Effect of chitosan on epithelial permeability and structure

Numerous studies have shown that chitosan, a mucoadhesive polymer, is a pot ential enhancer for transmucosal drug delivery. To further understand the m echanisms involved in chitosan action on the mucosal barrier, the activity of chitosan on the function and structure of monolayers of intestinal epith elial cells was investigated. In Caco-2 cells, chitosan caused a reversible , time and dose-dependent decrease in transepithelial electrical resistance . The effect of chitosan on tight junctions was confirmed by an increased p ermeability coefficient for mannitol transport when cells were treated with 0.1-0.5% w/v chitosan solution for 60 min compared to control cells. Invol vement of tight junctions was visualized by confocal scanning microscopy us ing occludin and ZO-1, tight junctional proteins. Following an incubation w ith 0.01 or 0.1% w/v chitosan, labeling of both proteins varied in localiza tion and decreased in fluorescent intensity at the cell periphery. In addit ion, a focal condensation of actin was observed preferentially at areas of cell-to-cell contacts. However, after 24-h recovery, the cell structure res embled untreated control cells. Simultaneous addition of cycloheximide, a p rotein synthesis inhibitor, prevented full recovery. This implied that prot ein synthesis was required for the cells to return to baseline levels. Chit osan treatment appeared to slightly perturb the plasma membrane as assessed by an increased release of lactate dehydrogenase. However, addition of 0.5 % chitosan for 60 mill did not affect cell viability as shown by Trypan blu e dye exclusion. These data suggest that chitosan increases cell permeabili ty by affecting paracellular and intracellular pathways of epithelial cells , in a reversible manner. (C) 1999 Published by Elsevier Science B.V. All r ights reserved.