Sputum Exosomal microRNAs as Non-Invasive Biomarkers in COPD: A Cross-Sectional Study

Background: Chronic obstructive pulmonary disease (COPD) is a heterogeneous condition marked by airway inflammation, airflow limitation, and structural remodeling. Exosomal microRNAs (exo-miRNAs) are stable, cell-free biomarkers reflecting airway molecular changes. While serum and BALF exosomal miRNAs have been examined, sputum-derived profiles remain underexplored. Methods: Induced sputum was collected from 20 clinically stable COPD patients and 10 age-matched healthy controls. Exosomes were isolated by polymer-based precipitation and verified by transmission electron microscopy and Western blotting for CD9 and CD81. Nine candidate miRNAs (miR-21, miR-155, miR-34a, miR-126, miR-210, miR-146a, miR-199a-5p, miR-223, miR-1246) were quantified by RT-qPCR. Group comparisons used the Mann-Whitney U test, correlations Pearson's r, and diagnostic accuracy ROC analysis. Results: Sputum-derived exosomes displayed characteristic morphology and canonical protein markers. COPD patients showed significant dysregulation of exosomal miRNAs, including upregulation of miR-21 (fold change = 3.4; 95% CI: 0.12-0.64 vs. 0.18-0.22; p < 0.001) and miR-223 (fold change = 2.1; 95% CI: 0.00-3.79 vs. 0.86-1.22; p = 0.004), and downregulation of miR-155 (fold change = 0.35; 95% CI: 0.43-0.67 vs. 0.86-1.22; p = 0.002), miR-126 (fold change = 0.42; 95% CI: 0.30-0.39 vs. 0.80-1.42; p = 0.009), and miR-146a (fold change = 0.28; 95% CI: 0.49-1.12 vs. 0.87-1.35; p = 0.006). miR-21 correlated with symptom burden (CAT; r = 0.445; p = 0.049). Among individual biomarkers, miR-155 exhibited the best diagnostic performance for COPD detection (AUC = 0.730; 95% CI: 0.53-0.93), which further improved when combined with miR-126 and miR-146a (AUC = 0.841; 95% CI: 0.69-0.98). For disease stratification, miR-126 most effectively discriminated mild from moderate-to-severe COPD (AUC = 0.728; 95% CI: 0.50-0.96). These results indicate that sputum-derived exosomal miRNAs-particularly miR-155, miR-126, and miR-146a-may serve as promising non-invasive biomarkers for COPD diagnosis and clinical phenotyping. Conclusions: Sputum exosomal miRNAs reveal a distinct COPD-specific signature reflecting inflammation, impaired repair, and immune dysregulation. Composite panels incorporating miR-155, miR-126, and miR-146a enhance diagnostic accuracy and could be integrated into non-invasive workflows for COPD detection and staging.