Interactions of halogenated industrial chemicals with transthyretin and effects on thyroid hormone levels in vivo

Organochlorine pesticides and risk of papillary thyroid cancer in U.S. military personnel: a nested case-control study

BACKGROUND

The effects of organochlorine pesticide (OCP) exposure on the development of human papillary thyroid cancer (PTC) are not well understood. A nested case-control study was conducted with data from the U.S. Department of Defense Serum Repository (DoDSR) cohort between 2000 and 2013 to assess associations of individual OCPs serum concentrations with PTC risk.

METHODS

This study included 742 histologically confirmed PTC cases (341 females, 401 males) and 742 individually-matched controls with pre-diagnostic serum samples selected from the DoDSR. Associations between categories of lipid-corrected serum concentrations of seven OCPs and PTC risk were evaluated for classical PTC and follicular PTC using conditional logistic regression, adjusted for body mass index category and military branch to compute odds ratios (OR) and 95% confidence intervals (CIs). Effect modification by sex, birth cohort, and race was examined.

RESULTS

There was no evidence of associations between most of the OCPs and PTC, overall or stratified by histological subtype. Overall, there was no evidence of an association between hexachlorobenzene (HCB) and PTC, but stratified by histological subtype HCB was associated with significantly increased risk of classical PTC (third tertile above the limit of detection (LOD) vs. Collapse

Key Words

• Hexachlorobenzene
• Hexachlorocyclohexane
• Organochlorine pesticides
• Papillary thyroid cancer

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MESH Headings

• Male
• Humans
• Female
• Military Personnel
• Thyroid Cancer, Papillary/epidemiology
• Hexachlorobenzene
• Case-Control Studies
• Pesticides
• Hydrocarbons, Chlorinated
• Thyroid Neoplasms/chemically induced
• Thyroid Neoplasms/epidemiology
• Hexachlorocyclohexane

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Grants

• R01ES020361 NIH HHS
• R01ES020361 NIH HHS
• National Institutes of Health
• Murtha Cancer Center Research Program
• Oak Ridge Associated Universities
• National Cancer Institute Intramural Research Program

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Affiliation(s)

Jennifer A Rusiecki Department of Preventive Medicine and Biostatistics, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Room E-2009, Bethesda, MD, 20814, USA.
Jordan McAdam Murtha Cancer Center Research Program, 4494 North Palmer Road, Bethesda, MD, USA Henry M. Jackson Foundation for the Advancement of Military Medicine, 1401 Rockville Pike, Rockville, MD, USA
Hristina Denic-Roberts Department of Preventive Medicine and Biostatistics, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Room E-2009, Bethesda, MD, 20814, USA Oak Ridge Institute for Science and Education (ORISE), Oak Ridge, TN, USA
Andreas Sjodin Division of Laboratory Sciences, Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA
Mark Davis Division of Laboratory Sciences, Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA
Richard Jones Division of Laboratory Sciences, Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA
Thanh D Hoang Division of Endocrinology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
Mary H Ward Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, MD, USA
Shuangge Ma Department of Biostatistics, Yale School of Public Health, New Haven, CT, USA
Yawei Zhang Department of Environmental Health Sciences, Yale School of Public Health, New Haven, CT, USA Department of Cancer Prevention and Control, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China

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Human transthyretin binding affinity of halogenated thiophenols and halogenated phenols: An in vitro and in silico study

Serious harmful effects have been reported for thiophenols, which are widely used industrial materials. To date, little information is available on whether such chemicals can elicit endocrine-related detrimental effects. Herein the potential binding affinity and underlying mechanism of action between human transthyretin (hTTR) and seven halogenated-thiophenols were examined experimentally and computationally. Experimental results indicated that the halogenated-thiophenols, except for pentafluorothiophenol, were powerful hTTR binders. The differentiated hTTR binding affinity of halogenated-thiophenols and halogenated-phenols were observed. The hTTR binding affinity of mono- and di-halo-thiophenols was higher than that of corresponding phenols; while the opposite relationship was observed for tri- and penta-halo-thiophenols and phenols. Our results also confirmed that the binding interactions were influenced by the degree of ligand dissociation. Molecular modeling results implied that the dominant noncovalent interactions in the molecular recognition processes between hTTR and halogenated-thiophenols were ionic pair, hydrogen bonds and hydrophobic interactions. Finally, a model with acceptable predictive ability was developed, which can be used to computationally predict the potential hTTR binding affinity of other halogenated-thiophenols and phenols. Taken together, our results highlighted that more research is needed to determine their potential endocrine-related harmful effects and appropriate management actions should be taken to promote their sustainable use.

Longitudinal Study of Thyroid Hormones between Conventional and Organic Farmers in Thailand

Many pesticides are endocrine-disrupting chemicals that can interfere with hormone levels. This study aimed to assess the longitudinal impact of exposure to pesticides on thyroid hormone levels, including Thyroid Stimulating Hormone (TSH), Free Triiodothyronine (FT3), Free Thyroxine (FT4), Triiodothyronine (T3), and Thyroxine (T4). Both conventional (i.e., pesticide using) and organic farmers were interviewed using questionnaires, and blood samples were collected at 7-9 a.m. to determine thyroid hormone levels for four rounds, with a duration of eight months between each round. A linear mixed model of the natural log of the individual hormone levels used random intercepts for subjects while controlling gender, baseline age, and body mass index (BMI) was used to compare between conventional and organic farmers or the impact of cumulative days of spraying insecticides, herbicides or fungicides. The estimated marginal means of the thyroid hormone levels (TSH, FT3, T3, and T4) estimated from the linear mixed models were significantly higher among the conventional farmers than organic farmers. As cumulative spray days of insecticide, herbicide or fungicide increased, TSH and FT3 increased significantly. FT4 decreased significantly as cumulative spray days of insecticide or fungicide increased. These findings suggest that the insecticides, herbicides, and fungicides sprayed by conventional farmers exert endocrine-disrupting activities, altering the hypothalamic-pituitary-thyroid (HPT) axis homeostasis.

Binding interactions of halo-benzoic acids, halo-benzenesulfonic acids and halo-phenylboronic acids with human transthyretin

The anionic form-dependent binding interaction of halo-phenolic substances with human transthyretin (hTTR) has been observed previously. This indicates that ionizable compounds should be the primary focus in screening potential hTTR disruptors. Here, the potential binding potency of halo-benzoic acids, halo-benzenesulfonic acids/sulfates and halo-phenylboronic acids with hTTR was determined and analyzed by competitive fluorescence displacement assay integrated with computational methods. The laboratorial results indicated that the three test groups of model compounds exhibited a distinct binding affinity to hTTR. All the tested halo-phenylboronic acids, some of the tested halo-benzoic acids and halo-benzenesulfonic acids/sulfates were shown to be inactive with hTTR. Other halo-benzoic acids and halo-benzenesulfonic acids/sulfates were moderate and/or weak hTTR binders. The binding affinity of halo-benzoic acids and halo-benzenesulfonic acids/sulfates with hTTR was similar. The low distribution ability of the model compounds from water to hTTR may be the reason why they exhibited the binding potency observed with hTTR. By introducing other highly hydrophobic compounds, we observed that the binding affinity between compounds and hTTR increased with increasing molecular hydrophobicity. Those results indicated that the highly hydrophobic halo-benzoic acids and halo-benzenesulfonic acids/sulfates may be high-priority hTTR disruptors. Finally, a binary classification model was constructed employing three predictive variables. The sensitivity (S_n), specificity (S_p), predictive accuracy (Q) values of the training set and validation set were >0.83, indicating that the model had good classification performance. Thus, the binary classification model developed here could be used to distinguish whether a given ionizable compound is a potential hTTR binder or not.

Assessment of the endocrine-disrupting effects of diethyl phosphate, a nonspecific metabolite of organophosphorus pesticides, by in vivo and in silico approaches

Organophosphorus pesticides (OPs) remain one of the most commonly used pesticides, and their detection rates and residues in agricultural products, foods and environmental samples have been underestimated. Humans and environmental organisms are at high risk of exposure to OPs. Most OPs can be degraded and metabolized into dialkyl phosphates (DAPs) in organisms and the environment, and can be present in urine as biomarkers for exposure to OPs, of which diethyl phosphate (DEP) is a high-exposure metabolite. Epidemiological and cohort studies have found that DAPs are associated with endocrine hormone disorders, especially sex hormone disorders and thyroid hormone disorders, but there has been no direct causal evidence to support these findings. Our study explored the effects of chronic exposure to DEP on endocrine hormones and related metabolic indicators in adult male rats at actual doses that can be reached in the human body. The results showed that chronic exposure to DEP could cause thyroid-related hormone disorders in the serum of rats, causing symptoms of hyperthyroidism in rats, and could also lead to abnormal expression of thyroid hormone-related genes in the rat liver. However, DEP exposure did not seem to affect serum sex hormone levels, spermatogenesis or sperm quality in rats. The molecular interactions between DEP and thyroid hormone-related enzymes/proteins were investigated by molecular docking and molecular dynamics methods in silico. It was found that DEP could strongly interact with thyroid hormone biosynthesis, blood transport, receptor binding and metabolism-related enzymes/proteins, interfering with the production and signal regulation of thyroid hormones. In vivo and in silico experiments showed that DEP might be a potential thyroid hormone-disrupting chemical, and therefore, we need to be more cautious and rigorous regarding organophosphorus chemical exposure.

Comparative thyroid disruption by o,p'-DDT and p,p'-DDE in zebrafish embryos/larvae

1,1-Trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl) ethane (o,p'-DDT) and 1,1-dichloro-2,2-bis (p-chlorophenyl)-ethylene (p,p'-DDE) cause thyroid disruption, but the underlying mechanisms of these disturbances in fish remain unclear. To explore the potential mechanisms of thyroid dysfunction caused by o,p'-DDT and p,p'-DDE, thyroid hormone and gene expression levels in the hypothalamic-pituitary-thyroid (HPT) axis were measured, and the developmental toxicity were recorded in zebrafish larvae. Zebrafish embryos/larvae were exposed to o,p'-DDT (0, 0.28, 2.8, and 28 nM; or 0, 0.1, 1, and 10 μg/L) and p,p'-DDE (0, 1.57, 15.7, and 157 nM; or 0, 0.5, 5, and 50 μg/L) for 7 days. The genes related to thyroid hormone synthesis (crh, tshβ, tg, nis and tpo) and thyroid development (nkx2.1 and pax8) were up-regulated in both the o,p'-DDT and p,p'-DDE exposure groups. Zebrafish embryos/larvae exposed to o,p'-DDT showed significantly increased total whole-body T4 and T3 levels, with the expression of ugt1ab and dio3 being significantly down-regulated. However, the p,p'-DDE exposure groups showed significantly lowered whole-body total T4 and T3 levels, which were associated with up-regulation and down-regulation expression of the expression of dio2 and ugt1ab, respectively. Interestingly, the ratio of T3 to T4 was significantly decreased in the o,p'-DDT (28 nM) and p,p'-DDE (157 nM) exposure groups, suggesting an impairment of thyroid function. In addition, reduced survival rates and body lengths and increased malformation rates were recorded after treatment with either o,p'-DDT or p,p'-DDE. In summary, our study indicates that the disruption of thyroid states was different in response to o,p'-DDT and p,p'-DDE exposure in zebrafish larvae.

Establishment of cumulative assessment groups of pesticides for their effects on the thyroid

Cumulative assessment groups of pesticides have been established for two specific effects on the thyroid: firstly hypothyroidism, and secondly parafollicular cell (C-cell) hypertrophy, hyperplasia and neoplasia. Sources of uncertainties resulting from the methodological approach and from the limitations in available data and scientific knowledge have been identified and considered. This report supports the publication of a scientific report on cumulative risk assessment to pesticides affecting the thyroid, in which all uncertainties identified for either the exposure assessment or the establishment of the cumulative assessment groups are incorporated into a consolidated risk characterisation.

Comparative Overview of the Mechanisms of Action of Hormones and Endocrine Disruptor Compounds

Endocrine Disruptor Compounds (EDCs) are synthetic or natural molecules in the environment that promote adverse modifications of endogenous hormone regulation in humans and/or in wildlife animals. In the present paper, we review the potential mechanisms of EDCs and point out the similarities and differences between EDCs and hormones. There was only one mechanism, out of nine identified, in which EDCs acted like hormones (i.e. binding and stimulated hormone receptor activity). In the other eight identified mechanisms of action, EDCs exerted their effects either by affecting endogenous hormone concentration, or its availability, or by modifying hormone receptor turn over. This overview is intended to classify the various EDC mechanisms of action in order to better appreciate when in vitro tests would be valid to assess their risks towards humans and wildlife.

Interspecies Variation between Fish and Human Transthyretins in Their Binding of Thyroid-Disrupting Chemicals

Thyroid-disrupting chemicals (TDCs) are xenobiotics that can interfere with the endocrine system and cause adverse effects in organisms and their offspring. TDCs affect both the thyroid gland and regulatory enzymes associated with thyroid hormone homeostasis. Transthyretin (TTR) is found in the serum and cerebrospinal fluid of vertebrates, where it transports thyroid hormones. Here, we explored the interspecies variation in TDC binding to human and fish TTR (exemplified by Gilthead seabream ( Sparus aurata)). The in vitro binding experiments showed that TDCs bind with equal or weaker affinity to seabream TTR than to the human TTR, in particular, the polar TDCs (>500-fold lower affinity). Crystal structures of the seabream TTR-TDC complexes revealed that all TDCs bound at the thyroid binding sites. However, amino acid substitution of Ser117 in human TTR to Thr117 in seabream prevented polar TDCs from binding deep in the hormone binding cavity, which explains their low affinity to seabream TTR. Molecular dynamics and in silico alanine scanning simulation also suggested that the protein backbone of seabream TTR is more rigid than the human one and that Thr117 provides fewer electrostatic contributions than Ser117 to ligand binding. This provides an explanation for the weaker affinities of the ligands that rely on electrostatic interactions with Thr117. The lower affinities of TDCs to fish TTR, in particular the polar ones, could potentially lead to milder thyroid-related effects in fish.

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.

Incident thyroid disease in female spouses of private pesticide applicators

BACKGROUND

Little is known about modifiable risk factors for thyroid disease. Several pesticides have been implicated in thyroid disruption, but clinical implications are not clear.

OBJECTIVE

We assessed associations between pesticide use and other farm exposures and incident hypothyroidism and hyperthyroidism in female spouses of farmers in the Agricultural Health Study (AHS).

METHODS

We used Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals for risk of thyroid disease in 24,092 spouses who completed at least one follow-up questionnaire.

RESULTS

We identified 1627 hypothyroid and 531 hyperthyroid cases over 20 years of follow-up. The fungicides benomyl, maneb/mancozeb, and metalaxyl, the herbicide pendimethalin, and among those over 60 years of age the insecticides parathion and permethrin (applied to crops) were associated with elevated hypothyroidism risk, with HR ranging from 1.56-2.44. Conversely, the insecticide phorate, and the herbicides imazethapyr and metolachlor were associated with decreased risk (HR ranging 0.63-0.73), as were long-term farm residence and other farm-related activities (HR ranging 0.69-0.84). For hyperthyroidism, the insecticide diazinon, the fungicides maneb/mancozeb, and the herbicide metolachlor were associated with increased risk (HR ranging 1.35-2.01) and the herbicide trifluralin with decreased risk (HR: 0.57).

CONCLUSIONS

Several individual pesticides were associated with increased risk of hypothyroidism and hyperthyroidism, although some pesticides were associated with decreased risk. Some of the findings, specifically associations with fungicides, are consistent with results from an earlier analysis of prevalent diseases in AHS spouses.

Pesticide Use and Incident Hypothyroidism in Pesticide Applicators in the Agricultural Health Study

BACKGROUND

Though evidence suggests that some pesticides may have thyroid-disrupting properties, prospective studies of associations between specific pesticides and incident thyroid disease are limited.

OBJECTIVE

We evaluated associations between use of specific pesticides and incident hypothyroidism in private pesticide applicators in the Agricultural Health Study (AHS).

METHODS

Self-reported incident hypothyroidism ([Formula: see text] cases) was studied in relation to ever-use and intensity-weighted cumulative days of pesticide use at study enrollment. We estimated adjusted hazard ratios (HRs) and 95% confidence intervals (CI) using Cox proportional hazards models applied to 35,150 male and female applicators followed over 20 y. All models were stratified by state and education to meet proportional hazards assumptions ([Formula: see text] for age x covariate interactions). Models of pesticides that did not meet proportional hazards assumptions were stratified by median attained age (62 y).

RESULTS

Hypothyroidism risk was significantly increased with ever- vs. never-use of four organochlorine insecticides (aldrin, heptachlor, and lindane among participants with attained age [Formula: see text]; chlordane in all participants), four organophosphate insecticides (coumaphos in those [Formula: see text]; diazinon, dichlorvos, and malathion in all participants) and three herbicides (dicamba, glyphosate, and 2,4-D in all participants). HRs ranged from 1.21; 95% CI: 1.04, 1.41 (chlordane) to 1.54; 95% CI: 1.23, 19.4 (lindane in those [Formula: see text]). Hypothyroidism risk was greatest among those with higher intensity-weighted lifetime days of using chlordane, lindane, coumaphos (over age 62), diazinon, permethrin, and 2,4-D.

CONCLUSIONS

Our findings support associations between exposure to several pesticides and increased hypothyroidism risk. These findings are generally consistent with prior analyses of prevalent hypothyroidism in the AHS. https://doi.org/10.1289/EHP3194.

Thyroid-disrupting chemicals and brain development: an update

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

Association of in utero exposure to organochlorine pesticides with thyroid hormone levels in cord blood of newborns

Organochlorine pesticides (OCPs) had been widely used in agriculture and disease prevention from the 1940s-1960s. Currently, OCPs are raising global concerns due to their associated prevalent contamination and adverse health effects, such as endocrine disruption. Several epidemiological studies have explored the underlying association of OCPs on thyroid hormone (TH) status in adults and newborns, but the results of studies performed on newborns are often inconclusive. This exploratory study was conducted with the purpose of assessing the potential association of the prenatal exposure to OCPs with the concentrations of TH in the cord blood of newborns from China. Cord blood and information on demographic characteristics were collected from 115 newborns between November 2013 and June 2014. The exposure levels of 17 OCPs were measured with a gas chromatography/mass spectrometry, and TH levels including free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) were detected using electrochemiluminescence immunoassay methods. After adjusting for confounding factors (the age of pregnant mothers, education level, monthly household income, parity, and sex of the newborns), we found marginally significant inverse associations of cord plasma measurements of ∑hexachlorcyclohexanes (∑HCHs), 1,1-dichloro-2,2-di(4-chlorophenyl)ethylene (ρ,ρ'-DDE) and methoxychlor with FT4 levels, but not with FT3 and TSH levels. Moreover, higher cord plasma levels of aldrin, dieldrin, ∑dichlorodiphenyltrichloroethanes (∑DDTs), ∑Drins, and ∑OCPs were found to be related to the increase in cord plasma TSH levels after the adjustment for confounders. The results of this exploratory study indicate that in utero exposure to certain OCPs may affect TH status in newborns, and therefore, pose potential effects on early human development. Further research, with larger sample sizes, should be conducted to confirm these findings.

Effects of sublethal Abamectin exposure on some hormonal profiles and testicular histopathology in male albino rats and the possible ameliorative role of Eruca sativa

The ameliorative role of Eruca sativa on some hormonal profile and testicular histopathology in male albino rats exposed to a sublethal dose of 1 mg/kg body weight (b.wt). Abamectin (Crater 3.37% EC) was evaluated. Eighteen male albino rats were divided into three groups: control group, Abamectin-treated group, and Abamectin + E. sativa-treated group. Rats of the second group were orally administrated 1 mg/kg b.wt. of Abamectin, the third group received a mixture of sublethal oral dose of Abamectin (1 mg/kg b.wt.) and E. sativa suspension (5 g/kg b.wt.) every 48 h for 28 days. At the end of the study, blood samples were collected from all groups to measure some hormonal parameters; also, rats were dissected and tissue sections from the testes were prepared and stained with hematoxylin and eosin for examination under light microscope. The results of the present study revealed a disturbance in the hormonal parameters and some testicular histopathological changes. In addition, administration of E. sativa might have a promising effect against Abamectin toxicity-induced disorders of thyroid hormones and impaired testicular functions, which were correlated with histopathological changes in the testes of male rats.

Dissimilar effects of organohalogenated compounds on thyroid hormones in glaucous gulls

The glaucous gull (Larus hyperboreus) is an arctic top predator and scavenger exposed to high levels of mixtures of organohalogenated contaminants (OHCs) of which many interfere with the thyroid hormone (TH) system. In the present study, we applied statistical modeling to investigate the potential combined influence of the mixture of chlorinated, brominated and perfluorinated organic compounds in plasma of glaucous gulls on their plasma TH concentrations. In females, there were significant negative associations between several organochlorinated compounds (OCs) and free thyroxin (FT4) and triiodothyronine (FT3), indicating additive negative effects on FT4 and FT3. However, in these females there was also a significant positive association between perfluorooctane sulfonate (PFOS) and FT3. The inverse associations between several OCs and FT3 and the contrasting positive association between PFOS and FT3, indicate that these two groups of OHCs may have dissimilar and antagonistic effects on FT3 in female glaucous gulls. In males, there were no associations between any of the OHCs and the THs. That OHCs affect THs in a complex manner involving both additive and antagonistic effects add to the challenge of interpreting the overall functional effect of thyroid disruptive chemicals in wildlife. However, experimental studies are needed to confirm or disprove such effects.

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.

Increased risk for hypothyroidism after anticholinesterase pesticide poisoning: a nationwide population-based study

PURPOSE

Previous animal studies have reported that acute anticholinesterase pesticide (organophosphate and carbamate) poisoning may affect thyroid hormones. However, there is no human study investigating the association between hypothyroidism and anticholinesterase pesticide poisoning, and therefore, we conducted a retrospective nationwide population-based cohort study to delineate this issue.

METHODS

We identified 10,372 anticholinesterase pesticide poisoning subjects and matched 31,116 non-anticholinesterase pesticide poisoning subjects between 2003 and 2012 from the Nationwide Poisoning Database and the Longitudinal Health Insurance Database 2000, respectively, in a 1:3 ratio by index date, age, and sex for this study. We compared the cumulative incidence of hypothyroidism between the two cohorts by following up until 2013. Independent predictors for hypothyroidism were also investigated.

RESULTS

In total, 75 (0.72%) anticholinesterase pesticide poisoning subjects and 184 (0.59%) non-anticholinesterase pesticide poisoning subjects were diagnosed with hypothyroidism during the follow-up. Cox proportional hazard regression analysis showed that anticholinesterase pesticide poisoning subjects had higher risk for hypothyroidism than did non-anticholinesterase pesticide poisoning subjects (adjusted hazard ratio: 1.47, 95% confidence interval: 1.11-1.95) after adjusting for age, sex, hypertension, malignancy, liver disease, renal disease, atrial fibrillation or flutter, thyroiditis, goiter, other endocrine disorders, and mental disorder. Stratified analysis showed that anticholinesterase pesticide poisoning subjects had higher risk for hypothyroidism than did non-anticholinesterase pesticide poisoning subjects in terms of the age subgroup of 40-64 years, female sex, past history of goiter, follow-up of <1 month, and anticholinesterase pesticide poisoning subjects without atropine treatment (incidence rate ratio [IRR]: 1.66, 95% confidence interval: 1.20-2.30). Female sex, malignancy, renal disease, thyroiditis, goiter, mental disorder, and anticholinesterase pesticide poisoning without atropine treatment were independent predictors for hypothyroidism.

CONCLUSIONS

Anticholinesterase pesticide poisoning is associated with increased risk for hypothyroidism. Early evaluation of thyroid function in anticholinesterase pesticide poisoning subjects is suggested, especially in subjects without atropine treatment, aged 40-64 years, female sex, and past history of goiter.

Weight-of-the-evidence evaluation of 2,4-D potential for interactions with the estrogen, androgen and thyroid pathways and steroidogenesis

A comprehensive weight-of-the-evidence evaluation of 2,4-dichlorophenoxyacetic acid (2,4-D) was conducted for potential interactions with the estrogen, androgen and thyroid pathways and with steroidogenesis. This assessment was based on an extensive database of high quality in vitro, in vivo ecotoxicological and in vivo mammalian toxicological studies. Epidemiological studies were also considered. Toxicokinetic data provided the basis for determining rational cutoffs above which exposures were considered irrelevant to humans based on exceeding thresholds for saturation of renal clearance (TSRC); extensive human exposure and biomonitoring data support that these boundaries far exceed human exposures and provide ample margins of exposure. 2,4-D showed no evidence of interacting with the estrogen or androgen pathways. 2,4-D interacts with the thyroid axis in rats through displacement of thyroxine from plasma binding sites only at high doses exceeding the TSRC in mammals. 2,4-D effects on steroidogenesis parameters are likely related to high-dose specific systemic toxicity at doses exceeding the TSRC and are not likely to be endocrine mediated. No studies, including high quality studies in the published literature, predict significant endocrine-related toxicity or functional decrements in any species at environmentally relevant concentrations, or, in mammals, at doses below the TSRC that are relevant for human hazard and risk assessment. Overall, there is no basis for concern regarding potential interactions of 2,4-D with endocrine pathways or axes (estrogen, androgen, steroidogenesis or thyroid), and thus 2,4-D is unlikely to pose a threat from endocrine disruption to wildlife or humans under conditions of real-world exposures.

Occupational exposure to pesticides and other biocides and risk of thyroid cancer

OBJECTIVES

To assess the associations between occupational exposure to biocides and pesticides and risk of thyroid cancer.

METHODS

Using data from a population-based case-control study involving 462 incident thyroid cancer cases and 498 controls in Connecticut collected in 2010-2011, we examined the association with occupational exposure to biocides and pesticides through a job-exposure matrix. We used unconditional logistic regression models to estimate OR and 95% CI, adjusting for potential confounders.

RESULTS

Individuals who were occupationally ever exposed to biocides had an increased risk of thyroid cancer (OR=1.65, 95% CI 1.16 to 2.35), and the highest risk was observed for the high cumulative probability of exposure (OR=2.18, 95% CI 1.28 to 3.73). The observed associations were similar when we restricted to papillary thyroid cancer and well-differentiated thyroid cancer. Stronger associations were observed for thyroid microcarcinomas (tumour size ≤1 cm). No significant association was observed for occupational exposure to pesticides.

CONCLUSIONS

Our study provides the first evidence linking occupational exposure to biocides and risk of thyroid cancer. The results warrant further investigation.

Pesticide exposure and thyroid function in an agricultural population in Brazil

Although numerous pesticides may interfere with thyroid function, however, epidemiological evidence supporting this relationship is limited, particularly regarding modern non-persistent pesticides. We sought to evaluate the association of agricultural work practices, use of contemporary-use pesticides, and OC pesticides residue levels in serum with circulating thyroid hormone levels in an agricultural population. A cross-sectional study was conducted with a random sample of 275 male and female farm residents in Farroupilha, South of Brazil. Information on sociodemographics, lifestyle and agricultural work was obtained through questionnaire. Blood samples were collected on all participants and analyzed for cholinesterase activity, serum residues of OC pesticides, and levels of free T4 (FT4), total T3 (TT3) and TSH. Non-persistent pesticides exposure assessment was based on questionnaire information on current use of pesticides, and frequency and duration of use, among others. Associations were explored using multivariate linear regression models. Total lifetime years of use of fungicides, herbicides and dithiocarbamates in men was associated with increased TSH accompanied by decrease in FT4, with evidence of a linear trend. In addition, there was an association between being sampled in the high pesticide-use season and increased TSH levels. Conversely, farm work and lifetime use of all pesticides were related with slight decrease in TSH and increased TT3 and FT4, respectively. In general, pesticide use was not associated with thyroid hormones in women. Subjects with detected serum concentrations of β-hexachlorocyclohexane, endrin, dieldrin, heptachlor epoxide B, γ-chlordane, transnonachlor, heptachlor, p,p'-dichlorodiphenylethane and endosulfan II experienced slight changes in TT3; however, associations were weak and inconsistent. These findings suggest that both cumulative and recent occupational exposure to agricultural pesticides may affect the thyroid function causing hypothyroid-like effects, particularly in men.

Pesticide use in the U.S. and policy implications: A focus on herbicides

This article examines herbicide use in the United States, providing estimates of poundage, land surface covered, distribution, and recent trends based on federal and state figures. Herbicides are by far the most widely used class of pesticide in the US, where 556 million lbs of herbicide active ingredients (AIs) were applied in 1995. Agriculture accounts for the majority of herbicide use, totaling 461 million lbs of AIs in 1995. Over 60% of the poundage of all agricultural herbicides consist of those that are capable of disrupting the endocrine and/or reproductive systems of animals. In addition, at least 17 types of `inert ingredients,' which can equal 90% or more of a pesticide product, have been identified as having potential endocrine-disrupting effects. Atrazine is the predominant herbicide used according to poundage, with 68-73 million lbs of AIs applied in 1995. However, 2,4-D is the most widespread herbicide, covering 78 million acres for agricultural uses alone. Both of these herbicides are reported endocrine disruptors. Acetolactate synthase (ALS) inhibitors, namely the sulfonylureas and imidazolinones, are one of the fastest growing classes of herbicides. Many of these herbicides are 100 times more toxic to select plant species than their predecessors, so they can be applied at rates approximately 100 times lower. Consequently, they can affect plant species at concentration levels so low that no standard chemical protocol can detect them. Due in part to these more potent herbicides, the poundage of herbicides used in the US has decreased since the mid-1980s; however, the available data suggest that the number of treated acres has not significantly declined. A thorough assessment of potential exposure to herbicides by wildlife and humans is limited due to the inaccessibility of production and usage data.

Identifying reference chemicals for thyroid bioactivity screening

Reference chemicals were selected based on thyroid bioactivity in 'Tier 1' screening assays used by the U.S. EPA's Endocrine Disruptor Screening Program. Active reference chemicals had significant effects on thyroid-responsive endpoints in the amphibian metamorphosis assay, and the male and female pubertal rat assays. In the absence of thyroid weight or histopathological effects, additional published studies providing mechanistic data on thyroid activity were required for active chemicals. Inactive reference chemicals had no significant effects on thyroid-responsive endpoints in Tier 1 assays, or in amphibian or rodent studies from several online databases. The 34 reference chemicals (29 active and five inactive) will be useful for performance-based validation of alternative, high throughput screening assays for thyroid bioactivity.

Exposure to non-persistent pesticides and thyroid function: A systematic review of epidemiological evidence

Numerous pesticides are recognized for their endocrine-disrupting properties. Non-persistent pesticides such as organophosphates, dithiocarbamates and pyrethroids may interfere with thyroid function as suggested by animal studies. However, the influence of chronic exposure to these compounds on thyroidal functions in humans remains to be determined. The present study aimed to review epidemiological evidence for an association between exposure to non-persistent pesticides and circulating levels of thyroid hormones (thyroxin [T4] and triiodothyronine [T3]) and thyroid-stimulating hormone (TSH). A systematic review was conducted using MEDLINE, SCOPUS and Virtual Health Library (BVS) databases. Articles were limited to original studies and reports published in English, Portuguese or Spanish. Nineteen epidemiological studies were identified, 17 of which were cross-sectional, 14 were of occupationally exposed workers and 11 used exposure biomarkers. Fungicides and organophosphates (OP) insecticides were the most studied pesticides. Although methodological heterogeneity between studies was noted, particularly regarding study design, exposure assessment, and control of confounding, most of them showed associations with changes in T3 and T4, and/or TSH levels, while results from a few of these are consistent with experimental data supporting the findings that non-persistent pesticide exposure exerts hypothyroid-like effects. However, reporting quality was moderate to poor in 50% of the studies, particularly regarding method of selection of participants and discussion of external validity. Overall, current knowledge regarding the impact of non-persistent pesticides on human thyroid function is still limited. Given the widespread use of pesticides, future research should assess effects of exposure to currently-used pesticides in cohort studies combining comprehensive questionnaire-based assessment and biomarkers. Investigators need to pay particular attention to exposure during critical windows of brain development and exposure in agricultural populations.

The diversity of mechanisms influenced by transthyretin in neurobiology: development, disease and endocrine disruption

Transthyretin (TTR) is a protein that binds and distributes thyroid hormones (THs). TTR synthesised in the liver is secreted into the bloodstream and distributes THs around the body, whereas TTR synthesised in the choroid plexus is involved in movement of thyroxine from the blood into the cerebrospinal fluid and the distribution of THs in the brain. This is important because an adequate amount of TH is required for normal development of the brain. Nevertheless, there has been heated debate on the role of TTR synthesised by the choroid plexus during the past 20 years. We present both sides of the debate and how they can be reconciled by the discovery of TH transporters. New roles for TTR have been suggested, including the promotion of neuroregeneration, protection against neurodegeneration, and involvement in schizophrenia, behaviour, memory and learning. Recently, TTR synthesis was revealed in neurones and peripheral Schwann cells. Thus, the synthesis of TTR in the central nervous system (CNS) is more extensive than previously considered and bolsters the hypothesis that TTR may play wide roles in neurobiological function. Given the high conservation of TTR structure, function and tissue specificity and timing of gene expression, this implies that TTR has a fundamental role, during development and in the adult, across vertebrates. An alarming number of 'unnatural' chemicals can bind to TTR, thus potentially interfering with its functions in the brain. One role of TTR is delivery of THs throughout the CNS. Reduced TH availability during brain development results in a reduced IQ. The combination of the newly discovered sites of TTR synthesis in the CNS, the increasing number of neurological diseases being associated with TTR, the newly discovered functions of TTR and the awareness of the chemicals that can interfere with TTR biology render this a timely review on TTR in neurobiology.

Bioaccumulation of hydroxylated polychlorinated biphenyls and pentachlorophenol in the serum of northern elephant seal pups (Mirounga angustirostris)

Northern elephant seals (NES) (Mirounga angustirostris) from the Año Nuevo State Reserve (CA, USA) were sampled at 1-, 4-, 7- and 10-week post-weaning. Concentrations of hydroxylated polychlorinated biphenyls (HO-PCBs) and their parent PCBs were measured in the serum of each individual. The ΣHO-PCB concentrations in the serum increased significantly between early and late fast (from 282 ± 20 to 529 ± 31 pg/mL). This increase might result from a mobilisation of HO-PCBs transferred from the mother during gestation and/or lactation and stored in the pup's liver. Food deprivation has been shown to exacerbate biotransformation capacities in mammals, birds and fish. The HO-penta-CBs was the predominant homologue group, followed by HO-hexa-CBs and HO-hepta-CBs. No preferential pathway for the metabolism of HO-PCBs (HO-direct insertion or NIH-shift of a chlorine atom) could be evidenced. The concentrations of pentachlorophenol (PCP) in the serum of weaned NES increased from 103 ± 7 pg/mL at early fast to 246 ± 41 pg/mL at late fast, which is within the range of PCP concentrations usually encountered in marine mammals.

PCB153 and p,p'-DDE disorder thyroid hormones via thyroglobulin, deiodinase 2, transthyretin, hepatic enzymes and receptors

Polychlorinated biphenyls (PCBs) and DDT are widespread environmental persistent organic pollutants that have various adverse effects on reproduction, development and endocrine function. In order to elucidate effects of PCBs and DDT on thyroid hormone homeostasis, Sprague-Dawley rats were dosed with PCB153 and p,p'-DDE intraperitoneally (ip) for five consecutive days and sacrificed within 24 h after the last dose. Results indicated that after combined exposure to PCB153 and p,p'-DDE, total thyroxine , free thyroxine, total triiodothyronine, and thyroid-stimulating hormone in serum were decreased, whereas free triiodothyronine and thyrotropin-releasing hormone were not affected. Thyroglobulin and transthyretin levels in serum were significantly reduced. mRNA expression of deiodinases 2 (D2) was also suppressed, while D1 and D3 levels were not significantly influenced after combined exposure. PCB153 and p,p'-DDE induced hepatic enzymes, UDPGTs, CYP1A1, CYP2B1, and CYP3A1 mRNA expressions being significantly elevated. Moreover, TRα1, TRβ1, and TRHr expressions in the hypothalamus displayed increasing trends after combined exposure to PCB153 and p,p'-DDE. Taken together, observed results indicate that PCB153 and p,p'-DDE could disorder thyroid hormone homeostasis via thyroglobulin, deiodinase 2, transthyretin, hepatic enzymes, and hormone receptors.

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.

An F1-extended one-generation reproductive toxicity study in Crl:CD(SD) rats with 2,4-dichlorophenoxyacetic acid

2,4-Dichlorophenoxyacetic acid (2,4-D) was assessed for systemic toxicity, reproductive toxicity, developmental neurotoxicity (DNT), developmental immunotoxicity (DIT), and endocrine toxicity. CD rats (27/sex/dose) were exposed to 0, 100, 300, 600 (female), or 800 (male) ppm 2,4-D in diet. Nonlinear toxicokinetic behavior was shown at high doses; the renal clearance saturation threshold for 2,4-D was exceeded markedly in females and slightly exceeded in males. Exposure was 4 weeks premating, 7 weeks postmating for P1 males and through lactation for P1 females. F1 offspring were examined for survival and development, and at weaning, pups were divided in cohorts, by sex and dose, and by systemic toxicity (10), DNT (10), DIT (20), and reproductive toxicity (≥ 23). Remaining weanlings were evaluated for systemic toxicity and neuropathology (10–12). Body weight decreased during lactation in high-dose P1 females and in F1 pups. Kidney was the primary target organ, with slight degeneration of proximal convoluted tubules observed in high-dose P1 males and in high-dose F1 males and females. A slight intergenerational difference in kidney toxicity was attributed to increased intake of 2,4-D in F1 offspring. Decreased weanling testes weights and delayed preputial separation in F1 males were attributed to decreased body weights. Endocrine-related effects were limited to slight thyroid hormone changes and adaptive histopathology in high-dose GD 17 dams seen only at a nonlinear toxicokinetic dose. 2,4-D did not cause reproductive toxicity, DNT, or DIT. The “No Observed Adverse Effect Level” for systemic toxicity was 300 ppm in both males (16.6mg/kg/day) and females (20.6mg/kg/day), which is approximately 6700- to 93 000-fold higher than that reported for 2,4-D exposures in human biomonitoring studies.

Accumulation of hydroxylated polychlorinated biphenyls (OH-PCBs) and implications for PCBs metabolic capacities in three porpoise species

The present study investigated polychlorinated biphenyls (PCBs) and hydroxylated metabolites of PCBs (OH-PCBs) in blood from three porpoise species: finless porpoises (Neophocaena phocaenoides), harbor porpoises (Phocoena phocoena), and Dall's porpoises (Phocoenoides dalli). The porpoises were found stranded or were bycaught along the Japanese coast. Concentrations of OH-PCB were the highest in Dall's porpoises (58pgg(-1) wet wt), second highest in finless porpoises (20pgg(-1) wet wt), and lowest in harbor porpoises (8.3pgg(-1) wet wt). The concentrations in Dall's porpoises were significantly higher than the concentrations in finless porpoises and harbor porpoises (p<0.05 and p<0.01, respectively). There was a positive correlation between PCB and OH-PCB concentrations (r=0.67, p<0.001), suggesting the possible concentration-dependent induction of CYP enzymes. The three porpoise species may have exceptionally low metabolic capacities compared with other marine and terrestrial mammals, because low OH-PCB/PCB concentration ratios were found, which were 0.0016 for Dall's porpoises, 0.0013 for harbor porpoises, and 0.00058 for finless porpoises. Distinct differences in the OH-PCB congener patterns were observed for the three species, even though they are taxonomically closely related.

Transthyretin-binding activity of contaminants in blood from polar bear (Ursus maritimus) cubs

We determined the transthyretin (TTR)-binding activity of blood-accumulating contaminants in blood plasma samples of approximately 4-months-old polar bear (Ursus maritimus) cubs from Svalbard sampled in 1998 and 2008. The TTR-binding activity was measured as thyroxine (T4)-like equivalents (T4-EQMeas). Our findings show that the TTR-binding activity related to contaminant levels was significantly lower (45%) in 2008 than in 1998 (mean ± standard error of mean: 1998, 2265 ± 231 nM; 2008, 1258 ± 170 nM). Although we cannot exclude a potential influence of between-year differences in capture location and cub body mass, our findings most likely reflect reductions of TTR-binding contaminants or their precursors in the arctic environment (e.g., polychlorinated biphenyls [PCBs]). The measured TTR-binding activity correlated positively with the cubs' plasma levels of hydroxylated PCBs (OH-PCBs). No such association was found between TTR-binding activity and the plasma levels of perfluoroalkyl substances (PFASs). The OH-PCBs explained 60 ± 7% and 54 ± 4% of the TTR-binding activity in 1998 and 2008, respectively, and PFASs explained ≤1.2% both years. Still, almost half the TTR-binding activity could not be explained by the contaminants we examined. The considerable levels of TTR-binding contaminants warrant further effect directed analysis (EDA) to identify the contaminants responsible for the unexplained part of the observed TTR-binding activity.

Halogenated organic contaminants and their correlations with circulating thyroid hormones in developing Arctic seabirds

Thyroid hormones are essential for normal growth and development and disruption of thyroid homeostasis can be critical to young developing individuals. The aim of the present study was to assess plasma concentrations of halogenated organic contaminants (HOCs) in chicks of two seabird species and to investigate possible correlations of HOCs with circulating thyroid hormone (TH) concentrations. Plasma from black-legged kittiwake (Rissa tridactyla) and northern fulmar (Fulmarus glacialis) chicks were sampled in Kongsfjorden, Svalbard in 2006. The samples were analyzed for thyroid hormones and a wide range of HOCs (polychlorinated biphenyls (PCBs), hydroxylated (OH-) and methylsulphoned (MeSO-) PCB metabolites, organochlorine pesticides (OCPs), brominated flame retardants (BFRs), and perfluorinated compounds (PFCs)). Concentrations of HOCs were generally low in kittiwake and fulmar chicks compared to previous reports. HOC concentrations were five times higher in fulmar chicks compared to in kittiwake chicks. PFCs dominated the summed HOCs concentrations in both species (77% in kittiwakes and 69% in fulmars). Positive associations between total thyroxin (TT4) and PFCs (PFHpS, PFOS, PFNA) were found in both species. Although correlations do not implicate causal relationships per se, the correlations are of concern as disruption of TH homeostasis may cause developmental effects in young birds.

Association between Perchlorate and Indirect Indicators of Thyroid Dysfunction in NHANES 2001-2002, a Cross-Sectional, Hypothesis-Generating Study

BACKGROUND

A previous study based on NHANES 2001-2002 observed that increased levels of urinary perchlorate were associated with increased levels of thyroid stimulating hormone among all women, and with decreased levels of thyroxine among women with low urinary iodine. No associations were observed for men.

METHODS

Using the same NHANES 2001-2002 data, associations of urinary perchlorate with indirect biomarkers of thyroid hormone disruption were investigated. Decreased levels of hemoglobin (HGB), hematocrit (HCT), and high density lipoprotein (HDL) have been observed among subjects with subclinical hypothyroidism. To investigate the suitability of these indicators for use in observational studies, subjects were divided into six groups: boys, age 6-19; men, age 20-85; girls, age 6-14; non-pregnant women, age 15-49; women, age 50-85; and pregnant women. Use of perchlorate quintiles (Q1-Q5) and continuous log-transformed perchlorate in the regression models allowed investigation of both non-linear and linear associations. Adjustments were made for age, urinary creatinine, race/ethnicity, body mass index, cotinine, poverty index, hours of fasting, thiocyanate, nitrate, daily kcal intake, C-reactive protein. Adjustment for alcohol consumption depended on availability. Adjustment for prescription drugs (beta-blockers, sex hormones, antihyperlipidemic and antidiabetic drugs) was made if it changed the perchlorate estimate by ≥10%.

RESULTS

Statistically significant decreases were observed for HGB and HCT among boys, men, women age 15-49, and pregnant women, and for HDL among men.

CONCLUSIONS

Although the mean response biomarkers were within normal range, their association with urinary perchlorate is of interest. HGB and HCT among pregnant women showed a stronger association with urinary perchlorate than non-pregnant women age 15-49. Statistically significant associations were observed for individual perchlorate quintiles. Assumption of linearity of log-transformed perchlorate may result in underestimation of some associations.

Perturbation of lipids and glucose metabolism associated with previous 2,4-D exposure: a cross-sectional study of NHANES III data, 1988-1994

BACKGROUND

Results from previous population studies showed that mortality rates from acute myocardial infarction and type-2 diabetes during the 1980s and 1990s in rural, agricultural counties of Minnesota, Montana, North and South Dakota, were higher in counties with a higher level of spring wheat farming than in counties with lower levels of this crop. Spring wheat, one of the major field crops in these four states, was treated for 85% or more of its acreage with chlorophenoxy herbicides. In the current study NHANES III data were reviewed for associations of 2,4-dichlorophenoxy acetic acid (2,4-D) exposure, one of the most frequently used chlorophenoxy herbicides, with risk factors that are linked to the pathogenesis of acute myocardial infarction and type-2 diabetes, such as dyslipidemia and impaired glucose metabolism.

METHODS

To investigate the toxicity pattern of chlorophenoxy herbicides, effects of a previous 2,4-D exposure were assessed by comparing levels of lipids, glucose metabolism, and thyroid stimulating hormone in healthy adult NHANES III subjects with urinary 2,4-D above and below the level of detection, using linear regression analysis. The analyses were conducted for all available subjects and for two susceptible subpopulations characterized by high glycosylated hemoglobin (upper 50th percentile) and low thyroxine (lower 50th percentile).

RESULTS

Presence of urinary 2,4-D was associated with a decrease of HDL levels: 8.6% in the unadjusted data (p-value = 0.006), 4.8% in the adjusted data (p-value = 0.08), and 9% in the adjusted data for the susceptible subpopulation with low thyroxine (p-value = 0.02). An effect modification of the inverse triglycerides-HDL relation was observed in association with 2,4-D. Among subjects with low HDL, urinary 2,4-D was associated with increased levels of triglycerides, insulin, C-peptide, and thyroid stimulating hormone, especially in the susceptible subpopulations. In contrast, subjects with high HDL did not experience adverse 2,4-D associated effects.

CONCLUSIONS

The results indicate that exposure to 2,4-D was associated with changes in biomarkers that, based on the published literature, have been linked to risk factors for acute myocardial infarction and type-2 diabetes.

Association between thyroid hormone levels and 4,4'-DDE concentrations in pregnant women (Valencia, Spain)

INTRODUCTION

Several epidemiological studies have reported that some organochlorine compounds (OCs), such as polychlorobiphenyls (PCBs) and 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (4,4'-DDE), may alter thyroid function.

OBJECTIVE

The aim of the present study was to investigate the association of maternal serum OC concentrations of 4,4'-DDE and the sum of seven PCB congeners (PCB 28, 52, 101, 118, 138, 153, and 180) with thyroid hormone (TH) status.

METHODS

We measured OC concentrations in 157 maternal serum samples at 12 weeks of pregnancy in a cohort from Valencia (Spain). Thyroid-stimulating hormone (TSH), total triiodothyronine (TT3), and free thyroxine (FT4) were measured as biomarkers of thyroid function in the same samples. Linear and logistic regression analyses were performed between OCs and TH levels, and variables were log transformed.

RESULTS

Mothers with higher levels of 4,4'-DDE had higher odds of having TSH levels >2.5 mIU/L (OR=2.53; 95% CI=1.36; 4.73; p=0.004), and we found a significant negative association between serum 4,4'-DDE concentrations and FT4 levels (beta=-0.03; 95% CI=-0.05; 0.00; p=0.050) after adjustment for covariates and total lipids. No association was found between sum of PCBs and TH levels.

CONCLUSION

Serum concentrations of 4,4'-DDE were associated with increased TSH and reduced FT4 but not TT3 levels. Our results suggest that some environmental chemicals may interfere with the thyroid system of pregnant women. The major role that maternal THs may play in fetal neurodevelopment makes these findings especially relevant.

The menace of endocrine disruptors on thyroid hormone physiology and their impact on intrauterine development

The delivery of the appropriate thyroid hormones quantity to target tissues in euthyroidism is the result of unopposed synthesis, transport, metabolism, and excretion of these hormones. Thyroid hormones homeostasis depends on the maintenance of the circulating 'free' thyroid hormone reserves and on the development of a dynamic balance between the 'free' hormones reserves and those of the 'bound' hormones with the transport proteins. Disturbance of this hormone system, which is in constant interaction with other hormone systems, leads to an adaptational counter-response targeting to re-establish a new homeostatic equilibrium. An excessive disturbance is likely to result, however, in hypo- or hyper- thyroid clinical states. Endocrine disruptors are chemical substances forming part of 'natural' contaminating agents found in most ecosystems. There is abundant evidence that several key components of the thyroid hormones homeostasis are susceptible to the action of endocrine disruptors. These chemicals include some chlorinated organic compounds, polycyclic aromatic hydrocarbons, herbicides, and pharmaceutical agents. Intrauterine exposure to endocrine disruptors that either mimic or antagonize thyroid hormones can produce permanent developmental disorders in the structure and functioning of the brain, leading to behavioral changes. Steroid receptors are important determinants of the consequences of endocrine disruptors. Their interaction with thyroid hormones complicates the effect of endocrine disruptors. The aim of this review is to present the effect of endocrine disruptors on thyroid hormones physiology and their potential impact on intrauterine development.

Polychlorinated biphenyls and their hydroxylated metabolites (OH-PCBS) in pregnant women from eastern Slovakia

OBJECTIVE

Our aim in the present study was to characterize and quantify the levels of polychlorinated biphenyls (PCBs) and specific polychlorobiphenylol (OH-PCB) metabolites in maternal sera from women delivering in eastern Slovakia.

DESIGN

During 2002-2004, blood samples were collected from women delivering in two Slovak locations: Michalovce district, where PCBs were formerly manufactured, and Svidnik and Stropkov districts, about 70 km north.

PARTICIPANTS

A total of 762 and 341 pregnant women were sampled from Michalovce and Svidnik/Stropkov, respectively, and OH-PCBs were measured in 131 and 31. EVALUATION/MEASUREMENTS: We analyzed PCBs using gas chromatography (GC)/electron capture detection. OH-PCBs and pentachlorophenol (PCP) were determined as methyl derivatives using GC-electron capture negative ionization/mass spectrometry. We characterized distributions in the full cohort using inverse sampling weights.

RESULTS

The concentrations of both PCBs and OH-PCB metabolites of Michalovce mothers were about two times higher than those of the Svidnik/Stropkov mothers (p < 0.001). The median weighted maternal serum levels of the sum of PCBs (sigmaPCBs) were 5.73 ng/g wet weight (Michalovce) and 2.82 ng/g wet weight (Svidnik/Stropkov). The median sum of OH-PCBs (ZOH-PCBs) was 0.55 ng/g wet weight in Michalovce mothers and 0.32 ng/g wet weight in Svidnik/Stropkov mothers. 4-OH-2,2',3,4',5,5',6-Heptachlorobiphenyl (4-OH-CB187) was a primary metabolite, followed by 4-OH-2,2',3,4',5,5'-hexachlorobiphenyl (4-OH-CB146). Only four PCB congeners-CBs 153, 138, 180, and 170--had higher concentrations than 4-OH-CB187 and 4-OH-CB146 (p < 0.001). The median ratio of the sigmaOH-PCBs to the sigmaPCBs was 0.10.

CONCLUSIONS

Mothers residing in eastern Slovakia are still highly exposed to PCBs, and their body burdens of these pollutants and OH-PCB metabolites may pose a risk for adverse effects on health for themselves and their children.

Pesticide exposure: the hormonal function of the female reproductive system disrupted?

Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation: 1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies, exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy, spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity, it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both in toxicological and epidemiological settings.

Human health implications of environmental contaminants in Arctic Canada: A review

The objectives of this paper are to: assess the impact of exposure to current levels of environmental contaminants in the Canadian Arctic on human health; identify the data and knowledge gaps that need to be filled by future human health research and monitoring; examine how these issues have changed since our first assessment [Van Oostdam, J., Gilman, A., Dewailly, E., Usher, P., Wheatley, B., Kuhnlein, H. et al., 1999. Human health implications of environmental contaminants in Arctic Canada: a review. Sci Total Environ 230, 1-82]. The primary exposure pathway for contaminants for various organochlorines (OCs) and toxic metals is through the traditional northern diet. Exposures tend to be higher in the eastern than the western Canadian Arctic. In recent dietary surveys among five Inuit regions, mean intakes by 20- to 40-year-old adults in Baffin, Kivalliq and Inuvialuit communities exceeded the provisional tolerable daily intakes (pTDIs) for the OCs, chlordane and toxaphene. The most recent findings in NWT and Nunavut indicate that almost half of the blood samples from Inuit mothers exceeded the level of concern value of 5 microg/L for PCBs, but none exceeded the action level of 100 microg/L. For Dene/Métis and Caucasians of the Northwest Territories exposure to OCs are mostly below this level of concern. Based on the exceedances of the pTDI and of various blood guidelines, mercury and to a lesser extent lead (from the use of lead shot in hunting game) are also concerns among Arctic peoples. The developing foetus is likely to be more sensitive to the effects of OCs and metals than adults, and is the age groups of greatest risk in the Arctic. Studies of infant development in Nunavik have linked deficits in immune function, an increase in childhood respiratory infections and birth weight to prenatal exposure to OCs. Balancing the risks and benefits of a diet of country foods is very difficult. The nutritional benefits of country food and its contribution to the total diet are substantial. Country food contributes significantly more protein, iron and zinc to the diets of consumers than southern/market foods. The increase in obesity, diabetes and cardiovascular disease has been linked to a shift away from a country food diet and a less active lifestyle. These foods are an integral component of good health among Aboriginal peoples. The social, cultural, spiritual, nutritional and economic benefits of these foods must be considered in concert with the risks of exposure to environmental contaminants through their exposure. Consequently, the contamination of country food raises problems which go far beyond the usual confines of public health and cannot be resolved simply by risk-based health advisories or food substitutions alone. All decisions should involve the community and consider many aspects of socio-cultural stability to arrive at a decision that will be the most protective and least detrimental to the communities.

Thyroid-hormone-disrupting chemicals: evidence for dose-dependent additivity or synergism

Endocrine disruption from environmental contaminants has been linked to a broad spectrum of adverse outcomes. One concern about endocrine-disrupting xenobiotics is the potential for additive or synergistic (i.e., greater-than-additive) effects of mixtures. A short-term dosing model to examine the effects of environmental mixtures on thyroid homeostasis has been developed. Prototypic thyroid-disrupting chemicals (TDCs) such as dioxins, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers have been shown to alter thyroid hormone homeostasis in this model primarily by up-regulating hepatic catabolism of thyroid hormones via at least two mechanisms. Our present effort tested the hypothesis that a mixture of TDCs will affect serum total thyroxine (T4) concentrations in a dose-additive manner. Young female Long-Evans rats were dosed via gavage with 18 different polyhalogenated aromatic hydrocarbons [2 dioxins, 4 dibenzofurans, and 12 PCBs, including dioxin-like and non-dioxin-like PCBs] for 4 consecutive days. Serum total T4 was measured via radioimmunoassay in samples collected 24 hr after the last dose. Extensive dose-response functions (based on seven to nine doses per chemical) were determined for individual chemicals. A mixture was custom synthesized with the ratio of chemicals based on environmental concentrations. Serial dilutions of this mixture ranged from approximately background levels to 100-fold greater than background human daily intakes. Six serial dilutions of the mixture were tested in the same 4-day assay. Doses of individual chemicals that were associated with a 30% TH decrease from control (ED30), as well as predicted mixture outcomes were calculated using a flexible single-chemical-required method applicable to chemicals with differing dose thresholds and maximum-effect asymptotes. The single-chemical data were modeled without and with the mixture data to determine, respectively, the expected mixture response (the additivity model) and the experimentally observed mixture response (the empirical model). A likelihood-ratio test revealed statistically significant departure from dose additivity. There was no deviation from additivity at the lowest doses of the mixture, but there was a greater-than-additive effect at the three highest mixtures doses. At high doses the additivity model underpredicted the empirical effects by 2- to 3-fold. These are the first results to suggest dose-dependent additivity and synergism in TDCs that may act via different mechanisms in a complex mixture. The results imply that cumulative risk approaches be considered when assessing the risk of exposure to chemical mixtures that contain TDCs.

Evaluation of mechanisms inducing thyroid toxicity and the ability of the enhanced OECD Test Guideline 407 to detect these changes

The OECD has developed an "enhanced Test Guideline 407" (TG 407) protocol for detecting endocrine effects during the course of a 28-day testing scheme. This protocol has gone through a validation process with (anti)estrogenic and (anti)androgenic compounds and substances that affect the thyroid (thyroxine and propylthiouracil). This review investigates whether a 28-day testing scheme would show up alterations in the thyroid-related parameters of the "enhanced TG 407" (T3, T4, TSH, thyroid weight and histopathology), irrespective of the mode of action. For each mode of action, a generally accepted reference chemical was selected and an in-depth literature survey was carried out, and the chemical was evaluated for treatment-related changes of thyroid-dependent parameters. The following model chemicals were selected: ion perchlorate, blockage of iodine uptake; propylthiouracil, inhibition of thyroid hormone synthesis; excess of iodine, blockage of thyroid hormone release; pyrazole, thyroid cytotoxicity; minocycline, thyroid pigmentation; amiodarone, inhibition of TSH synthesis; diethylstilbestrol, competition for thyroid hormone binding globulin; selenium-deficient diet, inhibition of thyroxine deiodination; FD&C Red No. 3, inhibition of peripheral 5'-deiodinase; cadmium, lipid peroxidation; phenobarbital, increase in thyroxine conjugation and biliary excretion; temelastine, thyroxine accumulation. Test data for treatments lasting approximately one month were available for most of these model chemicals, and these demonstrated the expected thyroid-related changes. Thus, it can be concluded that a 28-day testing scheme allows for the detection of thyroid-disrupting chemicals. The literature data also were evaluated according to whether preference can be given to any of the thyroid-related parameters (thyroid/pituitary hormones, thyroid weight and histopathology) with regard to dose-related sensitivities. Due to different study designs (such as treatment duration, application mode, dose selection and parameters used), no clear picture emerged. Therefore, consideration should be given to all of these parameters, which should also help to define the mode of action. Overall, this literature review provides support for the contention that the newly developed "enhanced TG 407" test protocol is well suited to the detection of chemicals that affect the thyroid gland.

Hydroxylated Polychlorinated Biphenyls Selectively Bind Transthyretin in Blood and Inhibit Amyloidogenesis: Rationalizing Rodent PCB Toxicity

Polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs) are known to bind to transthyretin (TTR) in vitro, possibly explaining their bioaccumulation, rodent toxicity, and presumed human toxicity. Herein, we show that several OH-PCBs bind selectively to TTR in blood plasma; however, only one of the PCBs tested binds TTR in plasma. Some of the OH-PCBs displace thyroid hormone (T4) from TTR, rationalizing the toxicity observed in rodents, where TTR is the major T4 transporter. Thyroid binding globulin and albumin are the major T4 carriers in humans, making it unlikely that enough T4 could be displaced from TTR to be toxic. OH-PCBs are excellent TTR amyloidogenesis inhibitors in vitro because they bind to the TTR tetramer, imparting kinetic stability under amyloidogenic denaturing conditions. Four OH-PCB/TTR cocrystal structures provide further insight into inhibitor binding interactions.

Effects of organochlorine contaminants on thyroid hormone levels in Arctic breeding glaucous gulls, Larus hyperboreus

Studies on glaucous gulls (Larus hyperboreus) breeding in the Barents Sea have reported that high blood levels of halogenated organic contaminants in this species might cause reproductive, behavioral, and developmental stress. However, potential endocrine system modulation caused by contaminant exposure has yet not been reported in this Arctic apical predator. In this present study we aimed to investigate whether the current levels of a selection of organochlorines (OCs) were associated with altered circulating levels of thyroid hormones (THs) in free-ranging adult glaucous gulls breeding at Bear Island in the Barents Sea. Blood concentrations of 14 polychlorinated biphenyls, hexachlorobenzene (HCB), oxychlordane, and p,p' -dichlorodiphenyldichloroethylene (p,p' -DDE) were quantified, in addition to free and total thyroxine (T4) and triiodothyronine (T3), in plasma of 66 glaucous gulls in the spring of 2001. Negative correlations were found between plasma levels of T4 and T4:T3 ratio, and blood levels of OCs in male glaucous gulls. Despite their relatively low contribution to the total OC fraction, HCB and oxychlordane were the most prominent compounds in terms of their negative effect on the variation of the T4:T3 ratio. Moreover, lower T4 levels and T4:T3 ratios were measured in glaucous gulls breeding in a colony exposed to high levels of OCs, compared with a less exposed colony. Levels of T3 were elevated in the high-OC-exposed colony. This may indicate that the glaucous gull is susceptible to changes to TH homeostasis mediated by exposure to halogenated organic contaminants.

Exploring associations between serum levels of select organochlorines and thyroxine in a sample of New York state sportsmen: the New York State Angler Cohort Study

This preliminary study investigated associations between environmental organochlorine compounds and thyroid function in a sample of 66 sportsmen selected from among participants in the New York State Angler Cohort Study. A cross-sectional design was employed with the primary goal of the analysis being the generation of specific testable hypotheses. Blood samples were analyzed for compounds based on a priori identified literature-cited evidence of thyroid disruption. These included hexachlorobenzene and polychlorinated biphenyl congeners 19, 28, 47, 118, 153, 169, 180, 183, and 187. Time of sample collection, serum triglycerides, cholesterol, high- and low-density lipoproteins, age, body mass index, and cigarette smoking were considered for each participant. Potential associations between organochlorine compounds and serum total thyroxine, controlling for potential confounders, were examined using multivariable linear regression models. The models reported consisted of all variates being entered ("full" model, R2=0.380, P=0.136) and stepwise selection of variates ("reduced" models, alpha=0.15) using the criterion of maximum partial correlation at each step. Several procedures were considered to address contaminant data below the limit of detection in the reduced models with no change in selected predictors. Hexachlorobenzene (beta=-0.113) and age (beta=0.007) were selected as predictors of serum T4 in the reduced models (R2=0.083, P=0.065). Power analysis suggested that by doubling the sample size the existing results would be statistically significant with a type I error of 0.05 and a power of 0.80. These findings are important in the design of a new specific study of thyroid function and environmental contaminants.

Increased [3H]phorbol ester binding in rat cerebellar granule cells and inhibition of 45Ca(2+) buffering in rat cerebellum by hydroxylated polychlorinated biphenyls

Our previous structure-activity relationship (SAR) studies indicated that the effects of polychlorinated biphenyls (PCBs) on neuronal Ca(2+) homeostasis and protein kinase C (PKC) translocation were associated with the extent of coplanarity. Chlorine substitutions at ortho position on the biphenyl, which increase the non-coplanarity, are characteristic of the most active congeners in vitro. In the present study, we investigated the effects of selected hydroxylated PCBs, which are major PCB metabolites identified in mammals, on the same measures where PCBs had differential effects based on structural configuration. These measures include PKC translocation as determined by [3H]phorbol ester ([3H]PDBu) binding in cerebellar granule cells, and Ca(2+) sequestration as determined by 45Ca(2+) uptake by microsomes isolated from adult rat cerebellum. All the selected hydroxy-PCBs with ortho-chlorine substitutions increased [3H]PDBu binding in a concentration-dependent manner and the order of potency as determined by E(50) (concentration that increases control activity by 50%) is 2',4',6'-trichloro-4-biphenylol (32 +/- 4 microM), 2',5'-dichloro-4-biphenylol (70 +/- 9 microM), 2,2',4',5,5'-pentachloro-4-biphenylol (80 +/- 7 microM) and 2,2',5'-trichloro-4-biphenylol (93 +/- 14 microM). All the selected hydroxy-PCBs inhibited microsomal 45Ca(2+) uptake to a different extent. Among the hydroxy-PCBs selected, 2',4',6'-trichloro-4-biphenylol is the most active in increasing [3H]PDBu binding as well as inhibiting microsomal 45Ca(2+) uptake. 3,5-Dichloro-4-biphenylol and 3,4',5-trichloro-4-biphenylol did not increase [3H]PDBu binding, but inhibited microsomal 45Ca(2+) uptake. This effect was not related to ionization of these two hydroxy-PCBs. Hydroxylated PCBs seemed to be as active as parent PCBs in vitro. These studies indicate that PCB metabolites such as hydroxy-PCBs might contribute significantly to the neurotoxic responses of PCBs.