Oxidative Modification of Lipoproteins: Mechanisms, Role in Inflammation and Potential Clinical Applications in Cardiovascular Disease

Abnormalities of lipid metabolism often lead to pathologic lipid accumulation in the vessel wall, oxidative and chronic inflammatory sequelae and the formation of atherosclerotic lesions, ultimately leading to clinical events. Oxidation of lipoproteins, and in particular low density lipoprotein (LDL), is a seminal even that mediates many pro-atherogenic and pro-inflammatory pathways. Many in vivo mechanisms exist to oxidize LDL, including transition metals such as divalent cations, heme, as well as a number of different enzyme systems, such as lipoxygenases, myeloperoxidase, NADPH oxidases, and nitric oxide synthases. Oxidized LDL is taken up in an unregulated fashion. By macrophages leading to foam cell formation, ultimately generating a potent pro-inflammatory milieu. Minimally modified LDL also induces proinflammatory effects in macrophages, including cytoskeletal rearrangements and macropinocytosis, generation of reactive oxygen species, survival of foam cells, reduced phagocytic capacity toward apoptotic cells, and expression of inflammatory genes, many of these effects mediated through toll-like receptor-4. Using the scientific knowledge gained from understanding these pathways, antibodies binding well-defined oxidation-specific epitopes have been generated and are being used in translational clinical applications. In particular, assays measuring oxidized phospholipids on apolipoprotein B-100 particles (OxPL/apoB) predict the presence and progression of femoral, carotid and coronary artery disease and predict new cardiovascular events independent of established risk factors. Human oxidation-specific antibodies have also been successfully used to image the extent and regression of experimental atherosclerotic lesions using nuclear and magnetic resonance imaging approaches. If validated and translated to humans, this imaging approach may provide a means to non-invasively detect, quantitate and monitor extent of atherosclerosis and potentially image high risk plaques. Further understanding of the role of oxidation of lipoproteins may allow more rational targeted diagnostic and therapeutic modalities in clinical applications.