Computational Investigation of Darapladib and Rilapladib Binding to Platelet Activating Factor Receptor. A Possible Mechanism of Their Involvement in Atherosclerosis

Abstract

Platelet Activating Factor (PAF), the most potent inflammatory mediator, is involved in a wide range of pathophysiological actions. PAF signal transduction is mediated through PAF receptors (PAFR) that are coupled with several isoforms of G-proteins. PAF hydrolysis is mediated through specific enzymes clustered as PAF acetylhydrolases (PAF-AH). The plasma isoform is known as lipoprotein-associated PLA2 (Lp-PLA2), and is considered a marker, or a mediator in the mechanism of atherosclerosis. Darapladib and rilapladib are selective Lp-PLA2 inhibitors. They are, thus, proposed as a novel therapeutic approach for cardiovascular disease (CVD). The data derived from the computational methods used in this paper suggest that darapladib and rilapladib are potential PAFR antagonists, predicted to bind inside the PAF-binding site with a comparable binding affinity to the endogenous agonist (?G = –11.1 Kcal mol–1). Darapladib (?G = –10.6 Kcal mol–1) exhibited a higher affinity than rilapladib (?G = –8.2 Kcal mol–1). The fact that darapladib down-regulates PAFR expression, while PAFR inhibitors down-regulate the expression of CD36, could be the biochemical explanation in the observed necrotic core reduction, both in animals and humans. The reported results in conjunction with bibliographical data lead to the hypothesis that the involvement of darapladib and rilapladib in atherosclerosis could be through direct inhibition of PAF activity as well as modification of PAF metabolism.