Characterization of the scavenger receptor on bovine cerebral endothelial cells in vitro

Primary cultures of bovine brain capillary endothelial cells (BCEC), possessing tight junctions and high levels of gamma-glutamyl transpeptidase, were used as an in vitro model for the blood-brain barrier. The interaction of acetylated low density lipoprotein (AcLDL) with BCEC was studied to characterize the scavenger receptor on these cells. A saturable high affinity binding site was found with a dissociation constant of AcLDL of 5.4 micrograms/ml (3.1 nM) and a maximal binding ranging from 284 to 626 ng of AcLDL/mg of cell protein for eight primary cultures, and independent of the presence of calcium. Cell association was coupled to degradation, and both could be effectively competed for by polyinosinic acid and AcLDL but not by low density lipoprotein or by high density lipoprotein. Prolonged incubation showed an accumulation of the ligand in the cells. The rate of degradation of AcLDL was approximately 10-20-fold lower in BECEC than that of peripheral endothelial cells. No evidence for lysosomal degradation could be obtained. Binding of 1,1'-dioctadecyl-3,3,3'-tetramethylindocarboxyamine perchlorate-labeled AcLDL by BCEC was observed, which could be competed for by an excess of unlabeled AcLDL and polyinosinic acid. We have shown that in vitro BCEC possesses specific binding sites for AcLDL, whereas these cells show a relatively low degradative capacity.