1 Introduction

There are over hundred million couples in the world who are not using any method of contraception in spite of the fact that they would like to stop or space child-bearing^[1]. Studies show that the unmet need for contraception is related to the number of contraceptive methods and services accessible to the potential users^[2]. The greatest unmet need is among those who have the least access to family planning programmes. Studies also show that for responsible parenthood, and for the good health of the family greater involvement of men is essential. Men must assume greater responsibility for sharing the burden of practising contraception and to protect the health and well being of their partners. It necessitates increasing awareness of and access to technologies and services with appropriate quality care. It also calls for expanding contraceptive choices for men by developing a wider array of effective fertility control methods. The recent studies suggest that male attitude towards family planning is much more favourable than originally believed. A multicountry study involving 1829 men showed that majority of them (44-83%) would welcome a new hormonal method of contraception when available^[3]. Similarly, when women were asked if they would trust their partners to use a contraceptive reliably almost 64 per cent replied in the affirmative^[4]. The results of these studies suggest that if effective, safe, reversible and affordable methods could be made available to men they would use such methods.

In spite of reassuring observations that men have a positive attitude towards sharing contraceptive responsibilities, the contraceptive options available to men are rather limited. The use of condom, when there is no perceived risk of infection, is not the preferred option for birth control. It is labeled as a method which interferes with sexual pleasure^[5]. The withdrawal method, in addition to having a high failure rate of almost 18 per cent^[6], requires interruption of sexual activity at a time when it is peaking. The vasectomy is still not fully reversible. It is quite surprising that there is no effective long-acting and reversible method of contraception for men. Is it that the efforts to develop effective male contraceptive methods are hindered by a lack of knowledge of male reproductive physiology, or is it that sufficient research efforts and financial inputs have not been made in this project? This paper reviews the status of research efforts to develop a contraceptive for men and analyze the constraints in the development of a widely acceptable method.

2 Possible targets for male contraception

Male reproductive system involves interaction between somatic cells and germinal cells as well as complex hormonal interactions with central nervous system controls. The primary sex organ, the testis, produce spermatozoa which travel through the epididymis, vas deference and passes through urethra along with secretions from prostate, seminal vesicle, glands of Littre and Cowper.  Proper functioning in a sequential and orchestrated manner of each organ is necessary for the production of spermatozoa with fertilizing ability. The modern research leading to the development of male contraceptives is targeting the following five areas: (i) inhibition of sperm production, (ii) interference with sperm function, (iii) interruption of sperm transport, (iv) prevention of sperm deposition, and (v) prevention of sperm-egg interaction.

2.1 Inhibition of sperm production

2.1.1 Spermatogenesis and steroidogenesis: possible sites of intervention

The testis produce gametes and sex hormones by the process called spermatogenesis and steroidogenesis. These processes occur in two compartments namely tubular and interstitial which are distinct both morphologically and physiologically. The tubular compartment, consisting of the seminiferous tubules, contains large number of germinal cells and supportive cells called the cells of Sertoli and peritubular cells. The interstitial compartment consists of Leydig cells, connective tissue cells, cells of the immune system, blood vessels, nerves and lymph vessels. The Leydig cells secrete testosterone, in response to luteinizing hormone (LH).  Testosterone gets into the circulation by simple diffusion into lymphatic or passing into capillaries. The Sertoli cells have multiple functions such as synthesis of peptide hormone  (e.g. inhibin) to create and maintain patency of the seminiferous tubules, testicular volume and support sperm production. The first interventional step could be to alter the permeability of the micro vasculature or net fluid flow across the endothelium and factors which can influence the synthesis and secretion of testosterone.

Second intervention could be at the level of spermatogenesis.  The process of spermatogenesis, from the stem cells, can be divided into three stages namely: (i) mitotic division of spermatogonia; (ii) meiotic division of spermatocytes to haploid spermatids; and (iii) transformation of haploid cells spermatids through a series of phases (spermiogenesis) to form spermatozoa.

The first stage of mitotic division of spermatogonia yields spermatocyte which initiate meiosis with concomitant DNA synthesis.  Intercellular bridges connect these two cells which form the basis and also may be a prerequisite for coordinated germ cell development and maturation. The process of maturation is irreversible.  Knowledge of spermatogonial proliferation and differentiation is limited. Alteration of this coordinated germ cell development will be yet another point of intervention, which is an attractive option but at the same time very difficult. However, with the advancement in molecular biology these processes can be well understood.

The different phases of meiotic division give rise to haploid germ cells. This is a very critical event in gametogenesis as it involves exchange of chromosomal material, reduction in chromosome number and development of spermatids.  Meiosis is the critical point in human spermatogenesis because of the remarkable germ cell loss and genetic recombination.  Further research is needed on the regulatory mechanisms and gene expression during meiosis.

Spermiogenesis is unique in a way that numerous new proteins are synthesized from stored paternal mRNA and transcription steps. The change in chromatin structure during this process for, yet unknown reasons, brings about the expression of additional genes. The expression of the haploid genome during the process of spermatogenesis leads to a large number of haploid spermatids. This could be a possible site for disrupting the intercellular regulatory sites.  This can lead to future strategies in the development of newer contraceptive technologies.

2.1.2 Approaches evaluated to inhibit sperm production

A number of approaches have been evaluated to inhibit sperm production, of which the use of hormones has given the most encouraging results so far.  Androgens either alone or in combination with progestins, and GnRH agonists and antagonists either alone or in combination with androgens have been most extensively investigated. Immunization against GnRH and FSH has also been tried in limited clinical trials.

2.1.2.1 Androgens

(a) Androgens alone

Testosterone is essential for the maintenance of spermatogenesis and libido, however, when given in pharmacological doses it has inhibitory effects on the secretion of gonadotrophins and consequently on spermatogenesis.  Long-term treatment of men aged 23-38 years with testosterone propionate (i.m., 25 mg/day) has been shown to induce complete suppression of spermatogenesis by 60 days^[7]. The effects were reversed within 150 days of the stoppage of treatment. sing a relatively longer acting androgen, testosterone enanthate (TE), the WHO has completed two multicentric clinical trials and has confirmed the contraceptive potential of androgens in men^[8,9]. In the two trials involving 670 men from seven countries, weekly i.m. treatment with TE (200 mg/week) induced azoospermia in about 70 per cent and severe oligospermia in most other men during the first six months of treatment.  The pregnancy rate, assessed during the 12-month efficacy phase following the initial 6 month treatment, was zero per cent among azoospermic men, and 8.1 per cent among those whose sperm concentration was reduced to the level of 0.1 million/mL to 3 million/mL. The inhibitory effects of TE on sperm production were reversed following stopping of treatment.  Normal sperm concentration (about 20 million/mL or more) was restored in 64 per cent of men in an average 112 days, and base-line concentration in 34 per cent cases in 203 days after the withdrawal of treatment.

Prolonged treatment with high doses of TE was associated with a number of side effects. The most common side effects were painful injections, acne, fatigue and weight gain^[10].  Gynecomastia and prostate problems were detected in almost 9 per cent and 4 per cent men, respectively.  Total cholesterol and its fractions as well as  HDL:LDL ratio were lowered during the treatment period.  Liver transaminases were increased significantly in the Chinese subjects.  Most of these androgen and dose-related effects have also been reported in previous studies^[11,12].

Nevertheless, these trials provided a number of highly significant observations. Firstly, prolonged treatment with TE impaired spermatogenesis, however, the residual spermatozoa still retained the fertilizing ability, suggesting thereby that the induction of azoospermia is essential for a hundred per cent effective regimen.

These studies also revealed heterogeneity in the spermatogenic response among Chinese and Caucasian men^[8]. Out of the 70 Chinese, from three centres, who completed the suppression phase in the trial 64 (91%) became azoospermic, whereas of the 155 Caucasian men 93 (60%) became azoospermic. The reasons for such differences are not yet known. 

Finally, even among the same ethnic groups a variable response to treatment with TE  in inhibiting the sperm production was observed. The reasons for polymorphism in response are not known. The base-line characteristics such as body mass index, size of the testis, sperm concentration and sperm motility did not differ significantly among those men who became either azoospermic or oligozoospermic^[13].  Similarly, the men in two groups did not respond significantly differently in terms of levels LH, FSH, free or total testosterone or estradiol levels^[13,14]. These results suggest that pharmacokinetics of testosterone or its pharmacodynamic effects at the hypothalamo-hypophyseal-gonadal axes may not account for varying response among men.  However, it has been shown that in men in which testosterone treatment induced oligozoospermia the activity of 5 -reductase was selectively increased after treatment, but similar rise was not observed in those becoming azoospermic^[15]. The difference in the androgenic milieu thus created may allow spermatogenesis to continue, although at a reduced rate, despite the apparent absence of gonadotrophins.

It is possible that the observed side effects are due to the high doses of TE used and fluctuations in the plasma levels by weekly i.m. injections in oil base. In view of this, a number of longer-acting androgens and improved drug-delivery systems are being developed and evaluated for anti-spermatogenic effects. A single i.m. injection of testosterone buciclate, an ester of testosterone, has been shown to maintain physiological levels of testosterone for 16-20 weeks^[16].  Treatment also impaired spermatogenesis in all 8 eugonadal volunteers, however, azoospermia was induced in only 3^[17]. Testosterone encapsulated into biodegradable polylactide-glycolide co-polymer microsheres^[18], transdermal delivery systems for testosterone^[19,20], and testosterone implants^[21,22] have been evaluated with the objective of maintaining physiological concentrations of androgens over an extended period of time.  It is hoped that when fully developed these longer-acting formulations will provide better approach for impairing male fertility while keeping the dose-related side effects to the minimal.

(b) Androgens in combination with progestins

Since progestins can act synergistically with androgens to block gonadotrophin function and consequently spermatogenesis, combination of a number of progestins with TE has been evaluated for its male contraceptive potential^[23-27]. The foreseen advantages of the combination regimen are reduced drug load on the body and dose-related side effects of androgens.

Daily oral administration of levonorgestrel (0.5 mg/day) followed by a weekly i.m. administration of TE (100 mg/week) to adult men has been shown to impair spermatogenesis^[28]. Induction of oligozoospermia and azoospermia was faster and in more number of subjects treated with a combination regimen as compared to those who were treated with only-androgen regimen.  However, the side effects observed in men treated with androgen-alone such as decrease in HDL-cholesterol, weight gain and acne were also observed in those treated with a combination regimen. The side effects could be due to the androgenic properties of levonorgestrel, which get attenuated when administered in conjunction with TE.

Medroxyprogesterone acetate, which is free of androgenic effects, has also been tried in combination with testosterone or 19-nortestosterone ester to suppress spermatogenesis, however, consistent suppression of spermatogenesis was not observed with this regimen in the non-Indonesian men^[29,30].  However, the Indonesian men were rendered azoospermic or nearly azoospermic by 3-weekly injection of TE or 19-nortestosterone ester plus DMPA at 6-week intervals^[31].

More recently, 3-ketodesogestrel has also been evaluated in combination with varying doses of testosterone^[32]. The advantage of 3-ketodesogestrel has been that this synthetic progestin is considered to have less androgenic properties than other 19-nortestosterone-derived gonane progestogens^[33].  Moreover, it is being used in combination with estrogens as a female contraceptive for almost 20 years and its use does not seem to upset the lipid profile. A limited clinical trial involving eight healthy men has shown that a daily oral dose of 300 g 3-ketodesogestrel followed by weekly i.m. injection of 50 mg TE induced azoospermia within 24 weeks in all the men^[32].  These results suggest that the combined dose of progestins and androgens is a promising approach to achieve reversible male contraception.  

(c) Androgens in combination with progestin having anti-androgenic activity

The observations that small amounts of intratesticular testosterone can maintain spermatogenesis, although at a  reduced rate, despite suppression of FSH^[34,35], prompted researchers to use progestins with antiandrogenic activity to block spermatogenesis.  The rational of using such progestins, such as cyproterone acetate (CPA), was that its progestational activity would suppress gonadotrophin mediated effects, while the antiandrogenic activity would block the stimulatory effects of androgens on sperm production at the testicular level. The antiandrogenic action of CPA is based on its ability to competitively inhibit the binding of testosterone and dihydrotestosterone to androgen receptors^[36,37].  The blocking of intratesticular testosterone effect by CPA is presumed to cause a decrease in cell-adhesion molecule concentrations and contribute to the premature sloughing of spermatids from the seminiferous epithelium^[38] thereby resulting in early disappearance of spermatozoa from the ejaculate.

In langur monkeys, oral daily treatment with CPA (1 mg/kg body wt) and i.m. TE (2mg/kg body wt/15 days) over a period of 90 days has been shown to induce severe oligozoospermia or azoospermia in all the animals^[39].  Circulating testosterone levels were maintained within the normal range and libido and sexual potency were unaffected.  In men also treatment with low doses of CPA has been shown to impair spermatogenesis^[40]. When treatment with CPA was combined with TE a more rapid and profound suppression of spermatogenesis was observed^[41,42]. The effects were dependent on the dose of CPA. Daily dose of 25 mg, 50 mg or 100 mg CPA followed by 100 mg TE/week induced azoospermia in all men^[42]. Further decrease in the dose of CPA to 12.5 mg  induced azoospermia in 3 out of 5 men^[43]. The anti-spermatogenic effects of combination regimen were more profound as compared to when TE was given alone.  Time to attain azoospermia was also significantly less in those treated with combination regimen as compared to TE alone group. The effects of this combination regimen were reversible, sperm counts returned to baseline levels in all men within 20 weeks of stopping the treatment.

Some concerns have been expressed with the possible CPA-induced adducts with DNA in liver cell cultures^[44].  However, in clinical trials liver function tests were not affected in men treated with CPA^[45]. The teratogenic, including carcinogenic effects of CPA , if any, need to be ruled out before embarking upon clinical trials involving its long-term use as a male contraceptive.

2.1.2.2 Gonadotrophin releasing hormones (GnRH)

GnRH secreted from hypothalamus stimulates the anterior pituitary to secrete LH and FSH that is required for normal spermatogenesis. However, prolonged treatment with GnRH desensitizes the GnRH receptors resulting in suppression of gonadotrophins and spermatogenesis. GnRH antagonists hold more promise because of their high affinity for GnRH receptors and slower dissociation from the receptors than  native GnRH or agonists.

(a) GnRH agonists

Twelve studies, involving 106 normal healthy men, were carried out between 1979 and 1992 to investigate the ability of GnRH agonists in combination with androgens to suppress spermatogenesis^[46]. The GnRH agonists decapeptyl, buserelin and nafarelin were administered at doses ranging from 5 g/day to 500  g/day for periods of 6-60 weeks.  Azoospermia was achieved only in a small proportion (~20%) of men.  Moreover, the combined GnRH agonist and testosterone regimen was less effective in suppressing spermatogenesis as compared to the androgen alone^[47], which was probably due to the inadequate suppression of FSH levels. While the treatment suppressed serum levels of LH and endogenous testosterone but levels of FSH returned to almost normal values five weeks after the GnRH agonist administration. This divergent effects of GnRH agonist on LH and FSH have been confirmed by other workers^[48,49]. Whether extremely high doses of GnRH agonists can suppress FSH over extended periods of time in normal men is not known. However, with the current GnRH agonists and the doses tested so far the combination of GnRH agonist plus androgen is not useful for male contraception.

(b) GnRH antagonists

GnRH antagonists produce a precipitous and prolonged fall in the serum levels of LH and FSH in men^[50-53].  Initial studies carried out in cynomolgus monkeys showed that GnRH antagonists and testosterone can effectively suppress spermatogenesis^[54].  Similarly, in the five clinical trials conducted, 35 out of the 40 volunteers became azoospermic within 3 months^[46]. In the latest two clinical trials reported^[55,56] all the 14 volunteers became azoospermic within the mean time of 6-8 weeks.  GnRH antagonist-androgen combination was more effective in suppressing spermatogenesis than androgen alone.  However, the doses of GnRH antagonists required are high i.e. 10-20 mg/day. Considering the high cost of GnRH antagonists, the need for daily s.c. administration of up to 20 mg/day renders the method impracticable.  There have been attempts to reduce the load of GnRH antagonists used to bring about azoospermia. Studies in monkeys suggested that the suppression of spermatogenesis achieved by GnRH antagonists could be maintained by substituting GnRH antagonists with testosterone preparation alone^[57]. However, this finding could not be confirmed in a clinical trial involving six volunteers^[56].  Another alternative strategy tried to reduce the amount of GnRH antagonist required to suppress spermatogenesis was to use a relatively high loading dose followed by a lower maintenance dose (~1 mg/day or less)^[53-56]. Once the gonadotrophins and testosterone were effectively suppressed, suppression could be maintained by much lower doses (1 mg/day or even less).

(c) The GnRH vaccine

Passive as well as active immunization against GnRH has been shown to suppress release of gonadotrophins thereby resulting in the regression of Leydig cells and suppression of testosterone production and spermatogenesis in rodents and non-human primates^[58]. These experiments proved the feasibility of inducing specific antibodies against GnRH in sufficient amounts to suppress the biological actions of native hormone using immunogens, carriers and adjuvants permissible for use in humans.  Immunization against GnRH also suppressed the libido of the animals. Preliminary experiment in rodents have revealed that maintenance of constant physiological levels of testosterone, delivered either by slow-releasing  implants or injections of  long-acting  testosterone 17-trans-4-n-butyl cylohexane carboxylate, can sustain normal ejaculatory behaviour  in the immunized animals.  Further, androgen replacement did not restore fertility in the immunized animals. Studies following long-term active immunization of primates with GnRH need to be conducted before embarking upon clinical trials for contraceptive use.

2.1.2.3 Gonadotrophins: FSH  vaccine

Active immunization of adult male bonnet monkeys (Macaca radiata) with purified ovine FSH, adsorbed on an adjuvant alhydrogel, produced high titre antibodies capable of neutralizing hFSH^[59]. Immunization resulted in reduction in sperm counts to acute oligozoospermia to azoospermia without causing any significant change in the serum testosterone levels.  Mating studies with proven fertile female monkeys revealed that none of the males were able to impregnate females, thereby demonstrating that FSH immunization had rendered the males infertile.

A limited clinical study involving five adult men has also shown that immunization against oFSH vaccine produces antibodies capable of both binding and neutralizing bioactivity of hFSH^[60].  Immunization caused reduction in sperm counts (30-74%) in some volunteers. The concentrations of LH, FSH, testosterone, thyroxine and triiodothyronine remained unaltered.  However, serum levels of prolactin were elevated in 3 volunteers. An extended phase I clinical trial evaluating the safety and efficacy of oFSH derived vaccine is warranted.

In an identical study, Srinath and co-workers immunized rhesus monkeys with FSH and observed impaired fertility after one year of immunization^[61].  However, during the third year the sperm counts returned to lower normal range and sperm motility and morphology remained generally normal. Spermatozoa from the immunized animals, in the third year, were also able to penetrate zona-pellucida free hamster eggs, indicating their return of functional integrity. Testosterone, maintained at the physiological levels throughout the immunization period, might have been responsible for the reinitiation of spermatogenesis qualitatively.  The authors believe that suppression or immunoneutralization of FSH alone may not be a viable method of male contraception^[62].

For fear of autoimmune reactions, reservations have been expressed whether immunization against a molecule so central in endocrine control should be pursued for developing contraceptive strategies^[63]. Recent studies show that immunization against the extracellular domain of the FSH receptor impairs sperm count and fertility in bonnet monkeys^[64]. Since FSH receptor expression is restricted to gonadal tissues, it is possible that approaches using  the FSH-receptor rather than FSH for immunization may be of advantage and deserves further exploration.

These studies also raise questions about the need for FSH for spermatogenesis in primates, which is pertinent to mention here.  Two reports using a mouse FSH- subunit knockout model^[65] and analysis of the infertile status of a group of homozygous men with an apparently inactivating mutation of the FSH receptor gene^[66] concluded that FSH is not required for maintenance of spermatogenesis and fertility in humans.  In contrast, there are reports to indicate the requirement of FSH for human male reproduction.  A patient with a congenital absence of FSH due to a mutation in the FSH- chain was reported to be infertile and hypogonadal^[67].  It has also been reported that a patient with activating FSH receptor mutation, who was hypophysectomized for a pituitary tumour, was fertile, inspite of absence of serum gonadotrophins and low levels of testicular testosterone, suggesting that FSH could autonomously sustain spermatogenesis even at low concentrations of testicular testosterone^[68].  A fair amount of clinical data hitherto available is supportive of FSH having a significant role in promoting quantitative spermatogenesis, leading to the sperm quality needed for successful fertilization.

2.2 Constraints in developing contraceptive based on inhibition of sperm production

Constraints in the further development of androgens as a male contraceptive are both biological and technological.  The biological constraints include (i) long duration of 72 days required to achieve suppression of spermatogenesis; (ii) the need to achieve azoospermia for 100 per cent efficacy; (iii) suppression of high density cholesterol; (iv) ethnic variations in the response to androgens.  The technological constraints include (i) non availability of sustained release delivery systems; (ii) non availability of androgens with increased biopotency; and (iii) high cost.  

Combination of GnRH antagonist and androgen have great potential to become an effective male contraceptive method.  But a number of issues have to be sorted out before this method becomes practical. (1)  The biopotency of currently available antagonists is relatively low and milligram amounts of these peptides are required to be administered systematically daily to achieve gonadotrophin suppression.  It is imperative to develop antagonists with increased biopotency,  so that the doses could be substantially reduced. (2)  Since the most potent GnRH antagonists invariably contain substitutions of the natural decapeptide with several unnatural synthetic amino acids, they are extremely expensive and complex compounds to produce.  It is absolutely essential to bring down the price of the GnRH antagonists if they have to become contraceptive agents. (3)  If the concept of a relatively high loading dose followed by a lower maintenance dose is generally feasible, attempts should be made to develop GnRH antagonist depot preparations.

There are indications that testosterone depot preparations such as testosterone buciclate or testosterone implants given together with GnRH antagonist may fulfil the requirements of a quick onset of contraceptive protection, high contraceptive efficacy and long inter-injection intervals. However, large scale clinical trials with such compounds have yet to be conducted.  Finally, attempts should be made to develop non-peptide GnRH antagonists which may be more economical to produce and also orally effective.

One should also consider whether during extended periods of interference with spermatogenesis, the maintenance of higher than normal level of stimulation of Leydig cells by LH is without risk.  The second point to be considered is the possible genetic abnormalities induced by interference with spermatogenesis.

2.3 Interference with sperm function

The epithelium of epididymis has characteristic population of epithelial cells and also population of wandering lymphocytes. This is the site of accumulation and storage of spermatozoa.  They also maintain a unique environment for the survival of spermatozoa, which is the main role of epididymis.  Epididymal secretions are important for the changes to be brought about in maturation of spermatozoa; the process by which sperms gain their ability to fertilize eggs.  However, very little is known about the functions and nature of these secretions in man.  Recent research points to some specific human epididymal secretions involved in gamete recognition^[60,70]. While there are some suggestions that sperm maturation may not be as important in human as in other animals and sperms from high in the epididymis or even from testicular spermatids may be capable of fertilization and initiating pregnancies^[71-73]. The above findings are from the experiences gained from  assisted reproductive technologies and the in vivo normal reproductive procedures do require sperms to be matured in the epididymis as the challenges faced by sperms in vivo are completely different from those encountered in vitro.  However, the possibility of inhibiting sperm maturation in the epididymis has to be given a serious consideration as a means of contraception.

An approach which will arrest the fertilizing ability of spermatozoa, either in the testis, the epididymis or the vas deferens, is likely to find better compliance than those methods which suppress sperm production.  Blocking of sperm function might be a rapid process both in onset and reversibility, and may not disrupt testicular endocrine function and thereby suppress libido.  Interference with sperm functional development could be at the level of sperm motility, formation of sperm organelles or both sperm function and sperm surface membrane integrity.

A number of chemical compounds have been identified which interfere with sperm maturation in the epididymis without affecting the sperm production. However, toxic effects of these compounds prohibited their long-term evaluation as antifertility agents. For example, oral treatment with -chlorohydrin and 6-chloro-6-deoxysugars has been shown to induce infertility in male monkeys, however, their neurotoxic effects^[74] preclude their development for use in humans. The identification of gossypol and its association with male sterility had raised high hopes of a male contraceptive. However, its use leads to severe potassium deficiency and irreversible damage to spermatogenesis^[75,76]. Similarly, the plant Trypterigium wilfordii, which reduces sperm motility, has immunosuppressive side effects^[77,78].  These studies nevertheless suggest that post-testicular blocking of sperm function is a viable approach. 

2.4 Constraints in the development of methods which interrupt sperm function

The approaches which do not affect sperm production but selectively impair sperm function would be preferable as male contraceptives. The feasibility of developing such an approach has also been demonstrated. However, the compounds evaluated so far have turned out to be highly toxic. This necessitates continued efforts to screen more compounds.  Meiosis and germ cell-specific enzymes that may be needed for sertoli cell-germ cell interaction could be used as targets for intervention. But very few non-toxic specific inhibitors have been identified to-date which may selectively perturb spermatogenesis.

2.5 Interruption of sperm transport

Interruption of sperm transport through the vas either by vasectomy or percutaneous injection of liquids which form cure-in-place plugs are attractive options for male contraception. In addition, non-occlusive devices which deviate the course of spermatozoa so that they are either voided in urine or destroyed are being evaluated for their contraceptive potential.

2.5.1 Vasectomy

Vasectomy is an effective, safe and easy to perform method of male contraception. However, in India only about 2 per cent men of reproductive age rely on vasectomy for birth control. Widespread acceptability of this method is low because (i) it is a surgical intervention; (ii) of the false apprehensions that the procedure reduces sexual potency; (iii) of the fear of cardiovascular sequelae; (iv) of the fear of an increased risk of prostate and testicular cancer among vasectomized mBecause of these events large number of spermatid target are possible for intervention and at least they offer a theoretical possibility of en; and (v) the procedure is considered permanent as reversal is difficult and the success rate, as determined by subsequent fertility, is low.

Studies carried out under the aegis of the Indian Council of Medical Research have shown that vasectomy had no adverse effects on the cardiovascular system^[79]. However, the possible association of vasectomy with increased risk for prostate cancer is still being debated. Results of a study of more than 1000 men in Mumbai suggested an association between vasectomy and prostate cancer, particularly among men who underwent vasectomy at least 20 years prior to the diagnosis of cancer or who were at least 40 years old when they had vasectomy^[80]. On the other hand, a review by the ICMR has concluded that there was no consensus about an increased risk of prostate cancer among vasectomized men^[81]. The overall morbidity and mortality rates due to cancer in vasectomized men are equal to or lower than those of community-matched controls. Regarding the association between vasectomy and testicular cancer, follow up on a study in Denmark in which 73,917 vasectomized men were identified from hospitals and pathology registers between 1977 and 1989 demonstrated no increased risk of testicular cancer in the group^[82].  These observations are quite reassuring to dispel any fear which vasectomized men or those thinking of opting for this approach for fertility regulation might have. 

The concern that the procedure is not reversible is justifiable. The couples would prefer to use a method which is hundred per cent reversible because the infant mortality rate in most of the developing countries is very high.  Since vasectomy reversal is requested in 2 to 7 per cent of men, research efforts to make vasectomy a reversible procedure must be pursued more vigorously. Identifying and correcting the reasons for low pregnancy rate in spite of high patency rate would improve success of vasectomy reversal and increase vasectomy acceptance. Secondly, the conventional vasectomy procedure requiring incision should be replaced with the no scalpel procedure. The no-scalpel method yields much fewer complications and is likely to find greater acceptance than the traditional methods. 

2.5.2 Vas occlusion

Vas occlusion-related methods include percutaneous injection of liquids such as polyurethane, silicone or styrene maleic anhydride (SMA) in the vas deferens. This approach is being developed to avoid the need for a skin incision.  However, the success of this approach lies in the precise injection of chemical mixture into the lumen of the vas deferens by correct grasping and stabilization of vas underneath the scrotal skin.

In a study involving 12,000 Chinese men who underwent vas occlusion using percutaneous injection of medical grade polyurethane elastomer, examination of semen samples collected from 500 men at the end of one year showed azoospermia in 490, severe oligospermia in 5 and in the other 5 the sperm concentrations were more than 4 million/mL^[83]. A similar azoospermia rate persisted for 100 men who agreed to provide semen after 2 and 3 years of vas occlusion.  The plug is removed following a longitudinal incision in the vas, under local anaesthesia. Usually the incision in the vas does not require a suture although the skin incision does. In men who had plug in place for over one year, removal of plug restored fertility within 1-2 years of the removal of plug^[84]. On the other hand the reversal was much faster in those who had plug in place for less than one year.  Although there have been no signs of long-term side effects from the use of this material since 1984, some concerns were raised about the possible formation of certain amines during polymerization. In addition, a study has reported rupturing of the vas and leakage of polyurethane elastomer^[85]. The authors suggest that the contraceptive action of elastomer is due to secondary obstruction due to tissue proliferation after the rupture of the vas deferens. Proper skill and practice to achieve percutaneous cannulation of the vas deferens seems to be of critical importance.

Guha and associates have shown that injection of SMA (60 mg) in a solvent system of dimethylsulphoxide into the vas deference induces complete azoospermia^[86]. Twelve adult healthy men who were administered the drug were rendered infertile over the one year study period and the procedure did not lead to any clinical complications in the urogenital system and other parts of the body.  These studies are being extended in larger number of volunteers.

Percutaneous injection of liquid silicone to occlude the vas has also been evaluated in a clinical trial. The injection of 0.1 to 0.16 mL in the vas of 14 men, produced occlusion of a 1-cm length of the vas^[87].  Azoospermia was achieved in all men by 9 months of the injection of silicone. Results of some studies carried out in Indonesia and China have shown a high frequency of vas rupture following percutaneous intravasal injection of silicone.  These studies need to be extended to determine the optimum volume and pressure characteristics needed to achieve complete vas occlusion without causing any damage to the vas.

2.6 Constraints in the development of methods for interruption of sperm transport

The long-term safety of vasectomy has been reaffirmed by several large scale epidemiological studies.  However, the reversibility of vasectomy, as measured by pregnancy rates, is usually less than 60 per cent.  The reasons for this functional failure, in spite of near 90 per cent patency rates are yet unanswered.  The vasovasostomy is more complicated and expensive as compared to vasectomy.  Moreover, not many surgeons have the desired skills for successful reversal of the procedure. In addition, increased incidence of formation of autoantibodies to spermatozoa in vasectomized men raises apprehensions about restoring fertility even after an accurate vasovasostomy.  Until near 100 per cent reversibility of vasectomy is assured, it should be promoted as a permanent method of contraception, or men should consider it permanent in their decision-making process.

The success of the approach of using chemical methods for vas occlusion lies in the precise injection of chemical mixture into the lumen of the vas deferens by correct grasping and stabilization of vas underneath the scrotal skin. As in the case of vasectomy, restoration of fertility after the removal of the plug might not be feasible in all men.  Histological studies show that four years after the vas occlusion using elastomers, the obstruction is no more confined to the area of injection but quite distal to the plug, raising doubts on the refertilization. Further research with vas occluding agents is warranted.

2.7 Prevention of sperm deposition

Condom has been promoted as an easy to use, comfortable and safe method of birth control.  In fact it is the only effective method to prevent both unwanted pregnancy and sexually transmitted diseases (STDs) including HIV/AIDS. However, contraceptive efficacy of condom in typical use is less than that of most methods which are at the disposal of women. Therefore it is essential to undertake research to identify the means to improve the acceptance and contraceptive effectiveness of condom.

In addition to promoting the use of condom, there is a need to assess the effectiveness of vaginal microbicides to prevent pregnancy as well as transmission of STDs.  Recent studies in Zimbabwe show that several men might prefer microbicides, if shown to be safe and effective, over condoms as the later interfere with the act and reduces pleasure.

2.8 Constraints in the development of methods which prevent sperm deposition

A number of studies show that large number of men, at least in stable marriages, do not prefer condom mainly because its use reduces sexual pleasure. A variety of flavoured, coloured, scented and ribbed condoms are being developed to enhance the acceptability of condom^[88]. In addition, the design of the condoms is being changed from tight fit to bagginess built for better sensation and friction at the right places. In addition to developing more acceptable condoms, there is a need for behavioural change to motivate men to use condoms to protect their families from disease. The condoms are used most often outside marriage where there is a risk of STDs. This also calls for empowerment of women to propose to their male partners, in case of perceived risk, to use condom without fear of their reaction.

2.9 Prevention of sperm-egg interaction

Spermatozoa, being sequestered from the immune system because of the blood-testis barrier, should be immunogenic in the male. Observations that up to 70 per cent of vasectomized men develop antisperm antibodies and up to 30 per cent of infertility is associated with antisperm antibodies in the male and/or the female partner of an infertile couple confirm the immunogenicity of spermatozoa.

A number of sperm antigens have been purified and characterized biochemically and immunologically. The antigens with potential application in immunocontraception are LDH-C4, PH-20, SP-10, HSA-63, FA-1, FA-2, CS-1, hSPI, 26 kDa and 80 kDa proteins.  Among the above mentioned antigens, hSPI and 26 kDa protein seem to be better candidates for male contraceptive vaccine development as hSPI is a sperm coating antigen and 26 kDa protein is of epididymal  origin^[89]. Antibodies to such antigens should have easier access to the target tissue, i.e., epididymis, as compared to antibodies to testicular antigens, to bind and agglutinate spermatozoa without causing autoimmune orchitis or disrupting spermatogenesis. These antigens and many others are at various stages of evaluation in laboratory animals and extensive work still needs to be carried out before any sperm-surface antigen could be clinically evaluated.

2.10 Constraints in the development of methods to prevent sperm-egg interaction

Although whole spermatozoa can produce an antibody response that is capable of inducing infertility in humans, they per se cannot be employed for the development of a vaccine. Besides the presence of numerous antigens common to somatic and sperm cells, there are several proteins on the sperm surface that are likely to be shared with various somatic cell plasma membranes. Thus, only those antigens that have been carefully analysed for sperm specificity should be employed for the development of an antisperm contraceptive vaccine. The advent of hybridoma technology, Western blotting and recombinant DNA technology have revolutionized the search for sperm-specific antigens that are relevant to fertility.

3 Conclusions

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