Differential expression of oxidation-specific epitopes and apolipoprotein(a) in progressing and ruptured human coronary and carotid atherosclerotic lesions

The relationships between oxidation-specific 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 macrophage-rich areas, lipid pools, and the necrotic core, and they were most specifically associated with unstable and ruptured plaques. Specific 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. These findings provide a rationale for targeting OSE for biotheranostic applications in humans.Oxidative pathways in the subendothelial space activate pro-inflammatory, 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-specific epitopes (OSE) are generated during oxidative modification of plaque components. These epitopes are not only expressed on modified lipoproteins but also on apoptotic cells and proteins in the extracellular matrix of atherosclerotic vessels (2).Extensive experimental data exists defining 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 significant 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-specific 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 significantly in size, and is associated with markers of plaque stabilization, such as increased collagen and smooth muscle cell (SMC) expression, and a decrease in reactive oxygen species and macrophages (6–8).Despite this wealth of animal data on the relationship of OSE and atherosclerosis, relatively little is known about their relationship to clinically relevant advanced, unstable, or ruptured plaques. Furthermore, a systematic analysis of the presence of OSE in human lesions has not been performed to date. Therefore, the purpose of this study was to determine the presence and relative distribution of well-characterized OSE in various stages of human atherosclerotic lesions, including native coronary lesions, carotid endarterectomy samples, and material from carotid and saphenous vein graft (SVG) embolic protection filters. Such knowledge may have significant clinical implications with the emergence in the clinical and translational arenas of oxidative biomarkers, molecular imaging, and therapeutic approaches, including immune modulation and vaccine approaches targeting these moieties (9–12), broadly characterized as “biotheranostic” (biomarker, therapeutic, diagnostic imaging) applications.