Sex-specific vitellogenin production in immature rainbow trout

Integrative multi-biomarker approach on caged rainbow trout: A biomonitoring tool for wastewater treatment plant effluents toxicity assessment

The complex mixtures of contaminants released in wastewater treatment plant (WWTP) effluents are a major source of pollution for aquatic ecosystems. The present work aimed to assess the environmental risk posed by WWTP effluents by applying a multi-biomarker approach on caged rainbow trout (Oncorhynchus mykiss) juveniles. Fish were caged upstream and downstream of a WWTP for 21 days. To evaluate fish health, biomarkers representing immune, reproductive, nervous, detoxification, and antioxidant functions were assayed. Biomarker responses were then synthesized using an Integrated Biomarker Response (IBR) index. The IBR highlighted similar response patterns for the upstream and downstream sites. Caged juvenile females showed increased activities of innate immune parameters (lysozyme and complement), histological lesions and reduced glycogen content in the hepatic tissue, and higher muscle cholinergic metabolism. However, the intensity of the observed effects was more severe downstream of the WWTP. The present results suggest that the constitutive pollution level of the Meuse River measured upstream from the studied WWTP can have deleterious effects on fish health condition, which are exacerbated by the exposure to WWTP effluents. Our results infer that the application of IBR index is a promising tool to apply with active biomonitoring approaches as it provides comprehensive information about the biological effects caused by point source pollution such as WWTP, but also by the constitutive pollutions levels encountered in the receiving environment.

The effect of bifenthrin on the dopaminergic pathway in juvenile rainbow trout (Oncorhynchus mykiss)

Bifenthrin is a type I pyrethroid pesticide, which has been shown to increase plasma estrogen concentrations in several fish models. The mechanism of action by which bifenthrin alters 17β-estradiol (E2) is unclear. E2 biosynthesis is regulated through pituitary follicle stimulating hormone, which is directly controlled by hypothalamic gonadotropin releasing hormone (GnRH2). Since dopaminergic signaling significantly influences GnRH2 release in fish, the goal of the study was to determine the effect of a 96 h and 2 weeks exposure to bifenthrin on dopaminergic signaling in juvenile rainbow trout (Oncorhynchus mykiss) (RT). Our results indicated that a decrease in dopamine receptor 2A (DR2A) expression was associated with a trend toward an increase in plasma E2 following exposure at 96 h and 2 weeks, and a significant increase in the relative expression of vitellogenin mRNA at 2 weeks. DR2A mRNA expression decreased 426-fold at 96 h and 269-fold at 2 weeks in the brains of 1.5 ppb (3.55 pM) bifenthrin treated RT. There was an increase in tyrosine hydroxylase transcript levels at 96 h, which is indicative of dopamine production in the brains of the 1.5 ppb (3.55 pM) bifenthrin treated RT. A significant increase in the relative expression of GnRH2 was observed at 96 h but a significant decrease was noted after 2 weeks exposure indicating potential feedback loop activation. These results indicate that the estrogenic-effects of bifenthrin may result in part from changes in signaling within the dopaminergic pathway, but that other feedback pathways may also be involved.

Exploring the impacts of two separate mixtures of pesticide and surfactants on estrogenic activity in male fathead minnows and rainbow trout

In this study, male fathead minnows (FHM) (Pimephales promelas) and juvenile rainbow trout (RT; Oncorhynchus mykiss) were exposed to two different surfactant mixtures of analytical-grade nonlyphenol, 4-tert octyphenol, octylphenol ethoxylates, nonylphenol ethoxylates, and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). After a 7-days exposure to environmentally relevant concentrations of these compounds, there was no difference in the relative mRNA expression of vitellogenin (VTG) in male juvenile RT exposed to individual compounds or the 2,4-D-surfactant mixture compared with the control. In male FHM, there was a significant increase in VTG mRNA expression in the high individual treatments of 2,4-D and the surfactants but not the 2,4-D-surfactant mixtures compared with the control. These results were compared with another study exposing male FHM to individual and a mixture of alkylphenols and alkylphenol ethoxylates in two different combinations with the herbicide diuron and the insecticide bifenthrin. There were no differences in the relative expression of VTG mRNA amongst individual exposures and the control. Interestingly, when the ethoxylate mixture was combined with diuron, there was a significant decrease in the relative mRNA expression of VTG compared with the control. However, when the ethoxylate mixture was combined with both diuron and bifenthrin, there was a significant increase in the relative mRNA expression of VTG in male compared with all other groups in the multichemical mixture. The results of this study highlight differences between species and measurements of VTG in assessing the risk of mixtures to aquatic organisms.

Reconstitution studies of pesticides and surfactants exploring the cause of estrogenic activity observed in surface waters of the San Francisco Bay Delta

To evaluate the potential role of endocrine disruption in the decline of pelagic fishes in the San Francisco Bay Delta of California, various surface water samples were collected, extracted, and found to elicit estrogenic activity in laboratory fish. Chemical analysis of the estrogenic samples indicated 2 pesticides (bifenthrin, diuron), 2 alkyphenols (AP), and mixtures of 2 types of alkyphenol polyethoxylates (APEOs). Evaluation of estrogenic activity was further characterized by in vitro bioassays using rainbow trout hepatocytes (Oncorhynchus mykiss) and in vivo studies with Japanese medaka (Oryzias latipes). In the in vitro bioassays, hepatocytes exposed to the pesticides alone or in combination with the AP/APEO mixtures at concentrations observed in surface waters failed to show estrogenic activity (induction of vitelloginin mRNA). In the in vivo bioassays, medaka exposed to individual pesticides or to AP/APEO alone did not have elevated VTG at ambient concentrations. However, when the pesticides were combined with AP/APEOs in the 7-day exposure a significant increase in VTG was observed. Exposure to a 5-fold higher concentration of the AP/APEO mixture alone also significantly induced VTG. In contrast to earlier studies with permethrin, biotransformation of bifenthrin to estrogenic metabolites was not observed in medaka liver microsomes and cytochrome P450 was not induced with AP/APEO treatment. These results showed that mixtures of pesticides with significantly different modes of action and AP/APEOs at environmentally relevant concentrations may be associated with estrogenic activity measured in water extracts and feral fish that have been shown to be in population decline in the San Francisco Bay Delta.

Clock genes and their genomic distributions in three species of salmonid fishes: Associations with genes regulating sexual maturation and cell cycling

Background

Clock family genes encode transcription factors that regulate clock-controlled genes and thus regulate many physiological mechanisms/processes in a circadian fashion. Clock1 duplicates and copies of Clock3 and NPAS2-like genes were partially characterized (genomic sequencing) and mapped using family-based indels/SNPs in rainbow trout (RT)(Oncorhynchus mykiss), Arctic charr (AC)(Salvelinus alpinus), and Atlantic salmon (AS)(Salmo salar) mapping panels.

Results

Clock1 duplicates mapped to linkage groups RT-8/-24, AC-16/-13 and AS-2/-18. Clock3/NPAS2-like genes mapped to RT-9/-20, AC-20/-43, and AS-5. Most of these linkage group regions containing the Clock gene duplicates were derived from the most recent 4R whole genome duplication event specific to the salmonids. These linkage groups contain quantitative trait loci (QTL) for life history and growth traits (i.e., reproduction and cell cycling). Comparative synteny analyses with other model teleost species reveal a high degree of conservation for genes in these chromosomal regions suggesting that functionally related or co-regulated genes are clustered in syntenic blocks. For example, anti-müllerian hormone (amh), regulating sexual maturation, and ornithine decarboxylase antizymes (oaz1 and oaz2), regulating cell cycling, are contained within these syntenic blocks.

Conclusions

Synteny analyses indicate that regions homologous to major life-history QTL regions in salmonids contain many candidate genes that are likely to influence reproduction and cell cycling. The order of these genes is highly conserved across the vertebrate species examined, and as such, these genes may make up a functional cluster of genes that are likely co-regulated. CLOCK, as a transcription factor, is found within this block and therefore has the potential to cis-regulate the processes influenced by these genes. Additionally, clock-controlled genes (CCGs) are located in other life-history QTL regions within salmonids suggesting that at least in part, trans-regulation of these QTL regions may also occur via Clock expression.

Do suspended sediments modulate the effects of octylphenol on rainbow trout?

A system was devised which allows particles to remain in suspension in a conventional 60 L aquarium without undue disturbance to resident fish. Using this system, juvenile rainbow trout were exposed for one week to 4-tert-octylphenol (OP, 10-1000 microg/L) with or without the presence of suspended sediments (10-20mg/L of natural suspended sediments from the River Calder, UK). About 8% of the added OP partitioned to the solid phase. Vitellogenin levels were determined in the plasma of the exposed rainbow trout and showed a dose-dependent increase with regards to OP exposure concentration. Considerable variation in the vitellogenin response was observed between separate runs with the same OP concentration. There was no statistically significant (at P < 0.05) difference in plasma VTG levels between the OP treatments with or without suspended sediments. This suggests that the dissolved concentration is the key factor and natural suspended sediment neither protects against, nor exacerbates, the endocrine disrupting effect of OP on fish.

Vitellogenin in the blood plasma of male cod (Gadus morhua): a sign of oestrogenic endocrine disruption in the open sea?

An ELISA for cod vitellogenin (VTG) has been set up using cod lipovitellin for plate coating and standardisation. The assay has been applied to plasma samples collected from male and female cod caught in three distinct areas around the UK, three areas off the Norwegian coast and also to cod reared initially at an aquaculture site and subsequently maintained at a research station. The aim of the study was to determine whether there were any signs of oestrogenic endocrine disruption in a fish species living offshore. VTG induction was found in male cod caught in the North Sea, the Shetland Box area, in Oslofjord and also in cultivated fish. There was a strong relationship between concentrations of VTG and fish size. There was no evidence that the presence of VTG in the plasma of males is a natural part of their life cycle. On the other hand, the size of fish at which these elevated VTG concentrations appear (ca. 5 kg) is about the size that cod change from feeding primarily on benthic invertebrates to mainly other fish, both benthic and pelagic. The possibility is suggested that large cod pick up oestrogenic endocrine disrupters through the food chain.

Waterborne ethynylestradiol induces vitellogenin and alters metallothionein expression in lake trout (Salvelinus namaycush)

Estrogenic contaminants isolated from waters receiving sewage treatment plant effluents are known to induce the egg yolk precursor vitellogenin (VTG) in male fish. Levels of the metal binding protein metallothionein (MT) have also been shown to be affected by estrogens in fish. It has been postulated that MT declines in estrogen exposed fish to facilitate transfer of the essential metal Zn to cellular components required for VTG synthesis. To examine the changes in MT and VTG concentrations in fish exposed to an estrogen contaminant, lake trout (Salvelinus namaycush) were exposed to waterborne ethynylestradiol at 0, 4, 40 or 400 ng/l(-1) for 21 days. Blood and tissues were collected after 21 days of exposure to measure circulating levels of VTG as well as MT concentrations in liver and kidney. VTG increased in male and female fish from all three exposure groups compared to control fish. MT in liver significantly decreased in males and females compared to the controls, in the two highest exposures. MT in kidney was significantly higher in both sexes of fish exposed to the two highest concentrations of ethynylestradiol. These data are supportive of a relationship between estrogen exposure and the regulation of MT. Further studies to examine the specific links between estrogen exposure, VTG induction and regulation of essential metals like Zn are required.

Estrogenic effect of dietary 4-tert-octylphenol in rainbow trout (Oncorhynchus mykiss)

The estrogenic effect of dietary 4-tert-octylphenol (octylphenol) in rainbow trout Oncorhynchus mykiss was investigated. Octylphenol was administered orally to sexually immature rainbow trout every second day for 11 days in doses between 0.4 and 50 mgkg(-1)2 d(-1). Plasma vitellogenin was measured at day 0, 6 and 11 and at the end of the experiments, the amounts of octylphenol retained in liver and muscle were determined. Increases in average plasma vitellogenin levels were seen at exposure to 40 mg octylphenol kg(-1) every second day; the most sensitive fish responded to 30 mgkg(-1). Doses below 20 mg octylphenol kg(-1)2 d(-1) had no effect. The ED(50) value for induction of vitellogenin synthesis was 35 mg octylphenol kg(-1)2 d(-1). Only 1 to 2 per thousand of the total amount of octylphenol administered orally over the 11 days experimental period was retained in muscle and liver at the end of the experiment. A clear dose-related increase was observed for concentrations of octylphenol in both liver and muscle of fish exposed to doses between 0.4 and 50 mgkg(-1)2 d(-1). A significant correlation was found between the concentrations of octylphenol in the liver and vitellogenin level in plasma.

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.

Uptake, metabolism and excretion of bisphenol A in the rainbow trout (Oncorhynchus mykiss)

The uptake, metabolism and excretion of the oestrogenic chemical bisphenol A (BPA) were studied in juvenile rainbow trout (Oncorhynchus mykiss). BPA was detectable in plasma, liver and muscle after 2 h of water exposure at 0.44 microM (100 microg BPA/l), and a steady state was reached within 12-24 h. The concentration of the glucuronidated degradation product in the plasma was about twice that of the parent compound. A plasma half life of BPA was calculated as 3.75 h following injection of the compound. The vitellogenin synthesis was measured in response to the BPA treatment, and a lag period of 5 and 7 days between injection of the compound and a significant vitellogenin response was observed for females and males, respectively. At the time of the vitellogenin response no BPA could be detected in the liver tissue from either male or female fish. These results indicate that fish briefly exposed to elevated levels of oestrogenic chemicals might develop a response several days later.

3,3'-diindolylmethane, a major condensation product of indole-3-carbinol, is a potent estrogen in the rainbow trout

Indole-3-carbinol (I3C), a compound found in Brassica vegetables has been widely studied for its chemopreventive properties. I3C has been shown to block tumor initiation and promotion; however, it also acts as a tumor promoter. I3C and some of its acid condensation products, particularly 3,3'-diindolylmethane (I33'), have exhibited antiestrogenic properties. We report that I33' acts as an estrogen in the rainbow trout liver in vitro and in vivo by inducing vitellogenin (Vg), a well-characterized biomarker for estrogens. Precision-cut liver slices from male rainbow trout, Oncorhynchus mykiss, were incubated at 14 degrees C for 96 h in media containing I3C, I33', or a mixture of I3C acid condensation products (RXN) (0-250 microM). I33' and RXN increased Vg levels in rainbow trout liver slices by over 300- and 20-fold, respectively, vs vehicle. The efficacy of I33' induction of Vg was comparable to 17 beta-estradiol (E(2)) with 2500-fold less potency. I33' and E(2) cotreatment resulted in additive Vg induction. Tamoxifen completely inhibited I33'-induced Vg induction, suggesting that Vg induction by I33' is entirely through the estrogen receptor. In vivo, juvenile male rainbow trout were fed I3C, RXN (0-2000 mg/kg), or I33' (0-250 mg/kg) for 2 weeks. At 2000 mg/kg, I3C induced Vg by over 100,000-fold compared to controls, which was comparable to 5 mg/kg 17 beta-estradiol (the dose resulting in maximum induction). I33' was five times as potent as I3C with equal efficacy. The potency of RXN was only 5% of I3C. Again, I33' and E(2) cotreatment resulted in additive Vg induction. I33' may have accounted for Vg increases observed in trout fed I3C as it is present in liver after oral dosing at concentrations (70 microM) expected to maximally induce Vg. In trout, results in vitro and in vivo document that I33' is estrogenic, consistent with our hypothesis that I3C promotes liver cancer in trout by estrogenic pathways.

The non-aromatizable androgen, dihydrotestosterone, induces antiestrogenic responses in the rainbow trout

In order to satisfy government mandates, numerous studies have been performed categorizing potential endocrine disrupting chemicals as (anti)estrogens or (anti)androgens. We report here that dihydrotestosterone (DHT), a potent, non-aromatizable androgen receptor agonist, induces antiestrogenic responses through direct and/or indirect modulation of vitellogenin (Vg), steroid hormone and total cytochrome P450 levels. DHT and two weak, aromatizable androgens, DHEA and androstenedione (0.05-50 mg/kg per day), were fed to juvenile trout for 2 weeks. DHEA and androstenedione significantly increased blood plasma Vg by up to 30- and 45-fold, respectively (P<0.05, t-test). 17beta-Estradiol (E2) increases were also observed with both androgens, albeit with lower sensitivity. DHT markedly decreased Vg and E2 levels, suggesting that DHEA and androstenedione increased Vg and E2 via conversion to E2 and not by estrogen receptor agonism. DHEA and androstenedione had no effect on total cytochrome P450 content, while DHT significantly decreased P450 content in a dose dependent fashion. These results indicate that alterations in metabolism mediated by androgen receptor binding may be responsible for the Vg and E2 decreases by DHT. In an attempt to decipher between receptor and non-receptor androgenic mechanisms of the observed DHT effects, DHT (0, 50 or 100 mg/kg per day) and flutamide (0-1250 mg/kg per day), an androgen receptor antagonist, were fed to juvenile rainbow trout for 2 weeks. Flutamide alone was as effective as DHT in decreasing E2 and Vg levels in males but did not significantly reverse DHT induced Vg decreases in either sex (P>0.05, F-test). DHT decreases in total P450 content were partially attenuated in males by flutamide co-treatment, but not females, suggesting a partial androgenic mechanism to the P450 decreases as well as a fundamental sex difference responding to androgen receptor binding. Moreover, flutamide alone decreased P450 content by up to 30% in males and 40% in females. These effects may be mediated through direct androgen receptor binding irrespective of whether the binding is agonistic or antagonistic. This study indicates that androgen receptor agonists/antagonists can elicit significant antiestrogenic effects that may not necessarily be mediated through classic receptor binding mechanisms and signal transduction pathways.

The oestrogenic potential of the phthalate esters

The phthalate esters represent a class of chemicals used widely and diversely in industry. Concern that phthalates might be oestrogenic arose from observations that the diesters inhibited the binding of 17beta-estradiol to isolated oestrogen receptors and stimulated the expression of cellular oestrogen-sensitive endpoints (gene expression, mitosis) in vitro. However, conflicting results have been found in comparable studies, and those studies that have demonstrated oestrogen mimicry have generally done so at concentrations approaching, or above, the limit of water solubility for the phthalates. The monoesters (the primary metabolites of the diesters in vivo) are inactive in similar in vitro tests. Furthermore, the diesters have not shown any oestrogenic activity in numerous and diverse studies in vivo at doses eliciting systemic toxicity. Consequently, the oestrogenic activity of phthalates identified in in vitro studies is not relevant to humans or the environment.

Determining relative estrogenicity by quantifying vitellogenin induction in rainbow trout liver slices

Precision cut tissue slices, by modeling the entire organ, are a valuable tool for studying protein induction or inhibition by test chemicals. This manuscript describes parameters to quantify relative estrogenicity of chemicals in rainbow trout liver slices by measuring vitellogenin (Vg) induction, a well-characterized biomarker of estrogen receptor signal transduction. Hank's medium (phenol-red free) supplemented with Hepes, sodium bicarbonate, and 1% bovine serum albumin was utilized. The experimental parameters were optimized using 1000 nM 17beta-estradiol, a potent estrogen in rainbow trout that induces Vg production in vivo. The addition of trout serum and retention of the media was essential, probably to allow for the accumulation of Vg in the slices and media. Histological examination and ATP analyses indicated no toxicity in control or 17beta-estradiol-treated liver slices after 120 h. Induction was 4-fold greater with 25% serum containing media compared to media with 10% serum. We observed Vg induction as great as 500-fold over controls at 96 h in liver slices and media containing 25% serum and 1000 nM 17beta-estradiol. Controls without 17beta-estradiol, incubated in media with 10 or 25% serum, exhibited no detectable Vg production, indicating that the induction seen was not from the media or serum. We observed that 48 h was required for significant Vg induction in the media and liver slices. Maximum induction in slices occurred at 96 h, whereas media Vg levels continued to increase to 120 h, suggesting a time delay between Vg production and excretion by the liver. The feasibility of this model to detect weak environmental estrogens was determined with 0-250 microM o,p'DDE and bisphenol A. Both compounds induced Vg in this model with EC50 values of 10(4) and 2x10(5) higher than E(2), respectively. Our results indicate the importance of media, serum, and time selection for optimal Vg induction. This model allows for the determination of relative estrogenicity of chemicals in a controlled in vitro system while utilizing the advantages of precision cut slice technology.