Enhanced cholesterol delivery to cells in culture by low density lipoproteins from hypercholesterolemic monkeys

Previous studies have shown that the large molecular weight low density lipoprotein (LDL) of abnormal composition isolated from hypercholesterolemic nonhuman primates stimulates greater cholesterol accumulation in cells in culture than does the same amount of normal LDL. The purpose of the present study was to determine if a correlation existed over a range of LDL molecular weights with cholesterol accumulation in cells in culture, if the differential in cholesterol accumulation was the result of increased delivery of cholesterol to the cells and to evaluate the extent to which this differential was dependent on a functional LDL receptor pathway. Monkey and human skin fibroblasts were incubated for 24 hours with LDL isolated from individual normal or hypercholesterolemic cynomolgus monkeys having LDL molecular weights ranging from 2.58-6.39 x 10(6), and the cellular free and esterified cholesterol contents were determined. There was no correlation of LDL molecular weight with accumulation of cellular free or esterified cholesterol with LDL from normal animals having molecular weight of 2.58 to 3.08 X 10(6) or from hypercholesterolemic animals with LDL molecular weights greater than 4.5 x 10(6). There was a positive and significant correlation of LDL molecular weight with the accumulation of cellular free and esterified cholesterol with LDL molecular weights of 3.0 x 4.5 x 10(6). These differences were present when the LDL were added at equivalent protein or cholesterol concentrations and cannot be entirely explained by the increased amounts of cholesterol in LDL particles of larger molecular weight. The enhanced cellular cholesterol accumulation with hypercholesterolemic LDL seems to be the result of increased delivery of LDL cholesterol to the cells as shown by the increased rate of suppression of cellular sterol synthesis and LDL receptor activity, the increased stimulation of cholesterol esterification, and the increased accumulation of cellular 3H-cholesterol from LDL labeled with 3H-cholesteryl oleate. This difference in cellular cholesterol accumulation requires that the LDL must be both bound and internalized by a functional LDL receptor pathway, since cells that lack LDL receptors or are unable to internalize their LDL receptors do not show increased accumulation of cholesterol when incubated with hypercholesterolemic LDL.