Physicochemical Characterization and Antioxidant Activity Evaluation of Idebenone/Hydroxypropyl-β-Cyclodextrin Inclusion Complex

Idebenone (IDE) is an antioxidant drug active at the level of the central nervous system (CNS), whose poor water solubility limits its clinical application. An IDE/2-hydroxypropyl-beta-cyclodextrin (IDE/HP-beta-CD) inclusion complex was investigated by combining experimental methods and theoretical approaches. Furthermore, biological in vitro/ex vivo assays were performed. Phase solubility studies showed an A(L) type diagram, suggesting the presence of a 1:1 complex with high solubility. Scanning electron microscopy (SEM) allowed us to detect the morphological changes upon complexation. The intermolecular interactions stabilizing the inclusion complex were experimentally characterized by exploring the complementarity of Fourier-transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR) with mid-infrared light, Fourier-transform near-infrared (FT-NIR) spectroscopy, and Raman spectroscopy. From the temperature evolution of the O-H stretching band of the complex, the average enthalpy Delta H-HB of the hydrogen bond scheme upon inclusion was obtained. Two-dimensional (2D) rotating frame Overhauser effect spectroscopy (ROESY) analysis and computational studies involving molecular modeling and molecular dynamics (MD) simulation demonstrated the inclusion of the quinone ring of IDE inside the CD ring. In vitro/ex vivo studies evidenced that complexation produces a protective effect of IDE against the H2O2-induced damage on human glioblastoma astrocytoma (U373) cells and increases IDE permeation through the excised bovine nasal mucosa.