Purpose: Lung inflammation from exposure to airborne particulate matter (PM) may be responsible for morbidity in asthma, but several studies using environmental monitoring data showed inconsistent results. Thus, the aim of this study was to evaluate the capability of induced sputum (IS) technology in order to biologically monitor PM in the lungs of urban asthmatic children.
Methods: We collected clinical, demographic, biological and environmental monitoring data on 136 children referred for asthma evaluations. The study participants were divided into two groups according to IS eosinophil counts of <3% (non-eosinophilic inflammation, n = 52) and ≥3% (eosinophilic inflammation, n = 84).
Results: The eosinophilic group displays significantly higher levels of fractional exhaled nitric oxide than the non-eosinophilic one (58.8 ± 47.5 vs 28.9 ± 34.2 ppm, p = 0.007). Particles (0-2.5 and 0-5 µm) comprised a strong risk factor for eosinophilic inflammation in IS (≥3%). Children with >80% of particles (0-2.5 µm) out of the total PM accumulated in the airways displayed the highest OR 10.7 (CI 2.052-56.4 p = 0.005) for an existing eosinophilic inflammation. Heme oxygenase-1 (HO-1) enzyme levels in IS positively correlated with % eosinophils and with particles in IS ranging between 2 and 3 μm. The level of HO-1 enzyme activity and FEV1/FVC in children with <3% eosinophils, but not ≥3%, was positively and significantly correlated, showing a protective effect of HO-1.
Conclusion: Accumulation of PM involves oxidative stress pathways and is a risk factor for developing eosinophilic inflammation in asthmatic children. IS can biologically monitor this process.