Characterization of the estrogenic response to genistein in Japanese medaka (Oryzias latipes)

Embryonic exposure to genistein induces anxiolytic and antisocial behavior in zebrafish: persistent effects until the adult stage

Genistein is a phytoestrogen, which is structurally similar to 17β-estradiol. It is present in plants, food, and as a contaminant in effluents. In this article, we demonstrate the effects of embryonic exposure to three different concentrations of genistein (10 μg/L, 40 μg/L, and 80 μg/L) which is similar to those found in effluents. Zebrafish eggs were exposed during the first 72 h post-fertilization (hpf). Heart rate was evaluated at 48 hpf and mortality rate was assessed during the first 72 hpf. The light/dark (LDT) and open field (OFT) behavioral tests were applied to the larvae (6 dpf), and the novel tank (NTT), social preference (SPT), light-dark (LDT), and sexing tests were performed on adult fish (90 dpf). Embryonic exposure to genistein caused anxiolytic-like behavior in both larvae and adult animals. In adult stage, we observed an increase in locomotor activity and antisocial behavior in the concentration of 40 μg/L. There was an increase in the mortality rate in all concentrations when compared to the control and an increase in heart rate at the concentration of 80 μg/L. Exposure to 10 μg/L generated a higher frequency of females when compared to the control group. Our results show that exposure to genistein during the embryonic phase brings damage in the short and long term as it increases the mortality rate and leads to behavioral disorders both in the larval stage, with perpetuation until adult stage. The anxiolytic-like effect and less social interaction are effects that harm fish survival.

The Gene Regulatory Roles of Herbal Extracts on the Growth, Immune System, and Reproduction of Fish

The crucial need for safe and healthy aquatic animals obligates researchers in aquaculture to investigate alternative and beneficial additives. Medicinal herbals and their extracts are compromised with diverse effects on the performances of aquatic animals. These compounds can affect growth performance and stimulate the immune system when used in fish diet. In addition, the use of medicinal herbs and their extracts can reduce oxidative stress induced by several stressors during fish culture. Correspondingly, aquatic animals could gain increased resistance against infectious pathogens and environmental stressors. Nevertheless, the exact mode of action where these additives can affect aquatic animals' performances is still not well documented. Understanding the mechanistic role of herbal supplements and their derivatives is a vital tool to develop further the strategies and application of these additives for feasible and sustainable aquaculture. Gene-related studies have clarified the detailed information on the herbal supplements' mode of action when administered orally in aquafeed. Several review articles have presented the potential roles of medicinal herbs on the performances of aquatic animals. However, this review article discusses the outputs of studies conducted on aquatic animals fed dietary, medicinal herbs, focusing on the gene expression related to growth and immune performances. Furthermore, a particular focus is directed to the expected influence of herbal supplements on the reproduction of aquatic animals.

Histological Evaluation of Gonad Impairments in Russian Sturgeon (Acipenser gueldenstaedtii) Reared in Recirculating Aquatic System (RAS)

Simple Summary

The growing interest in sturgeon aquaculture necessitates the constant development of rearing techniques with special emphasis on the maintenance of high fish reproduction performance. However, there is a substantial lack of knowledge regarding gonadal impairments in sturgeons, even though the occurrence of such disorders poses a significant threat to the future of both commercial and conservation farming. Therefore, the aim of the research was to determine potential pathologies in the gonads of over-four-year old Russian sturgeon (Acipenser gueldenstaedtii) reared in the controlled conditions of recirculating aquatic systems (RAS). RAS have gained popularity in recent years, as they are considered the most environmentally friendly way of producing fish. Nevertheless, there are many issues that need to be resolved regarding sturgeon RAS farming, including its effect on gonadal development and, therefore, fish reproduction capacity. A detailed histological analysis revealed multiple gonadal disorders in the analyzed sturgeon, some of which can contribute to decreased fish fertility or even sterility. The female-biased sex ratio and the character of the identified impairments indicates that the observed germinal tissue disruptions might originate from estrogenic endocrine disturbances. Therefore, for the further sustainable development of sturgeon RAS aquaculture, there is an urgent need to identify and eliminate the causes of such disruptions.

Abstract

The aim of the study was to raise an issue concerning gonadal impairments in sturgeon reared in recirculating aquatic systems (RAS). In the present study, an in-depth histological evaluation in terms of gonadal pathologies was performed on over-4-year-old (1600 days post-hatching) Russian sturgeon (Acipenser gueldenstaedtii) reared under indoor RAS. A female-biased sex ratio, intersex occurrence, ovarian fat overgrowth, T-cell infiltration and follicle atresia were the most commonly observed disorders in the analyzed gonads. The combined processes of oocyte autophagy and follicular cell apoptosis were engaged in follicular atresia; however, atretic follicles showed a varied morphology, whereas oogonia and oocytes in the early stages of meiosis, as well as spermatogonia, underwent degeneration by apoptosis. The most severe pathology was observed in females with abundant intra-ovarian fat deposition. The extremely fatty ovaries were noted to lose the majority of ovarian follicles, which directly leads to fish sterility. The identified impairments might be related to estrogenic endocrine disruption, as feminization and unspecific vitellogenin synthesis were detected, although the sources of the observed pathologies can be diverse. Therefore, the presented research lays the groundwork for further studies on reproductive disorders in this prized and endangered fish species.

Opposite pH-dependent roles of hydroxyl radicals in ozonation and UV photolysis of genistein

Phytoestrogens were frequently detected in municipal or industrial wastewater, and raised great attentions due to potential risks to humans or organisms. Until now, transformation mechanisms of phytoestrogens in advanced wastewater treatments were largely unknown. Here, pH influence mechanisms on transformations of phytoestrogens during two typical advanced wastewater treatments (ozonation and photolysis) were investigated, employing genistein (Gs) as a case. Removal efficiencies of Gs decreased significantly with increases of pH during ozonation, while photolytic rates increased by 44 or 200 times from pH 4.9 to 11.6 under irradiations without or with UVC. pH increases caused both dissociation of Gs and formation of hydroxyl radicals (OH) in ozonation or photolysis, however, led to opposite changes to degradation rates. This was because that OH played negatively as a competitor for O₃ in ozonation, but acted as an accelerating species inducing self-sensitized photooxidation of Gs under UV light. Ozonation and photolytic products of Gs were similar at pH 4.9 or 8.6, but were totally different at pH 11.6. Most of the transformation products maintained isoflavone structures, and might possess phytoestrogenic effects. This study provided a deep insight into the pH influencing mechanism on typical advanced wastewater treatment processes of phytoestrogens. MAIN FINDING OF THE WORK: Opposite pH-dependent degradation mechanisms caused by hydroxyl radicals (OH) were elucidated for ozonation and UV photolysis of phytoestrogens, taking genistein as a case.

Medaka as a model for studying environmentally induced epigenetic transgenerational inheritance of phenotypes

Ability of environmental stressors to induce transgenerational diseases has been experimentally demonstrated in plants, worms, fish, and mammals, indicating that exposures affect not only human health but also fish and ecosystem health. Small aquarium fish have been reliable model to study genetic and epigenetic basis of development and disease. Additionally, fish can also provide better, economic opportunity to study transgenerational inheritance of adverse health and epigenetic mechanisms. Molecular mechanisms underlying germ cell development in fish are comparable to those in mammals and humans. This review will provide a short overview of long-term effects of environmental chemical contaminant exposure in various models, associated epigenetic mechanisms, and a perspective on fish as model to study environmentally induced transgenerational inheritance of altered phenotypes.

Toxicological relevance of endocrine disruptors in the Tagus River estuary (Lisbon, Portugal)

The Tagus is the longest Iberian river, notwithstanding, the levels of natural and xenoestrogenic endocrine-disrupting compounds (EDCs) were never measured in its estuary. Suspecting for their presence, we made a major survey of 17 EDCs that include: (i) natural (17β-oestradiol and estrone) and pharmaceutical oestrogens (17α-ethynylestradiol); (ii) industrial and household pollutants (octylphenols, nonylphenols and their mono and diethoxylates, and bisphenol A); (iii) phytoestrogens (biochanin A, daidzein, formononetin, genistein); and (iv) the phytosterol (sitosterol). Water samples from the Tagus estuary were taken from nine locations every 2 months over a 1-year period and analysed by gas chromatography. Oestrogens, industrial/household pollutants were consistently higher at two sites-at Tagus River mouth and close to the Trancão tributary, both at Lisbon region. The overall oestrogenic load, in ethynylestradiol equivalents, was 13 ng/L for oestrogens, 2.3 ng/L for industrial/household pollutants and 43 ng/L for phytoestrogens; well in the range of toxicological significance. Water physicochemical parameters also indicated anthropogenic pollution, mainly at the two above-referred sampling sites.

Phytoestrogens β -sitosterol and genistein have limited effects on reproductive endpoints in a female fish, Betta splendens

Phytoestrogens are produced by plants and may cause endocrine disruption in vertebrates. The present study hypothesizes that phytoestrogen exposure of female Siamese fighting fish (Betta splendens) may disrupt endogenous steroid levels, change agonistic behavior expression, and potentially also disrupt oocyte development. However, only the pharmacologic dose of β-sitosterol had a significant effect on opercular flaring behavior, while we did not find significant effects of β-sitosterol or genistein on steroids or gonads. These findings are in direct contrast with previous studies on the effects of phytoestrogens in female fish. Results of the current study support previous work showing that the effects of phytoestrogen exposure may be less acute in mature female B. splendens than in other fish.

Transcriptome alterations in zebrafish embryos after exposure to environmental estrogens and anti-androgens can reveal endocrine disruption

Exposure to environmental chemicals known as endocrine disruptors (EDs) is in many cases associated with an unpredictable hazard for wildlife and human health. The identification of endocrine disruptive properties of chemicals certain to enter the aquatic environment relies on toxicity tests with fish, assessing adverse effects on reproduction and sexual development. The demand for quick, reliable ED assays favored the use of fish embryos as alternative test organisms. We investigated the application of a transcriptomics-based assay for estrogenic and anti-androgenic chemicals with zebrafish embryos. Two reference compounds, 17α-ethinylestradiol and flutamide, were tested to evaluate the effects on development and the transcriptome after 48h-exposures. Comparison of the transcriptome response with other estrogenic and anti-androgenic compounds (genistein, bisphenol A, methylparaben, linuron, prochloraz, propanil) showed commonalities and differences in regulated pathways, enabling us to classify the estrogenic and anti-androgenic potencies. This demonstrates that different mechanism of ED can be assessed already in fish embryos.

Studying the effects of genistein on gene expression of fish embryos as an alternative testing approach for endocrine disruption

Assessment of endocrine disruption currently relies on testing strategies involving adult vertebrates. In order to minimize the use of animal tests according to the 3Rs principle of replacement, reduction and refinement, we propose a transcriptomics and fish embryo based approach as an alternative to identify and analyze an estrogenic activity of environmental chemicals. For this purpose, the suitability of 48 h and 7 days post-fertilization zebrafish and medaka embryos to test for estrogenic disruption was evaluated. The embryos were exposed to the phytoestrogen genistein and subsequently analyzed by microarrays and quantitative real-time PCR. The functional analysis showed that the genes affected related to multiple metabolic and signaling pathways in the early fish embryo, which reflect the known components of genistein's mode of actions, like apoptosis, estrogenic response, hox gene expression and steroid hormone synthesis. Moreover, the transcriptomic data also suggested a thyroidal mode of action and disruption of the nervous system development. The parallel testing of two fish species provided complementary data on the effects of genistein at gene expression level and facilitated the separation of common from species-dependent effects. Overall, the study demonstrated that combining fish embryo testing with transcriptomics can deliver abundant information about the mechanistic effects of endocrine disrupting chemicals, rendering this strategy a promising alternative approach to test for endocrine disruption in a whole organism in-vitro scale system.

Occurrence of phytoestrogens in municipal wastewater and surface waters

Phytoestrogens (isoflavones, enterolignans and coumestrol) in wastewater samples and surface water samples have been analysed by LC-ESI-MS(n). In wastewater samples, high levels of enterolactone (581-2111 ng/L), daidzein (341-1688 ng/L) and enterodiol (60-834 ng/L) were detected in raw sewage, but the vast majority of the analysed phytoestrogens were removed effectively in the treatment process. The removal rates of the analysed phytoestrogens in the two advanced tertiary treatment plants were >99%; a case study in one of the treatment plants showed that most of the residual phytoestrogens were removed by biological treatment using activated sludge. In surface water samples, daidzein was found at concentrations ranging from 2 ng/L to 33 ng/L in samples from two creeks, and up to 120 ng/L in surface water (pond) on a dairy farm. The analytical results suggest that direct excretions of livestock discharged from farmyards can be another potential source of phytoestrogen contamination in the aquatic environment.

The phytoestrogen genistein affects zebrafish development through two different pathways

BACKGROUND

Endocrine disrupting chemicals are widely distributed in the environment and derive from many different human activities or can also be natural products synthesized by plants or microorganisms. The phytoestrogen, genistein (4', 5, 7-trihydroxy-isoflavone), is a naturally occurring compound found in soy products. Genistein has been the subject of numerous studies because of its known estrogenic activity.

METHODOLOGY/PRINCIPAL FINDINGS

We report that genistein exposure of zebrafish embryos induces apoptosis, mainly in the hindbrain and the anterior spinal cord. Timing experiments demonstrate that apoptosis is induced during a precise developmental window. Since adding ICI 182,780, an ER antagonist, does not rescue the genistein-induced apoptosis and since there is no synergistic effect between genistein and estradiol, we conclude that this apoptotic effect elicited by genistein is estrogen-receptors independent. However, we show in vitro, that genistein binds and activates the three zebrafish estrogen receptors ERalpha, ERbeta-A and ERbeta-B. Furthermore using transgenic ERE-Luciferase fish we show that genistein is able to activate the estrogen pathway in vivo during larval stages. Finally we show that genistein is able to induce ectopic expression of the aromatase-B gene in an ER-dependent manner in the anterior brain in pattern highly similar to the one resulting from estrogen treatment at low concentration.

CONCLUSION/SIGNIFICANCE

TAKEN TOGETHER THESE RESULTS INDICATE THAT GENISTEIN ACTS THROUGH AT LEAST TWO DIFFERENT PATHWAYS IN ZEBRAFISH EMBRYOS: (i) it induces apoptosis in an ER-independent manner and (ii) it regulates aromatase-B expression in the brain in an ER-dependent manner. Our results thus highlight the multiplicity of possible actions of phytoestrogens, such as genistein. This suggests that the use of standardized endpoints to study the effect of a given compound, even when this compound has well known targets, may carry the risk of overlooking interesting effects of this compound.

Dietary red clover (Trifolium pratense) induces oviduct growth and decreases ovary and testes growth in Japanese quail chicks

To determine whether drought-stress alters phytoestrogens in red clover and whether red clover in the diet influences sexual development in Japanese quail, we fed chicks diets containing irrigated or non-irrigated clover. Irrigation altered phytoestrogenic activity of red clover (determined using an in vitro bioassay), with extracts of irrigated clover diet containing more estrogenic activity than extracts of non-irrigated clover diet. Chick growth was negatively correlated with the amount of irrigated or non-irrigated clover in the diet. Dietary red clover also depressed both absolute and relative gonad weights; however, relative oviduct weight was increased by the irrigated diet. Diets did not affect serum vitellogenin. These results reveal a negative influence of drought-stress on phytoestrogenic potency of clover, and that red clover in the diet can inhibit avian growth and development independent of irrigation state. Thus, phytoestrogens may affect reproductive development in wild birds, and environmental stressors may influence levels of phytoestrogens in the field.

Effects of phytoestrogens on testosterone secretion by Leydig cells from Biłgoraj ganders (Anser anser)

The aim of this study was to examine ganders at different stages of the reproductive season and the effect of: (1) diets with high phytoestrogen content and (2) in vitro phytoestrogen treatment on testosterone secretion by isolated Leydig cells. Thirty-six male Biłgoraj geese were fed control diets with low phytoestrogen content (containing grass meal) and diets with high phytoestrogens (containing alfalfa meal and soy). Testes were obtained from both groups of ganders at three different times of the breeding season: peak of reproductive activity (March), second half of reproductive activity (May) and beginning of photorefractoriness (July). Isolated Leydig cells were incubated with LH as well as genistein, daidzein, equol and coumestrol and the concentration of testosterone in the medium was determined by radioimmunoassay. The mean weight of testes from ganders in May and July decreased relative to their weights in March, but no significant differences among experimental groups were noted. No differences were observed in basal and LH-stimulated testosterone secretion by Leydig cells of ganders fed the control diets and the diets with higher phytoestrogen content. In July, LH did not stimulate testosterone secretion in either group. In vitro treatment with genistein, daidzein and equol (5 and 50 microM) inhibited basal and LH-stimulated testosterone production by Leydig cells from both groups. Coumestrol (5 and 50 microM) inhibited basal testosterone secretion only in March in the control group. Dietary exposure to phytoestrogens had a slight effect on in vitro testicular secretion in ganders. In vitro treatment with phytoestrogen inhibited testosterone production by Leydig cells. Genistein showed the strongest effect and coumestrol had the weakest influence on testicular secretion.

Contaminant-induced feminization and demasculinization of nonmammalian vertebrate males in aquatic environments

Many chemicals introduced into the environment by humans adversely affect embryonic development and the functioning of the male reproductive system. It has been hypothesized that these developmental alterations are due to the endocrine-disruptive effects of various environmental contaminants. The endocrine system exhibits an organizational effect on the developing embryo. Thus, a disruption of the normal hormonal signals can permanently modify the organization and future function of the male reproductive system. A wide range of studies examining wildlife either in laboratories or in natural settings have documented alterations in the development of males. These studies have begun to provide the causal relationships between embryonic contaminant exposure and reproductive abnormalities that have been lacking in pure field studies of wild populations. An understanding of the developmental consequences of endocrine disruption in wildlife can lead to new indicators of exposure and a better understanding of the most sensitive life stages as well as the consequences of exposure during these periods.