October 28, 2010
Discovery Of Taste Receptors May Help Asthma Victims Breathe Easier
(Ivanhoe Newswire) -- Taste receptors in the lungs? Researchers have discovered that bitter taste receptors aren't just in the mouth, but in the lungs as well. Learning about the taste receptors could revolutionize the treatment of asthma and other obstructive lung diseases.
"The detection of functioning taste receptors on smooth muscle of the bronchus in the lungs was so unexpected that we were at first quite skeptical ourselves," the study's senior author, Stephen B. Liggett, M.D., professor of medicine and physiology at the University of Maryland School of Medicine and director of its Cardiopulmonary Genomics Program was quoted as saying.
Dr. Liggett, a pulmonologist, says his team found the taste receptors by accident, during an earlier, unrelated study of human lung muscle receptors that regulate airway contraction and relaxation. The airways are the pathways that move air in and out of the lungs, one of several critical steps in the process of delivering oxygen to cells throughout the body. In asthma, the smooth muscle airways contract or tighten, impeding the flow of air, causing wheezing and shortness of breath.
The taste receptors in the lungs are the same as those on the tongue. On the tongue the receptors are clustered in taste buds that send signals to the brain. The receptors in the lung aren't clustered in taste buds and don't send signals to the brain, but they do respond to bitter-tasting substances.
In this study, bitter-tasting compounds were exposed to human and mouse airways, individual airway smooth muscles cells, and to mice with asthma.
Most plant-based poisons are bitter, so the researchers thought the purpose of the lung's taste receptors was similar to the tongue's- to warn against poisonsHowever, there are thousands of compounds that activate the body's bitter taste receptors but are not toxic in appropriate doses. Many are synthetic agents, developed for different purposes, and others come from natural origins, such as certain vegetables, flowers, berries and trees.
The researchers tested a few standard bitter substances known to activate these receptors. "It turns out that the bitter compounds worked the opposite way from what we thought," says Dr. Liggett. "They all opened the airway more profoundly than any known drug that we have for treatment of asthma or chronic obstructive pulmonary disease (COPD)." Dr. Liggett says this observation could have implications for new therapies.
Quinine and chloroquine have been used to treat completely different diseases (such as malaria), but are also very bitter. Both of these compounds opened contracted airways profoundly in laboratory models. Even saccharin, which has a bitter aftertaste, was effective at stimulating these receptors. The researchers also found that administration of an aerosolized form of bitter substances relaxed the airways in a mouse model of asthma, showing that they could potentially be an effective treatment for this disease.
SOURCE: Nature Medicine, published online October 24, 2010