A new experiment testing a non-hormonal, injectable form of contraception on male monkeys has proven successful, bringing us one step closer to long-term birth control for men.
In a yearslong study involving 16 adult rhesus monkeys, scientists found that a gel-like polymer called Vasalgel, injected into ducts in the monkey’s testes, successfully blocked their sperm and prevented female monkeys from conceiving. The experiment showed that the monkeys with Vasalgel in their testes did not reproduce with female monkeys who shared their habitat, even though scientists observed them participating in normal breeding behavior.
“Importantly, we show that the method of Vasalgel placement is safe and produced fewer complications than usually occur with a vasectomy,” said lead author Catherine VandeVoort of the California National Primate Research Center, where the experiment was conducted.
The Need For Better Male Contraception
Giving men a highly reliable, long-acting reversible contraception option, or LARC, would give men more autonomy over their reproductive timetable and take the pressure off women, who have to bear the burden of refilling birth control pills or inserting hormonal implants and IUDs.
Currently, the only contraceptive options for men include condoms, which are not as effective as hormonal methods of contraception, vasectomies, which are generally permanent and can be difficult to reverse if a man later decides he does want to have children, and withdrawal, which has a failure rate of 4 percent if performed perfectly every time.
Vasalgel is just one of a handful of male contraceptive methods in trials right now. A recent global clinical trial to test the effectiveness of hormonal shots for men found that they successfully suppressed sperm production in 96 percent of participants who completed the study. However, the shot may need to be reformulated or retested to address the high number of mostly mild adverse reactions participants reported.
While women currently carry most of the responsibility when it comes to contraception, surveys reveal that most men are more than willing to take over. Among 9,000 men surveyed in Europe, the Americas and Asia in 2005, 55 percent said they’d be willing or very willing to try hormonal contraception for men. An estimated 40 percent of pregnancies worldwide are unintended.
Researchers have been conducting clinical trials on male contraception since the 1970s, but no viable solution has ever emerged from the experiments.
The Vasalgel Experiment
The California National Primate Research Center study involved 16 adult male rhesus monkeys, 10 of which had already sired offspring in the past. Researchers sedated the monkeys and inserted Vasalgel into their vas deferens — two ducts that bring sperm from each testicle to the urethra.
After spending a week recovering, the monkeys were allowed to enter their normal habitats at the primate research center, where they lived and interacted with female monkeys in heat for up to two years.
Under these circumstances, scientists typically expect an 80 percent pregnancy rate during the monkeys’ breeding season, which lasts from September until about May. All of the experimental monkeys spent at least one breeding season with female monkeys. The Vasalgel proved 100 percent effective at preventing pregnancy for the length of the experiment.
Three monkeys experienced mild complications. The Vasalgel had been incorrectly inserted into one monkey’s left vas deferens and was leaking, so scientists treated it by performing a vasectomy on that side, leaving Vasalgel in the right duct.
In another monkey, scientists noticed a small, one-centimeter sperm granuloma, or a lump filled with leaking sperm, near the surgical site. This is a common side effect of vasectomies in human beings, and tends to resolve itself over time. Surgeons removed the lump and resolved the leak with a vasectomy on the affected vas deferens, while leaving the Vasalgel in the left testes.
Finally, a third monkey got into a biting fight with other monkeys one week after receiving the Vasalgel treatment and was partially castrated. This surgery was likely not related to any complication with the Vasalgel, but rather a normal breeding season conflict between competitive male monkeys.
This experiment follows previous animal studies that found Vasalgel to be safe and reversible in rabbits. Future experiments should explore whether these monkeys can have their Vasalgel insertions successfully reversed and their fertility restored.
Based on the success of the monkey study, scientists at the Berkeley, California-based Parsemus Foundation, which funded the experiment, are preparing for Vasalgel’s first clinical trials in human beings.
The foundation funds studies for low-cost therapies that get little attention from the pharmaceutical industry, such as male contraceptives. While the Parsemus Foundation is a nonprofit, its social venture subsidiary, Revolution Contraceptives LLC, actually developed Vasalgel, the foundation says.
This study on rhesus macaques was published in the journal Basic and Clinical Andrology.
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