Next Stop for Male Contraception: The Vas Deferens

Men today have two options when it comes to birth control: condoms or vasectomy.  Condoms are a low-tech barrier method and can prevent both pregnancy and transmission of STDs.  However, the effectiveness of a condom is dramatically decreased if not used correctly, and studies have shown a more realistic 15% failure rate.  Vasectomy promises permanent birth control, through an invasive procedure which cuts the vas deferens, creating a block in the tube which sperm pass through before ejaculation.  While the surgery alone may turn off some men, the delay in effectiveness is also unappealing, since it can take up to 3 months for a vasectomy to be successful.  Some men experience swelling of the epididymis due to the blocking of fluid passing through the vas deferens, a condition called epididymitis.  While vasectomy reversal is an option, often fertility does not return to pre-vasectomy levels.  Vasectomy is not ideal for many men due to the need for surgical incision, a delay in effectiveness, and reduced fertility following reversal.

When we track the complete cycle of male fertility, other possibilities for male contraception emerge.  Male fertility begins with the production of sperm in the testes, followed by the sperm's journey through the male reproductive tract.  This voyage starts in the epididymis (a set of tightly twisted tubes where sperm are stored and mature) and continues in the vas deferens, a second tube that connects to the epididymis and serves as the passageway for sperm when they are released from the body.  Researchers are exploiting the fact that sperm make this journey before reaching the egg (in the female reproductive tract) by targeting sperm in the vas deferens or immediately after they released.  These targeted male contraceptive approaches are non-hormonal, resulting in fewer systemic side effects.    

One of the most promising non-hormonal male contraceptives in the pipeline is RISUG, or Reversible Inhibition of Sperm Under Guidance.  Researchers in India have developed a polymer gel that once injected into the vas deferens coats the wall of the tube.  This gel will come in contact with sperm passing through the vas deferens and burst the cell membranes, leaving sperm unable to fertilize an egg.  The polymer does not completely block the vas deferens and allows for fluid to pass through, diminishing the chances of fluid buildup and subsequent epididymitis.  It only takes minutes for the polymer to bind and contraceptive effects are seen immediately, within days not months like a vasectomy.  Both application and reversal of RISUG use no-scalpel methods, and therefore do not involve cutting of the vas deferens.  Despite the non-invasive and immediate effectiveness of RISUG, the beauty of this contraceptive lies in its name:  RISUG is reversible.  A simple injection can flush out the polymer and restore fertility within 150 days; however, this has only been tested in primates.  The obvious next step would be to test reversibility on human subjects, some of which have been using RISUG for over 10 years.  RISUG is in phase III clinical trials in India as of March 2007.  Clinical studies of RISUG must be repeated on a larger scale using US and international guidelines before it can be considered for human studies in other countries. 

Another very similar non-hormonal male contraceptive is the intra vas device, or IVD.  This method requires much less cutting when compared to a vasectomy, and works by a plug inserted into the vas deferens.  Clinical trials in Minnesota are using a soft silicone based plug while Chinese scientists are using a plug made from urethane and nylon.  This approach prevents sperm from passing through the vas deferens, but allows for some fluid to pass through.  Again, reversibility has only been tested in primates, but the results are very promising with fertility returning to pre-IVD levels one month following removal.  The FDA approved clinical trials of the IVD in 2006 and it is currently in clinical trials on 90 individuals across the US.   

While devices that effect sperm passing though the male reproductive tract are effective contraceptives, they do not provide any STD protection.  Spermicides that are also microbicides can offer both contraceptive and STD protection. They are often used as lubrication alone or with condoms and work by binding to the sperm membrane, thereby blocking sperm movement.  Nonoxynol-9 , a popular detergent-based spermicide, was shown to promote HIV and HPV transmission through vaginal and cervical abrasions caused by detergents.  Taking into consideration the adverse side effects, the FDA has mandated warning labels on nonoxynol-9 containing products, leaving a void of safe and effective spermicides available for consumers.  However, there are a few promising non-detergent based spermicides that offer both contraceptive and STD protection.  These include spermicides which create a physical barrier (UsherCell and Pro2000) and ones which acidify the environment and utilize natural defense mechanisms (BufferGel and Acidform).  Many of these spermicides are in clinical trials; however, there still remains a concern about the effectiveness of spermicides as contraceptives.  Alone they have a high failure rate of 29% with typical use, however when used in combination with condoms, spermicides can increase the effectiveness of both products. 

Finally, it is easy to imagine a contraceptive that would block sperm from binding to the egg.  The closest to this is a "sugar pill", in simple terms, an enzyme inhibitor being developed by a US scientist that mimics the sugary coating of the egg.  This sugar mimic is added to sperm in the epididymis and binds to the sperm head, thus preventing treated sperm from binding to the egg.  This contraceptive is in early developmental stages, as it was found to be 90% effective in rats with no side effects. 

Scientists across the world are working toward developing a safe and effective male contraceptive.  They are using a diverse set of approaches, including arresting sperm production, blocking sperm entry into the female reproductive tract, and interfering with sperm-egg binding.  Compared to systemic hormonal methods, targeted mechanisms promise fewer side effects.  However, the future of male contraception depends upon not only the bright minds that fuel the research, but the funds to support the development and testing required for implementation.  With an increase in public interest hopefully we will find a rise in funding, with the ultimate goal of developing an effective, non-hormonal, male contraceptive.