Increased matrix metalloproteinase-9 (MMP-9) activity observed in chronic wound fluid is related to the clinical severity of the ulcer

Background The pathology of chronic wounds is often characterized by elevated levels of proinflammatory cytokines [e.g. tumour necrosis factor (TNF)-alpha and interleukin (IL)-1 beta], proteases [e.g. matrix metalloproteinases (MMPs)] and neutrophil elastase. MMPs specifically have been implicated by a number of studies as the major protease family responsible for the degradation of key factors critical to the ulcer's ability to heal. Objectives To assess individual MMPs in chronic wound fluid (CWF) in order to develop improved treatments for chronic ulcers. Methods Collagen type I and IV zymography, immunoprecipitation followed by a substrate activity assay, and an indirect enzyme-linked immunosorbent assay were all used to analyse MMP levels in CWF. Results Our studies demonstrate that there is excessive protease activity in CWF compared with both human serum and acute wound fluid (AWF), which can be specifically attributed to MMPs as determined through a MMP-inhibitor study. Multiple MMPs were immunoprecipitated from the CWF samples and MMP-9 was identified as the predominant protease in CWF, with significantly elevated activity levels in CWF compared with AWF. In addition, the clinical status of the ulcer is directly associated with the amounts of MMP-9 present in the wound fluid. Therefore, this study suggests that higher levels of MMP-9 in chronic wound fluid correlate with a clinically worse wound. Conclusions In view of these results, it is hypothesized that a specific inhibitor of MMP-9 could potentially be more therapeutically effective than general MMP inhibitors in modulating chronic ulcers towards a healing state.