Objective: 

Chitosan is employed as an absorption enhancer for development of novel drug delivery strategies. As detailed information concerning mechanisms is limited, we have investigated the rapid effects on epithelial barrier function of the intestinal epithelial cell model HT-29/B6.

Methods: 

Monolayers of HT-29/B6 cells were grown on permeable supports, mounted in Ussing chambers, and transepithelial resistance and flux of permeability markers was measured. Western blots and confocal laser scanning immunofluorescence microscopy were performed to analyze tight junction proteins.

Results: 

Chitosan induced a rapid and reversible decrease in transepithelial resistance (R^t). Two-path impedance spectroscopy revealed effects on both, the paracellular (R^para) and the transcellular (R^trans) resistance. pH-dependence and inhibition of both effects by a negatively charged macromolecule, heparin, indicated a chitosan action only in the protonated form. The decrease in R^trans was mediated by activation of a chloride-bicarbonate exchanger involved in intracellular pH regulation. This activation was coupled to the decrease in R^para which was associated with an increase in ion permeability and permeability for paracellular flux markers up to 10 kDa. No effects on expression and subcellular distribution of tight junction proteins or the actin cytoskeleton were observed.

These results suggest that the absorption-enhancing effect of chitosan is due to changes in intracellular pH caused by the activation of a chloride-bicarbonate exchanger resulting in an opening of the tight junction, facilitating the passage of macromolecules of up to 10 kDa.