Enhancing effect of N-octyl-O-sulfate chitosan on etoposide absorption

P-glycoprotein (P-gp), expressed in the apical membranes of the epithelial cells of the intestine, can reduce the oral bioavailability of a wide range of drugs. Many surfactants/excipients have been demonstrated to potentially increase drug absorption by inhibiting P-gp. The purpose of the present study was to evaluate the effect of N-octyl-O-sulfate chitosan (NOSC) on the absorption of etoposide (VP16), a substrate of P-gp with low water solubility. The rat intestinal circulating perfusion in situ and Caco-2 cell uptake and monolayer membrane penetration in vitro were performed to investigate the enhancing ability of NOSC in comparison with some other P-gp inhibitors. The results indicated that various concentrations of NOSC all increased the intestinal absorption of VP16 in rat jejunum and ileum obviously and there was no significant difference in ileum between the enhancing effects of NOSC and other P-gp inhibitors. The VP16 uptake of Caco-2 cell was increased by NOSC solution with different concentrations. As the NOSC concentration was close to its critical micelle concentration (CMC), the cell uptake of VP16 reached to a maximum value. Both NOSC and verapamil (Ver) enhanced dramatically the transport of VP16 from apical side to basolateral side in Caco-2 cell monolayers. Moreover, they both decreased notably the transport of VP16 from basolateral side to apical side, but this effect of NOSC was weaker than that of Ver. However, transepithelial electrical resistance (TEER) of Caco-2 cell monolayers had no significant change during the study. These studies demonstrated that NOSC had the potential by inhibiting P-gp to improve the absorption of oral drugs which were P-gp substrates.