WASHINGTON, July 16 (Reuters) - An ingredient in curry may help stimulate immune system cells that gobble up the brain-clogging proteins that mark Alzheimer's disease, U.S. researchers said on Monday.

They said they isolated a compound in turmeric, a yellow spice that gives Indian curry powder its distinctive color, that appears to stimulate a specific response against Alzheimer's symptoms.

It may be possible to infuse this compound into patients and treat the incurable and fatal brain condition, Dr. Milan Fiala of the University of California Los Angeles and colleagues said.

Other research has shown that curcumin, an antioxidant found in turmeric, can help prevent tumors from forming in the laboratory and in rats.

Writing in the Proceedings of the National Academy of Sciences, Fiala's team said they had shown earlier that curcumin may affect the brain cells of Alzheimer's patients. But they wanted to pinpoint the precise factor in curcumin, which is a complex compound.

They isolated bisdemethoxycurcumin and determined it was the most active ingredient in curcumin.

Using blood samples from Alzheimer's patients, they found that bisdemethoxycurcumin boosted immune cells called macrophages to clear a protein called amyloid beta, which clogs the brains of Alzheimer's patients and kills brain cells.

Macrophages are the immune cells that literally engulf and destroy deformed cells and attack invaders, like bacteria or viruses.

The researchers said it is not clear if people can eat enough curcumin to get this level of activity, but said bisdemethoxycurcumin was active at a level that could easily be achieved by infusion.

Some studies have suggested that people who eat a lot of curry may be less prone to cancer and Alzheimer's, but whether curry is responsible is unclear.

Companies are working to make an Alzheimer's vaccine that would stimulate the production of antibodies against amyloid beta. This approach would stimulate a different type of immune response and might be less likely to cause harmful side effects, like brain inflammation, the researchers said.

"Our results may provide an entirely different direction to therapeutic opportunities in Alzheimer's disease through the repair of the functional and transcriptional deficits of Alzheimer's disease macrophages by curcuminoids," the researchers wrote.

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