Chemical Radioprotection in Mammals and in Man

Experiments with enzymes in vitro (Barron et al. 1949) and in microorganisms (Latarjet and Ephrati 1948) have shown that certain chemicals are able to moderate the biologic effects of radiation. Patt et al. (1949) were the first to use a radioprotective agent, cysteine, in mammals exposed to whole-body X-irradiation. These authors observed a marked protective effect in rats that had been injected with cysteine just prior to irradiation (Patt et al. 1949, 1950). However, the agent did not confer protection when administered after the exposure. This phenomenon is illustrated by the experimental results of Bacq et al. (1951) with the agent mercaptoethylamine (HS-CH2-CH2-NH2), or cyste-amine, in mice. As Fig. 5.1 shows, a radioprotective effect does not occur when the drug is administered after irradiation. On the other hand, experiments in animals with reduced metabolism have shown that chemical radioprotection is possible even after the exposure has occurred.