Developmental exposure to progestins causes male bias and precocious puberty in zebrafish (Danio rerio)

Transgenerational effects of the levonorgestrel-based birth control pill in zebrafish offspring

The consumption of hormone-derived medicines, such as levonorgestrel (LNG), is increasing worldwide, and its discharge into the environment reaches non-target organisms. In our previous study, we exposed the parental generation of zebrafish to environmentally relevant concentrations of LNG during the developmental phase. Subsequently, they had grown in a tank with clean water until adulthood. Now, we allowed this parental generation to reproduce to obtain F1 progeny unexposed to LGN, in order to analyze the transgenerational effects of parental LNG exposure on the survival and hatching of unexposed F1 embryos and the stress and behavior of F1 larvae. Here, we found decreased survival rates with higher LNG concentrations, providing a transgenerational effect. This highlights the environmental impact of exposure to LNG, causing damage at the individual and population level and affecting the next generation at the beginning of development, impacting qualities in the survival of the species.

Effects of mifepristone, a model compound with anti-progestogenic activity, on the development of African clawed frog (Xenopus laevis)

The objective of this study was to assess the effects of a model substance with anti-progestogenic activity on development of African clawed frog (Xenopus laevis) from tadpole to juvenile stage. Mifepristone, a synthetic progesterone receptor-blocking steroid hormone used in medicine as an abortifacient, was chosen as a model compound with anti-progestogenic activity. In the experiment, African clawed frog tadpoles were exposed to mifepristone at three concentrations (2, 21, and 215 ng L-1). A control group was exposed to dimethyl sulfoxide (DMSO; 0.001 %). The experiment started when tadpoles reached stages 47-48 according to Nieuwkoop and Faber (NF; 1994) and continued until stage NF 66, when metamorphosis was complete. Exposure to mifepristone had no significant effect on the rate of tadpole development, occurrence of morphological anomalies, weight, body length, or sex ratio. Mortality was within an acceptable range of 0-3.6 % throughout the test and did not differ among the groups. Histopathological examination of the gonads and thyroid gland revealed no significant changes. Therefore, we can conclude that mifepristone had no negative effect on development of the African clawed frog up to juvenile stage. Nevertheless, at the highest tested mifepristone concentration (215 ng L-1), gene expression analysis revealed up-regulation of mRNA expression of nuclear progesterone receptor (npr), membrane progesterone receptor (mpr), estrogen receptor beta (esrβ), and luteinizing hormone (lh) in the brain-pituitary complex of exposed frogs at stage NF 66. Higher mRNA expression of npr was also found in frogs exposed to 22 ng L-1 mifepristone compared to the solvent control. These findings confirmed the anti-progestogenic activity of mifepristone in frogs because the up-regulation of progesterone receptors occurs if progesterone availability in the body is reduced. All the observed changes in combination may have negative consequences for reproduction and reproductive behavior later in life.

Norethindrone suppress the germ cell development via androgen receptor resulting in male bias

Progestins are widely used and detected in surface waters, and can affect gonad development and sexual differentiation in fish. However, the toxicological mechanisms of sexual differentiation induced by progestins are not well understood. Here, we investigated the effects of norethindrone (NET) and androgen receptor (AR) antagonist flutamide (FLU) on gonadal differentiation in zebrafish from 21 dpf (days post-fertilization) to 49 dpf. The results showed that NET caused male bias, while FLU resulted in female bias at 49 dpf. The NET and FLU mixtures significantly decreased the percentage of males compared to the NET single exposure. Molecular docking analysis showed that FLU and NET had similar docking pocket and docking posture with AR resulting in competitively forming the hydrogen bond with Thr334 of AR. These results suggested that binding to AR was the molecular initiating event of sex differentiation induced by NET. Moreover, NET strongly decreased transcription of biomarker genes (dnd1, ddx4, dazl, piwil1 and nanos1) involved in germ cell development, while FLU significantly increased transcription of these target genes. There was an increase in the number of juvenile oocytes, which was consistent with the female bias in the combined groups. The bliss independence model analysis further showed that NET and FLU had antagonistic effect on transcription and histology during gonadal differentiation. Thus, NET suppressed the germ cell development via AR, resulting in male bias. Understanding the molecular initiation of sex differentiation in progestins is essential to provide a comprehensive biological basis for ecological risk assessment.

Fate of progesterone and norgestrel in anaerobic/anoxic/oxic (A/A/O) process: Insights from biotransformation and mass flow

Progesterone (P4) and norgestrel (NGT) are two steroid progestogens that can pose adverse effects on aquatic organisms at ng/L levels. Despite increasing concern on their occurrence and removal in wastewater, their fate in the wastewater treatment process has not been well documented. This study identified the transformation products (TPs) of P4 and NGT in anaerobic/anoxic/oxic (A/A/O) process. Potential functional genes involved in biotransformation of P4 and NGT were explored. The elimination or formation behavior of P4, NGT and convinced TPs along various units of A/A/O process was revealed through the mass flow. Results showed that 12 and 13 TPs were identified in the P4 and NGT groups respectively, wherein 10 identical TPs and C-19 structures transformation pathways were observed in both groups. Six genes were found that may be involved in dehydrogenation and isomerization reactions in the pathways. Mass flow indicated that P4 and NGT were mainly eliminated in anaerobic and anoxic units, while convinced TPs mainly formed in anaerobic and anoxic units and were then eliminated in aerobic unit. Further, the ecological risks of the effluent should not be ignored as residual compounds including P4 or NGT and their TPs in the effluent still posed adverse effects on zebrafish transcript levels.

Dydrogesterone and levonorgestrel at environmentally relevant concentrations have antagonist effects with rhythmic oscillation in brain and eyes of zebrafish

Synthetic progestins levonorgestrel (LNG) and dydrogesterone (DDG) are frequency detected in surface water. Combined effects of LNG and DDG on gonad differentiation are similar to LNG single exposure in juvenile zebrafish. However, LNG and DDG mixtures have stronger effects on spermatogenesis in testes of adult zebrafish, which show variable at different life stage. Effects of LNG and DDG mixtures on eyes and brain remain unknown. Here we investigated effects of LNG, DDG and their mixtures on eyes and brain. Zebrafish were exposed to LNG, DDG and their mixtures from 2 hpf to 144 dpf. Rhythm and vision related biological processes were enriched in eyes and brain in LNG and DDG treatments, which indicated rhythmic oscillation in eyes and brain. The qPCR data revealed that both LNG and DDG decreased transcription of arntl2 and clocka, while increased transcription of per1a, per1b, rpe65a and tefa in eyes and brain. However, DDG and LNG mixtures had slight effect on transcription of genes related to rhythm and vision. In addition, LNG and DDG reduced the thickness of inner nuclear layer in the eyes. Bliss independent model revealed that LNG and DDG had antagonist effects on transcription and histology in eyes and brain. Moreover, LNG and DDG formed the same hydrogen bonds with green-sensitive opsin-4 and rhodopsin kinase GRK7a. Taken together, LNG and DDG competed with each other for the same binding residues resulting in antagonist effect in their mixtures treatments, and have significant ecological implications to assess combined effects of progestins mixtures on fish in different organs.

Endocrine disrupting effects induced by levonorgestrel linked to altered DNA methylation in rare minnow (Gobiocypris rarus)

Progestins are worldwide environmental contaminants, however, their ecotoxicological risks and underlying molecular mechanisms of effects are not fully understood. In this study, newly hatched rare minnow (Gobiocypris rarus) larvae were exposed to environmentally realistic concentrations (1 and 10 ng/L) of levonorgestrel (LNG) for 6 months. The sex ratios were not affected by LNG at both concentrations, but the growth was significantly inhibited at 10 ng/L while promoted at 1 ng/L. Histological analysis revealed impaired gonadal development. Plasma concentrations of estradiol in females and testosterone in both sexes were significantly induced after exposure to 1 ng/L LNG; plasma concentrations of 11-ketotestosterone were markedly increased in females exposed to 10 ng/L LNG and in males exposed to both concentrations of LNG. The transcription of cyp19a1a was significantly up-regulated in ovaries exposed to LNG at both concentrations, while cyp17a1 was down-regulated in testes exposed to 10 ng/L LNG. The global DNA methylation level was significantly decreased in testes exposed to 10 ng/L LNG, which might be associated with inhibited spermatogenesis. Gender-specific changes in CpG methylation patterns were induced by LNG in the 5' flanking region of cyp19a1a, with hypomethylation in ovaries but hypermethylation in testes, which was linked to the regulation of cyp19a1a transcription. The results suggest that LNG could induce endocrine disrupting effects in fish at environmentally realistic concentrations, which may be linked to altered DNA methylation. This study indicates potentially high ecological risk of LNG to fish populations, and warrants researches on regulatory mechanisms of epigenetic modifications in progestin-induced effects.

Synthetic Progestins in Waste and Surface Waters: Concentrations, Impacts and Ecological Risk

Synthetic progestins (PGs) are a large family of hormones used in continuously growing amounts in human and animal contraception and medicinal therapies. Because wastewater treatment plants (WWTPs) are unable to eradicate PGs after excretion, they are discharged into aquatic systems, where they can also be regenerated from conjugated PG metabolites. This review summarises the concentrations of 12 PGs in waters from 2015 to 2021. The selected PGs were considered of particular interest due to their wide use, activity, and hormonal derivation (from testosterone, progesterone, and spirolactone). We concluded that PGs had been analysed in WWTPs influents and effluents and, to a lesser extent, in other matrices, including surface waters, where their concentrations range from ng/L to a few µg/L. Because of their high affinity for cell hormone receptors, PGs are endocrine disruptor compounds that may alter the reproductive fitness and development of biota. This review focused on their biological effects in fish, which are the most used aquatic model organisms to qualify the impacts of PGs, highlighting the risks that environmental concentrations pose to their health, fecundity, and fertility. It is concluded that PGs research should be expanded because of the still limited data on their environmental concentrations and effects.

Effects of endocrine disrupting chemicals on gonad development: Mechanistic insights from fish and mammals

Over the past century, evidence has emerged that endocrine disrupting chemicals (EDCs) have an impact on reproductive health. An increased frequency of reproductive disorders has been observed worldwide in both wildlife and humans that is correlated with accidental exposures to EDCs and their increased production. Epidemiological and experimental studies have highlighted the consequences of early exposures and the existence of key windows of sensitivity during development. Such early in life exposures can have an immediate impact on gonadal and reproductive tract development, as well as on long-term reproductive health in both males and females. Traditionally, EDCs were thought to exert their effects by modifying the endocrine pathways controlling reproduction. Advances in knowledge of the mechanisms regulating sex determination, differentiation and gonadal development in fish and rodents have led to a better understanding of the molecular mechanisms underlying the effects of early exposure to EDCs on reproduction. In this manuscript, we review the key developmental stages sensitive to EDCs and the state of knowledge on the mechanisms by which model EDCs affect these processes, based on the roadmap of gonad development specific to fish and mammals.

17β-Trenbolone binds to androgen receptor, decreases number of primordial germ cells, modulates expression of genes related to sexual differentiation, and affects sexual differentiation in zebrafish (Danio rerio)

Exposure to 17β-trenbolone caused a skewed sex ratio in fish. However, the molecular initiating event and key molecular event(s) remain unknown. In this study, zebrafish were exposed to 17β-trenbolone at nominal concentrations of 2 ng/L, 20 ng/L, 200 ng/L, and 2000 ng/L from fertilization to 60 days post fertilization (dpf). First, the sex ratio at 60 dpf was calculated to evaluate adverse outcomes on sexual differentiation. 17β-Trenbolone caused a skewed sex ratio toward males, with intersex individuals observed in the 20 ng/L group and all-male populations found in the 200 ng/L and 2000 ng/L groups. Then, the distribution and number of primordial germ cells, the expression of sex differentiation-related genes, and plasma vitellogenin concentrations were detected in wild-type zebrafish and the EGFP-nanos-3'UTR transgenic line using whole-mount in situ hybridization, real-time PCR, EGFP fluorescence quantification, and enzyme-linked immunosorbent assay. The results indicated that 17β-trenbolone exposure decreased the number of primordial germ cells at 1 dpf and 3 dpf, decreased expression of ovarian differentiation-related genes foxl2 and cyp19a1a at 60 dpf, increased expression of testis differentiation-related genes dmrt1, sox9a, and amh at 60 dpf, and decreased plasma vitellogenin levels at 60 dpf, revealing the key molecular events at different time points involved in affected sexual differentiation by 17β-trenbolone. Finally, molecular docking showed that 17β-trenbolone docked into ligand-binding domain of zebrafish androgen receptor with high binding energy (-3.72 kcal/mol), suggesting that binding to androgen receptor is the molecular initiating event affecting sexual differentiation by 17β-trenbolone. We found that 17β-trenbolone can bind to the zebrafish androgen receptor, decrease the number of primordial germ cells during the early embryonic stage, modulate the expression of genes related to sexual differentiation during gonadal differentiation, and eventually cause a skewed sex ratio toward males in adults.

Levonorgestrel and dydrogesterone affect sex determination via different pathways in zebrafish

Levonorgestrel (LNG) and dydrogesterone (DDG) are two commonly used synthetic progestins that have been detected in aquatic environments. They could affect fish sex differentiation, but the underlying mechanisms remain unknown. Here we investigated the effects of LNG (5 ng L^-1 and 50 ng L^-1), DDG (100 ng L^-1) and their mixtures on gonadal differentiation and sex determination in zebrafish at transcriptomic and histological levels from 2 hours post-fertilization (eleutheroembryos) to 144 days post-fertilization (sexual maturity). Germ cell development and oogenesis pathways were significantly enriched in LNG and the mixture of LNG and DDG treatments, while insulin and apoptosis pathways in the DDG treatment. LNG and the mixture of LNG and DDG strongly decreased transcripts of germ cell development and oogenesis related genes, while DDG increased the transcripts of insulin and apoptosis related genes at 28 days post fertilization (dpf) and 35 dpf. Furthermore, DDG caused ∼ 90% males, and LNG and the mixture of LNG and DDG resulted in 100% males on all sampling dates. Specifically, most males in LNG and the mixture of LNG and DDG treatments were "Type I" males without juvenile oocytes at 28 dpf and 35 dpf, while those in DDG treatment were "Type II" and "Type III" males with a few juvenile oocytes. These results indicated that LNG and DDG promoted testicular differentiation via different pathways to cause male bias. LNG and DDG mixtures have similar effect on testicular differentiation to LNG alone. The findings from this study could have significant ecological implications to fish populations.

Brightened body coloration in female guppies (Poecilia reticulata) serves as an in vivo biomarker for environmental androgens: The example of 17β-trenbolone

In vivo testing systems for environmental androgens are scarce. The aim of this study was to evaluate the potential of male-specific brightened body coloration in female guppies (Poecilia reticulata) to serve as an in vivo biomarker of environmental androgens using 17β-trenbolone as an example. The high bioaccumulation of 17β-trenbolone in the skin of female guppies suggests that it is a potential target tissue of environmental androgens. The coloration index, pigment cell ultrastructure, pigment levels, sexual attractiveness, and reproductive capability of female guppies were analyzed following 28 days of exposure to 20 ng/L, 200 ng/L, and 2000 ng/L 17β-trenbolone. Increases in the coloration index caused by 17β-trenbolone exposure were attributable to increased pteridine and melanin levels. Decreases in the sexual attractiveness, number of offspring, and survival rate of offspring suggested that the changes in body coloration translated into adverse outcomes. Finally, mRNA sequencing indicated that 17β-trenbolone increased pteridine levels by activating genomic effects of androgen receptor on xanthine dehydrogenase and increased melanin levels by exerting non-genomic effects targeting microphthalmia-associated transcription factor, tyrosinase, and tyrosinase-related protein 1 that were mediated by mitogen-activated protein kinase and calcium signaling pathways. We have derived a robust adverse outcome pathway of environmental androgens, and our findings suggest that indicators at different biological levels related to brightened body coloration in female guppies can serve as less-invasive or noninvasive in vivo biomarkers of short-term exposure to environmental androgens.

Harmonized Cross-Species Assessment of Endocrine and Metabolic Disruptors by Ecotox FACTORIAL Assay

Environmental pollution is a threat to humans and wildlife species. Of particular concern are endocrine disrupting chemicals (EDCs). An important target of EDCs is nuclear receptors (NRs) that control endocrine and metabolic responses through transcriptional regulation. Owing in part to structural differences of NRs, adverse effects of EDCs vary significantly among species. Here, we describe a multiplexed reporter assay (the Ecotox FACTORIAL) enabling parallel assessment of compounds' effects on estrogen, androgen, thyroid, and PPARγ receptors of representative mammals, birds, reptiles, amphibians, and fish. The Ecotox FACTORIAL is a single-well assay comprising a set of species-specific, one-hybrid GAL4-NR reporter constructs transiently transfected into test cells. To harmonize cross-species assessments, we used a combination of two approaches. First, we used the same type of test cells for all reporters; second, we implemented a parallel detection of reporter RNAs. The assay demonstrated excellent quality, reproducibility, and insignificant intra-assay variability. Importantly, the EC50 values for NR ligands were consistent with those reported for conventional assays. Using the assay allowed ranking the hazard potential of environmental pollutants (e.g., bisphenols, polycyclic aromatic hydrocarbons, and synthetic progestins) across species. Furthermore, the assay permitted detecting taxa-specific effects of surface water samples. Therefore, the Ecotox FACTORIAL enables harmonized assessment of the endocrine and metabolic disrupting activity of chemicals and surface water in humans as well as in wildlife species.

Effects of new generation progestins, including as mixtures and in combination with other classes of steroid hormones, on zebrafish early life stages

Fish are exposed to progestins and steroid mixtures in contaminated waters but the ecotoxicological implications are not sufficiently known. Here we analyze effects of the new generation progestin dienogest (DNG) followed by investigating effects of mixtures of new generation progestins containing DNG, cyproterone acetate and drospirenone and the hormone progesterone. Furthermore, effects of this mixture were studied after adding 17β-estradiol (E2) and clobetasol propionate (CLO) in zebrafish embryos and larvae at concentrations between 0.01 and 10 μg/L. DNG showed only very minor transcriptional alterations among the 24 assessed genes with downregulation of the fshb transcript only. The progestin mixture caused weak induction of the lhb, cyp2k22 and sult2st3 transcripts. Addition of E2 to the mixture caused strong induction vtg1, cyp19b, esr1 and lhb, as well as downregulation of fshb from 0.01 μg/L onwards. Besides altering the same transcripts, addition of CLO altered glucocorticoid regulated genes mmp-9, mmp-13, g6pca, fkbp5 and irg1l. While each steroid class exhibited its specific activity independently in the mixture, sult2st3 and cyp2k22 were regulated by both E2 and CLO. Furthermore, CLO alone and in mixtures decreased spontaneous muscle contractions, increased heartrate and induced edema. Our study highlights the prominent effects of E2 and CLO in environmental steroid mixtures, while new generation progestins show relatively low activity.

Changes in fish sex ratio as a basis for regulating endocrine disruptors

Fish sex ratio (SR) is an endpoint potentially indicating both endocrine activity and adversity, essential elements for identifying Endocrine Disrupting Chemicals (EDCs) as required by the EU regulations. Due to different protocols and methods in the literature studies, SR data vary greatly. This study analyses literature SR data and discusses important considerations for using SR data in the regulatory context for the hazard identification, classification, PBT (persistent, bioaccumulative and toxic) assessment, testing, and risk assessment. A total number of 106 studies were compiled for SR of zebrafish, medaka and fathead minnow exposed to 84 chemicals or mixtures. About 53% of literature studies determined SR by methods different from the standard histology method, leading to uncertainty of quantifying SR and differential sensitivity. SR was determined after depuration in 40 papers, which may lead to chemical-induced SR changes reversible to the control. SR was responsive to chemicals with EAS (estrogen, androgen, steoroidogenesis) activity and also to those with thyroid and progesterone activity. Besides, SR was influenced by non-chemical factors, e.g., inbreeding and temperature, leading to difficulty in data interpretation. The ECHA/EFSA/JRC Guidance suggests that SR and gonad histology data can be used for identifying EDCs. Due to reversibility, influence of confounding factors, and responsiveness to chemicals with endocrine activity other than EAS, this study suggests that SR/gonad histology should be combined with certain mode of action evidence for identifying EDCs. Important considerations for using SR data in the identification, classification, PBT assessment, testing, and risk assessment are discussed.

Medroxyprogesterone acetate affects sex differentiation and spermatogenesis in zebrafish

Medroxyprogesterone acetate (MPA) is a widely used synthetic progestin and it has been frequently detected in aquatic environments. However, its effects on aquatic organisms remain largely unknown. Here we investigated the chronic effects of MPA on sex differentiation and gonad development in zebrafish. Zebrafish larvae at 20 days post fertilization (dpf) were exposed to 4.32, 42.0, and 424 ng L^-1 of MPA until they reached 140 dpf. The results showed that chronic exposure to 42.0 ng L^-1 of MPA caused 60% proportion of males as well as significant up-regulation of dmrt1 (˜1.79 fold) and hsd17b3 (˜1.92 fold). Histological analysis showed MPA significantly increased the frequency of immature spermatocytes accompanied with the increased transcription of dmrt1 (˜2.06 fold) and ar (˜1.73 fold) in the testes. Meanwhile, MPA exposure significantly increased the transcription of lhb at all exposure concentrations in the males. In contrast, it significantly suppressed the transcription of lhb (˜-8.06-fold) and fshb (˜-6.35-fold) at 42.0 ng L^-1 in the females. Collectively our results demonstrated that MPA had androgenic activity, and could affect sex differentiation and spermatogenesis in zebrafish at environmentally relevant concentrations. The findings from this study suggest that MPA in the aquatic environment may pose potential androgenic risks to fish populations.

Endocrine disrupting effects of tebuconazole on different life stages of zebrafish (Danio rerio)

Tebuconazole is a widely used fungicide that has been detected in water ecosystems, of which the concentrations may affect the endocrine function of aquatic organisms. At present study, tissue-specific bioaccumulation of tebuconazole was found in ovary of adult zebrafish, indicating a potential risk of endocrine disruption. In order to evaluate the potential endocrine disrupting effects, three life stages (2 hpf (hours post-fertilization) -60 dpf (days post-fertilization), Stage I; 60-120 dpf, Stage II; 180-208 dpf, Stage III) of zebrafish (Danio rerio) were chronically exposed to tebuconazole at the concentrations ranging from 0.05 mg/L to 1.84 mg/L. Result showed that exposed to tebuconazole could lead to a male-biased sex differentiation in juvenile zebrafish and significant decrease of the percentage of germ cells in sexually-mature zebrafish. Egg production was significantly inhibited by 57.8% and 19.2% after Stage II- and Stage III-exposures, respectively. The contents of 17β-estradiol in gonad decreased by 63.5% when exposed to 0.20 mg/L tebuconazole at Stage II and by 49.5% after exposed to 0.18 mg/L tebuconazole at Stage III, respectively. For all stages exposure, reductions in 17β-estradiol/testosterone ratio were observed, indicating an imbalance in steroids synthesis. Additionally, tebuconazole reduced the expression of cyp19a, which was consistent with the decrease of E2 level. In overall, the present findings indicated that, playing as an anti-estrogen-like chemical, tebuconazole inhibited the expression of Cyp19, thereby impairing steroid hormones biosynthesis, leading to a diminished fecundity of zebrafish.

Rapid masculinization and effects on the liver of female western mosquitofish (Gambusia affinis) by norethindrone

Natural and synthetic progestins in receiving streams can disrupt the normal endocrine systems of fish. Norethindrone (NET) is a widely used synthetic progestin that often appears in wastewater effluents. For this research, adult female western mosquitofish (Gambusia affinis) were exposed to NET at three concentrations. The effects of NET on the following biological factors were evaluated: the histology of the ovaries and livers, the anal fin morphology, and transcription of genes related to steroidogenesis signaling pathways in the livers. After 42 d exposure to NET at 33.0 ng L^-1 and 347.5 ng L^-1, rapid masculinization, an increase in the number of atretic and postovulatory follicles in the ovary, enhanced vascularization, degenerated hepatocytes and irregular nuclei in the livers were observed. Exposure to NET did not affect the expression of the androgenic and estrogenic receptor genes and Cyp19a except for a significant up-regulation of Erα. However, the expression of Vtg A, Vtg B, and Vtg C were markedly inhibited in the females exposed to three concentrations of NET. Compared to the control female, exposure to NET at 33.0 ng L^-1 and 347.5 ng L^-1 caused a 4.4- and 5.8-fold increase in the expression of Hsd17β3 in the livers, respectively. The results demonstrate that NET can cause rapid masculinization of female G. affinis, hepatopathological alterations and inhibited expressions of Vtg A, Vtg B, and Vtg C. The results imply that G. affinis populations might be threatened in NET-contaminated environment.

Dydrogesterone affects the transcription of genes in GnRH and steroidogenesis pathways and increases the frequency of atretic follicles in zebrafish (Danio rerio)

Dydrogesterone (DDG) is a synthetic progestin broadly used in human and veterinary medicine and has been widely detected in aquatic environments. However, its potential effects on aquatic organisms are little documented. Here we investigate the short-term effects of DDG on the transcriptional and histological responses in adult zebrafish (Danio rerio). Adult zebrafish were exposed to 32.0, 305 and 2490 ng L^-1 of DDG for 14 days. Real time quantitative PCR analysis showed that DDG significantly increased transcripts of most genes involved in the gonadotropin-releasing hormone (GnRH) pathway in the brain of female. In contrast, apparent down-regulation of these gene transcriptions was observed in the brain of males. The transcription of cyp19a1a in the ovary had a 2.3 fold increase at 2490 ng L^-1 of DDG and the transcription of hsd17b2 at 305 and 2490 ng L^-1 in the testis was enhanced by approximately 2.0 fold and 2.4 fold, respectively. Histopathological analysis revealed exposure to 2490 ng L^-1 DDG significantly increased the percentage of atretic follicles in the ovary. The results of this study suggest that DDG has potential endocrine disrupting effects and affects the ovarian development in zebrafish.

Endocrine disruption in Chinese rare minnow (Gobiocypris rarus) after long-term exposure to low environmental concentrations of progestin megestrol acetate

Synthetic progestins are widely used pharmaceutical agents that have become common contaminants in the aquatic environment. The potential adverse effects of long-term exposure on aquatic wildlife, however, are not fully understood. The aim of this study was to investigate the endocrine disruption in Chinese rare minnow (Gobiocypris rarus) in response to megestrol acetate (MTA) exposure. Newly-hatched Chinese rare minnow larvae were exposed to MTA at a nominal concentration of either 1 ng/L (detected concentrations ranged from 0.18 to 0.93 ng/L) or 10 ng/L (detected concentrations ranged from 4.27 to 9.64 ng/L) for 6 months and the effects on growth, sex steroid hormones, gonadal histology, and steroidogenic genes expression were determined. After 6 months of exposure to a nominal concentration of 10 ng/L MTA, the body weight and condition factors were significantly increased in fish of both sexes. Exposure to a nominal concentration of 10 ng/L MTA significantly reduced plasma concentrations of estradiol and 11-ketotestosterone in female fish while also reducing testosterone and 11-ketotestosterone in male fish. Gonad histology revealed significantly reduced proportions of vitellogenic oocytes in female fish exposed to a nominal concentration of 10 ng/L MTA and induction of atretic follicles in female fish exposed to both nominal concentrations of MTA. The expression of cyp19a1a and cyp17a1 in the gonads was up-regulated in the ovaries while down-regulated in the testes. Our results indicate that MTA can induce endocrine disruption in Chinese rare minnow at the low concentrations found in contaminated environments. This indicates a potentially high ecological risk from MTA to fish populations in MTA-contaminated aquatic environments in China and may also in other regions.

Do progestins contribute to (anti-)androgenic activities in aquatic environments?

Unknown compounds with (anti-)androgenic activities enter the aquatic environment via municipal wastewater treatment plants (WWTPs). Progestins are well-known environmental contaminants capable of interfering with androgen receptor (AR) signaling pathway. The aim of the present study was to determine if 15 selected progestins have potential to contribute to (anti-)androgenic activities in municipal wastewaters and the respective recipient surface waters. AR-specific Chemically Activated LUciferase gene eXpression bioassay in agonistic (AR-CALUX) and antagonistic (anti-AR-CALUX) modes and liquid chromatography tandem atmospheric pressure chemical ionization/atmospheric photoionization with hybrid quadrupole/orbital trap mass spectrometry operated in high resolution product scan mode (LC-APCI/APPI-HRPS) methods were used to assess (anti-)androgenic activity and to detect the target compounds, respectively. The contribution of progestins to (anti-)androgenic activities was evaluated by means of a biologically and chemically derived toxicity equivalent approach. Androgenic (0.08-59 ng/L dihydrotestosterone equivalents - DHT EQs) and anti-androgenic (2.4-26 μg/L flutamide equivalents - FLU EQs) activities and progestins (0.19-75 ng/L) were detected in selected aquatic environments. Progestins displayed androgenic potencies (0.01-0.22 fold of dihydrotestosterone) and strong anti-androgenic potencies (9-62 fold of flutamide). Although they accounted to some extent for androgenic (0.3-29%) and anti-androgenic (4.6-27%) activities in influents, the progestins' contribution to (anti-)androgenic activities was negligible (≤2.1%) in effluents and surface waters. We also tested joint effect of equimolar mixtures of target compounds and the results indicate that compounds interact in an additive manner. Even if progestins possess relatively strong (anti-)androgenic activities, when considering their low concentrations (sub-ng/L to ng/L) it seems unlikely that they would be the drivers of (anti-)androgenic effects in Czech aquatic environments.

Dydrogesterone Causes Male Bias and Accelerates Sperm Maturation in Zebrafish ( Danio rerio)

Synthetic progestins are widely used in human and veterinary medicine. They can enter aquatic environments mainly via wastewater discharge and agricultural runoff, thus affecting fish populations in receiving waters. Here, we investigated the chronic effects of dydrogesterone (DDG) on zebrafish from 21 to 140 days post-fertilization (dpf) at 3.39, 33.1, and 329 ng L^-1. The results showed that the male ratio increased with the exposure concentration, and after 120 days of exposure to 329 ng L^-1, 98% of the fish were males. The DDG exposure during sex differentiation significantly increased the transcription of dmrt1 (1.83-fold) and apoptosis-related genes but suppressed the transcription of cyp19a1a (3.16-fold). Histological analysis showed that the exposure to DDG at 329 ng L^-1 caused 61.5% of mature spermatocytes in males, while the exposure to DDG at 33.1 ng L^-1 resulted in 14.7% of atretic follicles in females. Microarray analysis identified spermatogenesis-related gene ontology (endothelial barrier and immune response) in the testes at all concentrations. Genes from phagosome, lysosome, and sphingolipid metabolism pathways were enriched and could be responsible for sperm maturation. The findings from this study demonstrate that DDG in the aquatic environment can cause male bias and accelerate sperm maturation in zebrafish, resulting in potential high ecological risks to fish populations.

The progestin norethindrone affects sex differentiation and alters transcriptional profiles of genes along the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes in juvenile zebrafish Dario renio

Natural and synthetic progestins may pose a threat to wild fish populations living in receiving waters. In this study, the effects of norethindrone (NET) on the sex differentiation of zebrafish (Dario renio) and the mechanisms underlying these effects were investigated. Juvenile zebrafish (20 days post fertilization, pdf) were exposed to environmentally relevant concentrations (5, 50, 500, and 1000 ng L^-1) for 45 d. Sex ratio of the NET-exposed populations, the histology of the gonads and the transcriptional profile of the regulatory genes involved in sex differentiation and steroidogenesis were examined. The results showed that a significantly higher ratio of male/female was induced in the zebrafish populations exposed to NET at concentrations higher than 32.3 ng L^-1. Exposure to NET caused acceleration of sexual mature in males and a delay in ovary maturation in female zebrafish. Among the genes regulating sexual differentiation, transcripts of Dmrt1 showed a dose-dependent increase while transcripts of Figa and Fox12 showed a dose-dependent decrease in response to exposure to NET. For genes regulating the steroidogenesis, the expressions of Cyp11a1, Cyp17, Cyp19a1a, and Cyp11b were significantly down-regulated by exposure to NET, while Hsd17b3 expression was significantly up-regulated by exposure to NET at 421.3 and 892.9 ng L^-1. For the receptor genes in the gonads, the transcriptional expression of Pgr, Ar, and Mr was significantly up-regulated at 421.3 and 892.9 ng L^-1 of NET. For genes involved in the hypothalamic-pituitary axis, the transcriptional expression of Gnrh3 and Pomc was significantly up-regulated by exposure to NET with the exception for Gnrh3 at 4.2 ng L^-1. The results demonstrated that exposure to NET at the juvenile stage could affect gonad differentiation and sex ratio, which might be accounted for by the alterations of the transcriptional expressions of genes along the hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-adrenal (HPA) axes.

Alterations of secondary sex characteristics, reproductive histology and behaviors by norgestrel in the western mosquitofish (Gambusia affinis)

Synthetic hormones in wastewater effluents released into the aquatic environments may interfere with the normal endocrine systems of fish in receiving streams. Norgestrel (NGT) is a synthetic progestin widely used in oral contraceptives and frequently detected in wastewater effluents. In this study, adult female mosquitofish (Gambusia affinis) were exposed to three environmentally relevant concentrations of norgestrel (NGT) (i.e., 3.6, 35.8, and 368.0 ng L-1) for 42 d, fin morphology, histology of the ovary, and reproductive behaviors were evaluated. The results showed that NGT at all three concentrations caused an increased frequency of atretic follicular cells in ovaries and impaired mating behaviors exhibited by males toward the NGT-exposed females. In mosquitofish exposed to NGT at 35.8 and 368 ng L^-1, the anal fin of females had an increased length ratio of ray4/ray 6, an increased width of ray 3, and increased number of segments in ray 3. The histopathological analysis showed that exposure to NGT increased the incidence of spermatogenesis in ovaries. Mating behavior was impaired 58.4%, 65.7%, and 76.4% (P < 0.01 in all cases) when mosquitofish were exposed to NGT at 3.6, 35.6 and 368.0 ng L^-1, respectively. The rapid masculinization, the increased frequency of atretic follicles, the incidence of spermatogenesis in the ovary of female fish, and the altered reproductive behaviors suggest that wild populations of mosquitofish could be similarly affected inhabiting in NGT contaminated environments.

Determination of progestogens in surface and waste water using SPE extraction and LC-APCI/APPI-HRPS

The aim of this study was to develop a reliable analytical method for the measurement of 17 selected progestogens in waste water and surface water. Automated whole water solid phase extraction (SPE) was used for sample concentration. Liquid chromatography tandem atmospheric pressure chemical ionization/atmospheric pressure photoionization with hybrid quadrupole/orbital trap mass spectrometry operated in high resolution product scan mode (LC-APCI/APPI-HRPS) was applied for the analyses. The whole-method recoveries ranged from 60% to 140% for all analytes at two different spike levels (5 and 50ng/L) in the studied matrices. The method is very sensitive with LOQs ranging from 0.02 to 0.87ng/L. The developed method was used for the determination of progestogens in real samples of waste water from three waste water treatment plants (WWTPs) and in surface water from the corresponding recipients. Progesterone was detected in all samples with concentrations in the range of 0.82 to 1.1ng/L in surface water and 0.11 to 110ng/L in waste water samples. Three synthetic progestogens, namely, megestrol acetate, medroxyprogesterone acetate, and dienogest, were detected most frequently in effluents; therefore, further attention should be paid to the monitoring of these compounds. To the best of our knowledge, this study is the first to present analysis of altrenogest, etonogestrel, dienogest, nomegestrol acetate and ulipristal acetate in waste water and surface water using a solid-phase extraction method.

Concentration and timing of application reveal strong fungistatic effect of tebuconazole in a Daphnia-microparasitic yeast model

Given the importance of pollutant effects on host-parasite relationships and disease spread, the main goal of this study was to assess the influence of different exposure scenarios for the fungicide tebuconazole (concentration×timing of application) on a Daphnia-microparasitic yeast experimental system. Previous results had demonstrated that tebuconazole is able to suppress Metschnikowia bicuspidata infection at ecologically-relevant concentrations; here, we aimed to obtain an understanding of the mechanism underlying the anti-parasitic (fungicidal or fungistatic) action of tebuconazole. We exposed the Daphnia-yeast system to four nominal tebuconazole concentrations at four timings of application (according to the predicted stage of parasite development), replicated on two Daphnia genotypes, in a fully crossed experiment. An "all-or-nothing" effect was observed, with tebuconazole completely suppressing infection from 13.5μgl^-1 upwards, independent of the timing of tebuconazole application. A follow-up experiment confirmed that the suppression of infection occurred within a narrow range of tebuconazole concentrations (3.65-13.5μgl^-1), although a later application of the fungicide had to be compensated for by a slight increase in concentration to elicit the same anti-parasitic effect. The mechanism behind this anti-parasitic effect seems to be the inhibition of M. bicuspidata sporulation, since tebuconazole was effective in preventing ascospore production even when applied at a later time. However, this fungicide also seemed to affect the vegetative growth of the yeast, as demonstrated by the enhanced negative effect of the parasite (increasing mortality in one of the host genotypes) at a later time of application of tebuconazole, when no signs of infection were observed. Fungicide contamination can thus affect the severity and spread of disease in natural populations, as well as the inherent co-evolutionary dynamics in host-parasite systems.

Tetrabromoethylcyclohexane affects gonadal differentiation and development in the frog Pelophylax nigromaculatus

Tetrabromoethylcyclohexane (TBECH), an additive brominated flame retardant, has been shown to have an androgenic activity in vitro. In the present study, we aimed to investigate the effects of TBECH on gonadal differentiation and development in the frog Pelophylax nigromaculatus, an amphibian species sensitive to androgenic chemicals, and to assess the androgenic activity of TBECH in vivo. P. nigromaculatus tadpoles were exposed to TBECH (1, 10, 100nM) from Gosner stage 24 to complete metamorphosis, and to 5α-dihydrotestosterone (DHT) as a positive control. We found that 1nM DHT resulted in 100% males, while the sex ratio in the solvent control group was close to 1:1. In all the TBECH treatment groups, sexually ambiguous gonads based on gross morphology and intersexualities with testicular and ovarian histological structures were found, but no abnormality occurred in the solvent control. In the 1, 10, 100nM TBECH treatment groups, the female percentages were 52%, 31%, 17%, with 36%, 56%, 66% for males and 12%, 13%, 17% for abnormal sexes, respectively. X²-test revealed significant differences in sex ratios between the three TBECH groups and the solvent control group, and the sex ratios in the two higher concentration groups were male-biased. These observations show that TBECH has a masculinizing effect on gonadal differentiation and development in P. nigromaculatus, suggesting an androgenic activity of TBECH in vivo. To our knowledge, this is the first study demonstrating that TBECH could induce gonadal masculinization in an animal, which raises new concerns for reproductive risk of TBECH exposure.

Lycium barbarum polysaccharide alleviates nonylphenol exposure induced testicular injury in juvenile zebrafish

Nonylphenol is an endocrine disrupting chemicals that can disrupt the organisms' reproductive system, and exists widely in rivers and lakes. Lycium barbarum polysaccharide (LBP) is the main active constituent (about 10%) in Lycium barbarum, which is used to protect reproductive health. In this study, we investigated whether LBP can alleviate nonylphenol exposure induced testicular injury in juvenile zebrafish. We detected histological alteration, anti-oxidant enzyme profile and P450 gene transcription to assess LBP effect on testicular development. The GSI reduced significantly due to nonylphenol exposure, while LBP can improve the GSI. The densities of sperms increased and non-celluar zone decreased after LBP treatment. Meanwhile, Cyp11b gene was up regulated to NP group, and cyp19a gene was down regulated to NP group. In sum, the LBP could repair the testicular injury in zebrafish. This findings provide a basis research to remit the estrogen effect of artificial endocrine disruptor.