A two-hybrid yeast assay to quantify the effects of xenobiotics on thyroid hormone-mediated gene expression

Evaluation of thyroid-disrupting effects of bisphenol F and bisphenol S on zebrafish (Danio rerio) using anti-transthyretin monoclonal antibody-based immunoassays

The thyroid disrupting chemicals (TDCs) have raised great concerns due to their adverse impacts on thyroid hormones (THs). In this study, we investigated the thyroid-disrupting effects of bisphenol F (BPF) and bisphenol S (BPS), two major BPA substitutes, on adult zebrafish (Danio rerio). Firstly, anti-transthyretin (TTR) monoclonal antibody (anti-TTR mAb) was prepared and used to establish an indirect ELISA, which had a working range of 15.6∼1000 ng/mL of a detection limit of 6.1 ng/mL. The immunoassays based on anti-TTR mAb showed that exposure to BPF (10 and 100 μg/L) and BPS (100 μg/L) significantly elevated the levels of TTR protein in the plasma, liver, and brain tissues. Moreover, immunofluorescence showed that 100 μg/L BPF and BPS induced the production of TTR protein in liver and brain tissues. In addition, BPF and BPS increased THs levels and damaged thyroid tissue structure in adult female zebrafish. Especially, 100 μg/L BPF significantly increased T4 and T3 levels by 2.05 and 1.14 times, and induced pathological changes of thyroid follicles. The changes in the expression levels of genes involved in the hypothalamus-pituitary-thyroid (HPT) axis further illustrated that BPF and BPS had significant adverse effects on THs homeostasis and thyroid function in zebrafish. Therefore, TTR immunoassays could be used for the evaluation of thyroid-disrupting effects in fish and BPF exhibited greater disruption than BPS.

The toxicological profile of polychlorinated naphthalenes (PCNs)

The legacy of polychlorinated naphthalenes (PCNs) manufactured during the last century continues to persist in the environment, food and humans. Metrological advances have improved characterisation of these occurrences, enabling studies on the effects of exposure to focus on congener groups and individual PCNs. Liver and adipose tissue show the highest retention but significant levels of PCNs are also retained by the brain and nervous system. Molecular configuration appears to influence tissue disposition as well as retention, favouring the higher chlorinated (≥ four chlorines) PCNs while most lower chlorinated molecules readily undergo hydroxylation and excretion through the renal system. Exposure to PCNs reportedly provokes a wide spectrum of adverse effects that range from hepatotoxicity, neurotoxicity and immune response suppression along with endocrine disruption leading to reproductive disorders and embryotoxicity. A number of PCNs, particularly hexachloronaphthalene congeners, elicit AhR mediated responses that are similar to, and occur within similar potency ranges as most dioxin-like polychlorinated biphenyls (PCBs) and some chlorinated dibenzo-p-dioxins and furans (PCDD/Fs), suggesting a relationship based on molecular size and configuration between these contaminants. Most toxicological responses generally appear to be associated with higher chlorinated PCNs. The most profound effects such as serious and sometimes fatal liver disease, chloracne, and wasting syndrome resulted either from earlier episodes of occupational exposure in humans or from acute experimental dosing of animals at levels that reflected these exposures. However, since the restriction of manufacture and controls on inadvertent production (during combustion processes), the principal route of human and animal exposure is likely to be dietary intake. Therefore, further investigations should include the effects of chronic lower level intake of higher chlorinated PCN congeners that persist in the human diet and subsequently in human and animal tissues. PCNs in the diet should be evaluated cumulatively with other similarly occurring dioxin-like contaminants.

Exploring the influence mechanism of dissolved organic matter on the bioavailability and thyroid hormone disrupting effect of zinc: A case study of effluents from galvanizing plants

The effect of dissolved organic matter (DOM) on metal bioavailability and toxicity is a complex process. Effluents from galvanizing plants containing large amounts of DOM and Zn were selected to investigate the potential influence and mechanism of DOM on Zn bioavailability and its role in inducing thyroid hormone disrupting effects. Thyroid hormone disrupting effects were evaluated using a recombinant thyroid hormone receptor β gene yeast assay. The results suggest that Zn could be the main metal contributor to the toxic effects. Then, Zn-binding characteristics with different fluorescent components of DOM were analyzed using three-dimensional excitation emission matrix fluorescence spectroscopy (3DEEM) and revealed that Zn was more susceptible to interactions with fulvic-like materials. Furthermore, DOM altered the cellular biouptake and compartmentalization processes of Zn by downregulating Zn transmembrane transport-related genes (ZRT1, ZRT2 and ZAP1) and upregulating detoxification-related genes (COT1 and ZRC1), thus altering thyroid toxicity. These results provide comprehensive insights into the influence and mechanism of DOM on bioavailability and thyroid toxicity of Zn and suggest that the influence is associated with complex physical, chemical and biological processes, indicating that more refined medium constraints along with subtle biological reactions should be considered when predicting the bioavailability and toxicity of Zn in environmental water samples.

Thyroid Hormone Disruption by Organophosphate Esters Is Mediated by Nuclear/Membrane Thyroid Hormone Receptors: In Vitro, In Vivo, and In Silico Studies

Earlier mechanistic studies of many prohibited flame retardants (FRs) highlighted their thyroid hormone-disrupting activity through nuclear thyroid hormone receptors (nTRs), whereas some alternative FRs such as organophosphate esters (OPEs) exerted weak nTR-disrupting effects. However, an increasing number of studies have revealed that OPEs also exert thyroid hormone-disrupting effects, and the underlying mechanism is unclear. Herein, the thyroid hormone-disrupting effects and mechanisms of 8 typical OPEs were investigated using integrated in vitro, in vivo, and in silico assays. All tested chemicals competitively bound to the membrane thyroid hormone receptor (mTR) [the 20% relative inhibitory concentration (RIC20): (3.5 ± 0.2) × 10¹ to (4.9 ± 1.0) × 10⁷ nM], and Cl-OPEs and alkyl-OPEs had lower RIC20 values. In contrast, only 4 OPEs showed nTR antagonistic activities at higher concentrations [≥ (4.8 ± 0.8) × 10³ nM]. Cl-OPEs and alkyl-OPEs preferentially interacted with mTR. Molecular docking illustrated that OPEs docked into mTRs, consistent with the competitive binding assay. In vivo analyses of zebrafish embryonic development confirmed that tris(1,3-dichloro-2-propyl) phosphate induced inappropriate expression of proteins, and these protein interactions might be associated with mTR according to the quantitative proteomic analysis. Based on the results, mTR might play a critical role in mediating the thyroid hormone-disrupting effects of OPEs.

Towards regulation of Endocrine Disrupting chemicals (EDCs) in water resources using bioassays - A guide to developing a testing strategy

Endocrine disrupting chemicals (EDCs) are found in every environmental medium and are chemically diverse. Their presence in water resources can negatively impact the health of both human and wildlife. Currently, there are no mandatory screening mandates or regulations for EDC levels in complex water samples globally. Bioassays, which allow quantifying in vivo or in vitro biological effects of chemicals are used commonly to assess acute toxicity in water. The existing OECD framework to identify single-compound EDCs offers a set of bioassays that are validated for the Estrogen-, Androgen-, and Thyroid hormones, and for Steroidogenesis pathways (EATS). In this review, we discussed bioassays that could be potentially used to screen EDCs in water resources, including in vivo and in vitro bioassays using invertebrates, fish, amphibians, and/or mammalians species. Strengths and weaknesses of samples preparation for complex water samples are discussed. We also review how to calculate the Effect-Based Trigger values, which could serve as thresholds to determine if a given water sample poses a risk based on existing quality standards. This work aims to assist governments and regulatory agencies in developing a testing strategy towards regulation of EDCs in water resources worldwide. The main recommendations include 1) opting for internationally validated cell reporter in vitro bioassays to reduce animal use & cost; 2) testing for cell viability (a critical parameter) when using in vitro bioassays; and 3) evaluating the recovery of the water sample preparation method selected. This review also highlights future research avenues for the EDC screening revolution (e.g., 3D tissue culture, transgenic animals, OMICs, and Adverse Outcome Pathways (AOPs)).

TDCPP mimics thyroid hormones associated with the activation of integrin αvβ3 and ERK1/2

Tri(1,3-dichloropropyl) phosphate (TDCPP) potentially damages the thyroid system in humans and animals. However, knowledge of its toxic effects and underlying mechanisms is limited. The present study was conducted to determine the thyroid hormone-disrupting effects of TDCPP and its major metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCPP) in rat pituitary cell lines (GH3). TDCPP and BDCPP, that mimic the thyroid hormone (TH), promoted GH3 cell proliferation and modulated the progression of the cell cycle at 20 and 200 μmol/L, respectively. Similar to T3, TDCPP and BDCPP also significantly upregulated c-fos and downregulated Tshβ gene expression. Although the binding affinity of these chemicals for thyroid receptor β (TRβ) was not measured, significant competition between these chemicals to bind to the membrane thyroid hormone receptor (integrin α_vβ₃) was found, suggesting that TDCPP and BDCPP were strongly bound to integrin α_vβ₃. Results from a molecular docking analysis provided further evidence of strong binding affinities of TDCPP and BDCPP for integrin α_vβ₃, and the ligand binding site of Arg-Gly-Asp (RGD) was identified. Real-time PCR also supported the supposition that, after binding to integrin α_vβ₃, TDCPP and BDCPP may induce the activation of the extracellular signal-regulated protein kinase (ERK1/2) signal transduction pathway. Taken together, our data suggest that TDCPP and BDCPP have the ability to mimic THs and that the underlying mechanism might be associated with their interactions with integrin α_vβ₃ and the activation of the ERK1/2 pathway, providing new insight into the mechanism of TDCPP- and BDCPP-induced cytotoxicity.

Competitive binding assays for measuring the binding affinity of thyroid-disrupting chemicals for integrin αvβ3

Some thyroid-disrupting chemicals (TDCs) affect thyroid function by activating the pathways mediated by a typical thyroid hormone (TH) membrane receptor, integrin α_vβ₃. The present study introduces improved competitive binding assays for the rapid and sensitive evaluation of the binding affinities of TDCs for integrin α_vβ_3. Based on different probes, two assays were modified: a fluorescence competitive binding assay and a radioligand competitive binding assay. The chemicals tested included the known TH, 3,3',5,5'-tetraiodo-l-thyronine (T4); a deaminated analog of T4, tetraiodothyroacetic acid (tetrac); and phthalate esters (PAEs). The relative binding potency of T4 was studied, and the concentration required to displace 50% of the ligands from their receptors (RIC50) of T4 was 4.9 × 10⁵ and 9.7 × 10⁴ nM for the fluorescence and radioligand competitive binding assays, respectively, suggesting that the radioligand competitive binding assay might be more sensitive for the evaluation of the binding affinity for integrin α_vβ₃. The three PAEs, including diethyl hexyl phthalate (DEHP), benzyl butyl phthalate (BBP) and dibutyl phthalate (DnBP), demonstrated binding affinities for integrin α_vβ₃ in the following order of potency: DnBP > DEHP > BBP tested by the radioligand competitive binding assay. A docking simulation of each of the three PAEs with integrin α_vβ₃ confirmed the calculated binding energies, which had a strong positive relationship with the log RIC20 values of the 3 PAEs (R = 0.99, p < 0.001). The present study shows that the established radioligand competitive binding assay could be used as a valuable tool for quantifying the affinity of TDCs for integrin α_vβ₃.

Thyroid-Disrupting Activities of Groundwater from a Riverbank Filtration System in Wuchang City, China: Seasonal Distribution and Human Health Risk Assessment

The recombinant thyroid hormone receptor (TR) gene yeast assay was used to evaluate thyroid disruption caused by groundwater from the riverbank filtration (RBF) system in Wuchang City, China. To investigate seasonal fluctuations, groundwater was collected during three seasons. Although no TR agonistic activity was found, many water samples exhibited TR antagonistic activity. The bioassay-derived amiodarone hydrochloride (AH) equivalents ranged from 2.99 to 274.40 μg/L. Water samples collected from the riverbank filtration system during the dry season had higher TR antagonistic activity. All samples presented adverse 3,3′,5-triiodo-L-thyronine (T3) equivalent levels, ranging from −2.00 to −2.12 μg/kg. Following exposure to water samples with substantial TR antagonist activity, predicted hormonal changes in humans of different gender and age ranged from 0.65 to 1.48 μg/kg of T3, being 47% to 231% of normal. No obvious difference was found between genders or among age groups. Overall, the results revealed that the RBF system could remove the thyroid-disrupting chemicals in the river water to some extent. Considering the varying degrees of risk to human health, further treatment is needed to remove the potential thyroid-disrupting chemicals in pumping water after riverbank filtration to ensure drinking water safety.

The molecular mechanism of the antagonistic activity of hydroxylated polybrominated biphenyl (OH-BB80) toward thyroid receptor β

Polybrominated biphenyls (PBBs) were widely used as additive brominated flame retardants. Their hydroxylated products (OH-PBBs) have been detected frequently in various marine mammals, causing an increased health risk. Till now, there lacks information on the potential disruption of OH-PBBs toward thyroid hormone receptor (TR) and the molecular characteristics of their interactions remain largely unknown. We herein in vitro and in silico evaluated the disrupting effect of 3,3',5,5'-tetrabromobiphenyl (BB80) and its metabolite 2,2'-dihydroxy- 3,3',5,5'-tetrabromobiphenyl (OH-BB80) toward human TR. The recombinant human TRβ two-hybrid yeast assay reveals the moderate antagonistic activity of OH-BB80 with IC₂₀ at 2 μmol/L, while BB80 shows no agonistic or antagonistic activity. OH-BB80 binds at the binding cavity of TRβ ligand binding domain (LBD) and forms one hydrogen bond with Phe272. Electrostatic interactions and hydrophobic interactions contribute much to their interactions. The binding of OH-BB80 quenches the intrinsic fluorescence of TRβ LBD at static quenching mode. Our study extends knowledge on the endocrine disrupting effect of OH-PBBs and suggests the full consideration of the biotransformation for further health risk assessment of PBBs and related structurally similar emerging contaminants.

Triple functional small-molecule-protein conjugate mediated optical biosensor for quantification of estrogenic activities in water samples

Establishing biosensors to map a comprehensive picture of potential estrogen-active chemicals remains challenging and must be addressed. Herein, we describe an estrogen receptor (ER)-based evanescent wave fluorescent biosensor by using a triple functional small-molecule-protein conjugate as a signal probe for the determination of estrogenic activities in water samples. The signal probe, consisting of a Cy5.5-labelled streptavidin (STV) moiety and a 17β-estradiol (E₂) moiety, acts simultaneously as signal conversion, signal recognition and signal report elements. When xenoestrogens compete with the E₂ moiety of conjugate in binding to the ER, the unbound conjugates are released, and their STV moiety binds with desthiobiotin (DTB) modified on the optical fiber via the STV-DTB affinity interactions. Signal probe detection is accomplished by fluorescence emission induced by an evanescent field, which positively relates with the estrogenic activities in samples. Quantification of estrogenic activity expressed as E₂ equivalent concentration (EEQ) can be achieved with a detection limit of 1.05 μg/L EEQ by using three times standard deviation of the mean blank values and a linear calibration range from 20.8 to 476.7 μg/L EEQ. The optical fiber system is robust enough for hundreds of sensing cycles. The biosensor-based determination of estrogenic activities in wastewater samples obtained from a full-scale wastewater treatment plant is consistent with that measured by the two-hybrid recombinant yeast bioassay.

Biotransformation of estrone, 17β-estradiol and 17α-ethynylestradiol by four species of microalgae

Natural and synthetic estrogens have been widely detected in wastewater treatment plant (WWTP) influent and effluent as well as in the corresponding receiving aqueous environment and other ecosystems. Microalgae can be used to remove nitrogen and phosphorus in wastewater, but the species-dependent removal of estrogens needs further investigation. In this study we investigated estrone, 17β-estradiol and 17α-ethynylestradiol removals and transformation products by four common microalgae Haematococcus pluvialis, Selenastrum capricornutum, Scenedesmus quadricauda, and Chlorella vulgaris. It was found that H. pluvialis, S. capricornutum and S. quadricauda could more effectively remove all three estrogens in synthetic wastewater effluent. The estrogenic activities i.e. 17β-estradiol equivalency determined by yeast estrogenic screening assay showed substantial estrogenic activity reductions after biotransformation by H. pluvialis, S. capricornutum, and S. quadricauda. Quadrupole Time-of-flight Mass Spectrometry results identified several possible ring-cleavage metabolites as well as their metabolic pathways, which had not been reported yet, confirming the estrogen degradation rather than mere absorption or uptake by microalgae. The findings demonstrate that not only can some specific bacteria degrade estrogens, but also the widely living microalgae are able to degrade these emerging pollutants, suggesting that microalgae could be an advanced treatment of WWTPs to remove nutrients and estrogens.

DnBP-induced thyroid disrupting activities in GH3 cells via integrin αvβ3 and ERK1/2 activation

Di-n-butylphthalate (DnBP) exhibits alarming thyroid disrupting activities. However, the toxic mechanism of DnBP is not completely understood. In this study, we investigated the mechanism of DnBP in thyroid disruption. Rat pituitary tumor cell lines (GH3) were treated with DnBP in different scenarios, and cell viabilities, target gene transcriptions and protein levels were measured accordingly. The results showed that after treatment with DnBP (20 μmol/L), cell proliferation increased to 114.69% (p < 0.01) and c-fos gene was up-regulated by 1.57-fold (p < 0.01). Both nuclear thyroid hormone receptor β (TRβ) and membrane TR (integrin α_v and integrin β₃) genes were up-regulated by 1.31-, 1.08- and 2.39-fold (p < 0.01), respectively, the latter was inhibited by Arg-Gly-Asp (RGD) peptides; the macromolecular DnBP-BSA was unable to bind nuclear TRs, but still promoted cell proliferation to 104.18% and up-regulated c-fos by 2.99-fold (p < 0.01); after silencing TRβ gene, cell proliferation (106.64%, p < 0.05) and up-regulation of c-fos (1.23-fold, p < 0.01) were also observed. All of these findings indicated the existence of non-genomic pathway for DnBP-induced thyroid disruption. Finally, DnBP activated the downstream extracellular regulated protein kinases (ERK1/2) pathway, up-regulating Mapk1 (1.15-, p < 0.05), Mapk3 (1.26-fold, p < 0.01) and increasing protein levels of p-ERK (p < 0.01); notably, DnBP-induced ERK1/2 activation along with c-fos up-regulation were attenuated by PD98059 (ERK1/2 inhibitor). Taken together, it could be suggested that integrin α_vβ₃ and ERK1/2 pathway play significant roles in DnBP-induced thyroid disruption, and this novel mechanism warrants further investigation in living organisms.

Enhanced Removal of Chlorophene and 17β-estradiol by Mn(III) in a Mixture Solution with Humic Acid: Investigation of Reaction Kinetics and Formation of Co-oligomerization Products

Reaction with soluble Mn(II) has been considered as a main decay pathway for superoxide in natural waters, accompanied by an important Mn redox cycling. In this study, the interaction of Mn(II) and humic acid (HA) was investigated in visible light irradiated water. Our results indicate that HA may play a dual role to act as a photosensitizer to produce superoxide anions (O₂^-) and as a strong ligand to stabilize the Mn(III), forming soluble Mn(III)_L species for substrate transformation. Furthermore, the reaction kinetics, products, and mechanisms of chlorophene (CP) and estradiol (E2) mixture in the Mn(II)/HA/visible light reaction systems were assessed. The removal of CP and E2 was enhanced by 24.3% and 13.2%, respectively, in mixture solution at initial concentration of 1.0 μM for each target contaminant, as compared to the case of single-compound degradation. Product identification and density functional theory calculations indicated that cross-coupling reaction of CP and E2 radicals was more likely to occur than the self-coupling reaction in mixture solution. In addition, estrogenic activities of initial reaction solution were also effectively decreased during the transformation process. These findings provide new insights into Mn(III)-mediated reactions to better understand the environmental fate of organic contaminant mixture in waters.

Occurrences, sources, and transport of hydrophobic organic contaminants in the waters of Fildes Peninsula, Antarctica

As a pristine continent, Antarctica provides a good opportunity to study the spatial transport and temporal accumulation of environmental contaminants and the impacts of anthropogenic activities, both of which have given rise to ongoing public concern. In this research, an approach of coupling aquatic time-integrated passive sampling with chemical analysis and bioassays was used to assess pollution by hydrophobic organic contaminants in Antarctic waters. Passive samplers were deployed in waters of Fildes Peninsula, Antarctica, and their extracts were used for chemical analyses of sixty-six hydrophobic organic contaminants belonging to five groups [organophosphorus flame retardants (PFRs), phthalic acid esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and polychlorinated biphenyls (PCBs)] and in vitro bioassays for endocrine disruption and genotoxicity. In total, twenty pollutants (six PFRs, one PAE, two PAHs, six OCPs, and five PCBs) were quantified, and six PFRs had concentrations that ranged from ND (not detected) to 44.37 ng L^-1 in Antarctic waters. The concentrations detected in the waters were generally low and insufficient to have significant in vitro endocrine disruption potential or genotoxicity. The source and transport pathways of PFRs and PAE in Fildes Peninsula were studied, and multiple local sources (wastewater, air traffic, research stations, and animal feces) for different PFRs were proposed. A spatial and temporal analysis showed slight changes in the exposure of OCPs and PCBs in Antarctic waters. Furthermore, a comparison among a variety of Antarctic water sampling cases revealed that passive sampling can be a tool for aquatic time-integrated investigations in polar regions.

Thyroid Disruption by Bisphenol S Analogues via Thyroid Hormone Receptor β: in Vitro, in Vivo, and Molecular Dynamics Simulation Study

Bisphenol S (4-hydroxyphenyl sulfone, BPS) is increasingly used as a bisphenol A (BPA) alternative. The global usage of BPS and its analogues (BPSs) resulted in the frequent detection of their residues in multiple environmental media. We investigated their potential endocrine-disrupting effects toward thyroid hormone receptor (TR) β. The molecular interaction of BPSs toward TRβ ligand binding domain (LBD) was probed by fluorescence spectroscopy and molecular dynamics (MD) simulations. BPSs caused the static fluorescence quenching of TRβ LBD. The 100 ns MD simulations revealed that the binding of BPSs caused significant changes in the distance between residue His435 at helix 11(H11) and residue Phe459 at H12 in comparison to no ligand-bound TRβ LBD, indicating relative repositioning of H12. The recombinant two-hybrid yeast assay showed that tetrabromobisphenol S (TBBPS) and tetrabromobisphenol A (TBBPA) have potent antagonistic activity toward TRβ, with an IC₁₀ of 10.1 and 21.1 nM, respectively. BPS and BPA have the antagonistic activity with IC₁₀ of 312 and 884 nM, respectively. BPSs significantly altered the expression level of mRNA of TRβ gene in zebrafish embryos. BPS and TBBPS at environmentally relevant concentrations have antagonistic activity toward TRβ, implying that BPSs are not safe BPA alternatives in many BPA-free products. Future health risk assessments for TR disruption and other adverse effects should focus more on the structure-activity relationship in the design of environmentally benign BPA alternatives.

Side Chains of Parabens Modulate Antiandrogenic Activity: In Vitro and Molecular Docking Studies

Parabens have been widely used in packaged foods, pharmaceuticals, and personal-care products. Considering their potential hydrolysis, we herein investigated structural features leading to the disruption of human androgen receptor (AR) and whether hydrolysis could alleviate such effects using the recombinant yeast two-hybrid assay. Parabens with an aryloxy side chain such as benzyl paraben and phenyl paraben have the strongest antiandrogenic activity. The antiandrogenic activity of parabens with alkyloxyl side chains decreases as the side chain length increases from 1 to 4, and no antiandrogenic effect occurred for heptyl, octyl, and dodecyl parabens with the number of alkoxyl carbon atoms longer than 7. The antiandrogenic activity of parabens correlates significantly with their binding energies (R² = 0.84, p = 0.01) and were completely diminished after the hydrolysis, particularly for parabens with aryloxy side chains. The K_m for the hydrolysis of parabens with aromatic moiety side chain is 1 order of magnitude higher than that of the parabens with alkyl side chains. Both in vitro and in silico data, for the first time, suggest parabens with aromatic side chains are less prone to hydrolysis. Our results provide an insight into risk of various paraben and considerations for design of new paraben-related substitutes.

Analysis of the sensitivity of in vitro bioassays for androgenic, progestagenic, glucocorticoid, thyroid and estrogenic activity: Suitability for drinking and environmental waters

The presence of endocrine disrupting chemicals in the aquatic environment poses a risk for ecosystem health. Consequently there is a need for sensitive tools, such as in vitro bioassays, to monitor endocrine activity in environmental waters. The aim of the current study was to assess whether current in vitro bioassays are suitable to detect endocrine activity in a range of water types. The reviewed assays included androgenic (n=11), progestagenic (n=6), glucocorticoid (n=5), thyroid (n=5) and estrogenic (n=8) activity in both agonist and antagonist mode. Existing in vitro bioassay data were re-evaluated to determine assay sensitivity, with the calculated method detection limit compared with measured hormonal activity in treated wastewater, surface water and drinking water to quantify whether the studied assays were sufficiently sensitive for environmental samples. With typical sample enrichment, current in vitro bioassays are sufficiently sensitive to detect androgenic activity in treated wastewater and surface water, with anti-androgenic activity able to be detected in most environmental waters. Similarly, with sufficient enrichment, the studied mammalian assays are able to detect estrogenic activity even in drinking water samples. Fewer studies have focused on progestagenic and glucocorticoid activity, but some of the reviewed bioassays are suitable for detecting activity in treated wastewater and surface water. Even less is known about (anti)thyroid activity, but the available data suggests that the more sensitive reviewed bioassays are still unlikely to detect this type of activity in environmental waters. The findings of this review can help provide guidance on in vitro bioassay selection and required sample enrichment for optimised detection of endocrine activity in environmental waters.

Pentachlorophenol affected both reproductive and interrenal systems: In silico and in vivo evidence

The present study investigated the effects on reproductive and interrenal system by pentachlorophenol (PCP) using in silico and in vivo assays. Molecular docking results indicated interacting potency of PCP with steroid receptors (ERα, ERβ, AR, GR) but not Cytochrome P450 enzymes (CYPs). In the in vivo assay, sexually matured rare minnow (Gobiocypris rarus) was exposed to environmental relevant concentrations of PCP (0, 0.5, 5, 50 μg L^-1). In male fish, 14-d exposure caused up-regulation of mRNA levels of hepatic erα, erβ, ar, gr, vtg and gonadal erα, vtg, ar, dmrt1, providing evidence for agonistic activities for steroid receptors by PCP. The up-regulated mRNA of gnrh, crf, pomc in the brain also indicated feed-forward responses of the hypothalamic-pituitary-gonadal/interrenal (HPG/I) axis. However, at 28th d the feed-forward response of the HPG axis seemed eased back and the HPI axis showed negative feedback responses. Corresponding changes including increases of plasma steroid hormones, inhibition of spermatogenesis, and decreased RSI were observed in male fish upon 28-d exposure to PCP. In the females, a transition from feed-forward responses to negative feedbacks of the HPG/I axis was also indicated by the transcriptional profiles at 14th and 28th day. Corresponding changes including increased E2, T and decreased C levels, degenerated ovaries, and decreased GSI and RSI were also observed. Overall, we concluded that PCP could interfere with steroid receptors, evoke responses of HPG/I axis, and finally result in adverse effects on reproductive and interrenal system in rare minnow at environmental relevant concentrations.

Evaluation and characterization of thyroid-disrupting activities in soil samples along the Second Songhua River, China

In this study, a recombinant thyroid receptor (TR) gene yeast assay combined with Monte Carlo simulation were used to evaluate and characterize soil samples collected from Jilin (China) along the Second Songhua River, for their ant/agonist effect on TR. No TR agonistic activity was found in soils, but many soil samples exhibited TR antagonistic activities, and the bioassay-derived amiodarone hydrochloride equivalents, which was calculated based on Monte Carlo simulation, ranged from not detected (N.D.) to 35.5μg/g. Hydrophilic substance fractions were determined to be the contributors to TR antagonistic activity in these soil samples. Our results indicate that the novel calculation method is effective for the quantification and characterization of TR antagonists in soil samples, and these data could provide useful information for future management and remediation efforts for contaminated soils.

Widely used pharmaceuticals present in the environment revealed as in vitro antagonists for human estrogen and androgen receptors

A considerable amount of scientific evidence indicates that a number of pharmaceuticals that could be detected in the environment can contribute towards the development of problems associated with human reproductive systems, as well as those of wildlife. We investigated the estrogenic and androgenic effects of select pharmaceuticals with high production volume and environmental relevance. We examined the receptor-binding activities of these pharmaceuticals in the T47D human cell line using altered secretion of cytokine CXCL12. Functional yeast-luciferase reporter gene assays were also employed to confirm the mechanism of receptor binding by estrogen and androgen. Non-steroidal anti-inflammatory drugs, namely ibuprofen, diclofenac and antiarrhythmic agent amiodarone showed strong anti-estrogenic effects in the T47D cell line. In the yeast-luciferase assay, these anti-inflammatory drugs also demonstrated anti-estrogenic potency and inhibited the E2 response in a concentration-dependent manner. Amiodarone did not exhibit any response in the yeast-luciferase assay; therefore, the endocrine disruption presumably occurred at a different level without directly involving the receptor. All the anti-inflammatory drugs considered in this study, including ketoprofen, naproxen and clofibrate, exhibited a dose-dependent antagonism towards the androgen receptor in the yeast-luciferase assays. Several other drugs, including the stimulant caffeine, did not show any response in the tests that were employed. A risk assessment analysis using 'Hazard Quotient' suggested a potential risk, especially in the cases of ibuprofen, ketoprofen, diclofenac and clofibrate. The results reveal the intrinsic endocrine disrupting nature of several pharmaceuticals and thus could contribute towards explaining a number of adverse health effects on humans and wildlife.

T-screen and yeast assay for the detection of the thyroid-disrupting activities of cadmium, mercury, and zinc

In the present study, a two-hybrid yeast bioassay and a T-screen were used to screen for the thyroid receptor (TR)-disrupting activity of select metallic compounds (CdCl2, ZnCl2, HgCl2, CuSO4, MnSO4, and MgSO4). The results reveal that none of the tested metallic compounds showed TR-agonistic activity, whereas ZnCl2, HgCl2, and CdCl2 demonstrated TR antagonism. For the yeast assay, the dose-response relationship of these metallic compounds was established, and the concentrations producing 20 % of the maximum effect of ZnCl2, HgCl2, and CdCl2 were 9.1 × 10(-5), 3.2 × 10(-6), and 1.2 × 10(-6) mol/L, respectively. The T-screen also supported the finding that ZnCl2, HgCl2, and CdCl2 decreased the cell proliferation at concentrations ranging from 10(-6) to 10(-4) mol/L. Furthermore, the thyroid-disrupting activity of metallic compounds in environmental water samples collected from the Guanting Reservoir, Beijing, China was evaluated. Solid-phase extraction was used to separate the organic extracts, and a modified two-hybrid yeast bioassay revealed that the metallic compounds in the water samples could affect thyroid hormone-induced signaling by decreasing the binding of the thyroid hormone. The addition of ethylenediaminetetraacetic acid (30 mg/L) could eliminate the effects. Thus, the cause(s) of the thyroid toxicity in the water samples appeared to be partly related to the metallic compounds.

A screening assay for thyroid hormone signaling disruption based on thyroid hormone-response gene expression analysis in the frog Pelophylax nigromaculatus

Amphibian metamorphosis provides a wonderful model to study the thyroid hormone (TH) signaling disrupting activity of environmental chemicals, with Xenopus laevis as the most commonly used species. This study aimed to establish a rapid and sensitive screening assay based on TH-response gene expression analysis using Pelophylax nigromaculatus, a native frog species distributed widely in East Asia, especially in China. To achieve this, five candidate TH-response genes that were sensitive to T3 induction were chosen as molecular markers, and T3 induction was determined as 0.2 nmol/L T3 exposure for 48 hr. The developed assay can detect the agonistic activity of T3 with a lowest observed effective concentration of 0.001 nmol/L and EC50 at around 0.118-1.229 nmol/L, exhibiting comparable or higher sensitivity than previously reported assays. We further validated the efficiency of the developed assay by detecting the TH signaling disrupting activity of tetrabromobisphenol A (TBBPA), a known TH signaling disruptor. In accordance with previous reports, we found a weak TH agonistic activity for TBBPA in the absence of T3, whereas a TH antagonistic activity was found for TBBPA at higher concentrations in the presence of T3, showing that the P. nigromaculatus assay is effective for detecting TH signaling disrupting activity. Importantly, we observed non-monotonic dose-dependent disrupting activity of TBBPA in the presence of T3, which is difficult to detect with in vitro reporter gene assays. Overall, the developed P. nigromaculatus assay can be used to screen TH signaling disrupting activity of environmental chemicals with high sensitivity.

The toxicity of sediments from Taihu Lake evaluated by several in vitro bioassays

In vitro bioassays are useful techniques for the determination of biological effects in sediment samples containing complex mixtures of contaminants. In this study, 28 surface sediment samples from Taihu Lake, East China, were collected for toxicity assessment using a battery of in vitro bioassays. The battery included a two-hybrid yeast bioassay for estrogenic and thyroidal effects, the H4IIE rat hepatoma cell bioassay for aryl hydrocarbon (Ah) receptor (Ah-agonists)-mediated effects as measured by ethoxyresorufin-O-deethylase (EROD) activity, and the SOS/umu bioassay for genotoxic effects. Toxicities were expressed as 17β-estradiol equivalents (EEQs), T3 (3,5,3'-triiodothyronine) equivalents (T3-EQs), 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs), and induction ratios (IRs) of β-galactosidase activity. The results showed that total estrogenic effects in sediment samples ranged from 0.0011 to 12.4 pg EEQ/g sediment [dry weight (d.w.)], the thyroidal effects ranged from 0.35 to 24.8 pg T3-EQ/g sediment (d.w.), the Ah-agonist effects varied from 2.70 to 37.8 pg TEQ/g sediment (d.w.), and the weight of soil required for the extracts to lead to a positive result (IR 2.0) in the SOS/umu bioassay was between 1.98 and 15.3 mg (d.w.) per well. Significantly positive correlations were only found between lgT3-EQs and lgEEQs, which indicated similar spatial distributions of estrogenic and thyroidal effects in Taihu Lake. These results suggested that the applied battery of in vitro bioassays represented an efficient (fast and cost-effective) screening system for the identification of emerging contaminants in Taihu Lake and provided meaningful information for further analysis and risk evaluation.

Identification of thyroid-receptor antagonists in water from the Guanting Reservoir, Beijing, China

Thyroid hormone (TH) has long been known to be essential for normal brain development in both humans and animals, and increasing evidence suggests that environmental components may disrupt TH signaling. In the present study, two-hybrid yeast bioassay and chemical analysis were used to evaluate and identify thyroid-receptor (TR) disruptors in water from the Guanting Reservoir, Beijing, China. Modified yeast bioassay showed that the water samples could affect TH signaling. The bioassay-derived amiodarone hydrochloride equivalents ranged from 33.8 ± 3.3 to 308.5 ± 31.8 µg/L. Solid-phase extraction was used to separate the organic extracts, which were subjected to bioassay and chemical analysis. The organic extracts significantly antagonized the TR, which accounted for >86.0 % of the total effects. Thus, organic extracts may play a major role in the TR-disruption activity of the water. Phenols, organochlorine pesticides, and phthalate esters were detected in the organic extracts. Chemical analysis and toxic-equivalent calculation showed that a major cause of the TR antagonism of the water was dibutyl phthalate (80.1 to 122.7 %).

Thyroid hormone disrupting activities of sediment from the Guanting Reservoir, Beijing, China

In the present study, yeast bioassays were used to evaluate and characterize the thyroid receptor (TR) disrupting activities of the organic extracts and elutriates of the sediments from the Guanting Reservoir, Beijing, China. An accelerated solvent extraction was used to separate the organic extracts, which were subjected to a yeast bioassay. The organic extracts could affect thyroid hormone signaling by decreasing the binding of the thyroid hormone. The TR antagonistic activity equivalents (TEQbio) referring to amiodarone hydrochloride were calculated and the observed TEQbio-organic extracts ranged from 25.4 ± 3.7 to 176.9 ± 18.0 μg/g. Elutriate toxicity tests using the modified yeast bioassay revealed that the elutriates also significantly antagonized the TR, with the TEQbio-elutriates ranging from N.D. to 7.8 ± 0.8 μg/L. To characterize the toxic compounds, elutriates were extracted by using a C18 cartridge or treated with ethylenediaminetetraacetic acid (EDTA, 30 mg/L). The results suggested that the addition of EDTA eliminated over 74.3% of the total effects, and the chemical analysis revealed that heavy metals, some of which exhibited TR disrupting potency, for example Zn and Cd, were detectable with higher concentrations in the elutriates. Thus, the cause(s) of toxicity in the elutriate appear to be partly related to the heavy metals.

Concurrent degradation of tetrabromobisphenol A by Ochrobactrum sp. T under aerobic condition and estrogenic transition during these processes

The effect of concurrent degradation of tetrabromobisphenol A (TBBPA) by the strain Ochrobactrum sp. T under aerobic condition was investigated. The results demonstrated that four extra energy source-addition systems still followed pseudo-first order kinetics. The addition of ethanol or glucose could promote the biodegradation ability of Ochrobactrum sp. T to TBBPA, and 90.1 percent and 77.5 percent of TBBPA (5mg L(-1)) could be removed with corresponding TBBPA half-lives of 26 and 36h, respectively, after 96h reaction. Comparatively, the degradation efficiency of the sole TBBPA system was only 72.9 percent under the same condition. In contrast, two other co-substrates 2,4,6-tribromophenol (TBP) and bisphenol A (BPA) showed a negative effect on the TBBPA biodegradation, and the degradation efficiencies of TBBPA were achieved as 44.7 percent and 67.4 percent, respectively. For the TBBPA+TBP system, the competitive inhibition for the TBBPA debromination was less than the inhibition of the toxicity to the bacterium. While for the TBBPA+BPA system, the degradation of TBBPA could be promoted at the beginning of the reaction, and was then inhibited slightly with further prolonging of reaction time. This is probably due to the substrates being oxidized, and BPA can consume partial oxygen and provide the electrons during the concurrent biodegradation process. In addition, although higher estrogenic activity could be detected for the debrominated intermediates in TBBPA co-degradation process than the original TBBPA, the estrogenicity of the whole system still decreased finally after 96h degradation.

A yeast bioassay for direct measurement of thyroid hormone disrupting effects in water without sample extraction, concentration, or sterilization

The present study introduces an improved yeast bioassay for rapid yet sensitive evaluation of thyroid hormone disruption at the level of thyroid receptor (TR) in environmental water samples. This assay does not require water sample preparation and thus requires very little hands-on time. Based on different β-galactosidase substrates, two modified bioassays, a colorimetric bioassay and a chemiluminescent bioassay, were developed. The compounds tested included the known thyroid hormone 3,3',5-triiodo-l-thyronine (T3), the specific TR antagonist amiodarone hydrochloride (AH) and phthalate esters (PAEs), which potentially disrupt thyroid hormone signaling. The EC50 values for T3 were similar to those previously obtained using a 96-well plate bioassay. TR antagonism by AH was studied in the presence of 2.5 × 10(-7)M T3, and the concentration producing 20% of the maximum effect (RIC20) for AH was 3.1 × 10(-7)M and 7.8 × 10(-9)M for the colorimetric bioassay and chemiluminescent bioassay, respectively. None of the tested PAEs induced β-galactosidase expression, but diethylhexyl phthalate, benzyl butyl phthalate and dibutyl phthalate demonstrated TR antagonism. Furthermore, water samples collected from Guanting reservoir in Beijing were evaluated. Although TR agonism was not observed, antagonism was detected in all water samples and is expressed as AH equivalents. The toxicology equivalent quantity values obtained by the chemiluminescent bioassay ranged from 21.2 ± 1.6 to 313.9 ± 28.8 μg L(-1) AH, and similar values were obtained for the colorimetric bioassay. The present study shows that the modified yeast bioassay can be used as a valuable tool for quantification of thyroid hormone disrupting effects in environmental water samples.

Unexpected phenotypes of malformations induced in Xenopus tropicalis embryos by combined exposure to triphenyltin and 9-cis-retinoic acid

Xenopus tropicalis embryos were exposed for 48 hr to the mixtures of 5 μg Sn/L triphenyltin (TPT), which is a well-known endocrine disruptor, and 0.25-5 μg/L 9-cis retinoic acid (9c-RA), which is the natural ligand of retinoid X receptor. The phenotypes induced by combined exposure were more variable than those resulting from single exposure to either TPT or 9c-RA. The prominent phenotypes included underdeveloped head structures, abnormal eyes, narrow fins, enlarged proctodaeum, etc. Especially, combined exposure induced unexpected notochord malformations, which ranged from small swellings of the surface of the tails to the extension and extrusion of notochord out of the posterior tails. Compared with the 5 μg Sn/L TPT-treated group, the index of fin deficiency was not affected, and the index of axis deficiency was significantly increased with increasing RA concentrations in the mixtures. Our results suggest that combined exposure to TPT and 9c-RA induced not only more variable phenotypes of malformations than exposure to single compound but also some new and unexpected phenotypes.

Development of yeast reporter assay for screening specific ligands of retinoic acid and retinoid X receptor subtypes

INTRODUCTION

Retinoic acids are essential for embryonic development, tissue organization, and homeostasis and act via retinoic acid receptors (RARs) that form heterodimers with retinoid X receptors (RXRs). Human RARs and RXRs include the three subtypes α, β, and γ, which have varying distributions and physiological functions among human tissues. Recent reports show that subtype-specific binding of several chemicals to RARs or RXRs may lead to endocrine disruption. To evaluate these ligand-like chemicals, convenient assay systems for each receptor subtype are required.

METHODS

We developed reporter assay yeasts to screen ligands for RXR subtype receptor homodimers. To screen RAR ligands, yeasts were engineered to express RAR subtypes with defective RXRα, which fails to bind to coactivators because of its shortened c-terminus.

RESULTS

These assay yeasts were validated using known RXR- and RAR-specific ligands and subtype-specific responses were clearly shown. Subtype-specific ligand activities of the suspected chemical RAR or RXR ligands o-t-butylphenol, triphenyltin chloride, tributyltin chloride, and 4-nonylphenol were determined.

DISCUSSION

The present assay yeasts may be valuable tools for subtype-specific assessments of unidentified environmental ligand chemicals and receptor-specific pharmaceuticals.

In vitro assessment of thyroid hormone disrupting activities in drinking water sources along the Yangtze River

The thyroid hormone disrupting activities of drinking water sources from the lower reaches of Yangtze River were examined using a reporter gene assay based on African green monkey kidney fibroblast (CV-1) cells. None of the eleven tested samples showed thyroid receptor (TR) agonist activity. Nine water samples exhibited TR antagonist activities with the equivalents referring to Di-n-butyl phthalate (DNBP) (TR antagonist activity equivalents, ATR-EQ(50)s) ranging from 6.92 × 10(1) to 2.85 × 10(2) μg DNBP/L. The ATR-EQ(50)s and TR antagonist equivalent ranges (ATR-EQ(30-80) ranges) for TR antagonist activities indicated that the water sample from site WX-8 posed the greatest health risks. The ATR-EQ(80)s of the water samples ranging from 1.56 × 10(3) to 6.14 × 10(3) μg DNBP/L were higher than the NOEC of DNBP. The results from instrumental analysis showed that DNBP might be responsible for the TR antagonist activities in these water samples. Water sources along Yangtze River had thyroid hormone disrupting potential.

Relationship between BDE 209 metabolites and thyroid hormone levels in rainbow trout (Oncorhynchus mykiss)

Decabromodiphenyl ether (BDE 209), the primary component in a commonly used flame retardants, has recently been shown to be metabolized by organisms. In the present study, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to BDE 209 at five nominal gradient concentrations from 50 to 1000 ng/g wet weight for 21 days via a single intraperitoneal injection. Then the liver, kidney and blood samples were collected to analyze for its debrominated, hydroxylated and methoxylated metabolites. The relationships between levels of BDE 209 metabolites in different tissues and thyroid hormone (TH) levels in plasma were evaluated. The results showed that BDE 209 could be metabolized into debrominated BDEs, methoxylated BDEs (MeO-BDEs) and hydroxylated BDEs (OH-BDEs). Levels of these three metabolites were tissue-dependent. The TH levels, including total thyroxine (TT(4)), free thyroxine (FT(4)), total triiodothyronine (TT(3)) and free triiodothyronine (FT(3)) in plasma, were significantly affected by BDE 209 metabolism. However, only FT(4) levels showed a negative correlation with MeO-BDE and OH-BDE metabolites, among which the correlation between FT(4) and OH-BDEs was the most significant.

Effects of chronic exposure to an environmentally relevant mixture of brominated flame retardants on the reproductive and thyroid system in adult male rats

Brominated flame retardants (BFRs) are incorporated into a wide variety of consumer products, are readily released into home and work environments, and are present in house dust. Studies using animal models have revealed that exposure to polybrominated diphenyl ethers (PBDEs) may impair adult male reproductive function and thyroid hormone physiology. Such studies have generally characterized the outcome of acute or chronic exposure to a single BFR technical mixture or congener but not the impact of environmentally relevant BFR mixtures. We tested whether exposure to the BFRs found in house dust would have an adverse impact on the adult male rat reproductive system and thyroid function. Adult male Sprague Dawley rats were exposed to a complex BFR mixture composed of three commercial brominated diphenyl ethers (52.1% DE-71, 0.4% DE-79, and 44.2% decaBDE-209) and hexabromocyclododecane (3.3%), formulated to mimic the relative congener levels in house dust. BFRs were delivered in the diet at target doses of 0, 0.02, 0.2, 2, or 20 mg/kg/day for 70 days. Compared with controls, males exposed to the highest dose of BFRs displayed a significant increase in the weights of the kidneys and liver, which was accompanied by induction of CYP1A and CYP2B P450 hepatic drug–metabolizing enzymes. BFR exposure did not affect reproductive organ weights, serum testosterone levels, testicular function, or sperm DNA integrity. The highest dose caused thyroid toxicity as indicated by decreased serum thyroxine (T4) and hypertrophy of the thyroid gland epithelium. At lower doses, the thickness of the thyroid gland epithelium was reduced, but no changes in hormone levels (T4 and thyroid-stimulating hormone) were observed. Thus, exposure to BFRs affected liver and thyroid physiology but not male reproductive parameters.

Occurrence of thyroid hormone activities in drinking water from eastern China: contributions of phthalate esters

Thyroid hormone is essential for the development of humans. However, some synthetic chemicals with thyroid disrupting potentials are detectable in drinking water. This study investigated the presence of thyroid active chemicals and their toxicity potential in drinking water from five cities in eastern China by use of an in vitro CV-1 cell-based reporter gene assay. Waters were examined from several phases of drinking water processing, including source water, finished water from waterworks, tap water, and boiled tap water. To identify the responsible compounds, concentrations and toxic equivalents of a list of phthalate esters were quantitatively determined. None of the extracts exhibited thyroid receptor (TR) agonist activity. Most of the water samples exhibited TR antagonistic activities. None of the boiled water displayed the TR antagonistic activity. Dibutyl phthalate accounted for 84.0-98.1% of the antagonist equivalents in water sources, while diisobutyl phthalate, di-n-octyl phthalate and di-2-ethylhexyl phthalate also contributed. Approximately 90% of phthalate esters and TR antagonistic activities were removable by waterworks treatment processes, including filtration, coagulation, aerobic biodegradation, chlorination, and ozonation. Boiling water effectively removed phthalate esters from tap water. Thus, this process was recommended to local residents to reduce certain potential thyroid related risks through drinking water.

In vitro thyroid disrupting effects of organic extracts from WWTPs in Beijing

It is generally known that there are many endocrine disrupting compounds (EDCs) in the effluents from wastewater treatment plants (WWTPs). Most research has focused on the occurrence of estrogenic or androgenic activities, while ignoring that there are environmental chemicals disrupting thyroid system, which is essential for growth and development in both humans and animals. In the present work, a two-hybrid yeast assay was conducted to evaluate the removal efficiencies of agonistic or antagonistic thyroid receptor (TR) mediated effects in different treatment processes of three WWTPs located in Beijing. We found no TR agonistic, but TR antagonistic activities in all processes from the WWTPs. The TR antagonistic activities in organic extracts of water samples were then calibrated regarding to a known TR-inhibitor, amiodarone hydrochloride (AH). The observed concentration of TR disrupting substances ranged from 2.35 x 10(-8) to 6.19 x 10(-7) mol/L AH in Gaobeidian WWTP, 3.76 x 10(-8) to 8.75 x 10(-8) mol/L AH in Lugouqiao WWTP, and 4.80 x 10(-9) to 2.55 x 10(-8) mol/L AH in Beixiaohe WWTP. Of the three WWTPs, the removal rates were 92.7%, 42.2%, and 23.1% respectively. Industrial sewage may contain more TR disrupting substances compared with domestic sewage. The recipient waters were found to contain considerable concentrations of TR disrupting substances that may cause adverse effects on the exposed organisms.

Estrogen-related receptor gamma disruption of source water and drinking water treatment processes extracts

Environmental chemicals in drinking water can impact human health through nuclear receptors. Additionally, estrogen-related receptors (ERRs) are vulnerable to endocrine-disrupting effects. To date, however, ERR disruption of drinking water potency has not been reported. We used ERRgamma two-hybrid yeast assay to screen ERRgamma disrupting activities in a drinking water treatment plant (DWTP) located in north China and in source water from a reservoir, focusing on agonistic, antagonistic, and inverse agonistic activity to 4-hydroxytamoxifen (4-OHT). Water treatment processes in the DWTP consisted of pre-chlorination, coagulation, coal and sand filtration, activated carbon filtration, and secondary chlorination processes. Samples were extracted by solid phase extraction. Results showed that ERRgamma antagonistic activities were found in all sample extracts, but agonistic and inverse agonistic activity to 4-OHT was not found. When calibrated with the toxic equivalent of 4-OHT, antagonistic effluent effects ranged from 3.4 to 33.1 microg/L. In the treatment processes, secondary chlorination was effective in removing ERRgamma antagonists, but the coagulation process led to significantly increased ERRgamma antagonistic activity. The drinking water treatment processes removed 73.5% of ERRgamma antagonists. To our knowledge, the occurrence of ERRgamma disruption activities on source and drinking water in vitro had not been reported previously. It is vital, therefore, to increase our understanding of ERRy disrupting activities in drinking water.

Dibutyl phthalate contributes to the thyroid receptor antagonistic activity in drinking water processes

It has long been recognized that thyroid hormone (TH) is essential for normal brain development in both humans and animals, and there is growing evidence that environmental chemicals can disrupt the thyroid system. In the present work, we used a two-hybrid yeast assay to screen for agonistic or antagonistic thyroid receptor (TR) mediated effects in drinking waters. We found no TR agonistic, but TR antagonistic activities in all samples from the drinking water processes. The TR antagonistic activities in organic extracts of water samples were then calibrated regarding to a known TR-inhibitor, NH3, and were expressed as the NH3 equivalents (TEQbio). The observed TEQbio in waters ranged from 180.8+/-24.8 to 280.2+/-48.2 microg/L NH3. To identify the specific compounds responsible for TR disrupting activities, the concentrations of potentially thyroid-disrupting chemicals including organochlorine pesticides (OCPs), phenols, and phthalates in organic extracts were quantitatively determined and their toxic equivalents with respect to NH3 (TEQcal) were estimated from their concentration-dependent relationships, respectively, using the same set of bioassays. Based on the TEQ approach, it was revealed that dibutyl phthalate (DBP) accounted for 53.7+/-8.2% to 105.5+/-16.7% of TEQbio. There was no effective removal of these potential thyroid disrupting substances throughout drinking water treatment processes.

Hormone activity of hydroxylated polybrominated diphenyl ethers on human thyroid receptor-beta: in vitro and in silico investigations

BACKGROUND

Hydroxylated polybrominated diphenyl ethers (HO-PBDEs) may disrupt thyroid hormone status because of their structural similarity to thyroid hormone. However, the molecular mechanisms of interactions with thyroid hormone receptors (TRs) are not fully understood.

OBJECTIVES

We investigated the interactions between HO-PBDEs and TRbeta to identify critical structural features and physicochemical properties of HO-PBDEs related to their hormone activity, and to develop quantitative structure-activity relationship (QSAR) models for the thyroid hormone activity of HO-PBDEs.

METHODS

We used the recombinant two-hybrid yeast assay to determine the hormone activities to TRbeta and molecular docking to model the ligand-receptor interaction in the binding site. Based on the mechanism of action, molecular structural descriptors were computed, selected, and employed to characterize the interactions, and finally a QSAR model was constructed. The applicability domain (AD) of the model was assessed by Williams plot.

RESULTS

The 18 HO-PBDEs tested exhibited significantly higher thyroid hormone activities than did PBDEs (p < 0.05). Hydrogen bonding was the characteristic interaction between HO-PBDE molecules and TRbeta, and aromaticity had a negative effect on the thyroid hormone activity of HO-PBDEs. The developed QSAR model had good robustness, predictive ability, and mechanism interpretability.

CONCLUSIONS

Hydrogen bonding and electrostatic interactions between HO-PBDEs and TRbeta are important factors governing thyroid hormone activities.

Analysis of environmental endocrine disrupting activities using recombinant yeast assay in wastewater treatment plant effluents

A battery of in vitro recombinant yeast bioassays was conducted to assess the estrogen receptor, androgen receptor, progesterone receptor and thyroid receptor ant/agonistic activities of effluents collected from Datansha wastewater treatment plant (WWTP), furthermore to evaluate the removal efficiencies of endocrine disrupting chemicals in the WWTP. The results showed that estrogenic, anti-androgenic, anti-progesteronic and anti-thyroidic activities were observed in influent. The removal efficiencies of these compounds were more than 80%, which suggested that the present wastewater treatment processes were good enough to remove most of all kinds of endocrine disruption chemicals.

Isolation and characterization of a novel 2-sec-butylphenol-degrading bacterium Pseudomonas sp. strain MS-1

A novel bacterium capable of utilizing 2-sec-butylphenol as the sole carbon and energy source, Pseudomonas sp. strain MS-1, was isolated from freshwater sediment. Within 30 h, strain MS-1 completely degraded 1.5 mM 2-sec-butylphenol in basal salt medium, with concomitant cell growth. A pathway for the metabolism of 2-sec-butylphenol by strain MS-1 was proposed on the basis of the identification of 3 internal metabolites—3-sec-butylcatechol, 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid, and 2-methylbutyric acid—by gas chromatography-mass spectrometry analysis. Strain MS-1 degraded 2-sec-butylphenol through 3-sec-butylcatechol along a meta-cleavage pathway. Degradation experiments with various alkylphenols showed that the degradability of alkylphenols by strain MS-1 depended strongly on the position (ortho ≫ meta = para) of the alkyl substitute, and that strain MS-1 could degrade 2-alkylphenols with various sized and branched alkyl chain (o-cresol, 2-ethylphenol, 2-n-propylphenol, 2-isopropylphenol, 2-sec-butylphenol, and 2-tert-butylphenol), as well as a dialkylphenol (namely, 6-tert-butyl-m-cresol).