Background: C-reactive protein (CRP), the prototypic marker of inflammation, is present in atherosclerotic plaques and appears to promote atherogenesis. Also, CRP has been localized to monocytes and tissue macrophages, which are present in the necrotic core of lesions prone to plaque rupture. Leukocyte-derived myeloperoxidase (MPO), primarily hosted in human polymorphonuclear cells (PMNs), has also been shown to be present in human atherosclerotic lesions. Because MPO and CRP concentrations are increased in acute coronary syndrome (ACS) patients and predict poor outcomes, we tested the effect of CRP on MPO release from PMNs and monocytes.
Methods: We treated human PMNs and monocytes with CRP (25 and 50 mg/L for 6 h) and measured MPO release as total mass and activity in culture supernatants. We also measured nitro-tyrosinylation (NO(2)-Tyr) of LDL as an indicator of biological activity of CRP-mediated MPO release. Furthermore, we explored the effect of human CRP on MPO release in the rat sterile pouch model.
Results: CRP treatment significantly increased release of MPO (both mass and activity) from human PMNs as well as monocytes (P < 0.05) and caused NO(2)-Tyr of LDL. Human CRP injection in rats resulted in increased concentrations of MPO in pouch exudates (P < 0.05), thus confirming our in vitro data.
Conclusions: CRP stimulates MPO release both in vitro and in vivo, providing further cogent data for the proinflammatory effect of CRP. These results might further support the role of CRP in ACS.