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

The impact of co-exposure to polystyrene microplastics and norethindrone on gill histology, antioxidant capacity, reproductive system, and gut microbiota in zebrafish (Danio rerio)

In recent years, studies have focused on the combined ecological risks posed by microplastics and other organic pollutants. Although both microplastics and progestin residues are frequently detected in the aquatic environments, their ecological implications remain unknown. Adult zebrafish were exposed to polystyrene microplastics (PS, 200 nm, 200 μg/L), norethindrone (NET, 69.6 ng/L), and their mixture (200 μg/L PS + 63.1 ng/L NET) for 30 days. The results demonstrated that exposure to PS and NET resulted in gill damage. Notably, the PS and PS+NET exhibited a significant decrease in glutathione (GSH) and oxidized glutathione (GSSG) content, as well as reduced antioxidase activity in the gills. The oxidative stress in PS+NET primarily originated from PS. The PS, NET, or their mixture resulted in a decrease in testosterone (T) and estradiol (E2) levels in female. Furthermore, compared to NET, the PS+NET showed a significant reduction in E2 levels, thereby augmenting the inhibitory effect on reproductive ability mediated by NET. However, males showed an increase in 11-ketodihydrotestosterone (11-KT) content, accompanied by a significant decrease in spermatogonia (Sg) and increase in spermatocytes (Sc). Consequently, it can be inferred that PS enhances the androgenic effect of NET. In female fish brain, NET alone resulted in transcriptional down-regulation of partial hormone receptors; however, co-administration of PS effectively mitigated the interference effects. Furthermore, transcriptional downregulation of 17-alpha-hydroxylase (cyp17), hydroxysteroid 3-beta dehydrogenase (hsd3b), estrogen receptor 1 (esr1), and estrogen receptor 2a (esr2b) genes in the ovary was found to be associated with the androgenic activity induced by NET. Moreover, in comparison to PS or NET alone, PS+NET resulted in a notable decrease in Cetobacterium abundance and an increase in Aeromonas population, suggesting that the co-exposure of PS+NET may exacerbate intestinal burden. The findings highlight the importance of studying the combined toxicity of PS and NET.

Characteristics of the Vasa Gene in Silurus asotus and Its Expression Response to Letrozole Treatment

The identification and expression of germ cells are important for studying sex-related mechanisms in fish. The vasa gene, encoding an ATP-dependent RNA helicase, is recognized as a molecular marker of germ cells and plays a crucial role in germ cell development. Silurus asotus, an important freshwater economic fish species in China, shows significant sex dimorphism with the female growing faster than the male. However, the molecular mechanisms underlying these sex differences especially involving in the vasa gene in this fish remain poorly understood. In this work, the vasa gene sequence of S. asotus (named as Savasa) was obtained through RT-PCR and rapid amplification of cDNA end (RACE), and its expression in embryos and tissues was analyzed using qRT-PCR and an in situ hybridization method. Letrozole (LT) treatment on the larvae fish was also conducted to investigate its influence on the gene. The results revealed that the open reading frame (ORF) of Savasa was 1989 bp, encoding 662 amino acids. The SaVasa protein contains 10 conserved domains unique to the DEAD-box protein family, showing the highest sequence identity of 95.92% with that of Silurus meridionalis. In embryos, Savasa is highly expressed from the two-cell stage to the blastula stage in early embryos, with a gradually decreasing trend from the gastrula stage to the heart-beating stage. Furthermore, Savasa was initially detected at the end of the cleavage furrow during the two-cell stage, later condensing into four symmetrical cell clusters with embryonic development. At the gastrula stage, Savasa-positive cells increased and began to migrate towards the dorsal side of the embryo. In tissues, Savasa is predominantly expressed in the ovaries, with almost no or lower expression in other detected tissues. Moreover, Savasa was expressed in phase I-V oocytes in the ovaries, as well as in spermatogonia and spermatocytes in the testis, implying a specific expression pattern of germ cells. In addition, LT significantly upregulated the expression of Savasa in a concentration-dependent manner during the key gonadal differentiation period of the fish. Notably, at 120 dph after LT treatment, Savasa expression was the lowest in the testis and ovary of the high concentration group. Collectively, findings from gene structure, protein sequence, phylogenetic analysis, RNA expression patterns, and response to LT suggest that Savasa is maternally inherited with conserved features, serving as a potential marker gene for germ cells in S.asotus, and might participate in LT-induced early embryonic development and gonadal development processes of the fish. This would provide a basis for further research on the application of germ cell markers and the molecular mechanisms of sex differences in S. asotus.

Occurrence and spatiotemporal distribution of natural and synthetic steroid hormones in soil, water, and sediment systems in suburban agricultural area of Guangzhou City, China

Steroid hormones are highly potent compounds that can disrupt the endocrine systems of aquatic organisms. This study explored the spatiotemporal distribution of 49 steroid hormones in agricultural soils, ditch water, and sediment from suburban areas of Guangzhou City, China. The average concentrations of Σsteroid hormones in the water, soils, and sediment were 97.7 ng/L, 4460 ng/kg, and 9140 ng/kg, respectively. Elevated hormone concentrations were notable in water during the flood season compared to the dry season, whereas an inverse trend was observed in soils and sediment. These observations were attributed to illegal wastewater discharge during the flood season, and sediment partitioning of hormones and manure fertilization during the dry season. Correlation analysis further showed that population, precipitation, and number of slaughtered animals significantly influenced the spatial distribution of steroid hormones across various districts. Moreover, there was substantial mass transfer among the three media, with steroid hormones predominantly distributed in the sediment (60.8 %) and soils (34.4 %). Risk quotients, calculated as the measured concentration and predicted no-effect concentration, exceeded 1 at certain sites for some hormones, indicating high risks. This study reveals that the risk assessment of steroid hormones requires consideration of their spatiotemporal variability and inter-media mass transfer dynamics in agroecosystems.

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.

Polymorphism in ovine ADCY8 gene and its association with residual feed intake in Hu sheep

Feed efficiency makes up a large part of sheep production, which also has a crucial impact on the economic benefits of producers. This study explores the polymorphism of Adenylyl cyclase 8 gene associated with feed efficiency and detects the expression characteristics of ADCY8 in ten tissues of Hu sheep. The polymorphism of ADCY8 was recognized by using PCR amplification and Sanger sequencing, KASPar technology was used for genotyping subsequently, and the relationship between SNP and RFI is also studied. The results indicated that an intronic mutation g.24799148 C > T (rs 423395741) was identified in ADCY8, and association analysis showed that the SNP g.24799148 C > T (rs 423395741) was significantly associated with RFI at 100-120, 100-140, 100-160, and 100-180 days (p < 0.05). The quantitative real-time PCR (qRT-PCR) result showed that ADCY8 was expressed in ten tissues, and the expression of ADCY8 gene in rumen tissue was significantly higher than in the other tested tissues. Therefore, these results indicated that the ADCY8 mutation locus may be used as a candidate molecular marker for evaluating the feed efficiency of Hu sheep.

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.

Occurrence, tissue distribution, and risk assessment of progestins, androgens, estrogens, and phenols in wild freshwater fish species

The presence of endocrine-disrupting chemicals (EDCs) in aquatic environments such as water, sediment, and sludge received more and more attention. However, the bioaccumulate properties of EDCs, particularly progestins and androgens, in various tissues of different wild freshwater fish species, as well as their effects on human health, have not been fully studied. The muscle, liver, and gills of three wild fish species obtained from the East Dongting Lake in southern China were examined for the presence of 19 EDCs (4 progestins, 5 androgens, 6 estrogens, and 4 phenols). Seventeen analytes were detected in all fish samples, and the concentrations of progestins, androgens, estrogens, and phenols ranged from ND-78.80 ng/g (wet weight, ww), ND-50.40 ng/g ww, ND-3573.82 ng/g ww, and ND-88.17 ng/g ww, respectively. The bioaccumulation of some EDCs in wild fish from East Dongting Lake was species-specific. Additionally, AND, EES, P4, and E2 were discovered in the liver at higher levels than in the muscle, suggesting that livers had a larger ability for enriching these EDCs than the muscle. Furthermore, the relationships between the fish sizes and the EDC concentrations indicated that total weight and length had a negligible impact on the bioaccumulation of EDCs in various fish species. Most importantly, the effects of EDCs on human health as a result of fish consumption were assessed. Although the estimated daily intakes (EDIs) of most EDCs were much lower compared with the corresponding acceptable daily intakes (ADIs) via consuming fish collected in this study, the EDI of EE2 in Silurus asotus was higher than the ADI of E2, indicating that Silurus asotus from East Dongting Lake should be eaten in moderation by local residents.

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.

Short-term exposure to norethisterone affected swimming behavior and antioxidant enzyme activity of medaka larvae, and led to masculinization in the adult population

Norethisterone (NET), one of the synthetic progestins, is detected with increasing frequency in the water environment and distributed in the ocean, with a potential toxicity risk to marine organisms. However, current studies on the adverse effects of progestins (including NET) in aquatic environments have focused on freshwater organisms, mainly fish. In the present, marine medaka (Oryzias melastigma) larvae were exposed to 91.31 ng/L NET for 10 days, and then the swimming behavior, oxidation-antioxidant-related enzyme activities, sex and thyroid hormone levels, and the gene transcription patterns of the larvae were measured. After NET treatment, medaka larvae were raised in artificial seawater until 5 months of age, and the sex ratio was counted. Ten-day exposure to 91.31 ng/L NET inhibited swimming behavior, of marine medaka larvae, which showed that the time in the resting state was significantly prolonged, while the time in the large motor state was significantly reduced; disrupted oxidative-antioxidant system, significantly up-regulated the enzymatic activities of reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione peroxidase (GSH-Px); affected the hormone levels of larvae, lowered 11- keto testosterone (11-KT) and triiodothyronine (T3) concentrations. RNA-seq results showed that 91.31 ng/L NET exposure for 10 days changed the transcript levels of 275 genes, of which 28 were up-regulated and 247 were down-regulated. Differentially expressed genes (DEGs) were mainly significantly enriched in piwi interacting RNA (piRNA), gonadal development, gametogenesis, and steroidogenesis biological processes, etc. After removing NET exposure and returning to breeding for 140 days, a significant increase in male proportions (69.67%) was observed in sexually mature medaka populations in the NET-treated group. These results show that exposure to 91.31 ng/L NET for 10 days can lead to various adverse effects on marine medaka larvae. These findings shed light on the potential ecological risks of synthetic progestins to marine organisms.

Effects of the synthetic progestin levonorgestrel on some aspects of thyroid physiology in common carp (Cyprinus carpio)

The objective of the present study was to assess the effects of levonorgestrel (LNG), a synthetic progestin, on early development and the thyroid system of carp using morphological, histological, immunohistochemical, and gene expression analysis. Fish were exposed to LNG at three levels (3, 31, and 310 ng L^-1) from eggs to the onset of juvenile stage (47 days). LNG had no significant effect on early development in common carp or on the occurrence of morphological anomalies. No pathological alterations of the thyroid follicles were found. Immunohistochemical examination of the thyroid follicles using antibodies against thyroxin did not show any differences in fish exposed to 310 ng L^-1 LNG compared to the controls. mRNA expression of iodothyronine deiodinases (dio1, 2, 3) was differentially affected by LNG treatment during carp development. Most importantly, dio3 was markedly downregulated in fish exposed to all three LNG levels compared to the controls at the conclusion of the experiment (47 days post-fertilization). A decrease in dio1 or dio3 or an increase in dio2 transcription observed at different time points of the study may be a sign of hypothyroidism. mRNA expression of genes npr, esr1, and esr2b in the body and npr and esr2b in the head of fish exposed to 310 ng L^-1 LNG was significantly upregulated compared to the solvent control group at the end of the test. Together, these results show that levonorgestrel caused parallel changes in the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-gonad axes.

Association of long-term effects of low-level sulfamethoxazole with ovarian lipid and amino acid metabolism, sex hormone levels, and oocyte maturity in zebrafish

Sulfamethoxazole (SMZ) is an important antibiotic used to prevent and treat infections in both clinical settings and animal husbandry. High levels of SMZ may exhibit endocrine toxicity. Environmental SMZ enters the human body via food and water; however, the toxicity of environmental doses of SMZ and its effects on reproductive health are unknown. In the present study, zebrafish were exposed to low concentrations of SMZ (1000 and 5000 ng/L) from 2 h post-fertilization to 120 d post-fertilization. Consequently, the proportion of mature oocytes in adult female zebrafish ovarian tissue increased by 98.2 %, indicating that SMZ promotes ovarian maturation. Metabolomics analysis revealed significant changes in ovarian lipid and amino acid levels after SMZ treatment. An enzyme-linked immunoassay used to detect sex hormones in the ovaries showed that SMZ exposure significantly increased the levels of estradiol, a follicle-stimulating hormone, and of luteinizing hormone. Furthermore, an association analysis showed that most of the differentially expressed metabolites in the ovary were strongly correlated with the levels of sex hormones secreted by the pituitary gland. Therefore, significantly increased transcript levels of gonadotropin-releasing hormone (GnRH) and follicle-stimulating hormone detected in brain tissue suggested that SMZ may exhibit ovarian toxicity via the hypothalamus. In vitro experiments were performed to demonstrate that SMZ targets neurons in the hypothalamus. Exposure to SMZ significantly increased the GnRH content in GnRH neurons. Finally, molecular docking simulations indicated the potential interaction of SMZ with G protein-coupled receptor 54; this molecular binding can activate, synthesize, and release GnRH in neurons. In conclusion, long-term environmental exposure to SMZ may induce ovarian toxicity by affecting the hypothalamus-pituitary-gonad axis.

Identification and functional analysis of Tex11 and Meig1 in spermatogenesis of Hyriopsis cumingii

Abstract: The process of spermatogenesis is complex and controlled by many genes. In mammals, Testis-expressed gene 11 (Tex11) and meiosis expressed gene 1 (Meig1) are typical spermatogenesis-related genes. In this study, we obtained the full length cDNAs for Tex11 (3143bp) and Meig1 (1649bp) in Hyriopsis cumingii by cloning. Among them, Hc-Tex11 contains 930 amino acids and Hc-Meig1 contains 91 amino acids. The protein molecular masses (MW) of Hc-Tex11 and Hc-Meig1 were 105.63 kDa and 10.95 kDa, respectively. Protein secondary structure analysis showed that Hc-TEX11 protein has three TPR domains. The expression of Hc-Tex11 and Hc-Meig1 in different tissues showed higher levels in testes. At different ages, the expression of Hc-Tex11 and Hc-Meig1 was higher levels in 3-year-old male mussels. During spermatogenesis, the mRNA levels of Hc-Tex11, Hc-Meig1 gradually increased with the development of spermatogonia and reached a peak during sperm maturation. Hc-Tex11 and Hc-Meig1 mRNA signals were detected on spermatogonia and spermatocytes by in situ hybridization. In addition, RNA interference (RNAi) experiments of Hc-Tex11 caused a down-regulated of Dmrt1, KinaseX, Tra-2 and Klhl10 genes and an up-regulated of β-catenin gene. Based on the above experimental results, it can be speculated that Hc-Tex11 and Hc-Meig1 are important in the development of the male gonadal and spermatogenesis in H. cumingii, which can provide important clues to better comprehend the molecular mechanism of Tex11 and Meig1 in regulating spermatogenesis of bivalves.

Robust strategies to eliminate endocrine disruptive estrogens in water resources

The widespread occurrence and ubiquitous distribution of estrogens, i.e., estrone (E1), estradiol (E2), and estriol (E3) in our water matrices, is an issue of global concern. Public and regulatory authorities are concerned and placing joint efforts to eliminate estrogens and related environmentally hazardous compounds, due to their toxic influences on the environmental matrices, ecology, and human health, even at low concentrations. However, most of the available literature is focused on the occurrence of estrogens in different water environments with limited treatment options. Thus, a detailed review to fully cover the several treatment processes is needed. This review comprehensively and comparatively discusses many physical, chemical, and biological-based treatments to eliminate natural estrogens, i.e., estrone (E1), estradiol (E2), and estriol (E3) and related synthetic estrogens, e.g., 17α-ethinylestradiol (EE2) and other related hazardous compounds. The covered techniques include adsorption, nanofiltration, ultrafiltration, ultrasonication, photocatalysis of estrogenic compounds, Fenton, Fenton-like and photo-Fenton degradation of estrogenic compounds, electro-Fenton degradation of estrogenic compounds, ozonation, and biological methods for the removal of estrogenic compounds are thoroughly discussed with suitable examples. The studies revealed that treatment plants based on chemical and biological approaches are cost-friendly for removing estrogenic pollutants. Further, there is a need to properly monitor and disposal of the usage of estrogenic drugs in humans and animals. Additional studies are required to explore a robust and more advanced oxidation treatment strategy that can contribute effectively to industrial-scale applications. This review may assist future investigations, monitoring, and removing estrogenic compounds from various environmental matrices. In concluding remarks, a way forward and future perspectives focusing on bridging knowledge gaps in estrogenic compounds removal are also proposed.

Biomarker Responses, Gene Expression Alterations, and Histological Changes in Zebrafish (Danio rerio) After In Vivo Exposure to Polychlorinated Diphenyl Ethers

Polychlorinated diphenyl ethers (PCDEs) have been detected in various aquatic matrices, which pose potential threats to aquatic ecosystem security. In this work, both micro and macro analysis methods were used to assess the toxicity of PCDEs to zebrafish. Results indicated that after in vivo PCDE exposure, the oxidative stress and related gene of Danio rerio were significantly changed. The higher concentration or longer exposure time could cause more severe oxidative stress in zebrafish tissues. Compared with among the five tested compounds, more obvious changes in the level of oxidative biomarkers of lower chlorinated PCDEs’ (4-mono-CDE and 4,4′-di-CDE) exposure groups were observed. The integrated biomarker response analysis and gene expression results also indicate a similar trend. Histopathological observation suggested that 4,4′-di-CDE could render liver nuclei enlargement and necrosis, hepatocyte vacuolation, and the development inhibition of ovarian cells. Transmission electron microscope photos showed that 4,4′-di-CDE caused organelle damage in the liver and ovary, including the rupture of the endoplasmic reticulum, swelling of mitochondria, and condensation of chromatin in the liver and mitochondria disappeared significantly in the ovary. The degree of damage is enhanced with the increasing exposure doses. In addition, PCDEs also significantly altered vitellogenin content and related gene (vtg1) expression, suggesting that PCDEs may be estrogen endocrine disruptors. Overall, these results provided some valuable toxicological data of PCDEs on aquatic species.

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.

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.

Spatiotemporal distribution, source apportionment and risk assessment of typical hormones and phenolic endocrine disrupting chemicals in environmental and biological samples from the mariculture areas in the Pearl River Delta, China

The present work studied the levels, distribution, potential sources, ecological and human health risks of typical hormones and phenolic endocrine disrupting chemicals (EDCs) in the mariculture areas of the Pearl River Delta (PRD), China. The environmental levels of 11 hormones (6 estrogens, 4 progestogens, and 1 androgen) and 2 phenolic EDCs were quantified in various matrices including water, sediment, cultured fish and shellfish. Ultrahigh performance liquid chromatography-triple quadrupole tandem mass spectrometry analyses showed that all the 13 target compounds were detected in biotic samples, whereas 10 were detected in water and sediment, respectively. The total concentrations ranged from 35.06-364.53 ng/L in water and 6.31-29.30 ng/g in sediment, respectively. The average contaminant levels in shellfish (Ostrea gigas, Mytilus edulis and Mimachlamys nobilis) were significantly higher than those in fish (Culter alburnus, Ephippus orbis and Ephippus orbis). Source apportionment revealed that the pollution of hormones and phenolic EDCs in PRD mariculture areas was resulted from the combination of coastal anthropogenic discharges and mariculture activities. The hazard quotient values of the contaminants were all less than 1, implying no immediate human health risk. Overall, the present study is of great significance for scientific mariculture management, land-based pollution control, ecosystem protection, and safeguarding human health.

Transgenerational effects of androstadienedione and androstenedione at environmentally relevant concentrations in zebrafish (Danio rerio)

Androgens androstadienedione (ADD) and androstenedione (AED) are predominant steroid hormones in surface water, and can disrupt the endocrine system in fish. However, little is known about the transgenerational effects of ADD and AED in fish. In the present study, F0 generation was exposed to ADD and AED from 21 to 144 days post-fertilization (dpf) at nominal concentrations of 5 (L), 50 (M) and 500 (H) ng L^-1, and F1 generation was domesticated in clear water for 144 dpf. The sex ratio, histology and transcription in F0 and F1 generations were examined. In the F0 generation, ADD and AED tended to be estrogenic in zebrafish, resulting in female biased zebrafish populations. In the F1 generation, ADD at the H level caused 63.5% females, while AED at the H level resulted in 78.7% males. In brain, ADD and AED had similar effects on circadian rhythm in the F0 and F1 generations. In the F1 eleutheroembryos, transcriptomic analysis indicated that neuromast hair cell related biological processes (BPs) were overlapped in the ADD and AED groups. Taken together, ADD and AED at environmentally relevant concentrations had transgenerational effects on sex differentiation and transcription in zebrafish.

CeO2 nanostructured electrochemical sensor for the simultaneous recognition of diethylstilbestrol and 17β-estradiol hormones

A new highly sensitive, selective, and inexpensive electrochemical method has been developed for simultaneously detecting diethylstilbestrol (DES) and 17β-estradiol (E2) in environmental samples (groundwater and lake water) using a graphite sensor modified by cerium oxide nanoparticles (CPE-CeO₂ NPs). The developed sensor and the materials used in its preparation were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The ab initio simulation was used to evaluate the adsorption energies between both DES and E2 with the surface of the sensor. The peak current of oxidation of both hormones showed two regions of linearity. The region of greatest sensitivity was observed for the linear range of 10 nM-100 nM. The detection and quantification limits for this concentration range were 0.8/2.6 nM and 1.3/4.3 nM for DES and E2, respectively. The analytical performance of the developed method showed high sensitivity, precision, repeatability, reproducibility, and selectivity. The CPE-CeO₂ NPs sensor was successfully applied to simultaneously detect DES and E2 in real samples with recovery levels above 98%.

Chronic Exposure to Climbazole Induces Oxidative Stress and Sex Hormone Imbalance in the Testes of Male Zebrafish

As the main active ingredient for the treatment of fungal infections, climbazole (CBZ) is commonly used in a variety of personal care products. After its use, CBZ enters the receiving environment directly or indirectly through domestic sewage. Its concentration can be up to several nanograms per liter in surface water. So far, the effects of CBZ on the reproductive system of female zebrafish have been systematically studied, but the potential toxicity mechanism of CBZ on male zebrafish still needs to be further explored. In this study, adult male zebrafish were exposed to CBZ at concentrations of 0.1, 10, and 1000 μg·L^-1 for 28 days, and their testes were collected for histological, mass-spectrometry-based metabolomics, and biochemical analyses. We found that CBZ caused a significantly abnormal metabolism of purine and glutathione and triggered oxidative stress in zebrafish testes, thereby inducing testicular cell apoptosis. In addition, CBZ could inhibit the synthesis of essential sex hormones in the testis and thus reduce the sperm production. The conclusions of this study fill the data gap on the reproductive toxicity of CBZ to male zebrafish and highlight the ecotoxicological application of untargeted metabolomics in the biomarker discovery.

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.

Hypothalamic and ovarian transcriptome profiling reveals potential candidate genes in low and high egg production of white Muscovy ducks (Cairina moschata)

In China, the low egg production rate is a major challenge to Muscovy duck farmers. Hypothalamus and ovary play essential role in egg production of birds. However, there are little or no reports from these tissues to identify potential candidate genes responsible for egg production in White Muscovy ducks. A total of 1,537 laying ducks were raised; the egg production traits which include age at first egg (days), number of eggs at 300 d, and number of eggs at 59 wk were recorded. Moreover, 4 lowest (LP) and 4 highest producing (HP) were selected at 59 wk of age, respectively. To understand the mechanism of egg laying regulation, we sequenced the hypothalamus and ovary transcriptome profiles in LP and HP using RNA-Seq. The results showed that the number of eggs at 300 d and number of eggs at 59 wk in the HP were significantly more (P < 0.001) than the LP ducks. In total, 106.98G clean bases were generated from 16 libraries with an average of 6.68G clean bases for each library. Further analysis showed 569 and 2,259 differentially expressed genes (DEGs) were identified in the hypothalamus and ovary between LP and HP, respectively. The KEGG pathway enrichment analysis revealed 114 and 139 pathways in the hypothalamus and ovary, respectively which includes Calcium signaling pathway, ECM-receptor interaction, Focal adhesion, MAPK signaling pathway, Apoptosis and Apelin signaling pathways that are involved in egg production. Based on the GO terms and KEGG pathways results, 10 potential candidate genes (P2RX1, LPAR2, ADORA1, FN1, AKT3, ADCY5, ADCY8, MAP3K8, PXN, and PTTG1) were identified to be responsible for egg production. Further, protein-protein interaction was analyzed to show the relationship between these candidate genes. Therefore, this study provides useful information on transcriptome of hypothalamus and ovary of LP and HP Muscovy ducks.

Effects of dexamethasone on the morphology, gene expression and hepatic histology in adult female mosquitofish (Gambusia affinis)

Glucocorticoids (GCs), including natural hormones as well as synthetic chemicals, can pose influences on physiological performance, development and reproduction of fish. Dexamethasone (DEX) is a synthetic glucocorticoid widely used as pharmaceutical and usually exists in effluents with varying degrees of concentrations. In this study, adult female mosquitofish (Gambusia affinis) were treated by DEX at concentrations of 0, 0.5, 5 and 50 μg/L for 60 days. Morphological parameters of anal fin and skeleton, mRNA expression abundance, and histological alterations of liver were investigated to assess effects of DEX on mosquitofish. The results showed that DEX increased number of sections of ray 3 in anal fin and decreased 16L, 15D and 16D in skeletal parameters, which indicates DEX could potentially lead to weak masculinization. Furthermore, transcriptional expression levels of ARα, ARβ, ERβ, VTGC and CYP19A genes were notably down-regulated by DEX, which will contribute to weak masculinization in females. In addition, the damage to liver tissue was also induced by DEX. Taken together, this research demonstrated that aquatic environments contaminated by DEX have negative effects on mosquitofish at a population level.

Metabolomics reveals the reproductive abnormality in female zebrafish exposed to environmentally relevant levels of climbazole

Climbazole (CBZ) ubiquitously detected in the aquatic environment may disrupt fish reproductive function. Thus far, the previous study has focused on its transcriptional impact of steroidogenesis-related genes on zebrafish, but the underlying toxic mechanism still needs further investigation at the metabolic level. In this study, adult zebrafish were chronically exposed to CBZ at concentrations of 0.1 (corresponding to the real concentration in surface water), 10, and 1000 μg/L and evaluated for reproductive function by egg production, with subsequent ovarian tissue samples taken for histology, metabolomics, and other biochemical analysis. After 28 days' exposure, fecundity was significantly decreased in all exposure groups, with the inhibition of oocytes in varying developmental stages to a certain degree. The decrease in retinoic acid and sex hormones, down-regulated genes important in steroidogenesis, and increase in oxidized/reduced glutathione ratio and occurrence of apoptotic cells were observed in zebrafish ovaries following exposure to CBZ even at environmentally realistic concentrations, suggesting that alternations in steroidogenesis and oxidative stress can play significant roles in CBZ-triggered reproductive toxicity. Besides, mass spectrometry imaging analysis validated the results from metabolomics analysis. Our findings provide novel perspectives for unveiling the mechanism of reproductive dysfunction by CBZ and highlight its risk to fish reproduction.

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.

Occurrence and distribution of natural and synthetic progestins, androgens, and estrogens in soils from agricultural production areas in China

The occurrence of biologically potent sex hormones in agricultural soils is of growing concern due to their ability to disrupt the endocrine systems of aquatic organisms after being transported to surface waters via runoff. This study, therefore, examined the large-scale occurrence of 34 natural and synthetic sex hormones (13 progestins, 16 androgens, and 5 estrogens) in soils from 7 provinces and 1 municipality in China. The target sex hormones were detected in 99.3% of the soil samples, indicating their widespread occurrence in most agricultural areas. Additionally, seven synthetic progestins were detected in soils for the first time. The total concentration of the 34 sex hormones (Σsex hormones) in the sampled soils ranged from below the method detection limit to 23.7 ng/g (mean of 4.72 ± 4.07 ng/g), with androgens and progestins being the most dominant hormone groups. Significant correlations were observed among the concentrations of Σestrogens, Σandrogens, and Σprogestins (r = 0.117-0.433, p < 0.001), suggesting similar sources of sex hormones. The mean concentration of Σsex hormones varied considerably across the selected provinces/municipality. Notably, the annual slaughter of poultry and swine (R² = 0.75-0.88), female population (R² = 0.57-0.58), and soil organic carbon content (R² = 0.20-0.55) in each province were significantly correlated with the concentrations or mean concentrations of Σsex hormones, Σestrogens, or Σprogestins. This finding implies that these parameters contributed to the occurrence and distribution of sex hormones in the studied soils. Finally, risk quotients for some sex hormones exceeded 0.01, indicating medium or high risks to agroecosystems. This study highlights the importance of designing an optimal manure fertilization strategy in order to mitigate the risks posed by sex hormones in agroecosystems.

The effects of norethindrone on the ontogeny of gene expression along the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes in zebrafish (Danio rerio)

Little is known about the molecular effects of progestins on the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes in fish prior to sexual differentiation. In this study, the effects of norethindrone (NET) on the ontogeny of HPG- and HPA-related genes in zebrafish embryo/early larvae prior to sexual differentiation were evaluated. Embryo/larvae were exposed to different concentrations (5, 50, 500 ng/L) of NET for 6 days. The levels of the transcripts of the genes closely related to the HPG and HPA axes were determined daily during 3 stages (embryo, embryo/larvae transition, and early larvae). The results showed that most genes were up-regulated and the ontogeny of genes in the HPA axis was earlier than that of HPG axis, especially for the upstream genes of both the HPG (gnrh2, gnrh3, fshb, lhb) and the HPA (crh, pomc, star) axes. In contrast, the transcriptional expressions of genes of the cortisol/stress pathway (cyp11b, mr) were inhibited and those of the progesterone pathway were not affected. More importantly, NET exposure induced the expressions of the genes (esr1, vtg1, hsd17b3, hsd11b2, ar) that are closely related to the steroid hormone pathways in the embryos/larvae stages, implying a precocious effects of NET in zebrafish. This study demonstrates that NET alters the expression of HPA- and HPG-axes related genes in zebrafish at early stages, pointing to the need for the same type of analysis during the zebrafish gonadal differentiation window.

The synthetic progestin norethindrone causes thyroid endocrine disruption in adult zebrafish

Synthetic progestin norethindrone (NET) widely used in oral contraceptives, hormonal therapy and livestock farming has been detected in various aquatic ecosystems. Recent studies have shown that NET can cause thyroid endocrine disruption in amphibians. However, studies are still lacking on thyroid axis of fish. In the present study, we investigated thyroid hormone levels (T3 and T4) and transcriptional patterns of 15 genes of the hypothalamic-pituitary-thyroid axis (HPT axis) in adult zebrafish that were exposed to solvent control and three measured concentrations of NET (7, 84 and 810 ng/L) for 90 days. The results indicated that NET significantly lowered T3 and T4 levels in both female and male zebrafish. Transcriptional expression profiles of some of the HPT-axis related genes were disrupted. Specifically, the expression levels of tshb and pax8 have increased significantly while dio2 and ugt1ab have decreased in females. In male, however, tshb expression levels were increased while ttr, ugt1ab, thra and thrb were decreased. The overall results demonstrate that NET disrupts thyroid endocrine system by interfering at multiple sites along HPT axis in adult zebrafish.

Norethindrone alters mating behaviors, ovary histology, hormone production and transcriptional expression of steroidogenic genes in zebrafish (Danio rerio)

The impact of progestins (i.e. synthetic forms of progesterone) on aquatic organisms has drawn increasing attention due to their widespread occurrence in the aquatic environments and potential effects on the endocrine system of fish. In this study, the effects of norethindrone (NET, a progestin) on the reproductive behavior, sex hormone production and transcriptional expressions were evaluated by exposing female zebrafish to NET at 0, 3.1, 36.2 and 398.6 ng L^-1 for 60 days. Results showed that NET impaired the mating behaviors of female at 36.2 and 398.6 ng L^-1 exhibited by males and increased the frequency of atretic follicular cells in the ovary exposed to NET at 398.6 ng L^-1. As for sex hormones, plasma testosterone concentration in zebrafish increased, while estradiol concentration decreased. Up-regulation of genes (Npr, Mpra, Mprβ, Fshβ, Lβ, Tshb, Nis and Dio2) was detected in the brain of fish exposed to NET at 398.6 ng L^-1. The transcriptional levels of genes (Esr1, Vtg1, Ar, Cyp19a, Cyp11b and Ptgs2) were generally inhibited in the ovary of zebrafish by NET at 398.6 ng L^-1. Moreover, the transcripts of genes (Vtg1, Esr1, Ar and Pgr) in the liver were reduced by NET at 36.2 and 398.6 ng L^-1. Our findings suggest that NET can potentially diminish the of fish populations not only by damaging their reproductive organs, but also by altering their mating behavior through the changes in the expressions of genes responsible for the production of sex hormones.