On the cytotoxicity of vitamin C and metal ions

Abstract

The toxicity of ascorbate towards phage .lambda. and the phages T2-T7 was investigated. At room temperature the T-odd and .lambda. bacteriophages were highly susceptible to ascorbate-induced damage; the T-even phages were practically resistant. The toxicity of ascorbate depended on the presence of Cu (or Fe) and O2, although O2, was not required in the presence of H2O2. H2O2 was essential for the ascorbate-induced phage inactivation and the damage was prevented by catalase. At the concentrations used, most Cu ions were bound to the phage particles. Chelating agents such as EDTA or His fully protected the phages; salicylate only reduced the rate of phage inactivation. OH scavengers such as sucrose, formate, mannitol, tert-butyl alcohol or poly(ethylene glycol) had no protective effect. Experiments with DNA labeled phages indicated that phage adsorption and DNA injection were impaired as a result of the exposure to ascorbate and Cu. The failure to express the viral genetic information as a result of single and double-strand breaks in the DNA, probably also contributed to the loss of the plaque-forming ability of the phages. The results were interpreted in terms of a site-specific Fenton mechanism according to which the binding of the transition metal ions to the biological target was a prerequisite for the production of damage. The bound metal ion was reduced by .**GRAPHIC**. ascorbate or other reductants and was subsequently reoxidized by H2O2 yielding OH. radicals. This cyclic redox reaction of the metal generated OH. radicals which reacted with vital macromolecules with a high probability of causing multi-hit damage. This site-specific formation of OH. radicals, which took place near the target molecules, accounted for the high damaging efficiency and for the failure of OH. scavengers to protect against it.