium supplementation effectively improved the redox status. DEHP affected biosynthesis, biotransformation, biotransport, and metabolism of THs, as well as thyrotropin releasing hormone receptor (TRHr) levels. Plasma selenium, thyroid peroxidase (TPO), deiodinase 1 (Dio1), and transthyretin (TTR) were downregulated, while Dio3, Ugt1a1, Sult1e1, CYP2b1, CYP3a1, and TRHr were upregulated by DEHP. However, selenium supplementation led to elevations of selenium, Dio1 and TTR, and reductions of Ugt1a1, Sult1e1, CYP2b1, and TRHr. TPO, Dio3, and CYP3a1 were not significantly affected by selenium supplementation. Taken together, selenium could ameliorate DEHP-caused TH dyshomeostasis via modulations of the redox status, Dio1, TTR, TRHr, and hepatic enzymes.

Maternal urinary phthalate metabolites during pregnancy and thyroid hormone concentrations in maternal and cord sera: The HOME Study

BACKGROUND

Phthalates, endocrine-disrupting chemicals that are commonly found in consumer products, may adversely affect thyroid hormones, but findings from prior epidemiologic studies are inconsistent.

OBJECTIVES

In a prospective cohort study, we investigated whether maternal urinary phthalate metabolite concentrations and phthalate mixtures measured during pregnancy were associated with thyroid hormones among pregnant women and newborns.

METHODS

We measured nine phthalate metabolites [monoethyl phthalate (MEP), mono-n-butyl phthalate, mono-isobutyl phthalate, monobenzyl phthalate (MBzP), and four monoesthers of di(2-ethylhexyl) phthalate] in urine collected at approximately 16 and 26 weeks' gestation among women in the Health Outcomes and Measures of the Environment Study (2003-2006, Cincinnati, Ohio). Thyroid stimulating hormone (TSH) and free and total thyroxine and triiodothyronine were measured in maternal serum at 16 weeks' gestation (n = 202) and cord serum at delivery (n = 276). We used multivariable linear regression to assess associations between individual urinary phthalate metabolites and concentrations of maternal or cord serum thyroid hormones. We used weighted quantile sum regression (WQS) to create a phthalate index describing combined concentrations of phthalate metabolites and to investigate associations of the phthalate index with individual thyroid hormones.

RESULTS

With each 10-fold increase in 16-week maternal urinary MEP, maternal serum total thyroxine (TT₄) decreased by 0.52 μg/dL (95% CI: -1.01, -0.03). For each 10-fold increase in average (16- and 26-week) maternal urinary MBzP, cord serum TSH decreased by 19% (95% CI: -33.1, -1.9). Among mothers, the phthalate index was inversely associated with maternal serum TT₄ (WQS beta = -0.60; 95% CI: -1.01, -0.18). Among newborns, the phthalate index was inversely associated with both cord serum TSH (WQS beta = -0.11; 95% CI: -0.20, -0.03) and TT₄ (WQS beta = -0.53; 95% CI: -0.90, -0.16).

CONCLUSION

Our results suggest that co-exposure to multiple phthalates was inversely associated with certain thyroid hormones (TT₄ in pregnant women and newborns, and TSH in newborns) in this birth cohort. These findings highlight the need to study chemical mixtures in environmental epidemiology.

Influence of DEHP on thyroid, sex steroid-related genes and gonadal differentiation in Rana chensinensis tadpoles

In the present study, responses of the Chinese brown frog (Rana chensinensis) to exposure to di-2-ethylhexyl phthalate (DEHP), a common plasticizer, during the larval period were characterized. The effects of DEHP on metamorphosis rate, thyroid hormone, thyroid histology and the expression of genes involved in the steroid hormone synthesis in gonad were investigated. Metamorphosis rate and 50 percent of the tadpoles to reach Gosner stage 42 (T_0.5 ) were significantly slower in all DEHP groups. The thyroid glands of the tadpoles exposed to DEHP clearly exhibited colloid depletion. In addition, decreased concentrations of T4 and T3 were observed in the tadpoles exposed to DEHP. Moreover, the highest DEHP exposure (10 µmol/L DEHP) showed increased ratio of females significantly. Also, up-regulation significantly of transcripts of cytochrome P450 aromatase (CYP19) gene was detected in male tadpoles exposed to DEHP. The present results indicate that this increase in estrogens could lead to female-biased sex ratio in DEHP exposure group. Taken together, the present study indicates that DEHP disrupt thyroid hormone and sex steroid signaling in R. chensinensis tadpoles. Our present observations support evidence of a crosstalk between TH and sex steroids in gonad differentiation.

Potential influence of the phthalates on normal liver function and cardiometabolic risk in males

Phthalates are ubiquitous environmental contaminants, massively used in industry as plasticizers and additives in cosmetics, which may impair the human endocrine system inducing fertility problems, respiratory diseases, obesity, and neuropsychological disorders. The aim of this study was to examine the influence of the monoethyl phthalate (MEP) and mono-(2-ethylhexyl) phthalate (MEHP) on the liver function and cardiometabolic risk factors in males. In this research, 102 male participants (51 normal weight and 51 overweight/obese) were enrolled and examined for phthalate metabolites exposure in urine samples after 12 h of fasting. MEP was found in 28.43% (29/102) volunteers, while MEHP was detected among 20.59% (21/102) participants. Statistically significant increment in transaminase serum levels was observed in MEP-positive normal weight subgroup. Linear correlation was obtained between MEP concentration in urine samples and triglyceride (TG) serum levels (r ² = 0.33; p < 0.01), visceral adiposity index (VAI) (r ² = 0.41; p < 0.01), lipid accumulation product (LAP) (r ² = 0.32; p < 0.01), and TG to high-density lipoprotein (HDL) ratio (r ² = 0.40, p < 0.01) among the obese. The MEHP-positive normal weight volunteers had statistically significant increment of body mass index (p = 0.03) compared to MEHP-negative participants. Urine MEHP concentrations were negatively correlated with HDL serum levels (r ² = 0.31; p < 0.05) in the normal weight subgroup. The phthalates exposure may be related to statistically significant ALT and AST serum levels increment as well as with increased BMI, while the phthalate levels in the urine may be correlated with increased TG and decreased HDL cholesterol serum levels and associated with indicators of cardiometabolic risk and insulin resistance as LAP and VAI.

Oral exposure to dibutyl phthalate exacerbates chronic lymphocytic thyroiditis through oxidative stress in female Wistar rats

Chronic lymphocytic thyroiditis (CLT) is a common autoimmune disorder. The possible pathogenic role and mechanism of dibutyl phthalate (DBP) in CLT is still controversial. Experiments were conducted after 35-days of oral exposure to the three concentrations of DBP or saline, and three immunizations with thyroglobulin (TG). Healthy female Wistar rats were randomly divided into ten exposure groups (n = 8 each): (A) saline control, (B) 0.5 mg/kg/d DBP, (C) 5 mg/kg/d DBP, (D) 50 mg/kg/d DBP, (E) TG-immunized group, (F) TG- combined with 0.5 mg/kg/d DBP, (G) TG- combined with 5 mg/kg/d DBP, (H) TG- combined with 50 mg/kg/d DBP, (I) TG- combined with 50 mg/kg/d DBP plus 100 mg/kg/d vitamin C; (J) 100 mg/kg/d vitamin C. We showed that oral exposure DBP can aggravate CLT in rats. This deterioration was concomitant with increased thyroid auto antibodies, Th1/Th2 imbalance and Th17 immune response, activated pro-inflammatory and apoptosis pathways, and increased thyroid dysfunction in rats. Our results also suggested that DBP could promote oxidative damage. The study also found that vitamin C reduced the levels of oxidative stress and alleviated CLT. In short, the study showed that DBP exacerbated CLT through oxidative stress.

Effects of Prenatal Phthalate Exposure on Thyroid Hormone Concentrations Beginning at The Embryonic Stage

Limited studies have consistently shown an association of phthalates exposure with thyroid hormones (THs) in pregnant women. However, it remains unknown on which specific phthalates can affect THs and whether any effects could differ by gestational age. In the present study, we investigated associations between serum concentrations of phthalate monoesters [monoethyl phthalate (MEP), mono-(n + iso)-butyl phthalate (MBP) and mono(2-ethylhexyl) phthalate (MEHP)] and THs [thyroid-stimulating hormone (TSH), total thyroxine (TT4) and free thyroxine (FT4)] in Chinese pregnant women. 1,397 women were recruited from the China-Anhui Birth Cohort. Maternal serum samples were collected and used to measure phthalate metabolites and THs. Covariate-adjusted linear regression analyses showed that natural log (Ln)-transferred concentrations of MBP and LnMEHP were negatively associated with TT4 (β = −0.277 and –0.461, respectively; p < 0.001). Stratification analyses by gestational weeks showed significant associations of LnMBP and LnMEHP with TT4 in gestational weeks 5 to 8, 9 to 12, and 13 to 20. Our findings suggest an association of serum phthalates with lower TT4. The influence of MBP and MEHP on TT4 concentrations throughout the early pregnancy may begin from the embryonic stage (gestational weeks 5 to 8).

Considering common sources of exposure in association studies - Urinary benzophenone-3 and DEHP metabolites are associated with altered thyroid hormone balance in the NHANES 2007-2008

Epidemiological studies have shown that thyroid hormone balances can be disrupted by chemical exposure. However, many association studies have often failed to consider multiple chemicals with possible common sources of exposure, rendering their conclusions less reliable. In the 2007-2008 National Health and Nutrition Examination Survey (NHANES) from the U.S.A., urinary levels of environmental phenols, parabens, and phthalate metabolites as well as serum thyroid hormones were measured in a general U.S. population (≥12years old, n=1829). Employing these data, first, the chemicals or their metabolites associated with thyroid hormone measures were identified. Then, the chemicals/metabolites with possible common exposure sources were included in the analytical model to test the sensitivities of their association with thyroid hormone levels. Benzophenone-3 (BP-3), bisphenol A (BPA), and a metabolite of di(2-ethylhexyl) phthalate (DEHP) were identified as significant determinants of decreased serum thyroid hormones. However, significant positive correlations were detected (p-value<0.05, r=0.23 to 0.45) between these chemicals/metabolites, which suggests that they might share similar exposure sources. In the subsequent sensitivity analysis, which included the chemicals/metabolite with potentially similar exposure sources in the model, we found that urinary BP-3 and DEHP exposure were associated with decreased thyroid hormones among the general population but BPA exposure was not. In association studies, the presence of possible common exposure sources should be considered to circumvent possible false-positive conclusions.

Phthalates and thyroid function in preschool age children: Sex specific associations

BACKGROUND

Research relating either prenatal or concurrent measures of phthalate exposure to thyroid function in preschool children is inconclusive.

METHODS

In a study of inner-city mothers and their children, metabolites of di-n-butyl phthalate, butylbenzyl phthalate, di-isobutyl phthalate, di(2-ethylhexyl) phthalate, and diethyl phthalate were measured in a spot urine sample collected from women in late pregnancy and from their children at age 3years. We measured children's serum free thyroxine (FT4) and thyroid stimulating hormone (TSH) at age 3. Linear regression models were used to investigate the associations between phthalate metabolites, measured in maternal urine during late pregnancy and measured in child urine at age 3 and thyroid function measured at age 3.

RESULTS

Mean concentrations (ranges) were 1.42ng/dL (1.02-2.24) for FT4, and 2.62uIU/mL (0.61-11.67) for TSH. In the children at age 3, among girls, FT4 decreased with increasing log_e mono-n-butyl phthalate [estimated b=-0.06; 95% CI: (-0.09, -0.02)], log_e mono-isobutyl phthalate [b=-0.05; 95% CI: (-0.09, -0.01)], log_e monoethyl phthalate [b=-0.04; 95% CI: (-0.07, -0.01)], and log_e mono(2-ethyl-5-hydroxyhexyl) phthalate [b=-0.04; 95% CI: (-0.07, -0.003)] and log_e mono(2-ethyl-5-oxy-hexyl) phthalate [b=-0.04; 95% CI: (-0.07, -0.004)]. In contrast, among boys, we observed no associations between FT4 and child phthalate metabolites at age 3. On the other hand, in late gestation, FT4 increased with increasing log_e mono-(2-ethylhexyl) phthalate [estimated b=0.04; 95% CI: (0.02, 0.06)] and no sex difference was observed. We found no associations between phthalate biomarkers measured in either the child or prenatal samples and TSH at age 3.

CONCLUSIONS

The data show inverse and sex specific associations between specific phthalate metabolites measured in children at age 3 and thyroid function in preschool children. These results may provide evidence for the hypothesis that reductions in thyroid hormones mediate associations between early life phthalate exposure and child cognitive outcomes.

Maternal prenatal urinary phthalate metabolite concentrations and visual recognition memory among infants at 27 weeks

BACKGROUND

Prior research has demonstrated inverse associations between maternal prenatal urinary phthalate metabolite concentrations and cognitive development assessed in preschool and school-aged children. While there are a limited number of studies that evaluated these associations during infancy, no study has evaluated whether these associations exist when using the Fagan Test of Infant Intelligence (FTII), which captures novelty preference as a function of visual recognition memory.

OBJECTIVE

We evaluated associations between phthalate metabolite concentrations in maternal prenatal urine and cognition in infancy using the FTII at 27 weeks and determine if these associations are sex-specific.

METHODS

Mono-n-butyl phthalate (MnBP), monobenzyl phthalate (MBzP), monoisobutyl phthalate (MiBP), mono-ethyl phthalate (MEP), mono-3-carboxypropyl phthalate (MCPP) and four di-2-ethylhexyl phthalate metabolites (DEHP) were quantified in urine samples collected from 168 minority women living in urban neighborhoods during their third trimester of pregnancy. The FTII was administered to infants at 27 weeks to measure visual recognition memory and was recorded as the novelty preference score.

RESULTS

There were no associations between prenatal phthalate metabolite concentrations and novelty preference score in the full sample. However, there was evidence of effect modification by infant sex. Sex-stratified models demonstrated that compared to girls in the lowest tertile of MBzP concentrations, girls in tertiles 2 and 3 had, on average, 3.98 and 4.65 points lower novelty preference scores (p-value=0.04 and 0.03, respectively). The relationship was similar for ΣDEHP, MiBP, and MEP. Effects among boys were inconsistent and generally not significant.

CONCLUSION

Maternal prenatal exposure to some phthalates was negatively associated with visual recognition memory as measured by the FTII among girls at age 27 weeks.

Associations between urinary phthalate metabolites and bisphenol A levels, and serum thyroid hormones among the Korean adult population - Korean National Environmental Health Survey (KoNEHS) 2012-2014

BACKGROUND

Phthalates and bisphenol A (BPA) have been used extensively in many consumer products, resulting in widespread exposure in the general population. Studies have suggested associations between exposure to phthalates and BPA, and serum thyroid hormone levels, but confirmation on larger human populations is warranted.

METHODS

Data obtained from nationally representative Korean adults (n=6003) recruited for the second round of the Korean National Environmental Health Survey (KoNEHS), 2012-2014, were employed. Three di-(2-ethylhexyl) phthalate (DEHP) metabolites, along with benzyl-butyl phthalate (BBzP) and di-butyl phthalate (DBP) metabolites, and BPA were measured in subjects' urine. Thyroxine (T4), total triiodothyronine (T3), and thyroid-stimulating hormone (TSH) were measured in serum. The associations between urinary phthalates or BPA and thyroid hormone levels were determined.

RESULTS

Urinary phthalate metabolites were generally associated with lowered total T4 or T3, or increased TSH levels in serum. Interquartile range (IQR) increases of mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) were associated with a 3.7% increase of TSH, and a 1.7% decrease of total T4 levels, respectively. When grouped by sex, urinary MEHHP levels were inversely associated with T4 only among males. Among females, mono-benzyl phthalate (MBzP) and mono-n-butyl phthalate (MnBP) levels were inversely associated with TSH and T3, respectively. In addition, negative association between BPA and TSH was observed.

CONCLUSIONS

Several phthalates and BPA exposures were associated with altered circulatory thyroid hormone levels among general Korean adult population. Considering the importance of thyroid hormones, public health implications of such alteration warrant further studies.

Does exposure to phthalates influence thyroid function and growth hormone homeostasis? The Taiwan Environmental Survey for Toxicants (TEST) 2013

BACKGROUND

Previous epidemiologic and toxicological studies provide some inconsistent evidence that exposure to phthalates may affect thyroid function and growth hormone homeostasis.

OBJECTIVE

To assess the relations between exposure to phthalates and indicators of thyroid function and growth hormone homeostasis disturbances both among adults and minors.

METHODS

We conducted a population-based cross-sectional study of 279 Taiwanese adults (≥18 years old) and 79 minors (<18 years old) in 2013. Exposure assessment was based on urinary biomarkers, 11 phthalate metabolites measured by using online liquid chromatography/tandem mass spectrometry. Indicators of thyroid function included serum levels of thyroxine (T₄), free T₄, triiodothyronine, thyroid-stimulating hormone, and thyroxine-binding globulin (TBG). Growth hormone homeostasis was measured as the serum levels of insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding protein 3 (IGFBP3). We applied multivariate linear regression models to examine these associations after adjusting for covariates.

RESULTS

Among adults, serum T₄ levels were negatively associated with urinary mono-(2-ethyl-5-hydroxyhexyl) phthalate (β=-0.028, P=0.043) and the sum of urinary di-(2-ethylhexyl) phthalate (DEHP) metabolite (β=-0.045, P=0.017) levels. Free T₄ levels were negatively associated with urinary mono-ethylhexyl phthalate (MEHP) (β=-0.013, P=0.042) and mono-(2-ethyl-5-oxohexyl) phthalate (β=-0.030, P=0.003) levels, but positively associated with urinary monoethyl phthalate (β=0.014, P=0.037) after adjustment for age, BMI, gender, urinary creatinine levels, and TBG levels. Postive associations between urinary MEHP levels and IGF-1 levels (β=0.033, P=0.006) were observed. Among minors, free T₄ was positively associated with urinary mono benzyl phthalate levels (β=0.044, P=0.001), and IGF-1 levels were negatively associated with the sum of urinary DEHP metabolite levels (β=-0.166, P=0.041) after adjustment for significant covariance and IGFBP3.

CONCLUSIONS

Our results are consistent with the hypothesis that exposure to phthalates influences thyroid function and growth hormone homeostasis.

Exposure to phthalates in children aged 5-7years: Associations with thyroid function and insulin-like growth factors

This study aimed to evaluate the associations between phthalate concentrations and thyroid function in preschool children. We collected demographic data and biological samples from 216 children aged 5-7years. We calculated urinary concentrations of eight mono-phthalate metabolites (mPAEs) separately for children from urban and rural areas and investigated their associations with thyroid function and growth hormones. mPAE concentrations were higher in children from the urban area than in those from the rural area, and most mPAEs were positively associated with free triiodothyronine and free thyroxine. The insulin-like growth factor 1 (IGF-1) concentration decreased 0.082ng/mL (95% confidence interval [CI]: -1.34, -0.113) with each 1ng/mL increase in monomethyl phthalate (MMP) and 0.132ng/mL (95% CI: -0.209, -0.055) with each 1ng/mL increase in mono-n-butyl phthalate. The insulin-like growth factor binding protein 3 concentration decreased by 0.01mg/L (95% CI: -0.001, -0.000) or 0.01mg/L (95% CI: -0.003, -0.000) with each 1ng/mL increase in MMP or monoethyl phthalate, respectively. Exposure to some phthalates at 5-7years of age might interfere with thyroid hormones and growth.

Di2-ethylhexyl phthalate disrupts thyroid hormone homeostasis through activating the Ras/Akt/TRHr pathway and inducing hepatic enzymes

Di(2-ethylhexyl) phthalate (DEHP), as a widespread environmental pollutant and an endocrine disruptor, can disturb the homeostasis of thyroid hormones (THs). In order to elucidate roles of the MAPK and PI3K/Akt pathways and hepatic enzymes in thyroid-disrupting effects of DEHP, Sprague-Dawley rats were dosed with DEHP by gavage for 30 consecutive days; Nthy-ori 3-1 cells were treated with DEHP with NAC, k-Ras siRNA or inhibitors (U0126 and wortmannin). Results showed that DEHP led to histopathologic changes in rat thyroid and liver, such as the decrease in thyroid follicular cavity diameter, hepatocyte edema. Triiodothyronine (T3), thyroxine (T4) and thyrotropin releasing hormone (TRH) were reduced. DEHP caused ROS production, oxidative stress and k-Ras upregulation, thereby activating the ERK and Akt pathways in vivo and in vitro. Moreover, TRH receptor (TRHr) level was elevated after the activation of the Akt pathway and was downregulated after the inhibition of the Akt pathway. However, TRHr was not modulated by the ERK pathway. Additionally, hepatic enzymes, including Ugt1a1, CYP2b1, Sult1e1, and Sult2b1, were significantly induced after DEHP exposure. Taken together, DEHP can perturb TH homeostasis and reduce TH levels. The activated Ras/Akt/TRHr pathway and induced hepatic enzymes play vital roles in thyroid-disrupting effects of DEHP.

Effects of Long-Term In Vivo Exposure to Di-2-Ethylhexylphthalate on Thyroid Hormones and the TSH/TSHR Signaling Pathways in Wistar Rats

Di-(2-ethylhexyl)phthalate (DEHP) was a widely used chemical with human toxicity. Recent in vivo and in vitro studies suggested that DEHP-exposure may be associated with altered serum thyroid hormones (THs) levels, but the underlying molecular mechanisms were largely unknown. To explore the possible molecular mechanisms, 128 Wistar rats were dosed with DEHP by gavage at 0, 150, 300, and 600 mg/kg/day for 3 months (M) and 6 M, respectively. After exposure, expression of genes and proteins in the thyroid, pituitary, and hypothalamus tissues of rats were analyzed by Q-PCR and western blot, while the sera and urine samples were assayed by radioimmunoassay and ELISA. Results showed that serum THs levels were suppressed by DEHP on the whole. DEHP treatment influenced the levels of rats’ thyrotropin releasing hormone receptor (TRHr), Deiodinases 1 (D1), thyroid stimulating hormone beta (TSHβ), sodium iodide symporter (NIS), thyroid stimulating hormone receptor (TSHr), thyroperoxidase (TPO), thyroid transcription factor 1 (TTF-1), and thyroglobulin (TG) mRNA/protein expression in the hypothalamus-pituitary-thyroid (HPT) axis and decreased urine iodine. Taken together, observed findings indicate that DEHP could reduce thyroid hormones via disturbing the HPT axis, and the activated TSH/TSHR pathway is required to regulate thyroid function via altering TRHr, TSHβ, NIS, TSHr, TPO, TTF-1 and TG mRNA/protein expression of the HPT axis.

Associations between Repeated Measures of Maternal Urinary Phthalate Metabolites and Thyroid Hormone Parameters during Pregnancy

BACKGROUND

Maintaining thyroid homeostasis during pregnancy is essential for normal fetal growth and development. Growing evidence suggests that phthalates interfere with normal thyroid function. Few human studies have investigated the degree to which phthalates may affect thyroid hormone levels in particularly susceptible populations such as pregnant women.

OBJECTIVES

We examined the associations between repeated measures of urinary phthalate metabolites and plasma thyroid hormone levels in samples collected at up to four time points per subject in pregnancy. Additionally, we investigated the potential windows of susceptibility to thyroid hormone disturbances related to study visit of sample collection.

METHODS

Data were obtained from pregnant women (n = 439) participating in a nested case-control study of preterm birth with 116 cases and 323 controls. We measured 9 phthalate metabolite concentrations in urine samples collected at up to four study visits per subject during pregnancy (median = 10, 18, 26, and 35 weeks of gestation, respectively). We also measured a panel of thyroid function markers in plasma collected at the same four time points per subject during pregnancy.

RESULTS

Although our results were generally null, in repeated measures analyses we observed that phthalate metabolites were largely inversely associated with thyrotropin and positively associated with free and total thyroid hormones. Cross-sectional analyses by study visit revealed that the magnitude and/or direction of these relationships varied by timing of exposure during gestation.

CONCLUSIONS

These results support previous reports showing the potential for environmental phthalate exposure to alter circulating levels of thyroid hormones in pregnant women. Citation: Johns LE, Ferguson KK, McElrath TF, Mukherjee B, Meeker JD. 2016. Associations between repeated measures of maternal urinary phthalate metabolites and thyroid hormone parameters during pregnancy. Environ Health Perspect 124:1808-1815; http://dx.doi.org/10.1289/EHP170.

Maternal phthalate exposure during the first trimester and serum thyroid hormones in pregnant women and their newborns

Animal and human studies have suggested that phthalate alters thyroid hormone concentrations. This study investigated the associations between phthalate exposure during the first trimester and thyroid hormones in pregnant women and their newborns. Pregnant women were enrolled from the prospective Ma'anshan Birth Cohort study in China. A standard questionnaire was completed by the women at the first antenatal visit. Seven phthalate metabolites were measured in one-spot urine at enrolment (10.0 ± 2.1 gestational weeks), as were thyroid hormone levels in maternal and cord sera. Multivariable linear regression showed that 1-standard deviation (SD) increase in natural log (ln)-transformed mono(2-ethylhexyl) phthalate (MEHP) and mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) was associated with 0.163 μg/dL (p = 0.001) and 0.173 μg/dL (p = 0.001) decreases in maternal total thyroxine (TT4). Both MEHP and MEHHP were negatively associated with maternal free thyroxine (FT4; β: -0.013, p < 0.001 and β: -0.011, p = 0.001, respectively) and positively associated with maternal thyroid-stimulating hormone (β: 0.101, p < 0.001; β: 0.132, p < 0.001, respectively). An inverse association was observed between monobenzyl phthalate and maternal TT4 and FT4. A 1-SD increase in ln-transformed monoethyl phthalate was inversely associated with maternal TT4 (β: -0.151, p = 0.002). By contrast, the concentrations of phthalate metabolites in urine were not associated with those of thyroid hormone in cord serum. Our analysis suggested that phthalate exposure during the first trimester disrupts maternal thyroid hormone levels.

Phthalates Are Metabolised by Primary Thyroid Cell Cultures but Have Limited Influence on Selected Thyroid Cell Functions In Vitro

Phthalates are plasticisers added to a wide variety of products, resulting in measurable exposure of humans. They are suspected to disrupt the thyroid axis as epidemiological studies suggest an influence on the peripheral thyroid hormone concentration. The mechanism is still unknown as only few in vitro studies within this area exist. The aim of the present study was to investigate the influence of three phthalate diesters (di-ethyl phthalate, di-n-butyl phthalate (DnBP), di-(2-ethylhexyl) phthalate (DEHP)) and two monoesters (mono-n-butyl phthalate and mono-(2-ethylhexyl) phthalate (MEHP)) on the differentiated function of primary human thyroid cell cultures. Also, the kinetics of phthalate metabolism were investigated. DEHP and its monoester, MEHP, both had an inhibitory influence on 3'-5'-cyclic adenosine monophosphate secretion from the cells, and MEHP also on thyroglobulin (Tg) secretion from the cells. Results of the lactate dehydrogenase-measurements indicated that the MEHP-mediated influence was caused by cell death. No influence on gene expression of thyroid specific genes (Tg, thyroid peroxidase, sodium iodine symporter and thyroid stimulating hormone receptor) by any of the investigated diesters could be demonstrated. All phthalate diesters were metabolised to the respective monoester, however with a fall in efficiency for high concentrations of the larger diesters DnBP and DEHP. In conclusion, human thyroid cells were able to metabolise phthalates but this phthalate-exposure did not appear to substantially influence selected functions of these cells.

Migration of phthalates on culture plates - an important challenge to consider for in vitro studies

Phthalates are endocrine disruptors of the reproductive system and suspected to influence many other organ and hormone systems. They are also semi-volatile organic compounds present in the gas phase in the environment. Their mode of action has been investigated in numerous in vitro studies. Multi-well culture plates are typically used to study phthalates in cell cultures. In a pilot study, we observed evidence of phthalate migration in 24-well culture plates. As this has not previously been described, we investigated the phenomenon in more detail. Primary human thyroid epithelial cell cultures (n = 8 cultures) were exposed to either di-ethyl phthalate (DEP), di-n-butyl phthalate (DnBP), mono-n-butyl phthalate (MnBP) or di-(2-ethylhexyl) phthalate (DEHP). Measurement of phthalate metabolites by mass spectrometry demonstrated that the short-branched DEP was able to migrate to adjacent wells when added to cell culture plates. DnBP also seemed to be able to migrate, unlike the long-branched DEHP or the monoester MnBP which did not seem to have this ability. High background levels of phthalate metabolites were also observed, which might compromise results from low dose phthalate studies. In conclusion, the migration of phthalates which is probably caused by their volatile properties might lead to false interpretation of study results.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Plasticizer endocrine disruption: Highlighting developmental and reproductive effects in mammals and non-mammalian aquatic species

Due to their versatility, robustness, and low production costs, plastics are used in a wide variety of applications. Plasticizers are mixed with polymers to increase flexibility of plastics. However, plasticizers are not covalently bound to plastics, and thus leach from products into the environment. Several studies have reported that two common plasticizers, bisphenol A (BPA) and phthalates, induce adverse health effects in vertebrates; however few studies have addressed their toxicity to non-mammalian species. The aim of this review is to compare the effects of plasticizers in animals, with a focus on aquatic species. In summary, we identified three main chains of events that occur in animals exposed to BPA and phthalates. Firstly, plasticizers affect development by altering both the thyroid hormone and growth hormone axes. Secondly, these chemicals interfere with reproduction by decreasing cholesterol transport through the mitochondrial membrane, leading to reduced steroidogenesis. Lastly, exposure to plasticizers leads to the activation of peroxisome proliferator-activated receptors, the increase of fatty acid oxidation, and the reduction in the ability to cope with the augmented oxidative stress leading to reproductive organ malformations, reproductive defects, and decreased fertility.

DEHP reduces thyroid hormones via interacting with hormone synthesis-related proteins, deiodinases, transthyretin, receptors, and hepatic enzymes in rats

Di-(2-ethylhexyl) phthalate (DEHP) is used extensively in many personal care and consumer products, resulting in widespread nonoccupational human exposure through multiple routes and media. Limited studies suggest that exposure to DEHP may be associated with altered thyroid function, but detailed mechanisms are unclear. In order to elucidate potential mechanisms by which DEHP disturbs thyroid hormone homeostasis, Sprague-Dawley (SD) rats were dosed with DEHP by gavage at 0, 250, 500, and 750 mg/kg/day for 30 days and sacrificed within 24 h after the last dose. Gene expressions of thyroid hormone receptors, deiodinases, transthyretin, and hepatic enzymes were measured by RT-PCR; protein levels of transthyretin were also analyzed by Western blot. Results showed that DEHP caused histological changes in the thyroid and follicular epithelial cell hypertrophy and hyperplasia were observed. DEHP significantly reduced thyroid hormones (T3, T4) and thyrotropin releasing hormone (TRH) levels, whereas thyroid stimulating hormone (TSH) was not affected. After exposure to DEHP, biosynthesis of thyroid hormones was suppressed, and sodium iodide symporter (NIS) and thyroid peroxidase (TPO) levels were significantly reduced. Additionally, levels of deiodinases and transthyretin were also affected. TSH receptor (TSHr) level was downregulated, while TRH receptor (TRHr) level was upregulated. Metabolism of thyroid hormones was accelerated due to elevated gene expression of hepatic enzymes (UDPGTs and CYP2B1) by DEHP. Taken together, observed findings indicate that DEHP could reduce thyroid hormones through influencing biosynthesis, biotransformation, biotransport, receptor levels, and metabolism of thyroid hormones.

Fetal and Childhood Exposure to Phthalate Diesters and Cognitive Function in Children Up to 12 Years of Age: Taiwanese Maternal and Infant Cohort Study

Few studies have examined the association between environmental phthalate exposure and children’s neurocognitive development. This longitudinal study examined cognitive function in relation to pre-and postnatal phthalate exposure in children 2–12 years old. We recruited 430 pregnant women in their third trimester in Taichung, Taiwan from 2001–2002. A total of 110, 79, 76, and 73 children were followed up at ages 2, 5, 8, and 11, respectively. We evaluated the children’s cognitive function at four different time points using the Bayley and Wechsler tests for assessing neurocognitive functions and intelligence (IQ). Urine samples were collected from mothers during pregnancy and from children at each follow-up visit. They were analyzed for seven metabolite concentrations of widely used phthalate esters. These esters included monomethyl phthalate, monoethyl phthalate, mono-butyl phthalate, mono-benzyl phthalate, and three metabolites of di(2-ethylhexyl) phthalate, namely, mono-2-ethylhexyl phthalate, mono(2-ethyl-5-hydroxyhexyl) phthalate, and mono(2-ethyl-5-oxohexyl) phthalate. We constructed a linear mixed model to examine the relationships between the phthalate metabolite concentrations and the Bayley and IQ scores. We found significant inverse associations between the children’s levels of urinary mono(2-ethyl-5-oxohexyl) phthalate and the sum of the three metabolites of di(2-ethylhexyl) phthalate and their IQ scores (β = -1.818; 95% CI: -3.061, -0.574, p = 0.004 for mono(2-ethyl-5-oxohexyl) phthalate; β = -1.575; 95% CI: -3.037, -0.113, p = 0.035 for the sum of the three metabolites) after controlling for maternal phthalate levels and potential confounders. We did not observe significant associations between maternal phthalate exposure and the children’s IQ scores. Children’s but not prenatal phthalate exposure was associated with decreased cognitive development in the young children. Large-scale prospective cohort studies are needed to confirm these findings in the future.

Urinary phthalate metabolites in relation to maternal serum thyroid and sex hormone levels during pregnancy: a longitudinal analysis

BACKGROUND

Increasing scientific evidence suggests that exposure to phthalates during pregnancy may be associated with an elevated risk of adverse reproductive outcomes such as preterm birth. Maternal endocrine disruption across pregnancy may be one pathway mediating some of these relationships. We investigated whether urinary phthalate metabolites were associated with maternal serum thyroid (free thyroxine [FT4], free triiodothyronine [FT3], and thyroid-stimulating hormone [TSH]), and sex (estradiol, progesterone, and sex hormone-binding globulin [SHBG]) hormone levels at multiple time points during pregnancy.

METHODS

Preliminary data (n = 106) were obtained from an ongoing prospective birth cohort in Northern Puerto Rico. We collected urine and serum sample at the first and third study visits that occurred at 18 +/- 2 and 26 +/- 2 weeks of gestation, respectively. To explore the longitudinal relationships between urinary phthalate metabolites and serum thyroid and sex hormone concentrations, we used linear mixed models (LMMs) adjusted for prepregnancy body mass index (BMI) and maternal age. An interaction term was added to each LMM to test whether the effect of urinary phthalate metabolites on serum thyroid and sex hormone levels varied by study visit. In cross-sectional analyses, we stratified BMI- and age-adjusted linear regression models by study visit.

RESULTS

In adjusted LMMs, we observed significant inverse associations between mono-3-carboxypropyl phthalate (MCPP) and FT3 and between mono-ethyl phthalate (MEP) and progesterone. In cross-sectional analyses by study visit, we detected stronger and statistically significant inverse associations at the third study visit between FT3 and MCPP as well as mono-carboxyisooctyl phthalate (MCOP); also at the third study visit, significant inverse associations were observed between FT4 and metabolites of di-(2-ethylhexyl) phthalate (DEHP). The inverse association between MEP and progesterone was consistent across study visits.

CONCLUSIONS

In this group of pregnant women, urinary phthalate metabolites may be associated with altered maternal serum thyroid and sex hormone levels, and the magnitude of these effects may depend on the timing of exposure during gestation.

Prenatal exposure to phthalate esters and behavioral syndromes in children at 8 years of age: Taiwan Maternal and Infant Cohort Study

BACKGROUND

Few studies have shown an association between prenatal phthalate exposure and adverse effects on neurodevelopment and behavior in young children.

OBJECTIVES

We aimed to assess the relationship between prenatal exposure to phthalate esters and behavior syndromes in children at 8 years of age.

METHODS

A total of 122 mother-child pairs from the general population in central Taiwan were studied from 2000 to 2009. Mono-methyl phthalate (MMP), mono-ethyl phthalate (MEP), mono-butyl phthalate (MBP), mono-benzyl phthalate (MBzP), and three di-(2-ethylhexyl) phthalate (DEHP) metabolites-mono-2-ethylhexyl, mono-2-ethyl-5-hydroxyhexyl, and mono-2-ethyl-5-oxohexyl phthalates (MEHP, MEHHP, and MEOHP)--were measured in maternal urine collected during the third trimester of pregnancy using liquid chromatography-electrospray ionization-tandem mass spectrometry. Behavioral syndromes of children at 8 years of age were evaluated using the Child Behavior Checklist (CBCL). Associations between log10-transformed creatinine-corrected phthalate concentrations and standardized scores of the CBCL were estimated using linear regression models or multinomial logistic regressions with adjustments for potential confounders.

RESULTS

Externalizing problem scores were significantly higher in association with a 1-unit increase in log10-transformed creatinine-corrected concentrations of maternal MBP (β = 4.29; 95% CI: 0.59, 7.99), MEOHP (β = 3.74; 95% CI: 1.33, 6.15), and MEHP (β = 4.28 ; 95% CI: 0.03, 8.26) after adjusting for the child's sex, intelligence, and family income. Meanwhile, MBP and MEOHP were significantly associated with Delinquent Behavior and Aggressive Behavior scores. The same pattern was found for borderline and/or clinical ranges.

CONCLUSIONS

Our findings suggest positive associations between maternal DEHP and dibutyl phthalate (DBP) exposure and externalizing domain behavior problems in 8-year-old children.

Phthalate exposure and childhood obesity

Phthalates are commonly used as plasticizers and vehicles for cosmetic ingredients. Phthalate metabolites have documented biochemical activity including activating peroxisome proliferator-activated receptor and antiandrogenic effects, which may contribute to the development of obesity. In vitro and in vivo studies suggest that phthalates have significant effects on the development of obesity, especially after prenatal exposure at low doses. Although few studies have examined the effects of phthalate on obesity development in humans, some work has shown that phthalates affect humans and animals similarly. In this paper, we review the possible mechanisms of phthalate-induced obesity, and discuss evidence supporting the role of phthalates in the development of obesity in humans.

Thyroid endocrine disruption in zebrafish larvae after exposure to mono-(2-ethylhexyl) phthalate (MEHP)

Phthalates are extensively used as plasticizers in a variety of daily-life products, resulting in widespread distribution in aquatic environments. However, limited information is available on the endocrine disrupting effects of phthalates in aquatic organisms. The aim of the present study was to examine whether exposure to mono-(2-ethylhexyl) phthalate (MEHP), the hydrolytic metabolite of di-(2-ethylhexyl) phthalate (DEHP) disrupts thyroid endocrine system in fish. In this study, zebrafish (Danio rerio) embryos were exposed to different concentrations of MEHP (1.6, 8, 40, and 200 μg/L) from 2 h post-fertilization (hpf) to 168 hpf. The whole-body content of thyroid hormone and transcription of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis were examined. Treatment with MEHP significantly decreased whole-body T4 contents and increased whole-body T3 contents, indicating thyroid endocrine disruption. The upregulation of genes related to thyroid hormone metabolism (Dio2 and UGT1ab) might be responsible for decreased T4 contents. Elevated gene transcription of Dio1 was also observed in this study, which might assist to degrade increased T3 contents. Exposure to MEHP also significantly induced transcription of genes involved in thyroid development (Nkx2.1 and Pax8) and thyroid hormone synthesis (TSHβ, NIS and TG). However, the genes encoding proteins involved in TH transport (transthyretin, TTR) was transcriptionally significantly down-regulated after exposure to MEHP. Overall, these results demonstrate that acute exposure to MEHP alters whole-body contents of thyroid hormones in zebrafish embryos/larvae and changes the transcription of genes involved in the HPT axis, thus exerting thyroid endocrine toxicity.