Researchers at University of Maryland’s School of Medicine have discovered that human lungs contain bitter taste receptors, identical to those on our tongues. In itself, this would be a surprising discovery, but as it turns out, these taste receptors may have a valuable potential medical application: They could be used to treat asthma more effectively than any current drug.
Most plant-based poisons are bitter, so the researchers thought the purpose of the lung’s taste receptors was similar to those in the tongue – to warn against poisons. “I initially thought the bitter-taste receptors in the lungs would prompt a ‘fight or flight’ response to a noxious inhalant, causing chest tightness and coughing so you would leave the toxic environment, but that’s not what we found,” says Dr. Liggett.
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 extensively 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. “New drugs to treat asthma, emphysema or chronic bronchitis are needed,” he says. “This could replace or enhance what is now in use, and represents a completely new approach.”
Liggett and his team found that the bitter antimalarials quinine and chloroquine are extremely effective at opening up the airways, and that even saccharine, the artificial sweetener with a bitter aftertaste, works; the next step is likely converting the most effective bitter substances to aerosol forms, allowing them to be applied using inhalers.
This research is still a ways away from widespread medical application, which could yet hit a dead end for some unforeseen reason. But it’s exciting because it makes use of a physiological pathway about which we already know quite a lot, that of taste, and presents the opportunity to apply that knowledge to treat a different, urgent problem. More than 300 million people worldwide have asthma — 23 million in the United States — and asthma rates have been steadily increasing over the past several decades as the world has become more industrialized. Aerosolized bitter substances could potentially be much cheaper than the beta-2 antagonists we currently use to treat asthma, and thus present more promise in the third world; moreover, they could be safer for young children.