Children with stable asthma have reduced airway matrix metalloproteinase-9 and matrix metalloproteinase-9/tissue inhibitor of metalloproteinase-1 ratio

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Abstract
Background Childhood asthma is characterized by inflammation of the airways. Structural changes of the airway wall may also be seen in some children early in the course of the disease. Matrix metalloproteinases (MMPs) are key mediators in the metabolism of the extracellular matrix (ECM). Objective To investigate the balance of MMP‐8, MMP‐9 and tissue inhibitor of metalloproteinases (TIMP)‐1 in the airways of children with asthma. Methods One hundred and twenty‐four children undergoing elective surgical procedures also underwent non‐bronchoscopic bronchoalveolar lavage (BAL). MMP‐8, MMP‐9 and TIMP‐1 were measured by ELISA. Results There was a significant reduction in MMP‐9 in atopic asthmatic children (n=31) compared with normal children (n=30) [median difference: 0.57 ng/mL (95% confidence interval: 0.18–1.1 ng/mL)]. The ratio of MMP‐9 to TIMP‐1 was also reduced in asthmatic children. Levels of all three proteins were significantly correlated to each other and to the relative proportions of particular inflammatory cells in BAL fluid (BALF). Both MMP‐8 and MMP‐9 were moderately strongly correlated to the percentage neutrophil count (r=0.40 and 0.47, respectively, P<0.001). Conclusions An imbalance of MMPs and their inhibitors occurs in children with well‐controlled asthma, which may indicate early derangement of the metabolism of the ECM.