The effect of chitosan and other polycations on tight junction permeability in the human intestinal Caco-2 cell line(1)

Chitosan is a polycationic compound widely employed as dietary supplement and also present in pharmaceutical preparations. Although it has been approved for human consumption, its possible side effects have not been widely investigated and the available data in the literature are still controversial. Several polycationic substances have been shown to affect tight junction permeability in epithelial cell models in vitro. In this study we have compared the effects of chitosan and other polycations (polyethylenimine, poly-L-lysines of different molecular weights) on the integrity of tight junctions and of the actin cytoskeleton in the human intestinal Caco-2 cell line. We have measured trans-epithelial electrical resistance and paracellular passage of the extracellular marker inulin, and we have localized F-actin and tight junctional proteins (ZO1 and occludin) in cell monolayers treated with various concentrations of each polycation. Fluorescent poly-L-lysines were also employed to determine their association with the cell monolayer. Our results indicate that all polycations investigated are able to induce a reversible increase in tight junction permeability. This effect is concentration and energy dependent, affected by the extracellular concentration of divalent cations (calcium, magnesium and manganese) and it is associated with morphological changes in the F-actin cytoskeleton, as well as in the localization of tight junctional proteins. Chitosan, in particular, was the only cationic polymer that displayed an irreversible effect on tight junctions at the highest concentration tested (0.01%). These results indicate that oral ingestion of chitosan may have more widespread health effects by altering intestinal barrier function, thus allowing the entrance into the circulation of potentially toxic and/or allergenic substances.