New therapy may be an option to surgical castration of cats – 06/15/2023 – Equilíbrio

For all the cats who share our homes as companion animals, there is a vast dark world of strays, a growing and rapidly breeding multitude.

Their lives are plagued by the threat of infectious disease, predators and fast cars. And they themselves are top predators, hunting millions of birds and small mammals annually.

Castration is indicated for all cats, but controlling populations of stray animals is an expensive and logistically complicated investment. Many communities, especially in countries outside the United States and Europe, lack the veterinary and economic resources to coordinate such efforts.

“Creating an alternative to surgery has been the goal of many people for decades, and there is simply nothing that has been shown to be effective,” says William Swanson, director of animal research at the Cincinnati Zoo and Botanical Gardens (USA).

Such a method may finally be closer. In a study published last week in the journal Nature Communications, a single dose of a gene therapy prevented cats from becoming pregnant for at least two years. The work was extremely small: six cats that received the gene therapy injection were compared to three that did not.

By limiting the study size to just a few animals, the researchers were able to screen each one extensively, analyzing 15,220 freeze-dried stool samples for estrogen and progesterone levels and examining 1,200 hours of videos of mating behavior, says Swanson.

The birth control injection delivers a gene that penetrates muscle cells, allowing them to pump out a substance called anti-Müllerian hormone, or AMH, which interferes with the development of egg follicles in the ovaries.

The researchers cautioned that more research is needed to test the preliminary results. And if larger studies confirm that the treatment — the first gene therapy developed specifically for animals — is safe and effective throughout a cat’s lifetime, controlling feline populations won’t require the surgical expertise of veterinarians, Swanson says.

David Pépin, a reproductive biologist at Massachusetts General Hospital in Boston, was originally studying AMH as a possible therapy for ovarian cancer, but decided to look at its effect on the ovaries. When he injected the hormone into female mice, their ovaries shrank to the size of a newborn, suggesting it might have contraceptive properties.

Pépin is investigating the hormone’s potential use in people, not as a gene therapy, but as a pill or injection that must be taken continuously. Most contraceptives today prevent ovulation, but AMH would act sooner, blocking follicles from maturing.

He thinks it could be useful for women who cannot take birth control pills with progesterone or estrogen for medical reasons, or that it will help women undergoing cancer treatments to preserve their fertility.

“It’s a hormone that we haven’t been able to deal with before and that potentially has many different applications for women’s health,” he says.

As a gene therapy that may be permanent, the use of AMH in people is unlikely. “But it’s actually the perfect tool to control cat overpopulation,” he said. Four female cats in the study did not exhibit behaviors that indicated they were ready to mate, and two allowed male cats to mate with them but did not ovulate.

Pépin and Swanson, an expert in feline reproduction (and a member of the scientific advisory board of the Michelson Found Animals Foundation, which funded the work), are planning a larger study that could support a request to the FDA to consider approving the therapy to be marketed and used in cats.

They’re also testing it on puppies, which can be treated as young as eight weeks old, as well as dogs, which also have huge stray populations.

“This is really exciting and I hope it works out,” says Julie Levy, a veterinarian at the University of Florida College of Veterinary Medicine in Gainesville, Florida, who was not involved in the study. “Wouldn’t it be great if we could send a technician into the field to inject cats and then release them?”

The study is an example of the Michelson Foundation’s practice of “pushing a lot of money into the problem” to find nonsurgical contraceptives for strays, says Levy, who works with cats in colonies and outdoor shelters.

But she cautioned that there is still a lot to learn from a larger study, such as how long the injection lasts, whether it is as safe as it seems and what percentage of cats will actually be protected from pregnancy, “because it probably won’t be 100%.”

Others note that it might not be so easy. If the shot is effective, long-lasting and less expensive than spaying and neutering surgery, it could be very valuable, says Autumn Davidson, a veterinarian at the University of California, Davis School of Veterinary Medicine. But in order to receive the injection, the animals need to be captured, and cats that are adept at escaping traps can still make population control difficult.

Translated by Luiz Roberto M. Gonçalves