Fat Hormone May Aid in Weight Loss

Hormone Adiponectin Speeds Metabolism, Burns Fat

April 23, 2004 -- Move over, leptin. Researchers have discovered another fat hormone that may aid in promoting weight loss.

Contact: Karen Kreeger
Karen.kreeger@uphs.upenn.edu
215-349-5658
University of Pennsylvania Medical Center

A new study suggests that the hormone adiponectin, found in fat tissue, can cause weight loss by boosting metabolism without affecting appetite. Researchers say that the finding may lead to better treatments for obesity and other metabolic disorders, such as diabetes.

Leptin, a related fat hormone, has been widely studied in recent years and has been shown in to produce weight loss in animals by decreasing appetite and increasing metabolism.

Researchers say both fat hormones work through the same pathway in the brain to control body weight and blood sugar (glucose). But these hormones may also control metabolism though other unique ways, and learning more about how they work may lead to more effective anti-obesity treatments.

Fat Hormone Boosts Metabolism

In the study, published in the April issue of Nature Medicine, researchers injected adiponectin into normal laboratory mice. They found that the mice lost weight even though the hormone didn't seem to alter appetite or cause changes in the amount of food the mice ate.

"The animal burns off more calories, so over time loses weight, which was very fascinating because we knew that leptin caused weight loss by suppressing appetite and increasing metabolic rate," says researcher Rexford Ahima, MD, PhD, assistant professor of medicine at the University of Pennsylvania, in a news release. "Here we have another fat hormone that can cause weight loss but without affecting intake."

Researchers say fat hormones, such as leptin and adiponectin, are of interest because they may aid in promoting long-term weight loss. Over time, weight loss becomes more difficult because the body compensates, in part, by lowering its metabolic rate -- the rate at which it burns calories.

If drugs can be developed that capitalize on the metabolism-boosting properties of these fat hormones, they may be able to sustain weight loss efforts over a longer period of time without adverse health effects.

"Adiponectin or its targets in the brain and other organs could be harnessed to sustain weight loss by maintaining a high metabolic rate," ways Ahima. "This is only a possibility. We're not suggesting at this point that adiponectin will become a drug."

Fat cell hormone causes weight loss

Penn discovery in animal model opens up potential for future therapy to tackle obesity

Penn (Philadelphia, PA) - Researchers at the University of Pennsylvania School of Medicine have established in an animal model that the hormone adiponectin secreted by fat tissue acts in the brain to reduce body weight. In contrast to leptin, a related hormone, adiponectin can cause weight loss by raising metabolic rate while not affecting appetite. This finding may have future implications in understanding and treating obesity and metabolic disorders like diabetes, says lead author, Rexford Ahima, MD, PhD, Assistant Professor of Medicine, Penn Diabetes Center. This research appears in the May issue of Nature Medicine.

When adiponectin, which is involved in glucose and lipid metabolism, was introduced into the cerebrospinal fluid of normal mice, they showed no changes in food intake, but their metabolism rose. "The animal burns off more calories, so over time loses weight, which was very fascinating because we knew that leptin caused weight loss by suppressing appetite and increasing metabolic rate," explains Ahima. "Here we have another fat hormone that can cause weight loss but without affecting intake."

For many dieters, it's easy, at first, to lose weight; but over time, it becomes more difficult because the body compensates, in part, by dropping its metabolic rate. "Adiponectin or its targets in the brain and other organs could be harnessed to sustain weight loss by maintaining a high metabolic rate," says Ahima. "This is only a possibility. We're not suggesting at this point that adiponectin will become a drug." In severely obese mice, adiponectin rapidly decreases blood glucose and lipids, while burning fat. Hence, adiponectin could be beneficial in the treatment of diabetes and heart disease associated with obesity.

These findings have far-reaching potential to help fight the war against obesity, which healthcare experts agree has reached epidemic proportions in the United States. "For years people used to think fat tissue was a passive player--just there to store excess energy," explains Ahima. This proved to be a simplistic view since hormones produced by fat tissue are released into the blood and are actively involved in the regulation of metabolism. The best known fat hormone, leptin, decreases body weight by decreasing appetite and increasing metabolic rate. Leptin also reduces glucose and lipids. The researchers found that both adiponectin and leptin require the melanocortin pathway in the brain to control body weight and glucose. However, these fat hormones also control metabolism through other distinct pathways in the brain. "We focus on the brain because it is a major coordinator of feeding, metabolism, and hormones, including insulin," says Ahima.

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SOURCES: Yong, Q. Nature Medicine, April 2004 advance online publication. News release, University of Pennsylvania Medical Center.