Environmental contaminants: Is male reproductive health at risk?

The FAK/occludin/ZO-1 complex is critical for cadmium-induced testicular damage by disruption of the integrity of the blood-testis barrier in chickens

Cadmium (Cd) is a well-known testis toxicant. The blood-testis barrier (BTB) is a crucial component of the testis. Cd can disrupt the integrity of the BTB and reproductive function. However, the mechanism of Cd-induced disruption of BTB and testicular damage has not been fully elucidated. Here, our study investigates the effects of Cd on BTB integrity and testicular dysfunction. 80 (aged 1 day) Hy-Line white variety chickens were randomly designed into 4 groups and treated for 90 days, as follows: control group (essential diet), 35 Cd, 70 Cd and 140 Cd groups (35, 70 and 140 mg/kg Cd). The results found that Cd exposure diminished volume of the testes and induced histopathological lesions in the testes. Exposure to Cd induced an inflammatory response, disrupted the structure and function of the FAK/occludin/ZO-1 protein complex and disrupted the tight junction and adherens junction in the BTB. In addition, Cd exposure reduced the expression of steroid-related proteins and inhibited testosterone synthesis. Taken together, these data elucidate that Cd disrupts the integrity of the BTB and further inhibits spermatogenesis by dissociating the FAK/occludin/ZO-1 complex, which provides a basis for further investigation into the mechanisms of Cd-induced impairment of male reproductive function and pharmacological protection.

Effects of postnatal exposure to cadmium on male sexual incentive motivation and copulatory behavior: Estrogen and androgen receptors expression in adult brain rat

There are numerous evidence showing that cadmium (Cd) is an endocrine disruptor that exerts multiple toxic effects at different reproductive levels, including male sexual behavior (MSB). The effect of early exposure to Cd on sexual incentive motivation (SIM) and MSB in adult stage, and the immunoreactivity of receptors for hormones such as estrogens and androgens in brain regions that are relevant for the SIM and MSB display, have not been studied until now. The present study evaluated the effects of 0.5 and 1 mg/kg CdCl2 from day 1-56 of postnatal life on SIM and MSB in adults rats, as well as serum testosterone concentrations, Cd concentration in blood, testis, and brain areas, and the immunoreactivity in estrogen receptors (ER-α and -β), and androgen receptor (AR) in the olfactory bulbs (OB), medial preoptic area (mPOA), and medial amygdala (MeA). Our results showed that both doses of Cd decreased SIM and MSB, accompanied by low serum concentrations of testosterone. Also, there was a significant reduction in immunoreactivity of ER-α and AR in mPOA, and a significant reduction in AR in MeA on male rats treated with Cd 1 mg/kg. These results show that exposure to high doses of Cd in early postnatal life could alter the correct integration of hormonal signals in the brain areas that regulate and display SIM and MSB in adult male rats.

Titanium dioxide nanoparticles perturb the blood-testis barrier via disruption of actin-based cell adhesive function

As one of the most commonly used nanoparticles, titanium dioxide nanoparticles (TiO₂-NPs) are widely used as coating reagents in cosmetics, medicine and other industries. The increasing risk of exposure to TiO₂-NPs raises concerns about their safety. In this study, we investigated the mechanism by which TiO₂-NPs cross the blood-testis barrier (BTB). TM-4 cells were selected as an in vitro Sertoli cell model of BTB. Cell viability, cell morphological changes, apoptosis, oxidative damage, and the expression levels of actin regulatory and tight junction (TJ) proteins were assessed in TM-4 cells treated with 3-nm and 24-nm TiO₂-NPs. Cells treated with 3-nm TiO₂-NPs exhibited increased cytotoxicity and decreased Annexin II expression, whereas cells treated with 24-nm TiO₂-NPs exhibited increased Arp 3 and c-Src expression. Both TiO₂-NPs induced significant oxidative stress, decreased the expression of TJ proteins (occludin, ZO-1 and claudin 5), damaged the TJ structure, and exhibited enlarged gaps between TM-4 cells. Our results indicated that both TiO₂-NPs crossed the BTB by disrupting actin-based adhesive junctions of TM-4 cells; however, apoptosis was not observed. Our results provide new insights into how TiO₂-NPs cross the BTB.

Glyphaeaside C- enriched extract of Glyphaea brevis restored the antioxidant and reproductive integrity of 1,4-Dinitrobenzene-intoxicated rats

This study assessed the fertility potential of methanol leaf extract of Glyphaea brevis (MGB) in rats exposed to 1,4-Dinitrobenzene (DNB), an environmental reprotoxicant. Male Wistar rats were orally exposed to 50 mg/kg DNB and administered 750 mg/kg MGB, 1500 mg/kg MGB or 300 mg/kg vitamin E for 21 days after 48 h of DNB exposure. Determination of serum reproductive hormone levels by enzyme-linked immunosorbent assays, evaluation of hematologic profile, computer-assisted sperm analyses (CASA) of sperm kinematics and morphology, assessment of testicular and spermatozoan antioxidant systems, and histopathological evaluation of reproductive tissues were performed. HPLC-DAD analysis identify Glyphaeaside C as the major component of the extract. In rats toxified with 50 mg/kg DNB, testicular and epididymal weights, serum levels of luteinizing hormone, testosterone and follicle-stimulating hormone, and packed cell volume, haemoglobin concentration, and white blood cell counts were decreased. There was altered sperm kinematics which reflected in increased sperm abnormalities. Treatment with the Glyphaeaside C -enriched MGB counteracted all DNB-induced changes and corrected DNB-induced aberrations in kinematic endpoints. Also, testicular and epididymal antioxidant systems were disrupted and there was damage to tissue histoarchitecture. Furthermore, our molecular docking study revealed that Glyphaeaside-C exhibited high binding affinities to the binding pocket of some free radical generating enzymes. Conclusively, the results indicated that Glyphaeaside C-enriched extract of Glyphaea brevis leaf enhanced the quality of semen and improved the functional capabilities of spermatozoa following exposure of rats to DNB which could translate to enhanced fertility.

The Impact of Endocrine-Disrupting Chemicals in Male Fertility: Focus on the Action of Obesogens

The current scenario of male infertility is not yet fully elucidated; however, there is increasing evidence that it is associated with the widespread exposure to endocrine-disrupting chemicals (EDCs), and in particular to obesogens. These compounds interfere with hormones involved in the regulation of metabolism and are associated with weight gain, being also able to change the functioning of the male reproductive axis and, consequently, the testicular physiology and metabolism that are pivotal for spermatogenesis. The disruption of these tightly regulated metabolic pathways leads to adverse reproductive outcomes. The permanent exposure to obesogens has raised serious health concerns. Evidence suggests that obesogens are one of the leading causes of the marked decline of male fertility and key players in shaping the future health outcomes not only for those who are directly exposed but also for upcoming generations. In addition to the changes that lead to inefficient functioning of the male gametes, obesogens induce alterations that are “imprinted” on the genes of the male gametes, establishing a link between generations and contributing to the transmission of defects. Unveiling the molecular mechanisms by which obesogens induce toxicity that may end-up in epigenetic modifications is imperative. This review describes and discusses the suggested molecular targets and potential mechanisms for obesogenic–disrupting chemicals and the subsequent effects on male reproductive health.

Environmental Factors-Induced Oxidative Stress: Hormonal and Molecular Pathway Disruptions in Hypogonadism and Erectile Dysfunction

Hypogonadism is an endocrine disorder characterized by inadequate serum testosterone production by the Leydig cells of the testis. It is triggered by alterations in the hypothalamic–pituitary–gonadal axis. Erectile dysfunction (ED) is another common disorder in men that involves an alteration in erectile response–organic, relational, or psychological. The incidence of hypogonadism and ED is common in men aged over 40 years. Hypogonadism (including late-onset hypogonadism) and ED may be linked to several environmental factors-induced oxidative stresses. The factors mainly include exposure to pesticides, radiation, air pollution, heavy metals and other endocrine-disrupting chemicals. These environmental risk factors may induce oxidative stress and lead to hormonal dysfunctions. To better understand the subject, the study used many keywords, including “hypogonadism”, “late-onset hypogonadism”, “testosterone”, “erectile dysfunction”, “reactive oxygen species”, “oxidative stress”, and “environmental pollution” in major online databases, such as SCOPUS and PUBMED to extract relevant scientific information. Based on these parameters, this review summarizes a comprehensive insight into the important environmental issues that may have a direct or indirect association with hypogonadism and ED in men. The study concludes that environmental factors-induced oxidative stress may cause infertility in men. The hypothesis and outcomes were reviewed critically, and the mechanistic approaches are applied through oxidant-sensitive pathways. This study also provides reccomendations on future therapeutic interventions and protective measures against such adverse environmental factors-induced hypogonadism and ED.

Delay in puberty indices of Wistar rats caused by Cadmium. Focus on the redox system in reproductive organs

Puberty is a transitional period from juvenile stage to adulthood, followed by the functional maturation of gonads and reproductive organs. This period is sensitive to environmental pollutants like cadmium (Cd), a heavy metal that represents a serious health risk. Cd is an endocrine disruptor that interferes with reproduction by causing oxidative stress in the reproductive organs, affecting the sexual function and decreasing testosterone (T) levels. However, little research has been done on the effects of Cd on puberty markers and antioxidant systems. In this study, we evaluated the effects of Cd on puberty markers: preputial separation, testes descent and T levels, and the antioxidant activity (SOD, CAT, GSH/GSSG and TAC) in the seminal vesicles, testis and epididymis. Male Wistar pups were treated with 1 mg/kg Cd or saline solution by i.p. injection from day 1 to 35; the other treatment was administrated for 49 days. At the end of treatment, the animals were sacrificed, and the tissues of interest dissected, weighed and prepared for the respective assays. Cd treated rats from birth to puberty showed a delay onset in the puberty markers and a low weight in reproductive organs. Also, Cd induced differential effects on the redox system in reproductive organs and decreased T levels, these effects played a pivotal role in the delay of puberty markers onset (testes descent and preputial separation), affecting the development and sexual maturity of the male rats.

Metformin Improves Fertility in Obese Males by Alleviating Oxidative Stress-Induced Blood-Testis Barrier Damage

Background/Aims

Obesity, which is related to increased oxidative stress in various tissues, is a risk factor for male infertility. Metformin is reported to have an antioxidant effect; however, the precise role of metformin in obesity-induced male infertility remains unknown. The current study is aimed at exploring the effects of metformin and characterizing its underlying mechanism in the fertility of obese males.

Methods

An obese male mouse model was generated by feeding mice with a high-fat diet; then, the mice were administered metformin in water for 8 weeks. Reproductive ability, metabolic parameters, and follicle-stimulating hormone (FSH) were assessed by cohabitation, enzymatic methods, and ELISA, respectively. Damage to the integrity of the blood-testis barrier (BTB), which ensures spermatogenesis, was assessed by transmission electron microscopy and immunofluorescence with a biotin tracer. Malondialdehyde (MDA), superoxide dismutase (SOD), and reactive oxygen species (ROS) were employed for the assessments of oxidative stress. BTB-related proteins were measured by immunoblotting. Nuclear factor κB (NF-κB) was assessed by immunofluorescence.

Results

High-fat-diet-fed mice presented evident lipid metabolic disturbances, disrupted BTB integrity, and decreased reproductive function. Metformin alleviated the decrease in male fertility, decreased ectopic lipid deposition in the testis, and increased serum FSH levels. A further mechanistic analysis revealed that metformin ameliorated the high-fat-diet-induced injury to the BTB structure and permeability and restored the disordered BTB-related proteins, which might be associated with an improvement in oxidative stress and a recovery of NF-κB activity in Sertoli cells (SCs).

Conclusion

Metformin improves obese male fertility by alleviating oxidative stress-induced BTB damage. These findings provide new insights into the effect of metformin on various diseases and suggest future possibilities in the treatment of male infertility.

Resveratrol Attenuates Malathion Induced Damage in Some Reproductive Parameters by Decreasing Oxidative Stress and Lipid Peroxidation in Male Rats

Objective: Malathion is the most organophosphates which capable to produce free radicals and induce disturbance on some of male reproductive parameter. Resveratrol is an herbal polyphenol and it has been beneficial antioxidant effects during short-term administration. This study was designed to evaluate the effects of Resveratrol against damage induced by Malathion to the reproductive parameter of male rats. Materials and methods: In this experimental study, 48 male rats were randomly assigned to 8 groups: normal control (saline) and Malathion control (250 mg/kg) groups; Resveratrol groups (2, 8, 20 mg/kg) and Malathion + Resveratrol (2, 8, 20 mg/kg). Treatments were administered intraperitoneally and gavage daily for 65 days. The sperm parameters, testis malondialdehyde (MDA), total antioxidant capacity (TAC), testosterone level and germinal layer height were evaluated and statistically analyzed. Results: The results displayed that the values of all parameters except MDA level (which increased) reduced significantly in the Malathion control group compared to the normal control group (p < 0.001). The Resveratrol and Resveratrol + Malathion treatments at all doses increased significantly all parameters except MDA level (which decreased) compared to the Malathion control group (p < 0.001). No significant modifications were observed in all Resveratrol groups compared to the normal control group (p > 0.05). Conclusion: Resveratrol attenuates toxic effect of Malathion on some of male reproductive parameters.

Toxic Effect of Cadmium, Lead, and Arsenic on the Sertoli Cell: Mechanisms of Damage Involved

Over the past decades, an increase has been described in exposure to environmental toxins; consequently, a series of studies has been carried out with the aim of identifying problems associated with health. One of the main risk factors is exposure to heavy metals. The adverse effects that these compounds exert on health are quite complex and difficult to elucidate, in that they act at different levels and there are various signaling pathways that are implicated in the mechanisms of damage. The Sertoli cells plays a role of vital importance during the process of spermatogenesis, and it has been identified as one of the principal targets of heavy metals. In the present review, cadmium, lead, and arsenic are broached as altering the physiology of the Sertoli cells, citing mechanisms that have been cited in the literature.

In Vitro Evaluation of Damage by Heavy Metals in Tight and Gap Junctions of Sertoli Cells

The Sertoli cell plays a vital role during the spermatogenesis process and has been identified as one of the main targets of the toxic action of heavy metals on the seminiferous epithelium. In the present work, the effect of lead (Pb), Arsenic (As), and Cadmium (Cd) in primary cultures of Sertoli cells was analyzed by measuring the expression of the genes Cldn11, Ocln, and Gja1 that participate in the tight and gap junctions, which are responsible for maintaining the blood-testis barrier. Sertoli cells were isolated from the testes of Wistar rats. Sertoli cell cultures were exposed separately and at the same concentrations of three heavy metals for 48 h. Subsequently, gene expression was measured by real-time polymerase chain reaction. In the morphological analysis of the cultures, after 24 h, the cultures exposed to Cd showed greatest detachment of the monolayer, followed by those exposed to As and Pb. As for gene expression patterns, As induced a decrease in the expression of the Cldn11 gene at 24 and 48 h (p < 0.01) and in that of Ocln at 24 (p < 0.001) and 48 h (p < 0.01), whereas Cd induced overexpression of the Gja1 gene from day 1 of exposure (p < 0.001) and subexpression of the Ocln gene (p < 0.05) at 24 h. Because each of these three metals generated different expression patterns in the three genes, we can postulate that the mechanisms of damage that they induce are different; therefore, the effect that they exert on the Sertoli cell occurs through different pathways, generating changes in structural proteins, altering Sertoli cell morphology, and compromising its function in the regulation of the spermatogenesis process.

Dialkyl phosphate urinary metabolites and chromosomal abnormalities in human sperm

BACKGROUND

The past decade has seen numerous human health studies seeking to characterize the impacts of environmental exposures, such as organophosphate (OP) insecticides, on male reproduction. Despite an extensive literature on OP toxicology, many hormone-mediated effects on the testes are not well understood.

OBJECTIVES

This study investigated environmental exposures to OPs and their association with the frequency of sperm chromosomal abnormalities (i.e., disomy) among adult men.

METHODS

Men (n=159) from a study assessing the impact of environmental exposures on male reproductive health were included in this investigation. Multi-probe fluorescence in situ hybridization (FISH) for chromosomes X, Y, and 18 was used to determine XX18, YY18, XY18 and total disomy in sperm nuclei. Urine was analyzed using gas chromatography coupled with mass spectrometry for concentrations of dialkyl phosphate (DAP) metabolites of OPs [dimethylphosphate (DMP); dimethylthiophosphate (DMTP); dimethyldithiophosphate (DMDTP); diethylphosphate (DEP); diethylthiophosphate (DETP); and diethyldithiophosphate (DEDTP)]. Poisson regression was used to model the association between OP exposures and disomy measures. Incidence rate ratios (IRRs) were calculated for each disomy type by exposure quartiles for most metabolites, controlling for age, race, BMI, smoking, specific gravity, total sperm concentration, motility, and morphology.

RESULTS

A significant positive trend was seen for increasing IRRs by exposure quartiles of DMTP, DMDTP, DEP and DETP in XX18, YY18, XY18 and total disomy. A significant inverse association was observed between DMP and total disomy. Findings for total sum of DAP metabolites concealed individual associations as those results differed from the patterns observed for each individual metabolite. Dose-response relationships appeared nonmonotonic, with most of the increase in disomy rates occurring between the second and third exposure quartiles and without additional increases between the third and fourth exposure quartiles.

CONCLUSIONS

This is the first epidemiologic study of this size to examine the relationship between environmental OP exposures and human sperm disomy outcomes. Our findings suggest that increased disomy rates were associated with specific DAP metabolites, suggesting that the impacts of OPs on testis function need further characterization in epidemiologic studies.

Phthalates might interfere with testicular function by reducing testosterone and insulin-like factor 3 levels

STUDY QUESTION

Do phthalates create a male reproductive hormone imbalance by down-regulating the secretion of testosterone and insulin-like factor 3 (INSL3)?

SUMMARY ANSWER

Our study suggests that exposure to phthalates is related to a reduction in the secretion of testosterone and INSL3 in adult males.

WHAT IS KNOWN ALREADY

There is evidence that exposure to phthalates, an abundant group of industrial plasticizers, negatively affects testosterone biosynthesis, but little is known about the mechanism in men. The hypothesis that exposure to phthalates reduces the levels of testosterone and INSL3, a marker of Leydig cell function, is underexplored.

STUDY DESIGN, SIZE, DURATION

This case-control study of 176 men ran from 2010 to 2012. Infertile men were recruited through infertility clinics in Taiwan, fertile men were recruited from childbirth preparation classes and all were categorized based on the World Health Organization definition of infertility and by the diagnoses of obstetricians.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Urinary concentrations of 11 phthalate metabolites were measured, along with serum levels of FSH, LH, total testosterone (TT), estradiol, sex hormone-binding globulin and Inhibin B. Androgen status indices including free testosterone (fT) and the free androgen index (FAI) were calculated. The circulating INSL3 level was evaluated using a radioimmunoassay. Non-parametric analyses, trend tests and linear regression models were used.

MAIN RESULTS AND THE ROLE OF CHANCE

Urinary mono-n-butyl phthalate (MnBP), mono-(2-ethylhexyl) phthalate (MEHP) and mono-2-ethyl-5-carboxypentyl phthalate were significantly higher in infertile than in fertile men. Serum Inhibin B, the Inhibin B : FSH ratio, the TT : LH ratio and INSL3 were significantly lower in infertile men. In multiple regression models controlled for potential confounders, there is an inverse association between urinary levels of mono-methyl phthalate (MMP), mono-iso-butyl phthalate (MiBP), MEHP, MEHP% and serum TT (P = 0.001, 0.007, 0.042 and 0.012, respectively). The inverse associations were also found between urinary levels of MiBP, monobenzyl phthalate (MBzP), MEHP, MEHP% and serum fT (P = 0.028, 0.017, 0.045 and 0.027, respectively); between urinary levels of MMP, MEHP, MEHP% and the TT : LH ratio (P = 0.004, 0.029 and 0.039, respectively); between urinary levels of MMP, MiBP, MnBP, MBzP, MEHP and the FAI (P = 0.002, 0.008, 0.037, 0.028, 0.042 and 0.016, respectively). Urinary MBzP and MEHP% were negatively associated with a decrease in serum INSL3 (P = 0.049 and <0.001). We also observed a strong inverse relationship between MEHP% quartiles and serum TT, fT, the TT : LH ratio and INSL3 (Ptrend = 0.003, 0.080, 0.002 and 0.012, respectively). Serum INSL3, TT, fT and the TT : LH ratio were lower for men in the highest MEHP% quartile than in the reference group (P = 0.007, 0.002, 0.090 and 0.001, respectively).

LIMITATIONS, REASONS FOR CAUTION

A potential limitation is using a single urine and blood sample to predict urinary phthalate metabolites and reproductive hormone status over long periods. However, there is evidence that a single measure provides a reliable result in population studies.

WIDER IMPLICATIONS OF THE FINDINGS

Non-occupational exposure to phthalates, including di-2-ethylhexyl phthalate, might lead to adverse effects on testicular/Leydig cell function and be of concern owing to the ubiquitous multisource exposure to phthalates among the general population. Although our findings are in agreement with recent experimental data, more studies are required to draw firm conclusions on the relation of INSL3 to phthalate exposure or testicular/Leydig cell function.

Toxic effects of cadmium on testis of birds and mammals: a review

In humans and other mammals, cadmium (Cd) causes various damages to different organs and tissues of the body. This review presents a comprehensive overview on the effect of Cd on the structure of seminiferous tubules, Leydig cells and blood vessels in the testis. The main observation of the effect of Cd is destruction of the seminiferous tubules with severe necrotic areas. Damage is to all stages of developing germ cells by inducing their structural changes and the apoptotic cell death. Sertoli supporting cells are considered the most vulnerable cells. Their damage results in cytoplasmic rearrangement and disruption of inter-Sertoli tight junctions resulting in increased permeability of the blood-testis barrier, structural changes in the Leydig cells and decreased testosterone secretion. After long time of Cd exposure an increase of the amount of interstitial connective tissue occurs. In blood vessels Cd exposure causes various morphological and physiological changes in vascular endothelial cells and smooth muscle cells. In humans and other mammals, the range of effect depends on the dose, route, ways, and duration of exposure. After necrosis of the sensitive cells Cd produced lesions in surrounding tissue and activate free cells. Atrophy of the seminiferous tubules is followed by Leydig cell regeneration and interstitial revascularization. In birds, spermatogenic cells underwent irreversible degeneration or atrophy of seminiferous tubules in the absence of significant vascular lesions.

Toxicants target cell junctions in the testis: Insights from the indazole-carboxylic acid model

There are numerous types of junctions in the seminiferous epithelium which are integrated with, and critically dependent on the Sertoli cell cytoskeleton. These include the basal tight junctions between Sertoli cells that form the main component of the blood–testis barrier, the basal ectoplasmic specializations (basal ES) and basal tubulobulbar complexes (basal TBC) between Sertoli cells; as well as apical ES and apical TBC between Sertoli cells and the developing spermatids that orchestrate spermiogenesis and spermiation. These junctions, namely TJ, ES, and TBC interact with actin microfilament-based cytoskeleton, which together with the desmosomal junctions that interact with the intermediate filament-based cytoskeleton plus the highly polarized microtubule-based cytoskeleton are working in concert to move spermatocytes and spermatids between the basal and luminal aspect of the seminiferous epithelium. In short, these various junctions are structurally complexed with the actin- and microtubule-based cytoskeleton or intermediate filaments of the Sertoli cell. Studies have shown toxicants (e.g., cadmium, bisphenol A (BPA), perfluorooctanesulfonate (PFOS), phthalates, and glycerol), and some male contraceptives under development (e.g., adjudin, gamendazole), exert their effects, at least in part, by targeting cell junctions in the testis. The disruption of Sertoli–Sertoli cell and Sertoli–germ cell junctions, results in the loss of germ cells from the seminiferous epithelium. Adjudin, a potential male contraceptive under investigation in our laboratory, produces loss of spermatids from the seminiferous tubules through disruption of the Sertoli cell spermatid junctions and disruption of the Sertoli cell cytoskeleton. The molecular and structural changes associated with adjudin administration are described, to provide an example of the profile of changes caused by disturbance of Sertoli-germ cell and also Sertoli cell-cell junctions.

Regulation of drug transporters in the testis by environmental toxicant cadmium, steroids and cytokines

The blood-testis barrier (BTB) provides an efficient barrier to restrict paracellular and transcellular transport of substances, such as toxicants and drugs, limiting their entry to the testis to cause injury. This is achieved by the coordinated actions of efflux and influx transporters at the BTB, which are integral membrane proteins that interact with their substrates, such as drugs and toxicants. An efflux transporter (e.g., P-glycoprotein) can either restrict the entry of drugs/toxicants into the testis or actively pump drugs/toxicants out of Sertoli and/or germ cells if they have entered the seminiferous epithelium via influx pumps. This thus provides an effective mechanism to safeguard spermatogenesis. Using Sertoli cells cultured in vitro with an established tight junction (TJ)-permeability barrier which mimicked the BTB in vivo and treated with cadmium chloride (CdCl2), and also in adult rats (~300 g b.w.) treated with CdCl2 (3 mg/kg b.w., via i.p.) to induce testicular injury, cadmium was found to significantly downregulate the expression of efflux (e.g., P-glycoprotein, Mrp1, Abcg1) and influx (e.g., Oatp3, Slc15a1, Scl39a8) transporters. For instance, treatment of Sertoli cells with cadmium induced significant loss of P-glycoprotein and Oatp-3 at the cell-cell interface, which likely facilitated cadmium entry into the Sertoli cell. These findings illustrate that one of the mechanisms by which cadmium enters the testis is mediated by downregulating the expression of drug transporters at the BTB. Furthermore, cytokines and steroids were found to have differential effects in regulating the expression of drug transporters. Summary, the expression of drug transporters in the testis is regulated by toxicants, steroids and cytokines.

Organic and inorganic transporters of the testis: A review

Transporters have a huge impact on the toxicology and pharmacological effects of xenobiotics in addition to being implicated in several diseases. While these important proteins have been well studied in organs such as the kidney or liver, characterization of transporters in the testis is still in the early stages. Knowledge of transporter function may greatly advance the field's understanding of the physiological and toxicological processes that occur in the testis. Several foundational studies involving both organic and inorganic transporters have been critical in furthering our understanding of how the testis interacts with endogenous and xenobiotic compounds. This review provides an overview of how transporters function, their clinical significance, and highlights what is known for many of the important transporters in the testis.

Sexually immature male ERE-Luc reporter mice to assess low dose estrogen-like effects of CdCl2 versus dietary Cd

CdCl2 salt is widely used in exposure oriented studies, while the biological exposure of Cadmium (Cd) occurs mostly through diet. Hence, we designed a in vivo imaging methodology with sexually immature male ERE-Luc reporter mice to test the estrogen-like (EL) effects of Cd as a natural component in wheat and flax bread based diets (containing 17.57 and 49.22 ug/kg Cd concentrations respectively) and CdCl2 per-oral dose of 1 ug/kg/bw/day. Total exposure of ingested and % bioaccumulation of Cd in selected organs were estimated as 547 ng (4.4%), 776 ng (0.3%) and 2131.8 ng (0.1%) corresponding to CdCl2, wheat and flax bread based diet treatments respectively. Cd from CdCl2 bioaccumulated more readily, despite the exposure of Cd is higher with bread based diets. Longitudinal in vivo imaging did not reveal significant changes in luciferase activity. White adipose tissue (WAT) and prostate were identified as novel target organs of Cd. Indeed, the rest of the observed EL effects, endogenous target gene expression and necropsy findings are not consistent to any particular organ or treatment. This implies that, the observed EL effects due to low doses of Cd (either from CdCl2 or dietary form) occur only as subtle changes at the molecular level, but inadequate to cause significant changes at the anatomo-pathological level during the 21 day exposure period. The study demonstrates the sensitivity of the methodology to assess EL effects of food embedded Cd and underlines the limitations of directly extrapolating the results of suspected chemicals in their pure form to dietary exposure scenarios.

Environmental toxicants perturb human Sertoli cell adhesive function via changes in F-actin organization mediated by actin regulatory proteins

STUDY QUESTION

Can human Sertoli cells cultured in vitro and that have formed an epithelium be used as a model to monitor toxicant-induced junction disruption and to better understand the mechanism(s) by which toxicants disrupt cell adhesion at the Sertoli cell blood-testis barrier (BTB)?

SUMMARY ANSWER

Our findings illustrate that human Sertoli cells cultured in vitro serve as a reliable system to monitor the impact of environmental toxicants on the BTB function.

WHAT IS KNOWN ALREADY

Suspicions of a declining trend in semen quality and a concomitant increase in exposures to environmental toxicants over the past decades reveal the need of an in vitro system that efficiently and reliably monitors the impact of toxicants on male reproductive function. Furthermore, studies in rodents have confirmed that environmental toxicants impede Sertoli cell BTB function in vitro and in vivo.

STUDY DESIGN, SIZE AND DURATION

We examined the effects of two environmental toxicants: cadmium chloride (0.5-20 µM) and bisphenol A (0.4-200 µM) on human Sertoli cell function. Cultured Sertoli cells from three men were used in this study, which spanned an 18-month period.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human Sertoli cells from three subjects were cultured in F12/DMEM containing 5% fetal bovine serum. Changes in protein expression were monitored by immunoblotting using specific antibodies. Immunofluorescence analyses were used to assess changes in the distribution of adhesion proteins, F-actin and actin regulatory proteins following exposure to two toxicants: cadmium chloride and bisphenol A (BPA).

MAIN RESULTS AND THE ROLE OF CHANCE

Human Sertoli cells were sensitive to cadmium and BPA toxicity. Changes in the localization of cell adhesion proteins were mediated by an alteration of the actin-based cytoskeleton. This alteration of F-actin network in Sertoli cells as manifested by truncation and depolymerization of actin microfilaments at the Sertoli cell BTB was caused by mislocalization of actin filament barbed end capping and bundling protein Eps8, and branched actin polymerization protein Arp3. Besides impeding actin dynamics, endocytic vesicle-mediated trafficking and the proper localization of actin regulatory proteins c-Src and annexin II in Sertoli cells were also affected. Results of statistical analysis demonstrate that these findings were not obtained by chance.

LIMITATIONS, REASONS FOR CAUTION

(i) This study was done in vitro and might not extrapolate to the in vivo state, (ii) conclusions are based on the use of Sertoli cell samples from three men and (iii) it is uncertain if the concentrations of toxicants used in the experiments are reached in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

Human Sertoli cells cultured in vitro provide a robust model to monitor environmental toxicant-mediated disruption of Sertoli cell BTB function and to study the mechanism(s) of toxicant-induced testicular dysfunction.

The apical ES-BTB-BM functional axis is an emerging target for toxicant-induced infertility

Testes are sensitive to toxicants, such as cadmium and phthalates, which disrupt a local functional axis in the seminiferous epithelium known as the 'apical ectoplasmic specialization (apical ES)-blood-testis barrier (BTB)-basement membrane (BM)'. Following exposure, toxicants contact the basement membrane and activate the Sertoli cell, which perturbs its signaling function. Thus, toxicants can modulate signaling and/or cellular events at the apical ES-BTB-BM axis, perturbing spermatogenesis without entering the epithelium. Toxicants also enter the epithelium via drug transporters to potentiate their damaging effects, and downregulation of efflux transporters by toxicants impedes BTB function such that toxicants remain in the epithelium and efficiently disrupt spermatogenesis. These findings support a novel model of toxicant-induced disruption of spermatogenesis that could be interfered with using small molecules.

Targeting testis-specific proteins to inhibit spermatogenesis: lesson from endocrine disrupting chemicals

INTRODUCTION

Exposure to endocrine disrupting chemicals (EDCs) has recently been linked to declining fertility in men in both developed and developing countries. Since many EDCs possess intrinsic estrogenic or androgenic activities, thus, the gonad is one of the major targets of EDCs.

AREAS COVERED

For the past 2 decades, studies found in the literature regarding the disruptive effects of these EDCs on reproductive function in human males and also rodents were mostly focused on oxidative stress-induced germ cell apoptosis, disruption of steroidogenesis, abnormal sperm production and disruption of spermatogenesis in particular cell adhesion function and the blood-testis-barrier (BTB) function. Herein, we highlight recent findings in the field illustrating testis-specific proteins are also targets of EDCs.

EXPERT OPINION

This information should be helpful in developing better therapeutic approach to manage ECD-induced reproductive toxicity. This information is also helpful to identify potential targets for male contraceptive development.

Estrogenic effect of three substituted deoxybenzoins

Deoxybenzoins (1-(2,4-dihydroxyphenyl)-2-(4-hydroxyphenyl)ethanone) are possible precursors or metabolites of isoflavanones which may have xenoestrogenic potential on estrogen receptor (ER). In this study we evaluated three 2'-substituted deoxybenzoin derivatives for their estrogenic effect based upon their ability to affect the proliferation of ERα(+) MCF7 cells, ERβ(+) PC3 cells and Hep2 cells stably transfected and expressing either ERα or ERβ. These compounds designated as CMPD3, CMPD6 and CMPD9 had -COOH, -(CH(2))(4)-CH(3) and -CH(3) substitutions, respectively on the 2'-position of the 2,4-dihydroxyphenyl ring of deoxybenzoin. We found that all three compounds increased the proliferation of ERα(+) MCF7 cells (EC(50)~1-12 μM) and ERα(+) Hep2 cells, while causing apoptosis in ERβ(+) PC3 cells (IC(50)~1-5 μM) and ERβ(+) Hep2 cells. The compounds also up-regulated the expression of estrogen sensitive genes, trefoil factor 1 (TFF1, previously known as pS2) and cathepsin-D (CTSD), in these cells. We performed in vitro ER transcription activation assays using Hep2 cells transiently co-transfected with estrogen response element driven luciferase and either ERα or ERβ vectors to ascertain the mechanism of action of these compounds through the 'classical' genomic pathway of estrogenic activity and to determine their ER subtype selectivity. Molecular docking of the compounds with the Ligand Binding Domain of ERα and ERβ showed similar docking scores (Glidescores of -6.5 to -8.5 kcal/mol) indicating that these compounds were ligands of both ERα and ERβ with similar affinity.

Intercellular adhesion molecule-2 is involved in apical ectoplasmic specialization dynamics during spermatogenesis in the rat

In this study, we investigated the role of intercellular adhesion molecule-2 (ICAM2) in the testis. ICAM2 is a cell adhesion protein having important roles in cell migration, especially during inflammation when leukocytes cross the endothelium. Herein, we showed ICAM2 to be expressed by germ and Sertoli cells in the rat testis. When a monospecific antibody was used for immunolocalization experiments, ICAM2 was found to surround the heads of elongating/elongated spermatids in all stages of the seminiferous epithelial cycle. To determine whether ICAM2 is a constituent of apical ectoplasmic specialization (ES), co-immunoprecipitation and dual immunofluorescence staining were performed. Interestingly, ICAM2 was found to associate with β1-integrin, nectin-3, afadin, Src, proline-rich tyrosine kinase 2, annexin II, and actin. Following CdCl₂ treatment, ICAM2 was found to be upregulated during restructuring of the seminiferous epithelium, with round spermatids becoming increasingly immunoreactive for ICAM2 by 6-16 h. Interestingly, there was a loss in the binding of ICAM2 to actin during CdCl₂-induced germ cell loss, suggesting that a loss of ICAM2-actin interactions might have facilitated junction restructuring. Taken collectively, these results illustrate that ICAM2 plays an important role in apical ES dynamics during spermatogenesis.

Lifestyle behaviors associated with exposures to endocrine disruptors

Identifying and characterizing sources of exposure to phthalates and bisphenol A (BPA) have proved challenging due to the presence of multiple co-exposures resulting from a wide variety of home environments and lifestyles. We hypothesized that the consistent lifestyle of an Old Order Mennonite (OOM) community would provide an ideal setting in which to characterize sources of exposure to BPA and phthalates. We obtained urine samples from ten mid-term pregnant OOM women (ages-21-39) to determine concentrations of 9 phthalate metabolites and BPA and collected a self-reported survey of participants' household environment, product use, and lifestyle within a 48-h period prior to urine collection. We compared their metabolite concentrations to pregnant women included in the National Health and Nutrition Examination Survey (NHANES 2007-2008). Although OOM participants reported some use of plastic and fragranced household products, concentrations of metabolites were lower and significantly less for BPA (p=0.002) and phthalate metabolites MEHP (p=0.0215), MiBP (p=0.0020) and MEP (p=0.021), when compared to NHANES pregnant women. Levels of other phthalate metabolites were also lower in this population. Our data suggest three practices that may contribute to these lower levels: (1) consuming mostly homegrown produce (ingestion), (2) no cosmetics and limited use of personal care products, and (3) transportation primarily by sources other than automobiles.