Male birth control: non-hormonal injection could be effective

Whereas women have several options for long-lasting contraception, men currently have a limited selection available to them. Vasectomy is the only effective long-acting method available for men, but a new, non-hormonal, injectable gel could change the game.

Is a non-hormonal, long-lasting contraceptive on the horizon for men?

Results of a study testing the effectiveness of the injectable male contraceptive, conducted in rabbits, are published in the journal Basic and Clinical Andrology.

According to the study, both the availability and use of contraceptives has major implications for public health and well-being. Around the world each year, an estimated 85 million unintended pregnancies happen, half of which end in abortion.

There is increasing demand for male contraceptive options. Although it is safe and effective, vasectomy is typically regarded as permanent because its reversal is expensive, difficult and has the chance of being unsuccessful in restoring fertility.

Recently, researchers reported on a birth control pill for men, which is being developed by tweaking the structure of chemical compounds that could potentially be used to inhibit male fertility.

There are, of course, concerns over potential side effects. Though scientists have focused on hormonal approaches to male birth control, the authors of this latest study note that many men prefer a non-hormonal option to avoid side effects and safety risks.

One target that appears to be a good starting point for male contraception is the vas deferens, which is the tube that carries sperm from each testicle.

'No detectable sperm in semen samples'

For their study, the researchers injected the gel - called Vasalgel - into the vas deferens of 12 rabbits. The gel is made of styrene-alt-maleic acid (SMA) that is dissolved in dimethyl sulfoxide.

The team tested two different formulations of the gel - either using 100% SMA acid or 80% SMA acid/20% SMA anhydride.

After analyzing the semen of the 12 rabbits, the researchers found that 11 of them were azoospermic in all samples, meaning that they had no detectable sperm in the semen samples.

Although one of the rabbits had a few samples containing small numbers of sperm, he, too, eventually became azoospermic. Furthermore, both formulations were equally effective.

The researchers say the contraceptive effect of the gel lasted during the 12-month study period, and the response of the rabbits' vas deferens "was minimal with characteristics of a normal foreign body response."

Will the gel work in humans?

The way the gel works is that, once it is injected into the vas deferens, it forms a hydrogel, which remains in a soft, gel-like state. This means it is able to flex and adhere to the walls of the vasa deferentia.

Because hydrogels allow many water-soluble molecules to pass through - but not larger structures, such as sperm - this technique could reduce pressure in the sperm storage and production areas, the researchers say.

In the rabbit model, the researchers were able to successfully remove the gel to return the sperm flow and thus restore fertility. However, whether this technique will work in humans remains to be seen. The first clinical trial in men is planned for late 2016.

Commenting on their findings, the researchers from the University of Illinois-Chicago, say:

"Results from our study in rabbits were even better than expected. Vasalgel produces a very rapid contraceptive effect which lasted throughout the study due to its unique hydrogel properties. These features are important considerations for a contraceptive product to be used in humans."

References:

1.  Azoospermia in rabbits following an intravas injection of Vasalgel , Donald Waller et al., Basic and Clinical Andrology, doi: 10.1186/s12610-016-0033-8, published 30 March 2016.
2.  Parmeus Foundation news release, accessed 30 March 2016 via EurekAlert.
3.  Additional source: Mayo clinic, Vasectomy reversal, accessed 30 March 2016.