WASHINGTON (AP)– Leptin, a hormone that acts in the brain to suppress appetite, also fights obesity by burning up fat within cells, researchers report.
Dr. Roger H. Unger of the University of Texas Southwestern Medical Center at Dallas said laboratory rats that are genetically altered to have high levels of leptin lose all the fat in their bodies within days.
The researchers say a study to be published on Tuesday in the Proceedings of the National Academy of Sciences shows for the first time that leptin is active inside body cells, not just in the brain.
“There is a huge effect in cells on the metabolism of fatty acids,” said Unger. “The fat never leaves the cells. It is burned up inside.”
Fat was depleted in cells that normally store fat and in muscle, liver and pancreas cells, he said.
“Within seven days, there is no fat detectable in the body at all,” said Unger.
Earlier studies of leptin showed that the hormone acts in the brain to blunt the appetite. Rats with high levels of leptin were found to eat about half the food of normal rats.
Unger and his associates transferred genes that boosted the leptin levels in lab rats to about 20 times normal.
Their appetites and feeding habits were then monitored.
For comparison, normal rats were fed the same amount of food as the high-leptin rats, said Unger.
Later, tissue from the rats was examined for fat content.
Unger said the normal rats lost fat, but only about half the amount shed by the leptin rodents. Also, the normal rats retained fat in their muscle cells.
The study suggested that leptin may be useful in controlling Type II diabetes, the form that often develops in older, overweight people. He said the study showed that by burning fat in the cells, leptin lowered blood sugar and made the cells more sensitive to insulin, the hormone that controls sugar levels. Diabetes develops when the body stops making or becomes insensitive to insulin.
Unger cautioned that the studies on the action of leptin in rat cells may not apply to humans. “That still needs to be tested,” he said.
An artificial form of leptin is now being tested as a weight-control drug in humans, but the results are still unknown, he said.