Scheme of preparation of the in vitro human BBB model. After subculturing the human cell lines for several days, the brain capillary endothelial cells were seeded on microporous filter membranes of 24-well tissue culture inserts (Greiner Bio-one®, transparent PET membrane, 3.0 μm pore size). The inserts were immediately transferred to a 24-well cell module of a CellZscope system which was placed inside an incubator (37°C and 5% CO2). TEER and CCL values were recorded on-line every hour. After 2–4 days (at the maximal TEER), paracellular permeability of Na-F and LY was assessed. To monitor barrier integrity after the assay, TEER and CCL values were again recorded real-time using the CellZscope system.