Association between environmental exposure to cadmium and human semen quality

NCOA4-mediated ferritinophagy participates in cadmium-triggered ferroptosis in spermatogonia

Cadmium (Cd) is a common pollutant with reproductive toxicity. Our previous study revealed that Cd triggered spermatogonia ferroptosis. However, the underlying mechanisms remain unclear. Nuclear receptor coactivator 4 (NCOA4) mediates ferritinophagy and specific degradation of ferritin through lysosomes, resulting in the release of ferrous ions. Excessive autophagy can lead to ferroptosis. This study investigated the role of autophagy in Cd-triggered ferroptosis using GC-1 spermatogonial (spg) cells which exposed to CdCl2 (5 μM, 10 μM, or 20 μM) for 24 without/with CQ. The cells which transfected with Ncoa4-siRNA were used to explore the role of NCOA4-mediated ferritinophagy in Cd-triggered ferroptosis. The results revealed that Cd caused mitochondrial swelling, rupture of cristae, and vacuolar-like changes. The Cd-treated cells exhibited more autophagosomes. Simultaneously, Cd increased intracellular iron, reactive oxygen species, and malondialdehyde concentrations while decreasing glutathione content and Superoxide Dismutase-2 activity. Moreover, Cd upregulated mRNA levels of ferritinophagy-associated genes (Ncoa4, Lc3b and Fth1), as well as enhanced protein expression of NCOA4, LC3B, and FTH1. While Cd decreased the mRNA and protein expression of p62/SQSTM1. These results showed that Cd caused ferritinophagy and ferroptosis. The use of chloroquine to inhibit autophagy ameliorated Cd-induced iron overload and ferroptosis. Moreover, Ncoa4 knockdown in spermatogonia significantly reduced intracellular iron concentration and alleviated Cd-triggered ferroptosis. In conclusion, our findings demonstrate that Cd activates the ferritinophagy pathway mediated by NCOA4, resulting in iron accumulation through ferritin degradation. This causes oxidative stress, ultimately initiating ferroptosis in spermatogonia. Our results may provide new perspectives and potential strategies for preventing and treating Cd-induced reproductive toxicity.

Melatonin counteracts cadmium-induced rat testicular toxicity via the mechanistic target rapamycin (mTOR) pathway

The protective action of melatonin (MLT) against the harmful effects of cadmium (Cd) on testicular activity in rats has been documented previously; however, the involved molecular mechanisms have yet to be elucidated. Herein, we investigate the involvement of the mammalian target of rapamycin (mTOR) on the ability of MLT to counteract the damage induced by Cd on the rat testicular activity. Our study confirmed that Cd has harmful effects on the testes of rats and the protective action exerted by MLT. We reported, for the first time, that the addition of rapamycin (Rapa), a specific mTOR inhibitor, to animals co-treated with Cd and MLT completely abolished the beneficial effects exerted by MLT, indicating that the mTOR pathway partially modulates its helpful effects on Cd testicular toxicity. Interestingly, Rapa-alone treatment, provoking mTOR inhibition, produced altered morphological parameters, increased autophagy of germ and somatic cells, and reduced serum testosterone concentration. In addition, mTOR inhibition also reduced protein levels of markers of steroidogenesis (3β-Hydroxysteroid dehydrogenase) and blood-testis barrier integrity (occludin and connexin 43). Finally, Rapa altered sperm parameters as well as the ability of mature spermatozoa to perform a proper acrosome reaction. Although further investigation is needed to better clarify the molecular pathway involved in MLT action, we confirm that MLT alleviating Cd effects can be used as a supplement to enhance testicular function and improve male gamete quality.

PBA alleviates cadmium-induced mouse spermatogonia apoptosis by suppressing endoplasmic reticulum stress

OBJECTIVE

Endoplasmic reticulum (ER) stress mediates Cd-caused germ cell apoptosis in testis. The effects of 4-phenylbutyric acid (PBA), a classical chaperone, were investigated on Cd-induced apoptosis in mouse GC-1 spermatogonia cells.

METHODS

The cells were pretreated with PBA before Cd exposure. TUNEL and flow cytometry assays were applied to determine apoptosis. Some key biomarkers of ER stress were analyzed using RT-PCR and western blot.

RESULTS

as expected, the apoptotic cells exposed to Cd apparently increased. The mRNA and protein expression levels of GRP78 and ATF6α, were elevated in the Cd groups. Additional experiments displayed that Cd notably increased IRE1α and JNK phosphorylation, and upregulated XBP-1 mRNA and protein expression. Moreover, p-eIF2α and CHOP expressions were clearly elevated in the Cd groups. Interestingly, PBA almost completely inhibited ER stress and protected spermatogonia against apoptosis induced by Cd.

CONCLUSION

PBA alleviated Cd-induced ER stress and spermatogonia apoptosis, and may have the therapeutic role in Cd-induced male reproductive toxicity.

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.

The impact of dietary fructose on gut permeability, microbiota, abdominal adiposity, insulin signaling and reproductive function

The excessive intake of fructose in the regular human diet could be related to global increases in metabolic disorders. Sugar-sweetened soft drinks, mostly consumed by children, adolescents, and young adults, are the main source of added fructose. Dietary high-fructose can increase intestinal permeability and circulatory endotoxin by changing the gut barrier function and microbial composition. Excess fructose transports to the liver and then triggers inflammation as well as de novo lipogenesis leading to hepatic steatosis. Fructose also induces fat deposition in adipose tissue by stimulating the expression of lipogenic genes, thus causing abdominal adiposity. Activation of the inflammatory pathway by fructose in target tissues is thought to contribute to the suppression of the insulin signaling pathway producing systemic insulin resistance. Moreover, there is some evidence that high intake of fructose negatively affects both male and female reproductive systems and may lead to infertility. This review addresses dietary high-fructose-induced deteriorations that are obvious, especially in gut permeability, microbiota, abdominal fat accumulation, insulin signaling, and reproductive function. The recognition of the detrimental effects of fructose and the development of relevant new public health policies are necessary in order to prevent diet-related metabolic disorders.

Evidence of the protective role of D-Aspartate in counteracting/preventing cadmium-induced oxidative stress in the rat testis

Cadmium (Cd), by producing oxidative stress and acting as an endocrine disruptor, is known to cause severe testicular injury, documented by histological and biomolecular alterations, such as decreased serum testosterone (T) level and impairment of spermatogenesis. This is the first report on the potential counteractive/preventive action of D-Aspartate (D-Asp), a well-known stimulator of T biosynthesis and spermatogenesis progression by affecting hypothalamic-pituitary-gonadal axis, in alleviating Cd effects in the rat testis. Our results confirmed that Cd affects testicular activity, as documented by the reduction of serum T concentration and of the protein levels of steroidogenesis (StAR, 3β-HSD, and 17β-HSD) and spermatogenesis (PCNA, p-H3, and SYCP3) markers. Moreover, higher protein levels of cytochrome C and caspase 3, together with the number of cells positive to TUNEL assay, indicated the intensification of the apoptotic process. D-Asp administered either simultaneously to Cd, or for 15 days before the Cd-treatment, reduced the oxidative stress induced by the metal, alleviating the consequent harmful effects. Interestingly, the preventive action of D-Asp was more effective than its counteractive effect. A possible explanation is that giving D-Asp for 15 days induces its significant uptake in the testes, reaching the concentrations necessary for optimum function. In summary, this report highlights, for the first time, the beneficial role played by D-Asp in both counteracting/preventing the adverse Cd effects in the rat testis, strongly encouraging further investigations to consider the potential value of D-Asp also in improving human testicular health and male fertility.

Genotoxicity in the absence of inflammation after tungsten inhalation in mice

Tungsten is used in several applications and human exposure may occur. To assess its pulmonary toxicity, we exposed male mice to nose-only inhalation of tungsten particles at 9, 23 or 132 mg/m³ (Low, Mid and High exposure) (45 min/day, 5 days/week for 2 weeks). Increased genotoxicity (assessed by comet assay) was seen in bronchoalveolar (BAL) fluid cells at Low and High exposure. We measured acellular ROS production, and cannot exclude that ROS contributed to the observed genotoxicity. We saw no effects on body weight gain, pulmonary inflammation, lactate dehydrogenase or protein in BAL fluid, pathology of liver or kidney, or on sperm counts. In conclusion, tungsten showed non-dose dependent genotoxicity in the absence of inflammation and therefore interpreted to be primary genotoxicity. Based on genotoxicity, a Lowest Observed Adverse Effect Concentration (LOAEC) could be set at 9 mg/m³. It was not possible to establish a No Adverse Effect Concentration (NOAEC).

Cadmium induced mouse spermatogonia apoptosis via mitochondrial calcium overload mediated by IP3R-MCU signal pathway

Cadmium (Cd) is a toxic metal and also a well-known reproductive toxicant. Cd could induce germ cells apoptosis in mouse testes, however, the mechanism remains unclear. This study designed in vitro using GC-1 spermatogonial (spg) cells to explore the cytotoxicity and the molecular mechanisms induced by cadmium chloride(CdCl₂). As expected, CdCl₂ elevated the levels of reactive oxygen species (ROS) and induced the release of AIF and Cyt-c from the mitochondria to the cytosol in spermatogonia. Correspondingly, CdCl₂ apparently increased the apoptotic rate in spermatogonia. Further researches found that CdCl₂ could activate IP₃R-MCU pathway, trigger Ca²⁺ transfer from endoplasmic reticulum to mitochondria, and cause mitochondrial Ca²⁺ overload. BAPTA acetoxymethyl ester (BAPTA-AM), a calcium chelator, almost completely attenuated IP₃R phosphorylation, inhibited the mRNA and protein expression levels of VDAC1, MCU and MCUR1 upregulated by CdCl₂, reduced the calcium ion content in the mitochondria. Moreover, BAPTA-AM could decrease the level of ROS, antagonize CdCl₂-induced release of AIF and Cyt-c from the mitochondria to the cytosol and alleviate CdCl₂-induced apoptosis in spermatogonia. As above, these results provided the evidence that CdCl₂ might induce apoptosis of spermatogonia via mitochondrial Ca²⁺ overload mediated by IP₃R-MCU signal pathway.

Potential protective effect of beta-caryophyllene against cadmium chloride-induced damage to the male reproductive system in mouse

Cadmium is a metal that can affect the male reproductive process, possibly leading to infertility. In contrast, beta-caryophyllene (BC) is a sesquiterpene that has shown antigenotoxic, anticancer, and antioxidant properties. Therefore, the aim of the present study was to determine the protective effect of BC against the deleterious effects of cadmium chloride (CC) on various mouse testicular and sperm parameters. We tested three doses of BC (20, 200, and 400 mg/kg) given before and during exposure to 3 mg/kg CC (six days after a single administration). Our results show significant alleviation of the damage induced by CC after the three doses of BC. Regarding the sperm concentration and morphology, the protection with the high dose was complete, and regarding sperm mobility and viability, the protection was more than 74%. In the comet assay, the highest dose showed a reduction of 92.5% in the damage induced by CC, and regarding the number of micronuclei in the spermatids, the reduction was 83.3%. In the oxidative evaluation, regarding sperm lipoperoxidation, the improvement was complete with the high dose, and in the ABTS^.+ test, the improvement in the response to the BC high dose was 26.3%. Regarding testicular lipoperoxidation and protein oxidation, the protective effects of the high BC dose were 87.6% and 89.9%, respectively. We also found that BC protected against the histological and morphometric alterations induced by CC. Therefore, our study clearly demonstrates the beneficial, chemopreventive effect of BC against the mouse sperm and testicular alterations induced by CC.

Mixture analysis of associations between exposure to low levels of multiple metals and semen quality and sperm DNA integrity

The objective of this study was to assess the association of exposure to metal mixtures with semen quality and sperm DNA integrity of coke oven workers (n = 96). Urinary six metals (cadmium, lead, arsenic, zinc, selenium, and copper) were quantified using inductively coupled-mass spectrometry. Semen quality parameters included sperm concentration, sperm concentration, sperm motility, sperm morphology, and sperm viability. Sperm DNA fragmentation and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) adducts served as biomarkers for assessing sperm DNA integrity. Bayesian kernel machine regression with the hierarchical variable selection process was used for analyzing both individual and joint effects of the metal mixture on the outcomes of semen samples, while adjusting for age, smoking, alcohol consumption, job length, and body mass index. The metal mixture was associated with reduced sperm concentration, motility, viability, and normal morphology. It was novel that a dose-response relationship was observed between exposure of the metal mixture and semen quality. Among the metals tested, cadmium had a reverse relationship with sperm motility, viability, and normal morphology, and a non-linear relationship with sperm viability and sperm motility. The metal mixture and individual metals were not associated with sperm DNA fragmentation and 8-oxodGuo. In conclusion, exposure to metal mixtures and cadmium may exert an association with semen quality and had no association with sperm DNA breakages.

Metal(loid)s and human semen quality: The LIFE Study

Multiple studies have demonstrated a global population-wide decline in semen quality, with sperm concentrations having fallen 50 % over the past 50 years. Several metal and metalloid ("metal(loid)") compounds are known to have testicular toxicity, raising concerns about their contribution to rising infertility. In the male reproductive tract, metal(loid)s can reduce semen quality and disturb function both directly, by inducing tissue damage, and indirectly, by disrupting hormone production and secretion. This study assessed associations between 15 creatinine-adjusted metal(loid)s and 7 measures of semen quality among 413 reproductive-aged men recruited from 16 U.S. counties between 2005-2009. Multi-metal(loid) multivariable linear regression models estimated associations between semen quality endpoints and urinary concentrations of chromium, cobalt, copper, molybdenum, selenium, zinc, antimony, arsenic, barium, cadmium, lead, thallium, tin, tungsten, and uranium. LASSO regression was employed to select model variables and account for multicollinearity of the metal(loid)s. A positive association was observed between tin and sperm morphology (β = 4.92 p = 0.045). Chromium (β = 1.87, p = 0.003) and copper (β= -1.30, p = 0.028) were positively and negatively associated with total sperm count, respectively. With respect to DNA fragmentation, cadmium (β = 12.73, p = 0.036) was positively associated and chromium was negatively associated (β = -5.08, p = 0.001). In this cohort of U.S. population-based men, there was evidence of both positive and negative associations between specific metal(loid)s and semen quality. Additional research is needed to determine interactions between metal(loid)s within a mixture, consistent with typical human exposure, and identify sperm effects resulting from cumulative metal(loid) exposures.

Mixture Analysis of Associations between Occupational Exposure to Polycyclic Aromatic Hydrocarbons and Sperm Oxidative DNA Damage

OBJECTIVE

This study aimed to determine (i) associations between levels of the polycyclic aromatic hydrocarbon (PAH) mixture with 16 targeted PAH compounds in the personal breathing zone area and sperm oxidative DNA damage, (ii) associations between levels of individual PAH compounds and sperm oxidative DNA damage, (iii) oxidative stress as the mode of action for the genotoxic effects on sperm, and (iv) any dose-response relationship between exposure to the PAH mixture and/or individual PAH compounds and sperm oxidative DNA damage.

METHODS

Sixteen targeted PAH compounds in the personal breathing zone area of 38 coke-oven workers and 24 control subjects were quantified using gas chromatography-mass spectrometry. Sperm oxidative damage and status were evaluated by measuring levels of sperm 7,8-dihydro-8-oxoguanie (8-oxodGuo), seminal malondialdehyde (MDA) and seminal reactive oxygen species (ROS). Bayesian kernel machine regression with hierarchical variable selection process was employed to determine associations of the PAH mixture and the biomarkers of sperm oxidative damage. A novel grouping approach needed for the hierarchical variable selection process was developed based on PAH bay region and molecular weight.

RESULTS

The PAH mixture exhibited a positive trend with increased sperm 8-oxodGuo levels at their lower percentiles (25th-50th). The exposure of the PAH mixture was associated with increased MDA levels in sperm. Bay and bay-like regions of the PAH mixture were the most important group for estimating the associations between the PAH mixture and sperm oxidative stress status. Benzo[a]anthracene was the main individual PAH compound that was associated with increased MDA levels.

CONCLUSION

Sperm oxidative DNA damage induced by occupational exposure to the PAH mixture had a suggestive association with increased MDA levels in coke-oven workers. Finally, the study identified that the individual PAH compound, benzo[a]anthracene, was the primary driver for the suggestive association between the PAH mixture and sperm oxidative damage.

Impact of Heavy Metals on Human Male Fertility-An Overview

Heavy metals are endocrine disruptors which interfere with processes mediated by endogenous hormones of the organism, negatively affecting endocrine functions. Some studies have correlated heavy metal exposure with male infertility. However, the number of studies conducted on humans are limited. Therefore, the aim of this study is to summarize the current knowledge on how heavy metals influence human male fertility. Hence, three distinct databases were consulted—PubMed, Scopus and Web of Science—using single keywords and combinations of them. The total number of identified articles was 636. Nevertheless, by using the inclusion and exclusion criteria, 144 articles were finally included in this work. Results display that the development of adequate instruments for heavy metal assessment may play an important function in human male fertility diagnosis and treatment. Furthermore, clinical trials could be useful to confirm the role of heavy metals in human male fertility diagnosis. Overall, further research is required to fully understand the molecular and cellular basis of the influence of environmental and occupational exposure to heavy metals on human male infertility and reproductive outcomes.

Burden of osteoporosis and costs associated with human biomonitored cadmium exposure in three European countries: France, Spain and Belgium

Cadmium (Cd) is a toxic heavy metal widespread in the environment leading to human exposure in particular through diet (when smoking is excluded), as documented by recent human biomonitoring (HBM) surveys. Exposure to Cd at environmental low-exposure levels has been associated with adverse effects such as renal toxicity and more recently bone effects. The implication, even if limited, of Cd in the etiology of osteoporosis can be of high importance at the population level given the significant prevalence of osteoporosis and the ubiquitous and life-long exposure to Cd. Therefore, the osteoporosis cases attributable to Cd exposure was estimated in three European countries (Belgium, France and Spain), based on measured urinary Cd levels from HBM studies conducted in these countries. The targeted population was women over 55 years old, for which risk levels associated with environmental Cd exposure were available. Around 23% of the cases were attributed to Cd exposure. Moreover, in a prospective simulation approach of lifelong urinary Cd concentrations assuming different intakes scenarios, future osteoporosis attributable cases were calculated, based on urinary Cd levels measured in women aged under 55. Between 6 and 34% of the considered populations under 55 years were at risk for osteoporosis. Finally, the costs associated to the burden of osteoporosis-related fractures attributable to Cd for each country targeted in this paper were assessed, standing for a major contributing role of Cd exposure in the overall social costs related to osteoporosis. Absolute costs ranged between 0.12 (low estimate in Belgium) and 2.6 billion Euros (high estimate in France) in women currently over 55 years old and at risk for fractures. Our results support the importance of reducing exposure of the general population to Cd.

Postnatal cadmium administration affects the presence and distribution of carbohydrates in the sperm membrane during maturation in the epididymis in adult Wistar rats

Cadmium (Cd) is a heavy metal related to a decrease in sperm parameters. The transit of spermatozoa through the epididymis is necessary to generate changes in the sperm membrane, such as the assembly of various carbohydrates that are added to the spermatazoan's surface to prepare it for successful fertilisation of the oocyte. No studies have yet analysed whether Cd alters the presence and distribution of these carbohydrates. We aimed to evaluate the changes induced by Cd in the distribution pattern of N-acetylglucosamine, sialic acid, mannose and fucose on the sperm membrane in the epididymis (e.g. caput, corpus, cauda) and if it alters the epididymal epithelium. Male Wistar pups were treated with Cd doses (0.125, 0.25 and 0.5mg/kg) on postnatal days 1-49. At postnatal day 90, they were humanely killed, sperm samples were obtained from the epididymis and tissue samples were taken for histological analysis. Cd concentrations in the blood and epididymis increased in proportion to the dose administered and decreased the serum testosterone levels and sperm quality. Histological analysis revealed alterations in the epithelium in all Cd-treated groups. Cd altered the distribution patterns of carbohydrates and fluorescence indices. All these alterations affected the structure and functioning of sperm.

Cadmium mediated redox modulation in germline stem cells homeostasis affects reproductive health of Drosophila males

Maintenance of male germline stem cells (GSCs) homeostasis is crucial for successful reproductive life of adults. New insights gained on dysfunction in stem cell maintenance could be the basis of stem cell dependent ailment during adulthood. Cadmium (Cd), a reported male reproductive toxicant, has been explored inadequately for its impact on male GSCs maintenance. The present study, therefore, has been aimed to evaluate the adverse effect of Cd on the homeostasis of GSCs by using Drosophila testis as an in vivo model. Following developmental exposure of environmentally relevant concentrations of Cd (5.0, 10.0 and 20.0 μg/mL) to Drosophila, we showed that a significantly increased level of reactive oxygen species (ROS) at 20.0 μg/mL of Cd resulted in alteration of GSCs number accompanied by inappropriate differentiation leading to reduced sperm number and eventually poor reproductive performance in exposed organism. Rescuing effect was evident by overexpressing sod in the early germ cell stage. The study suggests that an alteration in GSCs homeostasis due to redox imbalance plays a pivotal role in Cd induced failure in male fertility. The study further advocates for the use of Drosophila as an alternative animal model for in vivo evaluation of male GSCs toxicity with minimal ethical concern.

Urinary biomarker of strontium exposure is positively associated with semen quality among men from an infertility clinic

Experimental studies have shown that nonradioactive strontium (Sr), in the form of Sr²⁺, have a positive effect on semen quality, but human evidence is lacking. This study aimed to examine the associations between nonradioactive Sr exposure and semen quality in Chinese men (n = 394). We recruited men who presented at an infertility clinic in Wuhan, China to seek for semen parameter analyses. Urinary Sr concentration as an exposure biomarker was measured using inductively coupled plasma mass spectrometer. We estimated the associations between urinary Sr concentrations and semen parameters using multivariable logistic and linear regression models. In multivariable linear regressions models, positive dose-response associations were estimated for sperm concentration, motility, and count across increasing urinary Sr quartiles (all p for trends<0.05), and the consistent positive associations were also observed for urinary Sr concentration modeled as a continuous exposure. In multivariable logistic models, decreased risks of below-reference sperm concentration, motility, and count were also estimated across increasing urinary Sr quartiles (all p for trends<0.05). Our results suggest that nonradioactive Sr exposure may have a beneficial effect on semen quality, but more investigations are warranted to confirm the results.

Comprehensive Review of Cadmium Toxicity Mechanisms in Male Reproduction and Therapeutic Strategies

Cadmium (Cd) has been widely studied as an environmental pollutant for many years. Numerous studies have reported that Cd exposure causes damage to the heart, liver, kidneys, and thyroid in vivo. The emerging evidence suggests that Cd exposure induces damage on male reproductive system, which is related to oxidative stress, inflammation, steroidogenesis disruption, and epigenetics. Current preclinical animal studies have confirmed a large number of proteins and intracellular signaling pathways involved in the pathological process of Cd-induced male reproductive damage and potential measures for prophylaxis and treatment, which primarily include antioxidants, anti-inflammatory agents, and essential ion supplement. However, explicit pathogenesis and effective treatments remain uncertain. This review collects data from the literatures, discusses the underlying mechanisms of Cd-induced toxicity on male reproductive function, and summarizes evidence that may provide guidance for the treatment and prevention of Cd-induced male reproductive toxicity.

Signaling Proteins That Regulate Spermatogenesis Are the Emerging Target of Toxicant-Induced Male Reproductive Dysfunction

There is emerging evidence that environmental toxicants, in particular endocrine disrupting chemicals (EDCs) such as cadmium and perfluorooctanesulfonate (PFOS), induce Sertoli cell and testis injury, thereby perturbing spermatogenesis in humans, rodents and also widelife. Recent studies have shown that cadmium (e.g., cadmium chloride, CdCl₂) and PFOS exert their disruptive effects through putative signaling proteins and signaling cascade similar to other pharmaceuticals, such as the non-hormonal male contraceptive drug adjudin. More important, these signaling proteins were also shown to be involved in modulating testis function based on studies in rodents. Collectively, these findings suggest that toxicants are using similar mechanisms that used to support spermatogenesis under physiological conditions to perturb Sertoli and testis function. These observations are physiologically significant, since a manipulation on the expression of these signaling proteins can possibly be used to manage the toxicant-induced male reproductive dysfunction. In this review, we highlight some of these findings and critically evaluate the possibility of using this approach to manage toxicant-induced defects in spermatrogenesis based on recent studies in animal models.

Interaction effect of polycyclic aromatic hydrocarbon metabolites and cadmium on semen quality in nonsmokers

Both cadmium (Cd) and polycyclic aromatic hydrocarbons (PAHs) are known reproductive toxicants, but their co-exposure and interaction effect on semen quality particularly in nonsmokers remain unknown. We included 333 nonsmoking men and analyzed their urine and semen samples for heavy metals and PAH metabolites. Restricted cubic spline models were used to explore the dose-response relationship between each OH-PAHs, Cd, and semen quality parameters; the generalized linear model was performed to examine the interaction of each urinary OH-PAH metabolite and Cd concentration on semen quality. Also, stratified analysis was applied to further illustrate the independent effect of PAHs on semen quality parameters in low and high concentration Cd subgroups. The dose-response and interaction effect of PAHs and Cd on male semen quality was observed. Stratified analysis in the high concentration Cd subgroup showed a negative association of 1-OHPyr concentration with semen motility. Our findings indicate that Cd not only modifies the association between PAHs and semen quality but can also exacerbate the toxic effect of pyrene on semen quality parameters. However, further studies with larger samples are needed to confirm the findings.

Protective effect of quercetin on rat testes against cadmium toxicity by alleviating oxidative stress and autophagy

Cadmium (Cd), a highly toxic heavy metal, adversely affects human and animal health. Quercetin (Que) is a kind of flavonoid that can protect many tissues from the toxic effect of heavy metals. Although many studies have explored the adverse effects of cadmium on rats and other animals, the mechanism of Cd-induced testicular autophagy and the antagonistic effect of Que on cadmium remain unclear. In this study, Sprague-Dawley rats were treated with Cd, Que or Cd, and Que supplements to explore the mechanisms of Que-alleviated testis injury caused by Cd exposure. The rat body weight and relative testicular weight were measured. Morphological changes in testes and indices of oxidative stress were also examined. The expression levels of autophagy-related genes were detected as well. Results showed that Cd decreased the rat body weight and relative testicular weight and induced pathological changes in testes. Conversely, Que alleviated these changes. We also found that Cd increased the malondialdehyde content and decreased the contents of total superoxide dismutase, glutathione peroxidase, catalase, and glutathione. Moreover, the protein expression levels of P62 and LC3-II increased under Cd exposure conditions. Conversely, Que obviously alleviated these toxic activities induced by Cd. Overall, this study showed that Cd accumulated in rat testes, leading to oxidative stress and autophagy. Que can reduce cadmium toxicity by reducing oxidative stress and inhibiting autophagy. The specific mechanism of Que antagonizing Cd toxicity can provide new insights into countering cadmium toxicity.

Paternal cadmium exposure increases the susceptibility to diet-induced testicular injury and spermatogenic disorders in mouse offspring

The impairments of gestational cadmium (Cd) exposure on testicular development and male fertility in offspring have been reported. Here, we investigated the effect of paternal low-concentration cadmium exposure on testicular development and spermatogenesis in offspring. Five-week-old male mice were exposed to cadmium chloride (100 mg/L) in drinking water for 20 weeks. Results presented that Cd did not affect the testicular histology and sperm count in mice. After mating with untreated females, pregnant mice and pups were then evaluated. No significant difference in the rate for successful pregnancy and the body weight of pups was observed in Cd-exposed mice compared to the controls. Male offspring were given with a chow and high-fat diet from postnatal day (PND) 35 to PND70. Our data indicated that high-fat diet obviously decreased No. of sperm in epididymides of adult offspring due to paternal Cd exposure. Testicular histology revealed that the percentage of seminiferous tubules in stages IX-XII and the atypical residual bodies positive tubules in CdH (paternal cadmium exposure and pubertal high-fat diet) group were higher than these in CdC (paternal cadmium exposure and pubertal chow diet) group. Further analysis demonstrated that high-fat diet markedly accelerated testicular apoptosis, as determined by TUNEL assay and immunostaining for cleaved caspase-3, in male offspring due to paternal Cd exposure. Collectively, high-fat diet exacerbates the damage of testicular development and spermatogenesis in offspring due to paternal cadmium exposure.

Cadmium-induced toxicity increases prolyl endopeptidase (PREP) expression in the rat testis

During the differentiation of the male gamete, there is a massive remodeling in the shape and architecture of all the cells of the seminiferous epithelium. The cytoskeleton, as well as many associated proteins with it, plays a pivotal role in this process. The testis is particularly susceptible to environmental pollutant, which can lead to injury and impairment of normal spermatozoa production. Cadmium (Cd) is one of the major chemical environmental toxicants in economically developed countries. Food and cigarettes are the main sources of exposure to this element. Here, the protective role of zinc (Zn) to prevent the testicular toxicity in male adult rats after prenatal and during lactation exposure to Cd has been assessed. Altered testicular histology at the interstitial and germinal levels was found, whereas Zn supply completely corrected Cd toxicity. Moreover, the effects of these metals on the testicular expression and localization of the protease prolyl endopeptidase (PREP) were evaluated. Interestingly, the results showed an increase of PREP messenger RNA and protein. Data were corroborated by immunofluorescence. This study raises the possibility of using PREP as a new fertility marker.

Association of liver and kidney functions with Klotho gene methylation in a population environment exposed to cadmium in China

Exposure to the heavy metal cadmium has adverse effects on human health, including DNA methylation. This study aimed to investigate the effects of cadmium on liver and kidney functions and Klotho gene methylation and to explore the relationship of methylation level with indicators of liver and kidney functions. Graphite furnace atomic absorption spectrometry was conducted to determine urinary cadmium, and an automatic biochemical analyzer was used to detect indices of liver and kidney functions. PCR pyrosequencing was performed to detect the methylation rate of Klotho. One-way ANOVA was adopted to compare the differences between groups, and the linear correlation to variables was analyzed. Cadmium exposure was negatively correlated with albumin level (r=-0.143, p=0.021) and positively correlated with urinary β₂-microglobulin level (r=0.229, p<0.001). However, the methylation levels of Klotho gene was decreased and increased by low and high doses of cadmium exposure, respectively. And Klothomethylation levels were negatively correlated with albumin levels and positively correlated with β₂-microglobulin levels.In this study, cadmium exposure affects liver and kidney functions as well as Klotho methylation levels, but the effect on Klotho methylation levels is not linear. Klotho methylation levels also influence liver and kidney functions.

Effect of astaxanthin nanoparticles in protecting the post-thawing quality of rooster sperm challenged by cadmium administration

The protective role of astaxanthin nanoparticles (Ast NPs, 25 mg/kg p.o) against cadmium (Cd, 1 mg/100 g b.w. SC), a known inductor of lipid peroxidation and changes in the antioxidant defense system in the Ross 308 breeder roosters sperm, was examined. Sperm motility (computer-assisted sperm motility analysis), membrane integrity (hypoosmotic swelling test), viability, total abnormality, and enzymatic parameters were assessed after thawing. The testis/body weight (mg/kg) ratio and HE staining results of testis were also performed. The obtained results showed that Cd induced detrimental effects on testis and sperm, while Cd treated by Ast NPs (Cd Ast) diminished this change compared to the Cd group. Cd-treated group resulted in significantly (P < 0.05) lowest total (37.29 ± 2.46) and progressive (5.84 ± 0.47) motility and decreased antioxidant enzyme activity (CAT, TAC, and GPx), as well as producing a significant (P < 0.05) decrease in testis weight (mg) compared to the control group. Treatment with Ast NPs (Ast NPs + Cd) had reversed Cd-induced changes in the antioxidant defense system and significantly prevented Cd-induced testis damage. In conclusion, the results of our work suggest that Ast NPs at 25 mg/kg act as a potent antioxidant in protecting rooster testes against oxidative stress induced by Cd.

Cadmium toxicity: effects on human reproduction and fertility

Background Cadmium (Cd) is a non-essential toxic heavy metal, an environmental toxicant, and toxic at a low concentration, and it has no known beneficial role in the human body. Its exposure induces various health impairments including hostile reproductive health. Objective The present review discusses the information on exposure to Cd and human reproductive health impairments including pregnancy or its outcome with respect to environmental and occupational exposure. Methods The present review provides current information on the reproductive toxic potential of Cd in humans. The data were collected using various websites and consulting books, reports, etc. We have included recent data which were published from 2000 onward in this review. Results Cd exposure affects human male reproductive organs/system and deteriorates spermatogenesis, semen quality especially sperm motility and hormonal synthesis/release. Based on experimental and human studies, it also impairs female reproduction and reproductive hormonal balance and affects menstrual cycles. Based on the literature, it might be concluded that exposure to Cd at low doses has adverse effects on both human male and female reproduction and affects pregnancy or its outcome. Further, maternal prenatal Cd exposure might have a differential effect on male and female offspring especially affecting more female offspring. Hence, efforts must be made to prevent exposure to Cd. Conclusion Cd affects both male and female reproduction, impairs hormone synthesis/regulation and deteriorates pregnancy rate or its outcome even at lower doses.

PM2.5 exposure impairs sperm quality through testicular damage dependent on NALP3 inflammasome and miR-183/96/182 cluster targeting FOXO1 in mouse

Exposure to ambient fine particular matter (PM2.5) has been clearly associated with male reproductive disorders. However, very limited toxicological studies were carried out to investigate the potential mechanisms underlying the PM2.5-induced sperm quality decline. In the present study, we established a real time whole-body PM2.5 exposure mouse model to investigate the effects of PM2.5 on sperm quality and its potential mechanisms. Sixty male C57BL/6 mice were randomly subjected to three groups: filtered air group, unfiltered air group and concentrated air group. Half of the mice from each group were sacrificed for study when the exposure duration accumulated to 8 weeks and the rest of the mice were sacrificed when exposed for 16 weeks. Our results suggested that PM2.5 exposure could induce significant increases in circulating white blood cells and inflammation in lungs. PM2.5 exposure induced apparently DNA damages and histopathologic changes in testes. There were significantly decreased sperm densities of mice, which were paralleled with the down-regulated testosterone levels in testes tissue of mice after exposure to PM2.5 for 16 weeks. The numbers of motile sperms were decreased and sperms with abnormal morphology were increased after PM2.5 exposure in a time-depended and dose-depended manner. PM2.5 exposure significantly increased the expression of the major components of the NACHT, LRR and PYD domains-containing protein3 (NALP3) inflammasome, accompanied by the increased expression of miR-183/96/182 targeting FOXO1 in testes. The present data demonstrated that sperm quality decline induced by PM2.5 could be partly explained by the inflammatory reaction in testes which might be a consequence of systemic inflammation. The molecular mechanism was depended on the activation of NALP3 inflammasome accompanied by miR-183/96/182 targeting FOXO1 in testes.

Water and soil pollution as determinant of water and food quality/contamination and its impact on male fertility

Over the past two decades, public health has focused on the identification of environmental chemical factors that are able to adversely affect hormonal function, known as endocrine disruptors (EDs). EDs mimic naturally occurring hormones like estrogens and androgens which can in turn interfere with the endocrine system. As a consequence, EDs affect human reproduction as well as post and pre-natal development. In fact, infants can be affected already at prenatal level due to maternal exposure to EDs. In particular, great attention has been given to those chemicals, or their metabolites, that have estrogenic properties or antagonistic effects on the activity of androgen or even inhibiting their production. These compounds have therefore the potential of interfering with important physiological processes, such as masculinization, morphological development of the urogenital system and secondary sexual traits. Animal and in vitro studies have supported the conclusion that endocrine-disrupting chemicals affect the hormone-dependent pathways responsible for male gonadal development, either through direct interaction with hormone receptors or via epigenetic and cell-cycle regulatory modes of action. In human populations, epidemiological studies have reported an overall decline of male fertility and an increased incidence of diseases or congenital malformations of the male reproductive system. The majority of studies point towards an association between exposure to EDs and male and/or female reproductive system disorders, such as infertility, endometriosis, breast cancer, testicular cancer, poor sperm quality and/or function. Despite promising discoveries, a causal relationship between the reproductive disorders and exposure to specific toxicants has yet to be established, due to the complexity of the clinical protocols used, the degree of occupational or environmental exposure, the determination of the variables measured and the sample size of the subjects examined. Despite the lack of consistency in the results of so many studies investigating endocrine-disrupting properties of many different classes of chemicals, the overall conclusion points toward a positive association between exposure to EDs and reproductive system. Future studies should focus on a uniform systems to examine human populations with regard to the exposure to specific EDs and the direct effect on the reproductive system.

Metal/metalloid levels in urine and seminal plasma in relation to computer-aided sperm analysis motion parameters

BACKGROUND

Exposure to high levels of metals/metalloids may impair semen quality. Computer-aided sperm analysis (CASA) can be used for kinematic analysis of spermatozoa, which provides additional insights into sperm motion characteristics.

OBJECTIVE

To explore the associations of urinary and seminal plasma metal/metalloid concentrations with CASA motion parameters and assess the degree of correspondence between the two sample types.

METHODS

Eighteen metals/metalloids in seminal plasma and repeated urine samples were determined among 746 men recruited from a reproductive center. We assessed their associations with 6 CASA motion parameters [i.e., straight-line velocity (VSL), curvilinear velocity (VCL), average path velocity (VAP), linearity (LIN), straightness (STR) and amplitude head displacement (ALH)] using multivariable linear regression models.

RESULTS

We found significantly inverse dose-dependent relationships between seminal plasma arsenic (As) and VSL, VCL and VAP, between seminal plasma selenium (Se) and VSL and VAP, between seminal plasma zinc (Zn) and STR and LIN, and between seminal plasma manganese (Mn) and LIN in single-metal models [all false discovery rate (FDR) adjusted P for trend < 0.05]. These dose-response relationships remained statistically significant based on multiple-metal models and restricted cubic spline functions. Metal/metalloid concentrations in urine poorly predicted the same-day seminal plasma concentrations [coefficient of determination (R²) < 0.15]. We didn't find any significant associations between urinary metal/metalloid concentrations and the CASA motion parameters.

CONCLUSION

Exposure to high levels of As, Se, Mn and Zn may impair sperm motion capacity. Concentrations of metals/metalloids in spot urine samples cannot accurately predict same-day seminal plasma exposure levels.

Ascorbic acid inhibits cadmium-induced disruption of the blood-testis barrier by regulating oxidative stress-mediated p38 MAPK pathways

Ascorbic acid (AA), one of the best-known reactive oxygen species (ROS) scavengers, exhibits numerous functions such as antioxidant, anti-cancer, and anti-inflammatory effects. Increasing evidence demonstrates that oxidative stress plays an important role in testicular toxicity. In the present study, we investigated the protective effect of AA against cadmium (Cd)-induced blood-testis barrier (BTB) disruption. Sprague-Dawley (SD) rats were divided into four groups: the Cd-treated group received a single dose (s.c.) of 2 mg/kg BW cadmium chloride; the AA antagonism group received an injection of AA at a dose of 400 mg/kg BW (200 mg 24 h prior to Cd treatment and 200 mg 24 h following Cd treatment); and the control groups received an equal volume of saline or an equal dose of AA. As expected, ROS expression was upregulated in the Cd-treated rats, accompanied by an increase in malondialdehyde (MDA). Interestingly, AA suppressed Cd-induced oxidative stress by decreasing the levels of ROS and MDA and increasing the activity of superoxide dismutase (SOD) and catalase (CAT). In addition, AA also reduced BTB disruption by inhibiting TGF-β3 activation and p38 MAPK phosphorylation. Significant decreases in occludin and claudin-11 expression were observed in the Cd-treated rats, whereas AA administration attenuated this effect. Moreover, testicular histopathology and transmission electron microscopy further demonstrated the protective effects of AA against Cd-induced BTB damage. In conclusion, the results of the present study suggest that AA protects BTB destruction via the inhibition of oxidative stress and the TGF-β3/p38 MAPK signalling pathway in the testis of Cd-exposed rats.

Role of autophagy in cadmium-induced testicular injury

The testis is sensitive to cadmium, but studies investigating cadmium-induced testicular injury have not yet clearly revealed the underlying mechanisms. This study aimed to investigate the injurious effects of cadmium on rat testes and the role that autophagy plays in this process. Wistar rats were randomly divided into four groups and intraperitoneally injected with 0.2 (low), 0.4 (middle), and 0.8 mg/kg·body weight (high) cadmium chloride for 5 weeks, while the control rats were injected with equal volume of saline. Rats exposed to cadmium appeared inactive and had reduced body weights and increased testicular organ coefficients at the end of treatment compared with control rats. Atomic absorption results showed that cadmium levels increased with increased cadmium exposure. Hematoxylin and eosin staining of testicular sections showed seminiferous tubular atrophy, decreased pipe diameter, spermatogonial stem cells falling off the inner lining, and reduced germ cell layers of disorderly arrangements in cadmium-treated rats. Immunohistochemical and western blot results both showed that levels of the autophagy-related proteins Beclin1 and microtubule-associated protein 1 light chain 3B (LC3B) increased with increased cadmium exposure. We also found that LC3B-II and calcium-sensing receptor (CSR) levels in cadmium-exposed rats significantly increased. By immunofluorescence, we found that the percentage of cells that expressed the CSR was significantly higher in LC3B-positive than LC3B-negative cells. Together, our results showed that cadmium accumulates in the testes causing testicular injury, which may be related to increased autophagy levels. Furthermore, calcium disorders associated with the CSR may reveal a potential way to activate autophagy.