Identification of two immortalized cell lines, ECV304 and bEnd3, for in vitro permeability studies of blood-brain barrier

To identify suitable cell lines for a mimetic system of in vivo blood-brain barrier (BBB) for drug permeability assessment, we characterized two immortalized cell lines, ECV304 and bEnd3 in the respect of the tightness, tight junction proteins, P-glycoprotein (P-gp) function and discriminative brain penetration. The ECV304 monoculture achieved higher transendothelial electrical resistance (TEER) and lower permeability to Lucifer yellow than bEnd3. However, co-culture with rat glioma C6 cells impaired the integrity of ECV304 and bEnd3 cell layers perhaps due to the heterogeneity among C6 cells in inducing BBB characteristics. The immunostaining of ZO-1 delivered distinct bands along cell borders on both cell lines while those of occludin and claudin-5 were diffused and weak. P-gp functionality was only proved in bEnd3 by Rhodamine 123 (R123) uptake assay. A permeability test of reference compounds displayed a similar rank order (digoxin < R123 < quinidine, verapamil < propranolol) in ECV304 and bEnd3 cells. In comparison with bEnd3, ECV304 developed tighter barrier for the passage of reference compounds and higher discrimination between transcellular and paracellular transport. However, the monoculture models of ECV304 and bEnd3 fail to achieve the sufficient tightness of in vitro BBB permeability models with high TEER and evident immunostaining of tight junction proteins. Further strategies to enhance the paracellular tightness of both cell lines to mimic in vivo BBB tight barrier deserve to be conducted.