EFFECTS OF VARIOUS FACTORS ON PULMONARY ABSORPTION OF PEPTIDE DRUGS USING IN VITRO EXPERIMENTAL SYSTEMS

Abstract

We examined the in vitro penetration characteristics of FITC-dextrans (FDs) with various molecular weights and peptides such as calcitonin and insulin across human lung carcinoma A-549 cell monolayer. The permeability coefficients of FDs through the A-549 monolayers (type-II like cells) were much larger than those in the rat alveolar epithelial cell monolayers (RAEMs: type-I like cells), which were established by Kim and coworkers. The high permeability characteristics of A-549 monolayers may be attributed to their morphological differences as compared with the RAEMs.
On the other hand, we studied the degradation characteristics of peptide drugs such as calcitonin and insulin using rat lung and A-549 cell homogenates. Calcitonin was rapidly disappeared than insulin in both homogenates. The apparent degradation clearance (Km/Vmax) values of these peptides were higher in the cytosol fraction than membrane fraction. In both homogenates, chymotrypsin activity was the highest among the six protease activities such as trypsin, elastase, chymotrypsin, Leu-aminopeptidase, aminopeptidase B and aminopeptidase N examined in this study. These results confirmed our previous report that the degradation of insulin in the rat lung homogenate was suppressed by the addition of soybean trypsin inhibitor.
Furthermore, the penetration characteristics of water soluble compounds, such as phenol red and FDs across the Xenopus isolated pulmonary membrane were examined with the modified Ussing chamber system. The permeability coefficients of FDs with various molecular weights through the Xenopus isolated pulmonary membrane were similarto those through the small and large intestine. A good correlation was observed between the penetrated amounts of drugs across the Xenopus isolated pulmonary membrane with the in vitro Ussing chamber system and their absorbed amounts calculated by deconvolution method in an in situ rat intrapulmonary absorption experiment. Three types of absorption enhancers, such as laurylmaltoside, mixed micelle and Na-caprate, increased the penetration of phenol red across the Xenopus isolated pulmonary membrane, while EDTA and Na-salicylate did not affect its penetration across the Xenopus isolated pulmonary membrane. These results were in agreement with our previous report of an in situ rat intrapulmonary experiment.