Novel male hormonal contraceptive combinations: the hormonal and spermatogenic effects of testosterone and levonorgestrel combined with a 5alpha-reductase inhibitor or gonadotropin-releasing hormone antagonist

Beyond the Condom: Frontiers in Male Contraception

Nearly half of all pregnancies worldwide are unplanned, despite numerous contraceptive options available. No new contraceptive method has been developed for men since the invention of condom. Nevertheless, more than 25% of contraception worldwide relies on male methods. Therefore, novel effective methods of male contraception are of interest. Herein we review the physiologic basis for both male hormonal and nonhormonal methods of contraception. We review the history of male hormonal contraception development, current hormonal agents in development, as well as the potential risks and benefits of male hormonal contraception options for men. Nonhormonal methods reviewed will include both pharmacological and mechanical approaches in development, with specific focus on methods which inhibit the testicular retinoic acid synthesis and action. Multiple hormonal and nonhormonal methods of male contraception are in the drug development pathway, with the hope that a reversible, reliable, safe method of male contraception will be available to couples in the not too distant future.

Gonadotropin suppression in men leads to a reduction in claudin-11 at the Sertoli cell tight junction

STUDY QUESTION

Are Sertoli cell tight junctions (TJs) disrupted in men undergoing hormonal contraception?

SUMMARY ANSWER

Localization of the key Sertoli cell TJ protein, claudin-11, was markedly disrupted by 8 weeks of gonadotropin suppression, the degree of which was related to the extent of adluminal germ cell suppression.

WHAT IS KNOWN ALREADY

Sertoli cell TJs are vital components of the blood-testis barrier (BTB) that sequester developing adluminal meiotic germ cells and spermatids from the vascular compartment. Claudin-11 knockout mice are infertile; additionally claudin-11 is spatially disrupted in chronically gonadotropin-suppressed rats coincident with a loss of BTB function, and claudin-11 is disorganized in various human testicular disorders. These data support the Sertoli cell TJ as a potential site of hormonal contraceptive action.

STUDY DESIGN, SIZE, DURATION

BTB proteins were assessed by immunohistochemistry (n = 16 samples) and mRNA (n = 18 samples) expression levels in available archived testis tissue from a previous study of 22 men who had undergone 8 weeks of gonadotropin suppression and for whom meiotic and post-meiotic germ cell numbers were available. The gonadotropin suppression regimens were (i) testosterone enanthate (TE) plus the GnRH antagonist, acyline (A); (ii) TE + the progestin, levonorgestrel, (LNG); (iii) TE + LNG + A or (iv) TE + LNG + the 5α-reductase inhibitor, dutasteride (D). A control group consisted of seven additional men, with three archived samples available for this study.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Immunohistochemical localization of claudin-11 (TJ) and other junctional type markers [ZO-1 (cytoplasmic plaque), β-catenin (adherens junction), connexin-43 (gap junction), vinculin (ectoplasmic specialization) and β-actin (cytoskeleton)] and quantitative PCR was conducted using matched frozen testis tissue.

MAIN RESULTS AND THE ROLE OF CHANCE

Claudin-11 formed a continuous staining pattern at the BTB in control men. Regardless of gonadotropin suppression treatment, claudin-11 localization was markedly disrupted and was broadly associated with the extent of meiotic/post-meiotic germ cell suppression; claudin-11 staining was (i) punctate (i.e. 'spotty' appearance) at the basal aspect of tubules when the average numbers of adluminal germ cells were <15% of control, (ii) presented as short fragments with cytoplasmic extensions when numbers were 15-25% of control or (iii) remained continuous when numbers were >40% of control. Changes in localization of connexin-43 and vinculin were also observed (smaller effects than for claudin-11) but ZO-1, β-catenin and β-actin did not differ, compared with control.

LIMITATIONS, REASONS FOR CAUTION

Claudin-11 was the only Sertoli cell TJ protein investigated, but it is considered to be the most pivotal of constituent proteins given its known implication in infertility and BTB function. We were limited to testis samples which had been gonadotropin-suppressed for 8 weeks, shorter than the 74-day spermatogenic wave, which may account for the heterogeneity in claudin-11 and germ cell response observed among the men. Longer suppression (12-24 weeks) is known to suppress germ cells further and claudin-11 disruption may be more uniform, although we could not access such samples.

WIDER IMPLICATIONS OF THE FINDINGS

These findings are important for our understanding of the sites of action of male hormonal contraception, because they suggest that BTB function could be ablated following long-term hormone suppression treatment.

STUDY FUNDING/COMPETING INTERESTS

National Health and Medical Research Council (Australia) Program Grants 241000 and 494802; Research Fellowship 1022327 (to R.I.M.) and the Victorian Government's Operational Infrastructure Support Program. None of the authors have any conflicts to disclose.

TRIAL REGISTRATION NUMBER

Not applicable.

Male hormonal contraception: looking back and moving forward

Despite numerous contraceptive options available to women, approximately half of all pregnancies in the United States and worldwide are unplanned. Women and men support the development of reversible male contraception strategies, but none have been brought to market. Herein we review the physiologic basis for male hormonal contraception, the history of male hormonal contraception development, currents agents in development as well as the potential risks and benefits of male hormonal contraception for men.

Endocrine control of spermatogenesis: Role of FSH and LH/ testosterone

Evaluation of testicular functions (production of sperm and androgens) is an important aspect of preclinical safety assessment and testicular toxicity is comparatively far more common than ovarian toxicity. This chapter focuses (1) on the histological sequelae of disturbed reproductive endocrinology in rat, dog and nonhuman primates and (2) provides a review of our current understanding of the roles of gonadotropins and androgens. The response of the rodent testis to endocrine disturbances is clearly different from that of dog and primates with different germ cell types and spermatogenic stages being affected initially and also that the end-stage spermatogenic involution is more pronounced in dog and primates compared to rodents. Luteinizing hormone (LH)/testosterone and follicle-stimulating hormone (FSH) are the pivotal endocrine factors controlling testicular functions. The relative importance of either hormone is somewhat different between rodents and primates. Generally, however, both LH/testosterone and FSH are necessary for quantitatively normal spermatogenesis, at least in non-seasonal species.

Steroid hormones for contraception in men

BACKGROUND

Male hormonal contraception has been an elusive goal. Administration of sex steroids to men can shut off sperm production through effects on the pituitary and hypothalamus. However, this approach also decreases production of testosterone, so 'add-back' therapy is needed.

OBJECTIVES

To summarize all randomized controlled trials (RCTs) of male hormonal contraception.

SEARCH METHODS

In January and February 2012, we searched the computerized databases CENTRAL, MEDLINE, POPLINE, and LILACS. We also searched for recent trials in ClinicalTrials.gov and ICTRP. Previous searches included EMBASE. We wrote to authors of identified trials to seek additional unpublished or published trials.

SELECTION CRITERIA

We included all RCTs that compared a steroid hormone with another contraceptive. We excluded non-steroidal male contraceptives, such as gossypol. We included both placebo and active-regimen control groups.

DATA COLLECTION AND ANALYSIS

The primary outcome measure was the absence of spermatozoa on semen examination, often called azoospermia. Data were insufficient to examine pregnancy rates and side effects.

MAIN RESULTS

We found 33 trials that met our inclusion criteria. The proportion of men who reportedly achieved azoospermia or had no detectable sperm varied widely. A few important differences emerged. 1) Levonorgestrel implants (160 μg daily) combined with injectable testosterone enanthate (TE) were more effective than levonorgestrel 125 µg daily combined with testosterone patches. 2) Levonorgestrel 500 μg daily improved the effectiveness of TE 100 mg injected weekly. 3) Levonorgestrel 250 μg daily improved the effectiveness of testosterone undecanoate (TU) 1000 mg injection plus TU 500 mg injected at 6 and 12 weeks. 4) Desogestrel 150 μg was less effective than desogestrel 300 μg (with testosterone pellets). 5) TU 500 mg was less likely to produce azoospermia than TU 1000 mg (with levonorgestrel implants). 6) Norethisterone enanthate 200 mg with TU 1000 mg led to more azoospermia when given every 8 weeks versus 12 weeks. 7) Four implants of 7-alpha-methyl-19-nortestosterone (MENT) were more effective than two MENT implants. We did not conduct any meta-analysis due to intervention differences.Several trials showed promising efficacy in percentages with azoospermia. Three examined desogestrel and testosterone preparations or etonogestrel and testosterone, and two examined levonorgestrel and testosterone.

AUTHORS' CONCLUSIONS

No male hormonal contraceptive is ready for clinical use. Most trials were small exploratory studies. Their power to detect important differences was limited and their results imprecise. In addition, assessment of azoospermia can vary by sensitivity of the method used. Future trials need more attention to the methodological requirements for RCTs. More trials with adequate power would also be helpful.

Alcohol consumption, finasteride, and prostate cancer risk: results from the Prostate Cancer Prevention Trial

BACKGROUND

Current research is inconclusive regarding the relation between alcohol consumption and prostate cancer risk. In this study, the authors examined the associations of total alcohol, type of alcoholic beverage, and drinking pattern with the risk of total, low-grade, and high-grade prostate cancer.

METHODS

Data for this study came from the 2129 participants in the Prostate Cancer Prevention Trial (PCPT) who had cancer detected during the 7-year trial and 8791 men who were determined by biopsy to be free of cancer at the trial end. Poisson regression was used to calculate relative risks (RRs) and 95% confidence intervals (95% CIs) for associations of alcohol intake with prostate cancer risk.

RESULTS

Associations of drinking with high-grade disease did not differ by treatment arm. In combined arms, heavy alcohol consumption (> or =50 g of alcohol daily) and regular heavy drinking (> or =4 drinks daily on > or =5 days per week) were associated with increased risks of high-grade prostate cancer (RR, 2.01 [95% CI, 1.33-3.05] and 2.17 [95% CI, 1.42-3.30], respectively); less heavy drinking was not associated with risk. Associations of drinking with low-grade cancer differed by treatment arm. In the placebo arm, there was no association of drinking with risk of low-grade cancer. In the finasteride arm, drinking > or =50 g of alcohol daily was associated with an increased risk of low-grade disease (RR, 1.89; 95% CI, 1.39-2.56); this finding was because of a 43% reduction in the risk of low-grade cancer attributable to finasteride treatment in men who drank <50 g of alcohol daily and the lack of an effect of finasteride in men who drank > or =50 g of alcohol daily (P(interaction) = .03).

CONCLUSIONS

Heavy, daily drinking increased the risk of high-grade prostate cancer. Heavy drinking made finasteride ineffective for reducing prostate cancer risk.

Male contraception: A realistic option?

This review illustrates the principle of hormonal male contraception and gives an overview of current trials aiming at the development of a marketable hormonal contraceptive for men. The principle of male hormonal contraception is based on strong suppression of gonadotropins in order to arrest spermatogenesis at the spermatogonial stem cell level, thus leading to azoospermia or severe oligozoospermia. Until now, it has not been possible to interrupt spermatogenesis effectively without simultaneously inhibiting the production of androgens by Leydig cells, resulting in a deficiency of extra-testicular androgens. Therefore, testosterone needs to be replaced. By administering exogenous testosterone alone azoospermia can be reached in East Asians, whereas azoospermia is only achieved in two-thirds of Caucasian volunteers so that in these men an additional agent is required. Currently injectable testosterone combined with gestagens or administered as implants are being tested for possible licensing. Although scrotal and non-scrotal testosterone patches, orally administered testosterone undecanoate and testosterone gels are generally well tolerated and provide stable testosterone levels in the normal range, their use showed generally disappointing efficacy due to insufficient gonadotropin suppression. Further large multi-centre studies are required to establish the contraceptive efficacy of the most promising steroid combinations.

Oral administration of the GnRH antagonist acyline, in a GIPET-enhanced tablet form, acutely suppresses serum testosterone in normal men: single-dose pharmacokinetics and pharmacodynamics

PURPOSE

GnRH analogs are useful for the treatment of prostate cancer, but require parenteral administration. The peptide GnRH antagonist acyline potently suppresses luteinizing hormone (LH) and testosterone in man; however, its clinical utility is limited by the requirement for frequent injections. The use of a proprietary enhancer system called GIPET, which is based on medium-chain fatty acids, facilitates the oral bioavailability of peptides. We hypothesized that GIPET enhancement would allow for the safe oral dosing of acyline for the treatment of prostate cancer.

METHODS

We enrolled eight healthy young men in a pharmacokinetic and pharmacodynamic study of 10, 20 and 40 mg doses of GIPET-enhanced oral acyline. Blood for measurement of serum LH, FSH, testosterone and acyline was obtained prior to each dose of GIPET-enhanced oral acyline and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24 and 48 h after dosing.

RESULTS

Serum LH, FSH and serum testosterone were significantly suppressed by all doses of GIPET-enhanced oral acyline after 6 h, with suppression reaching a nadir 12 h after dosing. In addition, the 20 and 40 mg doses demonstrated sustained suppression of testosterone for 12-24 h. All hormone concentrations returned to normal 48 h after administration. There were no treatment-related serious adverse events, and laboratory assessments, including liver function tests and creatinine, were unaffected by treatment.

CONCLUSIONS

Oral administration of GIPET-enhanced acyline significantly suppresses testosterone and gonadotropins in normal men without untoward side effects and might have utility in the management of prostate cancer.

Serum steroid and sex hormone-binding globulin concentrations and the risk of incident benign prostatic hyperplasia: results from the prostate cancer prevention trial

The authors conducted a nested case-control study of serum steroid concentrations and risk of benign prostatic hyperplasia (BPH), using data from the placebo arm of the Prostate Cancer Prevention Trial (1993-2003). Incident BPH over 7 years (n = 708) was defined as receipt of treatment, a report of 2 International Prostate Symptom Score (IPSS) values greater than 14, or 2 increases of 5 or more from baseline IPSS values with at least 1 value greater than or equal to 12. Controls (n = 709) were selected from men who reported no BPH treatment or any IPSS greater than 7. Baseline serum was analyzed for testosterone, estradiol, estrone, 5alpha-androstane-3alpha, 17beta-diol-glucuronide, and sex hormone-binding globulin. Covariate-adjusted odds ratios contrasting the highest quartiles with the lowest quartiles of testosterone, estradiol, and testosterone:17beta-diol-glucuronide ratio were 0.64 (95% confidence interval (CI): 0.43, 0.95; P(trend) = 0.04), 0.72 (95% CI: 0.53, 0.98; P(trend) = 0.09), and 0.64 (95% CI: 0.46, 0.89; P(trend) = 0.004), respectively. Findings did not differ by age, body mass index, time to BPH endpoint, or type of BPH endpoint. High testosterone levels, estradiol levels, and testosterone:17beta-diol-glucuronide ratio are associated with reduced BPH risk, which may reflect decreased activity of 5-alpha-reductase. Genetic or environmental factors that affect the activity of 5-alpha-reductase may be important in the development of symptomatic BPH.

transient scrotal hyperthermia and levonorgestrel enhance testosterone-induced spermatogenesis suppression in men through increased germ cell apoptosis

CONTEXT

In rodents and monkeys, a combination of hormonal and physical agents accelerates germ cell death.

OBJECTIVE

A "proof of concept" study was performed to investigate whether addition of heat exposure or a progestin to an androgen induces germ cell death and more complete and rapid spermatogenesis suppression.

DESIGN AND SETTINGS

A randomized clinical trial was performed at academic medical centers.

PARTICIPANTS

We treated four groups of healthy male volunteers (18 per group) for 18 wk: 1) testosterone undecanoate (TU) 1000 mg im (first dose), followed by 500 mg im every 6 wk; 2) submersion of scrota at 43 C in water for 30 min/d for 6 consecutive days; 3) TU plus heat; and 4) TU plus oral levonorgestrel (LNG) 250 microg/d.

MAIN OUTCOME MEASURES

Semen parameters, testicular histology, and germ cell apoptosis were the main outcome measures.

RESULTS

Heat alone and TU plus heat suppressed sperm counts more than TU alone by wk 6. By wk 9, recovery began in the heat only group, whereas spermatogenesis remained suppressed in the TU plus heat group. Oral LNG plus TU suppressed spermatogenesis earlier and more severely than TU alone. At wk 2, significantly greater germ cell apoptosis occurred in heat and heat plus TU subjects, but not in subjects without heat treatment, compared with pretreatment subjects. By 9 wk, markedly smaller seminiferous tubule diameters and fewer spermatocytes and spermatids were noted in all 12 biopsies from men receiving TU, TU plus LNG, with most dramatic differences for the TU plus heat group, whereas no differences from pretreatment biopsies were observed in men who received heat treatment only.

CONCLUSIONS

Heat causes a rapid and transient suppression of spermatogenesis. TU plus heat resulted in low-sperm output that was maintained by continuous treatment with TU. Addition of an oral progestin accelerated spermatogenesis suppression by TU alone. Increased germ cell apoptosis contributed to suppression of spermatogenesis.

The effect of 5alpha-reductase inhibition with dutasteride and finasteride on semen parameters and serum hormones in healthy men

CONTEXT

Dutasteride and finasteride are 5alpha-reductase inhibitors (5ARIs) that dramatically reduce serum levels of dihydrotestosterone (DHT).

OBJECTIVE

Because androgens are essential for fertility, we sought to determine the impact of 5ARI administration on serum testosterone (T), DHT, and spermatogenesis. DESIGN, SETTING, SUBJECTS, AND INTERVENTION: We conducted a randomized, double-blinded, placebo-controlled trial in 99 healthy men randomly assigned to receive dutasteride (D; 0.5 mg) (n = 33), finasteride (F; 5 mg) (n = 34), or placebo (n = 32) once daily for 1 yr.

MAIN OUTCOME MEASURES

Blood and semen samples were collected at baseline and 26 and 52 wk of treatment and 24 wk after treatment and were assessed for T, DHT, and semen parameters.

RESULTS

D and F significantly (P < 0.001) suppressed serum DHT, compared with placebo (D, 94%; F, 73%) and transiently increased serum T. In both treatment groups, total sperm count, compared with baseline, was significantly decreased at 26 wk (D, -28.6%; F, -34.3%) but not at 52 wk (D, -24.9%; F, -16.2%) or the 24-wk follow-up (D, -23.3%; F, -6.2%). At 52 wk, semen volume was decreased (D, -29.7%; F, -14.5%, significantly for D) as was sperm concentration (D, -3.2%; [corrected] F, -7.4%, neither significant). There was a significant reduction of -6 to 12% in sperm motility during treatment with both D and F and at follow-up. Neither treatment had any effect on sperm morphology.

CONCLUSIONS

This study demonstrates that the decrease in DHT induced by 5ARIs is associated with mild decreases in semen parameters that appear reversible after discontinuation.

Steroid hormones for contraception in men

BACKGROUND

Male hormonal contraception has been an elusive goal. Administration of sex steroids to men can shut off sperm production through effects on the pituitary and hypothalamus. However, this approach also decreases production of testosterone, so 'add-back' therapy is needed.

OBJECTIVES

To summarize all randomized controlled trials of male hormonal contraception.

SEARCH STRATEGY

We searched the computerized databases CENTRAL, MEDLINE, EMBASE, POPLINE, and LILACS (each from inception to March 2006) for randomized controlled trials of hormonal contraception in men. We wrote to authors of identified trials to seek unpublished or published trials that we might have missed.

SELECTION CRITERIA

We included all randomized controlled trials in any language that compared a steroid hormone with another contraceptive. We excluded non-steroidal male contraceptives, such as gossypol. We included both placebo and active-regimen control groups. All trials identified included only healthy men with normal semen analyses.

DATA COLLECTION AND ANALYSIS

Azoospermia (absence of spermatozoa on semen examination) was the primary outcome measure. Data were insufficient to examine pregnancy rates and side effects.

MAIN RESULTS

We found 30 trials that met our inclusion criteria. The proportion of men who achieved azoospermia varied widely in reports to date. A few important differences emerged from these trials: levonorgestrel implants combined with injectable testosterone enanthate (TE) were more effective than levonorgestrel 125 microg daily combined with testosterone patches; levonorgestrel 500 mug daily improved the effectiveness of TE 100 mg injected weekly; desogestrel 150 mug was less effective than desogestrel 300 mug (with testosterone pellets); testosterone undecanoate (TU) 500 mg was less likely to produce azoospermia than TU 1000 mg (with levonorgestrel implants); norethisterone enanthate 200 mg with TU 1000 mg led to more azoospermia when given every 8 weeks versus 12 weeks; four implants of 7-alpha-methyl-19-nortestosterone (MENT) were more effective than two MENT implants. Several trials showed promising efficacy in terms of percentages with azoospermia. Three examined desogestrel and testosterone preparations or etonogestrel (metabolite of desogestrel) and testosterone, and two examined levonorgestrel and testosterone.

AUTHORS' CONCLUSIONS

No male hormonal contraceptive is ready for clinical use. Most trials were small exploratory studies. As a result, their power to detect important differences was limited and their results imprecise. In addition, the definition of oligozoospermia has been imprecise or inconsistent. To avoid bias, future trials need more attention to the methodological requirements for randomized controlled trials. More trials with adequate power would also be helpful.

Contraceptions masculines non déférentielles : revue de la littérature

OBJECTIVES

To review the state of progress of the various male contraceptive methods (with the exception of deferential methods).

MATERIAL AND METHODS

A review of the literature was performed by using the key words: male/contraception, limiting the search to original articles in English and French. Articles on vasectomy and the other deferential methods of contraception are not considered in the present review.

RESULTS

Three methods of male contraception are widely used at the present time: withdrawal, male condom and vasectomy, although other types of male contraception have been shown to be effective, including hormonal contraception, which appears to be the most promising technique and the subject of the majority of research. Other contraceptive methods (immunological, thermal...) could constitute possible alternatives.

CONCLUSION

Male contraception remains under-used, as only male condoms are commonly used (apart from withdrawal and vasectomy). Consequently, new research protocols in the field of male contraception must be strongly encouraged.

Testosterone gel combined with depomedroxyprogesterone acetate is an effective male hormonal contraceptive regimen and is not enhanced by the addition of a GnRH antagonist

INTRODUCTION

Exogenous androgens plus progestins can be used to suppress spermatogenesis, resulting in effective male hormonal contraception; however, induction of azoospermia can require 3-6 months, and these methods require injectable or implantable androgens. We hypothesized that testosterone (T) transdermal gel (T gel) could be combined with a depot formulation of the progestin, depomedroxyprogesterone acetate (DMPA), with or without the potent GnRH antagonist, acyline, to suppress spermatogenesis conveniently, rapidly, and reversibly.

OBJECTIVES

The objectives of the study were: 1) to determine the rate of severe oligospermia (< or = 1 million sperm/ml) using T gel+DMPA; and 2) to determine whether the addition of acyline to T gel+DMPA during the first 12 wk of the regimen would accelerate and improve suppression of spermatogenesis.

METHODS

Forty-four healthy men, ages 18-55 yr, were randomized to T gel (100 mg daily)+DMPA (300 mg/3 months) or acyline (300 microg/kg.2 wk x 12 wk)+T gel+DMPA. Thirty-eight men completed the 24-wk treatment protocol.

RESULTS

All men had dramatic suppression of spermatogenesis; 90% of the subjects became severely oligospermic, a rate comparable to implantable and injectable T+progestin combinations. The addition of acyline did not significantly accelerate spermatogenic suppression or improve rates of severe oligospermia. There were no serious adverse events, and there were minimal changes in weight, serum lipids, and prostate-specific antigen.

CONCLUSIONS

The combination of T gel+DMPA is a promising new regimen in male contraception. The addition of the GnRH antagonist acyline, as part of an induction phase in a male contraception regimen, has limited clinical utility. Additional studies using T gel for male contraception are warranted.

Direct effect of progestogen on gene expression in the testis during gonadotropin withdrawal and early suppression of spermatogenesis

CONTEXT

Testicular production of steroids and gametes is under gonadotropin support, but there is little information as to the molecular mechanisms by which these are regulated in the human. The testicular response to gonadotropin withdrawal is important for the development of effective contraceptive methods.

OBJECTIVE

Our objective was investigation of expression of genes in the normal human testis reflecting steroidogenesis, Sertoli cell function, and spermatogenesis after short-term gonadotropin withdrawal and the effects of activating testicular progesterone receptors.

DESIGN AND SETTING

We conducted a randomized controlled trial at a research institute.

PATIENTS

Thirty healthy men participated.

INTERVENTIONS

Subjects were randomized to no treatment or gonadotropin suppression by GnRH antagonist (cetrorelix) with testosterone (CT group) or with additional administration of the gestogen desogestrel (CTD group) for 4 wk before testicular biopsy. Gene expression was quantified by RT-PCR.

RESULTS

Both treatment groups showed similar suppression of gonadotropins and sperm production and markedly reduced expression of steroidogenic enzymes. Addition of progestogen in the CTD group resulted in reduced expression of 5alpha-reductase type 1 compared with both controls and the CT group. Inhibin-alpha and the spermatocyte marker acrosin-binding protein were significantly lower in the CTD but not CT groups, compared with controls, but did not differ between treated groups. Men who showed greater falls in sperm production also showed reduced expression of these three genes but not of the spermatid marker protamine 1.

CONCLUSIONS

These data provide evidence for direct progestogenic effects on the testis and highlight steroid 5alpha-reduction and disruption of spermiation as important components of the testicular response to gonadotropin withdrawal.

Significant impact of 5alpha-reductase type 2 polymorphisms on sperm concentration and motility

Androgens, including 5alpha-dihydrotestosterone (DHT), are known to play a role for spermatogenesis and accessory sex gland function. The enzyme 5alpha-reductase (SRD5A) catalyses the conversion of testosterone to DHT. Our objective was to investigate whether polymorphisms in the SRD5A2 gene influence semen parameters in the general population. DNA from 182 Swedish military conscripts was examined for the A49T, V89L, and R227Q polymorphisms in the SRD5A type 2 gene. Ejaculates were analysed according to WHO guidelines. In addition, sperm motility was assessed using computer-aided sperm analysis (CASA). Seminal markers of epididymal (neutral alpha-glucosidase), prostatic (prostate specific-antigen and zinc), and seminal vesicles function (fructose) were measured. The A49TT-allele was associated with significantly higher sperm concentration compared with the wild type A-allele (mean: 102 x 10(6)/mL vs. 57 x 10(6)/mL, p = 0.02). The V89LV-genotype was correlated with significantly higher proportion progressive motile spermatozoa compared with the L-variant (mean: 55% vs. 48%, p = 0.04). The same trend was found regarding the CASA motile spermatozoa (mean: 52% vs. 41%, p = 0.02). No association between any of the polymorphisms and biochemical markers was found. SRD5A2 gene variants were associated with sperm concentration and motility, but not with epididymal and accessory sex gland markers. This effect on sperm parameters might therefore be exerted via a direct effect of DHT on spermatogenesis.

Male hormonal contraception: concept proven, product in sight?

Current male hormonal contraceptive (MHC) regimens act at various levels within the hypothalamic pituitary testicular axis, principally to induce the withdrawal of the pituitary gonadotrophins and in turn intratesticular androgen production and spermatogenesis. Azoospermia or severe oligozoospermia result from the inhibition of spermatogonial maturation and sperm release (spermiation). All regimens include an androgen to maintain virilization, while in many the suppression of gonadotrophins/spermatogenesis is augmented by the addition of another anti-gonadotrophic agent (progestin, GnRH antagonist). The suppression of sperm concentration to 1 x 10(6)/ml appears to provide comparable contraceptive efficacy to female hormonal methods, but the confidence intervals around these estimates remain relatively large, reflecting the limited number of exposure years reported. Also, inconsistencies in the rapidity and depth of spermatogenic suppression, potential for secondary escape of sperm into the ejaculate and onset of fertility return not readily explainable by analysis of subject serum hormone levels, germ cell number or intratesticular steroidogenesis, are apparent. As such, a better understanding of the endocrine and genetic regulation of spermatogenesis is necessary and may allow for new treatment paradigms. The development of an effective, consumer-friendly male contraceptive remains challenging, as it requires strong translational cooperation not only between basic scientists and clinicians but also between public and private sectors. At present, a prototype MHC product using a long-acting injectable testosterone and depot progestin is well advanced.

Drug Insight: recent advances in male hormonal contraception

As there are limitations to current methods of male contraception, research has been undertaken to develop hormonal contraceptives for men, analogous to the methods for women based on estrogen and progestogens. When testosterone is administered to a man, it functions as a contraceptive by suppressing the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. Since these hormones are the main stimulatory signals for spermatogenesis, low levels of LH and FSH markedly impair sperm production. After 3-4 months of testosterone treatment, 60-70% of men no longer have sperm in their ejaculate, and most other men exhibit markedly diminished sperm counts. Male hormonal contraception is well tolerated, free of serious adverse side effects, and 95% effective in the prevention of pregnancy. Importantly, male hormonal contraception is reversible, with sperm counts usually recovering within 4 months of the discontinuation of hormone treatment. Because exogenous testosterone administration alone does not completely suppress sperm production in all men, researchers have combined testosterone with second agents, such as progestogens or gonadotropin-releasing-hormone antagonists, to further suppress secretion of LH and FSH and improve suppression of spermatogenesis. Recent trials have used combinations of long-acting injectable or implantable forms of testosterone with progestogens, which can be administered orally, by injection or by a long-acting implant. Such combinations suppress spermatogenesis to zero without severe side effects in 80-90% of men, with near-complete suppression in the remainder of individuals. One of these testosterone and progestogen combination regimens might soon bring the promise of male hormonal contraception to fruition.

Analysis of the Human Sperm Proteome

As part of our effort to identify putative protein targets for the development of male contraceptives, we performed an in-depth proteomic analysis of human sperm by liquid chromatography and tandem mass spectrometry. Motile sperm were collected from a single fertile individual and fractionated into detergent-soluble and detergent-insoluble fractions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis separation of these fractions, followed by manual cutting of the gel, yielded 35 gel sections for each fraction to include proteins across the full range of electrophoretic mobility. Proteomic analysis of these gel sections identified more than 1,760 proteins with high confidence, with 1,350 proteins identified in the soluble fraction, 719 identified in the insoluble fraction, and 309 identified in both fractions. This characterization of the human sperm proteome provides a high-resolution, physiologically relevant index of the proteins that comprise human sperm.

Male Hormonal Contraceptives

Because of the shortcomings of currently available methods of male contraception, efforts have been made to develop additional forms of contraception for men. The most promising approach to male contraceptive development involves hormones, and requires the administration of exogenous testosterone. When administered to a healthy man, testosterone functions as a contraceptive by suppressing the secretion of luteinizing hormone and follicle-stimulating hormone from the pituitary, thereby depriving the testes of the signals required for normal spermatogenesis. After 2-3 months of treatment, low levels of pituitary gonadotropins lead to markedly decreased sperm counts and effective contraception in the majority of men. Treatment with exogenous testosterone has proven not to be associated with serious adverse effects and is well tolerated by men. In addition, sperm counts uniformly normalize when testosterone is discontinued. Thus, male hormonal contraception is safe, effective, and reversible; however, spermatogenesis is not suppressed to zero in all men, meaning that some diminished potential for fertility persists. Because of this, recent studies have combined testosterone with progestogens and/or gonadotropin-releasing hormone antagonists to further suppress pituitary gonadotropins and optimize contraceptive efficacy. Current combinations of testosterone and progestogens completely suppress spermatogenesis in 80-90% of men without severe adverse effects, with significant suppression in the remainder of individuals. Recent trials with newer, long-acting forms of injectable testosterone, which can be administered every 8 weeks, combined with progestogens, administered either orally or by long-acting implant, have yielded promising results and may soon result in the marketing of a safe, reversible, and effective hormonal contraceptive for men.