Effect of metal ions on radical intensity and cytotoxic activity of ascorbate.

Various metal ions were investigated for their ability to modify the radical intensity and cytotoxic activity of sodium ascorbate or ascorbic acid. The addition of metal ions, such as Cu+, Cu2+, Fe2+, Zn2+, Mn2+ and Fe3+, dose-dependently enhanced the ascorbyl radical intensity whereas Na+, K+, Ca2+ and Mg2+ were totally inactive. The enhancement of ascorbyl radical intensity by metal ions was tightly coupled with the accelerated degradation of ascorbate. Addition of either serum or albumin significantly reduced the stimulation effect of Cu2+, and almost completely eliminated that of Fe3+ and Zn2+. The noncytotoxic concentration of Cu2+ significantly enhanced the cytotoxicity of ascorbate against cultured human glioblastoma T98G cell line. The present data suggest the possible role of metal ions in the regulation of the biological activity of ascorbate.