Reducing Compounds in Radioprotection and Radio-sensitization: Model Experiments Using Ascorbic Acid

SummaryAscorbic acid has been used in model experiments to investigate the possible roles of reducing agents in radioprotection and radiosensitization.The repair of organic radicals by their reaction with ascorbic acid has been demonstrated directly using pulse radiolysis. Absolute rate constants for the reaction of the vitamin with hydroxyl radicals and secondary inorganic radical anions have been determined. In the presence of ascorbic acid, the rapid reactions of the sensitizer triacetoneamine-N-oxyl (TAN), with the thymine hydroxyl adduct, or the isopropanol radical, were not observed. This was attributed to the rapid thermal reduction of the stable free radical. The resultant loss in radiosensitizing properties was confirmed by bacteriological studies using Serratia marcescens. In contrast, ascorbic acid had only an insignificant effect on the sensitizing action of the relatively stable compound p.nitroacetophenone (PNAP).