ALPHA-KETOACIDS SCAVENGE H2O2 IN-VITRO AND IN-VIVO AND REDUCE MENADIONE-INDUCED DNA INJURY AND CYTOTOXICITY

We demonstrate that alpha-ketoacids reduce and, in some instances, abr ogate menadione-induced DNA damage and cytotoxicity in the human breas t cancer cell line, MCF7. We confirm that alpha-ketoacids quench the c opious amounts of H2O2 generated by menadione while these alpha-ketoac ids undergo nonenzymatic oxidative decarboxylation; our data thus supp ort enhanced H2O2 production as an important pathway for menadione-ind uced DNA damage and cytotoxicity. We also demonstrate that alpha-ketoa cids scavenge H2O2 generated by mitochondria and microsomes when these organelles are exposed to menadione; additionally, alpha-ketoacids pr otect oxidant-vulnerable enzymes against functional impairment induced by H2O2. Finally, we provide the first in vivo demonstration that acu te elevations in concentrations of alpha-ketoacids in rat tissues and urine scavenge H2O2. We conclude that enhanced H2O2 production is a ma jor pathway for menadione-induced DNA damage and cytotoxicity and that the diverse alpha-ketoacids present within the cell must be considere d, along with glutathione peroxidase and catalase, as part of the intr acellular antioxidant defense mechanisms that regulate the ambient lev els of H2O2.