Reproductive and transcriptional effects of the antiandrogenic progestin chlormadinone acetate in zebrafish (Danio rerio)

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

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

Multigenerational exposure to gamma radiation affects offspring differently over generations in zebrafish

Mutigenerational studies are now of great interest in ecotoxicology and previous studies have shown the importance of conducting multigenerational studies when assessing radiation toxicity in fish. In our study, the first objective was to study the early life stages (embryo-larval stages) and critical functions such as reproduction (which are generally studied in the context of ecological risk assessment (ERA)), in order to assess the sensitivity of zebrafish to ionizing radiation. The second objective was to assess acquisition of phenotypic effects at select life stages over generations. To our knowledge, this was the first time that irradiation of zebrafish (0.05 and 5 mGy.h^-1) up to generation F2 was maintained with the following two exposure conditions: (1) recovery, only F0 genitors were irradiated and the progeny were placed in control condition, (2) irradiated condition, all generations were exposed. Multigenerational irradiation affected F1 parental reproductive capacity (reproductive success) mainly over the first reproductive cycle (104d) and larval survival rate. Unexpected yet significant effects on sex ratio were observed in F1 progeny after parental irradiation (mainly at 5 mGy.h^-1). These effects were observed for both conditions -irradiated and recovery- suggesting transmitted effects from F0 genitors to offspring. All studied life stages were affected by ionizing radiation (IR), suggesting an alteration of vital physiological functions (reproduction and sexual determination). Such results highlight the hypothesis that IR affects population dynamics. In addition, the clear evidence of transmitted effects suggests worsening of effects at the population scale over generations. This approach is closer to environmental conditions to assess wild population fate, and thus highlights the importance of multigenerational studies to support ERA of ionizing radiation in fish.

Pyriproxyfen induced impairment of reproductive endocrine homeostasis and gonadal histopathology in zebrafish (Danio rerio) by altered expression of hypothalamus-pituitary-gonadal (HPG) axis genes

Pyriproxyfen (PPF), a broad-spectrum insecticide known to cause reproductive and endocrine disruption in invertebrates, while the data is scarce in aquatic vertebrates. The goal of this study is to investigate the impact of PPF on reproductive endocrine system of male and female zebrafish along hypothalamus-pituitary-gonadal (HPG) axis. In brain, PPF caused significant alteration in the transcripts of erα, lhβ, and cyp19b genes in male and fshβ, lhβ, and cyp19b genes in female zebrafish. The downstream genes of steroidogenic pathway like, star, 3βhsd, 17βhsd, and cyp19a expression were significantly altered in gonad of both sexes. Subsequent changes in circulatory steroid hormone levels lead to imbalance in hormone homeostasis as revealed from estradiol/testosterone (E₂/T) ratio. Further, the vitellogenin transcript level was enhanced in hepatic tissues and their blood plasma content was increased in male (16.21%) and declined in female (21.69%). PPF also induced histopathological changes in gonads such as, reduction of mature spermatocytes in male and vitellogenic oocytes in female zebrafish. The altered E₂/T ratio and gonadal histopathology were supported by the altered transcript levels of HPG axis genes. Overall, these findings provide new insights of PPF in zebrafish reproductive system and highlights for further investigations on its potential risks in aquatic environment.

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.

Embryo/larval toxicity and transcriptional effects in zebrafish (Danio rerio) exposed to endocrine active riverbed sediments

Sediment toxicity plays a fundamental role in the health of inland fish communities; however, the assessment of the hazard potential of contaminated sediments is not a common objective in environmental diagnostics or remediation. This study examined the potential of transcriptional endpoints investigated in zebrafish (Danio rerio) exposed to riverbed sediments in ecotoxicity testing. Embryo-larval 10-day tests were conducted on sediment samples collected from five sites (one upstream and four downstream of the city of Milan) along a polluted tributary of the Po River, the Lambro River. Sediment chemistry showed a progressive downstream deterioration in river quality, so that the final sampling site showed up to eight times higher concentrations of, for example, triclosan, galaxolide, PAH, PCB, BPA, Ni, and Pb, compared with the uppermost site. The embryo/larval tests showed widespread toxicity although the middle river sections evidenced worse effects, as evidenced by delayed embryo development, hatching rate, larval survival, and growth. At the mRNA transcript level, the genes encoding biotransformation enzymes (cyp1a, gst, ugt) showed increasing upregulations after exposure to sediment from further downstream sites. The genes involved in antioxidant responses (sod, gpx) suggested that more critical conditions may be present at downstream sites, but even upstream of Milan there seemed to be some level of oxidative stress. Indirect evidences of potential apoptotic activity (bcl2/bax < 1) in turn suggested the possibility of genotoxic effects. The genes encoding for estrogen receptors (erα, erβ1, erβ2) showed exposure to (xeno)estrogens with a progressive increase after exposure to sediments from downstream sites, paralleled by a corresponding downregulation of the ar gene, likely related to antiandrogenic compounds. Multiple levels of thyroid disruption were also evident particularly in downstream zebrafish, as for thyroid growth (nkx2.1), hormone synthesis and transport (tg, ttr, d2), and signal transduction (trα, trβ). The inhibition of the igf2 gene reasonably reflected larval growth inhibitions. Although none of the sediment chemicals could singly explain fish responses, principal component analysis suggested a good correlation between gene transcripts and the overall trend of contamination. Thus, the combined impacts from known and unknown covarying chemicals were proposed as the most probable explanation of fish responses. In summary, transcriptional endpoints applied to zebrafish embryo/larval test can provide sensitive, comprehensive, and timeliness information which may greatly enable the assessment of the hazard potential of sediments to fish, complementing morphological endpoints and being potentially predictive of longer studies.

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.

Ferredoxin 1b Deficiency Leads to Testis Disorganization, Impaired Spermatogenesis, and Feminization in Zebrafish

The roles of steroids in zebrafish sex differentiation, gonadal development, and function of the adult gonad are poorly understood. Herein, we used ferredoxin 1b (fdx1b) mutant zebrafish to explore such processes. Fdx1b is an essential electron-providing cofactor to mitochondrial steroidogenic enzymes, which are crucial for glucocorticoid and androgen production in vertebrates. Fdx1b-/- zebrafish mutants develop into viable adults in which concentrations of androgens and cortisol are significantly reduced. Adult fdx1b-/- mutant zebrafish display predominantly female secondary sex characteristics but may possess either ovaries or testes, confirming that androgen signaling is dispensable for testicular differentiation in this species, as previously demonstrated in androgen receptor mutant zebrafish. Adult male fdx1b-/- mutant zebrafish exhibit reduced characteristic breeding behaviors and impaired sperm production, resulting in infertility in standard breeding scenarios. However, eggs collected from wild-type females can be fertilized by the sperm of fdx1b-/- mutant males by in vitro fertilization. The testes of fdx1b-/- mutant males are disorganized and lack defined seminiferous tubule structure. Expression of several promale and spermatogenic genes is decreased in the testes of fdx1b-/- mutant males, including promale transcription factor sox9a and spermatogenic genes igf3 and insl3. This study establishes an androgen- and cortisol-deficient fdx1b zebrafish mutant as a model for understanding the effects of steroid deficiency on sex development and reproductive function. This model will be particularly useful for further investigation of the roles of steroids in spermatogenesis, gonadal development, and regulation of reproductive behavior, thus enabling further elucidation of the physiological consequences of endocrine disruption in vertebrates.

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

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

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

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

Reproductive effects of synthetic progestin norgestrel in zebrafish (Danio rerio)

The aim of this study was to assess the adverse effects of synthetic progestin norgestrel (NGT) on the reproduction of zebrafish by measuring the egg production, histology and transcriptional expression profiles along the hypothalamic-pituitary-gonadal (HPG) axis in adult zebrafish. After a pre-exposure period of 7 days, adult zebrafish were exposed to 6, 29 and 69 ng L^-1 NGT for 21 days. The results showed that exposure to 69 ng L^-1 NGT led to a significant up-regulation of follicle stimulating hormone, beta polypeptide (fshb), luteinizing hormone, beta polypeptide (lhb), progesterone receptor (pgr), estrogen receptor 1 (esr1) and androgen receptor (ar) genes in the brains, as well as significant up-regulation of hydroxysteroid 20-beta dehydrogenase (hsd20b) and hydroxysteroid 11-beta dehydrogenase 2 (hsd11b2) genes and down-regulation of 11-beta-hydroxylase (cyp11b) gene in the ovaries of females. In the testes of males, an overall down-regulation of steroidogenic acute regulatory protein (star), cytochrome P450-mediated side-chain cleavage enzyme (cyp11a1), cyp11b, hsd20b, hydroxysteroid 17-beta dehydrogenase type 3 (hsd17b3), hsd11b2 and ar genes were observed following exposure to different treatments of NGT. These transcriptional alterations imply that NGT could exhibit the potent progestogenic and androgenic activities in zebrafish. Egg production as well as histology in the ovaries and testes was not affected by NGT. Taken together, the overall results demonstrated that NGT could significantly affect transcriptional expression levels of genes related to HPG axis in zebrafish, and whether that change translates to additional physiological effects is needed further research.

Hepatic gene expression profiles of a non-model cyprinid (Barbus plebejus) chronically exposed to river sediments

In this study, we characterized the gene expression responses of the Padanian barbel (Barbus plebejus), a native benthivorous cyprinid with a very compromised presence within the fish community of the River Po. Barbel juveniles were exposed in the laboratory to two river sediments reflecting an upstream/downstream gradient of increasing contamination and collected from one of the most anthropized tributaries of the River Po. After 7months of exposure, hepatic transcriptional changes that were diagnostic of sediment exposure were assessed. We investigated a set of 24 genes involved in xenobiotic biotransformation (cyp1a, gstα, ugt), antioxidant defense (gpx, sod, cat, hsp70), trace metal exposure (mt-I, mt-II), DNA repair (xpa, xpc), apoptosis (bax, casp3), growth (igf2), and steroid (erα, erβ1, erβ2, ar, vtg) and thyroid (dio1, dio2, trα, trβ, nis) hormone signaling pathways. In a consistent overall picture, the results showed that long-term sediment exposure mainly increased the levels of mRNAs encoding proteins involved in xenobiotic metabolism, oxidative stress defense, repair of DNA damage and activation of the apoptotic process. Transcript up-regulation of three receptor genes (erβ2, ar, trβ), likely representing compensatory responses to antagonistic/toxic effects, was also observed, confirming the exposure to disruptors of the reproductive and thyroidal axes. In contrast to expectations, a few genes showed no response (e.g., casp3) or even downregulation (vtg), further suggesting that the timing of exposure/assessment, potential compensatory effects or post-transcriptional modifications interact to modify the gene expression profiles, particularly during exposure to mixtures of contaminants.