The influence of various endocrine disruptors on the reproductive system

Various stimulants (VS) are chemicals that disrupt the endocrine system - endocrine homeostasis of the reproductive system - which also known as endocrine-disrupting chemicals (EDCs). These substances are found in the human body, in both the blood and urine, amniotic fluid, or, among others, the adipose tissue. This article presents the current state of knowledge of the effect of EDCs and additional factors such as smoking, alcohol consumption, and cannabis on the gonads. The article is an overview of the impact of EDCs and their mechanism of action, with particular emphasis on gonads, based on databases such as PubMed, EMBASE and Google Scholar, and Web of Science available until May 2022. The impact of human exposure to bisphenol A (BPA) is not fully understood, but it has been shown that phthalates show a negative correlation in anti-androgenic activity in the case of men and women for the anti-Müllerian hormone (AMH). Smoking cigarettes and passive exposure to tobacco have a huge impact on the effects of endocrine disorders in both women and men, especially during the reproductive time. Also, the use of large amounts of cannabinoids during the reproductive years can lead to similar disorders. It has been documented that excessive alcohol consumption leads to disturbed function of the hypothalamus-pituitary-gonadal axis (HPG). Excess caffeine consumption may adversely affect male reproductive function, although this is not fully proven. Therefore, the following publication presents various stimulants (BPA, phthalates, nicotine, alcohol, cannabis) that disrupt the function of the endocrine system and, in particular, affect the function of the gonads.

Reproductive Deficits Induced by Prenatal Antimüllerian Hormone Exposure Require Androgen Receptor in Kisspeptin Cells

Polycystic ovary syndrome (PCOS) is a common reproductive disorder characterized by elevated androgens and antimüllerian hormone (AMH). These hormones remain elevated throughout pregnancy, and potential effects of hormone exposure on offspring from women with PCOS remain largely unexplored. Expanding on recent reports of prenatal AMH exposure in mice, we have fully characterized the reproductive consequences of prenatal AMH (pAMH) exposure throughout the lifespan of first- and second-generation offspring of both sexes. We also sought to elucidate mechanisms underlying pAMH-induced reproductive effects. There is a known reciprocal relationship between AMH and androgens, and in PCOS and PCOS-like animal models, androgen feedback is dysregulated at the level of the hypothalamus. Kisspeptin neurons express androgen receptors and play a critical role in sexual development and function. We therefore hypothesized that pAMH-induced reproductive phenotypes would be mediated by androgen signaling at the level of kisspeptin cells. We tested the pAMH model in kisspeptin-specific androgen receptor knockout (KARKO) mice and found that virtually all pAMH-induced phenotypes assayed are eliminated in KARKO offspring compared to littermate controls. By demonstrating the necessity of androgen receptor in kisspeptin cells to induce pAMH phenotypes, we have advanced understanding of the interactions between AMH and androgens in the context of prenatal exposure, which could have significant implications for children of women with PCOS.

Effects of trophic 2,2', 4,4'-tetrabromodiphenyl ether (BDE-47) exposure in Oreochromis niloticus: A multiple biomarkers analysis

Polybrominated diphenyl esters are emerging environmental contaminants with few toxicological data, being a concern for the scientific community. This study evaluated the effects of BDE-47 on the health of Oreochromis niloticus fish. The animals were exposed to three doses of BDE-47 (0, 0.253, 2.53, 25.3 ng g^-1) every 10 days, for 80 days. The BDE-47 affected the hepatosomatic and gonadosomatic index in female and the condition factor by intermediate dose in both sexes. The levels of estradiol decreased and the T4 are increased, but the vitellogenin production was not modulated in male individuals. Changes in AChE, GST, LPO and histopathology were observed while the integrated biomarker response index suggests that the lowest dose of BDE-47 compromised the activity of antioxidant enzymes. The oral exposure to BDE-47 in environmental concentrations is toxic to O. niloticus and the use of multiple biomarkers is an attribution in ecotoxicology studies and biomonitoring programs.

Global expression response of genes in sex-undifferentiated Nile tilapia gonads after exposure to trace letrozole

The aromatase inhibitor letrozole can be found in rivers, effluents, and even drinking water. Studies have demonstrated that letrozole affects various metabolic pathways and may cause reproductive toxicity, especially in fish exposed during development. However, studies on the effect of a low concentration of letrozole at the whole-gonad transcriptomic level in the early stage of fish sexual development have not been investigated. The aim of our study was to explore the potential effects of a low concentration of letrozole on the gonad transcriptome of Nile tilapia at an early stage of sexual development. In this study, 9 dpf (days postfertilization) Nile tilapia were exposed to trace letrozole for 12 days. Letrozole exposure from 9 dpf to 21 dpf persistently altered phenotypic sex development and induced the male-biased sex ratio. The transcriptome results showed that 1173 differentially expressed genes (DEGs) were present in the female control vs 1.5 μg/L letrozole-treated female comparison group and that 1576 DEGs were present in the 1.5 μg/L letrozole-treated female vs male control comparison group. Differentially expressed gene enrichment analysis revealed several crucial pathways, including the drug metabolism-cytochrome P450 pathway, the ErbB-PI3K/Akt/mTOR pathway, and the calcium signalling pathway. Further analysis of these identified DEGs indicated that some key genes correlated with metabolism and epigenetic regulation were significantly affected by letrozole, such as UDP-glucuronosyltransferase (Ugt), glutathione S-transferase omega-1 (Gsto1), lysine-specific demethylase 6bb (Kdm6bb, original name is Kdm6a), jumonji and AT-rich interaction domain containing 2 (Jarid2b, original name is Jarid2), growth arrest and DNA damage inducible gamma (Gadd45g), and chromobox protein 7 (Cbx7). The qRT-PCR validation results for twelve DEGs showed that the Pearson's correlation of the log₁₀^{fold change} values between the qPCR and RNA-Seq results was 0.90, indicating the accuracy and reliability of the RNA-Seq results. Our study is the first to report the effect of letrozole on the transcriptome of gonads from fish during early-stage sexual development. These findings will be useful for understanding the toxic effects and molecular mechanisms of letrozole exposure at the early stage of gonad development on the sexual development of aquatic organisms.

Combined Effects of Temperature and Toxic Algal Abundance on Paralytic Shellfish Toxic Accumulation, Tissue Distribution and Elimination Dynamics in Mussels Mytilus coruscus

This study assessed the impact of increasing seawater surface temperature (SST) and toxic algal abundance (TAA) on the accumulation, tissue distribution and elimination dynamics of paralytic shellfish toxins (PSTs) in mussels. Mytilus coruscus were fed with the PSTs-producing dinoflagellate A. catenella under four simulated environment conditions. The maximum PSTs concentration was determined to be 3548 µg STX eq.kg⁻¹, which was four times higher than the EU regulatory limit. The increasing SST caused a significant decline in PSTs levels in mussels with rapid elimination rates, whereas high TAA increased the PSTs concentration. As a result, the PSTs toxicity levels decreased under the combined condition. Additionally, toxin burdens were assessed within shellfish tissues, with the highest levels quantified in the hepatopancreas. It is noteworthy that the toxin burden shifted towards the mantle from gill, muscle and gonad at the 17th day. Moreover, variability of PSTs was measured, and was associated with changes in each environmental factor. Hence, this study primarily illustrates the combined effects of SST and TAA on PSTs toxicity, showing that increasing environmental temperature is of benefit to lower PSTs toxicity with rapid elimination rates.

Occurrence and ecotoxicity of cytostatic drugs 5-fluorouracil and methotrexate in the freshwater unionid Elliptio complanata

Municipal effluents continuously release cytostatic drugs with unknown consequences in aquatic organisms. The purpose of the study was to examine the sublethal toxicity of 2 commonly-found cytostatic drugs 5-fluouracile (5-FLU) and methotrexate (MTX) to endemic Elliptio complanata freshwater mussels. The mussels were exposed of each drugs at 0, 4, 20 and 100 μg/L for 96 h t 15 °C. After the exposure period, glutathione S-transferase (GST) and dehydrofolate reductase (DHFR) activities, DNA damage and lipid peroxidation (LPO) were determined. The drugs were detected in mussel tissues with no evidence of accumulation with either drugs. The drug 5-FLU gave a larger spectrum of effects than MTX such as increased DHFR, decreased LPO and DNA strand breaks (repair activity) suggesting that the mussels were metabolically hindered and reduced DNA repair activity. The drug MTX only increased DHFR activity in the gonad. Hence, the data suggest that these drugs are biologically active in freshwater mussels and based on the reported maximum levels of these drugs in municipal effluents, the observed effects are likely in sessile freshwater mussel species downstream urban sources of pollution.

Circulating miR-30b levels increase during male puberty

OBJECTIVE

The role of miRNA as endocrine regulators is emerging, and microRNA mir-30b has been reported to repress Mkrn3. However, the expression of miR-30b during male puberty has not been studied.

DESIGN AND METHODS

Circulating relative miR-30b expression was assessed in sera of 26 boys with constitutional delay of growth and puberty (CDGP), treated with low-dose testosterone (T) (n =11) or aromatase inhibitor letrozole (Lz) (n =15) for 6 months and followed up to 12 months (NCT01797718). The associations between the relative expression of miR-30b and hormonal markers of puberty were evaluated.

RESULTS

During the 12 months of the study, circulating miR-30b expression increased 2.4 ± 2.5 (s.d.) fold (P = 0.008) in all boys, but this change did not correlate with corresponding changes in LH, testosterone, inhibin B, FSH, or testicular volume (P = 0.25-0.96). Lz-induced activation of the hypothalamic-pituitary-gonadal (HPG) axis was associated with more variable miR-30b responses at 3 months (P < 0.05), whereas those treated with T exhibited significant changes in relative miR-30b levels in the course the study (P < 0.01-0.05).

CONCLUSIONS

Circulating miR-30b expression in boys with CDGP increases in the course of puberty, and appears to be related to the activity of the HPG axis.

Micropollutants impair the survival of Oreochromis niloticus and threat local species from Iguaçu River, Southern of Brazil

The wastewater contamination of urban rivers is a concern for biodiversity and a consequence from poor urban conservation policies. In the current study, the impact of urban and industrial activities was investigated in Iguaçu river (Southern Brazil) using juvenile Oreochromis niloticus, after trophic and chronic exposure (25, 50 and 100 %), over 81 days. After exposure liver, gills, gonads, brain, muscle, and blood were sampled for chemical, biochemical, histopathological, genotoxic and molecular analyses. Water levels of persistent organic pollutants such as polychlorinated biphenyls, organochlorine pesticides, polycyclic aromatics hydrocarbon (PAHs) and metals were investigated. The redox unbalance, histopathological and increase in vitellogenin expression in fish revealed both the bioavailability of micropollutants and their harmful effects. According to the results, the level of Iguaçu river pollution negatively impacts the health of O. niloticus revealing and highlighting the risk of this pollution exposure to biota and human populations.

Differential Disrupting Effects of Prolonged Low-Dose Exposure to Dichlorodiphenyltrichloroethane on Androgen and Estrogen Production in Males

Dichlorodiphenyltrichloroethane (DDT) is the most widespread, persistent pollutant and endocrine disruptor on the planet. Although DDT has been found to block androgen receptors, the effects of its low-dose exposure in different periods of ontogeny on the male reproductive system remain unclear. We evaluate sex steroid hormone production in the pubertal period and after maturation in male Wistar rats exposed to low doses of o,p'-DDT, either during prenatal and postnatal development or postnatal development alone. Prenatally and postnatally exposed rats exhibit lower testosterone production and increased estradiol and estriol serum levels after maturation, associated with the delayed growth of gonads. Postnatally exposed rats demonstrate accelerated growth of gonads and higher testosterone production in the pubertal period. In contrast to the previous group, they do not present raised estradiol production. All of the exposed animals exhibit a reduced conversion of progesterone to 17OH-progesterone after sexual maturation, which indicates putative attenuation of sex steroid production. Thus, the study reveals age-dependent outcomes of low-dose exposure to DDT. Prenatal onset of exposure results in the later onset of androgen production and the enhanced conversion of androgens to estrogens after puberty, while postnatal exposure induces the earlier onset of androgen secretion.

Efficacy of Sex Steroid Therapy Without Progestin or GnRH Agonist for Gonadal Suppression in Adult Transgender Patients

CONTEXT

Testosterone (T) or estradiol (E2) are administered to suppress gonadal function in female-to-male (FTM) and male-to-female (MTF) transgender patients. How often sex steroids cause adequate suppression without GnRH agonist (GnRHa) or progestin therapy has not been reported.

OBJECTIVES

(1) To determine how often T and E2 therapy alone can effectively suppress gonadal function in MTF and FTM transgender patients, and (2) to determine the frequency and range of serum E2 levels above the normal male range in FTM patients receiving T therapy.

DESIGN

Retrospective cohort study.

SETTING

Outpatient reproductive endocrinology clinic at an academic medical center.

PATIENTS

A total of 65 FTM and 33 MTF patients were included who were > 18 years of age and not receiving progestin or GnRHa therapy.

INTERVENTION

Female-to-male patients were receiving T through injections or gel. Male-to-female patients were receiving oral or subcutaneous E2.

MAIN OUTCOME MEASUREMENTS

In FTM patients the indicator of ovary suppression was amenorrhea. In MTF patients, the indicator of testes suppression was T levels <50 ng/dL.

RESULTS

Median serum total T level for FTM patients was 712 ng/dL (range, 370-1164 ng/dL). On T therapy alone, 90.8% of patients achieved amenorrhea and 49.2% of patients had serum E2 levels above the normal range for women. For MTF patients, the median serum E2 level was 129.2 pg/mL (range, 75-197 pg/mL). On E2 therapy alone, 84.8% of MTF patients had adequate suppression of testicular function.

CONCLUSIONS

Testosterone and E2 therapy are usually effective without progestin or GnRHa therapy to suppress gonadal function in transgender patients. Progestin and/or GnRHa therapy should only be initiated in those patients who do not have adequate gonadal suppression on optimized doses of T or E2 alone.

Complete Androgen Insensitivity Syndrome: From Bench to Bed

Complete androgen insensitivity syndrome (CAIS) is due to complete resistance to the action of androgens, determining a female phenotype in persons with a 46,XY karyotype and functioning testes. CAIS is caused by inactivating mutations in the androgen receptor gene (AR). It is organized in eight exons located on the X chromosome. Hundreds of genetic variants in the AR gene have been reported in CAIS. They are distributed throughout the gene with a preponderance located in the ligand-binding domain. CAIS mainly presents as primary amenorrhea in an adolescent female or as a bilateral inguinal/labial hernia containing testes in prepubertal children. Some issues regarding the management of females with CAIS remain poorly standardized (such as the follow-up of intact testes, the timing of gonadal removal and optimal hormone replacement therapy). Basic research will lead to the consideration of new issues to improve long-term well-being (such as bone health, immune and metabolic aspects and cardiovascular risk). An expert multidisciplinary approach is mandatory to increase the long-term quality of life of women with CAIS.

Sex steroids and steroidogenesis-related genes in the sea cucumber, Holothuria scabra and their potential role in gonad maturation

The sea cucumber Holothuria scabra is an economically valuable marine species which is distributed throughout the Asia-Pacific region. With the natural population declining due to over fishing, aquaculture of this species is deemed necessary. Hence, it is essential to understand the mechanisms regulating the reproduction in order to increase their populations. Sex steroids, including estrogens, androgens and progestogens, play an important role in reproduction in most vertebrates and several invertebrates. It has been proposed that sea cucumbers have the same sex steroids as vertebrates but the steroidogenic pathway in the sea cucumbers is still unclear. In this study, we demonstrated by using liquid chromatography-tandem mass spectrometry (LC-MS/MS) that sex steroids (estradiol, progesterone, and testosterone) were present in H. scabra neural and gonadal tissues. In silico searches of available sea cucumber transcriptome data identified 26 steroidogenesis-related genes. Comparative analysis of encoded proteins for the steroidogenic acute regulatory protein (HscStAR), CYP P450 10, 17 and 3A (HscCYP10, HscCYP17, HscCYP3A) and hydroxysteroid dehydrogenases (Hsc3β-HSD, Hsc17β-HSD) with other species was performed to confirm their evolutionary conservation. Gene expression analyses revealed widespread tissue expression. Real-time PCR analysis revealed that HscStAR, HscCYP10, Hsc3β-HSD, and Hsc17β-HSD gene expressions were similar to those in ovaries and testes, which increased during the gonad maturation. HscCYP17 mRNA was increased during ovarian development and its expression declined at late stages in females but continued high level in males. The expression of the HscCYP3A was high at the early stages of ovarian development, but not at other later stages in ovaries, however it remained low in testes. Moreover, a role for steroids in reproduction was confirmed following the effect of sex steroids on vitellogenin (Vtg) expression in ovary explant culture, showing upregulation of Vtg level. Collectively, this study has confirmed the existence of steroids in an echinoderm, as well as characterizing key genes associated with the steroidogenic pathway. We propose that sex steroids might also be associated with the reproduction of H. scabra, and the identification of biosynthetic genes enables future functional studies to be performed.

Hypothalamo-Pituitary axis and puberty

Puberty is a complex process that culminates in the acquisition of psychophysical maturity and reproductive capacity. This elaborate and fascinating process marks the end of childhood. Behind it lies a complex, genetically mediated neuroendocrine mechanism through which the gonads are activated thanks to the fine balance between central inhibitory and stimulating neuromodulators and hormones with both central and peripheral action. The onset of puberty involves the reactivation of the hypothalamic-pituitary-gonadal (HPG) axis, supported by the initial "kiss" between kisspeptin and the hypothalamic neurons that secrete GnRH (the GnRH "pulse generator"). This pulsatile production of GnRH is followed by a rise in LH and, consequently, in gonadal steroids. The onset of puberty varies naturally between individuals, and especially between males and females, in the latter of whom it is typically earlier. However, pathological variations, namely precocious and delayed puberty, are also possible. This article reviews the scientific literature on the physiological mechanisms of puberty and the main pathophysiological aspects of its onset.

Vasopressinergic Activity of the Suprachiasmatic Nucleus and mRNA Expression of Clock Genes in the Hypothalamus-Pituitary-Gonadal Axis in Female Aging

The important involvement of the suprachiasmatic nucleus (SCN) and the activity of vasopressinergic neurons in maintaining the rhythmicity of the female reproductive system depends on the mRNA transcription-translation feedback loops. Therefore, circadian clock function, like most physiological processes, is involved in the events that determine reproductive aging. This study describes the change of mRNA expression of clock genes, Per2, Bmal1, and Rev-erbα, in the hypothalamus-pituitary-gonadal axis (HPG) of female rats with regular cycle (RC) and irregular cycle (IC), and the vasopressinergic neurons activity in the SCN and kisspeptin neurons in the arcuate nucleus (ARC) of these animals. Results for gonadotropins and the cFos/AVP-ir neurons in the SCN of IC were higher, but kisspeptin-ir was minor. Change in the temporal synchrony of the clock system in the HPG axis, during the period prior to the cessation of ovulatory cycles, was identified. The analysis of mRNA for Per2, Bmal1, and Rev-erbα in the reproductive axis of adult female rodents shows that the regularity of the estrous cycle is guaranteed by alternation in the amount of expression of Bmal1 and Per2, and Rev-erbα and Bmal1 between light and dark phases, which ceases to occur and contributes to determining reproductive senescence. These results showed that the desynchronization between the central and peripheral circadian clocks contributes to the irregularity of reproductive events. We suggest that the feedback loops of clock genes on the HPG axis modulate the spontaneous transition from regular to irregular cycle and to acyclicity in female rodents.

Effect of EPA on Neonatal Pig Sertoli Cells "In Vitro": A Possible Treatment to Help Maintain Fertility in Pre-Pubertal Boys Undergoing Treatment With Gonado-Toxic Therapies

The incidence of cancer in pre-pubertal boys has significantly increased and, it has been recognized that the gonado-toxic effect of the cancer treatments may lead to infertility. Here, we have evaluated the effects on porcine neonatal Sertoli cells (SCs) of three commonly used chemotherapy drugs; cisplatin, 4-Hydroperoxycyclophosphamide and doxorubicin. All three drugs induced a statistical reduction of 5-hydroxymethylcytosine in comparison with the control group, performed by Immunofluorescence Analysis. The gene and protein expression levels of GDNF, were significantly down-regulated after treatment to all three chemotherapy drugs comparison with the control group. Specifically, differences in the mRNA levels of GDNF were: 0,8200 ± 0,0440, 0,6400 ± 0,0140, 0,4400 ± 0,0130 fold change at 0.33, 1.66, and 3.33μM cisplatin concentrations, respectively (**p < 0.01 at 0.33 and 1.66 μM vs SCs and ***p < 0.001 at 3.33μM vs SCs); 0,6000 ± 0,0340, 0,4200 ± 0,0130 fold change at 50 and 100 μM of 4-Hydroperoxycyclophosphamide concentrations, respectively (**p < 0.01 at both these concentrations vs SCs); 0,7000 ± 0,0340, 0,6200 ± 0,0240, 0,4000 ± 0,0230 fold change at 0.1, 0.2 and 1 µM doxorubicin concentrations, respectively (**p < 0.01 at 0.1 and 0.2 μM vs SCs and ***p < 0.001 at 1 μM vs SCs). Differences in the protein expression levels of GDNF were: 0,7400 ± 0,0340, 0,2000 ± 0,0240, 0,0400 ± 0,0230 A.U. at 0.33, 1.66, and 3.33μM cisplatin concentrations, respectively (**p < 0.01 at both these concentrations vs SCs); 0,7300 ± 0,0340, 0,4000 ± 0,0130 A.U. at 50 and 100 μM of 4- Hydroperoxycyclophosphamide concentrations, respectively (**p < 0.01 at both these concentrations vs SCs); 0,6200 ± 0,0340, 0,4000 ± 0,0240, 0,3800 ± 0,0230 A.U. at 0.l, 0.2 and 1 µM doxorubicin concentrations, respectively (**p < 0.01 at 0.1 and 0.2 μM vs SCs and ***p < 0.001 at 1 μM vs SCs). Furthermore, we have demonstrated the protective effect of eicosapentaenoic acid on SCs only at the highest concentration of cisplatin, resulting in an increase in both gene and protein expression levels of GDNF (1,3400 ± 0,0280 fold change; **p < 0.01 vs SCs); and of AMH and inhibin B that were significantly recovered with values comparable to the control group. Results from this study, offers the opportunity to develop future therapeutic strategies for male fertility management, especially in pre-pubertal boys.

Molecular mechanism of reproductive toxicity induced by beta-cypermethrin in zebrafish

Beta-cypermethrin, a type II synthetic pyrethroid insecticide, is widely used in pest control. Several studies have demonstrated that beta-cypermethrin can affect the reproductive system of mammals. However, there is still a scarcity of information about the reproductive toxicity to fish induced by beta-cypermethrin and its molecular mechanism. Therefore, this study was conducted to address this scientific question, in which the adult zebrafish were exposed to 0 (blank control), 0 (acetone solvent control), 0.1, 0.5, and 2.5 μg/L of beta-cypermethrin for 21 days. A decrease in cumulative egg production of zebrafish was observed, indicating that beta-cypermethrin had a negative impact on reproductive capacity of zebrafish. Regarding the histomorphological analysis of gonads, the delay of gonadal development was observed after exposure for 21 days. In addition, significant changes in plasma 17β-estradiol (E2) and testosterone (T) were found in zebrafish. Further exploration showed that the transcription levels of hypothalamic-pituitary-gonadal (HPG) axis-related genes were remarkably changed, which corresponded well with the alterations of hormone levels. These results demonstrated that beta-cypermethrin might have an adverse effect on the reproduction system of zebrafish through delaying gonadal development, disturbing sex hormone secretion, and affecting HPG axis gene expression. This study suggests that beta-cypermethrin poses a potential threat to the reproduction of fish populations, and the toxicity assessment of beta-cypermethrin plays a vital role in the environmental risk assessment of pesticides.

A 30-Year Study of Impacts, Recovery, and Development of Critical Effect Sizes for Endocrine Disruption in White Sucker (Catostomus commersonii) Exposed to Bleached-Kraft Pulp Mill Effluent at Jackfish Bay, Ontario, Canada

Jackfish Bay is an isolated bay on the north shore of Lake Superior, Canada that has received effluent from a large bleached-kraft pulp mill since the 1940s. Studies conducted in the late 1980s found evidence of reductions in sex steroid hormone levels in multiple fish species living in the Bay, and increased growth, condition and relative liver weights, with a reduction in internal fat storage, reduced gonadal sizes, delayed sexual maturation, and altered levels of circulating sex steroid hormones in white sucker (Catostomus commersonii). These early studies provided some of the first pieces of evidence of endocrine disruption in wild animals. Studies on white sucker have continued at Jackfish Bay, monitoring fish health after the installation of secondary waste treatment (1989), changes in the pulp bleaching process (1990s), during facility maintenance shutdowns and during a series of facility closures associated with changing ownership (2000s), and were carried through to 2019 resulting in a 30-year study of fish health impacts, endocrine disruption, chemical exposure, and ecosystem recovery. The objective of the present study was to summarize and understand more than 75 physiological, endocrine, chemical and whole organism endpoints that have been studied providing important context for the complexity of endocrine responses, species differences, and challenges with extrapolation. Differences in body size, liver size, gonad size and condition persist, although changes in liver and gonad indices are much smaller than in the early years. Population modeling of the initial reproductive alterations predicted a 30% reduction in the population size, however with improvements over the last couple of decades those population impacts improved considerably. Reflection on these 30 years of detailed studies, on environmental conditions, physiological, and whole organism endpoints, gives insight into the complexity of endocrine responses to environmental change and mitigation.

Effects of the Thyroid Endocrine System on Gonadal Sex Ratios and Sex-Related Gene Expression in the Pufferfish Takifugu rubripes

To examine the effect and mechanism of thyroid hormone on gonadal sex differentiation, Takifugu rubripes larvae were treated with goitrogen (methimazole, MET, 1000 g/g), and thyroxine (T4, 2nM) from 25 to 80 days after hatching (dah). Gonadal histology and sex ratios of fish were then determined at 80 dah. MET treatment induced masculinization, but T4 treatment did not induce feminization in T. rubripes larvae. Transcriptomic analysis of gonads at 80 dah was then conducted. Among the large number of differentially expressed genes between the groups, the expression of foxl2, cyp19a1a, and dmrt1 was altered. The expression of foxl2, cyp19a1a, dmrt1 and gsdf at 25, 40, 55 days after treatment (dat) was further analyzed by qPCR. MET treatment suppressed the expression of foxl2 and cyp19a1a, and induced the expression of dmrt1 in genetic females (p < 0.05). Additionally, T4 treatment induced an increase in the expression of cyp19a1a in genetic XY gonads only at 25 dat. However, the increase in cyp19a1a expression did not continue to 40 and 55 dat. This may explain why feminization of larvae was not found in the T4-treated group. Thus, the present study provides the first evidence that MET treatment causes masculinization in teleost fish. The effects of MET-induced masculinization in T. rubripes may act primarily via suppression of the expression of foxl2 and cyp19a1a, and stimulation of the expression of dmrt1. Moreover, the effects of higher concentrations of T4 or different concentrations of T3, on sex differentiation require further testing.

Functional differences in the hypothalamic-pituitary-gonadal axis are associated with alternative reproductive tactics based on an inversion polymorphism

The evolution of social behavior depends on genetic changes, yet, how genomic variation manifests itself in behavioral diversity is still largely unresolved. Chromosomal inversions can play a pivotal role in producing distinct behavioral phenotypes, in particular, when inversion genes are functionally associated with hormone synthesis and signaling. Male ruffs exhibit alternative reproductive tactics (ARTs) with an autosomal inversion determining two alternative morphs with clear behavioral and hormonal differences from the ancestral morph. We investigated hormonal and transcriptomic differences in the pituitary and gonads. Using a GnRH challenge, we found that the ability to synthesize testosterone in inversion carriers is severely constrained, whereas the synthesis of androstenedione, a testosterone precursor, is not. Inversion morphs were able to produce a transient increase in androstenedione following the GnRH injection, supporting the view that pituitary sensitivity to GnRH is comparable to that of the ancestral morph. We then performed gene expression analyses in a second set of untreated birds and found no evidence of alterations to pituitary sensitivity, gonadotropin production or gonad sensitivity to luteinizing hormone or follicle-stimulating hormone across morphs. Inversion morphs also showed reduced progesterone receptor expression in the pituitary. Strikingly, in the gonads, inversion morphs over-expressed STAR, a gene that is located outside of the inversion and responsible for providing the cholesterol substrate required for the synthesis of sex hormones. In conclusion, our results suggest that the gonads determine morph-specific differences in hormonal regulation.

Parental exposure to polystyrene microplastics at environmentally relevant concentrations has negligible transgenerational effects on zebrafish (Danio rerio)

Waterborne exposure to highly persistent microplastic pollutants is a major concern for aquatic species worldwide. There are still gaps in knowledge on microplastics' potential transgenerational effects on offspring generation. Using zebrafish, this study investigated the survival and early development of offspring through a 21-day continuous parental treatment with polystyrene microplastics. The results showed that continuous waterborne exposure to high concentrations (>100 μg/L) of polystyrene microplastics (1 μm) for 21 days resulted in notable microplastic accumulation in adult fish intestines. Exposure at microplastic concentrations greater than 100 μg/L also induced significant changes in steroidogenic mRNA expression in zebrafish gonads. However, no significant changes in the cumulative number of eggs spawned and fertilization rate were observed at any parental exposure concentrations when compared to the control. Early development of derived offspring, in terms of hatching rate, body length, malformation rate and mortality rate, did not significantly differ from that of the control. This study showed that transgenerational effects of parental exposure to polystyrene microplastics in zebrafish might be negligible or recoverable. This study provided new results and insights on the transgenerational effects of microplastics on a freshwater fish species and can help to understand impacts of microplastics on freshwater ecosystems.

Endocrine-Disrupting Air Pollutants and Their Effects on the Hypothalamus-Pituitary-Gonadal Axis

Anthropogenic endocrine-disrupting chemicals (EDCs) can contaminate air, soil, and water. Human exposures to EDCs occur through inhalation, absorption, and ingestion. EDCs act by disrupting various pathways in the endocrine system. When the hypothalamic–pituitary–gonadal (HPG) axis is disrupted by EDCs, there can be effects on fertility in both men and women. Not only can fertility be indirectly affected by EDC disruptions of the HPG axis, but EDCs can also directly affect the menstrual cycle and sperm morphology. In this review, we will discuss the current findings on EDCs that can be inhaled. This review examines effects of exposure to prominent EDCs: brominated and organophosphate flame retardants, diesel exhaust, polycyclic aromatic hydrocarbons, cadmium and lead, TCDD, and polychlorinated biphenyls on fertility through alterations that disrupt the HPG axis and fertility through inhalation. Although the studies included herein include multiple exposure routes, all the studies indicate receptor interactions that can occur from inhalation and the associated effects of all compounds on the HPG axis and subsequent fertility.

Effects of 17α-ethinylestradiol on sex ratio, gonadal histology and perianal hyperpigmentation of Cnesterodon decemmaculatus (Pisces, Poeciliidae) during a full-lifecycle exposure

The effects of 17α-ethinylestradiol (EE₂) on sex ratio, gonopodium morphology, and gonadal histology of C. decemmaculatus were assessed by a full-lifecycle exposure experiment. Newborn fish were waterborne exposed to 30, 100, and 300 ng EE₂/L for 90 d, using 50 fish per treatment. Additionally, in December of 2016, a field survey was conducted on a C. decemmaculatus population inhabiting the Girado Creek downstream of the Chascomus city wastewater effluent discharge. After 90 d of exposure, EE₂ was able to histologically skew the sex ratio toward females and inhibit the full gonopodium development since the lowest tested concentration (LOEC = 30 ng/L). At higher concentrations, EE₂ was toxic, inducing mortality in a concentration-dependent fashion (90 d-LC₅₀ = 109.9 ng/L) and altering the gonadal histoarchitecture, causing neither testes nor ovaries discernible histologically (LOEC = 100 ng/L). In addition, a novel response, perianal hyperpigmentation, was discovered been induced by the EE₂ exposure in a concentration-dependent fashion (90 d-EC₅₀ = 39.3 ng/L). A higher proportion of females and perianal hyperpigmentation were observed in wild fish collected from the Girado Creek. The major reached conclusions are: i) EE₂ induce different effects on the sexual traits of C. decemmaculatus when exposed from early-life or adult stages. ii) The most sensitive effects observed in the laboratory occur in a creek receiving wastewater effluent. iii) The perianal hyperpigmentation comes-up as a promising biomarker of exposure to estrogenic compounds.

Exposure of zebrafish to environmentally relevant concentrations of mercury during early life stages impairs subsequent reproduction in adults but can be recovered in offspring

Mercury (Hg) is a global pollutant that poses potential threats to health of fishes. Although effects of Hg on reproduction of fishes have been documented, little is known about effects of exposure to Hg²⁺ during early life stages on subsequent reproductive fitness of adults or whether these effects can be transferred to offspring. In this study, zebrafish embryos were exposed to environmentally relevant concentrations of Hg²⁺ (0.6, 3 or 15 μg/L) for 5 days and then depurated in clean water for another 115 days. Exposure to Hg²⁺ during early life stages disturbed the balance of sex hormones and gametogenesis by altering expression of mRNA for genes involved in the hypothalamic-pituitary-gonadal axis, which resulted in delayed gonadal development and lesser gonado-somatic index, thereby resulting in lesser fecundity. A similar, but less pronounced effect was observed in F₁ females that were not exposed directly to Hg, whereas such damage was neither observed in F₁ males nor either sex during the F₂ generation. Exposure to Hg²⁺ during early life can impair subsequent reproduction in adults and has intergenerational effects on F₁ females, but this reproductive damage can be recovered in F₁ males and in F₂ females.

Tissues injury and pathological changes in Hyla intermedia juveniles after chronic larval exposure to tebuconazole

Tebuconazole (TBZ), an azole pesticide, is one of the most frequently detected fungicides in surface water. Despite its harmful effects, mainly related to endocrine disturbance, the consequences of TBZ exposure in amphibians remain poorly understood. Here, we investigated the adverse and delayed effects of TBZ chronic exposure on a native anuran species, often inhabiting cultivated areas, the Italian tree frog (Hyla intermedia). To disclose the multiple mechanisms of action through which TBZ exerts its toxicity we exposed tadpoles over the whole larval period to two sublethal TBZ concentrations (5 and 50 μg/L), and we evaluated histological alterations in three target organs highly susceptible to xenobiotics: liver, kidney, and gonads. We also assessed morphometric and gravimetric parameters: snout-vent length (SVL), body mass (BM), liver somatic index (LSI), and gonad-mesonephros complex index (GMCI) and determined sex ratio, gonadal development, and differentiation. Our results show that TBZ induces irreversible effects on multiple target organs in H. intermedia, exerting its harmful effects through several pathological pathways, including a massive inflammatory response. Moreover, TBZ markedly affects sexual differentiation also by inducing the appearance of sexually undetermined individuals and a general delay of germ cell maturation. Given the paucity of data on the effects of TBZ in amphibians, our results will contribute to a better understanding of the environmental risk posed by this fungicide to the most endangered group of vertebrates.

The impact of endocrine-disrupting chemical exposure in the mammalian hypothalamic-pituitary axis

The hypothalamic-pituitary axis (HP axis) plays a critical and integrative role in the endocrine system control to maintain homeostasis. The HP axis is responsible for the hormonal events necessary to regulate the thyroid, adrenal glands, gonads, somatic growth, among other functions. Endocrine-disrupting chemicals (EDCs) are a worldwide public health concern. There is growing evidence that exposure to EDCs such as bisphenol A (BPA), some phthalates, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and biphenyls (PBBs), dichlorodiphenyltrichloroethane (DDT), tributyltin (TBT), and atrazine (ATR), is associated with HP axis abnormalities. EDCs act on hormone receptors and their downstream signaling pathways and can interfere with hormone synthesis, metabolism, and actions. Because the HP axis function is particularly sensitive to endogenous hormonal changes, disruptions by EDCs can alter HP axis proper function, leading to important endocrine irregularities. Here, we review the evidence that EDCs could directly affect the mammalian HP axis function.

Exogenous Oestrogen Impacts Cell Fate Decision in the Developing Gonads: A Potential Cause of Declining Human Reproductive Health

The increasing incidence of testicular dysgenesis syndrome-related conditions and overall decline in human fertility has been linked to the prevalence of oestrogenic endocrine disrupting chemicals (EDCs) in the environment. Ectopic activation of oestrogen signalling by EDCs in the gonad can impact testis and ovary function and development. Oestrogen is the critical driver of ovarian differentiation in non-mammalian vertebrates, and in its absence a testis will form. In contrast, oestrogen is not required for mammalian ovarian differentiation, but it is essential for its maintenance, illustrating it is necessary for reinforcing ovarian fate. Interestingly, exposure of the bi-potential gonad to exogenous oestrogen can cause XY sex reversal in marsupials and this is mediated by the cytoplasmic retention of the testis-determining factor SOX9 (sex-determining region Y box transcription factor 9). Oestrogen can similarly suppress SOX9 and activate ovarian genes in both humans and mice, demonstrating it plays an essential role in all mammals in mediating gonad somatic cell fate. Here, we review the molecular control of gonad differentiation and explore the mechanisms through which exogenous oestrogen can influence somatic cell fate to disrupt gonad development and function. Understanding these mechanisms is essential for defining the effects of oestrogenic EDCs on the developing gonads and ultimately their impacts on human reproductive health.

Assessment of reproductive and developmental effects of graphene oxide on Japanese medaka (Oryzias latipes)

Due to its unique properties, graphene oxide (GO) has potential for biomedical and electronic applications, however environmental contamination including aquatic ecosystem is inevitable. Moreover, potential risks of GO in aquatic life are inadequately explored. Present study was designed to evaluate GO as an endocrine disrupting chemical (EDC) using the model Japanese medaka (Oryzias latipes). GO was injected intraperitoneally (25-200 μg/g) once to breeding pairs and continued pair breeding an additional 21 days. Eggs laid were analyzed for fecundity and the fertilized eggs were evaluated for developmental abnormalities including hatching. Histopathological evaluation of gonads, liver, and kidneys was made 21 days post-injection. LD₅₀ was found to be sex-dependent. Fecundity tended to reduce in a dose-dependent manner during early post-injection days; however, the overall evaluation showed no significant difference. The hatchability of embryos was reduced significantly in the 200 μg/g group; edema (yolk and cardiovascular) and embryo-mortality remained unaltered. Histopathological assessment identified black particles, probably agglomerated GO, in the gonads of GO-treated fish. However, folliculogenesis in stromal compartments of ovary and the composition of germinal elements in testis remained almost unaltered. Moreover, granulosa and Leydig cells morphology did not indicate any significant EDC-related effects. Although liver and kidney histopathology did not show GO as an EDC, some GO-treated fish accumulated proteinaceous fluid in hepatic vessels and induced hyperplasia in interstitial lymphoid cells (HIL) located in kidneys. GO agglomerated in medaka gonads after 21-days post-injection. However, gonad histopathology including granulosa and Leydig cells alterations were associated with GO toxicity rather than EDC effects.

Comparing the effect of triadimefon and its metabolite on male and female Xenopus laevis: Obstructed growth and gonad morphology

Amphibians are the most endangered class of vertebrates. In this study, Xenopus laevis frogs were exposed to 0, 1 and 10 mg/L of triadimefon or triadimenol. After 14 or 28 days of exposure, high levels of triadimefon or triadimenol obstructed the growth of frogs. However, low levels of triadimefon induced the growth of females after the longer period of exposure. We also found that the antioxidant enzyme activity and LDH levels in males were higher than those in females after 28-days exposure. In histopathology tests, triadimenol exerted more effect on the ovary while triadimefon exerted more effect on the testes. Additionally, the levels of Estradiol in all 14-day treatments, except 1 mg/L triadimenol, were significantly decreased, however, there was no difference in testosterone levels. Furthermore, triadimefon and triadimenol disrupted the expression of genes controlling hormone homeostasis and reproduction, and this effect depended on the exposure time and the gender of the organism. Our experiments explored the effect of triadimefon and its metabolite on the gonads of frogs and highlighted the role that pesticides are likely to play in the global decline of amphibians.

Assessment of reproductive and developmental effects of graphene oxide on Japanese medaka (Oryzias latipes)

Due to its unique properties, graphene oxide (GO) has potential for biomedical and electronic applications, however environmental contamination including aquatic ecosystem is inevitable. Moreover, potential risks of GO in aquatic life are inadequately explored. Present study was designed to evaluate GO as an endocrine disrupting chemical (EDC) using the model Japanese medaka (Oryzias latipes). GO was injected intraperitoneally (25-200 μg/g) once to breeding pairs and continued pair breeding an additional 21 days. Eggs laid were analyzed for fecundity and the fertilized eggs were evaluated for developmental abnormalities including hatching. Histopathological evaluation of gonads, liver, and kidneys was made 21 days post-injection. LD50 was found to be sex-dependent. Fecundity tended to reduce in a dose-dependent manner during early post-injection days; however, the overall evaluation showed no significant difference. The hatchability of embryos was reduced significantly in the 200 μg/g group; edema (yolk and cardiovascular) and embryo-mortality remained unaltered. Histopathological assessment identified black particles, probably agglomerated GO, in the gonads of GO-treated fish. However, folliculogenesis in stromal compartments of ovary and the composition of germinal elements in testis remained almost unaltered. Moreover, granulosa and Leydig cells morphology did not indicate any significant EDC-related effects. Although liver and kidney histopathology did not show GO as an EDC, some GO-treated fish accumulated proteinaceous fluid in hepatic vessels and induced hyperplasia in interstitial lymphoid cells (HIL) located in kidneys. GO agglomerated in medaka gonads after 21-days post-injection. However, gonad histopathology including granulosa and Leydig cells alterations were associated with GO toxicity rather than EDC effects.

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.

Effects of BPA on zebrafish gonads: Focus on the endocannabinoid system

Bisphenol A (BPA), a monomer used for polycarbonate manufacture, has been widely reported as an endocrine-disrupting chemical (EDC). Among other alterations, BPA induces reproductive dysfunctionalities. Changes in the endocannabinoid system (ECS) have been recently shown to be associated with reproductive disorders. The ECS is a lipid-based signaling system (cannabinoid receptors, endocannabinoids and enzymatic machinery) involved in several physiological functions. The main goal of the present study was to assess the effects of two environmental concentrations of BPA (10 and 20 μg/L) on the ECS in 1-year old zebrafish gonads. In males, BPA increased the gonadosomatic index (GSI) and altered testicular levels of endocannabinoids as well as reduced the testicular area occupied by spermatogonia. In male liver, exposure to 20 μg/L BPA significantly increased vitellogenin (vtg) transcript levels. In female zebrafish, BPA altered ovarian endocannabinoid levels, elevated hepatic vtg mRNA levels as well as increased the percentage of vitellogenic oocytes in the ovaries. In conclusion, exposure to two environmentally relevant concentrations of BPA altered the ECS and consequently, gonadal function in both male and female zebrafish.

Opioids and the Hypothalamic-Pituitary-Gonadal (HPG) Axis

CONTEXT

Hypogonadism is a well-established consequence of opioid use. It has been reported in both men and women, although more widely studied in men.

EVIDENCE ACQUISITION

PubMed was searched for articles in English until December 2019 for opioids and hypogonadism. Bibliography of retrieved articles was searched for relevant articles.

EVIDENCE SYNTHESIS

The prevalence of opioid-induced hypogonadism (OIH) varies between studies but was reported to be 69% in a recent systematic review. There is large heterogeneity in the studies, with different factors shown to have stronger association with hypogonadism such as specific types of opioids, higher doses, and longer durations of use. The consequences of OIH include sexual dysfunction, depression, decreased quality of life, and low bone density. There is paucity of randomized controlled trials assessing the efficacy of testosterone replacement therapy (TRT) for OIH in men, and even less studies on treating OIH in women. TRT studies in men reported varying outcomes with some studies favoring and others showing no clear benefit of TRT on different measures.

CONCLUSIONS

Despite the high prevalence of OIH, it remains underrecognized and undertreated with multiple endocrine and metabolic consequences. A reasonable approach in patients using opioids includes informing them of this complication and its potential consequences, screening for signs and symptoms of hypogonadism then sex hormone levels if prolonged opioid use > 3 months, and treating patients diagnosed with hypogonadism, if and when clinically indicated, with sex hormones if chronic opioids are planned to be continued for ≥ 6 months.

Effects of Whole-Lake Additions of Ethynylestradiol on Leech Populations

Leeches are widespread, found in many freshwater habitats, and have diverse dietary habits. Despite their close phylogenetic relationships to Mollusca, a phylum with species affected by exogenous estrogens, it is unclear whether Hirudinea may also be impacted. A whole-lake experiment was done at the Experimental Lakes Area in Ontario, Canada, to assess whether 17α-ethynylestradiol (EE2) affected fishes and other species. Herein, we examined whether EE2 impacted leech community composition, species abundance, growth rates, gonad size, and cocoon production, when compared with reference lakes using a before-after-control-impact design. Each month baited leech traps were set overnight in the littoral zone at 10 sites around experimental Lake 260 and 2 reference lakes, and individuals were identified, weighed, and measured. Male and female organs of common species Haemopis marmorata were measured. Across all lakes, 9 species representing 3 families were collected. There were no apparent effects of EE2 on numbers, species richness, or community composition; however, condition in 1 of 5 species increased significantly after EE2 exposures. Total gonadosomatic index (GSI) and the GSI for all male or all female organs combined for H. marmorata were not affected by EE2 additions. However, some individual reproductive organs including relative sperm sac length (+), relative epididymis weight (-), relative vaginal bulb length (+), and relative ovisac + albumen gland length (+) changed after EE2 additions. Finally, whereas overall cocoon production was similar, it occurred earlier in the EE2-amended lake. In summary, few individual through community measures of leeches responded to low ng/L concentrations of EE2, suggesting that Hirudinea are less sensitive to this endocrine disruptor than other invertebrates and vertebrates. Environ Toxicol Chem 2020;39:1608-1619. © 2020 SETAC.

Transcriptional changes caused by estrogenic endocrine disrupting chemicals in gonad-mesonephros complexes of genetic male Xenopus laevis: Multiple biomarkers for early detection of testis differentiation disruption

Our recent study revealed some early molecular and cellular events in which 17β-estradiol (E2) disrupted testis differentiation and resulted in feminization in Xenopus laevis (the African clawed frog), an ideal species for studying reproductive endocrine disruption by estrogenic endocrine disrupting chemicals (EDCs). On this basis, we aimed to develop multiple biomarkers for early detection of testis differentiation disruption by estrogenic EDCs in X. laevis. Tadpoles at stage 45/46 were exposed to four known estrogenic EDCs with different estrogenic activities, including E2, diethylstilbestrol (DES), mestranol (MES) and 4-n-nonyphenol (NP). At stage 53, gonadal morphological and histological changes as well as altered sex-dimorphic gene expression in gonad-mesonephros complexes (GMCs) showed that these estrogenic EDCs disrupted testis differentiation and caused feminization to different degrees. Then we measured transcriptional changes of 48 candidate genes, which are believed to be associated with E2-induced testis differentiation alterations, in GMCs at stage 50. As a result, 19 genes were found to be transcriptionally altered by all test chemicals and proposed as promising biomarkers for early detection of testis differentiation disruption by estrogenic EDCs. Finally, all biomarker responses were integrated as integrated biomarker response (IBR) index to characterize testis differentiation disruption by these estrogenic EDCs in X. laevis. Compared with the methods used in previous studies, the multiple biomarker test using X. laevis at early developmental stages largely shortens the exposure duration, thereby achieving the goal of rapid detection. Certainly, the biomarker test needs further validations in the future study.

Environmental estrogen exposure converts lipid metabolism in male fish to a female pattern mediated by AMPK and mTOR signaling pathways

Environmental estrogens, including bisphenol A (BPA) and 17β-estradiol (E2), which are widely used in industries and medicine, pose a severe ecological threat to fish due to feminization induction. However, the related metabolic basis for reproductive feminization in male fish has not been well addressed. We first found that female zebrafish exhibited higher lipid accumulation and lipogenesis activity than males. Next, we exposed male and female zebrafish to E2 (200 ng/L) or BPA (100 μg/L) for six weeks, and observed an early-phase reproductive feminization in males, accompanied with reduced spermatids, significant fat deposition and lipogenic gene expressions that mimicked female patterns. Cellular signaling assays revealed that, E2 or BPA modulated lipid metabolism in males mainly through lowering 5' AMP-activated protein kinase (AMPK) and upregulating the lipogenic mechanistic target of rapamycin (mTOR) pathways. For the first time, we show that environmental estrogens could alter lipid metabolism in male fish to a female pattern (metabolic feminization) prior to gonad feminization in male fish, to allows males to accumulate efficiently lipids to harmonize with the feminized gonads. This study suggests that negative effects of environmental estrogens, as hazardous materials, on vertebrate health are more complicated than originally thought.

Chronic exposure to di-n-butyl phthalate causes reproductive toxicity in zebrafish

Di-n-butyl phthalate (DBP) is known to have adverse effects on reproduction in mammals and is pervasive in the aquatic environment. The objective of the present study was to investigate whether long-term exposure to low concentrations of DBP can affect fish reproduction. In this study, zebrafish (Danio rerio) embryos (F₀ ) were exposed to low concentrations (4.9, 13.6 and 43.8 μg/L) of DBP from 2 hours post-fertilization until sexual maturation. The results demonstrate that chronic exposure to DBP (43.8 μg/L) impaired the reproductive function of zebrafish, as verified by reduced egg production and modifications to gonadal histology of the treated fish. Plasma 17β-estradiol levels in female zebrafish decreased significantly in a concentration-dependent manner, while testosterone levels in males increased significantly when fish were exposed to 43.8 μg/L DBP. Real-time polymerase chain reaction was performed to examine selected genes in the hypothalamic-pituitary-gonadal (HPG) axis and liver. Hepatic vitellogenin gene transcription was downregulated in both males and females, suggesting that DBP possesses anti-estrogenic activity. The disturbed steroid hormones were accompanied by the significant alterations in gene expression along the HPG axis. Additionally, parental exposure to DBP caused reduced hatching and survival rate as well as decreased growth in the F₁ generation. Taken together, these results demonstrate that long-term exposure to low concentrations of DBP in zebrafish could cause reproductive toxicity, implying that DBP could have significant adverse effects on fish populations, particularly in a highly DBP-contaminated aquatic environment.

Temperature-Dependent Biomarkers of Estrogenic Exposure in a Piscivore Freshwater Fish

The biological effects of endocrine-active compounds and increasing water temperatures as a result of climate change have been studied extensively and independently, but there is a dearth of research to examine the combined effect of these factors on exposed organisms. Recent data suggest that estrogenic exposure and rising ambient temperatures independently impact predator-prey relationships. However, establishing these connections in natural settings is complex. These obstacles can be circumvented if biomarkers of estrogenic exposure in resident fish can predict changes in predator-prey relationships. To test the effects of estrone and temperature, the piscivore bluegill sunfish (Lepomis macrochirus) was exposed for 30 days to estrone at concentrations (90 ± 17.6 ng/L [mean ± standard deviation] and 414 ± 146 ng/L) previously shown to reduce prey-capture success. Exposures were conducted at four temperatures (15 °C, 18 °C, 21 °C, 24 °C) to simulate breeding season ambient temperatures across the natural range of this species. A suite of morphological and physiological biomarkers previously linked to estrogenic exposures were examined. Biomarkers of estrone exposure were more commonly and severely impacted in male fish than in female fish. Notably, the gonadosomatic index was lower and gonads were less mature in exposed males. Additionally, temperature modulated the effects of estrone similarly in males and females with fish exposed at higher temperatures typically exhibiting a decreased morphological index. This study provides evidence that alterations in hepatic function and gonadal function may cause shifts in metabolism and energy allocation that may lead to declining prey capture performance.

Effect of Copper Sulphate (CuSO4) on Freshwater Snail, Physa acuta Draparnaud, 1805: A Histopathological Evaluation

In this study, freshwater snail (Physa acuta) was investigated to determine histopathological effects of CuSO₄ on digestive gland, foot, mantle and ovotestis under laboratory conditions. The snails were exposed to different sublethal concentrations of CuSO₄ (0.05 mg/L, 0.1 mg/L and 0.2 mg/L) periods of 10, 20 and 30 days. The relationship between CuSO₄ concentration and mortality rate in snails was calculated as Y = 8.8 + 125.14X, R² = 0.9444. The histopathological examinations revealed that CuSO₄ caused significant histopathological changes in all the tissues of the snail. The severity of these lesions in tissues increased with increasing CuSO₄ concentration and duration of exposure. The results showed that freshwater snail, Physa acuta can be considered to be a suitable bioindicator to demonstrate the toxic effect of copper in aquatic environments.

Disruptive effects of nonylphenol on reproductive hormones, antioxidant enzymes, and histology of liver, kidney and gonads in Caspian trout smolts

The endocrine-disrupting effect of pollutants such as alkylphenols has been considered a major concern during recent years. Although the effects of nonylphenol on the reproductive hormones of fish have been investigated in several studies, the effect of this endocrine disruptor on reproductive hormones of immature fish and salmonid smolts has been less addressed. The present work studied the effects of 1, 10 and 100 μg/l concentrations of nonylphenol on the levels of plasma reproductive hormones and liver antioxidant enzymes as well as on histopathology of reproductive and non-reproductive organs of male and female Caspian brown trout (Salmo trutta caspius) smolts after 21 days of exposure. The results of the present study showed that environmentally relevant concentrations of nonylphenol affected plasma levels of sex steroids; gonadotropins, phosphorus, estradiol to testosterone ratio, and also caused histopathological lesions in liver, kidney and testis tissues of immature Caspian brown trout during smolting. Nonylphenol significantly increased the levels of estradiol in plasma of both male and female smolts exposed to nonylphenol compared with the control groups. Exposure to nonylphenol decreased testosterone and FSH levels in both genders. It has also increased plasma levels of LH in females but did not affect LH levels in male fish. Liver SOD and CAT content was decreased in nonylphenol-exposed smolts. Therefore, the release of this economically valuable and endangered species into the rivers contaminated with nonylphenol should be avoided as it can have significant effects on the development and reproductive function of smolts.

The comparative toxicity of rainfall overflows and a municipal effluent plume in Elliptio complanata using a novel qPCR array approach

Municipal effluents have the potential to disrupt the endocrine system involved in reproduction in aquatic organisms. The purpose of this study was to develop a novel a quantitative polymerase chain reaction (qPCR) array for the freshwater mussel Elliptio complanata to compare the toxic properties of municipal effluents and rainfall overflows. Mussels were caged for 3 months at upstream and downstream sites of a municipal effluent discharge point and 2 rainfall overflow sites in the Saint-Lawrence River. The data revealed that exposure to municipal effluents and overflow sites lead to increased expression of vitellogenin (VTG) in male mussels, altered sexual differentiation in females, gene expression involved in oxidative stress (superoxide dismutase, glutathione S-transferase) and DNA damage (chromosome mismatch and repair of covalently-bound DNA adducts). Mussels at the downstream site accumulated also large amounts of heterotrophic bacteria but not at the overflow sites. However, mussels at the overflow sites had decreased expression in ABC transporter gene expression. Scaling analysis revealed that the following gene expression were related to effects at higher level of biological organization such as total RNA levels, gonad mass and gonad somatic index: DNA repair of covalent DNA adducts, mistmach chromosomal recombination during meiosis and undifferentiated cells in gonads. In conclusion, exposure to rainfall overflow sites have similar effects to municipal effluents based on VTG and oxidative stress responses at the transcriptomic levels only but the effects at the DNA integrity and sexual differentiation were involved in adverse outcome pathways of urban pollution in Elliptio complanata mussels.

3-(4-Methylbenzylidene) camphor induced reproduction toxicity and antiandrogenicity in Japanese medaka (Oryzias latipes)

To assess the toxic effects of 3-(4-Methylbenzylidene) camphor (4-MBC) at environmentally relevant concentrations on the reproduction and development of Japanese medaka (Oryzias latipes), adult paired medaka (F0) were exposed to 5, 50, and 500 μg/L 4-MBC for 28 d in the current study. The fecundity and fertility were significantly decreased at 500 μg/L 4-MBC (p < 0.05). Histological observations showed that spermatogenesis in F0 males was significantly inhibited at 50 and 500 μg/L 4-MBC, similar to the effects obtained with all treatments of plasma 11-ketotestosterone (p < 0.05). Moreover, the plasma vitellogenin and estradiol levels in F0 females were significantly increased at 5 μg/L 4-MBC (p < 0.05). All the transcripts of hypothalamic-pituitary-gonadal (HPG) axis-related genes tested in the brains and gonads of males were significantly increased at all treatments, similar to the effects obtained for erα, erβ and vtg in the livers and in contrast to those found for arα in the livers (p < 0.05). Equal numbers of embryos were exposed to tap water and 4-MBC solutions. Significantly increased times to hatching, decreased hatching rates and decreased body lengths at 14-day post-hatching (dph) were obtained at 500 μg/L 4-MBC treatment (p < 0.05). The cumulative death rates at 14 dph were significantly increased with all the treatments (p < 0.05). Therefore, our results showed that long-term exposure to 50 and 500 μg/L 4-MBC causes reproductive and developmental toxicity and thus provide new insight into antiandrogenicity and the mechanism of 4-MBC in Japanese medaka.

Climate change impacts on fish reproduction are mediated at multiple levels of the brain-pituitary-gonad axis

Anthropogenic emissions of carbon dioxide in the atmosphere have generated rapid variations in atmospheric composition which drives major climate changes. Climate change related effects include changes in physico-chemical proprieties of sea and freshwater, such as variations in water temperature, salinity, pH/pCO₂ and oxygen content, which can impact fish critical physiological functions including reproduction. In this context, the main aim of the present review is to discuss how climate change related effects (variation in water temperature and salinity, increases in duration and frequency of hypoxia events, water acidification) would impact reproduction by affecting the neuroendocrine axis (brain-pituitary-gonad axis). Variations in temperature and photoperiod regimes are known to strongly affect sex differentiation and the timing and phenology of spawning period in several fish species. Temperature mainly acts at the level of gonad by interfering with steroidogenesis, (notably on gonadal aromatase activity) and gametogenesis. Temperature is also directly involved in the quality of released gametes and embryos development. Changes in salinity or water acidification are especially associated with reduction of sperm quality and reproductive output. Hypoxia events are able to interact with gonad steroidogenesis by acting on the steroids precursor cholesterol availability or directly on aromatase action, with an impact on the quality of gametes and reproductive success. Climate change related effects on water parameters likely influence also the reproductive behavior of fish. Although the precise mechanisms underlying the regulation of these effects are not always understood, in this review we discuss different hypothesis and propose future research perspectives.

Evaluation of the effects of low concentrations of bisphenol AF on gonadal development using the Xenopus laevis model: A finding of testicular differentiation inhibition coupled with feminization

Developmental exposures to estrogenic chemicals possibly cause structural and functional abnormalities of reproductive organs in vertebrates. Bisphenol AF (BPAF), a bisphenol A (BPA) analogue, has been shown to have higher estrogenic activity than BPA, but little is known about the effects of BPAF on gonadal development, particularly gonadal differentiation. We aimed to determine whether low concentrations of BPAF could disrupt gonadal differentiation and subsequent development using Xenopus laevis, a model species for studying feminizing effects of estrogenic chemicals. X. laevis tadpoles were exposed to BPAF (1, 10, 100 nM) or 17β-estradiol (E2, positive control) from stages 45/46 to 53 and 66 in a semi-static exposure system, with a prolonged treatment with the highest concentration to the eighth week post-metamorphosis (WPM8). Gonadal morphology and histology as well as sexually dimorphic gene expression were examined to evaluate the effects of BPAF. All concentrations of BPAF caused changes in testicular morphology at different developmental stages compared with controls. Specifically, at stage 53, BPAF like E2 resulted in decreases in both the size and the number of gonadal metameres (gonomeres) in testes, looking like ovaries. Some of BPAF-treated testes remained segmented and even became discontinuous and fragmented at subsequent stages. Histological abnormalities were also observed in BPAF-treated testes, such as ovarian cavity at stages 53 and 66 and poorly developed seminiferous tubules on WPM8. At the molecular level, BPAF inhibited expression of male highly expressed genes in testes at stage 53. Correspondingly, BPAF, like E2, inhibited cell proliferation in testes at stage 50. All results show that low concentrations of BPAF inhibited testicular differentiation and subsequent development in X. laevis, along with feminizing effects to some degree. Our finding implies a risk of BPAF to the male reproductive system of vertebrates including humans.

Assessing cadmium-based quantum dots effect on the gonads of the marine mussel Mytilus galloprovincialis

This study assesses the sex-specific effects induced by CdTe QDs, on the marine mussel Mytilus galloprovincialis in comparison to its dissolved counterpart. A 14 days exposure to CdTe QDs and dissolved Cd was conducted (10 μg Cd L^-1), analysing Cd accumulation, oxidative stress, biotransformation, metallothionein and oxidative damage in the gonads. Both Cd forms caused significant antioxidant alterations, whereby QDs were more pro-oxidant, leading to oxidative damage, being females more affected. Overall, biochemical impairments on gonads of M. galloprovincialis demonstrate that the reproductive toxicity induced by CdTe QDs in mussels are sex-dependent and mediated by oxidative stress and lipid peroxidation. It is crucial to acknowledge how gametes are affected by metal-based nanoparticles, such as Cd-based QDs. As well as understanding the potential changes they may undergo at the cellular level during gametogenesis, embryogenesis and larval development potentially leading to serious impacts on population sustainability and ecosystem health.

2,2',4,4'-tetrabromodipheny ether (BDE-47) disrupts gonadal development of the Africa clawed frog (Xenopus laevis)

Previous studies have shown that BDE-47, one of the most abundant polybrominated diphenyl ethers (PBDEs) congeners, has a weak estrogenic activity, but it has remained unclear whether BDE-47 disrupts gonadal development and causes male-to-female sex reversal in lower vertebrates, with limited and controversial data. The present study aimed to determine the effects of BDE-47 on gonadal development in Xenopus laevis, a model amphibian species for studying adverse effects of estrogenic chemicals on reproductive development. X. laevis at stage 45/46 were exposed to BDE-47 (0.5, 5, 50 nM) in semi-static system, with 1 nM 17β-estradiol (E2) as the positive control. When reaching stage 53, tadpoles were examined for gonadal morphology, histology and sex-dimorphic gene expression. The phenotypic sex (gonadal morphology and histology) of each BDE-47-treated tadpole matched its genetic sex, showing no sex-reversal, whereas one half of genetic males treated with E2 displayed ovarian-like features. However, some genetic males (26%) in the 50 nM BDE-47 treatment group were found to contain more germ cells clumping together in the medulla, along with an increasing tendency of the gonad length/kidney length ratio in males, resembling feminizing outcomes of E2. These observations seem to suggest that BDE-47 exerted weak feminizing effects. However, BDE-47 induced increases in expression of both female-biased genes and male-biased genes in two sexes, which disagrees with feminizing outcomes, suggesting complicated effects of BDE-47 on gonadal development. Taken together, all results demonstrate that nanomolar BDE-47 disrupted gonadal development and exerted weak feminizing effects, but not resulted in male-to-female sex reversal in X. laevis.

Acute exposure to physiological doses of triiodothyronine does not induce gonadal caspase 3 activity in goldfish in vitro

Seasonally spawning fish rely on a dynamic and complex hormonal interplay to regulate cycles of gonadal development and the regression. Thyroid hormones have been shown to be a key player during gonadal development, and can regulate the activity of a number of essential reproductive hormones. Apoptosis is a vital cellular process that contributes to the hormonal control of gonadal development and regression, but the roles of thyroid hormones on gonadal apoptosis in goldfish have not been explored. The present study examines the role of acute T3 exposure on caspase 3-dependent apoptosis in dispersed goldfish gonadal tissue in vitro. We examined the levels of caspase 3 activity in early, mid, and late recrudescent gonadal tissue after exposure to physiological doses of T3 for up to 24 h. Acute treatment with T3 did not alter basal caspase 3 activity in goldfish gonads in vitro in these reproductive stages. This initial study suggests that transient increases in T3 levels are unlikely to directly contribute to basal caspase 3-dependent apoptosis in the gonadal tissue of goldfish, although we cannot rule out an interaction of T3 with other hormones involved in the control of apoptosis in the testis and ovary.

Dietary ω3-and ω6-Polyunsaturated fatty acids reconstitute fertility of Juvenile and adult Fads2-Deficient mice

Objective

Polyunsaturated fatty acids (PUFAs), including essential fatty acids linoleic and α-linolenic acid and derived long chain and very long chain ω3-and ω6-polyunsaturated fatty acids, are vital structures in mammalian membrane systems and signaling molecules, pivotal in brain development, lipid, and energy metabolism and in female and male fertility during human evolution. Numerous nutritional studies suggest imbalance of PUFA metabolism as a critical factor in the pathogenesis of several human lifestyle diseases: dyslipoproteinemia, obesity, cardiovascular and neurodegenerative diseases, and infertility. The lack of unbiased animal models impedes molecular interpretation of the role of synthesized and dietary supplied PUFAs in these conditions. In this study, we used a Δ6 fatty acid desaturase (FADS2) deficient mouse mutant lacking key enzyme activity in the biosynthesis of ω3-and ω6-PUFAs from EFAs to address the molecular role of PUFAs in female and male fertility. Infertility is a hallmark of the pleiotropic but auxotrophic fads2−/− phenotype and is therefore helpful for stringent dietary studies on the role of individual PUFAs.

Methods

Feeding regimens: Age- and gender-matched infertile fads2−/− mice were maintained on defined diets, normal diet containing essential fatty acids, and supplemented with ω6-arachidonic acid, ω3-docosahexaenoic acid, and arachidonic/docosahexaenoic acid, starting (a) after weaning and (b) initiated in 4-month-old female and male fads2−/− mice. Phospho- and sphingolipidomes of ovarian and testicular membrane lipid bilayers in each cohort were established and the impact on the expression and topology of membrane marker proteins, membrane morphology, germ cell development, and female and male fertility in the respective cohorts was elaborated.

Results

PUFA synthesis deficiency caused a halt to folliculogenesis, atresia of oocytes, and infertility of fads2−/− female mice. A PUFA-deficient membrane lipid bilayer core structure led to the disassembly of the gap junction network of the follicular granulosa cells. In fads2−/− testis, the blood-testis barrier was disrupted and spermatogenesis arrested, leading to infertility. Sustained supply of combined AA and DHA remodeled the PUFA-deficient ovarian and testicular membrane lipidomes, facilitating the reassembly of the functional gap junction network for regular ovarian cycles and the reconstitution of the blood-testis barrier in Sertoli cells, reconstituting fertility not only in developing newborns, but surprisingly also in adult infertile fads2−/− mice.

Conclusions

These findings demonstrate the previously unrecognized membrane structure-based molecular link between nutrient ω3-and ω6-PUFAs, gonadal membrane structures, and female and male fertility and might foster studies of the pivotal role of dietary PUFAs in human fertility.

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PUFA-depletion disrupts membrane lipid scaffolds of ovarian GJ- and TJ-complexes of the testicular BTB

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Nutrient AA/DHA reconstitute the gonadal membrane bilayer architecture in auxotrophioc fads2-/- mice

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AA/DHA replenished lipid-bilayers promote the assembly of follicular GJ- and BTB-protein complexes in fads2-/- mice

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Nutrient AA/DHA release arrest of oo- and spermatogenesis, restoring fertility of newborn and adult fads2-/- mice

An estradiol-17β/miRNA-26a/cyp19a1a regulatory feedback loop in the protogynous hermaphroditic fish, Epinephelus coioides

Cyp19a1a is a key gene responsible for the production of estradiol-17β (E₂), the main functional estrogen and a major downstream regulator of reproduction in teleost fish. It is widely known that CYP19 gene expression, aromatase activity, and E₂ production can influence gonadal differentiation and sex reversal in teleost fish, but the feedback mechanisms whereby E₂ regulates cyp19a1a remain poorly understood, especially regarding the potential roles of endogenous small RNA molecules (miRNAs). Here, we identified miR-26a-5p as a regulatory factor of its predicted target gene (cyp19a1a). In vitro and in vivo studies showed that miR-26a-5p can decrease cyp19a1a expression. Furthermore, high doses of E₂ act as a repressor of miR-26a-5p. This study proposes a regulatory feedback loop whereby E₂ regulates cyp19a1a through miR-26a-5p, and suggests that this positive feedback is an important aspect of the control of E₂ production.

Expression Profile of Chicken Sex Chromosome Gene BTF3 is Linked to Gonadal Phenotype

In birds, the female is heterogametic (ZW) and the male homogametic (ZZ). The small W chromosome comprises only 28 protein coding genes (homologues to Z chromosome counterparts) and a number of repeat regions. Here, we report our analysis of one of these genes, BTF3 (basic transcription factor 3), which exhibits differential expression during gonadogenesis. We measured RNA levels of both Z and W homologues and BTF3 protein levels in male and female gonads during development of the chicken embryo. In addition, BTF3 RNA and protein levels were compared in female gonads (ovary) and in female gonads following treatment to induce sex reversal (testis). Combined BTF3 RNA levels were higher in female gonads than male gonads, while BTF3-Z was expressed at similar levels in males and females. Surprisingly, BTF3 protein levels were higher in male gonads than female gonads at embryonic day 6 (E6), suggesting translational rather than transcriptional regulation. BTF3 protein was expressed in both somatic and germ cells and was restricted to the medulla of the developing ovary in females and the sex cords of the developing testis in males. In addition, in gonadal sex-reversed females, RNA and protein levels of BTF3 were similar to those normally found in male gonads, suggesting that BTF3 expression correlated with the gonadal phenotype.

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

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