Leptin levels in infertile male patients are correlated with inhibin B, testosterone and SHBG but not with sperm characteristics

MiOXSYS® and OxiSperm® II assays appear to provide no clinical utility for determining oxidative stress in human sperm-results from repeated semen collections

BACKGROUND

Oxidative stress in semen contributes up to 80% of all infertility diagnosis. Diagnostics to measure oxidative stress in semen was recently added to the 6th edition WHO methods manual, although diagnostic predictive values need to be interpreted with caution as there are still several research questions yet to be answered.

OBJECTIVES

To determine the natural fluctuations in semen redox indicators (MiOXSYS® and OxiSperm® II) within and between men and their association with markers of sperm oxidative stress.

MATERIALS AND METHODS

Total, 118 repeat semen samples from 31 generally healthy men aged 18-45 years, over 6 months. Standard semen analysis as per 5th WHO manual. Semen redox levels measured via MiOXSYS® and OxiSperm® II. Additional attributes of sperm quality; HBA® binding assay and sperm hyperactivation and oxidative stress; DNA fragmentation (Halo® Sperm) and lipid peroxidation (BODIPY™ 581/591 C11) were assessed.

RESULTS

Samples with high redox-potential (MiOXSYS® ≥1.47 sORP/106 sperm/ml) had lower sperm, motility, morphology and higher DNA fragmentation (P < 0.05). Upon further analysis, these associations were driven solely by the adjustment of sperm concentration (106 /ml) in normalised redox-potential. No significant associations between NBT-reactivity (OxiSperm® II) and measures of the sperm function or oxidative stress were observed (P > 0.05). Fluctuations in semen redox levels varied greater between men than within men over the study period.

DISCUSSION

Neither MiOXSYS® nor OxiSperm® II assays were predictive of sperm function or sperm oxidative stress. This was likely due at least in part to limited understanding of their biochemistry and clinical application. As a result, these assays seem to provide no additional clinical utility beyond that of a standard semen analysis, highlighting the imperative for the development of new robust point-of-care devices for accurately determining sperm oxidative stress.

CONCLUSION

These findings suggest that MiOXSYS® and OxiSperm® II systems for the measurement of sperm oxidative stress may have limited diagnostic potential.

A cross-sectional study of the association between circulating sex hormone-binding globulin levels and selected adipokines in women with polycystic ovary syndrome

INTRODUCTION

Changes in the proportion of pro-inflammatory and anti-inflammatory adipokines may reflect the accumulation of lipids in the liver and the development of insulin resistance. Both liver steatosis and insulin resistance result in decreased sex hormone-binding globulin (SHBG) synthesis. This study aimed to analyze associations between circulating SHBG and adipokines levels in women with polycystic ovary syndrome (PCOS).

MATERIAL AND METHODS

A cross-sectional cohort study involved 87 women with phenotype A of PCOS (39 normal weight and 48 obese). Body mass, height, and waist circumference were measured, and BMI was calculated. In addition, body composition was assessed using the bioimpedance method. Serum SHBG levels and plasma apelin-36 and apelin-12, adiponectin, leptin, omentin-1, and RBP-4 were determined by using the ELISA method. The participants were divided into subgroups with SHBG concentrations above and below this lower limit [N = 35 (40.2%) and N = 52 (59.8%), respectively].

RESULTS

The median adiponectin, apelin-12, and apelin-36 levels were significantly lower, and leptin levels were significantly higher in the subgroup with low SHBG levels than that in the subgroup above the lower limit of the reference range, while there were no differences in median omentin-1 and RBP-4 between the study subgroups. There were positive correlations between SHBG and omentin-1, adiponectin, apelin-36, and apelin-12 levels, as well as negative correlation with leptin levels. However, after adjustment by BMI, waist circumference, and body fat percentage, only the association between SHBG and omentin-1 remained significant.

CONCLUSION

Our results show associations between circulating SHBG and adipokine levels in women with PCOS and support the role of hormonal dysfunction of the adipose tissue in the pathogenesis of PCOS.

Leptin and prolactin reduce cryodamage in normozoospermic human semen samples during cryopreservation

OBJECTIVES

Cryopreservation has destructive effects on the function and structure of spermatozoa. It is known that leptin and prolactin play an active role in decreasing the rates of reactive oxygen species and DNA fragmentation, as well as enhancing sperm motility. Hence, this experiment aimed to investigate the effects of leptin and prolactin as pro-survival factors on the normozoospermic human semen samples during cryopreservation.

MATERIAL AND METHODS

Semen samples were collected from 15 healthy, fertile men ranging from 25 to 40 years. Cryopreservation of the samples was performed in liquid nitrogen over a period of two weeks, using five varying concentrations of leptin/prolactin, 0, 10, 100, 500, and 1000ng/ml respectively. Sperm motility, total caspase activity, and mitochondrial and cytosolic ROS were measured by flowcytometry, TUNEL, and other appropriate tests after thawing of the samples.

RESULTS

Both hormones were observed to have positive effects on the motility of the samples post-cryopreservation, the highest improvement being in the 100ng/ml concentration leptin and prolactin in comparison to the control group (P=0.01 and P=0.041, respectively). A significant reduction of mitochondrial ROS was also observed in 100 and 1000ng/ml of leptin (P=0.042), and there was a considerable decrease in the cytosolic ROS in the 100ng/ml of prolactin in comparison to the control group (P=0.048). Total caspase activity was also highly reduced in the 100, 500, and 1000ng/ml of leptin compared to the control group (P=0.039). Interestingly, both hormones also significantly decreased DNA fragmentation in 1000ng/ml compared to the control group (P=0.042).

CONCLUSION

It can be concluded that leptin and prolactin act as protective agents against cryodamage to spermatozoa during cryopreservation.

Obesity and male infertility: multifaceted reproductive disruption

Background

The global prevalence of obesity has soared to a concerning height in the past few decades. Interestingly, the global decline in semen quality is a parallel occurrence that urges researchers to evaluate if obesity is among the most essential causatives of male infertility or subfertility.

Main body

Obesity may alter the synchronized working of the reproductive-endocrine milieu, mainly the hypothalamic-pituitary-gonadal (HPG) axis along with its crosstalks with other reproductive hormones. Obesity-mediated impairment in semen parameters may include several intermediate factors, which include physical factors, essentially increased scrotal temperature due to heavy adipose tissue deposits, and systemic inflammation and oxidative stress (OS) initiated by various adipose tissue-derived pro-inflammatory mediators. Obesity, via its multifaceted mechanisms, may modulate sperm genetic and epigenetic conformation, which severely disrupt sperm functions. Paternal obesity reportedly has significant adverse effects upon the outcome of assisted reproductive techniques (ARTs) and the overall health of offspring. Given the complexity of the underlying mechanisms and rapid emergence of new evidence-based hypotheses, the concept of obesity-mediated male infertility needs timely updates and pristine understanding.

Conclusions

The present review comprehensively explains the possible obesity-mediated mechanisms, especially via physical factors, OS induction, endocrine modulation, immune alterations, and genetic and epigenetic changes, which may culminate in perturbed spermatogenesis, disrupted sperm DNA integrity, compromised sperm functions, and diminished semen quality, leading to impaired male reproductive functions.

Systematic Review of Literature Documenting the Link Between BMI, Sperm Parameters, and Leptin

Background: Leptin administration to rats causes adverse effects on sperm that resemble those reported in obese males. The purpose of this review is, therefore, to examine whether human and animal studies have taken this information on board and have attempted to link the poor sperm quality in obese or overweight individuals to leptin in their methodology, data analysis, and discussion. The review also documents the link between low sperm quality in the obese and leptin.

Method: A search was made for articles reporting body mass index (BMI), sperm parameters, and leptin, published until September 2020 in PubMed, Science Direct, Google Scholar, and Springer Link using a number of search terms.

Results: Forty-four of the 53 human and animal studies on BMI and sperm parameters reported abnormal sperm parameters in the obese but only 9 of those had measured serum leptin. None, however, attempted to link sperm abnormalities to leptin. Nine animal studies report of adverse effects of leptin on sperm in normal weight rats that were found to be similar to those reported in obese males.

Conclusion: Although none of the human studies had actually linked the raised leptin to sperm abnormalities in the obese, there is nevertheless, convincing evidence linking leptin to obesity-related poor sperm quality and male infertility. There is a need, therefore, to include measures that will help reduce the impact of raised leptin levels on male reproductive function, particularly, in obese infertile or subfertile males.

Measuring Reactive Oxygen Species in Semen for Male Preconception Care: A Scientist Perspective

Oxidative stress and elevated levels of seminal and sperm reactive oxygen species (ROS) may contribute to up to 80% of male infertility diagnosis, with sperm ROS concentrations at fertilization important in the development of a healthy fetus and child. The evaluation of ROS in semen seems promising as a potential diagnostic tool for male infertility and male preconception care with a number of clinically available tests on the market (MiOXSYS, luminol chemiluminescence and OxiSperm). While some of these tests show promise for clinical use, discrepancies in documented decision limits and lack of cohort studies/clinical trials assessing their benefits on fertilization rates, embryo development, pregnancy and live birth rates limit their current clinical utility. In this review, we provide an update on the current techniques used for analyzing semen ROS concentrations clinically, the potential to use of ROS research tools for improving clinical ROS detection in sperm and describe why we believe we are likely still a long way away before semen ROS concentrations might become a mainstream preconception diagnostic test in men.

Environmental and occupational exposures associated with male infertility

The upsurge in male infertility over the last two decades, possibly due to environmental exposure, has raised significant interest, particularly boosted by reports from fertility clinics, which showed that chronic diseases and hereditary or other medical conditions might only partially explain current incidence of male infertility. Both environmental and occupational settings may have a significant role in exposure to complex mixtures of endocrine disruptors (ED), which play a major role in fertility disorders. The aim of this review is to give an insight into the current knowledge on exposure settings which may be associated with male infertility. Our study relied on a systematic search of PubMed, Scopus, and Web of Science for articles published between January 2000 and September 2020. It showed that some well documented factors associated with male infertility include smoking, and physiological disturbances or chronic diseases such as obesity and diabetes, which in turn, may also reflect lifestyle choices and environmental exposures, especially to EDs such as phthalates, bisphenols, pesticides, and flame retardants. However, the number of studies on the aetiology of male infertility is still too low in comparison with the size of affected population. Occupational health follow-ups and medical surveillance do not collect any data on male infertility, even though ED chemicals are part of many technological processes.

Seminal and serum leptin levels in male patients with varicocele and isolated asthenozoospermia before and after repair

BACKGROUND AND AIM

Varicocele is one of the most common causes of male infertility. Leptin that has a role in sperm motility may have a role of varicocele. We aimed to study the effect of varicocelectomy on the serum and seminal leptin in patients with asthenozoospermia and the correlation between leptin levels, sperm parameters and varicocele grade.

METHODS

Thirty-six male patients with varicocele having isolated asthenozoospermia were included in this study. Thirty normal fertile controls were included. Semen analysis, serum and seminal leptin measurements were performed for all participants at baseline and for patients three months after varicocelectomy. Microsurgical varicocelectomy has been performed for patients.

RESULTS

Seminal and serum leptin levels were significantly higher in patients than controls. Seminal leptin was positively correlated with varicocele grade (r = 0.357, p < .05) while no correlation was found between serum leptin varicocele grade (r = 0.056, p = .37). Both seminal and serum leptin were inversely correlated with sperm motility (r = -0.92 and r = -0.87, p < .001; respectively). Seminal and serum leptin were significantly improved after varicocelectomy.

CONCLUSION

Varicocele is associated with higher levels of seminal and serum leptin especially in higher grads and this was correlated with negative effects on sperm motility. Leptin levels were significantly decreased after repair.

Pubertal development and reproductive hormone levels of singleton ICSI offspring in adolescence: results of a prospective controlled study

STUDY QUESTION

Are there any differences in the pubertal development and reproductive hormone status during adolescence between singletons following ICSI therapy or spontaneous conception (SC)?

SUMMARY ANSWER

Pubertal development and reproductive hormone levels are largely similar between ICSI and SC adolescents, except for a tendency towards lower inhibin B levels as well as significantly higher estradiol levels and a lower testosterone-to-estradiol-ratio in male adolescents.

WHAT IS KNOWN ALREADY

Previous data are scarce and partly inconclusive regarding pubertal development in female ICSI adolescents as well as demonstrating a tendency towards lower inhibin B serum levels in male ICSI offspring.

STUDY DESIGN, SIZE, DURATION

Prospective controlled study including 274 singleton ICSI-conceived adolescents (141 girls, 133 boys) followed up for the third time, and 273 SC controls (142 girls, 131 boys) from seven German registration offices (Aachen, Eichstätt, Erfurt, Lübeck, Hamburg, Heidelberg and Schwerin).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Pubertal development assessed by Tanner staging (breast, genital and pubic hair development), age at menarche and reproductive hormone levels were analyzed in ICSI and SC adolescents at the mean age of 16.5 years. Differences were analyzed by multinomial regression (Tanner stages) or t test and linear regression for hormonal assessments.

MAIN RESULTS AND THE ROLE OF CHANCE

Both female and male ICSI and SC adolescents showed adequate pubertal maturation according to their age, and the mean age at menarche (at 12.7 versus 12.8 years) was similar. Tanner stages as well did not display any relevant or significant differences between the groups. Reproductive hormone levels in female adolescents not using hormonal contraception were largely similar before and after adjustment for several factors such as preterm birth, Tanner stages, BMI or physical activity. In male ICSI adolescents, a tendency towards lower inhibin B (−14.8 pg/ml, 95% CI: −34.2 to 4.6 pg/ml), significantly higher estradiol (2.6 ng/l, 95% CI: 0.0 to 5.2 ng/l) and a significantly lower testosterone-to estradiol ratio (−0.047, 95% CI: −0.089 to −0.004) was found.

LIMITATIONS, REASONS FOR CAUTION

The all-over response rate and the willingness to participate in the blood test and medical examination were very low in the control group. Participating control families may have greater health awareness, and selection bias cannot be ruled out. Hormonal data in the females were measured irrespective of the cycle day and restricted to those not using hormonal contraception. Some parameters from the questionnaire data such as usage of hormonal contraception might suffer from reporting bias. As this is an observational study, we can draw only limited causal conclusions from the findings.

WIDER IMPLICATIONS OF THE FINDINGS

Differences in male reproductive hormones may indicate altered testicular function. However, at this time possible consequences for later reproductive success are unknown.

STUDY FUNDING/COMPETING INTEREST(S)

DFG research grant KA 1643/4-1. The authors declare no conflict of interest.

Chronic epididymitis and leptin and their associations with semen characteristics in men with infertility

PROBLEM

The aim of this study was to ascertain the associations between serum leptin levels and chronic epididymitis and semen parameters in patients with infertility.

METHOD OF STUDY

A total of 846 patients who were diagnosed as primary infertility were enrolled and divided into four groups. The general information, blood lipids, reproductive hormones, and semen parameters were collected. Receiver operating characteristic (ROC) curves of leptin were plotted for diagnosis of the poor sperm quality. We used Student's t test and the chi-squared test to analyze their relationships and used logistic regression analysis to evaluate potential confounding factors.

RESULTS

Receiver operating characteristic curve revealed that leptin had better sensitivity and specificity at the concentration of 6.02 (0.565 and 0.917). Isolated epididymitis or elevated leptin had no effect on sperm concentration and sperm membrane function, but the combination of these conditions would reduce the concentration and normal morphology rate both (P = 0.002, P = 0.005). Epididymitis or elevated leptin can affect the motility of sperms, the former presented more significance (P = 0.000), and the co-existence would further reduce the sperm motility (P = 0.001).

CONCLUSION

Low sperm motility and sperm normal morphology were found to be associated with chronic epididymitis and high leptin. Simultaneously suffering from chronic epididymitis and high leptin could produce a more serious effect on sperm quality.

Body fat content, fat distribution and adipocytokine production and their correlation with fertility markers in young adult men and women conceived by intracytoplasmic sperm injection (ICSI)

OBJECTIVE

Differences in body fat content during childhood and adolescence have been described in offspring conceived by in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI). However, data on body fat and its distribution as well as on adipocytokine production in young adults conceived by ICSI are nonexistent. We investigated if young adult men and women conceived by ICSI have a normal body fat patterning and adipocytokine production.

DESIGN

Cohort study.

PATIENTS

One hundred twenty-seven young adults conceived by ICSI and 138 peers born after spontaneous conception.

MEASUREMENTS

Anthropometric parameters (skinfold thickness, hip and waist circumferences), dual X-ray absorptiometry (whole body and regional) measurements and adipocytokine levels (leptin and adiponectin) were analysed in relation to fertility markers (serum anti-Mullerian hormone (AMH) and inhibin B).

RESULTS

While at age 18 years, a normal body fat distribution and normal leptin and adiponectin production was found in both male and female ICSI offspring, young men conceived by ICSI had a higher peripheral fat deposition in comparison with spontaneously conceived peers. No correlation between AMH and inhibin B with leptin or adiponectin was observed.

CONCLUSION

While men conceived by ICSI, but not women, had a higher peripheral fat deposition, body fat distribution as well as mean levels of adipocytokines were not affected by the mode of conception.

Review of the role of leptin in the regulation of male reproductive function

Since discovered in 1994, leptin has been thought to be a pleiotropic hormone that regulates food intake, controls energy balance in the body and influences multiple tissues in the body. Leptin plays an important mediating role in the regulation of neuroendocrine and can transmit the nutritional status signals to the reproductive-related central nervous system. Many studies have shown that leptin may play an important role in the control of reproductive function. Leptin can act on all levels of the hypothalamus-pituitary-gonadal (HPG) axis and may have local effects on the function of testis and spermatogenesis. Leptin is critical for puberty initiation and can also modulate testosterone synthesis by downregulating cAMP-dependent activation of steroidogenic genes expressions. Leptin is found to be higher in infertile men than in normal subjects. Yet, the exact role of leptin in the regulation of male reproductive function remains incomplete. The purpose of this review was to summarise the recent research about the biological effects of leptin on male reproductive system. In-depth study of leptin in reproductive system will help to reveal the pathogenesis of infertility and provide new treatment ideas for human assisted reproductive technology.

Decreased Implantation Number After In Utero Artificial Insemination Can Reflect an Impairment of Fertility in Adult Male Rats After Exogenous Leptin Exposure

Leptin is a protein secreted by the adipocytes, which serves as a link between fat and brain. Its main action is to decrease appetite and increase energy expenditure, but it is also involved in the control of different neuroendocrine systems, including gonadal axis. Although the effects of leptin deficiency on reproduction are well recognized, the effect of excess leptin on male reproductive function is not clear. The aim of this study was to evaluate fertility and sperm parameters of male rats exposed to exogenous leptin. A group of adult male rats received exogenous leptin intraperitoneally (30 μg/kg/day) for 42 days, and a control group received only the vehicle during the same period. After the treatment, animals were evaluated for sperm count, sperm motility, and fertility after intrauterine artificial insemination. There was no statistically significant difference between the groups related to sperm production, sperm concentration, and sperm motility. However, fertility evaluation after artificial insemination showed a quantitative decrease in the uterus plus fetuses weight, number of implantation sites, and number of live fetuses. The fertility potential showed a reduction of about 40%, whereas the preimplantation loss rate increased more than 2-fold in leptin-treated animals. In conclusion, leptin administration to nonobese male rats impairs ability of treated animals to generate offspring, since the occurrence of implantation was diminished. So leptin can impair sperm quality, affecting the reproductive capacity.

The Disappearing Sperms: Analysis of Reports Published Between 1980 and 2015

Reports regarding the changes in sperm concentration in different counties of the world are inconsistent. Furthermore, the reports that sprung up from specific epidemiological and experimental examinations did not include data of prior studies or geographical variations. The current study, following a previous report of massive fall in semen volume over the past 33 years, attempts to delineate the trend of altering sperm concentrations and factors responsible for this by reviewing article published from 1980 to July 2015 with geographic differences. The current study identified an overall 57% diminution in mean sperm concentration over the past 35 years ( r = -.313, p = .0002), which, when analyzed for each geographical region, identified a significant decline in North America, Europe, Asia, and Africa. An increasing trend of sperm concentration was identified only in Australia. The association of male age with such a trend ( R² = .979) is reported. The authors also correlated male fertility with sperm concentration. Thus, this comprehensive, evidence-based literature review aims to concisely and systematically present the available data on sperm concentration from 1980 to 2015, as well as to statistically analyze the same and correlate male health with the declining pattern of sperm count in a single scientific review to serve the scientific research zone related to reproductive health. It points to the threat of male infertility in times ahead.

Male obesity and subfertility, is it really about increased adiposity?

The prevalence of overweight and obesity in reproductive-aged men is increasing worldwide, with >70% of men >18 years classified as overweight or obese in some western nations. Male obesity is associated with male subfertility, impairing sex hormones, reducing sperm counts, increasing oxidative sperm DNA damage and changing the epigenetic status of sperm. These changes to sperm function as a result of obesity, are further associated with impaired embryo development, reduced live birth rates and increased miscarriage rates in humans. Animal models have suggested that these adverse reproductive effects can be transmitted to the offspring; suggesting that men's health at conception may affect the health of their children. In addition to higher adiposity, male obesity is associated with comorbidities, including metabolic syndrome, hypercholesterolemia, hyperleptinemia and a pro-inflammatory state, all which have independently been linked with male subfertility. Taken together, these findings suggest that the effects of male obesity on fertility are likely multifactorial, with associated comorbidities also influencing sperm, pregnancy and subsequent child health.

Obesity is associated with increased seminal insulin and leptin alongside reduced fertility parameters in a controlled male cohort

BACKGROUND

Obesity appears to be associated with male reproductive dysfunction and infertility, although this has been inconsistent and inconclusive. Insulin and leptin are known mediators and modulators of the hypothalamus-pituitary-testes axis, contributing to the regulation of male reproductive potential and overall wellbeing. These hormones are also present in semen influencing sperm functions. Although abdominal obesity is closely associated with insulin resistance (hyperinsulinaemia), hyperleptinaemia and glucose dysfunction, changes in seminal plasma concentrations of insulin, leptin and glucose in obese males has not previously been investigated.

METHODS

This small case controlled study assessed serum and seminal concentrations of insulin, leptin and glucose in obese (BMI > =30; n = 23) and non-obese (BMI < 30; n = 19) males. Following a detailed medical history and examination, participants meeting the inclusion criteria were entered for data analysis. Body parameters such as BMI, waist and hip circumference and the waist hip ratio were measured. Serum and semen samples were collected and assayed for insulin, leptin and glucose. Semen samples also underwent a standard semen analysis, with sperm mitochondrial membrane potential (MMP) and DNA fragmentation (DF).

RESULTS

Obesity was associated with increased serum and seminal insulin and leptin, with no significant difference in seminal glucose. Serum and seminal concentrations of insulin and leptin were positively correlated. Furthermore, obesity was associated with decreased sperm concentration, sperm vitality and increased MMP and DF, with a non-significant impact on motility and morphology.

CONCLUSIONS

Hyperinsulinaemia and hyperleptinaemia are associated with increased seminal insulin and leptin concentrations, which may negatively impact male reproductive function in obesity. Insulin was also found to be highly concentrated in the seminal plasma of both groups. This data will contribute to the contradictive information available in the literature on the impact of obesity and male reproduction.

The impact of obesity on male reproduction: its biological significance

Since obesity and male subfertility have increased in parallel during the last decades, the hypothesis of an association between these two phenomena has been explored by several researchers. Although there is no consensus apparently obesity impacts men's reproductive potential by several mechanisms, like alterations on the hypothalamus-pituitary-testicular axis, modifications of spermatogenesis and semen quality and/or impairment of men's sexual health. This review intends to summarize the underlying bases of such alterations and propose new ones, without miscalculating their biological significance. Obesity is not rigorously related to subfertility; in addition, the existence of a genetic predisposition to obesity-linked sterility is currently under investigation. Nonetheless, the impact of obesity on male reproductive potential must be fully elucidated since the prevalence of obesity is increasing and consequently, the number of obese men with reduced fertility will also rise.

BMI in relation to sperm count: an updated systematic review and collaborative meta-analysis

BACKGROUND The global obesity epidemic has paralleled a decrease in semen quality. Yet, the association between obesity and sperm parameters remains controversial. The purpose of this report was to update the evidence on the association between BMI and sperm count through a systematic review with meta-analysis. METHODS A systematic review of available literature (with no language restriction) was performed to investigate the impact of BMI on sperm count. Relevant studies published until June 2012 were identified from a Pubmed and EMBASE search. We also included unpublished data (n = 717 men) obtained from the Infertility Center of Bondy, France. Abstracts of relevant articles were examined and studies that could be included in this review were retrieved. Authors of relevant studies for the meta-analysis were contacted by email and asked to provide standardized data. RESULTS A total of 21 studies were included in the meta-analysis, resulting in a sample of 13 077 men from the general population and attending fertility clinics. Data were stratified according to the total sperm count as normozoospermia, oligozoospermia and azoospermia. Standardized weighted mean differences in sperm concentration did not differ significantly across BMI categories. There was a J-shaped relationship between BMI categories and risk of oligozoospermia or azoospermia. Compared with men of normal weight, the odds ratio (95% confidence interval) for oligozoospermia or azoospermia was 1.15 (0.93-1.43) for underweight, 1.11 (1.01-1.21) for overweight, 1.28 (1.06-1.55) for obese and 2.04 (1.59-2.62) for morbidly obese men. CONCLUSIONS Overweight and obesity were associated with an increased prevalence of azoospermia or oligozoospermia. The main limitation of this report is that studied populations varied, with men recruited from both the general population and infertile couples. Whether weight normalization could improve sperm parameters should be evaluated further.

Functional relationship between obesity and male reproduction: from humans to animal models

BACKGROUND

The increase in the incidence of obesity has a substantial societal health impact. Contrasting reports have been published on whether overweight and obesity affect male fertility. To clarify this, we have reviewed published data on the relation between overweight/obesity, semen parameters, endocrine status and human male fertility. Subsequently, we have used results obtained in animal models of obesity to explain the human data.

METHODS

Pubmed, Scopus, Web of Science and Google Scholar databases were searched between September 2009 and October 2010 for a comprehensive publication record. Available studies on adult human males were examined. The included animal studies examined obesity and fertility, and focused on leptin, leptin receptor signaling, kisspeptins and/or NPY.

RESULTS

Most overweight/obese men do not experience significant fertility problems, despite the presence of reduced testosterone alongside normal gonadotrophin levels. Only a subgroup of subjects suffers from hypogonadotropic hypogonadism. Animal models offer several explanations and show that reduced leptin signaling leads to reduced GnRH neuronal activity. This may be due to decreased hypothalamic Kiss1 expression, a potent regulator of GnRH/LH/FSH release. As the Kiss1 neurons express leptin receptors, the Kiss1 system may participate in transmitting metabolic information to the GnRH neurons, thus providing a bridge between metabolic regulation and fertility.

CONCLUSIONS

Infertility in overweight/obese males may be explained by leptin insensitivity. This implies a possible role for the KISS1 system in human obesity-related male infertility. If substantiated, it will pave the way for methods to restore fertility in these subjects.

Mechanisms of obesity-induced male infertility

Male infertility, characterized by hypogonadism, decreased semen quality or ejaculatory dysfunction, accounts for approximately 20% of infertility cases. Obesity and metabolic dysfunction have been identified, among other causal factors, to contribute to male infertility. In the context of the Western world's 'obesity epidemic', this article discusses three main biological mechanisms linking obesity to impaired male reproductive function: hypogonadism, testicular heat stress/hypoxia-induced apoptosis and endocrine disruption by 'obesogens'. Among these, obesity-induced hypogonadism is undoubtedly the most clinically significant and is easily assessed. Rapidly expanding areas of research in this area include leptin modulation of kisspeptins and hypothalamic-pituitary-testicular hormone pathways, and roles of other adipocytokines in male infertility, as well as the impact of exposure to obesogens on the quality of semen.

The effect of obesity on sperm disorders and male infertility

The results of several studies point to an increased likelihood of abnormal semen parameters among overweight men, and an elevated risk for subfertility among couples in which the male partner is obese. Obesity is, therefore, associated with a higher incidence of male factor infertility. Several mechanisms might account for the effect of obesity on male infertility, both directly and indirectly, by inducing sleep apnea, alterations in hormonal profiles (reduced inhibin B and androgen levels accompanied by elevated estrogen levels) and increased scrotal temperatures, ultimately manifesting as impaired semen parameters (decreased total sperm count, concentration and motility; increased DNA fragmentation index). Neither the reversibility of obesity-associated male infertility with weight loss nor effective therapeutic interventions have been studied in-depth. The increasing prevalence of obesity calls for greater clinical awareness of its effects on fertility, better understanding of underlying mechanisms, and exploration into avenues of treatment.

Semen parameters and hormonal profile in obese fertile and infertile males

OBJECTIVE

To study the changes in semen parameters, gonadotropic and sex hormones, and serum leptin in obese fertile and infertile oligozoospermic men.

DESIGN

Prospective.

SETTING

University hospital.

PATIENT(S)

Forty-two obese fertile and 80 obese infertile oligozoospermic men (body mass index [BMI] >30).

INTERVENTION(S)

The BMI calculation, semen analysis, and serum FSH, LH, T, E(2), PRL, and leptin estimation.

MAIN OUTCOME MEASURE(S)

Semen and hormonal profiles.

RESULT(S)

Obese oligozoospermic patients had significant increase in mean BMI, serum FSH, LH, E(2), PRL, and leptin compared with obese fertile controls. The BMI had significant positive correlation with abnormal sperm morphology, LH, serum leptin and significant negative correlation with sperm concentration, sperm motility, serum T. Serum leptin demonstrated significant positive correlation with patients' age, abnormal sperm morphology, serum FSH, LH, PRL and significant negative correlation with sperm concentration, sperm motility, and serum T.

CONCLUSION(S)

Serum leptin mediates a link between obesity and male infertility.