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 (K_D) 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 B_max 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.