The inhibitory activity of xanthine oxidase (XO) is a combination of uric acid formation inhibition and superoxide anion (O2-) generation suppression. The inhibition of uric acid formation by XO is useful for the screening of natural compounds that prevent gout, while the suppression of O2- generation is useful for treating oxidative stress. Many edible plants contain abundant phenolic compounds and alk(en)yl phenols, and some of these compounds display XO inhibitory activity. This review focuses on XO inhibitory activity since this activity is used to characterize natural products. Recently, it was demonstrated that the inhibitory activity could be characterized using assays for XO inhibition, the suppression of O2- generation, DPPH radical scavenging and O2- radical scavenging. The inhibitory activity was divided three reaction types. The first is XO inhibition, the second O2- generation suppression by modification of enzyme molecules and the third two forms of O2- scavenging. It was demonstrated that these three activities are related to both the hydroxy group arrangement in the phenol portion and the alk(en)yl chains. This characterization is useful for pursuing XO inhibitors and antioxidants in natural compounds.
Keywords: Antioxidant property; Superoxide anion scavenging; Superoxide anion suppression; Xanthine oxidase inhibition; Xanthine oxidase modification.
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