The uremic solute indoxyl sulfate acts as an antioxidant against superoxide anion radicals under normal-physiological conditions.

The effect of the uremic solute indoxyl sulfate (IS) on scavenging superoxide anion radicals (O(2)(*-)) generated from both the xanthine/xanthine oxidase (X/XO) system and activated neutrophils was investigated by electron paramagnetic resonance spectroscopy, combined with 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-1-oxide (EMPO). The findings show that the presence of normal-physiological serum concentrations of IS (0.1-10 microM) resulted in decreased formation of EMPO-superoxide adduct without affecting XO activity. Furthermore, IS showed scavenging activity against cell-derived O(2)(*-) generated from activated neutrophils. In addition, IS also eliminated hydroxyl radicals. These findings suggest that IS acts as a novel endogenous antioxidant under normal-physiological conditions. Copyright 2010. Published by Elsevier B.V.