Maternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin suppresses male reproductive functions in their adulthood

Impact of dioxins on reproductive health in female mammals

Extensive research has been conducted to investigate the toxicological impact of dioxins on mammals, revealing profound effects on the female reproductive system in both humans and animals. Dioxin exposure significantly disrupts the intricate functions of the ovary, a pivotal organ responsible for reproductive and endocrine processes. This disruption manifests as infertility, premature ovarian failure, and disturbances in sex steroid hormone levels. Comprehensive studies, encompassing accidental human exposure and experimental animal data, have raised a wealth of information with consistent yet varied conclusion influenced by experimental factors. This review begins by providing an overarching background on the ovary, emphasizing its fundamental role in reproductive health, particularly in ovarian steroidogenesis and hormone receptor regulation. Subsequently, a detailed examination of the Aryl hydrocarbon Receptor (AhR) and its role in governing ovarian function is presented. The review then outlines the sources and toxicity of dioxins, with a specific focus on AhR involvement in mediating reproductive toxicity in mammals. Within this context, the impact of dioxins, notably 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), on Folliculogenesis and Preimplantation embryos is discussed. Furthermore, the review delves into the disruptions of the female hormonal system caused by TCDD and their ramifications in endometriosis. Notably, variations in the effects of TCDD on the female reproductive and hormonal system are highlighted in relation to TCDD dose, animal species, and age. As a forward-looking perspective, questions arise regarding the potential involvement of molecular mechanisms beyond AhR in mediating the female reproductive toxicity of dioxins.

Protective effect of didymin against 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin-induced reproductive toxicity in male rats

PURPOSE

2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin (TCDD) is one of the most potent environmental toxicants, which causes oxidative stress and adversely affects the male reproductive system. The current study aimed to evaluate the ameliorative role of didymin (DDM) against TCDD-induced testicular toxicity.

METHODS

Forty-eight male Sprague-Dawley rats were divided into four equal groups (n=12). (i) Control group, (ii) TCDD-induced group was provided with 10 μg/kg/day of TCDD, (iii) TCDD + DDM group received 10 μg/kg/day of TCDD and 2 mg/kg/day of DDM, and (iv) DDM-treated group was administered with 2 mg/kg/day of DDM. After 56 days of treatment, biochemical, steroidogenic, hormonal, spermatogenic, apoptotic, and histopathological parameters were estimated.

RESULTS

TCDD affected the biochemical profile by reducing the activities of antioxidant enzymes, while increasing the levels of malondialdehyde (MDA) and reactive oxygen species (ROS). Furthermore, it decreased the expressions of steroidogenic enzymes, 3β-hydroxysteroid dehydrogenase (HSD), 17β-HSD, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (CYP11A1), and 17α-hydroxylase/17, 20-lyase (CYP17A1), as well as reduced the levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and plasma testosterone. Besides, epididymal sperm count, viability, and motility were decreased, while sperm morphological anomalies were increased. Moreover, TCDD altered the apoptotic profile by up-regulating the expressions of Bax and caspase-3, while downregulated the Bcl-2 expression. Additionally, histopathological damages were prompted due to TCDD administration. However, DDM restored all the TCDD-induced damages owing to its antioxidant, anti-apoptotic, and androgenic potential.

CONCLUSION

Our data suggested that DDM might play its role as a therapeutic agent against TCDD-prompted testicular toxicity.

2,3,7,8-tetrachlorodibenzo-p-dioxin induces multigenerational testicular toxicity and biosynthetic disorder of testosterone in BALB/C mice: Transcriptional, histopathological and hormonal determinants

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent environmental contaminant, is an endocrine disrupter with a proven reproductive toxicity in mammals. However, its effects on male fertility across generations are still elusive. The current work evaluates the toxicity of dioxin on male reproductive system in two separate groups of BALB/C mice; a group of pubertal males directly exposed to TCDD (referred to as DEmG), and a group of indirectly exposed males (referred to as IDEmG) comprises of F1, F2 and F3 males born from TCDD-exposed pregnant females. Both groups were exposed to 25 μg TCDD/kg body weight for a week. Our data show that males of TCDD-DEmG exhibited significant alterations in the expression of certain genes involved in the detoxification of TCDD and the biosynthesis of testosterone. This was accompanied with testicular pathological symptoms, including a sloughing in the germinal epithelium and a congestion of blood vessels in interstitial tissue with the presence of multinuclear cells into seminiferous tubule, with a 4-fold decline in the level of serum testosterone and reduced sperm count. Otherwise, the male reproductive toxicity across F1, F2 and F3 generations from TCDD-IDEmG was mainly characterized by: i) a reduce in body and testis weight. ii) a decrease in gene expression of steriodogenesis enzyme, e.g., AhR, CYP1A1, CYP11A1, COX1, COX2, LOX5 and LOX12. iii) a remarked and similar testicular histopathology that found for DEmG, iv) a serious decline in serum testosterone. v) a decreased male-to-female ratio. vi) a low sperm count with increasing abnormalities. Thus, pubertal or maternal exposure to TCDD provokes multigenerational male reproductive toxicity in mice, ultimately affecting the spermatogenesis and suggesting that the hormonal alternation and sperm abnormality are the most marked effects of the indirect exposure of mammalian male to TCDD.

Transcriptional, hormonal and histological alterations in the ovaries of BALB/c mice exposed to TCDD in connection with multigenerational female infertility

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener of dioxins, has a proven reproductive toxicity. Due to the lack of evidence on the multigenerational female reproductive toxicity of TCDD through the maternal exposure, the current study aims to evaluate, on the one hand, the acute reproductive toxicity of TCDD on adult female pre-gestational exposed to a critical single dose of TCDD (25 μg/kg) for a week (group referred to as AFnG; adult female/non-gestation). On the other hand, the transcription, hormonal and histological effects of TCDD on the females of two generations F1 and F2, were also investigated after the exposure of pregnant females to TCDD on gestational day 13 (GD13) (group referred to as AFG; adult female/gestation). First, our data showed alternations in the ovarian expressional pattern of certain key genes involved in the detoxification of TCDD as well as in the biosynthesis of steroidal hormones. The expression of Cyp1a1 was highly induced in TCDD-AFnG group, but reduced in both F1 and F2. While the transcripts levels of Cyp11a1 and 3βhsd2 were decreased, Cyp19a1 transcripts were increased as a function of TCDD exposure. This was synchronized with a dramatic increase in the level of estradiol hormone in the females of both experimental groups. Beside a significant reduce in their size and weight, ovaries of TCDD-exposed females showed serious histological alterations marked by atrophy of the ovary, congestion in the blood vessels, necrosis in the layer of granular cells, dissolution of the oocyte and nucleus of ovarian follicles. Finally, the female fertility was dramatically affected across generations with a reduced male\female ratio. Our data indicate that the exposure of pregnant female to TCDD has serious negative effects in the female productive system across generations and suggest the use of hormonal alternation as biomarker to monitor and assess the indirect exposure of these generations to TCDD.

Hyperandrogen-induced polyol pathway flux increase affects ovarian function in polycystic ovary syndrome via excessive oxidative stress

AIMS

Polycystic ovary syndrome (PCOS) is a common endocrine disorder in the women of childbearing age. It is characterized by hyperandrogenism and abnormal follicular growth and ovulation. The polyol pathway is a glucose metabolism bypass pathway initiated by aldose reductase (ADR). Androgen induces the expression of ADR in the male reproductive tract, which has a general physiological significance for male reproductive function. Here we investigate whether hyperandrogenemia in PCOS leads to increased flux of the polyol pathway in ovarian tissue, which in turn affects follicular maturation and ovulation through oxidative stress.

MAIN METHODS

We used clinical epidemiological methods to collect serum and granulosa cells from clinical subjects for a clinical case-control study. At the same time, cell biology and molecular biology techniques were used to conduct animal and cell experiments to further explore the mechanism of hyperandrogen-induced ovarian polyol pathway hyperactivity and damage to ovarian function.

KEY FINDINGS

Here, we find that hyperandrogenism of PCOS can induce the expression of ovarian aldose reductase, which leads to the increase of the polyol pathway flux, and affects ovarian function through excessive oxidative stress.

SIGNIFICANCE

Our research has enriched the pathological mechanism of PCOS and may provide a new clue for the clinical treatment of PCOS.

Temporal decline of sperm concentration: role of endocrine disruptors

INTRODUCTION

Male infertility is a widespread disease with an etiology that is not always clear. A number of studies have reported a decrease in sperm production in the last forty years. Although the reasons are still undefined, the change in environmental conditions and the higher exposure to endocrine-disrupting chemicals (EDCs), namely bisphenol A, phthalates, polychlorinated biphenyls, polybrominated diphenyl esters, dichlorodiphenyl-dichloroethylene, pesticides, and herbicides, organophosphates, and heavy metals, starting from prenatal life may represent a possible factor justifying the temporal decline in sperm count.

AIM

The aim of this study is to provide a comprehensive description of the effects of the exposure to EDCs on testicular development, spermatogenesis, the prevalence of malformations of the male genital tract (cryptorchidism, testicular dysgenesis, and hypospadias), testicular tumor, and the mechanisms of testicular EDC-mediated damage.

NARRATIVE REVIEW

Animal studies confirm the deleterious impact of EDCs on the male reproductive apparatus. EDCs can compromise male fertility by binding to hormone receptors, dysregulating the expression of receptors, disrupting steroidogenesis and hormonal metabolism, and altering the epigenetic mechanisms. In humans, exposure to EDCs has been associated with poor semen quality, increased sperm DNA fragmentation, increased gonadotropin levels, a slightly increased risk of structural abnormalities of the genital apparatus, such as cryptorchidism and hypospadias, and development of testicular tumor. Finally, maternal exposure to EDCs seems to predispose to the risk of developing testicular tumors.

CONCLUSION

EDCs negatively impact the testicular function, as suggested by evidence in both experimental animals and humans. A prenatal and postnatal increase to EDC exposure compared to the past may likely represent one of the factors leading to the temporal decline in sperm counts.

Rhamnazin ameliorates 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin-evoked testicular toxicity by restoring biochemical, spermatogenic and histological profile in male albino rats

2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) is a potential environmental toxin that has the ability to affect male reproductive tract. Rhamnazin is a naturally present flavone that displays multiple medicinal properties. Therefore, the current study was designed to determine the mitigative role of rhamnazin against TCDD induced reproductive damage. 48 adult male albino rats were randomly separated into four groups: control, TCDD (10 µgkg-1), TCDD + rhamnazin (10 µgkg-1 + 5 mgkg-1 respectively) and rhamnazin (5 mgkg-1). The trial was conducted for 56 days. TCDD intoxication notably affected superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GSR) and catalase (CAT) activities, besides reactive oxygen species (ROS) and malondialdehyde (MDA) concentrations were augmented. TCDD administration also lowered sperm motility, viability, sperm number, while it augmented the sperm morphological (tail, neck/midpiece and head) anomalies. Moreover, it decreased the levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and plasma testosterone. Moreover, TCDD reduced steroidogenic enzymes i.e., 17-beta hydroxysteroid dehydrogenase (17β-HSD), steroidogenic acute regulatory protein (StAR) and 3-beta hydroxysteroid dehydrogenase (3β-HSD) as well as B-cell lymphoma 2 (Bcl-2) expressions, but increased the expressions of Bcl-2-associated X protein (Bax) and cysteine-aspartic acid protease (Caspase-3). Furthermore, TCDD exposure also induced histopathological anomalies in testicular tissues. However, the supplementation of rhamnazin recovered all the mentioned damages in the testicles. The outcomes revealed that rhamnazin can ameliorate TCDD induced reproductive toxicity due to its anti-oxidant, anti-apoptotic and androgenic nature.

Effects of dioxins on animal spermatogenesis: A state-of-the-art review

The male reproductive system is especially affected by dioxins, a group of persistent environmental pollutants, resulting in irreversible abnormalities including effects on sexual function and fertility in adult males and possibly on the development of male offspring. The reproductive toxicity caused by dioxins is mostly mediated by an aryl hydrocarbon receptor (AhR). In animals, spermatogenesis is a highly sensitive and dynamic process that includes proliferation and maturation of germ cells. Spermatogenesis is subject to multiple endogenous and exogenous regulatory factors, including a wide range of environmental toxicants such as dioxins. This review discusses the toxicological effects of dioxins on spermatogenesis and their relevance to male infertility. After a detailed categorization of the environmental contaminants affecting the spermatogenesis, the exposure pathways and bioavailability of dioxins in animals was briefly reviewed. The effects of dioxins on spermatogenesis are then outlined in detail. The endocrine-disrupting effects of dioxins in animals and humans are discussed with a particular focus on their effects on the expression of spermatogenesis-related genes. Finally, the impacts of dioxins on the ratio of X and Y chromosomes, the status of serum sex hormones, the quality and fertility of sperm, and the transgenerational effects of dioxins on male reproduction are reviewed.

Pathological effects of graded doses of aflatoxin B1 on the development of the testes in juvenile white leghorn males

Current experiment was planned to investigate the deleterious effects of the graded doses of aflatoxin B1 (AFB1) on white leghorn male birds. For this purpose, one-hundred birds of 8 weeks of age were divided into 4 equal groups and reared on feed contaminated with different doses of AFB1 for 10 weeks. Group A was kept as a control group and was fed with normal toxin-free diet; groups B, C, and D were offered feed containing 100 ppb, 200 ppb, and 400 ppb of AFB1, respectively. The birds were euthanized at the 4th and 10th week of the experiment. Clinical signs, behavioral changes, absolute and relative organ weight of the testes, and sperm motility were measured. Cellular immune response was observed through carbon clearance assay (CCA), P-HAP, and antibody response against sheep red blood cells (SRBC). Results showed a dose-dependent decline in the immune response of birds with the increase in the level of AFB1 in the feed. A significant decrease in the serum levels of testosterone, prolactin, and LH were observed at the end of the study. Grossly, testicular size and volume were reduced in ABF1 fed birds, while histological examination showed moderate to severe necrosis of testicular parenchyma, with partial to complete arrest of spermatogenesis. Very few spermatozoa were found in group C, while they were almost absent in group D which was offered a diet containing 400 ppb AFB1. The motility of sperms was reduced in all treated groups except control. The abovementioned results showed that AFB1 had severe toxic effects on the reproductive and immunological parameters of WLH male birds in a dose-dependent manner.

Endocrine-Disrupting Chemicals and Disorders of Penile Development in Humans

This paper reviews the current knowledge on the environmental effects on penile development in humans. The specific focus is on endocrine-disrupting chemicals (EDCs), a heterogeneous group of natural or manmade substances that interfere with endocrine function, and whether they can induce hypospadias and micropenis in male neonates. Epidemiological data and animal observations first raised suspicions about environmental effects, leading to the testis dysgenesis syndrome (TDS) hypothesis. More recent research has provided stronger indications that TDS may indeed be the result of the direct or indirect effects of EDCs. Drawing on epidemiological and toxicological studies, we also report on the effects of maternal diet and substances like pesticides, phthalates, bisphenol A, and polychlorinated biphenyls. Proximity to contamination hazards and occupational exposure are also suspected to contribute to the occurrence of hypospadias and micropenis. Lastly, the cumulative effects of EDCs and the possibility of transgenerational effects, with the penile development of subsequent generations being affected, raise concerns for long-term public health.

Experimental Evidence of 2,3,7,8-Tetrachlordibenzo-p-Dioxin (TCDD) Transgenerational Effects on Reproductive Health

Previous studies have demonstrated that endocrine disruptors (EDs) can promote the transgenerational inheritance of disease susceptibility. Among the many existing EDs, 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) affects reproductive health, including in humans, following direct occupational exposure or environmental disasters, for instance the Agent Orange sprayed during the Vietnam War. Conversely, few studies have focused on TCDD multigenerational and transgenerational effects on human reproductive health, despite the high amount of evidence in animal models of such effects on male and female reproductive health that mimic human reproductive system disorders. Importantly, these studies show that paternal ancestral TCDD exposure substantially contributes to pregnancy outcome and fetal health, although pregnancy outcome is considered tightly related to the woman’s health. In this work, we conducted a systematic review of the literature and a knowledge synthesis in order (i) to describe the findings obtained in rodent models concerning TCDD transgenerational effects on reproductive health and (ii) to discuss the epigenetic molecular alterations that might be involved in this process. As ancestral toxicant exposure cannot be changed in humans, identifying the crucial reproductive functions that are negatively affected by such exposure may help clinicians to preserve male and female fertility and to avoid adverse pregnancy outcomes.

Animal Toxicology Studies on the Male Reproductive Effects of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin: Data Analysis and Health Effects Evaluation

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental poison that exist in the environment for many years. However, its effect on the male reproductive system has not been clearly stated. We conducted a meta-analysis of the effect of TCDD on the male reproductive system of rodents about TCDD. Results showed that that TCDD exposure reduced the testis weight (weighted mean difference [WMD]: -0.035, 95% confidence interval [CI]: -0.046 to -0.025), sperm count (WMD: -35, 95% CI: -42.980 to -27.019), and blood testosterone concentration (WMD: -0.171, 95% CI: -0.269 to -0.073). According to our research results, TCDD can cause damage to the male reproductive system of rodents through direct or indirect exposure. In order to further explore the potential hazards of TCDD to humans, more human-related research needs to be carried out.

Endocrine-disrupting chemicals and male reproductive health

BACKGROUND

A number of different types of endocrine-disrupting chemicals (EDCs) including bisphenol A, phthalates, pesticides, and other environmental chemicals have been shown to adversely impact upon male reproductive health. Understanding the potential effects of EDCs on male reproductive health may enable the development of novel treatments and early prevention of the effects of EDCs on male infertility and their potential long-term sequelae. This review critically evaluates the research performed in this area and explores potential harmful effects of EDCs in animals and humans, including the possibility of trans-generational transmission.

METHODS

A literature review was conducted using electronic databases using the following terms: 'endocrine disrupt*' OR 'endocrine disruptors' OR 'endocrine disruptor chemicals' OR 'EDC' AND 'sperm*' OR 'spermatozoa' OR 'spermatozoon' OR 'male reproductive health' OR' male fertility'.

MAIN FINDINGS

Several studies have shown that EDCs have a variety of pathophysiological effects. These include failure of spermatogenesis, embryonic development, the association with testicular cancer, and long-term metabolic effects.

CONCLUSIONS

Several studies observe correlations between chemical doses and at least one sperm parameter; however, such correlations are sometimes inconsistent between different studies. Mechanisms through which EDCs exert their pathophysiological effects have not yet been fully elucidated in human studies.

Serum dioxin levels and sperm DNA methylation age: Findings in Vietnam war veterans exposed to Agent Orange

Exposure to dioxin, a known endocrine disruptor and carcinogen, is associated with poor reproductive outcomes. Yet, few studies have explored the role of DNA methylation in these relationships. Utilizing a publicly available dataset from 37 male Air Force Health Study participants exposed to dioxin-contaminated Agent Orange during the Vietnam war, we cross-sectionally examined the relationship of serum dioxin levels with a novel DNA methylation-based measure of sperm age (DNAm-agesperm). DNAm-agesperm was calculated using CpG sites on the Illumina HumanMethylation450 BeadChip. We estimated associations of dioxin levels with DNAm-agesperm using linear regression models adjusted for chronological age, body mass index, and smoking status. Chronological age was highly correlated with DNAmagesperm (r = 0.80). In fully-adjusted linear models, a one percent increase in serum dioxin levels was significantly associated with a 0.0126-year (i.e. 4.6-day) increase in DNAm-agesperm (95%CI: 0.003, 0.022, p = 0.01). Further analyses demonstrated significant negative associations of dioxin levels (β = -0.0005, 95%CI: -0.0010, 0.00004, P = 0.03) and DNAm-agesperm (β = -0.02, 95%CI: -0.04, -0.001, P = 0.03) with methylation levels of FOXK2 - a gene previously reported to be hypomethylated in infertile men. In sum, we demonstrate associations of dioxin with increased methylation aging of sperm. DNAm-agesperm may provide utility for understanding how dioxin levels impact sperm health and potentially male reproductive capacity in human population studies. Moreover, our pilot study contributes further evidence that some environmental toxicants are associated with methylation aging. Additional studies are necessary to confirm these findings, and better characterize dioxin and sperm methylation relationships with male reproductive health.