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

The effects of 17α-methyltestosterone on gonadal histology and gene expression along hypothalamic-pituitary-gonadal axis, germ cells, sex determination, and hypothalamus-pituitary-thyroid axis in zebrafish (Danio rerio)

As a synthetic androgen, 17α-methyltestosterone (MT) is widely used in aquaculture to induce sex reversal and may pose a potential risk to aquatic organisms. This ecological risk has attracted the attention of many scholars, but it is not comprehensive enough. Thus, the adverse effects of MT on zebrafish (Danio rerio) were comprehensively evaluated from gonadal histology, as well as the mRNA expression levels of 47 genes related to hypothalamic-pituitary-gonadal (HPG) axis, germ cell differentiation, sex determination, and hypothalamus-pituitary-thyroid (HPT) axis. Adult zebrafish with a female/male ratio of 5:7 were exposed to a solvent control (0.001% dimethyl sulfoxide) and three measured concentrations of MT (5, 51 and 583 ng/L) for 50 days. The results showed that MT had no significant histological effects on the ovaries of females, but the frequency of late-mature oocytes (LMO) showed a downward trend, indicating that MT could induce ovarian suppression to a certain extent. The transcriptional expression of activating transcription factor 4b1 (atf4b1), activating transcription factor 4b2 (atf4b2), calcium/calmodulin-dependent protein kinase II delta 1 (camk2d1), calcium/calmodulin-dependent protein kinase II delta 2 (camk2d2) and calcium/calmodulin-dependent protein kinase II inhibitor 2 (camk2n2) genes in the brain of females increased significantly at all treatment groups of MT, and the mRNA expression of forkhead box L2a (foxl2) and ovarian cytochrome P450 aromatase (cyp19a1a) genes in the ovaries were down-regulated by 5 and 583 ng/L group, which would translate into inhibition of oocyte development. As compared to females, MT had relatively little effects on the reproductive system of males, and only the transcriptional alterations of synaptonemal complex protein 3 (sycp3) and 17-alpha-hydroxylase/17,20-lyase (cyp17) genes were observed in the testes, not enough to affect testicular histology. In addition, MT at all treatments strongly increased corticotropin-releasing hormone (crh) transcript in the brain of females, as well as deiodinase 2 (dio2) transcript in the brain of males. The paired box protein 8 (pax8) gene was significantly decreased at 51 or 583 ng/L of MT in both female and male brains. The above results suggest that MT can pose potential adverse effects on the reproductive and thyroid endocrine system of fish.

Experimental exploration of estrogenic effects of norethindrone and 17α-ethinylestradiol on zebrafish (Danio rerio) gonads

Synthetic progestins and xenoestrogens found in aquatic habitats are currently gaining attention on global scale. The current study aimed to investigate the time-and dose-dependent effects of synthetic progestin Norethindrone (NET; 100, 500 and 1000 ng/L) and estrogen 17α-ethinylestradiol (EE2; 100 ng/L) individually as well as in binary mixture (1000 ng/L NET + 100 ng/L EE2) on reproductive histology and transcriptional expression profile of genes in adult zebrafish. For this, 20 female (3.15 ± 0.18 cm & 0.33 ± 0.06 g) and 20 male zebrafish in each group (2.93 ± 0.13 cm & 0.29 ± 0.04 g) were exposed to drugs dissolved in water for 30 days in 12 L rectangular tanks. We found that both NET and EE2 exposure reduced the gonadosomatic index in females, while only EE2 exposure caused significant reduction in males (p ≤ 0.05). Interestingly, NET delayed oocyte maturation in females and accelerated spermatogenesis in males, while EE2 consistently suppressed sperm maturation throughout the experiment. Further, qRT-PCR results revealed differential expression pattern of the study genes (er-α, er-β1, er-β2, pgr, vegfaa and p53) in male and female zebrafish. Co-exposure indicated potential inconsistencies in steroidal function in mixtures rather than single exposures. Our findings imply that changes in gonadal histology after NET and EE2 exposure may result from unique regulation of steroid hormone receptors. Additionally, significantly reduced p53 levels (p ≤ 0.05) following co-exposure in both sexes may suggest an elevated risk of neoplastic transformations. Further research with mammalian models will help to explore the mechanisms behind differing effects of alone and co-exposures.

Deleterious effect of gestagens from wastewater effluent on fish reproduction in aquatic environment: A review

Gestagens are common pollutants accumulated in the aquatic ecosystem. Gestagens are comprised of natural gestagens (i.e. progesterone) and synthetic gestagens (i.e. progestins). The major contributors of gestagens in the environment are paper plant mill effluent, wastewater treatment plants, discharge from pharmaceutical manufacturing, and livestock farming. Gestagens present in the aquatic environment interact with progesterone receptors and other steroid hormone receptors, negatively influencing fish reproduction, development, and behavior. In fish, the gonadotropin induces 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) production, an important steroid hormone involved in gametogenesis. DHP interacts with the membrane progestin receptor (mPR), which regulates sperm motility and oocyte maturation. Gestagens also interfere with the hypothalamic-pituitary-gonadal (HPG) axis, which results in altered hormone levels in fish. Moreover, recent studies showed that even at low concentrations exposure to gestagens can have detrimental effects on fish reproduction, including reduced egg production, masculinization, feminization in males, and altered sex ratio, raising concerns about their impact on the fish population. This review highlights the hormonal regulation of sperm motility, oocyte maturation, the concentration of environmental gestagens in the aquatic environment, and their detrimental effects on fish reproduction. However, the long-term and combined impacts of multiple gestagens, including their interactions with other pollutants on fish populations and ecosystems are not well understood. The lack of standardized regulations and monitoring protocols for gestagens pollution in wastewater effluent hampers effective control and management. Nonetheless, advancements in analytical techniques and biomonitoring methods provide potential solutions by enabling better detection and quantification of gestagens in aquatic ecosystems.

Dydrogesterone disrupts lipid metabolism in zebrafish brain: A study based on metabolomics and Fourier transform infrared spectroscopy

Brain is a potential target for neuroprogestogens and/or peripheral progestogens. Previous studies reported that expression of genes about steroidogenesis, reproduction, cell cycle, and circadian rhythm in zebrafish brain could be affected by progestogens. However, there are limited information from metabolites or biomacromolecules aspects, leaving an enormous gap in understanding toxic effects of progestogens on fish brain. In this study, we exposed zebrafish embryos to 2.8, 27.6, and 289.8 ng/L dydrogesterone (DDG, a synthetic progestogen) until sexual maturity (140 days). LC-MS and GC-MS based untargeted metabolomics and Fourier-transform infrared (FTIR) spectroscopy were then performed to investigate the metabolic profiles and macromolecular changes of brain of these zebrafish. The results from multivariate statistical analysis of metabolite features showed a clear separation between different treatment groups of both female and male zebrafish brains. DDG exposure increased the levels of cholesterol, saturated fatty acids, and nucleoside monophosphates, but decreased the contents of polyunsaturated fatty acids (PUFAs), lysophosphatides, and nucleosides in dose-dependent manner. FTIR results indicated that DDG exposure led to accumulation of saturated lipids, reduction of nucleic acids and carbohydrates, and alteration of protein secondary structures. The findings from this study demonstrated that DDG could affect contents of metabolites and biomacromolecules of zebrafish brain, which may finally lead to brain dysfunctions.

Norethindrone alters growth, sex differentiation and gene expression in marine medaka (Oryzias melastigma)

Norethindrone (NET) is a widely used synthetic progestin, which appears in water environments and threatens aquatic organisms. In this study, marine medaka (Oryzias melastigma) larvae were exposed to 7.6 and 80.1 ng/L NET for 190 days. The effects of NET on growth, sex differentiation, gonad histology and transcriptional expression profiles of hypothalamic-pituitary-gonadal (HPG) axis-related genes were determined. The results showed that exposure to 80.1 ng/L NET caused an all-male marine medaka population and significantly decreased the growth of males. Exposure to 7.6 ng/L NET increased the ratio of males/females in the marine medaka population, decreased the growth of males and delayed the ovary maturation in females. However, the sperm maturation was accelerated by 7.6 or 80.1 ng/L NET. In females, the transcription levels of cytochrome P450 aromatase (cyp19a1a) and progesterone receptor (pgr) in ovaries, glucocorticoid receptor (gr) and vitellogenin (vtg) in livers were suppressed after exposure to 7.6 ng/L NET, which may cause delayed ovary maturation. In males, NET significantly decreased the transcription levels of follicle stimulating hormone β (fshβ) and Luteinizing hormone β (lhβ)in the brain, Estrogen receptor β (erβ)，gr and pgr in the liver, and vitellogenin receptor (vtgr) in the testes, while NET of 80.1 ng/L led to a significant up-regulation of steroidogenic acute regulatory protein (star) in the testes of males. These results showed that NET could influence growth, sex differentiation and gonadal maturation and significantly alter the transcriptional expression levels of HPG axis-related genes.

Long term exposure to tris (2-chloroethyl) phosphate (TCEP) causes alterations in reproductive hormones, vitellogenin, antioxidant enzymes, and histology of gonads in zebrafish (Danio rerio): In vivo and computational analysis

In aquatic milieus, tris (2-chloroethyl) phosphate (TCEP) was detected as an emerging environmental contaminant. In this study, in vivo experiment and in-silico docking was integrated systematically to explore the toxic mechanisms of TCEP using zebrafish (Danio rerio). Fish (mean weight of 0.24 ± 0.02 g) were exposed to 100 and 1500 μg L^-1 concentrations of TCEP for 28 days under the static renewal method. During chronic exposure, plasma steroid hormones such as testosterone (T) and 17β estradiol (E2), plasma vitellogenin (Vtg) and antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and lipid peroxidation (LPO) in gonads were significantly (P < 0.05) altered in TCEP exposed group (1500 μg L^-1) compared to the control group. However, the alterations of these parameters were not significant on the 14th day (except Vtg and GR in testis) in 100 μg L^-1 of TCEP exposed groups. There were no significant differences (p > 0.05) in the growth parameters comparing TCEP exposed groups with the control group. The gonads of fish exposed to TCEP showed significant histopathological changes when compared to the control groups. A docking study observed that TCEP possessed binding affinity with the estrogen receptor (ERβ) and androgen receptor (AR). These data indicate that TCEP at tested concentrations adversely affects the aquatic organisms.

Dydrogesterone Affects the Transcription of Genes in Innate Immune and Coagulation Cascade in Zebrafish Embryos

Dydrogesterone (DDG) acts on the reproduction but also affects the functioning of non-reproductive system. So far, the knowledge about other effects of DDG remains limited. Here we investigated the effects of DDG on the transcription of genes in innate immune and coagulation cascade in zebrafish embryos. The zebrafish embryos were exposed to DDG at 49.0, 527 and 5890 ng L^- 1 for 144 hour post fertilization (hpf). The results showed that DDG significantly decreased the transcription of marker genes (e.g. tnfa, il8 and cc-chem) involved in the innate immune response at environmental concentrations. Moreover, DDG also down-regulated the transcription of genes in coagulation cascade (e.g. fga, fgb, fgg and f2). These results indicated that DDG had potential effects on the innate immune and coagulation cascade functions in the early life zebrafish, thus further affecting fish growth and health.

Histological and transcriptional effects of androstenedione in adult zebrafish (Danio rerio)

As a natural androgen, androstenedione (AED) may pose potential risks to aquatic organisms due to its ubiquitousness in aquatic environments. Here we assessed the adverse effects of AED on histology of gonads, as well as mRNA expression levels of 34 genes concerned with hypothalamic-pituitary-gonadal (HPG) axis, germ-cell differentiation and sex differentiation in zebrafish (Danio rerio). Adult zebrafish were exposed to solvent control and three measured concentrations of 0.2, 2.3 and 23.7 μg/L AED for 60 days. The results showed that AED did not induce any obvious histological effects in the ovaries and testes. Of the investigated genes, transcriptional expression levels of amh and cyp11c1 genes in the ovaries of females were significantly increased by AED at 2.3 or 23.7 μg/L. However, different exposure concentrations of AED significantly inhibited mRNA expression of gnrh3, atf4b1 and cyp19a1b in the brain of males. In the testes of males, AED at 2.3 μg/L led to a significant induction of sox9b gene, but it at 23.7 μg/L down-regulated nr5a1b gene. These observed transcriptional changes indicated that AED could pose potential androgenic effects in zebrafish.

Progesterone affects the transcription of genes in the circadian rhythm signaling and hypothalamic-pituitary-gonadal axes and changes the sex ratio in crucian carp (Carassius auratus)

Progesterone (P4) is an extensively applied progestin in human and veterinary medicine that has been widely detected in ambient aquatic environments, which can be detrimental to the health of aquatic organisms. Here we investigate the long-term effects of P4 on the transcription of genes related to the circadian rhythm signaling pathway and hypothalamic-pituitary-gonadal (HPG) axes in the crucian carp, which may have a potentially negative on endocrine-disrupting and sex differentiation impacts. Our results suggest that the expression of genes associated with the circadian rhythm signaling pathway are altered following exposure for 10, 20, 30, 40, 50 and 60 d, leading to disorders in the endocrine system disorders and the regulation of HPG axes-related gene expression. These maladies may affect gonadal development and the reproductive systems of crucian carp and provide a plausible mechanism for the observed change in sex ratio toward females after 180 d.

The progestin norethindrone alters growth, reproductive histology and gene expression in zebrafish (Danio rerio)

The aim of this study was to assess the long-term effects of synthetic progestin norethindrone (NET) on the growth, reproductive histology, and transcriptional expression profiles of genes associated with the hypothalamic-pituitary-gonadal (HPG) axis and germ cells in adult zebrafish. Adult zebrafish were exposed to 7, 84 and 810 ng/L NET for 90 days. The results showed that exposure to 810 ng/L NET caused a significant decrease in growth of females and males. The ovary weight and GSI was significantly reduced by NET at concentrations of 84 or 810 ng/L, which came along with the delay of ovary maturation in females. However, NET at all treatments resulted in acceleration of sperm maturation in males. In the ovaries of females, a strong inhibition of cyp19a1a gene was observed following exposure to NET at 810 ng/L. Similarly, NET at the highest treatment led to a significant down-regulation of cyp17, cyp19a1a, vasa, nanos1, dazl and dmc1 genes in the testes of males. Taken together, the overall results demonstrated that NET could impact growth and gonadal maturation, with significant alterations of transcriptional expression genes along HPG axis and germ cells.

Dysregulation of endocrine disruption, apoptosis and the transgenerational toxicity induced by spirotetramat

Spirotetramat (SPT) is a new tetronic acid derivative insecticide used to control scales and aphids; the potential for endocrine disruptor effects in fish could not be finalized with the available data. In this study, zebrafish were selected to assess the endocrine-disrupting effects. Significant decrease of plasma estradiol (E2), testosterone (T) and 11-ketotestosterone (11-KT) were observed in both male and female following the spirotetramat exposure; the vitellogenin (VTG) level in females significantly decreased. The expression of the hypothalamic-pituitary-gonad (HPG) axis genes fshr, lhr and esr1 showed significant increase in the gonads, which expression in males is higher than in females. In addition, the activities of capspase-3 and caspase-9 significantly decreased in both males and females liver, while the capspase-3 and caspase-9 were increased in male testis, the mRNA expression levels of genes expression related to the apoptosis pathway were also significantly altered after the spirotetramat exposure. Additionally, we found the parental zebrafish exposed to spirotetramat induced the development delay of its offspring. Above all, the adverse effects induced by spirotetramat suggesting that spirotetramat is a potential exogenous hazardous agent.

Dydrogesterone affects the transcription of genes in visual cycle and circadian rhythm network in the eye of zebrafish

Dydrogesterone (DDG) is a synthetic progestin used in contraception and hormone replacement therapy. Our previous transcriptome data showed that the response to light stimulus, photoperiodism and rhythm related gene ontology (GO) terms were significantly enriched in the brain of zebrafish after chronic exposure to DDG. Here we investigated the effects of DDG on the eye of zebrafish. Zebrafish were exposed to DDG at three concentration levels (3.39, 33.1, and 329 ng L^-1) for 120 days. Based on our previous transcriptome data, the transcription of genes involved in visual cycle and circadian rhythm network was examined by qPCR analysis. In the visual cycle network, exposure to all concentrations of DDG significantly decreased transcription of grk7a, aar3a and guca1d, while increased the transcription of opn1mw4 and opn1sw2 at the low concentration. Importantly, exposure to all concentrations of DDG down-regulated the transcription of rep65a that encodes a critical enzyme to catalyze the conversion from all-trans-retinal to 11-cis-retinal in the eye of male zebrafish. In the circadian rhythm network, DDG enhanced the transcription of clocka, arntl2 and nifil3-5 at all three concentrations, while it decreased the transcription of cry5, per1b, nr1d2b and si:ch211.132b12.7. In addition, DDG decreased the transcription of tefa in both males and females. Moreover, histological analysis showed the exposure to 329 ng L^-1 of DDG decreased the thickness of retinal ganglion cell in the eye of male zebrafish. These results indicated that DDG exposure could affect the transcription of genes in visual cycle and circadian rhythm network in the eyes of zebrafish. This suggests that DDG has potential negative impact on the normal eye function.

Male-biased zebrafish sex differentiation and metabolomics profile changes caused by dydrogesterone

Some progestins, including the widely used dydrogesterone (DDG), have been shown to cause male-biased sex ratio in teleost. However, there is a gap to fully understand the mechanisms of the sex differentiation disturbance by progestins, particularly from the metabolic aspect. We thus aimed to examine the sex changes by exposing zebrafish embryos to 4.4 (L), 44 (M) and 440 (H) ng/L DDG for up to 140 days, and investigated metabolomic profile changes during the critical period of sex differentiation at fry stage (35 dpf). DDG increased the percentage of male zebrafish in a dose-dependent manner, with 98% male fish in the high concentration group. In zebrafish fry, DDG increased the levels of some free fatty acids, monoglycerides, acylcarnitines, organic acids, free amino acids, while decreased lysophospholipids, uric acid and bile acids. DDG exposure also decreased the nucleoside monophosphates and UDP-sugars while increased nucleosides and their bases. These metabolite changes, namely increase in n-3 PUFAs (polyunsaturated fatty acids), myo-inositol, taurine, palmitoleic acid, oleic acid, lactic acid, fumaric acid, and uracil, and decrease in uric acid and bile acids, might account for the male-biased sex ratio in zebrafish. It appears that many of these metabolites could inhibit several pathways that regulate zebrafish gonad differentiation, including NF-κB/COX-2 and Wnt/β-catenin pathways, and activate p53 pathway. Thus we proposed a hypothesis that DDG might induce oocytes apoptosis through the above pathways and finally lead to female-to-male sex reversal. The results from this study suggest that DDG at environmentally relevant concentrations could affect zebrafish metabolomic profiles and finally disturb fish sex differentiation.

Dydrogesterone exposure induces zebrafish ovulation but leads to oocytes over-ripening: An integrated histological and metabolomics study

Dydrogesterone (DDG) is a synthetic progestin widely used in numerous gynecological diseases. DDG has been shown to disturb fish reproduction, however, the mechanism is still unclear. Here we studied the histological changes and differences of metabolome between exposed and control fish gonads after exposure of zebrafish (Danio rerio) embryos to 2.8, 27.6, and 289.8 ng/L DDG until sexual maturity for a total of 140 days. Dydrogesterone exposure led to male-biased zebrafish sex ratios. Histological examination revealed that DDG induced postovulatory follicles and atretic follicles in the ovary of the female fish. Postovulatory follicles indicated the occurrence of ovulation. DDG also increased spermatids and spermatozoa in the male fish testis, suggesting promotion of spermatogenesis. Ovarian metabolome showed that DDG increased the concentrations of free amino acids, urea, putrescine, free fatty acids, acylcarnitines, lysophospholipids, and other metabolites catabolized from phospholipids. Most of these metabolites are biodegradation products of proteins and lipids, suggesting the existence of ovulated oocytes over-ripening. Further, DDG upregulated arachidonic acid (AA) and its 5‑lipoxygenase (5-LOX) metabolites 5‑oxo‑6,8,11,14‑eicosatetraenoic acid (5-oxo-ETE) in the ovary, which could lead to suppression of AA cyclooxygenase (COX) metabolite prostaglandin F2α (PGF2α). It is believed that AA induced oocyte maturation, while 5-oxo-ETE and related metabolites in purinergic signaling promoted ovulation. Whereas, the suppression of PGF2α production might block spawning and damaged follicular tissue digestion, which explained the oocytes over-ripening and atretic follicles in the treated ovary. Overall, our results suggested that DDG exposure induced zebrafish oocyte maturation and ovulation but led to oocytes over-ripening via the AA metabolic pathway and purinergic signaling.