Published July 27, 2012
A potential new weight-loss drug created by scientists may help people shed pounds and keep them off, researchers say.
In the study, obese mice treated with the drug ate less, lost weight and experienced improved metabolic health, such as reduced insulin resistance, compared with obese mice not given the drug.
The drug appears to work by increasing the body's sensitivity to leptin, a hormone that suppresses appetite. It's thought that obese people become desensitized to leptin, meaning their bodies do not respond to it.
"By sensitizing the body to naturally occurring leptin, the new drug could not only promote weight loss, but also help maintain it," said study researcher George Kunos, of the National Institute on Alcohol Abuse and Alcoholism.
Because the study was conducted in mice, it's not clear whether the effects will translate to people. The researchers plan to start tests of the drug in people if it passes a safety test required by the National Institutes of Health, Kunos said.
New drug, tried method
Because obese people become desensitized to leptin, simply giving people supplements of the hormone does not promote weight loss, studies have shown. The desensitization process is thought to involve cannabinoid receptors — the same receptors that are activated by chemicals in marijuana.
Activating cannabinoid receptors is known to promote feelings of hunger in marijuana smokers, and blocking these receptors has been shown to cause weight loss. However, a previously developed weight- loss drug, called rimonabant, that blocked cannabinoid receptors also caused serious psychiatric side effects, including anxiety and depression. Rimonabant was sold in Europe beginning in 2006, but was taken off the market a few years later.
The drug tested in the new study, called JD5037, was designed to not enter the brain as a way to reduce psychiatric side effects. The drug blocks cannabinoid receptors in other parts of the body, including the liver and muscle, Kunos said.
Obese mice given JD5037 daily for about a month lost 28 percent of their body weight, and reached the weight of a normal-size mouse, Kunos said. Moreover, the mice lost the weight while continuing to eat the high-fat diet that led to their obesity in the first place. The mice appeared to lose most of the weight in the first two weeks, and maintained it after that.
The mice showed no signs of psychiatric side effects.
Another weight-loss drug?
Although our appetites are controlled by our brains, the new drug does not need to get inside the brain to do its work, Kunos said. Instead, the drug reduces leptin levels by inhibiting leptin production by fat cells and increasing the clearance of leptin, which in turn, makes the body more sensitive to the hormone, Kunos said.
Two weight-loss drugs, Belviq and Qsymia, were recently approved by the Food and Drug Administration. But because of the vastness of the obesity epidemic, medications that act in different ways are badly needed to help the problem, Kunos said.
Before Qsymia, which was previously called Qnexa, was approved, there had been concerns about the drug's side effects, including its potential to cause a fast heart rate.
Belviq may also cause serious side effects, including serotonin syndrome, a potentially life-threatening drug reaction that causes the body to have too much serotonin, a chemical produced by nerve cells, according to the National Institutes of Health.
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