Primary rat Sertoli and interstitial cells exhibit a differential response to cadmium

The Role of Chlorella vulgaris in Attenuating Infertility Induced by Cadmium Chloride via Suppressing Oxidative Stress and Modulating Spermatogenesis and Steroidogenesis in Male Rats

Cadmium (Cd) is an environmental pollutant known as endocrine disruptor . Cd has been reported to induce perturbations of the testicular functions and the subsequent decline of the male fertility of both animals and humans. Chlorella vulgaris (ChV) a species of green microalga has been reported to have multiple beneficial activities such as anti-inflammatory, antioxidant, and antiapoptotic effects. Thus, this work was conducted to declare the benefits of Chlorella vulgaris (ChV) (500 mg/kg doses) against cadmium chloride CdCl2 (2 mg/kg doses) toxicity on the main and accessory reproductive organs' weight, structure, and function of male rats. Briefly, 40 adult male rats in 4 groups (n = 10) were used as follows; control, ChV, CdCl2, and CdCl2+ChV. (i) The 1st group was kept as control fed on pellet chow and water ad libitum. (ii) The second group is Chlorella vulgaris (ChV) group fed with C. vulgaris alga for 10 days (500 mg/kg BW). (iii) The third group was administrated CdCl2 (2mg/kg BW) via subcutaneous injection (S/C) daily for 10 days. (iv) The fourth group administered both CdCl2 and ChV with the abovementioned doses daily for successive 10 days. Our observations declared that cadmium exhibited an adverse influence on the testes and prostate gland architecture indicated by seminiferous tubule destruction, testicular edema, degeneration of Leydig cells, and prostate acini damage. All together affect the epididymal semen quality and quantity including sperm viability, motility, and count. Interestingly, ChV could restore the testicular architecture and spermatozoa regeneration accompanied by semen quality improvement and increased reproductive hormones including testosterone. On the other side, ChV suppresses reactive oxygen species (ROS) formation via enhancement the antioxidant-related genes in the testicular tissue including SOD, CAT, GSH, and MDA and maintaining spermatocyte survival via suppression of apoptotic related genes including caspase3 and activating steroidogenic related genes including StAR and HSD17β3 in the cadmium-treated testes. In this study, ChV could enhance male fertility under normal or stressful conditions and ameliorate the adverse effects of hazardous heavy metals that are widely distributed in our environment.

An in vitro testicular organoid model for the study of testis morphogenesis, somatic cell maturation, endocrine function, and toxicological assessment of endocrine disruptors

Male reproductive capacity has fallen considerably in recent decades; in addition, the incidence of testicular cancer has increased in many developed countries. The cause of this phenomenon is unknown, but environmental toxicants are considered a major contributing factor. To study potential reproductive toxicants, robust in vitro testis models are needed. We have recently established a porcine testis organoid system with a high resemblance to the architectures of innate testis tissue. Here, we further investigated the testis morphogenesis, cell maturation, and endocrine function of the testis organoids. We also challenged this system with abiraterone, a steroidogenic inhibitor, to validate its suitability as an in vitro platform for endocrine toxicology tests. Our results showed that the testis cells in the organoids reorganize into testis cordal structures, and the cordal relative areas increase in the organoids over time of culture. Moreover, the diameters and cell numbers per cross-section of the cordal structures increased over time. Interestingly, Sertoli cells in the organoids gradually underwent maturational changes by showing increased expression of androgen receptors, decreased expression of the anti-müllerian hormone, and formation of the blood-testis barrier. Next, we confirmed that the organoids respond to hormonal stimulation and release multiple sex hormones, including testosterone, estradiol, and progesterone. Finally, we showed that the production of testosterone and estradiol in this system can be inhibited in response to the steroidogenic inhibitor. Taken together, our organoid system provides a promising in vitro platform for male reproductive toxicology studies on testis morphogenesis, somatic cell maturation, and endocrine production.

Environmental and occupational exposure to cadmium associated with male reproductive health risk: a systematic review and meta-analysis based on epidemiological evidence

There is an abundance of epidemiological evidence and animal experiments concerning the correlation between cadmium exposure and adverse male reproductive health outcomes. However, the evidence remains inconclusive. We conducted a literature search from PubMed, Embase, and Web of Science over the past 3 decades. Pooled r and 95% confidence intervals (CIs) were derived from Cd levels of the type of biological materials and different outcome indicators to address the large heterogeneity of existing literature. Cd was negatively correlated with semen parameters (r = - 0.122, 95% CI - 0.151 to - 0.092) and positively correlated with sera sex hormones (r = 0.104, 95% CI 0.060 to 0.147). Among them, Cd in three different biological materials (blood, semen, and urine) was negatively correlated with semen parameters, while among sex hormones, only blood and urine were statistically positively correlated. In subgroup analysis, blood Cd was negatively correlated with semen density, sperm motility, sperm morphology, and sperm count. Semen Cd was negatively correlated with semen concentration. As for serum sex hormones, blood Cd had no statistical significance with three hormones, while semen Cd was negatively correlated with testosterone. In summary, cadmium exposure might be associated with the risk of a decline in sperm quality and abnormal levels of sex hormones.

Impacts of cadmium on male fertility: Lessons learnt so far

Cadmium (Cd) is one of the most dangerous heavy metals in the world. Globally, toxicities associated with cadmium and its attendant negative impact on humans and animals cannot be under-estimated. Cd is a heavy metal, and people are exposed to it through contaminated foods and smoking. Cd exerts its deleterious impacts on the testes (male reproductive system) by inducing oxidative stress, spermatogenic cells apoptosis, testicular inflammation, decreasing androgenic and sperm cell functions, disrupting ionic homeostasis, pathways and epigenetic gene regulation, damaging vascular endothelium and blood testes barrier. In association with other industrial by-products, Cd has been incriminated for the recent decline of male fertility rate seen in both man and animals. Understanding the processes involved in Cd-induced testicular toxicity is vital for the innovation of techniques that will help ameliorate infertility in males. In this review, we summed up recent studies on the processes of testicular toxicity and male infertility due to Cd exposure. Also, the usage of different compounds including phytochemicals, and plant extracts to manage Cd reprotoxicity will be reviewed.

Cadmium and immunologically-mediated homeostasis of anatomical barrier tissues

Cadmium (Cd) is a toxic heavy metal that when absorbed into the body causes nephrotoxicity and effects in other tissues.Anatomical barrier tissues are tissues that prevent the entry of pathogens and include skin, mucus membranes and the immune system. The adverse effects of Cd-induced immune cell's activity are the most extensively studied in the kidneys and the liver. There are though fewer data relating the effect of this metal on the other tissues, particularly in those in which cells of the immune system form local circuits of tissue defense, maintaining immune-mediated homeostasis. In this work, data on the direct and indirect effects of Cd on anatomical barrier tissue of inner and outer body surfaces (the lungs, gut, reproductive organs, and skin) were summarized.

Hypomethylation of LINE-1 retrotransposons is associated with cadmium-induced testicular injury

Retrotransposons, as vital regulator of male fertility, are essential for spermatogenesis. Cadmium (Cd) is an environmental toxicant and endocrine disruptor, targeting the reproductive system. Growing evidence shows that Cd exposure can induce male infertility in mammals. In this study, we generated a male C57BL/6 J mice model with consecutive 35 days cadmium chloride (CdCl₂) in different concentrations of 0, 0.25, 0.5, 1.0, and 2.0 mg/kg. The results indicated that 1.0 and 2.0 mg/kg CdCl₂ significantly affected the body weight. Meanwhile, the highest dose group with 2.0 mg/kg CdCl₂ presented low fertility. Furthermore, the expression of retrotransposon mRNA was markedly increased in the higher doses group. We examined methylcytosine (mC) levels of the three active LINE-1 subfamilies TfI, A, and GfII in testis. Conclusively, Cd exposure probably undermines the male mice fertility by disrupting DNA methylation to regulate the retrotransposons. Further studies are required for identifying whether retrotransposon activation has any significant impacts on genome structure, stability, and expression in Cd-induced testicular injury, laying foundation for the treatment for male infertility.

Characterization of rodent Sertoli cell primary cultures

Sertoli cells play a vital role in spermatogenesis by offering physical and nutritional support to the differentiating male germ cells. They form the blood-testis barrier and secrete growth factors essential for germ cell differentiation. Sertoli cell primary cultures are critical for understanding the regulation of spermatogenesis; however, obtaining pure cultures has been a challenge. Rodent Sertoli cell isolation protocols do not rule out contamination by the interstitial or connective tissue cells. Sertoli cell-specific markers could be helpful, but there is no consensus. Vimentin, the most commonly used marker, is not specific for Sertoli cells since its expression has been reported in peritubular myoid cells, mesenchymal stem cells, fibroblasts, macrophages, and endothelial cells, which contaminate Sertoli cell preparations. Markers based on transcription and growth factors also have limitations. Thus, the impediment to obtaining pure Sertoli cell cultures pertains to both the method of isolation and marker usage. The aim of this review is to discuss improvements to current methods of rodent Sertoli cell primary cultures, assess the properties of prepubertal versus mature Sertoli cell cultures, and propose steps to improve cellular characterization. Potential benefits of using contemporary approaches, including lineage tracing, specific cell ablation, and RNA-seq for obtaining Sertoli-specific transcript markers are discussed. Evaluating the specificity and applicability of these markers at the protein level to characterize Sertoli cells in culture would be critical. This review is expected to positively impact future work using primary cultures of rodent Sertoli cells.

The environment and male reproduction: The effect of cadmium exposure on reproductive function and its implication in fertility

Cadmium is an environmental pollutant known as endocrine disruptor. Testis is particularly susceptible to cadmium, and testis injury occurs at high but even low levels of exposure. Cadmium reproductive toxicity is mediated by multiple mechanisms, including structural damage to testis vasculature and blood-testis barrier, inflammation, cytotoxicity on Sertoli and Leydig cells, oxidative stress mainly by means of mimicry and interference with essential ions, apoptosis, interference with selected signaling pathways and epigenetic regulation of genes involved in the regulation of reproductive function, and disturbance of the hypothalamus-pituitary-gonadal axis. The current review outlines epidemiological observational findings from environmental and occupational exposure in humans, and reports experimental studies in humans and animals. Lastly, a focus on the pathogenetic mechanisms of cadmium toxicity and on the specific mechanisms of cadmium sensitivity and resistance, particularly assessed in animal models, is included. Despite convincing experimental findings in animals and supporting evidences in humans identifying cadmium as reproductive toxicant, observational findings are controversial, suffering from heterogeneity of study design and pattern of exposure, and from co-exposure to multiple pollutants.

Early signs of toxicity in testes and sperm of rats exposed to low cadmium doses

The cadmium (Cd) concentration in the environment has increased as a consequence of anthropogenic activity. The objective of this study was to determine early signs of Cd toxicity in testes and sperm as possible biomarkers. The dose orally administered to Wistar rats was within the range where chronic toxicity can appear. At the light microscopic level, gonads presented preserved cytoarchitecture throughout treatment; however, after the second month, transmission electron microscopy (TEM) revealed disruption of the blood–testis barrier. The study of sperm with light microscopy showed defects in gamete morphology after 2 months of treatment. Another parameter that revealed alteration was sperm motility after 3 months of treatment. TEM was used to analyze the flagellum, which in the midpiece showed aberrant mitochondria and displacement of outer dense fibers in relation to the central axoneme after 2 months. The data obtained were associated with Cd concentration in the testes, an increase in its levels being observed in a time-dependent manner. The results provided in this study demonstrated that early signs of Cd toxicity were observed in gonads and gametes during the second month of the treatment, generating morphological and functional alterations in the sperm that could lead to infertility.

Cell-specific ablation in the testis: what have we learned?

Testicular development and function is the culmination of a complex process of autocrine, paracrine and endocrine interactions between multiple cell types. Dissecting this has classically involved the use of systemic treatments to perturb endocrine function, or more recently, transgenic models to knockout individual genes. However, targeting genes one at a time does not capture the more wide‐ranging role of each cell type in its entirety. An often overlooked, but extremely powerful approach to elucidate cellular function is the use of cell ablation strategies, specifically removing one cellular population and examining the resultant impacts on development and function. Cell ablation studies reveal a more holistic overview of cell–cell interactions. This not only identifies important roles for the ablated cell type, which warrant further downstream study, but also, and importantly, reveals functions within the tissue that occur completely independently of the ablated cell type. To date, cell ablation studies in the testis have specifically removed germ cells, Leydig cells, macrophages and recently Sertoli cells. These studies have provided great leaps in understanding not possible via other approaches; as such, cell ablation represents an essential component in the researchers’ tool‐kit, and should be viewed as a complement to the more mainstream approaches to advancing our understanding of testis biology. In this review, we summarise the cell ablation models used in the testis, and discuss what each of these have taught us about testis development and 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.

Cadmium-induced testicular injury

Cadmium (Cd) is an environmental toxicant and an endocrine disruptor in humans and rodents. Several organs (e.g., kidney, liver) are affected by Cd and recent studies have illustrated that the testis is exceedingly sensitive to Cd toxicity. More important, Cd and other toxicants, such as heavy metals (e.g., lead, mercury) and estrogenic-based compounds (e.g., bisphenols) may account for the recent declining fertility in men among developed countries by reducing sperm count and testis function. In this review, we critically discuss recent data in the field that have demonstrated the Cd-induced toxicity to the testis is probably the result of interactions of a complex network of causes. This is likely to involve the disruption of the blood-testis barrier (BTB) via specific signal transduction pathways and signaling molecules, such as p38 mitogen-activated protein kinase (MAPK). We also summarize current studies on factors that confer and/or regulate the testis sensitivity to Cd, such as Cd transporters and metallothioneins, the impact of Cd on the testis as an endocrine disruptor and oxidative stress inducer, and how it may disrupt the Zn(2+) and/or Ca(2+) mediated cellular events. While much work is needed before a unified mechanistic pathway of Cd-induced testicular toxicity emerges, recent studies have helped to identify some of the likely mechanisms and/or events that take place during Cd-induced testis injury. Furthermore, some of the recent studies have shed lights on potential therapeutic or preventive approaches that can be developed in future studies by blocking or minimizing the destructive effects of Cd to testicular function in men.

Cadmium accumulation and binding characteristics in intact Sertoli/germ cell units, and associated effects on stage-specific functionsin vitro: insights from a shark testis model

The increased human use of cadmium (Cd) and its increased occurrence in the environment is of concern. The testis is sensitive to Cd because of the steroid-mediated regulation of spermatogenesis, high levels of DNA synthesis and gene transcription, all of which varies in a stage-related manner. Validated techniques (acridine orange vital staining to detect apoptosis and dextran-rhodamine exclusion to assess blood-testis barrier function) were recently developed and the shark testis was proposed as an alternative model for assessing stage-specific functions in living testicular tissue and to study toxicant actions on spermatogenesis. The present paper shows that 109Cd accumulation and binding in vitro was stage-dependent (premeiotic, PrM > meiotic, M > postmeiotic, PoM), rapid and persisted in spermatocysts (intact germ cell/Sertoli cell units) 49 h after washout. In competitive binding analyses of all three spermatocyst stages, Hg, but not Zn, could replace bound 109Cd, suggesting that Cd binding was specific. These findings were associated with a biphasic apoptotic response in the PrM spermatocysts, which was maximal at 10 microm CdCl2 and 1 microm CdCl2 after 2 and 4 days in culture, respectively. Although Cd uptake in PoM cysts was more than 2-fold less than uptake in PrM cysts, the percentage dextran-rhodamine permeant PoM cysts was approximately 8-fold greater than in controls in the presence of both 10 microm CdCl2 and 30 microm CdCl2 after 4 days culture, indicating that blood-testis barrier function in PoM spermatocysts was compromised. These findings demonstrate that this model has utility for use in screening assays of environmental toxicants.

Is cadmium chloride-induced inter-sertoli tight junction permeability barrier disruption a suitable in vitro model to study the events of junction disassembly during spermatogenesis in the rat testis?

The events of germ cell movement during spermatogenesis are composed of intermittent phases of junction disassembly and reassembly. Although primary Sertoli cells cultured in vitro can be used to study junction reassembly, an in vitro model to study the events of junction disassembly is still lacking. We have assessed whether the CdCl(2)-induced inter-Sertoli tight junction (TJ) permeability barrier disruption in vitro can fill this gap. When Sertoli cells (1.2 x 10(6) cells/cm(2)) were cultured on Matrigel-coated bicameral units to allow the assembly of inter-Sertoli TJs, it was manifested by a steady rise in transepithelial electrical resistance across the Sertoli cell epithelia. Exposure of these cells on day 1 (i.e. 24 h after their isolation) to CdCl(2) at 5-10 microM for 8 h could perturb the inter-Sertoli TJ assembly dose dependently without any apparent cytotoxicity. Likewise, when cells were exposed to CdCl(2) (0.1-5 microM) on day 4 for 8 h after inter-Sertoli TJs were already assembled, CdCl(2) also perturbed the maintenance of inter-Sertoli TJ permeability barrier dose dependently without signs of cell cytotoxicity. Although the perturbed inter-Sertoli TJs were not capable of resealing even after the removal of CdCl(2), the presence of testosterone (T) at 1 x 10(-9) M allowed resealing of the inter-Sertoli TJ barrier after CdCl(2) was removed, whereas the presence of 2 x 10(-7) M testosterone even protected Sertoli cells from CdCl(2)-induced damage. More important, the reassembly of inter-Sertoli TJs after CdCl(2)-induced TJ disruption was accompanied by changes in cellular gene expression of occludin and urokinase plasminogen activator, which mimicked their patterns during inter- Sertoli TJ assembly in vitro without CdCl(2) treatment. Based on these results, it is apparent that CdCl(2)-induced inter-Sertoli TJ disassembly is a potential in vitro model to study the events of junction disassembly.

Sensitivity of Sertoli and Leydig cells to xenobiotics in in vitro models

Different chemicals are known to cause testicular damage in the human male and experimental animals. However, the ability to assess the potential and mechanism of action leading to chemically-induced damage in men has been hampered by a lack of good predictive models. Although many of these chemicals were found to impair reproductive capacity in various laboratory animals, only some have caused reproductive damage in men. Mammalian spermatogenesis takes places within the avascular seminiferous tubules of the testis. Specialized tight junctions, which form between adjacent Sertoli cells at the time of puberty, divide the tubular space into the basal and adluminal compartments, and create a "blood-testis" barrier that restricts passage of substances and ions from the circulation. Thus, the completion of meiosis and post-meiotic germ cell differentiation, which take place in the adluminal compartment, are isolated from circulating substances unable to cross the blood-testis barrier. It seems feasible, therefore, that damage to the germ cells induced by testicular toxicants may be mediated through other cells in the testis such as the Sertoli, peritubular, or Leydig cells. A recently developed two-compartment system for culture of testicular cells can simulate, to some degree, the normal physiologic conditions. In principle, Sertoli cells isolated from mammalian testes are cultured on a permeable support (that is millipore filter) between two fluid compartments. They form a highly polarized epithelial layer with characteristic tight junctions that restrict the passage of substances between the two compartments, in analogy to the blood-testis barrier. We believe this system provides an excellent in vitro model for determining the ability of chemicals to: a) alter the permeability of the blood-testis barrier, b) impair the secretory function of Sertoli cells, or c) affect their viability, all of which could indirectly affect the germ cells. We have utilized this system for examining the effects of cadmium chloride (CdCl2) and other toxic substances known to affect the testis. The Leydig cell toxicity was investigated in testicular perfusion system or cultures of isolated Leydig cells.

Effect of cadmium chloride on transepithelial electrical resistance of Sertoli cell monolayers in two-compartment cultures--a new model for toxicological investigations of the "blood-testis" barrier in vitro

The effect of various doses (0.75-24 microM) of cadmium chloride (CdCl2) on the development of intercellular tight junctions by immature rat Sertoli cells (Sc) was investigated in vitro using the two-compartment culture system. The status of tight junctions was monitored by repeated measurements of the transepithelial electrical resistance (TER). For defining the specificity of CdCl2 effects, the TER changes were correlated with Sc secretory activity (immunoactive inhibin), the cell number (DNA content), and viability (MTT test). The effects of CdCl2 depended on the concentration of the toxicant as well as on the onset and duration of exposure (4 and 18 hr on Day 1 or 5 of culture). The observed effects could be divided into four categories: (1) At highest doses employed, the TER values decreased significantly and irreversibly during 13 days of culture, and the decrease was accompanied by a significant and irreversible drop in inhibin secretion, cell viability, and cell number. (2) Within a narrow range of doses, the irreversible, or only partially reversible, decrease of TER was accompanied by a transient decrease, or no change, of the secretory activity and no significant changes in Sc cell number and/or viability. (3) With still lower doses, the TER values rapidly decreased and then returned to control level within 3-4 days. In this group, no changes in either inhibin secretion or cell viability were observed. (4) Exposure to the lowest doses of CdCl2 caused a delayed, but significant increase in TER. This increase was not accompanied by noticeable changes in other parameters evaluated. These data suggest that CdCl2 may selectively compromise, at least in vitro, the development and maintenance of the inter-Sc tight junctions, without affecting the secretory activity or the cell number and viability. However, increasing cumulative doses of CdCl2 (concentration multiplied by the time of exposure) led to decreased inhibition secretion and cell viability and then, finally, to irreversible cell damage and death. We believe that the experimental model and approach reported in this paper should be very useful for investigating the mechanism of action of known or potential testicular toxicants, particularly those suspected to compromise the integrity of the "blood-testis" barrier.