Adenovirus-mediated gene transfer of Lp-PLA 2 reduces LDL degradation and foam cell formation in vitro

Oxidation of LDL generates biologically active platelet-activating factor (PAF)-like phospholipid derivatives, which have potent proinflammatory activity. These products are inactivated by lipoprotein-associated phospholipase A 2 (Lp-PLA 2 ), an enzyme capable of hydrolyzing PAF-like phospholipids. In this study, we generated an adenovirus (Ad) encoding human Lp-PLA 2 and injected 10 8, 10 9, and 10 10 plaque-forming unit doses of Adlp-PLA 2 and control AdlacZ intra-arterially into rabbits to achieve overexpression of Lp-PLA 2 in liver and in vivo production of Lp-PLA 2 -enriched LDL. As a result, LDL particles with 3-fold increased Lp-PLA 2 activity were produced with the highest virus dose. Increased Lp-PLA 2 activity in LDL particles decreased the degradation rate in RAW 264 macrophages after standard in vitro oxidation to 60–80% compared with LDL isolated from LacZ-transduced control rabbits. The decrease was proportional to the virus dose and Lp-PLA 2 activity. Lipid accumulation and foam cell formation in RAW 264 macrophages were also decreased when incubated with oxidized LDL containing the highest Lp-PLA 2 activity. Inhibition of the Lp-PLA 2 activity in the LDL particles led to an increase in lipid accumulation and foam cell formation. It is concluded that increased Lp-PLA 2 activity in LDL attenuates foam cell formation and decreases LDL oxidation and subsequent degradation in macrophages.