Oxidized low density lipoprotein can reduce the pinocytic activity in cultured human endothelial cells as measured by cellular uptake of [ 14C]sucrose

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The effect of low density lipoprotein (LDL) on the pinocytic activity in human endothelial cells in culture, as measured by the uptake of [ 14C]sucrose, was studied. The cells were preincubated for 48 h with a low concentration of LDL (25 μg protein/ml) or a high concentration of LDL (150 μg protein/ml) in the presence of lipoprotein deficient serum. Then the pinocytic activity of the cells was measured in a subsequent incubation by measuring the uptake of [ 14C]sucrose. The higher LDL concentration resulted in a reduced cellular uptake of [ 14C]sucrose compared to the lower concentration of LDL When the additional LDL (the lower concentration subtracted from the higher) was replaced by high density lipoprotein, albumin or gamma globulin, no reduction of the uptake of [ 14C]sucrose was observed. The inhibitory effect of LDL on the uptake of [ 14C]sucrose was seen in endothelial cell cultures of different age and cell density. When the endothelial cell proliferation was arrested by gamma irradiation, the reducing effect of LDL on the pinocytic activity was unchanged as compared to nonirradiated controls. LDL prepared in the presence of EDTA and glutathione did not have the same reducing effect on the uptake of [ 14C]sucrose as control LDL prepared in the absence of antioxidants. Thus, oxidized LDL reduced the pinocytic activity in cultured endothelial cells. The inhibitory effect of LDL on the rate of pinocytosis was present before endothelial cell injury could be observed.