High Density Lipoprotein Inhibits Low Density Lipoprotein Binding and Uptake by Bovine Aortic Endothelial Cells

Abstract

The antiatherogenic effect of high density lipoprotein (HDL) has been attrib uted to either an inhibition of cholesterol uptake or to reversed cholesterol transport from peripheral cells. In order to determine whether HDL competi tively blocks receptor-mediated low density lipoprotein (LDL) binding and up take, bovine aortic enothelial cells (BAECs) were cultured in Dulbecco's modified Eagles Medium (DMEM) containing 10% LDL-free fetal bovine serum, and incubated with 125I-LDL in concentrations of either 10 or 25 μg protein/mL. Varying amounts of HDL (0-200 μg/mL) were added to the media. Following a twenty-four hour incubation period at 37°C, 125I-LDL binding and uptake were measured. At the lower concentration of 125I-LDL, which represents high-affinity recep tor binding, there was no significant difference in either binding or uptake within the range of HDL concentrations studied. At the higher concentration of LDL, however, there was a marked inhibition of 125I-LDL binding (p<.006) and uptake (p<,001; ANOVA), which did not saturate at the highest HDL concentrations used. These data suggest that HDL does not influence high-affinity, receptor-me diated binding and uptake of LDL but that its effect is seen at a concentration of LDL representing nonspecific binding. The lack of saturation at increasing concentrations of HDL also indicates that HDL-receptor interaction is not essen tial for the effect.