VITAMIN C TOXICITY

Although there is no compelling evidence that vitamin C has antitumor activity in humans, clinical trials are testing the hypothesis that ascorbic acid (AA) will enhance the efficacy of arsenic trioxide (As2O3) in myeloma. In vitro, AA cytotoxicity depends on its interaction with free transition metal ions in culture media leading to the generation of H2O2 and other reactive oxygen species (ROSs). Vitamic C was found to generate cytotoxic concentrations of H2O2 in culture medium without cells and copper/iron chelators inhibited this reaction. However, Vitamin C did not generate H2O2 in simple buffer or human plasma. Direct incubation with Vitamin C resulted in increased intracellular ROSs, whereas DHA incubation decreased it.