Radioprotectors

chemical compounds used to protect living organisms—microorganisms, plants, animals, and man—from ionizing radiation. Radioprotectors are introduced into the environment or directly into the organism before or during irradiation. Effective radioprotectors include compounds containing sulfhydryl (thiol) groups (—SH), such as cysteine, mercaptoamines and indolylalkylamines. Radioprotectors generally diminish the consequences of irradiation, that is, its fatal and nonfatal effects, including genetic effects. They also reduce the intracellular or interstitial oxygen pressure and increase the amount of endogenous thiols, which is accompanied by a decrease in the oxidation-reduction potential.

The effectiveness of radioprotectors is expressed by a dose reduction factor, which is equal to the ratio of radiation doses producing identical effects in the presence or absence of radioprotectors. The dose reduction factor depends on the conditions of the irradiation and the physical properties of the radiation: with irradiation during a state of hypoxia, the factor is less than with irradiation in the presence of oxygen. The factor is less during radiation with high linear energy transfer (α particles, neutrons, and heavy ions) than during radiation with low linear energy transfer (X rays and γ rays). The effect of radioprotectors also depends on the properties of the organism. Thus, some radioprotectors may protect microorganisms and cells in a culture and not protect mammals.