A new compound that leads to weight loss in obese mice could help in the development of a new class of anti-obesity drugs for humans, scientists say – though this could take many years.
The drug works by increasing sensitivity to the body’s appetite-suppressing hormone, leptin. It is not known exactly how this mechanism works but American researchers suspect the body’s cannabinoid receptors, which mediate feelings of hunger, play a role.
“By sensitizing the body to naturally occurring leptin, the new drug could not only promote weight loss, but also help maintain it,” said senior study author George Kunos of the United States’ National Institute on Alcohol Abuse and Alcoholism.
The results are published today in the journal [Cell Metabolism](http://www.cell.com/.
A similar drug that targeted cannabinoid receptors, rimonabant, was sold in Europe in 2006 but was withdrawn after it was found to cause serious psychiatric side effects, including depression, mood changes and suicidal thoughts. It was never available in Australia.
Rimonabant works by blocking cannabinoid receptors in the brain, which caused brain-based side effects in some patients, according to Joseph Proietto, Professor of Medicine at the University of Melbourne. The researchers therefore aimed to produce a compound that did not enter the brain.
“What this group has done is they have modified the original structure into one that does not enter the brain. So the drug is now only blocking the receptors that are in the rest of the body,” he said.
The new drug has delivered similar weight loss results in the mice as rimonabant but the animals have not shown signs of anxiety or other behavioural problems.
The drug will now have to undergo several years of testing before it can be submitted for approval to the regulatory authorities, including toxicity tests and phase one, two and three clinical trials to ensure it is safe and effective at maintaining weight loss. “We’re talking close to ten years before it’s ready to be submitted for approval,” said Professor Proietto.
Two weight-loss drugs are currently available in Australia: Duromine, an appetite-suppressant which was released about 50 years ago, for which there is very little evidence; and Orlistat, which reduces fat absorption and has been shown to keep weight off for a few years.
The United States Food and Drug Administration recently approved two new weight-loss drugs, which could make their way to Australia over the next few years.
Associate Professor John Dixon, Senior Research Fellow at the Baker IDI Heart and Diabetes Institute, said better therapies were desperately needed to treat obesity and prevent long-term weight gain.
Professor Dixon said the new drug was “just a concept at the moment” but it marked an exciting development. “While this is a long way off, we watch optimistically, such that perhaps in ten years time we have a range of treatments like we do for treating diabetes and hypertension,” he said.
“Perhaps if we had truly effective drug therapies, people would have a different view of this serious disease.”