Effects of short-term in vivo exposure to polybrominated diphenyl ethers on thyroid hormones and hepatic enzyme activities in weanling rats

Endocrine-disrupting chemicals as prostate carcinogens

Endocrine-disrupting chemicals (EDCs) are natural or synthetic compounds that are ubiquitous in the environment and in daily-usage products and interfere with the normal function of the endocrine system leading to adverse health effects in humans. Exposure to these chemicals might elevate the risk of metabolic disorders, developmental and reproductive defects, and endocrine-related cancers. Prostate cancer is the most common hormone-dependent cancer in men, and the fifth leading cause of cancer-related mortality, partly owing to a lack of knowledge about the mechanisms that lead to aggressive castration-resistant forms. In addition to the dependence of early-stage prostate cancer on androgen actions, the prostate is a target of oestrogenic regulation. This hormone dependence, along with the fact that exogenous influences are major risk factors for prostate cancer, make the prostate a likely target of harmful actions from EDCs. Various sources of EDCs and their different modes of action might explain their role in prostate carcinogenesis.

Distribution of polybrominated diphenyl ethers (PBDEs) in placental tissues of maternal and fetal origin in exposed Wistar rats and associations with thyroid hormone levels

In utero exposure to polybrominated diphenyl ethers (PBDEs) is linked to adverse pregnancy and fetal health outcomes, including altered thyroid hormone (TH) levels. Despite their phase-out, PBDEs are still commonly detected in newborn cord blood. While PBDEs can cross the placenta, few studies have separately assessed PBDEs or THs in the maternal and fetal placental tissues. Additionally, no studies have separately assessed THs in these tissues across mid- and late gestation, during the onset of fetal TH synthesis. To address these gaps, we conducted a study with Wistar rats and examined PBDE accumulation in the maternal and fetal placenta. Pregnant dams were exposed daily to sesame oil vehicle, a low dose, or high dose PBDE mixture. At GD15 and 20, dams were sacrificed and placental tissues were collected. Tissues were analyzed for PBDEs, T3, rT3, and T4 using mass spectrometry. BDE-47, -99, -100, and -209 were frequently detected in both the fetal and maternal placenta. At GD15, higher concentrations of BDE-99, -100, and -209 were measured in the fetal placenta; however, this trend reversed by GD20, with higher maternal placental concentrations. Placental T3 and T4 were significantly impacted by exposure, tissue, and exposure × tissue at GD15, with significant reductions in both THs following low-dose exposure in the maternal placenta. By GD20, maternal placental T3 was only significantly reduced in the high exposure groups and there was no effect on placental T4. Overall, these results highlight the rapid developmental changes that occur throughout gestation between the maternal and fetal placenta, and the differential impacts of gestational PBDE exposure on placental T3 and T4 across mid- and late gestation.

Associations of cord serum polybrominated diphenyl ether (PBDE) mixture with birth outcomes and mediating role of thyroid function: Evidence from the Sheyang Mini Birth Cohort Study

BACKGROUND

Polybrominated diphenyl ethers (PBDEs), a series of worldwide applied flame retardants, may influence fetal growth and interfere with thyroid function. The study intended to explore the relationship between in-utero exposure to PBDE mixture and newborn anthropometric indexes and to further examine the potential mediating role of thyroid function.

METHODS

Demographics and laboratory measures of 924 mother-infant pairs were obtained from the database of the Sheyang Mini Birth Cohort Study. We applied gas chromatography-mass spectrometry (GC-MS) and electrochemiluminescence immunoassay to measure nine PBDE congeners and seven thyroid function parameters in umbilical cord serum samples, respectively. We fitted generalized linear models and Bayesian kernel machine regression (BKMR) to evaluate associations of lipid-adjusted cord serum PBDEs, as individuals and as a mixture, with newborn anthropometric and cord serum thyroid function parameters. We applied causal mediation analysis to test our hypothesis that thyroid function parameters act as a mediator between PBDEs and birth outcomes.

RESULTS

The molarity of cord serum ∑9PBDE had a median value of 31.23 nmol/g lipid (IQR 19.14 nmol/g lipid, 54.77 nmol/g lipid). BDE-209 was the most dominant congener. Birth length was positively associated with both single exposure to BDE-28 and cumulative exposure to PBDEs. Correspondingly, ponderal index (PI) was negatively associated with BDE-28 and the total effects of PBDE mixture. Free triiodothyronine had a negative trend with BDE-209 and PBDE mixture. In the sex-stratified analysis, BDE-153 concentrations were positively correlated with PI among males (β = 0.03; 95%CI: 0.01, 0.05; P = 0.01) but not among females. Cord serum thyrotropin mediated 14.92% of the estimated effect of BDE-153 on PI.

CONCLUSIONS

In-utero mixture exposure to PBDEs was associated with birth outcomes and thyroid function. Thyroid function might act as a mediator in the process in which PBDEs impact the growth of the fetus.

Endocrine disrupting chemical mixture exposure and risk of papillary thyroid cancer in U.S. military personnel: A nested case-control study

Single-pollutant methods to evaluate associations between endocrine disrupting chemicals (EDCs) and thyroid cancer risk may not reflect realistic human exposures. Therefore, we evaluated associations between exposure to a mixture of 18 EDCs, including polychlorinated biphenyls (PCBs), brominated flame retardants, and organochlorine pesticides, and risk of papillary thyroid cancer (PTC), the most common thyroid cancer histological subtype. We conducted a nested case-control study among U.S. military servicemembers of 652 histologically-confirmed PTC cases diagnosed between 2000 and 2013 and 652 controls, matched on birth year, sex, race/ethnicity, military component (active duty/reserve), and serum sample timing. We estimated mixture odds ratios (OR), 95% confidence intervals (95% CI), and standard errors (SE) for associations between pre-diagnostic serum EDC mixture concentrations, overall PTC risk, and risk of histological subtypes of PTC (classical, follicular), adjusted for body mass index and military branch, using quantile g-computation. Additionally, we identified relative contributions of individual mixture components to PTC risk, represented by positive and negative weights (w). A one-quartile increase in the serum mixture concentration was associated with a non-statistically significant increase in overall PTC risk (OR = 1.19; 95% CI = 0.91, 1.56; SE = 0.14). Stratified by histological subtype and race (White, Black), a one-quartile increase in the mixture was associated with increased classical PTC risk among those of White race (OR = 1.59; 95% CI = 1.06, 2.40; SE = 0.21), but not of Black race (OR = 0.95; 95% CI = 0.34, 2.68; SE = 0.53). PCBs 180, 199, and 118 had the greatest positive weights driving this association among those of White race (w = 0.312, 0.255, and 0.119, respectively). Findings suggest that exposure to an EDC mixture may be associated with increased classical PTC risk. These findings warrant further investigation in other study populations to better understand PTC risk by histological subtype and race.

EFSA Panel on Contaminants in the Food Chain (CONTAM), Schrenk D, Bignami M, Bodin L, Chipman JK, del Mazo J, Grasl‐Kraupp B, Hogstrand C, (Ron) Hoogenboom L, Leblanc J, Nebbia CS, Nielsen E, Ntzani E, Petersen A, Sand S, Schwerdtle T, Wallace H, Benford D, Fürst P, Hart A, Rose M, Schroeder H, Vrijheid M, Ioannidou S, Nikolič M, Bordajandi LR, Vleminckx C. Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

A comprehensive review on the decabromodiphenyl ether (BDE-209)-induced male reproductive toxicity: Evidences from rodent studies

Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardants (BFRs), are employed in various manufactured products to prevent fires, slow down their spread and reduce the resulting damages. Decabromodiphenyl ether (BDE-209), an example of PBDEs, accounts for approximately 82 % of the total production of PBDEs. BDE-209 is a thyroid hormone (TH)-disrupting chemical owing to its structural similarity with TH. Currently, increase in the level of BDE-209 in biological samples has become a major issue because of its widespread use. BDE-209 causes male reproductive toxicity mainly via impairment of steroidogenesis, generation of oxidative stress (OS) and interference with germ cell dynamics. Further, exposure to this chemical can affect metabolic status, sperm concentration, epigenetic regulation of various developmental genes and integrity of blood-testis barrier in murine testis. However, the possible adverse effects of BDE-209 and its mechanism of action on the male reproductive health have not yet been critically evaluated. Hence, the present review article, with the help of available literature, aims to elucidate the reproductive toxicity of BDE-209 in relation to thyroid dysfunction in rodents. Further, several crucial pathways have been also highlighted in order to strengthen our knowledge on BDE-209-induced male reproductive toxicity. Data were extracted from scientific articles available in PubMed, Web of Science, and other databases. A thorough understanding of the risk assessment of BDE-209 exposure and mechanisms of its action is crucial for greater awareness of the potential threat of this BFR to preserve male fertility.

Assessment of five typical environmental endocrine disruptors and thyroid cancer risk: a meta-analysis

Introduction

There are conflicting reports on the association between environmental endocrine disruptors (EEDs) and thyroid cancer. This meta-analysis aimed to elucidate the relationship between EEDs and thyroid cancer.

Methods

We searched for epidemiological studies on EEDs and thyroid cancer published in PubMed and Web of Science up to December 2022. We then screened the articles that could extract data on EEDs concentration levels in both thyroid cancer patients and healthy controls. We excluded articles that could not calculate effect sizes, focused on other thyroid diseases, or lacked controls. Standardized mean difference (SMD) was calculated to analyze the association between EEDs and thyroid cancer. We measured the heterogeneity among the included studies using I2, assessed publication bias by Egger's and Begg's test, and evaluated article quality using the Newcastle-Ottawa Quality Score (NOS). In the end, fifteen eligible case-control studies were included.

Results

Our comprehensive analysis revealed that polychlorinated biphenyls (PCBs) were negatively associated with thyroid cancer{ SMD = -0.03, 95% confidence interval (CI) = (-0.05, -0.00), P = 0.03}, while polybrominated diphenyl ethers (PBDEs), phthalates (PAEs), and heavy metals were positively associated with thyroid cancer{PBDEs: SMD = 0.14, 95%CI = (0.04, 0.23), P = 0.007; PAEs: SMD = 0.30, 95%CI = (0.02, 0.58), P = 0.04; heavy metals: SMD = 0.21, 95%CI = (0.11, 0.32), P < 0.001}. We did not find a statistically significant relationship between bisphenol A (BPA) and thyroid cancer. Most of the included studies did not show publication bias, except for those on PCBs.

Discussion

Our results indicate that exposure to certain EEDs, such as PBDEs, PAEs, and heavy metals, increases the risk of thyroid cancer. However, further large-scale epidemiological studies and mechanism studies are needed to verify these potential relationships and understand the underlying biological mechanisms.

Toxic Effects and Mechanisms of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDEs) are a group of flame retardants used in plastics, textiles, polyurethane foam, and other materials. They contain two halogenated aromatic rings bonded by an ester bond and are classified according to the number and position of bromine atoms. Due to their widespread use, PBDEs have been detected in soil, air, water, dust, and animal tissues. Besides, PBDEs have been found in various tissues, including liver, kidney, adipose, brain, breast milk and plasma. The continued accumulation of PBDEs has raised concerns about their potential toxicity, including hepatotoxicity, kidney toxicity, gut toxicity, thyroid toxicity, embryotoxicity, reproductive toxicity, neurotoxicity, and immunotoxicity. Previous studies have suggested that there may be various mechanisms contributing to PBDEs toxicity. The present study aimed to outline PBDEs' toxic effects and mechanisms on different organ systems. Given PBDEs' bioaccumulation and adverse impacts on human health and other living organisms, we summarize PBDEs' effects and potential toxicity mechanisms and tend to broaden the horizons to facilitate the design of new prevention strategies for PBDEs-induced toxicity.

Parental and transgenerational impairments of thyroid endocrine system in zebrafish by 2,4,6-tribromophenol

Many environmental contaminants could be transmitted from parents and generate impairments to their progeny. The 2,4,6-tribromophenol (TBP), a novel brominated flame retardant which has been frequently detected in various organisms, was supposed to be bioaccumulated and intergenerational transmitted in human beings. Previous studies revealed that TBP could disrupt thyroid endocrine system in zebrafish larvae. However, there is no available data regarding the parental and transgenerational toxicity of this contaminant. Thus, in this study adult zebrafish were exposed to environmental contaminated levels of TBP for 60 days to investigate the parental and transgenerational impairments on thyroid endocrine system. Chemical analysis verified the bioaccumulation of TBP in tested organs of parents (concentration: liver>gonads>brain) and its transmission into eggs. For adults, increased thyroid hormones, disturbed transcriptions of related genes and histopathological changes in thyroid follicles indicate obvious thyroid endocrine disruptions. Transgenerational effects are indicated by the increased thyroid hormones both in eggs (maternal source) and in developed larvae (newly synthesized), as well as disrupted transcriptional profiles of key genes in HPT axis. The overall results suggest that the accumulated TBP could be transmitted from parent to offspring and generate thyroid endocrine disruptions in both generations.

Effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on reproductive and endocrine function in female zebrafish (Danio rerio)

BACKGROUND

Polybrominated diphenyl ethers (PBDEs), a group of brominated flame retardants (BFRs), were reported exist extensively in various ecological environmental. Studies have indicated that PBDEs induce reproductive toxic effects on human health, but the mechanisms remain poorly understood. In this study, the adult female zebrafish were used to investigate the effects of 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47) on the reproductive endocrine system and its mechanism.

METHODS

Female zebrafish (AB strains) were continuously exposed to BDE-47 at the concentrations of 0, 10, 50, 100 and 500 µg/L till 21 days. The morphology of ovary were stained and evaluated with hematoxylin-eosin (H&E), and levels of sex hormones including follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T) and 17β-estradiol (E₂) and the biomarkers of oxidative stress such as superoxide dismutase (SOD) and malondialdehyde (MDA), were measured via ELISA. Subsequently, the expression of genes along the hypothalamic pituitary-gonad (HPG) and oxidative stress were determined using quantitative real-time PCR (qRT-PCR).

RESULT

The results showed that exposure to high level of BDE-47 reduced the index of condition factor (CF) and gonadosomatic index (GSI). Treatment with BDE-47 impaired the normal development and structure of oocytes in zebrafish ovary. Moreover, the steroid hormone of FSH, LH, T and E₂ were significantly decreased in BDE-47 exposure group. A dose-dependent elevation in SOD activity and MDA levels were recorded. Meanwhile, the transcription level of cyp19a, cyp19b, fshβ, lhβ were up-regulated while the transcription of fshr, lhr, cyp17a, 17βhsd were down-regulated in the gonad of female adult zebrafish.

CONCLUSION

Exposure to BDE-47 have detrimental impact on the development of ovary, decreasing sex hormone levels, inducing oxidative damage as well as altering HPG axis-related genes.

Dietary microplastics: Occurrence, exposure and health implications

The increasing use of plastic materials generates an enormous amount of waste. In the aquatic environment, a significant part of this waste is present in the form of microplastics (MPs)- particles with a diameter of between 0.1 μm and 5 mm. The arrival of these small plastics in the food chain has been recently documented. MPs have been reported in fishery products, drinking water and sea salt among other foods. Their intestinal absorption is considered limited due to their size, however, they contain a mixture of chemicals intentionally added during their manufacture, which could cross the intestinal barrier. Currently there are not enough data to allow an accurate assessment of the risk associated with dietary exposure to MPs. The lack of robust methodologies is undoubtedly one of the main problems. There is limited information on occurrence in dietary sources (drinking water and food), human intake, toxicokinetics and long term toxicity of these contaminants. The present review describes the studies published so far and points to the need for improved knowledge in order to have a more accurate view of the problems posed by MPs.

Global PBDE contamination in cetaceans. A critical review

This review summarizes the most relevant information on PBDEs' occurrence and their impacts in cetaceans at global scale, with special attention on the species with the highest reported levels and therefore the most potentially impacted by the current and continuous release of these substances. This review also emphasizes the anthropogenic and environmental factors that could increase concentrations and associated risks for these species in the next future. High PBDE concentrations above the toxicity threshold and stationary trends have been related to continuous import of PBDE-containing products in cetaceans of Brazil and Australia, where PBDEs have never been produced. Non-decreasing levels documented in cetaceans from the Northwest Pacific Ocean might be linked to the increased e-waste import and ongoing production and use of deca-BDE that is still allowed in China. Moreover, high levels of PBDEs in some endangered species such as beluga whales (Delphinapterus leucas) in St. Lawrence Estuary and Southern Resident killer whales (Orcinus Orca) are influenced by the discharge of contaminated waters deriving from wastewater treatment plants. Climate change related processes such as enhanced long-range transport, re-emissions from secondary sources and shifts in migration habits could lead to greater exposure and accumulation of PBDEs in cetaceans, above all in those species living in the Arctic. In addition, increased rainfall could carry greater amount of contaminants to the marine environment, thereby, enhancing the exposure and accumulation especially for coastal species. Synergic effects of all these factors and ongoing emissions of PBDEs, expected to continue at least until 2050, could increase the degree of exposure and menace for cetacean populations. In this regard, it is necessary to improve current regulations on PBDEs and broader the knowledge about their toxicological effects, in order to assess health risks and support regulatory protection for cetacean species.

Towards a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny-part III: how is substance-mediated thyroid hormone imbalance in pregnant/lactating rats or their progeny related to neurodevelopmental effects?

This review investigated which patterns of thyroid- and brain-related effects are seen in rats upon gestational/lactational exposure to 14 substances causing thyroid hormone imbalance by four different modes-of-action (inhibition of thyroid peroxidase, sodium-iodide symporter and deiodinase activities, enhancement of thyroid hormone clearance) or to dietary iodine deficiency. Brain-related parameters included motor activity, cognitive function, acoustic startle response, hearing function, periventricular heterotopia, electrophysiology and brain gene expression. Specific modes-of-action were not related to specific patterns of brain-related effects. Based upon the rat data reviewed, maternal serum thyroid hormone levels do not show a causal relationship with statistically significant neurodevelopmental effects. Offspring serum thyroxine together with offspring serum triiodothyronine and thyroid stimulating hormone appear relevant to predict the likelihood for neurodevelopmental effects. Based upon the collated database, thresholds of ≥60%/≥50% offspring serum thyroxine reduction and ≥20% and statistically significant offspring serum triiodothyronine reduction indicate an increased likelihood for statistically significant neurodevelopmental effects; accuracies: 83% and 67% when excluding electrophysiology (and gene expression). Measurements of brain thyroid hormone levels are likely relevant, too. The extent of substance-mediated thyroid hormone imbalance appears more important than substance mode-of-action to predict neurodevelopmental impairment in rats. Pertinent research needs were identified, e.g. to determine whether the phenomenological offspring thyroid hormone thresholds are relevant for regulatory toxicity testing. The insight from this review shall be used to suggest a tiered testing strategy to determine whether gestational/lactational substance exposure may elicit thyroid hormone imbalance and potentially also neurodevelopmental effects.

Zearalenone affects the growth of endometriosis via estrogen signaling and inflammatory pathways

Endometriosis is a chronic, inflammatory, estrogen-dependent gynecological disease characterized by the growth of endometrial stromal cells and glands outside the uterine cavity in response to hormones, which commonly occurs in reproductive-age women. Zearalenone (ZEA) is a toxic metabolite produced by Fusarium, which acts as estrogen activity because of the similarity of its structure to estrogen. In this study, we used an endometriosis mouse model: 15 days after ovariectomy, endometrial fragments were sutured on the pelvic wall, and exogenous estrogen was supplied using an estrogen-releasing silicone tube embedded subcutaneously. Mice were treated with different doses of ZEA by gavage for 21 days. The results show that ZEA significantly inhibited the growth of ectopic endometrium in a dose-dependent manner. The proliferation of cells decreased while apoptosis increased in the ectopic tissues of ZEA-treated mice compared to the vehicle group. The expression of estrogen receptor-α and its downstream targets MUC1 and p-AKT decreased, indicating an impaired estrogen signaling activity by ZEA treatment. In addition, the decreased expression of pro-inflammatory cytokine Tnf-α, Il-1β, and Il-6, the lower number of macrophages and neutrophils cells, and the inhibited NF-κB signaling pathway suggest the inflammatory response in the ectopic endometrium was also suppressed by ZEA treatment. However, when the exogenous estrogen supply is removed, ZEA, in turn, plays an estrogen-like role that promotes cell proliferation in the ectopic endometrium. In summary, our data suggest ZEA acts as an antagonist in endometriotic tissue when estrogen is sufficient but turns to estrogenic activity in the absence of estrogen in the development of endometriosis. ZEA also inhibits ectopic tissue growth by inhibiting inflammatory response in the endometriosis model.

Environmental, Health, and Legislation Considerations for Rational Design of Nonreactive Flame-Retardant Additives for Polymeric Materials: Future Perspectives

Increasing polymer usage has demanded functional additives that decrease fire hazards for end users. While traditional flame-retardant (FR) additives, such as halogenated, phosphorus, and metal hydroxides, greatly reduce flammability and associated fire hazards, research has continually exposed a litany of health and environmental safety concerns. This perspective aims to identify the key components of a successful FR additive and address material, environmental, and health concerns of existing additives. Legislation surrounding FRs and persistent organic pollutants is also discussed to highlight political perception that has resulted in the increased chemical regulations and subsequent banning of FR additives. Finally, future directions of this field regarding nonreactive additives, focusing on the use of bioinspired materials and transition metal chemistries to produce alternatives for polymers with efficacies surpassing traditional additives are presented.

Isoflucypram: Combining in vivo and NAMs data in a weight of evidence approach to demonstrate the human non-relevance of the mode of action leading to the subtle thyroid effects observed in the rat

Isoflucypram (ISY) is a new cereal fungicide with an overall favorable toxicity profile. As the thyroid was identified as a target organ only in the rat, following repeat dosing; short term in vivo (rat) and in vitro mechanistic studies were conducted to substantiate the thyroid changes as being secondary to liver enzyme induction via PXR/CAR activation and to determine the human non-relevance of the thyroid effects. The in vivo studies established ISY as a weak prototypical hepatic PXR/CAR enzyme inducer (P450 and T4-UDP-glucuronosyltransferase (T4-UDPGT) activities), with the induction being associated with increased liver weight/hepatocellular hypertrophy/proliferation. Thyroid effects (minimal follicular cell hypertrophy/proliferation, slight, statistically significantly increased thyroid stimulating hormone) occurred at doses where liver stimulation was already established. Direct thyroid effects (in vitro thyroid peroxidase and sodium iodide symporter inhibition) were excluded. Marked quantitative species differences were identified when comparing rat and human hepatic enzyme activities in vitro, particularly for T4-UDPGT. Specifically, basal T4-UDPGT was 4-fold lower in human compared to rat hepatocytes. In addition, T4-UDPGT was induced in vitro in rat but not in human hepatocytes following ISY treatment. Overall, the weight of evidence supports a liver mediated mode of action for the isoflucypram-induced slight rat thyroid changes as well as the human non-relevance of these findings.

Thyroid Dysfunction of Zebrafish (Danio rerio) after Early-Life Exposure and Discontinued Exposure to Tetrabromobiphenyl (BB-80) and OH-BB-80

3,3',5,5'-Tetrabromobiphenyl (BB-80) was once used as additive flame retardants. Whether its early exposure and discontinued exposure alter thyroid function remains unknown. We investigate adverse effects after early-life exposure and discontinued exposure to BB-80 and hydroxylated BB-80 (OH-BB-80) on thyroid hormone (TH) levels, thyroid tissue, and transcriptome profiles in zebrafish larvae. BB-80 at 10 μg/L induces pathological changes of thyroid with reduced thyroid follicles in larvae (P < 0.05), whereas OH-BB-80 significantly increases T4 and T3 contents (1.8 and 2.5 times of the control, P < 0.05) at 14 days postfertilization (dpf) without morphological thyroid alterations. BB-80 and OH-BB-80 cause transcriptome aberrations with key differentially expressed genes involved in the disruption of TH synthesis and signal transduction (BB-80 at 14 dpf) or TH pathway activation (OH-BB-80 at 21 dpf). After 7 days of discontinued exposure, thyroglobulin (tg) and thyroid peroxidase (tpo) genes are downregulated (P < 0.05) by 52 and 48% for BB-80 and by 49 and 39% for OH-BB-80, respectively; however, the whole-body TH levels fail to fully recover, and the locomotor activity is impaired more by BB-80. Our results indicate significant adverse impacts of BB-80 and OH-BB-80 on TH homeostasis and thyroid function of zebrafish.

High-fat diet exacerbated decabromodiphenyl ether-induced hepatocyte apoptosis via intensifying the transfer of Ca2+ from endoplasmic reticulum to mitochondria

Polybrominated diphenyl ether (PBDE) as the flame retardant is heavily used in daily necessities, causing adverse health effects on humans. This study aimed to evaluate the hepatotoxicity of decabromodiphenyl ether (BDE-209), the most widely used PBDE, in lean and high-fat diet (HFD)-treated obese mice and elucidate the underlying mechanism. Firstly, the increasing levels of TG and proinflammatory factors in the liver and ALT and AST in serum demonstrated the hepatic damage caused by BDE-209 and further exacerbated by HFD. Tunel image revealed that BDE-209 induced more severe hepatocyte apoptosis with the assistant of HFD. Next, the mechanism analysis showed that the pro-apoptotic action of BDE-209 was in an endoplasmic reticulum (ER)/Ca²⁺ flux/mitochondria-dependent manner, concluded from the impairment of mitochondrial membrane potential, the enhancive protein expression of p-PERK/PERK, p-IRE1/IRE1, ATF6, CHOP, Bax/Bcl-2, cleaved caspase-3/caspase-3, IP3R1 and Sig-1R, and the over-transfer of Ca²⁺ from ER to mitochondria. Such proposed mechanism was further confirmed by the IP3R1 siRNA transfection cell experiment, where apoptotic rate was reduced in parallel with the reduced mitochondrial Ca²⁺ level. Finally, the higher expression of PACS-2 protein and the expanded ER contributed to the enriched ER-mitochondria interaction, reflected by the closer distance between ER and mitochondria visually displayed in the TEM image in HFD groups. This change was conducive to the rapid delivery of apoptosis signals via Ca²⁺, as proven, mechanically explaining the strengthening effect of HFD on BDE-209 hepatotoxicity. These findings detailedly explained the mechanism of BDE-209 hepatotoxicity and clarified the auxiliary effect of HFD, providing a theoretical basis for further studying other analogs.

Adrenal Corticosteroid Perturbation by the Endocrine Disruptor BDE-47 in a Human Adrenocortical Cell Line and Male Rats

Polybrominated diphenyl ethers (PBDEs) have been previously shown to alter various endocrine biosynthetic pathways. Growing epidemiological evidence suggests that PBDEs alter cardiovascular function. The goal of this study was to examine the effects of BDE-47 on adrenal corticosteroid pathways that play vital roles in cardiovascular homeostasis and pathophysiology. The effect of BDE-47 on aldosterone and cortisol secretion was characterized in a human adrenocortical cell line. HAC15 cells were exposed to various concentrations of BDE-47 (1 nM to 100 μM). Cell viability, corticosteroid secretion, gene expression of enzymes involved in corticosteroid synthesis, and metabolic activity was examined. Additionally, Sprague Dawley male rats were orally exposed to BDE-47 (10 or 100 µg/kg), 5 days per week for 16 weeks. Organ weights and plasma corticosteroid levels were measured. In HAC15 cells, basal and stimulated aldosterone and cortisol secretion was significantly increased by BDE-47. Gene expression of several enzymes involved in corticosteroid synthesis and mitochondrial metabolism also increased. In Sprague Dawley rats, adrenal but not heart, kidney, or liver weights, were significantly increased in BDE-47 treatment groups. Plasma corticosterone levels were significantly increased in the 100 µg BDE-47/kg treatment group. No change in plasma aldosterone levels were observed with BDE-47 exposure. These data indicate that BDE-47 disrupts the regulation of corticosteroid secretion and provides further evidence that PBDEs are potential endocrine disruptors. Future studies will determine the underlying molecular mechanism of altered corticosteroid production and examine whether these alterations result in underlying cardiovascular disease in our rodent model of 16-week BDE-47 exposure.

Determination of benchmark doses for linear furanocoumarin consumption associated with inhibition of cytochrome P450 1A2 isoenzyme activity in healthy human adults

Millions of individuals globally consume traditional herbal medicines (THMs), which contain abundant amounts of linear furanocoumarins. Linear furanocoumarins (i.e., 8-methoxypsoralen, 5-methoxypsoralen, and isopimpinellin) are inhibitors of cytochrome P450 (CYP) isoenzymes including 1A2, a major enzyme involved in drug metabolism and carcinogen bioactivation. Despite the high consumption of furanocoumarin-containing THMs, no studies have measured the furanocoumarin consumption level that triggers an inhibition to CYP1A2 activity in humans. The first objective was to verify if the potencies of the three furanocoumarins are additive towards the inhibition of CYP1A2 activity in vitro using concentration-addition and whole-mixture chemical-mixture-assessment models. A second objective was to determine the benchmark dose (BMD) with the mixtures of furanocoumarin oral doses, expressed as 8-MOP equivalents, and to assess the in vivo CYP1A2 activity, expressed as inhibition percentages. The in vitro results indicated that the three furanocoumarin inhibitory potencies were additive in the THM extracts, validating the use of the concentration-addition model in total furanocoumarin dose-equivalent calculations. Using the USEPA BMD software, the BMD was 18.9 μg 8-MOP equivalent/kg body weight. This information is crucial for furanocoumarin-related health-assessment studies and the regulation of THMs. Further studies should be performed for the remaining major metabolic enzymes to complete the safety profile of furanocoumarin-containing THMs and to provide accurate warning labelling.

Mitigating the Adverse Effects of Polychlorinated Biphenyl Derivatives on Estrogenic Activity via Molecular Modification Techniques

The aim of this paper is to explore the mechanism of the change in oestrogenic activity of PCBs molecules before and after modification by designing new PCBs derivatives in combination with molecular docking techniques through the constructed model of oestrogenic activity of PCBs molecules. We found that the weakened hydrophobic interaction between the hydrophobic amino acid residues and hydrophobic substituents at the binding site of PCB derivatives and human oestrogen receptor alpha (hERα) was the main reason for the weakened binding force and reduced anti-oestrogenic activity. It was consistent with the information that the hydrophobic field displayed by the 3D contour maps in the constructed oestrogen activity CoMSIA model was one of the main influencing force fields. The hydrophobic interaction between PCB derivatives and oestrogen-active receptors was negatively correlated with the average distance between hydrophobic substituents and hydrophobic amino acid residues at the hERα-binding site, and positively correlated with the number of hydrophobic amino acid residues. In other words, the smaller the average distance between the hydrophobic amino acid residues at the binding sites between the two and the more the number of them, and the stronger the oestrogen activity expression degree of PCBS derivative molecules. Therefore, hydrophobic interactions between PCB derivatives and the oestrogen receptor can be reduced by altering the microenvironmental conditions in humans. This reduces the ability of PCB derivatives to bind to the oestrogen receptor and can effectively modulate the risk of residual PCB derivatives to produce oestrogenic activity in humans.

In Utero and Lactational Exposure to an Environmentally Relevant Mixture of Brominated Flame Retardants Induces a Premature Development of the Mammary Glands

In utero and prepubertal development of the mammary glands occurs minimally in a hormone independent manner until puberty where maturation of the hypothalamic-pituitary-gonadal axis drives an extensive remodeling. Nevertheless, because the immature glands contain functional hormone receptors, they are especially vulnerable to the effects of endocrine disruptors, such as brominated flame retardants (BFRs). BFRs are widespread chemicals added to household objects to reduce their flammability, and to which humans are ubiquitously exposed. We previously reported that in utero and lactational exposure to BFRs resulted in an impaired mammary gland development in peripubertal animals. Here, we assessed whether BFR-induced disruption of mammary gland development could manifest earlier in life. Dams were exposed prior to mating until pups' weaning to a BFR mixture (0, 0.06, 20, or 60 mg/kg/day) formulated according to levels found in house dust. The mammary glands of female offspring were collected at weaning. Histo-morphological analyses showed that exposure to 0.06 mg/kg/day accelerates global epithelial development as demonstrated by a significant increase in total epithelial surface area, associated with a tendency to increase of the ductal area and thickness, and of lumen area. Significant increases of the Ki67 cell proliferation index and of the early apoptotic marker cleaved caspase-9 were also observed, as well as an upward trend in the number of thyroid hormone receptor α1 positive cells. These molecular, histologic, and morphometric changes are suggestive of accelerated pubertal development. Thus, our results suggest that exposure to an environmentally relevant mixture of BFRs induces precocious development of the mammary gland.

Plasma polybrominated diphenyl ethers, urinary heavy metals and the risk of thyroid cancer: A case-control study in China

The incidence of thyroid cancer (TC) has increased rapidly worldwide in recent years. Exposure to endocrine disruptors can affect thyroid hormones and is probably carcinogenic to humans. The effects of polybrominated diphenyl ethers (PBDEs), some heavy metals (Cd, Pb, As and Hg) on risk of TC have been rarely reported. Hence, we aimed to examine the associations of TC risk with exposure to PBDEs and four heavy metals. This case-control study involved 308 TC cases and 308 age- and sex-matched controls. Plasma PBDEs concentrations were determined by gas chromatograph-mass spectrometry. Concentrations of heavy metals concentrations in urine specimens were detected by graphite furnace atomic absorption spectrometry or inductively coupled plasma optical emission spectrometry. Conditional logistic regression models were used to explore associations of PBDEs and 4 heavy metals exposures with TC risk. A joint-effect interaction term was inserted into the logistic regression models to assess the multiplicative interaction effects of PBDEs-heavy metals on TC risk. Some PBDE congeners (BDE-028, -047, -099, -183, -209) were positively correlated with TC risk. As and Hg were also associated with the increased TC risk. Compared with low exposure levels, participants with high exposure levels of As and Hg were 5.35 and 2.98 times more likely to have TC, respectively. Co-exposure to BDE-209 and Pb had a negative interaction effect on TC risk. Some PBDE congeners (e.g. BDE-028, -047, -209) and Hg had a significant positive interaction effect on the risk of TC. The joint exposure of BDE-183 and Hg showed a negative interaction effect on TC risk, but the corresponding OR value was still statistically significant. Exposure to PBDEs, As and Hg may be associated with TC development. Joint exposure to PBDEs and Pb or Hg has interaction effects on TC risk. Further prospective research with large sample is required to confirm these findings.

Bioconcentration of 2,4,6-tribromophenol (TBP) and thyroid endocrine disruption in zebrafish larvae

2,4,6-tribromophenol (TBP) is generally used as a brominated flame retardant but is produced in the degradation of tetrabromobisphenol-A. Although TBP is frequently detected in the environment and in various biota, including fish species, we still know little about its toxicity and environmental health risk. Here we investigated the bioconcentration and effects of TBP on the thyroid endocrine system by using zebrafish as a model. Zebrafish embryos (2 h post-fertilization, hpf) were exposed to five concentrations of TBP (0, 0.3, 1, 10, and 100 μg/L) until 144 hpf. According to our chemical analysis, TBP underwent bioconcentration in zebrafish larvae. However, acute exposure to TBP did not affect the hatching of embryos or their risk of malformation, nor the growth and survival of larvae, indicating low developmental toxicity of TBP. The whole-body thyroxine (T4) contents were significantly increased in zebrafish larvae after exposure to TBP, indicating thyroid endocrine disruption occurred. Gene transcription levels in the hypothalamic-pituitary-thyroid (HPT) axis were also examined in larvae; these results revealed that the transcription of corticotrophin-releasing hormone (crh), thyrotropin-releasing hormone (trh), and thyroid-stimulating hormone (tshβ) were all significantly downregulated by exposure to TBP. Likewise, genes encoding thyronine deiodinases (dio1, dio2, and dio3a/b) and thyroid hormone receptors (trα and trβ) also had their transcription downregulated in zebrafish. Further, the gene transcription and protein expression of binding and transport protein transthyretin (TTR) were significantly increased after TBP exposure. Taken together, our results suggest the bioavailability of and potential thyroid endocrine disruption by TBP in fish.

Pentabromoethylbenzene Exposure Induces Transcriptome Aberration and Thyroid Dysfunction: In Vitro, in Silico, and in Vivo Investigations

Pentabromoethylbenzene (PBEB), as one of the novel brominated flame retardants (NFBRs), has caused increasing public concern for health risks. Till now, information regarding potential effects of PBEB on thyroid function remains unclear. Herein, we investigated thyroid disruption of PBEB in vitro and in silico and evaluated thyroid dysfunction induced by PBEB using Sprague-Dawley rats. PBEB showed thyroid receptor (TR) β antagonistic activity with IC₅₀ of 9.82 × 10^-7 M in the dual-luciferase reporter gene assay and induced relative reorientation of helix 11 (H11) and H12 of the TR ligand binding domain as revealed by molecular dynamics simulations. PBEB (0.2, 2, 20 mg/kg BW/d) markedly altered the transcriptome profile of thyroid with induction of 17, 42, and 119 differentially expressed genes (DEGs) involved in thyroid hormone signaling and synthesis pathway, of which transthyretin and albumin are common DEGs. The 28-d exposure to PBEB significantly decreased the triiodothyronine level (from 7.23 to 5.67 ng/mL) and increased the thyrotropin level (from 7.88 to 12.86 mU/L) for female rats. PBEB consequently reduced thyroid weight and altered its morphology with more depleted follicles. Overall, our study provides the first account of evidence on PBEB exerted thyroid disruption, transcriptome aberration, and morphological alteration, facilitating health risk assessment of PBEB and structurally related NBFRs.

Accumulation and translocation of polybrominated diphenyl ethers into plant under multiple exposure scenarios

Plant foliar uptake is an essential part of the overall biogeochemical cycling of semivolatile organic compounds. Chambers were therefore designed to expose wheat to polybrominated diphenyl ethers (PBDEs) via various combinations of exposure routes (i.e., soil, air and particle). Under the simulated scenarios, most of PBDEs in wheat leaves originated from foliar uptake (including gaseous and particle-bound depositions) rather than translocation from root uptake. Our results further revealed that higher brominated PBDEs (h-PBDEs; i.e. hepta- through deca-BDEs) were inclined to enter wheat leaves via particle-bound deposition while gaseous deposition could not be ignored for less-brominated PBDEs (l-PBDEs; i.e., tri- through hexa-BDEs). Sequential extraction of wheat leaf displayed that the transfer velocities of h-PBDEs were lagged behind l-PBDEs during their deposition to leaf cuticle and subsequent erosion to mesophyll, where a large fraction of the target chemicals were ultimately stored (29-93% of total PBDEs burden). Applying McLachlan's framework to our data suggested that the uptake of PBDEs was controlled primarily by kinetically limited gaseous deposition for l-PBDEs and by particle-bound deposition for h-PBDEs. The combined use of exposure chamber measurement and framework provides a robust tool for interpreting the behaviors of PBDEs between the atmosphere and plant foliage.

Regulation of Thyroid-disrupting Chemicals to Protect the Developing Brain

Synthetic chemicals with endocrine disrupting properties are pervasive in the environment and are present in the bodies of humans and wildlife. As thyroid hormones (THs) control normal brain development, and maternal hypothyroxinemia is associated with neurological impairments in children, chemicals that interfere with TH signaling are of considerable concern for children's health. However, identifying thyroid-disrupting chemicals (TDCs) in vivo is largely based on measuring serum tetraiodothyronine in rats, which may be inadequate to assess TDCs with disparate mechanisms of action and insufficient to evaluate the potential neurotoxicity of TDCs. In this review 2 neurodevelopmental processes that are dependent on TH action are highlighted, neuronal migration and maturation of gamma amino butyric acid-ergic interneurons. We discuss how interruption of these processes by TDCs may contribute to abnormal brain circuitry following developmental TH insufficiency. Finally, we identify issues in evaluating the developmental neurotoxicity of TDCs and the strengths and limitations of current approaches designed to regulate them. It is clear that an enhanced understanding of how THs affect brain development will lead to refined toxicity testing, reducing uncertainty and improving our ability to protect children's health.

Perinatal low-dose PBDE-47 exposure hampered thyroglobulin turnover and induced thyroid cell apoptosis by triggering ER stress and lysosomal destabilization contributing to thyroid toxicity in adult female rats

Evidence demonstrates that 2,2',4,4'-tetrabromodiphenyl ether (PBDE-47) is able to disturb thyroid hormones (THs) homeostasis, yet the mechanisms remain unknown. We sought to investigate the effects of PBDE-47 on endoplasmic reticulum (ER) and lysosomes in thyroids. Using female Sprague-Dawley rats orally administered PBDE-47 at environmentally relevant doses (0.1, 1.0, 10 mg/kg/day) beginning ten days before breeding and ending at weaning, we showed that perinatal PBDE-47 exposure resulted in a reduction in serum THs levels and relative thyroid weight in adult female rats. These were accompanied by thyroid structural abnormalities with cell apoptosis. Mechanistically, PBDE-47 caused ER stress and activation of unfolded protein response (UPR). Moreover, PBDE-47 elicited lysosomal membrane permeabilization and the release of cathepsin. Importantly, the apoptotic cells co-localized with IRE1α, a stress sensor protein of UPR branch that mediates ER stress-induced apoptosis, or cathepsin B, a lysosomal cysteine protease that is involved in thyroglobulin, the precursor of THs, degradation and apoptosis induction. Interestingly, thyroglobulin was accumulated and predominantly presented in cells harboring compromised ER or lysosomal activity. Collectively, our findings suggest that perinatal low-dose PBDE-47 exposure hampers thyroglobulin turnover and induces thyroid cell apoptosis by triggering ER stress and lysosomal destabilization contributing to thyroid toxicity in adult female rats.

Associations between Exposure to Persistent Organic Pollutants and Thyroid Function in a Case-Control Study of East China

Animal studies have indicated that persistent organic pollutants (POPs) affect thyroid hormone homeostasis, while epidemiological studies involving human have not shown consistent results. In this study, we investigated the associations between POP exposure and thyroid function among adult population of East China. One hundred eighty-six participants diagnosed with thyroid disease and 186 participants without thyroid disease from Shandong, China were enrolled in the case-control study during 2016 to 2017. We found that POP exposure was significantly and positively associated with the risk of thyroid disease. The association of thyroid disease with a sum of 17 POPs followed a nonmonotonic dose response, with an adjusted odds ratio of 2.09 (95% confidence intervals: 1.13-3.87, p = 0.019) for the second quartile. Among 186 participants in the control group, concentrations of POPs showed negative associations with triiodothyronine (T3), free T3 (FT3), thyroxine (T4), and free T4 (FT4) in males and positive associations with T4 and FT4 in females. Taken together, these findings suggest that POP exposure can disrupt thyroid hormone homeostasis and increase the risk of thyroid disease.

Sodium perchlorate induces non-alcoholic fatty liver disease in developing stickleback

Perchlorate is a pervasive, water-soluble contaminant that competitively inhibits the sodium/iodide symporter, reducing the available iodide for thyroid hormone synthesis. Insufficient iodide uptake can lead to hypothyroidism and metabolic syndromes. Because metabolism, obesity and non-alcoholic fatty liver disease (NAFLD) are tightly linked, we hypothesized that perchlorate would act as an obesogen and cause NAFLD via accumulation of lipids in liver of developing threespine stickleback (Gasterosteus aculeatus). We performed an upshift/downshift exposure regime (clean water to perchlorate treated water or perchlorate treated water to clean water) on stickleback embryos at two concentrations (30 mg/L and 100 mg/L) plus the control (0 mg/L) over the course of 305 days. Adult stickleback were euthanized, H&E stained and analyzed for liver morphology. Specifically, we counted the number of lipid droplets, and measured the area of each droplet and the total lipid area of a representative section of liver. We found that perchlorate treated fish had more and larger lipid droplets, and a larger percentage of lipid in their liver than control fish. These data indicate that perchlorate causes NAFLD and hepatic steatosis in stickleback at concentrations commonly found at contaminated sites. These data also indicate the potential of perchlorate to act as an obesogen. Future studies should investigate the obesogenic capacity of perchlorate by examining organ specific lipid accumulation and whether perchlorate induces these effects at concentrations commonly found in drinking water. Work is also needed to determine the mechanisms by which perchlorate induces lipid accumulation.

Bioconcentration, Biotransformation, and Thyroid Endocrine Disruption of Decabromodiphenyl Ethane (Dbdpe), A Novel Brominated Flame Retardant, in Zebrafish Larvae

The brominated flame retardant decabromodiphenyl ethane (DBDPE), an alternative to decabrominated diphenyl ether (BDE209), has become a widespread environmental contaminant, but its possible toxic effects to wildlife remain unknown. Using zebrafish as a model, we investigated the bioconcentration and impact of DBDPE on thyroid endocrine function after water-borne exposure, compared to BDE209. Zebrafish embryos were exposed to DBDPE or BDE209 (0, 3, 10, 30, 100, 300 nM) for 6 or 14 days. Chemical analysis revealed that DBDPE and BDE209 were bioconcentrated in zebrafish larvae, with similar magnitudes of accumulated concentrations. Based on screened by chromatograms, at least seven unknown compounds were observed in DBDPE-treated larvae, indicating biotransformation of the chemical. Significant increases in whole body content of triiodothyronine (T3) and thyroxine (T4) were detected in DBDPE-treated larvae, but decreased in BDE209-treated groups. Alterations in gene transcription along the related hypothalamic-pituitary-thyroid (HPT) axis were observed. Furthermore, the binding and transport protein transthyretin (TTR) was significantly increased in DBDPE exposure groups. Histological examination and stereological analysis showed no obvious pathological changes in the thyroid gland. The present study demonstrates for the first time the bioavailability, biotransformation and thyroid endocrine disruption associated with DBDPE exposure in fish. Further studies are warranted to identify the metabolites of DBDPE and to define its environmental risks to aquatic organisms.

Pre- and Postnatal Polybrominated Diphenyl Ether Concentrations in Relation to Thyroid Parameters Measured During Early Childhood

Background: Penta-brominated diphenyl ethers (PentaBDEs) are endocrine-disrupting chemicals that structurally resemble thyroid hormones and were widely used as flame retardants in household consumer products from 1975 to 2004. Polybrominated diphenyl ethers (PBDEs) cross the placenta, and evidence suggests that for many children, body burdens may peak during the toddler years. This study aimed to understand the impact of exposure timing by examining both pre- and postnatal exposure to BDE-47, the predominant penta-brominated diphenyl ether congener detected in humans, in relation to thyroid hormone parameters measured during early childhood. Methods: The Columbia Center for Children's Environmental Health Mothers and Newborns Study is a prospective birth cohort of African American and Dominican maternal-child pairs. Pregnant women were recruited from two prenatal clinics in Northern Manhattan and the South Bronx between 1998 and 2006. Participants included 158 children with (i) plasma PBDE concentrations measured at birth and in the toddler years (age 2-3 years), and (ii) serum thyroid parameters measured at three and/or five years of age. Outcomes included concentrations of serum thyrotropin, free thyroxine, and total thyroxine. Results: Children with high exposure to BDE-47 during the prenatal period (-17% [confidence interval -29 to -2]) or toddler age (-19% [confidence interval -31 to -5]) had significantly lower geometric mean thyrotropin levels compared to children with low BDE-47 exposure throughout early life. Associations with thyroxine were also inverse; however, they did not reach statistical significance at the p = 0.05 level. Sex-stratified models suggest associations with postnatal exposure may be stronger among boys compared to girls. Conclusions: The thyroid regulatory system may be sensitive to BDE-47 during pre- and postnatal periods.

Evaluation of PCDD/Fs, dioxin-like PCBs and PBDEs in sperm whales from the Mediterranean Sea

Numerous studies to date have reported concentrations of Persistent Organic Pollutants (POPs) in different marine mammal species worldwide. Yet data on sperm whales are scarce from rich and unique biodiverse areas such as the Mediterranean Sea. This work aimed to assess levels of dioxin-like polychlorinated biphenyls (dl-PCBs), polybrominated diphenyl ethers (PBDEs), and polychlorodibenzo-p-dioxins and furans (PCDD/Fs) in blubber of sperm whales stranded along the Italian coast between 2008 and 2016. POP mean concentrations (dl-PCBs: 6410 ng/g l.w.; PBDEs: 612 ng/g l.w.; PCDD/Fs: 57.8 pg/g l.w.) were mostly in line with what has been previously reported on the same species in the Mediterranean environment and tended to be higher than those reported from other geographical regions. The relative abundance followed the order dl-PCBs > PBDEs ≫ PCDD/Fs. Interestingly, the non-ortho dl-PCB pattern (126 > 169 > 77) was similar to that described in other studies worldwide and different from what is described in its main prey. This could be linked to particular metabolic activities in sperm whales against these highly toxic contaminants. Total TEQs ranged from 275 to 987 pg/g l.w. and showed the pattern Σnon-ortho-dl-PCBs > Σortho-dl-PCBs > PCDDs > PCDFs, with PCBs' contribution about 96%. These findings highlight the high abundance of PCBs still found in the Mediterranean environment despite having been banned for decades. All sperm whales analyzed in this study surpassed the threshold of 210 pg WHO-TEQ/g l.w. proposed as starting point of immunosuppression in harbour seals; a level of contamination that may have contributed to an impairment of their immune system.

Designing modified polybrominated diphenyl ether BDE-47, BDE-99, BDE-100, BDE-183, and BDE-209 molecules with decreased estrogenic activities using 3D-QSAR, pharmacophore models coupled with resolution V of the 210-3 fractional factorial design and molecular docking

A 3D-QSAR model was constructed to predict polybrominated diphenyl ether (PBDE) estrogenic activities expressed as median effective concentrations (pEC₅₀), and resolution V of the 2^10-3 fractional factorial design and a pharmacophore model were used to modify the target PBDE molecules BDE-47, BDE-99, BDE-100, BDE-183, and BDE-209 to decrease the estrogenic activities. The persistent-organic-pollutant-related and flame-retardant properties of the modified molecules were evaluated. The mechanisms involved in decreasing PBDE estrogenic activities were explored through molecular docking. The 3D-QSAR model gave a cross-validated correlation coefficient (q²) of 0.682 (i.e., >0.5) and a non-cross-validated correlation coefficient (r²) of 0.980 (i.e., >0.9). Mono- and di-substitutions and hydrophobic substituent groups gave 40 modified molecules with decreased estrogenic activities, including modified BDE-47 and BDE-99 with pEC₅₀ decreased by >10% and modified BDE-100, BDE-183, and BDE-209 with pEC₅₀ decreased by >20%. The modified molecules had similar flame-retardancy to the unmodified molecules, and lower biotoxicities (by a maximum of 17.27%), persistences (by a maximum of 55.68%), bioconcentration (by 4.28%-23.91%), and long-range transport potentials (by 0.72%-18.47%). Docking indicated that hydrophobic interactions were the main factors affecting PBDE estrogenic activities. The results provide a theoretical basis for designing less estrogenic flame retardants than are currently available.

A bibliometric analysis of investigations of polybrominated diphenyl ethers (PBDEs) in biological and environmental matrices from 1992 - 2018

The aim of this bibliometric analysis is to review the status and research evolution on the analysis of polybrominated diphenyl ethers (PBDEs) on biological and environmental matrices from January 1992 to February 2018 in the Web of Science focusing on original articles and reviews. One thousand four hundred and eighty two articles were found in the databases of the Web of Science on the analysis of PBDEs. Quantitative and qualitative parameters (countries, number of articles, frequency, average article citations and total average citations) were used to analyse each article and ranking of countries based on productivity, authors and article citation. Complementary analysis based on keywords was also done. The last decade experienced an increase in the analysis of this pollutant with the year 2012 recording the highest number of published articles (n = 137). High rate of collaboration with a very rich research network exists amongst institutions in Asian, European and America countries. China and USA are ranked 1st and 2nd on countries based on productivity, publishing 30% and 21.7% of the total articles respectively. South Africa was the only African country found in the category of countries based on productivity occupying the 17th position. The spectacular growth of research by researchers domiciled in China suggests the dominance of China in scientific research. This study suggests high research interest on this class of pollutant in developed countries. Additionally, lack of funds and sophisticated analytical tools may be responsible for lack of PBDEs-related studies in developing countries especially in Africa.

Association of polybrominated diphenyl ethers in two fat compartments with increased risk of insulin resistance in obese individuals

BACKGROUND

Polybrominated diphenyl ethers (PBDEs), a widely utilized class of flame retardants in various commercial products, represent a prominent source of environmental contaminants. PBDEs tend to accumulate in adipose tissue, potentially altering the function of this endocrine organ and increasing risk of insulin resistance. The aim of this study was to compare levels of PBDEs in adipose tissues from two metabolically distinct obese groups; the insulin sensitive (IS) and the insulin resistant (IR).

METHODS

Levels of 28 PBDE congeners were assessed in subcutaneous and omental adipose tissues from 34 obese Qatari individuals (11 IS and 23 IR) using gas chromatography (Trace GC Ultra) coupled to a TSQ Quantum triple Quadrupole mass spectrometer. Correlations of identified PBDEs and mediators of metabolic disease were established and effects of PBDEs treatment on insulin signaling in primary omental preadipocytes were determined.

RESULTS

Out of 22 detectable PBDEs in subcutaneous and omental adipose tissues, PBDEs 28, 47, 99 and 153 were predominant in omental adipose tissues from obese Qatari subjects. PBDEs 99, 28, and 47 were significantly higher in IR individuals compared to their IS counterparts. Significant positive correlations were identified between PBDEs 28 and 99 in the omental tissues and with fasting insulin levels. When considering PBDEs congeners, penta congeners were also higher in IR compared to IS individuals, while no significant differences were detected in mono, tri, tertra, hexa, hepta and octa congeners between the two studied groups. Treatment of human omental preadipocytes from insulin sensitive individuals with PBDE28 caused inhibition of phosphorylation of GSK3 α/β (Ser²¹/Ser⁹), mTOR (Ser²⁴⁴⁸), p70 S6 kinase (Thr³⁸⁹) and S6 ribosomal protein (Ser²³⁵/Ser²³⁶) and activation of PTEN (Ser³⁸⁰) phosphorylation, suggesting inhibition of insulin signaling.

CONCLUSION

This pilot data suggests that accumulation of specific PBDEs in human adipose tissues is associated with insulin resistance in obese individuals. Further investigation of the functional role of PBDEs in the pathology of insulin resistance should help developing therapeutic strategies targeting obese individuals at higher risk.

The Role of Polybrominated Diphenyl Ethers in Thyroid Carcinogenesis: Is It a Weak Hypothesis or a Hidden Reality? From Facts to New Perspectives

In the last decades, the incidence of thyroid cancer has increased faster than that of any other malignant tumor type. The cause of thyroid cancer is likely multifactorial and a variety of both exogenous and endogenous has been identified as potential risk factors. Polybrominated diphenyl ethers (PBDEs), used since the 1970s as flame retardants, are still widespread and persistent pollutants today, although their production was definitely phased out in the western countries several years ago. Polybrominated diphenyl ethers are known endocrine disruptors, and the endocrine system is their primary target. Whereas animal studies have ascertained the ability of PBDEs to affect the normal functionality of the thyroid, evidence in humans remains inconclusive, and only a few epidemiological studies investigated the association between exposure to PBDEs and thyroid cancer. However, a number of clues suggest that a prolonged exposure to these chemicals might act a trigger of the most common malignancy of the endocrine system, whereas further studies with an advanced design are suggested.

Effects of Polybrominated Diphenyl Ethers on Child Cognitive, Behavioral, and Motor Development

Polybrominated Diphenyl Ether (PBDE) flame retardants are environmental chemicals that cross the placenta during pregnancy and have shown evidence of neurotoxicity. As the in utero period is a sensitive developmental window, such exposure may result in adverse childhood outcomes. Associations between in utero PBDE exposure and neurodevelopment are found in animal models and increasingly in human population studies. Here, we review the epidemiological evidence of the association between prenatal exposure to PBDEs and motor, cognitive, and behavioral development in infants and children. Published work suggests a negative association between PBDE concentrations and neurodevelopment despite varying PBDE congeners measured, bio-specimen matrix used, timing of the biological sampling, geographic location of study population, specific developmental tests used, age of children at time of testing, and statistical methodologies. This review includes 16 published studies that measured PBDE exposure in maternal blood during pregnancy or in cord blood at delivery and performed validated motor, cognitive, and/or behavioral testing at one or more time during childhood. We evaluate possible mediation through PBDE-induced perturbations in thyroid function and effect measure modification by child sex. While the majority of studies support an adverse association between PBDEs and neurodevelopment, additional research is required to understand the mechanism of action, possibly through the perturbations in thyroid function either in the pregnant woman or in the child, and the role of biologically relevant effect modifiers such as sex.

Emissions of selected brominated flame retardants from consumer materials: the effects of content, temperature, and timescale

The ubiquitous presence of brominated flame retardants (BFRs) in indoor air, dust, and even in human tissue could be attributed to their emissions from BFR-containing products. Nevertheless, the emission behavior of BFRs, especially novel BFRs from consumer materials, to the indoor environment has still not been well understood. To evaluate the effects of chemical content, temperature, and time on the emissions of BFRs, we used a batch of small glass chambers to conduct emission tests on carpet, computer casings, sound insulation, circuit boards, decorative laminate, and PVC floors at temperatures from 20 to 80 °C, as well as different emission times of up to 35 days. Seven BFRs were extracted from the tested materials with contents ranging from 50 to 35,803 μg g^-1, and four BFRs were detected with emission rates between 5.9 and 418 pg g^-1 h^-1 at room temperature (20 °C); 1,2,5,6,9,10-hexabromocyclododecane (HBCD) was considered to be the dominant compound, which was found in and could be emitted from all of the tested materials. Emission rates are significantly and positively correlated with both the contents of tested materials and the elevated temperature. These results indicate that BFR-containing products have the potential to be a major source of indoor contamination.

Polybrominated diphenyl ether (PBDE) exposures and thyroid hormones in children at age 3 years

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) reduce serum thyroid hormone concentrations in animal studies, but few studies have examined the impact of early-life PBDE exposures on thyroid hormone disruption in childhood.

METHODS

We used data from 162 mother-child pairs from the Health Outcomes and Measures of the Environment Study (2003-2006, Cincinnati, OH). We measured PBDEs in maternal serum at 16 ± 3 weeks gestation and in child serum at 1-3 years. Thyroid hormones were measured in serum at 3 years. We used multiple informant models to investigate associations between prenatal and early-life PBDE exposures and thyroid hormone levels at age 3 years.

RESULTS

Prenatal PBDEs were associated with decreased thyroid stimulating hormone (TSH) levels at age 3 years. A 10-fold increase in prenatal ∑PBDEs (BDE-28, -47, -99, -100, and -153) was associated with a 27.6% decrease (95% CI -40.8%, -11.3%) in TSH. A ten-fold increase in prenatal ∑PBDEs was associated with a 0.25 pg/mL (0.07, 0.43) increase in free triiodothyronine (FT3). Child sex modified associations between prenatal PBDEs and thyroid hormones, with significant decrements in TSH among females and decreased free T4 (FT4) in males. Prenatal ∑PBDEs were not associated with TT4, FT4, or total T3.

CONCLUSIONS

These findings suggest an inverse relationship between prenatal ∑PBDEs and TSH at 3 years. Associations may be sexually dimorphic, with an inverse relationship between prenatal BDE-47 and -99 and TSH in females and null associations among males.

Overview of Cadmium Thyroid Disrupting Effects and Mechanisms

Humans are exposed to a significant number of chemicals that are suspected to produce disturbances in hormone homeostasis. Hence, in recent decades, there has been a growing interest in endocrine disruptive chemicals. One of the alleged thyroid disrupting substances is cadmium (Cd), a ubiquitous toxic metal shown to act as a thyroid disruptor and carcinogen in both animals and humans. Multiple PubMed searches with core keywords were performed to identify and evaluate appropriate studies which revealed literature suggesting evidence for the link between exposure to Cd and histological and metabolic changes in the thyroid gland. Furthermore, Cd influence on thyroid homeostasis at the peripheral level has also been hypothesized. Both in vivo and in vitro studies revealed that a Cd exposure at environmentally relevant concentrations results in biphasic Cd dose-thyroid response relationships. Development of thyroid tumors following exposure to Cd has been studied mainly using in vitro methodologies. In the thyroid, Cd has been shown to activate or stimulate the activity of various factors, leading to increased cell proliferation and a reduction in normal apoptotic activity. Evidence establishing the association between Cd and thyroid disruption remains ambiguous, with further studies needed to elucidate the issue and improve our understanding of Cd-mediated effects on the thyroid gland.

Disruption in Thyroid Signaling Pathway: A Mechanism for the Effect of Endocrine-Disrupting Chemicals on Child Neurodevelopment

Thyroid hormones are crucial in normal brain development. Transient and mild thyroid hormone insufficiency in pregnancy is also associated with impaired neurodevelopment in the offspring (e.g., 3-4 IQ score loss in association with maternal free thyroxine in the lowest fifth percentile). While inadequate iodine intake remains the most common underlying cause of mild thyroid hormone insufficiency in vulnerable populations including pregnant women, other factors such as exposure to environmental contaminants have recently attracted increasing attention, in particular in interaction with iodine deficiency. Endocrine-disrupting chemicals (EDCs) are natural and synthetic substances with ubiquitous exposure in children and adults including pregnant women. EDCs interfere, temporarily or permanently, with hormonal signaling pathways in the endocrine system by binding to hormone receptors and modifying gene expression. Other mechanisms involve alterations in production, metabolism, and transfer of hormones. Experimental studies have shown that exposures to EDCs affect various brain processes such as neurogenesis, neural differentiation and migration, as well as neural connectivity. Neuroimaging studies confirm brain morphological abnormalities (e.g., cortical thinning) consistent with neurodevelopmental impairments as a result of EDC exposures at standard use levels. In this review, we provide an overview of present findings from toxicological and human studies on the anti-thyroid effect of EDCs with a specific attention to fetal and early childhood exposure. This brief overview highlights the need for additional multidisciplinary studies with a focus on thyroid disruption as an underlying mechanism for developmental neurotoxicity of EDC, which can provide insight into modifiable risk factors of developmental delays in children.

The Role of MicroRNAs in Environmental Risk Factors, Noise-Induced Hearing Loss, and Mental Stress

SIGNIFICANCE

MicroRNAs (miRNAs) are important regulators of gene expression and define part of the epigenetic signature. Their influence on every realm of biomedicine is established and progressively increasing. The impact of environment on human health is enormous. Among environmental risk factors impinging on quality of life are those of chemical nature (toxic chemicals, heavy metals, pollutants, and pesticides) as well as those related to everyday life such as exposure to noise or mental and psychosocial stress. Recent Advances: This review elaborates on the relationship between miRNAs and these environmental risk factors.

CRITICAL ISSUES

The most relevant facts underlying the role of miRNAs in the response to these environmental stressors, including redox regulatory changes and oxidative stress, are highlighted and discussed. In the cases wherein miRNA mutations are relevant for this response, the pertinent literature is also reviewed.

FUTURE DIRECTIONS

We conclude that, even though in some cases important advances have been made regarding close correlations between specific miRNAs and biological responses to environmental risk factors, a need for prospective large-cohort studies is likely necessary to establish causative roles. Antioxid. Redox Signal. 28, 773-796.