Abstract
Alkyl caffeates are strong antioxidants and inhibitors of xanthine oxidase. However, it is unclear about the effect of caffeic acid and alkyl caffeates on superoxide anion (O2−) generation catalyzed by xanthine oxidase. Effects of caffeic acid and alkyl caffeates on the uric acid formation and O2− generation catalyzed by xanthine oxidase were analyzed. The scavenging activities of 1,1-diphenyl-2-picryhydrazyl (DPPH) radical and O2− generated with phenazine methosulfate (PMS) and NADH were examined. Caffeic acid derivatives equally suppressed O2− generation, and the suppression is stronger than inhibition of xanthine oxidase. Scavenging activity of O2− is low compared to the suppression of O2− generation. Suppression of O2− generation catalyzed by xanthine oxidase with caffeic acid derivatives was not due to enzyme inhibition or O2− scavenging but due to the reduction of xanthine oxidase molecules. Alkyl caffeates are effective inhibitors of uric acid and O2− catalyzed by xanthine oxidase as well as antioxidants for edible oil.