Vanillic Acid as a Promising Xanthine Oxidase Inhibitor: Extraction from Amomum villosum Lour and Biocompatibility Improvement via Extract Nanoemulsion.

Gout is an oxidative stress-related disease. Food-derived vanillic acid, a promising xanthine oxidase inhibitor, could potentially be used as a safe, supportive, and therapeutic product for gout. The extraction of vanillic acid from a classic Chinese herbal plant Amomum villosum with ethanol was investigated in the study. The optimum conditions were determined as extraction time of 74 min, extraction temperature of 48.36 °C, and a solid-to-liquid ratio of 1:35 g·mL -1 using the Box-Behnken design (BBD) of response surface methodology (RSM). The experimental extraction yield of 9.276 mg·g -1 matched with the theoretical value of 9.272 ± 0.011 mg·g -1 predicted by the model. The vanillic acid in Amomum villosum was determined to be 0.5450 mg·g -1 by high-performance liquid chromatography-diode array detection (HPLC-DAD) under the optimum extraction conditions and exhibited xanthine oxidase (XO) inhibitory activity, with the half-maximal inhibitory concentration (IC50) of 1.762 mg·mL -1 . The nanoemulsion of Amomum villosum extract consists of 49.97% distilled water, 35.09% S mix (mixture of tween 80 and 95% ethanol with 2:1 ratio), and 14.94% n-octanol, with a particle size of 110.3 ± 1.9 nm. The nanoemulsion of Amomum villosum extract exhibited markable XO inhibitory activity, with an inhibition rate of 58.71%. The result demonstrated the potential benefit of Amomum villosum as an important dietary source of xanthine oxidase inhibitors for gout.