Physicochemical transfer of [3H]cholesterol from plasma lipoproteins to cultured human fibroblasts

Abstract

The transfer of free cholesterol from [3H]cholesterol-labelled plasma lipoproteins to cultured human lung fibroblasts was studied in a serum-free medium. The uptake of [3H]cholesterol depended upon time of incubation, concentration of lipoprotein in the medium, and temperature. Modified (reduced and methylated) low-density lipoprotein (LDL), which did not enter the cells by the receptor pathway, gave a somewhat lower transfer rate than unmodified LDL, but if the transfer values for native LDL were corrected for the receptor-mediated uptake of cholesterol the difference was eliminated. The initial rates of transfer of [3H]cholesterol from LDL and high-density lipoprotein (HDL) were of the same order of magnitude (0.67 +/- 0.05 and 0.75 +/- 0.06 nmol of cholesterol/h per mg of cell protein, respectively) while that from very-low-density lipoprotein (VLDL) was much lower (0.23 +/- 0.02 nmol of cholesterol/h per mg) (means +/- S.D., n = 5). The activation energy for transfer of cholesterol from reduced, methylated LDL to fibroblasts was determined to be 57.5 kJ/mol. If albumin was added to the incubation medium the transfer of [3H]cholesterol was enhanced, while that of [14C]dipalmitoyl phosphatidylcholine was decreased compared with the protein-free system. The results demonstrate that, in spite of its low water solubility, free cholesterol can move from lipoproteins to cellular membranes, probably by aqueous diffusion. We propose that physicochemical transfer of free cholesterol may be a significant mechanism for net uptake of the sterol into the artery during atherogenesis.

Deposition of Free Cholesterol in the Blood Vessels of Patients with Coronary Artery Disease: a Possible Novel Mechanism for Atherogenesis

“…The possibility that LDL FC may detach from the lipoprotein and move by aqueous diffusion to cellular membranes was raised by Lundberg and Suominen in an in vitro study with fibroblasts [24]. They postulated that unesterified cholesterol from LDL can move by aqueous transport, despite its low water solubility, and this transfer is facilitated by the addition of albumin to the medium.…”

Lipid utilization by human lymphocytes is correlated with high-density-lipoprotein binding site activity

“…The mechanism of cholesterol exchange between cells and HDL has been the subject of much investigation and controversy, in part because the outcome (delivery/removal) varies depending on the cell types and the experimental procedures. Three mecha- Interactions of high-density lipoproteins with human lymphocytes nisms have been suggested: (1) reverse cholesterol transport from the surface of extrahepatic cells [3,24], (2) establishment of a bidirectional equilibration of cholesterol between cell and HDL particle [25][26][27], and (3) a postulated unidirectional selective uptake of HDL cholesterol by the cells with or without degradation of the HDL particle [5][6][7][8]28,29]. We 1).…”

Structural and functional characterization of human apolipoprotein E 72-166 peptides in both aqueous and lipid environments

“…The detailed procedures for the LDLR binding assay have been described previously [ 22 , 37 , 38 ]. Briefly, human hepatoblastoma cells (HepG2) were incubated in DMEM with 10% fetal bovine serum at 37°C followed by incubation with DMEM containing 3 H-LDL and different receptor binding competitors (apoE proteins) at 4°C for 2 h. After washing, cells were released, lysed, and the radioactivity was determined using a liquid scintillation counter (Beckman, Fullerton, CA).…”