Photoproducts of indomethacin exhibit decreased hydroxyl radical scavenging and xanthine oxidase inhibition activities

Gi-Shih Lien ^a, Chien-Shu Chen ^b, Wei-Yu Chen ^c, Shih-Hao Huang ^d, Kur-Ta Cheng ^e, Chun-Mao Lin ^e,*,1, Su-Hui Chao ^e,1

a Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan, ROC
b School of Pharmacy, China Medical University, Taichung, Taiwan, ROC
c Department of Pathology, College of Medicine, Taipei Medical University, Taipei, Taiwan, ROC
d Department of Food and Beverage Management, Taipei College of Maritime Technology, Taipei, Taiwan, ROC
e Department of Biochemistry, College of Medicine, Taipei Medical University, Taipei, Taiwan, ROC

Indomethacin (IN) is a widely used nonsteroidal anti-inflammatory drug. In this study, four photoproducts of IN (IN1-IN4) were produced and isolated from photoirradiated IN. This study investigated the abilities of IN and its photoproducts to scavenge hydroxyl radicals and inhibit xanthine oxidase (XO). The hydroxyl radical-scavenging activity was measured in vitro by electron spin resonance spectrometry using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trapping agent. Enzyme activity was measured by continuous monitoring of uric acid formation, using xanthine as a substrate. The results showed that, among all the related products, IN has the strongest hydroxyl radical-scavenging (IC50 = 65 mM) and XO inhibitory (IC50 = 86 mM) effects. To further understand the stereochemistry of the reactions between these IN derivatives and XO, we performed computer-aided molecular modeling. IN was the most potent inhibitor with the most favorable interaction in the reactive site. Various photoproducts exhibited affinity toward XO as a result of the absence of hydrogen bonding with molybdopterin domain.

Keywords: Electron spin resonance, Hydroxyl radical, Indomethacin, Molecular modeling, Photoproduct, Xanthine oxidase