Limited mutagenesis of myelokaryocytes following acute external irradiation as a protective mechanism of miliacin in radiation-induced immunosuppression

Antimutagenic effect of the plant triterpenoid miliacin was studied, in order to characterize its protective properties in a model of acute irradiation immunosuppression using outbred male mice. Ionizing irradiation at different doses (0.5; 1.0; 2.0; 4.0 Gy) was used for experimental (miliacin-treated), and control animals that received the miliacin solvent. Miliacin was administered three times intraperitoneally at a single dose of 4.0 mg/kg with 24-hour intervals between injections. The last dose was applied 1 day before irradiation. Myelokaryocytes served as test objects, the analysis of which was carried out 24 hours after irradiation. Miliacin had a certain protective effect by limiting the post-radiation myeloablation, reducing the number of aberrant cells and the total number of aberrations. Protective effect of triterpenoids showed inverse relation to the radiation dose, being most pronounced at the dose of 0.5 Gy. Higher values of chromatid aberrations at radiation doses of 1.0 and 2.0 Gy in animals from the experimental group versus control mice, probably, due to anti-apoptotic effect of the triterpenoid, thus ensuring higher survival rates of mutated cells with severe damage to their genome. The protective effect of miliacin at 24 hours after radiation exposure may indicate its effect on the primary radiochemical stage of radiation injury. It is suggested that the mechanism of protective action of triterpenoid is mediated by its previously shown antioxidant activity, due to its ability to stabilize membranes and normalize expression of genes encoding antioxidant protection enzymes. Thus, the antimutagenic activity of miliacin after irradiation is an important characteristic of its immunoprotective effect during the radiation-induced immunosuppression. With respect to its ability to limit the mutagenic effect, miliacin may be classified as a weak radioprotective antimutagen with a protection efficiency of 20-40% at the dose range of 0.5 to 1.0 Gray.