N-alkylation of highly quaternized chitosan derivatives affects the paracellular permeation enhancement in bronchial epithelia in vitro

This study describes the structure-activity relationship for carefully characterized N-alkyl-N-quaternary chitosan derivatives as permeation enhancers for drugs that are mainly absorbed through the paracellular pathway, such as macromolecular drugs and hydrophilic drugs, in a well defined bronchial epithelial cell line. The 0-methyl free derivatives used in the study were fully trimethylated (100%) N,N,N-trimethyl chitosan (TMC) and N-propyl-(QuatPropyl), N-butyl-(QuatButyl) and N-hexyl (QuatHexyl)-N,N-dimethyl chitosan, with 85-91% degree of quaternization. The fully trimethylated TMC, from 0.25 mg/ml, decreased transepithelial electrical resistance (TER) in a reversible manner and enhanced the permeation of the macromolecule FITC-dextran 4 kDa (FD4) 2-5 fold. TMC did not cause any alterations in the tight junction (TJ) protein claudin-4 or in F-actin architecture. QuatHexyl was the most effective polymer to produce enhanced permeation and decreased TER from 0.016 mg/ml. Nevertheless, this enhanced permeation was accompanied by reduced viability and dissociation of F-actin and claudin-4 proteins. The structure-activity relationship suggests that more lipophilic derivatives show more permeation enhancement, TJ disassembly, and less viability in the order of hexyl approximate to butyl > propyl > methyl and demonstrates that the permeation effect is not only mediated by permanent positive charge but also by the extent of Nalkylation. These results are relevant to elucidate the structural factors contributing to the permeation enhancement of chitosan derivatives and for potential use in pulmonary applications. (C) 2013 Elsevier B.V. All rights reserved.