Nature Communications has just published the findings of a study coordinated by Jochen Buck of Weill Cornell Medicine (United States), which claims that inhibitors of an enzyme called soluble adenylyl cyclase (sAC) can reduce sperm motility in mice and humans. sAC is an enzyme that is essential for activating the sperm’s ability to move and mature, so that they can travel through the female reproductive tract and fertilize the oocyte. All the man would have to do is to take a birth control pill containing these inhibitors shortly before having sex to avoid pregnancy.

The sperm of a man taking a sAC-based contraceptive inhibitor would have impaired motility, leaving them unable to cross the cervix and to remain trapped in the vagina, so they would not persist for long after the sexual act.

According to the article, a single dose of a sAC inhibitor makes male mice temporarily infertile. They exhibit normal mating behavior, and full fertility returns the next day. This method would be completely different from known methods currently under study, which work by blocking the production of testicular sperm and require months of continuous use before the sperm count drops to subfertile levels. When the man wants to end the treatment, these methods also need months to recover normal counts. With the new drug, the man would be temporarily infertile shortly after taking a single dose, and his fertility levels would be fully restored the next day.

So far, the study has been conducted only in mice, but the researchers say their work provides evidence that sAC inhibitors have the potential to provide a safe, on-demand, non-hormonal and reversible oral contraceptive for men.

The team needs to conduct further research to determine whether these drugs will work effectively in humans and to identify possible side effects, and is already working on making sAC inhibitors more suitable for use in humans. They will also repeat the experiments in another animal model, which would lay the groundwork for clinical trials in humans that would prove the effect of sAC inhibition on sperm motility in healthy men.

According to Nature, at present, nearly half of all pregnancies are unintended and men currently have two contraceptive options: condoms and vasectomy.

Bioethical assessment

If the usefulness and safety of this new male contraceptive option are eventually proven, it would constitute an alternative to both the use of the condom, which has limited effectiveness, and vasectomy, which is irreversible. This new method, besides being reversible, would not affect the survival of the embryo, since it would act by a contraceptive mechanism, that is to say, by preventing fertilization. In this sense, it would present advantages over surgical methods such as vasectomy and female contraceptives that act by interfering with the implantation of the embryo in the uterus, i.e., by an abortive mechanism.

Julio Tudela

Bioethics Observatory – Institute of Life Sciences

Catholic University of Valencia


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