Evidence for an exclusive association of matrix metalloproteinase-9 with dysfunctional high-density lipoprotein: a novel finding.

High-density lipoprotein is a heterogeneous class of lipoprotein with diverse antiatherogenic functions. However, these antiatherogenic properties of HDL can be compromised in atherosclerotic conditions. We have recently identified dysfunctionality in HDL even among healthy subjects, during systemic inflammation. This study was carried out with the objective of examining whether dysfunctional HDL is associated with pro-inflammatory proteins other than the acute phase proteins as reported earlier. Serum HDL was isolated by three different methods-density gradient ultracentrifugation, PEG precipitation and electroelution. The antioxidant property of HDL was assessed as change in oxidation of LDL based on Dichloro-dihydro-fluorescein diacetate assay. HDL was subjected to gelatin zymography and western blot for assessment of MMP 9 activity. Dysfunctional HDL did not prevent the auto-oxidation of LDL. On the contrary the oxidation was enhanced. The zymogram data indicated enhanced MMP-9 activity selectively in dysfunctional HDL, irrespective of HDL isolation methods. This was confirmed by western blot of HDL probed with antibody specific to MMP 9. We also observed that dysfunctional HDL induced inflammatory response in monocyte/macrophages as evidenced by enhanced TNF-α and decreased IL-10 production. Further, invitro incubation of functional HDL with MMP-9 provided direct evidence for the association of MMP-9 with HDL and the role of MMP-9 in HDL dysfunction. A remarkable finding in the present study is the previously unrecognized association of MMP-9 with dysfunctional HDL and its proinflammatory property, indicating a novel molecular connection that can enhance the risk of cardiovascular disease in subjects with dysfunctional HDL.