Development of a stably transfected estrogen receptor-mediated luciferase reporter gene assay in the human T47D breast cancer cell line

Next generation risk assessment of human exposure to estrogens using safe comparator compound values based on in vitro bioactivity assays

In next generation risk assessment (NGRA), the Dietary Comparator Ratio (DCR) can be used to assess the safety of chemical exposures to humans in a 3R compliant approach. The DCR compares the Exposure Activity Ratio (EAR) for exposure to a compound of interest (EARtest) to the EAR for an established safe exposure level to a comparator compound (EARcomparator), acting by the same mode of action. It can be concluded that the exposure to a test compound is safe at a corresponding DCR ≤ 1. In this study, genistein (GEN) was selected as a comparator compound by comparison of reported safe internal exposures to GEN to its BMCL05, as no effect level, the latter determined in the in vitro estrogenic MCF7/Bos proliferation, T47D ER-CALUX, and U2OS ERα-CALUX assay. The EARcomparator was defined using the BMCL05 and EC50 values from the 3 in vitro assays and subsequently used to calculate the DCRs for exposures to 14 test compounds, predicting the (absence of) estrogenicity. The predictions were evaluated by comparison to reported in vivo estrogenicity in humans for these exposures. The results obtained support in the DCR approach as an important animal-free new approach methodology (NAM) in NGRA and show how in vitro assays can be used to define DCR values.

Estrogenic flavonoids and their molecular mechanisms of action

Flavonoids are a major group of phytoestrogens associated with physiological effects, and ecological and social impacts. Although the estrogenic activity of flavonoids was reported by researchers in the fields of medical, environmental and food studies, their molecular mechanisms of action have not been comprehensively reviewed. The estrogenic activity of the respective classes of flavonoids, anthocyanidins/anthocyanins, 2-arylbenzofurans/3-arylcoumarins/α-methyldeoxybenzoins, aurones/chalcones/dihydrochalcones, coumaronochromones, coumestans, flavans/flavan-3-ols/flavan-4-ols, flavanones/dihydroflavonols, flavones/flavonols, homoisoflavonoids, isoflavans, isoflavanones, isoflavenes, isoflavones, neoflavonoids, oligoflavonoids, pterocarpans/pterocarpenes, and rotenone/rotenoids, was summarized through a comprehensive literature search, and their structure-activity relationship, biological activities, signaling pathways, and applications were discussed. Although the respective classes of flavonoids contained at least one chemical mimicking estrogen, the mechanisms varied, such as those with estrogenic, anti-estrogenic, non-estrogenic, and biphasic activities, and additional activities through crosstalk/bypassing, which exert biological activities through cell signaling pathways. Such mechanistic variations of estrogen action are not limited to flavonoids and are observed among other broad categories of chemicals, thus this group of chemicals can be termed as the "estrogenome". This review article focuses on the connection of estrogen action mainly between the outer and the inner environments, which represent variations of chemicals and biological activities/signaling pathways, respectively, and form the basis to understand their applications. The applications of chemicals will markedly progress due to emerging technologies, such as artificial intelligence for precision medicine, which is also true of the study of the estrogenome including estrogenic flavonoids.

Extensive chemical and bioassay analysis of polycyclic aromatic compounds in a creosote-contaminated superfund soil following steam enhanced extraction

Polycyclic aromatic compounds (PACs) are organic compounds commonly found in contaminated soil. Previous studies have shown the removal of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soils during steam enhanced extraction (SEE). However, less is known about the removal of alkyl-PAHs and heterocyclic compounds, such as azaarenes, and oxygen- and sulfur-heterocyclic PACs (OPACs and PASHs, respectively). Further, the impact of SEE on the freely dissolved concentration of PACs in soil as well as the soil bioactivity pre- and post-SEE have yet to be addressed. To fulfil these research gaps, chemical and bioanalytical analysis of a creosote-contaminated soil, collected from a U.S. Superfund site, pre- and post-SEE were performed. The decrease of 64 PACs (5-100%) and increase in the concentrations of nine oxygenated-PAHs (OPAHs) (150%) during SEE, some of which are known to be toxic and can potentially contaminate ground water, were observed. The freely dissolved concentrations of PACs in soil were assessed using polyoxymethylene (POM) strips and the concentrations of 66 PACs decreased post-SEE (1-100%). Three in vitro reporter gene bioassays (DR-CALUX®, ERα-CALUX® and anti-AR CALUX®) were used to measure soil bioactivities pre- and post-SEE and all reporter gene bioassays measured soil bioactivity decreases post-SEE. Mass defect suspect screening tentatively identified 27 unique isomers of azaarenes and OPAC in the soil. As a remediation technique, SEE was found to remove alkyl-PAHs and heterocyclic PACs, reduce the concentrations of freely dissolved PACs, and decrease soil bioactivities.

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)).

In vitro profiling of toxic effects of environmental polycyclic aromatic hydrocarbons on nuclear receptor signaling, disruption of endogenous metabolism and induction of cellular stress

Polycyclic aromatic hydrocarbons (PAHs) may interact with multiple intracellular receptors and related signaling pathways. We comprehensively evaluated the toxicity profiles of six environmentally relevant PAHs differing in structure, genotoxicity and their ability to activate the aryl hydrocarbon receptor (AhR). We focused particularly on their impact on intracellular hormone-, xenobiotic- and lipid-sensing receptors, as well as on cellular stress markers, combining a battery of human reporter gene assays and qRT-PCR evaluation of endogenous gene expression in human hepatocyte-like HepaRG cells, with LC/MS-MS analysis of cellular sphingolipids. The effects of PAHs included: activation of estrogen receptor α (in case of fluoranthene (Fla), pyrene (Pyr), benz[a]anthracene (BaA), benzo[a]pyrene (BaP)), suppression of androgen receptor activity (Fla, BaA, BaP and benzo[k]fluoranthene (BkF)), enhancement of dexamethasone-induced glucocorticoid receptor activity (chrysene (Chry), BaA, and BaP), and potentiation of triiodothyronine-induced thyroid receptor α activity (all tested PAHs). PAHs also induced transcription of endogenous gene targets of constitutive androstane receptor (Fla, Pyr), or repression of target genes of pregnane X receptor and peroxisome proliferator-activated receptor α (in case of the AhR-activating PAHs - Chry, BaA, BaP, and BkF) in HepaRG cells. In the same cell model, the AhR agonists reduced the expression of glucose metabolism genes (PCK1, G6PC and PDK4), and they up-regulated levels of glucosylceramides, together with a concomitant induction of expression of UGCG, glucosylceramide synthesis enzyme. Finally, both BaP and BkF were found to induce expression of early stress and genotoxicity markers: ATF3, EGR1, GDF15, CDKN1A/p21, and GADD45A mRNAs, while BaP alone increased levels of IL-6 mRNA. Overall, whereas low-molecular-weight PAHs exerted significant effects on nuclear receptors (with CYP2B6 induction observed already at nanomolar concentrations), the AhR activation by 4-ring and 5-ring PAHs appeared to be a key mechanism underlying their impact on nuclear receptor signaling, endogenous metabolism and induction of early stress and genotoxicity markers.

Insights into estrogen receptor alpha modulation by cholestenoic acids

Oxysterols are a family of over 25 cholesterol metabolites naturally produced by enzymatic or radical oxidation. They are involved in many physiological and pathological pathways. Although their activity has been mainly attributed to the modulation of the Liver X Receptors (LXR), it is currently accepted that oxysterols are quite promiscuous compounds, acting at several targets at the same time. The promiscuity of the oxysterols with the Estrogen Receptor α (ERα) is crucial in several pathologies such as ER⁺ breast cancer, inflammation and atherosclerosis. Regarding this matter, we have previously reported the synthesis, LXR activity and binding mode of a family of cholestenoic acid analogs with a modified side chain. Here we report the transcriptional activity on the ERα triggered by these compounds and details on the molecular determinants involved in their activities in order to establish structure-activity relationships to shed light over the molecular basis of the promiscuity of these compounds on ER/LXR responses. Our results show that 3β-hydroxy-5-cholestenoic acid can interact with the ERα receptor in a way similar to 26-hydroxycholesterol and is an agonist of the receptor. Using molecular dynamics simulations, we were able to predict the ERα activity of a set of cholestenoic acid analogs with changes in the flexibility and/or steric requirements of the side chain, some of which exhibited selective activation of ERα or LXR.

Assessment of Five Pesticides as Endocrine-Disrupting Chemicals: Effects on Estrogen Receptors and Aromatase

Pesticides are widely applied all over the world, and pesticide exposure can induce different biological effects posing a possible threat to human health. Due to their effects on the endocrine system, some pesticides are classified as endocrine disruptors. The aim of the study is to assess the interference of five pesticides on estrogen biosynthesis and estrogen signaling. Three neonicotinoid insecticides (Acetamiprid, Clothianidin, and Thiamethoxam), a carbamate insecticide (Methiocarb) and a herbicide (Oxadiazon) were tested. The effect of pesticides on estrogen biosynthesis was studied through an ELISA assay using a recombinant form of human aromatase, the enzyme that catalyzes the transformation of androgens to estrogens. Moreover, the effect of pesticides on estrogen signaling was assessed using a gene reporter assay on MELN cells, which measures estrogen receptor-mediated estrogenic activity. The results of the ELISA assay showed that the pesticides did not alter aromatase activity (no interference with estrogen biosynthesis), while the results of the gene reporter assay showed that only Methiocarb was able to alter estrogen signaling at high doses. The estrogenic activity of Methiocarb, expressed as 17β-estradiol equivalency factor (EEF), was equal to 8.0 × 10⁻⁸. In conclusion, this study suggested that Methiocarb should be considered a potential endocrine disruptor.

Identification of known and novel nonpolar endocrine disruptors in human amniotic fluid

BACKGROUND

Prenatal exposure to endocrine-disrupting compounds (EDCs) may contribute to endocrine-related diseases and disorders later in life. Nevertheless, data on in utero exposure to these compounds are still scarce.

OBJECTIVES

We investigated a wide range of known and novel nonpolar EDCs in full-term human amniotic fluid (AF), a representative matrix of direct fetal exposure.

METHODS

Gas chromatography high-resolution mass spectrometry (GC-HRMS) was used for the targeted and non-targeted analysis of chemicals present in nonpolar AF fractions with dioxin-like, (anti-)androgenic, and (anti-)estrogenic activity. The contribution of detected EDCs to the observed activity was determined based on their relative potencies. The multitude of features detected by non-targeted analysis was tentatively identified through spectra matching and data filtering, and further investigated using curated and freely available sources to predict endocrine activity. Prioritized suspects were purchased and their presence in AF was chemically and biologically confirmed with GC-HRMS and bioassay analysis.

RESULTS

Targeted analysis revealed 42 known EDCs in AF including dioxins and furans, polybrominated diphenyl ethers, pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. Only 30% of dioxin activity and <1% estrogenic and (anti-)androgenic activity was explained by the detected compounds. Non-targeted analysis revealed 14,110 features of which 3,243 matched with library spectra. Our data filtering strategy tentatively identified 121 compounds. Further data mining and in silico predictions revealed in total 69 suspected EDCs. We selected 14 chemicals for confirmation, of which 12 were biologically active and 9 were chemically confirmed in AF, including the plasticizer diphenyl isophthalate and industrial chemical p,p'-ditolylamine.

CONCLUSIONS

This study reveals the presence of a wide variety of nonpolar EDCs in direct fetal environment and for the first time identifies novel EDCs in human AF. Further assessment of the source and extent of human fetal exposure to these compounds is warranted.

Endocrine disruptors of sex hormone activities

Sex hormones, such as androgens, estrogens and progestins are naturally occurring compounds that tightly regulate endocrine systems in a variety of living organisms. Uncontrolled environmental exposure to these hormones or their biological and synthetic mimetics has been widely documented. Furthermore, water contaminants penetrate soil to affect flora, fauna and ultimately humans. Because endocrine systems evolved to respond to very small changes in hormone levels, the low levels found in the environment cannot be ignored. The combined actions of sex hormones with glucocorticoids and other nuclear receptors disruptors creates additional level of complexity including the newly described "dynamic assisted loading" mechanism. We reviewed the extensive literature pertaining to world-wide detection of these disruptors and created a detailed Table on the development and current status of methods used for their analysis.

Key parameter optimization using multivariable linear model for the evaluation of the in vitro estrogenic activity assay in T47D cell lines (CXCL-test)

In comparison to analytical tools, bioassays provide higher sensitivity and more complex evaluation of environmental samples and are indispensable tools for monitoring increasing in anthropogenic pollution. Nevertheless, the disadvantage in cellular assays stems from the material variability used within the assays, and an interlaboratory adaptation does not usually lead to satisfactory test sensitivities. The aim of this study was to evaluate the influence of material variability on CXCL12 secretion by T47D cells, the outcome of an estrogenic activity assay, the CXCL-test. For this purpose, the cell line sources, sera suppliers, experimental and seeding media, and the amount of cell/well were tested. The multivariable linear model (MLM), employed as an innovative approach in this field for parameter evaluation, identified that all the tested parameters had significant effects. Knowledge of the contributions of each parameter has permitted step-by-step optimization. The most beneficial approach was seeding 20,000 cells/well directly in treatment medium and using DMEM for the treatment. Great differences in both basal and maximal cytokine secretions among the three tested cell lines and different impacts of each serum were also observed. Altogether, both these biologically based and highly variable inputs were additionally assessed by MLM and a subsequent two-step evaluation, which revealed a lower variability and satisfactory reproducibility of the test. This analysis showed that not only parameter and procedure optimization but also the evaluation methodology must be considered from the perspective of interlaboratory method adaptation. This overall methodology could be applied to all bioanalytical methods for fast multiparameter and accurate analysis.

Identification of the EdcR Estrogen-Dependent Repressor in Caenibius tardaugens NBRC 16725: Construction of a Cellular Estradiol Biosensor

In this work, Caenibius tardaugens NBRC 16725 (strain ARI-1) (formerly Novosphingobium tardaugens) was isolated due to its capacity to mineralize estrogenic endocrine disruptors. Its genome encodes the edc genes cluster responsible for the degradation of 17β-estradiol, consisting of two putative operons (OpA and OpB) encoding the enzymes of the upper degradation pathway. Inside the edc cluster, we identified the edcR gene encoding a TetR-like protein. Genetic studies carried out with C. tardaugens mutants demonstrated that EdcR represses the promoters that control the expression of the two operons. These genetic analyses have also shown that 17β-estradiol and estrone, the second intermediate of the degradation pathway, are the true effectors of EdcR. This regulatory system has been heterologously expressed in Escherichia coli, foreseeing its use to detect estrogens in environmental samples. Genome comparisons have identified a similar regulatory system in the edc cluster of Altererythrobacter estronivorus MHB5, suggesting that this regulatory arrangement has been horizontally transferred to other bacteria.

The Green toxicology approach: Insight towards the eco-toxicologically safe development of benign catalysts

Green toxicology is a novel approach increasingly applied for the development of materials and chemicals that are more benign to the environment and human health than their conventional counterparts. It includes predictive eco-toxicological assessments of chemicals during the early developmental process to exclude adverse effects. In the present study, two guanidine zinc catalysts for the ring-opening polymerization of lactide were investigated using eco-toxicological tools. Namely, the fish embryo toxicity assay for teratogenic effects, the ER (α) CALUX assay for endocrine activity and the Ames fluctuation assay for mutagenic potential were applied. Both complexes showed no endocrine activity, mutagenicity or acute aquatic toxicity, however a delayed hatch could be observed, therefore suggesting potential effects on a molecular level. This proof-of-concept study aims to assess the toxicity of guanidine zinc catalysts and is a first step towards the incorporation of toxicological assessments into chemical developmental processes to achieve a sustainable and safe production of catalysts.

Seasonal variation in oestrogenic potency and biological effects of wastewater treatment works effluents assessed using ERE-GFP transgenic zebrafish embryo-larvae

Effluents from wastewater treatment works (WwTW) exhibit both temporal and spatial variation in oestrogenicity, however few studies have attempted to quantify how this variation affects biological responses in fish. Here we used an oestrogen-responsive green fluorescent protein (ERE-GFP) transgenic zebrafish (Danio rerio) to quantify oestrogenic activity and health effects for exposure to three different WwTW effluents. Endpoints measured included survival/hatching rate, GFP induction (measured in target tissues or gfp mRNA induction in whole embryos) and vtg mRNA induction in whole embryos. Exposure to one of the study effluents (at 100%), resulted in some mortality, and exposure to all three effluents (at 50% and 100%) caused decreases in hatching rates. Higher levels of vtg mRNA corresponded with higher levels of steroidal oestrogens in the different effluents, with lowest-observed-effect concentrations (LOECs) between 31 ng/L and 39 ng/L oestradiol equivalents (EEQs). Tissue patterns of GFP expression for all three WwTWs effluents reflected the known targets for steroidal oestrogens and for some other oestrogenic chemicals likely present in those effluents (i.e. nonylphenol or bisphenolic compounds). GFP induction was similarly responsive to vtg mRNA induction (a well-established biomarker for oestrogen exposure). We thus demonstrate the ERE-GFP transgenic zebrafish as an effective model for monitoring the oestrogenic potency and health effects for exposure to complex mixtures of chemicals contained within WwTW effluents.

Potential risk of BPA and phthalates in commercial water bottles: a minireview

The global water bottling market grows annually. Today, to ensure consumer safety, it is important to verify the possible migration of compounds from bottles into the water contained in them. Potential health risks due to the prevalence of bisphenol A (BPA) and phthalates (PAEs) exposure through water bottle consumption have become an important issue. BPA, benzyl butyl phthalate (BBP), di-n-butyl phthalate (DBP) and di (2-ethylhexyl) phthalate (DEHP) can cause adverse effects on human health. Papers of literature published in English, with BPA, BBP, DBP and DEHP detections during 2017, by 2019 by liquid chromatography and gas chromatography analysis methods were searched. The highest concentrations of BPA, BBP, DBP and DEHP in all the bottled waters studied were found to be 5.7, 12.11, 82.8 and 64.0 μg/L, respectively. DBP was the most compound detected and the main contributor by bottled water consumption with 23.7% of the Tolerable Daily Intake (TDI). Based on the risk assessment, BPA, BBP, DBP and DEHP in commercial water bottles do not pose a serious concern for humans. The average estrogen equivalent level revealed that BPA, BBP, DBP and DEHP in bottled waters may induce adverse estrogenic effects on human health.

Effect-based evaluation of ozone treatment for removal of micropollutants and their transformation products in waste water

The aim of this interdisciplinary research project in North Rhine-Westphalia (NRW), Germany, entitled "Elimination of pharmaceuticals and organic micropollutants from waste water" involved the conception of cost-effective and innovative waste-water cleaning methods. In this project in vitro assays, in vivo assays and chemical analyses were performed on three municipal waste-water treatment plants (WWTP). This publication focuses on the study of the in vitro bioassays. Cytotoxic, estrogenic, genotoxic and mutagenic effects of the original as well as enriched water samples were monitored before and after wastewater treatment steps using MTT and PAN I, ER Calux and A-YES, micronucleus and Comet assays as well as AMES test. In most cases, the measured effects were reduced after ozonation, but in general, the biological response depended upon the water composition of the WWTP, in particular on the formed by-products and concentration of micropollutants. In order to be able to assess the genotoxic and/or mutagenic potential of waste-water samples using bioassays like Ames test, Comet assay or micronucleus test an enrichment of the water sample via solid-phase extraction is recommended. This is in agreement with previous studies such as the "ToxBox"-Project of the Environmental Agency in Germany.

Environmental six-ring polycyclic aromatic hydrocarbons are potent inducers of the AhR-dependent signaling in human cells

The toxicities of many environmental polycyclic aromatic hydrocarbons (PAHs), in particular those of high-molecular-weight PAHs (with MW higher than 300), remain poorly characterized. The objective of this study was to evaluate the ability of selected environmentally relevant PAHs with MW 302 (MW302 PAHs) to activate the aryl hydrocarbon receptor (AhR), since this represents a major toxic mode of action of PAHs. A large number of the evaluated compounds exhibited strong AhR-mediated activities, in particular in human models. The studied MW302 PAHs also significantly contributed to the overall calculated AhR activities of complex environmental mixtures, including both defined standard reference materials and collected diesel exhaust particles. The high AhR-mediated activities of representative MW302 PAHs, e.g. naphtho[1,2-k]fluoranthene, corresponded with the modulation of expression of relevant AhR target genes in a human lung cell model, or with the AhR-dependent suppression of cell cycle progression/proliferation in estrogen-sensitive cells. This was in a marked contrast with the limited genotoxicity of the same compound(s). Given the substantial levels of the AhR-activating MW302 PAHs in combustion particles, it seems important to continue to investigate the toxic modes of action of this large group of PAHs associated with airborne particulate matter.

Estrogenic activity of biological samples as a biomarker

Biological assays can evaluate the cumulative effect of a mixture, considering synergistic/antagonistic interactions and effects of unknown/unconsidered compounds. Therefore, their application could increase in the next years also to analyse biological samples. The aim of this review is to discuss the methodological approach and the application of estrogenic activity assays in human biological samples. 75 research articles were analysed and divided according to whether they used these assays: i) to quantify the level of estrogens and/or as a biomarker of estrogenic status ii) as a biomarker of exposure to endocrine disrupting chemicals (EDCs). For the first purpose, some authors extracted biological samples while others tested them directly without any treatment. The study of these methodologies outlined that the methodology applied influenced the specificity of analysis. The estrogenic activity biomarker was used to analyse physiological variations of estrogens, pediatric diseases, hormone-dependent diseases and estrogen suppression/enhancement after pharmaceutical treatments. For the second purpose, some authors extracted samples while others tested them directly, some authors divided endogenous estrogens from xenoestrogens while others tested samples without separation. The analysis of these methodologies outlined some limitations related to the efficiency of extraction and the incorrect separation of some compounds. The studies which applied this EDC biomarker showed that it was correlated with some EDCs, it varied according to the exposure of the population and it allowed the identification of some relationships between EDC exposure and breast cancer, type 1 diabetes and adverse health effects on children. In conclusion, the estrogenic activity of biological samples can be a useful tool: to quantify low levels of 17β-estradiol, to assess the combined effect of endogenous estrogens and xenoestrogens, to estimate the estrogenic status providing considerable insight into physiological or pathological conditions, to evaluate EDC presence implementing the existing knowledge about EDC exposure and adverse health effects.

Culture Conditions Affect Chemical-Induced Developmental Toxicity In Vitro: The Case of Folic Acid, Methionine and Methotrexate in the Neural Embryonic Stem Cell Test

In vitro tests are increasingly applied in chemical hazard assessment. Basic culture conditions may affect the outcome of in vitro tests and should be optimised to reduce false predictions. The neural embryonic stem cell test (ESTn) can predict early neurodevelopmental effects of chemicals, as it mimics the differentiation of stem cells towards the neuroectodermal lineage. Normal early neural differentiation depends crucially on folic acid (FA) and methionine (MET), both elements of the one-carbon (1C) cycle. The aim of this study was to assess the concentration-dependent influence of FA and MET on neural differentiation in the ESTn, and its consequences for assay sensitivity to methotrexate (MTX), a compound that interferes with the 1C cycle. Neural differentiation was inhibited below 0.007 mM and above 0.22 mM FA, while both stem cell viability (< 0.097 mM, > 1.52 mM) and neural differentiation (< 0.181 mM, > 1.35 mM) were affected when changing MET concentrations. A 10-day exposure to 13 nM MTX inhibited neural differentiation, especially in FA- and MET-deficient conditions. However, a 24-hour exposure to 39 nM MTX decreased neural cell and neural crest cell differentiation markers only when the concentration of FA in the medium was three times the standard concentration, which was expected to have a protective effect against MTX. These results show the importance of nutrient concentrations, exposure scenarios and timing of read-outs for cell differentiation and compound sensitivity in the ESTn. Caution should be taken when interpreting results from a single in vitro test, especially when extrapolating to effects on complex morphogenetic processes, like neural tube development.

Chemical Screening of Nuclear Receptor Modulators

Nuclear receptors are ligand-inducible transcriptional factors that control multiple biological phenomena, including proliferation, differentiation, reproduction, metabolism, and the maintenance of homeostasis. Members of the nuclear receptor superfamily have marked structural and functional similarities, and their domain functionalities and regulatory mechanisms have been well studied. Various modulators of nuclear receptors, including agonists and antagonists, have been developed as tools for elucidating nuclear receptor functions and also as drug candidates or lead compounds. Many assay systems are currently available to evaluate the modulation of nuclear receptor functions, and are useful as screening tools in the discovery and development of new modulators. In this review, we cover the chemical screening methods for nuclear receptor modulators, focusing on assay methods and chemical libraries for screening. We include some recent examples of the discovery of nuclear receptor modulators.

Combining Different In Vitro Bioassays to Evaluate Genotoxicity of Water-Accommodated Fractions from Petroleum Products

Genotoxicity assessment is of high relevance for crude and refined petroleum products, since oil compounds are known to cause DNA damage with severe consequences for aquatic biota as demonstrated in long-term monitoring studies. This study aimed at the optimization and evaluation of small-scale higher-throughput assays (Ames fluctuation, micronucleus, Nrf2-CALUX^®) covering different mechanistic endpoints as first screening tools for genotoxicity assessment of oils. Cells were exposed to native and chemically dispersed water-accommodated fractions (WAFs) of three oil types varying in their processing degree. Independent of an exogenous metabolic activation system, WAF compounds induced neither base exchange nor frame shift mutations in bacterial strains. However, significantly increased chromosomal aberrations in zebrafish liver (ZF-L) cells were observed. Oxidative stress was indicated for some treatments and was not correlated with observed DNA damage. Application of a chemical dispersant increased the genotoxic potential rather by the increased bioavailability of dissolved and particulate oil compounds. Nonetheless, the dispersant induced a clear oxidative stress response, indicating a relevance for general toxic stress. Results showed that the combination of different in vitro assays is important for a reliable genotoxicity assessment. Especially, the ZF-L capable of active metabolism and DNA repair seems to be a promising model for WAF testing.

Environmental exposure to nonylphenol and cancer progression Risk-A systematic review

Environmental exposure to nonylphenol (NP) can adversely affect human and wildlife health. A systematic review was conducted to evaluate the relationship between environmental NP exposure and cancer progression risk. Literature surveys were conducted within several international databases using appropriate keywords. A comprehensive search yielded 58 eligible studies involving a wide range of adverse effects, exposure assessment methods, study designs, and experimental models. Most studies reported that NP strongly induced breast cancer progression in intended experiments. Positive associations between NP exposure and ovarian, uterine, pituitary, and testicular cancers were also reported. Although some studies reported no relation between environmental NP exposure and tumour and/or cancer progression, NP (a known endocrine disrupting chemical) induced action mechanisms in multiple experimental models and may interfere with/hyper-activate oestrogen signalling. Secretion of oestrogen and development of reproductive tissues like breasts, uteruses, and ovaries showed strong associations with possible neoplasia (i.e., uncontrolled development of tumours and/or malignant cancers). Findings of this study are important for informing policymakers to pass legislation limiting the use of environmental contaminants such as NP before all adverse effects of exposure have been determined.

Mechanisms of action of agrochemicals acting as endocrine disrupting chemicals

Agrochemicals represent a significant class of endocrine disrupting chemicals that humans and animals around the world are exposed to constantly. Agrochemicals can act as endocrine disrupting chemicals through a variety of mechanisms. Recent studies have shown that several mechanisms of action involve the ability of agrochemicals to mimic the interaction of endogenous hormones with nuclear receptors such as estrogen receptors, androgen receptors, peroxisome proliferator activated receptors, the aryl hydrocarbon receptor, and thyroid hormone receptors. Further, studies indicate that agrochemicals can exert toxicity through non-nuclear receptor-mediated mechanisms of action. Such non-genomic mechanisms of action include interference with peptide, steroid, or amino acid hormone response, synthesis and degradation as well as epigenetic changes (DNA methylation and histone modifications). This review summarizes the major mechanisms of action by which agrochemicals target the endocrine system.

Real-time measurement of E2: ERα transcriptional activity in living cells

Kinetic analyses of diverse physiological processes have the potential to unveil new aspects of the molecular regulation of cell biology at temporal levels. 17β-estradiol (E2) regulates diverse physiological effects by binding to the estrogen receptor α (ERα), which primarily works as a transcription factor. Although many molecular details of the modulation of ERα transcriptional activity have been discovered including the impact of receptor plasma membrane localization and its relative E2-evoked signaling, the knowledge of real-time ERα transcriptional dynamics in living cells is lacking. Here, we report the generation of MCF-7 and HeLa cells stably expressing a modified luciferase under the control of an E2-sensitive promoter, which activity can be continuously monitored in living cells and show that E2 induces a linear increase in ERα transcriptional activity. Ligand-independent (e.g., epidermal growth factor) receptor activation was also detected in a time-dependent manner. Kinetic profiles of ERα transcriptional activity measured in the presence of both receptor antagonists and inhibitors of ERα plasma membrane localization reveal a biphasic dynamic of receptor behavior underlying novel aspects of receptor-regulated transcriptional effects. Finally, analysis of the rate of the dose-dependent E2 induction of ERα transcriptional activity demonstrates that low doses of E2 induce an effect identical to that determined by high concentrations of E2 as a function of the duration of hormone administration. Overall, we present the characterization of sensitive stable cell lines were to study the kinetic of E2 transcriptional signaling and to identify new aspects of ERα function in different physiological or pathophysiological conditions.

Receptor-mediated estrogenicity of native and chemically dispersed crude oil determined using adapted microscale reporter gene assays

Endocrine disrupting compounds (EDCs) emerged as a major concern for water quality in the last decade and have been studied extensively since. Besides typical natural and synthetic estrogens also petroleum product compounds such as some PAHs have been identified as potential EDCs, revealing endocrine disruption to be a relevant mode of action for crude oil toxicity. Hence, in the context of a comprehensive retro- or prospective risk assessment of oil spills the implementation of mechanism-specific toxicity such as endocrine disruption is of high importance. To evaluate the exposure risk for the aquatic biota, research focuses on water-soluble fractions underlying an oil slick that could be simulated via water-accommodated fractions (WAF). Against this background human (ERα-CALUX®) and yeast based (A-YES®) reporter gene bioassays were successfully optimized for the application in estrogenicity evaluation of the water-accommodated fraction (WAF) from a crude oil. Combining different approaches, the estrogenicity of the WAFs from a naphthenic North Sea crude oil was tested with and without the addition of a chemical dispersant addressing specific aspects of estrogenicity including the influence of biotransformation capacities and different salinity conditions. Both the WAF free from droplets (LEWAF) as well as the chemically dispersed WAF (CEWAF) gave indications of an ER-mediated estrogenicity with much stronger ERα agonists in the CEWAF treatment. Resulting estradiol equivalents of the WAFs were above the established effect-based trigger values for both bioassays. Results indicate that the dispersant rather increased the fraction of ER-activating crude oil compounds instead of interacting with the receptor itself. Only slight changes in estrogenic responses were observed when cells capable of active metabolism (T47D) were used instead of cells without endogenous metabolism (U2-OS) in the recombinant ER transactivation CALUX assay. With the yeast cells a higher estrogenic activity was observed in the experiments under elevated salinity conditions (6‰), which was in contrast to previous expectations due to typical decrease in dissolved PAH fraction with increasing salinity (salting-out effect) but might be related to increased cell sensitivity.

Applicability of the OECD 455 in-vitro assay for determination of hERa agonistic activity of isoflavonoids

The Organisation for Economic Co-operation and Development (OECD)-validated transactivation assay using the human estrogen receptor alpha (hERα) Hela9903 cell line is used for activity evaluation of hERα agonists and antagonists. Due to many advantages, this assay is broadly used as an initial screening process. However, response significantly higher from that of 17-β estradiol (E2) was observed with phytoestrogens for concentrations commonly above 1 μM in previous studies. The main aim of this study was thus to ascertain the applicability of OECD protocol 455 for evaluation of estrogenic activity of natural flavonoids, including known phytoestrogens. The estrogenic activities of aglycones as well as of O-methylated and glycosylated flavonoids were evaluated. Supra-maximal luciferase activity was seen for most of the flavonoids tested at concentrations even below 1 μM. hERα-mediated luciferase expression was confirmed with the competition assay specified in OECD protocol 455. However, at concentrations above 1 μM, non-specific interactions were also observed. Instead of EC₅₀ values, which could not be determined for most of the isoflavonoids tested, the concentrations corresponding to 10% (PC₁₀) and 50% (PC₅₀) of the maximum activity of the positive control, E2, were used for quantitative determination of estrogenic activities. Appropriate evaluation of the data obtained with the current OECD protocol 455 validated assay represents a valuable tool for initial screening of natural flavonoids for estrogenic activity.

Development of a neural rosette formation assay (RoFA) to identify neurodevelopmental toxicants and to characterize their transcriptome disturbances

The first in vitro tests for developmental toxicity made use of rodent cells. Newer teratology tests, e.g. developed during the ESNATS project, use human cells and measure mechanistic endpoints (such as transcriptome changes). However, the toxicological implications of mechanistic parameters are hard to judge, without functional/morphological endpoints. To address this issue, we developed a new version of the human stem cell-based test STOP-tox_(UKN). For this purpose, the capacity of the cells to self-organize to neural rosettes was assessed as functional endpoint: pluripotent stem cells were allowed to differentiate into neuroepithelial cells for 6 days in the presence or absence of toxicants. Then, both transcriptome changes were measured (standard STOP-tox_(UKN)) and cells were allowed to form rosettes. After optimization of staining methods, an imaging algorithm for rosette quantification was implemented and used for an automated rosette formation assay (RoFA). Neural tube toxicants (like valproic acid), which are known to disturb human development at stages when rosette-forming cells are present, were used as positive controls. Established toxicants led to distinctly different tissue organization and differentiation stages. RoFA outcome and transcript changes largely correlated concerning (1) the concentration-dependence, (2) the time dependence, and (3) the set of positive hits identified amongst 24 potential toxicants. Using such comparative data, a prediction model for the RoFA was developed. The comparative analysis was also used to identify gene dysregulations that are particularly predictive for disturbed rosette formation. This 'RoFA predictor gene set' may be used for a simplified and less costly setup of the STOP-tox_(UKN) assay.

Primary endometrial 3D co-cultures: A comparison between human and rat endometrium

Human and rat reproductive systems differ significantly with respect to hormonal cyclicity and endometrial cell behavior. However, species-differences in endometrial cell responses upon hormonal stimulation and exposure to potentially toxic compounds are poorly characterized. In this study, human and rat endometrial hormonal responses were assessed in vitro using a 3D co-culture model of primary human and rat endometrial cells. The models were exposed to the aryl hydrocarbon receptor (AHR) ligands 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), laquinimod, and its AHR active metabolite DELAQ. In both the human and rat endometrial models, estrogen receptor and progesterone receptor gene expression was modulated by the hormonal treatments, comparable to the in vivo situation. AHR gene expression in the human endometrial model did not change when exposed to hormones. In contrast, AHR expression decreased 2-fold in the rat model when exposed to predominantly progesterone, which resulted in a 2.8-fold attenuation of gene expression induction of cytochrome P450 1A1 (CYP1A1) by TCDD. TCDD and DELAQ, but not laquinimod, concentration-dependently induced CYP1A1 gene expression in both human and rat endometrial models. Interestingly, the relative degree of DELAQ to induce CYP1A1 was higher than that of TCDD in the human model, while it was lower in the rat model. These data clearly show species-differences in response to hormones and AHR ligands between human and rat endometrial cells in vitro, which might greatly affect the applicability of the rat as translational model for human endometrial effects. This warrants further development of human relevant, endometrium-specific test methods for risk assessment purposes.

Aryl Hydrocarbon Receptor-Dependent Metabolism Plays a Significant Role in Estrogen-Like Effects of Polycyclic Aromatic Hydrocarbons on Cell Proliferation

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants that interact in a complex manner with both the aryl hydrocarbon receptor (AhR) and estrogen receptors (ER). Their potential endocrine-disrupting activities may depend on both inhibitory AhR-ER cross-talk and on AhR-dependent metabolic production of estrogenic PAH metabolites. Here, we analyzed the impact of AhR on estrogen-like effects of PAHs, such as benzo[a]pyrene (BaP), in particular, on control of cell cycle progression/cell proliferation. Using AhR knockout variant of estrogen-sensitive human breast cancer MCF-7 cells (MCF-7 AhRKO cells), we observed that the AhR-dependent control of cytochrome P450 family 1 (CYP1) expression played a major role in formation of estrogenic BaP metabolites, most notably 3-OH-BaP, which contributed to the ER-dependent induction of cell cycle progression/cell proliferation. Both BaP metabolism and the BaP-induced S-phase transition/cell proliferation were inhibited in MCF-7 AhRKO cells, whereas these cells remained sensitive towards both endogenous estrogen 17β-estradiol or hydroxylated BaP metabolites. BaP was found to increase the activity of ER-dependent luciferase reporter gene in wild-type MCF-7 cells; however, unlike its hydroxylated metabolite, BaP failed to stimulate luciferase activity in MCF-7 AhRKO cells. Similarly, estrogen-like effects of other known estrogenic PAHs, such as benz[a]anthracene or 3-methylcholanthrene, were diminished in MCF-7 AhRKO cells. Ectopic expression of human CYP1A1 and CYP1B1 enzymes partly restored both BaP metabolism and its effects on cell proliferation. Taken together, our data suggest that the AhR-dependent metabolism of PAHs contributes significantly to the impact of PAHs on cell proliferation in estrogen-sensitive cells.

A Pharmacological Overview of Alpinumisoflavone, a Natural Prenylated Isoflavonoid

Over the last decade, several studies demonstrated that prenylation of flavonoids enhances various biological activities as compared to the respective nonprenylated compounds. In line with this, the natural prenylated isoflavonoid alpinumisoflavone (AIF) has been explored for a number of biological and pharmacological effects (therapeutic potential). In this review, we summarize the current information on health-promoting properties of AIF. Reported data evidenced that AIF has a multitherapeutic potential with antiosteoporotic, antioxidant and anti-inflammatory, antimicrobial, anticancer, estrogenic and antiestrogenic, antidiabetic, and neuroprotective properties. However, research on these aspects of AIF is not sufficient and needs to be reevaluated using more appropriate methods and methodology. Further series of studies are needed to confirm these pharmacological effects, and this review should lay the basis for the design of respective investigations. Overall, despite the drawbacks of studies recorded, AIF exhibits a potential as drug candidate.

Leaching of endocrine disrupting chemicals from marine microplastics and mesoplastics under common life stress conditions

Microplastics (MPs) and mesoplastics are able to sorb harmful substances and often contain additives, e.g., endocrine disrupting chemicals (EDCs), that can cause adverse effects to organisms. The present study aims to determine EDC concentrations and their endocrine activities in leachates of field-collected marine MPs and mesoplastics under stress conditions that are known to occur during the plastic life cycle. Estrogens were the dominant EDCs on plastic particles and were either concentrated from the surrounding water or originated from plastic manufacturing. Bisphenol A had the highest detection frequency (75%) with an average concentration of 475 ± 882 μg/kg, followed by bisphenol S, octylphenol and nonylphenol. Moreover, smaller marine MPs leached greater quantities of EDCs because the sorption from surrounding seawater is more efficient for smaller particles. It was found that normal life stresses such as microwaving (MW) and autoclaving (AC) can decrease EDC concentrations, but solar irradiation (solar) can increase EDC concentrations in leachates. Even though organisms with higher metabolic ability exhibited greater estrogenic effects, the comprehensive toxicity of plastic leachates after common life treatments was still limited (below the EC₁₀ value) if 0.1% is taken as the EDC uptake from plastic. In future studies, the accurate contribution of plastic bound EDCs needs to be further explored, and the monitoring of MPs and mesoplastics in the human diet remains important because the concentrations of these plastics may change in the future.

A β1-tubulin-based megakaryocyte maturation reporter system identifies novel drugs that promote platelet production

During maturation, megakaryocytes (MKs) express β1-tubulin (TUBB1) and rearrange their microtubule components to enlarge, form proplatelets, and eventually release platelets. The development of a platform to identify in vitro conditions that would efficiently promote MK development could potentially enable large-scale platelet production. Here, we show that an immortalized MK cell line (imMKCL) genetically modified to express the β1-tubulin-Venus reporter provides a practical system to efficiently monitor the in vitro production of platelet-like particles (PLPs). The Venus transgene was inserted downstream of the TUBB1 locus in imMKCLs using CRISPR/Cas9, and the expression was visualized by Venus fluorescence intensity. This imMKCL reporter line was then used for high-throughput drug screening. We identified several compounds that significantly improved the efficiency of PLP production in vitro under feeder-free conditions and showed a significant tendency to recover platelets in vivo in a mouse thrombocytopenia model induced by anti-GPIbα antibody administration. Interestingly, most of these compounds, including a WNT signaling pathway inhibitor, Wnt-C59, antagonized the aryl hydrocarbon receptor (AhR) to increase PLP production, confirming the crucial role of AhR inhibition in MK maturation. Consistently, small interfering RNA treatment against AhR increased the Venus intensity and PLP production. TCS 359, an FLT3 inhibitor, significantly increased PLP production independently of FLT3 or AhR. This study highlights the usefulness of the β1-tubulin reporter MK line as a useful tool to study the mechanisms underlying thrombopoiesis and to identify novel inducers of ex vivo platelet production.

Modulation of endocrine nuclear receptor activities by polyaromatic compounds present in fractionated extracts of diesel exhaust particles

Organic pollutants associated with diesel exhaust particles (DEP), such as polycyclic aromatic hydrocarbons (PAHs) and their derivatives, may negatively impact human health. However, a comprehensive overview of their effects on endocrine nuclear receptor activities is still missing. Here, we evaluated the effects of extracts and chromatographic fractions (fractionated according to increasing polarity) of two standard reference materials derived from distinct types of diesel engines (SRM 2975, SRM 1650b), on activation of androgen receptor (AR), estrogen receptor alpha (ERα), peroxisome proliferator-activated receptor γ (PPARγ), glucocorticoid receptor (GR) and thyroid receptor α (TRα), using human cell-based reporter gene assays. Neither DEP standard modulated AR or GR activities. Crude extracts and fractions of SRM 1650b and SRM 2975 suppressed ERα-mediated activity in the ER-CALUX™ assay; however, this effect could be partly linked to their cytotoxicity in this cell line. We observed that only SRM 2975 extract and its fractions were partial PPARγ inducers, while SRM 1650b extract was not active towards this receptor. Importantly, we found that both extracts and polar fractions of SRM activated TRα and significantly potentiated the activity of endogenous TRα ligand, triiodothyronine. Based on a detailed chemical analysis of both extracts and their polar fractions, we identified several oxygenated PAH derivatives, that were present at relatively high levels in the analyzed DEP standards, including 3-nitrobenzanthrone (3-NBA), anthracene-9,10-dione, phenanthrene-9,10-dione, 9H-fluoren-9-one or benzo[a]anthracene-7,12-dione, to activate TRα activity. Nevertheless, these compounds provided only a minor contribution to the overall TRα activity identified in polar fractions. This suggests that yet unidentified polar polyaromatic compounds associated with DEP may, apart from their known impact on the aryl hydrocarbon receptor or steroid signaling, deregulate activities of additional nuclear receptors, in particular of TRα. This illustrates the need to better characterize endocrine disrupting activities of DEP.

The Role of Endocrine and Dioxin-Like Activity of Extracts of Petroleum Substances in Developmental Toxicity as Detected in a Panel of CALUX Reporter Gene Assays

Recent evidence suggests that the interaction of polycyclic aromatic hydrocarbons (PAHs), present in some petroleum substances (PS), with particular nuclear-hormone-receptors and/or the dioxin (aryl hydrocarbon receptor [AhR]) receptor, may play a role in the prenatal developmental toxicity (PDT) induced by these substances. To address this hypothesis, we evaluated the possible endocrine and dioxin-like activity of the dimethylsulfoxide (DMSO)-extracts of 9 PS, varying in PAH content, and 2 gas-to-liquid (GTL) products, containing no PAHs but having similar other properties as PS, using a series of Chemical Activated LUciferase gene eXpression (CALUX) assays. The results show that the extracts of PS tested in this study possess various endocrine and dioxin-like activities and these in vitro potencies are associated with the quantity and type of PAHs they contain. All tested DMSO-extracts of PS show a strong AhR agonist activity and rather weak antiprogesterone, antiandrogen, and estrogenic activities. In the assays that evaluate thyroid-related and antiestrogen activity, only minor effects of specific extracts, particularly those with a substantial amount of 4–5 ring PAHs, ie, sample No. 34, 98, and 99, were observed. None of the GTL extracts interacted with the selected receptors. Of all assays, the AhR agonist activity correlates best (R² = 0.80) with the in vitro PDT of the substances as quantified previously in the embryonic stem cell test, suggesting an important role of the AhR in mediating this effect. Hierarchic clustering of the combined CALUX data clustered the compounds in line with their chemical characteristics, suggesting a PS class-specific effects signature in the various CALUX assays, depending on the PAH profile. To conclude, our findings indicate a high potential for endocrine and dioxin-like activity of some PS extracts which correlates with their in vitro PDT and is driven by the PAHs present in these substances.

Evaluation of mixture effects of endocrine active substances in wastewater using CALUX reporter-gene assays

Endocrine active substances (EAS), which are commonly used in pharmaceuticals and personal care products, are released into surface water mainly through WWTP effluents and have been shown to cause adverse effects in aquatic organisms. In wastewater, a variety of EAS with different hormonal activities is present, which can lead to additive effects or mask an endocrine activity. To investigate hormonal combination effects, with a focus on estrogen and androgen-modulators, influent samples from municipal and hospital wastewater treatmenr plants were spiked with 17α-ethinylestradiol, toremifene, 17α-methyltestosterone and bicalutamide and analyzed using in vitro reporter gene CALUX assays. All wastewaters caused endocrine activities in human cells, which were modified by adding one or several endocrine active substances. As expected, estrogenic activity was reduced in presence of the anti-estrogenic toremifene and androgenic activity decreased with the anti-androgen bicalutamide. In general, substance addition caused a similar trend in altered endocrine activities; however, their intensities differed between the wastewaters. Our results indicate that masking effects, leading to a suppressed biological signal, are of significant importance in the assessment of complex water samples, and combination effects rather than single substances determine the final biological effect. This emphasizes the need of effect-based tools in the assessment of water samples.

The effect of individual and mixtures of mycotoxins and persistent organochloride pesticides on oestrogen receptor transcriptional activation using in vitro reporter gene assays

The mycotoxins zearalenone (ZEN) and alpha-zearalenone (α-ZOL), which are common contaminants of agri-food products, are known for their oestrogenic potential. In addition to mycotoxins, food may also contain pesticides with oestrogenic properties such as 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (p,p'-DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (p,p'-DDE), raising the question on the potential effects of individual and combinations of these xeno-oestrogens on the action of natural oestrogens. The present study employed a mammalian reporter gene assay to assess the effects individual and binary combinations of these environmental and food-borne contaminants on oestrogen nuclear receptor (ER) transactivation. As expected, α-ZOL and ZEN exhibited the strongest oestrogenic potency (EC₅₀: 0.27 ± 0.121 nM and 1.32 ± 0.0956 nM, respectively) whereas p,p'-DDT and p,p'-DDE had weak ER agonistic activity with the maximal response of 28.70 ± 2.97% and 18.65 ± 1.77%, respectively. Concurrent treatment of the mycotoxins and/or pesticides, individually or in binary combination, with 17β-oestradiol (E₂) showed either additive, synergistic or antagonistic interactive effects on E₂-mediated ER response, depending on the combination ratios, the concentration range of xeno-oestrogens, and the concentration of E₂. This study highlights the importance of assessing the mixture effects of chemical contaminants in risk assessment, especially in the area of reproductive and developmental toxicity.

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

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

Screening Estrogen Receptor Modulators in a Paper-Based Breast Cancer Model

The health risks associated with acute and prolonged exposure to estrogen receptor (ER) modulators has led to a concerted effort to identify and prioritize potential disruptors present in the environment. ER agonists and antagonists are identified with end-point assays, quantifying changes in cellular proliferation or gene transactivation in monolayers of estrogen receptor alpha expressing (ER+) cells upon exposure. While these monolayer cultures can be prepared, dosed, and analyzed in a highly parallelized manner, they are unable to predict the potencies of ER modulators in vivo accurately. Physiologically relevant model systems that better predict tissue- or organ-level responses are needed. To address this need, we describe here a screening platform capable of quantitatively assessing ER modulators in 96 chemically isolated 3D cultures. These cultures are supported in wax-patterned paper scaffolds whose design has improved performance and throughput over previously described paper-based setups. To highlight the potential of paper-based cultures for toxicity screens, we measured the potency of known ER modulators with a luciferase-based reporter assay. We also quantified the proliferation and invasion of two ER+ cell lines in the presence of estradiol. Despite the inability of the current setup to better predict in vivo potencies of ER modulators than monolayer cultures, the results demonstrate the potential of this platform to support increasingly complex and physiologically relevant tissue-like structures for environmental chemical risk assessment.

Integrated assessment of persistent toxic substances in sediments from Masan Bay, South Korea: Comparison between 1998 and 2014

Complexity of anthropogenic influences on coastal ecosystems necessitates use of an integrated assessment strategy for effective interpretation and subsequent management. In this study a multiple lines of evidence (LOE) approach for sediment assessment, that combined use of chemistry, toxicity, and benthic community structure in the sediment quality triad was used to assess spatiotemporal changes and potential risks of persistent toxic substances (PTSs) in sediments of Masan Bay highlighting "long-term changes" between 1998 and 2014. Specific target objectives encompassed sedimentary PTSs (PAHs, alkylphenols (APs), and styrene oligomers), potential aryl hydrocarbon receptor (AhR; H4IIE-luc assay)- and estrogen receptor (ER; MVLN assay)-mediated activities, and finally several ecological quality (EcoQ) indices of benthic community structure. Concentrations of target PTSs in Masan Bay sediments were generally less by half in 2014 compared to those measured in 1998. Second, AhR-mediated potencies in sediments also decreased during this time interval, whereas ER-mediated potencies increased (+3790%), indicating that there has been substantial ongoing, input of ER agonists over the past 16 years. Potency balance analysis revealed that only 3% and 22% of the AhR- and ER-mediated potencies could be explained by identified known chemicals, such as PAHs and APs, respectively. This result indicated that non-targeted AhR and ER agonists had a considerable presence in the sediments over time. Third, EcoQ indices tended to reflect PTSs contamination in the region. Finally, ratio-to-mean values obtained from the aforementioned three LOEs indicated that quality of sediments from the outer region of the bay had recovery more during the period of 16-years than did the inner region. Overall, the results showed that even with the progress supported by recent efforts from the Korean governmental pollution control, PTSs remain a threat to local ecosystem, especially in the inner region of Masan Bay.

Stable cellular models of nuclear receptor PXR for high-throughput evaluation of small molecules

Pregnane & Xenobiotic Receptor (PXR) is one of the 48 members of the ligand-modulated transcription factors belonging to nuclear receptor superfamily. Though PXR is now well-established as a 'xenosensor', regulating the central detoxification and drug metabolizing machinery, it has also emerged as a key player in several metabolic disorders. This makes PXR attractive to both, researchers and pharmaceutical industry since clinical success of small drug molecules can be pre-evaluated on PXR platform. At the early stages of drug discovery, cell-based assays are used for high-throughput screening of small molecules. The future success or failure of a drug can be predicted by this approach saving expensive resources and time. In view of this, we have developed human liver cell line-based, dual-level screening and validation protocol on PXR platform having application to assess small molecules. We have generated two different stably transfected cell lines, (i) a stable promoter-reporter cell line (HepXREM) expressing PXR and a commonly used CYP3A4 promoter-reporter i.e. XREM-luciferase; and (ii) two stable cell lines integrated with proximal PXR-promoter-reporter (Hepx-1096/+43 and Hepx-497/+43). Employing HepXREM, Hepx-1096/+43 and Hepx-497/+43 stable cell lines > 25 anti-cancer herbal drug ingredients were screened for examining their modulatory effects on a) PXR transcriptional activity and, b) PXR-promoter activity. In conclusion, the present report provides a convenient and economical, dual-level screening system to facilitate the identification of superior therapeutic small molecules.

Genomic integration and ligand-dependent activation of the human estrogen receptor α in the crustacean Daphnia magna

The freshwater crustacean Daphnia have a long history in water quality assessments and now lend themselves to detection of targeted chemicals using genetically encoded reporter gene due to recent progress in the development of genome editing tools. By introducing human genes into Daphnia, we may be able to detect chemicals that affect the human system, or even apply it to screening potentially useful chemicals. Here, we aimed to develop a transgenic line of Daphnia magna that contains the human estrogen receptor alpha (hERα) and shows a fluorescence response to exposure of estrogens. We designed plasmids to express hERα in Daphnia (EF1α1:esr1) and to report estrogenic activity via red fluorescence (ERE:mcherry) under the control of estrogen response element (ERE). After confirmation of functionality of the plasmids by microinjection into embryos, the two plasmids were joined, a TALE site was added and integrated into the D. magna genome using TALEN. When the resulting transgenic Daphnia named the ES line was exposed to Diethylstilbestrol (DES) or 17β-Estradiol (E2), the ES line could reliably expressed red fluorescence derived from mCherry in a ligand-dependent manner, indicating that an estrogen-responsive line of D. magna was established. This is the first time a human gene was expressed in Daphnia, showcasing potential for further research.

In vitro profiling of toxic effects of prominent environmental lower-chlorinated PCB congeners linked with endocrine disruption and tumor promotion

The mechanisms contributing to toxic effects of airborne lower-chlorinated PCB congeners (LC-PCBs) remain poorly characterized. We evaluated in vitro toxicities of environmental LC-PCBs found in both indoor and outdoor air (PCB 4, 8, 11, 18, 28 and 31), and selected hydroxylated metabolites of PCB 8, 11 and 18, using reporter gene assays, as well as other functional cellular bioassays. We focused on processes linked with endocrine disruption, tumor promotion and/or regulation of transcription factors controlling metabolism of both endogenous compounds and xenobiotics. The tested LC-PCBs were found to be mostly efficient anti-androgenic (within nanomolar - micromolar range) and estrogenic (at micromolar concentrations) compounds, as well as inhibitors of gap junctional intercellular communication (GJIC) at micromolar concentrations. PCB 8, 28 and 31 were found to partially inhibit the aryl hydrocarbon receptor (AhR)-mediated activity. The tested LC-PCBs were also partial constitutive androstane receptor (CAR) and pregnane X receptor (PXR) agonists, with PCB 4, 8 and 18 being the most active compounds. They were inactive towards other nuclear receptors, such as vitamin D receptor, thyroid receptor α, glucocorticoid receptor or peroxisome proliferator-activated receptor γ. We found that only PCB 8 contributed to generation of oxidative stress, while all tested LC-PCBs induced arachidonic acid release (albeit without further modulations of arachidonic acid metabolism) in human lung epithelial cells. Importantly, estrogenic effects of hydroxylated (OH-PCB) metabolites of LC-PCBs (4-OH-PCB 8, 4-OH-PCB 11 and 4'-OH-PCB 18) were higher than those of the parent PCBs, while their other toxic effects were only slightly altered or suppressed. This suggested that metabolism may alter toxicity profiles of LC-PCBs in a receptor-specific manner. In summary, anti-androgenic and estrogenic activities, acute inhibition of GJIC and suppression of the AhR-mediated activity were found to be the most relevant modes of action of airborne LC-PCBs, although they partially affected also additional cellular targets.

Atropisomers of 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) exhibit stereoselective effects on activation of nuclear receptors in vitro

PCB 136 is an environmentally relevant chiral PCB congener, which has been found in vivo to be present in form of rotational isomers (atropisomers). Its atropselective biotransformation or neurotoxic effects linked with sensitization of ryanodine receptor suggest that it might interact also with other intracellular receptors in a stereospecific manner. However, possible atropselective effects of PCB 136 on nuclear receptor transactivation remain unknown. Therefore, in this study, atropselective effects of PCB 136 on nuclear receptors controlling endocrine signaling and/or expression of xenobiotic and steroid hormone catabolism were investigated. PCB136 atropisomers were found to exert differential effects on estrogen receptor (ER) activation; (+)-PCB 136 was estrogenic, while (-)-PCB 136 was antiestrogenic. In contrast, inhibition of androgen receptor (AR) activity was not stereospecific. Both PCB136 stereoisomers induced the constitutive androgen receptor (CAR)-dependent gene expression; however, no significant stereospecificity of PCB 136 atropisomers was observed. PCB136 was a partial inducer of the pregnane X receptor (PXR)-dependent gene expression. Here, (-)-PCB 136 was a significantly more potent inducer of PXR activity than (+)-PCB 136. Taken together, the present results indicate that at least two nuclear receptors participating in endocrine regulation or metabolism, ER and PXR, could be regulated in an atropselective manner by chiral PCB 136. The enantioselective enrichment of PCB atropisomers in animal and human tissues may thus have significant consequences for endocrine-disrupting effects of chiral ortho-substituted PCB congeners.

Effect-directed analysis (EDA) of Danube River water sample receiving untreated municipal wastewater from Novi Sad, Serbia

The release of a multitude of pollutants from untreated municipal wastewater (UMWW) to surface waters may have adverse effects on aquatic wildlife including endocrine disruption. For effect-directed analysis (EDA), a Danube river water sample downstream of emission of UMWW in Novi Sad, Serbia was extracted on-site and after processing in the lab was subjected to reporter gene assays which revealed pronounced estrogenic (ERα), androgenic (AR) and oxidative stress response (OSR). The sample was fractionated with reversed-phase high performance liquid chromatography (RP-HPLC) collecting thirty fractions at two-minute intervals. Biological analysis identified 5 ERα- and 3 AR-active fractions while none of the fractions showed considerable activity with regards to OSR. It appeared that OSR of parent sample (PS) distributed over all fractions. Chemical analysis of active fractions by LC-MS/MS and LC-HRMS/MS found female reproductive hormones (estrone (E1), estradiol (E2), estriol (E3)) as cause of ERα activity while male reproductive hormones (testosterone, dihydrotestosterone (DHT)) and gestagens (progesterone and medroxyprogesterone) were active in the AR bioassay. Designed chemical mixtures in concentration ratios detected in the active fractions were tested with the bioassays. The identified chemicals quantitatively explained the observed bioactivity with no substantial contribution attributable to xenobiotics. In terms of bioanalytical equivalent concentrations (BEQs), detected chemicals explained 5-159% of ERα-active fraction's biological effect and 31-147% for AR-active fractions. Estradiol and dihydrotestosterone were the compounds dominating the most of the effect in this study. In summary, androgenic compounds were found to be as potent as estrogenic compounds while OSR was found to be the cumulative effect of the mixture of many compounds present in the sample rather than the mixture effect dominated by individual chemicals. The obtained results stress the importance of wastewater treatment plant (WWTP) to minimize the pollutant load from UMWW in order to reduce the risk of endocrine disruption to the aquatic life as well as to improve the status of receiving freshwater ecosystem.

Validation of Arxula Yeast Estrogen Screen assay for detection of estrogenic activity in water samples: Results of an international interlaboratory study

Endocrine-active substances can adversely impact the aquatic ecosystems. A special emphasis is laid, among others, on the effects of estrogens and estrogen mimicking compounds. Effect-based screening methods like in vitro bioassays are suitable tools to detect and quantify endocrine activities of known and unknown mixtures. This study describes the validation of the Arxula-Yeast Estrogen Screen (A-YES®) assay, an effect-based method for the detection of the estrogenic potential of water and waste water. This reporter gene assay, provided in ready to use format, is based on the activation of the human estrogen receptor alpha. The user-friendly A-YES® enables inexperienced operators to rapidly become competent with the assay. Fourteen laboratories from four countries with different training levels analyzed 17β-estradiol equivalent concentrations (EEQ) in spiked and unspiked waste water effluent and surface water samples, in waste water influent and spiked salt water samples and in a mixture of three bisphenols. The limit of detection (LOD) for untreated samples was 1.8ng/L 17β-estradiol (E2). Relative repeatability and reproducibility standard deviation for samples with EEQ above the LOD (mean EEQ values between 6.3 and 20.4ng/L) ranged from 7.5 to 21.4% and 16.6 to 28.0%, respectively. Precision results are comparable to other frequently used analytical methods for estrogens. The A-YES® has been demonstrated to be an accurate, precise and robust bioassay. The results have been included in the ISO draft standard. The assay was shown to be applicable for testing of typical waste water influent, effluent and saline water. Other studies have shown that the assay can be used with enriched samples, which lower the LOD to the pg/L range. The validation of the A-YES® and the development of a corresponding international standard constitute a step further towards harmonized and reliable bioassays for the effect-based analysis of estrogens and estrogen-like compounds in water samples.

Biosensing estrogenic endocrine disruptors in human blood and urine: A RAPID cell-free protein synthesis approach

Many diseases and disorders are linked to exposure to endocrine disrupting chemicals (EDCs) that mimic the function of natural estrogen hormones. Here we present a Rapid Adaptable Portable In-vitro Detection biosensor platform (RAPID) for detecting chemicals that interact with the human estrogen receptor β (hERβ). This biosensor consists of an allosteric fusion protein, which is expressed using cell-free protein synthesis technology and is directly assayed by a colorimetric response. The resultant biosensor successfully detected known EDCs of hERβ (BPA, E2, and DPN) at similar or better detection range than an analogous cell-based biosensor, but in a fraction of time. We also engineered cell-free protein synthesis reactions with RNAse inhibitors to increase production yields in the presence of human blood and urine. The RAPID biosensor successfully detects EDCs in these human samples in the presence of RNAse inhibitors. Engineered cell-free protein synthesis facilitates the use of protein biosensors in complex sample matrices without cumbersome protein purification.

In vitro assessment of sex steroids and related compounds in water and sediments - a critical review

Detection of endocrine disrupting compounds in water and sediment samples has gained much importance since the evidence of their effects was reported in aquatic ecosystems in the 1990s. The aim of this review is to highlight the advances made in the field of in vitro analysis for the detection of hormonally active compounds with estrogenic, androgenic and progestogenic effects in water and sediment samples. In vitro assays have been developed from yeast, mammalian and in a few cases from fish cells. These assays are based either on the hormone-mediated proliferation of sensitive cell lines or on the hormone-mediated expression of reporter genes. In vitro assays in combination with various sample enrichment methods have been used with limits of detection as low as 0.0027 ng L^-1 in water, and 0.0026 ng g^-1 in sediments for estrogenicity, 0.1 ng L^-1 in water, and 0.5 ng g^-1 in sediments for androgenicity, and 5 ng L^-1 in water for progestogenicity expressed as equivalent concentrations of standard reference compounds of 17β-estradiol, dihydrotestosterone and progesterone, respectively. The experimental results and limits of quantification, however, are influenced by the methods of sample collection, preparation, and individual laboratory practices.