Glabridin smartPearls—Silica selection, production, amorphous stability and enhanced solubility

Abstract

Glabridin, a compound in the root extract of Glycyrrhiza glabra, has been identified as an effective tyrosinase inhibitor. Applied on skin, melanin synthesis is inhibited, making glabridin an interesting candidate for skin whitening or for the treatment of age spots. However, main obstaclefor its practical use is its low dermal bioavailability, caused by its poor water solubility. In this work smartPearls technology was used to increase the glabridins water solubility. smartPearls consist of silica particles with mesopores in which actives can be loaded. By this, actives are stabilized in amorphous state and simultaneously finely distributed in nm-range. Both amorphization and nanoization are well known approaches to increase saturation solubilities. In smartPearls these approaches are combined. In the first step, glabridin smartPearls formulation was developed, screening systematically the suitability of 4 different silicas varying in their pore sizes (3, 6, 10, 17 nm). Also, most suited filling level of glabridin was determined (25, 50, 80% referred to total pore volume of respective silica). Silica loading was performed by the immersion-evaporation method, resulting in pores filled with glabridin from bottom to top. By light microscopy, dynamic scanning calorimetry and X-ray diffraction the sample with 6 nm pore size and filling levels of 25% and 50% have been verified to be completely amorphous. Highest physical storage stability of 7 months up to now was obtained for the…