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Researchers at the University of Maryland School of Medicine in Baltimore have found that the human lungs have bitter taste receptors much like those located in the mouth, which could lead to improved treatment of asthma and other lung diseases.

Stephen B. Liggett, M.D., lead author of the study and professor of medicine and physiology at the University of Maryland School of Medicine; Deepak A. Deshpande, Ph.D., author of the study and assistant professor of medicine at the University of Maryland School of Medicine; and John Hopkins University researchers Steven S. An and James S. K. Sham have discovered bitter taste receptors in the human lungs on accident while studying human lung muscle receptors, which regulate airway relaxation and contraction.

"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," said Liggett.

The bitter taste receptors on the lungs, unlike taste receptors in the mouth, are not clustered in taste buds and do not send signals to the brain. However, they do respond to items that have a bitter taste. The researchers originally thought the purpose of these taste receptors were to prompt coughing and tightness of the chest when bitter poisons came in contact with the receptors, as a way of warning the individual of a toxic environment. But Liggett and his fellow researchers discovered that this hypothesis was incorrect after finding that thousands of compounds, which activate bitter taste receptors, are not toxic in moderate doses.

"It turns out that the bitter compounds worked the opposite way from what we thought," said Liggett. "They all opened the airway more extensively than any known drug that we have for treatment of asthma or chronic obstructive pulmonary disease (COPD).

"New drugs to treat asthma, emphysema or chronic bronchitis are needed. This could replace or enhance what is now in use, and represents a completely new approach."

Researchers came to this conclusion after exposing bitter-tasting compounds to individual airway smooth muscle cells in both human and mouse airways. Chloroquine, quinine and saccharine are a few bitter compounds that proved to open contracted airways in laboratory models. But Liggett warns that just eating bitter tasting food would not be enough to open airways.

"Based on our research, we think that the best drugs would be chemical modifications of bitter compounds, which would be aerosolized then inhaled into the lungs with an inhaler," said Liggett.

This improved treatment would be ideal for asthma, since this chronic inflammatory disease cause the smooth muscle airways to tighten, making the act of breathing difficult. Asthma affects 23 million Americans, and COPD is the fourth leading cause of death in the U.S. Together, asthma and COPD affects 300 million people globally.

"The work of this team exemplifies what it takes to make real improvements in treating certain diseases," said E. Albert Reece, M.D., Ph.D., M.B.A., dean of the University of Maryland School of Medicine. "These researchers were willing to take chances and ask questions about an unlikely concept. Why are taste receptors in the lungs? What do they do? Can we take advantage of them to devise a new therapy? In the end, their discoveries are in the best tradition of scientific research."

This study was published in Nature Medicine.