Chemical coupling of thiolated chitosan to preformed liposomes improves mucoadhesive properties

Kerstin Gradauer,1 Caroline Vonach,1 Gerd Leitinger,2,3 Dagmar Kolb,2,3 Eleonore Fröhlich,3 Eva Roblegg,4 Andreas Bernkop-Schnürch,5 Ruth Prassl1,61Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Graz, Austria; 2Institute of Cell Biology, Histology, and Embryology, Medical University of Graz, Graz, Austria; 3Center for Medical Research, Medical University of Graz, Graz, Austria; 4Institute of Pharmaceutical Sciences/Pharmaceutical Technology, Karl-Franzens University, Graz, Austria; 5Department of Pharmaceutical Technology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria; 6Ludwig Boltzmann Institute for Lung Vascular Research, Graz, AustriaAim: To develop mucoadhesive liposomes by anchoring the polymer chitosan-thioglycolic acid (chitosan-TGA) to the liposomal surface to target intestinal mucosal membranes.Methods: Liposomes consisting of phosphatidylcholine (POPC) and a maleimide-functionalized lipid were incubated with chitosan-TGA, leading to the formation of a thioether bond between free SH-groups of the polymer and maleimide groups of the liposome. Uncoated and newly generated thiomer-coated liposomes were characterized according to their size, zeta potential, and morphology using photon correlation spectroscopy and transmission electron microscopy. The release behavior of calcitonin and the fluorophore/quencher-couple ANTS/DPX (8-aminonaphthalene-1,3,6-trisulfonic acid/p-xylene-bis- pyridinium bromide) from coated and uncoated liposomes, was investigated over 24 hours in simulated gastric and intestinal fluids. To test the mucoadhesive properties of thiomer-coated and uncoated liposomes in-vitro, we used freshly excised porcine small intestine.Results: Liposomes showed a concentration-dependent increase in size – from approximately 167 nm for uncoated liposomes to 439 nm for the highest thiomer concentration used in this study. Likewise, their zeta potentials gradually increased from about –38 mV to +20 mV, clearly indicating an effective coupling of chitosan-TGA to the surface of liposomes. As a result of mucoadhesion tests, we found an almost two-fold increase in the mucoadhesion of coupled liposomes relative to uncoupled ones. With fluorescence microscopy, we saw a tight adherence of coated particles to the intestinal mucus.Conclusion: Taken together, our current results indicate that thiomer-coated liposomes possess a high potential to be used as an oral drug-delivery system.Keywords: thiomer, liposome, mucoadhesion, chitosan-thioglycolic acid, oral drug deliver

The stabilization and release performances of curcumin-loaded liposomes coated by high and low molecular weight chitosan

A comprehensive stability evaluation for curcumin-loaded liposomes (Cur-LP) coated by low (LCS) or high (HCS) molecular weight chitosan with three gradient concentrations (L: low; M: medium; H: high) was the main objective of this study. Apart from leading to a higher encapsulation efficiency (>90%), all chitosan-coated Cur-LP displayed an improved stability with respect to resistant to salt, sunlight, heat, accelerated centrifugation and long-term storage at 4 °C. Increasing the molecular weight and concentration of chitosan could effectively improve the stability of Cur-LP, in which HCS-H coatings displayed the best performance. According to the fluorescence probe analysis, the mechanical reinforcement of liposomes and the concomitant reduction in membrane fluidity accounts for the major contribution to vesicle stability. Secondly, a simulated digestion model was used to prove the applicability of sustained curcumin release, achieved by adjusting the molecular weight and concentration of the chitosan stabilizer for Cur-LP. The results of this study show that high molecular weight chitosan used at relatively high concentrations, is a promising coating material for improving the stability and sustained release of Cur-LP in vitro