Evidence that the reactions of nickel in the presence of vitamin C do not produce toxic oxygen intermediates such as hydroxyl but ascorbate and carbon radicals

A variety of reactions containing different amounts of nickel ions together with vitamin C were prepared and used in spin trapping experiments designe d to show nickel is not a Fenton active metal. Carbon based radicals were o bserved at low ratios of ascorbate to nickel, and ascorbate radical was obs erved at high ratios of ascorbate to nickel. No buffer effects were observe d. There was no evidence for oxygen intermediates as products of the reacti on with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) or alpha-(4-pyridyl-1-oxide )-N-tert-butylnitrone (POBN), seeming to indicate nickel is not a Fenton me tal. To test this hypothesis further trapping studies were run with the sin glet oxygen trap 2,2,6,6-tetramethyl-4-piperidone hydrochloride, in which d ioxygen was found not to affect the formation of carbon radicals. These res ults help to explain the damage to DNA observed in the presence of vitamin C and nickel in vitro.