Issues arising when interpreting results from an in vitro assay for estrogenic activity

Interferences in the yeast estrogen screen (YES) assay for evaluation of estrogenicity in environmental samples, chemical mixtures, and individual substances

The Yeast Estrogen Screen (YES) has a specific mechanism of action that allows for the analysis of estrogenic EDC at low concentrations, and it has been broadly used to estimate the estrogenic potential of environmental samples. However, the experimental parameters of this assay still demand an investigation, such as cell density, incubation time, wavelength on the experimental outcome, cytotoxicity, and estrogenic activity adsorbed on suspended solids. We studied these interferences and applied the assay to single substances, mixtures, and environmental matrices from different sources. The increase in cell density amplifies the assay sensitivity only to a limited extent, while the reduction in incubation time decreased assay sensitivity - although it was not significant for surface water, no differences were observed between estradiol-equivalents derived of 48 h and 72 h measurements. The particulate phase was of utmost importance for the total estrogenic activity of the landfill leachate and surface water. Surface waters, landfill leachates and sediments also showed antiestrogenic activity and the integration of both estrogenic and antiestrogenic endpoints provided deeper insights into the potential risk associated with EDC. This study elucidated experimental interferences that may arise during the implementation and use of this assay, bringing more understanding to experimental parameters during the application of the assay for estrogenicity screening.

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)).

Yeast-Based Fluorescent Sensors for the Simultaneous Detection of Estrogenic and Androgenic Compounds, Coupled with High-Performance Thin Layer Chromatography

The persistence of endocrine disrupting compounds (EDCs) throughout wastewater treatment processes poses a significant health threat to humans and to the environment. The analysis of EDCs in wastewater remains a challenge for several reasons, including (a) the multitude of bioactive but partially unknown compounds, (b) the complexity of the wastewater matrix, and (c) the required analytical sensitivity. By coupling biological assays with high-performance thin-layer chromatography (HPTLC), different samples can be screened simultaneously, highlighting their active components; these may then be identified by chemical analysis. To allow the multiparallel detection of diverse endocrine disruption activities, we have constructed Saccharomyces cerevisiae-based bioreporter strains, responding to compounds with either estrogenic or androgenic activity, by the expression of green (EGFP), red (mRuby), or blue (mTagBFP2) fluorescent proteins. We demonstrate the analytical potential inherent in combining chromatographic compound separation with a direct fluorescent signal detection of EDC activities. The applicability of the system is further demonstrated by separating influent samples of wastewater treatment plants, and simultaneously quantifying estrogenic and androgenic activities of their components. The combination of a chemical separation technique with an optical yeast-based bioassay presents a potentially valuable addition to our arsenal of environmental pollution monitoring tools.

Estrogenic activity of food contact materials-evaluation of 20 chemicals using a yeast estrogen screen on HPTLC or 96-well plates

Food contact materials (FCM) may contain complex mixtures of estrogenic chemicals. A yeast estrogen screen performed on high performance thin-layer chromatography plates (planar-YES, P-YES) is promising for analysis of such mixtures, as it could allow for better elucidation of effects compared with established methods in microtiter plates. However, the P-YES has not been directly compared with established methods. We compared the performance of a microtiter plate YES (lyticase-YES, L-YES) to P-YES on silica gel HPTLC plates using 17β-estradiol (E2), 20 chemicals representative of migrants from plastic FCM, and three migrates of coated metal food cans. Effective doses (ED10, ED50) and estradiol equivalencies were calculated for each chemical. Thirteen chemicals had calculable EDs in the L-YES or P-YES, with average EDs 13-fold (range 0.63-36) more potent in P-YES than in the L-YES. Normalized to E2, the median estrogenicity was within 1.5-fold (0.43-8.8) between the assays. Therefore, P-YES was as or more sensitive than L-YES but potencies relative to E2 were comparable between assays. With chromatography, the P-YES detected estrogenicity in coated metal cans, effects that were unmeasurable in L-YES. With the sample preparation methods used in this study, both YES assays are sufficiently sensitive to detect bisphenol A below the specific migration limit for plastic packaging (0.05 mg/kg food). This study demonstrates that P-YES outperforms L-YES because it is more sensitive, provides comparable estradiol equivalents, and circumvents confounding mixture effects. The P-YES will be useful for routine monitoring of FCM and toxicant identification in problematic materials. Graphical abstract.

Time-Resolved Freely Dissolved Concentrations of Semivolatile and Hydrophobic Test Chemicals in In Vitro Assays-Measuring High Losses and Crossover by Headspace Solid-Phase Microextraction

In vitro assays are normally conducted in plastic multiwell plates open to exchange with the ambient air. The concentration of test substances freely available to cells is often not known, can change over time, and is difficult to measure in the small volumes in microplates. However, even a well-characterized toxicological response is of limited value if it cannot be linked to a well-defined exposure level. The aim of this study was to develop and apply an approach for determining time-resolved freely dissolved concentrations of semivolatile and hydrophobic organic chemicals (SVHOCs) in in vitro assays: (1) free fractions were measured by a new medium dilution method and (2) time-resolved loss curves were obtained by measurements of total concentrations in 96-well plates during incubations at 37 °C. Headspace solid-phase microextraction was used as an analytical technique for 24 model chemicals spanning 6 chemical groups and 4-5 orders of magnitude in K_ow and K_aw. Free fractions were >30% for chemicals with log K_ow < 3.5 and then decreased with increasing log K_ow. Medium concentrations declined significantly (>50%) within 24 h of incubation for all 20 chemicals having log K_ow > 4 or log K_aw > -3.5 in serum-free medium. Losses of chemicals were lower for medium containing 10% fetal bovine serum, most significantly for chemicals with log K_ow > 4. High crossover to neighboring wells also was observed below log K_ow of 4 and log K_aw of -3.5. Sealing the well plates had limited effect on the losses but clearly reduced crossover. The high losses and crossover of most tested chemicals question the suitability of multiwell plates for in vitro testing of SVHOCs and call for (1) test systems that minimize losses, (2) methods to control in vitro exposure, (3) analytical confirmation of exposure, and (4) exposure control and confirmation being included in good in vitro reporting standards.

Combination of yeast-based in vitro screens with high-performance thin-layer chromatography as a novel tool for the detection of hormonal and dioxin-like compounds

The combination of classic in vitro bioassays with high-performance thin-layer chromatography (HPTLC) is a promising technique to directly link chemical analysis of contaminants to their potential adverse biological effects. With respect to endocrine disruption, much work is focused on estrogenicity. While a direct combination of HPTLC and the yeast estrogen screen is already developed, it is well accepted that further endocrine effects are relevant for monitoring environmental wellbeing. Here we show that non-estrogenic specific biological endpoints, (partly) related to the endocrine system, can also be addressed by combining respective yeast reporter gene assays with HPTLC to support effect-directed analysis (EDA). These are: androgenicity (YAS), thyroidogenicity (YTS), dioxin-like effects (YDS), effects on the vitamin D (YVS) and the retinoic acid receptor (YRaS). A proof of principle is demonstrated within this study by the characterization of dose-dependent responses to different model compounds for the respective receptors with and without chromatographic development of the HPTLC-plate. Limits of quantification (LOQ) for several model compounds were determined, e.g. 37 pg for testosterone (p-YAS), 0.476 ng for β-naphthoflavone (p-YDS) and 1.02 ng for calcipotriol hydrate (p-YVS) with chromatographic development. The LOQ for p-YTS and p-YRaS were 10.16 pg for 3,3',5-triiodothyroacetic acid (p-YTS) and 0.41 pg for tamibarotene (p-YRaS), without chromatographic separation. Furthermore, we challenged the developed methodology using environmental samples, demonstrating an elimination efficiency of androgenic activity from municipal wastewater by a wastewater treatment plant between 99.4 and 100%. We anticipate our methodology to substantially broaden the spectrum of specific endpoints combined with HPTLC for an efficient and robust screening of environmental samples to guide a subsequent in-depth EDA.

Estrogenic activity of cylindrospermopsin and anatoxin-a and their oxidative products by FeIII-B*/H2O2

The cyanotoxins released into waters during cyanobacterial blooms can pose serious hazards to humans and animals. Apart from their toxicological mechanisms, cyanotoxins have been shown to be involved in estrogenic activity by in vivo and in vitro assays; however, there is limited information on the change in estrogenicity of cyanotoxins following chemical oxidation. In this study, the estrogenic activity of cylindrospermopsin (CYL) and anatoxin-a (ANA) at concentrations ranging from 2.4 × 10^-7 M to 2.4 × 10^-12 M (CYL) and 7.1 × 10^-6 M to 7.1 × 10^-11 M (ANA), and after treatment by the Fe^III-B*/H₂O₂ catalyst system, was investigated by the yeast estrogen screen (YES) assay. The results indicate that CYL and ANA acted as agonists in the YES assay (CYL logEC₅₀ = -8.901; ANA logEC₅₀ = -6.789), their binding affinity to estrogen receptors is associated with their intrinsic properties, including ring structures and toxicant properties. CYL and ANA were shown to simulate endocrine disrupting chemicals (EDCs) to modulate the 17β-estradiol-induced estrogenic activity, resulting in non-monotonic dose responses. The treated CYL showed a significantly altered estrogenicity compared to the untreated CYL (T₍₂₎ = 8.168, p ≤ .05), while the estrogenicity of the treated ANA was not significantly different to the untreated ANA (T₍₂₎ = 1.295, p > .05). Intermediate products generated from CYL and ANA oxidized by Fe^III-B*/H₂O₂ were identified using Q-Exactive Tandem Mass Spectrometry (LC-MS/MS). Treatment with Fe^III-B*/H₂O₂ yielded open-ring by-products which likely resulted in CYL's reduced binding affinity to estrogen receptors. The insignificant change in the estrogenicity of treated ANA was possibly a result of its multiple ring structure products, which were likely able to bind to estrogen receptors. The comparisons for the estrogenicity of these cyanotoxins before and after Fe^III-B*/H₂O₂ treatment suggest that the reductions in estrogenicity achieved by oxidation were dependent on the levels of cyanotoxins removed, as well as the estrogenicity of the degradation products. This is the first study on the change in the estrogenicity of CYL and ANA upon oxidation by Fe^III-B*/H₂O₂, a high activity catalyst system.

Investigating the androgenic activity of ozonation transformation products of testosterone and androstenedione

This study investigates the impact of ozonation on the concentration of two androgen steroid hormones, testosterone and androstenedione, and on androgenic activity as measured using the YAS assay. While these compounds are remarkably similar in chemical structure and showed comparable removal profiles in the presence and absence of a hydroxyl scavenger (isopropanol), large differences between percent removal of target compounds using chemical analysis and percent removal of bioactivity was observed when small ozone doses were applied. The dynamic change and initial increase in bioactivity during ozonation can be attributed to transformation products. These results demonstrate the importance of combining chemical analysis and bioanalytical techniques not only to perform a comprehensive assessment of environmental risks but also as a tool to optimize treatment technologies proposed as a mean to mitigate the impact of contaminants of emerging concern.

Investigation of the presence and endocrine activities of pesticides found in wastewater effluent using yeast-based bioassays

This study investigated the presence of a variety of pesticides (herbicides, fungicides, and insecticides) in effluent of three wastewater treatment plants as well as their endocrine activities using yeast-based in vitro assays. Although the presence of these contaminants of emerging concern is frequently reported to be present throughout the environment, their presence in wastewater treatment plants has been seldom studied. Of the 18 compounds investigated in this study, imidacloprid was the only compound not detected in all three WWTPs. Concentrations measured ranged from 3ng/L to 27μg/L for fluconazole. The yeast estrogenic and yeast androgenic screen assays were performed on target compounds in order to investigate their endocrine disruption and potential environmental risks to receiving waters. It was found that of the 14 compounds investigated 12 showed either antiestrogenic or antiandrogenic activity and seven compounds showed pleiotropic effects. In addition to confirming endocrine activities of pesticides using the yeast-based assays this study is one of the first to report activities for novel compounds including three neonicotinoids.

Avoiding False Positives and Optimizing Identification of True Negatives in Estrogen Receptor Binding and Agonist/Antagonist Assays

The potential for chemicals to affect endocrine signaling is commonly evaluated via in vitro receptor binding and gene activation, but these assays, especially antagonism assays, have potential artifacts that must be addressed for accurate interpretation. Results are presented from screening 94 chemicals from 54 chemical groups for estrogen receptor (ER) activation in a competitive rainbow trout ER (rtER) binding assay and a trout liver slice vitellogenin mRNA expression assay. Results from true competitive agonists and antagonists, and inactive chemicals with little or no indication of ER binding or gene activation were easily interpreted. However, results for numerous industrial chemicals were more challenging to interpret, including chemicals with: (1) apparent competitive binding curves but no gene activation, (2) apparent binding and gene inhibition with evidence of either cytotoxicity or changes in assay media pH, (3) apparent binding but non-competitive gene inhibition of unknown cause, or (4) no rtER binding and gene inhibition not due to competitive ER interaction but due to toxicity, pH change, or some unknown cause. The use of endpoints such as toxicity, pH, precipitate formation, and determination of inhibitor dissociation constants (Ki) for interpreting the results of antagonism and binding assays for diverse chemicals is presented. Of the 94 chemicals tested for antagonism only two, tamoxifen and ICI-182780, were found to be true competitive antagonists. This report highlights the use of two different concentrations of estradiol tested in combination with graded concentrations of test chemical to provide the confirmatory evidence to distinguish true competitive antagonism from apparent antagonism.

Quantifying Hormone Disruptors with an Engineered Bacterial Biosensor

Endocrine disrupting compounds are found in increasing amounts in our environment, originating from pesticides, plasticizers, and pharmaceuticals, among other sources. Although the full impact of these compounds is still under study, they have already been implicated in diseases such as obesity, diabetes, and cancer. The list of chemicals that disrupt normal hormone function is growing at an alarming rate, making it crucially important to find sources of contamination and identify new compounds that display this ability. However, there is currently no broad-spectrum, rapid test for these compounds, as they are difficult to monitor because of their high potency and chemical dissimilarity. To address this, we have developed a new detection strategy for endocrine disrupting compounds that is both fast and portable, and it requires no specialized skills to perform. This system is based on a native estrogen receptor construct expressed on the surface of Escherichia coli, which enables both the detection of many detrimental compounds and signal amplification from impedance measurements due to the binding of bacteria to a modified electrode. With this approach, sub-ppb levels of estradiol and ppm levels of bisphenol A are detected in complex solutions. Rather than responding to individual components, this system reports the total estrogenic activity of a sample using the most relevant biological receptor. As an applied example, estrogenic chemicals released from a plastic baby bottle following microwave heating were detectable with this technique. This approach should be broadly applicable to the detection of chemically diverse classes of compounds that bind to a single receptor.

Hormonal activity, cytotoxicity and developmental toxicity of UV filters

Ultraviolet (UV) filters are commonly used compounds in personal care products and polymer based materials, as they can absorb solar energy in the UVA and UVB spectrum. However, they are able to bind to hormone receptors and have several and different types of hormonal activities determined by in vitro assays. One of the aims of this work was to measure the hormonal and cytotoxic activities of four frequently used UV filters using bioluminescence based yeast test organisms. Using Saccharomyces cerevisiae BLYES and BLYAS strains allowed the rapid and reliable detection of agonist and antagonist hormonal activities, whereas BLYR strain served to measure cytotoxicity. Results confirmed that all tested UV filters show multiple hormonal activities. Cytotoxicity is detected only in the case of benzophenone-3. Research data on the toxic effects of benzophenone-3, especially on aquatic organisms are scarce, so further investigations were carried out regarding its cytotoxic and teratogenic effects on bacteria and zebrafish (Danio rerio) embryos, respectively. Results revealed the cytotoxicity of benzophenone-3 not only to yeasts but to bacteria, as well as its ability to influence zebrafish embryo hatching and development.

High-Content and Semi-Automated Quantification of Responses to Estrogenic Chemicals Using a Novel Translucent Transgenic Zebrafish

Rapid embryogenesis, together with genetic similarities with mammals, and the desire to reduce mammalian testing, are major incentives for using the zebrafish model in chemical screening and testing. Transgenic zebrafish, engineered for identifying target gene expression through expression of fluorophores, have considerable potential for both high-content and high-throughput testing of chemicals for endocrine activity. Here we generated an estrogen responsive transgenic zebrafish model in a pigment-free "Casper" phenotype, facilitating identification of target tissues and quantification of these responses in whole intact fish. Using the ERE-GFP-Casper model we show chemical type and concentration dependence for green fluorescent protein (GFP) induction and both spatial and temporal responses for different environmental estrogens tested. We also developed a semiautomated (ArrayScan) imaging and image analysis system that we applied to quantify whole body fluorescence responses for a range of different estrogenic chemicals in the new transgenic zebrafish model. The zebrafish model developed provides a sensitive and highly integrative system for identifying estrogenic chemicals, their target tissues and effect concentrations for exposures in real time and across different life stages. It thus has application for chemical screening to better direct health effects analysis of environmental estrogens and for investigating the functional roles of estrogens in vertebrates.

Determination of estrogenic activity in the river Chienti (Marche Region, Italy) by using in vivo and in vitro bioassays

Environmental estrogen-like compounds (i.e. xenoestrogens) are a variety of pollutants, ranging from synthetic to natural occurring molecules, that are found in surface and waste waters over a wide range of concentrations. In aquatic environment, the overall estrogenic activity is often due to the presence of a mixture of chemicals and their degraded products which can induce synergistic effects. Current strategies for monitoring estrogen-like chemicals are based on the use of a battery of in vivo and in vitro ecotoxicological tests. In this regard, the aim of the present work was to carry out a bio-monitoring study for testing estrogenicity of the Chienti river (Marche Region, Italy) by using both an E-screen and a vitellogenin (Vtg) induction assay in juvenile goldfish. Three sites were used for analysis, localized at the mouth (sampling point 1), in the middle (sampling point 2) and at the origin (sampling point 3) of Chienti river. For most of the water samples (i.e. samples collected at sampling points 2 and 3), clear estrogenic activity was detected in the E-screen assay suggesting different proliferation activities in function of the collecting site. In contrast, the Vtg ELISA demonstrated that water samples collected from each sampling point were estrogenic. Overall, we showed for the first time that the estrogenic activities in water samples from the Chienti river were significant in both in vivo and in vitro; we also observed a different sensitivity between bioassays.

Chemical and biological assessment of endocrine disrupting chemicals in a full scale dairy manure anaerobic digester with thermal pretreatment

Concentrated animal feeding operations are important sources of estrogens and their conjugates, which are introduced into the environment through manure land application. In this study, concentrations of estrogens were measured in an anaerobic co-digestion system with thermal pasteurization pretreatment. Free estrogens (estrone (E1), 17α-estradiol (E2α), 17β-estradiol (E2β), estriol (E3)) were analyzed by gas chromatography with mass spectrometry (GC/MS), and conjugated estrogens (sulfate- and glucuronide-conjugates) were analyzed by liquid chromatography with tandem mass spectrometry (LC/MS/MS). Additionally, yeast estrogen screen assay was used to determine the estrogenic potential of the manure. The total hormone concentrations (mainly E1, E2α, E2β, and sulfated estrogens) were observed at concentrations up to a total of 7100ng/L in the liquid fraction, while free estrogen levels were 630ng/kg in the solid fraction of the untreated manure. The total hormone concentration did not decrease significantly during digestion, however, the relative composition of the estrogens changed from E2α (65%) being the predominant species before digestion to mostly E1 (72%) after digestion. This conversion process has important implications because E1 is more estrogenic than E2α. Total E2 equivalents associated with E1, E2α and E2β concentrations as determined by GC/MS indicate that E1 is the most important contributor to the endocrine-disruption activity of the treated manure.

A Workflow to Investigate Exposure and Pharmacokinetic Influences on High-Throughput in Vitro Chemical Screening Based on Adverse Outcome Pathways

BACKGROUND

Adverse outcome pathways (AOPs) link adverse effects in individuals or populations to a molecular initiating event (MIE) that can be quantified using in vitro methods. Practical application of AOPs in chemical-specific risk assessment requires incorporation of knowledge on exposure, along with absorption, distribution, metabolism, and excretion (ADME) properties of chemicals.

OBJECTIVES

We developed a conceptual workflow to examine exposure and ADME properties in relation to an MIE. The utility of this workflow was evaluated using a previously established AOP, acetylcholinesterase (AChE) inhibition.

METHODS

Thirty chemicals found to inhibit human AChE in the ToxCast™ assay were examined with respect to their exposure, absorption potential, and ability to cross the blood-brain barrier (BBB). Structures of active chemicals were compared against structures of 1,029 inactive chemicals to detect possible parent compounds that might have active metabolites.

RESULTS

Application of the workflow screened 10 "low-priority" chemicals of 30 active chemicals. Fifty-two of the 1,029 inactive chemicals exhibited a similarity threshold of ≥ 75% with their nearest active neighbors. Of these 52 compounds, 30 were excluded due to poor absorption or distribution. The remaining 22 compounds may inhibit AChE in vivo either directly or as a result of metabolic activation.

CONCLUSIONS

The incorporation of exposure and ADME properties into the conceptual workflow eliminated 10 "low-priority" chemicals that may otherwise have undergone additional, resource-consuming analyses. Our workflow also increased confidence in interpretation of in vitro results by identifying possible "false negatives."

CITATION

Phillips MB, Leonard JA, Grulke CM, Chang DT, Edwards SW, Brooks R, Goldsmith MR, El-Masri H, Tan YM. 2016. A workflow to investigate exposure and pharmacokinetic influences on high-throughput in vitro chemical screening based on adverse outcome pathways. Environ Health Perspect 124:53-60; http://dx.doi.org/10.1289/ehp.1409450.

Screening breeding sites of the common toad (Bufo bufo) in England and Wales for evidence of endocrine disrupting activity

Anuran amphibians are often present in agricultural landscapes and may therefore be exposed to chemicals in surface waters used for breeding. We used passive accumulation devices (SPMD and POCIS) to sample contaminants from nine breeding sites of the Common toad (Bufo bufo) across England and Wales, measuring endocrine activity of the extracts in a recombinant yeast androgen screen (YAS) and yeast estrogen screen (YES) and an in vitro vitellogenin induction screen in primary culture of Xenopus laevis hepatocytes. We also assessed hatching, growth, survival, and development in caged larvae in situ, and sampled metamorphs for gonadal histopathology. None of the SPMD extracts exhibited estrogen receptor or androgen receptor agonist activity, while POCIS extracts from two sites in west-central England exhibited concentration-dependent androgenic activity in the YAS. Three sites exhibited significant estrogenic activity in both the YES and the Xenopus hepatocyte. Hatching rates varied widely among sites, but there was no consistent correlation between hatching rate and intensity of agricultural activity, predicted concentrations of agrochemicals, or endocrine activity measured in YES/YAS assays. While a small number of intersex individuals were observed, their incidence could not be associated with predicted pesticide exposure or endocrine activitity measured in the in vitro screens. There were no significant differences in sex ratio, as determined by gonadal histomorphology among the study sites, and no significant correlation was observed between proportion of males and predicted exposure to agrochemicals. However, a negative correlation did become apparent in later sampling periods between proportion of males and estrogenic activity of the POCIS sample, as measured in the YES. Our results suggest that larval and adult amphibians may be exposed to endocrine disrupting chemicals in breeding ponds, albeit at low concentrations, and that chemical contaminants other than plant protection products may contribute to endocrine activity of surface waters in the agricultural landscape.

In vitro and in vivo studies of the endocrine disrupting potency of cadmium in roach (Rutilus rutilus) liver

Cadmium has been reported to exert estrogenic, antiestrogenic or both effects in vertebrate species. To elucidate the endocrine disrupting action of CdCl2, ex vivo and in vivo experiments were performed in roach (Rutilus rutilus). Roach liver explants were exposed to a range of CdCl2 concentrations alone (0.1-50μM) or with an effective concentration (100nM) of 17β-estradiol (E2). In addition, juvenile roach were intraperitoneally injected with CdCl2 (0.1-2.5mg/kg) with or without 1mg E2/kg. Subsequent analysis evaluated the effect of CdCl2 on vitellogenin (VTG) synthesis both at the mRNA and protein level, on estrogen receptors (erα and erβ1) and on androgen receptor (ar) mRNA expression. Ex vivo and in vivo experiments indicated that CdCl2 is strongly anti-estrogenic as, when co-exposed to E2, CdCl2 significantly inhibited VTG production as well as vtg and erα mRNA expressions. Moreover, CdCl2 compromised the E2-mediated induction of the ar mRNA expression in vivo.

Synthesis and characterization of 14C-labelled sulfate conjugates of steroid oestrogens

Steroid oestrogens are typical endocrine-disrupting compounds in the environment and are excreted from the human and animals mainly as conjugates, including sulfate and glucuronide salts. The oestrogen conjugates are largely biologically inactive, but they can be de-conjugated and release free oestrogens, which usually exhibit strong oestrogenicity. Therefore, it is important to study the fate of oestrogen conjugates in the environment. However, because of the complexity of environmental matrixes, time-consuming pre-treatments of samples are usually required to reduce the interference of the matrixes. (14)C radioisotope can trace target substances and their degradation products at low concentrations in complex environmental samples and is therefore essential in such studies. We synthesized three oestrogen sulfates with (14)C-labelling at the ring, i.e. [3-(14)C]-estrone-3-sulfate ammonium salt, [3-(14)C]-17β-estradiol-17-sulfate ammonium salt, and [3-(14)C]-17β-estradiol-3,17-disulfate diammonium salt with radiochemical purities of >98% by sulfation of [3-(14)C]-labelled estrone and 17β-estradiol in dry pyridine with SO3 -triethylamine at room temperature or 90-95 °C, followed by hydrolysis with KOH-methanol solution and purification by preparative thin-layer chromatography on silica gel using an ammonia-containing eluent. The products were characterized by mass spectrometry and (13)C and (1)H nuclear magnetic resonance spectroscopy, using their corresponding non-labelled compounds. The (14)C-labelled oestrogen conjugates provide possibilities for studying their fate in soil and sediment environments as well as in the animal manure.

Principles of sound ecotoxicology

We have become progressively more concerned about the quality of some published ecotoxicology research. Others have also expressed concern. It is not uncommon for basic, but extremely important, factors to apparently be ignored. For example, exposure concentrations in laboratory experiments are sometimes not measured, and hence there is no evidence that the test organisms were actually exposed to the test substance, let alone at the stated concentrations. To try to improve the quality of ecotoxicology research, we suggest 12 basic principles that should be considered, not at the point of publication of the results, but during the experimental design. These principles range from carefully considering essential aspects of experimental design through to accurately defining the exposure, as well as unbiased analysis and reporting of the results. Although not all principles will apply to all studies, we offer these principles in the hope that they will improve the quality of the science that is available to regulators. Science is an evidence-based discipline and it is important that we and the regulators can trust the evidence presented to us. Significant resources often have to be devoted to refuting the results of poor research when those resources could be utilized more effectively.

Effects of ethinylestradiol and of an environmentally relevant mixture of xenoestrogens on steroidogenic gene expression and specific transcription factors in zebrafish

In natural environments fish are exposed to endocrine disrupting compounds (EDCs) present at low concentrations and with different modes of actions. Here, adult zebrafish of both sexes were exposed for 21 days to an estrogenic mixture (Mix) of eleven EDCs previously quantified in Douro River estuary (Portugal) and to 100 ng/L 17α-ethinylestradiol (EE2) as positive control. Vitellogenin mRNA and HSI in males confirmed both exposure regimes as physiologically active. Potential candidates for estrogenic disturbance of steroidogenesis were identified (StAR, 17β-HSD1, cyp19a1), but Mix only affected cyp19a1 in females. Significant differences in the response of FSHβ, cypa19a2, 20β-HSD were observed between EE2 and Mix. Mtf-1 and tfap2c transcription factor binding sites were discovered in the putative promoter regions and corresponding transcription factors were found to be differentially expressed in response to Mix and EE2. The results suggest that "non-classical effects" of estrogenic EDC in fish are mediated via transcription factors.

PCR-ELISA detection of estrogen receptor β mRNA expression and plasma vitellogenin induction in juvenile sole (Solea solea) exposed to waterborne 4-nonylphenol

In this study, the effect of 4-nonylphenol (4NP) on reproductive axis of sole (Solea solea) has been investigated by using selected biomarkers of estrogenic effects: vitellogenin (VTG) and estrogen receptor β (ERβ) mRNA. Furthermore, an enzyme linked immunosorbent assay (ELISA) detection system of reverse transcriptase-polymerase chain reaction (RT-PCR) products for the analysis of sole ERβ mRNA expression was developed and validated. The proposed method allows large-scale analyses of different mRNAs in fast and not expensive way. Our results have demonstrated that the PCR-ELISA method developed shows high sensitivity, good reproducibility and also the potential for semi-quantitative analysis of hepatic ERβ mRNAs. Both plasma VTG level and ERβ mRNA expression were increased in tested animals following a short exposure to environmental relevant concentrations (10(-6)M) of 4NP, confirming the functional role of ERβ in the regulation of xenoestrogens-induced production of VTG. The methodology provided in the present study together with the preliminary results on the hepatic expression of ERβ may be useful in environmental xenoestrogens monitoring studies, using flatfish as "sentinel" species.

Lignans as food constituents with estrogen and antiestrogen activity

Phytoestrogens are plant-derived food ingredients assumed to contribute to the prevention of hormone-dependent cancers, osteoporosis, cardiovascular disease, and menopausal symptoms. Lignans occur in numerous food plants and various structures; they are common constituents of human diet, and estrogen activity has been assessed for lignan metabolites formed in the mammalian intestine. We examined natural lignans and semisynthetic norlignans for estrogen and antiestrogen activity. A transformed yeast strain (Saccharomyces cerevisiae) expressing the estrogen receptor alpha and a reporter system was applied as test system. Some plant lignans showed estrogen activity while others and the semisynthetic norlignans were moderately active antiestrogens. Docking of lignans to protein models of estrogen receptor alpha in the active and inactive form sustained the results of the yeast estrogen assay and supported the concept of plant lignans as phytoestrogens.

Nutraceutical value and safety of tomato fruits produced by mycorrhizal plants

Tomato fruit has assumed the status of 'functional food' due to the association between its consumption and a reduced likelihood of certain types of cancers and CVD. The nutraceutical value of tomatoes can be affected by the cultivation conditions, e.g. the phytochemical content of the fruits may increase with the establishment of beneficial mycorrhizal symbioses in the plants. A multidisciplinary study was carried out to gain knowledge on the antioxidant, oestrogenic/anti-oestrogenic and genotoxic activity of tomato fruits produced by mycorrhizal plants. The present results showed that the symbiosis positively affected the growth and mineral nutrient content of tomato plants and enhanced the nutritional and nutraceutical value of tomato fruits through modifications of plant secondary metabolism, which led to increased levels of lycopene in fruits obtained from mycorrhizal plants, compared with controls. Moreover, such changes did not result in the production of mutagenic compounds, since tomato extracts induced no in vitro genotoxic effects. Fruit extracts, both hydrophilic and the lipophilic fractions, originating from mycorrhizal plants strongly inhibited 17-β-oestradiol-human oestrogen receptor binding, showing significantly higher anti-oestrogenic power compared with controls. The present study shows that beneficial plant symbionts, such as mycorrhizal fungi, can lead to the production of safe and high-quality food, which is an important societal issue strongly demanded by both consumers and producers.

Antiestrogenicity and estrogenicity in leachates from solid waste deposits

A great deal of effort has been devoted to developing new in vitro and in vivo methods to identify and classify endocrine disrupting chemicals that have been identified in environmental samples. In this study an in vitro test based on recombinant yeast strains transfected with genes for the human estrogen receptor α was adapted to examine the presence of estrogenic and antiestrogenic substances in six Swedish landfill leachates. Antiestrogenic effects were measured as inhibition of the estradiol induced response with the human estrogen receptor α, and quantified by comparison with the corresponding inhibitory effects of a known antiestrogen, hydroxytamoxifen. The estrogenicity was within the range of that determined in domestic sewage effluents, from below the limit of detection to 29 ng estradiol units L(-1). Antiestrogenicity was detected in some of the investigated landfill leachates, ranging between <38 and 3800 μg hydroxytamoxifen equivalents L(-1). There was no apparent relation between the type of waste deposited on the landfills and the antiestrogenic effect. Fractionation of a landfill leachate showed that estrogenic compounds were located in two dominant fractions. Three estrogenic compounds were found that accounted for the estrogenic activity in extracts of leachates: bisphenol A, estradiol, and ethinylestradiol. The bisphenol may have been released from decomposing plastic waste and the estrogenic steroids from earlier deposits of municipal sewage sludge and pharmaceutical waste. Fractionation of leachates from three parts of a landfill showed that the antiestrogenic activity was distributed in at least four fractions and somewhat different in different flows of leachate. This indicated a heterogeneous mixture of antiestrogenic substances.

The arrival and discharge of conjugated estrogens from a range of different sewage treatment plants in the UK

The occurrence of free and conjugated estrogens was examined in a survey of eleven sewage treatment plants (STPs) and their discharge water in the United Kingdom using grab sampling. The STPs included trickling filter with and without tertiary treatment, and activated sludge with tertiary treatment. For three activated sludge plants both influent and effluent samples were compared. For a further 8STPs only the effluent was examined. The estrone-3-sulphate, estradiol-3-sulphate and estriol-3-sulphate concentrations (up to 20 ng L(-1)) were typically 5-fold that of the respective free estrogen concentration in the effluents. This represents a substantial additional 'potential' estrogen load arriving in the receiving waters. Estrone-3-glucuronide was found at 9 ng L(-1), estradiol-3-glucuronide at 7 ng L(-1), and estriol-3-glucuronide at 32 ng L(-1) in sewage influent. Except on one occasion, no glucuronide conjugates could be found in the effluent. The results suggest in most cases glucuronide conjugates will be completely transformed in sewage treatment whilst sulphate conjugates will only be partially removed.

Chlorinated isomers of nonylphenol differ in estrogenic and androgenic activity

Technical mixtures of nonylphenol (NP) contain over 20 p-substituted isomers. Mono- and di-chlorinated derivatives are generated during the chlorination process in water treatment. Four NP isomers (i.e. 4n-, p353-, p33-, p363-NP) and their mono- (MCl) and di-chlorinated (DCl) derivatives were tested for their estrogenic and androgenic potency using yeast estrogenic and androgenic assay. The p353-NP and 4n-MClNP isomers showed the highest and the lowest estrogenic potency, respectively. The p363-MClNP exhibits estrogenic potency comparable to the parent isomer, whereas all p-DClNP compounds displayed a decrease in the estrogenic potency. In the anti-androgenic screen, all substances exhibited a positive response; the mono- and di-chlorinated derivatives exhibit lower potency than the parent isomers. The isomer p363-NP and its corresponding mono- and di-chlorinated derivatives were almost inactive. Furthermore, all compounds were tested for anti-estrogenic and androgenic assays, but none of them showed a positive response. These results indicate that for assessing the xeno-hormone potency of chlorinated derivatives of NP, the use of pure compounds is essential because the mixtures are not representative. In fact the concentrations of NP isomers differ in technical mixtures according to the producers; after chlorination different technical mixtures can generate dissimilar ratios of chlorinated derivatives. Finally, the chlorinated derivatives of NP didn't show an increase in xeno-hormone potency compared to the parent isomers, and for this reason the many oxidized by-products generated during chlorination process mask the xeno-hormone potency of the pure chlorinated isomers of NP.

Interaction of Galaxolide® with the human and trout estrogen receptor-α

Synthetic musks have been detected in sewage effluents, surface waters, and fish tissues where the polycyclic musk compound, HHCB (Galaxolide®) is the dominant compound in those matrices. In the present study, the Galaxolide® formulation was tested in the yeast estrogenicity screening (YES) assay, and also tested in in vitro and in vivo teleost systems to determine whether it interacts with the estrogen receptor as either an agonist or antagonist. In those tests, Galaxolide® did not act as an estrogen agonist, however there was strong evidence of antagonistic activity as Galaxolide® inhibited the estrogenic activity of 17β-estradiol (E2). In the YES assay based on a recombinant strain of yeast containing the human estrogen receptor (i.e. hERα), Galaxolide® inhibited the effects of E2 in a dose-dependent manner (IC50=1.63×10(-5)M). In a luciferase reporter gene assay based on the rainbow trout estrogen receptor (i.e. rtER) transfected into a rainbow trout gonadal (RTG-2) cell line, the IC50 for the antagonistic effect of Galaxolide® was 2.79×10(-9)M. In an in vivo assay based on modulation of vitellogenin in rainbow trout, Galaxolide® i.p. injected into trout at a dose of 3.64mg/kg caused inhibition of E2-induced vitellogenin production. That dose is within the range of concentrations of Galaxolide® that have been detected in tissues of fish from contaminated locations.

Quantifying the antiestrogen activity of wastewater treatment plant effluent using the yeast estrogen screen

The yeast estrogen screen (YES) assay was used to measure both estrogenic and antiestrogenic activity of wastewater treatment plant (WWTP) effluent for the purpose of developing a method to quantify antiestrogenic activity. Wastewater treatment plant effluent samples were concentrated by solid-phase extraction (SPE) and serially diluted. Five microliters of each dilution plus 195 microl of assay medium was placed in well plates and tested for estrogenic substances. Antiestrogen activity in WWTP effluent samples was indirectly measured by an effluent-volume-dependent suppression of the beta-galactosidase activity induced by an estradiol (E2) standard. Antiestrogens and estrogens were quantified by median inhibition concentration (IC50) and median effective concentration (EC50) statistics, respectively, and were expressed in terms of effluent volume (prior to concentration by SPE). Antiestrogen IC50 and estrogen EC50 values, calculated by standard linear regression methods, averaged 25.6 microl and 22.1 microl effluent, respectively. Taken together, these values suggest that antiestrogens were responsible for approximately a 50% reduction in estrogen-induced activity in WWTP effluent. Therefore, measurements of estrogenicity by the YES assay in WWTP effluent that typically contains a mixture of estrogenic and antiestrogenic substances should be considered net estrogenic activity. The potential for false-positive antiestrogen activity was addressed by assays of beta-galactosidase activity in effluent, by measurements of yeast cell turbidity, and by stirred cell ultrafiltration for removal of solid-phase coextracted organic substances.

Rapid determination of free and conjugated estrogen in different water matrices by liquid chromatography-tandem mass spectrometry

This article describes the development of a short pre-treatment method that allows the simultaneous analysis of free estrogens (estrone, 17beta-estradiol, estriol and 17 alpha-ethynylestradiol) and their sulphate and glucuronide conjugated forms. For a range of matrices, from sewage effluent to river water, the developed methodology based on solid-phase extraction and fractionation technique with ultra-performance liquid chromatography system showed effective separation of the targeted estrogens. The detection limits of this method ranged from 0.2 to 0.8 ng L(-1) for river water. The recoveries for river water and sewage effluent varied from 63% to 127%. The problems of matrix effects and ion suppression or enhancement were allowed quantitatively for in the analysis using standard addition. The developed method was used successfully to detect estrogens and their conjugates in both raw and treated wastewater, and river water at a location in Japan. High concentrations of the free estrogens estrone, 17beta-estradiol and estriol were found in the influent (22.6, 77.2, 64.6 ng L(-1), respectively) but only E1 was still present at a high concentration in the effluent which was reflected in the downstream river concentration. Estrone-3-sulphate was detected up to 18.0 ng L(-1) in influent water sample and 1.1 ng L(-1) in downstream water. For the sulphate conjugates, removal efficiencies varied from 35 to 88%. Glucuronide conjugates were detected only once in the sewage influent.

Toxic masking and synergistic modulation of the estrogenic activity of chemical mixtures in a yeast estrogen screen (YES)

BACKGROUND, AIM AND SCOPE

Estrogenic and non-estrogenic chemicals typically co-occur in the environment. Interference by non-estrogenic chemicals may confound the assessment of the actual estrogenic activity of complex environmental samples. The aim of the present study was to investigate whether, in which way and how seriously the estrogenic activity of single estrogens and the observed and predicted joint action of estrogenic mixtures is influenced by toxic masking and synergistic modulation caused by non-estrogenic chemical confounders.

MATERIALS AND METHODS

The yeast estrogen screen (YES) was adapted so that toxicity and estrogenicity could be quantified simultaneously in one experimental run. Mercury, two organic solvents (dimethyl sulfoxide (DMSO) and 2,4-dinitroaniline), a surfactant (LAS-12) and the antibiotic cycloheximide were selected as toxic but non-estrogenic test chemicals. The confounding impact of selected concentrations of these toxicants on the estrogenic activity of the hormone 17ss-estradiol was determined by co-incubation experiments. In a second step, the impact of toxic masking and synergistic modulation on the predictability of the joint action of 17ss-estradiol, estrone and estriol mixtures by concentration addition was analysed.

RESULTS

Each of the non-estrogenic chemicals reduced the apparent estrogenicity of both single estrogens and their mixtures if applied at high, toxic concentrations. Besides this common pattern, a highly substance- and concentration-dependent impact of the non-estrogenic toxicants was observable. The activity of 17ss-estradiol was still reduced in the presence of only low or non-toxic concentrations of 2,4-dinitroaniline and cycloheximide, which was not the case for mercury and DMSO. A clear synergistic modulation, i.e. an enhanced estrogenic activity, was induced by the presence of slightly toxic concentrations of LAS-12. The joint estrogenic activity of the mixture of estrogens was affected by toxic masking and synergistic modulation in direct proportion to the single estrogens, which allowed for an adequate adaptation of concentration addition and thus unaffected predictability of the joint estrogenicity in the presence of non-estrogenic confounders.

DISCUSSION

The modified YES proved to be a reliable system for the simultaneous quantification of yeast toxicity and estrogen receptor activation. Experimental results substantiate the available evidence for toxic masking as a relevant phenomenon in estrogenicity assessment of complex environmental samples. Synergistic modulation of estrogenic activity by non-estrogenic confounders might be of lower importance. The concept of concentration addition is discussed as a valuable tool for estrogenicity assessment of complex mixtures, with deviations of the measured joint estrogenicity from predictions indicating the need for refined analyses.

CONCLUSIONS

Two major challenges are to be considered simultaneously for a reliable analysis of the estrogenic activity of complex mixtures: the identification of known and suspected estrogenic compounds in the sample as well as the substance- and effect-level-dependent confounding impact of non-estrogenic toxicants.

RECOMMENDATIONS AND PERSPECTIVES

The application of screening assays such as the YES to complex mixtures should be accompanied by measures that safeguard against false negative results which may be caused by non-estrogenic but toxic confounders. Simultaneous assessments of estrogenicity and toxicity are generally advisable.

Occurrence of pharmaceuticals and personal care products along the West Prong Little Pigeon River in east Tennessee, USA

Presence of pharmaceuticals and personal care products (PPCPs) in the environment has received a great attention due to their potential impacts on public health. This study examined the occurrence of PPCPs in West Prong Little Pigeon River in east Tennessee. As wastewater is a major source for environmental occurrence of PPCPs, both wastewater and river water samples were analyzed for nine target PPCPs and their estrogenicity. No estrogens were detected in influent, secondary effluent, and river samples. However, ibuprofen, caffeine, triclosan, bisphenol A, and bis(2-ethylhexyl)phthalate (DEHP) were detected in the influent. Ibuprofen, triclosan, and DEHP were detected in the secondary effluent samples. Only ibuprofen and triclosan were detected in river water collected near a wastewater outfall. Based on yeast estrogenic screening (YES) assays, estrogenic activities were observed in all influent, secondary effluent, and river water samples. Increased estrogenic activities were observed in river right after receiving effluent discharge, and the activities decreased as river water flowing away from the outfall. The estrogenicities of water samples measured from YES assays were much higher than those estimated from PPCP concentrations and their known estrogenicities, suggesting the presence of other unknown estrogenic compounds and/or additive effects of mixtures of estrogenic compounds at low concentrations. Results of this study demonstrated that wastewater contributed to environmental occurrence of PPCPs in the receiving water. As there is a myriad of known and unknown PPCPs in wastewater, in additional to chemical analysis, estrogenic bioassays are needed for assessing estrogenicity of environmental samples.

Towards high-throughput identification of endocrine disrupting compounds with mass spectrometry

High-mass matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with chemical cross-linking has the ability to monitor the ligand-dependent dimerization of the human estrogen receptor alpha ligand binding domain (hERalpha LBD) in solution. Because only ER ligands enhance the homodimer abundance, we evaluated the ability of this label-free approach for identifying endocrine disrupting compounds (EDCs) in a high-throughput manner. This was achieved by combining an automated liquid handler with an automated MS acquisition procedure, which allowed a five-fold gain in operator time compared to a fully manual approach. To detect ligand binding with enough confidence, the receptor has to be incubated with at least a 10 microM concentration of the test compound. Based on the increase of the measured homodimer intensity, eight compounds with a relative binding affinity (RBA, relative to the natural hormone estradiol) >7% were identified as ER ligands among the 28 chemicals tested. Two other compounds, quercetin and 4-tert-amylphenol, were also identified as ER ligands, although their RBAs have been reported to be only 0.01% and 0.000055%, respectively. This suggests that these two ligands have a higher affinity for hERalpha LBD than reported in the literature. The high-mass MALDI approach thus allows identifying high affinity EDCs in an efficient way.

Abiotic degradation of four phthalic acid esters in aqueous phase under natural sunlight irradiation

Abiotic degradability of four phthalic acid esters (PAEs) in the aquatic phase was evaluated over a wide pH range 5-9. The PAE solutions in glass test tubes were placed either in the dark and under the natural sunlight irradiation for evaluating the degradation rate via hydrolysis or photolysis plus hydrolysis, respectively, at ambient temperature for 140 d from autumn to winter in Osaka, Japan. The efficiency of abiotic degradation of the PAEs with relatively short alkyl chains, such as butylbenzyl phthalate (BBP) and di-n-butyl phthalate (DBP), at neutral pH was significantly lower than that in the acidic or alkaline condition. Photolysis was considered to contribute mainly to the total abiotic degradation at all pH. Neither hydrolysis nor photolysis of di-ethylhexyl phthalate (DEHP) proceeded significantly at any pH, especially hydrolysis at neutral pH was negligible. On the other hand, the degradation rate of di-isononyl phthalate (DINP) catalyzed mainly by photolysis was much higher than those of the other PAEs, and was almost completely removed during the experimental period at pH 5 and 9. As a whole, according to the half-life (t1/2) obtained in the experiments, the abiotic degradability of the PAEs was in the sequence: DINP (32-140 d) > DBP (50-360 d), BBP (58-480 d) > DEHP (390-1600 d) under sunlight irradiation (via photolysis plus hydrolysis). Although the abiotic degradation rates for BBP, DBP, and DEHP are much lower than the biodegradation rates reported, the photolysis rate for DINP is comparable to its biodegradation rate in the acidic or alkaline condition.

Estrogenicity of alkylphenols and alkylated non-phenolics in a rainbow trout (Oncorhynchus mykiss) primary hepatocyte culture

Alkylphenols act as estrogen mimics by binding to and transactivating estrogen receptors (ERs) in fish. In the present study, activation of ER-mediated production of the estrogenic biomarker vitellogenin (vtg) in a primary culture of rainbow trout (Oncorhynchus mykiss) hepatocytes was used to construct a structure-activity relationship for this ubiquitous group of aquatic pollutants. The role of alkyl chain length and branching, substituent position, number of alkylated groups, and the requirement of a phenolic ring structure was assessed. The results showed that most alkylphenols were estrogenic, although with 3-300 thousand times lower affinity than the endogenous estrogen 17beta-estradiol. Mono-substituted tertiary alkylphenols with moderate (C4-C5) and long alkyl chain length (C8-C9) in the para position exhibited the highest estrogenic potency. Substitution with multiple alkyl groups, presence of substituents in the ortho- and meta-position and lack of a hydroxyl group on the benzene ring reduced the estrogenic activity, although several estrogenic alkylated non-phenolics were identified. Co-exposures with the natural estrogen 17beta-estradiol led to identification of additional estrogenic compounds as well as some anti-estrogens. A combination of low affinity for the ER and cytotoxicity was identified as factors rendering some of the alkylphenols non-estrogenic in the bioassay when tested alone.

Structure-activity relationships of synthetic progestins in a yeast-based in vitro androgen bioassay

The recent identification of tetrahydrogestrinone (THG), a non-marketed designer androgen used for sports doping but previously undetectable by established mass spectrometry-based urine drug screens, and its production by a facile chemical modification of gestrinone has raised concerns about the risks of developing designer androgens from numerous marketed progestins. We therefore have used yeast-based in vitro androgen and progesterone bioassays to conduct a structure-activity study assessing the intrinsic androgenic potential of commercially available progestins and their derivatives, to identify those compounds or structures with the highest risk of forming a basis for such misapplication. Progestins had a wide range of androgenic bioactivity that was not reliably predicted for individual steroids by their progestin bioactivity. 17alpha-Hydroxyprogesterone and 19-norprogesterone derivatives with their bulky 17beta-substituents were strong progestins but generally weak androgens. 17alpha-Ethynylated derivatives of testosterone, 19-nortestosterone and 18-methyl-19-nortestosterone such as gestrinone, ethisterone, norethisterone and norgestrel had the most significant intrinsic androgenicity of all the commercially marketed progestins. Facile chemical modification of the 17alpha-ethynyl group of each of these progestins produces 17alpha-methyl, ethyl and allyl derivatives, including THG and norbolethone, which further enhanced androgenic bioactivity. Thus by using the rapid and sensitive yeast bioassay we have screened a comprehensive set of progestins and associated structures and identified the ethynylated testosterone, 19-nortestosterone and 18-methyl-19-nortestosterone derivatives as possessing the highest risk for abuse and potential for conversion to still more potent androgens. By contrast, modern progestins such as progesterone, 17alpha-hydroxyprogesterone and 19-norprogesterone derivatives had minimal androgenic bioactivity and pose low risk.

Endocrine modulation and toxic effects of two commonly used UV screens on the aquatic invertebrates Potamopyrgus antipodarum and Lumbriculus variegatus

The two UV screens 3-benzylidene-camphor (3-BC) and 3-(4'-methylbenzylidene)-camphor (4-MBC) were tested regarding their toxicity and estrogenic activity. The Yeast Estrogen Screen (YES) and two sediment assays with the freshwater invertebrates Lumbriculus variegatus and Potamopyrgus antipodarum were performed. In the YES, both substances activated the human estrogen receptor alpha with EC50 values of 44.2 microM for 3-BC and 44.3 microM for 4-MBC, whereby 4-MBC attained only 8% of the maximal response of 17beta-estradiol. For P. antipodarum embryo production increased after exposure to both substances (EC50 of 4.60 microM 4-MBC=1.17 mg kg(-1)dw) while mortality increased at high concentrations. The reproduction of L. variegatus was decreased by 3-BC with an EC50 of 5.95 microM (=1.43 mg kg(-1)dw) and also by 4-MBC, where no EC50 could be calculated. While reproduction decreased, the worms' weight increased after exposure to 3-BC with an EC50 of 26.9 microM (=6.46 mg kg(-1) dw), hence the total biomass remained unaffected.