Effects of TCDD in modulating the expression of Sertoli cell secretory products and markers for cell–cell interaction

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.

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.

Bisphenol A Deranges the Endocannabinoid System of Primary Sertoli Cells with an Impact on Inhibin B Production

Bisphenol A (BPA) is an endocrine disruptor that negatively affects spermatogenesis, a process where Sertoli cells play a central role. Thus, in the present study we sought to ascertain whether BPA could modulate the endocannabinoid (eCB) system in exposed mouse primary Sertoli cells. Under our experimental conditions, BPA turned out to be cytotoxic to Sertoli cells with an half-maximal inhibitory concentration (IC₅₀) of ~6.0 µM. Exposure to a non-cytotoxic dose of BPA (i.e., 0.5 μM for 48 h) increased the expression levels of specific components of the eCB system, namely: type-1 cannabinoid (CB₁) receptor and diacylglycerol lipase-α (DAGL-α), at mRNA level, type-2 cannabinoid (CB₂) receptor, transient receptor potential vanilloid 1 (TRPV1) receptors, and DAGL-β, at protein level. Interestingly, BPA also increased the production of inhibin B, but not that of transferrin, and blockade of either CB₂ receptor or TRPV1 receptor further enhanced the BPA effect. Altogether, our study provides unprecedented evidence that BPA deranges the eCB system of Sertoli cells towards CB₂- and TRPV1-dependent signal transduction, both receptors being engaged in modulating BPA effects on inhibin B production. These findings add CB₂ and TRPV1 receptors, and hence the eCB signaling, to the other molecular targets of BPA already known in mammalian cells.

Etoxazole induces testicular malfunction in mice by dysregulating mitochondrial function and calcium homeostasis

Epidemiological relationships between pesticide use and male infertility have been suggested for a long time. Etoxazole (ETX), an oxazoline pesticide, has been extensively used for pest eradication. It is considered relatively safe and has low mammalian toxicity because it specifically inhibits chitin synthesis. However, ETX may have toxic effects on the reproductive system. In this study, we examined the effects of ETX on the reproductive system using mouse testis cell lines (TM3 for Leydig cells and TM4 for Sertoli cells) and C57BL/6 male mice. We confirmed that ETX has anti-proliferative effects on the TM3 and TM4 cell lines. Moreover, ETX induced mitochondrial dysfunction and hampers calcium homeostasis. Western blot analysis of MAPK and Akt signaling cascades was performed to demonstrate the mode of action of ETX at a molecular level. Moreover, ETX induced misregulation of genes related to testicular function. Upon oral administration of ETX in C57BL/6 male mice, testis weight was reduced and transcriptional expression related to testis function was altered. These results indicate that ETX induces testicular toxicity by inducing mitochondrial dysfunction and calcium imbalance and regulating gene expression.

Can resveratrol attenuate testicular damage in neonatal and adult rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin during gestation?

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is considered one of the most toxic dioxins. The effects of TCDD are exerted via binding to the aryl hydrocarbon receptor (AhR). The aim of the present study was to evaluate the possible protective effects of resveratrol, an AhR antagonist, against testicular damage caused by TCDD exposure during pregnancy. Pregnant female Sprague-Dawley rats were divided into four groups: a control group; a group treated with 1 µg kg−1, p.o., TCDD on Gestational Day (GD) 15; a group treated with 20 µg kg−1, p.o., resveratrol on GD10–21; and a group treated with both TCDD and resveratrol. Rats were weighed and killed, and neonatal testes were collected for histopathological analysis on Postnatal Day (PND) 1. At PND90, adult male rats were killed and the testes collected for histopathological analysis and determination of sperm count. Resveratrol had a protective effect against the effects of TCDD on Sertoli cell number in adult and neonate testes, as well as against the effects of TCDD on abnormal seminiferous tubules in adults. Combined administration of TCDD and resveratrol altered the kinetics of spermatogenesis and the proportion of neonatal testicular compartments compared with the control group In addition, combined TCDD and resveratrol treatment decreased seminiferous tubule diameter in adult male rats compared with the control group. In conclusion, resveratrol may protect against some TCDD-induced testicular damage, but, based on the parameters assessed, the administration of resveratrol and TCDD in combination may result in more severe toxicity than administration of either drug alone.

Review on crosstalk and common mechanisms of endocrine disruptors: Scaffolding to improve PBPK/PD model of EDC mixture

Endocrine disruptor compounds (EDCs) are environment chemicals that cause harmful effects through multiple mechanisms, interfering with hormone system resulting in alteration of homeostasis, reproduction and developmental effect. Many of these EDCs have concurrent exposure with crosstalk and common mechanisms which may lead to dynamic interactions. To carry out risk assessment of EDCs' mixture, it is important to know the detailed toxic pathway, crosstalk of receptor and other factors like critical window of exposure. In this review, we summarize the major mechanism of actions of EDCs with the different/same target organs interfering with the same/different class of hormone by altering their synthesis, metabolism, binding and cellular action. To show the impact of EDCs on life stage development, a case study on female fertility affecting germ cell is illustrated. Based on this summarized discussion, major groups of EDCs are classified based on their target organ, mode of action and potential risk. Finally, a conceptual model of pharmacodynamic interaction is proposed to integrate the crosstalk and common mechanisms that modulate estrogen into the predictive mixture dosimetry model with dynamic interaction of mixture. This review will provide new insight for EDCs' risk assessment and can be used to develop next generation PBPK/PD models for EDCs' mixture analysis.

The aryl hydrocarbon receptor is important for proper seminiferous tubule architecture and sperm development in mice

The aryl hydrocarbon receptor (AHR) is known for its roles in xenobiotic metabolism and essential physiologic processes such as cell growth, death, and differentiation. AHR is also an important regulator of male reproductive processes. However, no studies have characterized the consequences of loss of AHR in spermatogenesis. We used Ahr knockout (Ahr(-/-)) mice to assess the effects of loss of AHR on the architecture and gene expression of the seminiferous epithelium and functional sperm outcomes. The histopathological defects of the Ahr(-/-)seminiferous epithelium included vacuoles, multinucleated giant cells, hypocellularity with widened intercellular spaces, apical sloughing, and an excess number of retained elongated spermatids. Quantitative real-time PCR revealed significant down-regulation of Testin and Magea4, indicating Sertoli cell and spermatogenic dysregulation. Moreover, the reduced expression of Hspa2, Prm1, and Prm2 as well as decreased expression of Nrf2, Sod2, and Ucp2 suggested poorly remodeled germ cells with increased vulnerability to oxidative stress. In wild-type sperm, AHR protein was localized to the acrosome and the principal piece of the mature sperm flagellum. The in vitro fertilization rate was significantly lower with Ahr(-/-) sperm as compared to wild-type sperm, and there were morphologic abnormalities of the Ahr(-/-) sperm head and tail. Taken together, our data indicate that AHR plays an important role in normal sperm development.

CYP19 expression is induced by 2,3,7,8-tetrachloro-dibenzo-para-dioxin in human glioma cells

Dioxins are the most concerned environmental pollutants. Recent studies have shown that these compounds could disrupt the proper functioning of our endocrine system. Estrogen is synthesized in glial cells of the brain. The hormone has been linked to the maintenance of normal brain operation, ranging from neurotransmission to synapse formation. Aromatase or CYP19 is the enzyme responsible for estrogen synthesis. In the present study, we demonstrated that 2,3,7,8-tetrachloro-dibenzo-para-dioxin (TCDD) stimulated the enzyme activity in human brain cells as low as 1pM. Increased brain-specific CYP19 mRNA species was also observed in these cells. Since the brain-specific promoter I.f of CYP19 contains two binding motifs for CCAAT/enhancer binding protein, electrophoretic mobility shift assay was performed to validate the activation. We further traced the triggering signal and found that the mitogen-activated protein kinases ERK-1/2 were activated. In summary, TCDD could induce CYP19 transcription in brain cells. Exposure to the pollutant might perturb the hormonal balance in the brain.

Endocrine disrupting chemicals: Multiple effects on testicular signaling and spermatogenesis

In the past 200 years, an enormous number of synthetic chemicals with diverse structural features have been produced for industrial, medical and domestic purposes. These chemicals, originally thought to have little or no biological toxicity, are widely used in our daily lives as well as are commonly present in foods. It was not until the first World Wildlife Federation Wingspread Conference held in 1994 were concerns about the endocrine disrupting (ED) effects of these chemicals articulated. The potential hazardous effects of endocrine disrupting chemicals (EDCs) on human health and ecological well-being are one of the global concerns that affect the health and propagation of human beings. Considerable numbers of studies indicated that endocrine disruption is linked to "the developmental basis of adult disease," highlighting the significant effects of EDC exposure on a developing organism, leading to the propensity of an individual to develop a disease or dysfunction in later life. In this review, we intend to provide environmental, epidemiological and experimental data to associate pollutant exposure with reproductive disorders, in particular on the development and function of the male reproductive system. Possible effects of pollutant exposure on the processes of embryonic development, like sex determination and masculinization are described. In addition, the effects of pollutant exposure on hypothalamus-pituitary-gonadal axis, testicular signaling, steroidogenesis and spermatogenesis are also discussed.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced cytotoxicity accompanied by oxidative stress in rat Sertoli cells: Possible role of mitochondrial fractions of Sertoli cells

TCDD, as an endocrine disruptor, is known to impair testicular functions and fertility. To elucidate the mechanism(s) underlying the testicular effects of TCDD, the potential toxicity of TCDD on Sertoli cells was investigated. Furthermore, the study aims to delineate whether mitochondrial fractions of Sertoli cells are involved in mediating the testicular effects of TCDD. Adult rat Sertoli cells were incubated with (5, 10 or 15nM) of TCDD for 6, 12 or 24h. Cell viability, lactate and LDH leakage into media along with lipid peroxidation, ROS generation, SOD, CAT, GPx, GR, γ-GT and β-glucuronidase activities, GSH content and Δψ(m) were measured. Superoxide anion production, COX and cardiolipin content were measured in mitochondrial fractions. Cell viability was significantly decreased while lactate and LDH leakage into media were increased. ROS generation along with lipid peroxidation was also increased. SOD, CAT, GPx, GR activities and GSH content were significantly decreased. γ-GT and β-glucuronidase activities were also decreased. Superoxide anion production was increased while COX activity and cardiolipin content were decreased in mitochondrial fractions. Moreover, the Δψ(m) was significantly decreased as measured in Sertoli cells. In conclusion, TCDD impairs Sertoli cell functions and this effect is, at least in part, attributed to oxidative stress. We have also found that TCDD increases mitochondrial superoxide anion production and decreases Δψ(m), COX activity and mitochondrial cardiolipin content. Our findings suggest that mitochondria may play an important role in ROS production, leading to the TCDD-induced oxidative stress response and resulting toxicological consequences in rat Sertoli cells.

Testicular spermiation failure in rats exposed prenatally to 3,3',4,4',5-pentachlorobiphenyl

Testicular spermatogenesis was studied in 7-, 10-, 13- and 17-week-old Sprague-Dawley rats whose dams had been administered intragastrically with 2.5, 25, or 250 ng of 3,3',4,4',5-pentachlorobiphenyl (PCB126) or vehicle on days 13-19 of gestation. The 250 ng groups among the 7-, 10- and 13-week-old offspring showed significant inhibition of mature spermatid release (spermiation), but 17-week-old offspring did not show this. These alterations were not observed in other PCB126 and vehicle groups, and no germ cell or Sertoli cell degeneration were observed in any group. Spermiation failure at puberty appeared in those rats born to dams exposed 250 ng/kg PCB126 on days 13-19 of gestation was reversible change that recovered at adulthood. Because the serum testosterone, luteinizing hormone and follicle-stimulating hormone concentrations were similar in the PCB126 and vehicle groups, a direct endocrine cause for the observed effects was unlikely.

Effect of Aroclor 1254 on Sertoli cellular antioxidant system, androgen binding protein and lactate in adult rat in vitro

Polychlorinated biphenyls (PCBs) are persistent and bioaccumulative environmental toxicants. Previous studies suggested that PCBs (Aroclor 1254) induce toxic effects including reproductive toxicity. The present study was designed to investigate the impact of Aroclor 1254 on Sertoli cellular function and antioxidant system of adult rat in vitro. Sertoli cells were isolated from adult rat testes and treated with various concentrations (10(-10) to 10(-7) M) of Aroclor 1254 for 6, 12 and 24 h. After the treatment period, cell viability was assessed and the Sertoli cellular antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), gamma-glutamyl transpeptidase (gamma-GT) and glutathione reductase (GR) and lipid peroxidation (LPO) were assayed. In addition, androgen binding protein (ABP) and lactate secretions were also quantified in Sertoli cell culture medium. Sertoli cellular viability and activity of antioxidant enzymes were significantly reduced in Aroclor 1254 (10(-10) to 10(-7) M) treatment for 6, 12 and 24 h whereas, the Sertoli cellular lipid peroxidation was significantly increased in a dose and duration dependent manner. In addition, ABP secretion diminished and lactate secretion was significantly elevated in the same manner. To conclude, the present study suggested that Aroclor 1254 disrupts Sertoli cellular metabolic functions such as ABP, lactate secretions and activity of antioxidant enzymes.