The permeability of large molecular weight solutes following particle delivery to air-interfaced cells that model the respiratory mucosa.

The transepithelial transport rates of compounds after deposition as aerosolised particles onto respiratory cell layers and allowing dissolution in the cell surface secretions has not been reported in a comprehensive manner to date. Here, the twin-stage impinger (TSI) was used to deposit potentially respirable particles (aerodynamically <6.4 microm) of varying molecular weight dextrans labelled with fluorescein isothiocyanate (FITC-dex) onto Calu-3 cells, a model of the bronchial epithelium. The TSI functioned as a particle size segregator, with >96% of the deposited particles being geometrically <6.4 microm (as measured by microscopy) and the particles being deposited discretely with a uniform distribution. Cell layers tolerated particle deposition at an air flow of 60 L/min. A small reduction in transepithelial electrical resistance (TER) of <10% occurred initially, but the original TER was recovered within 10 min and there was no significant effect on apparent permeability (P(app)) of FITC-dex 4 over 4 h. Interleukin 8 (IL-8) secretion in the apical and basolateral directions over 24 h was not increased by exposure to the TSI and particle deposition. The rate of FITC-dex 4 (4 kDa) transport across the cell layer after deposition and dissolution of the particles in the cell surface secretions was approximately 20-fold higher (P<0.05) than if applied as a solution. The volume of cell surface secretions was estimated by tracer dilution (3.44+/-1.90 microl, mean+/-SEM) and this value was used to calculate the P(app) of compound once deposited as a particle. The Papp value was found to be similar to that obtained when the compound was applied in solution (P<0.05). Thus, the increased transport rate was attributable to the differences in donor chamber solute concentration rather than any change in the permeability of the cell layer itself. Following particle deposition, transport of FITC-dex with molecular weights between 4 and 70 kDa correlated well (r(2)=0.918) with reported in vivo canine pulmonary clearance after intratracheal instillation of dextrans of similar molecular weight. The use of the TSI and the Calu-3 cell line for the assessment of compound dissolution and transport rates after particle deposition may allow more realistic analyses to be made with respect to the in vivo situation.