Prenatal exposure to endocrine disrupting chemicals in relation to thyroid hormone levels in infants - a Dutch prospective cohort study

Emerging perfluoroalkyl substances retard skeletal growth by accelerating osteoblasts senescence via ferroptosis

Due to the persistent nature and significant negative impacts of perfluorooctanoic acid (PFOA) on human health and other organisms, the emergence of new PFOA alternatives, such as perfluoro (2-methyl-3-oxhexanoic) acid (GenX) and perfluoro-3,6,9-trioxyundecanoic acid (PFO3TDA), have drawn significant attention. However, the toxic effects of PFOA and its substitutes on bones remain limited. In this study, we administered different concentrations of PFOA, GenX, and PFO3TDA via gavage to 3-week-old male BALB/C mice for four weeks. X-ray and micro-CT scans revealed shortening of the femur and tibia and significant reduction in bone density. Additionally, PFOA, GenX, and PFO3TDA promoted osteoblast senescence and impaired osteogenic capabilities. This was characterized by a decrease in the expression of osteogenesis-related genes (OCN, ALP, Runx2, etc.) and an increase in the expression of aging and inflammation-related factors (p16INK4a, P21, MMP3, etc). Furthermore, RNA sequencing revealed activation of the ferroptosis pathway in PFOA-treated osteoblasts, characterized by notable lipid peroxidation and excessive iron accumulation. Finally, by inhibiting the ferroptosis pathway with ferrostatin-1 (Fer-1), we effectively alleviated the senescence of MC3T3-E1 cells treated with PFOA, GenX, and PFO3TDA, and improved their osteogenic capabilities. Therefore, our study provides a new therapeutic insight into the impact of PFOA and its substitutes on bone growth and development.

A co-twin control study of in utero exposure to poly- and perfluoroalkyl substances and associations with neonatal thyroid-stimulating hormone

Research quantifying associations between early-life exposure to poly- and perfluoroalkyl substances (PFAS) and neonatal thyroid hormone levels is limited and reports inconsistent results. This study aimed to examine the associations of in utero PFAS exposure with neonatal thyroid-stimulating hormone (TSH), and to verify whether genetic and familial factors contribute to these associations. Within Wuhan Twin Birth Cohort study, we included 148 mother-twin pairs recruited between March 2016 and January 2018. Maternal plasma PFAS concentrations were measured at three different trimesters and averaged. Additionally, we measured cord plasma PFAS concentrations for twin newborns and retrieved their TSH levels from the medical system. Multivariable linear regression, generalized estimation equation, and linear mixed models were used to examine the covariate-adjusted associations. For maternal PFAS analyses, a 2-fold increment of average maternal perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) concentrations was linked with a 15% (95% CI: 2.5%, 28%) and 14% (95% CI: 2.4%, 28%) increase in neonatal TSH, respectively. For twin newborns discordant for PFAS exposure, a 2-fold increment of cord plasma PFOA, PFDA, perfluoroundecanoic acid (PFUdA), and perfluorohexanesulfonic acid (PFHxS) concentrations was related to a 7.1% (95% CI: 0.31%, 14%), 12% (95% CI: 4.8%, 20%), 7.5% (95% CI: 0.30%, 15%), and 8.5% (95% CI: 3.0%, 14%) increase in TSH among twins as individuals, respectively. Although these associations were mainly observed between twin pairs, certain PFAS exposure might have an independent association with increased TSH. Our present study suggests that higher maternal and cord plasma PFAS concentrations are associated with increased neonatal TSH, and genetic and familial factors contribute to these associations.

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 Between Prenatal and Early Postnatal Exposure to Perfluoroalkyl Substances and IQ Score in 7-Year-Old Children From the Odense Child Cohort

Perfluoroalkyl substances (PFAS) are persistent chemicals capable of crossing the placenta and passing into breast milk. Evidence suggests that PFAS exposure may affect brain development. We investigated whether prenatal or early postnatal PFAS exposure was associated with intelligence quotient (IQ) scores in schoolchildren from the Odense Child Cohort (Denmark, 2010-2020). We assessed concentrations of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA) in maternal serum collected during the first trimester of pregnancy and in child serum at age 18 months. At 7 years of age, children completed an abbreviated version of the Wechsler Intelligence Scale for Children, Fifth Edition, from which Full Scale Intelligence Quotient (FSIQ) and Verbal Comprehension Index scores were estimated. In multiple linear regression analyses conducted among 967 mother-child pairs, a doubling in maternal PFOS and PFNA concentrations was associated with a lower FSIQ score, while no significant associations were observed for PFOA, PFHxS, or PFDA. PFAS concentrations at age 18 months and duration of breastfeeding were strongly correlated, and even in structural equation models it was not possible to differentiate between the opposite effects of PFAS exposure and duration of breastfeeding on FSIQ. PFAS exposure is ubiquitous; therefore, an association with even a small reduction in IQ is of public health concern.

Per- and polyfluoroalkyl substances (PFAS) and thyroid hormone measurements in dried blood spots and neonatal characteristics: a pilot study

BACKGROUND

Pediatric thyroid diseases have been increasing in recent years. Environmental risk factors such as exposures to chemical contaminants may play a role but are largely unexplored. Archived neonatal dried blood spots (DBS) offer an innovative approach to investigate environmental exposures and effects.

OBJECTIVE

In this pilot study, we applied a new method for quantifying per- and polyfluoroalkyl substances (PFAS) to 18 archived DBS from babies born in California from 1985-2018 and acquired thyroid hormone measurements from newborn screening tests. Leveraging these novel data, we evaluated (1) changes in the concentrations of eight PFAS over time and (2) the relationship between PFAS concentrations, thyroid hormone concentrations, and neonatal characteristics to inform future research.

METHODS

PFAS concentrations in DBS were measured using ultra-high-performance liquid chromatography-mass spectrometry. Summary statistics and non-parametric Wilcoxon rank-sum and Kruskal-Wallis tests were used to evaluate temporal changes in PFAS concentrations and relationships between PFAS concentrations, thyroid hormone concentrations, and neonatal characteristics.

RESULTS

The concentration and detection frequencies of several PFAS (PFOA, PFOS, and PFOSA) declined over the assessment period. We observed that the timing of specimen collection in hours after birth was related to thyroid hormone but not PFAS concentrations, and that thyroid hormones were related to some PFAS concentrations (PFOA and PFOS).

IMPACT STATEMENT

This pilot study examines the relationship between concentrations of eight per- and polyfluoroalkyl substances (PFAS), thyroid hormone levels, and neonatal characteristics in newborn dried blood spots (DBS) collected over a period of 33 years. To our knowledge, 6 of the 22 PFAS we attempted to measure have not been quantified previously in neonatal DBS, and this is the first study to examine both PFAS and thyroid hormone concentrations using DBS. This research demonstrates the feasibility of using newborn DBS for quantifying PFAS exposures in population-based studies, highlights methodological considerations in the use of thyroid hormone data for future studies using newborn DBS, and indicates potential relationships between PFAS concentrations and thyroid hormones for follow-up in future research.

Public health evaluation of PFAS exposures and breastfeeding: a systematic literature review

Per- and polyfluoroalkyl substances (PFAS) are a class of man-made chemicals that are persistent in the environment. They can be transferred across the placenta to fetuses and through human milk to infants. The American Academy of Pediatrics advises that the benefits of breastfeeding infants almost always outweigh the potential risks of harm from environmental chemicals. However, there are few chemical-specific summaries of the potential harms of exposure to PFAS during the neonatal period through breastfeeding. This systematic review explores whether exposure to PFAS through breastfeeding is associated with adverse health outcomes among infants and children using evidence from human and animal studies. Systematic searches identified 4297 unique records from 7 databases. The review included 37 total articles, including 9 animal studies and 1 human study measuring the direct contribution of exposure of the infant or pup through milk for any health outcome. Animal studies provided evidence of associations between exposure to PFOA through breastfeeding and reduced early life body weight gain, mammary gland development, and thyroid hormone levels. They also provided limited evidence of associations between PFOS exposure through breastfeeding with reduced early life body weight gain and cellular changes in the hippocampus. The direct relevance of any of these outcomes to human health is uncertain, and it is possible that many adverse health effects of exposure through breastfeeding have not yet been studied. This review documents the current state of science and highlights the need for future research to guide clinicians making recommendations on infant feeding.

Trimester-specific associations of maternal exposure to bisphenols with neonatal thyroid stimulating hormone levels: A birth cohort study

BACKGROUND

Growing evidence suggests that exposure to bisphenol A (BPA) during pregnancy could interfere with neonatal thyroid function. Bisphenol F (BPF) and bisphenol S (BPS) are increasingly used as the substitutes of BPA. However, little is known about the effects of maternal exposure to BPS and BPF on neonatal thyroid function. The current study was aimed to investigate the trimester-specific associations of maternal exposure to BPA, BPS, and BPF with neonatal thyroid stimulating hormone (TSH) levels.

METHODS

Between November 2013 and March 2015, a total of 904 mother-newborn pairs were recruited from the Wuhan Healthy Baby Cohort Study, providing maternal urine samples in the first, second, and third trimesters for bisphenol exposure assessment, and neonatal heel prick blood samples for TSH measurement. Multiple informant model and quantile g-computation were used to evaluate the trimester-specific associations of bisphenols individually and mixture with TSH, respectively.

RESULTS

Each doubling concentration increase of maternal urinary BPA in the first trimester was significantly related to a 3.64 % (95% CI: 0.84 %, 6.51 %) increment in neonatal TSH. Each doubling concentration increase of BPS in the first, second and third trimesters were associated with 5.81 % (95 % CI: 2.27 %, 9.46 %), 5.70 % (95 % CI: 1.99 %, 9.55 %), 4.36 % (95 % CI: 0.75 %, 8.11 %) higher neonatal blood TSH, respectively. No significant association between trimester-specific BPF concentration and TSH was observed. The relationships between exposures to BPA/BPS and neonatal TSH were more evident in female infants. Quantile g-computation indicated that maternal co-exposure to bisphenols in the first trimester was significantly associated with neonatal TSH levels in a non-linear fashion.

CONCLUSION

Maternal exposure to BPA and BPS were positively associated with neonatal TSH levels. The results indicated the endocrine disrupting effect of prenatal exposure to BPS and BPA, which should be of particular concern.

Chronic exposure to tebuconazole alters thyroid hormones and plumage quality in house sparrows (Passer domesticus)

Triazoles belong to a family of fungicides that are ubiquitous in agroecosystems due to their widespread use in crops. Despite their efficiency in controlling fungal diseases, triazoles are also suspected to affect non-target vertebrate species through the disruption of key physiological mechanisms. Most studies so far have focused on aquatic animal models, and the potential impact of triazoles on terrestrial vertebrates has been overlooked despite their relevance as sentinel species of contaminated agroecosystems. Here, we examined the impact of tebuconazole on the thyroid endocrine axis, associated phenotypic traits (plumage quality and body condition) and sperm quality in wild-caught house sparrows (Passer domesticus). We experimentally exposed house sparrows to realistic concentrations of tebuconazole under controlled conditions and tested the impact of this exposure on the levels of thyroid hormones (T3 and T4), feather quality (size and density), body condition and sperm morphology. We found that exposure to tebuconazole caused a significant decrease in T4 levels, suggesting that this azole affects the thyroid endocrine axis, although T3 levels did not differ between control and exposed sparrows. Importantly, we also found that exposed females had an altered plumage structure (larger but less dense feathers) relative to control females. The impact of tebuconazole on body condition was dependent on the duration of exposure and the sex of individuals. Finally, we did not show any effect of exposure to tebuconazole on sperm morphology. Our study demonstrates for the first time that exposure to tebuconazole can alter the thyroid axis of wild birds, impact their plumage quality and potentially affect their body condition. Further endocrine and transcriptomic studies are now needed not only to understand the underlying mechanistic effects of tebuconazole on these variables, but also to further investigate their ultimate consequences on performance (i.e. reproduction and survival).

Derivatized versus non-derivatized LC-MS/MS techniques for the analysis of estrogens and estrogen-like endocrine disruptors in human plasma

Bisphenols, parabens, alkylphenols and triclosan are anthropogenic substances with a phenolic group that have been introduced to the environment in recent decades. As they possess hormone-like effects, they have been termed endocrine disruptors (EDs), and can interfere with steroid pathways in organisms. To evaluate the potential impact of EDs on steroid biosynthesis and metabolism, sensitive and robust methods enabling the concurrent measurement of EDs and steroids in plasma are needed. Of crucial importance is the analysis of unconjugated EDs, which possess biological activity. The aim of the study was to develop and validate LC-MS/MS methods with and without a derivatization step for the analysis of unconjugated steroids (estrone-E1, estradiol-E2, estriol-E3, aldosterone-ALDO) and different groups of EDs (bisphenols, parabens, nonylphenol-NP and triclosan-TCS), and compare these methods on a set of 24 human plasma samples using Passing-Bablok regression analysis. Both methods were validated according to FDA and EMA guidelines. The method with dansyl chloride derivatization allowed 17 compounds to be measured: estrogens (E1, E2, E3), bisphenols (bisphenol A-BPA, BPS, BPF, BPAF, BPAP, BPZ, BPP), parabens (methylparaben-MP, ethylparaben-EP, propylparaben-PP, butylparaben-BP, benzylparaben-BenzylP), TCS and NP, with lower limits of quantification (LLOQs) between 4 and 125 pg/mL. The method without derivatization enabled 15 compounds to be analyzed: estrogens (E1, E2, E3), ALDO, bisphenols (BPA, BPS, BPF, BPAF, BPAP, BPZ), parabens (MP, EP, PP, BP, BenzylP) with LLOQs between 2 and 63 pg/mL, and NP and BPP in semiquantitative mode. Adding 6 mM ammonium fluoride post column into mobile phases in the method without derivatization achieved similar or even better LLOQs than the method with the derivatization step. The uniqueness of the methods lies in the simultaneous determination of different classes of unconjugated (bioactive) fraction of EDs together with selected steroids (estrogens + ALDO in the method without derivatization), which provides a useful tool for evaluating the relationships between EDs and steroid metabolism.

Exposure to a mixture of non-persistent environmental chemicals and neonatal thyroid function in a cohort with improved exposure assessment

BACKGROUND

In vitro and toxicological studies have shown that non-persistent environmental chemicals can perturb thyroid hormone homeostasis. Epidemiological studies with improved exposure assessment (i.e., repeated urine samples) are needed to evaluate effects of these compounds, individually or as a mixture, in humans. We studied the associations between prenatal exposure to non-persistent environmental chemicals and neonatal thyroid hormones.

METHODS

The study population consisted of 442 mother-child pairs from the French SEPAGES mother-child cohort recruited between July 2014 and July 2017. For each participant, four parabens, five bisphenols, triclosan, triclocarban, benzophenone-3 as well as metabolites of phthalates and of di(isononyl)cyclohexane-1,2-dicarboxylate were assessed in two pools of repeated urine samples (median: 21 spot urines per pool), collected in the 2nd and 3rd trimesters of pregnancy, respectively. Thyroid stimulating hormone (TSH) and total thyroxine (T4) levels were determined in newborns from a heel-prick blood spot. Maternal iodine and selenium were assessed in urine and serum, respectively. Adjusted linear regression (uni-pollutant model) and Bayesian Kernel Machine Regression (BKMR, mixture model) were applied to study overall and sex-stratified associations between chemicals and hormone concentrations.

RESULTS

Interaction with child sex was detected for several compounds. Triclosan, three parabens, and one phthalate metabolite (OH-MPHP) were negatively associated with T4 among girls in the uni-pollutant model. BKMR also suggested a negative association between the mixture and T4 in girls, whereas in boys the association was positive. The mixture was not linked to TSH levels, and for this hormone the uni-pollutant model revealed associations with only a few compounds.

CONCLUSION

Our study, based on repeated urine samples to assess exposure, showed that prenatal exposure to some phenols and phthalates disturb thyroid hormone homeostasis at birth. Furthermore, both uni-pollutant and mixture models, suggested effect modification by child sex, while, to date underlying mechanisms for such sex-differences are not well understood.

Urinary levels of phthalate esters and heavy metals in adolescents with thyroid colloid cysts

We aimed to evaluate 14 urinary phthalate metabolites and 4 toxic metals in adolescents having thyroid colloid cyst (TCC) and compare with age and sex-matched others without TCC. Phthalate metabolites were analysed with UPLC-MS/MS and heavy metals with ICP-MS. TCC ratios in tertile subgroups of pollutants were compared with multiple logistic regression analysis after adjusting for age, sex, z-scores for body mass index and urinary creatinine values. Adolescents having the highest tertile of mono (2-ethylhexyl) phthalic acid and mercury had increased odds and those with the highest tertiles of monocarboxy-isononyl phthalate, mono (3-carboxypropyl) phthalate, monoisobutyl phthalate had lower odds for TCC than counterparts. The odds of TCC were lower for those in the second and the third tertiles. No differences in TCC ratios were detected with other pollutants. Given phthalate esters' and toxic metals' specific interactions on TCC, further studies were necessary to assess the influence of chemicals on TCC.

The association between prenatal perfluoroalkyl substance exposure and symptoms of attention-deficit/hyperactivity disorder in 8-year-old children and the mediating role of thyroid hormones in the Hokkaido study

BACKGROUND

Disruption of thyroid hormone (TH) levels during pregnancy contributes to attention deficit hyperactivity disorder (ADHD). Exposure to perfluoroalkyl substances (PFAS) during gestation may affect levels of maternal and neonatal TH; however, little is known about the effect of PFAS on ADHD mediated by TH.

OBJECTIVES

We investigated the impact of maternal PFAS exposure on children's ADHD symptoms with the mediating effect of TH.

METHODS

In a prospective birth cohort (the Hokkaido study), we included 770 mother-child pairs recruited between 2002 and 2005 for whom both prenatal maternal and cord blood samples were available. Eleven PFAS were measured in maternal serum obtained at 28-32 weeks of gestation using ultra-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry. TH and thyroid antibody, including thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) were measured in maternal blood during early pregnancy (median 11 gestational weeks) and in cord blood at birth. ADHD symptoms in the children at 8 years of age were rated by their parents using the ADHD-Rating Scale (ADHD-RS). The cut-off value was set at the 80th percentile for each sex.

RESULTS

Significant inverse associations were found between some PFAS in maternal serum and ADHD symptoms among first-born children. Assuming causality, we found only one significant association: maternal FT4 mediated 17.6% of the estimated effect of perfluoroundecanoic acid exposure on hyperactivity-impulsivity among first-born children.

DISCUSSION

Higher PFAS levels in maternal serum during pregnancy were associated with lower risks of ADHD symptoms at 8 years of age. The association was stronger among first-born children in relation to hyperactivity-impulsivity than with regard to inattention. There was little mediating role of TH during pregnancy in the association between maternal exposure to PFAS and reduced ADHD symptoms at 8 years of age.

Relationship between thyroid hormone parameters and exposure to a mixture of organochlorine pesticides, mercury and nutrients in the cord blood of newborns

The fetus is prenatally exposed to a mixture of organochlorine pesticides (OCPs), mercury (Hg), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and selenium (Se) through maternal seafood consumption in real-life scenario. Prenatal exposure to these contaminants and nutrients has been suggested to affect thyroid hormone (TH) status in newborns, but the potential relationships between them are unclear and the joint effects of the mixture are seldom analyzed. The aim of the study is to investigate the associations of prenatal exposure to a mixture of OCPs, Hg, DHA, EPA and Se with TH parameters in newborns. 228 mother-infant pairs in Shanghai, China were included. We measured 20 OCPs, total Hg, DHA, EPA and Se in cord blood samples as exposure variables. The total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH) levels and the FT3/FT4 ratio in cord serum were determined as outcomes. Using linear regression models, generalized additive models and Bayesian kernel machine regression, we found dose-response relationships of the mixture component with outcomes: among the contaminants, p,p'-DDE was the most important positive predictor of TT3, while HCB was predominantly positively associated with FT3 and the FT3/FT4 ratio, indicating different mechanisms underlying these relationships; among the nutrients, EPA was first found to be positively related to the FT3/FT4 ratio. Additionally, we found suggestive evidence of interactions between p,p'-DDE and HCB on both TT3 and FT3, and EPA by HCB interactions for TT3, FT3 and FT3/FT4 ratio. However, the overall effects of the mixture on thyroid hormone parameters were not significant. Our result suggests that prenatal exposure to p,p'-DDE, HCB and EPA as part of a mixture might affect thyroid function of newborns in independent and interactive ways. The potential biological mechanisms merit further investigation.

Combining in vitro assays and mathematical modelling to study developmental neurotoxicity induced by chemical mixtures

Prenatal and postnatal co-exposure to multiple chemicals at the same time may have deleterious effects on the developing nervous system. We previously showed that chemicals acting through similar mode of action (MoA) and grouped based on perturbation of brain derived neurotrophic factor (BDNF), induced greater neurotoxic effects on human induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes compared to chemicals with dissimilar MoA. Here we assessed the effects of repeated dose (14 days) treatments with mixtures containing the six chemicals tested in our previous study (Bisphenol A, Chlorpyrifos, Lead(II) chloride, Methylmercury chloride, PCB138 and Valproic acid) along with 2,2'4,4'-tetrabromodiphenyl ether (BDE47), Ethanol, Vinclozolin and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)), on hiPSC-derived neural stem cells undergoing differentiation toward mixed neurons/astrocytes up to 21 days. Similar MoA chemicals in mixtures caused an increase of BDNF levels and neurite outgrowth, and a decrease of synapse formation, which led to inhibition of electrical activity. Perturbations of these endpoints are described as common key events in adverse outcome pathways (AOPs) specific for DNT. When compared with mixtures tested in our previous study, adding similarly acting chemicals (BDE47 and EtOH) to the mixture resulted in a stronger downregulation of synapses. A synergistic effect on some synaptogenesis-related features (PSD95 in particular) was hypothesized upon treatment with tested mixtures, as indicated by mathematical modelling. Our findings confirm that the use of human iPSC-derived mixed neuronal/glial models applied to a battery of in vitro assays anchored to key events in DNT AOP networks, combined with mathematical modelling, is a suitable testing strategy to assess in vitro DNT induced by chemical mixtures.

Perinatal effects of persistent organic pollutants on thyroid hormone concentration in placenta and breastmilk

Thyroid hormones (TH) are known to play a critical role in regulating many biological processes including growth and development, energy homeostasis, thermogenesis, lipolysis and metabolism of cholesterol. Severe TH deficiency especially during fetal development results in cretinism, but can also lead to an imbalance in metabolism with, among others, an alteration in body weight composition. Over the past two decades, increasing evidence has shown that certain persistent organic pollutants (POP) can interfere with the endocrine system. These POP referred to as "endocrine disrupting chemicals" are widely present in the environment and populations are exposed globally. Moreover, epidemiological studies have shown that a particularly sensitive period is the pre- and postnatal time. Indeed, perinatal exposure to such chemicals could lead to the onset diseases in later life. It is known, that, maternal thyroid hormones are transported by the placenta to the fetus from 6 weeks of gestation and it seems that during the first trimester, and part of the second, the fetus is entirely dependent on maternal TH supply for its development. Interferences in the TH-network as a consequence of the exposure to such pollutants could cause variations in TH concentration. Only small changes in maternal thyroid hormone levels in early stages of pregnancy can influence fetal neurological and cardiovascular development, as well as according to recent studies, have effect on childhood body composition. With this review, we will report the most recent and important studies concerning the association between thyroid hormone concentration and POP levels measured during the perinatal period. We will mostly focus on the data recently reported on placenta and breastmilk as main sources for understanding the potential consequences of exposure. The possible link between exposure to pollutants, TH dysregulation and possible adverse outcome will also be briefly discussed. From our literature search, several studies support the hypothesis that pre- and postnatal exposure to different pollutants might play a role in causing variation in thyroid hormone concentration. However, few research papers have so far studied the relationship linking exposure to pollutants, TH concentration and possible health consequences. Therefore, this review highlights the need for further research in this direction.

Association between exposure to polyfluoroalkyl chemicals and increased fractional exhaled nitric oxide in adults

BACKGROUND

Perfluoroalkyl chemicals (PFCs) are widely detected in the environment and human body, and they have been linked to asthma and a number of respiratory responses in children and mice. However, no previous studies have investigated the association between exposure to PFCs and airway inflammation in adults.

OBJECTIVES

To evaluate the associations between serum PFCs and fractional exhaled nitric oxide (FeNO), a biomarker of airway inflammation, in adults.

METHODS

A cross-sectional study of 3630 adults aged 20-79 years who participated in the National Health and Nutrition Examination Survey (NHANES, 2007-2012) was conducted. Serum concentrations of five major PFCs were measured using SPE-HPLC-TIS-MS/MS method, including perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), and perfluorodecanoic acid (PFDE). The detection rates of them were all >85%. Weighted multivariable linear regression and Bayesian kernel machine regression (BKMR) analyses were applied to examine the associations between serum PFCs and FeNO.

RESULTS

After adjusted for potential confounding factors, linear regression analyses found that compared with their lowest tertiles, highest tertiles of PFOS, PFDE and PFOA were significantly associated with 5.02% (95% CI: 1.40%, 8.77%), 3.77% (95% CI: 0.30%, 7.36%) and 6.34% (95% CI: 2.81%, 10.01%) increases in FeNO, respectively. The second tertile of PFNA was significantly correlated with a 4.79% (95% CI: 1.41%, 8.29%) increase in FeNO compared with the lowest tertile. In the BKMR analysis, the mixture effect of PFCs on FeNO increased significantly when the PFC levels were at or above the 60th percentiles compared to those at their medians. PFOS and PFOA displayed significant positive single-exposure effects on FeNO when all the other PFCs are set at a particular threshold.

CONCLUSIONS

This study provided preliminary evidence that serum PFCs were positively associated with increased FeNO in adults.

Prenatal exposure to per- and polyfluoroalkyl substances and cognitive development in infancy and toddlerhood

BACKGROUND/OBJECTIVE

Per- and polyfluoroalkyl substances (PFAS) have neurobehavioral toxicity in experimental studies. Evidence on associations between prenatal PFAS exposure and child's cognitive development is inconsistent partly due to differences in assessment time points and tools. We examined associations of prenatal maternal serum PFAS concentrations with child's cognitive development assessed at multiple time points in infancy and toddlerhood.

METHODS

We included 140 mother-child pairs from MARBLES (Markers of Autism Risk in Babies - Learning Early Signs), a longitudinal cohort of children with a first degree relative who was diagnosed with autism spectrum disorder followed from birth. Study children's cognitive development was assessed at 6, 12, 24, and 36 months of age using the Mullen Scales of Early Learning (MSEL) which provides an overall Early Learning Composite (normative mean of 100 and SD of 15) and four subscales (i.e., fine motor, visual reception, receptive language, and expressive language abilities; normative mean of 50 and SD of 10). Nine PFAS were quantified in maternal serum collected during pregnancy. We examined associations of log 2-transformed prenatal maternal serum PFAS concentrations with the MSEL Composite and each of the subscale scores at each time point as well as longitudinal changes in the scores over the four time points. We also classified trajectories into low- and high-score groups and fit Poisson regression models to estimate associations expressed as relative risks (RR).

RESULTS

Among six PFAS detected in more than 60% of the samples, prenatal maternal serum perfluorooctanoate (PFOA) was inversely associated with child's Composite score at 24 months (β = -5.22, 95% CI: -8.27, -2.17) and 36 months of age (β = -5.18, 95% CI: -9.46, -0.91), while other five PFAS were not strongly associated with Composite score at any time points. When assessing longitudinal changes in the scores over the four time points, PFOA was associated with trajectories having a negative slope for Composite scores and all four subscales. When examining trajectories of the scores between low- and high-score groups, PFOA was associated with having lower and/or decreasing Composite scores (RR = 1.49, 95% CI: 1.09, 2.03).

CONCLUSIONS

Prenatal PFOA appears to adversely affect child's cognitive development in toddlerhood in this study population. Because a large fraction of MARBLES children is at risk for atypical development, population-based studies are needed to confirm our findings.

Could Glyphosate and Glyphosate-Based Herbicides Be Associated With Increased Thyroid Diseases Worldwide?

The increased incidence of thyroid diseases raises a series of questions about what the main predisposing factors are nowadays. If dietary restriction of iodine was once a major global health concern, today, the processes of industrialization of food and high exposure to a wide variety of environmental chemicals may be affecting, directly or indirectly, thyroid function. The homeostasis of hypothalamus-pituitary-thyroid (HPT) axis is finely regulated through the negative feedback mechanism exerted by thyroid hormones. Allostatic mechanisms are triggered to adjust the physiology of HPT axis in chronic conditions. Glyphosate and glyphosate-based herbicides are pesticides with controversial endocrine disrupting activities and only few studies have approached their effects on HPT axis and thyroid function. However, glyphosate has an electrophilic and nucleophilic zwitterion chemical structure that may affect the mechanisms involved in iodide oxidation and organification, as well as the oxidative phosphorylation in the ATP synthesis. Thus, in this review, we aimed to: (1) discuss the critical points in the regulation of HPT axis and thyroid hormones levels balance, which may be susceptible to the toxic action of glyphosate and glyphosate-based herbicides, correlating the molecular mechanisms involved in glyphosate toxicity described in the literature that may, directly or indirectly, be associated to the higher incidence of thyroid diseases; and (2) present the literature regarding glyphosate toxicity in HPT axis.

The association between perfluoroalkyl substances and lipid profile in exposed pregnant women in the Veneto region, Italy

BACKGROUND

Residents of a large area of North-Eastern Italy were exposed for decades to high concentrations of perfluoroalkyl and polyfluoroalkyl substances (PFAS) via drinking water. Serum PFAS levels have been consistently associated with elevated serum lipids, but few studies have been conducted among pregnant women, and none has stratified analyses by trimester of gestation. Elevated serum lipid levels during pregnancy can have both immediate and long-lasting effects on pregnant women and the developing fetus. We evaluated the association between perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and perfluoro-hexanesulfonate (PFHxS) levels in relation to lipid profiles in highly-exposed pregnant women.

METHODS

A cross-sectional analysis was conducted in 319 pregnant women (age 14-48 years) enrolled in the Regional health surveillance program. Non-fasting blood samples were obtained in any trimester of pregnancy and analyzed for PFOA, PFOS and PFHxS, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C). Low-density lipoprotein cholesterol (LDL-C) was calculated. The associations between ln-transformed PFAS (and categorized into quartiles) and lipids were assessed using generalized additive models. Analyses were adjusted for potential confounders and stratified according to pregnancy trimester.

RESULTS

The geometric means of PFOA, PFOS and PFHxS were 14.78 ng/mL, 2.67 ng/mL and 1.89 ng/mL, respectively. The plasma levels of TC, HDL-C and LDL-C increased steadily throughout the trimesters. In the 1st trimester, PFOS was positively associated with TC and PFHxS with HDL-C. In the 3rd trimester, instead, an inverse relationship was seen between PFOA and PFHxS and both TC and LDL-C.

CONCLUSIONS

Results suggest the associations between PFAS concentrations and lipid profiles in pregnant women might differ by trimesters of pregnancy. In the first trimester, patterns are similar to those of non-pregnant women, while they differ late in pregnancy. Different independent behavior of PFAS and lipid levels throughout the pregnancy might explain our observations. These findings support the ubiquitous exposure to PFAS and possible influence on lipid metabolisms during pregnancy and suggest a careful evaluation of the timing of PFAS measurement, when examining effects of PFAS during pregnancy on gestational outcomes related to serum lipids amounts.

Human Biomonitoring (HBM)-I values for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) - Description, derivation and discussion

In 2016, the German Human Biomonitoring Commission (HBM-C) published a statement on its decision to develop HBM-I values for Perfluorooctanoic acid (PFOA) and Perfluorooctanesulfonic acid (PFOS) (Bundesgesundheitsbl 2016, 59:1364 DOI 10.1007/s00103-016-2437-1). The HBM-I value corresponds to the concentration of a substance in a human biological material below which no adverse health effects are expected, according to current knowledge and assessment by the HBM-C, and, consequently, there is no need for action. Evidence for associations between PFOA- and PFOS-body burden and health outcomes was found for fertility and pregnancy, weights of newborns at birth, lipid metabolism, immunity, sex hormones and age at puberty/menarche, thyroid hormones, onset of menopause as well as uric acid metabolism. Significant contrasts were reported for human blood plasma concentrations between 1 and 10 ng PFOA/mL, and 1-15 ng PFOS/mL, respectively. Within the reported ranges, the HBM-C has decided to set the HBM-I-values at 2 ng PFOA/mL and 5 ng PFOS/mL blood plasma. The underlying pathomechanisms do not appear to be sufficiently clarified to provide an unambiguous explanation of the effects observed. Consistency of toxicological and epidemiological data has been considered. The available data do not indicate an unequivocal proof of a genotoxicity of PFOA and PFOS.

Maternal and Newborn Thyroid Hormone, and the Association With Polychlorinated Biphenyls (PCBs) Burden: The EHF (Environmental Health Fund) Birth Cohort

Background: Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants found in human tissues. PCBs can be transferred through the placenta and may disrupt the maternal thyroid homeostasis, and affect fetal thyroid hormone production. Several studies have shown that intrauterine exposure to PCBs might be associated with abnormal levels of thyroid hormones in mothers and their offspring. Objectives: To examine the associations between environmental exposure to PCBs and thyroid hormone levels in mothers and newborns. Methods: The EHF-Assaf-Harofeh-Ichilov cohort includes 263 mothers-newborns dyads. A total of 157 mother-newborn dyads had both PCBs and thyroid function measures. Regression models were used to estimate associations between maternal PCB exposure and maternal and newborn thyroid function, controlling for possible confounders. Results: Four PCBs congeners were analyzed: PCBs 118, 138, 153, and 180. ∑PCBs median (IQR) level was 14.65 (2.83-68.14) ng/g lipids. The median maternal thyroid-stimulating hormone (TSH) level was 2.66 (0.70-8.23) μIU/ml, the median maternal free thyroxine (FT4) level was 12.44 (11.27-13.53) μg/dL, the median maternal thyroid peroxidase antibodies (TPO Ab) level was 9.6 (7.36-12.51) IU/mL. Newborns' median total thyroxine (T4) level was 14.8 (7.6-24.9) μg/dL. No association was found between exposure to different congeners or to ∑PCBs and maternal TSH, FT4, thyroglobulin autoantibodies (Tg Ab), TPO Ab and newborn total T4 levels. In multivariable analysis a 1% change in ∑PCBs level was significantly associated with a 0.57% change in maternal TSH levels in women with body mass index (BMI) < 19. The same association was observed for each of the studied PCB congeners. Maternal TPO Ab levels statistically significantly increased by 0.53 and 0.46% for 1% increase in PCB 118 and 153 congeners, respectively. In women with BMI > 25, the association between the PCBs levels and maternal TSH levels was in the opposite direction. No association was found in women with normal BMI (19-24.9). Conclusions: Background exposure to environmentally relevant concentrations of some PCBs can alter thyroid hormone homeostasis in pregnant women and might be associated with abnormal TSH levels and TPO-Ab in women with low BMI. However, these findings require further investigation.

Early-life exposure to multiple persistent organic pollutants and metals and birth weight: Pooled analysis in four Flemish birth cohorts

BACKGROUND AND AIMS

Prenatal chemical exposure has frequently been associated with reduced fetal growth although results have been inconsistent. Most studies associate single pollutant exposure to this health outcome, even though this does not reflect real life situations as humans are exposed to many pollutants during their life time. The objective of this study is to investigate the association between prenatal exposure to a mixture of persistent environmental chemicals and birth weight using multipollutant models.

METHODS

We combined exposure biomarker data measured in cord blood samples of 1579 women from four Flemish birth cohorts collected over a 10 years' time period. The common set of available and detectable exposure measures in these cohorts are three polychlorinated biphenyls (PCB) congeners (138, 153 and 180), hexachlorobenzene (HCB), dichlorodiphenyldichloroethylene (p,p'-DDE) and the metals cadmium and lead. Multiple linear regression (MLR), Bayesian Information Criterion (BIC), penalized regression using minimax concave penalty (MCP) and Bayesian Adaptive Sampling (BAS) were applied to assess the influence of multiple pollutants in a single analysis on birth weight, adjusted for a priori selected covariates.

RESULTS

In the pooled dataset, a median (P25-P75) birth weight and gestational age of 3420 (3140-3700) grams and 39 (39-40) weeks was observed respectively. The median contaminant levels in cord blood were: 15.8, 26.5, 18.0, 16.9 and 91.5 ng/g lipid for PCB 138, PCB 153, PCB 180, HCB and p,p'-DDE, respectively, 0.075 µg/L for cadmium and 9.7 µg/L for lead. According to the applied statistical methods for multipollutant assessment, p,p'-DDE and PCB 180 were most consistently associated with birth weight. In addition, PCB 153 was selected when applying MCP and BAS. An inverse association with birth weight was found for the PCB congeners, while an increased birth weight was observed for elevated levels of p,p'-DDE.

CONCLUSIONS

Assessing the health risk of combinations of exposure biomarkers reflects better real-world situations and thereby allows more effective risk assessment. Our results add to the existing evidence based on detrimental effects of PCBs on birth weight and indicate a possible increase in birth weight due to p,p'-DDE (while correcting for PCBs).

Prenatal exposure to perfluoroalkyl substances and thyroid hormone concentrations in cord plasma in a Chinese birth cohort

BACKGROUND

Evidence of associations between prenatal exposure to perfluoroalkyl substances (PFASs) and fetal thyroid hormones (THs) is controversial, and few studies have estimated the associations, while addressing the high correlations among multiple PFASs. We aimed to examine the associations between prenatal PFAS exposure and thyroid hormone concentrations in cord blood.

METHODS

A total of 300 mother-infant pairs from the Shanghai-Minhang Birth Cohort Study were included. We measured the concentrations of eight PFASs in maternal plasma samples collected at 12-16 gestational weeks, as well as those of total thyroxine (T4), free T4 (FT4), total triiodothyronine (T3), free T3 (FT3), and thyroid stimulating hormone (TSH) in cord plasma. We estimated the associations between maternal PFAS concentrations and TH concentrations using linear regression and Bayesian kernel machine regression (BKMR) models.

RESULTS

In BKMR models, higher PFAS mixture concentrations were associated with increased T3 concentrations, and there were suggestive associations with increased FT3 concentrations. For single-exposure effects in BKMR models, a change in PFDA, PFUdA, and PFOA concentrations from the 25th to 75th percentile was associated with a 0.04 (95%CrI: - 0.01, 0.09), 0.02 (95%CrI: - 0.03, 0.07), and 0.03 (95%CrI: - 0.001, 0.06) nmol/L increase in T3 concentrations, respectively. PFOA, PFNA, and PFDA were the predominant compounds in PFASs-FT3 associations, and the corresponding estimates were 0.11 (95% CrI: 0.02, 0.19), - 0.17 (95% CrI: - 0.28, - 0.07), and 0.12 (95% CrI: - 0.004, 0.24) pmol/L, respectively. A change in PFNA and PFOA concentrations from the 25th to 75th percentile was associated with a - 1.69 (95% CrI: - 2.98, - 0.41) μIU/mL decrease and a 1.51 (95% CrI: 0.48, 2.55) μIU/mL increase in TSH concentrations. The associations of PFOA and PFNA with T3/FT3 were more pronounced in boys, while those with TSH were more pronounced in girls.

CONCLUSION

Our results suggest that prenatal exposure to multiple PFASs was associated with thyroid hormones in cord blood. However, individual PFAS had varied effects-differing in magnitude and direction-on fetal thyroid hormones.

Exposure characteristics for congeners, isomers, and enantiomers of perfluoroalkyl substances in mothers and infants

Per- and polyfluoroalkyl substances (PFASs) are ubiquitous in the environment, making it inevitable for humans to be exposed to these pollutants. The exposure begins while in utero and continues in infancy, during the potentially most sensitive early stages of life. This review summarizes the current knowledge on pre- and neo-natal exposures based on more than 200 articles published from 2000 to date. All relevant biological matrices used in the cited studies were included, such as maternal blood, umbilical cord blood, breast milk, placenta, amniotic fluid, fetal organs, newborns' dried blood spots, and infant serum. We show that such exposures are geographically global with significant discrepancies among countries and continents, and that while the levels of major legacy PFASs (PFOS and PFOA) have declined since 2000, those of others may have not. We also show that levels of PFOS and PFOA exceed those of some major environmental toxins, such as p,p'-DDE, BDE-47, PCB-153, PBB-153, and OH-PBDEs in maternal blood. Given that the behavior and potential effects have an origin in molecular structure, biomonitoring and research at the levels of isomers and enantiomers are critically important. Through critical analysis of these works, we summarize the major achievements, consensus, and the deficiencies of existing research. To our knowledge, this is the first review on the overall internal exposure status of mothers and infants to PFASs during pregnancy and lactation.

PFAS Environmental Pollution and Antioxidant Responses: An Overview of the Impact on Human Field

Due to their unique properties, perfluorinated substances (PFAS) are widely used in multiple industrial and commercial applications, but they are toxic for animals, humans included. This review presents some available data on the PFAS environmental distribution in the world, and in particular in Europe and in the Veneto region of Italy, where it has become a serious problem for human health. The consumption of contaminated food and drinking water is considered one of the major source of exposure for humans. Worldwide epidemiological studies report the negative effects that PFAS have on human health, due to environmental pollution, including infertility, steroid hormone perturbation, thyroid, liver and kidney disorders, and metabolic disfunctions. In vitro and in vivo researches correlated PFAS exposure to oxidative stress effects (in mammals as well as in other vertebrates of human interest), produced by a PFAS-induced increase of reactive oxygen species formation. The cellular antioxidant defense system is activated by PFAS, but it is only partially able to avoid the oxidative damage to biomolecules.

Exposure to Perflouroalkyl acids and foetal and maternal thyroid status: a review

BACKGROUND

Exposure to perfluorinated-alkyl-acids (PFAAs) is ubiquitous. PFAAs are hormone-disrupting compounds that are strongly suspected to affect mother-child-health such as fetal growth. Thyroid disruption is a plausible mechanism of action. We aim to summarize the epidemiological evidence for the relation between prenatal and postnatal exposure to PFAAs and disruption of thyroid homeostasis in mothers and/or infants.

METHOD

Fifteen original publications on PFAAs concentrations and thyroid hormones (TH) in pregnant women and/or infants were found upon a literature search in the PubMed database. Information on exposure to seven PFAAs congeners [Perfluorooctane sulfonate (PFOS), Perfluorooctanoate (PFOA), Perfluorohexane sulfonate (PFHxS), Perfluorononanoic acid (PFNA), Perfluorodecanoic acid (PFDA), Perfluoroundecanoic acid (PFUnA), and Perfluorododecanoic acid (PFDoA)] and thyroid stimulating hormone (TSH), free and total thyroxine (FT4 and TT4), free and total triiodothyronine (FT3 and TT3), T3RU (Free triiodothyronine resin uptake) and FT4-index (FT4I) levels were recorded. We evaluated sampling of maternal TH by trimester, and infant TH by sex stratification. Reported associations between mother or infant PFAAs and TH were not uniformly assessed in the selected studies.

RESULTS

Ten out of the fifteen studies examined maternal PFAAs concentration and TSH level. Seven studies showed significant associations between TSH and exposure to six PFAAs congeners, most of them were positive. Maternal T4 and T3 were investigated in nine studies and five studies found inverse associations between exposure to six PFAAs congeners and TH (TT3, TT4, FT3, FT4 and FT4I) levels. Eight of the fifteen studies investigated PFAAs concentrations and infant TSH. Infant TSH level was significantly affected in four studies, positively in three studies. Nine studies investigated infant T4 and T3 and seven studies found significant associations with PFAAs exposure. However, both inverse and positive significant associations with infant TH were found eliciting no clear direction.

CONCLUSION

Results indicate a mainly positive relationship between maternal PFAAs concentrations and TSH levels, and suggestion of an inverse association with T4 and/or T3 levels. Associations of infant TH with PFAAs concentration were less consistent.

Assessment of perfluoroalkyl substances in placenta by coupling salt assisted liquid-liquid extraction with dispersive liquid-liquid microextraction prior to liquid chromatography-tandem mass spectrometry

The widespread use of perfluoroalkyl substances (PFAS) is resulting in a broad human exposure to these endocrine disrupting chemicals (EDCs), prompting biomonitoring research to evaluate its magnitude and impact, especially during critical windows of exposure such as fetal and perinatal periods. This study was focused on developing a method to determine 10 PFAS in placental tissue by combining salt-assisted liquid-liquid extraction with dispersive liquid-liquid microextraction and using liquid chromatography-tandem mass spectrometry. Chemometric strategies were applied to optimize the experimental parameters. The limit of quantification was 0.02 ng g^-1 for all analytes, and the inter-day variability (as relative standard deviation) ranged from 7.9% to 13.8%. Recoveries ranged from 88.2% to 113.9%. The suitableness of the procedure was demonstrated by assessing the targeted compounds in 20 placenta samples. The highest concentrations were recorded for perfluorooctanoic acid and perfluorooctane sulfonate, with maximum concentrations of 0.62 and 1.02 ng g^-1 and median concentrations of 0.13 and 0.53 ng g^-1, respectively. Median concentrations of the other PFAS ranged from detected values to 0.08 ng g^-1. This analytical procedure yields useful data on fetal exposure to PFAS.

Acrylamide induces a thyroid allostasis-adaptive response in prepubertal exposed rats

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Acrylamide acts as endocrine disruptor for the thyroid gland function.

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Acrylamide increases the transcript expression of proteins related to THs synthesis.

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Exposure to acrylamide alters the hypothalamus-pituitary-thyroid axis homeostasis.

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Acrylamide induces allostatic regulation of the hypothalamus-pituitary-thyroid axis.

Some endocrine-disrupting chemicals (EDCs) can affect the endocrine system through covalent interactions with specific sites, leading to deregulation of physiological homeostasis. The acrylamide (AA) present in some fried or baked foods is an example of an electrophile molecule that is able to form adducts with nucleophilic regions of nervous system proteins leading to neurological defects. A positive correlation between increased urinary AA metabolite concentration and reduced levels of thyroid hormones (TH) was described in adolescents and young adults. Thus, this study aimed to evaluate whether AA affects the physiology of the hypothalamus-pituitary-thyroid (HPT) axis and the possible repercussions in peripheral TH-target systems. For this, male Wistar rats were exposed to doses of 2.5 or 5.0 mg AA/Kg/day, based on the LOAEL (Lowest Observed Adverse Effect Level) during prepubertal development. The expression of molecular markers of HPT functionality was investigated in the hypothalamus, pituitary, thyroid, heart and liver, as well as the hormonal and lipid profiles in blood samples. Herein, we showed that AA acts as EDCs for thyroid gland function, increasing the transcript expression of several proteins related to TH synthesis and altering hypothalamus-pituitary-thyroid axis homeostasis, an effect evidenced by the higher levels of THs in the serum. Compensatory mechanisms were observed in TH-target tissues, such as an increase in Dio3 mRNA expression in the liver and a reduction in Mct8 transcript content in the hearts of AA-treated rats. Together, these results pointed out an allostatic regulation of the HPT axis induced by AA and suggest that chronic exposure to it, mainly associated with food consumption, might be related to the higher prevalence of thyroid dysfunctions.

Assessment of developmental neurotoxicity induced by chemical mixtures using an adverse outcome pathway concept

BACKGROUND

In light of the vulnerability of the developing brain, mixture risk assessment (MRA) for the evaluation of developmental neurotoxicity (DNT) should be implemented, since infants and children are co-exposed to more than one chemical at a time. One possible approach to tackle MRA could be to cluster DNT chemicals in a mixture on the basis of their mode of action (MoA) into 'similar' and 'dissimilar', but still contributing to the same adverse outcome, and anchor DNT assays to common key events (CKEs) identified in DNT-specific adverse outcome pathways (AOPs). Moreover, the use of human in vitro models, such as induced pluripotent stem cell (hiPSC)-derived neuronal and glial cultures would enable mechanistic understanding of chemically-induced adverse effects, avoiding species extrapolation.

METHODS

HiPSC-derived neural progenitors differentiated into mixed cultures of neurons and astrocytes were used to assess the effects of acute (3 days) and repeated dose (14 days) treatments with single chemicals and in mixtures belonging to different classes (i.e., lead(II) chloride and methylmercury chloride (heavy metals), chlorpyrifos (pesticide), bisphenol A (organic compound and endocrine disrupter), valproic acid (drug), and PCB138 (persistent organic pollutant and endocrine disrupter), which are associated with cognitive deficits, including learning and memory impairment in children. Selected chemicals were grouped based on their mode of action (MoA) into 'similar' and 'dissimilar' MoA compounds and their effects on synaptogenesis, neurite outgrowth, and brain derived neurotrophic factor (BDNF) protein levels, identified as CKEs in currently available AOPs relevant to DNT, were evaluated by immunocytochemistry and high content imaging analysis.

RESULTS

Chemicals working through similar MoA (i.e., alterations of BDNF levels), at non-cytotoxic (IC20/100), very low toxic (IC5), or moderately toxic (IC20) concentrations, induce DNT effects in mixtures, as shown by increased number of neurons, impairment of neurite outgrowth and synaptogenesis (the most sensitive endpoint as confirmed by mathematical modelling) and increase of BDNF levels, to a certain extent reproducing autism-like cellular changes observed in the brain of autistic children.

CONCLUSIONS

Our findings suggest that the use of human iPSC-derived mixed neuronal/glial cultures applied to a battery of assays anchored to key events of an AOP network represents a valuable approach to identify mixtures of chemicals with potential to cause learning and memory impairment in children.

The association between prenatal exposure to organochlorine compounds and neonatal thyroid hormone levels: a systematic review

In this systematic review, the association between prenatal exposure to organochlorine pesticides (OCPs) and neonatal thyroid hormone levels was studied. A systematic search of scientific literature was performed from the PubMed, SCOPUS and ISI web of science electronic bibliographic databases. The search strategy for the review was [(organochlorine OR "organochlorine pesticides" OR "organochlorine pollutants" OR "organochlorine pollutant") AND ("thyroid hormone" OR triiodothyronine OR Thyroxine OR "fetal thyroid function" OR "thyroid function" OR "Thyroid Stimulating Hormone" AND "prenatal" AND "maternal exposure")] in English sources. In this review, 305 papers (PubMed: 30; Scopus: 29; ISI: 246) were identified through an electronic database search. Twenty-seven articles were assessed for eligibility, from which 16 qualified articles were selected for the final evaluation. The most common OCP metabolites which were evaluated in order were hexachlorobenzene (HCB) (13 studies), pp-dichlorodiphenyldichloroethylene (pp-DDE) (13 studies), hexachlorocyclohexane (HCH) (10 studies) and dichlorodiphenyltrichlorethane (DDT) (eight studies). A review of the documents related to the association of prenatal exposure of OCPs with fetal or neonatal thyroid function tests provides us with heterogeneous data in this field. Factors such as differences in the studied populations and their area, ethnic and genetic background, time and rate of exposure, possible interaction of other thyroid-disrupting environmental factors and dietary intake of micronutrients such as iodine and/or selenium are considered the main limitations for making an accurate conclusion. For some OCPs including DDT, DDE, HCH and HCB, there are supporting evidences, and it is suggested that their exposure could potentially alter the fetal thyroid function and consequently impair the neurodevelopment process of the infants.

Association between perfluoroalkyl substance exposure and thyroid hormone/thyroid antibody levels in maternal and cord blood: The Hokkaido Study

BACKGROUND

Thyroid antibodies (TAs) are the most common cause of hypothyroidism during gestation. Although previous studies found that prenatal exposure to perfluoroalkyl substances (PFASs) disrupts thyroid hormones (THs) in humans, their effects on TAs during the perinatal period have not been investigated.

OBJECTIVE

To explore the associations between prenatal exposure to eleven different PFASs from two different groups (carboxylates and sulfonates) and the expression of THs and TAs in maternal and cord blood while considering maternal TA status.

METHODS

In a prospective birth cohort (the Hokkaido Study), we included 701 mother‑neonate pairs recruited in 2002-2005 for whom both prenatal maternal and cord blood samples were available. Eleven PFASs were measured in maternal plasma obtained at 28-32 weeks of gestation using ultra-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry. THs and TAs including thyroid stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) were measured in maternal blood during early pregnancy (median 11 gestational weeks), and in cord blood at birth.

RESULTS

The median levels of TgAb and TPOAb in maternal serum were 15.0 and 6.0 IU/mL, respectively. The median TgAb level in neonates was 38.0 IU/mL, and TPOAb were detected in only 12.3% of samples. Maternal FT3 level was positively associated with PFAS levels in both TA-positive and TA-negative mothers. Maternal perfluorooctanoate was inversely associated with maternal TPOAb. Among boys, some maternal PFASs were associated with higher TSH and lower FT3 levels in maternal TA-negative group, while perfluorodecanoic acid was associated with lower TSH in maternal TA-positive group. Among girls, some PFAS of mothers showed associations with lower TSH and higher FT3 in maternal TA-negative group, while perfluorododecanoic acid was associated with lower FT4 in maternal TA-positive. Maternal PFASs showed associations with boy's TgAb inversely in maternal TA-negative group and with girl's TgAb positively in maternal TA-positive group.

CONCLUSIONS

Our results suggest thyroid disrupting effects of PFAS exposure and susceptibility vary depending on maternal TA levels.

Maternal exposures to persistent organic pollutants are associated with DNA methylation of thyroid hormone-related genes in placenta differently by infant sex

Exposure to persistent organic pollutants (POPs) during pregnancy is associated with a disruption in thyroid hormone balance. The placenta serves as an important environment for fetal development and also regulates thyroid hormone supply to the fetus. However, epigenetic changes of thyroid regulating genes in placenta have rarely been studied. This study was conducted to evaluate the association between several POP concentrations in maternal serum and DNA methylation of thyroid hormone-related genes in the placenta. The placenta samples were collected from 106 Korean mother at delivery, and the promoter methylation of the placental genes was measured by a bisulfite pyrosequencing. The deiodinase type 3 (DIO3), monocarboxylate transporter 8 (MCT8), and transthyretin (TTR) genes were selected as the target genes as they play an important role in the regulation of fetal thyroid balance. Because people are exposed to multiple chemicals at the same time, a multiple-POP model using principal component analysis (PCA) was applied to evaluate the association between the multiple POPs exposure and the epigenetic change in placenta. In addition, a single-POP model which includes one chemical each in the statistical model for association was conducted. Based on the single-POP models, serum concentrations of p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) and brominated diphenyl ether-47 (BDE-47) were significantly associated with an increase in placental DIO3 methylation, but only among female infants. Among male infants, a positive association between serum p,p'-DDT and MCT8 methylation level was found. According to the multiple-POP models, serum DDTs were positively associated with DIO3 methylation in the placenta of female infants, while a positive association with MCT8 methylation was observed in those of the male infants. Our observation showed that in utero exposure to DDTs may influence the DNA methylation of DIO3 and MCT8 genes in the placenta, in a sexually dimorphic manner. These alterations in placental epigenetic regulation may in part explain the thyroid hormone disruption observed among the newborns or infants followed by in utero exposure to POPs.

Perfluoroalkyl and polyfluoroalkyl substances and fetal thyroid hormone levels in umbilical cord blood among newborns by prelabor caesarean delivery

BACKGROUND

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) have been reported to disrupt the thyroid function. But epidemiological evidence on the association between PFAS and thyroid hormone (TH) levels in cord blood is scarce and controversial. We aimed to examine the association between cord blood PFAS concentrations and TH levels in prelabor caesarean deliveries.

METHODS

We measured ten PFAS and three THs in cord blood in 568 prelabor caesarean deliveries. The associations between PFAS and TH levels were examined using multiple linear regression model and sparse partial least squares (SPLS) regression model.

RESULTS

In SPLS analyses, thyroid stimulating hormone (TSH) level decreased with increasing concentrations of perfluorooctane sulfonate (PFOS, β = -0.012, 95% confidence interval [CI]: -0.019, -0.005), perfluorononanoic acid (PFNA, β = -0.012, 95% CI: -0.019, -0.005), perfluorodecanoic acid (PFDA, β = -0.012, 95% CI: -0.02, -0.005), perfluoroundecanoic acid (PFUA, β = -0.013, 95% CI: -0.021, -0.006) and perfluorododecanoic acid (PFDoA, β = -0.013, 95% CI: -0.023, -0.006). Moreover, we found a positive association between PFDoA and free thyroxine (FT4) levels (β = 0.190, 95% CI: 0.063, 0.304) after adjusting for potential confounders. Free tri-iodothyronine (FT3) levels were positively associated with concentrations of PFOS (β = 0.059, 95% CI: 0.023, 0.100), but negatively associated with PFDoA (β = -0.153, 95% CI: -0.212, -0.106). We also observed gender disparity in the associations of PFAS exposure and FT3, FT4, TSH levels.

CONCLUSION

Our results suggest that prenatal exposure to certain PFAS may disrupt fetal thyroid function. The effect may be gender-specific.

Longitudinal analysis reveals early-pregnancy associations between perfluoroalkyl sulfonates and thyroid hormone status in a Canadian prospective birth cohort

Serum perfluoroalkyl acids (PFAAs) have been linked to disruption of maternal thyroid hormone homeostasis, but results have varied between studies which we hypothesized was due to timing of the thyroid hormone measurements, variability in PFAA isomer patterns, or presence of other stressors. In a longitudinal study design, we investigated the time-dependency of associations between PFAA isomers and thyroid hormones during pregnancy and post-partum while considering thyroid peroxidase antibody (TPOAb) status and mercury (Hg) co-exposure. In participants of a prospective Canadian birth cohort (n = 494), free thyroxine (FT4), free triiodothyronine (FT3), thyroid stimulating hormone (TSH) and TPOAb were quantified in maternal plasma collected in each trimester and 3-months postpartum, and 25 PFAAs (15 linear and 10 branched) and Hg were quantified in samples collected during the second trimester. Perfluorohexane sulfonate (PFHxS) and total branched isomers of perfluorooctane sulfonate (PFOS) were positively associated with TSH in mixed-effect models, with strongest associations early in gestation. Throughout pregnancy and post-partum, PFHxS was inversely associated with FT4, consistent with elevated TSH, while Hg was inversely associated with FT3. In TPOAb-positive women, negative associations were found between PFUnA and FT4, and 1m-PFOS and TSH, supporting previous studies that thyroid disorder could increase susceptibility to PFAA-mediated hormone dysregulation. Hg did not confound associations but was a significant interaction term, revealing further positive associations between PFOS isomers (∑3m+4m-PFOS) and TSH. Higher perfluoroalkyl sulfonate exposures were associated with higher TSH and/or lower FT4, strongly suggestive that PFHxS and branched PFOS isomers are risk factors for subclinical maternal hypothyroidism. Isomer-specific analysis is important in future studies, as crude measures of 'total-PFOS' masked the associations of branched isomers. A concerning result was for PFHxS which had consistent negative associations with FT4 at all time points and a positive association with TSH in early pregnancy when fetal development is most sensitive to disruption.

Advancing human health risk assessment

The current/traditional human health risk assessment paradigm is challenged by recent scientific and technical advances, and ethical demands. The current approach is considered too resource intensive, is not always reliable, can raise issues of reproducibility, is mostly animal based and does not necessarily provide an understanding of the underlying mechanisms of toxicity. From an ethical and scientific viewpoint, a paradigm shift is required to deliver testing strategies that enable reliable, animal-free hazard and risk assessments, which are based on a mechanistic understanding of chemical toxicity and make use of exposure science and epidemiological data. This shift will require a new philosophy, new data, multidisciplinary expertise and more flexible regulations. Re-engineering of available data is also deemed necessary as data should be accessible, readable, interpretable and usable. Dedicated training to build the capacity in terms of expertise is necessary, together with practical resources allocated to education. The dialogue between risk assessors, risk managers, academia and stakeholders should be promoted further to understand scientific and societal needs. Genuine interest in taking risk assessment forward should drive the change and should be supported by flexible funding. This publication builds upon presentations made and discussions held during the break-out session 'Advancing risk assessment science - Human health' at EFSA's third Scientific Conference 'Science, Food and Society' (Parma, Italy, 18-21 September 2018).

Concentrations of perfluoroalkyl substances (PFASs) in human embryonic and fetal organs from first, second, and third trimester pregnancies

BACKGROUND

The persistent environmental contaminants perfluoroalkyl substances (PFASs) have gained attention due to their potential adverse health effects, in particular following early life exposure. Information on human fetal exposure to PFASs is currently limited to one report on first trimester samples. There is no data available on PFAS concentrations in fetal organs throughout all three trimesters of pregnancy.

METHODS

We measured the concentrations of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnA), and perfluorohexane sulfonic acid (PFHxS) in human embryos and fetuses with corresponding placentas and maternal serum samples derived from elective pregnancy terminations and cases of intrauterine fetal death. A total of 78 embryos and fetuses aged 7-42 gestational weeks were included and a total of 225 fetal organs covering liver, lung, heart, central nervous system (CNS), and adipose tissue were analyzed, together with 71 placentas and 63 maternal serum samples. PFAS concentrations were assayed by liquid chromatography/triple quadrupole mass spectrometry.

RESULTS

All evaluated PFASs were detected and quantified in maternal sera, placentas and embryos/fetuses. In maternal serum samples, PFOS was detected in highest concentrations, followed by PFOA > PFNA > PFDA = PFUnA = PFHxS. Similarly, PFOS was detected in highest concentrations in embryo/fetal tissues, followed by PFOA > PFNA = PFDA = PFUnA. PFHxS was detected in very few fetuses. In general, PFAS concentrations in embryo/fetal tissue (ng/g) were lower than maternal serum (ng/ml) but similar to placenta concentrations. The total PFAS burden (i.e. the sum of all PFASs) was highest in lung tissue in first trimester samples and in liver in second and third trimester samples. The burden was lowest in CNS samples irrespective of fetal age. The placenta:maternal serum ratios of PFOS, PFOA and PFNA increased across gestation suggesting bioaccumulation in the placenta. Further, we observed that the ratios were higher in pregnancies with male fetuses compared to female fetuses.

CONCLUSIONS

Human fetuses were intrinsically exposed to a mixture of PFASs throughout gestation. The compounds were detected in all analyzed tissues, suggesting that PFASs reach and may affect many types of organs. Collectively, our results demonstrate that PFASs pass the placenta and deposit to embryo and fetal tissues, calling for risk assessment of gestational exposures.

Risk to human health related to the presence of perfluorooctane sulfonic acid and perfluorooctanoic acid in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in food. Regarding PFOS and PFOA occurrence, the final data set available for dietary exposure assessment contained a total of 20,019 analytical results (PFOS n = 10,191 and PFOA n = 9,828). There were large differences between upper and lower bound exposure due to analytical methods with insufficient sensitivity. The CONTAM Panel considered the lower bound estimates to be closer to true exposure levels. Important contributors to the lower bound mean chronic exposure were 'Fish and other seafood', 'Meat and meat products' and 'Eggs and egg products', for PFOS, and 'Milk and dairy products', 'Drinking water' and 'Fish and other seafood' for PFOA. PFOS and PFOA are readily absorbed in the gastrointestinal tract, excreted in urine and faeces, and do not undergo metabolism. Estimated human half-lives for PFOS and PFOA are about 5 years and 2-4 years, respectively. The derivation of a health-based guidance value was based on human epidemiological studies. For PFOS, the increase in serum total cholesterol in adults, and the decrease in antibody response at vaccination in children were identified as the critical effects. For PFOA, the increase in serum total cholesterol was the critical effect. Also reduced birth weight (for both compounds) and increased prevalence of high serum levels of the liver enzyme alanine aminotransferase (ALT) (for PFOA) were considered. After benchmark modelling of serum levels of PFOS and PFOA, and estimating the corresponding daily intakes, the CONTAM Panel established a tolerable weekly intake (TWI) of 13 ng/kg body weight (bw) per week for PFOS and 6 ng/kg bw per week for PFOA. For both compounds, exposure of a considerable proportion of the population exceeds the proposed TWIs.

Developmental Exposure to Di-(2-ethylhexyl) Phthalate Induces Cerebellar Granule Cell Apoptosis via the PI3K/AKT Signaling Pathway

Di-(2-ethylhexyl) phthalate (DEHP) is an ubiquitous environmental contaminant because of its extensive use in plastics and its persistence. As an environmental endocrine disruptor, it is suspected to interfere with neurodevelopment in people. However, evidence of the effects of maternal DEHP exposure on cerebellar development in offspring is scarce. The objective of this study was to investigate maternal exposure to DEHP and its effect on apoptosis of cerebellar granule cells (CGCs) and related mechanisms. Pregnant Wistar rats were administrated DEHP (0, 30, 300 and 750 mg/kg/d) by gavage from gestational day (GD) 0 to postnatal day (PN) 21. Primary CGCs were also exposed to mono-(2-ethylhexyl) phthalate (MEHP), the main metabolite of DEHP, for 24 h with concentrations of 0, 25, 100 and 250 µM. The CGCs of male offspring from 300 and 750 mg/kg/d DEHP exposure groups showed significantly increased apoptosis. In addition, the PI3K/AKT signaling pathway was inhibited in the male offspring of the 300 and 750 mg/kg/d DEHP exposure groups. However, effects on female pups were not obvious. Apoptosis was also elevated and the PI3K/AKT signaling pathway was inhibited after primary CGCs were exposed to MEHP. Furthermore, apoptosis was reduced after treatment with the PI3K/AKT signaling pathway activator, insulin-like growth factor (IGF) 1, and increased after treatment with LY294002, an inhibitor of the PI3K/AKT signaling pathway. These results suggested that maternal DEHP exposure induced apoptosis in the CGCs of male pups via the PI3K/AKT signaling pathway, and the apoptosis could be rescued by IGF1 and aggravated by LY294002.

Risk to human health related to the presence of perfluorooctane sulfonic acid and perfluorooctanoic acid in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in food. Regarding PFOS and PFOA occurrence, the final data set available for dietary exposure assessment contained a total of 20,019 analytical results (PFOS n = 10,191 and PFOA n = 9,828). There were large differences between upper and lower bound exposure due to analytical methods with insufficient sensitivity. The CONTAM Panel considered the lower bound estimates to be closer to true exposure levels. Important contributors to the lower bound mean chronic exposure were 'Fish and other seafood', 'Meat and meat products' and 'Eggs and egg products', for PFOS, and 'Milk and dairy products', 'Drinking water' and 'Fish and other seafood' for PFOA. PFOS and PFOA are readily absorbed in the gastrointestinal tract, excreted in urine and faeces, and do not undergo metabolism. Estimated human half-lives for PFOS and PFOA are about 5 years and 2-4 years, respectively. The derivation of a health-based guidance value was based on human epidemiological studies. For PFOS, the increase in serum total cholesterol in adults, and the decrease in antibody response at vaccination in children were identified as the critical effects. For PFOA, the increase in serum total cholesterol was the critical effect. Also reduced birth weight (for both compounds) and increased prevalence of high serum levels of the liver enzyme alanine aminotransferase (ALT) (for PFOA) were considered. After benchmark modelling of serum levels of PFOS and PFOA, and estimating the corresponding daily intakes, the CONTAM Panel established a tolerable weekly intake (TWI) of 13 ng/kg body weight (bw) per week for PFOS and 6 ng/kg bw per week for PFOA. For both compounds, exposure of a considerable proportion of the population exceeds the proposed TWIs.

Analysis of Lipid Metabolism, Immune Function, and Neurobehavior in Adult C57BL/6JxFVB Mice After Developmental Exposure to di (2-ethylhexyl) Phthalate

Background: Developmental exposure to di (2-ethylhexyl) phthalate (DEHP) has been implicated in the onset of metabolic syndrome later in life. Alterations in neurobehavior and immune functions are also affected by phthalate exposure and may be linked to the metabolic changes caused by developmental exposure to DEHP. Objectives: Our goal was to study the effects of developmental exposure to DEHP in the context of metabolic syndrome by integrating different parameters to assess metabolic, neurobehavioral, and immune functions in one model. Methods: Female C57BL/6J mice were exposed to DEHP through the diet during gestation and lactation at doses ranging from 3.3 to 100,000 μg/kg body weight/day (μkd). During a 1-year follow-up period, a wide set of metabolic parameters was assessed in the F1 offspring, including weekly body weight measurements, food consumption, physical activity, glucose homeostasis, serum lipids, and endocrine profile. In addition, neurobehavioral and immune functions were assessed by sweet preference test, object recognition test, acute phase protein, and cytokines production. Animals were challenged with a high fat diet (HFD) in the last 9 weeks of the study. Results: Increased free fatty acids (FFA) and, high density lipoprotein (HDL-C) were observed in serum, together with a decrease in glycated hemoglobin levels in blood of 1-year old male DEHP-exposed offspring after HFD challenge. For the most sensitive endpoint measured (FFA), a lower bound of the 90%-confidence interval for benchmark dose (BMD) at a critical effect size of 5% (BMDL) of 2,160 μkd was calculated. No persistent changes in body weight or fat mass were observed. At 33,000 μkd altered performance was found in the object recognition test in males and changes in interferon (IFN)γ production were observed in females. Conclusions: Developmental exposure to DEHP combined with HFD in adulthood led to changes in lipid metabolism and neurobehavior in male offspring and cytokine production in female offspring. Our findings contribute to the evidence that DEHP is a developmental dyslipidemic chemical, however, more research is needed to further characterize adverse health outcomes and the mechanisms of action associated with the observed sex-specific effects.

Associations between longitudinal serum perfluoroalkyl substance (PFAS) levels and measures of thyroid hormone, kidney function, and body mass index in the Fernald Community Cohort

Perfluoroalkyl substances (PFAS) are a diverse class of manufactured compounds used in a wide range of industrial processes and consumer products and have been detected in human serum worldwide. Previous cross-sectional and cohort studies in humans have suggested exposure to PFAS is associated with a wide array of chronic diseases, including endocrine disruption, developmental health effects, cancer and metabolic changes. We examined the associations between a panel of eight PFAS and indicators of thyroid disruption, kidney function, and body mass index (BMI), all of which were measured at repeated time points (1990-2008) over the course of the study. Participants (N = 210) were selected from the Fernald Community Cohort based on household water supply from a PFAS-contaminated aquifer. In adjusted repeated measures models, we observed several notable associations between serum PFAS and thyroid hormones as well as kidney function as measured by estimated glomerular filtration rate (eGFR). An interquartile (IQR) increase in serum PFOS was associated with a 9.75% (95% CI = 1.72, 18.4) increase in thyroid stimulating hormone. An IQR increase in serum PFNA, PFHxS, and PFDeA was associated with a -1.61% (95% CI = -3.53, -0.59), -2.06% (95% CI = -3.53, -0.59), and -2.20% (95% CI = -4.25, -0.14) change in eGFR, respectively. On the other hand, an IQR increase in serum Me-PFOSA was associated with a 1.53% (95% CI = 0.34, 2.73) increase in eGFR. No significant associations with BMI and serum PFAS were noted. Our findings are in agreement with previous reports that serum PFAS are associated with altered kidney and thyroid function.

Strategies to improve the regulatory assessment of developmental neurotoxicity (DNT) using in vitro methods

Currently, the identification of chemicals that have the potential to induce developmental neurotoxicity (DNT) is based on animal testing. Since at the regulatory level, systematic testing of DNT is not a standard requirement within the EU or USA chemical legislation safety assessment, DNT testing is only performed in higher tiered testing triggered based on chemical structure activity relationships or evidence of neurotoxicity in systemic acute or repeated dose toxicity studies. However, these triggers are rarely used and, in addition, do not always serve as reliable indicators of DNT, as they are generally based on observations in adult rodents. Therefore, there is a pressing need for developing alternative methodologies that can reliably support identification of DNT triggers, and more rapidly and cost-effectively support the identification and characterization of chemicals with DNT potential. We propose to incorporate mechanistic knowledge and data derived from in vitro studies to support various regulatory applications including: (a) the identification of potential DNT triggers, (b) initial chemical screening and prioritization, (c) hazard identification and characterization, (d) chemical biological grouping, and (e) assessment of exposure to chemical mixtures. Ideally, currently available cellular neuronal/glial models derived from human induced pluripotent stem cells (hiPSCs) should be used as they allow evaluation of chemical impacts on key neurodevelopmental processes, by reproducing different windows of exposure during human brain development. A battery of DNT in vitro test methods derived from hiPSCs could generate valuable mechanistic data, speeding up the evaluation of thousands of compounds present in industrial, agricultural and consumer products that lack safety data on DNT potential.

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.

Association between serum polybrominated diphenyl ethers, new flame retardants and thyroid hormone levels for school students near a petrochemical complex, South China

As surrogates of polybrominated diphenyl ethers (PBDEs), new flame retardants (NFRs) include a series of chlorinated and brominated flame retardants. Though the NFRs are thought to induce similar thyroid hormone (TH) disrupting effects as PBDEs, few studies have focused on them. Given the increasing levels of NFRs in the environment, more in depth investigation of the potential TH disrupting effects of NFRs is warranted. This research involved a health survey to collect data and examine the associations between PBDEs, NFRs and TH. 174 school students lived near a petrochemical complex in South China participated in the survey, completing questionnaires and providing blood samples. Thirteen congeners of PBDEs, eight species of NFRs, TH and thyroid-stimulating hormone (TSH) were measured. The median levels of ΣPBDE (sum of thirteen congeners of PBDEs) and ΣNFR (sum of eight species of NFRs) for students were 140 and 240 ng g^-1 lipid, respectively. Nonmonotonic relationships were observed between quartile levels of PBDEs, NFRs and corresponding TH. In contrast to ΣPBDE that was positively associated with triidothyrine (T₃) level, ΣNFR was not statistically associated with TH. ΣPBDE + NFR (sum of thirteen congeners of PBDEs and eight species of NFRs) was significantly associated with T₃ level.

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.

Disruption in Thyroid Signaling Pathway: A Mechanism for the Effect of Endocrine-Disrupting Chemicals on Child Neurodevelopment

Thyroid hormones are crucial in normal brain development. Transient and mild thyroid hormone insufficiency in pregnancy is also associated with impaired neurodevelopment in the offspring (e.g., 3-4 IQ score loss in association with maternal free thyroxine in the lowest fifth percentile). While inadequate iodine intake remains the most common underlying cause of mild thyroid hormone insufficiency in vulnerable populations including pregnant women, other factors such as exposure to environmental contaminants have recently attracted increasing attention, in particular in interaction with iodine deficiency. Endocrine-disrupting chemicals (EDCs) are natural and synthetic substances with ubiquitous exposure in children and adults including pregnant women. EDCs interfere, temporarily or permanently, with hormonal signaling pathways in the endocrine system by binding to hormone receptors and modifying gene expression. Other mechanisms involve alterations in production, metabolism, and transfer of hormones. Experimental studies have shown that exposures to EDCs affect various brain processes such as neurogenesis, neural differentiation and migration, as well as neural connectivity. Neuroimaging studies confirm brain morphological abnormalities (e.g., cortical thinning) consistent with neurodevelopmental impairments as a result of EDC exposures at standard use levels. In this review, we provide an overview of present findings from toxicological and human studies on the anti-thyroid effect of EDCs with a specific attention to fetal and early childhood exposure. This brief overview highlights the need for additional multidisciplinary studies with a focus on thyroid disruption as an underlying mechanism for developmental neurotoxicity of EDC, which can provide insight into modifiable risk factors of developmental delays in 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.

Thyroid-disrupting chemicals and brain development: an update

This review covers recent findings on the main categories of thyroid hormone-disrupting chemicals and their effects on brain development. We draw mostly on epidemiological and experimental data published in the last decade. For each chemical class considered, we deal with not only the thyroid hormone-disrupting effects but also briefly mention the main mechanisms by which the same chemicals could modify estrogen and/or androgen signalling, thereby exacerbating adverse effects on endocrine-dependent developmental programmes. Further, we emphasize recent data showing how maternal thyroid hormone signalling during early pregnancy affects not only offspring IQ, but also neurodevelopmental disease risk. These recent findings add to established knowledge on the crucial importance of iodine and thyroid hormone for optimal brain development. We propose that prenatal exposure to mixtures of thyroid hormone-disrupting chemicals provides a plausible biological mechanism contributing to current increases in the incidence of neurodevelopmental disease and IQ loss.