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

Abstract 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 O -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 ≈ butyl > propyl > methyl and demonstrates that the permeation effect is not only mediated by permanent positive charge but also by the extent of N -alkylation. These results are relevant to elucidate the structural factors contributing to the permeation enhancement of chitosan derivatives and for potential use in pulmonary applications.