Selenoneine scavenges hydroxyl radicals by self-oxidation in hydrogen peroxide and by forming seleninic acid, which is reduced back to selenoneine

Abstract Selenoneine (SEN), a selenium analog of ergothioneine (EGT), is widely distributed in marine fishes and is a strong radical scavenger. Electron spin resonance (ESR) spectrometry showed that SEN monomer and dimer directly scavenged ·OH generated by irradiating hydrogen peroxide (H2O2) with ultraviolet light. The radical scavenging capacity was stronger for SEN monomer, dimer and EGT in that order. Mass spectrometry analyses revealed that the monomer and dimer were oxidized to SEN seleninic acid (SEN-seleninic acid) in the presence of H2O2, and that SEN-seleninic acid was reduced to SEN monomer by reduced glutathione (GSH). These reactions proceeded at physiological concentrations of H2O2 and GSH. Our findings suggest that SEN scavenges ·OH directly by a rapid, repetitive non-enzymatic reaction via self-oxidation and by its reduction back to SEN.