Environment and endocrinology: The case of thyroidology

Spatiotemporal variation of childhood hyperthyroidism: a 10-year nationwide study

OBJECTIVE

Childhood hyperthyroidism is mostly caused by Graves' disease, a rare autoimmune disease in children. Epidemiological data are scarce and the variability of within-region incidence is unknown. We aimed to provide the first description of temporal trends in pediatric hyperthyroidism in France and to explore spatial trends, with a view to identifying possible environmental triggers.

DESIGN AND METHODS

We performed an observational population-based study on data collected from the National Health Data System, covering the 2008-2017 period and the whole of France. We identified patients with an indicator reflecting incident cases of treated hyperthyroidism, in children aged 6 months-17.9 years, localized at the scale of the département (equivalent to a county) of residence. We performed descriptive analyses of incidence rate by sex, age, and year, and used a spatiotemporal model for estimation at département level.

RESULTS

We identified 4734 incident cases: 3787 girls (80%) and 947 boys (20%). The crude incidence rate was 3.35 (95% CI: 3.26; 3.45) per 100 000 person-years over the study period. We estimated the increase in incidence between 2008 and 2017 at 30.1% (19.0%; 42.3%). Annual incidence rate increased linearly over the 10-year period in both girls and boys, rising similarly in all age groups and in all départements. The spatial model highlighted marked heterogeneity in the risk of childhood hyperthyroidism across France.

CONCLUSION

The trend toward increasing incidence observed may reflect changes in genetic and environmental interactions, and the marked spatial heterogeneity may reflect localized ethnic or environmental factors worthy of further investigation.

Iodine as a potential endocrine disruptor-a role of oxidative stress

PURPOSE

Iodine is an essential micronutrient required for thyroid hormone biosynthesis. However, overtreatment with iodine can unfavorably affect thyroid physiology. The aim of this review is to present the evidence that iodine-when in excess-can interfere with thyroid hormone synthesis and, therefore, can act as a potential endocrine-disrupting chemical (EDC), and that this action, as well as other abnormalities in the thyroid, occurs-at least partially-via oxidative stress.

METHODS

We reviewed published studies on iodine as a potential EDC, with particular emphasis on the phenomenon of oxidative stress.

RESULTS

This paper summarizes current knowledge on iodine excess in the context of its properties as an EDC and its effects on oxidative processes.

CONCLUSION

Iodine does fulfill the criteria of an EDC because it is an exogenous chemical that interferes-when in excess-with thyroid hormone synthesis. However, this statement cannot change general rules regarding iodine supply, which means that iodine deficiency should be still eliminated worldwide and, at the same time, iodine excess should be avoided. Universal awareness that iodine is a potential EDC would make consumers more careful regarding their diet and what they supplement in tablets, and-what is of great importance-it would make caregivers choose iodine-containing medications (or other chemicals) more prudently. It should be stressed that compared to iodine deficiency, iodine in excess (acting either as a potential EDC or via other mechanisms) is much less harmful in such a sense that it affects only a small percentage of sensitive individuals, whereas the former affects whole populations; therefore, it causes endemic consequences.

Impact of Chemical Endocrine Disruptors and Hormone Modulators on the Endocrine System

There is growing concern regarding the health and safety issues of endocrine-disrupting chemicals (EDCs). Long-term exposure to EDCs has alarming adverse health effects through both hormone-direct and hormone-indirect pathways. Non-chemical agents, including physical agents such as artificial light, radiation, temperature, and stress exposure, are currently poorly investigated, even though they can seriously affect the endocrine system, by modulation of hormonal action. Several mechanisms have been suggested to explain the interference of EDCs with hormonal activity. However, difficulty in quantifying the exposure, low standardization of studies, and the presence of confounding factors do not allow the establishment of a causal relationship between endocrine disorders and exposure to specific toxic agents. In this review, we focus on recent findings on the effects of EDCs and hormone system modulators on the endocrine system, including the thyroid, parathyroid glands, adrenal steroidogenesis, beta-cell function, and male and female reproductive function.

Neurodevelopmental impact of the offspring by thyroid hormone system-disrupting environmental chemicals during pregnancy

Everyday use chemicals have been demonstrated to be endocrine disruptors. Since normal thyroid function during pregnancy is transcendental for the neurodevelopment of the offspring, knowledge of endocrine disrupting chemicals (EDC) is of main importance. The aim of our study is to recognize and describe EDC actions in pregnant women and focus on neurodevelopmental processes that can lead to neurotransmitter imbalance and cognitive impairment, and the possible clinical outcomes in the newborn and child. We searched PubMed databases for animal studies and clinical trials evaluating chemicals recognized as thyroid disruptors -perchlorate, phthalates, bisphenol A-, as well as chemicals with potential thyroid disruption activity -parabens, pesticides and persistent organic pollutants, on thyroid hormones (THs) levels and their bioavailability during pregnancy, and the outcome in newborns, infants and children. We also exhibit evidence from worldwide cohort studies to this regard. The publications reviewed show: 1) known endocrine disruptors have an association with hormonal thyroid levels, where an effect of increase or decrease in TH concentrations has been reported depending on the chemical exposed 2) associations between TH, EDCs and neurocognitive disorders have been addressed, such as ADHD, though no conclusive impact on potential related disorders as autism has been established, 3) perchlorate has demonstrated effects on thyroid levels on iodine uptake. In conclusion, detrimental risks and long-term consequences after in-utero exposure to EDCs are being reported in several cohort studies and further research must be conducted to establish a well-known cause-effect association.

The Association of Myo-Inositol and Selenium Contrasts Cadmium-Induced Thyroid C Cell Hyperplasia and Hypertrophy in Mice

Previous studies have demonstrated that, in addition to inducing structural changes in thyroid follicles, cadmium (Cd) increased the number of C cells. We examined the effects of myo-inositol (MI), seleno-L-methionine (Se), MI + Se, and resveratrol on C cells of mice exposed to cadmium chloride (Cd Cl2), as no data are currently available on the possible protective effects of these molecules. In contrast, we have previously shown this protective effect against CdCl2 on the thyroid follicles of mice. Ninety-eight C57 BL/6J adult male mice were divided into 14 groups of seven mice each: (i) 0.9% NaCl (vehicle; 1 ml/kg/day i.p.); (ii) Se (0.2 mg/kg/day per os); (iii) Se (0.4 mg/kg/day per os); (iv) MI (360 mg/kg/day per os); (v) Se (0.2 mg/kg/day) + MI; (vi) Se (0.4 mg/kg/day) + MI; (vii) resveratrol (20 mg/kg); (viii) CdCl2 (2 mg/kg/day i.p.) + vehicle; (ix) CdCl2 + Se (0.2 mg/kg/day); (x) CdCl2 + Se (0.4 mg/kg/day); (xi) CdCl2 + MI; (xii) CdCl2 + Se (0.2 mg/kg/day) + MI; (xiii) CdCl2 + Se (0.4 mg/kg/day) + MI; (xiv) CdCl2 + resveratrol (20 mg/kg). After 14 days, thyroids were processed for histological, immunohistochemical, and morphometric evaluation. Compared to vehicle, Cd significantly decreased follicle mean diameter, increased CT-positive cells number, area and cytoplasmic density, and caused the disappearance of TUNEL-positive C cells, namely, the disappearance of C cells undergoing apoptosis. Se at either 0.2 or 0.4 mg/kg/day failed to significantly increase follicular mean diameter, mildly decreased CT-positive cells number, area and cytoplasmic density, and was ineffective on TUNEL-positive C cells. Instead, MI alone increased significantly follicular mean diameter and TUNEL-positive cells number, and decreased significantly CT-positive cells number, area and cytoplasmic density. MI + Se 0.2 mg/kg/day or MI + Se 0.4 mg/kg/day administration improved all five indices more markedly. Indeed, follicular mean diameter and TUNEL-positive cells number increased significantly, while CT-positive cells number, area and cytoplasmic density decreased significantly. Thus, all five indices overlapped those observed in vehicle-treated mice. Resveratrol improved significantly all the considered parameters, with a magnitude comparable to that of MI alone. In conclusion, the association Myo + Se is effective in protecting the mouse thyroid from the Cd-induced hyperplasia and hypertrophy of C cells. This benefit adds to that exerted by Myo + Se on thyrocytes and testis.

Endocrine-Disrupting Chemicals' (EDCs) Effects on Tumour Microenvironment and Cancer Progression: Emerging Contribution of RACK1

Endocrine disruptors (EDCs) can display estrogenic and androgenic effects, and their exposure has been linked to increased cancer risk. EDCs have been shown to directly affect cancer cell regulation and progression, but their influence on tumour microenvironment is still not completely elucidated. In this context, the signalling hub protein RACK1 (Receptor for Activated C Kinase 1) could represent a nexus between cancer and the immune system due to its roles in cancer progression and innate immune activation. Since RACK1 is a relevant EDCs target that responds to steroid-active compounds, it could be considered a molecular bridge between the endocrine-regulated tumour microenvironment and the innate immune system. We provide an analysis of immunomodulatory and cancer-promoting effects of different EDCs in shaping tumour microenvironment, with a final focus on the scaffold protein RACK1 as a pivotal molecular player due to its dual role in immune and cancer contexts.

Effect of myrtle (Myrtus communis L.) essential oil on oxidant-antioxidant balance in rats with propylthiouracil-induced hypothyroidism

Among today's health problems, metabolic diseases are at the forefront. Hypothyroidism (HT) is a disease characterized by increased TSH, decreased T3&T4 concentrations in serum, with overall metabolic slowdown. Although there are many studies in the literature about oxidative status in HT, statements in these studies are contradictory. In our study, the effect of essential oils obtained from the leaves, flowers, and roots of Myrtus communis L. on oxidative metabolism in an HT model induced by propylthiouracil (PTU) in rats was investigated. A total of 36 Wistar albino rats were randomly divided into six groups as follows: (1) Control, (2) PTU, (3) M. communis L. oil 200 (MO 200), (4) M. communis L. oil 400 (MO 400), (5) PTU + MO 200, and (6) PTU + MO 400. In our study, while oxidative status deteriorates in groups given PTU, antioxidant activity increases in groups given M. communis L. oil. PRACTICAL APPLICATIONS: Essential oils are aromatic oily liquids derived from different parts of plants. M. communis L. is one of the best-known herbs in the class of aromatic and medicinal plants. This paper emphasizes the effect of M. communis L. oil on the negative oxidative state that occurs in HT conditions. The present study provides a positive effect of essential oils obtained from the M. communis L. on the oxidative state seen in HT. In light of this information, it may be beneficial to use M. communis L. oil due to its antioxidative effect in HT conditions.

Risk to human health related to the presence of perfluoroalkyl substances in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluoroalkyl substances (PFASs) in food. Based on several similar effects in animals, toxicokinetics and observed concentrations in human blood, the CONTAM Panel decided to perform the assessment for the sum of four PFASs: PFOA, PFNA, PFHxS and PFOS. These made up half of the lower bound (LB) exposure to those PFASs with available occurrence data, the remaining contribution being primarily from PFASs with short half-lives. Equal potencies were assumed for the four PFASs included in the assessment. The mean LB exposure in adolescents and adult age groups ranged from 3 to 22, the 95th percentile from 9 to 70 ng/kg body weight (bw) per week. Toddlers and 'other children' showed a twofold higher exposure. Upper bound exposure was 4- to 49-fold higher than LB levels, but the latter were considered more reliable. 'Fish meat', 'Fruit and fruit products' and 'Eggs and egg products' contributed most to the exposure. Based on available studies in animals and humans, effects on the immune system were considered the most critical for the risk assessment. From a human study, a lowest BMDL 10 of 17.5 ng/mL for the sum of the four PFASs in serum was identified for 1-year-old children. Using PBPK modelling, this serum level of 17.5 ng/mL in children was estimated to correspond to long-term maternal exposure of 0.63 ng/kg bw per day. Since accumulation over time is important, a tolerable weekly intake (TWI) of 4.4 ng/kg bw per week was established. This TWI also protects against other potential adverse effects observed in humans. Based on the estimated LB exposure, but also reported serum levels, the CONTAM Panel concluded that parts of the European population exceed this TWI, which is of concern.

Protective Effects of Myo-Inositol and Selenium on Cadmium-Induced Thyroid Toxicity in Mice

Cadmium (Cd) damages the thyroid gland. We evaluated the effects of myo-inositol (MI), seleno-L-methionine (Se) or their combination on the thyroids of mice simultaneously administered with Cd chloride (CdCl₂). Eighty-four male mice were divided into 12 groups (seven mice each). Six groups (controls) were treated with 0.9% NaCl (vehicle), Se (0.2 mg/kg/day), Se (0.4 mg/kg/day), MI (360 mg/kg/day), MI+Se (0.2 mg/kg) and MI+Se (0.4 mg/kg). The other six groups were treated with CdCl₂ (2 mg/kg), CdCl₂+MI, CdCl₂+Se (0.2 mg/kg), CdCl₂+Se (0.4 mg/kg), CdCl₂+MI+Se (0.2 mg/kg) and CdCl₂+MI+Se (0.4 mg/kg). An additional group of CdCl₂-challenged animals (n= 7) was treated with resveratrol (20 mg/kg), an effective and potent antioxidant. All treatments lasted 14 days. After sacrifice, the thyroids were evaluated histologically and immunohistochemically. CdCl₂ reduced the follicular area, increased the epithelial height, stroma, and cells expressing monocyte chemoattractant protein-1 (MCP-1) and C-X-C motif chemokine 10 (CXCL10). CdCl₂+Se at 0.2/0.4 mg/kg insignificantly reversed the follicular and stromal structure, and significantly decreased the number of MCP-1 and CXCL10-positive cells. CdCl₂+MI significantly reversed the thyroid structure and further decreased the number of MCP-1 and CXCL10-positive cells. CdCl₂+MI+Se, at both doses, brought all indices to those of CdCl₂-untreated mice. MI, particularly in association with Se, defends mice from Cd-induced damage. The efficacy of this combination was greater than that of resveratrol, at least when using the follicular structure as a read-out for a comparison. We suggest that the use of these nutraceuticals, more specifically the combination of MI plus SE, can protect the thyroid of Cd-exposed subjects.

Evaluation of potential sodium-iodide symporter (NIS) inhibitors using a secondary Fischer rat thyroid follicular cell (FRTL-5) radioactive iodide uptake (RAIU) assay

The Fischer rat thyroid follicular cell line (FRTL-5) endogenously expresses the sodium-iodide symporter (NIS) and has been used to identify environmental chemicals that perturb thyroid hormone homeostasis by disruption of NIS-mediated iodide uptake. Previously, a high-throughput radioactive iodide uptake (RAIU) screening assay incorporating the hNIS-HEK293T-EPA cell line was used to identify potential human NIS (hNIS) inhibitors in 1028 ToxCast Phase I (ph1_v2) and Phase II chemicals. In this study, the FRTL-5 cell line was evaluated and applied as a secondary RAIU assay coupled with cell viability assays to further prioritize highly active NIS inhibitors from the earlier screening. Assay validation with ten reference chemicals and performance assessment by chemical controls suggest the FRTL-5 based assays are robust and highly reproducible. Top-ranked chemicals from the ToxCast screening were then evaluated in both FRTL-5 and hNIS RAIU assays using newly sourced chemicals to strengthen the testing paradigm and to enable a rat vs. human species comparison. Eighteen of 29 test chemicals showed less than 1 order of magnitude difference in IC₅₀ values between the two assays. Notably, two common perfluorinated compounds, perfluorooctanesulfonic acid (PFOS) and perfluorohexane sulfonate (PFHxS), demonstrated strong NIS inhibitory activity [IC₅₀ - 6.45 (PFOS) and - 5.70 (PFHxS) log M in FRTL-5 RAIU assay]. In addition, several chemicals including etoxazole, methoxyfenozide, oxyfluorfen, triclocarban, mepanipyrim, and niclosamide also exhibited NIS inhibition with minimal cytotoxicity in both assays and are proposed for additional testing using short-term in vivo assays to characterize effects on thyroid hormone synthesis.

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

BACKGROUND

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

OBJECTIVES

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

DISCUSSION

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

Thyroid Hormones and Derivatives: Endogenous Thyroid Hormones and Their Targets

More than a century after the discovery of L-Thyroxine, the main thyroid hormone secreted solely by the thyroid gland, several metabolites of this iodinated, tyrosine-derived ancestral hormone have been identified. These are utilized as hormones during development, differentiation, metamorphosis, and regulation of most biochemical reactions in vertebrates and their precursor species. Among those metabolites are the thyromimetically active 3,3',5-Triiodo-L-thyronine (T3) and 3,5-Diiodo-L-thronine, reverse-T3 (3,3',5'-Triiodo-L-thyronine) with still unclear function, the recently re-discovered thyronamines (e.g., 3-Iodo-thyronamine), which exert in part T3-antagonistic functions, the thyroacetic acids (e.g., Tetrac and Triac), as well as various sulfated or glucuronidated metabolites of this panel of iodinated signaling compounds. In the blood most of these hydrophobic metabolites are tightly bound to the serum distributor proteins thyroxine binding globulin (TBG), transthyretin (TTR), albumin or apolipoprotein B100. Cellular import and export of these charged, highly hydrophobic amino acid derivatives requires a number of cell-membrane transporters or facilitators such as MCT8 or MCT10 and members of the OATP and LAT families of transporters. Depending on their structure, the thyroid hormone metabolites exert their cellular action by binding and thus modulating the function of various receptors systems (e.g., ανβ3 integrin receptor and transient receptor potential channels (TRPM8) of the cell membrane), in part linked to intracellular downstream kinase signaling cascades, and several isoforms of membrane-associated, mitochondrial or nuclear thyroid hormone receptors (TR), which are members of the c-erbA family of ligand-modulated transcription factors. Intracellular deiodinase selenoenzymes, which obligatory are membrane integrated enzymes, ornithine decarboxylase and monoamine oxidases control local availability of biologically active thyroid hormone metabolites. Inactivation of thyroid hormone metabolites occurs mainly by deiodination, sulfation or glucuronidation, reactions which favor their renal or fecal elimination.

Variations in biocorona formation related to defects in the structure of single walled carbon nanotubes and the hyperlipidemic disease state

Ball-milling utilizes mechanical stress to modify properties of carbon nanotubes (CNTs) including size, capping, and functionalization. Ball-milling, however, may introduce structural defects resulting in altered CNT-biomolecule interactions. Nanomaterial-biomolecule interactions result in the formation of the biocorona (BC), which alters nanomaterial properties, function, and biological responses. The formation of the BC is governed by the nanomaterial physicochemical properties and the physiological environment. Underlying disease states such as cardiovascular disease can alter the biological milieu possibly leading to unique BC identities. In this ex vivo study, we evaluated variations in the formation of the BC on single-walled CNTs (SWCNTs) due to physicochemical alterations in structure resulting from ball-milling and variations in the environment due to the high-cholesterol disease state. Increased ball-milling time of SWCNTs resulted in enhanced structural defects. Following incubation in normal mouse serum, label-free quantitative proteomics identified differences in the biomolecular content of the BC due to the ball-milling process. Further, incubation in cholesterol-rich mouse serum resulted in the formation of unique BCs compared to SWCNTs incubated in normal serum. Our study demonstrates that the BC is modified due to physicochemical modifications such as defects induced by ball-milling and physiological disease conditions, which may result in variable biological responses.

Epidemiological trends of iodine-related thyroid disorders: an example from Slovenia

The epidemiology of thyroid disorders is significantly associated with iodine supply. In 1999, Slovenia increased iodine content in kitchen salt from 10 mg to 25 mg of potassium iodide per kg of salt. According to the WHO criteria, Slovenia shifted from a mildly iodine-deficient country to a country with adequate iodine intake. Ten years after the increase in iodine intake, the incidence of diffuse goitre and thyroid autonomy decreased. Now patients with diffuse goitre and thyroid autonomy reach older age than the patients before the increase in iodine intake. In addition, patients with thyroid autonomy are less frequently hyperthyroid than ten years ago and iodine-induced hyperthyroidism is less severe. The incidence of highly malignant thyroid carcinoma has also dropped. However, the incidence of Hashimoto's thyroiditis increased, most probably in genetically predisposed individuals. Over the last ten years, many animal and in vitro studies evaluated the effects of endocrine disrupting chemicals (EDC) on various aspects of the thyroid function. They mostly studied the effects of polychlorinated biphenyls (PCBs) and dioxins, brominated flame retardants, phthalates, bisphenol A, perfluorinated chemicals, and perchlorate. However, human studies on the effects of EDCs on the thyroid function are very scarce, especially the long-term ones. What they do suggest is that PCBs and dioxins interfere with the transport of thyroid hormones and adversely affect the thyroid function. Many authors agree that iodine deficiency predisposes the thyroid gland to harmful effects of EDCs. Therefore the effects of EDCs in iodine-deficient areas could be more severe than in areas with adequate iodine intake.

Maternal total T4 during the first half of pregnancy: physiologic aspects and the risk of adverse outcomes in comparison with free T4

AIM

We aimed to investigate TT4 physiological aspects and associations with clinical end-points.

BACKGROUND

Total T4 (TT4) has been suggested as a marker for maternal thyroid function during pregnancy because as compared to FT4 (i) TT4 measurement is not affected by binding protein interference, (ii) TT4 is considered to be more stable from the second trimester onwards, and (iii) TT4 better reflects changes in the hypothalamic-pituitary-thyroid axis. However, this is based on data from small studies, and, more importantly, it is unknown whether TT4 is associated with adverse pregnancy or child outcomes.

METHODS

We selected 5647 mother-child pairs from a large population-based prospective cohort with data on maternal TSH, FT4 and TT4 during early pregnancy (median 13·2 weeks, 95% range 9·8-17·6). We used multivariable (non)linear and logistic regression models to study the association of maternal TT4 with pre-eclampsia, premature delivery, birthweight and offspring IQ and compare the results with previously obtained results for FT4.

RESULTS

The change of mean TT4 levels was 27·5% compared to 20·2% for FT4. There was a log-linear association of TT4 and FT4 with TSH, but the explained variability of TSH was much lower for TT4 than for FT4 (R-squared TT4: 2·5% vs 8·0% for FT4). In contrast to FT4, there was no independent association of maternal TT4 with pre-eclampsia, premature delivery, birthweight or offspring IQ.

CONCLUSION

Maternal TT4 levels are highly variable in the first half of pregnancy and are poorly related to maternal TSH. This study shows that maternal TT4 levels are either not associated, or not better associated as compared to FT4, with adverse pregnancy or child outcomes. This suggests that the maternal TT4 is inferior to FT4 in the assessment of maternal thyroid function during the first half of pregnancy.

Silychristin, a Flavonolignan Derived From the Milk Thistle, Is a Potent Inhibitor of the Thyroid Hormone Transporter MCT8

Thyroid hormones (THs) are charged and iodinated amino acid derivatives that need to pass the cell membrane facilitated by thyroid hormone transmembrane transporters (THTT) to exert their biological function. The importance of functional THTT is affirmed by the devastating effects of mutations in the human monocarboxylate transporter (MCT) 8, leading to a severe form of psychomotor retardation. Modulation of THTT function by pharmacological or environmental compounds might disturb TH action on a tissue-specific level. Therefore, it is important to identify compounds with relevant environmental exposure and THTT-modulating activity. Based on a nonradioactive TH uptake assay, we performed a screening of 13 chemicals, suspicious for TH receptor interaction, to test their potential effects on THTT in MCT8-overexpressing MDCK1-cells. We identified silymarin, an extract of the milk thistle, to be a potent inhibitor of T3 uptake by MCT8. Because silymarin is a complex mixture of flavonolignan substances, we further tested its individual components and identified silychristin as the most effective one with an IC50 of approximately 100 nM. The measured IC50 value is at least 1 order of magnitude below those of other known THTT inhibitors. This finding was confirmed by T3 uptake in primary murine astrocytes expressing endogenous Mct8 but not in MCT10-overexpressing MDCK1-cells, indicating a remarkable specificity of the inhibitor toward MCT8. Because silymarin is a frequently used adjuvant therapeutic for hepatitis C infection and chronic liver disease, our observations raise questions regarding its safety with respect to unwanted effects on the TH axis.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Selenium and the thyroid

PURPOSE OF REVIEW

This article provides an update on the role of the essential trace element selenium and its interaction with the other trace elements iodine and iron that together contribute to adequate thyroid hormone status. Synthesis, secretion, metabolism and action of thyroid hormone in target tissues depend on a balanced nutritional availability or supplementation of these elements. Selenium status is altered in benign and malignant thyroid diseases and various selenium compounds have been used to prevent or treat widespread diseases such as goiter, autoimmune thyroid disease or thyroid cancer.

RECENT FINDINGS

Several studies, most with still too low numbers of cases, indicate that selenium administration in both autoimmune thyroiditis (Hashimoto thyroiditis) and mild Graves' disease improves clinical scores and well-being of patients and reduces thyroperoxidase antibody titers. However, published results are still conflicting depending on basal selenium status, dose, time and form of selenium used for intervention. Evidence for sex-specific selenium action, lack of beneficial effects in pregnancy and contribution of genetic polymorphisms (selenoprotein S) has been presented.

SUMMARY

Adequate nutritional supply of selenium that saturates expression of circulating selenoprotein P, together with optimal iodine and iron intake, is required for a healthy and functional thyroid during development, adolescence, adulthood and aging.

An Improved Nonradioactive Screening Method Identifies Genistein and Xanthohumol as Potent Inhibitors of Iodothyronine Deiodinases

BACKGROUND

Deiodinases (DIO1, 2, and 3) are key enzymes in thyroid hormone (TH) activation and inactivation with impact on energy metabolism, development, cell differentiation, and a number of other physiological processes. The three DIO isoenzymes thus constitute sensitive rate-limiting components within the TH axis, prone to dysregulation by endocrine disruptive compounds or disease state. In animal models and cell culture experiments, they serve as readout for local TH status and disarrangement of the hormonal axis. Furthermore, some human diseases are characterized by apparent deiodinase dysregulation (e.g., the low triiodothyronine syndrome in critical illness). Consequently, these enzymes are targets of interest for the development of pharmacological compounds with modulatory activities. Until now, the portfolio of inhibitors for these enzymes is limited. In the clinics, the DIO1-specific inhibitor propylthiouracil is in use for treatment of severe hyperthyroidism. Other well-known inhibitors (e.g., iopanoic acid or aurothioglucose) are nonselective and block all three isoenzymes. Furthermore, DIO3 was shown to be a potential oncogenic gene, which is strongly expressed in some tumors and might, in consequence, protect tumor tissue form differentiation by TH. With respect to its role in tumorigenesis, specific inhibitors of DIO3 as a potential target for anticancer drugs would be highly desirable. To this end, a flexible and convenient assay for high-throughput screening is needed. We recently described a nonradioactive screening assay, utilizing the classic Sandell-Kolthoff reaction as readout for iodide release from the substrate molecules. While we used murine liver as enzyme source, the assay was limited to murine DIO1 activity testing. Here, we describe the use of recombinant proteins as enzyme sources within the assay, expanding its suitability from murine Dio1 to human DIO1, DIO2, and DIO3.

METHODS

As proof-of-concept, deiodination reactions catalyzed by these recombinant enzymes were monitored with various nonradioactive substrates and confirmed by liquid chromatography-tandem mass spectrometry.

RESULTS

The contrast agent and known DIO inhibitor iopanoic acid was characterized as readily accepted substrate by DIO2 and Dio3. In a screening approach using established endocrine disrupting compounds, the natural food ingredient genistein was identified as a further DIO1-specific inhibitor, while xanthohumol turned out to potently block the activity of all three isoenzymes.

CONCLUSIONS

A rapid nonradioactive screening method based on the Sandell-Kolthoff reaction is suitable for identification of environmental, nutritive and pharmacological compounds modulating activities of human deiodinase enzymes.

Chemical contamination and the thyroid

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

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

INTRODUCTION

Environmental exposure to harmful chemicals may produce severe consequences.

AIM

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

METHOD

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

RESULTS

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

CONCLUSIONS

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

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.

Endocrine-disrupting chemicals: associated disorders and mechanisms of action

The incidence and/or prevalence of health problems associated with endocrine-disruption have increased. Many chemicals have endocrine-disrupting properties, including bisphenol A, some organochlorines, polybrominated flame retardants, perfluorinated substances, alkylphenols, phthalates, pesticides, polycyclic aromatic hydrocarbons, alkylphenols, solvents, and some household products including some cleaning products, air fresheners, hair dyes, cosmetics, and sunscreens. Even some metals were shown to have endocrine-disrupting properties. Many observations suggesting that endocrine disruptors do contribute to cancer, diabetes, obesity, the metabolic syndrome, and infertility are listed in this paper. An overview is presented of mechanisms contributing to endocrine disruption. Endocrine disruptors can act through classical nuclear receptors, but also through estrogen-related receptors, membrane-bound estrogen-receptors, and interaction with targets in the cytosol resulting in activation of the Src/Ras/Erk pathway or modulation of nitric oxide. In addition, changes in metabolism of endogenous hormones, cross-talk between genomic and nongenomic pathways, cross talk with estrogen receptors after binding on other receptors, interference with feedback regulation and neuroendocrine cells, changes in DNA methylation or histone modifications, and genomic instability by interference with the spindle figure can play a role. Also it was found that effects of receptor activation can differ in function of the ligand.

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.

Thyroid cancer in Denmark 1943-2008, before and after iodine supplementation

Thyroid cancer incidence has increased worldwide during the previous decades. In this nationwide study, we aimed to identify the overall incidence of thyroid cancer in Denmark during 66 years (1943-2008) and incidences of the four main histological types of thyroid cancer from 1978 to 2008. Data were obtained from the nationwide Danish Cancer Registry, and we focused especially on the period after implementation of compulsory iodine supplementation, which was established on a national level in 2000. We calculated age-standardized incidence rates per 100,000 person-years, and age-period-cohort models were fitted to describe trends in incidence. To quantify trends in incidence over time, log-linear Poisson models were used to estimate annual percentage change. From 1943 to 2008, 1,947 men (29%) and 4,682 women (71%) were diagnosed with thyroid cancer. The age-standardized incidence increased in both sexes; in men from 0.41 to 1.57 per 100,000 and from 0.90 to 4.11 per 100,000 in women, corresponding to a significant average annual percentage change of 1.7 and 1.8%, respectively. The incidence increased with younger birth cohorts. The rise was almost exclusively caused by papillary carcinomas, and it was particularly present during the last decades of the study period. It cannot be ruled out that iodine supplementation may play a role for the risk of thyroid cancer, but as the strongest increase in incidence began in the years before the implementation, it is likely that improvement in diagnostic modalities increased diagnostic activity, and/or new unknown risk factors are also important contributors to the increase.

Extrapolation of hypothalamic-pituitary-thyroid axis perturbations and associated toxicity in rodents to humans: case study with perchlorate

Functional aspects of the Hypothalamic-Pituitary-Thyroid (HPT) axis in rats and humans are compared, exposing why extrapolation of toxicant-induced perturbations in the rat HPT axis to the human HPT axis cannot be accomplished using default risk assessment methodology. Computational tools, such as biologically based dose response models for the HPT axis, are recommended to perform complex animal to human extrapolations involving the HPT axis. Experimental and computational evidence are presented that suggest perchlorate acts directly on the thyroid gland in rats. The apparent escape from perchlorate-induced inhibition of thyroidal uptake of radioactive iodide in humans is discussed along with "rebound" or increased thyroidal uptake of radioactive iodide observed after discontinued clinical treatment with perchlorate.

Xanthohumol, a prenylated chalcone from hops, modulates hepatic expression of genes involved in thyroid hormone distribution and metabolism

In the present study, we analyzed the influence of xanthohumol (XN) on thyroid hormone (TH) distribution and metabolism in rats. A potent and selective competition of XN for thyroxine (T4) binding to transthyretin (IC(50)=1 microM at 1.7 nM [(125)I]T4) was found in human and rat sera in vitro. Female rats treated orally with XN showed increased hepatic expression of T4-binding globulin and decreased transthyretin and albumin. Thyrotropin levels and hepatic type 1 deiodinase activity were moderately increased. Northern blot analysis revealed diminished expression of liver sulfotransferase (Sult1a1) and uridine-diphosphate glucuronosyltransferase (Ugt1a1) after XN treatment. The transcript levels of constitutive androstane receptor (CAR), known to be involved in regulation of enzymes metabolizing hormones, drugs and xenobiotics, was lower in rats treated with >10 mg XN/kg body weight per day. Immunoblot analysis indicates reduced amounts of CAR protein. The phenobarbital-inducible cytochrome P450 mRNA level was decreased in rats treated with >10 mg XN/kg/day, in agreement with reduced CAR protein. Although only moderate changes in TH serum levels were observed, the XN-dependent altered expression of components involved in TH homeostasis might be important not only for hormone metabolism, but also for hepatic phase I and II elimination of drug metabolites and xenobiotics.

Effects of prenatal and postnatal exposure to a low dose of bisphenol A on behavior and memory in rats

Endocrine disruptors (EDs) are increasingly common chemicals in the environment. Bisphenol A (BPA), used to manufacture polycarbonate plastics, is an ED recognized for its estrogenic, anti-estrogenic, and anti-androgenic effects. Behavior is considered a vital characteristic for an animal's life cycle. This study evaluated the effect of exposure to low doses of BPA during pregnancy and/or lactation on several aspects of rat behavior, including memory, locomotion, and the exploratory instinct. Pups at 16 weeks of age (females and males) were divided into groups according to the mother's exposure to BPA (40μg/kg/day): CON (vehicle only); PRE (during pregnancy); LAC (during lactation); PRE-LAC (during both pregnancy and lactation). In the PRE-LAC group, exposure to BPA impaired both short-term (STM) and long-term memory (LTM) in inhibitory avoidance and the object recognition task, and also affected locomotor activity and spatial memory. Some sex-specific behavioral characteristics disappeared in the LAC group. Sex-specific memory and behavior impairment were caused by BPA exposure during brain organogenesis and differentiation.

Perchlorate and thiocyanate exposure and thyroid function in first-trimester pregnant women

CONTEXT

Thyroid hormone, requiring adequate maternal iodine intake, is critical for fetal neurodevelopment. Perchlorate decreases thyroidal iodine uptake by competitively inhibiting the sodium/iodide symporter. It is unclear whether environmental perchlorate exposure adversely affects thyroid function in pregnant women. Thiocyanate, derived from foods and cigarette smoke, is a less potent competitive sodium/iodide symporter inhibitor than perchlorate.

OBJECTIVE

Our objective was to determine whether environmental perchlorate and/or thiocyanate exposure is associated with alterations in thyroid function in pregnancy.

DESIGN AND SETTING

We conducted a cross-sectional study at health centers in Cardiff, Wales, and Turin, Italy.

PATIENTS

During 2002-2006, 22,000 women at less than 16 wk gestation were enrolled in the Controlled Antenatal Thyroid Screening Study. Subsets of 261 hypothyroid/hypothyroxinemic and 526 euthyroid women from Turin and 374 hypothyroid/hypothyroxinemic and 480 euthyroid women from Cardiff were selected based on availability of stored urine samples and thyroid function data.

MAIN OUTCOME MEASURES

Urinary iodine, thiocyanate, and perchlorate and serum TSH, free T(4) (FT(4)), and thyroperoxidase antibody were measured.

RESULTS

Urinary iodine was low: median 98 microg/liter in Cardiff and 52 microg/liter in Turin. Urine perchlorate was detectable in all women. The median (range) urinary perchlorate concentration was 5 microg/liter (0.04-168 microg/liter) in Turin and 2 microg/liter (0.02-368 microg/liter) in Cardiff. There were no associations between urine perchlorate concentrations and serum TSH or FT(4) in the individual euthyroid or hypothyroid/hypothyroxinemic cohorts. In multivariable linear analyses, log perchlorate was not a predictor of serum FT(4) or TSH.

CONCLUSIONS

Low-level perchlorate exposure is ubiquitous but did not affect thyroid function in this cohort of iodine-deficient pregnant women.

Health effects from long-range transported contaminants in Arctic top predators: An integrated review based on studies of polar bears and relevant model species

The aim of this review is to provide a thorough overview of the health effects from the complexed biomagnified mixture of long-range transported industrial organochlorines (OCs), polybrominated diphenyl ethers (PBDEs), perfluorinated compounds (PFCs) and mercury (Hg) on polar bear (Ursus maritimus) health. Multiple scientific studies of polar bears indicate negative relationships between exposure to these contaminants and health parameters; however, these are all of a correlative nature and do not represent true cause-and-effects. Therefore, information from controlled studies of farmed Norwegian Arctic foxes (Vulpes lagopus) and housed East and West Greenland sledge dogs (Canis familiaris) were included as supportive weight of evidence in the clarification of contaminant exposure and health effects in polar bears. The review showed that hormone and vitamin concentrations, liver, kidney and thyroid gland morphology as well as reproductive and immune systems of polar bears are likely to be influenced by contaminant exposure. Furthermore, exclusively based on polar bear contaminant studies, bone density reduction and neurochemical disruption and DNA hypomethylation of the brain stem seemed to occur. The range of tissue concentration, at which these alterations were observed in polar bears, were ca. 1-70,000 ng/g lw for OCs (blood plasma concentrations of some PCB metabolites even higher), ca. 1-1000 ng/g lw for PBDEs and for PFCs and Hg 114-3052 ng/g ww and 0.1-50 microg/g ww, respectively. Similar concentrations were found in farmed foxes and housed sledge dogs while the lack of dose response designs did not allow an estimation of threshold levels for oral exposure and accumulated tissue concentrations. Nor was it possible to pinpoint a specific group of contaminants being more important than others nor analyze their interactions. For East Greenland polar bears the corresponding daily SigmaOC and SigmaPBDE oral exposure was estimated to be 35 and 0.34 microg/kg body weight, respectively. Furthermore, PFC concentrations, at which population effect levels could occur, are likely to be reached around year 2012 for the East Greenland polar bear subpopulation if current increasing temporal trends continue. Such proposed reproductive population effects were supported by physiological based pharmacokinetic (PBPK) modelling of critical body residues (CBR) with risk quotients >or=1 for SigmaPCB, dieldrin, SigmaPFC and SigmaOHC (organohalogen contaminant). The estimated daily TEQ for East Greenland polar bears and East Greenland sledge dogs were 32-281-folds above WHO SigmaTEQ guidelines for humans. Compared to human tolerable daily intake (TDI), these were exceeded for PCBs, dieldrin, chlordanes and SigmaHCH in East Greenland polar bears. Comparisons like these should be done with caution, but together with the CBR modelling and T-score estimations, these were the only available tools for polar bear risk evaluation. In conclusion, polar bears seem to be susceptible to contaminant induced stress that may have an overall sub-clinical impact on their health and population status via impacts on their immune and reproductive systems.

Increase incidence of thyroid cancer in Florianopolis, Brazil: comparative study of diagnosed cases in 2000 and 2005

OBJECTIVE

To provide epidemiological information about thyroid cancer (TC) in the Metropolitan area of Florianopolis and investigate some factors that could be associated with this type of cancer.

METHOD

This study analyzed data of patients who had TC diagnosed and underwent surgical treatment in 2000 and 2005. Epidemiological factors about patients, tumors and surgical procedures were evaluated.

RESULTS

In 2000 and 2005, an increasing incidence of TC at a rate of 132.33% was detected. The increased rate was mainly observed for tumors measuring less than 1 cm (p = 0.004). Results also showed an increase in the number of multifocal tumors (p = 0.02) and in the rate of total thyroidectomy (p = 0.002).

CONCLUSIONS

The increasing incidence of TC in the Metropolitan area of Florianopolis is probably due to more invasive thyroid nodule management. Future studies are necessary to establish potential predicting factors for papillary thyroid microcarcinoma aggressiveness, as well as predictors of follicular lesion malignancy to identifying more accurately the appropriate therapy approach.

Environmental pollutants and the thyroid

Common environmental exposures may affect thyroid function in humans. Foetuses and infants are most vulnerable to these effects because they need thyroid hormone for normal neurodevelopment. Perchlorate, thiocyanate and nitrate are all competitive inhibitors of the sodium/iodine symporter (NIS) in pharmacologic doses, but their effects on human thyroid function at environmental exposure levels remain unclear. Many compounds, including polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs), bisphenol-A (BPA) and triclosan, may have direct actions on the thyroid hormone receptor, but these effects are complex and are not yet well understood. Isoflavones inhibit thyroperoxidase (TPO) activity, and, therefore, may cause goitre and hypothyroidism if ingested at high levels, particularly in iodine-deficient individuals. Organochlorine pesticides and dioxins may decrease serum T(4) half-life by activating hepatic enzymes. Additional studies are needed to further elucidate the risk posed by these and other potentially thyroid-disrupting compounds.

Chronic dietary exposure to environmental organochlorine contaminants induces thyroid gland lesions in Arctic foxes (Vulpes lagopus)

The impact of dietary organochlorine (OC) exposure on thyroid gland pathology was studied in farmed male Arctic foxes (Vulpes lagopus). The exposed group (n=16) was fed a diet based on wild minke whale (Balaenoptera acutorostrata) blubber as a main fat source in order to mimic the exposure to OC cocktails in the Artic environment. This resulted in an exposure of approximately 17 microg Sigma OC/kg day and a Sigma OC residue adipose tissue and liver concentration of 1700 and 4470 ng/gl.w., respectively, after 16 months of exposure. Control foxes (n=13) were fed a diet with pork (Sus scrofa) fat as a main fat source containing significantly lower OC concentrations. The food composition fed to the control and exposed group was standardized for nutrient contents. Four OC-related histopathological changes were found: (1) flat-epithelial-cell true thyroid cysts (TC) characterized by neutral content; (2) remnants of simple squamous epithelial-cell embryonic ducts containing neutral debris (EDN); (3) remnants of stratified squamous epithelial-cell embryonic ducts containing acid mucins often accompanied with debris of leukocyte inflammatory nature (EDM) and (4) disseminated thyroid C-cell hyperplasia (HPC). Of these, the prevalence of TC, EDN and HPC was significantly highest in the exposed group (chi(2) test: all p<0.04). The study shows that the OC mixture in minke whale blubber may cause development of thyroid gland cysts, C-cell hyperplasia and increase the prevalence of cystic remnants of embryonic ducts. The mechanism causing these effects could include endocrine disruption of the hypothalamus-pituitary-thyroid (HPT) axis, a disturbance of the calcium homeostasis/metabolism or energy metabolism or immune suppression. Because concentrations of OCs are higher in wild Arctic foxes, it is likely that these animals could suffer from similar OC-induced thyroid gland pathological and functional changes.