Role of leptin and the leptin receptor in the pathogenesis of varicocele-induced testicular dysfunction

Elevated seminal plasma leptin may correlate with varicocele presence and BMI

OBJECTIVES

Male infertility affects 20-30 % of infertile couples worldwide, and varicocele being a common cause. The relationship between leptin, a hormone involved in energy homeostasis and reproduction, and male fertility parameters remains incompletely understood, particularly in the context of varicocele and obesity. Thus, the current study sought to assess the associations between seminal plasma leptin and other clinical and demographic data of infertile patients.

METHODS

In this cross-sectional study, 90 men (29 with varicocele, 61 without) were evaluated from November 2023 to March 2024. Seminal plasma leptin levels were measured using ELISA. Study subjects were classified into three weight classifications using body mass index (BMI) measurements: normal weight, overweight, and obese. Semen analysis, reproductive hormones assessment, and correlation analyses were performed to examine relationships between leptin levels and various clinical parameters.

RESULTS

Patients with varicocele demonstrated significantly higher seminal plasma leptin levels compared to those without (9.27 vs. 7.65 ng/mL, p<0.05), this association persisted following statistical adjustment for demographic and clinical variables. In addition, BMI was the strongest independent predictor of seminal plasma leptin levels (β=0.26, p<0.01). Interestingly, overweight individuals showed higher leptin levels than both normal weight and obese participants. A significant inverse relationship found between leptin concentrations and luteinizing hormone levels (ρ=-0.375, p<0.05), while a positive association was found with progressive motility of sperm (ρ=0.225, p<0.05).

CONCLUSIONS

Higher levels of leptin were found in seminal specimens of varicocele-diagnosed subjects and strongly correlate with BMI in this Middle Eastern population. These results together propose that leptin's level in semen could be useful as a biological indicator for varicocele-associated male fertility issues.

The role of leptin in the male reproductive system

Leptin is a hormone produced from adipose tissue, targeting the hypothalamus and regulating energy expenditure, adipose tissue mass, and reproductive function. Leptin concentration reflects body weight and the amount of energy stored, as well as the level of reproductive hormones and male fertility. In this review, the aim was to focus on leptin signaling mechanisms and the significant influence of leptin on the male reproductive system and to summarize the current knowledge of clinical and experimental studies. The PubMed database was searched for studies on leptin and the male reproductive system to summarize the mechanism of leptin in the male reproductive system. Studies have shown that obesity-related, high leptin levels or leptin resistance negatively affects male reproductive functions. Leptin directly affects the testis by binding to the hypothalamic-pituitary-gonadal axis and the receptors of testicular cells, and thus the location of leptin receptors plays a key role in the regulation of the male reproductive system with the negative feedback mechanism between adipose tissue and hypothalamus. Based on the current evidence, leptin may totally inhibit male reproduction, and investigation of this role of leptin has established a potential interaction between obesity and male infertility. The mechanism of leptin in the male reproductive system should be further investigated and possible treatments for subfertility should be evaluated, supported by better understanding of leptin and associated signaling mechanisms.

Melatonin alleviates oxidative stress damage in mouse testes induced by bisphenol A

We investigated the effect of melatonin on bisphenol A (BPA)-induced oxidative stress damage in testicular tissue and Leydig cells. Mice were gavaged with 50 mg/kg BPA for 30 days, and concurrently, were injected with melatonin (10 mg/kg and 20 mg/kg). Leydig cells were treated with 10 μmol/L of BPA and melatonin. The morphology and organ index of the testis and epididymis were observed and calculated. The sperm viability and density were determined. The expressions of melatonin receptor 1A and luteinizing hormone receptor, and the levels of malonaldehyde, antioxidant enzymes, glutathione, steroid hormone synthases, aromatase, luteinizing hormone, testosterone, and estradiol were measured. TUNEL assay was utilized to detect testicular cell apoptosis. The administration of melatonin at 20 mg/kg significantly improved the testicular index and epididymis index in mice treated with BPA. Additionally, melatonin promoted the development of seminiferous tubules in the testes. Furthermore, the treatment with 20 mg/kg melatonin significantly increased sperm viability and sperm density in mice, while also promoting the expressions of melatonin receptor 1A and luteinizing hormone receptor in Leydig cells of BPA-treated mice. Significantly, melatonin reduced the level of malonaldehyde in testicular tissue and increased the expression of antioxidant enzymes (superoxide dismutase 1, superoxide dismutase 2, and catalase) as well as the content of glutathione. Moreover, melatonin also reduced the number of apoptotic Leydig cells and spermatogonia, aromatase expression, and estradiol level, while increasing the expression of steroid hormone synthases (steroidogenic acute regulatory protein, cytochrome P450 family 17a1, cytochrome P450 17α-hydroxylase/20-lyase, and, 17β-hydroxysteroid dehydrogenase) and the level of testosterone. Melatonin exhibited significant potential in alleviating testicular oxidative stress damage caused by BPA. These beneficial effects may be attributed to melatonin's ability to enhance the antioxidant capacity of testicular tissue, promote testosterone synthesis, and reduce testicular cell apoptosis.

Leptin Receptor Gln223Arg Polymorphism of Human Spermatozoa Associated with Male Infertility in a Chinese Population

Background

Leptin (LEP) is believed to play a crucial role in male reproduction, while the molecular mechanisms through which LEP affects the male reproductive system are unclear. LEP acts by binding to a leptin receptor (LEPR) which mediates its physiological action, but there are only limited studies on the function of LEPR in human sperm.

Purpose

This study aimed to determine the Gln223Arg polymorphisms of the LEPR gene in human spermatozoa and evaluate their possible relationship with semen variables.

Methods

The study was performed on Chinese men: 115 healthy subjects and 108 patients with primary and 98 with secondary infertility. Semen samples were obtained from all patients, and semen variables were analyzed. The genotypic and allelic frequencies of Gln223Arg polymorphism in spermatozoa were determined by PCR and restriction fragment length polymorphism (RFLP) analyses. Statistical analyses were performed using the chi-square test, the Kruskal-Wallis test, and the Mann-Whitney test.

Results

There were no significant differences in genotypic or allelic frequency distributions of Gln223Arg polymorphism among men with primary infertility, secondary infertility, and controls. Similarly, semen volume and sperm concentration did not differ with the different genotypes in all groups of men. The percentages of motile sperm for AA + AG genotypes in men with primary infertility (31.98%) were significantly lower than those in secondary infertility, and control men with GG genotypes were 34.41% and 59.36%, respectively. At the same time, the percentages of normal morphology sperm for AA + AG genotypes in men with primary infertility (2.93%) were significantly lower than those in secondary infertility and control men with GG genotypes 3.71% and 6.54%, respectively.

Conclusion

This study reveals a possible association between the Gln223Arg polymorphism of the LEPR gene in spermatozoa affecting spermatozoal membrane integrity and having a direct role in sperm motility.

Beneficial effects of combination therapy with testosterone and hydrogen sulfide by reducing oxidative stress and apoptosis: Rat experimental varicocele model

BACKGROUND

Despite the effectiveness of testosterone therapy in conditions associated with testosterone deficiency, including varicocele, several dose-dependent side effects limit the clinical use of testosterone therapy. Hydrogen sulfide, a toxic gas in high concentrations but a beneficial molecule in low concentrations, acts as both a major effector and an important inducer of testosterone.

OBJECTIVE

This study investigated whether a subeffective dose of testosterone combined with a subeffective dose of hydrogen sulfide donor sodium hydrosulfide (NaHS) can be effective in an experimental varicocele model through a possible additive effect.

MATERIALS AND METHODS

Thirty Wistar rats weighing 200-250 gr were divided into 5 groups as (n = 6/each): sham, varicocele, testosterone (200 µg/kg, 5 times per wk for 4 consecutive weeks), NaHS (15 μmol/L, daily for 4 consecutive wk) and testosterone + NaHS (200 µg/kg, 5 times per wk + 15 μmol/L, daily, both for 4 consecutive wk). All animals, except in the sham group, underwent varicocele induction.

RESULTS

The coadministration of testosterone and NaHS significantly increased serum testosterone (10.23 ± 0.95, p = 0.01), testicular H2S levels (608.94 ± 21.09, p < 0.001), and testicular superoxide dismutase activity (66.14 ± 1.56, p < 0.001), decreased malondialdehyde levels (0.77 ± 0.52, p < 0.001), and B-cell lymphoma 2-associated X protein to B-cell lymphoma 2 (0.16 ± 0.01, p < 0.001) protein expression ratio in the testicular tissues and improved sperm parameters and testicular histopathology compared to the varicocele group.

CONCLUSION

The combination therapy of subeffective doses of testosterone and NaHS can attenuate the varicocele-induced damages by reducing testicular oxidative stress and apoptosis and thus can be considered an effective approach with fewer side effects.

Varicocele associated male infertility: cellular and molecular perspectives of pathophysiology

BACKGROUND

Varicocele is a common risk factor associated with reduced male fertility potential. The current understanding of varicocele pathophysiology does not completely explain the clinical manifestation of infertility. The present treatment options such as antioxidant supplementation and varicocelectomy only helps ∼35% of men to achieve spontaneous pregnancy.

OBJECTIVE

This review aims to summarize the available knowledge on cellular and molecular alterations implicated to varicocele associated male infertility and also highlights the new knowledge generated by 'Omics' technologies.

MATERIALS AND METHODS

PubMed, MEDLINE, Cochrane and Google Scholar databases are searched using different combinations of keywords (varicocele, infertile/fertile men with varicocele, cellular changes, molecular mechanisms, proteome, epigenome, transcriptome and metabolome). A total of 229 relevant human and animal studies published till 2021 were included in this review.

RESULTS

Current understanding advocates oxidative stress (OS) as a major contributory factor to the varicocele associated male infertility. Excessive OS causes alteration in testicular microenvironment and sperm DNA fragmentation which further contributes to infertility. Molecular and omics studies have identified several promising biomarkers such as AAMP, SPINT1, MKI67 (genetic markers), sperm quality and function related protein markers, global sperm DNA methylation level (epigenetic marker), Hspa2, Protamine, Gadd7, Dynlt1 and Beclin1 (mRNA markers), PRDX2, HSPA, APOA2, YKL40 (seminal protein markers), total choline and PHGDH (metabolic markers).

DISCUSSION

Mature spermatozoa harbours a plethora of molecular information in form of proteome, epigenome and transcriptome; which could provide very important clues regarding pathophysiology of varicocele associated infertility. Recent molecular and omics studies in infertile men with varicocele have identified several promising biomarkers. Upon further validation with larger and well-defined studies, some of these biomarkers could aid in varicocele management.

CONCLUSION

The present evidences suggest inclusion of OS and sperm DNA fragmentation tests could be useful to the diagnostic workup for men with varicocele. Furthermore, including precise molecular markers may assist in diagnostics and prognostics of varicocele associated male infertility. This article is protected by copyright. All rights reserved.

The Head-to-Toe Hormone: Leptin as an Extensive Modulator of Physiologic Systems

Leptin is a well-known hunger-sensing peptide hormone. The role of leptin in weight gain and metabolic homeostasis has been explored for the past two decades. In this review, we have tried to shed light upon the impact of leptin signaling on health and diseases. At low or moderate levels, this peptide hormone supports physiological roles, but at chronically higher doses exhibits detrimental effects on various systems. The untoward effects we observe with chronically higher levels of leptin are due to their receptor-mediated effect or due to leptin resistance and are not well studied. This review will help us in understanding the non-anorexic roles of leptin, including their contribution to the metabolism of various systems and inflammation. We will be able to get an alternative perspective regarding the physiological and pathological roles of this mysterious peptide hormone.