Production and release of myeloperoxidase (MPO) from granules is known to occur in both neutrophils and monocytes. MPO is involved in several processes that modulate atherogenesis and coronary inflammation. For example, MPO has the ability to oxidize low-density lipoprotein (LDL) cholesterol, to break down nitric oxide (NO), to regulate endothelial homeostasis, and to modulate NO function in inflammatory processes.18
Elevated levels of MPO have been demonstrated in patients with coronary artery disease and have been implicated as having a role in plaque destabiliza-tion.19 An elevated level of MPO at the time of presentation with an ACS was associated with a worse prognosis irrespective of troponin T level,20 emphasizing the importance of the underlying inflammatory state. It is plausible that the presence of persistent inflammation may contribute to future events. Therefore, the role of MPO as a "marker of the vulnerable plaque" even in the troponin-negative ACS patient has been suggested.21
MPO serves to highlight the role of neutrophils in initiation of the events leading to ACS and events occurring immediately after MI. In addition to prognostic value, it provides a direct indication of underlying plaque instability in those with suspected ACS.
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