Extracellular matrix remodeling in children with airway foreign-body aspiration

The purpose of this study was to observe extracellular matrix remodeling in children with airway foreign-body aspiration (FBA) by detecting the expression of matrix metalloproteinase-9 (MMP-9), tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), and hydroxyproline (HYP) in bronchoalveolar lavage fluid (BALF). Forty-six children with FBA and 12 control subjects from 2002-2003 were enrolled in this study. The former were divided into three subgroups according to duration of foreign-body (FB) retention (subgroup 1, <7 days; subgroup 2, 7-30 days; subgroup 3, >30 days). Cell count, and levels of MMP-9, TIMP-1, and HYP in BALF were measured. The total number of cells and differential counts detected in BALF did not differ significantly between patients and controls (P > 0.05), while mast cells were found only in the BALF of patients. The positive rates of MMP-9 in controls, subgroup 1, subgroup 2, and subgroup 3 were 33.3%, 62.5%, 80.0%, and 93.3%, respectively, with a significant difference (P = 0.006). The positive rate of TIMP-1 in controls and subgroups 1, 2, and 3 were 33.3%, 62.5%, 80.0%, and 93.3%, respectively, with a significant difference (P < 0.001) as well. HYP levels in subgroups 2 and 3 were significantly more increased than in subgroup 1 and controls (all P < 0.001). Levels of MMP-9, TIMP-1, and HYP in patients were positively correlated with duration of FB retention (all P < 0.05), and levels of MMP-9 and TIMP-1 were also positively correlated with percentage of mast cells in BALF (all P < 0.05). The differences in MMP-9 and TIMP-1 before and after FB removed were not significant (P > 0.05), while HYP levels decreased significantly after FB were removed (P = 0.001). Our findings support the hypothesis that FBA may contribute not only to mechanical airway obstruction, but also possibly to eventual airway remodeling by generation of MMPs and TIMPs.