A new non-surgical one-shot contraceptive can make both male and female animals infertile for years.
The method, so far only tested in mice, could be used as an alternative to spaying and neutering feral animals, researchers say.
Earlier studies have shown an adeno-associated virus (AAV)—a small, harmless virus that is unable to replicate on its own—has been useful in gene-therapy trials and can be used to deliver sequences of DNA to muscle cells, causing them to produce specific antibodies that are known to fight infectious diseases, such as HIV, malaria, and hepatitis C.
For the new study, published in the journal Current Biology, researchers thought the same approach could be used to produce infertility. They used the virus to deliver a gene that directs muscle cells to produce an antibody that neutralizes gonadotropin-releasing hormone (GnRH) in mice.
GnRH is what the researchers refer to as a “master regulator of reproduction” in vertebrates—it stimulates the release of two hormones from the pituitary that promote the formation of eggs, sperm, and sex steroids. Without it, an animal is rendered infertile.
In the past, other teams have tried neutralizing GnRH through vaccination. However, the loss of fertility that was seen in those cases was often temporary. In the new study, researchers saw that the mice—both male and female—were unable to conceive after about two months, and the majority remained infertile for the remainder of their lives.
“Inhibiting GnRH is an ideal way to inhibit fertility and behaviors caused by sex steroids, such as aggression and territoriality,” says Bruce Hay, professor of biology and biological engineering at California Institute of Technology.
The study also shows that female mice can be rendered infertile using a different antibody that targets a binding site for sperm on the egg. “This target is ideal when you want to inhibit fertility but want to leave the individual otherwise completely normal in terms of reproductive behaviors and hormonal cycling.”
The researchers have dubbed the new approach “vectored contraception” and say that there are many other proteins that are thought to be important for reproduction that might also be targeted by the technique.
The researchers are particularly excited about the possibility of replacing spay–neuter programs with single injections.
“Spaying and neutering of animals to control fertility, unwanted behavior, and population numbers of feral animals is costly and time consuming, and therefore often doesn’t happen,” Hay says. “There is a strong desire in many parts of the world for quick, nonsurgical approaches to inhibiting fertility. We think vectored contraception provides such an approach.”
As a next step, researchers are working with Bill Swanson at the Cincinnati Zoo’s Center for Conservation and Research of Endangered Wildlife, to try this approach in female domestic cats. Swanson’s team spends much of its time working to promote fertility in endangered cat species, but it is also interested in developing humane ways of managing populations of feral domestic cats through inhibition of fertility, as these animals are often otherwise trapped and euthanized.
The Gordon and Betty Moore Foundation, the Beckman Institute, and the National Institutes of Health funded the work.