Assessment of antioxidant properties of alpha-keto acids in vitro and in vivo

The antioxidant properties of three alpha-keto acids, pyruvate, oxaloacetate and alpha-ketoglutarate were tested in vitro and in vivo. In vitro, the keto acids demonstrated a good H2O2-scavenging activity, but were less effective as scavengers of free radicals or reductants of oxidized compounds. Alpha-ketoglutarate was a more effective H2O2 scavenger as well as HO center dot in Fe3+-ascorbate-EDTA-H2O2 system than other keto acids. All keto acids did not demonstrate iron-chelating activity. It was supposed that ability of keto acids to inhibit HO center dot production in the Fenton reaction could be mainly conditioned by their H2O2-scavenging activity. In vivo experiments, the addition of alpha-keto acids to the incubation medium significantly increased the resistance of exponentially growing yeast Saccharomyces cerevisiae cells to H2O2, transition metal ions (Fe2+), but not to menadione, a superoxide anion-generating compound. Similar results were obtained on fruit fly Drosophila melanogaster. In particular, co-treatment with alpha-ketoglutarate enhanced resistance of adult flies to H2O2 and did not prevent menadione-induced death of flies. Collectively, the results obtained indicate that exogenous alpha-keto acids as antioxidants are able efficiently to protect living organisms against stressors in which effects are mediated by H2O2. Therefore, they can be considered as available natural supplements to alleviate the harmful effects of reactive oxygen species.