Background. Early detection is essential to ensure prompt treatment selection for many lung disorders, which are on the rise in the population. Unfortunately, invasive methods are often used to investigate the distal parts of the lungs for diagnosis as well as to establish biomarkers for these diseases. Thus, the use of a non-invasive particles in exhaled air (PExA) method to sample distal airways is gaining attention. Aims. To propose an optimized method and to determine if PExA samples may be utilised to detect and quantify microRNA (miRNA) in the lungs. In addition, to see if PExA can represent samples from the distal airways. Methods. We tested multiple PExA sampling and processing conditions due to the limitations of the collected material and risk of the RNA degradation. miRNA low input kits were used to extract and process total RNA, then miRNA sequencing was performed. Results. Even though the content of PExA samples is scarce, a list of mature miRNAs was detected. The most abundant miRNAs identified in PExA match those shown in extracellular vesicles secreted by primary human airway epithelial cells (1). We also identified miRNAs found in other types of lung samples, such as bronchoalveolar lavage fluid, indicating that PExA samples can represent the distal airways. Conclusions. We were able to detect miRNAs in PExA samples after successfully optimising the sampling and handling procedures, which were shown to originate from the distal airways. These first step verifying the possibility to studying the role of this biomolecule in lung disorders using this non-invasive technique will be further validated for quantitative analysis and data validation.

1) Koeppen, K. et al. PNAS 2021; 118 (28).