Amelioration of atherosclerosis in apolipoprotein E-deficient mice by inhibition of lipoprotein-associated phospholipase A2

Purpose: Lipoprotein-associated phospholipase A2 (Lp-PLA2) is involved in the pathogenesis of atherosclerosis, especially in advanced plaques. In the present study, the abilities of darapladib, a selective Lp-PLA2 inhibitor, and lentivirus-mediated Lp-PLA2 silencing on inflammation and atherosclerosis in apolipoprotein E-deficient mice were compared. Methods: Apolipoprotein E-deficient mice were fed on a high-fat diet and a constrictive collar was placed around the left carotid artery to induce plaque formation. The mice were randomly divided into control, negative control (NC), darapladib and RNA interference (RNAi) groups. Eight weeks after surgery, lentivirus-mediated RNAi construct or darapladib were used to decrease the expression of Lp-PLA2. Plaques were collected five weeks later for histological analysis. Inflammatory gene expression in the atherosclerotic lesions were then determined at the mRNA and protein level. Results: The expression of pro-inflammatory cytokines was significantly reduced in the treatment group, compared to nontreatment group, whereas the plasma concentration of anti-inflammatory cytokines increased markedly. Moreover, our results demonstrated a significant reduction in plaque lipid content, as well as a rise in collagen content following Lp-PLA2 inhibition. Interestingly, when comparing the two methods of Lp-PLA2 inhibition, animals treated with Lp-PLA2 RNAi were found to exhibit lower plaque areas and enhanced improvement of plaque stability as compared with animals treated with darapladib. Darapladib had no attenuating effect on atherosclerotic plaque area. These therapeutic effects were independent of plasma lipoprotein levels. Conclusions: Lp-PLA2 inhibition by darapladib or lentivirus-mediated RNAi ameliorated inflammation and atherosclerosis in apolipoprotein E-deficient mice. The effect was more prominent in the RNAi group.