Oxidative pathways in the subendothelial space activate pro-infl ammatory, immunogenic, and atherogenic processes, resulting in endothelial dysfunction, plaque growth and destabilization, platelet activation, and thrombosis, ultimately leading to clinical events ( 1 ). A variety of oxidation-specifi c epitopes (OSE) are generated during oxidative modifi cation of plaque components. These epitopes are not only expressed on modifi ed lipoproteins but also on apoptotic cells and proteins in the extracellular matrix of atherosclerotic vessels ( 2 ).Extensive experimental data exists defi ning the role of oxidation in both progression and regression of atherosclerosis. Atherosclerotic lesions of hypercholesterolemic animal models, which represent primarily early and intermediate stage atherosclerosis, contain signifi cant amounts of OSE, often in proportion to plaque burden. OSE in the vessel wall of atherosclerotic animals can also be imaged with nuclear and magnetic resonance techniques using murine and human oxidation-specifi c antibodies, such as MDA2, E06, and IK17 ( 3-5 ). Dietary interventions in hypercholesterolemic animals that promote regression result in more rapid removal of OSE than apoB, which occurs prior to plaques diminishing signifi cantly in size, and is associated with markers of plaque stabilization, such Abstract The relationships between oxidation-specifi c epitopes (OSE) and lipoprotein (a) [Lp(a)] and progressive atherosclerosis and plaque rupture have not been determined. Coronary artery sections from sudden death victims and carotid endarterectomy specimens were immunostained for apoB-100, oxidized phospholipids (OxPL), apo(a), malondialdehyde-lysine (MDA), and MDA-related epitopes detected by antibody IK17 and macrophage markers. The presence of OxPL captured in carotid and saphenous vein graft distal protection devices was determined with LC-MS/MS. In coronary arteries, OSE and apo(a) were absent in normal coronary arteries and minimally present in early lesions. As lesions progressed, apoB and MDA epitopes did not increase, whereas macrophage, apo(a), OxPL, and IK17 epitopes increased proportionally, but they differed according to plaque type and plaque components. Apo(a) epitopes were present throughout early and late lesions, especially in macrophages and the necrotic core. IK17 and OxPL epitopes were strongest in late lesions in macrophagerich areas, lipid pools, and the necrotic core, and they were most specifi cally associated with unstable and ruptured plaques. Specifi c OxPL were present in distal protection devices. Human atherosclerotic lesions manifest a differential expression of OSEs and apo(a) as they progress, rupture, and become clinically symptomatic.
