Canadian semen quality: an analysis of sperm density among eleven academic fertility centers

Impact of Nanoparticles on Male Fertility: What Do We Really Know? A Systematic Review

The real impact of nanoparticles on male fertility is evaluated after a careful analysis of the available literature. The first part reviews animal models to understand the testicular biodistribution and biopersistence of nanoparticles, while the second part evaluates their in vitro and in vivo biotoxicity. Our main findings suggest that nanoparticles are generally able to reach the testicle in small quantities where they persist for several months, regardless of the route of exposure. However, there is not enough evidence that they can cross the blood-testis barrier. Of note, the majority of nanoparticles have low direct toxicity to the testis, but there are indications that some might act as endocrine disruptors. Overall, the impact on spermatogenesis in adults is generally weak and reversible, but exceptions exist and merit increased attention. Finally, we comment on several methodological or analytical biases which have led some studies to exaggerate the reprotoxicity of nanoparticles. In the future, rigorous clinical studies in tandem with mechanistic studies are needed to elucidate the real risk posed by nanoparticles on male fertility.

Geographic variation in semen parameters from data used for the World Health Organization semen analysis reference ranges

OBJECTIVE

To study geographic variations in sperm parameters using data from the trials that defined the reference ranges of the World Health Organization 2021 manual.

DESIGN

Retrospective evaluation of the data used to define the World Health Organization reference ranges.

SETTING

Not applicable.

PATIENT(S)

Data from 11 studies, including 3,484 participants across 5 continents.

INTERVENTION(S)

The data were divided according to geographic locations.

MAIN OUTCOME MEASURE(S)

Differences in sperm parameters.

RESULT(S)

The semen volume was significantly lower in samples from Asia and Africa than in other regions. The sperm concentration was the lowest in Africa and highest in Australia. The total motile sperm count (TMSC) and total motile progressive sperm count (TMPS) were significantly lower in Africa than in other regions. The TMSC and TMPS in Asia and the United States were significantly lower than in Europe and Australia. The 5th percentile of the sperm concentration was lowest in the United States (12.5 × 10⁶/mL). The 5th percentile for the normal sperm morphology was lowest in the United States (3%) and highest in Asia (5%). The 5th percentile for the TMSC and TMPS were lowest in Africa (TMSC, 15.08 million; TMPS, 12.06 million) and the United States (TMSC, 18.05 million; TMPS, 16.86 million) and highest in Australia (TMSC, 29.61 million; TMPS, 25.80 million).

CONCLUSION(S)

Significant geographic differences in sperm parameters exist, and regional fertility societies should consider adding their own reference ranges on the basis of local experience and treatment outcomes.

Spatiotemporal trends in human semen quality

Over the past four decades, studies of various designs have reported spatial and temporal trends in human semen quality. Several standardized-methodology studies in homogeneous populations that compare specific cities within a country or a continent provide clear evidence of geographical differences in sperm production, even over short distances within the same country. Human sperm production is widely believed to be declining over time, but evidence from the scientific literature is less clear. Studies based on repeated cross-sectional data from a single centre have shown mixed results. Among the numerous retrospective studies conducted in a single centre, only some included homogeneous groups of men and appropriate methods, and most of them suggest a temporal decrease in human sperm production in the geographical areas considered. Conclusions reporting temporal trends in sperm production that came from existing retrospective multicentre studies based on individual semen data and those using means, medians or estimates of sperm production are questionable, owing to intrinsic limitations in the studies performed. Regardless of study design, studies on the percentage of motile or morphologically normal spermatozoa are still limited by the inherent variability in assessment. Overall, available data do not enable us to conclude that human semen quality is deteriorating worldwide or in the Western world, but that a trend is observed in some specific areas. To understand these trends and contrasts in sperm and semen quality, prospective studies should be encouraged and combined with assessment of the male exposome.

Several studies over the past few decades have suggested that sperm quality varies by geographical region and might be subject to a temporal decline worldwide. However, the data supporting these conclusions have come from studies of various methodologies and heterogeneous populations, making them unreliable. In this in-depth Review, Chevrier and colleagues discuss the data surrounding discussion of spatiotemporal trends in semen parameters and consider how these trends and the factors promoting them interact.

The vast literature on human semen quality trends is extremely heterogeneous in terms of the populations studied and study designs, and so these studies have been unable to draw firm conclusions.

Understanding the data around spatiotemporal semen trends requires a focus on the methodological choices and application of criteria to filter findings from the studies with optimal design.

Numerous appropriately designed studies suggest unambiguous geographical contrasts in human sperm production; however, evidence of a decline in sperm production is reliable only in specific populations and cities in which studies with a complete set of quality criteria have been conducted.

By contrast, suggestions of a worldwide drop in human semen quality on the basis of retrospective multicentre studies cannot be substantiated, owing to intrinsic limitations in the studies performed.

Many and varied factors of variation, in particular the diverse modalities of assessment, do not enable us to conclude that clear temporal trends of sperm motility and normal morphology are present.

Progress in our understanding of the highlighted trends and their causal factors requires prospective studies that minimize all known biases combined with the assessment of men’s exposome.

Hope for male fecundity: clinically insignificant changes in semen parameters over 10 years at a single clinic while assessing an infertility population

PURPOSE

What is the trend in sperm parameters in a group of men attending a single reproductive center, over a 10-year period?

METHODS

A retrospective study was conducted on 12,188 semen samples obtained from unique individuals who attended a university reproductive clinic from 2009 to 2018, inclusively. Semen analysis was done using computer-assisted sperm analysis and verified by an andrologist. Analysis was done after dividing the dataset into two groups: above WHO 2010 lower reference limits (ARL) (N = 6325) and below the reference limits (BRL) (N = 5521).

RESULTS

Volume increased slightly (ARL, p = 0.049) before returning to baseline or was stable (BRL, p = 0.59). Sperm concentration and total count of the BRL and ARL group declined initially and then recovered slightly (p < 0.0001, in all cases). Although these changes were statistically significant, this was due to the large study population; clinically, these changes were quite mild and would not have been significant for fertility. Sperm total motility and progressive motility of both the BRL group and the ARL group increased slightly from 2009 until 2015 and then decreased back to baseline (p < 0.0001). This change offset the decrease in count seen in those years. A spurious change was observed with sperm morphology that declined after the first 2 years and remained stable thereafter (p < 0.0001, in both groups). However, this change was attributed to a contemporaneous change in the method of analyzing strict morphology which happened when the change occurred.

CONCLUSION

While statistically significant changes were found, clinically, these changes were quite mild and would not have been significant for fertility.

One size does not fit all: variations by ethnicity in demographic characteristics of men seeking fertility treatment across North America

OBJECTIVE

To compare racial differences in male fertility history and treatment.

DESIGN

Retrospective review of prospectively collected data.

SETTING

North American reproductive urology centers.

PATIENT(S)

Males undergoing urologist fertility evaluation.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Demographic and reproductive Andrology Research Consortium data.

RESULT(S)

The racial breakdown of 6,462 men was: 51% White, 20% Asian/Indo-Canadian/Indo-American, 6% Black, 1% Indian/Native, <1% Native Hawaiian/Other Pacific Islander, and 21% "Other". White males sought evaluation sooner (3.5 ± 4.7 vs. 3.8 ± 4.2 years), had older partners (33.3 ± 4.9 vs. 32.9 ± 5.2 years), and more had undergone vasectomy (8.4% vs. 2.9%) vs. all other races. Black males were older (38.0 ± 8.1 vs. 36.5 ± 7.4 years), sought fertility evaluation later (4.8 ± 5.1 vs. 3.6 ± 4.4 years), fewer had undergone vasectomy (3.3% vs. 5.9%), and fewer had partners who underwent intrauterine insemination (8.2% vs. 12.6%) compared with all other races. Asian/Indo-Canadian/Indo-American patients were younger (36.1 ± 7.2 vs. 36.7 ± 7.6 years), fewer had undergone vasectomy (1.2% vs. 6.9%), and more had partners who underwent intrauterine insemination (14.2% vs. 11.9%). Indian/Native males sought evaluation later (5.1 ± 6.8 vs. 3.6 ± 4.4 years) and more had undergone vasectomy (13.4% vs. 5.7%).

CONCLUSION(S)

Racial differences exist for males undergoing fertility evaluation by a reproductive urologist. Better understanding of these differences in history in conjunction with societal and biologic factors can guide personalized care, as well as help to better understand and address disparities in access to fertility evaluation and treatment.

Decline in semen concentration of healthy Chinese adults: evidence from 9357 participants from 2010 to 2015

The present study aims to analyze sperm concentration trends among young and healthy Chinese adults in Wuhan, Central China, from 2010 to 2015. Semen analysis data from 9357 participants were collected and analyzed using a general linear model and the Cochran–Armitage trend test. A significant decline was observed in sperm concentration (β [standard deviation]: −1.53 [0.16]; P < 0.001). In addition, a decline in sperm density was observed by stratifying student versus nonstudent sperm donors and by analyzing the year of birth or birth year cohort of the participants. Furthermore, the percentage of participants with sperm densities of over 40 × 10⁶ ml⁻¹ significantly decreased with year. Notably, a dramatic decline in sperm density was recorded over the first 5 years of study. This research reported a decline in sperm concentration among young adults in Wuhan, Central China, in 2010–2015.

Declining Sperm Counts… or Rather Not? A Mini Review

Importance

Temporal global trends of sperm quality remain a matter of debate.

Objective

The aim of this study was to present a comprehensive review of studies reporting on sperm quality counts, summarize the main end points, and assess the main reasons for potential discrepancies.

Evidence Acquisition

An evidence-based review of PubMed and Scopus databases was performed regarding studies reporting on modification of sperm quality counts, independently of study character, study language, or date.

Results

Since the meta-analysis of Carlsen et al in 1992 (Br Med J 1992;305:609-613) that suggested an annual decline in sperm count of 1%, several reports confirmed the decline in sperm quality, whereas others disproved them, suggesting a slight increase or absence of change in sperm count. Such controversies may be attributed to geographical and time-related variability in sperm values and also to several confounding factors that influence the semen parameters. Intrinsic weaknesses of the studies include heterogeneity of subjects recruited, lack of adjustment for confounding factors, and samples that do not always represent the general population.

Conclusions

No consensus exists on whether sperm counts actually decrease because studies' results are often controversial or inconclusive with methodological deficiencies. More prospective, large-scale, population based studies are needed in order to provide sound evidence of possible global trends in sperm count.

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.

Changes in the semen quality among 5739 men seeking infertility treatment in Northern Norway over past 20 years (1993–2012)

Semen quality plays a pivotal role in sustaining the fertility rate and healthy population growth. Therefore, assessment of temporal trends in the semen quality provides valuable public health information. We analyzed the semen quality parameters of 5739 North Norwegian men among consecutive couples attending the fertility clinic of University Hospital of North Norway for investigation and/or treatment from 1993 to 2012. The seminal fluid volume, sperm concentration, and total sperm count were found to have gradually decreased during the past 20 years. The proportion of hypospermic, azoospermic, and oligozoospermic men had increased by 24.6% ( p < 0.001), 109.5% ( p < 0.001), and 9.5% ( p = 0.05), respectively, in the last decade (2003–2012) compared to the first decade (1993–2002). The parameters of semen quality are rapidly deteriorating in North Norwegian men seeking fertility treatment.

The reference values for semen parameters of 1213 fertile men in Guangdong Province in China

Semen samples were collected from 1213 fertile men whose partners had a time-to-pregnancy (TTP) ≤12 months in Guangdong Province in Southern China, and semen parameters including semen volume, sperm concentration, total counts, motility, and morphology were evaluated according to the World Health Organization (WHO) 2010 guideline. All semen parameters analyzed were normal in ~62.2% of the total samples, whereas ~37.8% showed at least one of the semen parameters below normal threshold values. The fifth centiles (with 95% confidence intervals) were 1.3 (1.2–1.5) ml for semen volume, 20 × 10⁶ (18×10⁶–20×10⁶) ml⁻¹ for sperm concentration, 40 × 10⁶ (38×10⁶–44×10⁶) per ejaculate for total sperm counts, 48% (47%–53%) for vitality, 39% (36%–43%) for total motility, 25% (23%–27%) for sperm progressive motility, 5.0% (4%–5%) for normal morphology. The pH values ranged from 7.2 to 8.0 with the mean ± standard deviation at 7.32 ± 0.17. No effects of age and body mass index were found on semen parameters. Occupation, smoking and alcohol abuse, varicocele appeared to decrease semen quality. Sperm concentration, but not sperm morphology, is positively correlated with TTP, whereas vitality is negatively correlated with TTP. Our study provides the latest reference values for the semen parameters of Chinese fertile men in Guangdong Province, which are close to those described in the new WHO guidelines (5^th Edition).

Decline in semen quality among infertile men in Brazil during the past 10 years

PURPOSE

To investigate whether the semen quality of men undergoing conventional semen analysis is deteriorating over time.

MATERIALS AND METHODS

We analyzed and compared the sperm count, motility and morphology of 2300 semen samples provided by males undergoing conventional seminal analysis, from years 2000 to 2002 and 2010 to 2012. The incidences of severe oligozoospermia and azoospermia over time were also compared.

RESULTS

A total of 764 sperm samples were analyzed in 2000-2002 and 1536 in 2010-2012. Over time, the mean sperm concentration/ml decreased significantly from 61.7 million in 2000-2002 to 26.7 million in 2010-2012 (R2 = 11.4%, p < 0.001), the total sperm concentration decreased significantly from 183.0 million to 82.8 million (R2 = 11.3%, p < 0.001), and the percentage of normal forms decreased significantly from 4.6% to 2.7% (R2 = 9.8%, p < 0.001). The incidence of severe oligozoospermia significantly increased from 15.7% to 30.3% (OR: 1.09, p < 0.001) and the incidence of azoospermia increased from 4.9% to 8.5% (OR: 1.06, p = 0.001).

CONCLUSIONS

This study demonstrated a significant time-related decline in semen quality of infertile patients. This finding might have implications on fertility and emphasizes the need for further studies addressing subject's life-style in order to find and reduce the causative agents. Future prospective and multicenter studies including representative samples of the general population are needed to confirm whether semen quality is really declining.

Shedding light on the controversy surrounding the temporal decline in human sperm counts: a systematic review

We systematically examined the evidence of declining sperm counts and the hypothesis that an increased exposure to environmental pollutants is responsible for such decline. Search engines, including PUBMED, MEDLINE, EMBASE, BIOSIS, and Cochrane library, were used to identify epidemiologic studies published from 1985 to 2013. We concluded that there is no enough evidence to confirm a worldwide decline in sperm counts. Also, there seems to be no scientific truth of a causative role for endocrine disruptors in the temporal decline of sperm production. Such assumptions are based on few meta-analyses and retrospective studies, while other well-conducted researches could not confirm these findings. We acknowledge that difficult-to-control confounding factors in the highly variable nature of semen, selection criteria, and comparability of populations from different time periods in secular-trend studies, the quality of laboratory methods for counting sperm, and apparently geographic variations in semen quality are the main issues that complicate the interpretation of the available evidence. Owing to the importance of this subject and the uncertainties still prevailing, there is a need not only for continuing monitoring of semen quality, reproductive hormones, and xenobiotics, but also for a better definition of fecundity.

Environmental toxins

This review comprehensively summarizes the effects of more than 15 mostly used pesticides on male reproductive physiology, as recent experimental and epidemiological research have indicated their alarming impact on overall human health. Mechanisms have described that pesticide exposure damages spermatozoa, alter Sertoli or Leydig cell function, both in vitro and in vivo and thus affects semen quality. But, the literature suggests a need for more intricate research in those pesticides that are defined as mutagens or carcinogens and directly affect the hypothalamic–pituitary–gonadal axis. This literature review also proposes specific solutions to overcome these health effects.

Semen quality of fertile Japanese men: a cross-sectional population-based study of 792 men

OBJECTIVES

To establish a base line for future studies on temporal trends, to describe potential geographical differences in semen quality and reference values for studies of men from the general population.

DESIGN

Cross-sectional study of fertile men from four areas in Japan. Inclusion criteria were: age 20-45 years at the time of invitation, and both the man and his mother had to be born in Japan. Additionally, the current pregnancy of the female partner had to be achieved by normal sexual relations without any fertility treatment.

SETTING

Four Japanese study centres at urban areas located in Sapporo, Osaka, Kanazawa and Fukuoka.

PARTICIPANTS

792 men, median age 31.4 years, included from 1999 to 2002.

OUTCOME MEASURES

Semen volume, sperm concentration, total sperm count, sperm motility and sperm morphology.

RESULTS

Semen volumes, percentages of motile spermatozoa and morphologically normal spermatozoa differed slightly between the four groups, whereas no differences in sperm concentrations or total sperm counts were found. In total, 1.2% of men had a sperm concentration below 5 million/ml, 2.1% below 10 million/ml, 3.5% below 15 million/ml and 16.3% below 40 million/ml. For morphology, 14.7% had less than 5% normal spermatozoa. Reproductive hormone levels varied significantly, however, only little from a biological point of view.

CONCLUSIONS

This is the first cross-sectional study on semen quality covering fertile men from the major regions of Japan. It showed that semen quality of fertile Japanese men is comparable to that of the best in European regions. The results may serve as reference values for studies of men from the general population.

Epigenetic mechanisms in the actions of endocrine-disrupting chemicals: gonadal effects and role in female reproduction

There is a heightened interest and concern among scientists, clinicians and regulatory agencies as well as the general public, regarding the effects of environmental endocrine-disrupting chemicals (EDCs). In this review, we identify the main epigenetic mechanisms and describe key ovarian processes that are vulnerable to the epigenetic actions of EDCs. We also provide an overview of the human epidemiological evidence documenting the detrimental effects of several common environmental EDCs on female reproduction. We then focus on experimental evidence demonstrating the epigenetic effects of these EDCs in the ovary and female reproductive system, with an emphasis on methoxychlor, an organochlorine pesticide. We conclude the review by describing several critical issues in studying epigenetic effects of EDCs in the ovary, including transgenerational epigenetic effects.

Dioxin-induced changes in epididymal sperm count and spermatogenesis

A single in utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on gestation day 15 decreased epididymal sperm count in adult rats and thus was used to establish a tolerable daily intake for TCDD. However, several laboratories have been unable to replicate these findings. Moreover, conflicting reports of TCDD effects on daily sperm production suggest that spermatogenesis may not be as sensitive to the adverse effects of TCDD as previously thought. We performed a PubMed search using relevant search terms linking dioxin exposure with adverse effects on reproduction and spermatogenesis. Developmental exposure to TCDD is consistently linked with decreased cauda epididymal sperm counts in animal studies, although at higher dose levels than those used in some earlier studies. However, the evidence linking in utero TCDD exposure and spermatogenesis is not convincing. Animal studies provide clear evidence of an adverse effect of in utero TCDD exposure on epididymal sperm count but do not support the conclusion that spermatogenesis is adversely affected. The mechanisms underlying decreased epididymal sperm count are unknown; however, we postulate that epididymal function is the key target for the adverse effects of TCDD.

Les différentes anomalies de la reproduction masculine sont-elles en augmentation ? Faits et controverses, possibles facteurs en cause: une analyse actualisée des données de la littérature et des registres

Au cours des dernières décennies, de nombreuses observations dans la faune sauvage d’anomalies relatives à l’appareil génital et à la fonction de reproduction mâle, certaines évoquant les données de la toxicologie expérimentale, ont conduit à s’interroger sur la toxicité de facteurs environnementaux pour la reproduction de l’homme. De plus, un certain nombre d’études suggère une augmentation de la prévalence des troubles de la reproduction de l’homme adulte au cours des dernières décennies dans de nombreux pays développés. Les données les mieux documentées concernent le cancer du testicule, son rythme de croissance suggérant le rôle de facteurs environnementaux et/ou de mode de vie. Toutefois, des différences régionales et ethniques considérables dans les taux d’incidence absolue pourraient impliquer des facteurs génétiques concomitants. Parallèlement, il semble que la qualité du sperme a diminué dans de nombreux pays, à en juger aussi bien par des méta-analyses que par des analyses statistiques de données d’un seul centre. Au début des années 2000, Skakkebæk et al. à Copenhague ont formulé l’hypothèse d’une origine commune à ces différentes anomalies lors du développement du testicule durant la gestation. Existe-t-il pour ces différentes conditions des données indiquant un lien de causalité avec une exposition environnementale/professionnelle à des composés reprotoxiques ? Ne serait-ce plutôt l’exposition chronique à de très nombreux composés chimiques à faible dose qui pourrait être impliquée ? Les facteurs de style de vie jouent-ils un rôle ? L’ensemble de ces questions se fondant sur une somme d’études, dont les résultats sont loin d’être univoques, a été la source de nombreux débats aussi bien au sein de la communauté scientifique que dans les médias. Les meilleures réponses possibles à ces questions complexes sont naturellement fondamentales pour les instances en charge de l’évaluation du risque et les politiques de santé publique qu’il convient d’adopter. La présente revue donne un état des lieux actualisé de ces questions.

Oxidative stress and antioxidants for idiopathic oligoasthenoteratospermia: Is it justified?

Oxidative stress contributes to defective spermatogenesis and the poor quality of sperm associated with idiopathic male factor infertility. The aim of this study was to review the current literature on the effects of various types of antioxidant supplements in patients to improve fertilization and pregnancy rates in subfertile males with idiopathic oligoasthenoteratozoospermia (iOAT). Review of recent publications through PubMed and the Cochrane database. Oxidative stress is implicated in impaired spermatogenesis leading to the poor semen parameters and increased DNA damage and apoptosis in iOAT. Strategies to modulate the level of oxidative stress within the male reproductive tract include the use of oral antioxidant compounds to reinforce the body's defence against oxidative damage. In our evaluation, carnitines were considered the most established pharmacotherapeutic agent to treat iOAT, as evidence and data concerning carnitine supplementation have been shown to be most consistent and relevant to the population of interest. Other therapies, such as combined vitamin E and C therapy, are still considered controversial as vitamin C can act as a pro-oxidant in certain instances and the results of randomized controlled trials have failed to show significant benefit to sperm parameters and pregnancy rates. There is a need for further investigation with randomized controlled studies to confirm the efficacy and safety of antioxidant supplementation in the medical treatment of idiopathic male infertility as well as the need to determine the dosage required to improve semen parameters, fertilization rates and pregnancy outcomes in iOAT.

Alcohol, drugs, caffeine, tobacco, and environmental contaminant exposure: reproductive health consequences and clinical implications

Reproductive function and fertility are thought to be compromised by behaviors such as cigarette smoking, substance abuse, and alcohol consumption; however, the strength of these associations are uncertain. Furthermore, the reproductive system is thought to be under attack from exposure to environmental contaminants, particularly those chemicals shown to affect endocrine homeostasis. The relationship between exposure to environmental contaminants and adverse effects on human reproductive health are frequently debated in the scientific literature and these controversies have spread into the lay press drawing increased public and regulatory attention. Therefore, the objective of the present review was to critically evaluate the literature concerning the relationship between lifestyle exposures and adverse effects on fertility as well as examining the evidence for a role of environmental contaminants in the purported decline of semen quality and the pathophysiology of subfertility, polycystic ovarian syndrome, and endometriosis. The authors conclude that whereas cigarette smoking is strongly associated with adverse reproductive outcomes, high-level exposures to other lifestyle factors are only weakly linked with negative fertility impacts. Finally, there is no compelling evidence that environmental contaminants, at concentrations representative of the levels measured in contemporary biomonitoring studies, have any effect, positive or negative, on reproductive health in the general population. Further research using prospective study designs with robust sample sizes are needed to evaluate testable hypotheses that address the relationship between exposure and adverse reproductive health effects.

Dioxin-induced changes in epididymal sperm count and spermatogenesis

BACKGROUND

A single in utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on gestation day 15 decreased epididymal sperm count in adult rats and thus was used to establish a tolerable daily intake for TCDD. However, several laboratories have been unable to replicate these findings. Moreover, conflicting reports of TCDD effects on daily sperm production suggest that spermatogenesis may not be as sensitive to the adverse effects of TCDD as previously thought.

DATA SOURCES

We performed a PubMed search using relevant search terms linking dioxin exposure with adverse effects on reproduction and spermatogenesis.

DATA SYNTHESIS

Developmental exposure to TCDD is consistently linked with decreased cauda epididymal sperm counts in animal studies, although at higher dose levels than those used in some earlier studies. However, the evidence linking in utero TCDD exposure and spermatogenesis is not convincing.

CONCLUSIONS

Animal studies provide clear evidence of an adverse effect of in utero TCDD exposure on epididymal sperm count but do not support the conclusion that spermatogenesis is adversely affected. The mechanisms underlying decreased epididymal sperm count are unknown; however, we postulate that epididymal function is the key target for the adverse effects of TCDD.

Temporal trends in bull semen quality: a comparative model for human health?

INTRODUCTION

A decline in human semen quality over the past 30-60 years has been reported in numerous epidemiological studies from the United States and Europe. We evaluated temporal trends in semen quality parameters in dairy bulls. The long-term management of dairy bulls for artificial insemination presented a unique opportunity to evaluate temporal trends in semen quality and explore this relationship as a potential animal model for reproductive abnormalities in humans.

MATERIALS AND METHODS

Bull semen analysis data from 1965 through 1995 were collected from a large artificial insemination organization. Semen analyses from 12- to 18-month-old Holstein dairy bulls were included in the study and consisted of daily sperm concentration, daily ejaculate volume, total daily sperm output, percentage of sperm with normal morphology, and percentage of sperm with normal post-thaw motility. Multiple regression analysis, logistic regression, and general linear modeling were used to determine temporal trends over the 30-year period.

RESULTS AND DISCUSSION

Semen quality appears to have declined from 1970 to 1980 or 1985 as manifested by declines in daily ejaculate volume, daily sperm concentration, and total daily sperm output. In contrast, sperm morphology and motility improved over the same period. In approximately 1980 or 1985, depending on the parameter, ejaculate volume, sperm concentration, total sperm, and motility improved. However, normal morphology began to deteriorate during this same period. Methodological inconsistencies over time introduce uncertainty in analyses of temporal trends in semen quality in this and previous human studies. However, changes in technology do not appear to be solely responsible for the temporal trends observed. The source of the decline in semen quality in the bulls studied is unknown. If the decline in semen quality were due to exposure to endocrine disrupting chemicals, then a continued decline or a leveling-off would be expected. Instead, a rise in semen quality was observed during the latter portion of the observation period.

Human exposure to endocrine disrupters and semen quality

Reproductive pathology in the male represents about 20% of infertility cases. Male infertility may be attributed to a number of causes, including genetic and congenital abnormalities, infection, multisystemic diseases, varicocele, and others; however, a significant number of cases are idiopathic. Global declines in semen quality were suggested to be associated with enhanced exposure to environmental chemicals that act as endocrine disrupters as a result of our increased use of pesticides, plastics, and other anthropogenic materials. A significant body of toxicology data based upon laboratory and wildlife animals studies suggests that exposure to certain endocrine disrupters is associated with reproductive toxicity, including (1) abnormalities of the male reproductive tract (cryptorchidism, hypospadias), (2) reduced semen quality, and (3) impaired fertility in the adult. There is, however, a relative paucity of studies designed to measure exposure to endocrine disrupters on semen quality parameters (sperm concentration, motility, morphology). An overview of the human semen quality literature is presented that examines the role of endocrine disrupters including organochlorines (OC), dioxins, phthalates, phytoestrogens, and chemical mixtures (pesticides and tobacco smoke).

Environmental contaminants and human infertility: hypothesis or cause for concern?

Throughout the 1980s and 1990s the crude human birth rate (live births per 1000 population) declined, indicating reduced fertility and suggesting a potential decline in fecundity (the potential to conceive). Detection of environmental contaminants in human tissues, together with reports of a global decline in semen quality, further fueled speculation that human infertility rates are increasing and environmental toxicants are potentially important causal agents associated with this change. However, there is little compelling evidence to suggest that infertility rates amongst the general population have changed over time. Moreover, recent studies suggest a rise in the fertility rates. While several studies documented increased time to pregnancy (TTP) in exposed study populations, other investigators were not able to replicate these findings. Nevertheless, studies involving occupational exposure together with results from animal experiments lend support to the conclusion that environmental contaminants potentially adversely affect fertility. Consequently, the impact of exposure to environmental contaminants on human fertility remains controversial. To test the hypothesis that environmental contaminant exposure was associated with enhanced risk of infertility, data concerning trends in fertility and infertility rates were examined to assess the impact of exposure of developing gametes to environmental contaminants. The relationship between exposure and reproductive outcomes was then examined to illustrate the range of adverse effects for reproductive toxicants with data sets of divergent depth and reliability. Data showed that only a weak association between exposure to environmental contaminants and adverse effects on human fertility exists. However, it is postulated that evidence of chemical exposure and potential health consequences of these exposures highlight the need for further research in this area.

Is sperm evaluation useful in predicting human fertility?

Traditionally, the diagnosis of male infertility has relied upon microscopic assessment and biochemical assays to determine human semen quality. The conventional parameters given most importance have been the concentration, motility, and morphology of sperm in the ejaculate. Most laboratories also include ‘sperm suitability’ tests where the subpopulations of sperm more likely to finish the marathon journey to the oocyte are separated by density centrifugation. These tests are essential to provide the fundamental information on which clinicians base their initial diagnosis. However, none of these parameters addresses sperm function and their clinical value in predicting fertility is questionable. The advent of intracytoplasmic sperm injection (ICSI) has further reduced the significance and perceived need for sperm quality tests since ICSI requires only one sperm, not subject to classic, or indeed any, tests for the procedure to be successful. Over the past decade, a number of laboratory tests have been developed to determine properties of sperm function. These include quantitative sperm motion parameters, capacitation, basal and induced acrosome reactions, sperm–zona pellucida interactions and nuclear and mitochondrial sperm DNA but few have been adopted into routine clinical use. International collaborations should be initiated to develop clinically relevant molecular and functional tests with agreed protocols and clinical thresholds as a matter of urgency.

Male idiopathic oligoasthenoteratozoospermia

Idiopathic oligoasthenoteratozoospermia (iOAT) affects approximately 30% of all infertile men. This mini-review discussed recent data in this field. Age, non-inflammatory functional alterations in post-testicular organs, infective agents (Chlamydia trachomatis, herpes virus and adeno-associated viruses), alterations in gamete genome, mitochondrial alterations, environmental pollutants and "subtle" hormonal alterations are all considered possible causes of iOAT. Increase of reactive oxygen species in tubules and in seminal plasma and of apoptosis are reputed to affect sperm concentration, motility and morphology. iOAT is commonly diagnosed by exclusion, nevertheless spectral traces of the main testicular artery may be used as a diagnostic tool for iOAT. The following can be considered therapies for iOAT: 1) tamoxifen citrate (20 mg/d) + testosterone undecanoate (120 mg/d) (pregnancy rate per couple/month [prcm]: 3.8%); 2) folic acid (66 mg/d) + zinc sulfate (5 mg/d); 3) L-carnitine (2 g/d) alone or in combination with acetyl-L-carnitine (1 g/d) (prcm: 2.3%); and 4) both carnitines = one 30 mg cinnoxicam suppository every 4 days (prcm: 8.5%). Alpha-blocking drugs improved sperm concentration but not morphology, motility or pregnancy rate. Tranilast (300 mg/d) increased sperm parameters and pregnancy rates in an initial uncontrolled study. Its efficacy on sperm concentration (but not on sperm motility, morphology or prcm) was confirmed in subsequent published reports. The efficacy of tamoxifen + testosterone undecanoate, tamoxifen alone, and recombinant follicle-stimulating hormone is still a matter for discussion.

Clinical correlates of environmental endocrine disruptors

Endocrine disrupting chemicals (EDCs), such as environmental estrogens, are hypothesized to be associated with a global decrease in sperm counts, other male reproductive tract problems and increasing rates of female breast cancer. Results of human population studies do not support the association between certain organochlorine EDCs and female breast cancer. Moreover, there is minimal evidence linking EDCs or exposure to other environmental chemicals with male reproductive tract problems. With the exception of the increasing incidence of testicular cancer, it is also questionable whether male reproductive tract problems are increasing, decreasing or unchanged. However, several studies report large differences in sperm count and quality and other endocrine-related problems within countries and regions, but the environmental, dietary and/or lifestyle factors responsible remain unknown.

Endocrine disruptors and human health: is there a problem

It has been hypothesized that endocrine-active chemicals (EACs) may be responsible for the increased incidence of breast cancer and disorders of the male reproductive tract. Synthetic chemicals with estrogenic activity (xenoestrogen) and the organochlorine environmental contaminants polychlorinated biphenyls (PCBs) and DDE have been the prime etiologic suspects. However, results of extensive research on PCBs and DDE does not show a correlation between PCB/DDE exposure and development of breast cancer. Studies also show that sperm count levels vary with demography, and the hypothesized coordinate global decrease in sperm counts and other disorders of the male reproductive tract is not supported by published data. In contrast, testicular cancer is increasing in most countries, and causal environmental/lifestyle factors for this disease are unknown.

Changes in semen quality in Jerusalem between 1990 and 2000: a cross-sectional and longitudinal study

The aim of the present study was to investigate whether sperm quality has changed during the years 1990-1999 among men residing in Jerusalem, Israel, who were involved in treatment by intrauterine insemination (IUI). Both cross-sectional and longitudinal analyses were performed. A total of 2638 male partners in couples that underwent treatment by IUI participated in the cross-sectional investigation. Of them, 417 men (16%) were included in the longitudinal study. Total sperm counts and percent motility were evaluated on an annual basis to assess changes over 10 years from 1990 through 1999. A significant downward trend in sperm count and motility was demonstrated in the cross-sectional study. Sperm count decreased by 5.2 x 10(6)+/-0.9 x 10(6) (p<.0001) each year and percent motility declined by 0.50+/-0.14% (p=.0003). Similar changes were found in the longitudinal evaluation, but they were not statistically significant. These data suggest that during the last decade in Jerusalem, sperm count and motility declined significantly among men involved in infertile relationships and treated by IUI.

Environmental estrogens: roles in male reproductive tract problems and in breast cancer

It has been hypothesized that endocrine disruptors and particularly synthetic estrogenic environmental contaminants (xenoestrogens) are etiologic factors in the global decrease of sperm counts and other problems of the male reproductive tract, including cryptorchidism, hypospadias, and testicular cancer. Xenoestrogens might also be linked to an increased incidence of breast cancer in women. These hypotheses have stimulated research addressing the current incidence rates and time-dependent changes in these human health problems, and the results do not support the hypotheses. With the exception of testicular cancer, the evidence does not indicate that sperm counts and other male reproductive tract problems are increasing, and correlations with xenoestrogen exposure have not been made. Moreover, initial observations that the level of certain organochlorine pollutants is higher in breast cancer patients vs. controls have not been duplicated in more recent studies. The results do not preclude an environmental eitology to some of these health problems or to susceptible subpopulations, and these areas require further research and critical scrutiny.

Age-related disease pattern in infertile men: increasing incidence of infections in older patients

In a cross-sectional retrospective study, the age-dependency of semen parameters of men with specific andrological diseases was investigated in 3,698 men (mean age 33 years; range 19-63 years) attending a tertiary referral clinic for couple infertility. In all, 1,853 patients suffered from idiopathic infertility (mean age 33.2 years; range 19-60 years), 388 from infections of the accessory glands (34.2; 20-61), 363 had a history of maldescended testes (32.0; 20-51) and 833 a varicocele (33.6; 20-63). In 172 patients, a varicocele and an infection (34.3; 24-54) and in 94 a varicocele and a history of maldecended testes (32.5; 21-53) were found. Semen analysis was performed according to WHO criteria. An age-related decrease in testicular volume was not observed in any group. Total sperm count decreased significantly with advancing age only in patients with an infection of the accessory glands. We found no evidence for age-dependent progressive deterioration of semen variables in the other groups. It may be concluded that the causes for the spermatogenetic defects in men with idiopathic infertility, a history of maldescended testes or varicocele are acquired before adolescence and do not progress during adulthood. In contrast, infections of the accessory glands may lead to decreased sperm counts by functional impairment or partial occlusion of the seminal ducts. Thus, if in the general population declining sperm counts are observed, genital tract infections may be suspected as a contributing factor.

Secular variations in sperm quality: fact or science fiction?

The debate concerning the possible degradation in human sperm quality began in the 1970s, was revived at the beginning of the 1990s and has continued to mobilize the scientific community ever since. After the meta-analysis by Carlsen et al. (1992) showing a decline in human semen quality over the last 50 years, several groups investigated the sperm characteristics of more or less homogeneous groups of men who had provided semen at the same center for 10 to 20 years. A significant decrease in sperm concentration was reported in some studies, but not in others. Meanwhile, there is an increasing number of reports suggesting that physical and chemical factors introduced and spread by human activity in the environment may have contributed to sperm decline. At the end of the 20th century the debate on declining semen quality is not closed. The lack of certainty and the serious consequences that such a decline would have on the fertility of human populations make this an important public health issue at the start of the 21st century. For this reason, intensive research should be developed in both fundamental and epidemiological domains, particularly in South America, where industrial and agricultural pollution pose a serious threat to the population.

Changes in male reproductive health and effects of endocrine disruptors in Scandinavian countries

Male reproductive health has deteriorated in many ways during the last decades. The incidence of testicular cancer has rapidly increased in Europe and European-derived populations. Sperm concentrations have declined and sperm motility and morphology have worsened in many areas. Both adverse trends have been shown to be associated with year of birth. Older birth cohorts have better reproductive health than the younger generations. Incidences of cryptorchidism and hypospadias have also increased according to several studies. The reasons for secular trends are unknown, but the rapid pace of the change points to environmental causes. Endocrine disrupting chemicals have been hypothesized to influence male reproductive health.

Occupational exposure to solvents and male infertility

OBJECTIVES

To determine whether, in a case-referent study of infertility patients, cases with low motile sperm count were more likely than referents to have had exposure to organic solvents.

METHODS

Occupations of men attending fertility clinics in Canada were assigned codes reflecting probable exposure to organic solvents, at four grades of intensity, using a job exposure matrix previously developed. A case referent design was used, with cases being defined as men with <12x10(6)/ml motile sperm. Information from 656 men in manual work attending a single clinic in Montreal in 1972-91 was used for the main study. A separate analysis was conducted with information for 574 men in manual work attending 10 further clinics across Canada in 1984-7.

RESULTS

In the Montreal series a significant association was found between intensity of exposure to solvents and clinical findings of <12x10(6)/ml motile sperm. Odds ratios (ORs), after allowing for confounding, were 2.07 (95% confidence interval (95% CI) 1.24 to 3.44) for moderate exposure to solvents and 3.83 (95% CI 1.37 to 10.65) for high exposure. In the second series of 568 men, the effect was confirmed at high exposure to solvents (OR 2.90, 95% CI 1.01 to 8.34) but not at moderate exposure (OR 1.01, 95% CI 0.53 to 1.92).

CONCLUSIONS

Exposure to organic solvents is common both at work and in recreational pursuits. The results of this study suggest that efforts should be made to identify the compounds hazardous to male fertility, and if the risk is confirmed, to regulate their use.