Increased permeability of primary cultured brain microvessel endothelial cell monolayers following TNF-alpha exposure

TNF-alpha is a cytokine that produces increased permeability in the periphe ral vasculature; however, little is known about the effects of TNF-alpha on the blood-brain barrier(BBB). Using primary cultured bovine brain microves sel endothelial cells (BBMEC) as an in vitro model of the BBB, this study s hows that TNF-alpha produces a reversible increase in the permeability of t he brain microvessel endothelial cells. The BBMEC monolayers were pre-treat ed with 100 ng/ml of TNF-alpha for periods ranging from 2 to 12 hours. Perm eability was assessed using three molecular weight markers, fluorescein (37 6 MW), fluorescein-dextran (FDX-4400; 4400 MW), and FD:Y-70000 (MW 70000). The permeability of BBMEC monolayers to all three fluorescent markers was i ncreased two-fold or greater in the TNF-alpha treatment group compared to c ontrol monolayers receiving no TNF-alpha. Significant changes in permeabili ty were also observed with TNF-alpha concentrations as low as 1 ng/ml. Thes e results suggest that TNF-alpha acts directly on the brain microvessel end othelial cells in a dynamic manner to produce a reversible increase in perm eability. Exposure of either the lumenal or ablumenal side of BBMEC monolay ers to TNF-alpha resulted in similar increases in permeability to small mac romolecules, e.g, fluorescein. However, when a higher molecular weight mark er was used (e.g. FDX-3000), there was a greater response following lumenal exposure to TNF-alpha. Together, these studies demonstrate a reversible an d time dependent increase in brain microvessel endothelial cell permeabilit y following exposure to TNF-alpha. Such results appear to be due to TNF's d irect interaction with the brain microvessel endothelial cell.