Debbie Nicholson

Bitter tasting foods help airways to relax

Bitter taste receptors (TAS2Rs), a G-protein-coupled receptor family long thought to be solely expressed in taste buds on the tongue, have recently been detected in airways. Bitter substances can activate TAS2Rs in airway smooth muscle to cause greater bronchodilation than β2 adrenergic receptor agonists, the most commonly used bronchodilators. However, the mechanisms underlying this bronchodilation remain elusive, according to the studies abstract.

University of Massachusetts Medical School researchers examined how bitter tasting foods can reverse the contraction of airway cells called bronchodilation. This effect someday may be applied to provide new treatments for airway obstructed diseases such as asthma and COPD.
Air can flow easily in and out of your lungs when your breathing is normal but when you’re having an asthma attack the smooth muscles around the outside of the tubes may tighten. The airways, or bronchial tubes, in the lungs become inflamed and swollen making breathing difficult. However, bitter substances are able to relax the smooth muscles suggest that they may be able to stop asthma attacks and in fact could even be an improvement over current treatments since the relaxation effects are quite fast.

Dr. Ronghua ZhuGe, PhD, Associate Professor, University of Massachusetts Medical School, Department of Microbiology & Physiological Systems, senior author of study and colleagues in order to uncover the mechanism underlying bitter tastant-induced bronchodilation as demonstrated in both in vitro and in vivo normal and asthmatic models of mice, and in vitro human airways. Researchers how bitter tastants affected both [Ca2+]i and ASM contraction in freshly isolated airway cells and tissues from mouse and human. Fluo-3 was used to assess the effect of bitter tastants on [Ca2+]i; chloroquine and denatonium, two substances commonly used to study bitter taste signaling, were used as bitter tastants.

During an asthma attack, channels on the membrane of smooth muscle cells in the airways open. This allows calcium to flow into the cell, causing it to contract. When the cells contract, the airway becomes narrower and makes breathing more difficult. The research team determined that bitter substances act by shutting down these calcium channels, allowing bronchodilation.

Bitter taste receptors, like most receptors, span the plasma membrane of the cell. Part of the receptor is outside the cell, able to bind (and hence "sense") bitter substances outside the cell. When a bitter compound binds to a bitter taste receptor, the receptor releases a G-protein, which then splits into two parts: a G alpha subunit and G beta-gamma dimer.

Kevin Fogarty, MS, Research Assistant Professor, Department, Program of Molecular Medicine at the University of Massachusetts Medical School and co-author of the study explains "It is the G beta-gamma dimer that likely acts to close the calcium channels on the plasma membrane.” "Once the channels are closed, the calcium level returns to normal and the cell relaxs," he said. "This ends the asthma attack."

In their discussion the research team writes “Our results demonstrate that bitter tastant's reversal of the rise in [Ca2+]i evoked by bronchoconstrictors is required for its bronchodilation effect. They also reveal that bitter tastants can generate different and opposing Ca2+ signals depending upon the cellular environment.”

Dr. ZhuGe comments "With this new understanding of how bitter substances are able to relax airways, we can focus our attention on studying these receptors and on finding even more potent bitter compounds with the potential to be used therapeutically to end asthma attacks.”
"I am excited that someday, with more research, there may be a new class of bronchodilatorswhich are able to reverse an asthma attack quicker and with fewer side effects than is currently available to patients.”

This study appears in Nature Medicine.

In 2010, researchers from the University Of Maryland School Of Medicine in Baltimore 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.

More information on lung diseases can be found online at the American Lung Associationwebsite.


Slideshow; Asthma and food

Associated Article; Bitter Tastes Reopens Tight Airways