Abstract

The possibility was explored of synthesizing, from commercially available lipids, high density lipoprotein (HDL)-like particles (neo-HDL) with the same physico-chemical and biological properties as native HDL. A preparation method involving egg yolk phosphatidylcholine, cholesterol, and apoproteins from HDL led to the formation of particles with a composition, size, electrophoretic mobility, and density similar to those of discoidal HDL. In vitro experiments with isolated parenchymal liver cells showed that unlabeled HDL and neo-HDL competed for the same high affinity binding sites as did radiolabeled neo-HDL, whereas an excess of unlabeled low density lipoprotein was ineffective. In vivo experiments with radio-labeled neo-HDL indicated that neo-HDL showed a slow decay upon injection into rats, whereas the liver uptake did not exceed > 10% of the injected dose. The small additional liver uptake of radioactivity from neo-HDL, compared with HDL, was due to enhanced uptake by endothelial and Kupffer cells. Lactosylation of neo-HDL led to a markedly increased decay rate and a rapid uptake by rat liver (80% in 10 min). Parenchymal cells accounted for > 90% of the total liver uptake of radiolabeled lactosylated neo-HDL. Because the liver uptake of lactosylated 125I-neo-HDL could be blocked by preinjection of N-acetylgalactosamine, we conclude that the asialoglycoprotein receptor, which is specifically localized on parenchymal liver cells, is responsible for the avid liver uptake. With a fibroblast cell line transfected with the human asialoglycoprotein receptor, it was found that lactosylated neo-HDL binds with high affinity (Kd, 40 nM), in a galactose-specific way. It can be concluded that, with commercially available lipid components, HDL-like particles (neo-HDL) with virtually the same characteristics as found for native apolipoprotein E-free HDL can be reconstituted. Lactosylated neo-HDL, which is rapidly taken up by galactose-specific receptors on parenchymal liver cells, might be used to transport antiviral drugs specifically to parenchymal liver cells.