Human small intestinal and colonic tissue mounted in the Ussing chamber as a tool for characterizing the intestinal absorption of drugs.

Abstract The purpose of this study was to validate human small intestinal and colonic tissue mounted in the Ussing chamber as a tool for predicting the oral drug absorption in humans with the main focus on moderately and poorly permeable compounds. The obtained apparent permeability coefficient ( P app ) of eleven test compounds was compared to their fraction absorbed (Fa) in humans taken from the literature. Beside the conventional P app a new parameter, the apparent permeability coefficient total ( P app,total ), involving both the apical-to-basolateral permeability and the time-dependent compound accumulation in the tissue was established. The permeability of lucifer yellow (LY), a fluorescent marker of the paracellular pathway and the test compounds showed no obvious differences between small intestine and colon. Furthermore, small intestinal and colonic tissue from a single donor showed similar permeability of both LY and a transcellularly transported compound metoprolol. All test compounds including low molecular weight hydrophilic compounds such as metformin, atenolol, sulpiride and famotidine showed adequate permeability reflecting human Fa values ( R 2  = 0.87). The P app values of digoxin, a P-glycoprotein (P-gp) substrate, were not significantly affected by the addition of verapamil, a P-gp inhibitor. In contrast, the P app,total values of digoxin increased approximately threefold in the presence of verapamil. In conclusion, both small intestinal and colonic tissue mounted in the Ussing chamber provide a good opportunity to predict the oral drug absorption rate in humans even for moderately and poorly absorbed compounds. The novel calculation of P app,total allows the study of the carrier-mediated drug–drug interactions in human intestine.