Perchlorate, iodine and the thyroid

Underlying Mechanisms of Pituitary-Thyroid Axis Function Disruption by Chronic Iodine Excess in Rats

BACKGROUND

Iodine is essential for thyroid hormone synthesis and is an important regulator of thyroid function. Chronic iodine deficiency leads to hypothyroidism, but iodine excess also impairs thyroid function causing hyperthyroidism, hypothyroidism, and/or thyroiditis. This study aimed to investigate the underlying mechanisms by which exposure to chronic iodine excess impairs pituitary-thyroid axis function.

METHODS

Male Wistar rats were treated for two months with NaI (0.05% and 0.005%) or NaI+NaClO₄ (0.05%) dissolved in drinking water. Hormone levels, gene expression, and thyroid morphology were analyzed later.

RESULTS

NaI-treated rats presented high levels of iodine in urine, increased serum thyrotropin levels, slightly decreased serum thyroxine/triiodothyronine levels, and a decreased expression of the sodium-iodide symporter, thyrotropin receptor, and thyroperoxidase mRNA and protein, suggesting a primary thyroid dysfunction. In contrast, thyroglobulin and pendrin mRNA and protein content were increased. Kidney and liver deiodinase type 1 mRNA expression was decreased in iodine-treated rats. Morphological studies showed larger thyroid follicles with higher amounts of colloid and increased amounts of connective tissue in the thyroid of iodine-treated animals. All these effects were prevented when perchlorate treatment was combined with iodine excess.

CONCLUSIONS

The present data reinforce and add novel findings about the disruption of thyroid gland function and the compensatory action of increased thyrotropin levels in iodine-exposed animals. Moreover, they draw attention to the fact that iodine intake should be carefully monitored, since both deficient and excessive ingestion of this trace element may induce pituitary-thyroid axis dysfunction.

Perchlorate Exposure Through Water and Milk in Istanbul

Perchlorate is a chemical pollutant that inhibits iodide uptake and may possibly impair thyroid function. Our previous study found widespread perchlorate exposure in non-pregnant, non-lactating, healthy women residing in Istanbul. The aim of this study is to assess the relative amounts of perchlorate exposure attributable to consumption of municipal water, bottled water and boxed milk available in Istanbul. Only trace levels of perchlorate were found in treated municipal water (58 % detectable, mean = 0.13 µg/L, maximum = 0.75 µg/L) and bottled water (7.4 % detectable, mean = <LOD, maximum = 0.19 µg/L). Conversely, all 30 boxed milk samples contained measurable levels of perchlorate (mean = 4.53 µg/L; maximum = 6.21 µg/L). Median perchlorate exposure attributable to water and milk (0.007 µg/kg/day) is small compared both to the reference dose (0.7 µg/kg/day) and to total perchlorate exposure (0.13 µg/kg/day) in Istanbul. Therefore, additional studies are needed to identify the major sources of perchlorate exposure in Istanbul.

Perchlorate in Water Supplies: Sources, Exposures, and Health Effects

Perchlorate exposure occurs from ingestion of natural or man-made perchlorate in food or water. Perchlorate is used in a variety of industrial products including missile fuel, fireworks, and fertilizers, and industrial contamination of drinking water supplies has occurred in a number of areas. Perchlorate blocks iodide uptake into the thyroid and decreases the production of thyroid hormone, a critical hormone for metabolism, neurodevelopment, and other physiologic functions. Occupational and clinical dosing studies have not identified clear adverse effects, but may be limited by small sample sizes, short study durations, and the inclusion of mostly healthy adults. Expanding evidence suggests that young children, pregnant women, fetuses, and people co-exposed to similarly acting agents may be especially susceptible to perchlorate. Given the ubiquitous nature of perchlorate exposure, and the importance of thyroid hormone for brain development, studying the impact of perchlorate on human health could have far-reaching public health implications.

Chlorine isotopic composition of perchlorate in human urine as a means of distinguishing among exposure sources

Perchlorate (ClO4(-)) is a ubiquitous environmental contaminant with high human exposure potential. Natural perchlorate forms in the atmosphere from where it deposits onto the surface of Earth, whereas synthetic perchlorate is manufactured as an oxidant for industrial, aerospace, and military applications. Perchlorate exposure can potentially cause adverse health effects in humans by interfering with the production of thyroid hormones through competitively blocking iodide uptake. To control and reduce perchlorate exposure, the contributions of different sources of perchlorate exposure need to be quantified. Thus, we demonstrate a novel approach for determining the contribution of different perchlorate exposure sources by quantifying stable and radioactive chlorine isotopes of perchlorate extracted from composite urine samples from two distinct populations: one in Atlanta, USA and one in Taltal, Chile (Atacama region). Urinary perchlorate from the Atlanta region resembles indigenous natural perchlorate from the western USA (δ(37)Cl=+4.1±1.0‰; (36)Cl/Cl=1 811 (±136) × 10(-15)), and urinary perchlorate from the Taltal, Chile region is similar to natural perchlorate in nitrate salt deposits from the Atacama Desert of northern Chile (δ(37)Cl=-11.0±1.0‰; (36)Cl/Cl=254 (±40) × 10(-15)). Neither urinary perchlorate resembled the isotopic pattern found in synthetic perchlorate. These results indicate that natural perchlorate of regional provenance is the dominant exposure source for the two sample populations, and that chlorine isotope ratios provide a robust tool for elucidating perchlorate exposure pathways.

Perchlorate as an emerging contaminant in soil, water and food

Perchlorate ( [Formula: see text] ) is a strong oxidizer and has gained significant attention due to its reactivity, occurrence, and persistence in surface water, groundwater, soil and food. Stable isotope techniques (i.e., ((18)O/(16)O and (17)O/(16)O) and (37)Cl/(35)Cl) facilitate the differentiation of naturally occurring perchlorate from anthropogenic perchlorate. At high enough concentrations, perchlorate can inhibit proper function of the thyroid gland. Dietary reference dose (RfD) for perchlorate exposure from both food and water is set at 0.7 μg kg(-1) body weight/day which translates to a drinking water level of 24.5 μg L(-1). Chromatographic techniques (i.e., ion chromatography and liquid chromatography mass spectrometry) can be successfully used to detect trace level of perchlorate in environmental samples. Perchlorate can be effectively removed by wide variety of remediation techniques such as bio-reduction, chemical reduction, adsorption, membrane filtration, ion exchange and electro-reduction. Bio-reduction is appropriate for large scale treatment plants whereas ion exchange is suitable for removing trace level of perchlorate in aqueous medium. The environmental occurrence of perchlorate, toxicity, analytical techniques, removal technologies are presented.

Thyroid nodules and thyroid autoimmunity in the context of environmental pollution

Evidence suggests that in most industrialized countries autoimmune disorders, including chronic lymphocytic thyroiditis, are increasing. This increase parallels the one regarding differentiated thyroid cancer, the increment of which is mainly due to the papillary histotype. A number of studies have pointed to an association between chronic lymphocytic thyroiditis and differentiated thyroid cancer. The upward trend of these two thyroid diseases is sustained by certain environmental factors, such as polluting substances acting as endocrine disrupting chemicals. Herein we will review the experimental and clinical literature that highlights the effects of environmental and occupational exposure to polluting chemicals in the development of autoimmune thyroid disease or differentiated thyroid cancer. Stakeholders, starting from policymarkers, should become more sensitive to the consequences for the thyroid resulting from exposure to EDC. Indeed, the economic burden resulting from such consequences has not been quantified thus far.

Perchlorate exposure does not modulate temporal variation of whole-body thyroid and androgen hormone content in threespine stickleback

Previously we showed that exposure of threespine stickleback (Gasterosteus aculeatus) to the endocrine disruptor perchlorate results in pronounced structural changes in thyroid and gonad, while surprisingly, whole-body thyroid hormone concentrations remain unaffected. To test for hormone titer variations on a finer scale, we evaluated the interactive effects of time (diel and reproductive season) and perchlorate exposure on whole-body contents of triiodothyronine (T3), thyroxine (T4), and 11-ketotestosterone (11-KT) in captive stickleback. Adult stickleback were exposed to 100ppm perchlorate or control water and sampled at 4-h intervals across the 24-hday and at one time-point (1100h) weekly across the reproductive season (May-July). Neither whole-body T3 nor T4 concentration significantly differed across the day in control or perchlorate treated stickleback. Across the reproductive season, whole-body T3 concentration remained stable while T4 significantly increased. However, neither hormone concentration was significantly affected by perchlorate, verifying our previous studies. The concentration of whole-body 11-KT, a major fish androgen, displayed significant diel variation and also steadily declined across the reproductive season in untreated males; perchlorate exposure did not influence the concentration of 11-KT in either diel or reproductive season schedules. Diel and reproductive season variations in 11-KT content in male stickleback are likely related to reproductive physiology and behavior. The observed increase in T4 content across the reproductive season may be reflective of increased energy investment in reproduction near the end of the life cycle.

Developmental timing of perchlorate exposure alters threespine stickleback dermal bone

Adequate levels of thyroid hormone are critical during development and metamorphosis, and for maintaining metabolic homeostasis. Perchlorate, a common contaminant of water sources, inhibits thyroid function in vertebrates. We utilized threespine stickleback (Gasterosteus aculeatus) to determine if timing of perchlorate exposure during development impacts adult dermal skeletal phenotypes. Fish were exposed to water contaminated with perchlorate (30mg/L or 100mg/L) beginning at 0, 3, 7, 14, 21, 42, 154 or 305days post fertilization until sexual maturity at 1year of age. A reciprocal treatment moved stickleback from contaminated to clean water on the same schedule providing for different stages of initial exposure and different treatment durations. Perchlorate exposure caused concentration-dependent significant differences in growth for some bony traits. Continuous exposure initiated within the first 21days post fertilization had the greatest effects on skeletal traits. Exposure to perchlorate at this early stage can result in small traits or abnormal skeletal morphology of adult fish which could affect predator avoidance and survival.

Perchlorate in Lake Water from an Operating Diamond Mine

Mining-related perchlorate [ClO4(-)] in the receiving environment was investigated at the operating open-pit and underground Diavik diamond mine, Northwest Territories, Canada. Samples were collected over four years and ClO4(-) was measured in various mine waters, the 560 km(2) ultraoligotrophic receiving lake, background lake water and snow distal from the mine. Groundwaters from the underground mine had variable ClO4(-) concentrations, up to 157 μg L(-1), and were typically an order of magnitude higher than concentrations in combined mine waters prior to treatment and discharge to the lake. Snow core samples had a mean ClO4(-) concentration of 0.021 μg L(-1) (n=16). Snow and lake water Cl(-)/ClO4(-) ratios suggest evapoconcentration was not an important process affecting lake ClO4(-) concentrations. The multiyear mean ClO4(-) concentrations in the lake were 0.30 μg L(-1) (n = 114) in open water and 0.24 μg L(-1) (n = 107) under ice, much below the Canadian drinking water guideline of 6 μg L(-1). Receiving lake concentrations of ClO4(-) generally decreased year over year and ClO4(-) was not likely [biogeo]chemically attenuated within the receiving lake. The discharge of treated mine water was shown to contribute mining-related ClO4(-) to the lake and the low concentrations after 12 years of mining were attributed to the large volume of the receiving lake.

The epidemiology of global micronutrient deficiencies

Micronutrients are essential to sustain life and for optimal physiological function. Widespread global micronutrient deficiencies (MNDs) exist, with pregnant women and their children under 5 years at the highest risk. Iron, iodine, folate, vitamin A, and zinc deficiencies are the most widespread MNDs, and all these MNDs are common contributors to poor growth, intellectual impairments, perinatal complications, and increased risk of morbidity and mortality. Iron deficiency is the most common MND worldwide and leads to microcytic anemia, decreased capacity for work, as well as impaired immune and endocrine function. Iodine deficiency disorder is also widespread and results in goiter, mental retardation, or reduced cognitive function. Adequate zinc is necessary for optimal immune function, and deficiency is associated with an increased incidence of diarrhea and acute respiratory infections, major causes of death in those <5 years of age. Folic acid taken in early pregnancy can prevent neural tube defects. Folate is essential for DNA synthesis and repair, and deficiency results in macrocytic anemia. Vitamin A deficiency is the leading cause of blindness worldwide and also impairs immune function and cell differentiation. Single MNDs rarely occur alone; often, multiple MNDs coexist. The long-term consequences of MNDs are not only seen at the individual level but also have deleterious impacts on the economic development and human capital at the country level. Perhaps of greatest concern is the cycle of MNDs that persists over generations and the intergenerational consequences of MNDs that we are only beginning to understand. Prevention of MNDs is critical and traditionally has been accomplished through supplementation, fortification, and food-based approaches including diversification. It is widely accepted that intervention in the first 1,000 days is critical to break the cycle of malnutrition; however, a coordinated, sustainable commitment to scaling up nutrition at the global level is still needed. Understanding the epidemiology of MNDs is critical to understand what intervention strategies will work best under different conditions.

The Relationship between Perchlorate in Drinking Water and Cord Blood Thyroid Hormones: First Experience from Iran

Background:

Considering the controversial information regarding the effects of perchlorate on thyroid function of high risk population as neonates, and given the high prevalence rate of thyroid disorders specially congenital hypothyroidism in our region, this study aims to investigate for the first time in Iran, the relationship between drinking groundwater perchlorate and cord blood thyroid hormones level in an industrial region.

Methods:

In this cross-sectional study, drinking groundwater perchlorate level of rural areas of Zarinshahr, Isfahan was measured. Simultaneously, cord blood level of thyroid hormones of neonates born in the studied region was measured. Thyroid function test of neonates in regions with low and high perchlorate level were compared.

Results:

In this study, 25 tap water samples were obtained for perchlorate measurement. Level of cord blood thyroid stimulating hormone (TSH), T4 and T3 of 25 neonates were measured. Mean (standard deviation) of perchlorate, TSH, T4 and T3 was 3.59 (5.10) μg/l, 7.81 (4.14) mIU/m, 6.06 (0.85) mg/dl, and 63.46 (17.53) mg/dl, respectively. Mean levels of thyroid function tests were not different in low (<5 μg/l) and high level of drinking ground water perchlorate (P > 0.05).

Conclusions:

Perchlorate did not appear to be related to thyroid function of neonates in the studied industrial region. It seems that iodine status of the regions, as well as other environmental contaminants and genetic background, could impact on its relation with thyroid function of neonates.

Gestational and early postnatal hypothyroidism alters VGluT1 and VGAT bouton distribution in the neocortex and hippocampus, and behavior in rats

Thyroid hormones are fundamental for the expression of genes involved in the development of the CNS and their deficiency is associated with a wide spectrum of neurological diseases including mental retardation, attention deficit-hyperactivity disorder and autism spectrum disorders. We examined in rat whether developmental and early postnatal hypothyroidism affects the distribution of vesicular glutamate transporter-1 (VGluT1; glutamatergic) and vesicular inhibitory amino acid transporter (VGAT; GABAergic) immunoreactive (ir) boutons in the hippocampus and somatosensory cortex, and the behavior of the pups. Hypothyroidism was induced by adding 0.02% methimazole (MMI) and 1% KClO4 to the drinking water starting at embryonic day 10 (E10; developmental hypothyroidism) and E21 (early postnatal hypothyroidism) until day of sacrifice at postnatal day 50. Behavior was studied using the acoustic prepulse inhibition (somatosensory attention) and the elevated plus-maze (anxiety-like assessment) tests. The distribution, density and size of VGluT1-ir and VGAT-ir boutons in the hippocampus and somatosensory cortex was abnormal in MMI pups and these changes correlate with behavioral changes, as prepulse inhibition of the startle response amplitude was reduced, and the percentage of time spent in open arms increased. In conclusion, both developmental and early postnatal hypothyroidism significantly decreases the ratio of GABAergic to glutamatergic boutons in dentate gyrus leading to an abnormal flow of information to the hippocampus and infragranular layers of the somatosensory cortex, and alter behavior in rats. Our data show cytoarchitectonic alterations in the basic excitatory hippocampal loop, and in local inhibitory circuits of the somatosensory cortex and hippocampus that might contribute to the delayed neurocognitive outcome observed in thyroid hormone deficient children born in iodine deficient areas, or suffering from congenital hypothyroidism.

Perchlorate in the Great Lakes: isotopic composition and origin

Perchlorate is a persistent and mobile contaminant in the environment with both natural and anthropogenic sources. Stable isotope ratios of oxygen (δ(18)O, Δ(17)O) and chlorine (δ(37)Cl) along with the abundance of the radioactive isotope (36)Cl were used to trace perchlorate sources and behavior in the Laurentian Great Lakes. These lakes were selected for study as a likely repository of recent atmospheric perchlorate deposition. Perchlorate concentrations in the Great Lakes range from 0.05 to 0.13 μg per liter. δ(37)Cl values of perchlorate from the Great Lakes range from +3.0‰ (Lake Ontario) to +4.0‰ (Lake Superior), whereas δ(18)O values range from -4.1‰ (Lake Superior) to +4.0‰ (Lake Erie). Great Lakes perchlorate has mass-independent oxygen isotopic variations with positive Δ(17)O values (+1.6‰ to +2.7‰) divided into two distinct groups: Lake Superior (+2.7‰) and the other four lakes (∼+1.7‰). The stable isotopic results indicate that perchlorate in the Great Lakes is dominantly of natural origin, having isotopic composition resembling that measured for indigenous perchlorate from preindustrial groundwaters of the western USA. The (36)Cl/Cl ratio of perchlorate varies widely from 7.4 × 10(-12) (Lake Ontario) to 6.7 × 10(-11) (Lake Superior). These (36)ClO4(-) abundances are consistent with an atmospheric origin of perchlorate in the Great Lakes. The relatively high (36)ClO4(-) abundances in the larger lakes (Lakes Superior and Michigan) could be explained by the presence of (36)Cl-enriched perchlorate deposited during the period of elevated atmospheric (36)Cl activity following thermonuclear bomb tests in the Pacific Ocean.

Environmental perchlorate exposure: potential adverse thyroid effects

PURPOSE OF REVIEW

This review will present a general overview of the sources, human studies, and proposed regulatory action regarding environmental perchlorate exposure.

RECENT FINDINGS

Some recent studies have reported significant associations between urinary perchlorate concentrations, thyroid dysfunction, and decreased infant intelligence quotient in groups who would be particularly susceptible to perchlorate effects. An update regarding the recently proposed regulatory actions and potential costs surrounding amelioration of perchlorate contamination is provided.

SUMMARY

The potential adverse thyroidal effects of environmental perchlorate exposure remain controversial, and further research is needed to further define its relationship to human health among pregnant and lactating women and their infants.

An evo-devo approach to thyroid hormones in cerebral and cerebellar cortical development: etiological implications for autism

The morphological alterations of cortical lamination observed in mouse models of developmental hypothyroidism prompted the recognition that these experimental changes resembled the brain lesions of children with autism; this led to recent studies showing that maternal thyroid hormone deficiency increases fourfold the risk of autism spectrum disorders (ASD), offering for the first time the possibility of prevention of some forms of ASD. For ethical reasons, the role of thyroid hormones on brain development is currently studied using animal models, usually mice and rats. Although mammals have in common many basic developmental principles regulating brain development, as well as fundamental basic mechanisms that are controlled by similar metabolic pathway activated genes, there are also important differences. For instance, the rodent cerebral cortex is basically a primary cortex, whereas the primary sensory areas in humans account for a very small surface in the cerebral cortex when compared to the associative and frontal areas that are more extensive. Associative and frontal areas in humans are involved in many neurological disorders, including ASD, attention deficit-hyperactive disorder, and dyslexia, among others. Therefore, an evo-devo approach to neocortical evolution among species is fundamental to understand not only the role of thyroid hormones and environmental thyroid disruptors on evolution, development, and organization of the cerebral cortex in mammals but also their role in neurological diseases associated to thyroid dysfunction.

Disruption of the thyroid system by the thyroid-disrupting compound Aroclor 1254 in juvenile Japanese flounder (Paralichthys olivaceus)

Polychlorinated biphenyls (PCBs) are a group of persistent organochlorine compounds that have the potential to disrupt the homeostasis of thyroid hormones (THs) in fish, particularly juveniles. In this study, thyroid histology, plasma TH levels, and iodothyronine deiodinase (IDs, including ID₁, ID₂, and ID₃) gene expression patterns were examined in juvenile Japanese flounder (Paralichthys olivaceus) following 25- and 50- day waterborne exposure to environmentally relevant concentrations of a commercial PCB mixture, Aroclor 1254 (10, 100, and 1000 ng/L) with two-thirds of the test solutions renewed daily. The results showed that exposure to Aroclor 1254 for 50 d increased follicular cell height, colloid depletion, and hyperplasia. In particular, hypothyroidism, which was induced by the administration of 1000 ng/L Aroclor 1254, significantly decreased plasma TT₄, TT₃, and FT₃ levels. Profiles of the changes in mRNA expression levels of IDs were observed in the liver and kidney after 25 and 50 d PCB exposure, which might be associated with a reduction in plasma THs levels. The expression level of ID₂ mRNA in the liver exhibited a dose-dependent increase, indicating that this ID isotype might serve as sensitive and stable indicator for thyroid-disrupting chemical (TDC) exposure. Overall, our study confirmed that environmentally relevant concentrations of Aroclor 1254 cause significant thyroid disruption, with juvenile Japanese flounder being suitable candidates for use in TDC studies.

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

CONTEXT

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

OBJECTIVE

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

DESIGN AND PATIENTS

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

MEASURES

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

RESULTS

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

CONCLUSIONS

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

Iodide transport: implications for health and disease

Disorders of the thyroid gland are among the most common conditions diagnosed and managed by pediatric endocrinologists. Thyroid hormone synthesis depends on normal iodide transport and knowledge of its regulation is fundamental to understand the etiology and management of congenital and acquired thyroid conditions such as hypothyroidism and hyperthyroidism. The ability of the thyroid to concentrate iodine is also widely used as a tool for the diagnosis of thyroid diseases and in the management and follow up of the most common type of endocrine cancers: papillary and follicular thyroid cancer. More recently, the regulation of iodide transport has also been the center of attention to improve the management of poorly differentiated thyroid cancer. Iodine deficiency disorders (goiter, impaired mental development) due to insufficient nutritional intake remain a universal public health problem. Thyroid function can also be influenced by medications that contain iodide or interfere with iodide metabolism such as iodinated contrast agents, povidone, lithium and amiodarone. In addition, some environmental pollutants such as perchlorate, thiocyanate and nitrates may affect iodide transport. Furthermore, nuclear accidents increase the risk of developing thyroid cancer and the therapy used to prevent exposure to these isotopes relies on the ability of the thyroid to concentrate iodine. The array of disorders involving iodide transport affect individuals during the whole life span and, if undiagnosed or improperly managed, they can have a profound impact on growth, metabolism, cognitive development and quality of life.

Regulation of iodide uptake in placental primary cultures

BACKGROUND

Maintenance of adequate iodide supply to the developing fetus is dependent not only on maternal dietary iodine intake but also on placental iodide transport. The objective of this study was to examine the effects of different pregnancy-associated hormones on the uptake of radioiodide by the placenta and to determine if iodide transporter expression is affected by hormone incubation.

METHODS

Primary cultures of placental trophoblast cells were established from placentas obtained at term from pre-labor caesarean sections. They were pre-incubated with 17β-estradiol, prolactin, oxytocin, human chorionic gonadotropin (hCG) and progesterone either singly or in combination over 12 h with (125)I uptake being measured after 6 h. RNA was isolated from placental trophoblasts and real-time RT-PCR performed using sodium iodide symporter (NIS) and pendrin (PDS) probes.

RESULTS

Significant dose response increments in (125)I uptake by trophoblast cells (p < 0.01) were observed following incubation with hCG (60% increase), oxytocin (45% increase) and prolactin (32% increase). Although progesterone (50-200 ng/ml) and 17β-estradiol (1,000-15,000 pg/ml) alone produced no significant differences in uptake, they facilitated increased uptake when combined with prolactin or oxytocin, with a combination of all four hormones producing the greatest increase (82%). Increased (125)I uptake was accompanied by corresponding increments in NIS mRNA (ratio 1.52) compared to untreated control cells. No significantly increased expression levels of PDS were observed.

CONCLUSIONS

Pregnancy-associated hormones, particularly oxytocin and hCG, have a role in promoting placental iodide uptake which may protect the fetus against iodine deficiency.

Impact of pregnancy and other factors on the levels of urinary perchlorate, thiocyanate, and nitrate among females aged 15-44 years: data from National Health and Nutrition Examination Survey: 2003-2008

Impact of pregnancy on levels of urinary perchlorate, thiocyanate, and nitrate has not been studied using large scale data. Data from National Health and Nutrition Examination Survey for the years 2003-2008 were used to evaluate risk factors that impact levels of these contaminants among females of child bearing age. In addition to pregnancy, other risk factors evaluated were: age, race/ethnicity, smoking status, serum triglyceride levels, and iodine deficiency status. Pregnancy did not affect the levels of perchlorate and nitrate but, new to this study, it was found that thiocyanate levels were statistically significantly lower among pregnant females as compared to non-pregnant females (p<0.01). Iodine deficient females had statistically significantly lower levels of these contaminates than iodine replete females (p<0.01). Levels of thiocyanate among smokers were about five times higher than among non-smokers. Non-Hispanic Blacks had the lowest and Mexican Americans had the highest levels of perchlorate and nitrate. The reverse was true for thiocyanate levels. There was an inverse association between nitrate and education levels. There was a positive association between serum triglyceride levels and the levels of these contaminants. Also, new to this study, of concern, was the fact that levels of these contaminants increased among females over the period 2005-2008. Levels of perchlorate, thiocyanate, and nitrate did not vary across pregnancy trimesters.

Increasing incidence of thyroid cancer: controversies explored

Thyroid cancer is the most common endocrine malignancy and its incidence has been increasing considerably in the past few decades. Many studies have been published providing evidence for this increase; however, why thyroid cancer incidence keeps rising is still debated and there are conflicting reports of factors leading to the increase in its incidence. In this article, Nature Reviews Endocrinology asks four experts their opinions on some of the controversies surrounding the changing trends in thyroid cancer incidence.

Metals in blood and urine, and thyroid function among adults in the United States 2007-2008

The thyroid is integral to regulation of development and metabolism. Certain metals have been shown to affect thyroid function in occupationally exposed persons, but few studies have been conducted in the general population. This study evaluates the association between biomarkers of metal exposure and thyroid hormones in the US population. Analyses included adults participating in the 2007-2008 National Health and Nutrition Examination Survey, with no history of thyroid disease or use of thyroid medications, and with data on metals in blood (lead, cadmium and mercury) and urine (lead, cadmium, mercury, barium, cobalt, cesium, molybdenum, antimony, thallium, tungsten and uranium), and thyroid hormones (TSH, free and total T3 and T4) in serum (N=1587). Multivariate linear regression was used to model the association between thyroid hormone levels, and metals in either urine (creatinine-adjusted) or blood. Metal concentrations were considered as both continuous and categorical variables. Models were adjusted for: age, sex, race, BMI, serum lipids, serum cotinine, pregnancy and menopausal status, and use of selected medications. Few participants (<5%) had free T3, free T4, or TSH levels outside the reference range. However, 9.2% (SE=1.2%) had low T3 and 9.4% (SE=1.1%) had low T4. Metals were detected in nearly all blood and urine samples, with the highest levels seen for urinary molybdenum (median 42.5μg/L). When including all blood metals, mercury was associated with decreases in T3 and T4, while cadmium was associated with decreased TSH. Urinary cadmium was associated with increases in both T3 and T4 (models including all metals measured in urine). Urinary thallium and barium were associated with decreased T4 (both) and T3 (barium). For TSH, cesium was associated with decreased, and tungsten with increased levels. Given the high prevalence of exposure to metals, associations of the size reported here could indicate an appreciable contribution of metals exposure to the prevalence of thyroid disorders. These findings indicate the importance of further research to further examine these relationships.

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

OBJECTIVE

Thyroid hormone, requiring adequate maternal iodine intake, is critical for neurodevelopment in utero. Perchlorate and, less so, thiocyanate decrease uptake of iodine into the thyroid gland by competitively inhibiting the sodium/iodide symporter (NIS). It remains unclear whether environmental perchlorate exposure adversely affects thyroid function in first-trimester pregnant women.

DESIGN

Cross-sectional.

PATIENTS

134 pregnant women from Athens, Greece, at mean ± SD 10·9 ± 2·3 weeks' gestation.

MEASUREMENTS

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

RESULTS

The median urinary iodide was 120 μg/l. Urinary perchlorate levels were detectable in all women: median (range) 4·1 (0·2-118·5) μg/l. Serum thyroperoxidase antibodies (TPO Ab) were detectable in 16% of women. Using Spearman's rank correlation analyses, there was no correlation between urinary perchlorate concentrations and serum TSH, although inverse correlations were seen between urine perchlorate and free T3 and free T4 values. In univariate analyses, urine thiocyanate was positively correlated with serum TSH, but was not associated with serum free T3 or free T4. Urine perchlorate was positively correlated with gestational age. In multivariate analyses adjusting for urinary iodide concentrations, urine thiocyanate, gestational age, maternal age and TPO Ab titres, urine perchlorate was not a significant predictor of thyroid function.

CONCLUSIONS

Low-level perchlorate and thiocyanate exposure is ubiquitous, but, in adjusted analyses, is not associated with alterations in thyroid function tests among mildly iodine-deficient Greek women in the first trimester of pregnancy.

The sodium iodide symporter (NIS) as an imaging reporter for gene, viral, and cell-based therapies

Preclinical and clinical tomographic imaging systems increasingly are being utilized for non-invasive imaging of reporter gene products to reveal the distribution of molecular therapeutics within living subjects. Reporter gene and probe combinations can be employed to monitor vectors for gene, viral, and cell-based therapies. There are several reporter systems available; however, those employing radionuclides for positron emission tomography (PET) or singlephoton emission computed tomography (SPECT) offer the highest sensitivity and the greatest promise for deep tissue imaging in humans. Within the category of radionuclide reporters, the thyroidal sodium iodide symporter (NIS) has emerged as one of the most promising for preclinical and translational research. NIS has been incorporated into a remarkable variety of viral and non-viral vectors in which its functionality is conveniently determined by in vitro iodide uptake assays prior to live animal imaging. This review on the NIS reporter will focus on 1) differences between endogenous NIS and heterologously-expressed NIS, 2) qualitative or comparative use of NIS as an imaging reporter in preclinical and translational gene therapy, oncolytic viral therapy, and cell trafficking research, and 3) use of NIS as an absolute quantitative reporter.

Summary of an NIH workshop to identify research needs to improve the monitoring of iodine status in the United States and to inform the DRI

The Office of Dietary Supplements (ODS) at the NIH sponsored a workshop on May 12-13, 2011, to bring together representatives from various NIH institutes and centers as a first step in developing an NIH iodine research initiative. The workshop also provided an opportunity to identify research needs that would inform the dietary reference intakes for iodine, which were last revised in 2001. Iodine is required throughout the life cycle, but pregnant women and infants are the populations most at risk of deficiency, because iodine is required for normal brain development and growth. The CDC monitors iodine status of the population on a regular basis, but the status of the most vulnerable populations remains uncertain. The NIH funds very little investigator-initiated research relevant to iodine and human nutrition, but the ODS has worked for several years with a number of other U.S. government agencies to develop many of the resources needed to conduct iodine research of high quality (e.g., validated analytical methods and reference materials for multiple types of samples). Iodine experts, scientists from several U.S. government agencies, and NIH representatives met for 2 d to identify iodine research needs appropriate to the NIH mission.

Adsorption of perchlorate from aqueous solution by the calcination product of Mg/(Al-Fe) hydrotalcite-like compounds

The calcination products containing Mg(II), Al(III), and Fe(III) in the brucite-like layers with varying Mg/Al/Fe molar ratios at 550°C were used as the adsorbent to remove perchlorate from aqueous solution, while the Mg/(Al-Fe) hydrotalcite compounds were synthesized by co-precipitation method at a constant pH value. The Mg/(Al-Fe) hydrotalcite compounds (HMAF) were characterized by XRD, FT-IR and TG-DTA. The characteristics showed that the layered double hydroxides structures in the HMAF were lost during calcination at 550°C, but were reconstructed subsequent to adsorption of perchlorate, indicating that the 'memory effect' appeared to play an important role in perchlorate adsorption. Batch adsorption studies were conducted under various equilibration conditions, such as molar ratios of Mg/Al/Fe, calcined temperature, different initial solution pH, adsorbent dose, initial perchlorate concentration, and co-existing anions. It was found that the existence of ferric iron in calcined Mg/(Al-Fe) hydrotalcite compound (CHMAF) was favorable to removal of perchlorate from water, and the best ratio of Mg/Al/Fe is 3:0.8:0.2 (CHMAF5%). This study demonstrated that the calcination product of Mg/(Al-Fe) hydrotalcite-like compound was a promising adsorbent for control of the perchlorate pollution in water.

Hypothyroidism among former workers of a nuclear weapons facility

BACKGROUND

Ionizing radiation alters thyroid function, and workers at a nuclear weapons facility may be exposed to above environmental levels of radiation.

METHODS

Hypothyroid status was determined for 622 former workers of a nuclear weapons facility located in Texas, using a combination of measured thyroid stimulating hormone (TSH) levels and thyroid medication history, as part of an on-going health surveillance program. We classified 916 unique job titles into 35 job categories.

RESULTS

According to the most stringent TSH definition used in this study (0.3-3.0 IU/ml), 174 (28.0%) former workers were considered to be hypothyroid; of these 66 (41.8%) were females and 108 (23.3%) were males. In logistic regression analysis adjusted for age, gender, and smoking status, only having worked as a material handler (n = 18) exhibited an elevated risk of developing hypothyroidism compared to other jobs (OR 3.88, 95% CI 1.43-11.07). This is one of the jobs with suspected exposure to radiation. No excess risk of hypothyroidism was observed for any of the other job categories.

CONCLUSIONS

There is suggestive evidence that only material handlers at this nuclear weapons facility may have elevated risk of hypothyroidism; further evaluation of thyroid health in this population is warranted.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Iodine and pregnancy

Iodine is a necessary element for the production of thyroid hormone. We will review the impact of dietary iodine status on thyroid function in pregnancy. We will discuss iodine metabolism, homeostasis, and nutritional recommendations for pregnancy. We will also discuss the possible effects of environmental contaminants on iodine utilization in pregnant women.

Role of iodine in thyroid physiology

Adequate levels of iodine, a trace element variably distributed on the earth, are required for the synthesis of the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃). The iodide cycle consists of a series of transport, oxidation and coupling steps in thyroid follicular cells to produce thyroid hormone. The sodium/iodide symporter (NIS) transports iodide into the thyrocyte. Competitive inhibitors of NIS, such as perchlorate and thiocyanate, can decrease the entrance of iodide into the follicular cell. Pendrin is the primary protein that is responsible for iodide efflux out of the thyrocyte and into the follicular lumen. T₄ is deiodinated in target tissues to produce the active form of thyroid hormone, T₃, and other metabolites. Exposure to excessive iodine or chronic iodine deficiency may result in various clinical disorders. The Wolff-Chaikoff effect and Jöd-Basedow phenomenon describe mechanisms of thyroid autoregulation and dysregulation, respectively, during iodine excess. Population studies have determined that iodine deficiency exists in approximately 38% of the world's population, is the leading cause of preventable mental retardation, and is of particular concern to women and their infants. Finally, the unique role of iodine utilization in thyroid physiology has applications in many important clinical areas.