Low Dose Radiation Induced Heart Disease In Rats And Its Mechanism

Objective: In this study,In this study,we established SD rat model with low-dose radiation-induced heart injury to observe the degree and morphological changes of RIHD caused by low-dose irradiation over time,and its potential pathology,molecular biology mechanism and influencing factors,aiming at providing some experimental basis for the treatment and prevention of RIHD.Methods:125 SD rats were used as experimental animals and randomly divided into 5 groups: 4different doses of irradiation groups and a control group,25 rats per group.Irradiation group were treated with 10 Gy,15Gy,20 Gy,25Gy chest irradiation,5Gy / times,once a day.At 1,2,3,6 months and 1 year after irradiation,5 rats were dissected in each group,and real-time quantitative PCR was performed to detect the expression of TGF-β1、CTGF mRNA in cardiac tissue;Western blotting was used to detect the expression of TGF-β1 and Smad3 protein.The degree of heart injury after irradiation was evaluated by hematoxylin-eosin staining,and the situation of myocardial fibrosis was assessed by Masson staing.Myocardial ultrastructure was observed by transmission electron microscope.Results: 1.Histological evaluation: 1.1 Results of HE staining optical microscope: In the early stage of radiation,the myocardium mainly exhibits inflammatory exudation,mild fibrosis began to appear in group 15 Gy at 3 months after irradiation,with the increase of dose,fibrosis gradually increased and spread to the interstitium of myocardium.Over time,20 Gy,25Gy group showed more obvious myocardial fibrosis and progressive increased.1.2 Masson staining results: 1.2.1 Two months after irradiation: Group 20Gy: a little blue fiber around the blood vessels can be observed.Group 25Gy: blue dye in myocardial cell interstitial and around the blood vessels slightly increased.1.2.2 Three months to one year after irradiation: Group 15Gy、20Gy、25Gy: myocardial fibrosis increases with increasing dose.2.Transmission electron microscopy observation results: Early RIHD was mainly manifested in mitochondrial damage,1 months after irradiation,only partialmitochondrial swelling was observed.At 2 months and 3 months after irradiation,20 Gy group and 25 Gy all showed different degrees of mitochondrial cristae deletion,cavitation and even medullary degeneration.Collagen fiber deposition appeared in the gap of cardiomyocytes at 3 months after irradiation.3.Detection results of TGF-β1and CTGF mRNA testing: 3.1 TGF-β1 mRNA levels: 1month after irradiation:compared with the normal group,the expression of TGF-β1 mRNA in each irradiated groups was higher than that in normal control group(P <0.05).The expression of TGF-β1 mRNA in Group 15 Gy and 25 Gy was significantly higher than that in control group(P <0.05).6 months and 1year after irradiation,the irradiated groups were higher than that of the control group,and there was significant difference in group25Gy(P < 0.05).3.2 CTGF mRNA levels: 1 month after irradiation,the expression of in the group 10 Gy was lower than that in the control group,but there was no significant difference(P > 0.05).The expression of groups 15 Gy,20Gy and 25 Gy were higher than those of control group and group 10 Gy,group 25 Gy was significantly higher(P < 0.05).At 6 months and 1 year after irradiation,the expression of CTGF mRNA in each irradiation group was higher than that in the control group,and the group 25 Gy was significantly higher than that in the control group(P < 0.05).4.Protein detection results: 4.1 Detection of TGF-β1 protein: 1month and 6months after irradiation,the expression of TGF-β1 protein was significantly increased in each irradiation group(P < 0.05);After irradiation for 1years compared with the control group,the expression of TGF-β1 protein increased significantly in group 25Gy(P < 0.05).Compared with group 10 Gy,the expression of TGF-β1 protein was significantly increased in group 25Gy(P < 0.05).4.2 Detection of Smad3 protein: the expression of Smad3 protein in 20 Gy and 25 Gy groups was significantly higher than that in control group(P <0.05).Compared with group 10 Gy,the expression of smad3 protein in group 20 Gy and 25 Gy was significantly higher(P<0.05).Compared with group 15 Gy,the expression of smad3 protein in group 20 Gy was significantly higher(P <0.05).6 months after irradiation the expression of Smad3 protein in group 20 Gy and group 25 Gy was significantly higher than that in control group(P <0.05).Compared with group 10 Gy,the expression of Smad3 protein ingroup 20 Gy and 25 Gy was significantly higher(P <0.05).Conclusion: 1.Early exposure to radiation can lead to the change of myocardial inflammation,over time20 Gy,25Gy irradiation appears more obvious fibrosis and progressive increased.2.10 Gy can also cause myocardial fibrosis in the late stage of irradiation.3.The occurrence of early RIHD may be related to radiation damage caused by mitochondrial metabolic abnormalities,oxidative stress and DNA damage.4.TGFbeta /Smad signaling pathway and its downstream mediator CTGF probably play a role in radiation-induced cardiac injury.