Mechanism and Functional Parameter of Myocardial Damage Induced by Low-Dose Radiation in Rats

Abstract

Radiation induced heart damage (RIHD) is the leading cause of non-cancer-related deaths in patients receiving thoracic radiotherapy. The mean cardiac dose (MHD) of normal tissue tolerance in NCCN guidelines for radiotherapy has been continuously decreased from 35 Gy in 2017 to 2020 20 Gy, indicating there is controversy of MHD that how much dose could control cardiac radiation damage better. In this study, 15 Gy/3f (BED = 40 Gy) low-dose irradiation of SD rat heart was used to explore the mechanism and functional parameter changes of RIDH caused by low-dose irradiation, and to explore the effect of combining recombinant human endostatin (E).75 SD adult male rats were randomly divided into control group (C, E, MHD25) and experimental group (MHD15, MHD15+E). A single dose 5 Gy/f, once per day, continuous irradiation 3d or 5d. After the irradiation, the E group and MHD15+E group were given recombinant human endostatin 6mg/kg intraperitoneal injection, once per day, for 14 consecutive days. At 24h, 48h and 15d after the intervention, the blood of the rats was taken to measure CK, CK-MB, LDH and CRP. At 1, 3 and 6 months, 5 rats after cardiac echocardiography was performed in each group were randomly killed and myocardial tissues were collected for Masson staining, Western Blot and qPCR. Two-way ANOVA statistics.There was no difference in LDH, CK, CK-MB, and CRP in the same time period among the groups at 24h, 48h, and 14d after intervention (P > 0. 05). Compared with group C, the EF and FS of the MHD25, MHD15 and MHD15+E group all decreased at 3 months (P < 0.05), and the degree was similar (P > 0.05). The EF and FS of the MHD25, MHD15 and MHD15+E group also decreased at 6 months (P < 0.05), and the degree was similar (P > 0.05). Comparing 6 months with 1 month, EF and FS of each group decreased (P < 0.01). Myocardial fibrosis MHD25 group appeared after 3 months of irradiation. Myocardial collagen volume fraction (CVF) increased (P < 0.05), and TGF-β1, P-smad2, Collagen-I protein expression increased (P < 0.05), and TGF-β1, Smad, Collagen-I gene expression increased (P < 0.05). The MHD15 and MHD15+E group showed the above changes at 6 months, and the degree of increase of the above-mentioned protein and gene expression was lower than that of the MHD25 group (P < 0.05). The expressions of the above-mentioned proteins and genes in the MHD15+E group were higher than those in the MHD15 group (P < 0.05). The protein level of Smad2 was similar in each group (P > 0.05).SD rat heart 15 Gy/3f (BED = 40 Gy) low-dose irradiation cause cardiac function damage in the early stage and myocardial fibrosis in the late stage, the appearance delayed and degree is lower than that of high-dose irradiation. On the basis of low-dose irradiation, combined with recombinant human endostatin increase the expression of related factors of TGF-β/Smad signaling pathway. Echocardiography may be able to predict the occurrence of RIDH early, but serological predictive indicators have yet to be found.