ERYTHROCYTE DEFENSES AGAINST HYDROGEN-PEROXIDE - THE ROLE OF ASCORBIC-ACID

Ascorbate has been reported to increase intracellular hydrogen peroxid e (H2O2) generation in human erythrocytes. In the present work, the ba sis for this prooxidant effect of the vitamin was investigated in the context of erythrocyte defenses against H2O2. Ascorbate added to eryth rocytes caused a dose-dependent increase in intracellular H2O2, which was measured as inactivation of endogenous catalase in the presence of 3-amino-1,2,4-triazole (aminotriazole). Ascorbate-induced catalase in activation was not observed when only the intracellular ascorbate conc entration was increased, when cells were incubated with ascorbate in p lasma, or when extracellular Fe3+ was chelated. Together, these result s suggest that the observed ascorbate-induced H2O2 generation is due t o Fe3+-catalyzed oxidation of extracellular, as opposed to intracellul ar, ascorbate by molecular oxygen. Rather than generate an oxidant str ess in erythrocytes, ascorbate was one of the most sensitive intracell ular antioxidants to H2O2 coming from outside the cells. On the other hand, intracellular ascorbate contributed little to the detoxification of H2O2, which was found to be mediated by both catalase and by the G SH system. (C) 1998 Elsevier Science B.V.