Cell viability assay

Cell viability was determined using a Cell Counting Kit-8 (Solarbio, CA1210). Briefly, 4 mL of 10% Cell Counting Kit-8 solution was added to the BBB Transwell system, such that the liquid level in the inner chamber was parallel to that in the outer chamber, and the system was incubated at 37°C for 2 hours. The culture media from the inner and outer chambers were then harvested and combined, and the absorbance at 450 nm was analyzed using a microplate reader. The viability of astrocytes and endothelial cells was calculated using the following formula: cell viability (%) = [optical density (OD)_experimental – OD_blank]/(OD_{negative control} – OD_blank) × 100.