Bitter substances bind to specific taste receptors in our mouths. The bitter taste receptors probably evolved to prevent us from eating poisonous plants and fruits. Many poisons have a bitter taste. A research team at the University of Maryland School of Medicine in Baltimore, was studying receptors in the lung that contract and relax smooth muscles in lung airways. The researchers found, to their surprise, bitter taste receptors in the lung, which when activated by bitter substances produced powerful dilation of bronchial airways.
Bitter substances better than anti-asthma drugs
In asthma and obstructive lung diseases, the smooth muscle cells that surround the airways contract and so prevent sufficient airflow, causing wheezing and shortness of breath. The researchers discovered the taste receptors in the lung after screening airway smooth muscle cells for genes that constrict or dilate airways. When they found the bitter taste receptors, they expected them to cause constriction. But when they tested both mouse and human smooth muscle tissue, they found that bitter substances, like quinine and chloroquine, relaxed the smooth muscle cells. When they compared the effect of standard anti-asthma drugs, the beta-adrenergic agonists, to the effect of the bitter substance on mouse airways, bitter substances dilated airways three times better than the anti-asthmatic drugs. The researchers also tested bitter substances and anti-asthma drugs in a mouse model of asthma, in which the mice had asthma-like symptoms. Substances and drugs were administered as an inhalent. The asthma-like symptoms were relieved much better by the bitter substances than by the anti-asthma drugs.
A promising new therapy
In the experiments, mouse airways were exposed to bitter substances by inhalation. The researchers don’t believe that just eating or drinking bitter substances could open up lung airways. Currently, researchers are working on bitter substances that can be added to inhalers to treat asthma and obstructive lung diseases. They write: “Given the need for efficacious bronchodilators for treating obstructive lung diseases, this pathway can be exploited for therapy with the thousands of known synthetic and naturally occurring bitter tastants” (Deshpande, D.A. et al.). Non-volatile bitter substances could be chemically modified to make them volatile for use in an inhaler. Unlike beta-adrenergic drugs, most bitter foods have no serious side effects. Targeting the bitter taste receptors in the lung could revolutionize the treatment of asthma and obstructive lung diseases.
Deshpande, D.A. et al. Bitter taste receptors on airway smooth muscle bronchodilate by localized calcium signaling and reverse obstruction. Nature Medicine (2010) 16: 1299