By Erin Hicks
Based on studies of mice, experts at Columbia University Medical Center in New York City are suggesting that leptin, a hormone involved in energy metabolism, appetite, fertility, and building bone mass, may play a key role in the link between asthma and obesity -- and possibly lead to development of a leptin-based treatment for weight-related asthma.
The researchers observed that some patients who are anorexic or obese also have asthma, which makes sense because both abnormally low or high body weight and fat mass can result in narrowing of the airways and diminished lung function.
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They suspected that asthma associated with anorexia or obesity might result from a signal coming from fat cells and affecting the lungs. That led them to leptin, a protein made by fat cells that circulates in the bloodstream and travels to the brain.
Leptin affects the airways by decreasing the activity of the parasympathetic nervous system, an area of the nervous system that hasn’t formerly been associated with the hormone, says lead study author Gerard Karsenty, MD, PhD. This study shows that leptin regulates airway diameter independently of body weight and appetite, according to a news release on the asthma study.
They also discovered that regulation of airway diameter occurs regardless of whether the bronchi are inflamed, a new finding since asthma has historically been linked with inflammation.
“Usually asthma is a disease caused by local inflammation. What we found is that, in fact, asthma in the obese or anorexic can develop and be treated without taking care of the [airway] inflammation,” says Dr. Karsenty.
Obese and Anorexic Mice
The researchers conducted two experiments on mice. In one, they took obese, asthmatic mice and gave them a substance that increases lung inflammation. When they infused leptin into the brains of the mice for four days, they found no effect on inflammation, but airway diameter and lung function were normal.
"This showed that, at least in the mouse, you can cure obesity-related asthma without affecting inflammation,” says Karsenty.
In the second experiment, researchers treated obese, asthmatic mice with drugs that decrease parasympathetic signaling. The asthma lessened after several days, suggesting that a treatment that affects parasympathetic signals can increase bronchi diameter — and therefore improve breathing — regardless of whether there is lung inflammation.
Leptin is thought to affect the lungs of anorexic patients the same way it affects the lungs of obese people, says Karsenty.
“In obese patients there is leptin resistance, and in anorexic patients, since they are so thin they have less leptin and less leptin signaling, therefore they have an increased parasympathetic tone and decreased airway diameter,” he explains.
Karsenty says that he and his research team hope that leptin may be a useful future treatment for asthma in obese patients.
Before that happens, he adds, “Clinical trials are needed before this or a more active and selective drug can be recommended for the treatment of body weight–associated asthma."
The study was published in the journal Cell Metabolism.
"Hormone May Play a Role in Asthma-Obesity Link" originally appeared on Everyday Health.