Vitellogenin: A Review of Analytical Methods to Detect (Anti) Estrogenic Activity in Fish

An international cross-laboratory survey on fish vitellogenin analysis: Methodological challenges and opportunities for best practice

Vitellogenin (VTG) is a biomarker for possible endocrine activity of chemicals acting via the estrogen, androgen, or steroidogenesis pathways. VTG is assessed in standardised fish guideline studies conducted for regulatory safety assessment of chemicals. VTG data can be highly variable leading to concerns for potential equivocal, false positive and/or negative outcomes. Consequently, additional fish testing may be required to address uncertainties in the VTG response, and possibly erroneous/missed identification of endocrine activity. To better understand the technical challenges of VTG assessment and reporting for regulatory purposes, a survey was sent to 27 testing laboratories performing these analyses. The survey results from 16 respondents (6 from the UK, 3 from the USA, and 7 from the EU) were analysed and discussed in a follow-up webinar. High variability in background VTG concentrations was widely acknowledged and thought to be associated with fish batch, husbandry, laboratory practices, and several methodological aspects. These include sample collection and storage, VTG quantification, data handling, and the benchmarks used for data acceptability. Information gathered in the survey provides a basis for improving and harmonizing the measurement of VTG in fish, and an opportunity to reassess the suitability of current acceptability criteria in test guidelines.

Are changes in vitellogenin concentrations in fish reliable indicators of chemical-induced endocrine activity?

Vitellogenin (VTG), a biomarker for endocrine activity, is a mechanistic component of the regulatory assessment of potential endocrine-disrupting properties of chemicals. This review of VTG data is based on changes reported for 106 substances in standard fish species. High intra-study and inter-laboratory variability in VTG concentrations was confirmed, as well as discrepancies in interpretation of results based on large differences between fish in the dilution water versus solvent control, or due to the presence of outlier measurements. VTG responses in fish were ranked against predictions for estrogen receptor agonist activity and aromatase inhibition from bioactivity model output and ToxCast in vitro assay results, respectively. These endocrine mechanisms explained most of the VTG responses in the absence of systemic toxicity, the magnitude of the VTG response being proportional to the in vitro potency. Interpretation of the VTG data was sometimes confounded by an alternative endocrine mechanism of action. There was evidence for both false positive and negative responses for VTG synthesis, but overall, it was rare for substances without endocrine activity in vitro to cause a concentration-dependent VTG response in fish in the absence of systemic toxicity. To increase confidence in the VTG results, we recommend improvements in the VTG measurement methodologies and greater transparency in reporting of VTG data (including quality control criteria for assay performance). This review supports the application of New Approach Methodologies (NAMs) by demonstrating that endocrine activity in vitro from mammalian cell lines is predictive for in vivo VTG response in fish, suggesting that in vitro mechanistic data could be used more broadly in decision-making to help reduce animal testing.

Physiologically Based Toxicokinetic Modeling of Bisphenols in Zebrafish (Danio rerio) Accounting for Variations in Metabolic Rates, Brain Distribution, and Liver Accumulation

Bisphenol A (BPA) is an industrial chemical, which has raised human health and environmental concerns due to its endocrine-disrupting properties. BPA analogues are less well-studied despite their wide use in consumer products. These analogues have been detected in water and aquatic organisms around the world, with some analogues showing toxic effects in various species including fish. Here, we present novel organ-specific time-course distribution data of bisphenol Z (BPZ) in female zebrafish (Danio rerio), including concentrations in the ovaries, liver, and brain, a rarely sampled organ with high toxicological relevance. Furthermore, fish-specific in vitro biotransformation rates were determined for 11 selected bisphenols. A physiologically based toxicokinetic (PBTK) model was adapted for four of these bisphenols, which was able to predict levels in the gonads, liver, and brain as well as the whole body within a 2-5-fold error with respect to experimental data, covering several important target organs of toxicity. In particular, predicted liver concentrations improved compared to currently available PBTK models. Predicted data indicate that studied bisphenols mainly distribute to the carcass and gonads and less to the brain. Our model provides a tool to increase our understanding on the distribution and kinetics of a group of emerging pollutants.

Systematic review of reptile reproductive toxicology to inform future research directions on endangered or threatened species, such as sea turtles

Threatened or endangered reptiles, such as sea turtles, are generally understudied within the field of wildlife toxicology, with even fewer studies on how contaminants affect threatened species reproduction. This paper aimed to better inform threatened species conservation by systematically and quantitatively reviewing available research on the reproductive toxicology of all reptiles, threatened and non-threatened. This review found 178 studies that matched our search criteria. These papers were categorized into location conducted, taxa studied, species studied, effects found, and chemicals investigated. The most studied taxa were turtles (n = 87 studies, 49%), alligators/crocodiles (n = 54, 30%), and lizards (n = 37, 21%). Maternal transfer, sex steroid alterations, sex reversal, altered sexual development, developmental abnormalities, and egg contamination were the most common effects found across all reptile taxa, providing guidance for avenues of research into threatened species. Maternal transfer of contaminants was found across all taxa, and taking into account the foraging behavior of sea turtles, could help elucidate differences in maternal transfer seen at nesting beaches. Sex steroid alterations were a common effect found with contaminant exposure, indicating the potential to use sex steroids as biomarkers along with traditional biomarkers such as vitellogenin. Sex reversal through chemical exposure was commonly found among species that exhibit temperature dependent sex determination, indicating the potential for both environmental pollution and climate change to disrupt population dynamics of many reptile species, including sea turtles. Few studies used in vitro, DNA, or molecular methodologies, indicating the need for more research using high-throughput, non-invasive, and cost-effective tools for threatened species research. The prevalence of developmental abnormalities and altered sexual development and function indicates the need to further study how anthropogenic pollutants affect reproductive output in threatened reptiles.

Summary of reference chemicals evaluated by the fish short-term reproduction assay, OECD TG229, using Japanese Medaka, Oryzias latipes

Under the Organisation for Economic Co-operation and Development (OECD), the Ministry of the Environment of Japan (MOE) added Japanese medaka (Oryzias latipes) to the test guideline fish short-term reproduction assay (FSTRA) developed by the United States Environmental Protection Agency (US EPA) using fathead minnow (Pimephales promelas). The FSTRA was designed to detect endocrine disrupting effects of chemicals interacting with the hypothalamic-pituitary-gonadal axis (HPG axis) such as agonists or antagonists on the estrogen receptor (Esr) and/or the androgen receptor (AR) and steroidogenesis inhibitors. We conducted the FSTRA with Japanese medaka, in accordance with OECD test guideline number 229 (TG229), for 16 chemicals including four Esr agonists, two Esr antagonists, three AR agonists, two AR antagonists, two steroidogenesis inhibitors, two progesterone receptor agonists, and a negative substance, and evaluated the usability and the validity of the FSTRA (TG229) protocol. In addition, in vitro reporter gene assays (RGAs) using Esr1 and ARβ of Japanese medaka were performed for the 16 chemicals, to support the interpretation of the in vivo effects observed in the FSTRA. In the present study, all the test chemicals, except an antiandrogenic chemical and a weak Esr agonist, significantly reduced the reproductive status of the test fish, that is, fecundity or fertility, at concentrations where no overt toxicity was observed. Moreover, vitellogenin (VTG) induction in males and formation of secondary sex characteristics (SSC), papillary processes on the anal fin, in females was sensitive endpoints to Esr and AR agonistic effects, respectively, and might be indicators of the effect concentrations in long-term exposure. Overall, it is suggested that the in vivo FSTRA supported by in vitro RGA data can adequately detect effects on the test fish, O. latipes, and probably identify the mode of action (MOA) of the chemicals tested.

Health risks of chlorothalonil, carbendazim, prochloraz, their binary and ternary mixtures on embryonic and larval zebrafish based on metabolomics analysis

Chlorothalonil (CTL), carbendazim (CBZ), and prochloraz (PCZ) are fungicides widely used in many countries. The use of these fungicides raises concerns because they are often applied together or used in the same agricultural area. However, the toxicity of these fungicides or mixtures, especially to aquatic organisms, has received limited attention. Here, embryonic and larval zebrafish were exposed to indicated concentrations of CTL, CBZ, and PCZ and their binary (CTL+CBZ, CTL+PCZ and CBZ+PCZ) and ternary (CTL+CBZ+PCZ) mixtures for 24 h. Based on metabolomics analysis, we observed that hundreds of metabolites were altered, and glycolysis metabolism and amino acid metabolism were the two most affected pathways. Interestingly, a total of 9 and 26 metabolites changed significantly in embryos and larvae treated with all fungicides, respectively. Among these altered metabolites, 2-aminoadipic acid (2-AAA) levels increased significantly in all groups, indicating that 2-AAA potentially represents a useful biomarker for evaluating the toxicity of fungicides. Furthermore, the joint effects of CTL+PCZ on embryos and larvae, especially on amino acid metabolism, were weaker than those in other groups, but combined treatment did not influence individual fungicidal activity. Data acquired from metabolomics provided important insight for understanding the mechanism by which fungicides or their mixtures affect zebrafish.

Detection of biomarkers to differentiate endocrine disruption from hepatotoxicity in zebrafish (Danio rerio) using proteomics

Measurement of specific biomarkers identified by proteomics provides a potential alternative method for risk assessment, which is required to discriminate between hepatotoxicity and endocrine disruption. In this study, adult zebrafish (Danio rerio) were exposed to the hepatotoxic substance acetaminophen (APAP) for 21 days, in a fish short-term reproduction assay (FSTRA). The molecular changes induced by APAP exposure were studied in liver and gonads by applying a previously developed combined FSTRA and proteomics approach. We observed a significant decrease in egg numbers, an increase in plasma hyaluronic acid, and the presence of single cell necrosis in liver tissue. Furthermore, nine common biomarkers (atp5f1b, etfa, uqcrc2a, cahz, c3a.1, rab11ba, mettl7a, khdrbs1a and si:dkey-108k21.24) for assessing hepatotoxicity were detected in both male and female liver, indicating hepatic damage. In comparison with exposure to fadrozole, an endocrine disrupting chemical (EDC), three potential biomarkers for liver injury, i.e. cahz, c3a.1 and atp5f1b, were differentially expressed. The zebrafish proteome response to fadrozole exposure indicated a significant regulation in estrogen synthesis and perturbed binding of sperm to zona pellucida in the ovary. This study demonstrates that biomarkers identified and quantified by proteomics can serve as additional weight-of-evidence for the discrimination of hepatotoxicity and endocrine disruption, which is necessary for hazard identification in EU legislation and to decide upon the option for risk assessment.

Medaka (Oryzias latipes) Multigeneration Test with Triclosan

The medaka extended one-generation reproduction test (MEOGRT) is a tier-2 study in the US Environmental Protection Agency's Endocrine Disruptor Screening Program and a level-5 study in the Organisation for Economic Co-operation and Development's conceptual framework. Integrating nonspecific apical and endocrine-specific mechanistic endpoints, results of a MEOGRT can be used, with other data, in a weight-of-evidence evaluation to establish a dose-response relationship for risk assessment and identify potential causal relationships between an endocrine mode of action and adverse effects. The MEOGRT test design was used to evaluate the multigenerational effects of the antimicrobial agent triclosan. Japanese medaka were exposed to nominal concentrations of 1.4, 2.8, 5.6, 11, and 23 μg/L triclosan and a dilution water control starting with adult medaka (F0) through hatch in the second generation (F2). No consistent or concentration-related responses occurred in the 182-d test that suggested an endocrine-mediated effect. There were no impacts on hepatic vitellogenin, secondary sex characteristics, or sex ratio that were linked to an adverse reproductive outcome. Histopathological responses were consistent with a toxic or stress effect, particularly when considered in context with observed reductions in growth. The overall population-relevant no-observed-effect concentration was 11 µg/L based on effects on growth. The results of the present study support a previously conducted weight-of-evidence evaluation concluding that triclosan does not act as an agonist or antagonist within estrogen, androgen, thyroid, or steroidogenic pathways. Environ Toxicol Chem 2019;38:1770-1783. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Mass spectrometry based detection of common vitellogenin peptides across fish species for assessing exposure to estrogenic compounds in aquatic environments

The identification of myriad of chemicals in the environment that mimic hormones and affect the endocrine functions of exposed organism is a daunting analytical challenge for environmental scientists and engineers. Many of these endocrine disrupting chemicals (EDCs) are present at very low concentrations in the aquatic systems, but yet affect the metabolic, developmental, and reproductive functions in exposed fish and wildlife. Vitellogenin (VTG) protein is a widely used biomarker in fish for assessing exposure to EDCs, and is commonly measured using species-specific immunochemical techniques. In this study, we developed a liquid chromatography tandem mass spectrometry (LC-MS/MS) method that can measure common peptides from digested VTG in multiple fish species. In the initial experiments using high resolution mass spectrometry, two peptides (ALHPELR and FIELIQLLR) were identified as common fragments in the digested VTG protein isolated from three different fish species (Pimephales promelas, Micropterus salmoides, and Fundulus heteroclitus). Then, a quantitative analysis using LC-MS/MS under selected reaction monitoring mode was developed for the detection of these two peptides in trypsin-digested plasma from female fish (positive control), estrogen-exposed male fish (test sample), and unexposed male fish (negative control) using two of the same species used for identifying the common peptides (P. promelas, and M. salmoides) and one new species (Ameiurus nebulosus) that was not included during the selection of peptides. Results from this study demonstrate the potential of LC-MS/MS as an effective cross-species method to detect VTG in fish, which can be an alternative analytical technique for assessing endocrine disruption in multiple fish species.

Development and evaluation of gene expression biomarkers for chemical pollution in common frog (Rana temporaria) tadpoles

Pollutants have been proposed as one factor in the worldwide declines of amphibian species and populations. Applying gene expression analysis of liver RNA in tadpoles would be a possible approach for biomarker measurements to increase knowledge of ecological health in amphibian populations. The major aim of this study was to explore the relevance of applying gene expression analyses of cytochrome p450 (cyp1a), metallothionein (mt), and vitellogenin (vtg) in Rana temporaria tadpoles. Therefore, tadpoles were exposed for 1 week to β-naphthoflavone (BNF), cadmium chloride (CdCl₂), and ethinylestradiol (EE2). Primers were developed for RT-qPCR to analyze gene expression in livers. The result showed that the methods for gene expression analyses of cyp1a, mt, and vtg as well as the reference gene β-actin (bact) were successful not only in R. temporaria but also in another amphibian, Rana arvalis. The gene expression of cyp1a was induced by BNF and the gene expression of mt was induced by CdCl₂ but no significant induction was recorded in vtg expression after exposure to EE2. Gene expressions varied throughout the tadpole metamorphosis development, in particular for vtg. Overall, the use of gene expression of cyp1a and mt as biomarkers in wild tadpoles seems promising while the use of vtg seems less relevant due to high natural variation and low background expression. The study shows that variations in gene expressions between tadpoles of different genetic origin are important to consider when evaluating the data. The present study has thus increased the background knowledge about gene expression applicability as biomarker for tadpoles.

Distinguishing between endocrine disruption and non-specific effects on endocrine systems

The endocrine system is responsible for growth, development, maintaining homeostasis and for the control of many physiological processes. Due to the integral nature of its signaling pathways, it can be difficult to distinguish endocrine-mediated adverse effects from transient fluctuations, adaptive/compensatory responses, or adverse effects on the endocrine system that are caused by mechanisms outside the endocrine system. This is particularly true in toxicological studies that require generation of effects through the use of Maximum Tolerated Doses (or Concentrations). Endocrine-mediated adverse effects are those that occur as a consequence of the interaction of a chemical with a specific molecular component of the endocrine system, for example, a hormone receptor. Non-endocrine-mediated adverse effects on the endocrine system are those that occur by other mechanisms. For example, systemic toxicity, which perturbs homeostasis and affects the general well-being of an organism, can affect endocrine signaling. Some organs/tissues can be affected by both endocrine and non-endocrine signals, which must be distinguished. This paper examines in vitro and in vivo endocrine endpoints that can be altered by non-endocrine processes. It recommends an evaluation of these issues in the assessment of effects for the determination of endocrine disrupting properties of chemicals. This underscores the importance of using a formal weight of evidence (WoE) process to evaluate potential endocrine activity.

Multigenerational Effects and Demographic Responses of Zebrafish ( Danio rerio) Exposed to Organo-Bromine Compounds

Long-term exposure to toxic chemicals often has deleterious effects on aquatic organisms. In order to support appropriate environmental management of chemicals, a mathematical model was developed to characterize the effects of chemicals on multigenerational population dynamics in aquatic animals. To parametrize the model, we conducted a multigenerational laboratory toxicity test in zebrafish ( Danio rerio) exposed to 2-bromo-4,6-dinitroaniline (BDNA). Long-term exposure to BDNA considerably reduced the fecundity of adult zebrafish (F₀ and F₁) and caused deformities in the offspring (F₂). Life history data, including changes in fecundity and population growth, were then integrated into the model to predict population dynamics of zebrafish exposed to two novel brominated flame retardants, bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB). The model predicted that the fecundity of adult zebrafish would be significantly impaired after exposure to 90.36 μM TBPH and 99.16 μM TBB. Thus, prolonged exposure to such levels over multiple generations could result in population extinction within 20 years. Our results provide an intensive temporal perspective to investigate a keystone that connects with individual response to chemicals, population dynamics, and ultimately ecosystem influences.

In vivo effects of PCB-126 and genistein on vitellogenin expression in zebrafish

In this study, the vitellogenin (Vtg) modulation by genistein and polychlorinated biphenyl-126 (PCB-126) exposure in zebrafishes has been investigated. Both PCB-126 and genistein have been identified as aquatic pollutants and can further increase estrogenicity of waterways. Vtg is egg yolk precursor protein release by the hepatocytes during vitellogenesis. This process occurs normally in the hepatocytes in response to the activation with the estrogens such as 17-β-estradiol. Our immunohistochemical findings showed a Vtg expression that increases at 12 h and at 72 h in the liver of treated fishes with both PCB-126 and genistein, individually and in combination. Furthermore, for the first time, also hepatic stellate cells (HSC) in the liver parenchyma were strongly positive for vitellogenin.

Vitellogenin concentrations in feral Danish brown trout have decreased: An effect of improved sewage treatment in rural areas?

Feminization of male and juvenile fish because of exposure to estrogens or estrogenic chemicals in effluents from central wastewater treatment plants (WWTPs) is a worldwide issue of concern. Intersex and induction of the female yolk protein, vitellogenin, in male and juvenile fish are robust biomarkers for estrogenic exposure, and feminized fish have been observed downstream of WWTP outlets in many countries. Danish central WWTPs reduce effluent estrogenicity effectively by advanced sewage treatment, and feminizations have not been observed downstream of central WWTP outlets. However, between 2000 and 2004, investigations of Danish streams not receiving sewage from central WWTPs revealed a high variation in vitellogenin concentrations of male juvenile brown trout (Salmo trutta); some individuals had high concentrations, probably as a result of estrogenic point sources, and the plasma concentration was >50 ng mL^-1 in 79% of the juvenile males. The streams were reinvestigated in 2010 to 2016, and the average male level had decreased to a hitherto unseen baseline level; in 2010 only 0.7% (one individual) of the males had a vitellogenin concentration >50 ng mL^-1 , which could indicate that the estrogenicity of the streams decreased after 2004. We examined possible estrogenic sources in streams unaffected by central WWTP effluents, and found that the reduced vitellogenin levels are most likely explained by a national effort to improve on-site wastewater treatment in scattered houses not connected to central WWTPs. Environ Toxicol Chem 2018;37:839-845. © 2017 SETAC.

Short-term induction of vitellogenesis in the immature male yellowfin seabream (Acanthopagrus latus) exposed to bisphenol A and 17β-estradiol

Bisphenol A (BPA) is a known environmental endocrine-disrupting chemical that is widely used in plastics manufacturing. BPA enters in the aquatic environment mainly through urban and industrial sewage effluents, thereby posing a potential threat to organisms living in these ecosystems. This study was conducted to investigate the effect of BPA on VTG production with direct (sodium dodecyl sulfate-polyarylamide gel electrophoresis) and indirect (alkali-labile phosphate (ALP), total plasma calcium and protein) methods in immature male yellowfin seabream ( Acanthopagrus latus) as a marine fish model. Fish were randomly distributed into seven groups that were administered 1, 10, 50, and 100 µg g−1 week−1 of BPA and 2 µg g−1week−1 of 17β-estradiol (E2) over a period of 2 weeks. Solvent controls received olive oil, whereas controls were not injected. The fish were sampled on days 0, 7, and 14, and their blood plasma and liver were obtained. The results showed that the hepatosomatic index of all treated fish was elevated in comparison with controls. Direct and indirect indicators showed that fish VTG protein was induced by BPA and E2 exposure. The protein was found to have two bands with molecular weights around 210 and 190 KDa. ALP, total plasma calcium and protein levels were increased in dose- and time-dependent manners. The results of this study demonstrated that short-term exposure of yellowfin seabream to BPA induced adverse effects in the reproductive system of hermaphrodite fish.

Evaluation of the scientific underpinnings for identifying estrogenic chemicals in nonmammalian taxa using mammalian test systems

The US Environmental Protection Agency has responsibility for assessing endocrine activity of more than 10 000 chemicals, a task that cannot reasonably be achieved solely through use of available mammalian and nonmammalian in vivo screening assays. Hence, it has been proposed that chemicals be prioritized for in vivo testing using data from in vitro high-throughput assays for specific endocrine system targets. Recent efforts focused on potential estrogenic chemicals-specifically those that activate estrogen receptor-alpha (ERα)-have broadly demonstrated feasibility of the approach. However, a major uncertainty is whether prioritization based on mammalian (primarily human) high-throughput assays accurately reflects potential chemical-ERα interactions in nonmammalian species. The authors conducted a comprehensive analysis of cross-species comparability of chemical-ERα interactions based on information concerning structural attributes of estrogen receptors, in vitro binding and transactivation data for ERα, and the effects of a range of chemicals on estrogen-signaling pathways in vivo. Overall, this integrated analysis suggests that chemicals with moderate to high estrogenic potency in mammalian systems also should be priority chemicals in nonmammalian vertebrates. However, the degree to which the prioritization approach might be applicable to invertebrates is uncertain because of a lack of knowledge of the biological role(s) of possible ERα orthologs found in phyla such as annelids. Further, comparative analysis of in vitro data for fish and reptiles suggests that mammalian-based assays may not effectively capture ERα interactions for low-affinity chemicals in all vertebrate classes. Environ Toxicol Chem 2016;35:2806-2816. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and, as such, is in the public domain in the United States of America.

Comprehensive transcriptomic analysis of the process of gonadal sex differentiation in the turbot (Scophthalmus maximus)

The turbot is a flatfish with a ZW/ZZ sex determination system but with a still unknown sex determining gene(s), and with a marked sexual growth dimorphism in favor of females. To better understand sexual development in turbot we sampled young turbot encompassing the whole process of gonadal differentiation and conducted a comprehensive transcriptomic study on its sex differentiation using a validated custom oligomicroarray. Also, the expression profiles of 18 canonical reproduction-related genes were studied along gonad development. The expression levels of gonadal aromatase cyp19a1a alone at three months of age allowed the accurate and early identification of sex before the first signs of histological differentiation. A total of 56 differentially expressed genes (DEG) that had not previously been related to sex differentiation in fish were identified within the first three months of age, of which 44 were associated with ovarian differentiation (e.g., cd98, gpd1 and cry2), and 12 with testicular differentiation (e.g., ace, capn8 and nxph1). To identify putative sex determining genes, ∼4.000 DEG in juvenile gonads were mapped and their positions compared with that of previously identified sex- and growth-related quantitative trait loci (QTL). Although no genes mapped to the previously identified sex-related QTLs, two genes (foxl2 and 17βhsd) of the canonical reproduction-related genes mapped to growth-QTLs in linkage group (LG) 15 and LG6, respectively, suggesting that these genes are related to the growth dimorphism in this species.

Altered transcription levels of endocrine associated genes in two fisheries species collected from the Great Barrier Reef catchment and lagoon

The Great Barrier Reef (GBR) is chronically exposed to agricultural run-off containing pesticides, many of which are known endocrine disrupting chemicals (EDCs). Here, we measure mRNA transcript abundance of two EDC biomarkers in wild populations of barramundi (Lates calcarifer) and coral trout (Plectropomus leopardus and Plectropomus maculatus). Transcription levels of liver vitellogenin (vtg) differed significantly in both species amongst sites with different exposures to agricultural run-off; brain aromatase (cyp19a1b) revealed some differences for barramundi only. Exposure to run-off from sugarcane that contains pesticides is a likely pathway given (i) significant associations between barramundi vtg transcription levels, catchment sugarcane land use, and river pesticide concentrations, and (ii) consistency between patterns of coral trout vtg transcription levels and pesticide distribution in the GBR lagoon. Given the potential consequences of such exposure for reproductive fitness and population dynamics, these results are cause for concern for the sustainability of fisheries resources downstream from agricultural land uses.

A novel framework for interpretation of data from the fish short-term reproduction assay (FSTRA) for the detection of endocrine-disrupting chemicals

The fish short-term reproduction assay (FSTRA) is a key component of the US Environmental Protection Agency's Endocrine Disruptor Screening Program (EDSP), which uses a weight-of-evidence analysis based on data from several assays to identify the potential for chemicals to act as agonists or antagonists of the estrogen or androgen receptors (ER and AR), or inhibitors of steroidogenic enzymes. The FSTRA considers a variety of mechanistic and apical responses in 21-d exposures with the fathead minnow (Pimephales promelas), including plasma steroid and vitellogenin (VTG; egg yolk protein) concentrations, secondary sex characteristics, gonad size and histopathology, and egg production. Although the FSTRA initially was described several years ago, recent data generation associated with implementation of the EDSP highlighted the need for more formal guidance regarding evaluation of information from the assay. The authors describe a framework for interpretation of FSTRA data relative to perturbation of endocrine pathways of concern to the EDSP. The framework considers end points individually and as suites of physiologically related responses relative to pathway identification. Sometimes changes in single end points can be highly diagnostic (e.g., induction of VTG in males by ER agonists, production of male secondary sex characteristics in females by AR agonists); in other instances, however, multiple, related end points are needed to reliably assess pathway perturbation (e.g., AR antagonism, steroid synthesis inhibition). In addition to describing an interpretive framework, the authors demonstrate its practical utility using publicly available FSTRA data for a wide range of known and hypothesized endocrine-disrupting chemicals. Environ Toxicol Chem 2014;33:2529-2540. Published 2014 Wiley Periodicals Inc., on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Short-term responses of selected endocrine parameters in juvenile rainbow trout (Oncorhynchus mykiss) exposed to 4-nonylphenol

The synthetic organic compound 4-nonylphenol (4-NP) has been shown to have a wide range of adverse effects on the endocrine system of various animals including fish. The present study evaluated the potential effects of 4-NP on vitellogenin (VTG) synthesis, steroid, and thyroid hormone concentrations in both juvenile male and female rainbow trout ( Oncorhynchus mykiss). Fish were exposed by intraperitoneal injection to different doses of 4-NP (1, 10, 50, and 100 μg g−1) or vehicle (coconut oil) over a period of 14 days. Blood samples were collected 7 and 14 days after initiation of treatment. Plasma VTG levels in 4-NP-treated fish were detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis as a high molecular weight protein band of 180 KDa. In addition, plasma VTG concentrations were quantified indirectly using plasma alkali-labile phosphate (ALP) and plasma calcium. Both ALP and calcium levels in plasma showed similar and parallel increase patterns after exposure to 4-NP that were significantly higher compared with controls. The analysis of plasma sex steroid levels revealed a significant increase in 17β-estradiol and testosterone in plasma of juvenile males and females, respectively. Furthermore, a significant increase was observed in plasma cortisol levels. On the other hand, 4-NP decreased both plasma triiodothyronine and thyroxine after 7 and 14 days of treatment. These results suggest that 4-NP can affect different parts of the endocrine system, which may lead to serious impairments in physiological homeostasis of juvenile rainbow trout.

The molecular and structural characterization of two vitellogenins from the free-living nematode Oscheius tipulae

This paper describes the purification of yolk proteins, which are important for the reproduction of egg-laying animals, and the structural characterization of two vitellogenins, VT1 and OTI-VIT-6, of the nematode Oscheius tipulae. O. tipulae is an alternative model organism to its relative, the widely used Caenorhabditis elegans, and is a good model to understand reproduction in insect parasitic nematodes of the genus Heterorhabditis. The native purified O. tipulae vitellogenin is composed of three polypeptides (VT1, VT2 and VT3), whereas in C. elegans, vitellogenin is composed of four polypeptides. The gene (Oti-vit-1) encoding yolk polypeptide VT1 has been recently identified in the genome of O. tipulae. Immunoblotting and N-terminal sequencing confirmed that VT1 is indeed coded by Oti-vit-1. Utilizing the same experimental approaches, we showed that the polypeptides VT2 and VT3 are derived from the proteolytic processing of the C- and N-terminal portions of the precursor OTI-VIT-6, respectively. We also showed that the recombinant polypeptide (P40), corresponding to the N-terminal sequence of OTI-VIT-6, preferentially interacts with a 100-kDa polypeptide found in adult worm extracts, as we have previously shown for the native vitellins of O. tipulae. Using the putative nematode vitellogenin amino acid sequences available in the UniProtKB database, we constructed a phylogenetic tree and showed that the O. tipulae vitellogenins characterized in this study are orthologous to those of the Caenorhabditis spp. Together, these results represent the first structural and functional comparative study of nematode yolk proteins outside the Caenorhabditis genus and provide insight into the evolution of these lipoproteins within the Nematode Phylum.

Seasonal variations in plasma vitellogenin and sex steroids in male and female Eastern Box Turtles, Terrapene carolina carolina

The Eastern Box Turtle (Terrapene carolina carolina) is a widespread species that has recently experienced precipitous declines throughout its range. Although many studies have documented aspects of reproduction in box turtles, reproductive physiology of free-ranging animals is unknown and can be crucial in this species' recovery. Over a two-year period, we measured reproductive parameters, (vitellogenin [Vtg], estradiol-17β [E2], and total testosterone [TT]), in plasma of 116 free-ranging Eastern Box Turtles across their active season. We found similar seasonal variations of Vtg and E2 within females. Mid-season, females showed a sharp peak in E2 that correlates with the putative beginning of the ovarian cycle. Individual females lacking these expected peaks of both Vtg and E2 suggest that some female T. c. carolina may not reproduce annually. Females typically expressed undetectable levels of TT, yet there was a small peak in TT early in the active season. Male Eastern Box Turtles exhibited a dual peak in TT. Elevated TT in males was significantly associated with observed sexual behaviors and smaller home ranges. Body condition had no effect on the concentration of TT or E2 in either sex. This is the first study to (1) document Vtg and sex steroid hormones in free-ranging animals of this genus, and (2) relate those metrics to individuals, the population, the purported annual cycle, and to other chelonian species.

Induction of vitellogenin synthesis in immature male yellowfin seabream (Acanthopagrus latus) exposed to 4-nonylphenol and 17β-estradiol

In the present study, the effects of xenoestrogen 4-nonylphenol (4-NP) and 17β-estradiol (E2) on the synthesis of vitellogenin (VTG) in immature male yellowfin seabream (Acanthoparus latus) were assessed to determine the potential use of this species as a biological model for studying endocrine disrupters in the Musa estuary in southern seawaters of Iran. A total number of 104 fish were injected by 10, 50, 100, 150 and 200 µg g(-) (1) week(-) (1) of 4-NP and 2 µg g(-) (1) week(-) (1) of E2, and their blood plasma was obtained for biochemical analysis on days 0, 7 and 14. The hepatosomatic index (HSI) of each fish was also recorded at each sampling time. The results showed that 4-NP significantly induced VTG synthesis in A. latus, which was detected by gel electrophoresis as two major protein bands (∼210 and 191 KDa). The induction of VTG was also determined indirectly by measuring the alkali-labile phosphate, total plasma calcium and protein. All of these VTG indicators significantly increased in the plasma of 4-NP- and E2-treated fish. Meanwhile, a significant dose-dependent increase was observed in HSI, indicating the activation of hepatic VTG production in 4-NP- and E2-injected fish. Furthermore, the plasma alanine aminotransferase and aspartate aminotransferase concentrations significantly increased in 4-NP-treated fish, presumably reflecting a situation of hepatic tissue damage due to 4-NP toxicity. Based on the results, it is suggested that A. latus could be used successfully as a model species for future studies of endocrine disrupting contaminants in the Musa estuary.

Adult fathead minnow, Pimephales promelas, partial life-cycle reproductive and gonadal histopathology study with bisphenol A

Bisphenol A (BPA) is an intermediate used to produce epoxy resins and polycarbonate plastics. Although BPA degrades rapidly in the environment with aquatic half-lives from 0.5 to 6 d, it can be found in aquatic systems because of widespread use. To evaluate potential effects from chronic exposure, fathead minnows were exposed for 164 d to nominal concentrations of 1, 16, 64, 160, and 640 µg/L BPA. Population-level endpoints of survival, growth, and reproduction were assessed with supplemental endpoints (e.g., vitellogenin, gonad histology), including gonad cell type assessment and quantification. No statistically significant changes in growth, gonad weight, gonadosomatic index, or reproduction variables (e.g., number of eggs and spawns, hatchability) were observed; however, there was a significant impact on male survival at 640 µg/L. Vitellogenin increased in both sexes at 64 µg/L or higher. Gonad cell type frequencies were significantly different from controls at 160 µg/L or higher in males with a slight decrease in spermatocytes compared with less mature cell types, and at 640 µg/L in females with a slight decrease in early vitellogenic cells compared with less mature cells. The decrease in spermatocytes did not correspond to a decrease in the most mature sex cell type (spermatozoa) and did not impair male fertility, as hatchability was not impacted. Overall, marginal shifts in gametogenic cell maturation were not associated with any statistically significant effects on population-relevant reproductive endpoints (growth, fecundity, and hatchability) at any concentration tested.

Reproductive endocrine disruption in smallmouth bass (Micropterus dolomieu) in the Potomac River basin: spatial and temporal comparisons of biological effects

A high prevalence of intersex or testicular oocytes (TO) in male smallmouth bass within the Potomac River drainage has raised concerns as to the health of the river. Studies were conducted to document biomarker responses both temporally and spatially to better understand the influence of normal physiological cycles, as well as water quality and land-use influences. Smallmouth bass were collected over a 2-year period from three tributaries of the Potomac River: the Shenandoah River, the South Branch Potomac and Conococheague Creek, and an out-of-basin reference site on the Gauley River. The prevalence of TO varied seasonally with the lowest prevalence observed in July, post-spawn. Reproductive maturity and/or lack of spawning the previous spring, as well as land-use practices such as application of manure and pesticides, may influence the seasonal observations. Annual, seasonal, and site differences were also observed in the percentage of males with measurable concentrations of plasma vitellogenin, mean concentration of plasma vitellogenin in females, and plasma concentrations of 17β-estradiol and testosterone in both sexes. Bass collected in the South Branch Potomac (moderate to high prevalence of TO) had less sperm per testes mass with a lower percentage of those sperm being motile when compared to those from the Gauley River (low prevalence of TO). An inverse relationship was noted between TO severity and sperm motility. An association between TO severity and wastewater treatment plant flow, percent of agriculture, total number of animal feeding operations, the number of poultry houses, and animal density within the catchment was observed.

Screening complex effluents for estrogenic activity with the T47D-KBluc cell bioassay: assay optimization and comparison with in vivo responses in fish

Wastewater treatment plant (WWTP) effluents can contain estrogenic chemicals, which potentially disrupt fish reproduction and development. The current study focused on the use of an estrogen-responsive in vitro cell bioassay (T47D-KBluc), to quantify total estrogenicity of WWTP effluents. We tested a novel sample preparation method for the T47D-KBluc assay, using powdered media prepared with direct effluent. Results of the T47D-KBluc assay were compared with the induction of estrogen receptor-regulated gene transcription in male fathead minnows (Pimephales promelas) exposed to the same effluents. Effluent samples for the paired studies were collected over the course of three months. According to the T47D-KBluc assay, the effluent estrogenicity ranged from 1.13 to 2.00 ng 17β-estradiol (E2) equivalents/L. Corresponding in vivo studies exposing male fathead minnows to 0, 10, 50, and 100% effluent dilutions demonstrated that exposure to 100% effluent significantly increased hepatic vitellogenin (VTG) and estrogen receptor α subunit transcripts relative to controls. The induction was also significant in males exposed to 250 ng E2/L or 100 ng E2/L. The in vitro and in vivo results support the conclusion that the effluent contains significant estrogenic activity, but there was a discrepancy between in vitro- and in vivo-based E2 equivalent estimates. Our results suggest that the direct effluent preparation method for the T47D-KBluc assay is a reasonable approach to estimate the estrogenicity of wastewater effluent.

The impacts of bisphenol A (BPA) on abalone (Haliotis diversicolor supertexta) embryonic development

The effects of bisphenol A (BPA) on abalone (Haliotis diversicolor supertexta) embryonic development were investigated by exposing the fertilized eggs to four different concentrations of BPA (0.05, 0.2, 2 and 10 μg mL(-1)). Toxicity endpoints including the embryo development parameters, the physiological features and the expression profile of several reference genes (prohormone convertase 1, PC1; cyclin B, CB; and cyclin-dependent kinase 1, CDK1) were assessed. The results showed that BPA could markedly reduce embryo hatchability, increase developmental malformation, and suppress the metamorphosis behavior of larvae. The possible toxicological mechanisms hidden behind of these effects (i.e. disturbing the embryogenesis) might result from three aspects: (1) BPA disturbance the cellular ionic homeostasis and osmoregulation of abalone embryos by changing the Na+-K+-ATPase and Ca2+-Mg2+-ATPase levels; (2) BPA induced oxidative damage of embryos by significantly altering the peroxidase (POD) activities and the malondialdehyde (MDA) production; and (3) the RT-PCR analysis further demonstrated that BPA perturbed the cellular endocrine regulation and cell cycle progression by down-regulating the PC1 gene, as well as over-expressing the CB and CDK1 genes. This is the first comprehensive study on the developmental toxicity of BPA to the marine abalone at morphological, physiological and molecular levels. The results in this study also indicated that the embryo tests can contribute to the ecological risk assessment of the endocrine disruptors in marine environment.

Distinguishing ovarian maturity of farmed white sturgeon (Acipenser transmontanus) by Fourier transform infrared spectroscopy: a potential tool for caviar production management

Fourier transform infrared spectroscopy (FT-IR, 4000-400 cm(-1)) was applied to blood plasma of farmed white sturgeon (N = 40) to differentiate and predict the stages of ovarian maturity. Spectral features of sex steroids (approximately 3000 cm(-1)) and vitellogenin (approximately 1080 cm(-1)) were identified. Clear segregation of maturity stages (previtellogenesis, vitellogenesis, postvitellogenesis, and follicular atresia) was achieved using principal component analysis (PCA). Progression of oocyte development in the late phase of vitellogenesis was also monitored using PCA based on changes in plasma concentrations of sex steroid and lipid content. The observed oocyte polarization index (PI, a measure of nuclear migration) was correlated with changes in plasma sex steroid levels revealed by FT-IR PCA results. A partial least squares (PLS) model predicted PI values within the range 0.12-0.40 (R = 0.95, SEP = 2.18%) from differences in spectral features. These results suggest that FT-IR may be a good tool for assessing ovarian maturity in farmed sturgeon and will reduce the need for the invasive ovarian biopsy required for PI determination.

Adverse outcome pathways: a conceptual framework to support ecotoxicology research and risk assessment

Ecological risk assessors face increasing demands to assess more chemicals, with greater speed and accuracy, and to do so using fewer resources and experimental animals. New approaches in biological and computational sciences may be able to generate mechanistic information that could help in meeting these challenges. However, to use mechanistic data to support chemical assessments, there is a need for effective translation of this information into endpoints meaningful to ecological risk-effects on survival, development, and reproduction in individual organisms and, by extension, impacts on populations. Here we discuss a framework designed for this purpose, the adverse outcome pathway (AOP). An AOP is a conceptual construct that portrays existing knowledge concerning the linkage between a direct molecular initiating event and an adverse outcome at a biological level of organization relevant to risk assessment. The practical utility of AOPs for ecological risk assessment of chemicals is illustrated using five case examples. The examples demonstrate how the AOP concept can focus toxicity testing in terms of species and endpoint selection, enhance across-chemical extrapolation, and support prediction of mixture effects. The examples also show how AOPs facilitate use of molecular or biochemical endpoints (sometimes referred to as biomarkers) for forecasting chemical impacts on individuals and populations. In the concluding sections of the paper, we discuss how AOPs can help to guide research that supports chemical risk assessments and advocate for the incorporation of this approach into a broader systems biology framework.

Optimization and validation of a California halibut environmental estrogen bioassay using a heterologous ELISA

Vitellogenin, the estrogen-inducible yolk protein precursor, serves as an indicator of exposure to estrogen mimicking environmental contaminants. An ELISA for the measurement of California halibut plasma vitellogenin was optimized and validated using a commercially-available antibody developed for another flatfish species, turbot. Attempts to enhance assay performance by addition of a biotinylated antibody, polyethylene glycol, and Tween-20, and altering the preincubation step are described. Inclusion of overnight preincubation was critical for low detection limits. Increasing the amount of Tween-20 to 0.05% in buffers was most effective in achieving accurate quantification of spiked plasma samples. At the IC50, the average recovery of spiked plasma samples was 104% and the interplate CV was 12%. The working range of the assay was 33-1000 ng/mL, while the detection limit in a plasma sample is 2.2 microg/mL. The performance of this assay compared very well to a homologous assay demonstrating that commercially-available antibodies can facilitate the development of bioassays for local environmentally-relevant species. The dose response relationship of halibut Vg to the model compounds 17beta-estradiol and pnonylphenol show that it is a suitable model for further studies of estrogen mimicking contaminants.

Establishment of ELISA for murrel vitellogenin and choriogenin, as biomarkers of potential endocrine disruption

Vitellogenin (Vg) and choriogenin (Chg) are sensitive biomarkers for testing endocrine disruption in fish. Therefore, we have developed immunoassays for Vg and Chg in the Indian freshwater murrel, Channa punctatus. Vg is a known precursor of egg-yolk proteins, whereas Chg contributes to the formation of egg-envelope. Vg and Chg were induced in male murrel by administration of estradiol-17beta. Chg had an apparent native molecular mass of 180 kDa. It consisted of a single peptide with a molecular mass of 110 kDa, whereas native Vg protein (530 kDa) contained 175 kDa peptide. Highly specific polyclonal antibodies against purified plasma proteins, Vg and Chg, were employed for developing competitive enzyme linked immunosorbent assays (ELISAs). The sensitivity of Vg assay was 3.9 ng/mL (working range 15-500 ng/mL) and of Chg assay was 1.56 ng/mL (working range 6-200 ng/mL). The inter- and intra-assay variations were well within acceptable limits. The two antisera did not cross-react with male plasma proteins. Antiserum to Vg did not cross-react with Chg. Similarly, antiserum to Chg showed no correlation with Vg. Further, immunofluorescence and Western blotting confirmed the specificity of Vg and Chg antisera.