Successful reversal of Vasalgel male contraceptive in rabbits

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Adapted Media Release

Results of a study of a
promising new male contraceptive called VasalgelTM were published in Basic and
Clinical Andrology. The polymer gel is injected into the vas deferens and
blocks the passage of sperm. The study followed the progress of seven rabbits successfully
contracepted for an average of 14 months before the gel was flushed out. Sperm
flow returned in all animals after reversal, confirming unobstructed sperm
transit (patency of the vas deferens) and warranting continued development of
this product.

Few current male contraceptive

When considering reproductive
control, couples often rely on female contraceptive methods, including daily
pills and long-acting products such as IUDs and implants. However, many women
cannot tolerate the side effects of hormonally-based contraceptives and grow
frustrated with the downsides of other methods.
Men who wish to control their
own reproduction or lift the burden of contraception from their partners have
even fewer options. No new male contraceptives have emerged in more than a
century, and men must rely on the old standbys: condoms, which are important
for reducing the incidence of sexually transmitted infections in new
relationships but result in high pregnancy rates in typical (imperfect) use;
withdrawal, which has an even higher pregnancy rate in typical use; and
vasectomy, which is very effective but should be considered permanent due to
the unpredictability of successful reversal. The need for a long-acting,
reversible male contraceptive – without the side effects of hormones – has been
demonstrated in international surveys and could be met by Vasalgel.

How Vasalgel works

Vasalgel functions like a
reversible vasectomy, blocking or filtering out sperm. The device is implanted
into the vasa deferentia (singular: vas deferens) — the small tubes that
transport sperm from the testes. It is composed of high molecular weight
polymer powder dissolved in dimethyl sulfoxide (DMSO), a biocompatible solvent.
The resulting Vasalgel implant remains in a soft gel-like state that allows
water-soluble molecules to pass but not larger structures such as spermatozoa.
This quality is thought to be a benefit for preventing back-pressure on sperm
storage areas. The contraceptive effect lasts for years, and, importantly, is developed
to be reversible by a second injection to dissolve the Vasalgel.

Demonstration of efficacy and
reversibility in rabbits

In a previous publication in
2016, the research team reported Vasalgel provided effective contraception in
rabbits. Vasalgel produced a rapid onset of azoospermia, with no live sperm in
semen samples collected as early as 29-36 days post-implantation, and the
effect was durable over a 12-month period. The device was safe and was
well-tolerated by the rabbits with minimal effects on the structure of the vasa
The follow-up study published
today reported the results of reversing the contraceptive effect of Vasalgel in
the same rabbits. Seven rabbits, successfully contracepted for 14 months
following Vasalgel implant, underwent a reversal procedure. A sodium
bicarbonate (baking soda) solution was injected into the vasa deferentia of
each rabbit to dissolve the implants and clear the blockage. Baking soda is
known for its ability to safely neutralize acids. In this case, the bicarbonate
solution neutralizes and breaks down the hydrogel structure of the polymer gel.
Sperm flow returned quickly, as evidenced by spermatozoa present in the semen
of all animals.
Further evaluation of the
sperm characteristics after reversal indicated sperm concentrations and sperm
motility were similar to baseline levels, an important first step to a return
of fertility. The sperm forward progression measurements were significantly
lower than the baseline measurements but increased consistently during six
months of follow-up semen collection.
Microscopic evaluation of the
vasa deferentia indicated that most had an intact epithelial lining (inner
lining tissue) and were clear of the gel. A smaller proportion of tissues
contained residual gel, and an occasional secondary intraluminal inflammatory
response (minor inflammation inside the vas deferens) was observed. Rabbits
have unusually large and thus vulnerable acrosomes (caps) on the heads of their
sperm, which were not observed following reversal. Residual material may have
impacted the sperm forward progression and caused loss of acrosomes during
transit through the vas.
“The results of the
Vasalgel reversibility study in rabbits indicate the implant could be removed
resulting in a quick return of sperm flow,” said lead author Donald
Waller, Ph.D. “We were pleased that the number of sperm and their motility
after reversal were no different from baseline measures. More flushing during
reversal may be needed to remove traces of the gel from the vas deferens, which
appeared to impact other sperm characteristics.”
The results of the study
provide momentum for continued development of Vasalgel as a male contraceptive.
Next steps

Vasalgel is being developed as
a non-hormonal, long-acting, reversible male contraceptive by Revolution
Contraceptives, LLC, a social venture subsidiary of Parsemus Foundation, a
nonprofit organization based in the San Francisco Bay Area.
Vasalgel has demonstrated
efficacy in monkeys and rabbits in previously published studies. This study is
the first to demonstrate reversibility. Reversal in larger animals has not been
confirmed and is an active research focus.
“This study gave us the
confidence to continue development of Vasalgel,” said Elaine Lissner,
founder and trustee of Parsemus Foundation. “We flushed out most of the
gel and restored full sperm flow. Now the thousands of followers of Vasalgel’s
progress are counting on us to refine and repeat this reversal success in
larger animals.”
With contraceptive efficacy
well-established in multiple species, preparations are being made for the first
contraceptive efficacy clinical trials in humans. Parsemus Foundation aims for
Vasalgel to be available worldwide, with a tiered international pricing
structure to ensure affordability to all men.
Article: Reversibility of
Vasalgel™ male contraceptive in a rabbit model, Donald Waller, David Bolick,
Elaine Lissner, Christopher Premanandan and Gary Gamerman, Basic and Clinical
Andrology, doi: 10.1186/s12610-017-0051-1, published 5 April 2017.

Kayode Ojo
Kayode Emmanuel Ojo is the Co-Founder and Managing Director at SHEFFA Limited. He is presently studying Computer Science at the National Open University, Victoria Island, Lagos.