Role of Lipoprotein-Associated Phospholipase A 2 in Atherosclerosis

Abstract

The development of atherosclerotic vascular disease is invariably linked to the formation of bioactive lipid mediators and accompanying vascular inflammation. Lipoprotein-associated phospholipase A 2 (Lp-PLA 2 ) is an enzyme that is produced by inflammatory cells, co-travels with circulating low-density lipoprotein (LDL), and hydrolyzes oxidized phospholipids in LDL. Its biological role has been controversial with initial reports purporting atheroprotective effects of Lp-PLA 2 thought to be a consequence of degrading platelet-activating factor and removing polar phospholipids in modified LDL. Recent studies, however, focused on pro-inflammatory role of Lp-PLA 2 mediated by products of the Lp-PLA 2 reaction (lysophosphatidylcholine and oxidized nonesterified fatty acids). These bioactive lipid mediators, which are generated in lesion-prone vasculature and to a lesser extent in the circulation (eg, in electronegative LDL), are known to elicit several inflammatory responses. The proinflammatory action of Lp-PLA 2 is also supported by a number of epidemiology studies suggesting that the circulating level of the enzyme is an independent predictor of cardiovascular events, despite some attenuation of the effect by inclusion of LDL, the primary carrier of Lp-PLA 2 , in the analysis. These observations provide a rationale to explore whether inhibiting Lp-PLA 2 activity and consequent interference with the formation of bioactive lipid mediators will abrogate inflammation associated with atherosclerosis, produce favorable changes in intermediate cardiovascular end points (eg, biomarkers, imaging, and endothelial function), and ultimately reduce cardiovascular events in high-risk patients. Recent studies suggest lipoprotein-associated phospholipase A 2 may play an important role in atherogenesis. This enzyme generates proinflammatory products implicated in every stage of atherosclerosis, from atheroma initiation to destabilization. The potential clinical benefit associated with Lp-PLA 2 inhibition is intriguing; however, more studies are needed to better define the biological role of this enzyme.