Breathomics in controlled asthma: identification of nonanoic and propanoic acids as volatile organic compounds

There is growing interest in identifying novel, non-invasive biomarkers reflecting endogenous inflammatory processes in asthma. This study aimed to evaluate the presence of volatile organic compounds (VOCs) in exhaled breath from patients with clinically controlled asthma and assess how tobacco exposure influences their expression.

Exhaled breath samples from 120 clinically controlled asthma patients and 89 healthy controls were collected using BioVOC breath samplers. Samples were analysed by gas chromatography-mass spectrometry, assessing five previously characterised VOCs: hexanal, heptanal, nonanal, propanoic acid and nonanoic acid.

Compared to healthy controls, asthma patients exhibited a lower frequency of propanoic acid exhalation (25.0% versus 53.9%; p<0.001) and higher frequencies of nonanoic acid (30.8% versus 15.7%; p=0.019). These differences persisted after adjusting for smoking status. Stratified analysis revealed reduced propanoic acid exhalation in both smoking and non-smoking asthma subgroups compared to their respective controls (21.0% versus 55.6% and 29.3% versus 51.4%, respectively; p<0.001). Additionally, asthma current and former smokers had significantly increased detection of nonanoic acid compared to controls (33.9% versus 11.1%; p=0.0359). Multivariate analysis identified propanoic acid as a protective factor against asthma (OR 0.2 (95% CI 0.1-0.4); p<0.001), whereas nonanoic acid significantly increased asthma risk (OR 4.5 (95% CI 1.8-12.6); p=0.003).

Exhaled propanoic and nonanoic acids may serve as complementary non-invasive biomarkers for monitoring controlled asthma, independently of tobacco exposure. VOC analysis has promising potential to improve asthma management, therapeutic monitoring and patient stratification.