Temperature-dependent vitellogenin-mRNA expression in primary cultures of rainbow trout (Oncorhynchus mykiss) hepatocytes at 14 and 18 degrees C

Fluctuating and Stable High Temperatures Differentially Affect Reproductive Endocrinology of Female Pupfish

For many fishes, reproductive function is thermally constrained such that exposure to temperatures above some upper threshold has detrimental effects on gametic development and maturation, spawning frequency, and mating behavior. Such impairment of reproductive performance at elevated temperatures involves changes to hypothalamic-pituitary-gonadal (HPG) axis signaling and diminished gonadal steroidogenesis. However, how HPG pathways respond to consistently high versus temporally elevated temperatures is not clear. Here, sexually mature Amargosa River Pupfish (Cyprinodon nevadensis amargosae) were maintained under thermal regimes of either stable ∼25°C (low temperature), diurnal cycling temperatures between ∼27 and 35°C (fluctuating temperature), or stable ∼35°C (high temperature) conditions for 50 days to examine effects of these conditions on HPG endocrine signaling components in the pituitary gland and gonad, ovarian and testicular gametogenesis status, and liver gene expression relating to oogenesis. Female pupfish maintained under stable high and fluctuating temperature treatments showed reduced gonadosomatic index values as well as a lower proportion of oocytes in the lipid droplet and vitellogenic stages. Females in both fluctuating and stable 35°C conditions exhibited reduced ovarian mRNAs for steroid acute regulatory protein (star), cholesterol side chain-cleavage enzyme, P450scc (cyp11a1), and 3β-hydroxysteroid dehydrogenase (3bhsd), while ovarian transcripts encoding 11β-hydroxysteroid dehydrogenase (11bhsd) and sex hormone-binding globulin (shbg) were elevated in females at constant 35°C only. Ovarian aromatase (cyp19a1a) mRNA levels were unaffected, but circulating 17β-estradiol (E2) was lower in females at 35°C compared to the fluctuating temperature condition. In the liver, mRNA levels for choriogenins and vitellogenin were downregulated in both the fluctuating and 35°C conditions, while hepatic estrogen receptor 2a (esr2a) and shbg mRNAs were elevated in 35°C females. Taken together, these results demonstrate the potential for elevated temperatures to impair ovarian steroidogenesis and reduce egg envelope and vitellogenin protein production in female C. n. amargosae pupfish, while also shedding light on how thermal regimes that only intermittently reach the upper thermal range for reproduction have differential impacts on reproductive endocrine pathways than constantly warm conditions.

Widespread alterations to hypothalamic-pituitary-gonadal (HPG) axis signaling underlie high temperature reproductive inhibition in the eurythermal sheepshead minnow (Cyprinodon variegatus)

Fish experiencing abnormally high or prolonged elevations in temperature can exhibit impaired reproduction, even for species adapted to warm water environments. Such high temperature inhibition of reproduction has been linked to diminished gonadal steroidogenesis, but the mechanisms whereby hypothalamic-pituitary-gonadal (HPG) axis signaling is impacted by high temperature are not fully understood. Here, we characterized differences in HPG status in adult sheepshead minnow (Cyprinodon variegatus), a eurythermal salt marsh and estuarine species of eastern North America, exposed for 14 d to temperatures of 27 °C or 37 °C. Males and females at 37 °C had lower gonadosomatic index (GSI) values compared to fish at 27 °C, and females at 37 °C had fewer spawning capable eggs and lower circulating 17β-estradiol (E₂). Gene transcripts encoding gonadotropin-inhibitory hormone (gnih) and gonadotropin-releasing hormone-3 (gnrh3) were higher in relative abundance in the hypothalamus of both sexes at 37 °C. While pituitary mRNAs for the β-subunits of follicle-stimulating hormone (fshβ) and luteinizing hormone (lhβ) were lowered only in males at 37 °C, Fsh and Lh receptor mRNA levels in the gonads were at lower relative levels in both the ovary and testis of fish at 37 °C. Females at 37 °C also showed reduced ovarian mRNA levels for steroid acute regulatory protein (star), P450 side-chain cleavage enzyme (cyp11a1), 3β-hydroxysteroid dehydrogenase (3βhsd), 17β-hydroxysteroid dehydrogenase (hsd17β3), and ovarian aromatase (cyp19a1a). Females at the higher 37 °C temperature also had a lower liver expression of mRNAs encoding estrogen receptor α (esr1) and several vitellogenin and choriogenin genes, but elevated mRNA levels for hepatic sex hormone-binding globulin (shbg). Our results substantiate prior findings that exposure of fish to high temperature can inhibit gonadal steroidogenesis and oogenesis, and point to declines in reproductive performance emerging from alterations at several levels of HPG axis signaling including increased hypothalamic Gnih expression, depressed gonadal steroidogenesis, and reduced egg yolk and egg envelope protein production in the liver.

Evaluating estrogenic and anti-estrogenic effect of endocrine disrupting chemicals (EDCs) by zebrafish (Danio rerio) embryo-based vitellogenin 1 (vtg1) mRNA expression

By measuring the vitellogenin 1 (vtg1) expression through quantitative PCR and in situ hybridization, we used the zebrafish embryo as an in vivo model to access the estrogenic or anti-estrogenic effects of several endocrine disrupting chemicals (EDCs), such as natural estrogen 17β-estradiol (E2), estriol (E3), synthetic hormones including diethylstilbestrol (DES), 4-octyl phenol (OP), bisphenol A (BPA), tamoxifen (TMX) and 3-(2,3-dibromopropyl) isocyanurate (TBC). According to our data, the estrogenic effect of the tested chemicals was ranked as: DES>E₂>E₃>OP>BPA, which is consistent with various in vivo and in vitro models. Therefore, the measurement of vtg1 gene expression in zebrafish embryos would be a valuable method for screening EDCs including both environmental estrogens and anti-estrogens.

Investigations to extend viability of a rainbow trout primary gill cell culture

The primary culture of fish gill cells can provide functional, cell diverse, model in vitro platforms able to tolerate an aqueous exposure analogous to in vivo tissues. The utility of such models could be extended to a variety of longer term exposure scenarios if a method could be established to extend culture viability when exposed to water for longer periods. Here we report findings of a series of experiments to establish increased longevity, as monitored by culture transepithelial electrical resistance (TEER) and concurrent histological developments. Experimental cultures improved TEER during apical freshwater exposure for a mean of twelve days, compared to previous viabilities of up to 3 days. Cultures with larger surface areas and the use of trout serum rather than foetal bovine serum (FBS) contributed to the improvement, while perfusion of the intact gill prior to cell harvest resulted in a significantly faster preparation. Detailed scanning electron microscopy analysis of cultures revealed diverse surface structures that changed with culture age. Cultures grown on membranes with an increased porosity, collagen coating or 3D structure were of no benefit compared to standard membranes. Increased culture longevity, achieved in this study and reported for the first time, is a significant breakthrough and opens up a variety of future experimentation that has previously not been possible. The extended viability facilitates exploration of in vitro chronic or pulse-exposure test paradigms, longer term physiological and environmental monitoring studies and the potential for interactive co-culture with other organoid micro-tissues.

Estrogen therapy offsets thermal impairment of vitellogenesis, but not zonagenesis, in maiden spawning female Atlantic salmon (Salmo salar)

In female Atlantic salmon (Salmo salar), exposure to warm summer temperatures causes a reduction in plasma 17β-estradiol (E2), which impairs downstream vitellogenesis and zonagenesis, and reduces egg fertility and embryo survival. The aim of the present study was to determine whether E2-treatment could offset thermal impairment of endocrine function and maintain egg quality in maiden (first-time-spawning) S. salar reared at 22 °C. Treatment with E2 at 22 °C stimulated vitellogenin (vtg) gene expression and subsequent protein synthesis which promoted oocyte growth and increased egg size relative to untreated fish at 14 and 22 °C. However, E2-treatment at 22 °C was not associated with an increase in egg fertility and embryo survival relative to untreated fish at 22 °C, despite the positive effects of E2-treatment on vitellogenesis and oocyte growth. As there was no evidence to suggest that the estrogen receptor alpha expression was suppressed by high temperature, this could be due to the lack of stimulation on zonagenesis by E2-treatment observed at high temperature during oocyte development. Our results demonstrate that treatment with E2 is not able to maintain zonagenesis or egg quality in maiden S. salar at high temperature, even when vtg gene expression, protein synthesis and subsequent oocyte growth is promoted. This implies that the mechanisms regulating zonagenesis, but not vitellogenesis are impaired at elevated temperature in female S. salar broodstock, and highlights the remarkable complexity of thermally induced endocrine disruption in fish.

Primary hepatocytes from Arctic char (Salvelinus alpinus) as a relevant Arctic in vitro model for screening contaminants and environmental extracts

Contaminants find their way to the Arctic through long-range atmospheric transport, transport via ocean currents, and through increased anthropogenic activity. Some of the typical pollutants reaching the Arctic (PAHs, PCBs) are known to induce cytochrome P450 1a (CYP1A) protein expression and ethoxyresorufin-O-deethylase (EROD) activity through the aryl hydrocarbon receptor (AhR). In addition, some endocrine disrupting chemicals (EDCs) such as estrogen mimics (xenoestrogens) have been documented in Arctic areas and they may interfere with natural sexual development and reproduction. In vitro assays that are capable of detecting effects of such pollutants, covering multiple endpoints, are generally based on mammalian or temperate species and there are currently no well-characterized cell-based in vitro assays for effect assessment from Arctic fish species. The present study aimed to develop a high-throughput and multi-endpoint in vitro assay from Arctic char (Salvelinus alpinus) to provide a non-animal (alternative) testing method for an ecologically relevant Arctic species. A method for isolation and exposure of primary hepatocytes from Arctic char for studying the toxic effects and mode of action (MoA) of pollutants was applied and validated. The multi-versatility of the bioassay was assessed by classical biomarker responses such as cell viability (membrane integrity and metabolic activity), phase I detoxification (CYP1A protein expression, EROD activity) and estrogen receptor (ER) mediated vitellogenin (Vtg) protein expression using a selection of model compounds, environmental pollutants and an environmental extract containing a complex mixture of pollutants. Primary hepatocytes from Arctic char were successfully isolated and culture conditions optimized to identify the most optimal assay conditions for covering multiple endpoints. The hepatocytes responded with concentration-dependent responses to all of the model compounds, most of the environmental pollutants and the environmental sample tested. The bioassay response and sensitivity of the hepatocytes from Arctic char differed slightly from closely related salmonid species, thus highlighting the need for developing in vitro assays relevant for Arctic species. The present multi-endpoint in vitro assay offer a highly versatile tool to screen potential effects of pollutants and complex samples relevant for Arctic exposure scenarios.

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.

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.

Effects of 17β-estradiol and bisphenol A on the formation of reproductive organs in planarians

Planarians have a remarkable capacity for regeneration after ablation, and they reproduce asexually by fission. However, some planarians can also reproduce and maintain their sexual organs. During the regenerative process, their existing sexual organs degenerate and new ones develop. However, little is known about hormonal regulation during the development of reproductive organs in planarians. In this study, we investigated the effects of 17β-estradiol (a steroid) and bisphenol A (an endocrine disrupter) on the formation of sexual organs in the hermaphroditic planarian Dugesia ryukyuensis. Under control conditions, all worm tissues regenerated into sexual planarians with sexual organs within 4 weeks after ablation. However, in the presence of bisphenol A or 17β-estradiol, although they apparently regenerated into sexual planarians, the yolk glands, which are one of the female sexual organs, failed to regenerate even 7 weeks after ablation. These data suggest that planarians have a steroid hormone system, which plays a key role in the formation and maturation of sexual organs.

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.

Water temperature and concomitant waterborne ethinylestradiol exposure affects the vitellogenin expression in juvenile brown trout (Salmo trutta)

Environmental estrogens have the potential to considerably affect the reproduction and development of aquatic vertebrates by interfering with the endocrine system. In addition to the potential risk of environmental estrogens, increasing water temperatures as a result of global warming have become a serious problem in many rivers and streams. To assess the degree of estrogenic exposure, the analysis of the estrogen-dependent protein vitellogenin (Vtg) is a frequently used biomarker in field studies. Little, however, is known regarding the potential interaction between ambient water temperature and the Vtg production induced by waterborne environmental estrogens. In order to test the influence of temperature on Vtg synthesis, we exposed juvenile brown trout to an environmentally relevant concentration of ethinylestradiol (EE(2)) and held them either at low or high temperatures (12 and 19 degrees C, respectively), but also at temperature cycles of 12-19 degrees C in order to simulate the field situation. The EE(2) exposure caused a 7-74-fold increase of hepatic Vtg mRNA. The synthesis of Vtg mRNA was clearly stimulated in fish held at higher water temperatures (12-19 degrees C and 19 degrees C, respectively). On the protein level, Vtg showed a similar pattern; the higher the temperature, the higher the concentration of Vtg in the plasma. The experiment further revealed a temperature-dependent increasing amount of hepatic estrogen receptor alpha mRNA (ERalpha) after exposure to waterborne EE(2). The gene expression of estrogen receptor beta-1 (ERbeta-1) and the glucocorticoid receptor (GR) in the liver of EE(2) exposed fish, however, showed no treatment-related alterations. In line with observed constant bile cortisol concentrations, our data do not indicate corresponding stress related effects on hepatic Vtg production. The present survey, however, clearly demonstrates that increased temperature significantly elevates the estrogen-induced expression of Vtg and therefore has to be considered when interpreting environmental monitoring studies.

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.

Vitellogenin, steroid plasma levels and spawning performance of cultured female Senegalese sole (Solea senegalensis)

The Senegalese sole (Solea senegalensis) is a high value market flatfish, which aquaculture is compromised by severe reproductive problems; these are mostly found in soles hatched and raised in captivity (F1 generation). To gain knowledge on the reproductive dysfunctions observed in cultured (F1) Senegalese sole, this work aimed at developing a specific vitellogenin (VTG) ELISA, for the measurement of plasma VTG levels in this species. Profiles of VTG were correlated with those of sexual steroids and spawning performance of an F1 broodstock, during three consecutive years. The Senegalese sole VTG (ssVTG) was purified by precipitation with MgCl(2)-EDTA and anion-exchange chromatography and showed a molecular mass of 172 kDa, by SDS-PAGE. Specific antibodies were obtained and used to develop a competitive ELISA, which had a sensitivity of 3.6 ng ml(-1), and inter- and intra-assay coefficients of variation of 9.5% (n=29) and 6.7% (n=12), respectively. Annual profiles of plasma VTG showed a major peak at pre-spawning, and a second minor rise around autumn, which mirrored plasma profiles of both estradiol (E(2)) and testosterone (T) levels. Spontaneous spawning occurred every year in the spring season, but no fertilized eggs were obtained. In conclusion, this study described, for the first time, the purification and development of a sensitive and specific ELISA for Senegalese sole VTG. The endocrine and spawning data suggested that F1 female broodstock showed normal VTG and steroid releasing profiles in captivity with occurrence of spontaneous spawning, but no fertilization of the eggs was recorded.

Synthetic endocrine disruptors in the environment and water remediation by advanced oxidation processes

The present study is an overview of the literature on classes and types of compounds described as "endocrine disruptors" and their treatability in water by advanced oxidation processes, which generate hydroxyl radicals in water. The review is limited to details of the destruction of three classes of endocrine disruptors, namely bisphenols, alkylphenols and phthalates, which are among the most highly suspected endocrine disrupting compounds that interfere with the hormonal system of wildlife. It was found that photocatalysis with titanium dioxide was the most frequently tested advanced oxidation method most likely due its potential to render complete mineralization. There is sufficient research also with direct and indirect photolysis and ozonation, which were less effective for the overall mineralization but more representative of the conditions existing in real water treatment plants.

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.

Application of Alamar blue/5-carboxyfluorescein diacetate acetoxymethyl ester as a noninvasive cell viability assay in primary hepatocytes from rainbow trout

We have adopted the application of two fluorescent indicator dyes to studying the viability of monolayers of primary rainbow trout hepatocytes. The two fluorescent dyes--Alamar blue, which indicates metabolic activity of a cell, and 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM), which is an indirect measure of cell membrane integrity-are noninvasive and can be monitored conveniently directly in multiwell plates. According to these dyes, L-15 culture medium supported hepatocyte viability over 96 h more stably than did M199. The two dyes proved to be capable of detecting a concentration-dependent toxic insult to hepatocytes caused by the model compound, pentachlorophenol. In contrast, a lack of impact on cell viability was indicated for up to 10(-5) M 17beta-estradiol, and that observation was supported by the induction of vitellogenin (VTG) mRNA/protein as indicator of hepatocyte-differentiated function. Application of the Alamar blue/CFDA-AM for 30 min did not alter gene expression either specifically as reflected by VTG or generally as reflected by a random selection of gene sequences that were amplified by differential display reverse transcription PCR (dd-rt-PCR). Thus, the assay represents a resource-efficient way of integrating measures of cell viability and gene expression that should aid in the interpretation of in vitro results. The assay can be applied repeatedly to the same set of cells and can be performed just prior to analysis of gene expression.

Androgenic and estrogenic effects of the synthetic androgen 17alpha-methyltestosterone on sexual development and reproductive performance in the fathead minnow (Pimephales promelas) determined using the gonadal recrudescence assay

The effects of the androgen, 17alpha-methyltestosterone were assessed on sexual development and reproductive performance in the fathead minnow (Pimephales promelas) using a gonadal recrudescence assay. In this assay, mature male and female fathead minnow, previously kept under simulated winter conditions (15 degrees C; 8:16 h light:dark regime) were transferred to simulated summer conditions (25 degrees C water temperature; 16:8 h light:dark regime) to induce gonadal recrudescence. To assess sexual development fish were exposed to nominal concentrations of 0, 0.1, 1, 5 and 50 microg/L 17alpha-methyltestosterone. After 3 weeks of chemical exposure, effects on condition (condition factor, CF), plasma vitellogenin (VTG), secondary sex characteristics, gonad growth (gonadosomatic index; GSI) and gonad histology were investigated. Reproductive performance, including reproductive output (egg production), spawning behaviour, and fertilisation rate were measured over a subsequent 3-week-period in breeding adults maintained in clean water. 17alpha-Methyltestosterone had no effects on the condition of fish at any of the doses tested. 17alpha-Methyltestosterone induced both androgenic and estrogenic effects with females generally more affected by 17alpha-methyltestosterone than males: atretic follicles and male-specific sex characteristics (androgenic effect) were induced in females at > or = 0.1 and > or = 1 microg/L 17alpha-methyltestosterone, respectively. An inhibitory effect on ovary growth occurred at an exposure concentration of 50 microg/L 17alpha-methyltestosterone. In males 1 microg/L 17alpha-methyltestosterone induced a concentration-response induction of plasma vitellogenin (estrogenic effect) likely due to its conversion into 17alpha-methylestradiol, rather to the competition with endogenous steroids and their cross reactivity with the estrogen receptor. In the fish breeding studies, concentration-dependent reductions in egg number, fertilisation rate and increases in abnormal sexual behaviour in females were observed. All of these effects occurred at exposure concentrations of > or = 5 microg/L 17alpha-methyltestosterone. Thus, it could be assumed that the observed estrogenic effects in male fathead minnow were likely to the conversion of 17alpha-methyltestosterone into the estrogen 17alpha-methylestradiol, rather to the acting of 17alpha-methyltestosterone itself. In conclusion to this, showing hormonally activity of 17alpha-methyltestosterone in fish down to 100 ng/L, indicates that its potency was close to the range of several naturally occurring estrogens.

Regulation of Arctic char (Salvelinus alpinus) egg shell proteins and vitellogenin during reproduction and in response to 17beta-estradiol and cortisol

Estrogens induce both vitellogenin (Vtg) and egg shell (zona pellucida; ZP) protein synthesis in salmonids. However, while Vtg is strictly under estrogenic control, recent reports suggest that additional mechanisms are involved in ZP protein synthesis. During sexual maturation both estrogen and glucocorticoid levels increase in the circulation of female fish. As glucocorticoids have been shown to interfere with Vtg induction in fish we investigated whether cortisol (F) had similar effects on ZP regulation. In the present study we determined both the natural variation in Vtg and ZP during an annual reproductive cycle in female Arctic char (Salvelinus alpinus), and the effect of co-treatment of juvenile Arctic char with 17beta-estradiol (E2) and F. During sexual maturation the expression of Vtg and ZP correlated to plasma levels of E2 and F. Determination of Vtg and ZP protein levels following co-treatment with E2 and F showed that F antagonized E2 induction of Vtg. However, F was observed to potentiate the expression of ZP protein in the same fish. These results indicate that in Arctic char Vtg and ZP proteins are not regulated by the same mechanisms and suggest that ZP protein expression does not necessarily imply exposure to estrogenic compounds alone, and may thus not be ideally suited as a biomarker of exposure to estrogenic compounds.

Estrogenicity of solid phase-extracted water samples from two municipal sewage treatment plant effluents and river Rhine water using the yeast estrogen screen

In the present study, the yeast estrogen screen (YES) was used to estimate the estrogenic potential of solid phase-extracted water samples from the effluents of two municipal sewage treatment plants (STPs 1 + 2) and from four lanes (left to right) of the river Rhine at Worms, Germany, i.e. downstream the STPs. Estrogenic activities of extracted water samples were expressed as 17beta-estradiol equivalents (E(2)-EQs). Estrogenic activity was detected in the effluents of both STPs with values of 0.242 +/- 0.038 nM (65.96 +/- 10.4 ng/l) and 0.125 +/- 0.026 nM E(2)-EQs (34.1 +/- 7.18 ng/l) at STP 1 and 2, respectively. In river Rhine water, estrogenic activity was lower, however, displaying significant differences between the left and right bank of the river (0.044 +/- 0.003 nM E(2)-EQs [11.97 +/- 0.7 ng/l] for lanes 1-3; 0.071 +/- 0.01 nM E(2)-EQs [19.42 +/- 2.8 ng/l] for lane 4). Chemical analysis of corresponding water samples resulted in a potential estrogenic response in the YES, expressed as E(2)-EQs for the known estrogens and phytoestrogens in the STP effluents with values up to 0.0662 nM E(2)-EQs (18.04 ng/l). In Rhine water from lane 4, however, total estrogenic activity of steroidal estrogens was equal to 0.014 nM E(2)-EQs (3.8 ng/l). Furthermore, total concentrations of flavonoids, fecal- and phytosteroids and resorcyclic lactones were about 1.2 microg/l at STP 1, 0.62 microg/l at STP 2 and 0.25 microg/l at the river Rhine, lane 4. Results indicate that estrogenic activity can clearly be measured in SPT effluents as well as in river Rhine water using the YES in combination with chemical analysis. Results from the bioassay, however, indicated a higher estrogenic potential (expressed as E(2)-EQs) than that obtained by chemical analysis.

Culture conditions affect induction of vitellogenin synthesis by estradiol-17 beta in primary cultures of tilapia hepatocytes

In vitro synthesis of vitellogenin (VTG), a female-specific protein, after estradiol-17 beta (E(2)) treatment was compared among different culture conditions using the hepatocytes of tilapia, Oreochromis mossambicus. VTG was measured by enzyme-linked immunosorbent assay. Comparison of Leibovitz's L-15 medium (L-15), Williams' medium E (WE) and Medium 199 (M199), which have been used for hepatocyte cultures in certain teleost fishes, showed that monolayer formation of the hepatocytes on the plate in WE and M199 was faster than in L-15 at the beginning of the culture. Morphological differences in the hepatocytes among the culture media were not evident by 96 h after culture. VTG synthesis in L-15 after E(2) treatment was higher than in WE and M199. A concentration of NaHCO(3) at 5 mM in L-15 resulted in faster monolayer formation of the cells and higher VTG synthesis than at 0 and 23 mM. Primary culture of the tilapia hepatocytes at 28 degrees C showed higher synthesis of VTG than at 23 and 33 degrees C. These results suggest that nutritional requirements are vitally different among species, and there are optimal ranges in the pH and the temperature in cultured hepatocytes.

Eggshell and egg yolk proteins in fish: hepatic proteins for the next generation: oogenetic, population, and evolutionary implications of endocrine disruption

The oocyte is the starting point for a new generation. Most of the machinery for DNA and protein synthesis needed for the developing embryo is made autonomously by the fertilized oocyte. However, in fish and in many other oviparous vertebrates, the major constituents of the egg, i.e. yolk and eggshell proteins, are synthesized in the liver and transported to the oocyte for uptake. Vitellogenesis, the process of yolk protein (vitellogenin) synthesis, transport, and uptake into the oocyte, and zonagenesis, the synthesis of eggshell zona radiata proteins, their transport and deposition by the maturing oocyte, are important aspects of oogenesis. The many molecular events involved in these processes require tight, coordinated regulation that is under strict endocrine control, with the female sex steroid hormone estradiol-17beta in a central role. The ability of many synthetic chemical compounds to mimic this estrogen can lead to unscheduled hepatic synthesis of vitellogenin and zona radiata proteins, with potentially detrimental effects to the adult, the egg, the developing embryo and, hence, to the recruitment to the fish population. This has led to the development of specific and sensitive assays for these proteins in fish, and the application of vitellogenin and zona radiata proteins as informative biomarkers for endocrine disrupting effects of chemicals and effluents using fish as test organisms. The genes encoding these important reproductive proteins are conserved in the animal kingdom and are products of several hundred million years of evolution.

Regulation of the membrane estrogen receptor-alpha: role of cell density, serum, cell passage number, and estradiol

We used modified immunocytochemical conditions to quantify a membrane form of estrogen receptor-alpha (mERalpha) in a rat pituitary tumor cell line, GH3/B6/F10. We studied the regulation of mERalpha vs. levels of intracellular ERalpha (iERalpha) using our 96-well plate immunoassay. The anti-ERalpha antibody C542 was used to label the ERalpha (via conjugated alkaline phosphatase) in fixed permeabilized (for iERalpha) vs. nonpermeabilized cells (for mERalpha). Expression of mERalpha was highest at low cell densities (<1000 cells/well) and decreased significantly at densities where cellular processes touched, whereas the more abundant iERalpha increased with increasing cell density over the same range. Serum starvation for 48 h caused increases in mERalpha, whereas iERalpha levels showed no significant changes. A large decline in mERalpha and iERalpha levels with cell passage number was observed. Minutes after nM 17beta-estradiol (E2) treatment, a portion of the cells rounded up and detached from the culture plate, whereas nM cholesterol had no such effect. Although E2 treatment did not change mERalpha levels, the antigen was reorganized from a fine particulate to aggregation into asymmetric large granules of staining. That common culturing conditions favor down-regulation of mERalpha may explain the relatively few reports of this protein in other experimental systems.

Vitellogenin precursors in the liver of the oviparous lizard, Podarcis sicula

In reptiles, as in the other oviparous vertebrates, vitellogenin (VTG) synthesis is stimulated in the liver by ovarian estrogens. In this article, the presence of VTG precursors was detected in liver subcellular fractions of the oviparous lizard, Podarcis sicula, in the reproductive period. The rough endoplasmic reticulum (RER) and the smooth microsomal fraction (SMF), which includes smooth endoplasmic reticulum and Golgi complex, were separated by means of two different sucrose gradients. The successful separation was controlled at the electron microscope. The contents of the different compartments were extracted by means of n-octyl-beta-D-glucopiranoside detergent and subjected to SDS-PAGE. Western Blotting with homologous anti/VTG antibody revealed two immunoreactive proteins of about 84 and 70 kDa in the RER, and four proteins of about 180, 150, 60, 50 kDa in the SMF; all these proteins appeared phosphorylated and glycosylated. The differences in the molecular weight of these VTG precursors are discussed.