Non-genomic effects of vitamin D in human spermatozoa

Vitamin D alleviates chronic stress-induced testicular steroidogenesis disruption in Wistar rats

Stress is associated with various health issues. Research has highlighted the relationship between chronic stress and male reproductive health. One of the primary mechanisms underlying stress-induced male reproductive dysfunction is impaired steroidogenesis. In the present study, we validated a chronic unpredictable stress (CUS) model and investigated testicular dysfunction in CUS rats. The CUS paradigm involved exposing rats to a variety of stressors daily for 8 weeks. Vitamin D (10 µg/kg/twice a week, p.o) was administered to CUS rats starting 2 weeks after the onset of stress exposure and continued until the end of study. The stress in rats was confirmed by the occurrence of anxiety and depressive-like behaviours through elevated plus-maze test & novelty-suppressed feeding test and rise in serum corticosterone levels. Testicular dysfunction in CUS rats was assessed via serum gonadotropins, testosterone, cytokines, oxidative stress, and testis-epididymis-sperm morphology. The reduction in steroidogenesis was confirmed via immunohistochemical analysis of 17β-hydroxysteroid dehydrogenase-3 (17β-HSD3), steroidogenic acute regulatory gene (StAR) and vitamin D receptor (VDR) expression. Further, we studied the role of vitamin D in alleviating stress-induced testicular damage and the potential mechanisms underlying steroidogenic alterations in CUS rats. Notably, vitamin D treatment prevented CUS-induced decline in testicular 17β-HSD3, StAR and VDR expression. Moreover, vitamin D ameliorated the CUS-induced reduction in serum testosterone levels. Histological assessment revealed that vitamin D prevented CUS-induced damage in sperm, testis and epididymis morphology. In conclusion, our findings suggest that CUS exposure induces testicular dysfunction, which can be prevented by vitamin D, potentially through the regulation of steroidogenic pathways.

Effects of Simulated Microgravity on Rat Reproductive System: Potential Benefits of Vitamin D3 Intervention

Gravity in space can have a negative impact on the reproductive system. Given that the reproductive system is one of vitamin D's objectives, this study will use a simulated microgravity model to evaluate its impact on the rat reproductive system.Twenty-two male Wistar rats were allocated into four groups at random. Under microgravity circumstances, the rats were housed in both special and standard cages. Each group was then separated into two subgroups, one of which received vitamin D3 and the other did not. Blood was drawn twice to determine blood levels of vitamin D3, LH, FSH, and testosterone. Rat testes were isolated for histological analysis, as well as a piece of epididymis for sperm count and morphological examination.Microgravity had a detrimental effect on testicular tissue, resulting in lower serum levels of LH and testosterone (p-value < 0.001). Spermatogenesis was largely inhibited under microgravity. During microgravity conditions, however, vitamin D3 had a good effect on testicular structure, and the total number of sperm. Simulated microgravity affects the male reproductive system, compromising testicular morphology, sperm parameters, and hormonal balance. However, this study shows that vitamin D3 supplementation can act as a preventative strategy, minimizing the negative consequences of microgravity. The beneficial effect of vitamin D3 on testicular health and sperm quality implies that it may be useful in protecting male reproductive function in space-related situations.

VDR promotes testosterone synthesis in mouse Leydig cells via regulation of cholesterol side chain cleavage cytochrome P450 (Cyp11a1) expression

BACKGROUND

The vitamin D receptor (VDR) mediates the pleiotropic biological actions that include osteoporosis, immune responses and androgen synthesis.VDR is widely expressed in testis cells such as Leydig cells, Sertoli cells, and sperm. The levels of steroids are critical for sexual development. In the early stage of steroidogenesis, cholesterol is converted to pregnenolone (precursor of most steroid hormones) by cholesterol side-chain lyase (CYP11A1), which eventually synthesizes the male hormone testosterone.

OBJECTIVE

This study aims to reveal how VDR regulates CYP11A1 expression and affects testosterone synthesis in murine Leydig cells.

METHODS

The levels of VDR, CYP11A1 were determined by quantitative real-time polymerase chain reaction (RT-qPCR) or western blot. Targeted relationship between VDR and Cyp11a1 was evaluated by dual-luciferase reporter assay. The levels of testosterone concentrations in cell culture media serum by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Phylogenetic and motif analysis showed that the Cyp11a1 family had sequence loss, which may have special biological functions during evolution. The results of promoter prediction showed that vitamin D response element (VDRE) existed in the upstream promoter region of murine Cyp11a1. Dual-luciferase assay confirmed that VDR could bind candidate VDREs in upstream region of Cyp11a1, and enhance gene expression. Tissue distribution and localizatio analysis showed that Cyp11a1 was mainly expressed in testis, and dominantly existed in murine Leydig cells. Furthermore, over-expression VDR and CYP11A1 significantly increased testosterone synthesis in mice Leydig cells.

CONCLUSIONS

Active vitamin D3 (VD3) and Vdr interference treatment showed that VD3/VDR had a positive regulatory effect on Cyp11a1 expression and testosterone secretion. VDR promotes testosterone synthesis in male mice by up-regulating Cyp11a1 expression, which played an important role for male reproduction.

Calcifediol: Mechanisms of Action

Due to its essential role in calcium and phosphate homeostasis, the secosteroid hormone calcitriol has received growing attention over the last few years. Calcitriol, like other steroid hormones, may function through both genomic and non-genomic mechanisms. In the traditional function, the interaction between the biologically active form of vitamin D and the vitamin D receptor (VDR) affects the transcription of thousands of genes by binding to repeated sequences present in their promoter region, named vitamin D-responsive elements (VDREs). Non-transcriptional effects, on the other hand, occur quickly and are unaffected by inhibitors of transcription and protein synthesis. Recently, calcifediol, the immediate precursor metabolite of calcitriol, has also been shown to bind to the VDR with weaker affinity than calcitriol, thus exerting gene-regulatory properties. Moreover, calcifediol may also trigger rapid non-genomic responses through its interaction with specific membrane vitamin D receptors. Membrane-associated VDR (mVDR) and protein disulfide isomerase family A member 3 (Pdia3) are the best-studied candidates for mediating these rapid responses to vitamin D metabolites. This paper provides an overview of the calcifediol-related mechanisms of action, which may help to better understand the vitamin D endocrine system and to identify new therapeutic targets that could be important for treating diseases closely associated with vitamin D deficiency.

Effect of vitamin D metabolites and gene expression of vitamin D receptor, and 1-alpha-hydroxylase related to the sperm quality

The incidence of male fertility disorders has increased greatly due to various genetic and lifestyle factors. Recently, it has been hypothesized that vitamin D may be involved with idiopathic infertility. The goal of the study was to determine the effect and relationship between blood vitamin D metabolites, intracellular sperm vitamin D levels, and gene expression of 1-α-hydroxylase and VDR, with regard to semen quality. Seventy volunteers aged 25-45 were involved in the study. According to spermogram analysis, participants were stratified into normozoospermic control group, non-normozoospermic target group, and oligoasthenoteratozoospermic group. Vitamin D metabolites (total 25-hydroxycholecalciferol, 1,25-dihydroxycholecalciferol) in blood and spermatozoa were determined by ELISA. Free and bioavailable 25-hydroxycholecalciferol were calculated using the Vermeulen equation. mRNA expression of VDR and 1-α hydroxylase was evaluated by qPCR. Free and bioavailable 25-hydroxycholecalciferol were significantly higher in the control group compared to the target group and compared to the oligoasthenoteratozoospermic group . Intracellular sperm 1,25-dihydroxycholecalciferol was higher in the control group compared to the target group. The mRNA levels of 1- α-hydroxylase were significantly higher in the control samples, while VDR expression was significantly higher in the target group. Significant positive correlations were established between free and bioavailable 25-hydroxycholecalciferol with sperm motility and morphology. Vitamin D metabolites in blood and intracellular sperm 1,25-dihydroxycholecalciferol seem to exert beneficial effects on sperm motility and morphology. Regarding sperm quality, these effects are more pronounced in the free and bioavailable 25OHD compared to the total 25OHD in blood. Higher expression of 1-α-hydroxylase likely leads to higher intracellular levels of 1,25-dihydroxycholecalciferol, which could contribute to sperm motility and morphology. Higher VDR expression may be a compensatory mechanism related to lower intracellular sperm 1,25-dihydroxycholecalciferol.

Vitamin D supplementation for improving sperm parameters in infertile men: A systematic review and meta-analysis of randomized clinical trials

OBJECTIVE

Vitamin D has been hypothesized to have a potential role in altering sperm motility and metabolism. However, experimental studies have demonstrated inconsistent results between vitamin D and sperm parameters. This study aims to investigate the role of vitamin D supplementation to improve sperm parameters in infertile men.

METHODS

This is a systematic review and meta-analysis study. We comprehensively conducted a search on ClinicalTrials.gov, IRCT.ir, Europe PMC, and PubMed and collected published studies on vitamin D supplementation and sperm parameters for infertile men. The risk of bias was assessed by using Risk of Bias version 2 (RoB v2) and the statistical analysis was performed by using Review Manager 5.4 software.

RESULTS

Five trials with a total of 648 infertile men were included. Our meta-analysis showed that supplementation with vitamin D may significantly improve total sperm motility [mean difference 4.96 (95% CI 0.38, 9.54), p = 0.03, I2 = 69%], progressive sperm motility [mean difference 4.14 (95% CI 0.25, 8.02), p = 0.04, I2 = 89%], and normal sperm morphology [mean difference 0.44 (95% CI 0.30, 0.57), p < 0.00001, I2 = 0%] better than placebo in infertile men. However, total sperm count (p = 0.15), sperm concentration (p = 0.82), and semen volume (p = 0.83) did not differ significantly between two groups.

CONCLUSIONS

Vitamin D supplementation may improve sperm motility, progressive sperm motility, and morphology in infertile men. Vitamin D supplementation may be considered in managing male fertility issue.

Vitamin D levels and human sperm DNA fragmentation: a prospective, cohort study

Background

Intracytoplasmic sperm injection (ICSI) has revolutionized the treatment of couples with male factor infertility but results remain suboptimal and suggest the need for further investigation into the molecular biology of spermatozoa. Vitamin D has been implicated in spermatogenesis and sperm function. Hypovitaminosis D has been associated with abnormal testicular function, including elevated sperm DNA fragmentation in a murine model. This study’s objective was to evaluate if there is a correlation between Vitamin D sufficiency and human spermatozoa DNA fragmentation index % (DFI%) in infertile couples.

Results

A prospective cohort study using a consecutive, convenience sample of subjects with infertility. The primary endpoint was the effect of Vitamin D sufficiency on human spermatozoa DFI%, and secondary outcomes included Vitamin D’s effect on moderate DFI%, high DFI%, High DNA stainability % (HDS%), sperm density (million/mL), sperm total motility (% total) and sperm strict morphology (% total). Of the 111 participating, 9 were excluded, leaving 102subjects. The subjects were stratified by vitamin D levels: deficient (< 20 ng/mL; n = 24), insufficient (20–30 ng/mL; n = 43),, and sufficient (> 30 ng/mL; n = 35). There were no statistical difference between the categories of serum vitamin D levels and sperm DFI% as well as the secondary outcomes. An increased BMI was associated with low serum vitamin D levels (p = 0.0012).

Conclusion

Vitamin D deficiency was not associated with sperm DFI% or routine sperm parameters. Previous animal and human studies have demonstrated conflicting results between sperm parameters and Vitamin D levels. Redundant pathways in Vitamin D and calcium homeostasis in the human male reproductive tract may maintain essential reproductive processes during Vitamin D insufficiency or deficiency.

Trial registration

Trial Registration Number: MOD00002311 (ClinicalTrials.gov).

Rapid Nontranscriptional Effects of Calcifediol and Calcitriol

Classically, a secosteroid hormone, vitamin D, has been implicated in calcium and phosphate homeostasis and has been associated with the pathogenesis of rickets and osteomalacia in patients with severe nutritional vitamin D deficiency. The spectrum of known vitamin D-mediated effects has been expanded in recent years. However, the mechanisms of how exactly this hormone elicits its biological function are still not fully understood. The interaction of this metabolite with the vitamin D receptor (VDR) and, subsequently, with the vitamin D-responsive element in the region of specific target genes leading to the transcription of genes whose protein products are involved in the traditional function of calcitriol (known as genomic actions). Moreover, in addition to these transcription-dependent mechanisms, it has been recognized that the biologically active form of vitamin D₃, as well as its immediate precursor metabolite, calcifediol, initiate rapid, non-genomic actions through the membrane receptors that are bound as described for other steroid hormones. So far, among the best candidates responsible for mediating rapid membrane response to vitamin D metabolites are membrane-associated VDR (VDRm) and protein disulfide isomerase family A member 3 (Pdia3). The purpose of this paper is to provide an overview of the rapid, non-genomic effects of calcifediol and calcitriol, whose elucidation could improve the understanding of the vitamin D₃ endocrine system. This will contribute to a better recognition of the physiological acute functions of vitamin D₃, and it could lead to the identification of novel therapeutic targets able to modulate these actions.

Is there a relationship between serum vitamin D and semen parameters? A cross-sectional sample of the Iranian infertile men

BACKGROUND

Recent studies suggest that serum vitamin D may be associated with semen parameters. In the present cross-sectional study, we attempted to investigate the association between serum vitamin D levels and semen parameters among Iranian sub-fertile men.

RESULTS

A total of 350 infertile men recruited for this cross-sectional study using a simple random sampling method with a mean age of 34.77 years old, body mass index of 26.67 kg/m², serum vitamin D of 20.17 ng/ml, semen volume of 3.82 mL, sperm count of 44.48 (10⁶/mL), sperm total motility of 38.10 %, and morphologically normal sperm of 7.0 %. After controlling for potential confounders, serum vitamin D was positively associated with semen volume (β = 0.63, 95 % CI: 0.06, 1.20), sperm count (β = 14.40, 95 % CI: 4.56, 24.25), sperm total motility (β = 18.12, 95 % CI: 12.37, 23.86), and sperm normal morphology (β = 1.95, 95 % CI: 1.07, 2.83).

CONCLUSIONS

The present findings suggest that higher serum vitamin D levels are positively associated with higher semen volume, sperm count, sperm total motility, and normal morphology rate. These findings, however, do not specify a cause-and-effect relationship, and there is a need for further research in this area to understand whether vitamin D supplementation can improve semen parameters.

In Vitro Non-Genomic Effects of Calcifediol on Human Preosteoblastic Cells

Several recent studies have demonstrated that the direct precursor of vitamin D₃, the calcifediol [25(OH)D₃], through the binding to the nuclear vitamin D receptor (VDR), is able to regulate the expression of many genes involved in several cellular processes. Considering that itself may function as a VDR ligand, although with a lower affinity, respect than the active form of vitamin D, we have assumed that 25(OH)D₃ by binding the VDR could have a vitamin’s D₃ activity such as activating non-genomic pathways, and in particular we selected mesenchymal stem cells derived from human adipose tissue (hADMSCs) for the in vitro assessment of the intracellular Ca²⁺ mobilization in response to 25(OH)D₃. Our result reveals the ability of 25(OH)D₃ to activate rapid, non-genomic pathways, such as an increase of intracellular Ca²⁺ levels, similar to what observed with the biologically active form of vitamin D₃. hADMSCs loaded with Fluo-4 AM exhibited a rapid and sustained increase in intracellular Ca²⁺ concentration as a result of exposure to 10⁻⁵ M of 25(OH)D₃. In this work, we show for the first time the in vitro ability of 25(OH)D₃ to induce a rapid increase of intracellular Ca²⁺ levels in hADMSCs. These findings represent an important step to better understand the non-genomic effects of vitamin D₃ and its role in endocrine system.

25-Hydroxy cholecalciferol, anti-Müllerian hormone, and thyroid profiles among infertile men

BACKGROUND AND AIM

We examined the relationship among vit.D₃, AMH, FT3, FT4, and TSH, in addition to the serum levels of reproductive hormones (FSH, LH, prolactin, and free testosterone), in oligoasthenoteratozoospermia and azoospermia patients in a cohort of infertile men from Egypt to establish a clinical marker/cause-effect relationship.

METHODS

This cross-sectional cohort study was carried out on 301 men (105 males with oligoasthenoteratozoospermia and 96 males with azoospermia), in addition to 100 controls. Measurements of serum vit.D₃, AMH, FT3, FT4, and TSH levels, in addition to reproductive hormone assays, were performed on all included subjects, using ELISA kits.

RESULTS

Overall, results showed significantly lower serum levels of vit.D₃ in infertile men than in the controls, with a greater decrease observed in men with azoospermia than in oligoasthenoteratozoospermia patients, (p < .05 for all). Significantly higher serum TSH and FSH levels and significantly lower serum free testosterone levels were observed in males with azoospermia than in males with oligoasthenoteratozoospermia and the controls (p < .05 for both). There were no significant differences between the studied groups in terms of AMH, FT3 or FT4 levels. LH levels were negatively correlated with TSH levels and positively correlated with AMH levels among men with oligoasthenoteratozoospermia, while among men with azoospermia, LH levels were positively correlated with vit.D₃ levels (p < .05 for all).

CONCLUSION

Decreased Vit.D₃ could play a role in male infertility, in addition to abnormal thyroid function, which needs further investigation.

Effects of Vitamin D on Apoptosis and Quality of Sperm in Asthenozoospermia

OBJECTIVE

Vitamin D receptor (VDR) is expressed in human spermatozoa. However, the role of vitamin D (VD) in human male reproduction has not yet been clarified. In this study, effects of VD on sperm parameters and its apoptosis in asthenozoospermic and healthy men were evaluated.

METHODS

The study was carried out on discharged semen samples of 80 asthenozoospermic and healthy men. The samples were divided into control and experimental groups (received 20 µMol of VD). This study assessed sperm motility using the Makler chamber, their morphology by Diff quick, apoptosis and necrosis by Annexin-V and TUNEL assays, and their chromatin integrity was assessed by Aniline blue and Toluidine blue staining, according to WHO guidelines.

RESULTS

The results revealed that: 1) the total number of motile sperms was increased by VD in both groups, but it was only significant in the asthenozoospermia group. 2) The progressive motility was increased with significant difference in both groups.3) Morphology of sperm did not show any changes due to VD in any of the groups. 4) Early apoptosis and necrosis of sperms were reduced in both groups, but the results of late apoptosis showed no statistical difference in these groups. 5) The percentage of positive toluidine blue was significantly decreased after using VD in the asthenozoospermia group.

CONCLUSION

VD could improve motility, early apoptosis, and sperm necrosis, especially in asthenozoospermic men and it could be used for therapeutic opportunities.

The effect of vitamin D on sperm motility and the underlying mechanism

Vitamin D deficiency is a common health issue around the world. We therefore evaluated the associations of semen quality with both serum and seminal plasma vitamin D levels and studied the mechanisms underlying these by incubating spermatozoa with 1,25(OH)₂D in vitro. Two hundred and twenty-two men were included in our study. Vitamin D was detected using an electrochemiluminescence method. Spermatozoa used for in vitro experiments were isolated by density gradient centrifugation. Positive relationships of serum 25(OH)D with semen volume and seminal plasma fructose were identified. Seminal plasma 25(OH)D level showed no relationship with serum 25(OH)D level, while it was inversely associated with sperm concentration and positively correlated with semen volume and sperm kinetic values. In vitro, sperm kinetic parameters increased after incubation with 1,25(OH)₂D, especially upon incubation for 30 min with it at a concentration of 0.1 nmol l⁻¹. Under these incubation conditions, the upward migration of spermatozoa increased remarkably with increasing adenosine triphosphate (ATP) concentration. The concentration of cyclic adenosine monophosphate (cAMP) and the activity of protein kinase A (PKA) were both elevated, and the PKA inhibitor, N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H89) reversed the increase of ATP production. The concentrations of cytoplasmic calcium ions and nicotinamide adenine dinucleotide (NADH) were both enhanced, while mitochondrial calcium uniporter (MCU) inhibitor, Ruthenium 360 (Ru360) did not reverse the increase of ATP production. Therefore, seminal plasma vitamin D may be involved in regulating sperm motility, and 1,25(OH)₂D may enhance sperm motility by promoting the synthesis of ATP both through the cAMP/PKA pathway and the increase in intracellular calcium ions.

Investigation of serum vitamin D and ischaemia-modified albumin levels in infertile Turkish men

Our aim was to explore the existence of a possible relationship of sperm motility with serum 25-hydroxyvitamin D3 (25-OH VD) levels and with ischaemia-modified albumin (IMA) levels in infertile Turkish men. A total of 30 men with nonobstructive azoospermia (no spermatozoa in ejaculate), 30 men with oligospermia (total progressive motile sperm count (TPMSC) <15 × 10⁶ /ml) and 33 fertile men with normospermia (with at least one child, as the control group) were enrolled in the study. The mean 25-OH VD levels for groups 1, 2 and 3 were 9.31 ± 6.46, 19.71 ± 12.80 and 30.52 ± 12.49 respectively (p < .05). There was a statistically significant difference in serum IMA levels among the groups (479.32 ± 307.56 vs. 296.37 ± 127.27 vs. 150.04 ± 81.05, respectively; p < .05). A positive correlation between serum 25-OH VD levels and TPMSC, and a negative correlation between TPMSC and serum IMA levels were determined. Infertile men had lower serum 25-OH VD and higher IMA levels than fertile men, with a positive correlation between serum 25-OH VD levels and TPMSC, and a negative correlation between TPMSC and serum IMA levels. Vitamin D supplementation may increase the sperm motility.

Association between polymorphisms in vitamin D receptor gene and adolescent idiopathic scoliosis: a meta-analysis

PURPOSE

This meta-analysis was performed to clarify whether the two single nucleotide polymorphisms (ApaI and BsmI) in vitamin D receptor (VDR) gene conferred susceptibility to adolescent idiopathic scoliosis (AIS).

METHODS

A comprehensive literature search in five online databases (PubMed, EMBASE, ISI Web of Science, CNKI, and Wanfang) was performed to identify studies that analyzed the association between VDR gene polymorphisms and risk of AIS. Observational studies met the predetermined inclusion criteria were selected for meta-analysis. The most appropriate genetic model was identified using a genetic model-free approach. Meta-analysis was performed using RevMan 5.3 software.

RESULTS

Five eligible studies were included in this meta-analysis, which involved a total of 717 cases and 554 controls. A statistically significant association was observed between BsmI polymorphism and AIS (OR 1.90, 95% CI 1.32, 2.62). In subgroup analysis by ethnicity, the association between BsmI polymorphism and AIS was significant in Asians (OR 2.06, 95% CI 1.56, 2.73) but not in Caucasians (OR 0.70, 95% CI 0.23, 2.19). However, the ApaI polymorphism was not associated with AIS. Moreover, no evidence of association between BMD and the two VDR gene polymorphisms was detected.

CONCLUSIONS

Meta-analysis of existing data suggested that BsmI was associated with increased risk of AIS in Asian populations. Nevertheless, further studies with rigorous design and more ethnic groups are encouraged to validate our findings. These slides can be retrieved under Electronic Supplementary Material.

Age-associated expression of vitamin D receptor and vitamin D-metabolizing enzymes in the male reproductive tract and sperm of Hu sheep

The cellular response to 1,25-dihydroxyvitamin D₃ (Vit D₃; biologically active form of Vitamin D) is complex and depends not only on Vitamin D receptor (VDR) expression but also on cellular uptake of circulating Vit D₃ and the presence and activity of Vitamin D-metabolizing enzyme. This study evaluated the expression of VDR and Vitamin D-metabolizing enzymes in the ram reproductive tract at different developmental stages and in spermatozoa. Nearly all cell types in the testes and epithelial cells of the caput, corpus, and cauda expressed VDR, CYP27B1, and CYP24A1 proteins. The mRNA and protein expression of CYP2R1, CYP27A1, and CYP27B1 in the testes and cauda increased significantly with increasing age (P < 0.05). However, epididymal VDR mRNA and protein expression showed no significant difference (P < 0.05) between adult (9- and 24-month-old) and prepubertal (3-month-old) rams. Furthermore, VDR and CYP24A1 were mainly concentrated in the mid-piece of ejaculated or cauda epididymis spermatozoa or both. Additionally, VDR and CYP27B1 mRNA and protein expression levels were significantly higher in ejaculated spermatozoa than in cauda epididymal spermatozoa (P < 0.05). Moreover, VDR and CYP24A1 expression was significantly higher in high-motility than in low-motility spermatozoa (P < 0.05). The diverse expression patterns of VDR and Vitamin D-metabolizing enzymes in the ram reproductive tract at different developmental stages and spermatozoa suggest it plays a potential role in spermatogenesis.

Occurrence and reproductive roles of hormones in seminal plasma

Only 2-5% of seminal fluid is composed of spermatozoa, while the rest is seminal plasma. The seminal plasma is a rich cocktail of organic and inorganic compounds including hormones, serving as a source of nutrients for sperm development and maturation, protecting them from infection and enabling them to overcome the immunological and chemical environment of the female reproductive tract. In this review, a survey of the hormones found in human seminal plasma, with particular emphasis on reproductive hormones is provided. Their participation in fertilization is discussed including their indispensable role in ovum fertilization. The origin of individual hormones found in seminal plasma is discussed, along with differences in the concentrations in seminal plasma and blood plasma. A part of review is devoted to methods of measurement, emphasising particular instances in which they differ from measurement in blood plasma. These methods include separation techniques, overcoming the matrix effect and current ways for end-point measurement, focusing on so called hyphenated techniques as a combination of chromatographic separation and mass spectrometry. Finally, the informative value of their determination as markers of male fertility disorders (impaired spermatogenesis, abnormal sperm parameters, varicocele) is discussed, along with instances where measuring their levels in seminal plasma is preferable to measurement of levels in blood plasma.

The role of vitamin D in male fertility: A focus on the testis

In the last decade, vitamin D has emerged as a pleiotropic molecule with a multitude of autocrine, paracrine and endocrine functions, mediated by classical genomic as well as non-classical non-genomic actions, on multiple target organs and systems. The expression of vitamin D receptor and vitamin D metabolizing enzymes in male reproductive system, particularly in the testis, suggests the occurrence of vitamin D synthesis and regulation as well as function in the testis. The role of vitamin D in the modulation of testis functions, including hormone production and spermatogenesis, has been investigated in animals and humans. Experimental studies support a beneficial effect of vitamin D on male fertility, by modulating hormone production through genomic and non-genomic actions, and, particularly, by improving semen quality essentially through non-genomic actions. However, clinical studies in humans are controversial. Indeed, vitamin D seems to contribute to the modulation of the bioavailable rather than total testosterone. Moreover, although an increased prevalence or risk for testosterone deficiency was reported in men with vitamin D deficiency in observational studies, the majority of interventional studies demonstrated the lack of effect of vitamin D supplementation on circulating levels of testosterone. The most consistent effect of vitamin D was reported on semen quality. Indeed, vitamin D was shown to be positively associated to sperm motility, and to exert direct actions on spermatozoa, including non-genomic driven modulation of intracellular calcium homeostasis and activation of molecular pathways involved in sperm motility, capacitation and acrosome reaction. The current review provides a summary of current knowledge on the role of vitamin D in male fertility, by reporting clinical and experimental studies in humans and animals addressing the relationship between vitamin D and testis function.

Elimination of cancer stem cells and reactivation of latent HIV-1 via AMPK activation: Common mechanism of action linking inhibition of tumorigenesis and the potential eradication of HIV-1

Although promising treatments are currently in development to slow disease progression and increase patient survival, cancer remains the second leading cause of death in the United States. Cancer treatment modalities commonly include chemoradiation and therapies that target components of aberrantly activated signaling pathways. However, treatment resistance is a common occurrence and recent evidence indicates that the existence of cancer stem cells (CSCs) may underlie the limited efficacy and inability of current treatments to effectuate a cure. CSCs, which are largely resistant to chemoradiation therapy, are a subpopulation of cancer cells that exhibit characteristics similar to embryonic stem cells (ESCs), including self-renewal, multi-lineage differentiation, and the ability to initiate tumorigenesis. Interestingly, intracellular mechanisms that sustain quiescence and promote self-renewal in adult stem cells (ASCs) and CSCs likely also function to maintain latency of HIV-1 in CD4⁺ memory T cells. Although antiretroviral therapy is highly effective in controlling HIV-1 replication, the persistence of latent but replication-competent proviruses necessitates the development of compounds that are capable of selectively reactivating the latent virus, a method known as the "shock and kill" approach. Homeostatic proliferation in central CD4⁺ memory T (T_CM) cells, a memory T cell subset that exhibits limited self-renewal and differentiation and is a primary reservoir for latent HIV-1, has been shown to reinforce and stabilize the latent reservoir in the absence of T cell activation and differentiation. HIV-1 has also been found to establish durable and long-lasting latency in a recently discovered subset of CD4⁺ T cells known as T memory stem (T_SCM) cells. T_SCM cells, compared to T_CM cells, exhibit stem cell properties that more closely match those of ESCs and ASCs, including self-renewal and differentiation into all memory T cell subsets. It is our hypothesis that activation of AMPK, a master regulator of cellular metabolism that plays a critical role in T cell activation and differentiation of ESCs and ASCs, will lead to both T cell activation-induced latent HIV-1 reactivation, facilitating virus destruction, as well as "activation", differentiation, and/or apoptosis of CSCs, thus inhibiting tumorigenesis. We also propose the novel observation that compounds that have been shown to both facilitate latent HIV-1 reactivation and promote CSC differentiation/apoptosis (e.g. bryostatin-1, JQ1, metformin, butyrate, etc.) likely do so through a common mechanism of AMPK activation.

Molecular actions of vitamin D in reproductive cell biology

Vitamin D (VitD) is an important secosteroid and has attracted attention in several areas of research due to common VitD deficiency in the population, and its potential to regulate molecular pathways related to chronic and inflammatory diseases. VitD metabolites and the VitD receptor (VDR) influence many tissues including those of the reproductive system. VDR expression has been demonstrated in various cell types of the male reproductive tract, including spermatozoa and germ cells, and in female reproductive tissues including the ovaries, placenta and endometrium. However, the molecular role of VitD signalling and metabolism in reproductive function have not been fully established. Consequently, the aim of this work is to review current metabolic and molecular aspects of the VitD–VDR axis in reproductive medicine and to propose the direction of future research. Specifically, the influence of VitD on sperm motility, calcium handling, capacitation, acrosin reaction and lipid metabolism is examined. In addition, we will also discuss the effect of VitD on sex hormone secretion and receptor expression in primary granulosa cells, along with the impact on cytokine production in trophoblast cells. The review concludes with a discussion of the recent developments in VitD–VDR signalling specifically related to altered cellular bioenergetics, which is an emerging concept in the field of reproductive medicine.

Association of vitamin D status with semen quality and reproductive hormones in Iranian subfertile men

Although vitamin D deficiency is one of the most common health problems throughout the world, including Iran, conflicting information exists on the potential association between serum vitamin D levels and semen quality. This study intended to evaluate the association between serum vitamin D [25(OH) D3] with semen quality and hormones in Iranian subfertile men. We also compared mean vitamin D and hormone levels in normospermic men with oligoasthenoteratozoospermia (OAT) men. This cross-sectional study was conducted on 278 men who were referred to Royan Infertility Clinic (Tehran, Iran) from March to September 2014. The participants were categorized into two groups; of 186 normospermic and 92 OAT patients according to World Health Organization 2010 criteria. Each participant provided informed consent prior to launching research. Participants completed two general questionnaires of nutritional status. Blood and semen samples were obtained for assessment, and all data were adjusted for age, body mass index (BMI), and season. Vitamin D levels were classified according to Institute of Medicine guidelines. Vitamin D deficiency, insufficiency, and normal levels were observed in 8.6%, 43.6%, 47.8% of participants, respectively. No association was found between daily dietary intake of vitamin D and calcium with sperm parameters. Serum vitamin D was inversely correlated with PTH (p < 0.045). In normospermic men, serum vitamin D levels categorized were not correlated with semen parameters and reproductive hormones (FSH, LH, testosterone(T), and FT), whereas sperm motility showed a positive correlation with vitamin D categorized in OAT men (rs = 0.131, p = 0.028). In conclusion, there was a high incidence of deficiency and insufficiency 25(OH) D Levels (<20ng/ml) observed in Iranian men (52.2%). Moreover, our findings showed a correlation between vitamin D levels and sperm motility in OAT men, which requires further studies.

Vitamin D deficiency and low ionized calcium are linked with semen quality and sex steroid levels in infertile men

STUDY QUESTION

Are low vitamin D levels linked with semen quality and sex steroids in infertile men?

SUMMARY ANSWER

Infertile men with vitamin D deficiency had lower sperm motility, total numbers of motile sperm, Inhibin B, sex-hormone-binding-globulin (SHBG) and testosterone/estradiol ratio, but higher levels of free sex steroids, than infertile men with normal vitamin D levels.

WHAT IS KNOWN ALREADY

Low vitamin D levels have been associated with decreased sperm motility in healthy men, but a relationship between vitamin D and calcium with semen quality and especially sex steroids has not been sufficiently described in infertile men.

STUDY DESIGN, SIZE, DURATION

This study comprises baseline characteristics of 1427 infertile men screened from 2011 to 2014 for inclusion in a randomized clinical trial, the Copenhagen-Bone-Gonadal Study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In total 1427 infertile men, consecutively referred to our tertiary andrological centre for fertility workup, underwent a physical examination and had semen quality assessed based on two samples and blood analysed for serum testosterone, SHBG, estradiol, inhibin B, luteinizing hormone, follicle-stimulating hormone (FSH), 25-hydroxyvitamin D (25-OHD), ionized calcium (Ca(2+)) and karyotype. There were 179 men excluded due to serious comorbidities or anabolic steroid usage, leaving 1248 patients for analyses.

MAIN RESULTS AND THE ROLE OF CHANCE

Men with 25-OHD >75 nmol/l had higher sperm motility and 66 and 111% higher total numbers of motile spermatozoa after 45 and 262 min, respectively, than men with 25-OHD <25 nmol/l (all P < 0.05). SHBG levels and testosterone/estradiol ratios were 15 and 14% lower, respectively, while free testosterone and estradiol ratios were 6 and 13% higher, respectively, in men with 25-OHD <25 nmol/l (all P < 0.05). Men with lower Ca(2+) levels had higher progressive sperm motility and inhibin B/FSH ratio but lower testosterone/estradiol ratio (all P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

All outcomes presented are predefined end-points but inferral of causality is compromised by the descriptive study design. It remains to be shown whether the links between vitamin D, calcium, semen quality and sex steroids in infertile men are causal.

WIDER IMPLICATIONS OF THE FINDINGS

The associations between vitamin D deficiency and low calcium with semen quality and sex steroids support the existence of a cross-link between regulators of calcium homeostasis and gonadal function in infertile men.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by the Danish Agency for Science, Technology and Innovation, Hørslev Fonden, Danish Cancer Society and Novo Nordisk Foundation. There are no conflicts of interest.

TRIAL REGISTRATION NUMBER

NCT01304927.

DATE OF TRIAL REGISTRATION

25 February 2011.

DATE OF ENROLMENT OF FIRST PATIENT

8 March 2011.

Vitamin D-induced ectodomain shedding of TNF receptor 1 as a nongenomic action: D3 vs D2 derivatives

As a nongenomic action, 1,25-dihydroxyvitamin D3 (1,25D3) induces L-type Ca(2+) channel-mediated extracellular Ca(2+) influx in human aortic smooth muscle cells (HASMCs), which activates a disintegrin and metalloprotease 10 (ADAM10) to cleave and shed the ectodomain of tumor necrosis factor receptor 1 (TNFR1). In this study, we examined the potencies of other vitamin D3 and D2 analogs to stimulate the ectodomain shedding of TNFR1 in HASMCs. 25-Hydroxyvitamin D3 (25D3), a precursor of 1,25D3, and elocalcitol, an analog of 1,25D3, caused ectodomain shedding of TNFR1 within 30 min, whereas 1,25-dihydroxyvitamin D2 (1,25D2) and paricalcitol, a derivative of 1,25D2, did not. Both 25D3 and elocalcitol rapidly induced extracellular Ca(2+) influx and markedly increased intracellular Ca(2+), while 1,25D2 and paricalcitol caused only small increases in intracellular Ca(2+). 25D3- and elocalcitol-induced TNFR1 ectodomain sheddings were abolished by verapamil and in Ca(2+)-free media. Both 25D3 and elocalcitol caused the translocation of ADAM10 to the cell surface, which was inhibited by verapamil, while 1,25D2 and paricalcitol did not cause ADAM10 translocation. When ADAM10 was depleted by ADAM10-siRNA, 25D3 and elocalcitol could not induce ectodomain shedding of TNFR1. The plasma membrane receptor, endoplasmic reticulum stress protein 57 (ERp57), but not the classic vitamin D receptor, mediated the nongenomic action of vitamin D to induce ectodomain shedding of TNFR1. In summary, like 1,25D3, 25D3 and elocalcitol caused ADAM10-mediated ectodomain shedding of TNFR1, whereas 1,25D2 and paricalcitol did not. The difference may depend on their affinities to ERp57 through which extracellular Ca(2+) influx is induced.

Vitamin D -- the sun hormone. Life in environmental mismatch

While some representatives of the animal kingdom were improving their biological mechanisms and properties for adapting to ever-changing life conditions, the genus Homo was developing backward: human individuals were losing their adaptation to life areas conquered earlier. Losing step-by-step their useful traits including the body hair cover, the primitive genus Homo retained his viability only under very favorable conditions of the equatorial Africa. Protection from UV radiation danger was provided only by pigmentation of skin, hair, and eyes. However, "impoverished" individuals of this genus gained the ability to walk upright. Their hands became free from participation in movement and became fine tools for producing useful instruments, from the stone knife to the computer. The major consequence of upright movement and hand development became the powerful development of the brain. A modern human, Homo sapiens, appeared capable of conquering very diverse new habitats. The human's expansion on the Earth occurred somewhat limited by his dependence on vitamin D. His expansion into new areas with lower Sun activity was partially associated with the loss of skin pigmentation. But there is an open question, whether under these new conditions he is satisfactorily provided with vitamin D. This paper discusses the following problems: how can we ensure a sufficient intake of vitamin D, how much does an individual require for his existence and optimal life, what will be consequences of vitamin D deficiency, and what are the prospects for better provision with vitamin D?

Plausible ergogenic effects of vitamin D on athletic performance and recovery

The purpose of this review is to examine vitamin D in the context of sport nutrition and its potential role in optimizing athletic performance. Vitamin D receptors (VDR) and vitamin D response elements (VDREs) are located in almost every tissue within the human body including skeletal muscle. The hormonally-active form of vitamin D, 1,25-dihydroxyvitamin D, has been shown to play critical roles in the human body and regulates over 900 gene variants. Based on the literature presented, it is plausible that vitamin D levels above the normal reference range (up to 100 nmol/L) might increase skeletal muscle function, decrease recovery time from training, increase both force and power production, and increase testosterone production, each of which could potentiate athletic performance. Therefore, maintaining higher levels of vitamin D could prove beneficial for athletic performance. Despite this situation, large portions of athletic populations are vitamin D deficient. Currently, the research is inconclusive with regards to the optimal intake of vitamin D, the specific forms of vitamin D one should ingest, and the distinct nutrient-nutrient interactions of vitamin D with vitamin K that affect arterial calcification and hypervitaminosis. Furthermore, it is possible that dosages exceeding the recommendations for vitamin D (i.e. dosages up to 4000-5000 IU/day), in combination with 50 to 1000 mcg/day of vitamin K₁ and K₂ could aid athletic performance. This review will investigate these topics, and specifically their relevance to athletic performance.

Vitamin D and male reproduction

Vitamin D is a versatile signalling molecule with a well-established role in the regulation of calcium homeostasis and bone health. The spectrum of vitamin D target organs has expanded and the reproductive role of vitamin D is highlighted by expression of the vitamin D receptor (VDR) and enzymes that metabolize vitamin D in testis, male reproductive tract and human spermatozoa. The expression levels of VDR and CYP24A1 in human spermatozoa serve as positive predictive markers of semen quality, and VDR mediates a nongenomic increase in intracellular calcium concentration that induces sperm motility. Interestingly, functional animal models show that vitamin D is important for estrogen signalling and sperm motility, while cross-sectional studies support the positive association between serum 25-hydroxyvitamin D level and sperm motility in both fertile and infertile men. Expression of VDR and enzymes that metabolize vitamin D in fetal testis indicates a yet unknown role during development, which may be extrapolated from invasive testicular germ cell tumours where 1α,25-dihydroxyvitamin D induces a mesodermal differentiation of the pluripotent testicular cancer cells. Taken together, vitamin D signalling has a positive effect on semen quality, increases estrogen responsiveness and differentiates germ cell tumours. Future studies are needed to determine when 1α,25-dihydroxyvitamin D acts in a paracrine manner and whether systemic changes, which are subject to pharmacological modulation, could influence male reproductive function.

Characterization of the testicular, epididymal and endocrine phenotypes in the Leuven Vdr-deficient mouse model: targeting estrogen signalling

Vitamin D is a key factor for calcium and bone homeostasis, but signalling through the vitamin D receptor (VDR) seems also to be important for testicular function. To test the functional role of vitamin D signalling we examined the male reproductive system of the Leuven Vdr-ablated (Vdr(-/-)) mice, previously established as a model for hereditary vitamin D-resistant rickets. We investigated reproductive hormones, changes in gene expression and histological phenotype of eleven Vdr(-/-), eight Vdr(+/-) and nine Vdr(+/+) mice. Testicular and epididymal histology were grossly normal in Vdr(-/-) mice. Accordingly, no differences were found in serum concentrations of testosterone, estradiol, LH, and FSH or testicular expression of Cyp19a1, Ersα, Cyp17a1, Star, Insl3, Inhbb, and Amh. However, a significantly lower ERβ expression was found in testis of Vdr(+/-) and Vdr(-/-) mice, conversely epididymal expressions of ERα and the estrogen-target gene Aqp9 were higher. In conclusion, vitamin D seems dispensable for murine spermatogenesis and sex hormone production, but aberrant estrogen-signalling may elicit some of the VDR-mediated effects on male reproduction.

Role of VDR in 1α,25-dihydroxyvitamin D3-dependent non-genomic activation of MAPKs, Src and Akt in skeletal muscle cells

1α,25-dihydroxyvitamin D3 [1,25D] is recognized as a steroid hormone that rapidly elicits intracellular signals in various tissues. In skeletal myoblasts, we have previously demonstrated that one of the 1,25D-induced non-genomic effects is the upstream stimulation of MAPKs through Src activation. In this work, the data obtained suggest that the classical receptor of vitamin D (VDR) participates in non-transcriptional actions of 1,25D. We significantly reduced VDR expression by infection of C2C12 murine myoblasts with lentiviral particles containing the pLKO.1 plasmid with information to express a shRNA against mouse VDR. In these cells (C2C12-shVDR), Western blot analyses show that 1,25D-induced p38 MAPK activation and Src tyr416 phosphorylation were abolished. In addition, 1,25D-dependent activity of ERK1/2 was diminished in cells lacking VDR but to a lesser extent (∼-60%). Phosphorylation of Akt by 1,25D, recently demonstrated in C2C12 cells, in the present work also appeared to be partially dependent on VDR expression (∼50% in C2C12-shVDR cells). Our results indicate that VDR is involved in 1,25D-induced rapid events related to survival/proliferation responses in skeletal muscle cells, providing relevant information on the mechanism of initiation of the non-genomic hormone signal. The participation of a VDR-independent non-genomic mechanism of action should also be taken into consideration. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Vitamin D metabolism and effects on pluripotency genes and cell differentiation in testicular germ cell tumors in vitro and in vivo

Testicular germ cell tumors (TGCTs) are classified as either seminomas or nonseminomas. Both tumors originate from carcinoma in situ (CIS) cells, which are derived from transformed fetal gonocytes. CIS, seminoma, and the undifferentiated embryonal carcinoma (EC) retain an embryonic phenotype and express pluripotency factors (NANOG/OCT4). Vitamin D (VD) is metabolized in the testes, and here, we examined VD metabolism in TGCT differentiation and pluripotency regulation. We established that the VD receptor (VDR) and VD-metabolizing enzymes are expressed in human fetal germ cells, CIS, and invasive TGCTs. VD metabolism diminished markedly during the malignant transformation from CIS to EC but was reestablished in differentiated components of nonseminomas, distinguished by coexpression of mesodermal markers and loss of OCT4. Subsequent in vitro studies confirmed that 1,25(OH)(2)D(3) (active VD) downregulated NANOG and OCT4 through genomic VDR activation in EC-derived NTera2 cells and, to a lesser extent, in seminoma-derived TCam-2 cells, and up-regulated brachyury, SNAI1, osteocalcin, osteopontin, and fibroblast growth factor 23. To test for a possible therapeutic effect in vivo, NTera2 cells were xenografted into nude mice and treated with 1,25(OH)(2)D(3), which induced down-regulation of pluripotency factors but caused no significant reduction of tumor growth. During NTera2 tumor formation, down-regulation of VDR was observed, resulting in limited responsiveness to cholecalciferol and 1,25(OH)(2)D(3) treatment in vivo. These novel findings show that VD metabolism is involved in the mesodermal transition during differentiation of cancer cells with embryonic stem cell characteristics, which points to a function for VD during early embryonic development and possibly in the pathogenesis of TGCTs.