A compound found in the root of the thunder god vine, a plant used for centuries in traditional Chinese herbal medicine, might be a key to weight loss, a study suggests.

Researchers say mice given high doses of the compound known as Celestrol for a week ate 80 percent less food than mice not given the compound, and after 3 weeks lost 45 percent of their body weight compared with the untreated mice, who lost no weight.

And weight loss was from body fat, not lean mass, they report in the journal Cell.

The compound's dramatic effect comes from its ability to greatly enhance the action of leptin, an appetite-suppressing hormone, they explain.

The hormone's effect has long been known, although efforts to harness that ability to improve weight loss have been unsuccessful.

Leptin, derived from fat cells, tells the brain when the body has sufficient fuel and energy. Researchers suspect that some people are insensitive to leptin, so those signals do not reach the brain even when leptin levels in the bloodstream increase.

That can lead to excessive food intake and obesity, the say.

"During the last two decades, there has been an enormous amount of effort to treat obesity by breaking down leptin resistance, but these efforts have failed," says senior study author Umut Ozcan, a Harvard Medical School endocrinologist. "The message from this study is that there is still hope for making leptin work, and there is still hope for treating obesity."

Analyzing a database of whole-genome gene expression profiles in human cells treated with molecules of various compounds showed Celastrol the most effective for producing a profile associated with improved leptin sensitivity in cells in the human body, the researchers said.

They emphasized caution should be exercised in any further research on the thunder god vine, suggesting toxicology studies and controlled clinical trials would be needed, since the plant's leaves, flowers and roots are all toxic.

"Celastrol is found in the roots of the thunder god vine in small amounts, but the plant's roots and flowers have many other compounds," Ozcan says. "As a result, it could be dangerous for humans to consume thunder god vine extracts to lose weight."

Still, the initial findings are sufficiently encouraging to merit more studies, he says.

"Celastrol is the first efficient leptin sensitizer and has a completely different mechanism of action than any other anti-obesity drug that has been reported to date," Ozcan says.

It is used in traditional medicine as a treatment for fever, chills and swelling, and it also is being studied as a possible treatment for some skin disorders and rheumatoid arthritis.