Effects on reproductive potential and endocrine status in the mummichog (Fundulus heteroclitus) after exposure to 17alpha-ethynylestradiol in a short-term reproductive bioassay

Effects on guppy brain aromatase activity following short-term steroid and 4-nonylphenol exposures

Brain estrogen production, performed by the enzyme aromatase, can be disrupted/affected in teleost fish exposed to endocrine disruptors found in polluted aquatic environments. The guppy (Poecilia reticulata) was previously studied and confirmed to suffer negative effects on reproductive behaviors following inhibition of the brain aromatase reaction. Here adult guppies (Poecilia reticulata) of both genders were subjected to known endocrine disruptors: the androgen androstenedione (A), the synthetic estrogen 17alpha-ethinylestradiol (EE(2)), and the estrogenic surfactant 4-nonylphenol (NP), at high (50 microg/L) and at environmentally relevant concentrations (10 ng/L EE(2), 5 microg/L NP, and 0.7 microg/L A) for 2 weeks followed by measurements of brain aromatase activity (bAA). In the adult males, bAA was stimulated by A and EE(2) at 50 microg/L. Female activity was also stimulated by the higher estrogenic treatment. At environmentally relevant concentrations only the EE(2) treatment affected bAA, and only in males. The alkylphenolic substance NP produced no effect in either of the experiments, not on males nor females. The results indicate that short-term steroid treatments have stimulatory effects on guppy brain aromatase even at concentrations that can be found in the environment. We thus suggest bAA of adult guppies to be a suitable bioindicator of endocrine disruptors.

An endocrine disrupting chemical changes courtship and parental care in the sand goby

Endocrine disrupting chemicals (EDCs) are a diverse group of compounds that can mimic, block or modulate the synthesis of natural hormones. They are known to cause impairment of reproduction of aquatic organisms at very low concentrations. The aim of this study was to examine how exposure from 10 to 31 days to 17alpha-ethinyl estradiol (EE2, 41 ng L(-1)) affects the courtship and parental care behaviour of male sand gobies (Pomatoschistus minutus). The sand goby exhibits a polygynous mating system, where males compete for females and provide paternal care. First, male courtship performance towards a stimulus female was recorded with video camera. Secondly, after the male had received eggs his parental care behaviour was video recorded. In addition to behavioural endpoints, we measured the expression of hepatic vitellogenin (Vtg) and zona radiata protein (Zrp) mRNA, as well as common somatic indices. Our study shows that exposure to EE2 affected male fanning behaviour during both courtship and parental care. Interestingly, small exposed males increased their courtship fanning to similar levels as larger control males. However, during parental care egg fanning was not related to male size, and all exposed males fanned more than control males. The EE2-exposure induced Vtg and Zrp mRNA expression in males and decreased hepatosomatic index (HSI), and increased gonadosomatic index (GSI). Females prefer males that fan more, which will favour the small EDC exposed males. This may lead to mating that favours males that are not strong enough to tend the eggs until they hatch, thus decreasing the reproductive success of individuals.

Hepatic transcriptomic and metabolomic responses in the Stickleback (Gasterosteus aculeatus) exposed to ethinyl-estradiol

An established three-spined stickleback (Gasterosteus aculeatus) cDNA array was expanded to 14,496 probes with the addition of hepatic clones derived from subtractive and normalized libraries from control males and males exposed to model toxicants. Microarrays and one-dimensional (1)H nuclear magnetic resonance (NMR) spectroscopy, together with individual protein and gene biomarkers were employed to investigate the hepatic responses of the stickleback to ethinyl-estradiol (EE(2)) exposure. Male fish were exposed via the water to EE(2), including environmentally relevant concentrations (0.1-100ng/l) for 4 days, and hepatic transcript and metabolite profiles, kidney spiggin protein and serum vitellogenin concentrations were determined in comparison to controls. EE(2) exposure did not significantly affect spiggin concentration but significantly induced serum vitellogenin protein at the threshold concentration of 32ng/l. (1)H NMR coupled with robust univariate testing revealed only limited changes, but these did support the predicted modulation of the amino acid profile by transcriptomics. Transcriptional induction was found for hepatic vitellogenins and choriogenins as expected, together with a range of other EE(2)-responsive genes. Choriogenins showed the more sensitive responses with statistically significant induction at 10ng/l. Real-time polymerase chain reaction (PCR) confirmed transcriptional induction of these genes. Phosvitinless vitellogenin C transcripts were highly expressed and represent a major form of the egg yolk precursors, and this is in contrast to other fish species where it is a minor component of vitellogenic transcripts. Differences in inducibility between the vitellogenins and choriogenins appear to be in accordance with the sequential formation of chorion and yolk during oogenesis in fish.

Disruption of the steroid metabolome in fish caused by exposure to the environmental estrogen 17alpha-ethinylestradiol

Exposure to environmental estrogens such as 17alpha-ethinylestradiol (EE2) has been associated with feminization and a decline in fertility of male fish. To investigate the effect of estrogen exposure on steroid homeostasis, we exposed roach (Rutilus rutilus) to EE2 (1-29 ng/L) for 18 days and analyzed steroid profiles in bile and plasma using targeted analyses and in liver and gonadal tissues using mass spectrometry metabolite profiling techniques (metabolomics). Exposure to EE2 resulted in a concentration dependent reduction of estrogens and androgens in bile and plasma of both male and female fish. At 10 ngEE2/L, significant reductions in concentrations of hydroxyprogesterone, androstenedione, 11-hydroxyandrostenedione, and 11-ketotestosterone were detected in the testes metabolome, indicating disruption of steroid biosynthesis upstream of androgen metabolism. Estrogen exposure also resulted in increased biosynthesis of cortisol and cortisone in testes and ovaries, respectively, but did not alter glucocorticoid concentrations in the liver or plasma. This first report on the effect of EE2 exposure on the steroid metabolome in fish tissues suggests that both sex steroid and glucocorticoid pathways are one of the primary targets of estrogen exposure in fish gonads and provides further insights into the mode of action of this endocrine disrupting chemical.

17alpha-ethinylestradiol induces an imbalance between apoptosis and cell proliferation to sex steroid disruption in a testis culture of gudgeon, Gobio gobio

The aim of this study was to investigate the effect of the most potent xenoestrogen currently found in the environment, ethinylestradiol (EE2), on some physiological events occurring during early spermatogenesis of gudgeon (Gobio gobio), a common European fish species. Physiological pathways studies were apoptosis, cell proliferation, and steroidogenesis on sex steroids (testosterone [T], 11-ketotestosterone [11-KT], and 17beta-estradiol [E2]). Testis pieces were cultured in vitro during 21 d at 10(-4), 10(-3), 10(-2), 10(-1), 1 and 10 microg/L of EE2 as well as in positive (10(-1) microg/L of E2) and ethanol control medium. Apoptosis and cell proliferation displayed opposite responses related to the EE2 concentration. When apoptosis inhibition was observed, cell proliferation was induced at 10(-2) and 10(-1) microg/L of EE2 as well as in the positive control. In contrast, a massive cell death was detected for high EE2 concentrations (1 and 10 microg/L). Steroidogenesis was also disrupted in a dose-related manner. 11-Ketotestosterone was depressed at 10(-2) and 10(-1) microg/L of EE2 whereas E2 was detectable in the medium only at 10(-3), 10(-2), and 10(-1) microg/L of EE2. High concentrations of T were detected in the medium at 10(-3), 10(-2), and 10(-1) microg/L of EE2 but depressed at 1 and 10 microg/L of EE2. In conclusion, intermediate EE2 concentrations (10(-2) and 10(-1) microg/L) used in this experimental design have obviously disrupted early spermatogenesis, leading to an imbalance between cell death and cell proliferation in a sex steroid environment toward E2. The results of the present study could be the basis conditions for oocyte development within the testis of a common teleost fish under xenoestrogen exposure.

Effects of 17alpha-ethynylestradiol on early-life development, sex differentiation and vitellogenin induction in mummichog (Fundulus heteroclitus)

Fertilized mummichog eggs retrieved from 17alpha-ethynylestradiol (EE(2)) exposed adult fish were raised in concentrations of EE(2) ranging from 0 to 100 ng/L (100 ng/L EE(2) estimated to have actual average exposure concentrations of 30% of nominal; 0.1-10 ng/L were below detect throughout 24-h exposure period) for 61 weeks post-hatch. Eggs exposed at 100 ng/L hatched sooner, the larvae were longer, and survival of juvenile fish from hatch to study termination was greater than all other treatments, though fewer hatched at this treatment. Sex ratios were skewed (>80% female phenotype) at 100 ng/L EE(2), and some gonadal male fish displayed female secondary sex characteristics. Condition factor, gonadosomatic index (GSI), and liver somatic index (LSI) were found to decrease in both sexes between 52 and 61 weeks post-hatch. Female fish had increased hepatic vitellogenin (VTG) at 52 weeks post-hatch. When exposed to 1, 10 and 100 ng/L EE(2), female fish had a higher proportion of vitellogenic follicles in the ovarian tissue. Males exposed at 100 ng/L may have had disruption at some endpoints (GSI, VTG) that is masked due to reduced sample size compared to other treatments. Fish exposed to concentrations of EE(2) at or below 10 ng/L showed inconsistent effects on development and reproductive potential. This study indicates the potential for population-level effects at the high range of environmental EE(2) at concentrations equivalent to those at which consistent effects in fecundity in the adult mummichog reproductive test have been measured. This work demonstrates that chronic EE(2) exposure causes developmental effects at concentrations similar to those which cause effects in the shorter-term adult mummichog reproductive test. Effects are at higher concentrations than have been noted for freshwater model species. Whether this is because of species sensitivity or due to differences between freshwater and saltwater availability of EE(2) or its uptake requires further study.

Disruption of sexual selection in sand gobies (Pomatoschistus minutus) by 17alpha-ethinyl estradiol, an endocrine disruptor

In aquatic environments, endocrine disrupting chemicals (EDCs) that interfere with the reproductive physiology of males form a threat to the reproduction of populations. This is often manifested as decreased sexual performance or sterility among males. We show that exposure to EDCs can directly affect the mating system of a marine fish, the sand goby (Pomatoschistus minutus). We exposed males for 1 to 4 weeks to two different concentrations (5 ng L(-1) and 24 ng L(-1)) of 17alpha-ethinyl estradiol (EE2); a synthetic compound mimicking estrogen and a water control. The sand goby exhibits a polygynous mating system, in which male mating success is typically skewed towards the largest males, resulting in strong sexual selection for increased male size. Our experiment shows that when males have been exposed to EE2, male size has a smaller effect on mating success, resulting in weaker sexual selection on male size as compared to the control. There was an interaction between treatment and exposure time on the expression of vitellogenin and zona radiata protein mRNAs. Males exposed to high EE2 reached much higher expression levels than males exposed to low EE2. Of the somatic markers, the hepatosomatic index was lower in males exposed to high EE2 than in the low EE2 and control males. Our results suggest that exposure to EDCs can have effects on the mating system before physiological changes are observable. These effects can be of profound nature as they interfere with sexual selection, and may in the long run lead to the loss of traits maintained through sexual selection.

Benzo(a)pyrene decreases brain and ovarian aromatase mRNA expression in Fundulus heteroclitus

The higher molecular weight polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BaP) are typically associated with genotoxicity, however, newer evidence suggests that these compounds may also act as endocrine system disruptors. We hypothesized that altered expression of the P450 enzyme aromatase genes could be a target for reproductive or developmental dysfunction caused by BaP exposure. Aromatase is at least partially responsible for estrogen homeostasis by converting androgens into estrogens. In fish, there are two isoforms of aromatase, a predominantly ovarian form, CYP19A1, and a brain form, CYP19A2. CYP19 mRNA expression was measured following BaP exposure (0, 10, 100 microg/L waterborne for 10 or 15 days) in Fundulus adults, juveniles and embryos by in situ hybridization. The CYP19A1 expression was significantly decreased after BaP exposure in the 3-month-old Fundulus immature oocytes, but BaP did not affect CYP19A1 expression at any stage in adult oocytes. In embryo brains, BaP significantly decreased CYP19A2 compared to controls by 3.6-fold at 14 days post-fertilization. In adults, CYP19A2 expression was decreased significantly in the pituitary and hypothalamus (81% and 85% of controls, respectively). Promoter regions of Fundulus CYP19s were cloned, and putative response elements in the CYP19A1 and CYP19A2 promoters such as CRE, AhR and ERE may be involved in BaP-mediated changes in CYP19 expression. In order to compare the mechanism of BaP-mediated inhibition with that of a known aromatase inhibitor, fish were also exposed to fadrozole (20 and 100 microg/L). Fadrozole did not significantly decrease the mRNA expression in embryos or adult Fundulus. However, aromatase enzyme activity was significantly decreased in adult ovary and brain tissues. These studies provide a greater molecular understanding of the mechanisms of action of BaP and its potential to impact reproduction or development.