Bitter Perception Is Altered in Asthma and Predicts its Severity

Abstract

To determine if bitter taste or n-propylthiouracil sensitivity is altered in patients with asthma and whether it correlates with disease characteristics.A total of 65 adults with confirmed asthma and 62 age- and sex-matched controls without asthma were studied. Exclusion criteria included but were not limited to patients with chronic obstructive pulmonary disease (COPD), >10 pack-years smoking history, and other conditions associated with dysgeusia.Patients rated their ability to smell and taste on a 10 cm visual analog scale. Asthma severity and medication step were assessed according to the Global Initiative for Asthma (GINA) guidelines. Gustatory sensitivity for sweet, sour, bitter salty, and umami (corresponding with monosodium glutamate taste) was assessed as perceived or not perceived by using a “Test Sprays” test and taste threshold assessed by using the “Taste Strips” test (TST). The TST measured each taste on a 0 to 4 point scale (cumulative score: 0–20). As another assessment of bitter perception, an impregnated test strip, was used to identify n-propylthiouracil “tasters” and “nontasters”Patients with asthma had significantly lower sensitivity for bitter (P = .026), salty (P = .035), umami (P < .001), and n-propylthiouracil (P = .001) than controls did. TST scores of 0 to 1 for individual tastes were more common in asthma patients, whereas scores of 3 to 4 were more common in controls without asthma. Taking medications with possible gustatory side effects (eg, cetirizine or formoterol) did not affect the results in the patients with asthma but had a moderate effect on salty and cumulative TST in the control group (P < .001 and P = .01, respectively). Among the asthma patients, asthma severity was negatively correlated with the bitter TST (P = −.28) and cumulative TST (P = −.37) scores. Similarly, the GINA treatment step was negatively correlated with the cumulative TST score (P = −.026) and bitter TST score (P = −.30). No other correlations between asthma severity or medication requirement and tastes were identified.There is a diminished gustatory sensitivity to bitter and n-propylthiouracil in patients with asthma that correlates with asthma severity. A simple n-propylthiouracil or quinine taste test may be a prognostic test to predict asthma severity.My first thought when I read this article was, “Who even knew there were taste receptors on airway smooth muscle and who thought to look in the first place?” Taste receptors (TAS2Rs) in human airway smooth muscle result in bronchodilation when activated. TAS2R polymorphisms are associated with more severe asthma. Increased expression of leukocyte TAS2Rs correlates with asthma severity in adults and children. The overexpression of TAS2Rs may be physiologic compensation for diminished functionality. With this study, the authors tell us 1 more thing that we did not know about asthma. There is much more yet to learn, including things we have not even considered. Unfortunately, we do not even know what we do not know!