Direct visualization of lipid deposition and reverse lipid transport in a perfused artery - Roles of VLDL and HDL

The major goal of this study was to determine the interactions of VLDL surf ace and core lipids with the artery wall. We first demonstrated in vitro th at surface lipid in VLDL could be traced using the phospholipid-like fluore scent probe 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine (DiI). The core of VLDL particles was traced by fluorescently labeling apolipoprot ein B with TRITC. The labeled VLDLs were perfused through rat carotid arter ies, and accumulation of the fluorescently labeled VLDL components in the a rterial walls was determined by quantitative fluorescence microscopy. Addit ion of lipoprotein lipase increased the accumulation of both DiI and TRITC by >2.3-fold. Histological examination showed that DiI and TRITC were prima rily localized to the endothelial layer; however, DiI also accumulated as s mall "lakes" deeper in the artery, in a subendothelial position. Addition o f HDL to the perfusion decreased the accumulation of surface lipid and apol ipoprotein B-containing particles and eliminated the DiI lakes. Moreover, t he increase in endothelial layer permeability associated with lipolysis was attenuated 21% by HDL. If VLDL surface lipid first was allowed to accumula te in the arterial wall, its subsequent rate of loss was more than twice as fast if HDL was included in the perfusate. These studies directly demonstr ate atherogenic effects of VLDL lipolysis and their inhibition by HDL.