Taste buds in lungs discovery could ease asthma

Image caption,
The taste receptors in the lungs do not send signals to the brain but they do respond to bitter substances

The discovery of "taste receptors" in the lungs rather than on the tongue could point the way to new medicines for asthma, it is suggested.

Experiments in mice revealed that bombarding the receptors with bitter-tasting compounds helped open the airways, which could ease breathing.

The University of Maryland study, published in Nature Medicine, may have implications for other lung diseases.

Asthma UK warned that any new drug would not arrive for some time.

The "taste receptors" discovered in the smooth muscle of the lungs are not the same as those clustered in taste buds in the mouth.

They do not send signals to the brain, and yet, when exposed to bitter substances, they still respond.

It was the nature of that response that surprised researchers, who assumed their presence was as a defence against noxious gases, triggering a tightening of the airways and coughing.

In fact, the mouse experiments revealed that exactly the reverse was true.

Protective response

When airway tissue from mice was treated with bitter substances, then exposed to allergens, there appeared to be a protective response.

Dr Stephen Liggett, leading the research, said: "They all opened the airway more profoundly than any known drug that we have for the treatment of asthma or chronic obstructive pulmonary disease."

In asthma, and other lung diseases, the smooth muscle lining the airway contracts, narrowing it, and drugs such as salbutamol help relax and open it, restoring normal breathing.

Dr Liggett said that an inhaler based on bitter substances such as quinine or even saccharine, which has a bitter after-taste, could "replace or enhance" current treatment.

He warned that simply eating bitter foods would not help protect from or relieve an asthma attack.

Dr Yassine Amrani, an asthma researcher at the University of Leicester, said the research was very "encouraging", potentially offering a new target for treatment.

He said future studies could focus on trying to reproduce the effect in human as well as mouse airway tissues, and making sure that the substances did not produce unwanted side effects such as inflammation.

He said: "The concept of having bitter taste receptors in the smooth muscle of the airways is a new one, and activating this receptor could offer a new way to relax them."

Leanne Metcalf, director of research at Asthma UK said that a significant number of the 5.4m asthmatics in the UK did not control their symptoms using existing drugs, and that research into new, more effective treatments, was "vital".

She said: "The effectiveness of bitter substances at overcoming the airway narrowing that causes asthma symptoms has so far only been tested in mice, however this somewhat surprising approach does make sense in terms of what we already know about the cell signalling processes involved in asthma.

"With further in-depth research, this approach could potentially pave the way for a new range of asthma treatments based on bitter substances which could either supplement or replace existing asthma treatments but if this were possible, it would be a long way into the future."

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