The Effects of Thorium-232 on the Bioluminescent Enzymatic System and Radioprotective Activity of Humic Substances

Abstract

The study of low-dose effects is relevant in connection with the expansion of areas with anthropogenic load. Thorium is one of the background-forming elements in natural ecosystems, its content can increase in the environment during the extraction of natural resources and the operation of thermal power plants. Of particular interest are the bioeffects of thorium in the presence of humic substances, natural detoxifiers. The aim of this study was to evaluate the neutralizing effect of humic substances under conditions of low-dose exposure to thorium-232 (<0.04 Gy). A bioluminescent system of enzymatic reactions, including bacterial luciferase and NAD(P)H:FMN-oxidoreductase, was used as a model biological object. Activation of bioluminescence at the initial stage of thorium-232 exposure (up to 50 min) and an increase in the content of reactive oxygen species after 50 min of exposure were observed. The relationship between the intensity of bioluminescence and the content of reactive oxygen species (correlation coefficient of –0.86) was shown. The presence of humic substances neutralized the activating effect of thorium and reduced the content of reactive oxygen species to a control level. The effect of humic substances on the rate of the NADH-dependent enzymatic redox process has been demonstrated. The results we obtained contribute to the understanding of the molecular mechanisms of thorium-232 exposure and the neutralization of its effect on enzymatic processes.