In Vivo Induction of Cytokine mRNA and Protein in Mice by the Radioprotectant Steroid 5-Androstenediol.

Abstract

We previously showed 5-androstenediol (5-AED) injected sc enhanced survival in mice exposed to whole-body gamma-irradiation, ameliorated radiation-induced neutropenia in mice, dogs, and monkeys, and induced increases in bone marrow GM-CFC in irradiated mice. Radiation-induced decreases in platelets, natural killer cells, red blood cells, and monocytes were also blunted by the steroid. Administration of 5-AED caused functional activation of circulating granulocytes (phagocytic ability), monocytes (oxidative burst), and natural killer cells (surface CD11b expression). To test our hypothesis that 5-AED acts via initiation of a cytokine cascade in hematopoietic tissue, we performed real time quantitative PCR on spleen samples taken from mice and correlated the results with serum ELISA. PCR was performed for mRNAs of GM-CSF, IL-6, IL-10, IL-12, and IFNg. Spleens and serum were taken at 3 time points: 4 h after 5-AED or vehicle (PEG-400) injection, and 4 or 24 h after irradiation (7.5 Gy whole-body gamma) or sham-irradiation. Each group contained 5 mice. Results were analyzed by 2-way ANOVA for PCR results 4 and 24 h after irradiation, and by a t-test 4 h after injection. Radiation alone induced increases in mRNAs for all cytokines at both 4 and 24 h, except for IFNg, which was not elevated at 4 h. 5-AED alone did not induce a significant increase for any cytokine, but the increases bordered on significance for IL-12 at 4 h after irradiation or sham-irradiation (28 h after injection, p = 0.07), and for GM-CSF 24 h after irradiation or sham-irradiation (48 h after injection, p = 0.08). There was a significant positive interaction between radiation and 5-AED for IL-6, 4 h after irradiation (p = 0.006). The interaction effect bordered on significance for IL-12 4 h after irradiation (p = 0.07) and for GM-CSF 24 h after irradiation (p = 0.10). ELISA for serum cytokine protein was measured for G-CSF, IL-6, IL-10, and IL-12. Results were analyzed by the Mann-Whitney test for exact p-values. IL-6 was not detected in serum. G-CSF was detected 4 and 24 h after irradiation or sham-irradiation only in 5-AED-treated mice. IL-10 and IL-12 were detected only 24 h after irradiation, and the values in 5-AED-treated mice were significantly higher than those in vehicle-treated mice (p = 0.02). The results support our hypothesis that the previously observed increases in numbers of circulating innate immune cells and platelets, and functional activation of granulocytes, monocytes, and NK cells, result from a cytokine cascade induced by 5-AED.