Reversible Male Contraception Shows Promising Results in Monkeys

Highlights

• No long-acting, reversible contraceptives are currently available for men.
• Many men say they would prefer a non-hormonal option because of the potential side effects and safety risks of hormones.
• Intravas injection of Vasalgel in sexually mature adult male rhesus monkeys was effective in preventing conception in a free-living, group environment.

Contraception options for men have not changed in over a century, and are currently limited to condoms and withdrawal (with high pregnancy rates in typical use), or vasectomy (meant to be permanent). No long-acting, reversible contraceptives are currently available for men. Surveys indicate that the majority of men would be interested in using a new contraceptive, and about 20% of couples already rely on existing male methods for reproductive control.

While research has uncovered a variety of new targets for male contraception, no new product has made it to market yet. Many men say they would prefer a non-hormonal option because of the potential side effects and safety risks of hormones.

Vasectomy has been the only male option available to non-human primate veterinarians who wish to reduce the pregnancy rate in their colonies.

A recent study finds the use of Vasalgel in groups of rhesus macaques - confirming previous preclinical findings in rabbits on the efficacy of the new device and offering a new tool to colony managers.

Vasalgel is a high molecular weight polymer that consists of styrene-alt-maleic acid (SMA) dissolved in dimethyl sulfoxide and could be the first long-acting, non-hormonal, potentially reversible male contraceptive to reach market.

The polymer forms a hydrogel after injection into the vas deferens, creating a blockage to the passage of sperm. It is thought that fluids are able to pass slowly through the gel, reducing back-pressure on the epididymis (the sperm storage area) that has been noted after vasectomy.

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The contraceptive effect of Vasalgel has been "reversed" in a rabbit model by flushing the material out with a simple sodium bicarbonate solution. Sperm flow quickly resumed.

Another experiment was done in monkeys to verify the effects in larger animals more anatomically similar to humans, before human use.

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Sixteen adult male rhesus monkeys received intravas injections of Vasalgel. After a one-week recovery, each male was returned to outdoor group housing, which included three to nine intact, breeding females with a successful reproductive history.

All males were monitored for at least one breeding season; 7 of the 16 were almost continually housed with females for two years.

The study authors reported that there were no conceptions after Vasalgel injections. Complications were minor and included one incident of incorrect placement of Vasalgel into the vas deferens and the development of a sperm granuloma in one animal.

Unilateral vasectomy was performed in each subject without further complication. One partial castration was performed due to an unrelated trauma incident. Histological examination in the removed testicle indicated that the presence of Vasalgel did not incite a localized inflammatory reaction (i.e., the Vasalgel was well-tolerated).

This finding is similar to that found in the rabbit, in which tissue response to the presence of Vasalgel was minimal. Additionally, the occurrence rate of sperm granulomas in the monkeys that received Vasalgel was lower than in an age- matched control group that received vasectomy.

Reference

1. Angela Colagross-Schouten et al., The contraceptive efficacy of intravas injection of Vasalgel™ for adult male rhesus monkeys, Basic and Clinical Andrology (2017) 10.1186/s12610-017-0048-9.

Source-Medindia