Evaluation of HO-1-u-1 cell line as an in vitro model for sublingual drug delivery involving passive diffusion—Initial validation studies

The aim of this study was to provide preliminary validation of a new sublingual mucosal cell line (HO-1-u-1) for use as in vitro sublingual drug delivery screening of compounds involving passive diffusion. HO-1-u-1 cells were seeded on cell culture inserts. The ultrastructure and integrity of cell layers, inter-passage variation and directionality of drug transport, and apparent permeability coefficient (Papp) of eight β-blockers (representing compounds involving passive diffusion) were determined. HO-1-u-1 cells grown on inserts formed stratified and epithelial-like structure and maintained the typical histological features of normal human sublingual epithelium. The maximal integrity of the cell layer was reached in 23 days. No significant inter-passage variation was found at the passages ranging from 2 to 11 when measured by radiolabeled transcellular and paracellular markers (testosterone and mannitol, respectively). Bidirectional transport studies confirmed the passive diffusion as the mechanism of transport for these markers. The Papp of eight β-blockers across HO-1-u-1 cell culture ranged from 2.89 ± 0.17 to 6.37 ± 0.37 × 10−6 cm/s and correlated well to the Papp obtained from porcine sublingual mucosa (r2 = 0.647 and 0.83 when excluding propranolol). The above results indicate that the HO-1-u-1 cells grown on inserts may offer as a potentially in vitro model for screening sublingual drug permeation involving passive diffusion.