Abstract 828: Adiponectin Enhanced ApoA-1- and HDL- mediated Cellular Cholesterol Efflux from Human Monocyte-Derived Macrophages
(Background) Plasma HDL-cholesterol levels are inversely correlated to the risk of CAD. HDL plays a crucial role as a shuttle carrying cholesterol derived from peripheral tissues and transporting it back to the liver. Recently, ATP-binding cassette transporters (ABCA1, ABCG1) have been identified as important membrane receptors to generate HDL by removing cholesterol and phospholipids from macrophage foam cells in the arterial wall. On the other hand, adiponectin (APN) abundantly secreted from adipocytes is one of the important molecules to inhibit the development of atherosclerosis. Epidemiological studies have revealed a positive correlation between plasma HDL-cholesterol and APN concentrations in humans, and APN levels are decreased in patients with CAD. In the current study, we investigated the role of APN on cellular cholesterol efflux from human macrophages.
(Methods) Recombinant human APN was prepared. Human monocyte-derived macrophages were isolated from whole blood of healthy volunteers and incubated with RPMI-1640 medium containing 10% type AB serum. After 7 days incubation, the indicated concentrations of recombinant APN were added to the medium containing 0.1% BSA and incubated for 24 hours. The expression of ABCA1 and ABCG1 was measured by real-time quantitative PCR and western blot analyses. Cholesterol efflux from macrophages, previously incubated with [3H]-labeled acetylated LDL, was measured with or without APN and expressed by a percentage of radioactivity of the medium to total radioactivity (cells plus medium). APN was added into the medium containing 0.1% BSA and apoA-1 (10 μg/ml) or HDL (50 μg/ml HDL protein) and incubated for 24 hours.
(Results) APN significantly up-regulated the mRNA and protein levels of ABCA1 in human macrophages by 3.6- and 2-fold, respectively. ApoA-1-mediated cholesterol efflux from macrophages was 8.1-fold-increased by APN treatment. Furthermore, the expression of ABCG1 was also significantly increased by APN. HDL-mediated cholesterol efflux was slightly increasd by APN.
(Conclusions) In conclusion, APN might act as a protective factor against atherosclerosis by increasing cholesterol efflux from human macrophages in both ABCA1- and ABCG1-dependent pathways.