IMPLICATIONS: The present study demonstrated increased matrix metalloproteinase (MMP)-9 levels in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) but not in patients receiving off-pump cardiac surgery. The corresponding increase in neutrophil MMP-9 expression and production suggests that MMP-9 is derived primarily from neutrophils and may contribute to the inflammatory response associated with CPB.

Leukocyte infiltration into tissues is essential to inflammation, and matrix metalloproteinases (MMPs) help support the extravasation and infiltration of leukocytes. MMPs belong to a family of more than 20 zinc-dependent endopeptidases, including collagenases, stromelysins, gelatinases, matrilysins, and membrane-type MMPs (1). In nature, they degrade the basement membrane and extracellular matrix to facilitate embryo development, morphogenesis, and angiogenesis. They also play a critical role in wound healing, inflammatory diseases, and tumor metastasis. MMP-9, also called gelatinase B, is mainly produced by inflammatory cells, such as neutrophils, monocytes/macrophages, and eosinophils (1). During an acute inflammatory response, neutrophils are chemo-attracted to the inflammatory site. MMP-9 is degranulated to degrade type IV collagen, the major constituent of basement membrane, and to facilitate neutrophil extravasation. Significant expression of MMP-9 in inflammatory diseases, such as rheumatoid arthritis (2), asthma (3), sepsis (4), and acute respiratory distress syndrome (ARDS)(5), has been demonstrated. Moreover, increased levels of plasma MMP-9 are detected in acute coronary syndrome (6) and myocardial ischemia-reperfusion (7) and may be predictive for ventricular remodeling after myocardial infarction (8).