Protective Effect Of Metformin On Ionizing Radiation-induced Injury Of Hematopoietic Immune System

The victims of nuclear accident and cancer patients treated with radiation therapy might develop different radiation injuries. The hematopoietic system is hypersensitive to radiation, which can lead to the bone marrow suppression and even individual death. There are currently no effective treatment methods for radiation injuries and newer strategies are urgently needed to protect hematopoietic system from radiation injury. Metformin is a widely used drug for treatment of type II diabetes. In recent years, studies have found that metformin has an antioxidant and anti-aging effect. And it inhibits mTOR activity through the LKB1-AMPK pathway. But its radioprotective effect has not yet been reported. In present study the protective effects of metformin on radiation injury of hematopoietic immune system and underlying mechanisms were investigated.In order to study the metformin protection in hematopoietic immune system of radiation injury mice, we divided C57BL/6 mice into three groups, including the control group, the irradiation group and the treatment group. Metformin can increase the survival rate of mice exposed to lethal dose (7.2Gy) total body irradiation(TBI) in 30 days survival experiment. In vivo experiments were studied in mice exposed to 4Gy TBI. Metformin can increase the irradiated mice’peripheral blood cell count, bone marrow nucleated cell count and the endogenous colony forming unit of spleen(endoCFUs). CFU-GM and CAFC experiments showed that 4Gy exposure can cause hematopoietic progenitor cell(HPC) and hematopoietic stem cell(HSC) injury. Metformin can improve HPC and HSC proliferation ability. In the experiments of bone marrow competition transplant, the studies have shown that metformin can improve HSC long-term replantation ability of irradiated mice. In addition, we also carried out a thorough research of radioprotective mechanism of metformin. Our studies have shown that metformin could reduce reactive oxygen species(ROS) level in irradiated mice hematopoietic cells. The qRT-PCR experiments have shown that metformin could reduce irradiated mice hematopoietic cells NOX4mRNA expression level, which is associated with lower level of ROS in the hematopoietic cells. Our research of p16mRNA expression and apoptosis of hematopoietic cells showed that metformin could reduce irradiated mice hematopoietic cells p16mRNA expression level and could not affect the cell apoptosis rate. The results indicate that metformin protection on radiation injury of hematopoietic system is associated with the aging of hematopoietic cells and irrelevant to the apoptosis pathway. The analysis results of genome-wide expression profile chip showed that mTOR, S6K, S6 gene expression in irradiation mice HSCs has been up-regulated. Metformin can inhibit the activity of mTOR pathway.In summary, we systematically studied the radioprotective effect of metformin on irradiated hematopoietic immune system for the first time. Our studies demonstrate that metformin has the protective effect on HSC damage in 4Gy irradiation mice. The protective effect was a result of decrease in oxidative stress levels and ageing in HSCs and HSC oxidative stress levels are associated with NOX4mRNA expression level. It might also be associated with metformin regulation of mTOR pathway. Our studies suggest that metformin could be an effective novel pharmacologic agent in treating hematopoietic system radiation injury and it could have potential value in improving the prognosis and survival of cancer patients undergoing radiotherapy and victims of radiation accident.