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Sodium ascorbate (vitamin C) has a reputation for inconsistent effects upon malignant tumor cells, which vary from growth stimulation to apoptosis induction. Melanoma cells were found to be more susceptible to vitamin C toxicity than any other tumor cells. The present study has shown that sodium ascorbate decreases cellular iron uptake by melanoma cells in a dose- and time-dependent fashion, indicating that intracellular iron levels may be a critical factor in sodium ascorbate-induced apoptosis. Indeed, sodium ascorbate-induced apoptosis is enhanced by the iron chelator, desferrioxamine (DFO) while it is inhibited by the iron donor, ferric ammonium citrate (FAC). Moreover, the inhibitory effects of sodium ascorbate on intracellular iron levels are blocked by addition of transferrin, suggesting that transferrin receptor (TfR) dependent pathway of iron uptake may be regulated by sodium ascorbate. Cells exposed to sodium ascorbate demonstrated down-regulation of TfR expression and this precedes sodium ascorbate-induced apoptosis. Taken together, sodium ascorbate-mediated apoptosis appears to be initiated by a reduction of TfR expression, resulting in a down-regulation of iron uptake followed by an induction of apoptosis. This study demonstrates the specific mechanism of sodium ascorbate-induced apoptosis and these findings support future clinical trial of sodium ascorbate in the prevention of human melanoma relapse.

• PMID: 15672419
• DOI: 10.1002/jcp.20286