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

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.

Thyroid endocrine disruption and neurotoxicity of gestodene in adult female mosquitofish (Gambusia affinis)

The frequent detection of progestins in various aquatic environments and their potential endocrine disruptive effects in fish have attracted increasing attention worldwide. However, data on their effects on thyroid function and neurotoxicity in fish are limited, and the underlying mechanisms remain unclear. Here, the effects of gestodene (GES, a common progestin) on the thyroid endocrine and nervous systems of mosquitofish (Gambusia affinis) were studied. Adult female fish were exposed to GES at environmentally relevant concentrations (4.4-378.7 ng/L) for 60 days. The results showed that exposure to 378.7 ng/L GES caused a significant decrease in fish growth compared with the control and a marked reduction in the total distance traveled (50.6%) and swimming velocity (40.1-61.9%). The triiodothyronine (T3) levels were significantly increased by GES in a dose-dependent manner, whereas those of tetraiodothyronine (T4) were significantly decreased only at the G500 concentration. The acetylcholinesterase (AChE) activity was decreased significantly in the 4.42 ng/L GES treatments, but increased significantly at 378.67 ng/L. In the brain, a strong increase in the transcriptional levels of bdnf, trh, and dio2 was observed in fish after the 378.7 ng/L treatment. In addition, chronic exposure to GES caused colloid depletion with a concentration-dependent manner in the thyroid, and angiectasis, congestion, and vacuolar necrosis in the brain. These findings provide a better understanding of the effects of GES and associated underlying mechanisms in G. affinis.

The Effect of Unpredictable Chronic Stress on Rare Minnow (Gobiocypris rarus): Growth, Behaviour and Physiology

Fishes often adjust their behaviour patterns and physiological responses to cope with changing environments, and different life experiences affect them differently. Fishes might adapt to short-term stress, whereas long-term unpredictable stress may lead to various adverse effects. Although some studies have constructed unpredictable stress models of fish, the effect of unpredictable chronic stress (UCS) in the laboratory is poorly understood in fishes. In the current study, we exposed adult rare minnow to an unpredictable chronic stress protocol over 7 and 14 days and measured their response in terms of growth performance, cortisol, neurotransmitter levels (DA, 5-HT, and related metabolites), and behaviour patterns to comprehensively assess the effects of UCS on laboratory rare minnow. We discovered that specific growth rates were significantly decreased, and cortisol levels were lowered in both 7-days and 14-days stress groups. In the behaviour test, the activity level of the 14-days stress group increased, but there was no significant difference in the number of crossings to the center areas, time spent in the center areas, or the speed. In addition, the levels of DA and 5-HT did not change in the stress groups, but the DOPAC and 5-HIAA levels in the 14 days stress group were significantly higher than those in the control group. These results suggested that UCS influences rare minnow growth performance, behaviour patterns, and cortisol levels, and similar stress should be minimised in the laboratory.

Persistent impairment of gonadal development in rare minnow (Gobiocypris rarus) after chronic exposure to chlorinated polyfluorinated ether sulfonate

The delayed and persistent adverse effects caused by developmental exposure to per- and poly-fluorinated substances are of significant concern. Juvenile rare minnows (Gobiocypris rarus), were exposed to chlorinated polyfluoroalkyl ether sulfonate (Cl-PFESA) at measured medium concentrations of 86.5 μg/L, 162 μg/L and 329 μg/L, for 4 weeks followed by 12 weeks of depuration. After 4 weeks of exposure, the body weight and length of the juvenile fish were increased compared to controls. Gene expression of gnrh3, lhβ, and cyp19a was decreased, and ar and erα were upregulated. Transcriptomic analysis revealed enrichment of multiple pathways related to gonadal development. After 12 weeks of depuration, the gonadosomatic indices were decreased in female fish in a concentration-dependent manner, with a significant decrease to 59% of control in 329 μg/L group. Histological analysis found increasing numbers of degenerating oocytes and perinucleolar oocytes, and decreasing numbers of mature vitellogenic oocytes in female fish treated by Cl-PFESA. Enlarged interstitial space of the testis was observed in the exposed male fish. Gene expression levels of gnrh3, lhβ, ar, erα, and vtg were upregulated in the adult fish. Chronic developmental exposure to Cl-PFESA caused persistent effects on gonadal development of fish, highlighting the necessity of a comprehensive ecological risk assessment.

Integrated estrogenic effects and semi-volatile organic pollutants profile in secondary and tertiary wastewater treatment effluents in North China

Endocrine-disrupting effects on aquatic organisms caused by wastewater discharging have raised extensive concerns. However, the efficiency of various wastewater treatment processes to remove estrogenic activity in effluents and the association with organic micropollutants was not well known. We evaluated the estrogenic activity using a well-characterized in vivo bioassay featuring the Chinese rare minnows (Gobiocypris rarus) and analyzed 886 semi-volatile organic compounds (SVOCs) in effluents from four secondary wastewater treatment plants (SWTP A-D) and a tertiary wastewater treatment plant (TTP E) that utilized various common treatment processes in northern China. The final effluents from SWTPs and TTP E all exhibited estrogenic effects, increasing male fish plasma vitellogenin (VTG) contents and estradiol/testosterone (E₂/T) ratios. Key regulating genes in the male fish liver including vtg1, vtg3, era, erβ, and cyp19a were upregulated. TTP E demonstrated high performance in reducing estrogenic activity in the effluents, with a reduction of 64% in integrative biomarkers of estrogenic response (IBR). UV disinfection at SWTPs removed IBR by 14%- 33%, while ozone disinfection at TTP E did not reduce IBR. Several SVOCs including alkanes, chlorobenzenes, and phthalates, detected at ng/L to µg/L level, significantly correlated with effluent estrogenic activity. Our findings suggest the necessity and the potential means to improve the efficiency of current wastewater treatment approaches to achieve better protection for aquatic organisms against the joint effects of mixtures of various categories of micropollutants in effluents.

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.

Transcriptomic and proteomic analysis of Chinese rare minnow (Gobiocypris rarus) larvae in response to acute waterborne cadmium or mercury stress

In this study, Chinese rare minnow (Gobiocypris rarus) larvae were exposed to the control group, Cd concentrations (0.5 and 2.5 mg/L), and Hg concentrations (0.1 and 0.3 mg/L) for 96 h. Transcriptome analysis showed that 816 and 1599 significantly differentially expressed genes (DEGs) were identified in response to 2.5 mg/L Cd²⁺ and 0.3 mg/L Hg²⁺, respectively. Functional enrichment analysis revealed that DEGs were mostly associated with immune responses after Cd exposure, such as antigen processing and presentation, phagosome, apoptosis, and lysosome. Similarly, functional enrichment analysis showed that many pathways were mostly involved in metabolism after Hg exposure, such as glutathione metabolism and starch and sucrose metabolism. Results of two-dimensional electrophoresis (2-DE) showed that the abundance of 10 protein spots was significantly altered in the Cd²⁺ treatments. The proteomic analysis demonstrated that Cd toxicity might impair cytoskeletal and cell motility-related protein activity in the liver of G. rarus. Similarly, the abundance of 24 protein spots was significantly altered in the Hg²⁺ treatments. Hg toxicity regulates the expression of proteins belonging to several functional categories, including cytoskeleton, oxidative stress, digestive system, and energy metabolism. This study provides valuable relevant insight into the molecular mechanisms in response to Cd or Hg toxicity in aquatic organisms and will help screen for potential biomarkers to respond to Cd and Hg pollutants.

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.

The Effect of Environmental Enrichment on Laboratory Rare Minnows (Gobiocypris rarus): Growth, Physiology, and Behavior

Simple Summary

Environmental enrichment is an important part of animal welfare. In this study, rare minnow in different rearing conditions underwent comprehensive evaluation regarding growth, anxiety-like behavior, and physiology parameters. Results showed that there were no differences in SGR, anxiety-like behavior, DA, DOPAC, and 5-HIAA levels between control and enriched groups. However, the enriched group had higher cortisol and 5-HT levels. Therefore, researchers should focus on the effect of environmental enrichment regarding the welfare of rare minnow and how it effects the validity of data from laboratory studies.

Abstract

Environmental enrichment is a method to increase environmental heterogeneity, which may reduce stress and improve animal welfare. Previous studies have shown that environmental enrichment can increase the growth rate, decrease aggressive and anxiety-like behaviors, improve learning ability and agility, and reduce cortisol levels in animals. These effects usually differ between species. Unfortunately, habitat enrichment on laboratory fish is poorly studied and seldom adopted in care guidance. Rare minnows (Gobiocypris rarus) have been cultured as a native laboratory fish in China in barren banks without environmental enrichment since 1990; they have been widely used in studies on ecotoxicology, environmental science, and other topics. The purpose of this study was to investigate the effect of environment enrichment on the growth, physiological status, and anxiety-like behavior of laboratory rare minnows. We observed and analyzed SGR, cortisol levels, DA, DOPAC, 5-HT and 5-HIAA, and anxiety-like behavior indexes after one month of treatment in barren (control) and enrichment tanks. We found that there were no significant differences in SGR, anxiety-like behavior, DA, DOPAC, or 5-HIAA levels between the two treatments. However, higher cortisol and 5-HT levels were observed in the enrichment tanks. This study suggests that rare minnows might be influenced by their living environment, and future related studies should consider their environmental enrichment.

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.

Effect-Directed Analysis of Progestogens and Glucocorticoids at Trace Concentrations in River Water

Effect-based monitoring is increasingly applied to detect and-in conjunction with chemical analysis-to identify endocrine-disrupting compounds (EDCs) in the environment. Although this approach of effect-directed analysis has been successfully demonstrated for estrogenicity and androgenicity, data on progestogens and glucocorticoids driving endocrine disruption are quite limited. We investigated progestogenic and glucocorticoid activities in Danube River water receiving untreated wastewater from Novi Sad, Serbia. After a 2-step fractionation, all fractions were tested with reporter gene bioassays for agonistic and antagonistic hormonal responses at progestogenic and glucocorticoid hormone receptors as well as with target and nontarget analytical screening of active fractions by liquid chromatography-high-resolution mass spectrometry. Due to masking by cytotoxic mixture components, the effects could not be detected in the raw water extract but were unraveled only after fractionation. Target chemical screening of the fraction that was active in the progesterone receptor (PR) assay revealed that progesterone and megestrol acetate were predominant drivers of PR-mediated activity along with medroxyprogesterone, dihydrotestosterone, androsterone, and epiandrosterone. Hydrocortisone was detected at sub-ng/L concentration in the active fraction in the glucocorticoid receptor (GR) assay but could not explain a significant fraction of the observed GR activity. The present study indicates that effect-based monitoring is a powerful tool to detect EDCs in the aquatic environment but that fractionation may be required to avoid masking effects of mixture components. Future effect-directed analysis studies are required to better understand the occurrence of EDCs and masking compounds in different lipophilicity windows, to finally reduce fractionation requirements for monitoring to a smart clean-up. Environ Toxicol Chem 2019;39:189-199. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Bioconcentration and depuration of cadmium in the selected tissues of rare minnow (Gobiocypris rarus) and the effect of dietary mulberry leaf supplementation on depuration

A 56-day trial was conducted to elucidate the bioconcentration and depuration of Cd in the liver and muscle of rare minnow (Gobiocypris rarus) and determine the effect of dietary mulberry leaf supplementation on depuration. Juvenile rare minnow were exposed to environmentally relevant doses of Cd (1 and 10 μg/L) for 28 days of uptake and then allowed 28 days of depuration. The bioaccumulation factors of the treated rare minnow in the liver and muscle were calculated to be between 4.13-4.675 and 1.76-1.94, respectively. This results suggested that Cd had high potential for bioconcentration in rare minnow. To investigate the effect of dietary mulberry leaf supplementation on depuration, the remaining fish of each group were allowed to depurate with different ratios (0%, 10%, and 30% dry weight) of dietary mulberry leaf supplementation for an additional 28 days. Fish weights did not differ significantly (p >  0.05) between the control and mulberry leaf treated groups. Mulberry leaf powder did not significantly affect Cd depuration in the 10 μg/L group or in the muscle of the 1 μg/L group, but caused a significant decrease in Cd content in the liver of the 1 μg/L group (p <  0.05). This work was the first to model the bioconcentration of Cd in rare minnow and showed that mulberry leaf supplementation decreased Cd residues in the liver of the 1μg/L group. Such a finding may promote the development of new approaches to mitigate the potential hazards of heavy metals to human health.

Progesterone affects sex differentiation and alters transcriptional of genes along circadian rhythm signaling and hypothalamic-pituitary-gonadal axes in juvenile Yellow River Carp (Cyprinus carpio var.)

Progesterone (P4) is a biologically active steroid hormone that is involved in the regulation of oocyte growth and maturation, as well as development of the endometrium and implantation in the uterus of humans. It can also stimulate oocyte maturation in female fish, as well as spermatogenesis and sperm motility in male fish. Thus, P4 has been extensively used in human and animal husbandry as a typical progestin. However, P4 remaining in the water environment will pose a potential hazard to aquatic organisms. For example, it can interfere with sex differentiation and reproduction in aquatic vertebrates such as fish. Therefore, we investigated the effects of prolonged progesterone exposure on the expression of genes related to circadian rhythm signaling and the hypothalamic-pituitary-gonadal (HPG) axes in Yellow River Carp, which may have a potential impact on their sex differentiation. Our results suggested that P4 exposure altered the expression of genes related to circadian rhythm signaling, which can lead to disorders in the endocrine system and regulate the HPG axes-related activities. Furthermore, the expression of genes related to the HPG axes was also altered, which might affect gonadal development and the reproductive systems of Yellow River Carp. In addition, these changes may provide a plausible mechanism for the observed shifts in their sex ratio toward females.