Early incorporation of cell-derived cholesterol into pre-.beta.-migrating high-density lipoprotein

Abstract

Cultures of human skin fibroblasts were labeled to high cholesterol specific activity with [3H]cholesterol and incubated briefly (1-3 min) with normal human plasma. The plasma was fractionated by two-dimensional agarose-polyacrylamide gel electrophoresis and the early appearance of cholesterol label among plasma lipoproteins determined. A major part of the label at 1-min incubation was in a pre-beta-migrating apo A-I lipoprotein fraction with a molecular weight of ca. 70,000. Label was enriched about 30-fold in this fraction relative to its content of apo A-I (1-2% of total apo A-I). The proportion of label in this lipoprotein was strongly correlated with its concentration in plasma. Further incubation (2 min) in the presence of unlabeled cells demonstrated transfer of label from this fraction to a higher molecular weight pre-beta apo A-I species, to low-density lipoprotein, and to the alpha-migrating apo A-I that made up the bulk (96%) of total apo A-I in plasma. The data suggest that a significant part of cell-derived cholesterol is transferred specifically to a pre-beta-migrating lipoprotein A-I species as part of a cholesterol transport transfer sequence in plasma.

Expression of Human Apolipoprotein A-I/C-III/A-IV Gene Cluster in Mice Induces Hyperlipidemia but Reduces Atherogenesis

“…Both apolipoproteins participate in RCT and promote cholesterol efflux from cultured cells. 1,23,25 In a normal background, new populations of HDLs appeared in the cluster Tg mice. All the human apoA-IV and a proportion of human apoA-I migrated to the pre-␤ position.…”

“…25 After the 2 electrophoreses, lipoproteins were electrotransferred on to nitrocellulose membranes. The filters were immunodecorated with rabbit anti-mouse or antihuman apoA-I, apoC-III, or apoA-IV antibodies, followed by secondary peroxidase-labeled antibodies directed against rabbit IgG.…”

Apolipoprotein A-I, Phospholipid Vesicles, and Cyclodextrins as Potential Anti-Atherosclerotic Drugs: Delivery, Pharmacokinetics, and Efficacy

“…The pre-b -migrating apoA-I LP fraction has a molecular weight of » 70,000Da (Castro and Fielding 1988), although recent estimates are 60,000Da (Kunitake et al 1992). This particle may be a particularly important factor for RCT (Fielding and Fielding 1980;Barbaras et al 1987;Castro and Fielding 1988;Francone et al 1989;Davidson et al 1995b).…”

“…This particle may be a particularly important factor for RCT (Fielding and Fielding 1980;Barbaras et al 1987;Castro and Fielding 1988;Francone et al 1989;Davidson et al 1995b). Transfer of carried cholesterol from this particle to a higher molecular weight pre-b apoA-I species, to LDL, and to the a -migrating apoA-I that makes up 96% of total apoA-I in plasma occurs (Castro and Fielding 1988). However, it is not known whether the smaller particles are converted to the larger particles along with their cholesterol loads.…”

“…The small size of the early acceptors of cholesterol may favor insertion of cholesterol (Castro and Phillips 1988). Their small size and greater diffusion coef cient would accelerate their entry into the unstirred water layer surrounding cells or to receptor sites on the membrane surface at rates greater than larger particles (Castro and Fielding 1988).…”