Binding of xenobiotics to hepatic estrogen receptor and plasma sex steroid binding protein in the teleost fish, the common carp (Cyprinus carpio)

Comparison and quantification of estrogen receptor-mediated responsiveness to endocrine disruptors in bivalves by using complementary model and a novel yeast assay approach

Endocrine disrupting chemicals (EDCs) in estuaries and coastal habitats have been widely detected over the world and caused global concern. Bivalves have been shown to be vulnerable to endocrine disruption. However, estrogen receptors (ERs) sensitivity to steroids and EDCs has long been considered to be restricted to vertebrates. In the present study, a computational simulation docking model was applied to qualitatively predict the binding behavior of two bivalve ERs to estradiol and compared the docking activity with zebra fish ERa. A novel reconstituted yeast system was constructed by using transcriptional activator GAL-4 consists of ER-expressing plasmid and ERE (estrogen responsive element)-containing plasmid. The assays showed that bivalve ER specifically activate transcription in response to tested steroids and EDCs, but the activation ability is weaker compared to zebra fish ERa. The results corroborate the presence of an active ER in bivalve molluscs and provide a promising tool for screening of marine environmental pollutants active in disturbing ERs of bivalves, as well as understanding the underlying mechanism across taxonomic groups and phyla.

Exploring toxicity of perfluorinated compounds through complex network and pathway modeling

Perfluorinated compounds (PFCs) have serious impacts on human health, which could interfere with the body's signal pathways and affect the normal hormone balance of humans. PFCs were reported to bind to many proteins causing a series of biological effects. It was quite possible that the in vivo action of PFCs was not a single target or a single pathway, suggesting the toxic effect was due to the disturbance of protein or gene network, not limited to the modification of a single target protein or gene. Thus, a PFCs-targets interaction network was constructed and the significant differences in the characteristics of complex networks between the branched PFCs and linear PFCs were observed. A molecular dynamics simulation proved that binding ability of the branched PFCs to the target protein was much weaker than that of the linear PFCs, explaining why the branched PFCs presented significantly difference from the linear PFCs in terms of complex network characteristics. In addition, four target genes were identified as the central node genes of the network. The four target genes were proved to present certain influences on some diseases, which suggested a high correlation between PFCs to these diseases, including obesity, hepatocellular carcinoma and diabetes. The present work was helpful to develop new approaches to identify the key toxic targets of compounds and to explore the toxicity effects on pathways. AbbreviationsARandrogen receptorBPAbisphenol AESR1estrogen receptor 1ESR2estrogen receptor 2GLTPglycolipid transfer proteinHbFthe fetal hemoglobinHBG1hemoglobin subunit γ-1hERαhuman ERαHSD17B1hydroxysteroid 17-β dehydrogenase 1KEGGKenya encyclopedia of genes and genomesMDmolecular dynamics simulationPFCsperfluorinated compoundsPFOAperfluorooctanoic acidPFOSperfluorooctane sulfonatePOPspersistent organic pollutantsRMSDroot-mean-square deviationSHBGsex hormone binding globulinSPC/Eextended simple point charge modelTRthyroid hormone receptorCommunicated by Ramaswamy H. Sarma.

Stage-specific testicular protein levels of the oestrogen receptors (ERα and ERβ) and Cyp19 and association with oestrogenic contamination in the lambari Astyanax rivularis (Pisces: Characidae)

Oestrogens participate in various biological processes such as oogenesis, vitellogenesis and testicular development, but studies regarding the distribution and protein levels of oestrogen receptors (ERα and ERβ) and aromatase (Cyp19) in testis are rarely investigated in fish species. The aim of the present study was to analyse the expression pattern of ERα, ERβ and Cyp19 in testis of Astyanax rivularis and, in addition, to verify if oestrogenic contamination interferes in the expression levels of these proteins. Quarterly, field samplings were carried out during a reproductive cycle in a stream of the Upper Velhas River with a good conservation status (site S1). In the gonadal maturation peak (June), when ripe stage was most abundant, fish collection was made in three streams: S1, reference site, and S2 and S3, sites contaminated by untreated sewage. The results of immunohistochemistry demonstrated labelling of Cyp19 in Leydig cells and acidophilic granulocytes, but spermatogonia, Sertoli cells, spermatids and spermatozoa were also labelled. ERα was more widely distributed than ERβ being found in all developmental germ cell phases. On the other hand, ERβ was found only in spermatogonia and spermatocytes. During testicular maturation, ELISA levels for Cyp19, ERα and ERβ followed the gonadosomatic index (GSI) with significant higher values in the ripe stage. Regarding to endocrine disruption, the males exposed to domestic sewage presented significant higher expression of Cyp19 and ERα when compared to the non-exposed fish. Together, our results demonstrate expression patterns of Cyp19, ERα and ERβ in the testis of A. rivularis. In addition, we indicate ERα and Cyp19 as sensitive biomarkers for monitoring of oestrogenic contamination in freshwater environments.

Development of QSAR models for predicting the binding affinity of endocrine disrupting chemicals to eight fish estrogen receptor

Endocrine disrupting effect has become a central point of concern, and various biological mechanisms involve in the disruption of endocrine system. Recently, we have explored the mechanism of disrupting hormonal transport protein, through the binding affinity of sex hormone-binding globulin in different fish species. This study, serving as a companion article, focused on the mechanism of activating/inhibiting hormone receptor, by investigating the binding interaction of chemicals with the estrogen receptor (ER) of different fish species. We collected the relative binding affinity (RBA) of chemicals with 17β-estradiol binding to the ER of eight fish species. With this parameter as the endpoints, quantitative structure-activity relationship (QSAR) models were established using DRAGON descriptors. Statistical results indicated that the developed models had satisfactory goodness of fit, robustness and predictive ability. The Euclidean distance and Williams plot verified that these models had wide application domains, which covered a large number of structurally diverse chemicals. Based on the screened descriptors, we proposed an appropriate mechanism interpretation for the binding potency. Additionally, even though the same chemical had different affinities for ER from different fish species, the affinity of ER exhibited a high correlation for fish species within the same Order (i.e., Salmoniformes, Cypriniformes, Perciformes), which consistent with that in our previous study. Hence, when performing the endocrine disrupting effect assessment, the species diversity should be taken into account, but maybe the fish species in the same Order can be grouped together.

Development of predictive models for predicting binding affinity of endocrine disrupting chemicals to fish sex hormone-binding globulin

Disturbing the transport process is a crucial pathway for endocrine disrupting chemicals (EDCs) exerting disrupting endocrine function. However, this mechanism has not received enough attention compared with that of hormones receptors and synthetase. Recently, we have explored the interaction between EDCs and sex hormone-binding globulin of human (hSHBG). In this study, interactions between EDCs and sex hormone-binding globulin of eight fish species (fSHBG) were investigated by employing classification methods and quantitative structure-activity relationships (QSAR). In the modeling, the relative binding affinity (RBA) of a chemical with 17β-estradiol binding to fSHBG was selected as the endpoint. Classification models were developed for two fish species, while QSAR models were established for the other six fish species. Statistical results indicated that the models had satisfactory goodness of fit, robustness and predictive ability, and that application domain covered a large number of endogenous and exogenous steroidal and non-steroidal chemicals. Additionally, by comparing the log RBA values, it was found that the same chemical may have different affinities for fSHBG from different fish species, thus species diversity should be taken into account. However, the affinity of fSHBG showed a high correlation for fishes within the same Order (i.e., Salmoniformes, Cypriniformes, Perciformes and Siluriformes), thus the fSHBG binding data for one fish species could be used to extrapolate other fish species in the same Order.

Does anti-androgen, flutamide cancel out the in vivo effects of the androgen, dihydrotestosterone on sexual development in juvenile Murray rainbowfish (Melanotaenia fluviatilis)?

The aim of the present study was to investigate if the effects of the androgen, dihydrotestosterone (DHT) on the sexual development in juvenile Murray rainbowfish (Melanotaenia fluviatilis) are canceled out by the anti-androgen, flutamide. Fish (60 days post hatch) were exposed to 250ng/L of DHT, 25μg/L of flutamide (Flu-low), 250μg/L of flutamide (Flu-high), DHT+Flu low and DHT+Flu high. After 35 days of exposure, lengths and weights of the fish were measured and the condition factor (CF) calculated; vitellogenin (VTG) concentrations were measured in tail tissue; sex steroid hormones (17β-estradiol [E2] and 11-keto testosterone [11-KT]) were measured in the head tissue and abdominal regions were used in histological investigation of the gonads. Treatment with DHT reduced the body-length of both male and female fish, an effect which was canceled out by low and high concentrations of flutamide. However, flutamide (low or high) could not nullify the DHT-induced reduction in the CF in either sex. The E2 levels were reduced only in female fish after exposure to DHT but returned to normal after treatment with Flu-high. DHT increased the levels of 11-KT and decreased the E2/11-KT ratio in both sexes. Flu-high, but not Flu-low, could nullify these effects. Both DHT and flutamide (low or high) induced VTG production and this effect persisted when both chemicals were co-administered. Treatment with DHT did not affect gonadal cell development in the testes. However, the female fish treated with DHT contained ovaries in early-vitellogenic stage in comparison to the pre-vitellogenic ovaries in control fish. Co-treatment with flutamide (low or high) resulted in oocyte atresia. The results from the present study suggest that treatment with Flu-high could cancel out DHT-induced effects only on the hormonal profile and body-length in both male and female fish. Juvenile fish co-treated with DHT and flutamide (low or high) had high VTG levels and low CF. In addition, the ovaries in female fish were atretic. These data represent potential adverse effects on the ability of the fish to reproduce successfully.

In vivo and in silico analyses of estrogenic potential of bisphenol analogs in medaka (Oryzias latipes) and common carp (Cyprinus carpio)

Various studies have demonstrated the estrogenic effect of bisphenol A (BPA), a member of bisphenol analogs (BPs), in in vitro and in vivo assays. However, limited data are available on the estrogenic potentials and risks of other BPs in aquatic organisms. In addition, the estrogenic effect of chemicals is known to have species-specific responses in teleost fish. The objective of this study was to evaluate the potential estrogenic effects of BPs on the medaka (Oryzias latipes) and common carp (Cyprinus carpio) using in vivo and in silico assays. Our quantitative real-time PCR analyses revealed that the expression levels of several hepatic estrogen-responsive biomarker genes in male medaka responded to various types and concentrations of BPs in a dose-response manner. The order of in vivo estrogenic potencies of BPs was as follows: BPC≈BPAF>BPB>BPA⋙BPP. To further investigate the interaction potential of BPs with medaka estrogen receptor α (ERα) in silico, a three-dimensional model of the ERα ligand-binding domain (LBD) was built and docking simulations were performed. The docking simulation analysis revealed that BPC interaction potential for medaka ERα LBD was the most potent, followed by BPAF and BPA. Comparing this with carp ERα LBD revealed that the interaction potentials of these BPs to medaka ERα LBD were more stable than to carp ERα LBD. Furthermore, we identified key amino acid residues in medaka ERα LBD that interacted with BPC (Glu356, Arg397, and Cys533), BPAF (Thr350 and Glu356), and BPA (Glu356 and Met424), and found some differences in these key amino acid residues between medaka and carp ERα LBDs. These results of in vivo and in silico analyses showed potential estrogenic effects of BPs in teleost fish, and they also indicated that the differences in interaction potentials and key amino acid residues between medaka and carp ERα LBDs may be due to the differences between the species and estrogenic potencies of the selected BPs.

Comparative responses to endocrine disrupting compounds in early life stages of Atlantic salmon, Salmo salar

Atlantic salmon (Salmo salar) are endangered anadromous fish that may be exposed to feminizing endocrine disrupting compounds (EDCs) during early development, potentially altering physiological capacities, survival and fitness. To assess differential life stage sensitivity to common EDCs, we carried out short-term (4 day) exposures using three doses each of 17 α-ethinylestradiol (EE2), 17 β-estradiol (E2), and nonylphenol (NP) on four early life stages; embryos, yolk-sac larvae, feeding fry and 1 year old smolts. Differential response was compared using vitellogenin (Vtg, a precursor egg protein) gene transcription. Smolts were also examined for impacts on plasma Vtg, cortisol, thyroid hormones (T4/T3) and hepatosomatic index (HSI). Compound-related mortality was not observed in any life stage, but Vtg mRNA was elevated in a dose-dependent manner in yolk-sac larvae, fry and smolts but not in embryos. The estrogens EE2 and E2 were consistently stronger inducers of Vtg than NP. Embryos responded significantly to the highest concentration of EE2 only, while older life stages responded to the highest doses of all three compounds, as well as intermediate doses of EE2 and E2. Maximal transcription was greater for fry among the three earliest life stages, suggesting fry may be the most responsive life stage in early development. Smolt plasma Vtg was also significantly increased, and this response was observed at lower doses of each compound than was detected by gene transcription suggesting plasma Vtg is a more sensitive indicator at this life stage. HSI was increased at the highest doses of EE2 and E2, and plasma T3 was decreased at the highest dose of EE2. Our results indicate that all life stages are potentially sensitive to endocrine disruption by estrogenic compounds and that physiological responses were altered over a short window of exposure, indicating the potential for these compounds to impact fish in the wild.

Modelling the binding affinity of steroids to zebrafish sex hormone-binding globulin

The circulating endogenous steroids are transported in the bloodstream. These are bound to a highly specific sex hormone-binding globulin (SHBG) and in lower affinity to proteins such as the corticosteroid-binding protein and albumin in vertebrates, including fish. It is generally believed that the glycoprotein SHBG protects these steroids from rapid metabolic degradation and thus intervenes in its availability at the target tissues. Endocrine disrupters binding to SHBG affect the normal activity of natural steroids. Since xenobiotics are primarily released in the aquatic environment, there is a need to evaluate the binding affinity of xenosteroid mimics on fish SHBG, especially in zebrafish (Danio rerio), a small freshwater fish originating in India and widely employed in ecotoxicology, toxicology, and genetics. In this context, a zebrafish SHBG (zfSHBG) homology model was developed using the human SHBG (hSHBG) receptor structure as template. It was shown that interactions with amino acids Ser-36, Asp-59 and Thr-54 were important for binding affinity. A ligand-based pharmacophore model was also developed for both zfSHBG and hSHBG inhibitors that differentiated binders from non-binders, but also demonstrated structural requirements for zfSHBG and hSHBG ligands. The study provides insights into the mechanism of action of endocrine disruptors in zebrafish as well as providing a useful tool for identifying anthropogenic compounds inhibiting zfSHBG.

A species comparison of 17-α-ethynylestradiol uptake and tissue-specific distribution in six teleost fish

Differences exist among fish species in their sensitivity to endocrine disruptors such as 17-α-ethynylestradiol (EE2). We examined whether there were corresponding differences in EE2 uptake rates and short-term internal distribution patterns. Six freshwater species: Japanese ricefish (medaka, Oryzias latipes), goldfish (Carassius auratus), zebrafish (Danio rerio), fathead minnow (Pimephales promelas), Atlantic killifish (Fundulus heteroclitus) and rainbow trout (Oncorhynchus mykiss) were exposed to waterborne radiolabelled EE2 (100ng/L) for 2-h measurements of uptake, tissue accumulation and oxygen consumption rates (MO2). EE2 uptake rate and MO2 were relatively consistent among species (2.5-3.0 fold variation), with the only significant differences being a lower EE2 uptake rate in medaka, and lower MO2 in medaka, goldfish, and zebrafish relative to the other species. EE2 accumulation, however, exhibited two distinct patterns, suggesting differences in metabolic processing. In killifish and medaka, the highest accumulation (~50%) occurred in the liver and gallbladder, whereas in minnow, goldfish, zebrafish and trout, >50% accumulated in the carcass. No significant sex differences were found in killifish or minnow, apart from lower gill tissue EE2 accumulation in minnow females. This study demonstrated that metabolic processing of EE2 may be species-specific and tissue specific EE2 distribution profiles vary. These could be indicative of differences in overall EE2 sensitivity among species.

Molecular signatures in rainbow darter (Etheostoma caeruleum) inhabiting an urbanized river reach receiving wastewater effluents

Rainbow darter (Etheostoma caeruleum) is a small benthic fish species found in North America that are abundant and distributed throughout the Grand River watershed, ON, Canada. Rainbow darter exhibit intersex in males at sites adjacent to municipal wastewater effluents (MWWE). In October 2010, female and male rainbow darter were collected at 3 sites (1 upstream reference and 2 downstream exposed sites) in the Grand River near the cities of Kitchener and Waterloo. The primary objectives of this research were (1) to characterize the responses of whole organism endpoints (i.e. condition factor (K), liversomatic (LSI) and gonadosomatic index (GSI), histopathology) to MWWEs and (2) to identify transcripts showing altered steady state abundance with exposure to MWWE in fish inhabiting municipal wastewater effluent-exposed areas. Genes measured in this study included vitellogenin, Sry-box containing protein 9 (sox9), forkhead box L2 (foxl2), doublesex and mab-3 related transcription factor 1 (dmrt1), cytochrome P450, family 11, subfamily A, polypeptide 1 (cyp11a) as well as estrogen (esr1, esrb) and androgen (ar) receptors. There were no changes in condition factor; however, there was a significant increase in LSI and a decrease in GSI in fish inhabiting downstream environments when compared with fish collected from the reference site. Males had a high incidence (∼ 70%) of intersex in downstream sites; characterized by the presence of oocytes within the testis. In the gonad, there were sex specific differences for genes related to sexual differentiation; dmrt1 was only expressed in males whereas foxl2 and sox9 were highly expressed in females compared to males. Expression levels of ar and esr1 were higher in females than males. Conversely, esrb was not differentially expressed between sexes or among sites. There were no differences detected for the genes investigated within sex among sites. This study is the first to report on gene expression changes in the rainbow darter, with emphasis on the differences in transcript abundance between sexes and how these changes relate to exposures to MWWEs. Molecular approaches are being investigated for their potential application to field ecotoxicology, and molecular bioassays for relevant, sentinel species in environmental monitoring programs are required to better understand the impact of anthropogenic impacts on species at risk in river systems.

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.

Laccase-mediated transformations of endocrine disrupting chemicals abolish binding affinities to estrogen receptors and their estrogenic activity in zebrafish

Endocrine disrupting chemicals (EDCs) are known to mainly affect aquatic organisms, producing negative effects in aquaculture. Transformation of the estrogenic compounds 17β-estradiol (E2), bisphenol-A (BPA), nonylphenol (NP), and triclosan (TCS) by laccase of Coriolopsis gallica was studied. Laccase is able to efficiently transform them into polymers. The estrogenic activity of the EDCs and their laccase transformation products was evaluated in vitro as their affinity for the human estrogen receptor alpha (hERα) and for the ligand binding domain of zebrafish (Danio rerio) estrogen receptor alpha (zfERαLBD). E2, BPA, NP, and TCS showed higher affinity for the zfERαLBD than for hERα. After laccase treatment, no affinity was found, except a marginal affinity of E2 products for the zfERαLBD. Endocrine disruption studies in vivo on zebrafish were performed using the induction of vitellogenin 1 as a biomarker (VTG1 mRNA levels). The use of enzymatic bioreactors, containing immobilized laccase, efficiently eliminates the endocrine activity of BPA and TCS, and significantly reduces the effects of E2. The potential use of enzymatic reactors to eliminate the endocrine activity of EDCs in supply water for aquaculture is discussed.

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

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

Effects of nonylphenol on early embryonic development, pigmentation and 3,5,3'-triiodothyronine-induced metamorphosis in Bombina orientalis (Amphibia: Anura)

Nonylphenol (NP) is an estrogenic endocrine disruptor in many aquatic species. In an effort to highlight the developmental toxicity of NP in amphibians, we examined the effects of NP on the embryonic survival, tadpole growth, melanophore development and metamorphosis of a native Korean amphibian species, Bombina orientalis (Anura). When treated to fertilized eggs, 1 μM NP significantly decreased embryonic survival at 48 h post fertilization (p.f.), suggesting that 1 μM NP can exert systemic toxicity in B. orientalis embryos. In the surviving embryos, there were no significant differences in malformation rates between NP-treated embryos and controls at 240 h p.f., suggesting no or low teratogenicity of NP in B. orientalis embryos. Below LC(50) NP significantly decreased body growth and development of melanophores at 0.1 μM, suggesting that NP far below the LC(50) targets multiple developmental events in tadpoles of this frog species. In metamorphosis assay using the premetamorphic tadpoles (corresponding to Nieuwkoop Faber stage 53 in Xenopus laevis) exogenous 3,5,3'-triiodothyronine (T3)-induced tail resorption was significantly decreased by 1 μM NP. However, NP (0.1 and 1 μM)-only treatment did not affected total body T3 and T4 levels, suggesting that NP at tested concentrations inhibits thyroid hormones action but not the synthesis of hormones during metamorphosis.

Diversity and biological significance of sex hormone-binding globulin in fish, an evolutionary perspective

In fish, two different genes, shbga and shbgb, exist that encode for very different proteins. Shbga is the ortholog of mammalian Shbg and was found in all investigated teleosts. In contrast, Shbgb is highly divergent and appears to be a salmonid-specific protein. Here, we review existing data on fish Shbga and Shbgb that have been obtained in chondrichthyes and osteichtyes. Even though other significant expression sites exist, existing data indicate that Shbga is mainly expressed in liver and subsequently secreted into the blood as a homodimer. In contrast, Shbgb is mainly expressed in the ovary, probably secreted as a monomer, and could contribute to the regulation of local steroid action. Binding studies indicate a specialization of circulating Shbg during evolution towards the preferential binding of estradiol and testosterone in teleosts. In contrast, specific fish steroids such as 11-oxo-androgens and oocyte maturation-inducing steroids that are crucial for reproduction are poorly bound by either form of Shbg.

Comparison of relative binding affinities to fish and mammalian estrogen receptors: the regulatory implications

Screening and testing of chemicals binding to estrogen receptors (ERs) emerge as an important issue in several regulatory programs or frameworks. Discrepancies exist, however, whether fish ERs should be included in the regulatory programs. In view of the differences in binding affinities to ERalpha and ERbeta and the significant contribution of ERbeta to biological effects of chemicals, it remains unknown whether both types of ERs are needed for the regulatory purposes. This study collected publications on binding affinities to both mammalian and fish ERs for 65 chemicals, covering a wide range of strong, moderate, weak and non-ER binders. Systematic evaluation of the data was performed in order to compare the difference in binding affinity of chemicals to fish and mammalian ERs and to subtypes of ERs. Except the reference estrogen 17beta-estradiol, all 64 chemicals have differential values of relative binding affinity (RBA), which result mostly from the inter-laboratory tests other than interspecies differences. It is concluded that ER binding in one vertebrate species or one subtype of ERs could be extrapolated to other species or subtypes of ERs for most of chemicals for the regulatory purpose. Fish ERs are likely more sensitive to some chemicals of weak binders than mammalian ERs, suggesting the importance of including fish ERs in the regulatory programs. Issues on data interpretation and testing strategy for the regulatory purpose have been discussed.

Sex hormone-binding globulin in fish gills is a portal for sex steroids breached by xenobiotics

As in most vertebrates, plasma sex hormone-binding globulin (SHBG) is produced in fish liver and regulates sex steroid access to target tissues. Low levels of SHBG mRNA are present in zebra fish gills but are unlikely to account for the high amounts of immunoreactive SHBG in filaments and lamellae. Although the uptake of steroids by fish from water has been reported to correlate with their affinity for SHBG, it is not known how this occurs. Our studies of zebra fish SHBG have revealed its preference for biological active androgen (testosterone), as well as for androstenedione, a sex steroid precursor that also acts as a pheromone in some fish. In addition to natural steroids, zebra fish SHBG has a high affinity for synthetic steroids, such as ethinylestradiol and progestins (levonorgestrel and norethindrone), that are present in waste water systems. Because steroids can pass across fish gills, we examined whether SHBG serves as a portal for natural and synthetic steroids controlling their flux between the blood and aquatic environment. The results indicate that SHBG ligands are rapidly and specifically removed from water by the fish through their gills, whereas the accumulated steroids are released slowly. The capacity of fish to sequester SHBG ligands from water is similar between sexes, independent of size, and characterized by a wide dynamic range. We conclude that SHBG controls the flux of sex steroids across fish gills and that this highly specialized function can be hijacked by xenobiotic ligands of fish SHBGs.

Binding of alkylphenols and alkylated non-phenolics to the rainbow trout (Oncorhynchus mykiss) plasma sex steroid-binding protein

Alkylphenols are well-known endocrine disrupters, mediating effects through the estrogen receptor (ER). Although the estrogenic properties of the alkylphenols are well documented, alternative mechanisms of action are poorly described. In the present work, the interaction of a range of alkyl-substituted phenols and alkyl-substituted non-phenolics with the rainbow trout (Oncorhynchus mykiss) sex steroid-binding protein (rtSBP) were determined by competitive ligand-binding studies. The role of alkyl chain length and branching, substituent position, number of alkylated groups, and the requirement of a phenolic ring structure were assessed. The results showed that the rtSBP binds to most chemical structures tested, although the highest affinity was obtained for mono-substituted alkylphenols with a chain length of four to eight methyl groups. Interestingly, rtSBP binding was also observed for non-phenolic compounds such as 4-t-butylcyclohexanol and 4-t-butylnitrobenzene suggesting that the rtSBP has a broad binding specificity for alkylphenols and alkylated non-phenolics.

An ecological assessment of bisphenol-A: Evidence from comparative biology

This review assesses the effects of environmental concentrations of bisphenol-A (BPA) on wildlife. Water concentrations of BPA vary tremendously due to proximity to point and non-point sources, but reported concentrations in stream/river water samples are less than 21 microg/L, and concentrations in landfill leacheate are less than 17.2mg/L. Extensive evidence indicates that BPA induces feminization during gonadal ontogeny of fishes, reptiles, and birds, but in all cases the amount of BPA necessary to cause such ontogenetic disruption exceeds concentrations in the environment. Extensive evidence also exists that adult exposure to environmental concentrations of BPA is detrimental to spermatogenetic endpoints and stimulates vitellogenin synthesis in model species of fish. Most of the reported effects of BPA on vertebrate wildlife species can be attributed to BPA acting as an estrogen receptor agonist, but mechanisms of disruption in invertebrates are less certain. A comparison of measured BPA environmental concentrations with chronic values suggests that no significant margin of safety exists for the protection of aquatic communities against the toxicity of BPA. Further studies should examine the most vulnerable vertebrate and invertebrate species.

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.

Development of methods for extraction and in vitro quantification of estrogenic and androgenic activity of wastewater samples

Chemicals released into the environment by anthropogenic activities have been linked to estrogenic or androgenic effects in exposed wildlife, and there is a need to develop and validate rapid and cost-effective methods to quantify the total estrogenic and androgenic activity of environmental water samples. In this study, estrogen receptors (ER) were isolated from sheep (Ovis aries) uteri and rainbow trout (Oncorhynchus mykiss) livers and androgen receptors (AR) were isolated from rainbow trout brains. The isolated receptors were used in competitive receptor binding assays to test the affinity of known estrogenic and androgenic chemicals for the receptor binding site, and results were compared with literature values for the rat uterine ER binding assay and the E-Screen. The relative binding affinities of the tested compounds to ER from different species were similar, and binding to the ER was a more responsive endpoint than the cellular effect measured in the E-Screen. Using the sheep ER binding assay in combination with solid-phase extraction, the estrogenic activity in a raw sewage sample from a municipal treatment plant in Brisbane (Queensland, Australia) was measured at 51-73 ng/L estradiol equivalents (EEq).

Bisphenol A induces superfeminization in the ramshorn snail Marisa cornuarietis(Gastropoda: Prosobranchia) at environmentally relevant concentrations

Previous investigations have shown that bisphenol A (BPA) induces a superfeminization syndrome in the freshwater snail Marisa cornuarietis at concentrations as low as 1 microg/L. Superfemales are characterized by the formation of additional female organs, enlarged accessory sex glands, gross malformations of the pallial oviduct, and a stimulation of egg and clutch production, resulting in increased female mortality. However, these studies were challenged on the basis of incomplete experimentation. Therefore, the objective of the current approach was to bridge several gaps in knowledge by conducting additional experiments. In an initial series of experiments, study results from the reproductive phase of the snails were evaluated in the sub-micrograms per liter range. Before and after the spawning season, superfemale responses were observed [NOEC (no observed effect concentration) 7.9 ng/L, EC10 (effective concentration at 10%) 13.9 ng/L], which were absent during the spawning season. A further experiment investigated the temperature dependence of BPA responses by exposing snails at two temperatures in parallel. The adverse effect of BPA was at least partially masked at 27 degrees C (EC10 998 ng/L) when compared with 20 degrees C (EC10 14.8 ng/L). In M. cornuarietis, BPA acts as an estrogen receptor (ER) agonist, because effects were completely antagonized by a co-exposure to tamoxifen and Faslodex. Antiandrogenic effects of BPA, such as a significant decrease in penis length at 20 degrees C, were also observed. Competitive receptor displacement experiments indicate the presence of androgen- and estrogen-specific binding sites. The affinity for BPA of the estrogen binding sites in M. cornuarietis is higher than that of the ER in aquatic vertebrates. The results emphasize that prosobranchs are affected by BPA at lower concentrations than are other wildlife groups, and the findings also highlight the importance of exposure conditions.

Differential effects of temperature and maturity stage on hepatic estrogen receptor characteristics of Atlantic salmon

In order to determine if elevated temperature during vitellogenesis had a detrimental effect on hepatic estrogen receptors of Atlantic salmon (Salmo salar), 3H-estradiol saturation binding analysis, using one- and two-site binding models, was carried out on extracts of hepatic cytosols from fish held at 14, 18 or 22 degrees C over the austral period of peak vitellogenesis (February to April). With one-site binding analysis, no temperature related difference in either receptor affinity (Kd) or number (Bmax) was found at each sampling point, but there was an apparent decrease in both affinity and number at each temperature over the period of the study. However, some analyses, notably at 22 degrees C during February, were best described using a two-site binding model. At this temperature and time, there was a clear separation of binding affinity into high and low components (Kd = 0.67+/-S.E. 0.05 and 20+/-S.E. 5.6 nM, respectively) (n = 4), which suggests that February was a critical time of temperature related hepatic sensitivity to estrogen. These results support those of other studies where we found that February was also a sensitive time with respect to temperature impairment of in vitro follicular estrogen synthesis, and the greatest period of in vivo temperature sensitivity.

Molecular and functional characterization of sex hormone binding globulin in zebrafish

SHBG (sex hormone binding globulin) transports androgens and estrogens in the blood of vertebrates including fish. Orthologs of SHBG in fish are poorly defined, and we have now obtained a zebrafish SHBG cDNA and characterized the zebrafish SHBG gene and protein through molecular biological, biochemical, and informatics approaches. Amino-terminal analysis of zebrafish SHBG indicated that its deduced precursor sequence includes a 25-residue secretion polypeptide and exhibits 22-27% homology with mammalian SHBG sequences and 41% with a deduced fugufish SHBG sequence. The 356-residue mature zebrafish SHBG (39,243 Da) sequence comprises a tandem repeat of laminin G-like domains typical of SHBG sequences; contains three N-glycosylation sites; and exists as a 105,000 +/- 8700 Da homodimer. Zebrafish SHBG exhibits a high affinity and specificity for sex steroids. An RT-PCR indicated that SHBG mRNA first appears in zebrafish larva, and SHBG mRNA was localized within the liver and gut at this stage of development by whole-mount in situ hybridization. In adult fish, SHBG mRNA was found in liver, testis, and gut. In the liver, immunoreactive SHBG was present in hepatocytes and concentrated in intrahepatic bile duct cells, whereas in the testis it was confined to cells surrounding the seminiferous tubule cysts. In the intestine, immunoreactive SHBG was present in the stroma and epithelial cells of the villous projections and the surrounding muscle. The production and presence of SHBG in the gut of developing and adult zebrafish suggests a novel role for this protein in regulating sex steroid action at this site.

Binding of xenoestrogens to the sex steroid-binding protein in plasma from Arctic charr (Salvelinus alpinus L.)

A specific sex steroid-binding protein (SBP) is believed to be involved in regulation of circulating sex steroids, steroid delivery to target cells and intracellular signalling in sex steroid-sensitive tissues. In the present work, interactions between xenoestrogens and the plasma SBP in Arctic charr (Salvelinus alpinus L.) were determined using ligand-protein binding studies. The test compounds were all able to displace tritiated 17 beta-estradiol (E2) from the Arctic charr SBP (acSBP) in a competitive and dose-dependent manner. The acSBP affinities for the xenoestrogens ranged over several orders of magnitude (17 beta-estradiol>>ethynylestradiol (EE2)>zearalenone (ZEA)>diethylstilbestrol (DES)>genistein (GEN)>bisphenol A (BPA), 4-t-octylphenol (OP)>>o,p'-DDT, and dieldrin (DIN)), but were consistently lower than that of 17 beta-estradiol (about 4 x 10(2) -10(6)-fold less potent). The relative binding affinity (RBA) for selected chemicals were independent of both gender, age and maturation status, as well as variations of acSBP binding affinity. The affinity of endogenous steroids and estrogen mimics for the acSBP shows a high correlation to the affinity for the rainbow trout SBP, thus suggesting a phylogenetically conserved ligand-binding site between closely related species. Furthermore, it is argued that interaction with the acSBP- and SBP-mediated processes may introduce novel pathways for endocrine disruption, which may work in concert with the classical receptor-mediated effects.

Interaction of xenobiotics with estrogen receptors alpha and beta and a putative plasma sex hormone-binding globulin from channel catfish (Ictalurus punctatus)

Estrogens are important regulators of physiological functions. Although environmental contaminants (xenoestrogens) which interfere with estrogen signaling are of increasing concern, there is only limited information about their ability to interact with estrogen-binding proteins (SHBG) or receptors (ER). Recombinant ERalpha and beta were obtained after transient transfection of COS-7 cells with channel catfish ER cDNA. Plasma from adult female channel catfish was the source of SHBG. Tritiated estradiol (3H-E2) was used in standard radioligand-binding assays to characterize the binding properties of channel catfish SHBG (ccfSHBG) and to estimate the inhibition constants for various estrogenic compounds. Binding of 3H-E2 to ccfSHBG was saturable and of high affinity with a Kd (+/-SE) of 1.9+/-0.14 nM and a Bmax of 14.3+/-2.4 pmol/mg protein ( n = 3 assays). Additionally, ccfSHBG displayed binding specificity for androgens and estrogens. Endosulfan, 4-nonylphenol, and 4-octylphenol displaced 3H-E2 binding to ccfSHBG albeit only at very high concentrations, whereas dieldrin and atrazine showed little displacement activity even at the highest concentrations used. The synthetic estrogen ethynylestradiol had higher affinity than E2 for ccfSHBG. This finding differs from results with human and rainbow trout SHBG. The alkylphenolic compounds (4-octylphenol and 4-nonylphenol) displayed some ability to displace 3H-E2 binding from ERalpha and beta at high concentrations, but dieldrin and atrazine had little binding activity for both ER subtypes and endosulfan for ERbeta. The xenobiotics tested generally showed equivalent or greater affinity for ERalpha than ERbeta, whereas natural estrogens had much greater affinity for ERbeta than ERalpha. These observations suggest that results of studies using fish tissue ER extracts must be interpreted with caution, since both ER subtypes may be present, and that the binding of xenoestrogens to SHBG must be taken into account for proper assessment of endocrine disruption caused by environmental contaminants.

Mechanistic basis for estrogenic effects in fathead minnow (Pimephales promelas) following exposure to the androgen 17alpha-methyltestosterone: conversion of 17alpha-methyltestosterone to 17alpha-methylestradiol

Exposure of adult fathead minnows (Pimephales promelas) to the androgen 17alpha-methyltestosterone (MT) produces both androgenic and estrogenic effects, manifested as nuptial tubercle formation in females, and vitellogenin production in males and females, respectively. The present study was conducted to determine if the unanticipated estrogenic effects are produced by conversion of MT via aromatase activity to 17alpha-methylestradiol (ME2). Aromatase activity at the end of a 7-day waterborne MT exposure (20, 200microg/l) was significantly decreased in ovarian microsomes and brain homogenates from exposed fish, to about 30-50% of control activity. Although aromatase activity was decreased by 7 days, it is possible that the conversion of MT to ME2 occurred soon after initial exposure. In support of this, ME2 was detected in plasma samples of the fish following the 7-day exposure, confirming their ability convert the androgen MT to the estrogen ME2. The concentration of ME2 in plasma was within the range of plasma 17ss-estradiol (E2) found in control female fathead minnows (4-5ng/ml). These results, in conjunction with competitive binding assays that indicate ME2 binds to the fathead minnow estrogen receptor with a relative binding affinity of 68.3% of E2, support the hypothesis that aromatization of MT to ME2 contributes to the estrogenic effects in fathead minnows following exposure to this androgen.

Functional changes of the LH-immunoreactive cells in adenohypophysis of the common carp (Cyprinus carpio) from rivers contaminated with estrogenic chemicals

The adverse effect of estrogenic chemicals on luteinizing hormone-immunoreactive (LH-ir) cells in the adenohypophysis of common carp (Cyprinus carpio) was examined using immunocytochemical and morphometric methods. Adult male fish were collected from two contaminated sites (Ishizu and Wada Rivers) and from a control pond at Agriculture, Food and Environmental Sciences, Research Center of Osaka Prefecture. The concentration of nonylphenol, bisphenol A and 17beta-estradiol in the Ishizu River was 3-4 times higher than that in the Wada River. The proportion and size of LH-ir cells were evaluated using the point-counting method by optical microscopy. In control carp, the proportion of LH-ir cells in the breeding season was significantly lower than in the pre- and post-breeding seasons. The same tendency was also found in Ishizu and Wada River carp, but without statistical significance. The proportion of LH-ir cells in Ishizu River carp was significantly lower than that of the control and the Wada River in all seasons. The LH-ir cells in control carp increased in size in the breeding season. LH-ir cells in Ishizu River carp were significantly (p<0.05) smaller than those in control fish, but not different from Wada River carp. A disturbance in the secretory function of LH-ir cells was found in carp from the Ishizu River; granulation and vacuolation were not in synchronization with those of control and Wada River fish. Our data suggest that the estrogenic chemicals in the Ishizu River interfere with functions of LH-ir cells directly or through the testis.

Potencies of estrogenic compounds in in vitro screening assays and in life cycle tests with zebrafish in vivo

The objective of this study was to compare the estrogenic potency of environmental estrogens at two testing tiers: at the initial level of in vitro screening assays, and at the level of definitive fish reproduction tests in vivo. The in vitro tests included a recombinant yeast estrogen receptor (ER) assay, a competitive radioreceptor assay using the hepatic ER of carp (Cyprinus carpio), and assays on vitellogenin induction in cultured hepatocytes of rainbow trout (Oncorhynchus mykiss) and carp. In vivo, full life cycle tests with zebrafish (Danio rerio) were performed, using fertilization success as estrogen-sensitive reproductive endpoint. The test compounds included the natural estrogen 17beta-estradiol (E2) (only applied in the in vitro assays); the synthetic estrogen ethynylestradiol (EE2); and two xenoestrogens, 4-tert-octylphenol (OP) and bisphenol A (BPA). Among the in vitro assays, differences were observed in the relative ranking of the test substances, and in the absolute sensitivity (EC50 values), although the interassay differences of EC50 values were within one order of magnitude. The in vivo activity of the test compounds was not accurately predicted by the in vitro assays, with respect to neither sensitivity nor ranking. The in vitro assays tended to overestimate the relative potency of the xenoestrogens; i.e. the ratio between the activity of the reference compound, EE2, and that of the test compound. The best prediction of the in vivo fish test results was obtained from the recombinant yeast assay.

The effects of pulp mill effluent on the sex steroid binding protein in white sucker (Catostomus commersoni) and longnose sucker (C catostomus)

The objective of this study was to characterize the effects of pulp mill effluent on the properties of the sex steroid binding protein (SBP) in the plasma of white sucker (Catostomus commersoni) and longnose sucker (C. catostomus). SBPs which specifically bind estradiol and testosterone with high affinity (k(D) approximately 3 nM) and low capacity (B(max) approximately 73-81 nM) were identified in both species. Subsequent studies determined if the properties of the SBP in white sucker exposed to bleached kraft mill effluent (BKME) at Terrace Bay, ON, and in longnose sucker exposed to BKME at Grande Prairie, AB. differed from appropriate reference fish. There were no effects of BKME exposure on the binding affinity (k(D)) of the SBP in either species, but there was a significant increase in the binding capacity (B(max)) of longnose sucker SBP exposed to BKME. The livers of nai;ve white sucker exposed to effluent at Terrace Bay or a bleached sulfite/groundwood mill in Edmundston, NB, rapidly accumulated compounds of differing hydrophobicity that bound to both the white sucker and goldfish (Carassius auratus) SBP. Conversely, there was reduced accumulation of SBP ligands in the bile of effluent-exposed fish. We have demonstrated that constituents present within pulp mill effluent bind to both the white sucker and goldfish SBP, and that native species residing downstream of pulp mill effluents may experience modifications in the properties of their SBP.

Amphibians as a model for the study of endocrine disruptors

Evidence shows that environmental compounds can interfere with the endocrine systems of wildlife and humans. The main sink of such substances, called endocrine disruptors (EDs), which are mainly of anthropogenic origin, is surface water; thus, aquatic vertebrates such as fishes and amphibians are most endangered. Despite numerous reports on EDs in fishes, information about EDs in amphibians is scarce, and this paucity of information is of particular concern in view of the worldwide decline of amphibians. EDs could contribute to changes of amphibian populations via adverse effects on reproduction and the thyroid system. In amphibians, EDs can affect reproduction by (anti)estrogenic and (anti)androgenic modes of action that produce severe effects including abnormal sexual differentiation. ED actions on the thyroid system cause acceleration or retardation of metamorphosis, which may also affect population levels. Our broad knowledge of amphibian biology and endocrinology indicates that amphibians are very suitable models for the study of EDs. In particular, effects of EDs on the thyroid system triggering metamorphosis can be determined easily and most sensitively in amphibians compared to other vertebrates. A new classification of EDs according to their biological modes of action is proposed because EDs have quite heterogeneous chemical structures, which do not allow prediction of their biological effects. Methods and strategies are proposed for identification and risk assessment of EDs, whether as pure test substances or as mixtures from environmental samples. Effects of EDs on the thyroid system of amphibians can be assessed by a single animal model (Xenopus laevis), whereas the various types of reproduction need comparative studies to investigate whether general endocrine principles do exist among several species of anurans and urodeles. Thus, at least one anuran and one urodelean model are needed to determine ED interference with reproduction.

Seasonal variation of plasmatic and hepatic vitellogenin and EROD activity in carp, Cyprinus carpio, in relation to sewage treatment plants

Concern about the health of aquatic fauna living in waters containing biologically active levels of estrogenic compounds is particularly focused on the effects on their reproductive success. To that end, carp, Cyprinus carpio, a feral fish living in warm waters of Southern Europe (NE Spain), were selected for signs of estrogenicity. The study area covered two tributaries (the Anoia and the Cardener) of the Llobregat River both known to be polluted by estrogenic compounds. The estrogenicity in the carp was measured as vitellogenin (VTG) presence in males and alterations in VTG levels in females, over a 6-month period, embracing both the pre- and post-spawning seasons. VTG content was measured in both the plasma and liver, the latter being the organ that synthesizes it. Also, hepatic 7-ethoxyresorufin O-deethylase (EROD) activity was recorded, as interactions of xenoestrogens and oestradiol have been reported to affect this enzymatic activity. The estrogenicity of these rivers was more evident in the Anoia at the location downstream from the sewage treatment plant (STP), by elevated levels of VTG in males and by the presence of some intersex individuals. In the Cardener, no intersex fish were found and male plasmatic VTG was not so highly elevated. However presence of hepatic VTG, in up to 54% of the male fish analyzed, proved exposure to xenoestrogens. In females, VTG fluctuated according to the biological cycle with a plasmatic peak in May and an earlier maximal in the liver. However, this pattern was altered in the locations with higher xenoestrogens presence. EROD activity showed differences between sexes, with higher activity in males than females, as well as site-related differences (up to one order of magnitude) in the same river. These differences were even greater than those detected between rivers. A seasonal trend was also seen in EROD activity with higher induction towards the summer in both males and females.

Assessing the estrogenic potential of organochlorine pesticides in primary cultures of male rainbow trout (Oncorhynchus mykiss) hepatocytes using vitellogenin as a biomarker

Many organochlorine pesticides are suspected of impairing natural hormonal function in organisms by mimicking endogenous estrogen. The aim of this study was to assess the estrogenic activity of the organochlorine pesticides o,p'-DDT, dieldrin, aldrin, heptachlor, mirex and DDT in rainbow trout hepatocyte cultures using vitellogenin (Vtg) as the biomarker. A wide range of pesticide concentrations (0.0001-100 microM) was evaluated. Among the pesticides tested, o,p'-DDT was the most potent inducer of Vtg. The lower potency of technical grade DDT relative to o,p'-DDT could be explained by the fact that this pesticide is a mixture of two different pesticides (18% o,p'-DDT and 77% p,p'-DDT). This suggests that o,p'-DDT is a stronger inducer of Vtg than p,p'-DDT. A simple hypothesis could be that pesticides mixed together competed for the same receptor to favor the formation of a complex with reduced activity towards EREs. If these compounds are classified according to the level of Vtg secreted, we observed the following decreasing order: 17beta-estradiol (E(2))>o,p'-DDT>dieldrin>aldrin>DDT. Non-toxic levels of these compounds competed with E(2) for binding to the estrogen receptor. Heptachlor and mirex did not induce Vtg. Since the latter compounds failed to stimulate Vtg production, the possibility that they could interfere with the estrogenic response by inhibiting E(2) action was tested. In the presence of heptachlor, Vtg production triggered by E(2) significantly decreased. The EC50 value for inhibition of ER binding by heptachlor was cytotoxic for hepatocytes in culture, and this could in part explain the lack of Vtg response observed with this compound at the concentrations tested. Our results indicate that organochlorine pesticides can act as positive or negative modulators of estrogenic function in rainbow trout.

Kinetic analysis of estrogen receptor/ligand interactions

Surface plasmon resonance biosensor technology was used to directly measure the binding interactions of small molecules to the ligand-binding domain of human estrogen receptor. In a screening mode, specific ligands of the receptor were easily discerned from nonligands. In a high-resolution mode, the association and dissociation phase binding responses were shown to be reproducible and could be fit globally to a simple interaction model to extract reaction rate constants. On average, antagonist ligands (such as tamoxifen and nafoxidine) were observed to bind to the receptor with association rates that were 500-fold slower than agonists (such as estriol and beta-estradiol). This finding is consistent with these antagonists binding to an altered conformation of the receptor. The biosensor assay also could identify subtle differences in how the same ligand interacted with two different isoforms of the receptor (alpha and beta). The biosensor's ability to determine kinetic rate constants for small molecule/protein interactions provides unique opportunities to understand the mechanisms associated with complex formation as well as new information to drive the optimization of drug candidates.

Intravenous injection of human sex steroid hormone-binding globulin in mouse decreases blood clearance rate and testicular accumulation of orally administered [2-125I]iodobisphenol A

Bisphenol A, an environmental compound with estrogenic activity, has been shown to bind human sex steroid hormone-binding globulin (hSHBG), the main plasma transport protein which regulates the metabolism of androgens and estrogens and limits their access to target organs. The present study was conducted to determine whether physiologically relevant concentrations of hSHBG can influence the blood clearance rate of bisphenol A and its accumulation in the testes. A radioactive [2-125I]iodobisphenol tracer was synthesized with an association constant (Ka) for binding to hSHBG of 0.14 +/- 0.01 x 10(6) M(-1) at 37 degrees C, a value much lower than for [2-125I]iodoestradiol, which was also synthesized. We used i.v. injection of immunopurified hSHBG in adult male mice to maintain hSHBG levels within the physiologically possible range for humans (27-267 nM) before gavage administration of [2-125I]iodobisphenol or [2-125I]iodoestradiol, for measuring the blood clearance rate of radioactive signal in blood samples taken during the following 120 min. Testicular accumulation of radioactivity was measured 24 h and 48 h after gavage of [2-125]iodobisphenol A. In mice receiving immunopurified hSHBG or vehicle, the time-dependent blood clearance of radioactivity exhibited a bi-exponential decrease which indicated alpha-diffusion and beta-elimination phases for both radioactive ligands. The presence of circulating hSHBG significantly and dose-dependently lowered the clearance rate of radioactivity. However, much higher circulating levels of hSHBG were required to retard the blood clearance of [2-125I]iodobisphenol A as compared to those required for [2-125I]iodoestradiol, in keeping with the important difference in their respective Ka value for binding to SHBG. In addition, mice treated with hSHBG exhibited significantly (P = 0.036) reduced testicular accumulation of radioactivity 24 h and 48 h after ingestion of [2-125I]iodobisphenol A. Provided that the binding properties of bisphenol A for hSHBG are not substantially different from those measured for [2-125I]iodobisphenol A, these findings suggest that, although hSHBG binds 2-mono-iodobisphenol A with a relatively low binding affinity, high enough concentrations of circulating hSHBG (range concentrations between 85 and 267 nM) are potentially able to exert a protective effect against exposure to bisphenol A.

Estrogen-mediated suppression of cytochrome P4501A (CYP1A) expression in rainbow trout hepatocytes: role of estrogen receptor

Hepatic CYP1A expression in fish can be modulated by the female sex hormone, 17beta-estradiol (E2), however neither the mechanism of E2 suppression of CYP1A nor the capacity for hormonal regulation to overcome CYP1A induction by xenobiotics are known. The present study investigates for the first time in fish if the estrogen receptor (ER) is involved in the suppressive action of E2 on CYP1A gene expression. The study further examines, if the E2 effect is able to overcome xenobiotic induction of CYP1A. As experimental model, in vitro cultures of rainbow trout, Oncorhynchus mykiss, hepatocytes were used. The effect of E2 on CYP1A was assessed by measuring the CYP1A-associated 7-ethoxyresorufin-O-deethylase (EROD) enzyme activity, and CYP1A mRNA contents. E2 at non-cytotoxic concentrations caused a significant time- and concentration-dependent decline of basal but not of induced hepatic EROD activities. The inhibitory action of E2 on basal CYP1A was also evident at the mRNA level. The presence of the ER antagonist tamoxifen abolished the inhibitory action of E2 on CYP1A expression. The results from these in vitro experiments provide evidence (a) that the ER is involved in the suppressive action of E2 on CYP1A, and (b) that E2 inhibitory action does not overcome xenobiotic induction of CYP1A.