In vitro vitellogenin production by carp (Cyprinus carpio) hepatocytes as a screening method for determining (anti)estrogenic activity of xenobiotics

In vitro biotransformation assays using fish liver cells: Comparing rainbow trout and carp hepatocytes

Biotransformation assays using primary hepatocytes from rainbow trout, Oncorhynchus mykiss, were validated as a reliable in vitro tool to predict in vivo bioconcentration factors (BCF) of chemicals in fish. Given the pronounced interspecies differences of chemical biotransformation, the present study aimed to compare biotransformation rate values and BCF predictions obtained with hepatocytes from the cold-water species, rainbow trout, to data obtained with hepatocytes of the warm-water species, common carp (Cyprinus carpio). In a first step, we adapted the protocol for the trout hepatocyte assay, including the cryopreservation method, to carp hepatocytes. The successful adaptation serves as proof of principle that the in vitro hepatocyte biotransformation assays can be technically transferred across fish species. In a second step, we compared the in vitro intrinsic clearance rates (CL_{in vitro, int}) of two model xenobiotics, benzo[a]pyrene (BaP) and methoxychlor (MXC), in trout and carp hepatocytes. The in vitro data were used to predict in vivo biotransformation rate constants (k_B) and BCFs, which were then compared to measured in vivo k_B and BCF values. The CL_{in vitro, int} values of BaP and MXC did not differ significantly between trout and carp hepatocytes, but the predicted BCF values were significantly higher in trout than in carp. In contrast, the measured in vivo BCF values did not differ significantly between the two species. A possible explanation of this discrepancy is that the existing in vitro-in vivo prediction models are parameterized only for trout but not for carp. Therefore, future research needs to develop species-specific extrapolation models.

An In Silico and In Vitro study for Investigating Estrogenic Endocrine Effects of Emerging Persistent Pollutants using Primary Hepatocytes from Grey Mullet (Mugil Cephalus)

There is growing concern about the environmentally relevant concentrations of new emerging persistent organic pollutants, such as perfluorinated compounds and pharmaceuticals, which are found to bioaccumulate in aquatic organisms at concentrations suspected to cause reproductive toxicity due to the activation of estrogen receptor (ER) α and β subtypes. Here, we use a combined in silico and in vitro approach to evaluate the impact of perfluorononanoic acid (PFNA) and Enalapril (ENA) on grey mullet (Mugil cephalus) hepatic estrogen signaling pathway. ENA had weak agonist activity on ERα while PFNA showed moderate to high agonist binding to both ERs. According to these effects, hepatocytes incubation for 48 h to PFNA resulted in a concentration-dependent upregulation of ER and vitellogenin gene expression profiles, whereas only a small increase was observed in ERα mRNA levels for the highest ENA concentration. These data suggest a structure–activity relationship between hepatic ERs and these emerging pollutants.

Chlorinated Polyfluoroalkylether Sulfonic Acids Exhibit Stronger Estrogenic Effects than Perfluorooctane Sulfonate by Activating Nuclear Estrogen Receptor Pathways

Chlorinated polyfluoroalkylether sulfonic acids (Cl-PFESAs) have been shown to have potential thyroid hormone (TH) disruption effects. Here, we further investigated their estrogenic effects and underlying mechanisms. In vivo results revealed that exposure of zebrafish to Cl-PFESAs induced disorder of sex hormones during the early embryonic stages and caused histopathological lesions in the gonads of adult zebrafish relative to control groups. To find out whether the estrogen receptor is the molecular target of Cl-PFESAs, the binding interaction between Cl-PFESAs and ERs was investigated using a series of in vitro assays. We found that all tested chemicals could bind directly to ERs and exhibit relatively weak agonistic activity toward ERs, suggesting that the ER-mediated signaling pathway is directly involved in the estrogenic effects of Cl-PFESAs. The internal dose of 8:2 Cl-PFESA was significantly higher than the others, which explained why it obviously displayed an ER agonistic effect despite its weak ER binding affinity. Taken together, these results uncover that, in addition to the TH disruption effect, Cl-PFESAs might also cause estrogenic effects by activating ER pathways.

Integrated Decision-tree Testing Strategies for Environmental Toxicity with Respect to the Requirements of the EU REACH Legislation

Liverpool John Moores University and FRAME recently conducted a research project sponsored by Defra on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with the REACH system. This paper focuses on the prospects for using alternative methods (both in vitro and in silico) for environmental (aquatic) toxicity testing. The manuscript reviews tests based on fish cells and cell lines, fish embryos, lower organisms, and the many expert systems and QSARs for aquatic toxicity testing. Ways in which reduction and refinement measures can be used are also discussed, including the Upper Threshold Concentration -- Step Down (UTC) approach, which has recently been retrospectively validated by ECVAM and subsequently endorsed by the ECVAM Scientific Advisory Committee (ESAC). It is hoped that the application of this approach could reduce the number of fish used in acute toxicity studies by around 65-70%. Decision-tree style integrated testing strategies are also proposed for acute aquatic toxicity and chronic toxicity (including bioaccumulation), followed by a number of recommendations for the future facilitation of aquatic toxicity testing with respect to environmental risk assessment.

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.

Characterizing combined effects of antiestrogenic chemicals on vitellogenin production in rainbow trout (Oncorhynchus mykiss) hepatocytes

Fish are exposed to a complex mixture of endocrine disrupting compounds (EDC), some of which display antiestrogenic activity leading to suppression of estrogen receptor (ER)- mediated reproductive processes. Although the main mode of action (MoA) of these antiestrogens is to directly interfere with natural ligand binding of the ER, several other MoA have been proposed. The aim of the present study was to characterize single and combined antiestrogenic effects of the aryl hydrocarbon receptor (AhR)-agonist β-naphthoflavone (BNF) and ER-antagonist 4-hydroxytamoxifen (OHT) on vitellogenin (Vtg) protein using primary rainbow trout (Oncorhynchus mykiss) hepatocytes. Supporting transcriptional analysis of ER-responsive genes (estrogen receptor-α (er-α), vitellogenin-1 (vtg-1), eggshell zona radiata protein (zrp)) and AhR-mediated genes (aryl hydrocarbon receptor-2β, cytochrome p450-1a (cyp1a)) was performed by qPCR to characterize the antiestrogenic influence on ER- and AhR-mediated responses. Data demonstrated that both BNF and OHT significantly reduced 17β-estradiol (E2)-induced Vtg protein expression in a concentration responsive manner, whereas exposure to a mixture of these produced an additive antiestrogenic effect. The results observed at the protein level were further supported by transcriptional analysis of ER-responsive genes (er-α, vtg-1, zrp), where only E2-induced vtg-1 gene expression was significantly decreased by OHT and the mixture of OHT and BNF. E2-induced er-α and zrp gene expression was not markedly altered. The significant reduction of E2-induced vtg-1 gene expression by OHT suggested that the antiestrogenic effect of this compound may be associated with ER signaling pathway. Specific genes involved in putative AhR-ER cross-talk were also investigated, however none were directly associated with the compound anti-estrogenic MoA. Although the MoA of the single compounds and mixture were not completely characterized, the present study enhanced our knowledge of the combined toxicity mediated by antiestrogens acting through different MoA.

Challenges in assigning endocrine-specific modes of action: Recommendations for researchers and regulators

As regulatory programs evaluate substances for their endocrine-disrupting properties, careful study design and data interpretation are needed to distinguish between responses that are truly endocrine specific and those that are not. This is particularly important in regulatory environments where criteria are under development to identify endocrine-disrupting properties to enable hazard-based regulation. Irrespective of these processes, most jurisdictions use the World Health Organization/International Programme on Chemical Safety definition of an endocrine disruptor, requiring that a substance is demonstrated to cause a change in endocrine function that consequently leads to an adverse effect in an intact organism. Such a definition is broad, and at its most cautious might capture many general mechanisms that would not specifically denote an endocrine disruptor. In addition, endocrine responses may be adaptive in nature, designed to maintain homeostasis rather than induce an irreversible adverse effect. The likelihood of indirect effects is increased in (eco)toxicological studies that require the use of maximum tolerated concentrations or doses, which must produce some adverse effect. The misidentification of indirect effects as truly endocrine mediated has serious consequences for prompting animal- and resource-intensive testing and regulatory consequences. To minimize the risk for misidentification, an objective and transparent weight-of-evidence procedure based on biological plausibility, essentiality, and empirical evidence of key events in an adverse outcome pathway is recommended to describe the modes of action that may be involved in toxic responses in nontarget organisms. Confounding factors such as systemic toxicity, general stress, and infection can add complexity to such an evaluation and should be considered in the weight of evidence. A recommended set of questions is proffered to help guide researchers and regulators in discerning endocrine and nonendocrine responses. Although many examples provided in this study are based on ecotoxicology, the majority of the concepts and processes are applicable to both environmental and human health assessments. Integr Environ Assess Manag 2017;13:280-292. © 2016 SETAC.

Kinetic determination of vitellogenin induction in the epidermis of cyprinid and perciform fishes: Evaluation of sensitive enzyme-linked immunosorbent assays

Induction of vitellogenin (VTG) in male and immature fish is a standardized endpoint in endocrine-disruption testing. To establish a nondestructive swab sampling method, VTG induction in the epidermis of Cypriniformes and Perciformes species was investigated. Both VTG and estrogen receptor genes are expressed in epidermal cells. Immunoaffinity and mass fingerprint analyses show induction of identical VTG peptides in liver and epidermis. Induction of VTG by estradiol (E2) and bisphenol A (BPA) in the epidermis was quantified with homolog enzyme-linked immunosorbent assays. Initial values in juveniles and males were below 1 ng VTG/mL extraction buffer. Exposure to E2 led to values between 200 ng/mL and 4600 ng/mL in cyprinids and between 10 ng/mL and 81 ng/mL in perciforms. Exposure to BPA increased VTG amounts to 250 ng/mL in fathead minnows, 1360 ng/mL in goldfish, 100 ng/mL in zebrafish, and 12 ng/mL in bluegills. Serum VTG contents demonstrated a similar dose-response pattern in the epidermis and the blood. These results show that VTG induction may be reliably assessed in the skin mucus of fishes, demonstrating the suitability of this biological sample for investigating estrogenic activity in compliance with Organisation for Economic Co-operation and Development standard protocols. This broadens the perspectives in toxicological screening and environmental monitoring, reducing the number of tested animals and minimizing harmful effects for animals, allowing for follow-up of individual induction profiles. Environ Toxicol Chem 2016;35:2916-2930. © 2016 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Regulation of vitellogenin (vtg1) and estrogen receptor (er) gene expression in zebrafish (Danio rerio) following the administration of Cd²⁺ and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

We evaluated the individual and joint estrogenic effects of cadmium (Cd(2+)) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the zebrafish liver (ZFL) cell line, zebrafish embryo, larvae and the liver of adult zebrafish. The mRNA expression of vtg1 was inhibited by Cd(2+), but unaffected by TCDD in ZFL cells. Similar changes in the mRNA levels of ERα, ERβ1, ERβ2 and GPER (G protein coupled estrogen receptor) in ZFL cells were also observed. Deletion mutants of vtg1 gene promoters were constructed to investigate transcriptional regulation, and we found that all of the constructs failed to respond to TCDD or Cd(2+). However, after co-transfection with a vtg1 promoter-luciferase construct to the ERα, ERβ1, ERβ2 and GPER expression vectors, decreased luciferase activity was observed in the ERα co-transfection group after treatment with Cd(2+), suggesting that ERα participates in vtg1 transcriptional regulation and is affected by Cd(2+). Differences in the regulation of the mRNA levels of these genes were also observed between different developmental stages and between the livers of male and female zebrafish.

17α-Ethinylestradiol (EE2) effect on global gene expression in primary rainbow trout (Oncorhynchus mykiss) hepatocytes

The potential impact of endocrine disrupting chemicals (EDCs) in the aquatic environment has driven the development of screening assays to evaluate the estrogenic properties of chemicals and their effects on aquatic organisms such as fish. However, obtaining full concentration-response relationships in animal (in vivo) exposure studies are laborious, costly and unethical, hence a need for developing feasible alternative (non-animal) methods. Use of in vitro bioassays such as primary fish hepatocytes, which retain many of the native properties of the liver, has been proposed for in vitro screening of estrogen receptor (ER) agonists and antagonists. The aim of present study was to characterize the molecular mode of action (MoA) of the ER agonist 17α-ethinylestradiol (EE2) in primary rainbow trout (Oncorhynchus mykiss) hepatocytes. A custom designed salmonid 60,000-feature (60k) oligonucleotide microarray was used to characterize the potential MoAs after 48h exposure to EE2. The microarray analysis revealed several concentration-dependent gene expression alterations including classical estrogen sensitive biomarker gene expression (e.g. estrogen receptor α, vitellogenin, zona radiata). Gene Ontology (GO) analysis displayed transcriptional changes suggesting interference of cellular growth, fatty acid and lipid metabolism potentially mediated through the estrogen receptor (ER), which were proposed to be associated with modulation of genes involved in endocrine function and reproduction. Pathway analysis supported the identified GOs and revealed modulation of additional genes associated with apoptosis and cholesterol biosynthesis. Differentially expressed genes (DEGs) related to impaired lipid metabolism (e.g. peroxisome proliferator-activated receptor α and γ), growth (e.g. insulin growth factor protein 1), phase I and II biotransformation (e.g. cytochrome P450 1A, sulfotransferase, UDP-glucuronosyltransferase and glutathione S-transferase) provided additional insight into the MoA of EE2 in primary fish hepatocytes. Results from the present study suggest that biotransformation, estrogen receptor-mediated responses, lipid homeostasis, growth and cancer/apoptosis in primary fish hepatocytes may be altered after short-term exposure to ER-agonists such as EE2. In many cases the observed changes were similar to those reported for estrogen-exposed fish in vivo. In conclusion, global transcriptional analysis demonstrated that EE2 affected a number of toxicologically relevant pathways associated with an estrogenic MoA in the rainbow trout hepatocytes.

Comparison of the sensitivity of four native Canadian fish species to 17-α ethinylestradiol, using an in vitro liver explant assay

Exposure to environmental estrogens and other endocrine-active chemicals can impact reproduction of freshwater fishes. While extensive data exists regarding the effect of estrogens on standard laboratory species, little is known about the sensitivity of freshwater fishes native to North America to these compounds. Current testing strategies for the toxicological assessment of contaminants still rely heavily on studies with live animals, which poses increasing concerns from an economical and ethical perspective. Therefore, the aim of the present study was to investigate the sensitivity of four native species, namely, northern pike (Esox lucius), walleye (Sander vitreus), white sucker (Catostomus commersoni), and juvenile white sturgeon (Acipenser transmontanus), to an environmental estrogen, 17α-ethinylestradiol (EE2), using an in vitro tissue explant approach. Transcript abundances of vitellogenin (VTG) as well as the estrogen receptors (ER) α and β were used as the measuring endpoints as they represent well established biomarkers previously used to assess exposure to estrogens. Transcript abundance of VTG was upregulated in a concentration-dependent manner in each species. Liver explants of male walleye were found to have the greatest sensitivity to EE2, with a lowest observable effect concentration of 300 ng/L (1.0 nM) for VTG transcript abundance, with juvenile white sturgeon having the greatest magnitude of VTG transcript upregulation in exposed tissue (15-fold relative to control). Exposure of liver explants to EE2 resulted in no alteration in transcript abundance of ERβ, whereas upregulation of ERα was observed in northern pike only. Based on in vitro expression of VTG, the species tested were among the species with greatest sensitivity to environmental estrogens tested to date.

Assessment of biomarkers for contaminants of emerging concern on aquatic organisms downstream of a municipal wastewater discharge

Contaminants of emerging concern (CECs), including pharmaceuticals, personal care products and estrogens, are detected in wastewater treatment plant (WWTP) discharges. However, analytical monitoring of wastewater and surface water does not indicate whether CECs are affecting the organisms downstream. In this study, fathead minnows (Pimephales promelas) and freshwater mussels Pyganodon grandis Say, 1829 (synonym: Anodonta grandis Say, 1829) were caged for 4 weeks in the North Saskatchewan River, upstream and downstream of the discharge from the WWTP that serves the Edmonton, AB, Canada. Passive samplers deployed indicated that concentrations of pharmaceuticals, personal care products, an estrogen (estrone) and an androgen (androstenedione) were elevated at sites downstream of the WWTP discharge. Several biomarkers of exposure were significantly altered in the tissues of caged fathead minnows and freshwater mussels relative to the upstream reference sites. Biomarkers altered in fish included induction of CYP3A metabolism, an increase in vitellogenin (Vtg) gene expression in male minnows, elevated ratios of oxidized to total glutathione (i.e. GSSG/TGSH), and an increase in the activity of antioxidant enzymes (i.e. glutathione reductase, glutathione-S-transferase). In mussels, there were no significant changes in biomarkers of oxidative stress and the levels of Vtg-like proteins were reduced, not elevated, indicating a generalized stress response. Immune function was altered in mussels, as indicated by elevated lysosomal activity per hemocyte in P. grandis caged closest to the wastewater discharge. This immune response may be due to exposure to bacterial pathogens in the wastewater. Multivariate analysis indicated a response to the CECs Carbamazepine (CBZ) and Trimethoprim (TPM). Overall, these data indicate that there is a 1 km zone of impact for aquatic organisms downstream of WWTP discharge. However, multiple stressors in municipal wastewater make measurement and interpretation of impact of CECs difficult since water temperature, conductivity and bacteria are also inducing biomarker responses in both fish and mussels.

Evaluation of the sensitivity, responsiveness and reproducibility of primary rainbow trout hepatocyte vitellogenin expression as a screening assay for estrogen mimics

Vitellogenin (Vtg) induction in primary fish hepatocytes has been proposed as an in vitro screening assay for ER agonists and antagonists, but has not yet been used extensively as a high-throughput screening tool due to poor reproducibility, sensitivity and overall feasibility. The present work has evaluated the role of seasonal variation, normalization, optimal culture and assay conditions on the sensitivity, responsiveness and reproducibility of in vitro vtg gene mRNA and protein expression in rainbow trout (Oncorhynchus mykiss) primary hepatocytes using the xenoestrogen 17α-ethynylestradiol (EE2) as a test chemical. The results show that primary hepatocytes display a relatively high individual and seasonal variation in both Vtg mRNA and protein induction potential, although less variance was observed in assay sensitivity. Data normalization of assay response to maximum (3 nM EE2) and minimum (DMSO) Vtg production dramatically reduced this variance and led to improved assay reproducibility. A time-dependent response was observed both for mRNA and protein expression, reaching maximum Vtg induction after 96 h of exposure, although reproducible concentration response curves for both Vtg mRNA and protein could be obtained already after 48 h. A need for chemical re-exposure of the hepatocytes was identified to be important for sustaining exposure concentrations in extended studies (>48 h), whereas different plate formats (96, 24 or 6 wells) did not affect the bioassay performance. In conclusion, standardization of hepatocyte bioassay and test conditions as well as data-normalization procedures are proposed to be instrumental for more consistent and comparable results in future use of this in vitro assay.

Luteinizing hormone receptor (lhcgr) as a marker gene for characterizing estrogenic endocrine-disrupting chemicals in zebrafish ovarian follicle cells

The adverse effects of endocrine-disrupting chemicals (EDCs) have been well documented; however, the action mechanisms of many EDCs remain elusive and controversial. Furthermore, the highly diversified chemical structures and low environmental concentrations of EDCs present a major challenge to their chemical detection. Clearly, there is an urgent need for simple and reliable bioassays to detect EDCs in the environment and unravel their action mechanisms. We have recently identified luteinizing hormone receptor (lhcgr) as a robust estradiol (E2)-responsive gene in cultured zebrafish ovarian follicle cells. The expression of lhcgr exhibited a distinct biphasic response to E2 over a 24-h time-course treatment, making this a unique system for characterizing estrogenic EDCs. This study was undertaken to validate this platform by testing a wide range of EDCs, including 17α-ethinylestradiol (EE2), diethylstilbestrol (DES), bisphenol A (BPA), genistein (GEN), 1,1,1-trichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethane (o,p'-DDT), vinclozolin (VIN), bis(2-ethylhexyl) phthalate (DEHP), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). Diethylstilbestrol (DES), EE2 and o,p'-DDT mimicked E2 and induced a biphasic expression of lhcgr while BPA and GEN stimulated a monophasic expression in the 24-h time-course. In contrast, BDE-47, DEHP and VIN had no effect, whereas TCDD decreased lhcgr expression. Dose-response experiment showed that E2, EE2 and DES had the highest potency, which was followed by GEN, BPA and o,p'-DDT. The effects of estrogenic EDCs were further confirmed by their potentiation of hCG-induced activin βA2 subunit (inhbab) expression. In conclusion, the present study showed that the expression of lhcgr in cultured zebrafish follicle cells and its biphasic response to estrogens provide a unique in vitro platform for screening and categorizing estrogenic substances and deciphering their action mechanisms.

Bacterial biosensors for evaluating potential impacts of estrogenic endocrine disrupting compounds in multiple species

To study the effects and possible mechanisms of suspected endocrine disrupting compounds (EDCs), a wide variety of assays have been developed. In this work, we generated engineered Escherichia coli biosensor strains that incorporate the ligand-binding domains (LBDs) of the β-subtype estrogen receptors (ERβ) from Solea solea (sole), and Sus scrofa (pig). These strains indicate the presence of ligands for these receptors by changes in growth phenotype, and can differentiate agonist from antagonist and give a rough indication of binding affinity via dose-response curves. The resulting strains were compared with our previously reported Homo sapiens ERβ biosensor strain. In initial tests, all three of the strains correctly identified estrogenic test compounds with a high degree of certainly (Z' typically greater than 0.5), including the weakly binding test compound bisphenol A (BPA) (Z' ≈ 0.1-0.3). The modular design of the sensing element in this strain allows quick development of new species-based biosensors by simple LBD swapping, suggesting its use in initial comparative analysis of EDC impacts across multiple species. Interestingly, the growth phenotypes of the biosensor strains indicate similar binding for highly estrogenic control compounds, but suggest differences in ligand binding for more weakly binding EDCs.

Alternatives to in vivo tests to detect endocrine disrupting chemicals (EDCs) in fish and amphibians--screening for estrogen, androgen and thyroid hormone disruption

Endocrine disruption is considered a highly relevant hazard for environmental risk assessment of chemicals, plant protection products, biocides and pharmaceuticals. Therefore, screening tests with a focus on interference with estrogen, androgen, and thyroid hormone pathways in fish and amphibians have been developed. However, they use a large number of animals and short-term alternatives to animal tests would be advantageous. Therefore, the status of alternative assays for endocrine disruption in fish and frogs was assessed by a detailed literature analysis. The aim was to (i) determine the strengths and limitations of alternative assays and (ii) present conclusions regarding chemical specificity, sensitivity, and correlation with in vivo data. Data from 1995 to present were collected related to the detection/testing of estrogen-, androgen-, and thyroid-active chemicals in the following test systems: cell lines, primary cells, fish/frog embryos, yeast and cell-free systems. The review shows that the majority of alternative assays measure effects directly mediated by receptor binding or resulting from interference with hormone synthesis. Other mechanisms were rarely analysed. A database was established and used for a quantitative and comparative analysis. For example, a high correlation was observed between cell-free ligand binding and cell-based reporter cell assays, between fish and frog estrogenic data and between fish embryo tests and in vivo reproductive effects. It was concluded that there is a need for a more systematic study of the predictive capacity of alternative tests and ways to reduce inter- and intra-assay variability.

In vitro and in vivo hepatoprotective and antioxidant effects of Astragalus polysaccharides against carbon tetrachloride-induced hepatocyte damage in common carp (Cyprinus carpio)

The present study is aiming at evaluating the hepatoprotective and antioxidant effects of Astragalus polysaccharide (APS) on the carbon tetrachloride (CCl(4))-induced hepatocyte and liver injury in common carp in vitro and in vivo. In vitro, APS (200, 400 and 800 μg/ml) was added to the carp primary hepatocytes before (pre-treatment), after (post-treatment) and both before and after (pre- and post-treatment) the incubation of the hepatocytes with CCl(4) at 8 mM in the culture medium. APS at concentrations of 200, 400 and 800 μg/ml significantly improved cell viability and inhibited the elevation of glutamate pyruvate transaminase (GPT), glutamate oxalate transaminase (GOT), lactate dehydrogenase (LDH) and malondialdehyde (MDA) and significantly increased the reduced level of superoxide dismutase (SOD). In vivo administration of APS at the doses of 1.5 and 3 g/kg in the diet for 60 days prior to CCl(4) intoxication significantly reduced the elevated activities of GPT, GOT and LDH and increased the reduced levels of total protein and albumin in the serum; meanwhile, the reduced levels of SOD, glutathione and total antioxidant capacity (T-AOC) were markedly increased and the MDA formation was significantly inhibited in liver tissue. Overall results proved the hepatoprotective action of APS, which is likely related to its antioxidant activity. The results support the use of APS as a hepatoprotective and antioxidant agent in fish.

Combined effects of oestrogen receptor antagonists on in vitro vitellogenesis

Some environmental compounds are known to have anti-oestrogenic activity and their modes of action (MoA) are believed to include competitive inhibition of 17β-estradiol (E2) binding to the oestrogen receptor (ER) or interference with ER-dependent processes. The presence of multiple compounds having the same MoA may cause concern, as exposure to multiple compounds at concentrations below their threshold for effect can interact with cellular targets to cause effects in combination. The combined effect of mixtures can be assessed using prediction models such as concentration addition (CA) and independent action (IA). The objective of the present study was to determine if the CA and IA prediction models could accurately characterise the combined effects of mixtures of ER antagonists in rainbow trout (Oncorhynchus mykiss) hepatocytes using the ER-mediated production of the oestrogenic biomarker vitellogenin (Vtg) as a screening assay. Model anti-oestrogens (4-hydroxytamoxifen and ZM 189.154) and environmentally relevant compounds (PCBs and PAHs) were tested to ensure inclusion of compounds from different chemical classes and with different MoAs. All eleven tested compounds had the ability to reduce the in vitro E2-induced production of Vtg in a concentration-dependent manner. The potency of the tested compounds differed by four orders of magnitude based on the concentrations for 50% inhibition (IC(50)). The observed order of potency was 2,3,7,8-tetrachlorodibenzo-p-dioxin>4-hydroxytamoxifen>3,3',4,4',5-pentachlorobiphenyl>benzo(k)fluoranthene>3,3',4,4'-tetrachlorobiphenyl>β-naphthoflavone>ZM 189.154>indeno[1,2,3-cd]pyrene>benzo(b)fluoranthene>benzo(a)pyrene>benzo(a)anthracene. The CA and IA models were able to predict the combined effects of mixtures of ER antagonists with similar MoA. The mixtures of certain ER-antagonists with different and/or complex MoA caused deviations from both the CA and the IA model by causing higher anti-oestrogenic activity than predicted from the potency of the compounds alone. The rationale for these deviations warrants additional studies to assess the potential impacts on the health of organisms.

Hepatoprotective and antioxidant effects of Glycyrrhiza glabra extract against carbon tetrachloride (CCl(4))-induced hepatocyte damage in common carp (Cyprinus carpio)

The present study is aiming at evaluating the hepatoprotective and antioxidant effects of Glycyrrhiza glabra extract (2.5, 5 and 10 μg/ml) on the carbon tetrachloride (CCl(4))-induced carp hepatocyte damage in vitro. Glycyrrhiza glabra extract was added to the carp primary hepatocytes before (pre-treatment), after (post-treatment) and both before and after (pre- and post-treatment) the incubation of the hepatocytes with CCl(4). CCl(4) at 8 mM in the culture medium produced significantly elevated levels of lactate dehydrogenase (LDH), glutamate oxalate transaminase (GOT), glutamate pyruvate transaminase (GPT) and malondialdehyde (MDA) and significantly reduced levels of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). Pre-treatment (5 μg/ml) and pre- and post-treatment (5 and 10 μg/ml) of the hepatocytes with Glycyrrhiza glabra extract significantly reduced the elevated levels of LDH, GOT, GPT and MDA and increased the reduced levels of SOD and GSH-Px by CCl(4); post-treatment of the hepatocytes with Glycyrrhiza glabra extract at 5 μg/ml reduced the GPT and GOT levels and increased the GSH-Px level, but had no effect on the other parameters at all the studied concentrations. The results support the use of Glycyrrhiza glabra extract as a hepatoprotective and antioxidant agent in fish.

A new in vitro screening bioassay for the ecotoxicological evaluation of the estrogenic responses of environmental chemicals using roach (Rutilus rutilus) liver explant culture

There is growing evidence that many chemicals released in the environment are able to disturb the normal endocrinology of organisms affecting the structure and function of their reproductive system. This has prompted the scientific community to develop appropriate testing methods to identify active compounds and elucidate mechanisms of action. Of particular interest are in vitro screening methods that can document the effects of these endocrine disrupting compounds on fish. In this study, an in vitro bioassay was developed in the roach (Rutilus rutilus) for evaluating the estrogenicity or antiestrogenicity potency of environmental pollutants by measuring vitellogenin (VTG) induction in cultured liver explants. The cell viability was assessed by the measurement of nonspecific esterase activity using a fluorescein diacetate hydrolysis assay. Results showed that explants could be cultured for 72 h without any significant loss of activity. Dose-dependent responses have been measured with estrogenic model compounds such as 17-β-estradiol (E2) and 17-α-ethynylestradiol (EE2) or antiestrogenic compounds such as tamoxifen. Lowest observable effective concentrations were 1 nM for E2, 1 nM for EE2, and 100 nM for tamoxifen, showing a good sensitivity of the test system. Estrogenicity of butyl 4-hydroxybenzoate, 4-nonylphenol, and bisphenol A was tested. bisphenol A (100 μM) or butylparaben induced a twofold increase in VTG production when compared with 100 nM E2, whereas this production was only 20% with 100 μM 4-nonylphenol. Overall, this study shows that the bioassay could provide valuable information on endocrine disrupting chemicals including metabolites and mixtures of compounds.

First evidence of estrogenic potential of the cyanobacterial heptotoxins the nodularin-R and the microcystin-LR in cultured mammalian cells

The estrogenic activity of cyanobacterial hepatotoxins microcystin-LR (MC-LR) and nodularin-R (NOD-R) was for the first time investigated invitro in a stably transfect cell line with an estrogen-regulated luciferase gene. Treatment of cells with NOD-R caused a dose-dependent increase in the luciferase activity. NOD-R gave rise to an induction of luciferase activity with an EC(50) value of 66.4 nM, whereas the positive control, 17beta-estradiol (E2) had an EC(50) of 9.6 pM. This indicates that NOD-R is a 6900-fold weaker inducer of luciferase than E2. In contrast, only a slight but significant activation of the luciferase gene was observed with MC-LR between 2.01 and 60.1 nM, and a maximal-induced response was observed with 10.1 nM, approximately 25% of the maximal effect obtained with 1 nM E2. The decrease in the luciferase activity at high MC-LR concentrations can be explained by a cytotoxic effect. No synergistic estrogenic effect was observed when each toxin was co-administrated with E2. However, the induction of the luciferase activity by NOD-R and MC-LR was inhibited by co-treatment with 1 microM of the pure estrogenic receptor (ER) antagonist ICI 182,780, thus proving the ER-dependency of the estrogenic effect.

Screening of chemicals with anti-estrogenic activity using in vitro and in vivo vitellogenin induction responses in zebrafish (Danio rerio)

Growing concern over possible adverse effects of endocrine-disrupting chemicals (EDCs) has driven the development of associated screening methods. The use of the vitellogenin (VTG) induction response in cultured teleost hepatocytes has been suggested as an in vitro screening assay for EDCs. However, current data do not sufficiently support this assay in the routine screening of chemicals. This study established and validated the use of primary cultured hepatocytes from zebrafish to screen chemicals for anti-estrogenic activities. Here we measured the transcript levels of selected hepatic estrogen-response genes, including vtg1, vtg2 and eralpha. Two model anti-estrogens, letrozole (LET), an aromatase inhibitor, and tamoxifen (TAM), a competitive estrogen receptor, were selected as representative chemicals. Additionally, comparisons between in vitro and in vivo assays were performed. As expected, there were concentration-dependent decreases for all three genes in the liver of female zebrafish exposed to LET in vivo for 72h. Similar responses were observed in males. As for in vitro testing, no discernable alterations in the gene transcripts were found in hepatocytes from males or females. In the case of TAM, exposure for 72h caused transcriptional reduction of hepatic estrogen-response genes in females in vivo and in vitro. In males, low concentrations of TAM resulted in increased expression of genes, while the expression decreased slightly at higher concentrations. Since these observations were in agreement with the pharmaceutical properties of two tested chemicals, the primary hepatocyte culture could be a promising tool for screening suspected EDCs.

Common carp (Cyprinus carpio) insulin-like growth factor binding protein-2 (IGFBP-2): molecular cloning, expression profiles, and hormonal regulation in hepatocytes

In the present study, we cloned IGFBP-2 cDNA from common carp (Cyprinus carpio) liver. The 1879 bp full-length cDNA encodes 274 amino acid residues containing a putative signal peptide of 22 residues. Two IGFBP-2 transcripts with estimated sizes of 2.2 and 1.5 kb have been detected with Northern blot analysis in liver. Relatively high levels of IGFBP-2 mRNA were observed in all regions of brain, liver, pituitary, ovary and testis. Intermediate levels were observed in white muscle, thymus gland and head kidney, while in retina, heart and other tissues IGFBP-2 mRNA levels were very low. A significant level of IGFBP-2 mRNA was firstly detected at lens formation stage, and it continued to increase to the highest level at blood cycling stage, and fell to a relatively high level until hatching. The expression pattern of IGFBP-2 mRNA was similar during different stages of testis and ovary. At recrudescing stage the expression level was extremely low, but it sharply increased to a high level at matured stage, and finally brought back to the very low level at regressed stage. Hepatocytes IGFBP-2 mRNA was greatly reduced by growth hormone but increased by insulin. PD-98059 and LY-294002, the specific inhibitor of MEK and PI3K, increased IGFBP-2 mRNA expression level and completely blocked the inhibitory effect of GH. It is suggested that the MAPK and PI3 kinase-signaling pathways were involved in the decrease of IGFBP-2 mRNA expression induced by GH in primary cultured hepatocytes.

The effect of in vivo co-exposure to estrone and AhR-ligands on estrogenic effect to vitellogenin production and EROD activity

We evaluated the effect of combination chemical exposure on estrogenic activity, in vivo using Japanese medaka (Oryzias latipes) during co-exposure to estrone (E1) and β-naphthoflavone (βNF) or α-naphthoflavone (αNF). We used E1 because which is one of the major estrogenic substances in the environment, and βNF or αNF are both AhR-ligands and usually used as a model substance of common environmental pollutants such as PAHs from physiological response standpoint. The results of present study demonstrate that both βNF and αNF inhibit the E1-induced production of plasma VTG in a concentration-dependent manner. These results indicate that estrogenic activity is suppressed by AhR-ligands in aquatic environment. At the same time, significant increase of EROD was observed in groups of βNF co-exposed with E1, conversely no significant alteration of EROD was observed in groups of αNF co-exposed with E1. Therefore, we conclude that the inhibition of VTG synthesis effect was not directly related to EROD.

Integrated decision-tree testing strategies for environmental toxicity with respect to the requirements of the EU REACH legislation

Liverpool John Moores University and FRAME recently conducted a research project sponsored by Defra on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with the REACH system. This paper focuses on the prospects for using alternative methods (both in vitro and in silico) for environmental (aquatic) toxicity testing. The manuscript reviews tests based on fish cells and cell lines, fish embryos, lower organisms, and the many expert systems and QSARs for aquatic toxicity testing. Ways in which reduction and refinement measures can be used are also discussed, including the Upper Threshold Concentration--Step Down (UTC) approach, which has recently been retrospectively validated by ECVAM and subsequently endorsed by the ECVAM Scientific Advisory Committee (ESAC). It is hoped that the application of this approach could reduce the number of fish used in acute toxicity studies by around 65-70%. Decision-tree style integrated testing strategies are also proposed for acute aquatic toxicity and chronic toxicity (including bioaccumulation), followed by a number of recommendations for the future facilitation of aquatic toxicity testing with respect to environmental risk assessment.

Beta-naphthoflavone inhibits the induction of hepatic oestrogen-dependent proteins by 17alpha-ethynylestradiol in mosquitofish (Gambusia holbrooki)

The interactive effects of an aryl hydrocarbon receptor (AhR) agonist and of a xenoestrogen on biomarker responses were studied in the liver of male mosquitofish (Gambusia holbrooki). Hepatic 7-ethoxyresorufin O-deethylase (EROD) enzymatic activity was measured as a biomarker of exposure to the model AhR agonist beta-naphthoflavone (bNF). Hepatic proteins indicating the exposure of males to the synthetic oestrogen 17alpha-ethynylestradiol (EE2) were monitored by Western blot analysis using immunoserum prepared for this study. After a semi-static exposure only to waterborne EE2, Western blot analysis of liver homogenate revealed the induction of two protein bands (a double band at 205 kDa and a single band at 125 kDa). The interaction between bNF and EE2 was investigated by analysing, on the one hand, EROD activity and, on the other hand, immunoreactivity corresponding to the two oestrogen-dependent protein bands in the liver of fish exposed to different concentrations of bNF for 2 days, then to the same concentrations of bNF plus 0.1 microg l(-1) EE2 for 5 days. EE2 changed neither the basal activity of EROD nor its rate of induction with 1.0 and 4.0 microg l(-1) bNF. On the other hand, the induction of oestrogen-dependent proteins with 0.1 microg l(-1) EE2 was inhibited by exposure to 4.0 microg l(-1) bNF. These results together with literature data suggest that field monitoring of xenoestrogen contamination through the analysis of oestrogen-dependent protein in male fish as a biomarker should take into account the possible negative interference of AhR agonists.

Biomarkers in fish from dioxin-contaminated fjords

The Grenland fjords, southern Norway, have been heavily contaminated by dibenzo-p-dioxins and dibenzofurans (dioxins) over decades through inputs from a magnesium smelter. Despite radically decreased inputs since 1990, there are still high levels of dioxins in both biotic and abiotic components of the fjords. The aim of the study was to establish whether biomarkers' responses in three fish species, Atlantic cod (Gadus morhua L.), sea-trout (anadromous brown trout, Salmo trutta L.) and flounder (Platichthys flesus L.), could be used to discern the effects in the most contaminated ecosystem, Frierfjord, from the effects in the adjacent, less-contaminated ecosystem, Eidangerfjord. Biomarker responses clearly indicated that the three fish species were affected by dioxin exposure. Phase I responses in cod and trout could be used to differentiate exposure in the two fjord ecosystems. Phase II responses (glutathione S-transferase) in cod and trout similarly indicated a higher dioxin exposure in Frierfjord compared with Eidangerfjord. Results for glutathione S-transferase and glutathione reductase indicated different exposure levels in the two fjords, but also showed seasonal variability, and the results highlighted the need for baseline data for these biomarkers.

Detection of estrogenic activity in municipal wastewater effluent using primary cell cultures from three-spined stickleback and chemical analysis

Environmental estrogens are substances that imitate the effects of endogenous estrogens. Effluents from municipal wastewater treatment plants are known to contain substances with estrogenic activity including steroidal estrogens and xenoestrogens. In the current study, a combination of biological and chemical analysis was applied to determine the estrogenic activity in municipal wastewater effluents in Finland. The male three-spined stickleback (Gasterosteus aculeatus) hepatocyte assay with vitellogenin induction as an endpoint was used for the detection of estrogenic activity in solid phase extracts of wastewater effluents, and 17beta-estradiol (E2) as a positive control. The wastewater extracts and E2 were found to induce vitellogenin production. The extracts were also subjected to chromatographic fractionation and the collected fractions were assayed. The only active fraction was the one in which E2, estrone and ethynylestradiol were eluted. Its activity corresponded to the activity of the original wastewater extract. The LC-MS/MS analyses of the wastewater extracts showed that the concentration of estrone was about 65 ng L(-1), the concentration of E2 was less than 1 ng L(-1), while estriol and 17alpha-ethynylestradiol could not be detected. These findings showed that the activity of the wastewater extracts and the chromatographic fraction was much higher than the activity which could have been expected on the base of the chemical analysis. This strongly indicates that other compounds, possibly acting by additivity or synergism, are playing a major role in the induced vitellogenin production by the hepatocytes.

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.

Effects of mammalian CYP3A inducers on CYP3A-related enzyme activities in grass carp (Ctenopharyngodon idellus): Possible implications for the establishment of a fish CYP3A induction model

Unexpected drug-drug interactions in fish are generally associated with the induction of CYP3A activity and may lead to the formation of drug residues and thus threaten the safety of fishery products. However, little information is available about CYP3A induction in fish. In the present study, we determined the in vivo and in vitro effects of typical mammalian CYP3A inducers (rifampicin, phenobarbital and dexamethasone) on CYP3A-related enzyme activities in a freshwater teleost, the grass carp (Ctenopharyngodon idellus). Our results showed that the response to rifampicin was similar for grass carp liver cell line (GCL), liver microsomes and the primary hepatocytes of grass carp, as indicated by the activity of aminopyrine N-demethylase (APND). When erythromycin N-demethylase (ERND) and 6beta-testosterone hydroxylase (6beta-TOH) were taken into consideration, the GCL displayed a greater capacity for conducting CYP3A metabolism and induction than the C. idellus kidney cell line (CIK). Using erythromycin and testosterone as substrates, we demonstrated that CYP3A catalysis exhibited non-Michaelis-Menten kinetics in GCL cells, and that V(max)/K(m) values were significantly increased due to rifampicin-treatment. Overall, this study may have implications for the use of GCL as a CYP3A induction model to identify physiological changes in fish as well as the similarities or differences between fish and mammals.

Evaluation of estrogenic activities and mechanism of action of perfluorinated chemicals determined by vitellogenin induction in primary cultured tilapia hepatocytes

Perfluorochemicals (PFCs) are emerging persistent organic pollutants (POPs) and are widely present in the environment, wildlife and humans. Recently, reports have suggested that PFCs may have endocrine-disrupting activities. In the present study, we have developed a non-competitive enzyme-linked immunosorbent assay (ELISA) method to investigate estrogenic activities of selected PFCs using vitellogenin (VTG) induction in primary cultured hepatocytes of freshwater male tilapia (Oreochromis niloticus). Cultured hepatocytes were exposed to various concentrations of perfluorooctanyl sulfonate (PFOS), pentadecafluorooctanoic acid (PFOA), 1H, 1H, 2H, 2H-nonafluoro-1-hexanol (4:2 FTOH), 1H, 1H, 2H, 2H-perfluorooctanol (6:2 FTOH) and 1H, 1H, 2H, 2H-perfluoro-1-decanol (8:2 FTOH) for 48 h, while 17beta-estradiol (E2) and 4-nonylphenol (4-NP) were used as positive controls. A dose-dependent induction of VTG was observed in E2-, 4-NP-, PFOS-, PFOA- and 6:2 FTOH-treated cells, whereas VTG levels remained unchanged in the 4:2 FTOH and 8:2 FTOH exposure groups at the concentrations tested. The estimated 48-h EC(50) values for E2, 4-NP, PFOS, PFOA and 6:2 FTOH were 4.7 x 10(-7), 7.1 x 10(-6), 1.5 x 10(-5), 2.9 x 10(-5) and 2.8 x 10(-5)M, respectively. In the time-course study, significant VTG induction took place at 24 h (E2), 6 h (4-NP), 48 h (PFOS), 48 h (PFOA), 72 h (4:2 FTOH), 12 h (6:2 FTOH), 72 h (8:2 FTOH), and increased further after 96 h of exposure. Co-exposure to binary mixtures of individual PFCs and E2 for 48 h significantly inhibited E2-induced hepatocellular VTG production in a dose-dependent manner except for 4:2 FTOH. The estimated 48-h IC(50) (concentration of a compound that elicits 50% inhibition of maximally E2-induced VTG) values for PFOS, PFOA, 6:2 FTOH and 8:2 FTOH were 3.1 x 10(-7), 5.1 x 10(-7), 1.1 x 10(-6) and 7.5 x 10(-7)M, respectively. In order to further investigate the estrogenic mechanism of PFCs, the hepatocytes were co-exposed to binary mixtures of individual chemicals (E2, 4-NP, PFOS, PFOA and 6:2 FTOH) and the known estrogen receptor inhibitor tamoxifen for 48 h; tamoxifen significantly inhibited the ability of these chemicals to stimulate vitellogenesis. The overall results demonstrated that PFOS, PFOA and FTOHs have estrogenic activities and that exposure to a combination of E2 and PFCs produced anti-estrogenic effects. The results of the estrogen receptor inhibition assay further suggested that the estrogenic effect of PFCs may be mediated by the estrogen receptor pathway in primary cultured tilapia hepatocytes.

Tamoxifen effects on the early life stages and reproduction of Japanese medaka (Oryzias latipes)

Tamoxifen is widely used in the treatment of breast cancer and can enter the aquatic environment in municipal wastewater. To evaluate potential effects on embryonic development of Japanese medaka, fertilized eggs were exposed to tamoxifen at 1-625μg/l for 14 days. Adverse effects on hatchability and time to hatching only occurred at 125 and 625μg/l. Reproductive effects were assessed by exposing adults for 21 days to the same dose range. At all concentrations tested, tamoxifen significantly increased plasma vitellogenin levels in males in a dose-dependent manner. Fecundity and fertility were detrimentally affected at 625μg/l. Additionally, F1 eggs were removed from tamoxifen-contaminated water to evaluate transgenerational effects. Hatchability was affected at 625μg/l but no morphological deformities were observed. A significant dose-dependent increase in the proportion of genotypic males occurred at all concentrations greater than 5μg/l.

Vitellogenin synthesis in primary cultures of fish liver cells as endpoint for in vitro screening of the (anti)estrogenic activity of chemical substances

Concern over possible adverse effects of endocrine-disrupting compounds on fish has caused the development of appropriate testing methods. In vitro screening assays may provide initial information on endocrine activities of a test compound and thereby may direct and optimize subsequent testing. Induction of vitellogenin (VTG) is used as a biomarker of exposure of fish to estrogen-active substances. Since VTG induction can be measured not only in vivo but also in fish hepatocytes in vitro, the use of VTG induction response in isolated fish liver cells has been suggested as in vitro screen for identifying estrogenic-active substances. The main advantages of the hepatocyte VTG assay are considered its ability to detect effects of estrogenic metabolites, since hepatocytes in vitro remain metabolically competent, and its ability to detect both estrogenic and anti-estrogenic effects. In this article, we critically review the current knowledge on the VTG response of cultured fish hepatocytes to (anti)estrogenic substances. In particular, we discuss the sensitivity, specificity, and variability of the VTG hepatocyte assay. In addition, we review the available data on culture factors influencing basal and induced VTG production, the response to natural and synthetic estrogens as well as to xenoestrogens, the detection of indirect estrogens, and the sources of assay variability. The VTG induction in cultured fish hepatocytes is clearly influenced by culture conditions (medium composition, temperature, etc.) and culture system (hepatocyte monolayers, aggregates, liver slices, etc.). The currently available database on estrogen-mediated VTG induction in cultured teleost hepatocytes is too small to support conclusive statements on whether there exist systematic differences of the VTG response between in vitro culture systems, VTG analytical methods or fish species. The VTG hepatocyte assay detects sensitively natural and synthetic estrogens, whereas the response to xenoestrogens appears to be more variable. The detection of weak estrogens can be critical due to the overshadow with cytotoxic concentrations. Moreover, the VTG hepatocyte assay is able to detect antiestrogens as well as indirect estrogens, i.e substances which require metabolic activation to induce an estrogenic response. Nevertheless, more chemicals need to be analysed to corroborate this statement. It will be necessary to establish standardized protocols to minimize assay variability, and to develop a set of pass-fail criteria as well as cut-offs for designating positive and negative responses.

Joint anti-estrogenic effects of PCP and TCDD in primary cultures of juvenile goldfish hepatocytes using vitellogenin as a biomarker

This work evaluated the joint anti-estrogenic effects of pentachlorophenol (PCP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) against 17beta-estradiol (E2) in juvenile goldfish (Carassius auratus) hepatocyte cultures. The level of vitellogenin (VTG) as a biomarker was determined by exposing hepatocytes to individual E2, PCP and TCDD, as well as to E2 in the presence of PCP, TCDD or their mixtures of various concentrations. PCP and TCDD did not exhibit estrogenicity. Both chemicals reduced the estrogenicity of E2, indicating the anti-estrogenic effects of PCP and TCDD. Their anti-estrogenic EC(50) values were calculated. The joint anti-estrogenic effects against E2 increased with increasing the PCP-to-TCDD ratio of mixture. Marking's indices were <0, suggesting an antagonism in anti-estrogenic effects between PCP and TCDD. The anti-estrogenic effects of PCP appeared to result primarily from the competitive binding to estrogen receptor. While TCDD may undergo an indirect binding process for its anti-estrogenic effects, the accurate mechanisms remain to be understood. The observed antagonism in anti-estrogenic effects resulted apparently from the mutual inhibition by PCP and TCDD.

Detection of endocrine disrupters: evaluation of a Fish Sexual Development Test (FSDT)

Managed by the Organisation for Economic Co-operation and Development (OECD), a comprehensive work is carried out in numerous laboratories to develop test guidelines for the detection of endocrine disrupting chemicals in humans, and various animal species. Development of tests to detect chemicals with endocrine disrupting properties in fish is a part of that work. A Fish Sexual Development Test (FSDT) (an extension of the existing OECD TG 210, fish early life stage toxicity test), proposed as an international test guideline for the detection of endocrine disrupting chemicals, was evaluated by water exposure of juvenile zebrafish to the three natural estrogens: estrone, 17beta-estradiol, and estriol and the synthetic androgen trenbolone (trenbolone acetate). As endpoints, vitellogenin induction and histological changes including changes in sex ratios were investigated. The sex ratio was significantly altered towards females from 49 ng/l estrone, 54 ng/l 17beta-estradiol and 22 microg/l estriol, respectively. An all male population was observed from exposure to 9.7 ng/l trenbolone and above. Significant vitellogenin induction in whole body homogenate was measured after exposure to 14 ng/l estrone, 54 ng/l 17beta-estradiol and 0.6 mug/l estriol, respectively. Significant vitellogenin reduction was measured after exposure to 193 ng/l trenbolone or higher. The present results provide strong evidence that the FSDT is a sensitive test toward estrogenic and especially androgenic exposure and the validation of the FSDT as an OECD test guideline should continue.

Inhibition of follicular development, vitellogenesis, and serum 17beta-estradiol concentrations in zebrafish following chronic, sublethal dietary exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent endocrine disruptor with the ability to affect several biologic processes, including reproduction. In fish, sublethal exposure to TCDD is known to modulate overall reproductive capacity, but impacts on follicular development and vitellogenesis are unknown. Here we show that chronic, dietary exposure to 0.08, 0.32, or 0.80 ng TCDD female(-1) day(-1) decreased egg production by more than 50% and that spawning success was reduced by as much as 96%. Serum estradiol concentrations were decreased more than twofold, accounting, in part, for observed decreases in serum vitellogenin concentrations by as much as 29%. Our data suggest that decreased egg production is likely the result of TCDD-mediated inhibition of the transition from pre-vitellogenic stage follicles to vitellogenic stage follicles, as well as the induction of follicular atresia. The majority of reproductive toxicity of TCDD is likely due to direct impacts on the ovary, yet histopathologic observations suggest liver toxicity could also contribute to observed impacts on vitellogenesis. Importantly, even when overall egg production is not significantly affected, our data show that subtle physiologic changes induced by TCDD can lead to altered gonadogenesis. This suggests that long-term exposure to very low concentrations of TCDD could greatly affect fecundity and reproductive success in fishes.

Effects of bisphenol A-related diphenylalkanes on vitellogenin production in male carp (Cyprinus carpio) hepatocytes and aromatase (CYP19) activity in human H295r adrenocortical carcinoma cells

The present study investigated the effects of the known xenoestrogen bisphenol A (BPA) relative to eight BPA-related diphenylalkanes on estrogen receptor (ER)-mediated vitellogenin (vtg) production in hepatocytes from male carp (Cyprinus carpio), and on aromatase (CYP19) activity in the human adrenocortical H295R carcinoma cell line. Of the eight diphenylalkanes, only 4,4'-(hexafluoropropylidene)diphenol (BHF) and 2,2'-bis(4-hydroxy-3-methylphenyl)propane (BPRO) induced vtg, i.e., to a maximum of 3% to 4% (at 100 microM) compared with 8% for BPA relative to the maximum induction by 17beta-estradiol (E2, 1 microM). Bisphenol A diglycidyl ether (BADGE) was a potent antagonist of vtg production with an IC50 of 5.5 microM, virtually 100% inhibition of vtg at 20 microM, and an inhibitive (IC50) potency about one-tenth that of the known ER antagonist tamoxifen (IC50, 0.6 microM). 2,2'-Diallyl bisphenol A, 4,4'-(1,4-phenylene-diisopropylidene)bisphenol, BPRO, and BHF were much less inhibitory with IC50 concentrations of 20-70 microM, and relative potencies of 0.03 and 0.009 with tamoxifen. Bisphenol ethoxylate showed no anti-estrogenicity (up to 100 microM), and 4,4'-isopropylidene-diphenol diacetate was only antagonistic at 100 microM. When comparing the (anti)estrogenic potencies of these bisphenol A analogues/diphenylalkanes, anti-estrogenicity occurred at lower concentrations than estrogenicity. 4,4'-Isopropylidenebis(2,6-dimethylphenol) (IC50, 2.0 microM) reduced E2-induced (EC50, 100 nM) vtg production due to concentration-dependent cytotoxicity as indicated by a parallel decrease in MTT activity and vtg, whereas the remaining diphenylalkanes did not cause any cytotoxicity relative to controls. None of the diphenylalkanes (up to 100 microM) induced EROD activity indicating that concentration-dependent, CYP1A enzyme-mediated metabolism of E2, or any Ah-receptor-mediated interaction with the ER, was not a likely explanation for the observed anti-estrogenic effects. At concentrations as great as 100 microM, none of the diphenylalkanes directly inhibited aromatase (CYP19) activity in H295R cells. Environmental exposure of fish to BPA and related diphenylalkanes, depending on the structure, may pose anti-estrogenic, and to a lesser extent estrogenic, risks to development and reproduction.

A novel enzyme-linked immunosorbent assay system for the quantitative analysis of Carassius auratus vitellogenin

A sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantitatively detect Carassius auratus vitellogenin (VTG) levels. The protein levels in fish plasma are useful aquatic biomarkers of estrogenic compounds. This procedure involved an ELISA using monoclonal antibodies of CVmA2 and CVmA7 against Carassius auratus VTG, and CVmA7 conjugated to horseradish peroxidase as the detection antibody. The assay range was between 1 and 401.5 ng/ml and the recovery of the VTG added to Carassius auratus plasma was 92.5-109%. An in vitro assay was performed to measure low levels of the VTG, using primary hepatocytes of Carassius auratus induced by 17-beta estradiol (E2). The detection limit was 1 ng/ml and 137 ng/ml at the maximum. Within each sex of wild Carassius auratus, VTG levels from the river next to sewage treatment works (STWs) were much higher than those from the feeding stream. The Carassius auratus VTG bioassay could be a sensitive and useful tool for quantification of estrogenic principles in aquatic environments.

In vitro induction of vitellogenin by estradiol 17 beta in isolated hepatocytes of catfish, Clarias gariepinus

Vitellogenin is a female-specific calcium-binding glycolipophosphoprotein synthesized in the hepatocytes of fishes. Its synthesis can be induced in fishes of either sex by estradiol or by xenoestrogens. To study the in vitro synthesis of vitellogenin, different culture conditions were set up using the hepatocytes of Clarias gariepinus. The present study reports on a non-enzymatic procedure for isolation and culture of hepatocytes from the liver of the catfish Clarias gariepinus, in order to study the effects of estradiol on vitellogenin synthesis in vitro. The procedure employs chelating properties of ethylenediamine tetracetic acid to achieve cell viability in excess of 95%. Equal numbers of isolated cells were incubated in different culture media viz. RPMI F1640, Medium-199, and Williams' Medium E. At 36 h, cell attachment and monolayer formation is faster in M-199 and Williams' Medium E than in RPMI. In order to study the effects of estradiol on vitellogenin synthesis, the isolated hepatocytes were seeded in Williams' Medium E in 24-well cell culture plates. 17 beta-estradiol (E(2)) was introduced in the culture plates at different concentrations and for different time periods. The media were assayed for vitellogenin using competitive ELISA. Vitellogenin appeared in the medium after 48 h of incubation with 10(-5) M estradiol whereas after 72 h of incubation 5x10(-7) M E(2) could elicit the synthesis.

Transcript and protein environmental biomarkers in fish--a review

The levels of contaminant-affected gene products (transcripts and proteins) are increasingly utilized as environmental biomarkers, and their appropriate implementation as diagnostic tools is discussed. The required characteristics of a gene product biomarker are accurate evaluation using properly normalized absolute units, aiming at long-term comparability of biomarker levels over a wide geographical range and among many laboratories. Quantitative RT-PCR and competitive ELISA are suggested as preferred evaluation methods for transcript and protein, respectively. Constitutively expressed RNAs or proteins which are part of the examined homogenate are suggested as normalizing agents, compensating for variable processing efficiency. Essential characterization of expression patterns is suggested, providing reference values to be compared to the monitored levels. This comparison would enable estimation of the intensity of biological effects of contaminants. Contaminant-independent reference expression patterns should include natural fluctuations of the biomarker level. Contaminant-dependent patterns should include dose response to model contaminants chronically administered in two environmentally-realistic routes, reaching extreme sub-lethal affected levels. Recent studies using fish as environmental sentinel species, applying gene products as environmental biomarkers, and implementing at least part of the depicted methodologies are reviewed.

Some polybrominated diphenyl ether (PBDE) flame retardants with wide environmental distribution inhibit TCDD-induced EROD activity in primary cultured carp (Cyprinus carpio) hepatocytes

Ethoxyresorufin-O-deethylase (EROD) activity, a catalytic function of the cytochrome P450 1A (CYP1A) microsomal oxygenase subfamily, is a popular biomarker for exposure to xenobiotics, polyhalogenated aromatic hydrocarbons (PHAHs) in particular. It has found wide use in aquatic pollution assessment both in vivo and in vitro. In such studies, subjects are often exposed to complex mixtures where various constituents can interfere with EROD-activity, possibly resulting in inadequate estimation of toxic hazard or biological response. The present study investigates the effects of polybrominated diphenyl ethers (PBDEs), a relatively new and increasingly detected group of environmental contaminants, on the validity of EROD activity as exposure marker in carp (Cyprinus carpio) hepatocytes. Freshly isolated hepatocytes of a genetically uniform strain of male carp were co-exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at concentrations of 0, 1, 3, 10, 30, and 100 pM, and one of the highly purified PBDE/PCB congeners (at concentrations of 0, 0.25, and 2.5 microM) or cleaned-up and untreated DE-71 samples (0, 0.1, and 1 microM). PBDEs were selected from the 209 possible congeners based on their relative abundance in environmental samples: BDE-47, BDE-99, BDE-100, and BDE-153. A tentative metabolite of BDE-47, 6OH-BDE-47, was also included. In addition, a commercial pentabrominated dipenylether mixture (DE-71) was tested for interference with EROD activity both with and without clean-up by carbon fractionating which removed possible planar contaminants. Polychlorinated biphenyl (PCB)-153, a reported inhibitor of EROD activity in flounder, was included for comparison. Cells were cultured for a total period of 8 days; exposure started at day 3 after cell isolation. After 5 days of exposure, cell pellets were frozen before EROD activity was determined. Upon exposure to TCDD, the cells responded with increased EROD activity as expected. Significant reduction of TCDD-induced EROD activity was found in the presence of BDE-47, BDE-99, and BDE-153, but not with BDE-100 and 6-hydroxylated BDE-47. Of these PBDE congeners, the most abundant congener in environmental samples, BDE-47, exhibited the strongest inhibition (down to 6% of the TCDD control value). The cleaned-up fraction of commercial penta-BDE (DE-71) mixture proved an even more potent inhibitor, resulting in reduction of EROD activity to 4% of the control values observed at 1.0 microM. BDE-47 and BDE-153 did not reduce TCDD-induced EROD activity when added shortly prior to measurement, suggesting possible interaction with TCDD at the level of CYP1A biosynthesis. PCB-153 did not show significant effects on EROD activity in carp in this study. The present results indicate that environmentally relevant PBDEs can interfere with determination of EROD activity in vitro, at levels reported earlier for PCBs. The observation that detected PBDE levels are rising, stresses the need for caution when interpreting EROD data on environmental samples.

EROD activities in a primary cell culture of grass carp (Ctenopharyngodon idellus) hepatocytes exposed to polychlorinated aromatic hydrocarbonas

Aryl hydrocarbon (Ah) receptor (Ah-agonist) effects of environmental samples containing polychlorinated aromatic hydrocarbons were evaluated using a 7-ethoxyresorufin-O-deethylase (EROD) assay of a primary hepatocyte culture from grass carp (Ctenopharyngodon idellus). The results were compared with those obtained from the assay using the rat hepatoma cell line H4IIE and chemical analysis using high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). A dose-response relationship was observed between the EROD activities, either from primary hepatocyte culture assay or from H4IIE assay, and concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The results showed that the assay based on the H4IIE cell line (EC50=0.83 pg/mL) is more sensitive to TCDD than the assay based on primary hepatocyte culture (EC50=9.7 pg/mL). In tests of environmental samples, the results from the assay using primary hepatocyte culture were comparable to those from the assay using the H4IIE cell line and chemical analysis of concentrations of mixtures of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/PCDF). The lack of a change in the activities of glutathione-S-transferase (GST) and lactate dehydrogenase (LDH) in cell culture upon exposure to TCDD indirectly indicates that the compound is persistent to biodegradation in the cell culture system.