Scientists turn fat cells into fat-burning machines

In what sounds like every dieter's dream, scientists have figured out a way to turn fat-storing cells into little fat-burning machines. Unfortunately, it has only been done in laboratory rats, and the human applications remain in the future. Nevertheless, the scientists say it could eventually lead to new ways to help Americans fight their expanding waistlines.

"This is in no way a cure for obesity," said Roger H. Unger of the University of Texas Southwestern Medical Center in Dallas, who led the work. "But it is a road map. It's a strategy for future research."

Unger and his colleagues injected rats with a virus genetically engineered to carry the gene for the hormone leptin, which is normally produced by fat cells. The virus infected the animals' livers, causing the organ to produce leptin. The resulting high levels of leptin in the animals' bloodstreams made the rats rapidly lose weight.

When Unger and his colleagues examined the animals' fat cells, they discovered that they had shriveled in size and were chock-full of an unusually large number of structures known as mitochondria, tiny energy-producing powerhouses inside cells, said a report in the Proceedings of the National Academy of Sciences.

The findings indicate that fat cells normally develop a defense against their own leptin, which would explain why injecting the hormone into the body has failed to make people lose weight. But when the hormone comes from another part of the body, it appears to bypass that defense. If researchers could identify that mechanism and harness it, that could lead to new weight-loss treatments, Unger said.

THE WASHINGTON POST