Citrate, a TCA cycle metabolite, plays a role as a hydroxyl radical scavenger in vitro

•We report metabolites of TCA cycle scavenge hydroxyl radicals. Reactive oxygen species, such as superoxide anions, hydrogen peroxide, and hydroxyl radicals, are strongly associated with diseases and aging. Superoxide anions and hydrogen peroxide are scavenged by superoxide dismutase and catalase, respectively. These scavenging reactions are supported by enzymes. In contrast, hydroxyl radicals are scavenged by non-enzymatic compounds, such as ascorbic acid, glutathione, and phenolic compounds. Recently, metabolites of glucose and ethanol have been shown to act as hydroxyl radical scavengers. In this study, we evaluated hydroxyl radical-scavenging activity of metabolites of the TCA cycle. We found that these metabolites have a scavenging activity against hydroxyl radicals. In particular, citrate exhibited significant scavenging activity at the cellular level. Additionally, citrate protected superoxide dismutase from hydroxyl radicals. We also confirmed the protective role of citrate against hydroxyl radical-induced DNA strand breakage. The previously reported rate constants and intracellular concentrations did not rule out a protective role in mitochondria. Collectively, our results indicate that citrate acts as a hydroxyl radical scavenger.