HIGH-DENSITY-LIPOPROTEIN INHIBITS LOW-DENSITY-LIPOPROTEIN BINDING AND UPTAKE BY BOVINE AORTIC ENDOTHELIAL-CELLS

The antiatherogenic effect of high density lipoprotein (HDL) has been attributed to either an inhibition of cholesterol uptake or to reversed cholesterol transport from peripheral cells. In order to determine whether HDL competitively blocks receptor-mediated low density lipoprotein (LDL) binding and uptake, bovine aortic enothelial cells (BAECs) were cultured in Dulbecco's modified Eagles Medium (DMEM) containing 10% LDL-free fetal bovine serum, and incubated with I-125-LDL in concentrations of either 10 or 25-mu-g protein/mL. Varying amounts of HDL (0-200-mu-g/mL) were added to the media. Following a twenty-four hour incubation period at 37-degrees-C, I-125-LDL binding and uptake were measured. At the lower concentration of I-125-LDL, which represents high-affinity receptor 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 I-125-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-mediated 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 essential for the effect.