Glycyrrhizic Acid Alleviates The Occurrence Of Radiation Pneumonia By Affecting The Polarization Of M1 Macrophages After Irradiation

Background: The essence of Radiation induced Lung Injury(RILI)is lung injury caused by radiation,which is well known as a common complication of thoracic radiotherapy for patients with thoracic malignant tumor.Radiation induced Pneumonia(RIP)is an early manifestation of RILI.At present,there are not enough drugs to treat radiation pneumonia.Corticosteroids are the most commonly used treatment for radiation-induced symptomatic pneumonia.Corticosteroids can relieve some symptoms,but do not prevent the development of RILI.Glycyrrhizic acid(GA)is a kind of biological agent extracted from licorice and has been widely used for liver protection and anti-inflammatory effects.GA plays a significant anti-inflammatory role in many inflammatory models(hepatitis,enteritis,etc.).At present,there are few reports on the anti-inflammatory effect of GA on RIP,and the anti-inflammatory mechanism of GA in radiation pneumonia is still unclear.Purpose: In this study,mononuclear macrophage RAW264.7 of mouse origin was taken as the research object,and the irradiated RAW264.7 was co-cultured with mouse lung epithelial cells MLE-12 to simulate the process of radiation lung injury in vitro,so as to explore the clinical application of GA that may help delay or reduce the occurrence of radiation pneumonia.Material and methods: RAW264.7 cells were treated with glycyrrhizic acid of different concentration gradients and irradiation of different dose gradients.The proliferation-inhibition of cells was detected by MTT method,and the histograms of drug concentration-growth inhibition rate and dose gradient-growth inhibition rate were drawn respectively.The levels of nitric oxide synthase(i NOS),a polarization marker in RAW264.7,were detected by Western blotting.The synthesis of RAW264.7inflammatory cytokines(tumor necrosis factor/TNF,Interleukin-6/IL-6,Interleukin-1β)were detected by ELISA.Results: MTT results showed that within a certain range,with the increase of GA concentration,the inhibition degree of RAW264.7 did not change significantly,glycyrrhizic acid had no obvious toxic and side effects on RAW264.7 cells.In a certain range,the inhibition degree of RAW264.7 increased with the increase of irradiation dose.The results of Western blot indicated that RT induced the production of more M1 polarization marker inducible nitric oxide synthase(INOS)in RAW264.7cells with the increase of dose,and induced its polarization toward M1 macrophages.At 5 Gy,obvious polarization began to appear.The addition of GA can reduce the polarization of macrophages after irradiation.Elisa results showed that GA significantly reduced the production of various inflammatory cytokines(TNF,IL-6,IL-1β).Conclusions: Glycyrrhizic acid can reduce or relieve the occurrence of inflammation by inhibiting the M1 polarization of macrophages after irradiation and inhibiting the release of proinflammatory cytokines in macrophages.The clinical application of glycyrrhizic acid may help to delay or reduce the occurrence of radiation pneumonia.