For centuries it has been known that time of day is important in asthma. Symptoms of uncontrolled asthma are worst around 4am, when airflow obstruction and airways inflammation are most severe. Many asthma treatments are taken in the morning, however there are data suggesting that steroids are more efficacious if taken mid-afternoon. Investigating the biological timing of asthma is crucial to better understand the pathogenesis of asthma and this may lead to the discovery of new drug targets, and the identification of dynamic biomarkers that change by time of day. We used an ‘omics’ approach to investigate the 24-hour time course of breath volatile organic compounds (VOCs) and serum lipids in asthmatics and healthy volunteers.
• Define new biochemical pathways involved in circadian rhythm in asthma
• Discover novel circadian biomarkers in asthma
Method: We recruited 10 atopic asthmatics and 10 healthy volunteers to complete four study visits, including an overnight stay. Blood, exhaled NO, induced sputum and breath were sampled at six-hour intervals, and physiological measurements made. Breath samples were analysed by gas chromatography/mass spectrometry. Gaussian process based statistical modelling was used to determine which of the identified VOCs were rhythmic. Serum samples were also analysed for rhythmic lipid mediators of the ceramide/sphingolipid pathways.
Results: Patients with asthma (mean age 42.8 years ±3.2 vs healthy 40.2years ±4.2 (ns)) with a mean FEV1 of 3.16L (compared to 3.64L in healthy (ns)), demonstrated significant reversibility of FEV1 to beta-agonist (265±43.85ml, vs 52±33.86ml in healthy). There was a high amplitude circadian change in FEV1 in asthmatics (the nadir is at 4am). Sputum eosinophils in asthmatics peaked at 4am, however, exhaled nitric oxide showed no diurnal variability in asthmatics (see Figure 1). Breathomic analysis demonstrated significant circadian variability in seven VOCs in asthma (but not in healthy volunteers), including 2-undecanal (Figure 1). Lipidomic analysis is currently underway.
Discussion: For the first time we have identified VOCs in breath that are uniquely rhythmic in asthma and may lead to identification of metabolic pathways important in the pathogenesis of asthma.