It is estimated that there are 600 million inhabitants cats in the world and 80% of them are strays. The only long-term solution to controlling the cat population is surgical sterilization. Therefore there is an urgent need for safe, effective and cost-effective alternatives for permanent contraception of strays.

Now, researchers from the Cincinnati Zoo and Botanical Garden, Harvard Medical School and the University of Massachusetts Chan School of Medicine have developed a potential new feline contraceptive method that shows promise: long-acting contraceptive injections that block ovulation. The impetus for the research was to address the issue of cat and dog overpopulation and the euthanasia of many animals in shelters, Dr. Bill Swanson, head of research at the Cincinnati Zoo and Botanical Garden and author of the published study, told CNN. in the journal Nature Communications.

A single dose of a viral vector containing anti-Müllerian hormone (AMH), a naturally occurring hormone, prevented ovulation and conception in female cats for at least two years, according to Massachusetts General Hospital researchers and their colleagues . AMH is a protein that plays a critical role in determining sex during fetal development and is found in the ovarian follicles of female cats.

Recent studies have shown that high levels of AMH can prevent follicular development and lead to permanent contraception in female mice when this is achieved through gene therapy using an adeno-associated virus (AAV) vector. Unlike traditional contraceptive methods, this one works by inhibiting the activation of the primordial follicles, the original structures that produce mature eggs. By preventing the activation of these early follicles, the contraceptive method effectively stops the reproductive process and prevents pregnancy.

In the present study, the researchers set out to develop a genetic approach to induce contraception in cats using an optimized AMH transgene and an adeno-associated serotype 9 (AAV9) vector to efficiently transfer the transgene into feline cells. AAV9 is a virus commonly used as a delivery system or vector in gene therapy. It was chosen because it prefers muscle tissues and is not usually blocked by antibodies in cats, making it an efficient gene transfer vehicle.

The researchers developed two versions of the AMH gene using genetic information from domestic cats, fcMISv1 and fcMISv2. The second version, fcMISv2, was modified to correct amino acid differences from the first. The modification increased the likelihood that the fcMISv2 gene would efficiently induce the desired physiological changes and provide the desired contraceptive effects when transferred to cats using the viral vector.

What the tests on mice and cats showed

For the initial test, the researchers used mice. By injecting the AAV9-fcMISv2 vector into immunodeficient mice, the researchers observed the production of the AMH protein in various tissues. They also observed a reduction in the size of the ovaries and the number of follicles in the treated mice compared to the control group. This meant the genes worked as intended and were ready to be tested in cats. AAV9-fcMISv2 was administered to nine female cats without significant adverse effects or immune responses.

The cats were followed for two years, during which the researchers observed that the animals continuously secreted hypernormal (higher than normal) levels of AMH while no antibodies against fcMISv2 were detected.

The researchers thus concluded that AAV9-fcMISv2 inhibits ovulation in the female domestic cat. However, the scientists stress that further research is needed to understand the physiological effects of high AMH levels on feline reproduction and to optimize the vector for effective contraception.

With information from Interesting Engineering, CNN