Chitosan Nanoparticles for Topical Co-Administration of the Antioxidants Glutathione and Idebenone: Characterization and In Vitro Release

Aims: The aim of this study was to explore the potential of novel nanoparticles (NPs) intended for topical administration of the hydrophilic antioxidant Glutathione and the lipophilic Idebenone. Glutathione was introduced into the NPs using two approaches: i) covalently bonded to Chitosan; ii) physically complexed with Idebenone and Sulfobutylether--cyclodextrin. Methodology: NPs were formulated using the ionic gelation technique, by dissolving the polysaccharide-forming matrix (Chitosan, Glycol chitosan, Glutathionyl Chitosan) in water or in slightly acidic solution. Idebenone was physically entrapped whereas glutathione was either physically entrapped or covalently bonded to chitosan. Physicochemical characterization of the resulting NPs included size, zeta potential measurements, antioxidant association efficiency, differential scanning calorimetry (DSC) and stability studies. Antioxidants in vitro release from the most stable NPs was assessed with Franz diffusion cells, and the in vitro antioxidant activity was evaluated by the 2,2- diphenyl-1-picrylhydrazyl (DPPH) radical test. NP cytotoxicity was assessed on immortalized human keratinocytes (HaCaT) cell line. Results: The NPs showed smaller particle size in acidic solution than in aqueous medium, whereas zeta potential values were always positive, irrespective of the medium. Stability studies led to the choice of the aqueous formulation where Glutathione was covalently bonded to Chitosan for this study. DSC highlighted amorphization of Idebenone in these NPs. In vitro release studies showed that only Idebenone was released from the NPs. The antioxidant activity test revealed a strong effect (close to 100%) of Idebenone loaded into NPs while its aqueous solution showed no activity. No cytotoxicity in human keratinocytes was observed for the investigated NPs. Conclusion: The results of this study suggest that Idebenone can be loaded into a hydrophilic delivery system without organic solvents, often used for its solubilization, possessing high antioxidant activity. Therefore, these nanocarriers represent a promising strategy for the design of formulations for topical treatments with antioxidants.