Synthesis and in vitro evaluation of a novel chitosan-glutathione conjugate

Purpose. It was the aim of this study to synthesize and characterize a novel chitosan-glutathione (GSH) conjugate providing improved mucoadhesive and permeation-enhancing properties. Methods. Mediated by carbodiimide and N-hydroxysuccinimide, glutathione was covalently attached to chitosan via the formation of an amide bond. The adhesive properties of chitosan-GSH conjugate were evaluated in vitro on freshly excised porcine mucosa via tensile studies and the rotating cylinder method. The cohesive properties and stability of the resulting conjugate were evaluated by disintegration test and by oxidation experiments, respectively. The permeation-enhancing effect of the chitosan-GSH/GSH system was evaluated in Ussing chambers by using rhodamine 123 as model compound. Results. The obtained conjugate displayed 265.5 mu mol immobilized free thiol groups and 397.9 mu mol disulfide bonds per gram polymer. Because of the formation of disulfide bonds within the polymer, the stability of matrix tablets could be strongly improved. In tensile studies, the total work of adhesion of the conjugate was determined to be 9.9-fold increased in comparison to unmodified chitosan. Results from the rotating cylinder method showed more than 55-fold increase in the adhesion time of thiolated chitosan vs. unmodified chitosan. In addition, the conjugate in combination with GSH displayed a 4.9-fold higher permeation-enhancing effect compared with unmodified chitosan. Conclusions. Because of the improved mucoadhesive and cohesive properties, and the strong permeation-enhancing effect of the chitosan-GSH conjugate/GSH system, the novel thiolated chitosan seems to represent a promising multifunctional excipient for various drug delivery systems.