Utility of in vitro test methods to assess the activity of xenoestrogens in fish

17β-Estradiol induces cyto-genotoxicity on blood cells of common carp (Cyprinus carpio)

17β-Estradiol, a natural hormone present at high concentrations in aquatic ecosystems, affects and modifies endocrine function in animals. In recent years research workers have expressed concern over its potential effects on aquatic organisms; however, little is known about its capacity to induce genetic damage or the pro-apoptotic effects of such damage on fish. Therefore, this study aimed to evaluate 17β-estradiol-induced cyto-genotoxicity in blood cells of the common carp Cyprinus carpio exposed to different concentrations (1 ng, 1 μg and 1 mg L^-1). Peripheral blood samples were collected and evaluated by comet assay, micronucleus test, determination of caspase-3 activity and TUNEL assay at 12, 24, 48, 72 and 96 h of exposure. Increases in frequency of micronuclei, TUNEL-positive cells and caspase-3 activity were observed, particularly at the highest concentration. In contrast, the comet assay detected significant increases at 24 and 96 h with the 1 μg and 1 ng L^-1 concentrations respectively. The set of assays used in the present study constitutes a reliable early warning biomarker for evaluating the toxicity induced by this type of emerging contaminants on aquatic species.

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

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

Influence of short-term exposure to low levels of 17α-ethynylestradiol on expression of genes involved in immunity and on immune parameters in rainbow trout, Oncorhynchus mykiss

Fish are exposed to endocrine-disrupting chemicals (EDC), which are well known to disturb not only the reproductive system but also the immune system in vertebrates. However, the mechanisms by which these compounds are able to modify fish immunity are not well understood. In order to test the EE2 effects on immunity in selected organs, we exposed rainbow trout male juveniles for 3 weeks to EE2 concentrations ranging from 0.01 to 1 μg/L. The results of this study suggest that EE2 affects the immunity of rainbow trout in a tissue dependent manner. This molecule affects both cellular and humoral immune systems. Indeed, blood leukocyte populations, as well as hepatic and plasma lysozyme, plasma MPO and renal complement activities, are modulated by EE2. Moreover, EE2 alters the gene expression of some mucus compounds, hepatic expression of complement sub-unit and lysozyme, or genes involved in the hepatic phagocytosis and transport of immunoglobulin across the liver.

Dehydroabietic acid (DHAA) alters metabolic enzyme activity and the effects of 17β-estradiol in rainbow trout (Oncorhynchus mykiss)

Recent studies have shown that dehydroabietic acid (DHAA), a resin acid present in pulp and paper mill effluent, affects liver energy metabolism and may have anti-estrogenic effects in fish. A chronic-exposure toxicity experiment using immature rainbow trout (Oncorhynchus mykiss) was conducted in order to assess the endocrine disrupting and liver metabolic effects of the model estrogen 17β-estradiol (E2) and the wood extractives DHAA and β-sitosterol (BS), regularly present in pulp and paper mill effluents. Exposure to 5ppm of E2 significantly increased hepatosomatic index (HSI), vitellogenin (VTG) and plasma sorbitol dehydrogenase (SDH). This latter effect was reduced by mixing E2 with DHAA, indicating that DHAA does not cause its endocrine disrupting effects indirectly due to liver damage. Exposure to 0.5ppm of DHAA as well as all the DHAA mixed treatments caused significant increases in liver citrate synthase (CS), activity after 7 days, however, the fish returned to control values by 28 days. Results indicate that DHAA may alter metabolic enzyme activity as well as alter the effects of E2 in juvenile rainbow trout.

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

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

In vivo and in vitro mixed-function oxygenase activity and vitellogenin induction in fish and in fish and rat liver cells by stilbenes isolated from scotch pine (Pinus sylvestris)

Many types of pulp and paper mill effluents have the ability to induce mixed-function oxygenase (MFO) activity and vitellogenin (VTG) protein in exposed male fish. The search for the compounds responsible for MFO induction has led to several classes of compounds, among them retene and stilbenes. The objective of this study was to investigate the biological activities of candidate stilbene compounds. Three stilbenes, 3,5-dihydroxystilbene (pinosylvin; P1), 3-hydroxy-5-methoxystilbene (P2), and 3,5-dimethoxystilbene (P3), were extracted from Scotch pine (Pinus sylvestris) and purified to evaluate their ability to induce MFO activity in vitro using ethoxyresorufin-O-deethylase (EROD) activity in a rat hepatoma cell line (H4IIE). As these compounds may be chlorinated during pulp bleaching, chlorination of P2 was undertaken, producing di- and trichlorinated isomers (Cl-P2), which were also tested. Compounds were tested for EROD-inducing ability in vivo by exposing juvenile rainbow tout (Oncorhynchus mykiss) to waterborne concentrations (0.010 to 1.0 mg/L) for 4 days. Compounds were also tested for their ability to induce VTG in trout primary liver cells in vitro. The stilbenes were weak inducers of EROD and VTG. H4IIE EROD was induced by all four compounds, with the most potent induction by P3, followed by P1, the Cl-P2 mixture, and then P2. Induction for all four stilbenes was from 3.13 × 10⁻³ to 3.57 × 10⁻⁴ as potent as retene and about 1.11 × 10⁻⁵ to 1.20 × 10⁻⁶ as potent as TCDD. Juvenile rainbow trout did not show EROD induction after exposures to P1, P2, or the Cl-P2 mixture, whereas P3 caused activity fourfold above that of controls. P1, P3, and Cl-P2 all weakly induced VTG in rainbow trout hepatocytes. The most potent inducer of VTG was Cl-P2, followed by P3 and P1. The results show the ability of wood-derived stilbenes to cause weak MFO induction in fish and in rat liver cells and to weakly induce vitellogenin in fish liver cells.

Estrogenic and anti-estrogenic effects of wood extractives present in pulp and paper mill effluents on rainbow trout

Wood extractives present in pulp and paper mill effluents may cause reproductive disturbances in fish. A chronic-exposure toxicity experiment using immature rainbow trout (Oncorhynchus mykiss) was conducted in order to assess the endocrine disrupting effects of two Chilean pulp and paper mill specific extracts (solid phase extraction, SPE) obtained from primary and secondary treated effluents. The (anti)estrogenic potencies and toxicity of the wood extractives regularly present in pulp mill effluent such as dehydroabietic acid (DHAA), beta-sitosterol (BS), and model estrogen 17beta-estradiol (E2) were evaluated by analysis of plasma vitellogenin (VTG) levels, gonadal somatic index (GSI) and liver ethoxyresorufin-O-deethylase (EROD) activity, respectively. The protocol involved the use of multiple intra-peritoneal injections (1 injection every 7 days for a total exposure period of 28 days). Analysis of variance/covariance, demonstrated no differences associated with fish gender other than GSI. The phytosterol BS, E2 and both pulp mill effluent extracts showed significant inductions of EROD and increased VTG levels after 4, 7, 14, 21 and 28 of exposure. While fish injected with secondary treated effluent extract showed a delayed induction in VTG levels compared to primary effluent injected fish, no effects on VTG and EROD levels were observed in DHAA injected fish. Moreover simultaneous injection of DHAA+E2 reduced the VTG levels found in E2 injected fish, indicating a potential indirect anti-estrogenic effect of this resin acid. The results of this study indicate that Chilean pulp and paper mill effluent extracts are estrogenic in rainbow trout males and females.

Effects of pulp and paper mill effluent extractives on aromatase CYP19a gene expression and sex steroid levels in juvenile triploid rainbow trout

We evaluated plasma testosterone (T) and 17beta-estradiol (E2) levels and ovarian aromatase CYP19a gene expression following a single intraperitoneal injection of Chilean pulp and paper mill effluent extracts into juvenile triploid rainbow trout. Fish injected with untreated effluent extracts had increased plasma T after 4 days, while plasma E2 concentration was increased in fish injected with both primary and secondary treated effluent extracts at the same sampling period. Ovarian CYP19a gene expression as measured by qRT-PCR was significantly induced in fish injected with the untreated, primary and secondary treated pulp and paper mill effluent extracts. Similar induction of CYP19a expression was found in fish injected with the androgens androstenedione (ADD) and T. A Principal Component Analysis (PCA) was conducted in order to identify structure in relationships between all measured variables and identifying which factors were most responsible for the variance observed within the plasma steroid levels, upregulation of ovarian CYP19a gene expression and the final estrogenic effect of increased plasma VTG levels. This analysis indicated a cluster correlation between plasma T levels and CYP19a gene expression (Factor 1, explaining 27.2% of total variance), a cluster including condition factor and liver somatic index (Factor 2, explaining 17.3%) and an additional cluster including plasma E2 and vitellogenin levels (Factor 3, explaining an additional 15.8%). The present results indicate that Chilean pulp and paper mill effluent extracts cause estrogenic effects in triploid rainbow trout. These effects could be related to the compounds present in the effluent that act as estrogen receptor agonists, or that induce changes leading to increased amounts of endogenous estrogens, reflected by increased E2 levels and induced aromatase expression/activity.

Responses of white sucker (Catostomus commersoni) to 20 years of process and waste treatment changes at a bleached kraft pulp mill, and to mill shutdown

The impacts of pulp mill effluents on white sucker (Catostomus commersoni) have been studied at Jackfish Bay, ON, Canada since the late 1980s. The site receives effluent from a large bleached kraft pulp mill which is the only source of chemical contamination in the area. Many laboratory studies have looked at the toxicological consequences of pulping process changes, but the benefit of these changes have not been looked at in wild fish. Jackfish Bay white sucker showed impacts on sexual maturity, gonad size, secondary sexual characteristics and circulating steroids hormone levels in the early years of the studies, and impacts were evaluated after installation of secondary treatment (1989), major pulping process changes (1995) and after the mill ceased pulp production and effluent release (2006). The addition of secondary treatment resulted in minor improvements in wild fish health, and the conversion to elemental chlorine free (ECF) bleaching at the mill was associated with more recovery in liver and gonad size. While some impacts persist at the exposure site, reproductive parameters showed further improvement during the mill shutdown period demonstrating that biologically active chemicals are still being discharged from modernized mills.

Gene expression responses in male fathead minnows exposed to binary mixtures of an estrogen and antiestrogen

Background

Aquatic organisms are continuously exposed to complex mixtures of chemicals, many of which can interfere with their endocrine system, resulting in impaired reproduction, development or survival, among others. In order to analyze the effects and mechanisms of action of estrogen/anti-estrogen mixtures, we exposed male fathead minnows (Pimephales promelas) for 48 hours via the water to 2, 5, 10, and 50 ng 17α-ethinylestradiol (EE₂)/L, 100 ng ZM 189,154/L (a potent antiestrogen known to block activity of estrogen receptors) or mixtures of 5 or 50 ng EE₂/L with 100 ng ZM 189,154/L. We analyzed gene expression changes in the gonad, as well as hormone and vitellogenin plasma levels.

Results

Steroidogenesis was down-regulated by EE₂ as reflected by the reduced plasma levels of testosterone in the exposed fish and down-regulation of genes in the steroidogenic pathway. Microarray analysis of testis of fathead minnows treated with 5 ng EE₂/L or with the mixture of 5 ng EE₂/L and 100 ng ZM 189,154/L indicated that some of the genes whose expression was changed by EE₂ were blocked by ZM 189,154, while others were either not blocked or enhanced by the mixture, generating two distinct expression patterns. Gene ontology and pathway analysis programs were used to determine categories of genes for each expression pattern.

Conclusion

Our results suggest that response to estrogens occurs via multiple mechanisms, including canonical binding to soluble estrogen receptors, membrane estrogen receptors, and other mechanisms that are not blocked by pure antiestrogens.

Identification of a transcriptional fingerprint of estrogen exposure in rainbow trout liver

The goal of this study was to identify a set of hepatic genes regulated by ligand-dependent activation of the estrogen receptor in juvenile rainbow trout (Oncorhynchus mykiss). A custom rainbow trout oligo DNA microarray, which contains probes targeting approximately 1450 genes relevant to carcinogenesis, toxicology, endocrinology, and stress physiology was utilized to identify transcriptional fingerprints of in vivo dietary exposure to 17 beta-estradiol (E2), tamoxifen (TAM), estradiol + tamoxifen (E2 + TAM), diethylstilbestrol (DES), dehydroepiandrosterone (DHEA), dihydrotestosterone (DHT), and cortisol (CORT). Estrogen exposure altered the expression of up to 49 genes involved in reproduction, immune response, cell growth, transcriptional regulation, protein synthesis and modification, drug metabolism, redox regulation, and signal transduction. E2, DES, and DHEA regulated 18 genes in common, mostly those associated with vitellogenesis, cell proliferation, and signal transduction. Interestingly, DHEA uniquely regulated several complement component genes of importance to immune response. While the effect of TAM on E2-induced changes in gene expression was mostly antagonistic, TAM alone increased expression of VTG1 and other genes associated with egg development and immune response. Few genes responded to CORT treatment, and DHT significantly altered expression of only one gene targeted by the OSUrbt array. Hierarchical cluster and principal components analyses revealed distinct patterns of gene expression corresponding to estrogens and non-estrogens, though unique patterns could also be detected for individual chemicals. A set of estrogen-responsive genes has been identified that can serve as a biomarker of environmental exposure to xenoestrogens.