Blood-brain barrier alterations in bacterial meningitis: Development of an in vitro model and observations on the effects of lipopolysaccharide

To further examine the effects of purified Haemophilus influenzae type b lipopolysaccharide (LPS) on blood-brain barrier permeability, we have developed an in vitro model of the BBB. Microvascular endothelial cells were isolated from rat cerebral cortices by enzymatic digestion, dextran centrifugation, and separation on percoll gradients. The cells were determined to be endothelial in origin by positive fluorescent staining for Factor VIII-related antigen and the ability to take up acetylated low density lipoproteins, and their cerebral origin by the formation of junctional complexes in vitro. Cells were seeded onto semipermeable polycarbonate filters and permeability assessed by measuring traversal of radioactive albumin across the monolayer. Treatment of the cells with LPS at concentrations of 1.0 μg/ml and 0.1 μg/ml for 4 h led to statistically significant increases in albumin permeability of 4.6% (P=0.001) and 5.6% (P<0.001), respectively, without evidence of cell death as assessed by release of lactate dehydrogenase into the media. These results indicate that LPS significantly increases albumin permeability across a monolayer of cerebral microvascular endothelial cells in the absence of host inflammatory cells. Future studies on the effects of LPS on intracellular regulation will determine the mechanisms responsible for these alterations.