Chemical Protection against 440-Mev Protons in Mice Pretreated with Mercaptoethylamine (MEA) or p-Aminopropiophenone (PAPP)

Abstract

We report in this paper studies on protection against lethality in mice totalbody-irradiated by 440-Mev protons after preirradiation treatment with mercaptoethylamine (MEA) or with p-aminopropiophenone (PAPP), and a comparison with similar effects in mice irradiated by 250-kvp X-rays. MEA and PAPP are known to protect a variety of biological systems against medium-energy and high-energy photon radiation, but their effectiveness against high-energy charged particle radiation has been little studied. For the specific situation of chemical protection of mammals from whole-body high-energy proton radiation, the only work known to the present authors is that of Yarmonenko and associates (1). These workers reported an increased survival in mice irradiated with 660-Mev protons by pretreatment with various mercapto and other coimpounds. Since the time-average spatial distribution of secondary particles resulting from the interaction of high-energy protons with matter is not identical with that resulting from high-energy photon interactions (although the space-average linear energy transfer is about the same), it appeared worth while to compare radioprotection between protectors for a given radiation, and between radiations for a given protector. The two protectors were selected chiefly on the basis of familiarity, and secondarily on the hypothesis (2) that they confer protection by two different but complementary phenomenological mechanisms: MEA by increasing the concentration of active sulfhydryl hydrogen in the cells, PAPP by decreasing the concentration of molecular oxygen in the cells.