Air-Liquid Interface (ALI) Culture of Human Bronchial Epithelial Cell Monolayers as an in vitro Model for Airway Drug Transport Studies

Serially passaged normal human bronchial epithelial (NHBE) cell monolayers were established on Transwell® inserts via an air-liquid interface (ALI) culture method. NHBE cells were seeded on polyester Transwell® inserts, followed by an ALI culture from day 3, which resulted in peak TEER value of 766 ± 154 Ω × cm2 on the 8th day. Morphological characteristics were observed by light microscopy and SEM, while the formation of tight junctions was visualized by actin staining, and confirmed successful formation of a tight monolayer. The transepithelial permeability (Papp) of model drugs significantly increased with the increase of lipophilicity and showed a good linear relationship, which indicated that lipophilicity is an important factor in determining the Papp value. The expression of P-gp transporter in NHBE cell monolayers was confirmed by the significantly higher basolateral to apical permeability of rhodamine123 than that of reverse direction and RT-PCR of MDR1 mRNA. However, the symmetric transport of fexofenadine · HCl in this NHBE cell monolayers study seems to be due to the low expression of P-gp transporter and/or to its saturation with high concentration of fexofenadine · HCl. Thus, the development of tight junction and the expression of P-gp in the NHBE cell monolayers in this study imply that they could be a suitable in vitro model for evaluation of systemic drug absorption via airway delivery, and that they reflect in vivo condition better than P-gp over-expressed cell line models.