Environmental pollutants and the thyroid

Comparison of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in the serum of hypothyroxinemic and euthyroid dogs

OBJECTIVE

To determine the profile of 14 polybrominated diphenyl ethers (PBDEs) and 23 polychlorinated biphenyls (PCBs) in serum of domestic canines and whether this was predictive of thyroid hormone status.

SAMPLES

Serum samples were collected from 51 client-owned dogs visiting the University of California Davis William R. Pritchard Veterinary Medical Teaching Hospital during 2012 to 2016 for routine appointments. Fifteen dogs were diagnosed with hypothyroxinemia while 36 were euthyroid.

PROCEDURES

Concentrations of PBDEs and PCBs in canine serum samples were measured by gas chromatography mass spectrometry. Logistic regression analysis was used to determine the association between the presence/absence of canine hypothyroxinemia and the serum concentration of individual PBDE or PCB congeners.

RESULTS

The median concentrations of total PBDE and PCB congeners in the hypothyroxinemic group were 660 and 1,371 ng/g lipid, respectively, which were higher than concentrations detected in the control group. However, logistic regression analysis determined that current concentrations of PBDEs and PCBs in canines were not significantly associated with hypothyroxinemia. BDE 183 was the only congener showing near significance (p = 0.068).

CONCLUSIONS

PBDE and PCB congeners were detected in all canine samples confirming ongoing exposure to these pollutants. Because household dogs share the human environment, they may serve as biosentinels of human exposure to these contaminants.

Disruption of thyroid hormone (TH) levels and TH-regulated gene expression by polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and hydroxylated PCBs in e-waste recycling workers

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) are the primary toxicants released by electronic waste (e-waste) recycling, but their adverse effects on people working in e-waste recycling or living near e-waste sites have not been studied well. In the present study, the serum concentrations of PBDEs, PCBs, and hydroxylated PCBs, the circulating levels of thyroid hormones (THs), and the mRNA levels of seven TH-regulated genes in peripheral blood leukocytes of e-waste recycling workers were analyzed. The associations of the hormone levels and gene expression with the exposure to these contaminants were examined using multiple linear regression models. There were nearly no associations of the TH levels with PCBs and hydroxylated PCBs, whereas elevated hormone (T₄ and T₃) levels were associated with certain lower-brominated BDEs. While not statistically significant, we did observe a negative association between highly brominated PBDE congeners and thyroid-stimulating hormone (TSH) levels in the e-waste workers. The TH-regulated gene expression was more significantly associated with the organohalogen compounds (OHCs) than the TH levels in these workers. The TH-regulated gene expression was significantly associated with certain PCB and hydroxylated PCB congeners. However, the expression of most target genes was suppressed by PBDEs (mostly highly brominated congeners). This is the first evidence of alterations in TH-regulated gene expression in humans exposed to OHCs. Our findings indicated that OHCs may interfere with TH signaling and/or exert TH-like effects, leading to alterations in related gene expression in humans. Further research is needed to investigate the mechanisms of action and associated biological consequences of the gene expression disruption by OHCs.

Perinatal exposure to glyphosate-based herbicide alters the thyrotrophic axis and causes thyroid hormone homeostasis imbalance in male rats

Glyphosate-based herbicides (GBHs) are widely used in agriculture. Recently, several animal and epidemiological studies have been conducted to understand the effects of these chemicals as an endocrine disruptor for the gonadal system. The aim of the present study was to determine whether GBHs could also disrupt the hypothalamic-pituitary-thyroid (HPT) axis. Female pregnant Wistar rats were exposed to a solution containing GBH Roundup®Transorb (Monsanto). The animals were divided into three groups (control, 5mg/kg/day or 50mg/kg/day) and exposed from gestation day 18 (GD18) to post-natal day 5 (PND5). Male offspring were euthanized at PND 90, and blood and tissues samples from the hypothalamus, pituitary, liver and heart were collected for hormonal evaluation (TSH-Thyroid stimulating hormone, T3-triiodothyronine and T4-thyroxine), metabolomic and mRNA analyses of genes related to thyroid hormone metabolism and function. The hormonal profiles showed decreased concentrations of TSH in the exposed groups, with no variation in the levels of the thyroid hormones (THs) T3 and T4 between the groups. Hypothalamus gene expression analysis of the exposed groups revealed a reduction in the expression of genes encoding deiodinases 2 (Dio2) and 3 (Dio3) and TH transporters Slco1c1 (former Oatp1c1) and Slc16a2 (former Mct8). In the pituitary, Dio2, thyroid hormone receptor genes (Thra1 and Thrb1), and Slc16a2 showed higher expression levels in the exposed groups than in the control group. Interestingly, Tshb gene expression did not show any difference in expression profile between the control and exposed groups. Liver Thra1 and Thrb1 showed increased mRNA expression in both GBH-exposed groups, and in the heart, Dio2, Mb, Myh6 (former Mhca) and Slc2a4 (former Glut4) showed higher mRNA expression in the exposed groups. Additionally, correlation analysis between gene expression and metabolomic data showed similar alterations as detected in hypothyroid rats. Perinatal exposure to GBH in male rats modified the HPT set point, with lower levels of TSH likely reflecting post-translational events. Several genes regulated by TH or involved in TH metabolism and transport presented varying degrees of gene expression alteration that were probably programmed during intrauterine exposure to GBHs and reflects in peripheral metabolism. In conclusion, the role of GBH exposure in HPT axis disruption should be considered in populations exposed to this herbicide.

Population Survey of Iodine Deficiency and Environmental Disruptors of Thyroid Function in Young Children in Haiti

CONTEXT

Iodine deficiency is the leading cause of preventable neurodevelopmental delay in children worldwide and a possible public health concern in Haiti.

OBJECTIVE

To determine the prevalence of iodine deficiency in Haitian young children and its influence by environmental factors.

DESIGN

Cross-sectional study, March through June 2015.

SETTING

Community churches in 3 geographical regions in Haiti.

PARTICIPANTS

299 healthy Haitian children aged 9 months to 6 years; one-third each enrolled in a coastal, mountainous, and urban region.

MAIN OUTCOME MEASURES

Urinary iodide, serum thyrotropin (TSH), goiter assessment, and urinary perchlorate and thiocyanate.

RESULTS

Mean age was 3.3±1.6 years, with 51% female, median family income USD 30/week, and 16% malnutrition. Median urinary iodide levels were normal in coastal (145 μg/L, interquartile range [IQR] 97 to 241) and urban regions (187 μg/L, IQR 92 to 316), but revealed mild iodine deficiency in a mountainous region (89 μg/L, IQR 56 to 129), P < 0.0001. Grade 1 goiters were palpated in 2 children, but TSH values were normal. Urinary thiocyanate and perchlorate concentrations were not elevated. Predictors of higher urinary iodide included higher urinary thiocyanate and perchlorate, breastfeeding, and not living in a mountainous region.

CONCLUSIONS

Areas of mild iodine deficiency persist in Haiti's mountainous regions. Exposure to two well-understood environmental thyroid function disruptors is limited.

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

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

MANAGEMENT OF ENDOCRINE DISEASE: Isolated maternal hypothyroxinemia during pregnancy: knowns and unknowns

Isolated maternal hypothyroxinemia (IMH) during pregnancy is defined as a low maternal T₄ in the absence of TSH elevation. As IMH is common, with a prevalence of 1-2% in iodine-sufficient populations, and early research has suggested adverse effects on fetal neurodevelopment, it has been the focus of many studies in the last decade. In the current review, we first discuss the significance of IMH based on data from animal models and recent discoveries regarding the role of thyroid hormone on neurodevelopment. We address issues surrounding the definition and prevalence of this entity and discuss new insights into the etiologies, clinical consequences and management of IMH. A number of large cohort studies have investigated the effects of IMH on the risk of various pregnancy complications and child neurodevelopment. We review these studies in detail and describe their limitations. We discuss the available research on management of IMH, including two recent randomized controlled trials (RCTs). Finally, we delineate the remaining uncertainties in this field and emphasize the need for a sufficiently powered, placebo-controlled RCT on the treatment of IMH early in the first trimester of pregnancy.

Environmental Issues in Thyroid Diseases

Environmental factors are determinant for the appearance of autoimmune thyroid diseases (AITD) in susceptible subjects. Increased iodine intake, selenium, and vitamin D deficiency, exposure to radiation, from nuclear fallout or due to medical radiation, are environmental factors increasing AITD. Cigarette smoking is associated with Graves' disease and Graves' ophthalmopathy, while it decreases the risk of hypothyroidism and thyroid autoimmunity. Viral infections are important environmental factors in the pathogenesis of AITD, too, particularly human parvovirus B19 (EVB19) and hepatitis C virus. Among the many chemical contaminants, halogenated organochlorines and pesticides variably disrupt thyroid function. Polychlorinated biphenyls and their metabolites and polybrominated diethyl ethers bind to thyroid transport proteins, such as transthyretin, displace thyroxine, and disrupt thyroid function. Among drugs, interferon- and iodine-containing drugs have been associated with AITD. Moreover intestinal dysbiosis causes autoimmune thyroiditis. To reduce the risk to populations and also in each patient, it is necessary to comprehend the association between environmental agents and thyroid dysfunction.

The role of micronutrients in the response to ambient air pollutants: Potential mechanisms and suggestions for research design

People living in regions of low socioeconomic status are thought to be prone to higher exposures to environmental pollutants, poor nutrition, and numerous preventable diseases and infections. Poverty correlates with pollution and malnutrition; however, limited studies examined their interrelationship. The well-studied, deleterious health effects attributed to environmental pollutants and poor nutrition may act in combination with produce more severe adverse health outcomes than any one factor alone. Deficiencies in specific nutrients render the body more susceptible to injury which may influence the pathways that serve as the mechanistic responses to ambient air pollutants. This review (1) explores specific micronutrients that are of global concern, (2) explains how these nutrients may impact the body's response to ambient air pollution, and (3) provides guidance on designing animal models of nutritional deficiency. It is likely that those individuals who reside in regions of high ambient air pollution are similarly malnourished. Therefore, it is important that research identifies specific nutrients of concern and their impact in identified regions of high ambient air pollution.

Comparison of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in the serum of hypothyroxinemic and euthyroid dogs

OBJECTIVE

To determine the profile of 14 polybrominated diphenyl ethers (PBDEs) and 23 polychlorinated biphenyls (PCBs) in serum of domestic canines and whether this was predictive of thyroid hormone status.

SAMPLES

Serum samples were collected from 51 client-owned dogs visiting the University of California Davis William R. Pritchard Veterinary Medical Teaching Hospital during 2012 to 2016 for routine appointments. Fifteen dogs were diagnosed with hypothyroxinemia while 36 were euthyroid.

PROCEDURES

Concentrations of PBDEs and PCBs in canine serum samples were measured by gas chromatography mass spectrometry. Logistic regression analysis was used to determine the association between the presence/absence of canine hypothyroxinemia and the serum concentration of individual PBDE or PCB congeners.

RESULTS

The median concentrations of total PBDE and PCB congeners in the hypothyroxinemic group were 660 and 1,371 ng/g lipid, respectively, which were higher than concentrations detected in the control group. However, logistic regression analysis determined that current concentrations of PBDEs and PCBs in canines were not significantly associated with hypothyroxinemia. BDE 183 was the only congener showing near significance (p = 0.068).

CONCLUSIONS

PBDE and PCB congeners were detected in all canine samples confirming ongoing exposure to these pollutants. Because household dogs share the human environment, they may serve as biosentinels of human exposure to these contaminants.

Thyroid Allostasis-Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming

The hypothalamus-pituitary-thyroid feedback control is a dynamic, adaptive system. In situations of illness and deprivation of energy representing type 1 allostasis, the stress response operates to alter both its set point and peripheral transfer parameters. In contrast, type 2 allostatic load, typically effective in psychosocial stress, pregnancy, metabolic syndrome, and adaptation to cold, produces a nearly opposite phenotype of predictive plasticity. The non-thyroidal illness syndrome (NTIS) or thyroid allostasis in critical illness, tumors, uremia, and starvation (TACITUS), commonly observed in hospitalized patients, displays a historically well-studied pattern of allostatic thyroid response. This is characterized by decreased total and free thyroid hormone concentrations and varying levels of thyroid-stimulating hormone (TSH) ranging from decreased (in severe cases) to normal or even elevated (mainly in the recovery phase) TSH concentrations. An acute versus chronic stage (wasting syndrome) of TACITUS can be discerned. The two types differ in molecular mechanisms and prognosis. The acute adaptation of thyroid hormone metabolism to critical illness may prove beneficial to the organism, whereas the far more complex molecular alterations associated with chronic illness frequently lead to allostatic overload. The latter is associated with poor outcome, independently of the underlying disease. Adaptive responses of thyroid homeostasis extend to alterations in thyroid hormone concentrations during fetal life, periods of weight gain or loss, thermoregulation, physical exercise, and psychiatric diseases. The various forms of thyroid allostasis pose serious problems in differential diagnosis of thyroid disease. This review article provides an overview of physiological mechanisms as well as major diagnostic and therapeutic implications of thyroid allostasis under a variety of developmental and straining conditions.

Refuse leachate exposure causes changes of thyroid hormone level and related gene expression in female goldfish (Carassius auratus)

To elucidate the potential thyroid disrupting effects of refuse leachate on females, female goldfish (Carassius auratus) were exposed to 0.5% diluted leachates from each step of a leachate treatment process (i.e. raw leachate before treatment, after membrane bioreactor treatment, and the final treated leachate) for 21days. Raw leachate exposure caused disturbances in the thyroid cascade of female fish, as evidenced by the elevated plasma 3,3',5-triiodo-l-thyronine (p<0.05) and thyroid-stimulating hormone (p<0.01) levels as well as up-regulated hepatic and gonadal type I deiodinase (p<0.01), type II deiodinase (p<0.01) and thyroid receptor (p<0.05) mRNA levels. Thyroid disrupting potency decreased markedly as raw leachate progressed through the "membrane bioreactor + reverse osmosis" treatment but could still be detected in the treated leachate. As our results indicated, thyroid system in female goldfish was more sensitive to leachate exposure than that of the male fish.

Environmentally relevant concentrations of nitrate increase plasma testosterone concentrations in female American alligators (Alligator mississippiensis)

Anthropogenic nitrogen is a ubiquitous environmental contaminant that is contributing to the degradation of freshwater, estuarine, and coastal ecosystems worldwide. The effects of environmental nitrate, a principal form of nitrogen, on the health of aquatic life is of increasing concern. We exposed female American alligators to three concentrations of nitrate (0.7, 10 and 100mg/L NO₃-N) for a duration of five weeks and five months from hatch. We assessed growth, plasma sex steroid and thyroid hormone concentrations, and transcription levels of key genes involved in steroidogenesis (StAR, 3β-HSD, and P450_scc) and hepatic clearance (Cyp1a, Cyp3a). Exposure to 100mg/L NO₃-N for both five weeks and five months resulted in significantly increased plasma testosterone (T) concentrations compared with alligators in the reference treatment. No differences in 17β-estradiol, progesterone, or thyroid hormones were observed, nor were there differences in alligator weight or the mRNA abundance of steroidogenic or hepatic genes. Plasma and urinary nitrate concentrations increased with increasing nitrate treatment levels, although relative plasma concentrations of nitrate were significantly lower in five month, versus five week old animals, possibly due to improved kidney function in older animals. These results indicate that environmentally relevant concentrations of nitrate can increase circulating concentrations of T in young female alligators.

Integrative and comparative reproductive biology: From alligators to xenobiotics

Dr. Louis J. Guillette Jr. thought of himself as a reproductive biologist. However, his interest in reproductive biology transcended organ systems, life history stages, species, and environmental contexts. His integrative and collaborative nature led to diverse and fascinating research projects conducted all over the world. He doesn't leave us with a single legacy. Instead, he entrusts us with several. The purpose of this review is to highlight those legacies, in both breadth and diversity, and to illustrate Dr. Guillette's grand contributions to the field of reproductive biology. He has challenged the field to reconsider how we think about our data, championed development of novel and innovative techniques to measure endocrine function, helped define the field of endocrine disruption, and lead projects to characterize new endocrine disrupting chemicals. He significantly influenced our understanding of evolution, and took bold and important steps to translate all that he has learned into advances in human reproductive health. We hope that after reading this manuscript our audience will appreciate and continue Dr. Guillette's practice of open-minded and passionate collaboration to understand the basic mechanisms driving reproductive physiology and to ultimately apply those findings to protect and improve wildlife and human health.

Autism genes are selectively targeted by environmental pollutants including pesticides, heavy metals, bisphenol A, phthalates and many others in food, cosmetics or household products

The increasing incidence of autism suggests a major environmental influence. Epidemiology has implicated many candidates and genetics many susceptibility genes. Gene/environment interactions in autism were analysed using 206 autism susceptibility genes (ASG's) from the Autworks database to interrogate ∼1 million chemical/gene interactions in the comparative toxicogenomics database. Any bias towards ASG's was statistically determined for each chemical. Many suspect compounds identified in epidemiology, including tetrachlorodibenzodioxin, pesticides, particulate matter, benzo(a)pyrene, heavy metals, valproate, acetaminophen, SSRI's, cocaine, bisphenol A, phthalates, polyhalogenated biphenyls, flame retardants, diesel constituents, terbutaline and oxytocin, inter alia showed a significant degree of bias towards ASG's, as did relevant endogenous agents (retinoids, sex steroids, thyroxine, melatonin, folate, dopamine, serotonin). Numerous other suspected endocrine disruptors (over 100) selectively targeted ASG's including paraquat, atrazine and other pesticides not yet studied in autism and many compounds used in food, cosmetics or household products, including tretinoin, soy phytoestrogens, aspartame, titanium dioxide and sodium fluoride. Autism polymorphisms influence the sensitivity to some of these chemicals and these same genes play an important role in barrier function and control of respiratory cilia sweeping particulate matter from the airways. Pesticides, heavy metals and pollutants also disrupt barrier and/or ciliary function, which is regulated by sex steroids and by bitter/sweet taste receptors. Further epidemiological studies and neurodevelopmental and behavioural research is warranted to determine the relevance of large number of suspect candidates whose addition to the environment, household, food and cosmetics might be fuelling the autism epidemic in a gene-dependent manner.

A meta-analysis of studies investigating the effects of occupational lead exposure on thyroid hormones

INTRODUCTION

Investigations of the effects of occupational exposure to lead on the concentrations of thyroid hormones in the blood have not produced consistent results. A meta-analysis was performed to assess the effect of occupational exposure to lead on thyroid hormone concentrations using the results from published studies.

METHODS

Group means from studies of the thyroid function of persons occupationally exposed to lead were used in a meta-analysis. Differences between the control and exposed groups, and the slopes between thyroid hormone concentrations and log10 blood lead concentrations or duration of exposure to lead were estimated using mixed models. The hormones analyzed were thyroid stimulating hormone, total and free thyroxine, and total and free triiodothyronine.

RESULTS

No differences in mean thyroid hormone concentrations were found between the exposed and control groups. No relationships were found between blood lead or the duration of exposure to lead and thyroid hormone concentrations.

CONCLUSION

The results of the analysis do not provide evidence for an effect of occupational lead exposure on thyroid function in men. Am. J. Ind. Med. 59:583-590, 2016. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Thyroid endocrine status of wild European eels (Anguilla anguilla) in the Loire (France). Relationships with organic contaminant body burdens

In teleost fish, thyroid function is involved in various critical physiological processes. Given the complexity of the hypothalamo-pituitary-thyroid (HPT) axis, a large number of genes and proteins can be the potential target of endocrine-disrupting compounds (EDCs). The aim of this study was to evaluate, in yellow and silver European eels (Anguilla anguilla), potential effects of EDCs on thyroid status by analyzing the associations between EDC body burdens and thyroid hormones (THs). In yellow individuals, greater free T3/T4 ratios (FT3/FT4) and lower plasma FT4 levels were associated with greater concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), as highlighted by significant correlations with many congeners. Few positive relationships with alkylphenols were noticed. In contrast, silver eels usually exhibited less significant correlations between THs and contaminant loads. Expression of a series of genes involved in the HPT axis was also investigated in the silver individuals. Concerning mRNA expression in silver females, some main correlations were noticed: thyroid-stimulating hormone (TSHβ) gene expression was significantly correlated to numerous PCBs, and hepatic mRNA levels of deiodinase 2 (Deio 2) were negatively correlated to 2-hydroxyfluorene (2-OHF) and 2-naphtol (2-OHNa). Thyroid receptor (TRα and TRβ) mRNA levels exhibited weak negative correlations with some PBDEs in silver females and males. Hepatic vitellogenin (Vtg) mRNA levels were detected in all silver males but at lower levels than in silver females. In males, Vtg mRNA levels were positively associated to FT4/TT4. In silver females, strong positive correlations were found between congeners of PCBs, PBDEs and PFAS suggesting potential estrogenic effects. Overall, the observed results indicate that several organic contaminants, mainly dl-, ndl-PCBs and PBDEs, could be associated with changes in thyroid homeostasis in these fish, via direct or indirect interactions with peripheral deiodination, metabolism of T4 and mechanisms involved in TSHβ, Deio 2 and Vtg gene transcription.

Serum concentrations of PCBs and OCPs among prepubertal Korean children

Although children are more vulnerable than adults to environmental hazards, due to their physiological and behavioral characteristics, few studies have assessed their internal exposure to persistent organic pollutants (POPs). The objective of this study was to determine the serum levels of certain polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) among pre-pubertal children in Korea and examine their variation with age and gender. We analyzed a total of 51 POPs in 214 children (age range, 7-9 years), using data from the Ewha Birth and Growth Cohort Study. To examine change over time, POP concentrations were measured at both 7 and 9 years of age in a sub-cohort of 26 children. The median and interquartile range (IQR, 25th to 75th percentiles) data for the sum of PCB congeners was 26.44 ng/g lipid (18.27-37.63 ng/g lipid). The median (IQR) concentration for the sum of OCPs was 74.82 ng/g lipid (51.11-112.45 ng/g lipid). Our results showed significant increases in serum concentrations of total PCBs with age (p = 0.0001), no gender dependence of total PCBs (p = 0.38) and total OCPs (p = 0.12), and strong correlations between individual POPs. Childhood exposure to POPs was relatively low compared to other studies carried out in different countries. However, even though the use of POPs has been banned since 2001, our results indicated that children in the general population are still exposed to various POPs. Because long-term, low-level exposure to POPs in the general population remains a concern for human health, future research should examine major routes of exposure and identification of risk factors.

Exposure to Polybrominated Diphenyl Ethers (PBDEs) and Hypothyroidism in Canadian Women

CONTEXT

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in a wide range of products, resulting in widespread human exposure. Epidemiological studies in some populations reported exposure to PBDEs and thyroid hormone levels but little epidemiological data are available among women from the general population.

OBJECTIVE

The objective of the study was to examine the association of PBDEs with hypothyroidism.

DESIGN AND SETTING

This was a cross-sectional analysis of the 2007-2009 Canadian Health Measures Survey.

PARTICIPANTS

A total of 745 women representative of Canadian women aged 30-79 years participated in the study. Main Outcome and Methods: We estimated the prevalence ratios (PRs) for hypothyroidism in relation to plasma concentrations of BDE-47, -99, -100, and -153 and their sum (ΣPBDEs). Women were identified as cases if they reported a doctor-diagnosed thyroid condition and underwent thyroid hormone replacement therapy (n = 90).

RESULTS

Higher plasma levels of brominated diphenyl ether (BDE)-47 and -100 and ΣPBDEs were associated with an increased prevalence of hypothyroidism. The PR for a 10-fold increase in ΣPBDEs was 1.7 (95% confidence interval [CI] 1.0, 3.0). Associations were consistently higher among women aged 30-50 years than among those 51-79 years for ΣPBDEs and the other PBDE congeners, although the interaction was significant only for BDE-100. For instance, in the younger age group, women with detectable levels of BDE-100 had a PR of 3.8 (95% CI 1.2, 12.3) compared with women with undetectable levels; the corresponding PR in the older age group was 1.2 (95% CI 0.6, 2.3). No association was observed for BDE-99 and -153.

CONCLUSION

Plasma PBDE levels were associated with an increased prevalence of hypothyroidism in Canadian women aged 30-50 years. Although the cross-sectional design of the study limits inferences of causality, these findings have important implications, given the key role of thyroid hormones in several biological mechanisms during reproductive age.

Thyroid endocrine disruption and external body morphology of Zebrafish

This study examined the effects thyroid-active compounds during early development on body morphology of Zebrafish (Danio rerio). Three-day postfertilization (dpf) larvae were exposed to goitrogen [methimazole (MZ, 0.15mM)], combination of MZ (0.15mM) and thyroxine (T4, 2nM), T4 (2nM), or control (reconstituted water) treatments until 33dpf and subsequently maintained in reconstituted water until 45dpf. Samples were taken at 33 and 45dpf for multivariate analysis of geometric distances between selected homologous landmarks placed on digital images of fish, and for histological assessment of thyrocytes. Body mass, standard length, and pectoral fin length were separately measured on remaining fish at 45dpf. Histological analysis confirmed the hypothyroid effect (increased thyrocyte height) of MZ and rescue effect of T4 co-administration. Geometric distance analysis showed that pectoral and pelvic fins shifted backward along the rostrocaudal axis under hypothyroid conditions at 45dpf and that T4 co-treatment prevented this shift. Pectoral fin length at 45dpf was reduced by exposure to MZ and rescued by co-administration of T4, but it was not associated with standard length. Methimazole caused a reduction in body mass and length at 45dpf that could not be rescued by T4 co-administration, and non-thyroidal effects of MZ on body shape were also recognized at 33 and 45dpf. Alterations in the length and position of paired fins caused by exposure to thyroid-disrupting chemicals during early development, as shown here for Zebrafish, could affect physical aspects of locomotion and consequently other important organismal functions such as foraging, predator avoidance, and ultimately survival and recruitment into the adult population. Results of this study also suggest the need to include rescue treatments in endocrine disruption studies that rely on goitrogens as reference for thyroid-mediated effects.

Various Possible Toxicants Involved in Thyroid Dysfunction: A Review

About 300 million people across the world suffer from thyroid gland dysfunction. Environmental factors play an important role in causation of autoimmune thyroid diseases in susceptible individuals. Genetics contributes to 70% of the risk. In order to reduce the risk, we need to understand the association of environmental agents with thyroid dysfunction. These factors are especially relevant for those at increased risk due to positive family history. The ideal study to see the impact of a thyroid toxicant consists of directly measuring the degree of exposure to toxicant in an individual with his thyroid status. Knowledge of various factors influencing thyroid dysfunction can help in interpreting the results of such studies in a better way. This article is an attempt to highlight the various possible toxicants affecting thyroid function so that adequate measures can be undertaken to control excessive exposure in future to reduce the prevalence of thyroid disorders.

Autoimmune thyroid disease in Colombian patients with systemic lupus erythematosus

OBJECTIVES

To determine the prevalence and the predictive factors of autoimmune hypothyroidism (AH) within a systemic lupus erythematosus (SLE) cohort and to analyse the current information concerning the prevalence and impact of autoimmune thyroid disease (AITD) and thyroid autoimmunity in patients with SLE.

METHODS

A total of 376 patients with SLE were assessed for the presence of the following: (i) confirmed AH, (ii) positive thy-roperoxidase/thyroglobulin antibodies [TPOAb/TgAb] without hypothyroidism, (iii) nonautoimmune hypothyroidism and (iv) SLE patients with neither. Multivariate analysis and a classification and regression tree model were used to analyse data. The current information was discussed through a systematic literature review (SLR).

RESULTS

In our cohort, the prevalence of confirmed AH was 12%. However, in euthyroid patients with SLE, TPOAb and TgAb were observed in 21% and 10%, respectively. Patients with confirmed AH were significantly older and had later age at onset of the disease. Smoking (adjusted odds ratio (AOR) 6·93, 95% CI 1·98-28·54, P = 0·004), Sjögren's Syndrome (SS) (AOR 23·2, 95% CI 1·89-359·53, P = 0·015) and positivity for anticyclic citrullinated peptide (anti-CCP) (AOR 10·35, 95% CI 1·04-121·26, P = 0·047) were associated with AH-SLE, regardless of gender and duration of the disease. Smoking and SS were confirmed as predictors of AH-SLE. In the SLR, the prevalence of AITD ranged from 1% to 60%. The factors associated with this polyautoimmunity were female gender, older age, smoking, certain autoantibodies, SS, and cutaneous and articular involvement.

CONCLUSIONS

AITD is frequent in SLE and does not affect the severity of SLE. Identified risk factors will assist clinicians in the search for AITD. Our results encourage smoke-free policies in patients with SLE.

Effects of nitrate on metamorphosis, thyroid and iodothyronine deiodinases expression in Bufo gargarizans larvae

Chinese toad (Bufo gargarizans) tadpoles were exposed to nitrate (10, 50 and 100mg/L NO3-N) from the beginning of the larval period through metamorphic climax. We examined the effects of chronic nitrate exposure on metamorphosis, mortality, body size and thyroid gland. In addition, thyroid hormone (TH) levels, type II iodothyronine deiodinase (Dio2) and type III iodothyronine deiodinase (Dio3) mRNA levels were also measured to assess disruption of TH synthesis. Results showed that significant metamorphic delay and mortality increased were caused in larvae exposed to 100mg/L NO3-N. The larvae exposed to 100mg/L NO3-N clearly exhibited a greater reduction in thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels. Moreover, treatment with NO3-N induced down-regulation of Dio2 mRNA levels and up-regulation of Dio3 mRNA levels, reflecting the disruption of thyroid endocrine. It seems that increased mass and body size may be correlated with prolonged metamorphosis. Interestingly, we observed an exception that exposure to 100mg/L NO3-N did not exhibit remarkable alterations of thyroid gland size. Compared with control groups, 100mg/L NO3-N caused partial colloid depletion in the thyroid gland follicles. These results suggest that nitrate can act as a chemical stressor inducing retardation in development and metamorphosis. Therefore, we concluded that the presence of high concentrations nitrate can influence the growth, decline the survival, impair TH synthesis and induce metamorphosis retardation of B. gargarizans larvae.

Correlation between urinary cadmium and thyroid hormones in outdoor workers exposed to urban stressors

OBJECTIVES

The aim of this study is to evaluate whether exposure to low concentrations of cadmium (Cd) can have effects on the thyroid hormone level of outdoor workers exposed to urban pollutants.

METHODS

The study was conducted on a final sample of 277 individuals (184 males and 93 females). The environmental monitoring of Cd was evaluated through the use of portable dosimeters, while the biological monitoring was achieved through the assessment of urinary Cd and thyroid hormones. The total sample was divided according to sex and task. The Pearson's correlation coefficient among the variables was calculated after subdivision on the basis of sex and task. The multiple linear regression was performed to take into account the major confounding factors.

RESULTS

Statistical tests showed a negative correlation between urinary Cd levels and free triiodothyronine and free thyroxine and a positive correlation between urinary Cd and thyroid-stimulating hormone levels.

CONCLUSIONS

Our early results seem to point out that occupational exposure to low concentrations of Cd present in urban air affects the thyroid hormone levels in exposed workers.

Correlation of Serum Thyroid Hormones Autoantibodies with Self-Reported Exposure to Thyroid Disruptors in a Group of Nonsegmental Vitiligo Patients

Vitiligo is a pigmentary disorder strongly associated with autoimmune thyroid disorders (ATD). Thyroid hormones antibodies (THAb) directed toward thyroxine (T3) and triiodothyronine (T4) (T3- and T4-Ab) are rare in the general population but are increased in individuals wit ATD and extrathyroid autoimmune disorders. Because it is known that alcohol, smoke, iodine, and some thyroid disruptors can elicit the appearance of ATD, the aim of our study was to evaluate possible correlation between T3- and T4-Ab expression and past toxic exposures in vitiligo patients. Seventy vitiligo patients were examined and self-reported exposure to thyroid disruptors (4,4'-isopropylidenediphenol, perchlorates, polychlorinated biphenyls (PCBs), hexachlorobenzene, resorcinol, dichlorodiphenyltrichloroethane, alachlor/amitriole, nitrate, thiocyanate, soy isoflavones), iodine intake, smoke, and alcohol consumption were investigated through standardized questionnaires. Immunoglobulin (Ig)M-T3-Ab, IgG-T3-Ab, IgM-T4-Ab,and IgG-T4-Ab were dosed by a radioimmunoprecipitation technique. Seventy-seven (95.7 %) patients had at least one type of THAb. Most of them had contemporarily both T3- and T4-Ab (50/70). We found a significant association between PCBs and T4-IgG-Ab (P = 0.039) and between food intake containing nitrate, thiocyanate, and soy isoflavones with (IgM + IgG)-T3-Ab (P = 0.041). Our study underlines a possible influence of diet and environment in vitiligo patients in eliciting THAb. Therefore, in the event of a positive exposure to thyroid disruptors, an evaluation of thyroid function might be useful to early detect possible associated thyroid autoantibodies such as THAb.

Tissue Distribution, Metabolism, and Excretion of 3,3'-Dichloro-4'-sulfooxy-biphenyl in the Rat

Polychlorinated biphenyls (PCBs) with less chlorine atoms exhibit a greater susceptibility to metabolism than their more-chlorinated counterparts. Following initial hydroxylation of these less-chlorinated PCBs, metabolic sulfation to form PCB sulfates is increasingly recognized as an important component of their toxicology. Because procedures for the quantitative analysis of PCB sulfates in tissue samples have not been previously available, we have now developed an efficient, LC-ESI-MS/MS-based protocol for the quantitative analysis of 4-PCB 11 sulfate in biological samples. This procedure was used to determine the distribution of 4-PCB 11 sulfate in liver, kidney, lung, and brain as well as its excretion profile following its intravenous administration to male Sprague-Dawley rats. Following initial uptake of 4-PCB 11 sulfate, its concentration in these tissues and serum declined within the first hour following injection. Although biliary secretion was detected, analysis of 24 h collections of urine and feces revealed recovery of less than 4% of the administered 4-PCB 11 sulfate. High-resolution LC-MS analysis of bile, urine, and feces showed metabolic products derived from 4-PCB 11 sulfate. Thus, 4-PCB 11 sulfate at this dose was not directly excreted in the urine but was instead redistributed to tissues and/or subjected to further metabolism.

Synergism between exposure to mercury and use of iodine supplements on thyroid hormones in pregnant women

OBJECTIVE

To evaluate the association between mercury exposure and thyroid-stimulating hormone (TSH), total triiodothyronine (TT3) and free thyroxine (FT4) levels during pregnancy as well as to explore if there is any synergic action between mercury and intake of iodine from different sources.

METHODS

The study population was 1407 pregnant women participating in the Spanish INMA birth cohort study. Total mercury concentrations were analyzed in cord blood. Thyroid hormones (THs) were measured in serum samples collected at 13.2±1.5 weeks of gestation. The association between mercury and TH levels was evaluated with multivariate linear regression models. Effect modification caused by iodine intake from supplements and diet was also evaluated.

RESULTS

The geometric means of TSH, TT3, FT4 and mercury were 1.1μU/L, 2.4nmol/L, 10.5pmol/L and 7.7μg/L, respectively. Mercury levels were marginally significantly associated with TT3 (β: -0.05; 95%CI: -0.10, 0.01), but were neither associated with TSH nor FT4. The inverse association between mercury and TT3 levels was stronger among the iodine supplement consumers (-0.08; 95%CI: -0.15, -0.02, interaction p-value=0.07). The association with FT4 followed the same pattern, albeit not significant.

CONCLUSION

Prenatal mercury exposure was inversely associated with TT3 levels among women who took iodine supplements during pregnancy. These results could be of public health concern, although further research is needed.

Metabolism and metabolites of polychlorinated biphenyls

Abstract The metabolism of polychlorinated biphenyls (PCBs) is complex and has an impact on toxicity, and thereby on the assessment of PCB risks. A large number of reactive and stable metabolites are formed in the processes of biotransformation in biota in general, and in humans in particular. The aim of this document is to provide an overview of PCB metabolism, and to identify the metabolites of concern and their occurrence. Emphasis is given to mammalian metabolism of PCBs and their hydroxyl, methylsulfonyl, and sulfated metabolites, especially those that persist in human blood. Potential intracellular targets and health risks are also discussed.

Comparison of the in vitro effects of TCDD, PCB 126 and PCB 153 on thyroid-restricted gene expression and thyroid hormone secretion by the chicken thyroid gland

The aim of this study was to compare the in vitro effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3',4,4',5-pentachlorobiphenyl (PCB 126; a coplanar PCB congener) and 2,2'4,4',5,5'-hexachlorobiphenyl (PCB153; non-coplanar PCB) on mRNA expression of thyroid-restricted genes, i.e. sodium iodide symporter (NIS), thyroid peroxidase (TPO) and thyroglobulin (TG), and thyroid hormone secretion from the thyroid gland of the laying chicken. Relative expression levels of NIS, TG and TPO genes and thyroxine (T4) and triiodothyronine (T3) secretion from the thyroidal explants were quantified by the real-time qPCR and RIA methods, respectively. In comparison with the control group, TCDD and PCB 126 significantly increased mRNA expression of TPO and TG genes. TCDD did not affect NIS mRNA levels, but PCB 126 decreased its expression. No effect of PCB 153 on the expression of these genes was observed. TCDD and PCB 126 significantly decreased T4 and T3 secretion. There was no significant effect of PCB 153 on these hormone secretions. In conclusion, the results obtained show that in comparison with non-coplanar PCB 153, TCDD and coplanar PCB 126 can directly affect thyroid hormone synthesis and secretion, and in consequence, they may disrupt the endocrine function of the thyroid gland of the laying chicken.

Chemical contamination and the thyroid

Industrial chemical contaminants have a variable impact on the hypothalamic-pituitary-thyroid axis, this depending both on their class and on confounding factors. Today, mounting evidence is pointing to the role of environmental factors, and specifically EDCs, in the current distressing upsurge in the incidence of thyroid disease. The unease is warranted. These substances, which are nowadays rife in our environments (including in foodstuffs), have been shown to interfere with thyroid hormone action, biosynthesis, and metabolism, resulting in disruption of tissue homeostasis and/or thyroid function. Importantly, based on the concept of the "nonmonotonic dose-response curve", the relationship between dose and effect has often been found to be nonlinear. Thus, small doses can induce unpredictable, adverse effects, one case being polychlorinated biphenyls (PCBs), of which congener(s) may centrally inhibit the hypothalamic-pituitary-thyroid axis, or dissociate thyroid receptor and selectively affect thyroid hormone signaling and action. This means that PCBs can act as agonists or antagonists at the receptor level, underlining the complexity of the interaction. This review highlights the multifold activity of chemicals demonstrated to cause thyroid disruption. It also represents a call to action among clinicians to undertake systematic monitoring of thyroid function and registering of the classes of EDs and additionally urges broader scientific collaborations to clarify these chemicals' molecular mechanisms of action, substances whose prevalence in our environments is disrupting not only the thyroid but all life on earth.

[Genetic and immune-toxicologic studies on abnormal thyroid functions in hospital employees exposed to cytostatic drugs]

INTRODUCTION

Environmental exposure to harmful chemicals may produce severe consequences.

AIM

The aim of the authors was to perform geno- and immune-toxicological monitoring in female employees occupationally exposed to cytostatic agents in hospitals and compare the findings to those obtained from controls.

METHOD

Altogether 642 women working in hospital who were occupationally exposed to cytostatic drugs and 262 control women participated in the study. Frequency of chromosome aberrations, immune phenotype and activation of lymphocytes, and the production of reactive oxygen-species in neutrophil granulocytes were determined.

RESULTS

Markedly higher number (n=39) of thyroid alterations was observed among exposed subjects as compared to controls (n=3). In persons with abnormal thyroid functions, the frequency of chromosome aberrations (3.69%) was significantly higher (3.69%) than in exposed subjects without thyroid alterations (2.43%) and in controls (1.70% and 1.60% in control subjects with and without thyroid alterations, respectively). Significantly increased ratio of helper T lymphocytes and decreased ratio of cytotoxic T cells and transferrin-receptor (CD71) expressing B cells were observed in exposed subjects having abnormal thyroid functions as compared to controls. In addition, the ratio of B cells, CD71 expressing T cells and production of reactive oxygen-intermediates was significantly decreased in exposed subjects with thyroid alterations in comparison to exposed subjects without thyroid alterations.

CONCLUSIONS

The results indicate increased geno- and immune-toxic effects among exposed subjects having thyroid alterations. Further data are needed to clearly establish the underlying pathophysiological mechanism of this finding.

The PI3K/Akt and ERK pathways elevate thyroid hormone receptor β1 and TRH receptor to decrease thyroid hormones after exposure to PCB153 and p,p'-DDE

PCBs and DDT cause the disturbance of thyroid hormone (TH) homeostasis in humans and animals. To test the hypothesis that the PI3K/Akt and MAPK pathways would play significant roles in TH imbalance caused by PCBs and DDT, Sprague-Dawley rats were dosed with PCB153 and p,p'-DDE intraperitoneally for 5 consecutive days, and human thyroid follicular epithelial (Nthy-ori 3-1 cell line) were treated with PCB153 and p,p'-DDE for different time. Results showed that serum total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3) and thyroid stimulating hormone (TSH) were decreased, whereas serum free triiodothyronine (FT3) and thyrotropin releasing hormone (TRH) were not changed. The PI3K/Akt and ERK pathways were activated in vivo and in vitro after the treatment with PCB153 and p,p'-DDE. Moreover, TH receptor β1 (TRβ1) was elevated after the activation of the PI3K/Akt pathway and was depressed after the inhibition of the PI3K/Akt pathway; TRH receptor (TRHr) was increased after the activation of the ERK pathway and was decreased after the inhibition of the ERK pathway. Though TH receptor α1 (TRα1) level was increased in the hypothalamus, TRα1 and TSHr were not influenced by the status of signaling pathways in in vitro study. Taken together, after exposure to PCB153 and p,p'-DDE, activated PI3K/Akt and ERK pathways disrupt the hypothalamic-pituitary-thyroid (HPT) axis via TRβ1 and TRHr and then decrease TH levels, and that would be a potential mechanism by which PCBs and DDT disturb TH homeostasis.

The influence of the environment on the development of thyroid tumors: a new appraisal

Most epidemiological studies concerning differentiated thyroid cancers (DTC) indicate an increasing incidence over the last two decades. This increase might be partially explained by the better access to health services worldwide, but clinicopathological analyses do not fully support this hypothesis, indicating that there are carcinogenetic factors behind this noticeable increasing incidence. Although we have undoubtedly understood the biology and molecular pathways underlying thyroid carcinogenesis in a better way, we have made very little progresses in identifying a risk profile for DTC, and our knowledge of risk factors is very similar to what we knew 30-40 years ago. In addition to ionizing radiation exposure, the most documented and established risk factor for DTC, we also investigated the role of other factors, including eating habits, tobacco smoking, living in a volcanic area, xenobiotics, and viruses, which could be involved in thyroid carcinogenesis, thus, contributing to the increase in DTC incidence rates observed.

Blood lead concentration and thyroid function during pregnancy: results from the Yugoslavia Prospective Study of Environmental Lead Exposure

BACKGROUND

Although maternal hypothyroidism increases the risk of adverse neonatal and obstetric outcomes as well as lower IQ in children, the environmental determinants of maternal thyroid dysfunction have yet to be fully explored.

OBJECTIVES

We aimed to examine associations between mid-pregnancy blood lead (BPb) and concomitant measures of thyroid function among participants in the Yugoslavia Prospective Study of Environmental Lead Exposure.

METHODS

As part of a population-based prospective study of two towns in Kosovo-one with high levels of environmental lead and one with low-women were recruited during the second trimester of pregnancy, at which time blood samples and questionnaire data were collected. We measured concentrations of BPb, free thyroxine (FT4), thyroid-stimulating hormone (TSH), and thyroid peroxidase antibodies (TPOAb) in archived serum samples.

RESULTS

Compared with women from the unexposed town, women from the exposed town had lower mean FT4 (0.91 ± 0.17 vs. 1.03 ± 0.16 ng/dL), higher mean TPOAb (15.45 ± 33.08 vs. 5.12 ± 6.38 IU/mL), and higher mean BPb (20.00 ± 6.99 vs. 5.57 ± 2.01 μg/dL). No differences in TSH levels were found. After adjustment for potential confounders, for each natural log unit increase in BPb, FT4 decreased by 0.074 ng/dL (95% CI: -0.10, -0.046 ng/dL), and the odds ratio for testing positive to TPOAb was 2.41 (95% CI: 1.53, 3.82). We found no association between BPb and TSH.

CONCLUSIONS

Prolonged lead exposure may contribute to maternal thyroid dysfunction by stimulating autoimmunity to the thyroid gland.

High prevalence of maternal hypothyroidism despite adequate iodine status in Indian pregnant women in the first trimester

BACKGROUND

Iodine requirements are increased during pregnancy to maintain maternal and fetal euthyroidism. There have been recent improvements in iodized salt coverage in India, but whether iodized salt is sufficient to sustain iodine requirements during pregnancy remains uncertain. Our aims were to measure thyroid status in first trimester pregnant women in southern India and assess potential determinants of thyroid function, including iodine status, thyroid autoimmunity, dietary patterns, body weight, and anemia.

METHODS

This was a cross-sectional study among 334 pregnant women of ≤ 14 weeks' gestation, in Bangalore, India. We measured anthropometrics, urinary iodine concentration (UIC), maternal thyroid volume (by ultrasound), and thyroid function. We applied a thyrotropin (TSH) upper limit of 2.5 mIU/L to classify thyroid insufficiency. Using a questionnaire, we obtained sociodemographic and dietary data, obstetric history, and use of iodized salt and iodine supplements.

RESULTS

Among the women, the mean (standard deviation) gestational age was 10.3 (2.5) weeks, 67% were nulliparous, 21% were vegetarian, 19% were anemic, and 23% were overweight or obese. Iodized salt was used by 98% of women, and they were iodine sufficient: median UIC (range) was 184.2 μg/L (8.1-1152 μg/L) and all had a normal thyroid volume. However, 18% of the women had thyroid insufficiency: 3.7% had overt hypothyroidism (83% with positive TPO-Ab), 9.2% had subclinical hypothyroidism, and 5.2% had hypothyroxinemia. Women consuming vegetarian diets did not have significantly lower iodine intakes or higher risk of hypothyroidism than those consuming mixed diets, but overweight/obesity and anemia predicted thyroid insufficiency.

CONCLUSION

In this urban population of southern India, pregnant women have adequate iodine status in the first trimester. Despite this, many have thyroid insufficiency, and the prevalence of overt hypothyroidism is more than fivefold higher than reported in other iodine sufficient populations of pregnant women.

Genetic and non-iodine-related factors in the aetiology of nodular goitre

Genetic and a large number of environmental non-iodine-related factors play a role in the cause of nodular goitre. Most evidence for the influence of genetic and environmental factors in the cause of goitre is from cross-sectional, population-based studies. Only a few studies have included prospective data on risk factors for nodular goitre, although few prospective data are available on the effect of iodine and tobacco smoking on goitre development. Goitre is not one single phenotype. Many epidemiological studies do not distinguish diffuse from nodular goitre, as the investigated parameter is often thyroid volume or frequency with increased thyroid volume. Moreover, information on the presence and effect of gene-environment, gene-gene, and environment-environment effect modifications is limited. Thus, firm conclusions about the relative contributions and causality of the investigated risk factors should be made with caution. Smoking seems to be an established risk factor for nodular goitre, possibly with effect modification from iodine intake, as the risk associated with smoking is smaller or absent in areas with sufficient iodine intake. The use of oral contraceptives might have protective effects against goitre, and childbirth is an increased risk factor for goitre in areas with non-optimal iodine intake. Insulin resistance is a recently investigated risk factor, and the risk of goitre may be reversible with metformin treatment. Iodine remains the major environmental risk factor for nodular goitre.

Biomarkers of nutrition for development--iodine review

The objective of the Biomarkers of Nutrition for Development (BOND) project is to provide state-of-the-art information and service with regard to selection, use, and interpretation of biomarkers of nutrient exposure, status, function, and effect. Specifically, the BOND project seeks to develop consensus on accurate assessment methodologies that are applicable to researchers (laboratory/clinical/surveillance), clinicians, programmers, and policy makers (data consumers). The BOND project is also intended to develop targeted research agendas to support the discovery and development of biomarkers through improved understanding of nutrient biology within relevant biologic systems. In phase I of the BOND project, 6 nutrients (iodine, vitamin A, iron, zinc, folate, and vitamin B-12) were selected for their high public health importance because they typify the challenges faced by users in the selection, use, and interpretation of biomarkers. For each nutrient, an expert panel was constituted and charged with the development of a comprehensive review covering the respective nutrient's biology, existing biomarkers, and specific issues of use with particular reference to the needs of the individual user groups. In addition to the publication of these reviews, materials from each will be extracted to support the BOND interactive Web site (http://www.nichd.nih.gov/global_nutrition/programs/bond/pages/index.aspx). This review represents the first in the series of reviews and covers all relevant aspects of iodine biology and biomarkers. The article is organized to provide the reader with a full appreciation of iodine's background history as a public health issue, its biology, and an overview of available biomarkers and specific considerations for the use and interpretation of iodine biomarkers across a range of clinical and population-based uses. The review also includes a detailed research agenda to address priority gaps in our understanding of iodine biology and assessment.

The association between perchlorate and thiocyanate exposure and thyroid function in first-trimester pregnant Thai women

CONTEXT

Thyroid hormone is critical for fetal neurodevelopment. Perchlorate and thiocyanate decrease thyroidal iodine uptake by competitively inhibiting the sodium/iodide symporter. It is clear that perchlorate and thiocyanate anions can influence thyroid function. However, as pollutants in the environment, their impact is conflicting.

OBJECTIVE

The objective was to determine the effects of environmental perchlorate and/or thiocyanate exposure on thyroid function in first-trimester pregnant women.

DESIGN AND PATIENTS

A cross-sectional study was conducted in 200 pregnant Thai women with a gestational age of 14 weeks or less.

MEASURES

Urinary iodide, perchlorate, thiocyanate, and serum thyroid function tests were measured.

RESULTS

The women were aged 28.6 ± 6.1 years and the mean gestational age was 9.6 ± 2.7 weeks. Median urinary iodide, perchlorate, and thiocyanate concentrations were 153.5 μg/L, 1.9 μg/L, and 510.5 μg/L, respectively. Using Spearman's rank correlation analyses, there were positive correlations between serum TSH and urine perchlorate to creatinine (r = 0.20, P = .005) and TSH and thiocyanate to creatinine ratios (r = 0.22, P = .001). There were negative correlations between free T4 and the perchlorate to creatinine ratio (r = -0.18, P = .01) and free T4 and the thiocyanate to creatinine ratio (r = -0.19, P = .008). In multivariate analyses adjusting for log thiocyanate to creatinine ratio, log iodide to creatinine ratio, and gestational age, log perchlorate to creatinine ratio was positively associated with log TSH (P = .002) and inversely associated with log free T4 (P = .002). Log thiocyanate to creatinine ratio was a significant positive predictor of log TSH (P = .02) in women with a urine iodide level of less than 100 μg/L.

CONCLUSIONS

Low-level environmental exposure to perchlorate and thiocyanate is common in Thailand. Low-level exposure to perchlorate is positively associated with TSH and negatively associated with free T4 in first-trimester pregnant women using multivariate analyses. In multivariate analyses, thiocyanate exposure is also positively associated with TSH in a subgroup of pregnant women with low iodine excretion.

Mechanisms of crosstalk between endocrine systems: regulation of sex steroid hormone synthesis and action by thyroid hormones

Thyroid hormones (THs) are well-known regulators of development and metabolism in vertebrates. There is increasing evidence that THs are also involved in gonadal differentiation and reproductive function. Changes in TH status affect sex ratios in developing fish and frogs and reproduction (e.g., fertility), hormone levels, and gonad morphology in adults of species of different vertebrates. In this review, we have summarized and compared the evidence for cross-talk between the steroid hormone and thyroid axes and present a comparative model. We gave special attention to TH regulation of sex steroid synthesis and action in both the brain and gonad, since these are important for gonad development and brain sexual differentiation and have been studied in many species. We also reviewed research showing that there is a TH system, including receptors and enzymes, in the brains and gonads in developing and adult vertebrates. Our analysis shows that THs influences sex steroid hormone synthesis in vertebrates, ranging from fish to pigs. This concept of crosstalk and conserved hormone interaction has implications for our understanding of the role of THs in reproduction, and how these processes may be dysregulated by environmental endocrine disruptors.

Occupation and thyroid cancer

Numerous occupational and environmental exposures have been shown to disrupt thyroid hormones, but much less is known about their relationships with thyroid cancer. Here we review the epidemiology studies of occupations and occupational exposures and thyroid cancer incidence to provide insight into preventable risk factors for thyroid cancer. The published literature was searched using the Web of Knowledge database for all articles through August 2013 that had in their text 'occupation' 'job' 'employment' or 'work' and 'thyroid cancer'. After excluding 10 mortality studies and 4 studies with less than 5 exposed incident cases, we summarised the findings of 30 articles that examined thyroid cancer incidence in relation to occupations or occupational exposure. The studies were grouped by exposure/occupation category, study design and exposure assessment approach. Where available, gender-stratified results are reported. The most studied (19 of 30 studies) and the most consistent associations were observed for radiation-exposed workers and healthcare occupations. Suggestive, but inconsistent, associations were observed in studies of pesticide-exposed workers and agricultural occupations. Findings for other exposures and occupation groups were largely null. The majority of studies had few exposed cases and assessed exposure based on occupation or industry category, self-report, or generic (population-based) job exposure matrices. The suggestive, but inconsistent findings for many of the occupational exposures reviewed here indicate that more studies with larger numbers of cases and better exposure assessment are necessary, particularly for exposures known to disrupt thyroid homeostasis.

Systematic analysis of the relationship between standardized biological levels of polychlorinated biphenyls and thyroid function in pregnant women and newborns

The impact polychlorinated biphenyl (PCB) exposure on thyroid status in pregnant women and newborns was investigated in various epidemiological studies, but findings show inconsistencies, and differences in biological indicators of exposure between studies limits comparison of results. The aim of this research was to use a procedure previously developed to standardize PCB biological concentration data between published studies to perform a systematic analysis of associations between PCB exposure and thyroid hormones (THs) (total and free T3 and T4) or thyroid stimulating hormone (TSH) in pregnant women and newborns. Biological concentrations from nineteen studies were expressed in total PCB equivalent per kg of lipids in maternal plasma (μg PCBMPEQ kg(-1) lipids). Systematic analysis of the "standardized biological concentration-thyroid parameters" relationship was conducted through the application of methodological criteria in both pregnant women and newborns. Standardization of PCB levels and application of methodological criteria led to assign higher confidence to ten of the reviewed studies. Among the retained studies in pregnant women, only one reported a significant association between PCBs and total T3 levels, but no association were observed when circulating TSH and free T4 levels were used to assess thyroid function. Regarding the association between prenatal PCB exposure and thyroid status in newborns, a lack of significant association was consistently obtained in the retained studies assigned an overall high confidence. The weight of evidence of a significant impact of PCB exposure on TSH and TH levels at the described biological levels in pregnant women and newborns (mean<1000 μg PCBMPEQ kg(-1) lipids) appears low according to this systematical analysis.

Modulation of lipocalin-type prostaglandin D2 synthase expression in catfish seminal vesicles by thyroid disrupting agents and hormones

Thyroid hormones play crucial role in several biological processes including reproduction. Disruption of normal thyroid status by environmental contaminants can cause severe impairment in reproductive functions. In our previous study, we reported down-regulation of a protein in seminal vesicular fluid of air-breathing catfish, Clarias gariepinus during experimentally induced hyperthyroidism. N-terminal amino acid sequence analysis followed by search in sequence database denoted it to be lipocalin-type prostaglandin D2 synthase (ptgds-b). In the present study, we cloned full-length cDNA of ptgds-b based on the N-terminal amino acid sequence. Surprisingly, Northern blot as well as RT-PCR analysis demonstrated the presence of ptgds-b transcript predominantly in seminal vesicles and developing testis. Further, ptgds-b mRNA significantly decreased in seminal vesicles following L-thyroxine overdose while there was an increased expression of ptgds-b after depletion of thyroid hormone by thiourea and withdrawal of the treatments reverted this effect. Treatment of catfish with human chorionic gonadotropin and estradiol significantly reduced ptgds-b expression. Taken together, we report ptgds-b as a thyroid hormone regulated protein in the seminal vesicles in addition to gonadotropin and estradiol. Further studies might explain the exclusive presence of ptgds-b in seminal vesicles and developing testis yet present data evaluated it as a putative biomarker for thyroid hormone disruption.

Impact of body mass index on thyroid functions in Indian children

OBJECTIVE

There is controversy about the relation of thyroid functions and body mass index. The present study was aimed to assess the relationship between thyroid function and body mass index in Indian school children.

DESIGN

Population survey.

PATIENTS

Data were collected from 25 schools in 19 cities across five different geographical zones of India. Children, who consented, were evaluated for anthropometry and blood tests. Children were categorized as overweight and obese based on standard BMI criteria.

MEASUREMENTS

Serum samples were analysed for free T3, free T4, TSH and anti-TPO antibodies.

RESULTS

A total of 13,691 children in the age group of 5-18 years formed the study population. The mean age and mean BMI were 11·9 ± 3·0 years and 18·48 ± 3·89 kg/m² respectively. Among these, 2119 (15·5%) children were overweight and 536 (3·9%) were obese. Subclinical hypothyroidism was present in 943 (6·9%) children.FT3 and TSH levels increased and FT4 levels decreased with increasing BMI in euthyroid boys and girls. Prevalence of SCH was significantly higher in obese/overweight children (9·0%, vs 6·5%; P = 0·034) as compared with normal BMI children.

CONCLUSIONS

Serum FT3 and TSH were positively while FT4 was negatively associated with BMI in apparently healthy euthyroid children.

Maternal hypothyroxinemia and effects on cognitive functioning in childhood: how and why?

Exposure to maternal hypothyroxinemia during pregnancy, which is characterized by low free T4 but normal thyroid-stimulating hormone (TSH) levels, can negatively affect the foetus. This review provides an overview of present findings concerning the association between maternal hypothyroxinemia during pregnancy and childhood cognitive functioning. Possible causes of maternal hypothyroxinemia and potential mechanisms underlying this association are also discussed. Clinical and epidemiological studies suggest that maternal hypothyroxinemia in the first half of pregnancy but not later in pregnancy impairs cognitive development in infancy and childhood. Animal models confirm that the first half of pregnancy may constitute a sensitive period in which maternal hypothyroxinemia alters neurogenesis and causes neuronal migration errors in the developing foetal brain. However, observational studies in humans cannot demonstrate causality of the association between hypothyroxinemia and neurodevelopment. In the only completed randomized trial of antenatal thyroid screening and subsequent levothyroxine treatment of mild maternal subclinical thyroid dysfunction, including hypothyroxinemia, the interventions did not affect offspring intelligence quotient (IQ). More randomized trials are needed investigating whether screening for hypothyroxinemia and its treatment earlier in the first trimester of pregnancy can improve child cognitive functioning or prevent neurodevelopmental changes. Long-term observational studies should identify molecular, neuroanatomical and neurophysiological factors involved in the association between maternal hypothyroxinemia and offspring cognitive functioning. Information on such mechanisms can be used for the development of innovative prevention and intervention studies that address maternal hypothyroxinemia and its potential consequences.

Effects of complex organohalogen contaminant mixtures on thyroid homeostasis in hooded seal (Cystophora cristata) mother-pup pairs

Many lipid-soluble and phenolic compounds present in the complex mixture of orgaohalogen contaminants (OHCs) that arctic wildlife is exposed to have the ability to interfere with the thyroid hormone (TH) system. The aim of this study was to identify compounds that might interfere with thyroid homeostasis in 14 nursing hooded seal (Cystophora cristata) mothers and their pups (1-4d old) sampled in the West Ice in March 2008. Multivariate modelling was used to assess the potential effects of measured plasma levels of OHCs on circulating TH levels of the measured free (F) and total (T) levels of triidothyrine (T3) and thyroxine (T4). Biological factors were important in all models (e.g. age and sex). In both mothers and pups, TT3:FT3 ratios were associated with α- and β-hexachlorocyclohexane (HCH), ortho-PCBs, chlordanes and DDTs. The similarities between the modelled TT3:FT3 responses to OHC levels in hooded seal mothers and pups most probably reflects similar exposure patterns, but could also indicate interconnected TH responses. There were some differences in the modelled TH responses of mothers and pups. Most importantly, the negative relationships between many OH-PCBs (particularly 3'-OH-CB138) and TT3:FT3 ratio and the positive relationships between TT4:FT4 ratios and polybrominated diphenyl ether [PBDE]-99, -100 and 4-OH-CB107 in pups, which was not found in mothers. Although statistical associations are not evidence per se of biological cause-effect relationships, the results suggest that thyroid homeostasis is affected in hooded seals, and that the inclusion of the fullest possible OHC mixture is important when assessing TH related effects in wildlife.

Endocrine effects of tobacco smoke exposure during lactation in weaned and adult male offspring

Children from pregnant smokers show more susceptibility to develop obesity in adult life. Previously, we failed to demonstrate a program for obesity in rat offspring only when the mothers were exposed to tobacco smoke during lactation. Here, we studied the short- and long-term effects of smoke exposure (SE) to both dams and their pups during lactation on endocrine and metabolic parameters. For this, we designed an experimental model where nursing rats and their pups were divided into two groups: SE group, exposed to smoke in a cigarette smoking machine (four times/day, from the third to the 21st day of lactation), and group, exposed to filtered air. Pups were killed at 21 and 180 days. At weaning, SE pups showed lower body weight (7%), length (5%), retroperitoneal fat mass (59%), visceral adipocyte area (60%), and higher subcutaneous adipocyte area (95%) with hypoinsulinemia (-29%), hyperthyroxinemia (59%), hypercorticosteronemia (60%), and higher adrenal catecholamine content (+58%). In adulthood, SE offspring showed higher food intake (+10%), body total fat mass (+50%), visceral fat mass (retroperitoneal: 55%; mesenteric: 67%; and epididymal: 55%), and lower subcutaneous adipocyte area (24%) with higher serum glucose (11%), leptin (85%), adiponectin (1.4-fold increase), total triiodothyronine (71%), free thyroxine (57%), TSH (36%), triglycerides (65%), VLDL cholesterol (+66%), and HDL cholesterol (91%) levels and lower corticosteronemia (41%) and adrenal catecholamine content (57%). Our present findings suggest that tobacco SE to both dams and their pups during lactation causes malnutrition in early life that programs for obesity and hormonal and metabolic disturbances in adulthood, only if the pups are submitted to the same smoke environment as the mother.

Sulfated metabolites of polychlorinated biphenyls are high-affinity ligands for the thyroid hormone transport protein transthyretin

BACKGROUND

The displacement of l-thyroxine (T4) from binding sites on transthyretin (TTR) is considered a significant contributing mechanism in polychlorinated biphenyl (PCB)-induced thyroid disruption. Previous research has discovered hydroxylated PCB metabolites (OH-PCBs) as high-affinity ligands for TTR, but the binding potential of conjugated PCB metabolites such as PCB sulfates has not been explored.

OBJECTIVES

We evaluated the binding of five lower-chlorinated PCB sulfates to human TTR and compared their binding characteristics to those determined for their OH-PCB precursors and for T4.

METHODS

We used fluorescence probe displacement studies and molecular docking simulations to characterize the binding of PCB sulfates to TTR. The stability of PCB sulfates and the reversibility of these interactions were characterized by HPLC analysis of PCB sulfates after their binding to TTR. The ability of OH-PCBs to serve as substrates for human cytosolic sulfotransferase 1A1 (hSULT1A1) was assessed by OH-PCB-dependent formation of adenosine-3',5'-diphosphate, an end product of the sulfation reaction.

RESULTS

All five PCB sulfates were able to bind to the high-affinity binding site of TTR with equilibrium dissociation constants (Kd values) in the low nanomolar range (4.8-16.8 nM), similar to that observed for T4 (4.7 nM). Docking simulations provided corroborating evidence for these binding interactions and indicated multiple high-affinity modes of binding. All OH-PCB precursors for these sulfates were found to be substrates for hSULT1A1.

CONCLUSIONS

Our findings show that PCB sulfates are high-affinity ligands for human TTR and therefore indicate, for the first time, a potential relevance for these metabolites in PCB-induced thyroid disruption.