The transfer of lipids from protein-free lipoprotein models to human fibroblasts in culture.
Lipid microemulsions were prepared by sonication of mixtures of cholesteryl ester, triacylglycerol, phosphatidylcholine and cholesterol in aqueous dispersions and were purified by gel filtration. The resulting emulsion particles were characterized by differential scanning calorimetry, electron microscopy and analytical gel filtration and were shown to have the size and general organization of low-density lipoprotein. The lipid microemulsions were used as protein-free plasma lipoprotein models for studies of the receptor-independent transfer of lipids to human fibroblasts in culture. The transfer rate of [3H]cholesterol increased with the donor concentration and with the molar ratio between cholesterol and phosphatidylcholine in the donor particles. A maximal transfer value of 1 nmol per mg protein per h was obtained for cholesterol/phosphatidylcholine 1:1 particles. There was a profound temperature effect on the cholesterol transfer. The effect of altering the core lipid of the emulsion particles on the [3H]cholesterol transfer rate was small giving a somewhat higher rate with cholesteryl oleate and cholesteryl stearate than with cholesteryl linoleate. Addition of trioleoylglycerol to the cholesteryl ester core had no effect on the transfer rate. The transfer rate of palmitoyl[14C]oleoylphosphatidylcholine was found to be about 1/5 of that obtained for [3H]cholesterol. About 50% of the cell-associated [14C]cholesteryl oleate was found in the trypsin-releasable pool, while 25% was internalized by the cells at a rate of 0.06 nmol X mg-1 X h-1. Trioleoylglycerol was internalized at the same rate as the cholesteryl ester. Our data suggest that the lipoprotein lipid composition may play a role in the receptor-independent cellular uptake of cholesterol.
D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism; D004655:Emulsions; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000378:metabolism*; D010316:Particle Size; D010713:Phosphatidylcholines / Q000378:metabolism; D013696:Temperature; D014304:Triolein / Q000378:metabolism
D002788:Cholesterol Esters; D004655:Emulsions; D008074:Lipoproteins; D010713:Phosphatidylcholines; D014304:Triolein; D002784:Cholesterol