Characterization of the Scavenger Receptor on Bovine Cerebral Endothelial Cells In Vitro

Abstract— Primary cultures of bovine brain capillary endo‐thelial cells (BCEC), possessing tight junctions and high levels of γ‐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 μg/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 ∼ 10–20‐fold lower in BCEC than that of peripheral endothelial cells. No evidence for lysosomal degradation could be obtained. Binding of 1,1′‐dioctadecyl‐3,3,3,3′‐tetramethylindocar‐boxyamine perchlorate‐labeled AcLDL by BCEC was observed, which could be competed for by an excess of un‐labeled 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

High-density lipoprotein and cerebral endothelial cells in vitro: Interactions and transport

Primary cultures of bovine cerebral endothelial cells were used as an in vitro model for the blood-brain barrier to study the transport and interactions of high-density lipoprotein (HDL) across monolayers of these cells. Transport of 125I-apoE free HDL across a monolayer of bovine cerebral endothelial cells occurred in a linear fashion up to a concentration of 70 μg/mL, suggesting paracellular transport of HDL. Bovine cerebral endothelial cells possess a high affinity binding site for HDL with a mean dissociation constant (KD) of 10.8 ± 2.6 μg/mL (N = 4). Maximal binding of apoE free HDL to cerebral endothelial cells proved to be temperature-dependent: at 4 ° a Bmax value of 42 ± 9.3 ng/mg cell protein was found, while at 37 ° this value was 177 ± 70.4 ng/mg cell protein. Cell association of 125I-HDL could be effectively displaced by HDL, not by low-density lipoprotein or acetylated low-density lipoprotein, and association was not coupled to degradation. The in vitro blood-brain barrier cell system possesses high affinity binding sites for HDL, which are probably not involved in the transport of HDL across cerebral endothelial cells