Increased ratio of matrix metalloproteinase-9 (MMP-9)/tissue inhibitor metalloproteinase-1 from alveolar macrophages in chronic asthma with a fast decline in FEV₁ at 5-year follow-up

Chronic asthma is associated with progressive airway remodeling, which may contribute to declining lung function. An increase in matrix metalloproteinases-9 (MMP-9)/tissue inhibitor metalloproteinase-1 (TIMP-1) may indicate airway inflammation and bronchial injury. Bronchial biopsy specimens and alveolar macrophages (AMs) were obtained from patients with asthma under regular treatment with inhaled corticosteroids or combination therapy and normal subjects (n = 10). Asthmatics included those with a slow forced expiratory volume in one second (FEV₁) decline (<30 mL/year, n = 13) and those with a fast FEV₁ decline (≥30 mL/year, n = 8) in 5-year follow-up. Immunostaining expression of MMP-9 and TIMP-1 was detected in airway tissues. MMP-9 and TIMP-1 was measured from AMs cultured for 24 h. After the 5-year treatment, the methacholine airway hyperresponsiveness of the slow FEV₁ decline group was decreased, but that of the fast FEV₁ decline group was increased (PC₂₀, provocative concentration causing a 20% decrease in FEV₁, 3.12 ± 1.10 to 1.14 ± 0.34 mg/dL, p < 0.05). AMs of asthma with a fast FEV₁ decline released a higher level of MMP-9 (8.52 ± 3.53 pg/mL, p < 0.05) than those of a slow FEV₁ decline (0.99 ± 0.20 pg/mL). The MMP-9/TIMP ratio in the fast FEV₁ decline group (0.089 ± 0.032) was higher than that of the slow FEV₁ decline group (0.007 ± 0.001, p < 0.01). The annual FEV₁ decline in 5 years was proportional to the level of MMP-9 (r = 57, p < 0.01) and MMP-9/TIMP-1 ratio (r = 0.58, p < 0.01). The airways of asthma with greater yearly decline in FEV₁ showed an increased thickness of submucosa and strong expression of MMP-9. An increase in MMP-9 and MMP-9/TIMP-1 in airways or AMs could be indicators of chronic airway inflammation and contribute to a greater decline in lung function of patients with chronic asthma.