Non-invasive biomarkers applied in a case-control study

Background: Exhaled breath contains various potential noninvasive biomarkers for airway disease. Aim: This study aims to evaluate the performance of known exhaled markers and to search for potential new markers in exhaled breath. Methods: Asthmatic (N=72) and healthy (N=67) children (6-12 years) donated exhaled breath condensate (EBC; RTube) and exhaled gasses (Tedlar bag). Fractional exhaled nitric oxide (FeNO) was measured (NIOX MINO). EBC pH was measured directly after sampling without deaeration, EBC 8- isoprostane was measured by ELISA (Cayman). Patterns of exhaled proteins and gasses were analysed by LC/MS or GC/MS to obtain a fingerprint of molecules which are indicative for the airway status. Results: Increased FeNO values were observed in the asthma group compared to the healthy controls (Mann-Whitney U test; p=0.057), and in the allergic asthmatic patients compared to the non-allergic asthmatic patients (p=0.01). EBC pH was significantly lower in the asthma group compared to healthy controls (p=0.047). EBC 8-isoprostane was comparable between children with asthma and healthy controls, but was significantly increased in allergic asthma patients compared to non-allergic patients (p=0.032). Various proteins that might be relevant in respiratory health outcomes were for the first time identified in EBC, amongst which annexin A1 and A2, calgranulin A and B, catalase, galectin-7, and prolactin-induced protein. Prediction models of selected proteolytic peptides or gasses were build (Support Vector Machine analysis) based on the health outcome asthma. Conclusion: Exhaled molecules are influenced by asthma or allergy status. This study identified new exhaled molecules that might be relevant for respiratory health.