Quaternization of high molecular weight chitosan for increasing intestinal drug absorption using Caco-2 cells as an in vitro intestinal model.

Potential use of a quaternized chitosan (MW 600 kDa) with 65% of 3-chloro-2-hydroxypropyltrimethylammonium (600-HPTChC(65)) as an absorptive enhancer was investigated in Caco-2 monolayers. 600-HPTChC(65) (0.005% w/v) quickly reduced transepithelial electrical resistance (TEER) to the maximum level in 40 min with full recovery within 6 h after removal. Its TEER reduction was corresponded to increased FD4 transport across the monolayers and disrupted localization of tight junction proteins ZO-1 and occludin at the cell borders. 600-HPTChC(65) was densely localized at the membrane surface and intercellular junctions. This chitosan (0.08-0.32% w/v) reduced the efflux ratio of [(3)H]-digoxin by 1.7- 2 folds, suggesting an increased [(3)H]-digoxin transport across the monolayers. Its binding with P-gp on Caco-2 monolayer increased the signal of fluorescence-labeled anti-P-gp (UIC2) reactivity due to conformational change. 600-HPTChC(65) (0.32% w/v) had no effect on P-gp expression in the Caco-2 monolayers. These results suggest that 600-HPTChC(65) could enhance drug absorption through tight junction opening and decreased P-gp function. Its interaction with the absorptive barrier mainly resulted in disrupting ZO-1 and occludin organization as well as changing in P-gp conformation.