Protection of Tissue-culture Cells against Ionizing Radiation

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Abstract
1. Using a plating technique of tissue-culture cells, as developed by Puck, an investigation was done to discover whether the radioprotective action of cysteamine could be explained by means of a hypoxia caused by its autoxidation, or whether another protective mechanism at the cellular level was involved. 2. The protective activity of a 4 and a 16 mM cysteamine solution and of anoxia is expressed by dose-reduction factors (DRF) of 1·9, 3·3 and 2·6, respectively. Under anoxic conditions the application of 4 and 16 mM cysteamine solutions resulted in a protection characterized by DRF's of 3 and 3·95. Since a high concentration of cysteamine provided a better protection than anoxia, and cysteamine gave an additional protection under anoxic conditions, it was concluded that the protective action of cysteamine cannot be explained by a hypoxia caused by its autoxidation. 3. Experiments were devised to obtain an intensive contact between air and a thin layer of a cysteamine solution to exclude the possibility of hypoxia. Chemical measurements indicated that cysteamine under this condition is oxidized rather quickly. The protective action of cysteamine in these experiments had a value that might be expected to be produced by the residual concentration of cysteamine present during irradiation. 4. Two hypotheses providing an explanation for the protective action of cysteamine at the cellular level are discussed.