Abstract. Macrophage cholesterol efflux is important in maintaining cellular lipid homeostasis and preventing the formation of lipid-laden foam cells. Although radioactive [ 3 H]-cholesterol is widely used as a tracer in cholesterol efflux assays, the lengthy and labor-intensive assay procedure, and the radioactivity disposal procedure limit the use of this assay for high-throughput screening. In the present study, a novel procedure using fluorescent N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino)-23,24-bisnor-5-xholen-3β-ol (NBD)-cholesterol was developed as a substitute for [ .872 for apoA-1; P<0.001). Furthermore, NBD-cholesterol efflux in the THP-1 cells exhibited a similar trend to that obseved in the PBMCs. In conclusion, the results of the present study suggested that fluorescent NBD-cholesterol can be used as a sensitive and specific probe in cholesterol efflux assays in THP-1-derived macrophages.
IntroductionCoronary artery disease (CAD) is the leading contributor to morbidity and mortality rates worldwide, and results in a mortality rate of >7,000,000 per year (1). Atherosclerotic plaques are key in the pathophysiology of CAD, in which macrophages initially become foam cells and initiate plaque formation. The imbalance of cholesterol uptake and efflux in macrophages may cause excessive accumulation of cholesterol and foam cell formation, which is a hallmark in the development of atherosclerosis (2). Cholesterol efflux from macrophages is a critical step in reverse cholesterol transport, which may prevent macrophages from becoming foam cells and thus reduce atherosclerosis (3,4). Free cholesterol is transported from macrophages in the arterial atherosclerotic plaque to an extracellular acceptors, including apoliporotein (apo) A-1 and high-density lipoprotein (HDL), and then back to the liver for bile acid synthesis and excretion (5). Previously, Khera et al reported a reverse correlation between cholesterol efflux capacity and atherosclerosis (6). To understand the underlying mechanism regulating cholesterol efflux, it is important to develop a reliable assay for measuring cholesterol efflux in vitro.Traditionally, radioisotope-labeled cholesterols have been used as probes in cholesterol efflux assays. However, the procedure is lengthy and labor-intensive, and the radioactivity disposal procedure can limit the use of this assay in high-throughput screening. By contrast, fluorescent