Interactions of persistent environmental organohalogens with the thyroid hormone system: mechanisms and possible consequences for animal and human health

Spatially Dependent Tissue Distribution of Thyroid Hormones by Plasma Thyroid Hormone Binding Proteins

Plasma thyroid hormone (TH) binding proteins (THBPs), including thyroxine-binding globulin (TBG), transthyretin (TTR), and albumin (ALB), carry THs to extrathyroidal sites, where THs are unloaded locally and then taken up via membrane transporters into the tissue proper. The respective roles of THBPs in supplying THs for tissue uptake are not completely understood. To investigate this, we developed a spatial human physiologically based kinetic (PBK) model of THs, which produces several novel findings. (1) Contrary to postulations that TTR and/or ALB are the major local T4 contributors, the three THBPs may unload comparable amounts of T4 in Liver, a rapidly perfused organ; however, their contributions in slowly perfused tissues follow the order of abundances of T4TBG, T4TTR, and T4ALB. The T3 amounts unloaded from or loaded onto THBPs in a tissue acting as a T3 sink or source respectively follow the order of abundance of T3TBG, T3ALB, and T3TTR regardless of perfusion rate. (2) Any THBP alone is sufficient to maintain spatially uniform TH tissue distributions. (3) The TH amounts unloaded by each THBP species are spatially dependent and nonlinear in a tissue, with ALB being the dominant contributor near the arterial end but conceding to TBG near the venous end. (4) Spatial gradients of TH transporters and metabolic enzymes may modulate these contributions, producing spatially invariant or heterogeneous TH tissue concentrations depending on whether the blood-tissue TH exchange operates in near-equilibrium mode. In summary, our modeling provides novel insights into the differential roles of THBPs in local TH tissue distribution.

Complex roles for sulfation in the toxicities of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are persistent organic toxicants derived from legacy pollution sources and their formation as inadvertent byproducts of some current manufacturing processes. Metabolism of PCBs is often a critical component in their toxicity, and relevant metabolic pathways usually include their initial oxidation to form hydroxylated polychlorinated biphenyls (OH-PCBs). Subsequent sulfation of OH-PCBs was originally thought to be primarily a means of detoxication; however, there is strong evidence that it may also contribute to toxicities associated with PCBs and OH-PCBs. These contributions include either the direct interaction of PCB sulfates with receptors or their serving as a localized precursor for OH-PCBs. The formation of PCB sulfates is catalyzed by cytosolic sulfotransferases, and, when transported into the serum, these metabolites may be retained, taken up by other tissues, and subjected to hydrolysis catalyzed by intracellular sulfatase(s) to regenerate OH-PCBs. Dynamic cycling between PCB sulfates and OH-PCBs may lead to further metabolic activation of the resulting OH-PCBs. Ultimate toxic endpoints of such processes may include endocrine disruption, neurotoxicities, and many others that are associated with exposures to PCBs and OH-PCBs. This review highlights the current understanding of the complex roles that PCB sulfates can have in the toxicities of PCBs and OH-PCBs and research on the varied mechanisms that control these roles.

Prenatal exposure to 209 PCBs in mother-infant pairs from two cities in China: Levels, congener profiles, and transplacental transfer

Prenatal exposure to polychlorinated biphenyls (PCBs) has been well researched, but studies covering all 209 congeners are limited. Recent literature suggests a shift in the dominant congeners and increasing levels of unintentionally-produced PCBs (UP-PCBs) in environmental samples in China. To investigate the exposure levels and profiles of PCBs in pregnant women and newborns, as well as the characteristics of transplacental transfer, we measured 209 PCBs in 80 pairs of maternal serum (MS) and cord serum (CS) from Hangzhou and Mianyang, China. The levels of ∑PCBs of participants in this study were lower than those in developed countries and followed the order of (ng/g lw): Hangzhou-MS (148) > Hangzhou-CS (107) > Mianyang-MS (63.8) > Mianyang-CS (57.9). UP-PCBs (mainly PCB-11) contributed around 50% of ∑PCBs in serum, which is consistent with the environmental samples. Environmental burden and dietary intake may account for the differences in the exposure levels, while the historical production and release may have impacted the homologue profiles. Prenatal exposure to PCB-126 was associated with increased birth weight (n = 80, adjusted β = 0.270, p = 0.030). The body burden of dioxin-like PCBs of newborns in Hangzhou was 82.4 pg TEQ/kg bw, suggesting certain health risks under WHO tolerable daily intake of 1-4 pg TEQ/kg bw. Log₁₀ K_OW was negatively correlated with log₁₀-transformed transplacental transfer efficiency (R² = 0.36, p < 0.001), serving its importance for PCBs' transplacental transfer. This study is the first to investigate maternal and fetal exposure to PCBs in China based on their levels, congener and homologue profiles, and potential adverse effects. Our findings help to provide insights into the processes and factors influencing the transplacental transfer of PCBs.

A minimal human physiologically based kinetic model of thyroid hormones and chemical disruption of plasma thyroid hormone binding proteins

The thyroid hormones (THs), thyroxine (T4) and triiodothyronine (T3), are under homeostatic control by the hypothalamic-pituitary-thyroid axis and plasma TH binding proteins (THBPs), including thyroxine-binding globulin (TBG), transthyretin (TTR), and albumin (ALB). THBPs buffer free THs against transient perturbations and distribute THs to tissues. TH binding to THBPs can be perturbed by structurally similar endocrine-disrupting chemicals (EDCs), yet their impact on circulating THs and health risks are unclear. In the present study, we constructed a human physiologically based kinetic (PBK) model of THs and explored the potential effects of THBP-binding EDCs. The model describes the production, distribution, and metabolism of T4 and T3 in the Body Blood, Thyroid, Liver, and Rest-of-Body (RB) compartments, with explicit consideration of the reversible binding between plasma THs and THBPs. Rigorously parameterized based on literature data, the model recapitulates key quantitative TH kinetic characteristics, including free, THBP-bound, and total T4 and T3 concentrations, TH productions, distributions, metabolisms, clearance, and half-lives. Moreover, the model produces several novel findings. (1) The blood-tissue TH exchanges are fast and nearly at equilibrium especially for T4, providing intrinsic robustness against local metabolic perturbations. (2) Tissue influx is limiting for transient tissue uptake of THs when THBPs are present. (3) Continuous exposure to THBP-binding EDCs does not alter the steady-state levels of THs, while intermittent daily exposure to rapidly metabolized TBG-binding EDCs can cause much greater disruptions to plasma and tissue THs. In summary, the PBK model provides novel insights into TH kinetics and the homeostatic roles of THBPs against thyroid disrupting chemicals.

Endocrine disruptors and endometriosis

Endometriosis is a hormone-dependent inflammatory gynecological disease of reproductive-age women. It is clinically and pathologically characterized by the presence of functional endometrium as heterogeneous lesions outside the uterine cavity. The two major symptoms are chronic pelvic pain and infertility, which profoundly affect women's reproductive health and quality of life. This significant individual and public health concerns underscore the importance of understanding the pathogenesis of endometriosis. The environmental endocrine-disrupting chemicals (EDCs) are exogenous agents that interfere with the synthesis, secretion, transport, signaling, or metabolism of hormones responsible for homeostasis, reproduction, and developmental processes. Endometriosis has been potentially linked to exposure to EDCs. In this review, based on the robust literature search, we have selected four endocrine disruptors (i) polychlorinated biphenyls (PCB)s (ii) dioxins (TCDD) (iii) bisphenol A (BPA) and its analogs and (iv) phthalates to elucidate their critical role in the etiopathogenesis of endometriosis. The epidemiological and experimental data discussed in this review indicate that these four EDCs activate multiple intracellular signaling pathways associated with proinflammation, estrogen, progesterone, prostaglandins, cell survival, apoptosis, migration, invasion, and growth of endometriosis. The available information strongly indicates that environmental exposure to EDCs such as PCBs, dioxins, BPA, and phthalates individually or collectively contribute to the pathophysiology of endometriosis. Further understanding of the molecular mechanisms of how these EDCs establish endometriosis and therapeutic strategies to mitigate the effects of these EDCs in the pathogenesis of endometriosis are timely needed. Moreover, understanding the interactive roles of these EDCs in the pathogenesis of endometriosis will help regulate the exposure to these EDCs in reproductive age women.

Thyroid Carcinoma: A Review for 25 Years of Environmental Risk Factors Studies

Environmental factors are established contributors to thyroid carcinomas. Due to their known ability to cause cancer, exposure to several organic and inorganic chemical toxicants and radiation from nuclear weapons, fallout, or medical radiation poses a threat to global public health. Halogenated substances like organochlorines and pesticides can interfere with thyroid function. Like phthalates and bisphenolates, polychlorinated biphenyls and their metabolites, along with polybrominated diethyl ethers, impact thyroid hormones biosynthesis, transport, binding to target organs, and impair thyroid function. A deeper understanding of environmental exposure is crucial for managing and preventing thyroid cancer. This review aims to investigate the relationship between environmental factors and the development of thyroid cancer.

AOP Report: Thyroperoxidase Inhibition Leading to Altered Visual Function in Fish Via Altered Retinal Layer Structure

Thyroid hormones (THs) are involved in the regulation of many important physiological and developmental processes, including vertebrate eye development. Thyroid hormone system-disrupting chemicals (THSDCs) may have severe consequences, because proper functioning of the visual system is a key factor for survival in wildlife. However, the sequence of events leading from TH system disruption (THSD) to altered eye development in fish has not yet been fully described. The development of this adverse outcome pathway (AOP) was based on an intensive literature review of studies that focused on THSD and impacts on eye development, mainly in fish. In total, approximately 120 studies (up to the end of 2021) were used in the development of this AOP linking inhibition of the key enzyme for TH synthesis, thyroperoxidase (TPO), to effects on retinal layer structure and visual function in fish (AOP-Wiki, AOP 363). In a weight-of-evidence evaluation, the confidence levels were overall moderate, with ample studies showing the link between reduced TH levels and altered retinal layer structure. However, some uncertainties about the underlying mechanism(s) remain. Although the current weight-of-evidence evaluation is based on fish, the AOP is plausibly applicable to other vertebrate classes. Through the re-use of several building blocks, this AOP is connected to the AOPs leading from TPO and deiodinase inhibition to impaired swim bladder inflation in fish (AOPs 155-159), together forming an AOP network describing THSD in fish. This AOP network addresses the lack of thyroid-related endpoints in existing fish test guidelines for the evaluation of THSDCs. Environ Toxicol Chem 2022;41:2632-2648. © 2022 SETAC.

The Association between Blood Concentrations of PCDD/DFs, DL-PCBs and the Risk of Type 2 Diabetes Mellitus and Thyroid Cancer in South Korea

Background and Objectives: Epidemiological studies have inconsistently shown an association between dioxin and risk of type 2 diabetes mellitus (T2DM) and cancer. This study aims to examine the effects of blood concentration of dioxin-like polychlorinated biphenyls (DL-PCBs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/DFs) on T2DM and thyroid cancer. Methods: We conducted a nested case–control study within the Korean cancer prevention study-II (KCPS-II) consisting of 15 thyroid cancer cases, 30 T2DM cases, and 55 controls. A total of 500 samples were used in 100 pooling samples. An average value of a pooled sample was calculated weighted by the blood volume of each sample. Results: The study population included 100 participants from the KCPS-II (median (IQR) baseline age, 54.06 [21.04] years; 48 women). The toxic equivalents of PCDD/DFs showed a significant positive association with T2DM and thyroid cancer, after adjustments for potential confounders (T2DM ORs  =  1.23; 95% CI  =  1.05–1.43; thyroid cancer ORs  =  1.34; 95% CI  =  1.12–1.61). Conclusion: In this study, both T2DM and thyroid cancer were associated with the blood concentrations of PCDD/DFs. The association between PCDD/DFs and T2D was found among women but not among men. Our findings suggest that further biochemical in vivo research and epidemiologic studies are needed to clarify the association between dioxins concentrations and diseases.

Dioxin-like Activity in Pregnant Women and Indices of Fetal Growth: The ACCEPT Birth Cohort

Exposure to lipophilic persistent organic pollutants (lipPOPs) elicits a number of species- and tissue-specific toxic responses, many of which involve the aryl hydrocarbon receptor (AhR). This study aims to measure the combined serum dioxin-like activity of lipPOPs in Greenlandic Inuit pregnant women and the associations with fetal growth indices. The combined dioxin-like activity of serum lipPOPs extracts was determined using the AhR reporter gene bioassay and expressed as pico-gram (pg) TCDD equivalent (TEQ) per gram serum lipid [AhR-TEQ (pg/g lipid)]. Significant AhR-TEQ was found in >87% of serum samples with the median level of 86.2 pg TEQ/g lipid. The AhR-TEQ level positively correlated with the marine food intake biomarker n-3/n-6 polyunsaturated fatty acids ratio, while negatively correlated with body mass index and parity. Women giving birth to infants with low birth weight (<2500 g) and length (<50 cm) had higher AhR-TEQ level compared to those with normal weight and length infants. For previous smokers, we found significant inverse associations between maternal AhR-TEQ level and fetal growth indices. In conclusion, exposure of Greenlandic Inuit pregnant women to dioxin-like compounds through traditional marine food can adversely influence the fetal growth via induced AhR activity. Smoking might have modifying effects.

The Effect of Early Life Exposure to Triclosan on Thyroid Follicles and Hormone Levels in Zebrafish

Triclosan (TCS) is an antimicrobial chemical widely used in personal care products. Most of the TCS component is discharged and enters the aquatic ecosystem after usage. TCS has a similar structure as thyroid hormones that are synthesized by thyroid follicular epithelial cells, thus TCS has a potential endocrine disrupting effect. It is still not clear how the different levels of the environmental TCS would affect early development in vivo. This study examines the effects of TCS on thyroid hormone secretion and the early development of zebrafish. The fertilized zebrafish eggs were exposed to TCS at 0 (control), 3, 30, 100, 300, and 900 ng/mL, and the hatching rate and the larvae mortality were inspected within the first 14 days. The total triiodothyronine (TT₃), total thyroxine (TT₄), free triiodothyronine (FT₃), and free thyroxine (FT₄) were measured at 7, 14, and 120 days post-fertilization (dpf). The histopathological examinations of thyroid follicles were conducted at 120 dpf. TCS exposure at 30-300 ng/mL reduced the hatching rate of larvae to 34.5% to 28.2 % in the first 48 hours and 93.8 .7 % to 86.8 % at 72 h. Extremely high TCS exposure (900 ng/mL) strongly inhibited the hatching rate, and all the larvae died within 1 day. Exposure to TCS from 3 to 300 ng/mL reduced the thyroid hormones production. The mean TT₃ and FT₃ levels of zebrafish decreased in 300 ng/mL TCS at 14 dpf (300 ng/mL TCS vs. control : TT₃ , 0.19 ± 0.08 vs. 0.39 ± 0.06; FT₃, 19.21 ± 3.13 vs. 28.53 ± 1.98 pg/mg), and the FT₄ decreased at 120 dpf ( 0.09 ± 0.04 vs. 0.20 ± 0.14 pg/mg). At 120 dpf , in the 300 ng/mL TCS exposure group, the nuclear area and the height of thyroid follicular epithelial cells became greater, and the follicle cell layer got thicker. This happened along with follicle hyperplasia, nuclear hypertrophy, and angiogenesis in the thyroid. Our study demonstrated that early life exposure to high TCS levels reduces the rate and speed of embryos hatching, and induces the histopathological change of thyroid follicle, and decreases the TT₃, FT₃, and FT₄ production in zebrafish.

Human hepatic microsomal sulfatase catalyzes the hydrolysis of polychlorinated biphenyl sulfates: A potential mechanism for retention of hydroxylated PCBs

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants that continue to be of concern due to their varied toxicities. Upon human exposure, many PCBs with lower numbers of chlorine atoms are metabolized to hydroxylated derivatives (OH-PCBs), and cytosolic sulfotransferases can subsequently catalyze the formation of PCB sulfates. Recent studies have indicated that PCB sulfates bind reversibly with a high affinity to human serum proteins, and that they are also taken up by cells and tissues. Since PCB sulfates might be hydrolyzed to the more toxic OH-PCBs, we have investigated the ability of human hepatic microsomal sulfatase to catalyze this reaction. Twelve congeners of PCB sulfates were substrates for the microsomal sulfatase with catalytic rates exceeding that of dehydroepiandrosterone sulfate as a comparison substrate for steroid sulfatase (STS). These results are consistent with an intracellular mechanism for sulfation and de-sulfation that may contribute to retention and increased time of exposure to OH-PCBs.

Determination of organic pollutants in meconium and its relationship with fetal growth. Case control study in Northwestern Spain

OBJECTIVES

Antenatal exposure to organic pollutants is a leading public health problem. Meconium is a unique matrix to perform prenatal studies because it enables us to retrospectively evaluate fetal exposure accumulated during the second and third trimester. The aim of the present study was to evaluate associations between organic pollutant levels in meconium and birth weight in NW Spain.

METHODS

In this study, we quantify the concentrations of 50 organic pollutants together with the total values of the most important chemical groups in meconium using gas chromatography coupled to tandem mass spectrometry.

RESULTS

Organochlorine pesticides, polychlorinated biphenyls and polybrominated diphenyl ethers were detected with the highest levels in meconium from small for gestational age newborns. It was estimated that several congeners were statistically significant (p<0.05). However, organophosphorus pesticides attained higher concentrations in newborns with an appropriate weight.

CONCLUSIONS

The occurrence of transplacental transfer can be confirmed. Prenatal exposure to organic pollutants was associated with a decrease in birth weight and, therefore, organic pollutants could have an impact on fetal growth. Nevertheless, these results need validation in larger sample sized studies.

Influence of perfluoroalkyl acids and other parameters on circulating thyroid hormones and immune-related microRNA expression in free-ranging nestling peregrine falcons

Exposure to certain perfluoroalkyl acids (PFAAs) can have considerable effects on the endocrine and immune systems, although such effects remain largely uncharacterized in wildlife. Using an apex avian predator, we investigated possible relationships of thyroid hormones (THs), specifically free (F) and total (T) thyroxine (FT4; TT4) and triiodothyronine (FT3; TT3), and the expression of an immune-related microRNA biomarker (i.e., miR-155), with the concentrations of 11 PFAAs in nestling peregrine falcons (Falco peregrinus). Nestling peregrines (n = 56; usually two chicks of each sex per nest) were blood sampled when 23 ± 4 days old in urban and rural regions of the Laurentian Great Lakes Basin (Ontario, Canada) in 2016 and 2018. The circulating concentrations of several PFAAs were significantly associated with THs and estimated thyroid gland activity (TT3:TT4; FT3:FT4), including PFHxS (FT3; FT3:FT4), PFDS (TT3; TT3:TT4), PFOA (TT4; FT3:FT4), PFTeDA (TT4; FT3:FT4), PFHxDA (TT4; TT3:TT4) and ΣPFCAs (TT4). Our novel evaluation of miR-155 in peregrine nestlings identified significantly negative relationships of plasma miR-155 counts with PFHxS and PFOA concentrations, indicating potential down-regulation of miR-155 expression and impaired immunity. Several PFAA homologues significantly predicted the variation in THs and miR-155 in conjunction with year (e.g., inter-annual differences in weather, ambient temperature, rainfall), region (urban/rural), nestling age, and/or diet (trophic position; δ¹⁵N), which suggests that multiple environmental and biological stressors, including PFAA exposure, influenced thyroid activity and immune function in these nestlings. Further research is warranted to identify the mechanisms and additional impacts of PFAA-related thyroid and immune disruption on the growth, development, and health risks in developing birds.

Unravelling the chemical exposome in cohort studies: routes explored and steps to become comprehensive

Environmental factors contribute to the risk for adverse health outcomes against a background of genetic predisposition. Among these factors, chemical exposures may substantially contribute to disease risk and adverse outcomes. In fact, epidemiological cohort studies have established associations between exposure against individual chemicals and adverse health effects. Yet, in daily life individuals are exposed to complex mixtures in varying compositions. To capture the totality of environmental exposures the concept of the exposome has been developed. Here, we undertake an overview of major exposome projects, which pioneered the field of exposomics and explored the links between chemical exposure and health outcomes using cohort studies. We seek to reflect their achievements with regard to (i) capturing a comprehensive picture of the environmental chemical exposome, (ii) aggregating internal exposures using chemical and bioanalytical means of detection, and (iii) identifying associations that provide novel options for risk assessment and intervention. Various complementary approaches can be distinguished in addressing relevant exposure routes and it emerges that individual exposure histories may not easily be grouped. The number of chemicals for which human exposure can be detected is substantial and highlights the reality of mixture exposures. Yet, to a large extent it depends on targeted chemical analysis with the specific challenges to capture all relevant exposure routes and assess the chemical concentrations occurring in humans. The currently used approaches imply prior knowledge or hypotheses about relevant exposures. Typically, the number of chemicals considered in exposome projects is counted in dozens-in contrast to the several thousands of chemicals for which occurrence have been reported in human serum and urine. Furthermore, health outcomes are often still compared to single chemicals only. Moreover, explicit consideration of mixture effects and the interrelations between different outcomes to support causal relationships and identify risk drivers in complex mixtures remain underdeveloped and call for specifically designed exposome-cohort studies.

Serum polychlorinated biphenyl (PCB) levels and risk of testicular germ cell tumors: A population-based case-control study in Connecticut and Massachusetts

The incidence rate of testicular germ cell tumors (TGCT) has continuously increased in Western countries over the last several decades. Some epidemiologic studies have reported that the endocrine disrupting polychlorinated biphenyls (PCBs) in serum may be associated with TGCT risk, but the evidence is inconsistent. Our goal was to investigate whether serum levels of PCBs are associated with the increase of TGCT risk. We conducted a population-based case-control study of 308 TGCT cases and 323 controls, all residents of Connecticut and Massachusetts. Serum levels of 56 PCBs congeners were measured using gas chromatography and unconditional logistic regression model was used to evaluate the risk of TGCT associated with total PCBs exposure, groups of PCBs categorized by Wolff's functional groups, and individual PCB congeners. The results showed that there was no association between total serum levels of PCBs and risk of TGCT overall (quartile 4 (Q4) vs. quartile 1 (Q1) odds ratio (OR) and 95% confidence interval (C.I.) = 1.0 (0.6-1.9), ρ trend = 0.9). However, strong positive association was observed between total serum levels of Wolff's Group 1 (potentially estrogenic) PCBs and risk of overall TGCT (Q4 vs. Q1 OR = 2.5, 95% CI = 1.3-4.7, ρ trend <0.05) as well as seminoma and non-seminoma subtypes. Wolff's Group 1 PCB congeners that showed an increased risk of TGCT included: 25, 44, 49, 52, 70, 101, 174, and 201/177. Considering the continuing increase of TGCT, these associations should be replicated in different populations with larger sample size.

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.

Life history and social structure as drivers of persistent organic pollutant levels and stable isotopes in Hawaiian false killer whales (Pseudorca crassidens)

False killer whales are long-lived, slow to mature, apex predators, and therefore susceptible to bioaccumulation of persistent organic pollutants (POPs). Hawaiian waters are home to three distinct populations: pelagic; Northwestern Hawaiian Islands (NWHI) insular; and main Hawaiian Islands (MHI) insular. Following a precipitous decline over recent decades, the MHI population was listed as "endangered" under the Endangered Species Act in 2012. This study assesses the risk of POP exposure to these populations by examining pollutant concentrations and ratios from blubber samples (n = 56) related to life history characteristics and MHI social clusters. Samples were analyzed for PCBs, DDTs, PBDEs, and some organochlorine pesticides. Skin samples (n = 52) were analyzed for stable isotopes δ¹³C and δ¹⁵N to gain insight into MHI false killer whale foraging ecology. Pollutant levels were similar among populations, although MHI whales had a significantly higher mean ratio of DDTs/PCBs than NWHI whales. The ∑PCB concentrations of 28 MHI individuals (68%) sampled were equal to or greater than suggested thresholds for deleterious health effects in marine mammals. The highest POP values among our samples were found in four stranded MHI animals. Eight of 24 MHI adult females have not been documented to have given birth; whether they have yet to reproduce, are reproductive senescent, or are experiencing reproductive dysfunction related to high POP exposure is unknown. Juvenile/sub-adults had significantly higher concentrations of certain contaminants than those measured in adults, and may be at greater risk of negative health effects during development. Multivariate analyses, POP ratios, and stable isotope ratios indicate varying risk of POP exposure, foraging locations and potentially prey items among MHI social clusters. Our findings provide invaluable insight into the ongoing risk POPs pose to the MHI population's viability, as well as consideration of risk for the NWHI and pelagic stocks.

Congener-specific determination of hydroxylated polychlorinated biphenyls by polar-embedded reversed-phase liquid chromatography-tandem mass spectrometry

This paper reports the development of an LC-ESI-MS² method for the sensitive determination of hydroxylated polychlorinated biphenyls (OH-PCBs) in human serum samples. Congener-specific separation was achieved by using a polar-embedded stationary phase, previously optimized for the working group, which provided better separation of isobaric compounds than the common octadecylsilane phases. MS fragmentation patterns and energies showed differences among OH-PCB congeners, mainly depending on the position of OH-group and the number of chlorine atoms in the molecule, although the most intense transitions were always those corresponding to the neutral loss of an HCl group from the quasi-molecular ion cluster. The method allowed the determination of OH-PCBs with good linearity (dynamic linear range of four orders of magnitude with R² higher than 0.995) and precision (relative standard deviations of absolute areas lower than 10%), and with better sensitivity than other similar methods previously described in the literature. Matrix effect has been evaluated and reduced to less than 10% by the addition of isotopically labeled standards and a 10-fold dilution of the final sample extract. The low iLODs provided by the developed method (from 1.2 to 5.4 fg µL^-1 for all the OH-PCBs studied, except 4'-OHCB108, whose iLOD was 61 fg µL^-1) allows dilution without losses of detected peaks. Finally, the applicability of the method has been demonstrated by analyzing human serum samples belonging to an interlaboratory exercise.

Halogen Bonding Interactions of Polychlorinated Biphenyls and the Potential for Thyroid Disruption

Polychlorinated biphenyl (PCB) flame retardants are persistent pollutants and inhibit neurodevelopment, particularly in the early stages of life. Halogen bonding (XB) to the iodothyronine deiodinases (Dio) that modulate thyroid hormones (THs) is a potential mechanism for endocrine disruption. Cl⋅⋅⋅Se XB interactions of PCBs with SeMe- , a small model of the Dio active site selenocysteine, are compared with previous results on polybrominated diphenylethers (PBDEs) and THs using density functional theory. PCBs generally display weaker XB interactions compared to PBDEs and THs, consistent with the dependence of XB strength on the size of the halogen (I>Br>Cl). PCBs also do not meet a proposed energy threshold for substrates to undergo dehalogenation, suggesting they may behave as competitive inhibitors of Dio in addition to other mechanisms of endocrine disruption. XB interactions in PCBs are position-dependent, with ortho interactions slightly more favorable than meta and para interactions, suggesting that PCBs may have a greater effect on certain classes of Dio. Flexibility of PCBs around the biphenyl C-C bond is limited by ortho substitutions relative to the biphenyl linkage, which may contribute to the ability to inhibit Dio and other TH-related proteins.

An investigation of physiological effects of the Deepwater Horizon oil spill on a long-distance migratory seabird, the northern gannet

Exposure to oil can have long-term impacts on migratory birds. Following the 2010 Deepwater Horizon blowout in the Gulf of Mexico (GOM), we investigated potential impacts of oil exposure on a population of northern gannets (Morus bassanus) that breed on Bonaventure Island (Québec, Canada) and winter in GOM and along the U.S. Atlantic coast (AC). Blood and feather samples were collected from adults previously equipped with geolocators to determine wintering locations. Parent and alkylated polycyclic aromatic hydrocarbons (PAHs); trace metals; stable isotopes of carbon, nitrogen, and hydrogen; and immune, thyroid, steroid, retinoid, and genetic endpoints were measured. PAH and trace metal concentrations did not differ between gannets using different wintering sites. Feather stable isotope values varied significantly between birds from different wintering locations. Gannets wintering in GOM showed higher feather corticosterone and plasma thyroid hormone levels, which may indicate increased energetic demands and/or greater exposure to environmental stressors.

Effects of perfluorooctanoic acid (PFOA) on the thyroid status, vitellogenin, and oxidant-antioxidant balance in the Murray River rainbowfish

Perfluorooctanoic acid's (PFOA) widespread use, presence and persistence in the aquatic environment has led to an increasing number of studies focusing on its toxicological effects. In Australia, PFOA has been detected in the aquatic environment, however its effects on Australian native fauna are unknown. In this study, male Australian native fish Murray River rainbowfish (Melanotaenia fluviatilis) were exposed to four different concentrations of PFOA (0.01, 0.1, 1 and 10 mg L^-1). Variations in thyroid hormones (Triiodothyronine (T3)/Thyroxine (T4)) and the presence of vitellogenin were determined in plasma. Oxidative stress responses were evaluated in gills and liver. Exposure of male fish to PFOA resulted in altered T3/T4 ratios and the presence of vitellogenin in the plasma. Activities of catalase (CAT) and glutathione- S-transferase (GST) were significantly increased in the gills and significantly reduced in the liver. Lipid peroxidation was observed in both tissues showing that vital organs could not neutralize the peroxides generated by oxidative stress resulting from exposure to PFOA. In natural populations exposed to PFOA, such hormonal disturbances can have negative effects, notably through altered capacity to respond to changes in environmental conditions.

Vitamin C improves liver and renal functions in hypothyroid rats by reducing tissue oxidative injury

Background: The effects of Vit C on liver and renal function and the tissues oxidative damage was investigated in hypothyroid rats. Materials and methods: The pregnant rats were divided into 5 groups (n=6): (1) Control; (2) Propylthiouracil (PTU; 0.005%), (3-5) PTU plus 10, 100 or 500 mg/kg b.w. Vit C. The drugs were added to the drinking water of the dams and their pups during lactation period and then continued for the offspring through the first 8 weeks of their life. Finally, 7 male offspring from each group were randomly selected. Results: Thyroxine, protein and albumin concentrations in the serum and thiol content and superoxide dismutase (SOD) and catalase (CAT) activities in renal and liver tissues of hypothyroid group was lower (all P<0.001) while, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALK-P), creatinine and blood urea nitrogen (BUN) concentrations in the serum and malondialdehyde (MDA) in the liver and renal tissues were higher than the control (all P<0.001). All doses of Vit C increased thyroxine, protein and albumin and thiol content in in renal and liver tissues while, decreased AST, ALT and ALK-P concentration and MDA in liver and renal tissues compared to PTU group (P<0.05-P<0.001). Creatinine, BUN and SOD and CAT were improved by both 100 and 500 mg/kg of Vit C in the renal (P<0.05-P<0.001) and by 100 mg/kg in the liver (P<0.05-P<0.001). Conclusion: Vit C improved liver and renal function of hypothyroid rats which might be due to its protective effects against tissues oxidative damage.

Pesticides With Potential Thyroid Hormone-Disrupting Effects: A Review of Recent Data

Plant Protection Products, more commonly referred to as pesticides and biocides, are used to control a wide range of yield-reducing pests including insects, fungi, nematodes, and weeds. Concern has been raised that some pesticides may act as endocrine disrupting chemicals (EDCs) with the potential to interfere with the hormone systems of non-target invertebrates and vertebrates, including humans. EDCs act at low doses and particularly vulnerable periods of exposure include pre- and perinatal development. Of critical concern is the number of pesticides with the potential to interfere with the developing nervous system and brain, notably with thyroid hormone signaling. Across vertebrates, thyroid hormone orchestrates metamorphosis, brain development, and metabolism. Pesticide action on thyroid homeostasis can involve interference with TH production and its control, displacement from distributor proteins and liver metabolism. Here we focused on thyroid endpoints for each of the different classes of pesticides reviewing epidemiological and experimental studies carried out both in in vivo and in vitro. We conclude first, that many pesticides were placed on the market with insufficient testing, other than acute or chronic toxicity, and second, that thyroid-specific endpoints for neurodevelopmental effects and mixture assessment are largely absent from regulatory directives.

Thyroid endocrine status and biochemical stress responses in adult male Wistar rats chronically exposed to pristine polystyrene nanoplastics

Toxicity evaluations of micro- or nano-sized plastics in rodent species commonly employed for toxicity analyses based on which risk assessment for humans could be performed are still largely lacking. Given this knowledge gap, the present work was aimed at determining the potential impact of chronic exposure to polystyrene nanoplastics (PS NPs) on the thyroid endocrine status and biochemical stress in a rat model. Young adult male rats were orally administered with PS NPs (1, 3, 6 and 10 mg kg^-1 day^-1) for five weeks. Thyroid hormones (THs) l-thyroxine (T4), l-triiodothyronine (T3), l-free triiodothyronine (FT3), and l-free thyroxine (FT4) as well as thyroid stimulating hormone (TSH) serum levels of normal rats and those exposed to PS NPs were compared. Serum levels of high-density lipoprotein (HDL), low-density lipoprotein (LDL), cholesterol, and creatinine, as well as glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) enzymes were also measured. Exposure to PS NPs suppressed the serum levels of T3 and circulating levels of THs, whereas TSH increased significantly. Though exposure to PS NPs did not affect the molar ratios of T3/T4, it induced a slight, but significant, increase in FT3/FT4. In addition, exposure to plastic nanoparticles showed signs of nephrotoxicity induction and kidney injury in exposed organisms as can be inferred from the significantly higher serum levels of creatinine in exposed groups. Our results provide clear evidence of an association between exposure to plastic NPs and thyroid endocrine disruption as well as metabolic deficit, and generate new leads for future research efforts.

Kanechlor 500-mediated changes in serum and hepatic thyroxine levels primarily occur in a transthyretin-unrelated manner

The effects of Kanechlor-500 (KC500) on the levels of serum total thyroxine (T₄ ) and hepatic T₄ in wild-type C57BL/6 (WT) and its transthyretin (TTR)-deficient (TTR-null) mice were comparatively examined. Four days after a single intraperitoneal injection with KC500 (100 mg/kg body weight), serum total T₄ levels were significantly decreased in both WT and TTR-null mice. The KC500 pretreatment also promoted serum [¹²⁵ I]T₄ clearance in both strains of mice administrated with [¹²⁵ I]T₄ , and the promotion of serum [¹²⁵ I]T₄ clearance in WT mice occurred without inhibition of the [¹²⁵ I]T₄ -TTR complex formation. Furthermore, the KC500 pretreatment led to significant increases in liver weight, steady-state distribution volume of [¹²⁵ I]T₄ , hepatic accumulation level of [¹²⁵ I]T₄ , and concentration ratio of the liver to serum in both strains of mice. The present findings indicate that the KC500-mediated decrease in serum T₄ level occurs in a TTR-unrelated manner and further suggest that KC500-promoted T₄ accumulation in the liver occurs through the development of liver hypertrophy and the promotion of T₄ transportation from serum to liver.

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

BACKGROUND

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

OBJECTIVES

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

DISCUSSION

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

Contaminant and Environmental Influences on Thyroid Hormone Action in Amphibian Metamorphosis

Aquatic and terrestrial environments are increasingly contaminated by anthropogenic sources that include pharmaceuticals, personal care products, and industrial and agricultural chemicals (i. e., pesticides). Many of these substances have the potential to disrupt endocrine function, yet their effect on thyroid hormone (TH) action has garnered relatively little attention. Anuran postembryonic metamorphosis is strictly dependent on TH and perturbation of this process can serve as a sensitive barometer for the detection and mechanistic elucidation of TH disrupting activities of chemical contaminants and their complex mixtures. The ecological threats posed by these contaminants are further exacerbated by changing environmental conditions such as temperature, photoperiod, pond drying, food restriction, and ultraviolet radiation. We review the current knowledge of several chemical and environmental factors that disrupt TH-dependent metamorphosis in amphibian tadpoles as assessed by morphological, thyroid histology, behavioral, and molecular endpoints. Although the molecular mechanisms for TH disruption have yet to be determined for many chemical and environmental factors, several affect TH synthesis, transport or metabolism with subsequent downstream effects. As molecular dysfunction typically precedes phenotypic or histological pathologies, sensitive assays that detect changes in transcript, protein, or metabolite abundance are indispensable for the timely detection of TH disruption. The emergence and application of 'omics techniques-genomics, transcriptomics, proteomics, metabolomics, and epigenomics-on metamorphosing tadpoles are powerful emerging assets for the rapid, proxy assessment of toxicant or environmental damage for all vertebrates including humans. Moreover, these highly informative 'omics techniques will complement morphological, behavioral, and histological assessments, thereby providing a comprehensive understanding of how TH-dependent signal disruption is propagated by environmental contaminants and factors.

Thyroid disruption properties of three indoor dust chemicals tested in Silurana tropicalis tadpoles

Indoor dust contains a multitude of industrial chemicals, and ingestion of dust is considered an important exposure route to organic contaminants. Some of these contaminants have been shown to interfere with the thyroid system, which may result in significant consequences on public health. The amphibian metamorphosis is a thyroid hormone-dependent process, which can be used as an in vivo model for studies on thyroid hormone-disrupting potency. Three contaminants of indoor dust were tested on metamorphosing Silurana (Xenopus) tropicalis tadpoles. The tested chemicals were Tris (1,3-dichloroisopropyl) phosphate (TDCiPP), tetrabromobisphenol-A (TBBPA) and propylparaben (PrP). Measurements reflecting general growth, development progress and thyroid epithelial cell height were performed on the exposed tadpoles as well as chemical analyses of the exposure water. It was shown that TDCiPP acts as a thyroid hormone-disrupting chemical in metamorphosing tadpoles by causing increased epithelial cell height in thyroid glands after exposure to a nominal concentration of 0.010 mg/L and in higher concentrations. TBBPA caused reductions in general growth of tadpoles at the nominal concentration 0.125 mg/L, and PrP caused acute toxicity at the nominal concentration 12.5 mg/L. However, no evident indications of specific thyroid-disrupting effects caused by TBBPA or PrP were observed.

Persistent Organic Pollutant-Mediated Insulin Resistance

Persistent organic pollutants (POPs) such as organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) have become wide-spread environmental contaminants as a consequence of their extensive use, long-range transport, and persistence. Because POPs are highly resistant to metabolic degradation, humans bioaccumulate these lipophilic and hydrophobic pollutants in fatty tissues for many years. Previous studies have demonstrated that POPs including PCBs are involved in the development of diabetes mellitus (DM) type 2 and insulin resistance. Numerous epidemiological studies suggest an association between POP burden and DM type 2/metabolic syndrome. In addition, several experimental studies have provided additional evidence supporting the association between POP exposure and DM type 2 or insulin resistance. Epidemiological and experimental studies have provided compelling evidence indicating that exposure to POPs increases the risk of developing insulin resistance and metabolic disorders. However, the detailed molecular mechanism underlying POP-induced insulin resistance is yet to be elucidated. In this article, we review literature that has reported on the association between POP burden and insulin resistance and the mechanism underlying POP-induced insulin resistance, and discuss implications for public health.

Association of maternal serum concentration of hydroxylated polychlorinated biphenyls with maternal and neonatal thyroid hormones: The Hokkaido birth cohort study

BACKGROUND

Evidence on the toxicity of hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs) for thyroid hormones (TH) is limited, and the underlying mechanism remains unknown.

OBJECTIVES

We aimed to investigate the effects of environmental prenatal exposure to OH-PCBs and maternal and neonatal TH levels, taking the maternal-fetal TH transfer into account.

METHODS

In this prospective birth cohort (the "Hokkaido study") we included 222 mother-neonate pairs. We measured five OH-PCB isomers in maternal serum samples either during pregnancy or within 5 days of delivery. Thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels were obtained from maternal blood samples at an early gestational stage (median; 11.1 weeks) and from heel prick samples of neonates between 4 and 7 days after birth. Multiple linear regression analysis and structural equation modeling (SEM) were performed to investigate the associations between maternal OH-PCB and maternal and neonatal TH levels.

RESULTS

Median concentration of ∑OH-PCBs was 25.37 pg/g wet weight. The predominant isomer was 4-OH-CB187, followed by 4-OH-CB146+3-OH-CB153. In the fully adjusted linear regression analysis, maternal ∑OH-PCBs was positively associated with maternal FT4, and 4-OH-CB187 was positively associated with both maternal and neonatal FT4 levels. Maternal OH-PCBs showed no significant association with TSH among mothers and neonates. Path analysis indicated the indirect pathway from 4-OH-CB187 exposure to increased neonatal FT4, via maternal THs and neonatal TSH.

CONCLUSIONS

These findings suggest that maternal exposure to OH-PCBs during pregnancy may increase both maternal and neonatal FT4 levels. Neonatal FT4 is presumed to be increased by prenatal 4-OH-CB187 indirectly, and this process may be mediated by maternal THs and neonatal TSH.

A combination of ternary classification models and reporter gene assays for the comprehensive thyroid hormone disruption profiles of 209 polychlorinated biphenyls

Computational toxicology is widely applied to screen tens and thousands of potential environmental endocrine disruptors (EDCs) for its great efficiency and rapid evaluation in recent years. Polychlorinated biphenyls (PCBs) with 209 congeners have not been comprehensively tested for their ability to interact with the thyroid receptor (TR), which is one of the most extensively studied targets related to the effects of EDCs. In this study, we aimed to determine the thyroid-disrupting mechanisms of 209 PCBs through the combination of a novel computational ternary classification model and luciferase reporter gene assay. The reporter gene assay was performed to examine the hormone activities of 22 PCBs via TR to classify their profiles as agonistic, antagonistic or inactive. Thus, six agonists, eleven antagonists and seven inactive chemicals against TR were identified in in vitro assays. Then, six relevant variables, including molecular structural descriptors and molecular docking scores, were selected for describing compounds. Machine learning methods (i.e., linear discriminant analysis (LDA) and support vector machines (SVM)) were used to build classification models. The optimal model was obtained by using SVM, with an accuracy of 88.24% in the training set, 80.0% in the test set and 75.0% in 10-fold cross-validation. The remaining 187 PCB congeners' hormone activities were predicted using the obtained models. Out of these PCBs, the SVM model predicted 38 agonists and 81 antagonists. The findings revealed that higher chlorinated PCBs tended to have TR-antagonistic activities, whereas lower chlorinated PCBs were agonists. This study provided a reference for further exploring PCBs' thyroid effect.

Effects of a complex contaminant mixture on thyroid hormones in breeding hooded seal mothers and their pups

There is a general lack of information on the possible effects of perfluoroalkyl substances (PFASs) on thyroid hormones (THs) in wildlife species. The effects of PFASs, which are known endocrine disruptors, on the TH homeostasis in hooded seals (Cystophora cristata) have yet to be investigated. Previously, correlations were found between plasma thyroid hormone (TH) concentrations in hooded seals, and organohalogen contaminants (OHCs) and hydroxyl (OH)-metabolites. Because animals are exposed to multiple contaminants simultaneously in nature, the effects of the complex contaminant mixtures that they accumulate should be assessed. Herein, we analyse relationships between plasma concentrations of multiple contaminants including protein-associated PFASs, hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs) and lipid soluble OHCs and plasma concentrations of free and total THs, i.e. triiodothyronine (FT3, TT3) and thyroxine (FT4, TT4) in hooded seal mothers and their pups. The perfluoroalkyl carboxylates (PFCAs) were the most important predictors for FT3 concentrations and TT3:FT3 ratios in the mothers. The FT3 levels decreased with increasing PFCA levels, while the TT3:FT3 ratios increased. In the pups, hexachlorocyclohexanes (HCHs) were the most important predictors for TT3:FT3 ratios, increasing with increasing HCHs levels. Additionally, perfluoroalkyl sulfonates (PFSAs) and PFCAs were important predictors for FT4:FT3 ratios in hooded seal pups, and the ratio increased with increasing concentrations. The study suggests that PFASs contribute to thyroid disruption in hooded seals exposed to complex contaminant mixtures that include chlorinated and fluorinated organic compounds.

Intracellular toxicity exerted by PCBs and role of VBNC bacterial strains in biodegradation

Polychlorinated biphenyls (PCBs) are xenobiotic compounds that persists in the environment for long-term, though its productivity is banned. Abatement of the pollutants have become laborious due to it's recalcitrant nature in the environment leading to toxic effects in humans and other living beings. Biphenyl degrading bacteria co-metabolically degrade low chlorinated PCBs using the active metabolic pathway. bph operon possess different genetic arrangements in gram positive and gram negative bacteria. The binding ability of the genes and the active sites were determined by PCB docking studies. The active site of bphA gene with conserved amino acid residues determines the substrate specificity and biodegradability. Accumulation of toxic intermediates alters cellular behaviour, biomass production and downturn the metabolic activity. Several bacteria in the environment attain unculturable state which is viable and metabolically active but not cultivable (VBNC). Resuscitation-promoting factor (Rpf) and Rpf homologous protein retrieve the culturability of the so far uncultured bacteria. Recovery of this adaptive mechanism against various physical and chemical stressors make a headway in understanding the functionality of both environmental and medically important unculturable bacteria. Thus, this paper review about the general aspects of PCBs, cellular toxicity exerted by PCBs, role of unculturable bacterial strains in biodegradation, genes involved and degradation pathways. It is suggested to extrapolate the research findings on extracellular organic matters produced in culture supernatant of VBNC thus transforming VBNC to culturable state.

Discovery and targeted monitoring of polychlorinated biphenyl metabolites in blood plasma using LC-TIMS-TOF MS

In the present work, the potential for rapid, targeted analysis of hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs) in diluted human blood plasma using liquid chromatography coupled with trapped ion mobility spectrometry and TOF high resolution mass spectrometry (LC-TIMS-TOF MS) was evaluated. Experimental OH-PCB collisional cross section (CCS_N2) and gas-phase candidate structures (<3% error) are reported for the first time and used, in addition to the LC retention time and accurate m/z, as OH-PCB identification features in order to increase the detection selectivity. The proposed LC-TIMS-TOF MS workflow combines a "dilute-and-shoot" sample preparation strategy, a robust liquid chromatography step, a high-resolving power mobility separation (R ~ 150-250) and high-resolution mass spectrometry (R ~ 30-40k) for the separation, identification and quantification of common OH-PCB isomers with limits of detection comparable to traditional workflows (e.g., LOD and LOQ of ~10 pg/mL and ~50 pg/mL, respectively). The higher selectivity and low detection limits provides multiple advantages compared to current methodologies that typically require long, labor-intensive preparation and/or derivatization steps prior to gas or liquid chromatography-mass spectrometry.

Early life exposure to air pollution particulate matter (PM) as risk factor for attention deficit/hyperactivity disorder (ADHD): Need for novel strategies for mechanisms and causalities

Epidemiological studies have demonstrated that air pollution particulate matter (PM) and adsorbed toxicants (organic compounds and trace metals) may affect child development already in utero. Recent studies have also indicated that PM may be a risk factor for neurodevelopmental disorders (NDDs). A pattern of increasing prevalence of attention deficit/hyperactivity disorder (ADHD) has been suggested to partly be linked to environmental pollutants exposure, including PM. Epidemiological studies suggest associations between pre- or postnatal exposure to air pollution components and ADHD symptoms. However, many studies are cross-sectional without possibility to reveal causality. Cohort studies are often small with poor exposure characterization, and confounded by traffic noise and socioeconomic factors, possibly overestimating the study associations. Furthermore, the mechanistic knowledge how exposure to PM during early brain development may contribute to increased risk of ADHD symptoms or cognitive deficits is limited. The closure of this knowledge gap requires the combined use of well-designed longitudinal cohort studies, supported by mechanistic in vitro studies. As ADHD has profound consequences for the children affected and their families, the identification of preventable risk factors such as air pollution exposure should be of high priority.

Hydroxylated and sulfated metabolites of commonly occurring airborne polychlorinated biphenyls inhibit human steroid sulfotransferases SULT1E1 and SULT2A1

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that are associated with varied adverse health effects. Lower chlorinated PCBs are prevalent in indoor and outdoor air and can be metabolized to their hydroxylated derivatives (OH-PCBs) followed by sulfation to form PCB sulfates. Sulfation is also a means of signal termination for steroid hormones. The human estrogen sulfotransferase (SULT1E1) and alcohol/hydroxysteroid sulfotransferase (SULT2A1) catalyze the formation of steroid sulfates that are inactive at steroid hormone receptors. We investigated the inhibition of SULT1E1 (IC50s ranging from 7.2 nM to greater than 10 μM) and SULT2A1 (IC50s from 1.3 μM to over 100 μM) by five lower-chlorinated OH-PCBs and their corresponding PCB sulfates relevant to airborne PCB-exposure. Several congeners of lower chlorinated OH-PCBs relevant to airborne PCB exposures were potent inhibitors of SULT1E1 and SULT2A1 and thus have the potential to disrupt regulation of intracellular concentrations of the receptor-active steroid substrates for these enzymes.

Polychlorinated biphenyls, indicators of thyroid function and thyroid autoantibodies in the Anniston Community Health Survey I (ACHS-I)

In this study, we examined associations between serum concentrations of 35 polychlorinated biphenyl (PCB) congeners, pesticides, and indicators of thyroid function in participants of the Anniston Community Health Survey (ACHS). Study subjects lived in the vicinity of a former PCB production facility and had PCB concentrations 2 to 3 times higher than similar age and race groups from the general population. We investigated associations among serum levels of thyroid hormones (thyroxin [T4], free thyroxin [fT4], triiodothyronine [T3], thyroid stimulation hormone [TSH]) and auto-antibodies (thyroglobulin antibody [TgAb] or thyroperoxidase antibody [TPOAb]) and combined indicators of thyroid function with the sum of PCBs, varying PCB groups, individual PCB congeners, and 8 pesticides. Logistic and linear regression models were adjusted for log10 transformed total lipids, age, sex, ethnicity, BMI, smoking, and family history of thyroid disease. We also performed analyses stratified by ethnicity and sex. Linear regression showed inverse associations between TT3 and thyroid-like PCBs (sum of PCBs 28, 52, 74, 101, 105, and 118; p = .0004), two pesticides (hexachlorobenzene, and pp'-DDE), and individual congeners (PCBs 74, 105). Null associations were observed between PCBs, pesticides, TSH, TT4, and fT4. Logistic regression analyses did not provide support for TT3 findings and found no association with other thyroid hormones, antibodies, or combined indicator of thyroid function. These results suggest there is little evidence that these chemicals have any major clinical effect on thyroid function in this highly PCB exposed population.

Aroclor 1254 and BDE-47 inhibit dopaminergic function manifesting as changes in locomotion behaviors in zebrafish embryos

Contamination with polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the environment is a major concern due to their persistent bioaccumulative toxicity that can disturb neurobehavioral functions including movements. Recently, it was reported that some PBDE including BDE-47 stimulates locomotor activities of zebrafish embryos by unknown mechanism. In this study, motor movements of the zebrafish embryo were used as a model system to evaluate the neuronal toxicity of a non-coplanar PCB-dominant mixture (Aroclor 1254) and BDE-47. Both organohalogens increased tail shaking and rotation of embryos in a concentration-dependent manner. Chemical inhibition and gene knock-down of tyrosine hydroxylase and vesicular monoamine transporter 2 (VMAT2) also induced hyperactivities. Hyperactivities induced by these treatments were all inhibited by supplementation of l-tyrosine and l-dopa, precursors of dopamine synthesis. Both organohalogens reduced dopamine contents and increased the 3,4-dihydroxyphenylacetic acid (DOPAC)/dopamine ratio in whole embryos. The results suggest that functional inhibition of dopaminergic neurons is involved in hyperactivities of zebrafish embryos caused by Aroclor 1254 and BDE-47.

Impact of Endocrine Disruptors on the Thyroid Hormone System

The thyroid hormone (TH) system plays a central role in central physiological processes of many species, including mammals and humans, ranging from growth and cell differentiation, energy metabolism, thermoregulation and phasing of hibernation or annual movements of migratory species, metamorphosis from larvae to adult forms, brain development, reproduction, or the cardiovascular system. Several chemicals are known to be TH-disrupting compounds (THDCs) and have been shown to interact with virtually all elements of TH homeostasis such as feedback mechanisms with the hypothalamus-pituitary axis, TH synthesis, TH storage and release from the thyroid gland, transport protein binding and TH distribution in tissues and organs, cellular TH uptake, intracellular TH metabolism, and TH receptor binding. Therefore, chemicals interfering with the TH homeostasis have the potential to interact with many of these important processes, and especially early-life stage exposure results in permanent alterations of tissue organization and homeostatic regulation of adaptive processes. This is not only of theoretical importance as the reported plasma concentrations of THDCs in human plasma fall well within the range of reported in vitro effect concentrations, and this is of even higher importance as the developing fetus and young children are in a sensitive developmental stage.

Thyroid Disrupting Chemicals

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

Biomarker Sensitivity to Vehicle Exhaust in Experimentally Exposed European Starlings

The effects of vehicle-related emissions on health has been a long-standing question in human health sciences; however, the toxicology of chronic exposure to environmentally relevant concentrations of these complex mixtures has not been characterized in wild birds. Adult European starlings (Sturnus vulgaris) were exposed to vehicle emissions, with combined benzene, toluene, ethylbenzene, and xylenes (BTEX) concentrations totaling 13.3 μg/m³ over 20 days of exposure for 5 h per day. Exposed birds had significantly lower cell-mediated immunity (measured using phytohaemagglutinin skin test, p < 0.0001), thyroxine (T4, p = 0.042), and glutathione (GSH, p = 0.034) concentrations than control birds. There was no difference in body condition, antibody response to vaccination, triiodothyronine (T3), hepatic biotransformation (7-ethoxyresorufin-O-deethylase activity), or oxidative stress (thiobarbituric acid-reactive substances and ratios of reduced to oxidized GSH) or organ masses between exposed and control birds. This study supports findings of previous studies examining wild birds exposed to these air contaminants and raises concern that environmentally relevant concentrations of common urban volatile pollutants may have measurable effects on health.

Evaluation on the thyroid disrupting mechanism of malathion in Fischer rat thyroid follicular cell line FRTL-5

Thyroid hormones are involved in many important physiological activities including regulation of energy metabolism, development of nervous system, maintenance of cerebral functions, and so on. Endocrine-disrupting chemicals (EDCs) that interfere with thyroid functions raise serious concerns due to their frequent misuse in areas where regulations are poorly implemented. In addition, chemicals that are originally regarded safe may now be considered as toxic with the development of life sciences. Malathion is an organophosphate insecticide that is widely applied and distributed in agricultural and residential settings. Due to the low acute toxicity and rapid degradation, malathion is not listed as a primary thyroid disrupting chemical. However, emerging evidences reported that malathion affected thyroperoxidase catalyzed iodide oxidation which in turn influenced thyroid hormone transportation, and enhanced parathyroid hyperplasia prevalence. Nevertheless, direct effect of malathion on thyroid hormone biosynthesis remains to be elucidated. This study investigated the effects of thyroid disruption of malathion in Fischer rat thyroid follicular cell line, FRTL-5. Transcriptional and translational analyses on thyroglobulin demonstrated that both mRNA and protein expression levels were significantly inhibited by malathion. Cellular cAMP level and TSH receptor expression were distinctly reduced by malathion (6.0 µg/ml). These results suggested that malathion directly disrupted the biosynthesis of thyroid hormone and the mechanism involved down-regulation of TSH receptor and cellular cAMP. This subsequently led to the suppression of TSH dependent signal transduction, TG transcription inhibition, and obstruction of thyroid hormone biosynthesis.

Differential neurotoxic effects of in utero and lactational exposure to hydroxylated polychlorinated biphenyl (OH-PCB 106) on spontaneous locomotor activity and motor coordination in young adult male mice

We investigated whether in utero or lactational exposure to 4-hydroxy-2',3,3',4',5'-pentachlorobiphenyl (OH-PCB 106) affects spontaneous locomotor activity and motor coordination in young adult male mice. For in utero exposure, pregnant C57BL/6J mice received 0.05 or 0.5 mg/kg body weight of OH-PCB 106 or corn oil vehicle via gavage every second day from gestational day 10 to 18. For lactational exposure, the different groups of dams received 0.05 or 0.5 mg/kg body weight of OH-PCB 106 or corn oil vehicle via gavage every second day from postpartum day 3 to 13. At 6-7 weeks of age, the spontaneous locomotor activities of male offspring were evaluated for a 24-hr continuous session in a home cage and in an open field for 30-min. Motor coordination function on an accelerating rotarod was also measured. Mice exposed prenatally to OH-PCB 106 showed increased spontaneous locomotor activities during the dark phase in the home cage and during the first 10-min in the open field compared with control mice. Mice exposed lactationally to OH-PCB 106, however, did not show a time-dependent decrease in locomotor activity in the open field. Instead, their locomotor activity increased significantly during the second 10-min block. In addition, mice exposed lactationally to OH-PCB 106 displayed impairments in motor coordination in the rotarod test. These results suggest that perinatal exposure to OH-PCB 106 affects motor behaviors in young adult male mice. Depending on the period of exposure, OH-PCB 106 may have different effects on neurobehavioral development.

Potentiation of ecological factors on the disruption of thyroid hormones by organo-halogenated contaminants in female polar bears (Ursus maritimus) from the Barents Sea

As apex predators, polar bears (Ursus maritimus) are among the most heavily polluted organisms in the Arctic. In addition to this anthropogenic stressor, climate warming has been shown to negatively affect their body condition, reproductive output and survival. Among potential underlying physiological mechanisms, thyroid hormones (THs), which control thermoregulation, metabolism and reproduction, can be affected by a variety of both natural and anthropogenic factors. While THs have been extensively used as proxies for pollution exposure in mammals, including polar bears, there is a lack of knowledge of their natural variations. In this context, we examined seasonal variations in body condition and circulating TH concentrations in free-ranging female polar bears. Females with variable reproductive status (i.e., solitary, with cubs of the year or with yearlings) were sampled from locations with contrasted sea ice conditions. Furthermore, we studied THs in relation to levels of organo-halogenated contaminants. As predicted, solitary females were in better condition than females caring for offspring, especially in spring. In addition, TH levels were lower in autumn compared to spring, although this seasonal effect was mainly observed in solitary females. Finally, the negative relationships between organochlorine and perfluoroalkyl substances and some THs suggest a possible alteration of homeostasis of THs. Since the latter relationships were only observed during spring, we emphasize the importance of considering the ecological factors when using THs as proxies for pollution exposure. Yet, the combined effects of natural and anthropogenic stressors on THs might impair the ability of polar bears to adapt to ongoing climate changes.

Serum Polybrominated Biphenyls (PBBs) and Polychlorinated Biphenyls (PCBs) and Thyroid Function among Michigan Adults Several Decades after the 1973-1974 PBB Contamination of Livestock Feed

BACKGROUND

In 1973-1974, Michigan residents were exposed to polybrominated biphenyls (PBBs) through an accidental contamination of the food supply. Residents were enrolled in a registry assembled after the incident, and they and their children participated in follow-up studies to assess subsequent health outcomes.

OBJECTIVES

We evaluated associations between serum PBBs and polychlorinated biphenyls (PCBs) and markers of thyroid function among Michigan adults.

METHODS

Serum concentrations of four PBB and four PCB congeners were measured at least once in 753 adults, including 79 women who participated in a 2004-2006 study and 683 women and men with follow-up during 2012-2015. Participants completed questionnaires on health conditions (including physician-diagnosed thyroid disease), behaviors, and demographics. Thyroid hormones were measured in a subset without thyroid disease (n=551). In multivariable linear regression models, PBB and PCB congener concentrations, on both the volume (nanogram/milliliter) and lipid (nanogram/gram lipid) basis, were assessed in relation to thyroid hormones. Logistic regression models were used to estimate associations between serum PBBs and PCBs and thyroid disease.

RESULTS

Thyroid disease was common (18% overall; 25% among women). Among women, all odds ratios (ORs) for PBB-153 and thyroid disease were positive for quintiles above the reference level, but estimates were imprecise and were without a monotonic increase. For an interquartile range (IQR) increase in PBB-153 (0.43 ng/mL), the OR (any thyroid disease)=1.12; (95% CI: 0.83, 1.52) (n=105 cases); for hypothyroidism, OR=1.35 (95% CI: 0.86, 2.13) (n=49 cases). There were 21 cases of thyroid disease in men [OR=0.69 (95% CI: 0.33); 1.44 for an IQR increase (0.75 ng/mL) in serum PBB-153]. PCB congeners were statistically significantly associated with greater total and free thyroxine and total triiodothyronine among women and with total and free triiodothyronine among men in lipid-standardized models.

CONCLUSIONS

We found some evidence to support associations of PBBs and PCBs with thyroid disease and thyroid hormone levels. https://doi.org/10.1289/EHP1302.

Halogenated phenolic compounds in wild fish from Canadian Areas of Concern

Concentrations of halogenated phenolic compounds were measured in the plasma of brown bullhead (Ameiurus nebulosus) from 4 Canadian Areas of Concern (AOCs), to assess exposure to suspected thyroid-disrupting chemicals. Hydroxylated polychlorinated biphenyls (OH-PCBs) were detected in every sample collected in 3 of the AOCs; the detection frequency was lower in samples from the Detroit River AOC. The OH-PCBs most frequently detected were pentachloro, hexachloro, and heptachloro congeners, which are structurally similar to thyroid hormones. Pentachlorophenol (PCP) was detected at highest concentrations (1.8 ng/g) in fish from Prince Edward Bay, the Bay of Quinte Lake reference site, and Hillman Marsh (the Wheatley Harbour reference site), suggesting local sources of contamination. Elevated PCP concentrations were also detected in the plasma of brown bullhead from exposed sites in the Toronto and Region AOC (0.4-0.6 ng/g). Triclosan was consistently detected in the Toronto and Region AOC (0.05-0.9 ng/g), consistent with wastewater emission. Greater concentrations were occasionally detected in the plasma of brown bullhead from the Bay of Quinte AOC. Concentrations of polybrominated diphenyl ethers were highest in the Toronto and Region AOC, and at 2 of the Bay of Quinte AOC exposed sites near Trenton and Belleville. Distribution patterns reflected the properties and usage of the compounds under investigation and the characteristics of each AOC. Environ Toxicol Chem 2017;36:2266-2273. © 2017 SETAC.

Perinatal exposure to organohalogen pollutants decreases vasopressin content and its mRNA expression in magnocellular neuroendocrine cells activated by osmotic stress in adult rats

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are environmental pollutants that produce neurotoxicity and neuroendocrine disruption. They affect the vasopressinergic system but their disruptive mechanisms are not well understood. Our group reported that rats perinatally exposed to Aroclor-1254 (A1254) and DE-71 (commercial mixtures of PCBs and PBDEs) decrease somatodendritic vasopressin (AVP) release while increasing plasma AVP responses to osmotic activation, potentially emptying AVP reserves required for body-water balance. The aim of this research was to evaluate the effects of perinatal exposure to A1254 or DE-71 (30mgkg/day) on AVP transcription and protein content in the paraventricular and supraoptic hypothalamic nuclei, of male and female rats, by in situ hybridization and immunohistochemistry. cFOS mRNA expression was evaluated in order to determine neuroendocrine cells activation due to osmotic stimulation. Animal groups were: vehicle (control); exposed to either A1254 or DE-71; both, control and exposed, subjected to osmotic challenge. The results confirmed a physiological increase in AVP-immunoreactivity (AVP-IR) and gene expression in response to osmotic challenge as reported elsewhere. In contrast, the exposed groups did not show this response to osmotic activation, they showed significant reduction in AVP-IR neurons, and AVP mRNA expression as compared to the hyperosmotic controls. cFOS mRNA expression increased in A1254 dehydrated groups, suggesting that the AVP-IR decrease was not due to a lack of the response to the osmotic activation. Therefore, A1254 may interfere with the activation of AVP mRNA transcript levels and protein, causing a central dysfunction of vasopressinergic system.