A Study Of The Impacts Of Human Mesenchymal Stem Cells On The Radiation-induced Lung Injury Of C57BL/6Mice

ObjectiveMesenchymal stem cells, with a capacity of self-renewal and a potential ofdifferentiation, originate in the early development stages of mesoderm and havecharacteristics of totipotent stem cells. Experiments show that mesenchymal stem cells areable to differentiate into a variety of systems, organs, tissues or cells in a specific cultureconditions, possessing advantages of low immunogenicity, immune regulation, targetedmigration. In recent years, mesenchymal stem cells provide new ideas and methods for thetreatment of many diseases, and showed preliminary efficacy. Besides, good results havebeen achieved in the treatment of myocardial infarction, traumatic spinal cord injury,congenital malformations of the neural tube, Parkinson’s, neurodegenerative diseases,diabetes, liver cell damage and other diseases. This study is aimed to explore the role ofhuman umbilical cord blood stem cell in the protection and repair of radiation-inducedlung injury. The first part aims to establish the animal model in line with the developmentprocesses of radiation-induced lung injury of humans, providing the foundation for thetreatment of human umbilical cord mesenchymal stem cells. The second part is to usethe animal models with acute radiation-induced lung injury, discussing the changes inlevels of proinflammatory cytokines and antiinflammatory cytokine and exploring thepreventive and therapeutic mechanisms of mesenchymal stem cells in radiation-inducedlung injury.MethodsPart one：Select the radiation-sensitive C57BL/6J mice as model carriers and randomly divide them into a control group, a small dose (6Gy) exposure group, a middledose (12Gy) irradiation group, a high-dose (18Gy) irradiation group. After the positioningof the simulator machine, according to different dosages, the whole lung of the mice is tobe irradiated and three different kinds of animal models of radiation-induced lung injuryare to be established. For a month, in4different time points, the mice’s general condition,average survival time, lung coefficient, the diagnosis of HE staining histological pathologyare to be observed and select the animal model group which is suitable for this experiment.In addition, detect the level of IL-1in the plasma of the mice and test the reliability of theanimal model.Part two：Devide randomly the animal model established in Part one into blankcontrol group, model+saline group and model+human umbilical cord mesenchymal stemcell therapy group. The latter two groups are established after their whole lungs aresuitably irradiated. Centrifugation and attachment culture are adopted to amplifymesenchymal stem cells.24hours later after the successful modeling, the culturedmesenchymal stem cells, via the tail vein, are to be injected into the mice group of themodel+human umbilical cord mesenchymal stem cell therapy group. For a month, in4different time points, observe the mice’s general condition, average survival time, lungcoefficient and the diagnosis of HE staining histological pathology and detect by ELISAthe levels of IL-1、IL-10、IL-13in the blood.ResultsAfter being radiated, there were increases in the lung water content in the three groupsof mice. For the mice group of small doses of radiation, their lung coefficient increase wasnot so significant. Compared to the blank control group, the increases of lung coefficient inthe group of middle doses of radiation and the group of large doses of radiation weredistinct（P＜0.05）. For the high-dose radiation group, at the seventh day after irradiation,their mortality was high. All mice died before the end of the experiment, and could notmeet the requirements of experimental observation. The three groups of mice have shownpathological manifestations of lung injury and the injuries are worsening with the increaseof the dosage. After detection, the vivo leukocyte interleukin-1in irradiated mice weresignificantly higher than normal levels (P <0.05). The radiation pneumonitis group and stem cell treatment group both had thepathological manifestations of lung injury, but comparatively speaking, the injuries in thelatter group decreased significantly. Besides, the two groups had dramatic differences inLung coefficient and pathological score（P＜0.05）. However, in average survival time,there were no significant differences between the two groups（P＞0.06）. ELISA analysisshowed that IL-1level in the radiation pneumonitis group were significantly higher thanthat in the control group (p <0.05). Compared with the radiation pneumonitis group,stem cell transplantation treatment group was significantly reduced (p <0.05). Comparedwith IL-10, IL-13levels in radiation pneumonitis model group, those levels in stem celltransplantation treatment group was significantly lower (p <0.05).Conclusion1. By irradiating the whole lung with ray irradiation of12Gy dose can animal modelsof radiation-induced lung injury in mice be successfully established; During the designingprocesses of animal models, the use of simulator machine has effectively guaranteed thecompleteness and accuracy of the irradiated lung field and in addition, it made the Brain,liver, kidney, spleen and other organs avoid the radiation line damage, reducingnon-experimental death of the mice and improving the success rate of the production ofanimal models.2. After being injected into the mice of radiation-induced lung injury via the tail vein,human umbilical cord mesenchymal stem cells can repair lung tissue damage, reduce thedevelopment of radiation pneumonitis and effectively keep radiation pneumonitis fromtransferring into the radiation-induced pulmonary fibrosis. It’s anti-inflammatorymechanism may be related to it’s inhibition of monocyte-macrophage cell’s synthesis andsecretion of IL-1and it’s promotion of monocyte-macrophage cell’s synthesis andsecretion of IL-10, IL-13.