Enhancement effect of geniposide on solubility and intestinal absorption of baicalin

Geniposide and baicalin, the main components of Huangqin-Zhizi herb pair, have been combined to increase the efficacy. To reveal the underlying compatibility mechanism of these two components, the synergistic effects of geniposide on the enhancement of solubility, apparent oil-water partition coefficient, and intestinal absorption of baicalin were investigated. The equilibrium solubility and apparent oil-water partition coefficient of baicalin in different solvents were determined through the shake-flask and high-performance liquid chromatography with diode array detection methods. The intestinal absorption of baicalin was investigated through the in situ single-pass intestinal perfusion method. When combined with different amounts of geniposide, the solubility and apparent oil-water partition coefficient of baicalin improved to 98.74-159.03μg/mL and 0.24-0.29, respectively, which were respectively 1.25-2.02-fold and 1.6-1.9-fold higher than those parameters in the baicalin-only control. The intestinal absorption study indicated that geniposide was an absorption-enhancer for baicalin and significantly increased the absorption rate constant value and the apparent absorption constant value of baicalin, especially in duodenum and jejunum when the compatibility concentrations were 1:1 and 1:2. Geniposide had synergistic effects in enhancing the solubility, apparent oil-water partition coefficient, intestinal absorption of baicalin. The study results provide scientific information elucidating the compatibility mechanism of the Huangqin-Zhizi herb pair and its primary components.