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

Health risk assessment of exposure to organochlorine pesticides in the general population in Seoul, Korea over 12 years: A cross-sectional epidemiological study

This study evaluated the 12-year trends in serum levels of 28 organochlorine pesticides (OCPs) in 880 adults living in Seoul, Korea. The OCP levels decreased from 2006 to 2017, and p,p'-dichlorodiphenyldichloroethylene was a predominant compound. OCP levels were higher in females than in males, and showed positive associations with BMI and age. The OCP concentrations had inverted U-shaped associations with low-density lipoprotein cholesterol and total cholesterol. Concentrations of β-hexachlorocyclohexane were significantly higher in patients with hypertension than in participants that were normotensive. OCP levels showed positive associations with uric acid, creatinine, and thyroid-stimulating hormone, but negative associations with free thyroxine. Participants with diabetes had significantly higher OCP levels than those without it. Principal component analysis suggested possible differences in disease manifestation depending on the composition of OCPs. These results suggest that OCPs might disturb renal transport and thyroid homeostasis. To our knowledge, the inverted U-shaped associations of heptachlor epoxide and endosulfan with cholesterol, the epidemiological associations of trans-nonachlor and endosulfan with thyroid hormones, and the association of p,p'-DDE with hyperuricemia have not been previously reported in general population. This is the first long-term study to show trends of 28 OCPs in serum and associations with various health indicators in Korea.

Interactions among thyroid hormones and serum lipid levels in association with PCB exposure in the Mohawk Akwesasne population

Alterations in thyroid function and serum lipid levels were assessed in relation to exposure to polychlorinated biphenyls (PCBs) and three chlorinated pesticides (DDE, hexachorobenzene and mirex) in a sample of Akwesasne Mohawk adults. This population is highly exposed to PCBs because of living in close proximity to three aluminum foundries that used PCBs as hydraulic fluids, which then contaminated local fish, wildlife, water, air and soils. The goal was to assess interactions between thyroid function (TSH, T3, T4 and fT4) and serum lipids (cholesterol, triglycerides and total serum lipids) in relation to concentrations of 101 PCB congeners and three chlorinated pesticides. Previous studies in this population have shown that elevated concentrations of PCBs resulted in suppression of thyroid function in adolescents, and increased risk of clinical hypothyroidism in adults, as well as an elevation in serum lipids. However in adjusted analyses of PCB concentrations of 703 adults we find only small and inconsistent associations between serum PCB levels and thyroid function. The most striking observations were strong significant positive associations between TSH and T3 with serum lipids and a negative association with fT4 in women. Because elevated serum lipids increase risks of other diseases the respective roles of thyroid hormones and PCBs in regulation of serum lipids requires additional study.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

Thyroid hormones are necessary for the normal functioning of physiological systems. Therefore, knowledge of any factor (whether genetic, environmental or intrinsic) that alters the levels of thyroid-stimulating hormone (TSH) and thyroid hormones is crucial. Genetic factors contribute up to 65% of interindividual variations in TSH and thyroid hormone levels, but many environmental factors can also affect thyroid function. This review discusses studies that have analyzed the impact of environmental factors on TSH and thyroid hormone levels in healthy adults. We included lifestyle factors (smoking, alcohol consumption, diet and exercise) and pollutants (chemicals and heavy metals). Many inconsistencies in the results have been observed between studies, making it difficult to draw a general conclusion about how a particular environmental factor influences TSH and thyroid hormone levels. However, lifestyle factors that showed the clearest association with TSH and thyroid hormones were smoking, body mass index (BMI) and iodine (micronutrient taken from the diet). Smoking mainly led to a decrease in TSH levels and an increase in triiodothyronine (T3) and thyroxine (T4) levels, while BMI levels were positively correlated with TSH and free T3 levels. Excess iodine led to an increase in TSH levels and a decrease in thyroid hormone levels. Among the pollutants analyzed, most studies observed a decrease in thyroid hormone levels after exposure to perchlorate. Future studies should continue to analyze the impact of environmental factors on thyroid function as they could contribute to understanding the complex background of gene-environment interactions underlying the pathology of thyroid diseases.

2,3',4,4',5-Pentachlorobiphenyl Induced Thyrocyte Autophagy by Promoting Calcium Influx via Store-Operated Ca2+ Entry

PCB118, a 2,3',4,4',5-pentachlorobiphenyl, has been shown to destroy thyroidal ultrastructure and induce thyrocyte autophagy. Previously, we reported that PCB118 promoted autophagosome formation in vivo and in vitro, but more details remain to be revealed. To explore the underlying mechanism by which PCB118 regulates thyrocyte autophagy, Fischer rat thyroid cell line-5 (FRTL-5) cells were exposed to different doses of PCB118 at 0, 0.25, 2.5, and 25 nM for 0-48 h. Western blot analysis of autophagy-related proteins P62, BECLIN1, and LC3 demonstrated that PCB118 induced autophagy formation in dose- and time-dependent manner. Moreover, laser scanning confocal microscopy and flow cytometry showed PCB118 treatment led to time- and dose-dependent increase in intracellular calcium concentration ([Ca2+]i). Additionally, PCB118 promoted store-operated Ca2+ entry (SOCE) channel followed by significant increase of ORAI1 and STIM1 protein levels. On the other hand, PCB118 induced thyroidal autophagy via class III β-tubulin (TUBB3)/death-associated protein kinase 2 (DAPK2)/myosin regulatory light chain (MRLC)/autophagy-related 9A (ATG9A) pathway in FRTL-5 cells. Pretreatment with SOCE inhibitor SKF96365 reduced cytosolic Ca2+, ORAI1, STIM1, and BECLIN1 levels as well as LC3 II/LC3 I ratio, while increased P62 expression. SKF96365 also inhibited TUBB3/DAPK2/MRLC/ATG9A pathway in FRTL-5 cells treated by PCB118. Our results provide evidence that PCB118 may induce thyroidal autophagy through TUBB3-related signaling pathway, and these effects are likely to be regulated by calcium influx via SOCE channel.

Environmental exposure to pesticides and risk of thyroid diseases

Occupational and environmental exposure to pesticides has been associated with thyroid dysfunction, particularly changes in circulating thyroid hormone levels (T3, T4) and thyroid stimulating hormone (TSH). This study assessed the association between environmental exposure to pesticides and the risk of developing thyroid diseases. A population-based case-control study was carried out among Spanish populations living in areas categorized as of high or low pesticide use according to agronomic criteria, which were used as surrogates for environmental exposure to pesticides. The study population consisted of 79.431 individuals diagnosed with goiter, thyrotoxicosis, hypothyroidism, and thyroiditis (according to the International Classification of Diseases, Ninth Revision) and 1.484.257 controls matched for age, sex and area of residence. Data were collected from computerized hospital records for the period 1998 to 2015. Prevalence rates and risk of having thyroid diseases were significantly higher in areas with higher pesticide use, with a 49% greater risk for hypothyroidism, 45% for thyrotoxicosis, 20% for thyroiditis and 5% for goiter. Overall, this study indicates an association between increased environmental exposure to pesticides as a result of a greater agricultural use and diseases of the thyroid gland, thus supporting and extending previous evidence. This study also provides support to the methodology proposed for real-life risk simulation, thus contributing to a better understanding of the real life threat posed by exposure to multiple pesticides from different sources.

Human exposure to bisphenol AF and diethylhexylphthalate increases susceptibility to develop differentiated thyroid cancer in patients with thyroid nodules

Pollutants represent potential threats to the human health, being ubiquitous in the environment and exerting toxicity even at low doses. This study aims at investigating the role of fifteen multiclass organic pollutants, assumed as markers of environmental pollution, most of which exerting endocrine-disrupting activity, in thyroid cancer development. The increasing incidence of differentiated thyroid cancer (DTC) may be related to the rising production and environmental dissemination of pollutants. Fifty-five patients, twenty-seven with diagnosis of benign thyroid nodules and twenty-eight suffering from differentiated thyroid cancer, were enrolled and the concentration levels of seven bisphenols, two phthalates (i.e. di(2-ethylhexyl) phthalate (DEHP) and its main metabolite, mono-(2-ethyl-hexyl) phthalate) (MEHP)), two chlorobenzenes, (1,4-dichlorobenzene and 1,2,4,5-tetrachlorobenzene), and 3 phenol derivatives (2-chlorophenol, 4- nonylphenol, and triclosan) were determined in their serum by using a validated analytical method based on high performance liquid chromatography with ultraviolet tandem fluorescence detection. A significant relationship was found between malignancy and the detection in the serum of both bisphenol AF and DEHP. Indeed, their presence confers a more than fourteen times higher risk of developing differentiated thyroid cancer. Relationship between these two pollutants and the risk of malignancy was dose-independent and not mediated by higher thyroid stimulating hormone levels. Even if a conclusive evidence cannot still be drawn and larger prospective studies are needed, the exposure to low doses of environmental endocrine-disrupting contaminants can be considered consistent with the development of thyroid cancer.

Pesticide exposure and thyroid function in an agricultural population in Brazil

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

A Preliminary Link between Hydroxylated Metabolites of Polychlorinated Biphenyls and Free Thyroxin in Humans

BACKGROUND

Polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (HO-PCBs) interfere with thyroid hormone action both in vitro and in vivo. However, epidemiologic studies on the link between PCB exposure and thyroid function have yielded discordant results, while very few data are available for HO-PCBs.

OBJECTIVES

Our study aimed at investigating the relationship between clinically available markers of thyroid metabolism and serum levels of both PCBs and HO-PCBs.

SUBJECTS AND METHODS

In a group of 180 subjects, thyroid-stimulating hormone (TSH) and free thyroxin (fT4), 29 PCBs (expressed both in lipid weight and in wet weight) and 18 HO-PCBs were measured in serum.

RESULTS

In regression models, adjusted for gender, age, current smoking behavior, BMI and total lipid levels, serum levels of 3HO-PCB118 and 3HO-PCB180, and PCB95(lw), PCB99(lw) and PCB149(lw) were independent, significant predictors of fT4. A stepwise, multiple regression with gender, age, current smoking behavior, BMI and total lipid levels and all five previously identified significant compounds retained age, BMI, PCB95(lw), PCB99(lw) and 3HO-PCB180 as significant predictors of fT4. TSH levels were not predicted by serum levels of any of the PCBs or HO-PCBs.

CONCLUSIONS

Our study indicates that in vivo, circulating fT4 levels can be linked to serum levels of several PCBs and hydroxylated PCB metabolites.

Molecular mechanisms of 2, 3', 4, 4', 5-pentachlorobiphenyl-induced thyroid dysfunction in FRTL-5 cells

Polychlorinated biphenyls (PCBs) can severely interfere with multiple animals and human systems. To explore the molecular mechanisms underlying 2, 3′, 4, 4′, 5- pentachlorobiphenyl (PCB118)-induced thyroid dysfunction, Fischer rat thyroid cell line-5(FRTL-5) cells were treated with either different concentrations of PCB118 or dimethyl sulfoxide (DMSO). The effects of PCB118 on FRTL-5 cells viability and apoptosis were assessed by using a Cell Counting Kit-8 assay and apoptosis assays, respectively. Quantitative real-time polymerase chain reaction was used to quantify protein kinase B (Akt), Forkhead box protein O3a (FoxO3a), and sodium/iodide symporter (NIS) mRNA expression levels. Western blotting was used to detect Akt, phospho-Akt (p-Akt), FoxO3a, phospho-FoxO3a (p-FoxO3a), and NIS protein levels. Luciferase reporter gene technology was used to detect the transcriptional activities of FoxO3a and NIS promoters. The effects of the constitutively active Akt (CA-Akt) and dominant-negative Akt (DN-Akt) plasmids on p-Akt, p-FoxO3a, and NIS levels were examined in PCB118-treated FRTL-5 cells. The effects of FoxO3a siRNA on FoxO3a, p-FoxO3a, and NIS protein levels were examined in the PCB118-treated FRTL-5 cells. The effects of pcDNA3 (plsmid vectors designed for high-level stable and transient expression in mammalian host)-FoxO3a on NIS promoter activity were examined in the PCB118-treated FRTL-5 cells. Our results indicated that relatively higher PCB118 concentrations can inhibit cell viability in a concentration- and time-dependent manner. Akt, p-Akt, and p-FoxO3a protein or mRNA levels increased significantly in PCB118-treated groups and NIS protein and mRNA levels decreased considerably compared with the control groups. FoxO3a promoter activity increased significantly, whereas NIS promoter activity decreased. These effects on p-FoxO3a and NIS could be decreased by the DN-Akt plasmid, enhanced by the CA-Akt plasmid, and blocked by FoxO3a siRNA. The overexpressed FoxO3a could reduce NIS promoter activity. Our results suggested that PCB118 induces thyroid cell dysfunction through the Akt/FoxO3a/NIS signaling pathway.

Monitoring chlorinated persistent organic pollutants in adolescents in Flanders (Belgium): concentrations, trends and dose-effect relationships (FLEHS II)

BACKGROUND

In 2007, the second cycle of the Flemish human biomonitoring survey started, with a main focus on 14-15 year-old adolescents.

OBJECTIVES

The main objectives were generating reference values for exposure markers, determining the pollution pressure in industrial hotspots and establishing dose-effect relationships between exposure to pollutants and hormone levels, sexual development, asthma and allergy, genotoxic and hematological markers.

METHODS

Geometric means with 95% confidence intervals (CI) were calculated for a reference population of 200 14-15 year-old adolescents. Stepwise multiple regression analyses with correction for confounders and covariates were performed to establish dose-effect relationships.

RESULTS

Geometric mean concentrations (with 95% CI) of 49.6 (45.7, 53.8), 70.8 (63.6, 78.8) and 8.34 (7.76, 8.97) n gg(-1) lipid for the sum of PCB 138, 153 and 180, p,p'-DDE and HCB were respectively 23%, 26% and 60% lower than those obtained five years earlier. Geometric mean concentrations of 108 (101, 114) and 32.1 (30.1, 34.2) pgCALUX-BEQg(-1) lipid were observed for the PCDD/Fs and dioxin-like PCBs, respectively. Multiple dose-effect relationships were observed between POPs and several effect markers, including positive (boys) and negative (girls) associations with data on sexual development and positive associations with asthma, animal allergy and free thyroxine (boys and girls).

CONCLUSIONS

Our findings suggest that chlorinated POP concentrations are decreasing over time and that even relatively low concentrations are associated with biological effects.

Long-term exposure to organochlorine pesticides and thyroid status in adults in a heavily contaminated area in Brazil

Organochlorine (OC) pesticides are endocrine disruptors altering the thyroid hormonal system. The aim of this study is to investigate the relationship between exposure to OC pesticides and thyroid status in adults from a rural area in Rio de Janeiro, Brazil, heavily contaminated with OC pesticides. A cross-sectional study was carried out in 303 men and 305 women >14 years old. Concentrations of 19 OC pesticides and levels of free thyroxine (T4), total triiodothyronine (T3), thyroid-stimulating hormone (TSH), anti-thyroperoxidase (TPOAb) and anti-thyroglobulin (TgAg) antibodies were analyzed in serum samples. Associations between OC pesticides concentrations and values of biochemical thyroid parameters were determined using multivariate regression models stratified by gender. Prevalence of subclinical hyperthyroidism and the presence of TPOAb antibodies were higher than those described for euthyroid populations elsewhere. After adjusting for confounders, total T3 levels were associated with lower concentrations of endosulphan 2 in men and with higher alpha-chlordane, p,p'-dichlorodiphenyltrichloroethane (DDT), endosulphan 2, and methoxychlor in women. Levels of free T4 showed inverse association with beta-hexachlorocyclohexane (HCH) and p,p'-DDT in men, and were positively associated with hexachlorobenzene (HCB), heptachlor, o,p'-DDT, and p,p'-DDT in women. TSH levels were associated with higher beta-HCH in men. A positive association was observed between exposure methoxychlor in males and presence of TPOAb, but no association with TPOAb was found in women. These results suggest that OC pesticides can affect the thyroid system through gender-specific mechanisms that may differ among compounds. Further detailed investigations and health monitoring should be warranted for this population.

Association between several persistent organic pollutants and thyroid hormone levels in serum among the pregnant women of Korea

Persistent organic pollutants such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs) are of global concern because of their widespread contamination and adverse health effects. Potential endocrine disruption, especially of thyroid status by PCBs has been repeatedly suggested in both experimental and epidemiological studies. However the associations with PBDEs or OCPs have been arguable especially in human populations. We investigated the associations between major groups of POPs and thyroid hormone balances among pregnant women. One hundred five pregnant women at delivery were recruited from four cities of Korea in 2011 and were investigated. Blood samples were collected within a day before delivery. Serum was then analyzed for 19 PCBs, 19 PBDEs, and 19 OCPs, along with five thyroid hormones (free and total T3 and T4, and TSH). Several PCBs such as PCB28, 52, and 118 showed negative associations with T3 or T4. BDE47 and total PBDEs showed significant associations with T3 or T4. For OCPs, dichlorodiphenyltrichloroethanes (DDTs) and hexachlorobenzene (HCB) were generally associated with reduction of T3 or T4. The thyroid hormone levels of all subjects were within the reference range, however exposure to several target POPs were clearly related with potential for disrupting thyroid hormone balance among pregnant women, at the current level of exposure. Although subtle, the changes in thyroid hormones should be seen with caution because even minor changes within pregnant women may have significant consequences especially on sensitive population like fetus.

Upstream adverse effects in risk assessment: a model of polychlorinated biphenyls, thyroid hormone disruption and neurological outcomes in humans

BACKGROUND

Increasing data on early biological changes from chemical exposures requires new interpretation tools to support decision-making.

OBJECTIVES

To test the possibility of applying a quantitative approach using human data linking chemical exposures and upstream biological perturbations to overt downstream outcomes.

METHODS

Using polychlorinated biphenyl (PCB) exposures and maternal thyroid hormone (TH) perturbations as a case study, we model three relationships: (1) prenatal PCB exposures and TH changes, using free T(4) (FT(4)); (2) prenatal TH and childhood neurodevelopmental outcomes; and (3) prenatal PCB exposures and childhood neurodevelopmental outcomes (IQ). We surveyed the epidemiological literature; extracted relevant quantitative data; and developed models for each relationship, applying meta-analysis where appropriate.

RESULTS

For relationship 1, a meta-analysis of 3 studies gives a coefficient of -0.27 pg/mL FT(4) per ln(sum of PCBs) (95% confidence interval [CI] -0.82 to 0.27). For relationship 2, regression coefficients from three studies of maternal FT(4) levels and cognitive scores ranged between 0.99 IQ points/(pg/mL FT(4)) (95% CI -0.31 to 2.2) and 7.6 points/(pg/mL FT(4)) (95% CI 1.2 to 16.3). For relationship 3, a meta-analysis of five studies produces a coefficient of -1.98 IQ points (95% CI -4.46 to 0.50) per unit increase in ln(sum of PCBs). Combining relationships 1 and 2 yields an estimate of -2.0 to -0.27 points of IQ per unit increase in ln(sum of PCBs).

CONCLUSIONS

Combining analysis of chemical exposures and early biological perturbations (PCBs and FT(4)) with analysis of early biological perturbations and downstream overt effects (FT(4) and IQ) yields estimates within the range of studies of exposures and overt effects (PCBs and IQ). This is an example approach using upstream biological perturbations for effect prediction.

Long term exposure to organochlorine pesticides and thyroid function in children from Cidade dos Meninos, Rio de Janeiro, Brazil

A pesticide factory in Cidade dos Meninos village, Duque de Caxias County, Rio de Janeiro, Brazil, ended its activity in 1961, leading to widespread contamination of the environment by several organochlorine pesticides. The aim of this study was to investigate the effects of chronic exposure to organochlorine pesticides on thyroid hormone levels in children residing in Cidade dos Meninos. In a population-based survey carried out between 2003 and 2004, serum concentration of 19 pesticides and levels of free thyroxine (T4), total triiodothyronine (T3) and thyroid-stimulating hormone (TSH) were determined in 193 children younger than 15 years old. Multivariate linear regression was conducted to examine thyroid hormone levels according to quintiles of organochlorine exposure, controlling for age, gender and serum lipid content. Free T4 and TSH levels were within reference values (0.7-1.8 ng/dl and 0.35-5.5 mU/l), whereas total T3 was above the reference range (80-180 ng/dl) in 28% of children. More than 60% of the children had detectable levels of most organochlorine pesticides. With the exception of heptachlor and methoxychlor, total T3 levels showed a significant increasing linear trend regardless of pesticide type to which children were exposed. Free T4 levels were positively and significantly associated only with exposure to p,p'-DDD, endosulfan 1, and dieldrin. No significant trend was found for TSH. Data showed that exposure of children to organochlorine pesticides produced a significant increase in serum total T3 concentrations. The clinical implications of such a total T3 elevation and subsequent development are uncertain and warrant the need for health monitoring of these children.

Adverse effects in risk assessment: modeling polychlorinated biphenyls and thyroid hormone disruption outcomes in animals and humans

There is a growing need for quantitative approaches to extrapolate relationships between chemical exposures and early biological perturbations from animals to humans given increasing use of biological assays to evaluate toxicity pathways. We have developed such an approach using polychlorinated biphenyls (PCBs) and thyroid hormone (TH) disruption as a case study. We reviewed and identified experimental animal literature from which we developed a low-dose, linear model of PCB body burdens and decrements in free thyroxine (FT(4)) and total thyroxine (TT(4)), accounting for 33 PCB congeners; extrapolated the dose-response from animals to humans; and compared the animal dose-response to the dose-response of PCB body burdens and TH changes from eleven human epidemiological studies. We estimated a range of potencies for PCB congeners (over 4 orders of magnitude), with the strongest for PCB 126. Our approach to developing toxic equivalency models produced relative potencies similar to the toxicity equivalency factors (TEFs) from the World Health Organization (WHO). We generally found that the dose-response extrapolated from the animal studies tends to under-predict the dose-response estimated from human epidemiological studies. A quantitative approach to evaluating the relationship between chemical exposures and TH perturbations, based on animal data can be used to assess human health consequences of thyroid toxicity and inform decision-making.

Thyroid effects of endocrine disrupting chemicals

In recent years, many studies of thyroid-disrupting effects of environmental chemicals have been published. Of special concern is the exposure of pregnant women and infants, as thyroid disruption of the developing organism may have deleterious effects on neurological outcome. Chemicals may exert thyroid effects through a variety of mechanisms of action, and some animal experiments and in vitro studies have focused on elucidating the mode of action of specific chemical compounds. Long-term human studies on effects of environmental chemicals on thyroid related outcomes such as growth and development are still lacking. The human exposure scenario with life long exposure to a vast mixture of chemicals in low doses and the large physiological variation in thyroid hormone levels between individuals render human studies very difficult. However, there is now reasonably firm evidence that PCBs have thyroid-disrupting effects, and there is emerging evidence that also phthalates, bisphenol A, brominated flame retardants and perfluorinated chemicals may have thyroid disrupting properties.

Do Thyroid Disrupting Chemicals Influence Foetal Development during Pregnancy?

Maternal euthyroidism during pregnancy is crucial for normal development and, in particular, neurodevelopment of the foetus. Up to 3.5 percent of pregnant women suffer from hypothyroidism. Industrial use of various chemicals—endocrine disrupting chemicals (EDCs)—has been shown to cause almost constant exposure of humans with possible harmful influence on health and hormone regulation. EDCs may affect thyroid hormone homeostasis by different mechanisms, and though the effect of each chemical seems scarce, the added effects may cause inappropriate consequences on, for example, foetal neurodevelopment. This paper focuses on thyroid hormone influence on foetal development in relation to the chemicals suspected of thyroid disrupting properties with possible interactions with maternal thyroid homeostasis. Knowledge of the effects is expected to impact the general debate on the use of these chemicals. However, more studies are needed to elucidate the issue, since human studies are scarce.

Incidence of thyroid disease following exposure to polybrominated biphenyls and polychlorinated biphenyls, Michigan, 1974-2006

Thyroid hormones, which influence body metabolism and development, could be affected by persistent organic pollutants. We sought to examine the relationship between polybrominated biphenyls (PBBs) and polychlorinated biphenyls (PCBs) and thyroid disease. We employed incidence density sampling to perform a nested case control analysis of the Michigan Long-Term PBB Cohort. Cohort members (n=3333) were exposed to PBBs through contaminated cattle feed in 1973-1974 and to PCBs through daily life. Those with detectable serum PBB and PCB concentrations at enrollment were categorized into tertiles of PBB and PCB exposure. Case-patients were cohort members answering "Yes" to "Has a healthcare provider ever told you that you had a thyroid problem?" during follow-up interviews; control-patients were cohort members answering "No". We used odds ratios (OR) with 95% confidence intervals (CI) to compare odds of thyroid disease by PBB and PCB exposure and by various risk factors. Total cumulative thyroid disease incidence after 33 years was 13.9% among women and 2.6% among men. After adjusting for body mass index, we found no statistically significant differences in odds of any type of thyroid disease among women or men with elevated PBB or PCB exposure. Compared to control-patients, women with thyroid disease had increased odds of being overweight/obese (OR=2.82, 95% CI: 1.94-4.11) and developing infertility (OR=1.71, 95% CI: 1.08-2.69), diabetes (OR=1.61, 95% CI: 1.04-2.51), or arthritis (OR=1.71, 95% CI: 1.18-2.50) during follow-up. Additional research should explore potential associations between PBBs/PCBs and thyroid disease among children exposed in utero.

The impacts of organochlorines and other persistent pollutants on thyroid and metabolic health

High prevalence of thyroid and metabolic disorders has been repeatedly observed in the population living in the area of eastern Slovakia highly polluted by a mixture of PCBs, DDE and HCB since about 50 years ago. Among thyroid disorders, increase of thyroid volume as measured by ultrasound volumetry may be suggested as one of notable findings which appeared possibly related to increased OCs levels and to autoimmunity signs (e.g. positive thyroperoxidase antibodies in blood and/or hypoechogenicity image obtained by ultrasound), while some participation of individual susceptibility and also of immunogenic effect of OCs and iodine in this iodine replete country cannot be excluded. Another notable finding has been the increase of blood FT4 and TT3 positively related to high PCBs level. Such increased FT4 level has been found associated with TSH level in hyperthyroid range in about 2% of examined population from polluted area. High prevalence of thyroid autoimmune disorders strongly supported the assumption on impaired immune system and thus also on presumably increased prevalence of other autoimmune disorders in highly exposed population. In addition, markedly increased prevalence of prediabetes and diabetes significantly related to major OCs (PCBs, DDE and HCB) levels and accompanied by increasing level of cholesterol and triglycerides has been observed. The observations also suggested a role of prenatal exposure to OCs in the development of several adverse health signs (e.g. increased prevalence of thyroid antibodies, impaired fasting glucose level, increased thyroid volume, decreased thymus volume, decreased neurobehavioral performance, increased hearing and dental disorders) in young generation born to highly exposed mothers in polluted area.

Polychlorinated biphenyls and thyroid hormones in adults: a systematic review appraisal of epidemiological studies

Reported evidence regarding relationships between polychlorinated biphenyls (PCBs) and thyroid homeostasis in adults has been considered contradictory. The objective of this systematic review is to determine a possible association between PCB exposure and the circulating thyroid hormones and thyrotropin (TSH) levels in adults, by analyzing the quality of published studies. A systematic review of epidemiological papers was conducted using PubMed. An evaluation of the quality of 22 studies was performed, and the papers were classified into two tiers: Tier I for studies with higher quality scores (eight) and Tier II for studies with lower quality scores (14). It appears that PCBs can interfere with thyroid hormone homeostasis; however epidemiological evidence is not entirely clear. For triiodothyronine (T3) and thyroxine (T4), Tier I studies showed either an inverse (four cases for T3; five cases for T4) or no significant association (two cases for T3; five cases for T4) with PCBs. In the case of free thyroxine and TSH, the Tier I papers observed no clear association with PCB levels. Rigorous study design, assessment of potential confounding factors, and fuller reporting of methods and results in future studies will facilitate understanding of whether PCB exposure is associated with changes in thyroid function.

Polychlorinated biphenyls and thyroid hormone serum concentrations among people living in a highly polluted area: a cross-sectional population-based study

BACKGROUND

Polychlorinated biphenyls (PCBs) may interact with several thyroid functions. Severe environmental pollution by PCBs has been observed in Brescia, Italy, due to the presence of a factory that produced these compounds until 1984.

OBJECTIVES

We aimed to investigate the correlation between serum levels of total PCBs and PCB 153 and thyroid hormone serum levels in adults in a cross-sectional population-based study.

METHODS

A total of 527 subjects were enrolled; they were face-to-face interviewed about their history of thyroid disease and provided a blood sample under fasting conditions. The serum levels of free and total triiodothyronine (FT3 and TT3), thyroxine (FT4 and TT4) and thyroid-stimulating hormone (TSH), anti-thyroperoxidase (anti-TPO) and anti-thyroglobulin (anti-TGA), and lipid-adjusted total PCBs and PCB 153 were determined.

RESULTS

There was no statistically significant difference in total PCB and PCB 153 concentrations in subjects with and without thyroid disease. Inverse, weak, statistically significant correlations were found between total PCBs and FT3 (Spearman's r=-0.09) and between total PCBs and PCB 153 and TSH (Spearman's r=-0.16 and -0.12, respectively). However, multiple regression analysis with FT3 and TSH serum levels as dependent variables and total PCBs and PCB 153 serum levels as predictors, including age, gender and BMI, showed a positive, rather than negative, association of PCBs and PCB 153 with FT3 and no association with TSH.

CONCLUSIONS

This study does not support the hypothesis that relatively high PCB environmental exposure can determine substantial alterations in thyroid function among adult people.

Gender differences in the effects of organochlorines, mercury, and lead on thyroid hormone levels in lakeside communities of Quebec (Canada)

Environmental chemicals can disrupt endocrine balance and in particular thyroid hormone (TH) homeostasis. However, studies differ with respect to thyroid profile changes and gender differences are rarely examined. This study investigated the THs, triodothyronine (T3), thyroxine (T4), and thyroid stimulating hormone (TSH), in relation to serum organochlorines (OCs), bioindicators of mercury (Hg) and blood lead (Pb) in 211 freshwater fish consumers (124 men and 87 women) from two communities in Canada. Thyroid hormones were within the normal range and the bioindicators of exposure were low compared to other reports on fish consumers. Stratified analysis showed that for women, serum T3 concentrations were negatively related to serum concentrations of PCB 138, PCB 153, the non-coplanar congeners, Arochlor 1260, and SigmaPCB, as well as p,p'-DDE. No relations were observed between T4 and any of the chemicals measured, but TSH was negatively related to blood Pb. For men, serum T4 was inversely related to PCB 138, non-ortho-substituted (dioxin-like) PCBs and SigmaPCB. A significant positive relationship was observed between serum TSH and different PCB congeners (PCB 138, PCB 180, non-coplanar congeners, mono-ortho coplanar congeners, dioxin-like PCBs), as well as SigmaPCB. Serum TSH increased with hair and blood Hg concentrations and was highest among those in the highest 50th percentile for both Hg and dioxin-like PCB congeners compared to the others. No associations were observed for T3 in men. These findings suggest that even at low concentrations, these environmental contaminants can interfere with thyroid status and effects may differ by gender.

Possible effects of environmental nitrates and toxic organochlorines on human thyroid in highly polluted areas in Slovakia

Heavy environmental pollution resulting from uncontrolled industrial and agricultural activities has occurred in several areas of Slovakia. So far, field surveys focused mainly on the thyroid have been conducted in one area polluted by nitrates and in a large area polluted mainly by organochlorinated toxicants. In children from the high nitrate area (HNA, n = 324) significantly higher thyroid volume (ThV) by ultrasound was found compared with age-matched children from surrounding areas with low nitrate (LNA, n = 764). In blood samples of 324 children from the HNA and of 100 children from the LNA no difference between areas was found in the level of total thyroxine (T4) and free triiodothyronine (T3). However, positive thyroid peroxidase antibodies (TPOAb) were found in 7/324 (2.2%) and thyrotropin (TSH) levels > 4.0 mIU/L in 13/324 (4.0%) of children from the HNA area, while no positive values were obtained in the LNA. In the area heavily polluted by an organochlorine (OC) cocktail consisting of polychlorinated biphenyls (PCBs), 2,2'-bis(4-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE), hexachlorobenzene (HCB), and dioxins and furans (polluted area) and in the background pollution area (background area) a total of 2046 adults were examined. In polluted area very high blood levels of OCs were found as well as increased ThV and prevalence of thyroid hypoechogenicity by ultrasound. For the evaluation of data the level of PCBs was used as a marker of all OCs. Increasing PCB levels were significantly associated with the increase of free T4 (p < 0.001) and total T3 (p < 0.05) in blood, while slight but not significant negative association of PCBs was observed with the level of TSH. In both women and men the prevalence of TPOAb was significantly higher in polluted area. Although the absolute TPOAb prevalence in both areas was higher in women than that in men, the increase in polluted vs. background area was more striking in men. From these data it appears that the effects of environmental pollution on the thyroid cannot be neglected.

Possible effects of persistent organochlorinated pollutants cocktail on thyroid hormone levels and pituitary-thyroid interrelations

In polluted district of Michalovce in East Slovakia (POLL) and two districts with background pollution (BCGR) 2046 adults (834 males and 1212 females aged 20-75 years) were examined. Serum levels of thyrotropin (TSH), free thyroxine (FT4), total triiodothyronine (TT3) and antithyroperoxidase antibodies (TPOab) were estimated by electrochemiluminiscent assay and also these of 15 polychlorinated biphenyl congeners (PCBs), p,p'-DDE, p,p'-DDT, hexachlorobenzene (HCB) and hexachlorocyclohexane were measured by high resolution gas chromatography/mass spectrometry. In addition, also dioxins, furans, coplanar- and mono-ortho-PCBs as well as selected hydroxylated and methylsulphonated PCBs and DDE metabolites were measured by appropriate methods based on gas chromatography/mass spectrometry principle. In POLL significantly higher levels of all organochlorines were found than these in BCGR. When pooled values from both areas were stratified in terms of PCBs level and treated as continuous variables, positive association of PCBs with FT4 and TT3 was found, the latter two being also mutually associated. However, within the category of PCBs level <530 ng/glipid (n=232) the association between PCBs and both the FT4 (p<0.09) and TT3 (p<0.03) was negative and any association of these was not found within the category of PCBs level of 531-1000 ng/g (n=691). In contrast, in the category of 531-2000 ng/g (n=1307) positive association appeared between PCBs and FT4 (p<0.001) as well as TT3 (p<0.05). Highly significant association of PCBs with FT4 (p<0.001) was further found in the categories with PCBs level of 1001-101414 ng/g (n=1307) and 2001-101414 (n=1123), while significant association with TT3 was observed only in the category of 531-2000 ng/g. Such findings suggest possible threshold level in positive effect of PCBs on FT4 and TT3 level which seems to be individual and located somewhere around the PCBs level of 1000 ng/g. However, highly significant negative association of both FT4 and TT3 with TSH was found in each of above indicated PCBs categories. Considerable difference in FT4 and TT3 level between large groups of subjects with the same range of PCBs level was also found suggesting different individual susceptibility to the effects of organochlorines. Among a total of 26 cases from POLL with very low TSH level (<0.5 mU l(-1)) 13 cases showed very high level of PCBs, FT4 and TT3, thus supporting a hypothesis on a novel sporadic form of high PCBs related peripheral subclinical hyperthyroidism possibly resulting from the long-term disruption of equilibrium between bound and free thyroxine in plasma by high PCBs level followed by a striking inhibition of TSH release from the pituitary.

Relationships of thyroid hormones with polychlorinated biphenyls, dioxins, furans, and DDE in adults

BACKGROUND

Thyroid hormone homeostasis can be disrupted by exposure to ubiquitous and bioaccumulative organochlorines such as polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins (PCDDs). Whereas investigations of health effects have generally focused on human populations with relatively high exposures through occupation, accident, or high fish consumption, general population exposures may also carry risk.

METHODS

We studied associations of total thyroxine (T(4)) and thyroid-stimulating hormone (TSH) with PCBs, dioxin-like toxic equivalents (TEQs), and p,p'-diphenyldichloroethene (DDE) in adult participants without thyroid disease who participated in the 1999-2002 National Health and Nutrition Examination Survey, a cross-sectional survey examining a random sample representative of the U.S. population.

RESULTS

We found inverse associations of total T(4) with exposure to TEQs in both sexes, with stronger associations in females. In women, mean T(4) was 8.2 microg/dL, and levels were on average 0.75 microg/dL lower (95% confidence interval, 0.04-1.46) in women in the highest quintile of TEQ exposure compared with the lowest two quintiles. Effects were stronger in people > 60 years of age, with negative associations of T(4) with PCBs and TEQs, and positive associations of TSH with PCBs and TEQs in older women, and a negative association of TSH with PCBs in older men.

CONCLUSIONS

The data show a dose-dependent decrease in total T(4) with exposure to TEQs at levels similar to those found in the general U.S. population. The effects were stronger in women. The results suggest that older adults, who have a high risk of thyroid disease, may be more at risk for disruption of thyroid hormone homeostasis by dioxin-like organochlorines than younger adults.

Serum PCBs, p,p'-DDE and HCB predict thyroid hormone levels in men

Polychlorinated biphenyls (PCBs) and some organochlorine pesticides, which continue to be measurable in a high proportion of blood samples from the general population, have been found to alter thyroid hormone levels in animals and humans. However, studies of these relationships in adult men are limited and results across studies have been inconsistent. In the present study, we measured serum levels of 57 PCB congeners, dichlorodiphenyldichloroethylene (p,p(')-DDE, a stable metabolite of DDT), and hexachlorobenzene (HCB), as well as free T(4), total T(3), and TSH, in 341 adult men recruited from an infertility clinic from 2000 to 2003. In multivariate linear regression, there were positive associations between p,p(')-DDE and both free T(4) and total T(3), and an inverse association between p,p(')-DDE and TSH. Conversely, for PCBs there was only a suggestive inverse association between PCB 153 and total T(3) when potential confounding variables were considered. However, when results were additionally adjusted for p,p(')-DDE, inverse associations with T(3) were significant for PCB 138, PCB 153, sum of PCBs and three different PCB groupings, and HCB, while the positive associations between p,p(')-DDE and T(3) also remained. In conclusion, serum concentrations of PCBs, p,p(')-DDE, and HCB were associated with circulating thyroid hormone levels in adult men.

ABBREVIATIONS

BMI, body mass index; CYP, cytochrome P450; DDT, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane; HCB, hexachlorobenzene; MDL, method detection limit; NHANES, national health and nutrition examination survey: p,p(')-DDE, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene; PCB, polychlorinated biphenyl; T(3), triiodothyronine; T(4), thryoxine; TSH, thyroid stimulating hormone (thyrotrophin); US, United States.

Associations of organochlorines with endogenous hormones in male Great Lakes fish consumers and nonconsumers

This study investigated the relationships of steroid and thyroid hormones with total noncoplanar polychlorinated biphenyls (PCBs), total toxic equivalents (TEQs) from dioxins-like organochlorines, and dichlorodiphenyl dichloroethene (DDE) in 56 male frequent and infrequent Great Lakes sport caught fish consumers. Significant negative associations were found for triiodothyronine (T3), thyroxine (T4), thyroid stimulating hormone (TSH), and sex hormone binding globulin (SHBG)-bound testosterone with PCBs, for TSH with total TEQs, and for estrone sulfate with DDE, adjusting for age, body mass index, and medication use. Follicle-stimulating hormone, luteinizing hormone, free testosterone, and SHBG were not significantly associated with organochlorines. Models that accounted for exposure to both PCBs and TEQs predicted T4, estrone sulfate, and SHBG-bound testosterone better than models that included either PCBs or TEQs alone, with the lowest hormone levels occurring in the participants with both higher PCB levels and lower TEQ levels. These data suggest that exposure to PCBs, dioxin-like organochlorines, and DDE, alone and potentially in combination, may be associated with effects on the endocrine system in adult males. Further studies should help delineate specific exposure effects and effects of exposures to other common environmental contaminants alone and in combination with PCBs.

Non-coplanar PCB-mediated modulation of human leukocyte phagocytosis: a new mechanism for immunotoxicity

Organochlorine (OC) contaminants, notably polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are ubiquitous in all ecosystems and found in the tissues of humans and wildlife. Although the immunotoxicity of coplanar, dioxinlike PCBs is well documented, the adverse effects exerted by non-coplanar, non-dioxinlike PCBs have received little attention. Direct causal relationship between PCB and dioxin exposure and the observed detrimental effects on the immune system has yet to be fully established in humans. The immunomodulatory potential of toxic coplanar PCB 169 and TCDD and abundant non-coplanar PCBs 138, 153, and 180 on human leukocyte phagocytosis, an important innate immune function that initiates the clearance of pathogens, was tested upon in vitro exposure. Mixture and concentration-response experiments demonstrated a suppression of phagocytosis by non-coplanar PCBs suggesting a previously unrecognized aryl hydrocarbon receptor (AhR)-independent pathway. Regression analysis revealed that reduction of phagocytosis was mostly explained by the non-coplanar congeners. The effects on phagocytosis could not be accurately predicted by either the currently used toxic equivalence (TEQ) approach or the mouse model, thus undermining the use of the traditional models in the risk assessment for OC mixtures containing non-coplanar congeners. Our results are cause for concern as they suggest an AhR-independent pathway through which non-coplanar PCBs modulate phagocytosis, the immune system's first line of defense, possibly increasing the risk to developing infectious disease.

Profiles of ortho-polychlorinated biphenyl congeners, dichlorodiphenyldichloroethylene, hexachlorobenzene, and Mirex among male Lake Ontario sportfish consumers: the New York State Angler cohort study

Great Lakes sportfish consumption is a recognized human exposure source to environmental organochlorine compounds. Using data collected as part of the New York State Angler Cohort Study, 203 males were considered with regard to history of Lake Ontario sportfish consumption and sera levels of 57 ortho-substituted polychlorinated biphenyl (PCB) congeners, dichlorodiphenyldichloroethylene, hexachlorobenzene, and Mirex. Consumption of six species of highly contaminated Lake Ontario sportfish during the years 1980 to 1990 was considered. Exposure was weighted by average annual frequency of consumption, whole-fish PCB estimates, and meal size to determine a continuous index of exposure. This index was dichotomized to compare "consumers" to "nonconsumers" in several procedures. Recovery and lipid-adjusted serum values for PCB congener IUPAC Nos. 138+163 (rsp=0.3), 183 (rsp=0.3), 187 (rsp=0.4), and 188 (rsp=0.3) and Mirex (rsp=0.4) were significantly correlated with the index of fish consumption (P<0.001). A logistic regression model, using forward stepwise selection procedures (alpha in/out=0.002/0.004), was employed to account for high intercorrelations among organochlorine predictor variables. Mirex was the sole statistically significant predictor variable of "consumer/nonconsumer." A one-unit increase in log Mirex was associated with a 92.0% increase in the odds of having reported sportfish consumption (OR=1.92, 95%CI=1.43, 2.58). Age, body mass index, cigarette smoking, water/wildfowl consumption, and year of sampling were considered covariates. The results of this study support the premise that long-term dietary consumption of Lake Ontario sportfish, even at comparatively low levels, contributes significantly to the body burden of organochlorine compounds in western New York anglers and sportsmen.

Thyroid function in relation to burden of PCBs, p,p'-DDE, HCB, mirex and lead among Akwesasne Mohawk youth: a preliminary study

The effects of endocrine disrupting environmental contaminants such as polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), p,p'-dichlorophenyldichloroethylene (p,p'-DDE), mirex, and lead, are examined in a sample of youth of the Akwesasne Mohawk Nation who are 10-16.9 years of age (n=115). The Akwesasne community is located adjacent to hazardous waste sites where PCBs and other toxicants have contaminated the local ecology. This study examines the relationship between measures of thyroid function and endocrine disrupting environmental toxicants. Both with and without statistical adjustment for other toxicants, as well as age, sex and lipid levels, several indicators of PCB burden are significantly, negatively related to levels of free thyroxine and total thyroxine, and positively to thyrotropin. Lead level was positively related to triidothyronine. Future testing of non-linear relationships is warranted. Despite the linear associations with thyrotropin, free and total thyroxine, PCBs were not related to increased occurrence of these hormones outside the clinically normal range for the testing laboratory.