Relationship between seminal plasma zinc concentration and spermatozoa-zona pellucida binding and the ZP-induced acrosome reaction in subfertile men

Trace and essential elements as vital components to improve the performance of the male reproductive system: Implications in cell signaling pathways

Successful male fertilization requires the main processes such as normal spermatogenesis, sperm capacitation, hyperactivation, and acrosome reaction. The progress of these processes depends on some endogenous and exogenous factors. So, the optimal level of ions and essential and rare elements such as selenium, zinc, copper, iron, manganese, calcium, and so on in various types of cells of the reproductive system could affect conception and male fertility rates. The function of trace elements in the male reproductive system could be exerted through some cellular and molecular processes, such as the management of active oxygen species, involvement in the action of membrane channels, regulation of enzyme activity, regulation of gene expression and hormone levels, and modulation of signaling cascades. In this review, we aim to summarize the available evidence on the role of trace elements in improving male reproductive performance. Also, special attention is paid to the cellular aspects and the involved molecular signaling cascades.

Progress on the roles of zinc in sperm cryopreservation

One of the effective methods for the long-term preservation of mammalian genetic resources is the cryopreservation of semen. However, a number of parameters, including diluents, the rate of freezing and thawing, cryoprotectants, etc., can easily alter the survival of frozen-thawed sperm. Numerous studies have documented the addition of a variety of zinc compounds, to the diluents used to cryopreserve sperm. The primary objective of this review is to briefly describe that adding zinc to diluents as an antioxidant significantly enhances frozen-thawed sperm quality. Second, a summary of the present understanding of zinc's molecular mechanism on semen cryopreservation is provided. Thirdly, this study addresses that nanoparticles of zinc can offer suggestions for raising cryopreservation effectiveness.

Oxidative Stress and Male Infertility: The Protective Role of Antioxidants

Oxidative stress is a significant factor in male infertility, compromising sperm function and overall reproductive health. As male infertility garners increasing attention, effective therapeutic interventions become paramount. This review investigates the therapeutic role of antioxidants in addressing male infertility. A detailed examination was conducted on antioxidants such as vitamin C, E, B12, D, coenzyme Q10, zinc, folic acid, selenium, l-carnitine, l-arginine, inositols, and alpha-lipoic acid. This analysis examines the methodologies, outcomes, and constraints of current clinical studies. Antioxidants show notable potential in counteracting the negative effects of oxidative stress on sperm. Based on the evidence, these antioxidants, individually or synergistically, can enhance sperm health and reproductive outcomes. However, certain limitations in the studies call for careful interpretation. Antioxidants are integral in tackling male infertility attributed to oxidative stress. The current findings underscore their therapeutic value, yet there's a pressing need for deeper, comprehensive research. Future studies should focus on refining dosage guidelines, identifying potential side effects, and discerning the most efficacious antioxidant combinations for male infertility solutions.

Blood metal/metalloid concentration of male subjects undergoing IVF/ICSI treatment outcomes: A prospective cohort study

BACKGROUND

Previous epidemiology studies reported that heavy metal/metalloid exposure is associated with the impairment of semen quality. However, it is still not clear whether the in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) treatment outcome will be affected after the heavy metal/metalloid exposure of the male partners.

METHODS

A prospective cohort study with a 2-year followed-up was conducted in a tertiary IVF center. A total of 111 couples undergoing IVF/ICSI treatment were initially recruited from November 2015 to November 2016. Male blood concentrations of heavy metal/metalloid including Ca, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Mo, Cd, Hg, and Pb were measured by inductively coupled plasma mass spectrometry, and the lab and pregnancy outcome data were followed up. The associations between male blood heavy metal/metalloid concentration and the clinical outcomes were analyzed by Poisson regression analysis.

RESULTS

Our results showed that none of the heavy metal/metalloid of male partners we investigated are significantly associated with the oocyte fertilization and good embryo (P ≥ 0.05); however, antral follicle count (AFC) was a protective factor for the oocyte fertilization (RR: 1.07, 95 % CI: 1.04-1.10). The blood Fe concentration of the male partner was positively associated (P < 0.05) with pregnancy in the first fresh cycle (RR:170.93, 95 % CI: 4.13-7082.04), cumulative pregnancy (RR: 23.61, 95 % CI: 3.25-171.64) and cumulative live birth (RR: 36.42, 95 % CI: 1.21-1092.54). In the first frozen embryo cycles, pregnancy was significantly associated (P < 0.05) with the blood Mn (RR: 0.01, 95 % CI:0.00-0.11) and Se concentration (RR: 0.01, 95 % CI:8.25 E-5-0.47) and female age (RR: 0.86, 95 % CI:0.75-0.99); live birth was significantly associated (P < 0.05) with the blood Mn concentration (RR: 0.00, 95 % CI: 1.14E-7-0.51).

CONCLUSIONS

Our results suggested that the higher male blood Fe concentration was positively associated with pregnancy in the fresh embryo transfer cycle, cumulative pregnancy, and cumulative live birth, whereas the higher male blood Mn and Se concentration were associated with lower chance of pregnancy and live birth in the frozen embryo transfer cycle. However, the underline mechanism of this finding still needs further investigation.

Comprehensive review on the positive and negative effects of various important regulators on male spermatogenesis and fertility

With the increasing global incidence of infertility, the influence of environmental factors, lifestyle habits, and nutrients on reproductive health has gradually attracted the attention of researchers. The quantity and quality of sperm play vital roles in male fertility, and both characteristics can be affected by external and internal factors. In this review, the potential role of genetic, environmental, and endocrine factors; nutrients and trace elements in male reproductive health, spermatozoa function, and fertility potency and the underlying mechanisms are considered to provide a theoretical basis for clinical treatment of infertility.

Expression Analysis of ZPB2a and Its Regulatory Role in Sperm-Binding in Viviparous Teleost Black Rockfish

Black rockfish is a viviparous teleost whose sperm could be stored in the female ovary for five months. We previously proposed that zona pellucida (ZP) proteins of black rockfish play a similar sperm-binding role as in mammals. In this study, SsZPB2a and SsZPB2c were identified as the most similar genes with human ZPA, ZPB1 and ZPB2 by Blastp method. Immunohistochemistry showed that ovary-specific SsZPB2a was initially expressed in the cytoplasm of oocytes at stage III. Then it gradually transferred to the region close to the cell membrane and zona pellucida of oocytes at stage IV. The most obvious protein signal was observed at the zona pellucida region of oocytes at stage V. Furthermore, we found that the recombinant prokaryotic proteins rSsZPB2a and rSsZPB2c could bind with the posterior end of sperm head and rSsZPB2a was able to facilitate the sperm survival in vitro. After knocking down Sszpb2a in ovarian tissues cultivated in vitro, the expressions of sperm-specific genes were down-regulated (p < 0.05). These results illustrated the regulatory role of ZP protein to the sperm in viviparous teleost for the first time, which could advance our understanding about the biological function of ZP proteins in the teleost.

Marginal Zinc Deficiency in Mice Increased the Number of Abnormal Sperm and Altered the Expression Level of Spermatogenesis-Related Genes

Marginal zinc deficiency is more common than severe zinc deficiency, and the effect of marginal zinc deficiency on male reproduction is unknown. This study investigated the effect of marginal zinc deficiency on spermatogenesis and its mechanism. Male ICR mice were fed normal zinc (30 mg/kg) and marginal zinc deficiency (10 mg/kg) diets for 35 days. Zinc-dependent proteins and enzymes were measured as biomarkers of zinc levels in the body. Metallothionein and Cu-Zn SOD levels in the control group were higher than those in the marginal zinc deficiency group. Hematoxylin and eosin staining showed that the marginal zinc deficiency diet caused histopathological changes in the testis and destruction of the sperm head under scanning electron microscopy. Sperm parameters and sex hormone levels were also affected by marginal zinc deficiency. In addition, marginal zinc deficiency led to alter expression level of several important spermatogenesis-related genes in the epididymis and testes. These results indicate that although zinc intake in marginal zinc deficiency is close to the recommended reference value, low zinc intake interferes with the expression of genes related to spermatogenesis and may lead to sperm abnormalities in mice.

Electrophysiology of Human Gametes: A Systematic Review

PURPOSE

Oocytes and spermatozoa are electrogenic cells with the ability to respond to electrical stimuli and modulate their electrical properties accordingly. Determination of the ionic events during the gamete maturation helps to design suitable culture media for gametes in assisted reproductive technology (ART). The present systematic review focuses on the electrophysiology of human gametes during different stages of maturation and also during fertilization.

MATERIALS AND METHODS

The reports published in the English language between January 2000 and July 2021 were extracted from various electronic scientific databases following the PRISMA checklist using specific MeSH keywords.

RESULTS

Subsequent to the screening process with defined inclusion and exclusion criteria, 60 articles have been included in this review. Among them, 11 articles were directly related to the electrophysiology of human oocytes and 49 physiology department to the electrophysiology of human spermatozoa.

CONCLUSIONS

Gametes generate electrical currents by ionic exchange, particularly Na+, K+, Cl-, H+, Zn2+, Cu2+, Se2+, Mg2+, HCO3-, and Ca2+ through specific ion channels in different stages of gamete maturation. The ionic concentrations, pH, and other physicochemical variables are modulated during the gametogenesis, maturation, activation, and the fertilization process following gamete function and metabolism. The electrical properties of human gametes change during different stages of maturation. Although it is demonstrated that the electrical properties are significant regulators of cell signaling and are fundamental to gamete maturation and fertilization, their exact roles in these processes are still poorly understood. Further research is required to unveil the intricate electrophysiological processes of human gamete maturation.

Low testicular zinc level, p53 expression and impairment of Sertoli cell phagocytosis of residual bodies in rat subjected to psychological stress

Psychological stress is a known aetiology of infertility. However, the mechanisms translating it to reproductive dysfunction are not fully elucidated. Three experiments were performed on Wistar rats were designed to evaluate Sertoli cell function under stress. In Experiment I, rats were randomised into three groups: saline baseline group given saline, ASEMA baseline group given aqueous extract of Massularia acuminata, zinc baseline group administered zinc orally. In Experiment II, exposure to psychological stress (for 1 hour per day) was layered on Experiment I while Experiment III substituted stress with administration of dexamethasone (DX). Six rats were sacrificed per group per experiment on days 7 and 14 and the right testis was excised and processed for PAS-haematoxylin staining and the left used for Zn determination. Results show significantly lower testicular Zn level as well more intensely immunoexpression of p53 in saline stress and saline DX groups compared with other groups. Also seen are the presence of residual bodies in the seminiferous tubular lumen of saline groups in Experiments II and III suggesting failure of residual bodies to be transported back towards the basement membrane. This study demonstrates that psychological stress impairs the ability of Sertoli cells to recycle residual bodies.

The Role of Zinc in Male Fertility

Several studies proposed the importance of zinc ion in male fertility. Here, we describe the properties, roles and cellular mechanisms of action of Zn²⁺ in spermatozoa, focusing on its involvement in sperm motility, capacitation and acrosomal exocytosis, three functions that are crucial for successful fertilization. The impact of zinc supplementation on assisted fertilization techniques is also described. The impact of zinc on sperm motility has been investigated in many vertebrate and invertebrate species. It has been reported that Zn²⁺ in human seminal plasma decreases sperm motility and that Zn²⁺ removal enhances motility. Reduction in the intracellular concentration of Zn²⁺ during epididymal transit allows the development of progressive motility and the subsequent hyper activated motility during sperm capacitation. Extracellular Zn²⁺ affects intracellular signaling pathways through its interaction with the Zn²⁺ sensing receptor (ZnR), also named GPR39. This receptor was found in the sperm tail and the acrosome, suggesting the possible involvement of Zn²⁺ in sperm motility and acrosomal exocytosis. Our studies showed that Zn²⁺ stimulates bovine sperm acrosomal exocytosis, as well as human sperm hyper-activated motility, were both mediated by GPR39. Zn²⁺ binds and activates GPR39, which activates the trans-membrane-adenylyl-cyclase (tmAC) to catalyze cAMP production. The NHE (Na⁺/H⁺-exchanger) is activated by cAMP, leading in increased pHi and activation of the sperm-specific Ca²⁺ channel CatSper, resulting in an increase in [Ca²⁺]_i, which, together with HCO₃⁻, activates the soluble adenylyl-cyclase (sAC). The increase in [cAMP]_i activates protein kinase A (PKA), followed by activation of the Src-epidermal growth factor receptor-Pphospholipase C (Src-EGFR-PLC) cascade, resulting in inositol-triphosphate (IP₃) production, which mobilizes Ca²⁺ from the acrosome, causing a further increase in [Ca²⁺]_i and the development of hyper-activated motility. PKA also activates phospholipase D1 (PLD1), leading to F-actin formation during capacitation. Prior to the acrosomal exocytosis, PLC induces phosphadidylinositol-4,5-bisphosphate (PIP₂) hydrolysis, leading to the release of the actin-severing protein gelsolin to the cytosol, which is activated by Ca²⁺, resulting in F-actin breakdown and the occurrence of acrosomal exocytosis.

Zinc supplementation within the reference ranges for zinc status in cattle improves sperm quality without modifying in vitro fertilization performance

Zinc (Zn) has important functions in mammalian reproductive processes. In cattle, Zn status can be classified as deficient, marginal, and adequate, depending on the plasma Zn concentration. In addition, Zn deficiency can lead to reproductive failure. The aim of this study was to investigate the effect of maternal Zn status at the beginning of a fixed-time artificial insemination (FTAI) treatment regimen on pregnancy rate in cattle, and evaluate the effect of supplementing in vitro fertilization (IVF) medium with Zn concentrations within the reference range for Zn status on sperm quality and IVF performance. Pregnancy rates of animals with marginal and adequate Zn status did not differ, and there were no Zn-deficient animals detected. Supplementation of 0.8 μg/mL Zn to IVF medium enhanced progressive motility, sperm viability, functional sperm membrane integrity (HOST), acrosomal integrity and sperm-zona binding, without modifying pronuclear formation, or development of embryos to the cleavage or blastocyst stage after IVF. In conclusion, the present results indicate pregnancy rates are not associated with maternal Zn status at the beginning of the FTAI treatment regimen if Zn status is marginal or adequate. Furthermore, supplementation of IVF medium with Zn at concentrations which is considered adequate for Zn status in cattle led to improved sperm quality, without having effects on embryo development in cattle.

Sperm Cohort-Specific Zinc Signature Acquisition and Capacitation-Induced Zinc Flux Regulate Sperm-Oviduct and Sperm-Zona Pellucida Interactions

Building on our recent discovery of the zinc signature phenomenon present in boar, bull, and human spermatozoa, we have further characterized the role of zinc ions in the spermatozoa’s pathway to fertilization. In boar, the zinc signature differed between the three major boar ejaculate fractions, the initial pre-rich, the sperm-rich, and the post-sperm-rich fraction. These differences set in the sperm ejaculatory sequence establish two major sperm cohorts with marked differences in their sperm capacitation progress. On the subcellular level, we show that the capacitation-induced Zn-ion efflux allows for sperm release from oviductal glycans as analyzed with the oviductal epithelium mimicking glycan binding assay. Sperm zinc efflux also activates zinc-containing enzymes and proteases involved in sperm penetration of the zona pellucida, such as the inner acrosomal membrane matrix metalloproteinase 2 (MMP2). Both MMP2 and the 26S proteasome showed severely reduced activity in the presence of zinc ions, through studies using by gel zymography and the fluorogenic substrates, respectively. In the context of the fertilization-induced oocyte zinc spark and the ensuing oocyte-issued polyspermy-blocking zinc shield, the inhibitory effect of zinc on sperm-borne enzymes may contribute to the fast block of polyspermy. Altogether, our findings establish a new paradigm on the role of zinc ions in sperm function and pave the way for the optimization of animal semen analysis, artificial insemination (AI), and human male-factor infertility diagnostics.

The importance of trace minerals copper, manganese, selenium and zinc in bovine sperm-zona pellucida binding

SummarySperm-zona pellucida (ZP) binding is a necessary event for successful fertilization. The aim of this study was to determine the effect of trace minerals such as copper (Cu), manganese (Mn), selenium (Se) and zinc (Zn) on bovine spermatozoa binding to ZP. Sperm viability, functional membrane integrity, acrosomal status (AS), total antioxidant capacity (TAC) and sperm lipid peroxidation (LPO) were also evaluated. For the present study, in vitro fertilization (IVF) medium was supplemented with Cu (0.4 µg/ml Cu), Mn (5 ng/ml Mn), Se (100 ng/ml Se), Zn (0.8 µg/ml Zn), all minerals (Cu+Mn+Se+Zn), or tested without supplement (Control). Considerably more sperm bound to ZP when Cu, Se or Zn were added to the IVF medium, but there were no difference compared with the Control, Mn and Cu+Mn+Se+Zn groups. After 1 h of incubation, viability was increased by the addition of Cu, Mn and Se with respect to the Control but, after 2 h, viability was higher only with the addition of Mn to IVF medium. Functional membrane integrity improved in sperm treated with Cu. Acrosome integrity was higher in sperm treated with Zn after 1 h of incubation. LPO was significantly higher in sperm treated with Cu or Cu+Mn+Se+Zn. The mean TACs of sperm treated with Cu, Mn, Zn or Cu+Mn+Se+Zn were lower than in the Control. In conclusion, the results obtained in the present study determined that the presence of Cu, Se and Zn in the IVF medium increased the number of spermatozoa bound to the ZP, highlighting the importance of these minerals in the fertilization process.

Effects of zinc deficiency on impaired spermatogenesis and male infertility: the role of oxidative stress, inflammation and apoptosis

Zinc (Zn) is necessary for the normal function of the male reproductive system and spermatozoa. Although influences of zinc deficiency on impaired spermatogenesis and male infertility have been widely considered, the molecular and cellular mechanisms of these abnormalities are not well understood. General abnormalities, including hypogonadism, Leydig cells damage, deficiency of sex hormone production and impaired spermatogenesis, as well as inflammation, antioxidant depletion, sperm death and male infertility can be observed during zinc deficiency. However, it is not obvious which pathways are relevant to the pathogenesis of zinc deficiency. Oxidative stress (OS) induced by reactive oxygen species is likely as the main mechanism of zinc deficiency which is associated with sperm DNA fragmentation, decrease in sperm membrane integrity, apoptosis, depletion of antioxidants, and consequently poor sperm quality and male infertility. Therefore, identification of these pathways will give valuable information regarding the mechanisms of zinc deficiency on the male reproductive system and the potential way for developing a better clinical approach. In this review, we aim to discuss the proposed cellular and molecular mechanisms of zinc deficiency on the male reproductive system, the importance of OS and mechanisms by which zinc deficiency induces OS and depletion of other antioxidants.

Impact of cigarette-smoking on sperm DNA methylation and its effect on sperm parameters

DNA methylation is an epigenetic modification of the genome. The purpose of this study was to determine the influence of cigarette-smoking on sperm DNA methylation from a genomewide survey of sperm samples and to ascertain its effect on sperm parameters. Twenty-eight sperm DNA samples (from 14 fertile smokers as a case study and 14 proven fertile nonsmokers as controls) were subjected to Infinium 450K BeadChip arrays to identify the changes in the DNA methylation level between the two groups. Then, deep bisulphite sequencing was used to validate five CpGs on 78 samples. The results from the Infinium 450K found that only 11 CpGs showed a significant difference in DNA methylation between the case and the control groups. Five CpGs of the eleven (cg00648582, cg0932376, cg19169023, cg23841288 and cg27391564) underwent deep bisulphite sequencing where cg00648582, related to the PGAM5 gene, and the cg23841288 CpGs, related to the PTPRN2 gene amplicons, showed a significant increase in their DNA methylation level in more than one CpG in the case group. In contrast, a significant decrease was found at cg19169023 and at its various neighbouring CpGs in the TYRO3 gene-related amplicons. Furthermore, this study demonstrated a significant correlation between the variation in sperm DNA methylation level and standard sperm parameters in the case group.

Zinc is an Essential Element for Male Fertility: A Review of Zn Roles in Men's Health, Germination, Sperm Quality, and Fertilization

Zinc (Zn) is the second most abundant trace element in human, which can't be stored in the body, thus regular dietary intake is required. This review explained the physiological and pathogenesis roles of zinc in men's health and its potentials in germination, quality of sperm, and fertilization. Our investigation showed that Zn contained many unique properties in human, especially males. The antioxidant quality is one of them. Also, the increased reactive oxygen species levels in the seminal plasma of men who are both infertile and smokers influence the Zn content of seminal plasma in a way that physiology of spermatozoa can be affected as well. Moreover, Zn acts as a toxic repercussionagainst heavy metals and cigarette inflammatory agents. Zinc as a hormone balancer helps hormones such as testosterone, prostate and sexual healthand functions as an antibacterial agent in men's urea system. It plays a role in epithelial integrity, showing that Zn is essential for maintaining the lining of the reproductive organs and may have a regulative role in the progress of capacitation and acrosome reaction. In contrast, Zn deficiency impedes spermatogenesis and is a reason for sperm abnormalities and has a negative effect on serum testosterone concentration. Based on these findings, Zn microelement is very essential for male fertility. It could be considered as a nutrient marker with many potentials in prevention, diagnosis, and treatment of male infertility.

Effect of metformin therapy and dietary supplements on semen parameters in hyperinsulinaemic males

Previous reports indicated that hyperinsulinaemic men may exhibit a higher percentage of poorly compacted DNA in their spermatozoa and less success in an IVF programme (Andrologia, 45, 2003, 18; Andrologia, 2014, doi: 10.1111/and.12227). The aim of this study was to investigate the effect of metformin (Glucophage®) and antioxidant treatment (StaminoGro®) on the semen parameters of hyperinsulinaemic men. Nineteen hyperinsulinaemic male patients were treated for 3 months with metformin alone (Group A), and fifteen patients used metformin in combination with the nutritional supplement (Group B). Combined data of the two groups (pre- and post-treatment) differ significantly regarding sperm morphology (P = 0.0003) and CMA3 (P < 0.0001) values. The improvement in sperm morphology after treatment was similar for the two respective groups (P < 0.05). The morphological normal sperm forms increased from the mean percentage of 3.9 to 5.5% and from 4.2 to 5.5% for Group A and B respectively. Where a combination of metformin and the supplement were used (Group B), the combination treatment proved to be superior in obtaining enhanced chromatin packaging quality although not statistically significant (P = 0.5929) when compared with the metformin (Group A) group. The chromatin packaging quality in Group B improved with 10% while the improvement in Group A was approximately 8.3%. Therefore, infertile hyperinsulinaemic men can benefit from metformin treatment and should be advised on the use of nutritional supplements with antioxidant properties.

Addition of zinc to human ejaculate prior to cryopreservation prevents freeze-thaw-induced DNA damage and preserves sperm function

PURPOSE

To study the effect of addition of zinc to human semen sample prior to cryopreservation on post-thaw sperm quality and function.

METHODS

Semen samples were collected from men attending university infertility clinic for semen analysis (n=109). Liquefied semen samples were cryopreserved in glycerol-egg yolk- citrate medium with or without the prior addition of zinc (100 μM) and stored in liquid nitrogen. After 10 days, the semen samples were thawed to assess the outcome. Sperm motility, DNA integrity, mitochondrial potential and the ability of spermatozoa to undergo capacitation and acrosome reaction was assessed in post-thaw samples.

RESULTS

Semen samples cryopreserved after addition of zinc had a significantly higher percentage of sperm with intact DNA (p<0.001), mitochondrial function (p<0.001) and progressive motility (p<0.01) compared to the semen samples cryopreserved without zinc supplementation. Apart from this, ability to undergo capacitation and acrosome reaction in vitro was significantly higher in semen samples cryopreserved with zinc (p<0.0001 and p<0.001 respectively).

CONCLUSIONS

Addition of zinc to semen samples prior to cryopreservation helps in preventing the freeze-thaw-induced sperm DNA damage and loss of sperm function.

Effects of manganese on routine semen quality parameters: results from a population-based study in China

Background

Manganese (Mn) is an essential element in humans but its effect on semen quality is unclear. This study therefore aimed to assess the effects of Mn on semen quality in healthy men with no occupational exposure to Mn.

Methods

Semen samples were obtained from healthy Chinese men 20–59 years old who were recruited from six provinces in China. Individuals with urogenital tract diseases, tuberculosis, or occupational exposure to heavy metals were excluded. A questionnaire survey was conducted, and the external genitalia, semen quality, and serum Mn levels were examined.

Results

A total of 1,179 volunteers were enrolled in this study. The median serum Mn concentration was 8.2 μg/L (25th percentile (P₂₅)=3.7 μg/L, P₇₅=16.2μg/L). After adjusted area (six provinces), abstinence interval, season, registered residence, age of subjects, education level, income, smoking, and drinking, the risk of teratospermia was increased at serum Mn concentrations >19.40 μg/L (P₈₀) group, with an adjusted odds ratio of 2.27 (95% confidence interval: 1.18–4.37).

Conclusion

High serum Mn levels appeared to have harmful effects on sperm morphology and motility among healthy men with no occupational exposure to Mn.

Could zinc prevent reproductive alterations caused by cigarette smoke in male rats?

The aim of the present study was to evaluate the effects of zinc on fertility through semen parameters, testosterone level and oxidative DNA damage to spermatozoa of rats exposed to cigarette smoke. Male Wistar rats (60 days old) were divided into four groups (n = 10 per group): control, cigarette-smoking (20 cigarettes per day), zinc (zinc chloride 20 mg kg–1 day–1) and zinc plus cigarette-smoking (zinc chloride 20 mg kg–1 day–1; 20 cigarettes per day). The treatment was applied for nine weeks and the following parameters were analysed: bodyweight, wet weights of the reproductive organs and the adrenal gland, plasma testosterone concentration, testicular function (seminal analysis and daily sperm production) and sperm DNA oxidative damage. The exposure to cigarette smoke decreased testosterone concentration, the percentage of normal morphology and the motility of spermatozoa. In addition, this exposure increased sperm DNA oxidative damage. Zinc treatment protected against the toxic damage that smoking caused to spermatozoa. This study showed a correlation between smoking and possible male infertility and subfertility, and also that the majority of smoking-induced changes in spermatozoa were prevented by zinc treatment. In conclusion, zinc, an antioxidant and stimulant of cell division, can be indicated as a promising treatment in men with infertility caused by the toxic components of cigarette smoke.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

A proper dialogue between spermatozoa and the egg is essential for conception of a new individual in sexually reproducing animals. Ca2+ is crucial in orchestrating this unique event leading to a new life. No wonder that nature has devised different Ca2+-permeable channels and located them at distinct sites in spermatozoa so that they can help fertilize the egg. New tools to study sperm ionic currents, and image intracellular Ca2+ with better spatial and temporal resolution even in swimming spermatozoa, are revealing how sperm ion channels participate in fertilization. This review critically examines the involvement of Ca2+ channels in multiple signaling processes needed for spermatozoa to mature, travel towards the egg, and fertilize it. Remarkably, these tiny specialized cells can express exclusive channels like CatSper for Ca2+ and SLO3 for K+, which are attractive targets for contraception and for the discovery of novel signaling complexes. Learning more about fertilization is a matter of capital importance; societies face growing pressure to counteract rising male infertility rates, provide safe male gamete-based contraceptives, and preserve biodiversity through improved captive breeding and assisted conception initiatives.

Relationship between seminal plasma zinc and semen quality in a subfertile population

RATIONALE:

Current knowledge on the relationship between seminal zinc levels and different parameters of human semen is inconsistent.

OBJECTIVES:

To assess the relationship between seminal plasma zinc and semen quality using two markers; zinc concentration (Zn-C) and total zinc per ejaculate (Zn-T).

DESIGN:

The study was carried out as a cross-sectional study.

SUBJECTS AND METHODS:

Semen parameters of 152 healthy men undergoing evaluation for subfertility were assessed. Seminal plasma zinc levels were determined using flame atomic absorption spectrometry. Zn-C, expressed as μg/mL, was multiplied by ejaculated volume to calculate Zn-T. Mann Whitney U test and Chi-square test were used to compare the zinc levels between different seminal groups when appropriate. Correlations were observed with Pearson’s correlation of coefficient. Analysis was carried out using SPSS 10.0 for windows software.

RESULTS:

Zn-C was low in 23 (15%) samples, while in 32 (21%) of the samples Zn-T was abnormal. The number of subnormal samples was high in the low-zinc groups compared with the normal-zinc groups, 15 vs. 8 (P > 0.05) for Zn-C and 28 vs. 4 (P < 0.001) for Zn-T. Zn-C was significantly high in the asthenozoospermics compared with the normal motile group; 138.11 μg/mL (83.92) vs. 110.69 11 μg/mL (54.59) (P < 0.05). Zn-T was significantly low in samples with hyperviscosity compared with samples with normal viscosity; 220.06 μg (144.09) vs. 336.34 μg (236.33) (P < 0.05). Conversely, Zn-T was high in samples with low viability compared with those with normal viability; 437.67 μg (283.88) vs. 305.15 μg (221.19) (P < 0.05). Weak correlations were found between Zn and some semen parameters. However, the correlation was negative between pH and Zn-C (r = –0.193, P < 0.05) as well as Zn-T (r = –0.280, P < 0.01). On the other hand, correlations were positive between Zn-T and sperm count (r = 0.211, P < 0.05).

CONCLUSION:

Count, motility, viability, pH and viscosity are affected by variations of seminal plasma zinc. Seminal plasma Zn-T is the better marker for assessing the relationship between zinc and semen quality.

Moderate zinc deficiency reduces testicular Zip6 and Zip10 abundance and impairs spermatogenesis in mice

Male infertility accounts for ~40% of cases of failure to conceive. Testes have a strict zinc (Zn) requirement and severe Zn deficiency compromises spermatogenesis, sperm viability, and motility, compromising fertility in men. Despite the high prevalence of marginal Zn deficiency in humans, less emphasis has been placed on understanding the consequences on male reproduction. Swiss Webster mice were used to visualize Zip protein expression during spermatogenesis using immunohistochemistry. Data suggest Zip5 imports Zn into Sertoli cells and spermatocytes, augmented by Zip10 (primary spermatocytes) and Zip8 (secondary spermatocytes). Zip6, 8, and 10 expression was retained in round spermatids, although Zip8 and Zip10 expression disappears during spermatid maturation. Zip1 and Zip6 expression was detected in mature, elongated spermatids. Zip14 was detected in undifferentiated spermatogonia and Leydig cells. Mice fed diets (n = 10/group) reduced in Zn concentration [marginal-Zn diet (MZD), 10 mg Zn/kg; low-Zn diet (ZD), 7 mg Zn/kg] for 30 d had >35% lower liver Zn concentrations than mice fed the control diet (C; 30 mg Zn/kg) (P < 0.05). Plasma Zn and testosterone concentrations and the testes Zn concentration and weight were not significantly lower than in controls. Plasma Zn was greater in the ZD group than in the C and MZD groups. Mice fed ZD had a reduced number of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells (~50%; P < 0.05), compromised seminiferous tubule structure, and reduced Zip10 and Zip6 abundance (>50%; P < 0.5) compared with mice fed C. Our data provide compelling evidence that reduced Zn intake may be associated with infertility in men, perhaps independent of decreased levels of circulating Zn or testosterone, which warrants further investigation in human populations.

Seminal Plasma Zinc Level May be Associated with the Effect of Cigarette Smoking on Sperm Parameters

The aim of this study was to investigate the effect of cigarette smoking on seminal plasma zinc levels and sperm parameters, and to examine the role of seminal plasma zinc. Semen samples from 79 non-smokers and 68 smokers were obtained. There was a significant decrease in seminal plasma zinc in smokers and a clear correlation between seminal plasma zinc levels and the extent of smoking. Sperm parameters (concentration, motility and morphology) among smokers were significantly lower in comparison to non-smokers. These parameters were also significantly decreased among smokers with abnormal zinc levels, while there was no significant difference between non-smokers with normal zinc and non-smokers with abnormal zinc levels. As previous studies have shown that seminal plasma zinc is associated with a decrease of anti-oxidant defences, seminal plasma zinc could be a contributor to the effects of cigarette smoking on sperm parameters. In conclusion, cigarette smoking can affect sperm parameters and this study may help towards providing a mechanistic explanation.