Immune System Protein Tied to Weight Loss

Mice without interleukin-18 quickly got fat, study found

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HealthDay Reporter

TUESDAY, June 19, 2007 (HealthDay News) -- A piece of the body's immune system might also help dampen appetite and help people lose weight, research in mice suggests.

The findings are preliminary, and so far there are only indications that the component -- a protein called interleukin-18 -- helps prevent mice from getting fat.

In the bigger picture, however, "we're really gaining a sense that there are molecules in the immune system that regulate appetite," said study lead author Eric Zorrilla, an assistant professor at The Scripps Research Institute in San Diego.

Appetitive suppressants do exist, but they're prone to major side effects, Zorrilla said. Scientists have been looking for alternatives that would be easier for people to tolerate.

Enter interleukin-18, an active part of the immune system. Zorrilla's team was studying the protein when they noticed that something unusual occurred in mice genetically engineered to lack the protein: They got fat.

The researchers then began studying the genetically engineered mice to see how they fared without the protein. Their findings were published this week in Proceedings of the National Academy of Sciences.

Mice without the protein overate and became fatter than the other mice, the researchers found.

It's not clear how the interleukin protein might keep appetite under control under normal circumstances. Nor is it understood why appetite seems to grow when the protein is missing.

One theory: Interleukin-18 might help animals lose their appetite when they're sick. Without the protein around to monitor things, the body loses its ability to properly track its food intake, the researchers speculated.

On the bright side, the protein may not be related to "the adverse parts of the sickness response, the part about actually feeling sick," Zorrilla said.

He said that researchers are years away from creating a drug that they could use on people. For now, Zorrilla said, "we're trying to understand the neurobiology of (the molecule), where in the brain it's acting. That would help us understand what side effects it might have."

Another expert agreed. Dr. Tae-Hwa Chun, a metabolism researcher at the University of Michigan, said that much more research is needed to make sure that tinkering with interleukin doesn't inadvertently lead to heart, blood vessel or liver problems.

More information

Learn more about fighting obesity from the U.S. National Institute of Diabetes and Digestive and Kidney Diseases.

SOURCES: Eric Zorrilla, Ph.D., assistant professor, The Scripps Research Institute, San Diego; and Tae-Hwa Chun, M.D., Ph.D., researcher, Department of Internal Medicine, University of Michigan, Ann Arbor; June 18-22, 2007, Proceedings of the National Academy of Sciences

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