Functional analysis of OCTN2 and ATB0,+ in normal human airway epithelial cells

Abstract

In human, OCTN2 (SLC22A5) and ATB0,+ (SLC6A14) transporters mediate the uptake of L-carnitine, essential for the transport of fatty acids into mitochondria and the subsequent degradation by {beta}-oxidation. Aim of the present study is to characterize L-carnitine transport in EpiAirway, a 3D organotypic in vitro model of primary human tracheal-bronchial epithelial cells that form a fully differentiated, pseudostratified columnar epithelium at air-liquid interface (ALI) condition. In parallel, Calu-3 monolayers grown at ALI were used as comparison. In EpiAirway, ATB0,+ was highly expressed and functional on the apical side while OCTN2 transporter was active on the basolateral side. Calu-3 cells showed a different pattern of expression and activity for ATB0,+: indeed, L-carnitine uptake on apical side was evident in Calu-3 at 8 days of culture but not in fully differentiated 21d ALI culture. As both ATB0,+ and OCTN2, beyond transporting L-carnitine, have a significant potential as delivery systems for drugs, the identification of these transporters in EpiAirway can open new fields of investigation in the studies of drug inhalation and pulmonary delivery.