Transport and permeability properties of human Caco-2 cells: An in vitro model of the intestinal epithelial cell barrier

When on nitrocellulose filters, in chambers, Caco-2 cells form a confluent monolayer with several properties characteristic of differentiated intestinal epithelial cells. The cell layers are morphologically polar and have well-developed brush borders at their apical surface. The monolayers are functional in the carrier-mediated transport of taurocholic acid and in the receptor-mediated endocytic transport of cobalamin-intrinsic factor. These active transport pathways, characteristic of the distal ileum, are specific and unidirectional (apical to basolateral). The Caco-2 model displays low permeability to the non-specific transepithelial passage of macromolecules. In addition, our results indicate that the model has potential for predicting in vivo absorption of low molecular weight drugs. The reproducibility and long-term viability of this human model, together with the ability to conveniently perform qualitative and quantitative transport studies across an intact epithelial layer, confer significant advantages over other in vitro models used f or absorption studies.