A critical role of follicle-stimulating hormone (Fsh) in mediating the effect of clotrimazole on testicular steroidogenesis in adult zebrafish

The azole biocide climbazole induces oxidative stress, inflammation, and apoptosis in fish gut

Climbazole is an azole biocide that has been widely used in formulations of personal care products. Climbazole can cause developmental toxicity and endocrine disruption as well as gut disturbance in aquatic organisms. However, the mechanisms behind gut toxicity induced by climbazole still remain largely unclear in fish. Here, we evaluate the gut effects by exposing grass carp (Ctenopharyngodon idella) to climbazole at levels ranging from 0.2 to 20 μg/L for 42 days by evaluating gene transcription and expression, biochemical analyses, correlation network analysis, and molecular docking. Results showed that climbazole exposure increased cyp1a mRNA expression and ROS level in the three treatment groups. Climbazole also inhibited Nrf2 and Keap1 transcripts as well as proteins, and suppressed the transcript levels of their subordinate antioxidant molecules (cat, sod, and ho-1), increasing oxidative stress. Additionally, climbazole enhanced NF-κB and iκBα transcripts and proteins, and the transcripts of NF-κB downstream pro-inflammatory factors (tnfα, and il-1β/6/8), leading to inflammation. Climbazole increased pro-apoptosis-related genes (fadd, bad1, and caspase3), and decreased anti-apoptosis-associated genes (bcl2, and bcl-xl), suggesting a direct reaction to apoptosis. The molecular docking data showed that climbazole could form stable hydrogen bonds with CYP1A. Mechanistically, our findings suggested that climbazole can induce inflammation and oxidative stress through CYP450s/ROS/Nrf2/NF-κB pathways, resulting in cell apoptosis in the gut of grass carp.

Impaired spermatogenesis and associated endocrine effects of azole fungicides in peripubertal Xenopus tropicalis

Early life exposure to endocrine disrupting chemicals (EDCs) has been suggested to adversely affect reproductive health in humans and wildlife. Here, we characterize endocrine and adverse effects on the reproductive system after juvenile exposure to propiconazole (PROP) or imazalil (IMZ), two common azole fungicides with complex endocrine modes of action. Using the frog Xenopus tropicalis, two short-term (2-weeks) studies were conducted. I: Juveniles (2 weeks post metamorphosis (PM)) were exposed to 0, 17 or 178 µg PROP/L. II: Juveniles (6 weeks PM) were exposed to 0, 1, 12 or 154 µg IMZ/L. Histological analysis of the gonads revealed an increase in the number of dark spermatogonial stem cells (SSCs)/testis area, and in the ratio secondary spermatogonia: dark SSCs were increased in all IMZ groups compared to control. Key genes in gametogenesis, retinoic acid and sex steroid pathways were also analysed in the gonads. Testicular levels of 3β-hsd, ddx4 were increased and cyp19 and id4 levels were decreased in the IMZ groups. In PROP exposed males, increased testicular aldh1a2 levels were detected, but no histological effects observed. Although no effects on ovarian histology were detected, ovarian levels of esr1, rsbn1 were increased in PROP groups, and esr1 levels were decreased in IMZ groups. In conclusion, juvenile azole exposure disrupted testicular expression of key genes in retinoic acid (PROP) and sex steroid pathways and in gametogenesis (IMZ). Our results further show that exposure to environmental concentrations of IMZ disrupted spermatogenesis in the juvenile testis, which is a cause for concern as it may lead to impaired fertility. Testicular levels of id4, ddx4 and the id4:ddx4 ratio were associated with the number of dark SSCs and secondary spermatogonia suggesting that they may serve as a molecular markers for disrupted spermatogenesis.

Evaluation of parental and transgenerational effects of clotrimazole in Daphnia magna - A multi-parametric approach

Azole antifungals inhibit the cytochrome P450 complex, decreasing the production of ergosterol in fungi, and compromising the biosynthesis of ecdysteroids in crustaceans, which are hormones regulating reproduction and ecdysis. The azole antifungal clotrimazole (CLO) raises environmental concerns due its toxicity. This work evaluated the effects on the number of moults, feeding rate, growth, reproduction, transgenerational reproductive effects on two different generations (F0, parental generation; and F1, organisms born from F0), and energetic balance in Daphnia magna. Neonates (<24 h) were exposed to sublethal concentrations (0, 2.7, and 3.4 mg/L) of CLO, to assess its effects on the moulting process. Neonates were also exposed to environmentally realistic concentrations of CLO (0, 30, 150, 750, and 3750 ng/L) for 24 and 96 h, to assess adverse effects on their feeding behaviour. Effects on energy reserves (fatty acids, glycogen, and protein levels) were also measured in animals exposed to CLO. A reproduction test was carried out to evaluate the amount and size of neonates from F0 and F1 generations. CLO exposure decreased the number of moults, and the size of organisms, but did not alter the feeding pattern of 5 days old individuals. However, neonates (<24 h) exposed to CLO had a significant decrease in their feeding pattern. CLO decreased the fatty acids content in exposed animals, but did not change glycogen and protein. CLO also decreased the size of adult daphnids from the third brood, born from animals exposed in F0; in F1 animals, the size of neonates from the third brood was decreased. This study evidenced the toxic effects caused by CLO on growth, feeding and reproduction of D. magna. Nevertheless, it is not possible to conclude whether the effects are due to the inhibition of cytochrome P450 enzymes, or to unspecific effects caused by general toxic stress and decreased nutrition.

Endocrine disruption by azole fungicides in fish: A review of the evidence

Azole fungicides are widely used chemicals in agriculture and medicine. Their antifungal activity involves inhibition of steroid biosynthesis via inhibition of several cytochrome p450 enzymes. Evidence is accumulating in fish species to suggest azole fungicides perturb multiple hormone signaling pathways. The objective of this review was to comprehensively review data for azole-mediated impacts on the teleost endocrine system. We emphasize aspects of azole-induced endocrine disruption in several fish species, with special focus on the hypothalamic-pituitary-gonadal (HPG), hypothalamus-pituitary-thyroid (HPT) and hypothalamic-pituitary-adrenal (HPA) axis. Histopathological, physiological, and molecular data suggest azole fungicides at environmentally relevant concentrations and above are endocrine disruptors in fish. Endocrine disruption has been well documented for some azoles (e.g., difenconazole, fadrozole, ketoconazole, tebuconazole, triadimefon), but there are little data for others (e.g., cyproconazole, expoxiconazole, imidazole, metoconazole, nocodazole) in fish, revealing a knowledge gap in our understanding of azole toxicity. Based upon literature, computational analyses of transcriptome responses revealed progesterone-mediated oocyte maturation, insulin signaling pathway, adrenergic signaling, and metabolism of angiotensinogen may be processes disrupted by azoles. However, hormonal regulation of the sympathetic nervous system and the cardiovascular system in response to azole exposure has yet to be investigated in fish. Recommendations for studies moving forward include focus on non-steroid endocrine pathways, mechanisms of neuroendocrine disruption, and transgenerational effects of azoles on fish. This critical review identifies knowledge gaps and future directions for environmental studies focused on the effects of azoles in aquatic species.

Igf3: a novel player in fish reproduction†

As in other vertebrates, fish reproduction is tightly controlled by gonadotropin signaling. One of the most perplexing aspects of gonadotropin action on germ cell biology is the restricted expression of gonadotropin receptors in somatic cells of the gonads. Therefore, the identification of factors conveying the action of gonadotropins on germ cells is particularly important for understanding the mechanism of reproduction. Insulin-like growth factors (Igfs) are recognized as key factors in regulating reproduction by triggering a series of physiological processes in vertebrates. Recently, a novel member of Igfs called Igf3 has been identified in teleost. Different from the conventional Igf1 and Igf2 that are ubiquitously expressed in a majority of tissues, Igf3 is solely or highly expressed in the fish gonads. The role of Igf3 in mediating the action of gonadotropin through Igf type 1 receptor on several aspects of oogenesis and spermatogenesis have been demonstrated in several fish species. In this review, we will summarize existing data on Igf3. This new information obtained from Igf3 provides insight into elucidating the molecular mechanism of fish reproduction, and also highlights the importance of Igf system in mediating the action of gonadotropin signaling on animal reproduction.

Multi-Parametric Portfolio to Assess the Fitness and Gonadal Maturation in Four Key Reproductive Phases of Brown Trout

Simple Summary

Brown trout is a freshwater fish with economic importance and with a great potential to be used as an environmental biosensor species. Despite being selected as a model species in distinct scientific contexts, in cultured specimens, there is a surprising lack of works investigating the morpho-physiological changes associated with the reproductive cycle; particularly concerning the gonads. In this study, a multi-parameter portfolio of biometric, biochemical, hormonal, and morphological analysis was established, which allowed a seasonal and sex characterization of the gonad status of adult brown trout males and females. Sampling included four reproductive phases: spawning capable (December), regressing (March), regenerating (July), and developing (November). Sex- and season-specific changes were described. The discriminative parameters characterized here stand now as normal baseline values against which abnormal patterns can be compared with. These parameters have the potential to be used as tools for the environmental monitoring of the reproductive status of wild populations and for the control of breeding stocks in aquaculture.

Abstract

Brown trout is an environmental freshwater sentinel species and is economically important for recreational fishing and aquaculture. Despite that, there is limited knowledge regarding morpho-physiological variations in adults throughout the reproductive cycle. Thus, this study aimed to analyze the fitness and gonadal maturation of cultured adult brown trout in four reproductive phases (spawning capable—December, regressing—March, regenerating—July, and developing—November). The systematic evaluation of males and females was based on biometric, biochemical, and hormonal parameters, along with a histomorphological grading of gonads and the immunophenotype location of key steroidogenic enzymes. The total weight and lengths reached the lowest levels in December. Gonad weights were higher in December and November, while the opposite pattern was found for liver weights. The lowest levels of cholesterol and total protein were also noted during those stages. The 11-ketotestosterone (11-KT) and testosterone (T) for males, and estradiol (E2) and T for females, mostly explained the hormonal variations. The immunohistochemistry of cytochrome P450c17 (CYP17-I), aromatase (CYP19), and 17β-hydroxysteroid dehydrogenase (17β-HSD) showed sex and site-specific patterns in the distinct reproductive phases. The sex- and season-specific changes generated discriminative multi-parameter profiles, serving as a tool for environmental and aquaculture surveys.

A comprehensive review on environmental toxicity of azole compounds to fish

BACKGROUND

Azoles are considered as one of the most efficient fungicides for the treatment of humans, animals, and plant fungal pathogens. They are of significant clinical importance as antifungal drugs and are widely used in personal care products, ultraviolet stabilizers, and in aircraft for its anti-corrosive properties. The prevalence of azole compounds in the natural environment and its accumulation in fish raises questions about its impact on aquatic organisms.

OBJECTIVES

The objective of this paper is to review the scientific studies on the effects of azole compounds in fish and to discuss future opportunities for the risk evaluation.

METHODS

A systematic literature search was conducted on Web of Science, PubMed, and ScienceDirect to locate peer-reviewed scientific articles on occurrence, environmental fate, and toxicological impact of azole fungicides on fish.

RESULTS

Studies included in this review provide ample evidence that azole compounds are not only commonly detected in the natural environment but also cause several detrimental effects on fish. Future studies with environmentally relevant concentrations of azole alone or in combination with other commonly occurring contaminants in a multigenerational study could provide a better understanding.

CONCLUSION

Based on current knowledge and studies reporting adverse biological effects of azole on fish, considerable attention is required for better management and effective ecological risk assessment of these emerging contaminants.

Identification and characteristics of insulin-like growth factor system in the brain, liver, and gonad during development of a seasonal breeding teleost, Pampus argenteus

Reproductive activity is closely related to the development and function of the brain and liver in teleosts, particularly in seasonal breeding teleosts. This study measured the involvement of the insulin-like growth factor (IGF) system in controlling the reproduction of the silver pomfret Pampus argenteus, a seasonal breeding tropical to temperate commercial fish. We cloned and characterized the cDNAs of igfs (igf2 and igf3) and igfrs (igf1ra, igf1rb, and igf2r) and examined their transcript levels in relation to seasonal reproduction. Phylogenetic analyses revealed that two types of IGFs (IGF-1 and IGF-2) and three types of IGFRs (IGF1RA, IGF1RB, and IGF2R) of the silver pomfret were clustered with those of teleosts; however, IGF-3 was a transmembrane protein different with the IGF-3 of other teleosts. The expression of IGF-3 was gonad-specific in the silver pomfret. The transcript levels of igf1 in the female brain were the highest, and the levels of igfrs in both sexes' brains increased during gametogenesis. Meanwhile, igfs and igfrs maintained high transcript levels in both sexes' liver and gonad during vitellogenesis and spermatogonia proliferation. We concluded that the development and activities of brain, liver, and gonad were related to the IGF system (IGFs and IGFRs). And the IGFs were mainly expressed in the liver. Nevertheless, gonadal development, especially vitellogenesis and spermatogonia proliferation, were related with IGFs in this species.

A critical role of foxp3a-positive regulatory T cells in maintaining immune homeostasis in zebrafish testis development

Suppressive regulatory T cells (Treg cells) play a vital role in preventing autoimmunity and restraining excessive immune response to both self- and non-self-antigens. Studies on humans and mice show that the Forkhead box p3 (Foxp3) is a key regulatory gene for the development and function of Treg cells. In zebrafish, Treg cells have been identified by using foxp3a as a reliable marker. However, little is known about the function of foxp3a and Treg cells in gonadal development and sex differentiation. Here, we show that foxp3a is essential for maintaining immune homeostasis in zebrafish testis development. We found that foxp3a was specifically expressed in a subset of T cells in zebrafish testis, while knockout of foxp3a led to deficiency of foxp3a-positive Treg cells in the testis. More than 80% of foxp3a^-/- mutants developed as subfertile males, and the rest of the mutants developed as fertile females with decreased ovulation. Further study revealed that foxp3a^-/- mutants had a delayed juvenile ovary-to-testis transition in definite males and sex reversal in about half of the definite females, which led to a dominance of later male development. Owing to the absence of foxp3a-positive Treg cells in the differentiating testis of foxp3a^-/- mutants, abundant T cells and macrophages expand to disrupt an immunosuppressive milieu, resulting in defective development of germ cells and gonadal somatic cells and leading to development of infertile males. Therefore, our study reveals that foxp3a-positive Treg cells play an essential role in the orchestration of gonadal development and sex differentiation in zebrafish.

Regulation of spermatogonial development by Fsh: The complementary roles of locally produced Igf and Wnt signaling molecules in adult zebrafish testis

Spermatogenesis is a cellular developmental process characterized by the coordinated proliferation and differentiation activities of somatic and germ cells in order to produce a large number of spermatozoa, the cellular basis of male fertility. Somatic cells in the testis, such as Leydig, peritubular myoid and Sertoli cells, provide structural and metabolic support and contribute to the regulatory microenvironment required for proper germ cell survival and development. The pituitary follicle-stimulating hormone (Fsh) is a major endocrine regulator of vertebrate spermatogenesis, targeting somatic cell functions in the testes. In fish, Fsh regulates Leydig and Sertoli cell functions, such as sex steroid and growth factor production, processes that also control the development of spermatogonia, the germ cell stages at the basis of the spermatogenic process. Here, we summarize recent advances in our understanding of mechanisms used by Fsh to regulate the development of spermatogonia. This involves discussing the roles of insulin-like growth factor (Igf) 3 and canonical and non-canonical Wnt signaling pathways. We will also discuss how these locally active regulatory systems interact to maintain testis tissue homeostasis.

Identification of a Novel Zebrafish Mutant Line that Develops Testicular Germ Cell Tumors

Testicular tumors are the most common solid malignant tumors in men 20-35 years of age. Although most of testicular tumors are curable, current treatments still fail in 15%-20% of patients. However, insufficient understanding of the molecular basis and lack of animal models limit development of more effective treatments. This study reports the identification of a novel zebrafish mutant line, ns1402, which develops testicular germ cell tumors (TGCTs). While both male and female ns1402 mutants were fertile at young age, male ns1402 mutants became infertile as early as 9 months of age. This infertility was associated with progressive loss of mature sperm. Failure of spermatogenesis was, at least in part, explained by progressive loss of mature Leydig cells, a source of testosterone that is essential for spermatogenesis. Interestingly, TGCTs in ns1402 mutants contained a large number of Sertoli cells and gene expression profiles of Sertoli cells were altered before loss of mature Leydig cells. This suggests that changes in Sertoli cell properties happened first, followed by loss of mature Leydig cells and failure of spermatogenesis. Taken together, this study emphasizes the importance of cell-cell interactions and cell signaling in the testis for spermatogenesis and tissue homeostasis.

In vitro effects of diosmin, naringenin, quercetin and indole-3-carbinol on fish hepatic CYP1A1 in the presence of clotrimazole and dexamethasone

Phytochemicals are widely present in fruits, vegetables and other plants and have great health benefits owing to their antioxidant properties. They are naturally found in the aquatic environment as well as discharged from sewage treatment plants after their large consumption. Little is known about their impact on fish; particularly in light of their interactions with pharmaceuticals. Therefore, this study was designed to determine the effects of diosmin, naringenin, quercetin and idole-3-carbinol on CYP1A-dependent 7-ethoxyresorufin-O-deethylase (EROD) activity on rainbow trout hepatic microsomes in the presence of two pharmaceuticals: clotrimazole and dexamethasone. The interactions between the phytochemicals and pharmaceuticals used in this study were determined using a combination index. Hepatic microsomes were exposed to two concentrations (1-or 50 μM) of phytochemicals and pharmaceuticals separately and in combinations. Singly, clotrimazole inhibited EROD activity 40% and 90% of control, while dexamethasone did not. Naringenin and diosmin inhibited EROD activity alone up to 90% and 55% respectively, but activities were further inhibited in the presence of either pharmaceutical. The preliminary study of combinations of clotrimazole with phytochemicals primarily showed synergistic effects. While EROD activity was not inhibited in the presence of quercetin or indole-3-carbinol, significant and synergistic inhibition was detected when either of these was combined with clotrimazole or dexamethasone.

Distinct and Cooperative Roles of amh and dmrt1 in Self-Renewal and Differentiation of Male Germ Cells in Zebrafish

Spermatogenesis is a fundamental process in male reproductive biology and depends on precise balance between self-renewal and differentiation of male germ cells. However, the regulative factors for controlling the balance are poorly understood. In this study, we examined the roles of amh and dmrt1 in male germ cell development by generating their mutants with Crispr/Cas9 technology in zebrafish. Amh mutant zebrafish displayed a female-biased sex ratio, and both male and female amh mutants developed hypertrophic gonads due to uncontrolled proliferation and impaired differentiation of germ cells. A large number of proliferating spermatogonium-like cells were observed within testicular lobules of the amh-mutated testes, and they were demonstrated to be both Vasa- and PH3-positive. Moreover, the average number of Sycp3- and Vasa-positive cells in the amh mutants was significantly lower than in wild-type testes, suggesting a severely impaired differentiation of male germ cells. Conversely, all the dmrt1-mutated testes displayed severe testicular developmental defects and gradual loss of all Vasa-positive germ cells by inhibiting their self-renewal and inducing apoptosis. In addition, several germ cell and Sertoli cell marker genes were significantly downregulated, whereas a prominent increase of Insl3-positive Leydig cells was revealed by immunohistochemical analysis in the disorganized dmrt1-mutated testes. Our data suggest that amh might act as a guardian to control the balance between proliferation and differentiation of male germ cells, whereas dmrt1 might be required for the maintenance, self-renewal, and differentiation of male germ cells. Significantly, this study unravels novel functions of amh gene in fish.

Antagonistic regulation of spermatogonial differentiation in zebrafish (Danio rerio) by Igf3 and Amh

Fsh-mediated regulation of zebrafish spermatogenesis includes modulating the expression of testicular growth factors. Here, we study if and how two Sertoli cell-derived Fsh-responsive growth factors, anti-Müllerian hormone (Amh; inhibiting steroidogenesis and germ cell differentiation) and insulin-like growth factor 3 (Igf3; stimulating germ cell differentiation), cooperate in regulating spermatogonial development. In dose response and time course experiments with primary testis tissue cultures, Fsh up-regulated igf3 transcript levels and down-regulated amh transcript levels; igf3 transcript levels were more rapidly up-regulated and responded to lower Fsh concentrations than were required to decrease amh mRNA levels. Quantification of immunoreactive Amh and Igf3 on testis sections showed that Fsh increased slightly Igf3 staining but decreased clearly Amh staining. Studying the direct interaction of the two growth factors showed that Amh compromised Igf3-stimulated proliferation of type A (both undifferentiated [A_und] and differentiating [A_diff]) spermatogonia. Also the proliferation of those Sertoli cells associated with A_und spermatogonia was reduced by Amh. To gain more insight into how Amh inhibits germ cell development, we examined Amh-induced changes in testicular gene expression by RNA sequencing. The majority (69%) of the differentially expressed genes was down-regulated by Amh, including several stimulators of spermatogenesis, such as igf3 and steroidogenesis-related genes. At the same time, Amh increased the expression of inhibitory signals, such as inha and id3, or facilitated prostaglandin E₂ (PGE₂) signaling. Evaluating one of the potentially inhibitory signals, we indeed found in tissue culture experiments that PGE₂ promoted the accumulation of A_und at the expense of A_diff and B spermatogonia. Our data suggest that an important aspect of Fsh bioactivity in stimulating spermatogenesis is implemented by restricting the different inhibitory effects of Amh and by counterbalancing them with stimulatory signals, such as Igf3.

Semicarbazide disturbs the reproductive system of male zebrafish (Danio rerio) through the GABAergic system

Semicarbazide (SMC), an emerging water contaminant, exerts anti-estrogenic effects in female zebrafish. However, the exact influence of SMC on male reproduction remains unclear. In this study, adult male zebrafish were exposed to 1-1000μg/L SMC in a semi-static system for 28 d prior to examining the testicular somatic index (TSI), testis histology, plasma sex hormone levels, and the transcription of genes involved in reproduction. The results showed that testicular morphology was altered and TSI was down-regulated by high concentrations of SMC (≥100μg/L and 1000μg/L, respectively). Plasma testosterone and 17β-estradiol concentrations were significantly decreased by all of the SMC treatments, along with down-regulation of the corresponding steroidogenic gene transcripts. These changes were associated with the inhibition of gamma-aminobutyric acid synthesis and function, in addition to the decreased expression of reproductive regulators. Our results contribute to elucidating the mechanisms underlying the adverse reproductive effects of SMC in male zebrafish.

Behavioural effect of low-dose BPA on male zebrafish: Tuning of male mating competition and female mating preference during courtship process

The ubiquity of environmental pollution by endocrine disrupting chemicals (EDCs) such as bisphenol A (BPA) is progressively considered as a major threat to aquatic ecosystems worldwide. Numerous toxicological studies have proved that BPA are hazardous to aquatic environment, along with alterations in the development and physiology of aquatic vertebrates. However, generally, there is a paucity in knowledge of behavioural and physiological effects of BPA with low concentration, for example, 0.22 nM (50 ng/L) and 2.2 nM (500 ng/L). Here we show that treatment of adult male zebrafish (Danio rerio) with 7 weeks low-dose (0.22 nM-2.2 nM) BPA, resulted in alteration in histological structure of testis tissue and abnormality in expression levels of genes involved in testicular steroidogenesis. Furthermore, low-dose BPA treatment decreased the male locomotion during courtship; and was associated with less courtship behaviours to female but more aggressive behaviours to mating competitor. Interestingly, during the courtship test, we observed that female preferred control male to male under low-dose BPA exposure. Subsequently, we found that the ability of female to chose optimal mating male through socially mutual interaction and dynamics of male zebrafish, which was based on visual discrimination. In sum, our results shed light on the potential behavioural and physiological effect of low-dose BPA exposure on courtship behaviours of zebrafish, which could exert profound consequences on natural zebrafish populations.

Sub-lethal effects and bioconcentration of the human pharmaceutical clotrimazole in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to characterize biomarker responses, haematological profiles, structural changes and uptake in juvenile rainbow trout exposed to clotrimazole (CLO) at three concentrations (0.01 - [lowest environmentally relevant concentration], 1.0 [highest environmentally relevant concentration] and 10 μg L(-1)) in a semi-static system over a period of 42 days. Antioxidant defence enzymes, which responded to CLO exposure, changed the oxidative stress status of cells, but no differences were observed in lipid peroxidation. Clotrimazole triggered a biphasic response of CYP3A-like activity in liver microsomes, which may indicate a detoxification process in the liver. Histopathological alterations were most pronounced in kidneys and testes in the group exposed to 10 μg L(-1). Structural changes in the kidney included tubulonephrosis and hyaline droplet degeneration in the tubular epithelial cells. The relative proportions of germ cells in testes were changed: The number of spermatozoa was reduced, and the spermatogonia and spermatocytes were increased. The highest CLO concentration was detected in fish liver (3710 ng per gram wet tissue) and kidney (4280 ng per gram wet tissue). Depuration half-life was estimated to be 72, 159, and 682 h in liver, muscle, and kidney, respectively. Taken together, these results provide valuable toxicological data on the effects of CLO on aquatic non-target organisms, which could be useful for further understanding of the potential risks in the real aquatic environment.

Genetic and structural analyses of cytochrome P450 hydroxylases in sex hormone biosynthesis: Sequential origin and subsequent coevolution

Biosynthesis of steroid hormones in vertebrates involves three cytochrome P450 hydroxylases, CYP11A1, CYP17A1 and CYP19A1, which catalyze sequential steps in steroidogenesis. These enzymes are conserved in the vertebrates, but their origin and existence in other chordate subphyla (Tunicata and Cephalochordata) have not been clearly established. In this study, selected protein sequences of CYP11A1, CYP17A1 and CYP19A1 were compiled and analyzed using multiple sequence alignment and phylogenetic analysis. Our analyses show that cephalochordates have sequences orthologous to vertebrate CYP11A1, CYP17A1 or CYP19A1, and that echinoderms and hemichordates possess CYP11-like but not CYP19 genes. While the cephalochordate sequences have low identity with the vertebrate sequences, reflecting evolutionary distance, the data show apparent origin of CYP11 prior to the evolution of CYP19 and possibly CYP17, thus indicating a sequential origin of these functionally related steroidogenic CYPs. Co-occurrence of the three CYPs in early chordates suggests that the three genes may have coevolved thereafter, and that functional conservation should be reflected in functionally important residues in the proteins. CYP19A1 has the largest number of conserved residues while CYP11A1 sequences are less conserved. Structural analyses of human CYP11A1, CYP17A1 and CYP19A1 show that critical substrate binding site residues are highly conserved in each enzyme family. The results emphasize that the steroidogenic pathways producing glucocorticoids and reproductive steroids are several hundred million years old and that the catalytic structural elements of the enzymes have been conserved over the same period of time. Analysis of these elements may help to identify when precursor functions linked to these enzymes first arose.

Occurrence, fate and ecological risk of five typical azole fungicides as therapeutic and personal care products in the environment: A review

Azole fungicides are widely used to treat fungal infection in human. After application, these chemicals may reach to the receiving environment via direct or indirect discharge of wastewaters, thus posing potential risks to non-target organisms. We aimed to review the occurrence, fate and toxicological effects of some representative household azole fungicides in the environment. Azole fungicides were widely detected in surface water and sediment of the aquatic environment due to their incomplete removal in wastewater treatment plants. These chemicals are found resistant to microbial degradation, but can undergo photolysis under UV irradiation. Due to different physiochemical properties, azole fungicides showed different environmental behaviors. The residues of azole fungicides could cause toxic effects on aquatic organisms such as algae and fish. The reported effects include regulation changes in expression of cytochrome P450-related genes and alteration in CYP450-regulated steroidogenesis causing endocrine disruption in fish. Further studies are essential to investigate the removal of azole fungicides by advanced treatment technologies, environmental fate such as natural photolysis, and toxic pathways in aquatic organisms.

Effects of pharmaceuticals present in aquatic environment on Phase I metabolism in fish

The fate of pharmaceuticals in aquatic environments is an issue of concern. Current evidence indicates that the risks to fish greatly depend on the nature and concentrations of the pharmaceuticals and might be species-specific. Assessment of risks associated with the presence of pharmaceuticals in water is hindered by an incomplete understanding of the metabolism of these pharmaceuticals in aquatic species. In mammals and fish, pharmaceuticals are primarily metabolized by cytochrome P450 enzymes (CYP450). Thus, CYP450 activity is a crucial factor determining the detoxification abilities of organisms. Massive numbers of toxicological studies have investigated the interactions of human pharmaceuticals with detoxification systems in various fish species. In this paper, we review the effects of pharmaceuticals found in aquatic environments on fish hepatic CYP450. Moreover, we discuss the roles of nuclear receptors in cellular regulation and the effects of various groups of chemicals on fish, presented in the recent literature.

In vitro and in vivo studies of the endocrine disrupting potency of cadmium in roach (Rutilus rutilus) liver

Cadmium has been reported to exert estrogenic, antiestrogenic or both effects in vertebrate species. To elucidate the endocrine disrupting action of CdCl2, ex vivo and in vivo experiments were performed in roach (Rutilus rutilus). Roach liver explants were exposed to a range of CdCl2 concentrations alone (0.1-50μM) or with an effective concentration (100nM) of 17β-estradiol (E2). In addition, juvenile roach were intraperitoneally injected with CdCl2 (0.1-2.5mg/kg) with or without 1mg E2/kg. Subsequent analysis evaluated the effect of CdCl2 on vitellogenin (VTG) synthesis both at the mRNA and protein level, on estrogen receptors (erα and erβ1) and on androgen receptor (ar) mRNA expression. Ex vivo and in vivo experiments indicated that CdCl2 is strongly anti-estrogenic as, when co-exposed to E2, CdCl2 significantly inhibited VTG production as well as vtg and erα mRNA expressions. Moreover, CdCl2 compromised the E2-mediated induction of the ar mRNA expression in vivo.

Localization of steroidogenic enzymes and Foxl2a in the gonads of mature zebrafish (Danio rerio)

In zebrafish, the identification of the cells expressing steroidogenic enzymes and their regulators is far from completely fulfilled though it could provide crucial information on the elucidation of the role of these enzymes. The aim of this study was to better characterize the expression pattern of steroidogenic enzymes involved in estrogen and androgen production (Cyp17-I, Cyp11c1, Cyp19a1a and Cyp19a1b) and one of their regulators (Foxl2a) in zebrafish gonads. By using immunohistochemistry, we localized the steroid-producing cells in mature zebrafish gonads and determined different expression patterns between males and females. All these steroidogenic enzymes and Foxl2a were detected both in the testis and ovary. In the testis, they were all localized both in Leydig and germ cells except Cyp19a1b which was only detected in germ cells. In the ovary, Cyp17-I, Cyp19a1a and Foxl2a were immunolocalized in both somatic and germ cells while Cyp19a1b was only detected in germ cells and Cyp11c1 in somatic cells. Moreover, Cyp19a1a and Foxl2a did not display exactly the same patterns of spatial localization but their expressions were correlated suggesting a possible regulation of cyp19a1a gene by Foxl2a in zebrafish. Comparative analysis revealed a dimorphic expression of Cyp11c1, Cyp19a1a, Cyp19a1b and Foxl2a between males and females. Overall, our study provides a detailed description of the expression of proteins involved in the biosynthesis of steroidal hormones at the cellular scale within gonads, which is critical to further elucidating the intimate roles of the enzymes and the use of the zebrafish as a model in the field of endocrinology.

Androgens directly stimulate spermatogonial differentiation in juvenile Atlantic salmon (Salmo salar)

We studied the effects of androgens on early stages of spermatogenesis along with androgen receptor binding characteristics and the expression of selected testicular and pituitary genes. To this end, immature Atlantic salmon postsmolts received testosterone (T), adrenosterone (OA, which is converted in vivo into 11-ketotestosterone, 11-KT) or a combination of the two androgens (T+OA). Treatment with OA and T elevated the plasma levels of 11-KT and T, respectively, and co-injection of OA with T lead to high 11-KT levels but prevented plasma T levels to reach the levels observed after injecting T alone. Clear stimulatory effects were recorded as regards pituitary lhb and gnrhr4 transcript levels in fish receiving T, and to a lesser extent in fish receiving OA (but for the lhb transcript only). The two androgen receptors (Ara1 and Ara2) we cloned bound T and 11-KT and responded to these androgens in a similar way. Both androgens down-regulated testicular amh and increased igf3 transcript levels after 1 week of treatment, but effects on growth factor gene expression required sustained androgen stimulation and faded out in the groups with the decreasing T plasma levels. In fish exhibiting a sustained elevation of 11-KT plasma levels (OA and T+OA groups) for 2 weeks, the number of differentiating spermatogonia had increased while the number of undifferentiated spermatogonia decreased. Previous work showed that circulating gonadotropin levels did not increase following androgen treatments of gonad-intact immature male salmonids. Taken together, androgen treatment of immature males modulated testicular growth factor expression that, when sustained for 2 weeks, stimulated differentiation, but not self-renewal, of undifferentiated type A spermatogonia.

Evaluation of HODE-15, FDE-15, CDE-15, and BDE-15 toxicity on adult and embryonic zebrafish (Danio rerio)

Diphenyl ether and its derivatives are widely used in the industry of spices, dyes, agrochemicals, and pharmaceuticals. Following the previous study, we selected 4,4'-dihydroxydiphenyl ether, 4,4'-difluorodiphenyl ether, 4,4'-dichlorodiphenyl ether, and 4,4'-dibromodiphenyl ether as research objects. The LC50 (96 h) values for these compounds in adult zebrafish were determined with the acute test. Also, developmental toxicities of the four substances to zebrafish embryos were observed at 24, 48, 72, and 96 hpf. All the LC50 (96 h) values of these compounds were between 1 and 10 mg/L, suggesting that they all had moderate toxicity to adult zebrafish. The embryonic test demonstrated that with increasing doses, 4,4'-dihydroxydiphenyl ether decreased the hatching rate, while 4,4'-difluorodiphenyl ether, 4,4'-dichlorodiphenyl ether, and 4,4'-dibromodiphenyl ether delayed the hatching time but had little effect on final hatchability at 96 hpf. All of these compounds inhibited larval growth, especially 4,4'-dihydroxydiphenyl ether. Exposure to these chemicals induced embryo yolk sac and pericardial edema. Spine deformation was visible in hatched larvae after 96 hpf 4,4'-dihydroxydiphenyl ether exposure, while tail curvature was observed for the halogenated compounds. The overall results indicated that 4,4'-dihydroxydiphenyl ether, 4,4'-difluorodiphenyl ether, 4,4'-dichlorodiphenyl ether, and 4,4'-dibromodiphenyl ether all had significant toxicity on adult and embryonic zebrafish.

Endocrine disrupting compounds affecting corticosteroid signaling pathways in Czech and Swiss waters: potential impact on fish

This study investigated the occurrence of corticosteroid signaling disruptors in wastewaters and rivers in the Czech Republic and in Switzerland. 36 target compounds were detected using HPLC-MS/MS, with up to 6.4 μg/L for azole antifungals that indirectly affect corticosteroid signaling. Glucocorticoid receptor (GR)-mediated activity was determined using the GR-CALUX bioassay with dexamethasone equivalent concentrations ranging from <LOD-2.6, 19-37, and 78-542 ng/L for river water, treated, and untreated wastewater, respectively. For most samples, the chemically predicted GR-mediated response was higher than that determined by the bioassay. Correspondingly, antiglucocorticoid activity was observed in some fractions. The fish plasma model (FPM), which predicts plasma concentrations, was applied to evaluate the potential of detected pharmaceuticals to cause receptor-mediated effects in fish. With one exception, medroxyprogesterone, the FPM applied to individual compounds predicted fish plasma concentrations to be below the level of human therapeutic plasma concentrations. To account for the activity of the sum of GR-active compounds, we introduce the "cortisol equivalents fish plasma concentration" approach, through which an increase in fish glucocorticoid plasma levels comparable to 0.9-83 ng/mL cortisol after exposure to the analyzed river waters was estimated. The results suggest that these chemicals may impact wild fish.

Gene expression profiling of key genes in hypothalamus-pituitary-gonad axis of rare minnow Gobiocypris rarus in response to EE2

The 17α-ethinylestradiol (EE2), which could induce estrogenic effects, is found in different aquatic systems. The current study aimed to assess in vivo effects of short-term EE2 exposure on the transcriptional activity of genes in the brain and gonad tissues in order to characterize the mode of action of EE2 on the hypothalamus-pituitary-gonad axis in rare minnow (Gobiocypris rarus). The full length cDNAs of fshβ, lhβ, fshr and lhr were first characterized in G. rarus. The homology and phylogenetic analyses of the amino acid sequences revealed that these four genes share high identity in cyprinid fish. The tissue distribution analysis by qRT-PCR showed that fshβ and lhβ were mainly expressed in the brain and fshr and lhr were mainly expressed in gonads. Adult G. rarus was exposed to EE2 at 1, 5, 25 and 125 ng/L for 3 and 6 days and the expression of brain cyp19a1b, fshβ and lhβ, estrogen receptors (esr1, esr2a, and esr2b) and gonadal fshr, lhr and cyp19a1a were assessed. Cyp19a1b was significantly up-regulated in the brains of female exposed to EE2 at 1-125 ng/L for 6 days. The brain lhβ, but not fshβ was strongly suppressed in most EE2 exposure groups of both sexes. The brain esr2b was inhibited in both sexes exposed to EE2 at all of the four concentrations for 6 days. Esr2a was up-regulated in the females by 6-day EE2 treatment at 1 and 25 ng/L. The high responsiveness of brain lhβ and esr2s to EE2 and their significant correlation in both sexes suggested that the transcriptional activity of Esr2s could play key roles in modulation of lhβ expression via direct action on gonadotropic cells in response to EE2. In gonads, fshr was strongly inhibited by EE2 in males, while lhr was significantly stimulated by EE2 in females. Cyp19a1a was inhibited by EE2 in both sexes. The positive correlations of gene expressions of both fshr and lhr with cyp19a1a in testes suggest that the suppression of 17α-estradiol (E2) synthesis in testis by exogenous estrogen could mediate via both Fsh/Fshr and Lh/Lhr signaling in male G. rarus.

Effects of low concentrations of the antiprogestin mifepristone (RU486) in adults and embryos of zebrafish (Danio rerio): 1. Reproductive and early developmental effects

Effects of synthetic progestins have recently been reported in fish, but potential effects of the synthetic antiprogestin mifepristone (MIF), also called RU486, have not been studied. The present study provides first insights into reproductive effects of MIF in zebrafish in comparison to the progesterone receptor agonist, progesterone (P4). We carried out a reproductive study using breeding groups of adult zebrafish. After a 14 day pre-exposure, zebrafish were exposed for 21 days to 5, 39, 77 ng/L MIF, 25 ng/L P4 and water and solvent controls. In addition, embryos originating from exposed adult fish were continuously exposed to 3, 15, 26 ng/L MIF, and 254 ng/L P4, respectively, for 96 h post fertilization. We found a significant U-shaped increase in egg production after exposure to 5 and 77 ng/L MIF, but no effects at 25 ng/L P4. Levels of sex steroid hormones in blood plasma of adult males (11-ketotestosterone) and females (17 β-estradiol) were not altered. In addition to an increase of mature vitellogenic oocytes in ovaries of females exposed to MIF and P4, we observed several histopathological changes in ovaries, including post-ovulatory follicles, atretic follicles and proteinaceous fluid. Male gonads showed no or less alterations and no histopathological effects. Fertility of eggs and hatching success of embryos (F1 generation) was not affected at 3-26 ng/L MIF and 254 ng/L P4, respectively. The data lead to the conclusion that trace quantities of MIF affect reproduction of zebrafish and ovaries of female zebrafish. Effects on transcriptional changes in adult and embryonic zebrafish of this study in comparison to in vitro effects are reported in the associated report (Blüthgen et al., 2013a).

Clotrimazole, but not dexamethasone, is a potent in vitro inhibitor of cytochrome P450 isoforms CYP1A and CYP3A in rainbow trout

The effects of clotrimazole (CLO) and dexamethasone (DEX), both detected in the aquatic environment, were assessed on inhibition of cytochrome P450 (CYP450) in hepatic microsomes of rainbow trout. Activity of three CYP450 isoforms: ethoxyresorufin O-deethylase (EROD; CYP1A), 7-benzyloxy-4-trifluoromethylcoumarin O-debenzylase (BFCOD; CYP3A) and p-nitrophenol hydroxylase (PNPH; CYP2E1-like protein) was investigated in the presence of four concentrations of CLO and DEX. Clotrimazole in a concentration range of 1-100μM decreased the activity of EROD and BFCOD. The inhibition was reversible, as pre-incubation of the microsomes with CLO, before addition of the substrate, had no effect. EROD activity was non-competitively inhibited with a Ki of 0.5μM, and BFCOD activity revealed competitive inhibition with a Ki of 0.04μM. The relatively low Ki for CLO inhibition of EROD and BFCOD activity may indicate that the ability of CYP1A and CYP3A to metabolize xenobiotics is reduced in the presence of CLO. PNPH activity was not affected by CLO. DEX showed no inhibitory potency on any investigated reaction. CLO, but not DEX, inhibited EROD and BFCOD activity by different mechanisms.

Effect of in vivo chronic exposure to clotrimazole on zebrafish testis function

Clotrimazole is an azole fungicide used as a human pharmaceutical that is known to inhibit cytochrome P450 (CYP) enzymatic activities, including several steroidogenic CYP. In a previous report, we showed that a 7-day exposure to clotrimazole induced the expression of genes related to steroidogenesis in the testes as a compensatory response, involving the activation of the Fsh/Fshr pathway. In this context, the aim of the present study was to assess the effect of an in vivo 21-day chronic exposure to clotrimazole (30-197 μg/L) on zebrafish testis function, i.e., spermatogenesis and androgen release. The experimental design combined (1) gene transcript levels measurements along the brain-pituitary-gonad axis, (2) 11-ketotestosterone (11-KT) quantification in the blood, and (3) histology of the testes, including morphometric analysis. The chronic exposure led to an induction of steroidogenesis-related genes and fshr in the testes as well as fshβ in the pituitary. Moreover, increases of the gonadosomatic index and of the volume proportion of interstitial Leydig cells were observed in clotrimazole-exposed fish. In accordance with these histological observations, the circulating concentration of 11-KT had increased. Morphometric analysis of the testes did not show an effect of clotrimazole on meiotic (spermatocytes) or postmeiotic (spermatids and spermatozoa) stages, but we observed an increase in the number of type A spermatogonia, in agreement with an increase in mRNA levels of piwil1, a specific molecular marker of type A spermatogonia. Our study demonstrated that clotrimazole is able to affect testicular physiology and raised further concern about the impact of clotrimazole on reproduction.

A progestin (17α,20β-dihydroxy-4-pregnen-3-one) stimulates early stages of spermatogenesis in zebrafish

Recently, evidence has been provided for multiple regulatory functions of progestins during the late mitotic and meiotic phases of spermatogenesis in teleost fish. For example, our previous studies suggested that 17α,20β-dihydroxy-4-pregnen-3-one (DHP), potentially via Sertoli cells that express the progesterone receptor (pgr) gene, can contribute to the regulation of zebrafish spermatogenesis. To further our understanding of the function of DHP at early spermatogenetic stages, we investigated in the present study the expression of genes reflecting Sertoli cell function and spermatogenic development in adult zebrafish testis after DHP treatment in tissue culture. Moreover, using an in vivo model of estrogen-mediated down-regulation of androgen production to interrupt adult spermatogenesis, we studied the effects of DHP on estrogen-interrupted spermatogenesis. In this model, DHP treatment doubled the testis weight, and all differentiating germ cell types, such as type B spermatogonia and primary spermatocytes, were abundantly present and incorporated the DNA-synthesis marker (BrdU). Accordingly, transcript levels of germ cell marker genes were up-regulated. Moreover, transcripts of two Sertoli cell-derived genes anti-müllerian hormone (amh) and gonadal soma-derived growth factor (gsdf) were up-regulated, as were three genes of the insulin-like growth factor signaling system, insulin-like growth factor 2b (igf2b), insulin-like growth factor 3 (igf3) and insulin-like growth factor 1b receptor (igf1rb). We further analyzed the relationship between these genes and DHP treatment using a primary zebrafish testis tissue culture system. In the presence of DHP, only igf1rb mRNA levels showed a significant increase among the somatic genes tested, and germ cell marker transcripts were again up-regulated. Taken together, our results show that DHP treatment induced the proliferation of early spermatogonia, their differentiation into late spermatogonia and spermatocytes as well as expression of marker genes for these germ cell stages. DHP-mediated stimulation of spermatogenesis and hence growth of spermatogenic cysts and the associated increase in Sertoli cell number may in part explain the elevated expression of Sertoli cell genes, but our data also suggest an up-regulation of the activity of the Igf signaling system.

FSH and LH have common and distinct effects on gene expression in rainbow trout testis

The general rules established from mammalian species for the regulation of spermatogenesis by gonadotropins may not be fully relevant in fish. Particularly, Fsh is as potent as Lh to stimulate steroidogenesis and the Fsh receptor is expressed in Leydig cells. In seasonal breeders, Fsh is likely the major gonadotropin involved in spermatogenesis onset and Lh is required to support spermatogenesis progression and gamete release. However, the genes that relay the action of Fsh and Lh have been poorly investigated in fish. The present study was aimed at identifying gonadotropin-dependent genes expressed in the testis during fish puberty. We cultured pubertal trout testicular explants for 96 h, with or without gonadotropin, and analyzed transcriptome variations using microarrays. Fsh and Lh had similar effects on a large group of genes while other genes were preferentially regulated by one or the other gonadotropin. We showed that most of the responsive genes were expressed in somatic cells and exhibited relevant patterns during the seasonal reproductive cycle. Some genes preferentially modulated by Lh could be involved in testicular cell fate (pvrl1 and bty) or sperm maturation (ehmt2 and racgap1) and will deserve further examination. Besides Fsh's effects on the steroidogenic pathway, our study demonstrates that Fsh coordinates relevant stimulatory and inhibitory paracrine factors known to regulate early germ cell proliferation and differentiation. Some of these genes belong to major regulatory pathways including the Igf pathway (igf1b/igf3 and igfbp6), the Tgfb pathway (amh, inha, inhba, and fstl3), the Wnt pathway (wisp1), and pleiotrophin (mdka).

Propiconazole inhibits steroidogenesis and reproduction in the fathead minnow (Pimephales promelas)

Conazoles are designed to inhibit cytochrome P450 (CYP) 14α-demethylase, an enzyme key to fungal cell wall formation. In vertebrates, conazoles may inhibit other CYPs, potentially disrupting processes like sex steroid synthesis. Propiconazole is a current-use pesticide that is among the first chemicals being tested in the U.S. Environmental Protection Agency endocrine disruptor screening program. Fathead minnows (Pimephales promelas) were exposed to 0, 5, 50, 500, or 1000 µg propiconazole/l in a 21-day study that evaluated apical reproductive endpoints (fecundity, fertility, hatch); measures of endocrine function and steroid synthesis, such as cholesterol, vitellogenin (VTG), and sex steroid (testosterone [T], 17β-estradiol [E2]) concentrations in the plasma; and changes in gonadal expression of steroidogenic genes. Plasma E2 and VTG concentrations in females were reduced by exposure to propiconazole, and egg production was decreased in the 500 and 1000 µg/l treatment groups. These in vivo effects coincided with inhibition of E2 synthesis by ovary explants exposed to propiconazole in vitro. We also observed a compensatory response in females exposed to propiconazole, manifested as increased gonad weight and upregulation of genes coding for key steriodogenic proteins, including CYP19 (aromatase), CYP17 (hydroxylase/lyase), CYP11A (cholesterol side-chain-cleavage), and steroidogenic acute regulatory protein. Other than an increase in relative testis weight, effects on endocrine function in males were less pronounced than in females. This study provides important data relative to the potential endocrine activity of propiconazole in fish and, more generally, to the further delineation of pathways for the reproductive effects of steroid synthesis inhibitors in fish.