Toxicity, radiation sensitivity modification, and metabolic effects of dehydroascorbate and ascorbate in mammalian cells,

Authors

  • Cameron J. Koch,

    1. Ontario Cancer Treatment and Research Foundation, London Clinic, Victoria Hospital, London, Ontario N6A 4G5
    2. Division of Radiation Biology, Department of Radiology, Case Western Reserve University, Cleveland, Ohio 44106
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  • John E. Biaglow

    1. Ontario Cancer Treatment and Research Foundation, London Clinic, Victoria Hospital, London, Ontario N6A 4G5
    2. Division of Radiation Biology, Department of Radiology, Case Western Reserve University, Cleveland, Ohio 44106
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  • Supported by the Ontario Cancer Treatment and Research Foundation, NCI Grant CA 13747 and the Medical Research Council of Canada.

  • Parts of this work were presented at the Twenty-Third Annual Meeting of the Radiation Research Society, Miami Beach, Florida, 1975.

Abstract

Dehydroascorbate, an electron affinic metabolite of vitamin C, sensitized Ehrlich ascites tumor cells, in vivo, to radiation and was selectively toxic to V79 Chinese hamster lung cells under hypoxic conditions (without radiation). The radiosensitization may involve both the electron affinic nature of dehydroascorbate as well as its ability to oxidize the intracelluar NAD(P)H and non-protein sulfhydryl. Dehydroascorbate's oxidation of NAD(P)H required higher concentrations than other sulfhydryl oxidants such as N-ethylmaleimide and diamide. The oxidation of NAD(P)H by dehydroascorbate could be reversed by glucose. Hypoxic cell radiosensitization of V79 cells in tissue culture by dehydroascorbate could not be easily demonstrated because of the rapid breakdown and appreciable cytotoxicity of the drug at high concentration. The cytotoxicity was found to occur with both high and low densities of V79 cells. With low cell densities small amounts of oxygen did not reduce the cytotoxicity of dehydroascorbate, but virtually eliminated the cytotoxicity of nitroaromatic electron affinic compounds (metronidazole and Ro-07-0582). The cytotoxicity to dense cell suspensions was found to depend upon the type of buffer included in the reaction medium. The maximum cytotoxicity was obtained in buffer free saline. The reduced form of dehydroascorbate, vitamin C, was found to be toxic only under aerobic conditions. The aerobic cytotoxicity could be prevented by the addition of catalase to the growth medium or by an increase in cell density, suggesting it was caused entirely by the production of H2O2 from the oxidation of vitamin C.

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