Endocrine disruptors and the thyroid gland--a combined in vitro and in vivo analysis of potential new biomarkers

Is there any association between urinary metabolites of polycyclic aromatic hydrocarbons and thyroid hormone levels in children and adolescents?

Considering the possible effects of polycyclic aromatic hydrocarbons (PAHs) on thyroid function, the current study aims to investigate the association of PAH urinary metabolites with the level of thyroid hormones in a sample of Iranian children and adolescents. This cross-sectional study was conducted from September 2015 to July 2016 in Isfahan, Iran. Participants were 150 students, aged 6-18 years, who were selected by multistage cluster random sampling from schools of Isfahan province. Blood and urine samples of participants were obtained for measurement of thyroid hormone levels (measured by immunoradiometric assay) and PAH urinary metabolites, including 1-hydroxynaphthalene, 2-hydroxynaphthalene, 9-hydroxyphenanthrene, and 1-hydroxypyrene. The association of serum thyroid-stimulating hormone (TSH) and PAH urinary metabolites was determined by correlation and regression analyses. Multivariate regression analysis revealed significant association between serum TSH and PAH urinary metabolites; this association remained significant after adjustment for gender and age. The corresponding figures were r = 0.85 for 1-naphthol, r = 0.86 for 2-naphthol, r = 0.87 for 1-hydroxypyrene, and r = 0.42 for 9-phenantrol, respectively, all p values < 0.001. The mean levels of 1-hydroxypyrene and 9-phenanthrol were higher in boys than those in girls (p < 0.05). The findings of this study indicated significant positive association between urinary PAH biomarkers and the TSH level in children and adolescents. It can be suggested that long-term exposure to PAHs might result in thyroid function impairment. The clinical implication of the current findings should be confirmed by future longitudinal studies.

Metabolism and disposition of 2-ethylhexyl-p-methoxycinnamate following oral gavage and dermal exposure in Harlan Sprague Dawley rats and B6C3F1/N mice and in hepatocytes in vitro

1. 2-Ethylhexyl-p-methoxycinnamate (EHMC) is commonly used as an ingredient in sunscreens, resulting in potential oral and dermal exposure in humans. 2. Clearance and metabolism of EHMC in hepatocytes and disposition and metabolism of EHMC in rodents following oral (8-800 mg/kg) intravenous (IV) (8 mg/kg) or dermal (0.8-80 mg/kg representing 0.1-10% formulation concentration) exposure to [¹⁴C]EHMC were investigated in rats and mice. 3. EHMC was rapidly cleared from rat and mouse hepatocytes (half-life ≤3.16 min) and less rapidly (half-life ≤48 min) from human hepatocytes. 4. [¹⁴C]EHMC was extensively absorbed and excreted primarily in urine by 72 h after oral administration to rats (65-80%) and mice (63-72%). Oral doses to rats were excreted to a lesser extent (3-8%) in feces and as CO₂ (1-4%). Radioactive residues in tissues were <1% of the dose. There were no sex or species differences in disposition in rats. 5. Following dermal application, 34-42% of an 8-mg/kg dose was absorbed in rats, and 54-62% in mice in 72-h. 6. Among numerous urinary metabolites associated with hydrolysis of the ester, two potential reproductive and developmental toxicants, 2-ethylhexanol and 2-ethylhexanoic acid were produced by metabolism of EHMC.

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

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

Evaluation of the endocrine-disrupting effects of homosalate (HMS) and 2-ethylhexyl 4-dimethylaminobenzoate (OD-PABA) in rat pups during the prenatal, lactation, and early postnatal periods

Homosalate (HMS) and 2-ethylhexyl 4-dimethylaminobenzoate (OD-PABA) are ultraviolet filters. We aimed to investigate the effects of dermal exposure to HMS and OD-PABA during the prenatal, lactation, and early infancy periods on pubertal development and thyroid function in male and female rats. The thyroid glands, uteri, testes, prostate glands, and seminal vesicles were excised and weighed, the reproductive organs were analyzed histologically, and the serum hormone levels were measured. In the prenatal period, the thyroxine (T4) levels increased in the female rats in the exposed groups ( p < 0.05); the thyroid weights, reproductive organ weights, and gonadal hormone levels were not altered. In males, the testosterone levels decreased ( p < 0.05), but the thyroid weights, T4 levels, prostate, and testis weights were not changed. In the lactation period, the weights of the thyroid glands increased in the exposed female groups ( p < 0.05), but the T4, gonadal hormone levels, and reproductive organ weights were not changed. In the males, the thyroid gland weights, T4 levels, reproductive organ weights, and gonadal hormone levels were not changed. During infancy, the thyroid gland weights increased in the female rats in the exposed groups ( p < 0.05), but the T4 levels, gonadal hormone levels, and reproductive organ weights were not affected. In the male rats in the exposed groups, the T4 levels were increased ( p < 0.05), but the thyroid and reproductive organ weights, gonadal hormone levels were not affected. Organ histopathology was not affected in all groups. HMS and OD-PABA do not have endocrine disruptor effects on thyroid function and the pubertal development of female and male rats.

Effects of the soya isoflavone genistein in early life stages of the Senegalese sole, Solea senegalensis: Thyroid, estrogenic and metabolic biomarkers

This study examines the effects induced by environmentally relevant concentrations of the isoflavone genistein (3mg/L and 10mg/L) during early life stages of the Senegalese sole. Throughout the hypothalamus-pituitary-thyroid (HPT) axis, several neurohormonal regulatory thyroid signalling patterns (thyroglobulin/Tg, thyroid peroxidase/TPO, transthyretin/TTR, thyroid receptors/TRβ, and iodothrynonine deiodinases, Dio2 and Dio3) were analysed. Furthermore, the expression patterns of estrogen receptor ERβ and haemoprotein Cyp1a were also evaluated. In the control larvae, progressive increases of constitutive hormonal signalling pathways have been evidenced from the pre-metamorphosis phase onwards, reaching the highest expression basal levels at the metamorphosis (Tg, TPO, Dio2) and/or during post-metamorphosis (TTR, TRβ, ERβ). When the early larvae were exposed to both genistein concentrations (3mg/L and 10mg/L), a statistically significant down-regulation of TPO, TTR and Tg mRNA levels was clearly detected at the metamorphic stages. In addition, the Dio2 and Dio3 transcript expression levels were also down and up-regulated when exposed to both genistein concentrations. In the larvae exposed to genistein, no statistically significant responses were recorded for the TRβ expression patterns. Nevertheless, the ERβ and Cyp1a transcript levels were up-regulated at the middle metamorphic stage (S2, at 16 dph) in the larvae exposed to high genistein concentrations and, only the ERβ was down-regulated (S1, at 12dph) at the lower doses. Finally, all these pointed out imbalances were only temporarily disrupted by exposure to genistein, since most of the modulated transcriptional signals (i.e. up or down-regulation) were quickly restored to the baseline levels. Additionally, the control and genistein-exposed Senegalese sole specimens showed characteristic ontogenetic patterns and completely suitable for an optimal development, metamorphosis, and growth.

Hormonally active agents in the environment: a state-of-the-art review

After the Second World War, infatuation with modern products has exponentially widened the spectrum of chemicals used. Some of them are capable of hijacking the endocrine system by blocking or imitating a hormone and are referred to as hormonally active chemicals or endocrine disruptors. These are chemicals that the body was not designed for evolutionarily and they are present in every matrix of the environment. We are living in a chemical world where the exposures are ubiquitous and take place in combinations that can interact with the endocrine system and some other metabolic activities in unexpected ways. The complexity of interaction of these compounds can be understood by the fact that they interfere with gene expression at extremely low levels, consequently harming an individual life form, its offspring or population. As the endocrine system plays a critical role in many biological or physiological functions, by interfering body's endocrine system, endocrine disrupting compounds (EDCs) have various adverse effects on human health, starting from birth defects to developmental disorders, deadly deseases like cancer and even immunological disorders. Most of these compounds have not been tested yet for safety and their effects cannot be assessed by the available techniques. The establishment of proper exposure measurement techniques and integrating correlation is yet to be achieved to completely understand the impacts at various levels of the endocrine axis.

Phenols and parabens in relation to reproductive and thyroid hormones in pregnant women

INTRODUCTION

Phenols and parabens are ubiquitous environmental contaminants. Evidence from animal studies and limited human data suggest they may be endocrine disruptors. In the current study, we examined associations of phenols and parabens with reproductive and thyroid hormones in 106 pregnant women recruited for the prospective cohort, "Puerto Rico Testsite for Exploring Contamination Threats (PROTECT)".

METHODS

Urinary exposure biomarkers (bisphenol A, triclosan, benzophenone-3, 2,4-dichlorophenol, 2,5-dichlorophenol, butyl, methyl and propyl paraben) and serum hormone levels (estradiol, progesterone, sex hormone-binding globulin (SHBG), free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone) were measured at up to two time points during pregnancy (16-20 weeks and 24-28 weeks). We used linear mixed models to assess relationships between exposure biomarkers and hormone levels across pregnancy, controlling for urinary specific gravity, maternal age, BMI and education. In sensitivity analyses, we evaluated cross-sectional relationships between exposure and hormone levels stratified by study visit using linear regression.

RESULTS

An IQR increase in methyl paraben was associated with a 7.70% increase (95% CI 1.50, 13.90) in SHBG. Furthermore, an IQR increase in butyl paraben as associated with an 8.46% decrease (95% CI 16.92, 0.00) in estradiol, as well as a 9.34% decrease (95% CI -18.31,-0.38) in estradiol/progesterone. Conversely, an IQR increase in butyl paraben was associated with a 5.64% increase (95% CI 1.26, 10.02) in FT4. Progesterone was consistently negatively associated with phenols, but none reached statistical significance. After stratification, methyl and propyl paraben were suggestively negatively associated with estradiol at the first time point (16-20 weeks), and suggestively positively associated with estradiol at the second time point (24-28 weeks).

CONCLUSIONS

Within this ongoing birth cohort, certain phenols and parabens were associated with altered reproductive and thyroid hormone levels during pregnancy. These changes may contribute to adverse health effects in mothers or their offspring, but additional research is required.

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.

Recent Advances on Endocrine Disrupting Effects of UV Filters

Ultraviolet (UV) filters are used widely in cosmetics, plastics, adhesives and other industrial products to protect human skin or products against direct exposure to deleterious UV radiation. With growing usage and mis-disposition of UV filters, they currently represent a new class of contaminants of emerging concern with increasingly reported adverse effects to humans and other organisms. Exposure to UV filters induce various endocrine disrupting effects, as revealed by increasing number of toxicological studies performed in recent years. It is necessary to compile a systematic review on the current research status on endocrine disrupting effects of UV filters toward different organisms. We therefore summarized the recent advances on the evaluation of the potential endocrine disruptors and the mechanism of toxicity for many kinds of UV filters such as benzophenones, camphor derivatives and cinnamate derivatives.

The effects of binary UV filter mixtures on the midge Chironomus riparius

Organic ultraviolet (UV) filters are used in a wide variety of products, including cosmetics, to prevent damage from UV light in tissues and industrial materials. Their extensive use has raised concerns about potential adverse effects in human health and aquatic ecosystems that accumulate these pollutants. To increase sun radiation protection, UV filters are commonly used in mixtures. Here, we studied the toxicity of binary mixtures of 4-methylbenzylidene camphor (4MBC), octyl-methoxycinnamate (OMC), and benzophenone-3 (BP-3), by evaluating the larval mortality of Chironomus riparius. Also molecular endpoints have been analyzed, including alterations in the expression levels of a gene related with the endocrine system (EcR, ecdysone receptor) and a gene related with the stress response (hsp70, heat shock protein 70). The results showed that the mortality caused by binary mixtures was similar to that observed for each compound alone; however, some differences in LC50 were observed between groups. Gene expression analysis showed that EcR mRNA levels increased in the presence of 0.1mg/L 4MBC but returned to normal levels after exposure to mixtures of 4MBC with 0.1, 1, and 10mg/L of BP-3 or OMC. In contrast, the hsp70 mRNA levels increased after exposure to the combinations tested of 4MBC and BP-3 or OMC mixtures. These data suggest that 4MBC, BP-3, and OMC may have antagonist effects on EcR gene transcription and a synergistic effect on hsp70 gene activation. This is the first experimental study to show the complex patterned effects of UV filter mixtures on invertebrates. The data suggest that the interactions within these chemicals mixtures are complex and show diverse effects on various endpoints.

Newer Approaches to Identify Potential Untoward Effects in Functional Foods

Globalization has greatly accelerated the numbers and variety of food and beverage products available worldwide. The exchange among greater numbers of countries, manufacturers, and products in the United States and worldwide has necessitated enhanced quality measures for nutritional products for larger populations increasingly reliant on functionality. These functional foods, those that provide benefit beyond basic nutrition, are increasingly being used for their potential to alleviate food insufficiency while enhancing quality and longevity of life. In the United States alone, a steady import increase of greater than 15% per year or 24 million shipments, over 70% products of which are food related, is regulated under the Food and Drug Administration (FDA). This unparalleled growth has resulted in the need for faster, cheaper, and better safety and efficacy screening methods in the form of harmonized guidelines and recommendations for product standardization. In an effort to meet this need, the in vitro toxicology testing market has similarly grown with an anticipatory 15% increase between 2010 and 2015 of US$1.3 to US$2.7 billion. Although traditionally occupying a small fraction of the market behind pharmaceuticals and cosmetic/household products, the scope of functional food testing, including additives/supplements, ingredients, residues, contact/processing, and contaminants, is potentially expansive. Similarly, as functional food testing has progressed, so has the need to identify potential adverse factors that threaten the safety and quality of these products.

Thyroid disrupting effects of polychlorinated biphenyls in ovariectomized rats: A benchmark dose analysis

Polychlorinated biphenyls (PCBs) are proved endocrine disrupting potentials. Reference points (RP) for PCBs are derived from dose-response relationship analysis by using the traditional no observed adverse effect or lowest observed adverse effect level (NOAEL/LOAEL) methods, or a more advanced benchmark dose (BMD) method. In present study, toxicological RP for PCBs' thyroid disruption was established and compared between NOAEL/LOAEL and BMD method in an ovariectomized (OVX) rat model. Sham and OVX controls were given corn oil while other OVX groups were administered with 0.1, 1.0, 5.0, and 10.0mg/kg bw of PCBs (aroclor 1254) respectively by gavage. Body weight change, liver type I 5'-deiodinase (5'-DI) activity, serum total thyroxine (tT4), triiodothyroxine (tT3), thyroid stimulating hormones (TSH), and thyroid histopathological changes were measured and analyzed. In PCBs-treated groups, serum tT4, tT3, TSH, and histopathological examinations showed significant changes with a dose-dependent manner compared with those in OVX control (P<0.05). The toxicological RP for PCBs affecting thyroid function of OVX rats was 0.02 mg/kg'bw based on BMD analysis.

CO-occurring exposure to perchlorate, nitrate and thiocyanate alters thyroid function in healthy pregnant women

BACKGROUND

Adequate maternal thyroid function during pregnancy is necessary for normal fetal brain development, making pregnancy a critical window of vulnerability to thyroid disrupting insults. Sodium/iodide symporter (NIS) inhibitors, namely perchlorate, nitrate, and thiocyanate, have been shown individually to competitively inhibit uptake of iodine by the thyroid. Several epidemiologic studies examined the association between these individual exposures and thyroid function. Few studies have examined the effect of this chemical mixture on thyroid function during pregnancy

OBJECTIVES

We examined the cross sectional association between urinary perchlorate, thiocyanate and nitrate concentrations and thyroid function among healthy pregnant women living in New York City using weighted quantile sum (WQS) regression.

METHODS

We measured thyroid stimulating hormone (TSH) and free thyroxine (FreeT4) in blood samples; perchlorate, thiocyanate, nitrate and iodide in urine samples collected from 284 pregnant women at 12 (±2.8) weeks gestation. We examined associations between urinary analyte concentrations and TSH or FreeT4 using linear regression or WQS adjusting for gestational age, urinary iodide and creatinine.

RESULTS

Individual analyte concentrations in urine were significantly correlated (Spearman's r 0.4-0.5, p<0.001). Linear regression analyses did not suggest associations between individual concentrations and thyroid function. The WQS revealed a significant positive association between the weighted sum of urinary concentrations of the three analytes and increased TSH. Perchlorate had the largest weight in the index, indicating the largest contribution to the WQS.

CONCLUSIONS

Co-exposure to perchlorate, nitrate and thiocyanate may alter maternal thyroid function, specifically TSH, during pregnancy.

Reproduction Symposium: does grazing on biosolids-treated pasture pose a pathophysiological risk associated with increased exposure to endocrine disrupting compounds?

Biosolids (processed human sewage sludge), which contain low individual concentrations of an array of contaminants including heavy metals and organic pollutants such as polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), and polychlorinated dibenzodioxins/polychlorinated dibenzofurans known to cause physiological disturbances, are increasingly being used as an agricultural fertilizer. This could pose a health threat to both humans and domestic and wild animal species. This review summarizes results of a unique model, used to determine the effects of exposure to mixtures of environmentally relevant concentrations of pollutants, in sheep grazed on biosolids-treated pastures. Pasture treatment results in nonsignificant increases in environmental chemical (EC) concentrations in soil. Whereas EC concentrations were increased in some tissues of both ewes and their fetuses, concentrations were low and variable and deemed to pose little risk to consumer health. Investigation of the effects of gestational EC exposure on fetal development has highlighted a number of issues. The results indicate that gestational EC exposure can adversely affect gonadal development (males and females) and that these effects can impact testicular morphology, ovarian follicle numbers and health, and the transcriptome and proteome in adult animals. In addition, EC exposure can be associated with altered expression of GnRH, GnRH receptors, galanin receptors, and kisspeptin mRNA within the hypothalamus and pituitary gland, gonadotroph populations within the pituitary gland, and regional aberrations in thyroid morphology. In most cases, these anatomical and functional differences do not result in altered peripheral hormone concentrations or reproductive function (e.g., lambing rate), indicating physiological compensation under the conditions tested. Physiological compensation is also suggested from studies that indicate that EC effects may be greater when exposure occurs either before or during gestation compared with EC exposure throughout life. With regard to human and animal health, this body of work questions the concept of safe individual concentration of EC when EC exposure typically occurs as complex mixtures. It suggests that developmental EC exposure may affect many different physiological systems, with some sex-specific differences in EC sensitivity, and that EC effects may be masked under favorable physiological conditions.

In vitro assessment of thyroidal and estrogenic activities in poultry and broiler manure

Among the many chemicals found in avian manure, endocrine disruptors (EDs), of natural or anthropogenic origin, are of special environmental concern. Nowadays, an increasing amount of estrogens is being released into the environment via the use of manure to fertilize agricultural land. While most research in this field has focused on estrogenic phenomena, little is known about alterations related to other endocrine systems, such as the thyroidal one. Here we simultaneously assessed the potential estrogenic and thyroidal activity of poultry and broiler litter manure using in vitro approaches based on estrogen receptor (Er) and thyroid receptor (Tr) transactivation assays. In addition, leaching experiments were performed to assess whether the EDs present in the manure pass through a soil column and potentially reach the groundwater. Manure from four broiler and four poultry farms was collected in two sampling campaigns carried out in two seasons (fall and spring). Extracts from broiler and poultry manure exhibited strong thyroidal activity. Only poultry manure showed estrogenic activity, which is consistent with the low levels of estrogens expected in hatchlings. Leakage experiments were performed in columns with two kinds of arable soils: sandy and loamy. No estrogenicity or thyroidal activity was detectable in soils treated with the manure or in the corresponding leachates. These results indicate that substances with estrogenic or thyroidal activity were degraded in the soil under our experimental conditions. However, the long-term effects associated with the constant and intensive application of manure to agricultural land in some regions require further research.

Molecular interactions of benzophenone UV filters with human serum albumin revealed by spectroscopic techniques and molecular modeling

Benzophenone (BP)-type UV filters have been widely used in many personal care products to protect human from UV exposure. Their dermal applications can cause direct human health risk following accumulation in bloodstream. Few studies have addressed whether BP-type UV filters could bind and alter the structure and function of human serum albumin (HSA), the major carrier protein in plasma. Four benzophenones, BP-1, BP-2, BP-3 and BP-8 were selected to investigate their potentially toxic interactions with HSA and the intrinsic binding mechanism using combined spectroscopies and molecular docking techniques. Four benzophenones significantly quench the intrinsic fluorescence of HSA via static mode. The competitive binding fluorescence assay and molecular docking both revealed that the benzophenones bind at site II of HSA. Their binding constants range from 1.91 × 10(4)M(-1) to 12.96 × 10(4)M(-1) at 296 K. BP-8 interacts with HSA mainly through hydrogen bonding interactions and van der Waals interactions, while hydrophobic interactions and electrostatic interactions are dominant for interactions between BP-1, BP-2, BP-3 and HSA. Molecular docking revealed that the changes in structural moiety and hydrophobicity of four benzophenones account for their different binding affinities. As further revealed by circular dichroism and time-resolved fluorescence decay, these benzophenones cause global and local structural changes of HSA, which illustrates their potential toxicity to cause structural damage of HSA. Two degradation products of BP-3 have higher binding affinities to HSA, suggesting higher potencies in causing adverse effects on human health.

Zebrafish embryos/larvae for rapid determination of effects on hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-interrenal (HPI) axis: mRNA expression

To identify and prioritize chemicals that may affect thyroid and adrenal/interregnal endocrine system and to reduce cost and animal use by conventional toxicity assay, an in vivo screening assay was developed using zebrafish embryos/larvae based on measurement of expression of genes that were suggested to play important roles in hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-interrenal (HPI) axis. Model chemicals that could modulate HPT and HPI axis in adult fish were selected in assay validation, including anti-thyroid agent 6-Propyl-2-thiouracil (PTU) and cytochrome P450 11B (Cyp11b) enzyme inhibitor metyrapone (MET). Zebrafish embryos were exposed to different concentrations of model chemical from 4h post-fertilization (hpf) to 5d post-fertilization (dpf). Exposure to PTU increased mRNA expression of sodium iodide symporter (nis) and thyroglobulin (tg) involved in HPT axis, and MET treatment up-regulated all the mRNA expression tested involved in HPI axis by a compensatory mechanism. These results suggested that HPT and HPI axis were active upon chemical exposure at least at 5 dpf zebrafish. Furthermore, we studied the effects of PTU or MET on the cross-talk between HPT and HPI axis. The results demonstrated that PTU and MET could affect cross-talk responses in zebrafish embryos/larvae.

Soy extracts suppressed iodine uptake and stimulated the production of autoimmunogen in rat thyrocytes

Soy consumption is associated with thyroid disorders such as hypothyroidism, goiter, and autoimmune thyroid disease (ATD) as well as increased iodine requirement in certain cases. However, the anti-thyroid component(s) in soy are yet to be identified and the molecular mechanism(s) involved remain unclear. This study examined the effects of soy isoflavones (ISF) on iodide uptake and expression of thyroglobulin (Tg) and sodium/iodide symporter (NIS) in thyrocytes. Fischer rat thyroid cells (FRTL) were treated with Novasoy (a soy alcohol extract containing 30% ISF) or major ISF aglycones or glycosides for 24 h. Iodide uptake was measured by a colorimetric assay. The protein level of Tg and NIS was measured by Western blotting. Cytotoxicity of tested compounds was determined by the MTT cell proliferation assay. Iodide uptake in FRTL cells was dose-dependently suppressed by Novasoy added into the cell culture (10, 25, or 50 µg/mL, P < 0.05). However, neither the major ISF aglycones nor glycosides alone or in combination had similar effects. Novasoy (up to 200 µg/mL) had no cytotoxic effect. Novasoy (1, 10, and 50 µg/mL) and genistein (1 and 10 µM) markedly increased the protein content of a 40 kDa Tg fragment (P40, a known autoimmunogen) and non-glycosylated NIS in the FRTL cells (P < 0.05). Overall, this study demonstrated that the alcohol soluble component(s) other than the major ISF in soy remarkably inhibited iodide uptake in the FRTL cells. Soy ISF, particularly genistein, induced the production of P40, which might be responsible for the higher incidence of ATD reported in soy infant formula-fed children.

Using whole mount in situ hybridization to examine thyroid hormone deiodinase expression in embryonic and larval zebrafish: a tool for examining OH-BDE toxicity to early life stages

Polybrominated diphenyl ethers (PBDEs) and their oxidative metabolites (hydroxylated PBDEs; OH-BDEs) are known endocrine disrupting contaminants that have been shown to disrupt thyroid hormone regulation both in mammals and in fish. The purpose of this study was to determine the precise organ and tissue locations that express genes critical to thyroid hormone regulation in developing zebrafish (Danio rerio), and to determine the effects of an OH-BDE on their expression. While RT-PCR can provide quantitative data on gene expression, it lacks spatial sensitivity to examine localized gene expression; and, isolation of organs from zebrafish embryos is technically difficult, if not impossible. For this reason, the present study used whole mount in situ hybridization to simultaneously localize and quantify gene expression in vivo. While PBDEs and OH-BDEs have been shown to inhibit the activity and expression of deiodionases, a family of enzymes that regulate thyroid hormone concentrations intracellularly, it is unclear whether or not they can affect regional expression of the different isoforms during early development. In this study we investigated deiodinase 1 (Dio1), deiodinase 2 (Dio2), and deiodinase 3 (Dio3) mRNA expression at the following life stages (2, 8, and 1k-cells; 50%-epiboly, 6 and 18-somites, 22, 24, 48, 72 hpf and/or 10 dpf) in zebrafish and found life stage specific expression of these genes that were highly localized. To demonstrate the use of this technique for investigating potential endocrine disrupting effects, zebrafish embryos were exposed to 1, 10 and 100nM 6-OH-BDE-47. Significant increases in mean intensity of Dio1 and Dio3 expression in the periventricular zone of brain and pronephric duct, respectively (quantified by measuring intensity of coloration using ImageJ analysis software) were observed, suggesting localized response at the HPT axis with the possibility of impacting neurodevelopment. Our results demonstrate effects of OH-BDEs on thyroid regulating gene expression and provide more insight into potential sites of injury during early life stages.

Endocrine-related effects of perfluorooctanoic acid (PFOA) in zebrafish, H295R steroidogenesis and receptor reporter gene assays

Perfluorooctanoic acid (PFOA), a persistent perfluorinated compound, is distributed widely in wildlife and humans. Recent studies showed that PFOA is a suspected endocrine disruptor. But the results are somewhat contradictory and the mechanisms are unclear. In this study, we investigated the endocrine-related effects of PFOA using a series of assays. The lower dose effect of PFOA on development and endocrine-related gene expression were assessed in a short-term zebrafish assay in vivo. To clarify the mechanism of PFOA, in vitro assays were performed. We tested the hormone receptor activities of ER, AR, and TR against PFOA using reporter gene assays. The hormone levels of estradiol (E2) and testosterone (T), the expression of major steroidogenic genes and the key steroidogenic gene regulator steroidogenic factors 1 (SF-1) were measured after PFOA exposure in H295R steroidogenesis assay. Exposure of zebrafish embryo to PFOA resulted in higher expression of esr1, hhex and pax. PFOA is able to interfere with hormone receptor ER and TR. In H295R cells, PFOA could increase the E2 production and decrease the T production, altered the expression of major steroidogenic genes and regulator SF-1. The current findings indicated the potential endocrine-related effects of PFOA and provided novel information for human risk assessment.

Peri-conceptional changes in maternal exposure to sewage sludge chemicals disturbs fetal thyroid gland development in sheep

Ewes were exposed to sewage sludge-fertilized pastures in a study designed investigate pre-conceptual and/or gestational exposure to environmental chemicals. The in utero impact on fetal thyroid morphology and function at day 110 (of 145) of pregnancy was then determined. Pre-conceptual exposure increased the relative thyroid organ weights in male fetuses. The number of thyroid follicles in thyroids of fetuses after pre-conceptual or gestational exposure was reduced. This correlated with an increase in Ki67 positive cells. Pre-conceptual exposure to sewage sludge reduced small blood vessels in fetal thyroids. Thyroid tissues of exposed fetuses contained regions where mature angio-follicular units were reduced exhibiting decreased immunostaining for sodium-iodide symporter (NIS). Fetal plasma levels of fT3 and fT4 in exposed animals, however, were not different from controls suggesting compensatory changes in the thyroid gland to maintain homeostasis in exposed fetuses. The regional aberrations in thyroid morphology may impact on the post-natal life of the exposed offspring.

Mechanism-based testing strategy using in vitro approaches for identification of thyroid hormone disrupting chemicals

The thyroid hormone (TH) system is involved in several important physiological processes, including regulation of energy metabolism, growth and differentiation, development and maintenance of brain function, thermo-regulation, osmo-regulation, and axis of regulation of other endocrine systems, sexual behaviour and fertility and cardiovascular function. Therefore, concern about TH disruption (THD) has resulted in strategies being developed to identify THD chemicals (THDCs). Information on potential of chemicals causing THD is typically derived from animal studies. For the majority of chemicals, however, this information is either limited or unavailable. It is also unlikely that animal experiments will be performed for all THD relevant chemicals in the near future for ethical, financial and practical reasons. In addition, typical animal experiments often do not provide information on the mechanism of action of THDC, making it harder to extrapolate results across species. Relevant effects may not be identified in animal studies when the effects are delayed, life stage specific, not assessed by the experimental paradigm (e.g., behaviour) or only occur when an organism has to adapt to environmental factors by modulating TH levels. Therefore, in vitro and in silico alternatives to identify THDC and quantify their potency are needed. THDC have many potential mechanisms of action, including altered hormone production, transport, metabolism, receptor activation and disruption of several feed-back mechanisms. In vitro assays are available for many of these endpoints, and the application of modern '-omics' technologies, applicable for in vivo studies can help to reveal relevant and possibly new endpoints for inclusion in a targeted THDC in vitro test battery. Within the framework of the ASAT initiative (Assuring Safety without Animal Testing), an international group consisting of experts in the areas of thyroid endocrinology, toxicology of endocrine disruption, neurotoxicology, high-throughput screening, computational biology, and regulatory affairs has reviewed the state of science for (1) known mechanisms for THD plus examples of THDC; (2) in vitro THD tests currently available or under development related to these mechanisms; and (3) in silico methods for estimating the blood levels of THDC. Based on this scientific review, the panel has recommended a battery of test methods to be able to classify chemicals as of less or high concern for further hazard and risk assessment for THD. In addition, research gaps and needs are identified to be able to optimize and validate the targeted THD in vitro test battery for a mechanism-based strategy for a decision to opt out or to proceed with further testing for THD.

Monitoring of deiodinase deficiency based on transcriptomic responses in SH-SY5Y cells

Iodothyronine deiodinase types I, II, and III (D1, D2, and D3, respectively), which constitute a family of selenoenzymes, activate and inactivate thyroid hormones through the removal of specific iodine moieties from thyroxine and its derivatives. These enzymes are important in the biological effects mediated by thyroid hormones. The expression of activating and inactivating deiodinases plays a critical role in a number of cell systems, including the neuronal system, during development as well as in adult vertebrates. To investigate deiodinase-disrupting chemicals based on transcriptomic responses, we examined differences in gene expression profiles between T3-treated and deiodinase-knockdown SH-SY5Y cells using microarray analysis and quantitative real-time RT-PCR. A total of 1,558 genes, consisting of 755 upregulated and 803 downregulated genes, were differentially expressed between the T3-treated and deiodinase-knockdown cells. The expression levels of 10 of these genes (ID2, ID3, CCL2, TBX3, TGOLN2, C1orf71, ZNF676, GULP1, KLF9, and ITGB5) were altered by deiodinase-disrupting chemicals (2,3,7,8-tetrachlorodibenzo-p-dioxin, polychlorinated biphenyls, propylthiouracil, iodoacetic acid, methylmercury, β-estradiol, methimazole, 3-methylcholanthrene, aminotriazole, amiodarone, cadmium chloride, dimethoate, fenvalerate, octylmethoxycinnamate, iopanoic acid, methoxychlor, and 4-methylbenzylidene-camphor). These genes are potential biomarkers for detecting deiodinase deficiency and predicting their effects on thyroid hormone production.

Inhibition of the thyroid hormone pathway in Xenopus laevis by 2-mercaptobenzothiazole

Determining the effects of chemicals on the thyroid system is an important aspect of evaluating chemical safety from an endocrine disrupter perspective. Since there are numerous chemicals to test and limited resources, prioritizing chemicals for subsequent in vivo testing is critical. 2-Mercaptobenzothiazole (MBT), a high production volume chemical, was tested and shown to inhibit thyroid peroxidase (TPO) enzyme activity in vitro, a key enzyme necessary for the synthesis of thyroid hormone. To determine the thyroid disrupting activity of MBT in vivo, Xenopus laevis larvae were exposed using 7- and 21-day protocols. The 7-day protocol used 18-357 μg/L MBT concentrations and evaluated: metamorphic development, thyroid histology, circulating T4, circulating thyroid stimulating hormone, thyroidal sodium-iodide symporter gene expression, and thyroidal T4, T3, and related iodo-amino acids. The 21-day protocol used 23-435 μg/L MBT concentrations and evaluated metamorphic development and thyroid histology. Both protocols demonstrated that MBT is a thyroid disrupting chemical at the lowest concentrations tested. These studies complement the in vitro study used to identify MBT as a high priority for in vivo testing, supporting the utility/predictive potential of a tiered approach to testing chemicals for TPO activity inhibition. The 7-day study, with more comprehensive, sensitive, and diagnostic endpoints, provides information at intermediate biological levels that enables linking various endpoints in a robust and integrated pathway for thyroid hormone disruption associated with TPO inhibition.

Exposure of zebrafish embryos/larvae to TDCPP alters concentrations of thyroid hormones and transcriptions of genes involved in the hypothalamic-pituitary-thyroid axis

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) has been frequently detected in the environment and in various biota, including fish, and has been implicated in disruption of the thyroid endocrine system. In the present study, zebrafish (Danio rerio) embryos were exposed to different concentrations of TDCPP (10, 50, 100, 300 and 600 μg/L) from 2 h post-fertilization (hpf) to 144 hpf. Developmental endpoints, and whole-body concentrations of thyroid hormones and transcriptional profiles of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis were examined. Exposure to TDCPP caused a dose-dependent developmental toxicity, including decreased body weight, reduced hatching, survival and heartbeat rates, and increased malformation (spinal curvature). Treatment with the positive control chemical 3,3',5-triiodo-l-thyronine (T3) significantly decreased whole-body thyroxin (T4) concentrations, increased whole-body T3 concentrations, and upregulated mRNA expression involved in the HPT axis as a compensatory mechanism. These results suggested that the HPT axis in 144-hpf zebrafish larvae was responsive to chemical exposure and could be used to evaluate the effects of chemicals on the thyroid endocrine system. TDCPP exposure significantly decreased whole-body T4 concentrations and increased whole-body T3 concentrations, indicating thyroid endocrine disruption. The upregulation of genes related to thyroid hormone metabolism (dio1 and ugt1ab) might be responsible for decreased T4 concentrations. Treatment with TDCPP also significantly increased transcription of genes involved in thyroid hormone synthesis (tshβ, slc5a5 and tg) and thyroid development (hhex, nkx2.1 and pax8) as a compensatory mechanism for decreased T4 concentrations. Taken together, these results suggest that TDCPP alters the transcription of genes involved in the HPT axis and changes whole-body concentrations of thyroid hormones in zebrafish embryos/larvae, thus causing an endocrine disruption of the thyroid system.

Thyroid disruption in the lizard Podarcis bocagei exposed to a mixture of herbicides: a field study

Pesticide exposure has been related with thyroid disrupting effects in different vertebrate species. However, very little is known about the effects of these compounds in reptiles. In the Mediterranean area, lacertid lizards are the most abundant vertebrate group in agroecosystems, and have been identified as potential model species for reptile ecotoxicology. The aim of this study was to understand if the herbicides applied in corn fields have thyroid disruptive effects in the lizard Podarcis bocagei. Adult male lizards were captured in north-western Portugal in corn fields treated with herbicides (exposed sites), and in organic agricultural fields (reference sites). Thyroid and male gonad morphology and functionality, and testosterone levels were investigated through histological, immunohistochemical and biochemical techniques. Lizards from exposed locations displayed thyroid follicular lumens with more reabsorption vacuoles and significantly larger follicular area than those from reference fields. Furthermore, testes of lizards from exposed locations had significantly larger seminiferous tubule diameters, significantly higher number of spermatogenic layers and displayed an up-regulation of thyroid hormone receptors when compared with lizards from reference areas. These findings strongly suggest that the complex mixture of herbicides that lizards are exposed to in agricultural areas have thyroid disrupting effects which ultimately affect the male reproductive system. Alachlor, which has demonstrated thyroid effects in mammals, may be largely responsible for the observed effects.

Studying the effects of genistein on gene expression of fish embryos as an alternative testing approach for endocrine disruption

Assessment of endocrine disruption currently relies on testing strategies involving adult vertebrates. In order to minimize the use of animal tests according to the 3Rs principle of replacement, reduction and refinement, we propose a transcriptomics and fish embryo based approach as an alternative to identify and analyze an estrogenic activity of environmental chemicals. For this purpose, the suitability of 48 h and 7 days post-fertilization zebrafish and medaka embryos to test for estrogenic disruption was evaluated. The embryos were exposed to the phytoestrogen genistein and subsequently analyzed by microarrays and quantitative real-time PCR. The functional analysis showed that the genes affected related to multiple metabolic and signaling pathways in the early fish embryo, which reflect the known components of genistein's mode of actions, like apoptosis, estrogenic response, hox gene expression and steroid hormone synthesis. Moreover, the transcriptomic data also suggested a thyroidal mode of action and disruption of the nervous system development. The parallel testing of two fish species provided complementary data on the effects of genistein at gene expression level and facilitated the separation of common from species-dependent effects. Overall, the study demonstrated that combining fish embryo testing with transcriptomics can deliver abundant information about the mechanistic effects of endocrine disrupting chemicals, rendering this strategy a promising alternative approach to test for endocrine disruption in a whole organism in-vitro scale system.

Sunscreens: are they beneficial for health? An overview of endocrine disrupting properties of UV-filters

Today, topical application of sunscreens, containing ultraviolet-filters (UV-filters), is preferred protection against adverse effects of ultraviolet radiation. Evidently, use of sunscreens is effective in prevention of sunburns in various models. However, evidence for their protective effects against melanoma skin cancer is less conclusive. Three important observations prompted us to review the animal data and human studies on possible side effects of selected chemical UV-filters in cosmetics. (1) the utilization of sunscreens with UV-filters is increasing worldwide; (2) the incidence of the malignant disorder for which sunscreens should protect, malignant melanoma, is rapidly increasing and (3) an increasing number of experimental studies indicating that several UV-filters might have endocrine disruptive effects. The selected UV-filters we review in this article are benzophenone-3 (BP-3), 3-benzylidene camphor (3-BC), 3-(4-methyl-benzylidene) camphor (4-MBC), 2-ethylhexyl 4-methoxy cinnamate (OMC), Homosalate (HMS), 2-ethylhexyl 4-dimethylaminobenzoate (OD-PABA) and 4-aminobenzoic acid (PABA). The potential adverse effects induced by UV-filters in experimental animals include reproductive/developmental toxicity and disturbance of hypothalamic-pituitary-thyroid axis (HPT). Few human studies have investigated potential side effects of UV-filters, although human exposure is high as UV-filters in sunscreens are rapidly absorbed from the skin. One of the UV-filters, BP-3, has been found in 96% of urine samples in the US and several UV-filters in 85% of Swiss breast milk samples. It seems pertinent to evaluate whether exposure to UV-filters contribute to possible adverse effects on the developing organs of foetuses and children.

Developmental triclosan exposure decreases maternal, fetal, and early neonatal thyroxine: a dynamic and kinetic evaluation of a putative mode-of-action

This work tests the mode-of-action (MOA) hypothesis that maternal and developmental triclosan (TCS) exposure decreases circulating thyroxine (T4) concentrations via up-regulation of hepatic catabolism and elimination of T4. Time-pregnant Long-Evans rats received TCS po (0-300mg/kg/day) from gestational day (GD) 6 through postnatal day (PND) 21. Serum and liver were collected from dams (GD20, PND22) and offspring (GD20, PND4, PND14, PND21). Serum T4, triiodothyronine (T3), and thyroid-stimulating hormone (TSH) concentrations were measured by radioimmunoassay. Ethoxy-O-deethylase (EROD), pentoxyresorufin-O-depentylase (PROD) and uridine diphosphate glucuronyltransferase (UGT) enzyme activities were measured in liver microsomes. Custom Taqman(®) qPCR arrays were employed to measure hepatic mRNA expression of select cytochrome P450s, UGTs, sulfotransferases, transporters, and thyroid hormone-responsive genes. TCS was quantified by LC/MS/MS in serum and liver. Serum T4 decreased approximately 30% in GD20 dams and fetuses, PND4 pups and PND22 dams (300mg/kg/day). Hepatic PROD activity increased 2-3 fold in PND4 pups and PND22 dams, and UGT activity was 1.5 fold higher in PND22 dams only (300mg/kg/day). Minor up-regulation of Cyp2b and Cyp3a expression in dams was consistent with hypothesized activation of the constitutive androstane and/or pregnane X receptor. T4 reductions of 30% for dams and GD20 and PND4 offspring with concomitant increases in PROD (PND4 neonates and PND22 dams) and UGT activity (PND22 dams) suggest that up-regulated hepatic catabolism may contribute to TCS-induced hypothyroxinemia during development. Serum and liver TCS concentrations demonstrated greater fetal than postnatal internal exposure, consistent with the lack of T4 changes in PND14 and PND21 offspring. These data support the MOA hypothesis that TCS exposure leads to hypothyroxinemia via increased hepatic catabolism; however, the minor effects on thyroid hormone metabolism may reflect the low efficacy of TCS as thyroid hormone disruptor or highlight the possibility that other MOAs may also contribute to the observed maternal and early neonatal hypothyroxinemia.

Identification of iopanoic acid as substrate of type 1 deiodinase by a novel nonradioactive iodide-release assay

Enzymatic 5'- and 5-deiodination are key reactions for local and systemic activation and inactivation of iodothyronines and thyronamines. Expression of the three deiodinase (DIO) isoenzymes is regulated by a number of parameters, including thyroid status, genotype, micronutrient availability, and disease-related signaling. In addition, DIO are potential targets of pharmacological as well as environmentally derived substances, which might affect their enzymatic activity (endocrine disruptors). With the classical DIO activity assay, testing depends on the availability of radioactively labeled substrates (e.g. (125)I-rT(3)) to monitor the release of radioactive iodide. Recently, liquid chromatography-tandem mass spectrometry was described as an alternative method apparently resolving this limitation. However, it has a high demand in technical equipment and analytical routine and is limited in sample number by considerable measuring time. We therefore combined the classical deiodination assay with an easily accessible photometric method taking advantage of the Sandell-Kolthoff reaction for measuring iodide release. In brief, iodine works as a catalyst within this redox reaction between Ce(4+) and As(3+) leading to an acceleration of destaining. Furthermore, the protocol was adapted to minimize handling effort and time consumption. Because this method is not dependent on radioactivity, it expands the substrate spectrum of the classical method. Suitability of this assay was tested with tissue samples from animal experiments (hepatic Dio1 activity in hypo- and hyperthyroid mice) and established DIO inhibitors. As a new but not unexpected finding, the alleged inhibitor iopanoic acid turned out to be a DIO substrate. This finding was confirmed by liquid chromatography-tandem mass spectrometry, and its potential clinical impact requires further studies.

Use of TSHβ:EGFP transgenic zebrafish as a rapid in vivo model for assessing thyroid-disrupting chemicals

Accumulating evidence indicates that a wide range of chemicals have the ability to interfere with the hypothalamic-pituitary-thyroid (HPT) axis. Novel endpoints should be evaluated in addition to existing methods in order to effectively assess the effects of these chemicals on the HPT axis. Thyroid-stimulating hormone subunit β (TSHβ) plays central regulatory roles in the HPT system. We identified the regulatory region that determines the expression level of zebrafish TSHβ in the anterior pituitary. In the transgenic zebrafish with EGFP driven by the TSHβ promoter, the similar responsive patterns between the expression levels of TSHβ:EGFP and endogenous TSHβ mRNA in the pituitary are observed following treatments with goitrogen chemicals and exogenous thyroid hormones (THs). These results suggest that the TSHβ:EGFP transgenic reporter zebrafish may be a useful alternative in vivo model for the assessment of chemicals interfering with the HPT system.

Triiodothyronine-induced changes in the zebrafish transcriptome during the eleutheroembryonic stage: implications for bisphenol A developmental toxicity

Thyroid disruption during early development is a current matter of concern due to its significant human health implications. We present here a transcriptome analysis of thyroid hormone-regulated genes in zebrafish during the eleutheroembryonic stage (days 2-5 post fertilization) to detect potential markers of thyroid disruption. Exposure to 3,5,3'-triiodo-l-thyroxine (T3, 50 nM) induced changes in a minor portion (less than 2%) of the zebrafish transcriptome, with a significant fraction of genes involved in the haematopoietic system, eye formation, and ossification/skeletal system, including the thyroid receptor thra gene. Some of the transcriptomic changes were reflected macroscopically, as an allometric decrease of eye size and an increase on thra hybridization signal in the skeletal tissue. Using this information, changes on transcription of three genes (adult alpha globin gene si:ch211-5 k11.6, embryonic globin gene hbae3, and long wavelength cone opsin gene opn1/w1) were analyzed to monitor the effect of the suspected thyroid disrupter bisphenol A (BPA) on the thyroid system during this period of development of zebrafish. BPA acted as a weak T3 agonist when tested alone, but it strongly enhanced the effect of subsaturating concentrations of T3. In thyroxine immunofluorescence quantitative disruption tests (TIQDT), BPA did not prevent the ability of thyroid follicles to synthesize thyroxine, a landmark for direct goitrogens. Our results suggest that BPA potentiates the effect of endogenous T3 in early development and demonstrate the requirement for the use of in vivo, multi-endpoint methods to evaluate thyroid disruption hazards on early developmental processes in vertebrates.

Identification of classifiers for increase or decrease of thyroid peroxidase activity in the FTC-238/hTPO recombinant cell line

Thyroid peroxidase (TPO) plays an important role in thyroid hormone biosynthesis, as it catalyzes all of the essential steps in iodide organification. TPO activity can be detected using the guaiacol assay; however, this assay is complex and very time-consuming. Therefore, we focused on devising a simplified method using microarrays to detect changes in TPO activity, which is a target for disruption of the thyroid hormone axis. These experiments have systematically assessed the potential utility of transcriptomic end points as enhancements to the guaiacol assay. Previously, we demonstrated that benzophenone-2, benzophenone, perfluorooctane sulfonate, bisphenol A bis ether, and vinclozolin decreased TPO activity, and that dibutyl phthalate, carbaryl, dibenzo(a,h)anthracene, benzo(a)pyrene, and methylmercury increased TPO activity. In this work, we used human oligonucleotide chips to examine changes in the gene expression profile of FTC-238 human follicular thyroid carcinoma cells expressing human recombinant TPO, after exposure of the cells to TPO activity-disrupting agents. We identified 362 classifiers that could predict the effect of the toxicants on TPO activity with about 70% accuracy. These classifiers are potential markers for predicting the effects of chemicals on thyroid hormone production.

Zebrafish eleutheroembryos provide a suitable vertebrate model for screening chemicals that impair thyroid hormone synthesis

Thyroxine-immunofluorescence quantitative disruption test (TIQDT) was designed to provide a simple, rapid, alternative bioassay for assessing the potential of chemical pollutants and drugs to disrupt thyroid gland function. This study demonstrated that zebrafish eleutheroembryos provided a suitable vertebrate model, not only for screening the potential thyroid disrupting effect of molecules, but also for estimating the potential hazards associated with exposure to chemicals directly impairing thyroxine (T4) synthesis. Amitrole, potassium perchlorate, potassium thiocyanate, methimazole (MMI), phloroglucinol, 6-propyl-2-thiouracil, ethylenethiourea, benzophenone-2, resorcinol, pyrazole, sulfamethoxazole, sodium bromide, mancozeb, and genistein were classified as thyroid gland function disruptors. Concordance between TIQDT on zebrafish and mammalian published data was very high and the physiological relevance of T4-intrafollicular content was clearly higher than regulation at the transcriptional level of tg or slc5a5. Moreover, concentration-response analysis provided information about the thyroid disrupting potency and hazard of selected positive compounds. Finally, the effect of perchlorate, but not MMI, was completely rescued by low-micromolar amounts of iodide. TIQDT performed on zebrafish eleutheroembryos is an alternative whole-organism screening assay that provides relevant information for environmental and human risk assessments.

Tissue-specific thyroid hormone regulation of gene transcripts encoding iodothyronine deiodinases and thyroid hormone receptors in striped parrotfish (Scarus iseri)

In fish as in other vertebrates, the diverse functions of thyroid hormones are mediated at the peripheral tissue level through iodothyronine deiodinase (dio) enzymes and thyroid hormone receptor (tr) proteins. In this study, we examined thyroid hormone regulation of mRNAs encoding the three deiodinases dio1, dio2 and dio3 - as well as three thyroid hormone receptors trαA, trαB and trβ - in initial phase striped parrotfish (Scarus iseri). Parrotfish were treated with dissolved phase T(3) (20 nM) or methimazole (3 mM) for 3 days. Treatment with exogenous T(3) elevated circulating T(3), while the methimazole treatment depressed plasma T(4). Experimentally-induced hyperthyroidism increased the relative abundance of transcripts encoding trαA and trβ in the liver and brain, but did not affect trαB mRNA levels in either tissue. In both sexes, methimazole-treated fish exhibited elevated dio2 transcripts in the liver and brain, suggesting enhanced outer-ring deiodination activity in these tissues. Accordingly, systemic hyperthyroidism elevated relative dio3 transcript levels in these same tissues. In the gonad, however, patterns of transcript regulation were distinctly different with elevated T(3) increasing mRNAs encoding dio2 in testicular and ovarian tissues and dio3, trαA and trαB in the testes only. Thyroid hormone status did not affect dio1 transcript abundance in the liver, brain or gonads. Taken as a whole, these results demonstrate that thyroidal status influences relative transcript abundance for dio2 and dio3 in the liver, provide new evidence for similar patterns of dio2 and dio3 mRNA regulation in the brain, and make evident that fish exhibit tr subtype-specific transcript abundance changes to altered thyroid status.

Effect of endocrine disruptor pesticides: a review

Endocrine disrupting chemicals (EDC) are compounds that alter the normal functioning of the endocrine system of both wildlife and humans. A huge number of chemicals have been identified as endocrine disruptors, among them several pesticides. Pesticides are used to kill unwanted organisms in crops, public areas, homes and gardens, and parasites in medicine. Human are exposed to pesticides due to their occupations or through dietary and environmental exposure (water, soil, air). For several years, there have been enquiries about the impact of environmental factors on the occurrence of human pathologies. This paper reviews the current knowledge of the potential impacts of endocrine disruptor pesticides on human health.

Evaluation of effect of isoflavone on thyroid economy & autoimmunity in oophorectomised women: a randomised, double-blind, placebo-controlled trial

BACKGROUND AND OBJECTIVES

The potential of soy isoflavones to interfere with thyroid function has been reported. However, there are limited data regarding their effect on thyroid function and autoimmunity in surgical menopausal women. The present study aimed to evaluate the effect of isoflavones on thyroid function and autoimmunity, menopausal symptoms, serum follicle stimulating hormone (FSH) and estradiol levels in oophorectomised women.

METHODS

A randomized, double blind, placebo-controlled trial was conducted in 43 oophorectomised women to evaluate the effect of soy isoflavones (75 mg/day for 12 wk) on serum thyroid profile (free T3, free T4, TSH, TBG and anti-TPO antibody titres) assessed at baseline, 6 and 12 wk after randomization. Assessment was also done for menopause symptom score (MSS) three weekly, and FSH and estradiol levels at baseline and at study completion.

RESULTS

There was a significant alteration in free T3 levels in the group receiving isoflavones (4.05 ± 0.36, 4.12 ± 0.69 and 3.76 ± 0.55 pmol/l at baseline, 6 and 12 wk, respectively; P=0.02). However, the mean change in various thyroid parameters at 12 wk from baseline was not significantly different between the two groups. MSS was also significantly decreased at 9 and 12 wk from baseline with isoflavones (12.47 ± 8.15, 9.35 ± 5.23 and 9 ± 5.14 at baseline, 9 and 12 wk respectively; P=0.004) with significant improvement in urogenital symptoms compared to placebo. Isoflavones did not significantly affect other parameters during study period. There were no serious adverse events reported and the proportion of patients experiencing adverse events was similar between the two groups.

INTERPRETATION AND CONCLUSIONS

Modest reduction in serum free T3 levels in the isoflavone group in the absence of any effect on other thyroid parameters might be considered clinically unimportant.

The obesogen hypothesis: a shift of focus from the periphery to the hypothalamus

The obesogen concept proposes that environmental contaminants may be contributing to the epidemic of obesity and its related pathology, metabolic disorder. The first references to such a notion appeared at the beginning of the current decade, with the hypothesis that the correlation between increasing incidence of obesity and enhanced industrial chemical production was not simply coincidental, but potentially causally related. The next event was the introduction of the term "obesogen" as representing an environmental pollutant that adversely affects various aspects of adipose tissue functions. More recently, the concept was extended to include substances that may modify metabolic balance at the central, hypothalamic level. The actions of two prime candidate obesogens, tributyltin (TBT) and tetrabromobisphenol A (TBBPA), acting at the central level are the main focus of this review. Having discussed the evidence for contaminant accumulation in the environment and in human tissues and the potential mechanisms of action, data are provided showing that these two widespread pollutants modify hypothalamic gene regulations. Our studies are based on maternal exposure and measurement of effects in the progeny, mainly based on in vivo gene reporter assays. Such models are obviously pertinent to testing current hypotheses that propose that early exposure might exert effects on later development and physiological functions. The potential molecular mechanisms involved are discussed, as are the broader physiological consequences of these hypothalamic dysregulations.

Perfluorooctane sulfonate increased hepatic expression of OAPT2 and MRP2 in rats

The toxicity of perfluorooctane sulfonate (PFOS), a persistent organic compound, is of great concern. Several studies have reported that PFOS decreases circulating thyroid hormone (TH) concentrations. However, the mechanisms involved remain to be determined. Female rats were exposed to (1) vehicle; (2) PFOS (0.2, 1.0, and 3.0 mg/kg); (3) propylthiouracil (PTU, 10 mg/kg); or (4) PTU (10 mg/kg) + PFOS (3.0 mg/kg) by gavage once a day for 5 consecutive days. Parameters including contents of total T4 (TT4) and total T3 (TT3) in both serum and bile, serum concentrations of transthyretin and thyroglobulin, as well as transcripts of transporters involved in hepatic uptake and efflux of T4 were determined in control and PFOS-exposed groups. TT4 and TT3 were also analyzed in PTU and PTU + PFOS groups in order to reflect the different hormone effects between PFOS, PTU, and PFOS + PTU. Results showed that serum TT4 and TT3 decreased, while bile TT4 and TT3 remained stable following PFOS exposure. Exposure to 3.0 mg/kg of PFOS significantly enhanced hepatic organic anion transporter OATP2 mRNA expression (1.43 times of control). Treatment with PFOS increased hepatic expression of multidrug resistance--associated protein MRP2, approximately 1.80 and 1.69 times of control in 1.0 and 3.0 mg/kg groups, respectively. Spearman's correlation coefficients revealed that MRP2 mRNA expression correlated well with serum TT4 level (r = -0.528, P = 0.012). Serum thyroglobulin and transthyretin levels remained stable. Serum TT3, bile TT4, and bile TT3 were significantly different between PFOS and PTU groups. No significant differences of TT4 and TT3 in both serum and bile were observed between PTU and PTU + PFOS (P > 0.05). In conclusion, PFOS increased hepatic expression of OAPT2, which could possibly enhance hepatic uptake and metabolism of T4 in rats. PFOS-induced TT4 deficiency is mainly due to the extrathyroidal metabolism of T4, which is probably different from the classic goitrogen, PTU.