MMP-9 protein level does not reflect overall MMP activity in the airways of patients with COPD

SummaryBackgroundAnimal and human studies have implicated an imbalance of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) in the pathogenesis of chronic obstructive pulmonary disease (COPD). MMP-9 protein is increased in COPD and we hypothesized that total MMP activity would be raised although this has not previously been measured.MethodsUsing fluorescence and biotin labelled MMP assays, RT-PCR, western blotting and enzyme-linked immunosorbent assay we examined total MMP activity, specific gelatinase, elastase, collagenase activity, TIMP-1 and TIMP-2 in induced sputum from smokers with COPD and smokers without COPD.ResultsInduced sputum was obtained from 15 smokers with COPD and 14 smokers without COPD. MMP-9 levels were higher in those with COPD compared with controls (p<0.05). Total MMP activity, specific gelatinase, collagenase and elastase activities were not higher in COPD patients. In addition, reduced MMP activity was correlated with increasing airflow obstruction in COPD (p=0.016).ConclusionMMP-9 protein but not MMP activity was higher in sputum of COPD patients compared with controls. These results suggest that MMP-9 levels may not reflect the overall MMP activity in the airways of patients with COPD suggesting a complex relationship between MMP-9 protein and activity. Further studies of MMPs in COPD should comprise activity measures in addition to protein levels.