Characterisation of drug transporters in human respiratory epithelial cells

Abstract

Cell culture models are an efficient and relatively cheap tool to study isolated mechanisms of an organ. The right cell model, carefully selected to allow highest benefits, can give valuable information in the area of active drug transport, a mechanism hardly understood in the lung. Whereas Caco-2 cells have been demonstrated to be an efficient model for absorption studies in the gastrointestinal region, in the lung a most suitable model for these investigations has not been declared. Little is known about the expression of membrane transporters within lung epithelium, and even less about regional differences that may exist within the different lung epithelial surfaces. My work demonstrated similarities and differences between human lung epithelial cells of different origins. Primary models were compared to cell lines, either isolated from cancer cells or obtained by immortalisation of normal cells. Each model showed a characteristic pattern of expression and activity of the drug transporters tested. Moreover, a number of variations regarding transporter expression in cell models of pulmonary compared to gastrointestinal origin were discovered. Traditional RT-PCR and quantitative RT-PCR analyses characterised mRNA transcript expression of a wide range of membrane carrier transporters in several in vitro lung epithelial cell models. Transporters studied included: 11 ABC transporters, 11 SLC transporters, and 9 SLCO transporters. Employed cell culture models included both established cell lines (A549, Calu-3, 16HBE14o-, BEAS-2B) and freshly isolated cells in primary culture (human bronchial and alveolar epithelial cells). Immunofluorescence microscopy confirmed MDR1 protein in hAEpC localised predominantly at the luminal membranes, which was in agreement with immunohistochemical staining for MDRl performed in normal human lung tissue and resulting in a positive signal