INTRODUCTION
In the last few decades, a significant leap has been made in the development of efficient contraceptive methods to achieve fertility regulation. One such advancement is the development of an injectable male contraceptive, reversible inhibition of sperm under guidance (RISUG®) as an alternative to vasectomy, to provide safe and long-term contraception in men. RISUG, a polymeric gel consisting of styrene maleic anhydride (SMA) dissolved in dimethyl sulfoxide (DMSO), is a nonhormonal and nontoxic method of contraception with the advantage of being a nonscalpel method and ability to attain easy reversibility. When injected into the vas deferens, it blocks the sperms that traverse through and destroys them by lowering the surrounding pH and creating charge disturbances in the sperm membrane.
Contraceptive efficacy of RISUG has been tested and demonstrated in several experimental models such as rats, rabbits, and langur monkeys. Subsequently, Phase I and Phase II clinical trials have been successfully completed. RISUG is presently under Phase III clinical trials across multiple centers in India.
Following the successful demonstration of RISUG as an effective contraceptive, studies have been carried out in experimental models to evaluate its functional reversal. In langur monkeys, noninvasive reversal was achieved by percutaneous squeezing of the vas deferens, along with synchronized application of electrical stimulation, suprapubic percussion, and prerectal digital massage of the vas segments. This method of reversal, however, may not be feasible in humans due to different anatomical location of the vas deferens.
Previous studies have shown that at higher pH, RISUG tends to dissolve since its components become unstable. Thus, RISUG can be unbound from the walls of the vas deferens by flushing it out with alkaline solution/solvents such as DMSO and sodium bicarbonate (NaHCO3). Hence, reversal studies have been attempted in rats using DMSO and NaHCO3. The efficacy of DMSO and NaHCO3 has been tested and their effects on spermatozoa and the surrounding tissues have been studied. These short-term studies on experimental models have reported that reversal of vas occlusion using both these agents results in reversal of azoospermia and restoration of complete fertility. Long-term reversal of vas occlusion in male rats using DMSO and NaHCO3 has been reported recently. This is the first report of functional reversal in rabbit model following short- and long-term RISUG-induced vas occlusion.
MATERIALS AND METHODS
Drug
RISUG® is a copolymer synthesized through gamma irradiation of the monomers, styrene, and maleic anhydride, dissolved in the solvent vehicle DMSO in 1:2 ratio. It was kindly contributed by Prof. Sujoy K Guha, School of Medical Science and Technology, Indian Institute of Technology, Kharagpur, West Bengal, India.
Animals
Thirty-five New Zealand adult male rabbits (Oryctolagus cuniculus), 6–8 months old, weighing 1.5–2.0 kg, were used in the present investigation. The animals were maintained in the Departmental Experimental Animal Facility with 12:12 h light and dark schedule in individual metallic cages (size 16 inch × 18 inch × 15 inch). The temperature in animal house during the study period was maintained at 23 ± 2°C and the relative humidity ranged between 40% and 70%. The animals were fed with rabbit pellet diet (Ashirwad Industries Limited, Chandigarh, India) and water ad libitum. The animals were maintained under perfect veterinary supervision in accordance with the guidelines of the regulation of scientific experiments on animals. The experiment protocol was approved by the Institutional Animal Ethics Committee (IAEC).
Experimental design
Rabbits were allocated equally into following seven groups containing five animals in each. Group I: sham-operated control; Group II: vas occlusion with RISUG for 90 days; Group III: vas occlusion with RISUG for 90 days and reversal with DMSO; Group IV: vas occlusion with RISUG for 90 days and reversal with 5% NaHCO3; Group V: vas occlusion with RISUG for 360 days; Group VI: vas occlusion with RISUG for 360 days and reversal with DMSO; and Group VII: vas occlusion with RISUG for 360 days and reversal with 5% NaHCO3.
Vas occlusion
Rabbits of Groups II–VII were subjected to bilateral vas occlusion under sodium thiopentone anesthesia (25 mg kg−1 body weight of intravenous injection; THIOSOL Sodium: Neon Laboratories Ltd., Mumbai, Maharashtra, India). A single median incision was made just above the scrotum to locate the vas of inguinal region. The 5–7 μl of the therapeutic dose of RISUG was injected into each vas deferens at initial segment of the vas by a microsyringe. The solidification of RISUG was catalyzed by application of cotton wetted with normal saline and solidified on contact with fluid medium in the vas. The syringe was slowly withdrawn. The vas was placed in its original position and the incision was closed by catgut suture in the inner layer and by silken suture outside. Animals of Group I served as sham-operated control. The vasa of Group I animals were exposed in the similar manner; however, no drug was injected. Postoperative care included antibiotic Ceftriaxone (Cefoat, A to Z Pharmaceuticals Ltd., Surat, Gujarat, India) and anti-inflammatory drug Meloxicam (Melonex, Intas Pharmaceuticals Ltd., Ahmedabad, Gujarat, India), injected in the gluteal muscles. The functional success of vas occlusion was confirmed by semen analysis at intervals of 15 days.
Vas occlusion reversal
Reversal of vas occlusion was performed after 90 days and 360 days of vas occlusion under sodium thiopentone anesthesia. The vas was exposed in a similar way as that of occlusion and injected bilaterally with 250–500 μl of DMSO to dissolve RISUG in Groups III and VI. Likewise, 500–700 μl of 5% NaHCO3 was injected to dissolve the copolymer in Groups IV and VII. The vas was returned to its original position and the incision was closed. Postoperative care was provided as described previously. The success of reversal was assessed after every 15 days semen analysis.
Parameters
The animals of sham-operated control, vas occlusion, and vas occlusion reversal were evaluated for the following parameters.
Seminal characteristics
Semen samples were collected by artificial vagina at an interval of 15 days in all the groups of animals and evaluated for macroscopic (volume, pH, color and consistency) as well as microscopic characteristics (sperm concentration, output, motility, viability, and abnormality) according to the World Health Organization (WHO) manual.
Morphology of ejaculated spermatozoa
Ejaculated spermatozoa of all the groups were processed for light microscopy by Papanicolaou staining method.
Scanning electron microscopy (SEM)
Ejaculated spermatozoa of all the experimental groups were washed twice with phosphate buffer and pelleted at 1500 rpm for 15 min. The sperm pellets were fixed in 2.5% glutaraldehyde for 30 min and washed thrice in phosphate buffer followed by distilled water. A thin film of spermatozoa was smeared on a clean glass slide, air dried, mounted on SEM stub with silver paint, sputter coated at 350 Å with gold and observed under scanning electron microscope (EVO 18, Carl Zeiss, Oberkochen, Germany).
Fertility test
Periodical fertility tests were carried out every 15 days in all experimental groups by cohabitating the male with proven fertile female at 1:2 ratio. Copulation was observed and successful mating was confirmed by wooing sound of the male followed by his falling off the female either backward or in sideways direction. The females used for fertility test were caged separately.
Female rabbits of full term delivery
Fifty percent of pregnant females mated with sham-operated and vas occluded reversed animals were allowed to complete the full term of pregnancy and their record of litters, namely, litter size, body weight, body length, and sex ratio, was maintained.
Female rabbits of cesarean
While the remaining 50% of the pregnant females were undergone cesarean on day 28 under an overdose of intravenous injection of sodium thiopentone. Uterine horns and ovaries were removed, freed from fat and adherent tissues. Weight of gravid uterus, placenta, and ovary was observed. Nongravid uteri were subjected to ammonium sulfide staining for confirmation of nonpregnant status. A number of corpora lutea, implantations, and resorptions were observed. The fetuses were removed by opening uterus and were placed in sequential manner in 0.9% saline solution. All dead and live fetuses were counted and their body weight, length, and sex ratio were studied.
Fertility
On account of the above-mentioned process, the total number delivered females and total number of live and dead litters were recorded to calculate percent of fertility of male rabbits in each group.
Statistical analysis
Values are represented as mean ± standard deviation (s.d.). The mean values were compared by statistical comparisons between sham-operated control group and vas occlusion and/or reversal groups for evaluation of significant changes by One-way Analysis of Variance test (ANOVA). The difference between means was analyzed by Holm-Sidak multiple comparison using the statistical software SPSS version 10.0 (SPSS Inc., Chicago, IL, USA). P < 0.05 was considered statistically significant.
RESULTS
Seminal characteristics
Semen pH, color, and consistency
The semen pH (7.3–7.6), color (white), and consistency (normal) did not show any marked changes in all the groups following vas occlusion and reversal (data not shown).
Semen volume
Semen volume during preinjection in all groups was observed between 0.57 ± 0.08 ml and 0.59 ± 0.09 ml. Following vas occlusion and reversal, semen volume was found between 0.39 ± 0.07 ml and 0.62 ± 0.05 ml (Group I); 0.37 ± 0.18 ml and 0.57 ± 0.08 ml (Group II); 0.35 ± 0.18 ml and 0.52 ± 0.05 ml (Group III); 0.40 ± 0.08 ml and 0.60 ± 0.07 ml (Group IV); 0.46 ± 0.05 ml and 0.56 ± 0.11 ml (Group V); 0.40 ± 0.14 ml and 0.62 ± 0.05 ml (Group VI); and 0.44 ± 0.05 ml and 0.59 ± 0.11 ml (Group VII), respectively. No significant alterations in semen volume were observed in Groups II–VII when compared with sham-operated control.
Sperm concentration and output
Sperm concentration and output during preinjection periods was recorded between 167.25 × 106 ± 29.86 × 106 ml−1 and 185.10 × 106 ± 31.27 × 106 ml−1, and 96.54 × 106 ± 16.63 × 106 per ejaculate and 104.85 × 106 ± 14.21 × 106 per ejaculate, respectively. The sperm concentration and output gradually decreased following vas occlusion in Groups II–VII. Complete azoospermia was noticed at 60 days in Group II, 45 days in Groups III, VI, and VII; and 30 days in Groups IV and V, respectively. Preceding reversal, animals showed azoospermia in first 3–4 ejaculations followed by oligozoospermia at 60 days in Groups III (19.80 × 106 ± 10.60 × 106 ml−1), IV (43.06 × 106 ± 11.06 × 106 ml−1), and VII (14.02 × 106 ± 9.74 × 106 ml−1), and 75 days in Group VI (51.16 × 106 ± 15.86 × 106 ml−1), respectively (Table 1). After 9–10 ejaculations, animals showed normozoospermia at 135 days in Groups III (121.52 × 106 ± 12.37 × 106 ml−1) and VII (164.52 × 106 ± 5.63 × 106 ml−1), and 150 days in Groups IV (157.81 × 106 ± 10.82 × 106 ml−1) and VI (166.61 × 106 ± 13.36 × 106 ml−1), respectively, comparable to control group. Normal sperm output was gained by the animals following reversal at 120 days in Groups III (50.83 × 106 ± 8.37 × 106 per ejaculate), IV (54.29 × 106 ± 8.32 × 106 per ejaculate), VI (72.60 × 106 ± 15.80 × 106 per ejaculate), and VII (54.56 × 106 ± 10.00 × 106 per ejaculate) subsequently, e.g., proportionate to control group.
Sperm motility
The sperm motility (presented as percentage) during preinjection period in all experimental groups was found between 51.60 ± 10.20 and 62.87 ± 14.58. A complete inhibition of sperm motility was observed following vas occlusion in all experimental groups. Following reversal, Groups III and VII recovered motility at 135 days, e.g., 54.20 ± 3.87 and 57.20 ± 5.71, respectively, whereas Groups IV and VI attained normal motility at 150 days, e.g., 54.56 ± 9.89 and 55.40 ± 3.44 subsequently (Table 2).
Sperm viability
The sperm viability (presented as percentage) during preinjection period ranged from 65.02 ± 15.33 to 78.05 ± 9.70. A steep declination in sperm viability was observed prior to attainment of azoospermia in Groups II (13.56 ± 4.61), III (15.80 ± 1.93), IV (15.95 ± 4.96), V (5.18 ± 2.58), VI (14.18 ± 3.72), and VII (9.88 ± 2.97), respectively. Normal viability was resumed after reversal at 105 days in Groups III (59.20 ± 6.97) and IV (63.20 ± 7.19), 120 days in Group VI (61.38 ± 7.99), and 75 days in Group VII (61.67 ± 7.34), respectively.
Sperm abnormality
The sperm abnormality (presented as percentage) during preinjection period in all experimental groups ranged between 21.77 ± 7.11 and 24.86 ± 5.74. The sperm abnormality detected at 15 days of vas occlusion was 26.79 ± 5.05 enhanced to 51.84 ± 6.73 at 45 days in all groups. Following 60–90 days of reversal, the sperm abnormality ranged from 29.50 ± 3.72 to 36.13 ± 3.22 in all groups. After few ejaculations, animals of reversal groups resumed normal morphology, e.g., comparable to control.
Sperm morphology
Semen samples were analyzed for sperm morphology by SEM. The SEM observations of spermatozoa of Group I showed normal morphology with typical oval-shaped head, slender mid-piece, and long tail (Figure 1a). During vas occlusion, prior to azoospermia and initial periods when spermatozoa reappeared during reversal various deformities, namely, acrosome damage, elongated head, head-tail separation, damaged, bulging and bent mid-piece, super-coiling in tail, and disrupted plasma membrane, were observed (Figure 1b–1f). Following 150 days of reversal period, the sperm morphology was comparable to control.
Figure 1
(a) Ejaculated sperm of Group I (sham-operated control) animals showing normal morphology with intact head, midpiece, and tail through scanning electron microscope. (b–f) Various types of abnormalities in ejaculated spermatozoa during initial period of vas occlusion in Groups II–IV animals showing damaged acrosome, bent and damaged neck, head tail separation, deformed midpiece, super-coiled tail and disrupted membrane (×40 000).
Fertility test
Female rabbits of full term delivery
The pregnancy record of females of full-term delivery mated with male rabbits following reversal with DMSO (Groups III and VI) and NaHCO3(Groups IV and VII) did not reveal any change in litter size, body weight and width, and sex ratio of litters when compared with sham-operated control.
Female rabbits of cesarean
Similarly, implantation records in cesarean females following reversal with DMSO and NaHCO3 also revealed no changes in weights of gravid uterus, placenta, ovary, and number of corpora lutea, implantations, resorptions, body weight, length, and sex ratio of fetuses as compared to sham-operated control.
Fertility
Group I showed 100% fertility throughout the study period. The animals of vas occlusion and reversal groups (II–VII) showed 100% of fertility during preinjection whereas 0% of fertility indicated by sterile mating was observed during vas occlusion and initial periods of reversal. Following reversal, fertility was restored at 90 days (Groups III, VI, and VII) and 105 days (Group IV), respectively (Table 3).
DISCUSSION
Many vas-based contraceptives have been attempted to achieve fertility regulation with several limitations of surgical intervention/complications as well as lack of reversibility. RISUG is proposed to be successful in terms of safety and efficacy without significant adverse effects. The present work was aimed to evaluate, in rabbits, short- and long-term reversal of RISUG-induced vas occlusion using DMSO and NaHCO3. The results revealed complete restoration of fertility in male rabbits as evidenced by presence of spermatozoa and normal sperm functional characteristics following reversal. The success of reproductive function retrieval was further confirmed from the pregnancy record of full-term and cesarean females mated with these sterility-reversed male rabbits which were comparable to control.
The preliminary study evaluated teratogenic potential of RISUG in males without affecting pregnant rabbits and their respective F1 generation at different dose regimen. Similarly, removal of SMA from the vas deferens of rats by the injection of DMSO was demonstrated by Sethi et al. in 1990. This short-term study showed restoration of normal mucosal epithelium of the vas deferens, which was compromised during vas occlusion, by 4 weeks following flushing out of RISUG with DMSO thus demonstrating its potential as an effective reversal agent. However, this study presented the reversibility status only at an anatomical level. Functional success of RISUG-induced vas occlusion reversal was evaluated by Lohiya et al. by studying the sperm characteristics and teratological observations of the F1 progenies of the reversed rats. Changes in sperm morphology such as bent/detached tail, acrosomal damage, and other aberrations in sperm head that were observed during vas occlusion and initial periods of reversal gradually returned to normal with 100% restoration of fertility after 90 days of reversal with DMSO. Teratological studies showed the F1 progeny to be normal and comparable to control which further highlighted DMSO's role as a reversal agent. In another study on reversal, Koul et al. reported successful restoration of fertility, following vas occlusion, by flushing of the vas deferens with 10% NaHCO3 by observing the presence of spermatozoa in the vaginal smear and pregnancy in female rats. The principle behind this method of flushing out of RISUG is that SMA is unstable in a basic environment. Hence, NaHCO3 serves as one of the ideal candidates for removal of the SMA bound to the vas deferens. In case of DMSO, since it is a solvent in which SMA dissolves to form a polymeric gel, injection of this chemical would result in dissolution of the polymer from the walls of the vas deferens, subsequently resulting in the appearance of the spermatozoa in the ejaculate. Moreover, genotoxicity studies on rats showed that RISUG-induced vas occlusion and its reversal using DMSO and 5% NaHCO3 were safe and did not cause any genotoxicity in the leukocytes and the testis of these rats thereby confirming the safety of this method of contraception and reversal.
As a further advancement of the short-term studies, evaluation of reversal efficacy have been assessed for a longer duration, e.g., 360 days, in RISUG-injected animals. Ansari et al. recently reported achievement of long-term reversal of vas occlusion in male rats using DMSO and NaHCO3. Periodical assessment of fertility status, pregnancy record, sperm characteristics, teratology of the F1 generation, and histological studies indicated that while 100% restoration of reproductive function could be achieved using both solvents, complete reversal with 5% NaHCO3 was earlier (e.g., in 30 days) than with DMSO infusion, wherein 100% of fertility was restored in 45 days. Histological studies of the vas deferens indicated complete regeneration of the vas epithelium, thereby indicating reliability of this methodology of contraception reversal.
In the present study, on rabbits, azoospermia was observed 30–60 days following RISUG injection and the sperm began to reappear around 60–75 days postreversal with DMSO and 5% NaHCO3. Sperm motility and viability began to recover gradually following reversal too. While sperm motility was restored between 105 days and 135 days in reversal groups, sperm viability improved and normalized between 75 days and 105 days in both reversal groups too. In addition, 100% fertility was attained in both groups between 90 days and 105 days. Further, pregnancy record of both full-term and cesarean females mated with male rabbits following reversal was comparable to control and the F1 progeny of reversed animals were found to be normal. However, in contrast to the reversal studies carried out on rats, in rabbits, recovery of sperm characteristics and fertility were observed to be longer. This delayed reversibility could be attributed to the anatomy and physiology of the experimental model used.
Reversal of RISUG-induced contraception has also been attempted in langur monkeys Presbytis entellus entellus, albeit, in a different way as compared to rats. Noninvasive reversal in langur monkeys was achieved by palpitation, percutaneous electrical stimulation and squeezing of the vas deferens, and forced vibratory movements, suprapubic percussion, and prerectal digital massage of the vas segments. This mechanism propels the SMA toward the urethra resulting in normospermia with normal sperm motility and viability and subsequently its fertilizing ability. Revival of sperm characteristics and fertilizing ability were confirmed using sperm functional tests and biochemical analysis. Electron microscopic studies of the vas deferens revealed repair of the ultrastructural changes that occurred during vas occlusion, beginning from 90 days postreversal. Restoration of normalcy in these tissues, as evidenced by presence of prominent plasma membrane, nucleus, and cytoplasmic organelles, was observed after 150 days of reversal. This method was suggested to be a faster and a noninvasive approach to achieve functional reversal of vas occlusion in monkeys.
However, the shortcoming of this method of reversal is that it may not be feasible in humans due to the fact that their vas deferens is difficult to palpate reliably proximal to the scrotum. Hence, reversal of RISUG-induced vas occlusion using DMSO and NaHCO3 is being developed as a reliable, efficient and a safe method. The drug regulatory agency (DCGI) has conveyed its approval for clinical trials.
CONCLUSION
The results of this rabbit study have demonstrated that reversal of long-term RISUG-induced vas occlusion using DMSO and NaHCO3 is feasible, effective, and safe, thus providing better option for reversible male contraception for men, on successful completion of clinical trials.
AUTHOR CONTRIBUTIONS
NKL and ASA conceived and designed the study; AB conducted the experiment and analyzed the data; ASA and KB drafted the manuscript; and NKL finally approved the version to be published. All authors read and approved the final manuscript.
COMPETING INTERESTS
All authors declare no competing interests.
ACKNOWLEDGMENTS
The study was supported by the Indian Council of Medical Research, New Delhi. The infrastructural facilities provided by the Head of the Department are gratefully acknowledged. The authors are thankful to Prof. Sujoy K Guha, School of Medical Science and Technology, Indian Institute of Technology, Kharagpur, West Bengal, India, for providing RISUG. The ultrastructural studies were carried out at the electron microscope facility of the University Science Instrumentation Centre, University of Rajasthan, Jaipur, Rajasthan, India.
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