Edaravone, a scavenger for multiple reactive oxygen species, reacts with singlet oxygen to yield 2-oxo-3-(phenylhydrazono)-butanoic acid

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is a synthetic antioxidant used as a drug to treat acute ischemic stroke in Japan and amyotrophic lateral sclerosis in Japan and the USA. Its pharmacological mechanism is thought to be scavenging of reactive oxygen species, which are intimately related with these diseases. Recently, the singlet oxygen (‍1O2) has attracted attention among reactive oxygen species. In this study, we investigated the reactivity of edaravone toward 1O2 and identified its reaction products. Edaravone showed a reactivity toward 1O2 greater than those of uric acid, histidine, and tryptophan, which are believed to be ‍1O2 scavengers in vivo. And we confirmed that 2-oxo-3-(phenylhydrazono)-butanoic acid was formed as an oxidation product. We propose a plausible mechanism for 2-oxo-3-(phenylhydrazono)-butanoic acid production by ‍1O2-induced edaravone oxidation. Since 2-oxo-3-(phenylhydrazono)-butanoic acid has already been identified as a radical-initiated oxidation product, free radical-induced oxidation should be seriously reconsidered. We also found that edaravone can react with not only hypochlorous anions but also ‍1O2 that are formed from myeloperoxidase. This result suggests that edaravone treatment can be beneficial against myeloperoxidase-related injuries such as inflammation.