Modulation of oxidative stress, inflammation, and atherosclerosis by lipoprotein-associated phospholipase A₂

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂), also known as platelet-activating factor acetylhydrolase (PAF-AH), is a unique member of the phospholipase A₂superfamily. This enzyme is characterized by its ability to specifically hydrolyze PAF as well as glycerophospholipids containing short, truncated, and/or oxidized fatty acyl groups at the sn-2 position of the glycerol backbone. In humans, Lp-PLA ₂ circulates in active form as a complex with low- and high-density lipoproteins. Clinical studies have reported that plasma Lp-PLA₂ activity and mass are strongly associated with atherogenic lipids and vascular risk. These observations led to the hypothesis that Lp-PLA₂ activity and/or mass levels could be used as biomarkers of cardiovascular disease and that inhibition of the activity could offer an attractive therapeutic strategy. Darapladib, a compound that inhibits Lp-PLA₂ activity, is anti-atherogenic in mice and other animals, and it decreases atherosclerotic plaque expansion in humans. However, disagreement continues to exist regarding the validity of Lp-PLA₂ as an independent marker of atherosclerosis and a scientifically justified target for intervention. Circulating Lp-PLA ₂ mass and activity are associated with vascular risk, but the strength of the association is reduced after adjustment for basal concentrations of the lipoprotein carriers with which the enzyme associates. Genetic studies in humans harboring an inactivating mutation at this locus indicate that loss of Lp-PLA₂function is a risk factor for inflammatory and vascular conditions in Japanese cohorts. Consistently, overexpression of Lp-PLA ₂ has anti-inflammatory and anti-atherogenic properties in animal models. This thematic review critically discusses results from laboratory and animal studies, analyzes genetic evidence, reviews clinical work demonstrating associations between Lp-PLA₂ and vascular disease, and summarizes results from animal and human clinical trials in which administration of darapladib was tested as a strategy for the management of atherosclerosis.