Life-cycle exposure to BDE-47 results in thyroid endocrine disruption to adults and offsprings of zebrafish (Danio rerio)

New insights on the protection of endangered aquatic species: Embryotoxicity effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) via integrin-mediated oxidative stress and inflammatory pathways in Siberian sturgeon, Acipenser baerii

Polybrominated diphenyl ethers (PBDEs), are emerging pollutants ubiquitous in the environment, posing a threat to aquatic ecosystems. This study investigates the toxicological effects of PBDEs on sturgeon embryos, focusing on BDE-47, a representative PBDEs homologues. Siberian sturgeon embryos were exposed to BDE-47, revealing significant reductions in hatching and survival rates and the occurrence of developmental abnormalities. Oxidative stress induction by BDE-47 was evidenced by increased antioxidant enzyme activities and the presence of oxidative damage biomarker MDA. Besides, transcriptome analysis unveiled the activation of integrin signaling pathways, with molecular docking indicating strong binding to integrin receptors (specifically ITG-α5, ITG-α8, and ITG-α11). Moreover, qPCR and correlation analysis showed that BDE-47 significantly upregulated inflammatory cytokines and keap1/nrf2 signaling through ITGs. Furthermore, cultivation of head kidney macrophages showed that ITGs antagonist Cilengitide significantly reversed the upregulation of the above factors induced by BDE-47, including nf-κb, il-6, tnf-α, gpx, and nrf2. These findings indicate that BDE-47 induced embryotoxicity in Siberian sturgeon, which was potentially via ITGs-mediated oxidative stress and inflammatory pathways. This study providing novel insights into the protein binding of BDE-47 in animals, contributes to understanding emerging pollutant toxicity in fish embryos and offering a new perspective for the improvement of hatchability and survival rate of cultured sturgeon embryos to guarantee the sustainable development of the sturgeon aquaculture industry, as well as providing evidence for wild sturgeon populations conservation and habitat restoration.

Dietary exposure to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) induces oxidative damage promoting cell apoptosis primarily via mitochondrial pathway in the hepatopancreas of carp, Cyprinus carpio

To investigate the mechanisms of BDE-47 on hepatotoxicity in fish, this study examined the effects of dietary exposure to BDE-47 (40 and 4000 ng/g) on carp for 42 days. The results showed that BDE-47 significantly increased carp's condition factor and hepatosomatic index. Pathological results revealed unclear hepatic cord structure, hepatocytes swelling, cellular vacuolization, and inflammatory cell infiltration in the hepatopancreas of carp. Further investigation showed that ROS levels significantly increased on days 7, 14, and 42. Moreover, the activities of antioxidant enzymes SOD, GSH, CAT, and GST increased significantly from 1 to 7 days, and the transcription levels of antioxidant enzymes CAT, Cu-Zn SOD, Mn-SOD, GST, and GPX, and antioxidant pathway genes Keap1, Nrf2, and HO-1 changed significantly at multiple time-points during the 42 days. The results of apoptosis pathway genes showed that the mitochondrial pathway genes Bax, Casp3, and Casp9 were significantly upregulated and Bcl2 was significantly downregulated, while the transcription levels of FADD and PERK were significantly enhanced. These results indicate that BDE-47 induced oxidative damage in hepatopancreas, then it promoted cell apoptosis mainly through the mitochondrial pathway. This study provides a foundation for analyzing the mechanism of hepatotoxicity induced by BDE-47 on fish.

The associations between concentrations of gestational bisphenol analogues and thyroid related hormones in cord blood: A prospective cohort study

Animal studies indicated that Bisphenol analogues (BPs) exhibited potential thyroid toxicity. However, little is known of the associations between maternal BPs exposure and offspring's thyroid related hormones in humans. On the basis of Shanghai-Minhang Birth Cohort study, we analyzed BPs in maternal urine collected at the third trimester of pregnancy. Thyroid related hormones (THs), including total triiodothyronine (TT3), free triiodothyronine (FT3), total thyroxine (TT4), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) were measured in cord blood samples. We performed multiple linear regression and Bayesian kernel machine regression (BKMR) models to explore the single and joint effects of gestational BPs exposure on thyroid related hormones in cord blood among 258 mother-child pairs. Statistically significant inverse associations of categorized BPA with FT3 and TT4 concentrations were observed. We also found a significant association between the mixture of BPs in maternal urine and increased concentration of TT3 in cord blood and a marginally significant association between BPs mixture and increased FT3 concentrations. Further associations of BPA with lower TT4/FT4 and of Bisphenol AF (BPAF) with higher TT3/FT3 were also suggestive, by BKMR model, when other BPs were fixed at 25th percentiles. It was concluded that prenatal BPs exposure was associated with THs in cord blood. Exposure to BPA and BPAF might have large contributions to the effects on thyroid function than other bisphenols.

Thyroid endocrine disruption induced by [C8mim]Br: An integrated in vivo, in vitro, and in silico study

Conventional thyroid-disrupting chemicals (TDCs) such as polybrominated diphenyl ethers, polychlorinated biphenyls, and bisphenols perturb animal's thyroid endocrine system by mimicking the action of endogenous thyroid hormones (THs), since they share a similar backbone structure of coupled benzene rings with THs. 1-methyl-3-octylimidazolium bromide ([C₈mim]Br), a commonly used ionic liquid (IL), has no structural similarity to THs. Whether it interferes with thyroid function and how its mode of action differs from conventional TDCs is largely unknown. Herein, zebrafish embryo-larvae experiments (in vivo), GH3 cell line studies (in vitro), and molecular simulation analyses (in silico) were carried out to explore the effect of [C₈mim]Br on thyroid homeostasis and its underlying mechanism. Molecular docking results suggested that [C₈mim]⁺ likely bound to retinoid X receptors (RXRs), which may compromise the formation of TH receptor/RXR heterodimers. This then perturbed the negative regulation of thyroid-stimulating hormone β (tshβ) transcription by T3 in GH3 cell line. The resulting enhancement of tshβ expression further caused hyperthyroidism and developmental toxicity in larval zebrafish. These findings provided a crucial aspect of the ecological risks of ILs, and presented a new insight into the thyroid-disrupting mechanisms for emerging pollutants that do not have structural similarity to THs.

Parental whole life-cycle exposure to tris (2-chloroethyl) phosphate (TCEP) disrupts embryonic development and thyroid system in zebrafish offspring

Tris (2-chloroethyl) phosphate (TCEP), an emerging environmental pollutant, has been frequently detected in natural waters. The objective of this study was to investigate possible parental transfer of TCEP and transgenerational effects on the early development and thyroid hormone homeostasis in F1 larvae following parental whole life-cycle exposure to TCEP. To this end, zebrafish (Danio rerio) embryos were exposed to environmentally relevant concentrations (0.8, 4, 20 and 100 μg/L) of TCEP for 120 days until sexual maturation. Parental exposure to TCEP resulted in significant levels of TCEP, developmental toxicity including decreased survival and final hatching rates, accelerated heart rate and elevated malformation rate, as well as induction of oxidative stress and cell apoptosis in F1 offspring. In F1 eggs, declined thyroxin (T4) levels were observed, consistent with those in plasma of F0 adult females, indicating the maternal transfer of thyroid endocrine disruption to the offspring. In addition, mRNA levels of several genes along the hypothalamic-pituitary-thyroid (HPT) axis were significantly modified in F1 larvae, which could be linked to transgenerational developmental toxicity and thyroid hormone disruption. For the first time, we revealed that the parental exposure to environmentally relevant levels of TCEP could cause developmental toxicity and thyroid endocrine disruption in subsequent unexposed generation.

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.

Exposure to Polybrominated Diphenyl Ether Flame Retardants Causes Deoxyribonucleic Acid Damage in Human Thyroid Cells In Vitro

INTRODUCTION

The incidence of papillary thyroid cancer (PTC) in the United States has tripled in the past 30 y. Polybrominated diphenyl ethers (PBDEs) are flame retardants that were ubiquitously used over that time period, and exposure to PBDEs has been associated with PTC prevalence. They are potential carcinogens via their induction of reactive oxygen species (ROS) formation and resultant deoxyribonucleic acid (DNA) damage. We sought to determine the effects of PBDE and tris(2-chloroethyl) phosphate (TCEP), another flame retardant implicated in PTC incidence, on thyrocytes in vitro and measure PBDE levels in human thyroid tissue to determine their carcinogenic potential.

METHODS

Nthy-Ori, an immortalized benign human thyroid follicular cell line was used as a model of normal human thyroid. MTT assays were used to measure cell viability after exposure to PBDEs and TCEP. ROS levels and double-stranded and single-stranded DNA breaks were measured to determine genotoxicity. DNA damage response protein levels were measured with immunoblotting.

RESULTS

Exposure to 20μM PBDE or TCEP for 48 h had minimal effects on thyrocyte viability. There was no significant increase in intracellular ROS up to 6 h following PBDE or TCEP exposure in thyrocytes; however, cells exposed to PBDE 47 showed evidence of DNA single-stranded and double-stranded breaks. There was a dose-dependent increase in γH2AX levels following exposure to PBDEs 47 and 209 in Nthy-Ori cells but not with TCEP treatment.

CONCLUSIONS

PBDE 47 and 209 demonstrated genotoxicity but not cytotoxicity in follicular thyrocytes in vitro. Therefore, PBDE 47 and 209 may be carcinogenic in human thyroid cells.

The associations of urinary DEHP metabolite levels, serum thyroid hormones, and thyroid-related genes among the adolescent students from China: a cross-sectional study

Our study aimed to investigate the associations between DEHP exposure and serum thyroid hormone levels in 347 adolescents and young adults. We measured DEHP metabolites including mono(2-ethylhexyl) phthalate (MEHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-carboxypentyl) phthalate (MECPP), and mono(2-carboxymethyl)hexyl phthalate (MCMHP) in their urine. Total thyroxine (TT4), total triiodothyronine, free triiodothyronine, free thyroxine (FT4), thyroid-stimulating hormone and the mRNA levels of thyroid peroxidase (TPO), thyroglobulin (TG), sodium iodide symporter (NIS), thyroid transcription factor 1 (TTF-1), and paired box gene 8 (PAX-8) in serum were measured. The results of statistical analysis showed that urinary DEHP metabolites were generally negatively associated with TT4 levels in serum. In the males, the FT4 levels showed positive associations with urinary MEHP, MECPP, MCMHP, and ∑DEHP. The mRNA level of TG was significantly positively correlated with the levels of MECPP, MCMHP, and ∑DEHP, while the levels of TTF-1 and PAX-8 mRNA were significantly positively correlated with the levels of DEHP metabolites. Taken together, DEHP may affect the synthesis of TG by altering the normal transcription of TTF-1 and PAX-8, leading to decreased TT4 levels in Chinese adolescents.

Decabromodiphenyl ether-induced PRKACA hypermethylation contributed to glycolipid metabolism disorder via regulating PKA/AMPK pathway in rat and L-02 cells

BDE-209 is the most prevalent congener of polybrominated diphenyl ethers and has high bioaccumulation in humans and animals. BDE-209 has been reported to disrupt glycolipid metabolism, but the mechanisms are still unclear. In this study, we found that BDE-209 induced liver tissue injury and hepatotoxicity, increased the glucose and total cholesterol levels in the serum of rats, and increased glucose and triglyceride levels in L-02 cells. BDE-209 exposure changed the PKA, p-PKA, AMPK, p-AMPK, ACC, and FAS expression in rats' liver and L-02 cells. Moreover, BDE-209 induced PRKACA-1 hypermethylation in L-02 cells. AMPK activator (AICAR) inhibited the changes of p-AMPK, ACC, and FAS expression and elevation of glucose and triglyceride levels induced by BDE-209. DNA methylation inhibitor (5-Aza-CdR) reversed BDE-209 induced alters of PKA/AMPK/ACC/FAS signaling pathway. These results demonstrated that BDE-209 could disrupt the glycolipid metabolism by causing PRKACA-1 hypermethylation to regulate the PKA/AMPK signaling pathway in hepatocytes.

Disruption by stealth - Interference of endocrine disrupting chemicals on hormonal crosstalk with thyroid axis function in humans and other animals

Thyroid hormones (THs) are important regulators of growth, development, and homeostasis of all vertebrates. There are many environmental contaminants that are known to disrupt TH action, yet their mechanisms are only partially understood. While the effects of Endocrine Disrupting Chemicals (EDCs) are mostly studied as "hormone system silos", the present critical review highlights the complexity of EDCs interfering with TH function through their interactions with other hormonal axes involved in reproduction, stress, and energy metabolism. The impact of EDCs on components that are shared between hormone signaling pathways or intersect between pathways can thus extend beyond the molecular ramifications to cellular, physiological, behavioral, and whole-body consequences for exposed organisms. The comparatively more extensive studies conducted in mammalian models provides encouraging support for expanded investigation and highlight the paucity of data generated in other non-mammalian vertebrate classes. As greater genomics-based resources become available across vertebrate classes, better identification and delineation of EDC effects, modes of action, and identification of effective biomarkers suitable for HPT disruption is possible. EDC-derived effects are likely to cascade into a plurality of physiological effects far more complex than the few variables tested within any research studies. The field should move towards understanding a system of hormonal systems' interactions rather than maintaining hormone system silos.

Microplastics habituated with biofilm change decabrominated diphenyl ether degradation products and thyroid endocrine toxicity

Microplastics (MPs) are rapidly colonized by microbial biofilms in a natural aquatic environment, and the nature of the microbial community and type of MP can result in different degradation products of organic pollutants. Here, we quantified the degradation products of a ubiquitously detected pollutant, decabrominated diphenyl ether (BDE-209), under both light-only and biota conditions and in the absence or presence of three kinds of MPs, styrofoam polystyrene, hard polyamide, and polypropylene film. The results showed that the BDE-209 concentration increased by 0.7-2.8 fold in the presence of MPs, probably due to the "sustained release" desorption effect. Under light-only conditions, the penta- and hexa-BDE concentrations in the presence of styrofoam or hard MPs were significantly reduced, which can be deemed a beneficial effect. However, when biota were present, the debromination products increased with the addition of MPs, particularly in the presence of styrofoam MPs. These products caused a 1.7-fold upregulation in triiodothyronine content and a 5.9-fold upregulation of thyroid stimulating hormone β expression in zebrafish larvae. The increase in debromination products could be attributed to the distinct high abundance of the bacteria Chloroflexi, Proteobacteria, and Basidiomycotina on styrofoam MPs that can participate in pollutant degradation. Collectively, our results indicate that MPs can alter the degradation pathways of BDE-209 and increase the toxicity to the endocrine system and the thyroid in aquatic organisms.

Effects of trophic 2,2', 4,4'-tetrabromodiphenyl ether (BDE-47) exposure in Oreochromis niloticus: A multiple biomarkers analysis

Polybrominated diphenyl esters are emerging environmental contaminants with few toxicological data, being a concern for the scientific community. This study evaluated the effects of BDE-47 on the health of Oreochromis niloticus fish. The animals were exposed to three doses of BDE-47 (0, 0.253, 2.53, 25.3 ng g^-1) every 10 days, for 80 days. The BDE-47 affected the hepatosomatic and gonadosomatic index in female and the condition factor by intermediate dose in both sexes. The levels of estradiol decreased and the T4 are increased, but the vitellogenin production was not modulated in male individuals. Changes in AChE, GST, LPO and histopathology were observed while the integrated biomarker response index suggests that the lowest dose of BDE-47 compromised the activity of antioxidant enzymes. The oral exposure to BDE-47 in environmental concentrations is toxic to O. niloticus and the use of multiple biomarkers is an attribution in ecotoxicology studies and biomonitoring programs.

Parental transfer of nanopolystyrene-enhanced tris(1,3-dichloro-2-propyl) phosphate induces transgenerational thyroid disruption in zebrafish

Plastic is a globally recognized superwaste that can affect human health and wildlife when it accumulates and is amplified in the food chain. Microplastics (plastic particles < 5 mm) and nanoplastics (plastic particles < 100 nm) can interact with organic pollutants already present in the aquatic environment, potentially acting as carriers for pollutants entering organisms and thus influencing the bioavailability and toxicity of those pollutants. In this study, we investigated the transfer kinetics and transgenerational effects of exposure to tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and polystyrene nanoplastics (PS-NPs) in F1 offspring. At 90 days postfertilization, zebrafish (Danio rerio) strain AB was exposed to either TDCIPP (0, 0.47, 2.64, or 12.78 μg/L) or PS-NPs (10 mg/L) or their combination for 120 days. The results showed that TDCIPP and PS-NPs accumulated in the gut, gill, head, and liver of the zebrafish in a sex-dependent manner. The presence of PS-NPs promoted the bioaccumulation of TDCIPP in the adult fish and increased the parental transfer of TDCIPP to their offspring. We demonstrate that parental exposure to TDCIPP alone or in combination with PS-NPs induces thyroid disruption in adults, and then leads to thyroid endocrine disruption in their larval offspring. Reduced thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels contributed to the observed transgenerational thyroid dysfunction, which inhibited developmental growth and disturbed the transcription of genes and expression of proteins involved in the hypothalamic-pituitary-thyroid (HPT) axis in the F1 larvae. The increased transfer of TDCIPP to the offspring in the presence of PS-NPs also enhanced transgenerational thyroid endocrine disruption, demonstrated by a further reduction in T4 and the upregulation of thyroglobulin (tg), uridine diphosphate-glucuronosyltransferase (ugt1ab), thyroid-stimulating hormone (tshβ), and thyroid hormone receptor (trα) expression in the F1 larvae compared with the effects of parental TDCIPP exposure alone. Overall, our results indicate that the presence of PS-NPs modifies the bioavailability of TDCIPP and aggravates transgenerational thyroid disruption in zebrafish.

Dietary Intake of Endocrine Disrupting Substances Presents in Environment and Their Impact on Thyroid Function

According to the available data, environmental pollution is a serious problem all over the world. Between 2015 and 2016, pollution was responsible for approximately nine million deaths worldwide. They also include endocrine disrupting chemicals (EDCs) that can interfere with the functioning of the thyroid gland. They are characterized by high persistence in the environment. These substances can enter the body through the gastrointestinal tract, respiratory system, as well as contact with the skin and overcome the placental barrier. EDC can be found in food, water, and personal care products. They can get into food from the environment and as a result of their migration to food products and cosmetics from packaging. EDCs can disrupt the functioning of the thyroid gland through a number of mechanisms, including disrupting the activation of thyroid receptors and the expression of genes that are related to the metabolism, synthesis, and transport of thyroid hormones (HT). There is a need to strengthen the food safety policy that aimed at the use of appropriate materials in direct contact with food. At the same time, an important action is to reduce the production of all waste and, when possible, use biodegradable packaging, which may contribute to the improvement of the quality of the entire ecosystem and the health of food, thus reducing the risk of developing thyroid diseases.

New understanding of novel brominated flame retardants (NBFRs): Neuro(endocrine) toxicity

Traditional brominated flame retardants (BFRs) negatively affect the environment and human health, especially in the sensitive (developing) nervous system. Considering the physicochemical similarities between novel brominated flame retardants (NBFRs) and BFRs, more and more evidence reveals the neurotoxic effects of NBFRs. We reviewed the neuro(endocrine) toxic effects of NBFRs in vivo and in vitro and discussed their action mechanisms based on the available information. The neurotoxic potential of NBFRs has been demonstrated through direct neurotoxicity and disruption of the neuroendocrine system, with adverse effects on neurobehavioral and reproductive development. Mechanistic studies have shown that the impact of NBFRs is related to the complex interaction of neural and endocrine signals. From disrupting the gender differentiation of the brain, altering serum thyroid/sex hormone levels, gene/protein expression, and so on, to interfere with the feedback effect between different levels of the HPG/HPT axis. In this paper, the mechanism of neurotoxic effects of NBFRs is explored from a new perspective-neuro and endocrine interactions. Gaps in the toxicity data of NBFRs in the neuroendocrine system are supplemented and provide a broader dataset for a complete risk assessment.

Misbalance of thyroid hormones after two weeks of exposure to artificial light at night in Eurasian perch Perca fluviatilis

Artificial light at night (ALAN) can affect the physiology and behavior of animals because it alters the natural rhythm of light and darkness. Thyroid hormones (TH) are partially regulated by the light information of photoperiod and are involved in metabolic adjustments to daily and seasonal changes in the environment, such as larval and juvenile development, somatic growth and reproduction. ALAN can change photoperiodic information and might thereby lead to changes in thyroid metabolism, but so far research on this topic is scarce. Therefore, we tested in two different experiments the effects of nocturnal illumination at a wide range of light intensities on TH in plasma of Eurasian perch (Perca fluviatilis). Total 3,3',5-triiodo-L-thyronine (T3) was significantly affected by ALAN and reduced at the highest tested intensity of 100 lx after only two weeks of exposure. Although total L-thyroxine (T4) was not significantly affected, the ratio of T3 to T4 tended to slightly decrease at 100 lx. In a second low-light experiment ALAN did not have clear effects on T3, T4 or the ratio of T3 to T4 at intensities between 0.01 lx and 1 lx. The results show first signs of endocrine disruption in thyroid metabolism after a relatively short ALAN exposure of two weeks under high-intensity streetlight conditions. Misbalanced thyroidal status can have serious implications for metabolic rates as well as developmental and reproductive processes.

Impaired sperm quantity and motility in adult rats following gestational and lactational exposure to environmentally relevant levels of PBDE-47: A potential role of thyroid hormones disruption

Polybrominated diphenyl ethers (PBDEs) are flame retardants and the congener 2, 2', 4, 4'-tetrabromodiphenyl ether (PBDE-47) is capable of inducing thyroid endocrine disruption and developmental toxicity. However, little is known about whether developmental PBDE-47 exposure-elicited alterations in semen quality is associated with thyroid hormones (THs) perturbation. In this research, we sought to explore the impacts of gestational and lactational PBDE-47 exposure on adult sperm quantity and motility, and its link with THs levels. For this purpose, female Sprague-Dawley rats were administered environmentally relevant PBDE-47 levels (0.1, 1.0, 10 mg/kg/day) by oral gavage from prepregnancy through lactation cessation to achieve early-life exposure of offspring and to mimic the actual exposure. Sperm quantity and motility together with serum THs levels from male offspring were determined on postnatal day 88. In utero and lactational exposure to PBDE-47 boosted the weight gain while reduced the relative testis weight in adult male offspring. These were accompanied with the reductions in sperm counts (total and living sperm counts), the percentage of progressive sperm motility, sperm velocities (curvilinear velocity, straight-line velocity and average path velocity), motion path (beat cross frequency, linearity and wobble) and linear motile sperm parameters (count, motility and concentration). Further studies identified that the levels of serum triiodothyronine (T₃) were increased by PBDE-47 exposure and negatively associated with those differential semen parameters on quantity and motility. Collectively, our results indicate that exposure to low-level PBDE-47 during early-life development impairs semen quality in adult rats, which could be mediated partially by abnormal T₃ levels.

Structural studies on the endocrine-disrupting role of polybrominated diphenyl ethers (PBDEs) in thyroid diseases

Polybrominated diphenyl ethers (PBDEs) are synthetic brominated flame retardants with extensive applications in daily-life consumer products. However, PBDEs have become ubiquitous environmental contaminants due to their leach-out capability. The hazardous human health effects and endocrine-disrupting activity of PBDEs have led many governmental organizations to impose ban on their manufacture, causing their gradual phase out from commercial products. However, PBDEs and their metabolites are still being detected from biological and environmental samples owing to their persistence and bioaccumulation. The PDBE metabolites in these samples are present in concentrations often higher and even with higher toxic potential than parent PBDEs. The two commonly detected environmental PBDE congeners, 2,2',4,4'-tetra-bromodiphenyl ether (BDE-47) and 2,2',4,4',5-penta-bromodiphenyl ether (BDE-99), and their HO- and MeO- metabolites were considered in this study for their potential disrupting activity on thyroid hormone transport. Specifically, the study involved structural binding characterization of BDE-47 and BDE-99 including their two HO- and two MeO- metabolites with thyroxine-binding globulin (TBG), which is the main thyroid hormone transport protein in blood. The results showed that the binding pattern and molecular interactions of above two PBDEs and their metabolites exhibited overall similarity to native ligand, thyroxine in dock score, binding energy, and amino acid interactions with TBG. The BDE-99 and its metabolites were predicted to have stronger binding to TBG than BDE-47 with the metabolite 5-MeO-BDE-99 showing equal binding affinity to that of thyroxine. It is concluded that BDE-47 and BDE-99 and their metabolites have the potential to disrupt thyroid hormone transport and interfere in thyroid function.

Antagonistic effects of multi-walled carbon nanotubes and BDE-47 in zebrafish (Danio rerio): Oxidative stress, apoptosis and DNA damage

In natural environments, organisms are often exposed to several environmental pollutants at any one time, and the potential effects of such co-exposures on human and environmental health are of considerable concern. It is thought that multi-walled carbon nanotubes (MWCNTs) may interact with other pollutants in aquatic systems and induce considerably different effects compared with exposure to a single contaminant. The objective of this study was to evaluate the potential acute combined effects of mixtures of MWCNTs and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on embryonic development stages, oxidative stress, apoptosis and DNA damage in developing zebrafish (Danio rerio). The embryos were treated with BDE-47 (5, 10, and 50 μg/L) and MWCNTs (50 mg/L), either combined or individually, for 96 h. Following exposure, BDE-47 induced significant acute toxicity, while the MWCNTs exhibited slight toxicity. When compared with BDE-47-only exposure, the inhibited growth induced by BDE-47 was weakened in the presence of MWCNTs. Similarly, the levels of oxidative stress biomarkers (reactive oxygen species, superoxide dismutase, catalase activities and malondialdehyde), apoptosis (apoptosis rate, caspase-3 and caspase-9 activities) and DNA damage (comet assay and comet olive tails) decreased in the presence of MWCNTs compared to those exposed to BDE-47 alone. These results demonstrate that MWCNTs can weaken the developmental inhibition, oxidative stress, apoptosis and DNA damage induced by BDE-47 in the early stages of zebrafish development.

Testing for thyroid hormone disruptors, a review of non-mammalian in vivo models

Thyroid hormones (THs) play critical roles in profound changes in many vertebrates, notably in mammalian neurodevelopment, although the precise molecular mechanisms of these fundamental biological processes are still being unravelled. Environmental and health concerns prompted the development of chemical safety testing and, in the context of endocrine disruption, identification of thyroid hormone axis disrupting chemicals (THADCs) remains particularly challenging. As various molecules are known to interfere with different levels of TH signalling, screening tests for THADCs may not rely solely on in vitro ligand/receptor binding to TH receptors. Therefore, alternatives to mammalian in vivo assays featuring TH-related endpoints that are more sensitive than circulatory THs and more rapid than thyroid histopathology are needed to fulfil the ambition of higher throughput screening of the myriad of environmental chemicals. After a detailed introduction of the context, we have listed current assays and parameters to assess thyroid disruption following a literature search of recent publications referring to non-mammalian models. Potential THADCs were mostly investigated in zebrafish and the frog Xenopus laevis, an amphibian model extensively used to study TH signalling.

Toxicological, gene expression and histopathological evaluations of environmentally realistic concentrations of polybrominated diphenyl ethers PBDE- 47, PBDE-99 and PBDE-209 on zebrafish embryos

Polybrominated diphenyl ethers (PBDEs) are brominated flame retardants. Biomonitoring studies have shown widespread presence of PBDEs in humans and their accumulation in food chain cause concern to human health, especially for foetus and infant development. The early-life stages are generally considered more sensitive to exposure to toxic compounds than juvenile or adults. For this reason the aim of this study was to evaluate the effects of the three most environmentally relevant BDE (BDE- 47, 99 and 209) on zebrafish embryos. The fish embryo toxicity (FET) OECD tests on zebrafish were performed followed by histopathogical examination to assess morphological changes. The gene expression of the thyroid stimulating hormone β (Tshβ), the transport proteins transthyretin (Ttr) and thyroxine-binding globulin (Tbg) as well as the enzyme iodothyronine deiodinase 1 (Dio1) was also assessed by Real-time PCR. BDE-47 and BDE-99 showed an increase of the severity of the effects at the lower concentrations while for the BDE-209 the effects were higher to the high concentrations. Although all compounds did not show any acute toxicity for none of the concentrations tested, they reported interesting sub-acute lesions, including yolk and pericardial edema, tail and head malformation, reduced and extremely reduced heart beat rate, blood stasis and spinal curvature, with the highest percentage recorded for BDE-209. Cardiac edema, damage of eye structure and hydrocephaly were confirmed also by histophatological examination. Furthermore, a toxic and dose-dependent liver vacuolization in BDE-209 was observed in all experimental groups. Although no statistically significant difference in gene expression was observed, BDE-209 up-regulated only Dio1 while the other congeners induced Tshβ, Ttr, Tbg and Dio1. Overall, this research highlighted that exposure to BDE-47, BDE-99 and BDE-209 at realistic concentrations caused lethal and sub-lethal alterations and impaired genes involved in thyroid hormones homeostasis leading to abnormal development of zebrafish embryos.

Two PBDEs exposure inducing feeding depression and disorder of digestive and antioxidative system of Daphnia magna

2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) and 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) are two typical polybrominated diphenyl ethers (PBDEs), and studies have proven that these PBDs can disrupt the behaviors and physical function of aquatic organisms. However, little is known about the compositional impacts of BDE-47/BDE-99 compound pollution on the feeding behavior of Daphnia magna. In this study, a response surface methodology (RSM) was introduced into the combined toxicity assessment of BDE-47 and BDE-99 on the feeding depression of D. magna. Low concentrations of BDE-47 (9.2 μg/L) and BDE-99 (5.4 μg/L) had no effect on the feeding behavior of D. magna; nevertheless, the feeding depression was strengthened, and a concentration-dependent effect was observed with increasing concentrations of BDE-47 and BDE-99. The results of RSM indicated that the mixture of BDE-47 and BDE-99 can enhance their toxicity on the feeding behavior of D. magna. Moreover, real-time PCR (qPCR) analysis showed that the down-regulation of α-amylase (AMS) appeared in most of the exposed D. magna. However, there were significant different in the gene expression of trypsin, superoxide dismutase (SOD) and catalase (CAT) between the exposure and control groups. The change in the enzyme activity of AMS, trypsin, SOD and CAT implied that BDE-47 and BDE-99 cause damage to the digestive and antioxidative systems of D. magna. Correlation analysis indicated that a significant positive correlation existed between the gene expression and enzyme activity of SOD and CAT. Our results contribute to the understanding of toxicity caused by BDE-47/BDE-99 compound pollution in D. magna and help to improve traditional toxicity assessment methods for aquatic environments.

Map and model-moving from observation to prediction in toxicogenomics

BACKGROUND

Chemicals induce compound-specific changes in the transcriptome of an organism (toxicogenomic fingerprints). This provides potential insights about the cellular or physiological responses to chemical exposure and adverse effects, which is needed in assessment of chemical-related hazards or environmental health. In this regard, comparison or connection of different experiments becomes important when interpreting toxicogenomic experiments. Owing to lack of capturing response dynamics, comparability is often limited. In this study, we aim to overcome these constraints.

RESULTS

We developed an experimental design and bioinformatic analysis strategy to infer time- and concentration-resolved toxicogenomic fingerprints. We projected the fingerprints to a universal coordinate system (toxicogenomic universe) based on a self-organizing map of toxicogenomic data retrieved from public databases. Genes clustering together in regions of the map indicate functional relation due to co-expression under chemical exposure. To allow for quantitative description and extrapolation of the gene expression responses we developed a time- and concentration-dependent regression model. We applied the analysis strategy in a microarray case study exposing zebrafish embryos to 3 selected model compounds including 2 cyclooxygenase inhibitors. After identification of key responses in the transcriptome we could compare and characterize their association to developmental, toxicokinetic, and toxicodynamic processes using the parameter estimates for affected gene clusters. Furthermore, we discuss an association of toxicogenomic effects with measured internal concentrations.

CONCLUSIONS

The design and analysis pipeline described here could serve as a blueprint for creating comparable toxicogenomic fingerprints of chemicals. It integrates, aggregates, and models time- and concentration-resolved toxicogenomic data.

Molecular mechanisms and tissue targets of brominated flame retardants, BDE-47 and TBBPA, in embryo-larval life stages of zebrafish (Danio rerio)

Brominated flame retardants are known to disrupt thyroid hormone (TH) homeostasis in several vertebrate species, but the molecular mechanisms underlying this process and their effects on TH-sensitive tissues during the stages of early development are not well characterised. In this study, we exposed zebrafish (Danio rerio) embryo-larvae to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and tetrabromobisphenol A (TBBPA) via the water for 96 h from fertilisation and assessed for lethality, effects on development and on the expression of a suite of genes in the hypothalamic-pituitary-thyroid (HPT) axis via both real time quantitative PCR (qRT-PCR) on whole body extracts and whole mount in situ hybridisation (WISH) to identify tissue targets. The 96-h lethal median concentration (96h-LC₅₀) for TBBPA was 0.9 μM and mortality was preceded by retardation of development (smaller animals) and morphological deformities including, oedemas in the pericardial region and tail, small heads, swollen yolk sac extension. Exposure to BDE-47 did not affect zebrafish embryo-larvae survival at any of the concentrations tested (1-100 μM) but caused yolk sac and craniofacial deformities, a curved spine and shorter tail at the highest exposure concentration. TBBPA exposure resulted in higher levels of mRNAs for genes encoding deiodinases (dio1), transport proteins (ttr), the thyroid follicle synthesis protein paired box 8 (pax8) and glucuronidation enzymes (ugt1ab) and lower levels of dio3b mRNAs in whole body extracts, with responses varying with developmental stage. BDE-47 exposure resulted in higher levels of thrb, dio1, dio2, pax8 and ugt1ab mRNAs and lower levels of ttr mRNAs in whole body extracts. TBBPA and BDE-47 therefore appear to disrupt the TH system at multiple levels, increasing TH conjugation and clearance, disrupting thyroid follicle development and altering TH transport. Compensatory responses in TH production/ metabolism by deiodinases were also evident. WISH analyses further revealed that both TBBPA and BDE-47 caused tissue-specific changes in thyroid receptor and deiodinase enzyme expression, with the brain, liver, pronephric ducts and craniofacial tissues appearing particularly responsive to altered TH signalling. Given the important role of TRs in mediating the actions of THs during key developmental processes and deiodinases in the control of peripheral TH levels, these transcriptional alterations may have implications for TH sensitive target genes involved in brain and skeletal development. These findings further highlight the potential vulnerability of the thyroid system to disruption by BFRs during early developmental windows.

Parental exposure to tris(1,3-dichloro-2-propyl) phosphate results in thyroid endocrine disruption and inhibition of growth in zebrafish offspring

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is a re-emerging environmental contaminant used as a suitable substitute for brominated flame retardants. The objective of this study was to evaluate the effects of TDCIPP on thyroid disruption and growth inhibition in zebrafish (Danio rerio) offspring after chronic parental exposure, and to examine the possible molecular mechanisms involved. When adult zebrafish (4 months old) were exposed to 5.66, 25.55, or 92.8 μg TDCIPP/L for 90 days, bioconcentration of TDCIPP and its metabolic product [bis(1,3-dichloro-2-propyl) phosphate, BDCIPP] was observed in 7-day postfertilization (dpf) F1 larvae, which suggests the transfer of this compound from adult fish to their offspring. Our results demonstrated that parental exposure to TDCIPP induced thyroid disruption in the offspring, demonstrated by significantly decreased thyroxine (T4) and increased 3,5,3'-triiodothyronine (T3) levels, and disruption of the transcription of several genes and expression of proteins involved in the hypothalamic-pituitary-thyroid (HPT) axis in F1 larvae. Parental exposure to TDCIPP resulted in developmental abnormalities in offspring; the smaller body length that was recorded might be partly the result of the perturbation of the HPT axis. In addition, the results revealed that growth inhibition also resulted from the downregulation of the transcription of genes and expression of proteins involved in the growth hormone/insulin-like growth factor (GH/IGF) axis. Our study provides a new set of evidence showing that parental exposure to TDCIPP can induce thyroid disruption and inhibition of growth in offspring, and that perturbation of the HPT axis and GH/IGF axis contribute to these adverse effects.

Toxic effects of pentachlorophenol and 2,2',4,4'-tetrabromodiphenyl ether on two generations of Folsomia candida

The standard Folsomia candida test (ISO 11267), in which only the survival and reproduction of the parental generation (F0) were determined, is insufficient to assess the toxicity of chemicals, like endocrine disrupting chemicals (EDCs), since the effects of EDCs could last for several generations and sometimes can be transgenerational. It's necessary to assess the effects on subsequent generations to address the long-term consequences of these chemicals exposure. In this study, the effects of pentachlorophenol (PCP) and 2,2',4,4'-tetrabromodiphenyl (BDE47) were assessed on F0 and the first filial generation (F1) of F. candida after 28-day or 10-day exposure of F0. In the 28-day exposure method, F0 was exposed to PCP or BD47 for 28 days and F1 was exposed for about 21 days. In the 10-day exposure method, F0 was exposed for 10 days and F1 was not exposed. The F. candida reproduction of F0 and F1 can be assessed in both methods, while transgenerational effects can further be evaluated in the 10-day exposure method. The numbers of F1 and F2 (second filial generation) juveniles in the 28-day exposure method and F1 juveniles in the 10-day exposure method decreased significantly for the PCP treatment. For BDE47, only the number of F1 juveniles in the 28-day exposure method significantly decreased. The EC50 values of F0 reproduction (the number of F1 juveniles) in the 28-day exposure method were 89 and 306 mg/kg dry soil for PCP and BDE47, respectively. Results suggested that PCP could affect F. candida egg hatching or juvenile survival and adult reproductive capacity, while BDE47 was more likely to affect egg hatchability or juvenile survival rather than adult reproductive capacity. It also indicated that F. candida exposed to PCP or BDE47 could recover in clean soil. Transgenerational effects were not observed for neither PCP nor BDE47 in this study.

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.

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.

Parental exposure to microcystin-LR induced thyroid endocrine disruption in zebrafish offspring, a transgenerational toxicity

Microcystin-LR is the most poisonous and commonly encountered hepatotoxin produced by cyanobacteria in an aquatic ecosystem, and it may cause thyroid dysfunction in fish. The present study aimed to reveal the effects of transgenerational toxicity of MCLR on the thyroid endocrine system under sub-chronic exposure conditions. Adult zebrafish (F0) were exposed to environmentally relevant concentrations (1, 5 and 25 μg/L) of MCLR for 45 days. The produced F1 embryos were then tested without further MCLR treatment. In the F0 generation, exposure to 25 μg/L MCLR reduced thyroxine (T4) but not 3, 5, 3'-triiodothyronine (T3) levels in females, while the T4 and T3 levels were unchanged in males. After parental exposure to MCLR, we observed a decreased hatching and growth retardation correlated with reduced thyroid hormone levels in the F1 offspring. The gene transcription and protein expression along the hypothalamic-pituitary-thyroid axis were detected to further investigate the possible mechanisms of MCLR-induced thyroid disruption. Our results indicated MCLR could disturb the thyroid endocrine system under environmentally relevant concentrations and the disrupting effects could be remarkably transmitted to its F1 offspring. We regard these adverse effects as a parental transgenerational toxicity of MCLR.

Teratogenic responses of zebrafish embryos to decabromodiphenyl ether (BDE-209) in the presence of nano-SiO2 particles

This study investigated the influence of nano-SiO₂ particles (nSiO₂) on the teratogenic responses of zebrafish embryos to decabromodiphenyl ether (BDE-209). Zebrafish embryos were exposed to BDE-209 in the absence and presence of nSiO₂ for 96 h post fertilization (hpf). Results showed that formation of nSiO₂-BDE-209 associates promoted both extracellular and intracellular uptake of BDE-209 by zebrafish embryos, thereby increasing the bioconcentration of BDE-209 on the chorion surface and the embryos. Results also showed embryos delay hatching temporarily when co-exposure to BDE-209 and nSiO₂ at 60 hpf. Furthermore, there was heartbeat decline (28.3 beats/10s) and increase in irregular heartbeat (45.8%) in zebrafish larvae at 96 hpf, compared to the sole exposure to BDE-209 (32.7 beats/10s and 0%). Malformation in terms of spinal curvature (SC), pericardial edema (PE) and yolk sac edema (YSE) were observed on zebrafish larvae at 33.9, 23.4, and 18%, respectively. Overall, abnormal development of zebrafish was apparent when co-exposure to BDE-209 and nSiO₂. All relevant evidence considered, nSiO₂ could facilitate the transport of BDE-209 towards zebrafish embryos and negatively impact the development of zebrafish.

Adverse effects of BDE-47 on in vivo developmental parameters, thyroid hormones, and expression of hypothalamus-pituitary-thyroid (HPT) axis genes in larvae of the self-fertilizing fish Kryptolebias marmoratus

2,2',4,4'-tetrabromodiphenylether (BDE-47) is known to have the potential to disrupt the thyroid endocrine system in fishes due to its structural similarity to the thyroid hormones triiodothyronine (T3) and thyroxine (T4). However, the effects of BDE-47 on thyroid function in fishes remain unclear. In this study, abnormal development (e.g. deformity, hemorrhaging) and an imbalance in thyroid hormone (TH) homeostasis was shown in the early developmental stages of the mangrove killifish Kryptolebias marmoratus in response to BDE-47 exposure. To examine the thyroid endocrinal effect of BDE-47 exposure in mangrove killifish K. marmoratus larvae, transcript levels of genes involved in TH homeostasis and hypothalamus-pituitary-thyroid (HPT) axis-related genes were measured. The expression of thyroid hormone metabolism-related genes (e.g. deiodinases, UGT1ab) and HPT axis-related genes was up-regulated and there were significant changes in TH levels (P < 0.05) in response to BDE-47 exposure. This study provides insights into the regulation of TH homeostasis at the transcriptional level and provides a better understanding on the potential impacts of BDE-47 on the thyroid endocrine system of fishes.

Acute toxicity, biochemical toxicity and genotoxicity caused by 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium tetrafluoroborate in zebrafish (Danio rerio) livers

The present study examined the potential toxicity of 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and 1-butyl-3- methylimidazolium tetrafluoroborate ([Bmim]BF₄) in the liver cells of zebrafish (Danio rerio) with different doses (20-160mg/L) on 7 and 14days. The effects of [Bmim]Cl and [Bmim]BF₄ on acute toxicity, reactive oxygen species (ROS), antioxidant enzymes, glutathione S-transferase (GST), malondialdehyde (MDA), and DNA damage degree in livers of zebrafish were determined. The 50% lethal concentration (LC₅₀) values after a 96-h exposure to [Bmim]Cl and [Bmim]BF₄ were 632.8±67.4 and 604.6±56.2mg/L, respectively, which indicated that the substances were practically harmless. The minor discrepancy may be caused by the different anions. The ROS levels were dose-dependent, which may cause the inhibition of antioxidant enzyme activity, lipid peroxidation, DNA damage and the stimulation of detoxifying enzyme activity. The present study can also provide scientific support for the future selection and evaluation of ionic liquids (ILs).