Circulating miRNA-21 and miRNA-155 Expression in Adult Patients With Bronchial Asthma and Its Association With Lung Function

Background & objectives: MicroRNAs (miRNAs) regulate post-transcriptional gene expression and have emerged as important contributors to the pathogenesis of asthma, as well as potential biomarker candidates. In this study, we evaluated the serum miRNA-21 and miRNA-155 expression in bronchial asthma and its association with lung function and inflammatory markers. Methods: In this pilot case-control study, a total of 72 participants were enrolled, including 36 adults with spirometry-confirmed asthma and 36 healthy controls recruited from hospital staff and attendants without respiratory symptoms or history of allergic disease. Spirometry was also performed in controls to exclude occult airflow limitation. A predefined exploratory hypothesis was that circulating miRNA-21 and miRNA-155 expression would differ between asthma and controls and may correlate with inflammatory biomarkers and lung function. Serum miRNA-21 and miRNA-155 expression was quantified by quantitative real-time polymerase chain reaction. Between-group comparisons were performed using the Mann-Whitney U test, and correlations with serum IgE, absolute eosinophil count (AEC), forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were examined using Spearman’s rank correlation coefficient. Results: miRNA-21 expression was significantly higher in patients compared to controls with median values of 0.191 (IQR 0.114-0.312) vs 0.054 (IQR 0.027-0.195), P=0.006. In contrast, miRNA-155 expression did not differ significantly between the groups (median 0.159 (IQR 0.068-0.363) vs 0.220 (IQR 0.107-0.338), P=0.240). Among correlation analyses, only miRNA-155 showed a significant positive correlation with serum IgE (Spearman’s ρ=0.654, P<0.001) and no significant association of miRNA-21 with the IgE level. Neither miRNA correlated significantly with AEC, FEV1 or FVC. Interpretation & conclusions: Serum miRNA-21 was significantly upregulated in bronchial asthma, supporting its possible association with asthma-related immune dysregulation. Although miRNA-155 was not differentially expressed between groups, its positive association with serum IgE suggests a possible relationship with atopic inflammatory pathways. These findings suggest that circulating miRNAs may reflect asthma-related inflammatory activity; however, their clinical biomarker utility requires further validation.