Assessment of male reproductive system in the CD-1 mice following oral manganese exposure

Exposure to manganese during sertoli cell formation and proliferation disturbs early testicular development in rats

Manganese (Mn) is a metal and important micronutrient. However, exposure to supraphysiological levels of Mn, which occur through fungicides, atmospheric emissions, drainages, and spills, has been related to health risks, including morphometric changes in the male reproductive organs and impairment on gametogenesis and sperm quality, impacting the fertile ability of adult animals. Despite the relevance of the fetal/perinatal period for toxicological studies on Mn, previous data only deal with the physical and neurological development of the offspring, without mentioning their reproductive development. The present study investigated whether exposure to Mn during fetal/perinatal phase, specifically during the period of formation and proliferation of Sertoli cells, impairs the reproductive development of male offspring in early postnatal life. Therefore, pregnant Wistar rats were randomly distributed into 3 experimental groups: Ctl (received saline solution), Mn-9 (received 9 mg/kg of MnCl2), and Mn-90 (received 90 mg/kg of MnCl2). The female rats received the experimental treatment by gavage from gestational day 13 to lactational day 15, i.e., postnatal day (PND) 15 of the pups. Oxidative damage to the genetic material of germ and Sertoli cells, together with a decrease in connexin 43 immunolabeling were observed in the testis of male pups evaluated at PND 15. In addition, an increase in the seminiferous tubules presenting slight epithelium vacuolization and cells with eosinophilic cytoplasm were observed, without apparent epididymal changes. In conclusion, it was demonstrated that Mn perturbed the initial testicular development by altering Sertoli cell integrity through oxidative insult, which may compromise the spermatogenesis in the long-term.

An Overview of Essential Microelements and Common Metallic Nanoparticles and Their Effects on Male Fertility

Numerous factors affect reproduction, including stress, diet, obesity, the use of stimulants, or exposure to toxins, along with heavy elements (lead, silver, cadmium, uranium, vanadium, mercury, arsenic). Metals, like other xenotoxins, can cause infertility through, e.g., impairment of endocrine function and gametogenesis or excess production of reactive oxygen species (ROS). The advancement of nanotechnology has created another hazard to human safety through exposure to metals in the form of nanomaterials (NMs). Nanoparticles (NPs) exhibit a specific ability to penetrate cell membranes and biological barriers in the human body. These ultra-fine particles (<100 nm) can enter the human body through the respiratory tract, food, skin, injection, or implantation. Once absorbed, NPs are transported to various organs through the blood or lymph. Absorbed NPs, thanks to ultrahigh reactivity compared to bulk materials in microscale size, disrupt the homeostasis of the body as a result of interaction with biological molecules such as DNA, lipids, and proteins; interfering with the functioning of cells, organs, and physiological systems; and leading to severe pathological dysfunctions. Over the past decades, much research has been performed on the reproductive effects of essential trace elements. The research hypothesis that disturbances in the metabolism of trace elements are one of the many causes of infertility has been unquestionably confirmed. This review examines the complex reproductive risks for men regarding the exposure to potentially harmless xenobiotics based on a series of 298 articles over the past 30 years. The research was conducted using PubMed, Web of Science, and Scopus databases searching for papers devoted to in vivo and in vitro studies related to the influence of essential elements (iron, selenium, manganese, cobalt, zinc, copper, and molybdenum) and widely used metallic NPs on male reproduction potential.

Effects of mine waste water on rat: bioaccumulation and histopathological evaluation

The highlighting of the bioaccumulation capacity of metals in the internal organs, the mode of distribution at the level of internal organs, the interactions between them, respectively, and the histological changes occurred at the level of the liver and kidneys are the main aspects addressed in the present study. The experiment was performed on 4 groups of Wistar rats: 3 groups which were administered water from rivers located in the vicinity of the Bor mining operation and 1 control group. The determination of the metal content in the administered water samples and in the internal organs was performed using the flame atomic absorption spectrophotometer. Tissue alterations were assessed by histological technique and hematoxylin-eosin staining. The metal retention capacity in the internal organs differs depending on the metal concentration in the administered water sample but also on the organ in which the determination was made. Also, correlations were established between the concentrations of metals at the level of the organs, showing (a) positive and significant correlations-at the level of the heart between Zn and Cu, Fe, and Mn and at the level of the lungs between Mn and Cd-but the most numerous were reported in the testicle; (b) moderate correlations at liver level between Fe and Zn, at spleen level between Cu and Mn and Cd and at the level of the kidneys between Pb and Zn, Cu, and Fe; (c) negative correlations at renal level between Pb and Mn; and (d) insignificant correlations between Pb and Fe. The histological changes identified at the level of the liver and kidney become more obvious, and their aggravation is registered with the increase of the metal content.

Response of male reproductive function to environmental heavy metal pollution in a free-living passerine bird, Passer montanus

Heavy metals affect male reproductive function by impairing reproductive organs, disturbing reproductive hormone levels or directly affecting sperm quality. However, little attention has been given to the effect of environmental heavy metals on reproductive function in wild male birds. The present study investigated the alterations of reproductive function in male tree sparrows (Passer montanus) exposed to environments contaminated by heavy metals in terms of testis parameters, reproductive hormone levels and sperm movement characteristics. Two plots, Baiyin (BY, mainly polluted by copper, zinc, lead and cadmium) and Liujiaxia (LJX, a relatively unpolluted area) were selected as sampling sites. The results showed that tree sparrows from BY (1) accumulated higher levels of cadmium in the testes, (2) showed lower superoxide dismutase (SOD) activity and malondialdehyde level, with higher total antioxidant capacity and apoptosis level in the testes, (3) showed higher plasma levels of estrogen, follicle stimulating hormone and luteinizing hormone (LH), and (4) had better sperm movement performance. Additionally, we found that testis size, SOD activity in testes and LH levels were decisive factors in sperm movement performance in tree sparrows. Heavy metal concentrations in testes negatively correlated with testis size, SOD activity in testes, and estrogen levels in tree sparrows. The present study indicates that heavy metals accumulating in testes of tree sparrows adversely affected some key indicators of male reproductive function. However, testicular function, reproductive hormone levels and sperm quality showed adaptive responses that tended to partially compensate for the negative effects in the heavy metal polluted area. This study further indicated that the regulation of testicular function and reproductive hormone levels was the main factor for better sperm quality in tree sparrows exposed to environments contaminated by heavy metals.

Manganese exposure caused reproductive toxicity of male mice involving activation of GnRH secretion in the hypothalamus by prostaglandin E2 receptors EP1 and EP2

Exposure to manganese (Mn) can cause male reproductive damage and lead to abnormal secretion of sex hormones. Gonadotropin-releasing hormone (GnRH) plays an important role in the neuromodulation of vertebrate reproduction. Astrocytes can indirectly regulate the secretion of GnRH by binding paracrine prostaglandin E₂ (PGE₂) specifically to the EP1 and EP2 receptors on GnRH neurons. Prior studies assessed the abnormal secretion of GnRH caused by Mn exposure, but the specific mechanism has not been reported in detail. This study investigated the effects of Mn exposure on the reproductive system of male mice to clarify the role of PGE₂ in the abnormal secretion of GnRH in the hypothalamus caused by exposure to Mn. Our data demonstrate that antagonizing the EP1 and EP2 receptors of PGE₂ can restore abnormal levels of GnRH caused by Mn exposure. Mn exposure causes reduced sperm count and sperm shape deformities. These findings suggest that EP1 and EP2, the receptors of PGE₂, may be the key to abnormal GnRH secretion caused by Mn exposure. Antagonizing the PGE₂ receptors may reduce reproductive damage caused by Mn exposure.

Dietary Manganese Exposure in the Adult Population in Germany-What Does it Mean in Relation to Health Risks?

Manganese is both an essential nutrient and a potential neurotoxicant. Therefore, the question arises whether the dietary manganese intake in the German population is on the low or high side. Results from a pilot total diet study in Germany presented here reveal that the average dietary manganese intake in the general population in Germany aged 14-80 years is about 2.8 mg day^-1 for a person of 70 kg body weight. This exposure level is within the intake range of 2-5 mg per person and day as recommended by the societies for nutrition in Germany, Austria, and Switzerland. No information on the dietary exposure of children in Germany can be provided so far. Although reliable information on health effects related to oral manganese exposure is limited, there is no indication from the literature that these dietary intake levels are associated with adverse health effects either by manganese deficiency or excess. However, there is limited evidence that manganese taken up as a highly bioavailable bolus, for example, uptake via drinking water or food supplements, could pose a potential risk to human health-particularly in certain subpopulations-when certain intake amounts, which are currently not well defined, are exceeded.

Relationship between cadmium content in semen and male infertility: a meta-analysis

Meta-analysis with high-quality studies can provide superior evidence. In this paper, we use meta-analysis to analyze the relationship between cadmium (Cd) content in semen and male infertility, and then objectively evaluate the effect of Cd on sperm quality. The objectives of this study were to update our understanding of infertility and to provide evidence to treat and prevent the infertility. We searched potentially relevant studies that were published from establishing database data to April 2018. Articles came from the databases of CNKI, Wanfang, VIP, PubMed, CMCI, and EMBASE. A total of 11 articles were included. We gathered the mean and variance of the infertility group and the control group to compare the Cd content in two groups. In total, the 11 studies include 1707 subjects, 1093 of which were in the infertility group and 614 of which were in the control group. We can get some information from this meta-analysis: SMD = 0.50 (95% Cl 0.39-0.61), Z = 8.92, P < 0.05; the funnel plot of the meta-analysis shows incomplete symmetry, which may have the publication bias. Therefore, the high content of Cd in semen is a causative factor of infertility. The Cd content in semen can be used as an indicator of sperm quality.

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.

Chronic Exposure to Water of Lake Qaroun Induced Metal-Related Testicular Damage and Endocrine Disruption in Male Fish

The uncontrolled releasing of hazardous wastes into Lake Qaroun was adversely impacting the aquatic environment and its biota. Therefore, this approach was designed to investigate the impact of these discharges on the reproductive and testicular function of Oreochromis niloticus. Several biomarkers were applied on the testicular tissues as metal bioaccumulation levels, histological examination with recording the ovotestis appearance and antioxidant status after 45 days of exposure to 0, 10, 20, & 30% of Lake Qaroun water (LQW). The bioaccumulated Cu, Mn, Fe, Pb, and Cd were unequally distributed in the testes but all these metals showed a significant concentration-dependent elevation among the studied groups. The exposure to LQW significantly increased the histological alterations in the testicular tissues as vacuolar degeneration, loss of tubular organization, and degeneration of Leydig cell. Based on the frequent appearance of histopathological abnormalities and ovotestis recording, the most deformed testicular tissues were observed in the 30% LQW-exposed groups. The ovotestis severity index (OSI) was significantly raised in LQW-exposed groups compared to the control group. The activities of superoxide dismutase, catalase as well as glutathione-reduced levels were significantly (p < 0.05) decreased in testes after chronic exposure to LQW. On the other pole, the activities of glutathione peroxidase enzyme and malondialdehyde formation were sharply increased. In view of the above, the exposure to LQW induced metal-related oxidative damage to the testicular tissues and impaired the male reproductive health. This study showed strong correlations between the anthropogenic activities around Lake Qaroun and the reproductive dysfunction in fish.

Could male reproductive system be the main target of subchronic exposure to manganese in adult animals?

Manganese (Mn) is one of the most common chemical elements on Earth and an essential micronutrient in animal organism. However, in supraphysiological levels and long-term exposures, it is a potential toxicant. Although nervous system is the most studied in relation to Mn toxicity, other tissues can have their function impaired by Mn in high doses. The present study investigated the possible adverse effects of subchronic exposure to supraphysiologic level of Mn (5 mg/kg or 15 mg/kg, intraperitoneally) on reproductive, neurobehavioral, renal and hepatic parameters of male rats. For the first time, the vulnerability of these parameters to Mn was concomitantly investigated. While our results demonstrate that Mn treatments were not sufficient to produce a marked effect of neurotoxic, hepatotoxic or renal toxicity in adult rats, we found typical indicators of reproductive toxicity such as histopathological changes (major in testes and epididymis) and impaired sperm concentration and quality. Mn, under these experimental conditions, seems to exert reproductive toxicity by different testicular mechanisms, i.e. direct and indirect action on germ cells. On the other hand, exposure to Mn did not change the pattern of cognitive and emotional behaviors and the histological organization of kidneys of experimental rats. The liver showed a weight increasement and hidropic degeneration, probable due to the detoxification overload. In summary, for the first time it was demonstrated that adult male reproductive system was more sensitive to Mn toxicity than nervous, hepatic and renal systems, although nervous system is known as the main target tissue of this metal.

Ebselen can Protect Male Reproductive Organs and Male Fertility from Manganese Toxicity: Structural and Bioanalytical Approach in a Rat Model

Ebselen (EBS) is a versatile compound that can protect the cellular components from oxidative and free radical-mediated damage. In the present study, we investigated the protective effect of EBS against manganese (Mn) toxicity on male reproductive organs. Thirty-two male rats were assigned into four groups, namely, negative control, EBS (15 mg/kg body weight (bw), as a single protective IP injection), MnCl₂ (50 mg/kg bw, orally for 30 consecutive days), and EBS + MnCl₂ (as mentioned before). The results showed that EBS ameliorated the alterations caused by MnCl₂ in the testicular, epididymal, and seminal vesicle tissues. MnCl₂ increased the sperm abnormalities, decreased gonadosomatic index (GSI), sperm motility, and sperm count. Further, it reduced the serum levels of testosterone (T) and luteinizing hormone (LH). The elevated levels of malondialdehyde (MDA), nitric oxide (NO), and 8-OH-2'-deoxyguanosine (8-OHdG) and decreased the levels of superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT) upon exposure to MnCl₂ indicated a disturbance in the activities of the testicular antioxidant enzymes and indices. Histologically, MnCl₂ decreased the diameter of seminiferous tubules (ST), the height of germinal epithelium, number of spermatogonia/ST, spermatocytes/ST, spermatids/ST, and Leydig cells/intertubular area (IA). Chemoprotection with EBS successfully mitigated most of the above-mentioned parameters concluding that EBS could be used as a useful prophylactic therapy whenever Mn toxicity is involved.

Quercetin Improves Neurobehavioral Performance Through Restoration of Brain Antioxidant Status and Acetylcholinesterase Activity in Manganese-Treated Rats

The present study investigated the neuroprotective mechanism of quercetin by assessing the biochemical and behavioral characteristics in rats sub-chronically treated with manganese alone at 15 mg/kg body weight or orally co-treated with quercetin at 10 and 20 mg/kg body weight for 45 consecutive days. Locomotor behavior was monitored using video-tracking software during a 10-min trial in a novel environment whereas the brain regions namely the hypothalamus, cerebrum and cerebellum of the rats were processed for biochemical analyses. Results indicated that co-treatment with quercetin significantly (p < 0.05) prevented manganese-induced locomotor and motor deficits specifically the decrease in total distance travelled, total body rotation, maximum speed, absolute turn angle as well as the increase in time of immobility and grooming. The improvement in the neurobehavioral performance of manganese-treated rats following quercetin co-treatment was confirmed by track and occupancy plot analyses. Moreover, quercetin assuaged manganese-induced decrease in antioxidant enzymes activities and the increase in acetylcholinesterase activity, hydrogen peroxide generation and lipid peroxidation levels in the hypothalamus, cerebrum and cerebellum of the rats. Taken together, quercetin mechanisms of ameliorating manganese-induced neurotoxicity is associated with restoration of acetylcholinesterase activity, augmentation of redox status and inhibition of lipid peroxidation in brain of rats.

Suppression of the brain-pituitary-testicular axis function following acute arsenic and manganese co-exposure and withdrawal in rats

Despite the fact that most environmental exposures to metals do not occur in isolation, the combined effects of metal mixtures on brain-pituitary-gonadal axis are poorly known. The present study investigated the impacts of co-exposure to arsenic (As) and manganese (Mn) on sperm characteristics, reproductive hormones and selected oxidative stress indices in the brain, testes and epididymis of rats following exposure for 15 consecutive days to 60mg/L of AsO₂Na and 30mg/L of MnCl₂ in drinking water. The results showed that while the brain weight remained unaffected, the fluid intake and the weights of testes and epididymis significantly (p<0.05) decreased in all the treatment groups. A significant decrease in the body weight gain when compared with control was noted only in the co-exposed rats. Moreover, the significant decreases in the antioxidant status in brain, testes and epididymis as well as in the circulatory concentrations of follicle-stimulating hormone, luteinizing hormone and testosterone were similar following separate or combined exposure of rats to As and Mn. The marked oxidative damage in the investigated tissues was accompanied by a significant decrease in the sperm quantity and quality in all the treated rats when compared with the control. Interestingly, most of the parameters determined immediately after the exposure period persisted in rats from the withdrawal experiment. Collectively, co-exposure to As and Mn suppressed the brain-pituitary-testicular axis function and the post-testicular events such as sperm function possibly via a mechanism involving persistent oxidative stress and endocrine disruption in the exposed rats.

Chemoprotective role of quercetin in manganese-induced toxicity along the brain-pituitary-testicular axis in rats

Reproductive dysfunction in response to manganese exposure has been reported in humans and animals. Quercetin, a bioflavonoid widely distributed in fruits, vegetables and beverages has been shown to possess antioxidant, anti-inflammatory and anti-apoptotic activities in different experimental model systems. However, there is dearth of scientific information on the influence of quercetin on manganese-induced reproductive toxicity. This study was designed to evaluate the influence of quercetin on manganese-induced functional alterations along the brain-pituitary- testicular axis in rats. Manganese was administered alone at 15 mg/kg body weight or orally co-treated with quercetin at 10 and 20 mg/kg body weight for 45 consecutive days. Results indicated that quercetin co-treatment significantly (p < 0.05) inhibited manganese-induced elevation in biomarkers of oxidative stress whereas it increased antioxidant enzymes activities and glutathione level in the brain, testes and epididymis of the treated rats. Furthermore, quercetin mediated suppression of inflammatory indices and caspase-3 activity was accompanied by preservation of histo-architectures of the brain, testes and epididymis in manganese-treated rats. The significant reversal of manganese-induced decreases in reproductive hormones (i.e. luteinizing hormone, follicle-stimulating hormone and testosterone) and testicular activities of acid phosphatase, alkaline phosphatase and lactate dehydrogenase by quercetin was complemented by an increase in sperm quality and quantity in the treated rats. Collectively, quercetin modulated manganese-induced toxicity along the brain-pituitary-testicular axis in rats via its intrinsic antioxidant, anti-inflammatory and anti-apoptotic activities, and may thus represent a potential pharmacological agent against manganese-induced male reproductive deficits in humans.

Evaluation of urinary metal concentrations and sperm DNA damage in infertile men from an infertility clinic

This study aimed to examine associations between urinary metal concentrations and sperm DNA damage. Thirteen metals [arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), molybdenum (Mo), mercury (Hg), nickel (Ni), selenium (Se), and zinc (Zn)] were detected in urine samples of 207 infertile men from an infertility clinic using inductively coupled plasma mass spectrometry, and also, sperm DNA damage (tail length, percent DNA tail, and tail distributed moment) were assessed using neutral comet assay. We found that urinary Hg and Ni were associated with increasing trends for tail length (both p for trend<0.05), and that urinary Mn was associated with increasing trend for tail distributed moment (p for trend=0.02). These associations did persist even when considering multiple metals. Our results suggest that environmental exposure to Hg, Mn, and Ni may be associated with increased sperm DNA damage.

Failure of manganese to protect from Shiga toxin

Shiga toxin (Stx), the main virulence factor of Shiga toxin producing Escherichia coli, is a major public health threat, causing hemorrhagic colitis and hemolytic uremic syndrome. Currently, there are no approved therapeutics for these infections; however manganese has been reported to provide protection from the Stx1 variant isolated from Shigella dysenteriae (Stx1-S) both in vitro and in vivo. We investigated the efficacy of manganese protection from Stx1-S and the more potent Stx2a isoform, using experimental systems well-established for studying Stx: in vitro responses of Vero monkey kidney cells, and in vivo toxicity to CD-1 outbred mice. Manganese treatment at the reported therapeutic concentration was toxic to Vero cells in culture and to CD-1 mice. At lower manganese concentrations that were better tolerated, we observed no protection from Stx1-S or Stx2a toxicity. The ability of manganese to prevent the effects of Stx may be particular to certain cell lines, mouse strains, or may only be manifested at high, potentially toxic manganese concentrations.

Manganese-induced effects on testicular trace element levels and crucial hormonal parameters of Hyline cocks

Manganese (Mn) is an essential element required for normal development and reproduction. However, little is known about the reproductive toxicity of Mn in birds. To investigate the Mn-induced toxicity on testicular trace element levels and crucial hormonal parameters on male reproduction in birds, 50-day-old male Hyline cocks were fed either a commercial diet or a Mn-supplemented diet. The changes in contents of copper (Cu), iron (Fe), zinc (Zn), and calcium (Ca) in testis were detected. Hormonal parameters were evaluated including the levels of testosterone (T), luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) in the serum. The mRNA levels of luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) were determined in this study. The results showed that Mn was accumulated in testis, and the content of Cu, Fe, Zn, and Ca decreased. Exposure to Mn significantly lowered the content of T, LH, FSH, and the mRNA expression levels of LHR and FSHR. Levels of T3 and T4 appeared with a decreased tendency, and TSH presented no obvious regularity. It indicated that Mn exposure resulted in the disbalance of testicular trace elements and influenced hormone levels in the molecular level, which may be possible underlying reproductive toxicity mechanism induced by Mn.

Seminal plasma metals concentration with respect to semen quality

The aim of the current study was to assess relationships between multiple metals burden in human seminal plasma and semen quality parameters. Levels of five metals (lead, manganese, copper, arsenic, and selenium) in human seminal plasma were determined by inductively coupled plasma mass spectrometry (ICP-MS), and the correlations between the metal concentrations and semen parameters (sperm concentration, sperm motility rate, and sperm morphology) were analyzed. The activities of acid phosphatase (ACP) and of α-glucosidase in human seminal plasma were also determined. Of the 100 subjects, 21 had fertility problems according to the World Health Organization criteria and were designated as "abnormal group." Significant inverse correlations were found between the concentrations of Cu, As, Pb, and the sperm concentrations (r (Cu) = -0.312, P (Cu) = 0.029; r (As) = -0.328, P (As) = 0.021; r (Pb) = -0.377, P (Pb) = 0.008). Moreover, the Cu, Mn, and Se concentrations were significantly higher in the abnormal group than that in the normal group (P (Cu) = 0.024, P (Mn) = 0.002, P (Se) = 0.002). The ACP activity was significantly higher in the normal group than that in the abnormal group (P = 0.021). We also found a significantly negative correlation between α-glucosidase activity and the levels of As (r = -0.367, P = 0.023). These findings provide evidence for relationships between human semen quality and metal exposures. These relationships are consistent with animal data, but additional human and mechanistic studies are needed.

Ambient Manganese Exposure is Negatively Associated With Human Sperm Motility and Concentration

BACKGROUND

Occupational and experimental animal studies indicate that exposure to high levels of manganese impairs male fertility, but the effects of ambient manganese in humans are not known.

METHODS

We measured blood levels of manganese and selenium in 200 infertility clinic clients in a cross-sectional study. Correlations between metals and semen variables were determined, adjusting for other risk factors. Outcomes were low motility (<50% motile), low concentration (<20 million/mL), or low morphology (<4% normal). We also investigated dose-response relationships between quartiles of manganese exposure and sperm parameters.

RESULTS

High manganese level was associated with increased risk of low sperm motility (odds ratio = 5.4; 95% confidence interval = 1.6-17.6) and low sperm concentration (2.4; 1.2-4.9). We saw a U-shaped dose-response pattern between quartiles of manganese exposure and all 3 sperm parameters.

CONCLUSION

Ambient exposure to manganese levels is associated with a reduction in sperm motility and concentration. No adverse effects were seen for high selenium.

Manganese acts centrally to activate reproductive hormone secretion and pubertal development in male rats

Manganese (Mn) is an important element for normal growth and reproduction. Because Mn accumulates in the hypothalamus and is capable of stimulating puberty-related hormones in female rats, we assessed whether this metal could cause similar effects in male rats. We have demonstrated that MnCl2, when administered acutely into the third ventricle of the brain, acts dose dependently to stimulate luteinizing hormone (LH) release. Furthermore, there was a dose dependent stimulation in the secretion of LH-releasing hormone (LHRH) from the medial basal hypothalamus in vitro, and administration of an LHRH receptor antagonist in vivo blocks Mn-induced LH release. To assess potential chronic effects of the metal, male pups were supplemented with 10 or 25 mg MnCl2 per kg by gastric gavage from day 15 until days 48 or 55, at which times developmental signs of spermatogenesis were assessed. Results demonstrate that while significant effects were not observed with the 10 mg/kg dose, the animals receiving the 25 mg/kg dose showed increased LH (p<0.05), FSH (p<0.01) and testosterone (p<0.01) levels at 55 days of age. Furthermore, there was a concomitant increase in both daily sperm production (p<0.05) and efficiency of spermatogenesis (p<0.05), demonstrating a Mn-induced acceleration in spermatogenesis. Our results suggest Mn is a stimulator of prepubertal LHRH/LH secretion and may facilitate the normal onset of male puberty. These data also suggest that the metal may contribute to male precocious pubertal development should an individual be exposed to low but elevated levels of Mn too early in life.