Abstract: GLD/HP-β-CD inclusion complexes were prepared by encapsulating glabridin (GLD) with hydroxypropyl (HP) and β-cyclodextrin (β-CD) to improve the solubility of GLD in water. The morphology, the existing form of GLD, the interaction between GLD and HP-β-CD and the spatial conformation of the inclusion complexes were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and molecular docking, respectively. Furthermore, the dissolution and release characteristics of GLD/HP-β-CD inclusion complexes were investigated in vitro in simulated gastric and intestinal fluids. The permeability of GLD/HP-β-CD through the mucus layer was studied using the Transwell method, and the spatial conformation and interaction of GLD and mucins were investigated by molecular docking. The small intestinal uptake of GLD in GLD/HP-β-CD inclusion complexes was studied using Caco-2 cells, and the effect of the vector HP-β-CD on GLD uptake and the possible underlying mechanism were investigated. The results showed that the encapsulation efficiency and drug loading of GLD in GLD/HP-β-CD were 90.03% and 14.51%, respectively, and HP-β-CD could significantly increase the saturation solubility of GLD in water to 109.36 mg/mL. SEM showed that the GLD/HP-β-CD solid inclusion complexes were irregularly flake-shaped. DSC showed that GLD in the GLD/HP-β-CD inclusion complexes was present in an amorphous non-crystalline form. FTIR and DSC fully demonstrated that HP-β-CD encapsulated GLD in the cavity to form an inclusion complex. Molecular docking showed that GLD molecules were able to completely enter the cavity of HP-β-CD, the optimal binding energy between GLD and HP-β-CD was −7.37 kcal/mol, and the interaction between molecules was mainly maintained by van der Waals force. Compared with free GLD, the cumulative dissolution rate of GLD/HP-β-CD at 1 h in simulated gastric and intestinal fluids was increased by 15.75 and 12.4 folds, respectively, and the total cumulative release rate at 24 h in simulated gastric and intestinal fluids was increased by 54 folds. The apparent permeability coefficient through the mucus layer was increased from 9.24 × 10-9 to 1.43 × 10-5 cm/s. Molecular docking showed a strong interaction between GLD and the mucin MUC2, and the uptake by Caco-2 cells was increased from 0.039 to 0.349 mg/g. The present study shows that GLD/HP-β-CD complexes can significantly increase the dissolution and release of GLD, and greatly improve the permeability of GLD through the mucus layer of the intestinal epithelial surface and the uptake of GLD by intestinal epithelial cells, thereby having the potential to enhance GLD absorption and improve the bioavailability of GLD.

Key words: glabridin; hydroxypropyl-β-cyclodextrin; dissolution; inclusion complex; release; mucus layer permeation; cellular uptake