Semen quality and male reproductive health: the controversy about human sperm concentration decline

Adverse trends in male reproductive health: we may have reached a crucial 'tipping point'

Healthy men produce an enormous number of sperms, far more than necessary for conception. However, several studies suggest that semen samples where the concentration of sperms is below 40 mill/mL may be associated with longer time to pregnancy or even subfertility, and specimens where the concentration of sperms is below 15 mill/mL may carry a high risk of infertility. Historic data from the 1940s show that the bulk of young men at that time had sperm counts far above 40 mill/mL with averages higher than 100 mill/mL. However, recent surveillance studies of young men from the general populations of young men in Northern Europe show that semen quality is much poorer. In Denmark approximately 40 percent of the men have now sperm counts below 40 mill/mL. A simulation assuming that average sperm count had declined from 100 mill/mL in ‘old times’ to a current level close to 40 mill/mL indicated that the first decline in average sperm number of 20–40 mill/mL might not have had much effect on pregnancy rates, as the majority of men would still have had counts far above the threshold value. However, due to the assumed decline in semen quality, the sperm counts of the majority of 20 year old European men are now so low that we may be close to the crucial tipping point of 40 mill/mL spermatozoa. Consequently, we must face the possibility of more infertile couples and lower fertility rates in the future.

Environment, testicular dysgenesis and carcinoma in situ testis

The testicular dysgenesis syndrome (TDS) hypothesis proposes that a proportion of the male reproductive disorders-cryptorchidism, hypospadias, infertility and testicular cancer-may be symptoms of one underlying developmental disease, TDS, which is most likely a result of disturbed gonadal development in the embryo. TDS may be caused by genetic factors, environmental/life-style factors, or a combination of both. Some rare disorders of sex development of genetic origin are among the best-known examples of severe TDS. Among the environmental and life-style factors that are suspected to influence the hormonal milieu of the developing gonad are the endocrine disrupters. A prenatal exposure to commonly used chemicals, e.g. phthalates, may result in a TDS-like phenotype in rats. Currently, this animal model is the best model for TDS. In humans the situation is much more complex, and TDS exists in a wide range of phenotypes: from the mildest and most common form, in which impaired spermatogenesis is the only symptom, to the most severe cases, in which the patient may develop testicular cancer. It is of great importance that clinicians in different specialties treating patients with TDS are aware of the association between the different symptoms.

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.

Self-rated health and semen quality among 3,457 young Danish men

OBJECTIVE

To study the relationship between self-rated health (SRH) and semen quality.

DESIGN

Cross-sectional study of men attending a compulsory physical examination to determine their fitness for military service from 1996 to 2005.

SETTING

Young men were approached when they were summoned for a compulsory physical examination to determine their fitness for military service in two major Danish cities.

PATIENT(S)

A total of 3,457 Danish young men delivered a semen sample, had a physical examination performed, and responded to a questionnaire including a question about SRH.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Semen quality and testis size.

RESULT(S)

After control for confounders, men with good and poor SRH had, respectively, 0.5 mL (95% CI: -0.8, -0.1) and 0.8 mL (95% CI: -2.4, 0.8) smaller testes size compared to men with very good SRH, the trend was statistically significant. Men with good and poor SRH had, respectively, 12.2% (95% CI: -21.2%, -2.2%) and 26.9% (95% CI: -55.7%, 20.8%) lower total sperm count compared to men with very good SRH, the trend was statistically significant, and had +0.4% (-1.4%, 2.2%) and 1.4% (-3.5%, 0.7%) fewer morphologically normal sperms (trend statistically significant). Percentages of motile spermatozoa and semen volume were not significantly associated with SRH.

CONCLUSION(S)

We found significant associations between SRH and semen quality and testicular size. Given the cross-sectional study design, we cannot establish a causal relationship but argue that SRH may be associated with semen quality. Our findings need to be validated and confirmed with other study designs (preferably prospective) and in populations of different age structure and fertility status.

Phthalate exposure and male infertility

Phthalates have been used as additives in industrial products since the 1930s, and are universally considered to be ubiquitous environmental contaminants. The general population is exposed to phthalates through consumer products, as well as diet and medical treatments. Animal studies showing the existence of an association between some phthalates and testicular toxicity have generated public and scientific concern about the potential adverse effects of environmental changes on male reproductive health. In particular, prenatal exposure to phthalates seems to play a relevant role in determining these adverse effects given that human exposure has been demonstrated to begin during the intrauterine life. Unprecedented declines in fertility rates and semen quality of antenatal origin have been reported during the last half of the 20th century in developed countries and increasing interest exists on the potential relationship between exposure to environmental contaminants, including phthalates, and human male reproductive health. Here we review the data that support or discounts the evidence existing to date linking phthalate exposure and the decline of human male fertility, especially in developed countries.

The sensitivity of the child to sex steroids: possible impact of exogenous estrogens

The current trends of increasing incidences of testis, breast and prostate cancers are poorly understood, although it is assumed that sex hormones play a role. Disrupted sex hormone action is also believed to be involved in the increased occurrence of genital abnormalities among newborn boys and precocious puberty in girls. In this article, recent literature on sex steroid levels and their physiological roles during childhood is reviewed. It is concluded that (i) circulating levels of estradiol in prepubertal children are lower than originally claimed; (ii) children are extremely sensitive to estradiol and may respond with increased growth and/or breast development even at serum levels below the current detection limits; (iii) no threshold has been established, below which no hormonal effects can be seen in children exposed to exogenous steroids or endocrine disruptors; (iv) changes in hormone levels during fetal and prepubertal development may have severe effects in adult life and (v) the daily production rates of sex steroids in children estimated by the Food and Drug Administration in 1999 and still used in risk assessments are highly overestimated and should be revised. Because no lower threshold for estrogenic action has been established, caution should be taken to avoid unnecessary exposure of fetuses and children to exogenous sex steroids and endocrine disruptors, even at very low levels.

Testicular dysgenesis syndrome: possible role of endocrine disrupters

The testicular dysgenesis syndrome (TDS) hypothesis proposes that the four conditions cryptorchidism, hypospadias, impaired spermatogenesis and testis cancer may all be manifestations of disturbed prenatal testicular development. The TDS hypothesis is based on epidemiological, clinical and molecular studies, all suggestive of an interrelation between the different symptoms. The aetiology of TDS is suspected to be related to genetic and/or environmental factors, including endocrine disrupters. Few human studies have found associations/correlations between endocrine disrupters, including phthalates, and the different TDS components. However, for ethical reasons, evidence of a causal relationship between prenatal exposure and TDS is inherently difficult to establish in human studies, rendering the recently developed animal TDS model an important tool for investigating the pathogenesis of TDS. Clinically, the most common manifestation of TDS is probably a reduced sperm concentration, whereas the more severe form may include a high risk of testis cancer. Clinicians should be aware of the interconnection between the different features of TDS, and inclusion of a programme for early detection of testis cancer in the management of infertile men with poor semen quality is recommended.

Characterization and quantification of mRNA transcripts in ejaculated spermatozoa of fertile men by serial analysis of gene expression

BACKGROUND

Accumulated evidence proves that mature spermatozoa contain a complex yet specific array of mRNA, which could provide information on the past events of spermatogenesis.

OBJECTIVE

To quantitatively microdissect these mRNA transcripts by a digital approach.

METHODS

Serial analysis of gene expression (SAGE) was used to study the mRNA transcripts from ejaculate of a fertile individual and of a pool of 10 fertile men. Online DAVID software suite was also utilized to cluster the UniGene data.

RESULTS

A SAGE library from the individual produced 20,237 raw tags representing 2459 unique tags and that from pooled 10 men generated 21,052 raw tags representing 2712 unique tags. When the unique tags occurring > or = 4 times were analysed, 564 overlapping tags were produced by 638 unique tags from the individual and 682 from the pooled library. Fifty-four of these overlapped tags were considered to be novel genes. Online analysis of the overlapping tags revealed 25 functional gene groups, with the dominant one comprising 96 nuclear protein genes involving transcription and transcription regulation and also a group with 84 ribosomal subunit genes involving protein synthesis.

CONCLUSION

A SAGE analysis of ejaculate from fertile men has revealed a large number of transcripts, which occur in steady frequencies and probably have important roles in spermatogenesis and fertilization.

Role of acid/base transporters in the male reproductive tract and potential consequences of their malfunction

Acid/base transporters play a key role in establishing an acidic luminal environment for sperm maturation and storage in the male reproductive tract. Impairment of the acidification capacity of the epididymis, via either genetic mutations or exposure to environmental factors, may have profound consequences on male fertility.

Disrupted sex differentiation and feminization of man and domestic animals

Genital malformations constitute the most common birth defects in man and domestic animals and occur frequently in males since the participation of many genes is required for sex differentiation to proceed in the male direction. The precise dose, timing, and coordination needed for their expression add to the proneness of various stages in male sex differentiation to external influences. The emerging insight, through the identification of genes involved in the sex differentiation cascade, is that over 85% of sex anomalies in human and domestic animal populations are not attributable to chromosome aberrations or to mutations in a known gene. Since a majority of severely malformed individuals are incapable of reproduction, the high rates of these defects have to be results either of new mutations or of collaboration of environmental factors with genes. Increase in specific malformations in domestic animals often indicates increased concentration of liability genes brought together in the conceptus by inbreeding. However, in human populations where inbreeding is not the norm such increases may reflect environment-induced new mutations or interaction of environmental agents with hormone-sensitive genes. This review summarizes the information currently available on the genetics of major events in male sex differentiation and briefly discusses the collaborative role that environment may play in disrupting different components of this process.

Sperm concentration and normal sperm morphology decrease and follicle-stimulating hormone level increases with age

OBJECTIVE

To assess hormone levels, testicular volume, and semen characteristics of fertile men of various age groups.

PATIENTS AND METHODS

The records of 889 men who sought a vasectomy between September 1999 and March 2003 were reviewed. Patients were divided into five groups by age; we evaluated semen volume, sperm concentration, motility, morphology and complex sperm motion variables. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone levels and both testicular volumes were compared.

RESULTS

There were no differences among the groups in the levels of LH, testosterone, or right and left testicular volumes. There were differences among the five groups in FSH levels, semen volume, sperm concentration and motility. Normal morphology according to the World Health Organisation criteria was significantly lower in patients aged > 45 years. From a linear regression analysis, semen volume, sperm concentration and motility decreased by 0.01 mL, 2.1%, and 0.27%, respectively, per year, and the FSH level increased by 0.27%.

CONCLUSIONS

Sperm concentration and motility decrease and FSH levels increase with age. Normal sperm morphology decreases from 45 years old. Thus, the ageing effect should be considered when proposing standard values for semen characteristics in routine semen analysis.

Time trends in waiting time to pregnancy among Danish twins

BACKGROUND

Little is known about time trends in fecundity because few population-based data are available. In a survey among female twins born from 1953 to 1976, their time to pregnancy did not differ from singletons and can be considered to represent the fecundity of the general population.

METHODS

Information was collected by interview about waiting time to first pregnancy (TTP) and any periods of subfecundity among both male and female twins born between 1931 and 1952. Trends were analysed by considering the year of birth of the index person (birth cohort effect) or year at which the first attempt started (period effect).

RESULTS

Eighty-five percent of male and 81.3% of female eligible twins participated. A total of 1598 male twins and 1653 female twins reported a TTP value and 1671 men and 1715 women had a value for their first attempt to conceive including unsuccessful attempts. No overall trends in either male or female TTP were observed with increasing year of birth or of starting time, after adjustment for confounders, but for attempts fecundity increased among female twins by year of birth or of starting the attempt. A decreasing risk of severe infertility with increasing year of birth or year for start of the attempt was observed among male twins, but this observation was based on only 81 men and was not seen among female twins.

CONCLUSION

No decreasing trend in fecundity was observed among Danish twins born between 1931 and 1952 who had completed their reproduction. Female twins had a slight increase in fecundity, and men a decrease in severe infertility. In addition, TTP was apparently well reported and recalled for up to 50 years among both male and female twins.

Selection bias in semen studies due to self-selection of volunteers

BACKGROUND

Reports of a secular decrease in semen quality remain controversial, particularly due to the possibility of selection bias. We aimed to describe the potential bias due to self-selection of volunteers in semen studies involving fecund men.

METHODS

Using data from the French multicentre study REPRHOM, we compared the characteristics of the partners of pregnant women for three levels of participation: completion of a refusal questionnaire (n = 698), agreement to complete the study questionnaires only (n = 676) and agreement to complete the study questionnaires and give a semen sample (n = 331, 13% of the subjects approached).

RESULTS

Poorly educated men refused more often to participate than highly educated men. Semen providers were more likely to have experienced unfavourable pregnancy outcomes (odds ratio 1.68, 95% confidence interval 1.14-2.49) compared with participants completing the questionnaires only. Time to pregnancy was similar for all participants.

CONCLUSIONS

This study demonstrates the existence of selection bias in semen studies associated with fertility and socio-demographic characteristics of men. The results of semen analysis for this population sample cannot be extrapolated to the whole population from which the volunteers originate. More information is required on who participates, and participation rates should be reported in semen studies to make it possible to interpret the results correctly.

Environmental versus genetic sex determination: a possible factor in dinosaur extinction?

This study examined the possibility that genetically based sex-determination mechanisms have evolved to ensure a balanced male/female ratio and that this temperature-independent checkpoint might have been unavailable to long-extinct reptiles, notably the dinosaurs. A review of the literature on molecular and phylogenetic relationships between modes of reproduction and sex determination in extant animals was conducted. Mammals, birds, all snakes and most lizards, amphibians, and some gonochoristic fish use specific sex-determining chromosomes or genes (genetic sex determination, GSD). Some reptiles, however, including all crocodilians studied to date, many turtle and tortoise species, and some lizards, use environmental or temperature-dependent sex determination (TSD). We show that various modes of GSD have evolved many times, independently in different orders. Animals using TSD would be at risk of rapid reproductive failure due to a skewed sex ratio favoring males in response to sustained environmental temperature change and favoring the selection of sex-determining genes. The disadvantage to the evolving male sex-determining chromosome, however, is its decay due to nonrecombination and the subsequent loss of spermatogenesis genes. Global temperature change can skew the sex ratio of TSD animals and might have played a significant role in the demise of long-extinct species, notably the dinosaurs, particularly if the temperature change resulted in a preponderance of males. Current global warming also represents a risk for extant TSD species.

KEY PARAMETERS OF SPERM MOTION IN RELATION TO MALE FERTILITY

This study was undertaken to detect key parameters of rat sperm motion in relation to male fertility by comparing the differences in sperm motion induced by treatment with alpha-chlorohydrin (ACH), known to produce spermatotoxicity, and nitrobenzene (NTB), known to produce testicular toxicity. Male rats received ACH (5 or 20 mg/kg/day) or NTB (60 mg/kg/day) for either 3 days or 18 days. Epididymal sperm was assessed for motility using a Hamilton-Thorne Sperm Analyzer (HTM-IVOS). Numerical data for statistical analysis and graphical renditions of sperm motion using parameters in radar charts and reconstructed sperm tracks were analyzed to evaluate sperm motion. Males were allowed to copulate with untreated females and cesarean sections were conducted in order to examine the effects of drug administration on male fertility. Linearity of sperm track (linearity (LIN) and/or straightness (STR)) decreased and/or beat cross frequency (BCF) increased only in ACH groups (5 or 20 mg/kg/day), although the percentage of motile sperm, sperm velocities (average path velocity (VAP), curvilinear (VCL), and straight line velocity (VSL)) and amplitude of lateral head displacement (ALH) decreased on Day 18 in both ACH and NTB (60 mg/kg/day) groups. Furthermore, from the individual reconstructed sperm tracks, it was clear that ACH-treated spermatozoa were characterized by abnormal motion ("jerking") with low vigor (low velocities) and little or no forward progression. Finally, only ACH treatment led to a reduction in pregnancy rate or infertility. Therefore, our results suggest that linearity (especially VSL, STR and LIN) in sperm motion is a key parameter for assessing a chemical's potential to induce male infertility.

Estrogenic effects of food wrap packaging xenoestrogens and flavonoids in female Wistar rats: a comparative study

The objective of this study was to compare the estrogenicity of xenoestrogens found in food wrap packaging and phytoestrogen flavonoids. Uterotrophic and vaginal cornification assays were performed on immature and ovariectomized rats. Genistein, bisphenol F, and octylphenol were identified as estrogenic only in immature rats. Using vaginal cornification as a more specific estrogenic parameter, all tested compounds except tangeretin were active in immature rats. While apigenin and kaempferol appeared to have low estrogenic activity, they potentialized the uterotrophic effect of 17beta-estradiol in immature rats. These data showed that (i) phytoestrogens like genistein can be as potent or even more estrogenic than compounds found in food wrap packaging, (ii) immature rats appear to be a more sensitive in vivo model than ovariectomized rats in term of estrogenicity, (iii) the vaginal cornification assay could be a sensitive and useful test to detect weak estrogenic compounds to which humans can be exposed via food.

Dithioerythritol (DTE) prevents inhibitory effects of triphenyltin (TPT) on the key enzymes of the human sex steroid hormone metabolism

Organotins are known to induce imposex (pseudohermaphroditism) in marine neogastropods and are suggested to act as specific endocrine disruptors, inhibiting the enzyme-mediated conversion of steroid hormones. Therefore, we investigated the in vitro effects of triphenyltin (TPT) on human 5alpha-reductase type 2 (5alpha-Re 2), cytochrome P450 aromatase (P450arom), 17beta-hydroxysteroid dehydrogenase type 3 (17beta-HSD 3), 3beta-HSD type 2 and 17beta-HSD type 1 activity. First, the present study demonstrates that significant amounts of TPT occurred in the blood of eight human volunteers (0.17-0.67 microg organotin cation/l, i.e. 0.49-1.92 nmolcation/l). Second, TPT showed variable inhibitory effects on all the enzymes investigated. The mean IC(50) values were 0.95 microM for 5alpha-Re 2 (mean of n=4 experiments), 1.5 microM for P450arom (n=5), 4.0 microM for 3beta-HSD 2 (n=1), 4.2 microM for 17beta-HSD 3 (n=3) and 10.5 microM for 17beta-HSD 1 (n=3). To exclude the possibility that the impacts of TPT are mediated by oxidizing essential thiol residues of the enzymes, the putative compensatory effects of the reducing agent dithioerythritol (DTE) were investigated. Co-incubation with DTE (n=3) resulted in dose-response prevention of the inhibitory effects of 100 microM deleterious TPT concentrations on 17beta-HSD 3 (EC(50) value of 12.9 mM; mean of n=3 experiments), 3beta-HSD 2 (0.90 mM; n=3), P450 arom (0.91 mM; n=3) and 17beta-HSD 1 (0.21 mM; n=3) activity. With these enzymes, the use of 10mM DTE resulted in an at least 80% antagonistic effect, whereas, the effect of TPT on 5alpha-Re 2 was not compensated. In conclusion, the present study shows that TPT acts as an unspecific, but significant inhibitor of human sex steroid hormone metabolism and suggests that the inhibitory effects are mediated by the interaction of TPT with critical cysteine residues of the enzymes.

Human exposure to endocrine disrupters: consequences of gastroplasty on plasma concentration of toxic pollutants

BACKGROUND

Body weight loss occurring after a hypoenergetic diet or a gastroplasty could be followed by an increase in blood concentration of potentially toxic pollutants that can interfere with the hormonal system (endocrine disrupters).

DESIGN

Thirty obese individuals recruited for gastroplasty were compared before and after treatment with 45 normal-weight people.

MEASUREMENTS

Blood samples were analyzed for DDT, DDE, HCB and PCBs no. 28, 52, 101, 118, 138, 153 and 180, by gas chromatography-mass spectrometry.

RESULTS

The results indicate clearly that body weight loss occurring after gastroplasty increases plasma concentration of lipophilic pollutants.

CONCLUSION

Gastroplasty increases plasma concentration of organochlorine pesticides and PCBs, which could be a risk factor of endocrine disruption. Future longitudinal research will have to determine if the advantages of body weight loss are reduced by this potentially harmful effect.

The hidden effect of estrogenic/antiandrogenic methoxychlor on spermatogenesis

Perinatal and juvenile oral treatment of rats with methoxychlor (MXC) only during development reduces testicular size and Sertoli cell number in those animals as adults. The objectives were to determine if MXC administered orally reduces numbers of spermatogonia and daily sperm production that parallel reduction in Sertoli cell number and if germ cell degeneration rate or function of individual Sertoli cells was also affected. Rat dams were gavaged with MXC at 0, 5, 50, or 150 mg/kg/day for the week before and after they gave birth. Resulting male pups (14-16 per group) then were dosed directly from postnatal day 7 to 42. Testes were fixed in Bouin's fixative, postfixed in osmium tetroxide, and embedded in Epon. Sections of 0.5 and 20 microm were evaluated stereologically. Across dose groups, body weight was not affected, but testicular weight was significantly reduced in a dose-dependent fashion. Spermatogenic potential based on number of spermatogonia and number of spermatids per testis was significantly reduced by treatment. There was no adverse effect on daily sperm production per gram of parenchyma based on spermatids; however, the number of spermatogonia per gram was reduced. The ratio of spermatid number per spermatogonia was higher in the MXC-treated groups. This difference indicated that the testis can compensate for the treatment-induced reduction in number of spermatogonia by reducing degeneration of their progeny. However, the reduced number of Sertoli cells prevented the compensation from recovering the daily sperm production per testis totally. Given that endocrine disruptors like MXC can induce compensation during spermatogenesis, it may reduce the ability of the testis to compensate during subsequent exposures.