The Charge and Phase State of Liposomes Dramatically Affects the Binding of Mannosylated Chitosan

Abstract

Liposomal complexes with mucoadhesive polymers, e.g., mannosylated chitosan, are considered as prospective antituberculosis drug delivery systems. The properties of such complexes can be critically affected by the charge and phase state of liposomes. The aim of our work was to study the interaction of mannosylated chitosan with liposomes of various compositions and to identify the key patterns of this process. We tracked the interaction by titrating the liposomes with an increasing base-molar excess using the DLS method and ATR-FTIR spectroscopy. Sorption isotherms were obtained using ATR-FTIR spectroscopy and linearized in the Scatchard coordinates to evaluate the dissociation constant (Kdis). The inclusion of cardiolipin (CL) in the lipid composition helps to reduce the Kdis of the complexes by an order of magnitude of 3.8 × 10−4 M and 6.4 × 10−5 M for dipalmitoylphosphatidylcholine (DPPC) and DPPC:CL 80:20 (weight ratio), respectively. Preheating at 37 °C of gel-like anionic liposomes helps to reduce the Kdis to 3.5 × 10−5 M. Anionic liposomes, both in liquid crystal and in the gel-like state, form multipoint non-covalent complexes with chitosan–mannose conjugates due to the partial neutralization of the charges on the surface of the vesicles. Meanwhile, neutral liposomes in both states form unstable heterogeneous complexes, probably due to the predominant sorption of the polymer on the vesicles. Complex formation provides preferable binding with the model mannose-binding receptor concanavalin A and sustained pH-sensitive release of the antituberculosis drug moxifloxacin.