PDTC Attenuates Radiation Induced Heart Damage Through Inhibition Of Inflammation Pathway In Rats

Objective: The aim of this study is to examine the histopathological changes of myocardium at early stage in a rat model of radiation induced heart damage(RIHD),and to explore the potential mechanisms,and further to examine cardioprotective effects of pyrrolidine dithiocarbamate(PDTC)on the inhibition of NF-?B activation on RIHD.Methods: 21 Male adult Sprague-Dawley(SD)rats were randomly divided into three groups: Control Group(Control),Irradiation Group(IR)and PDTC + Irradiation Group(PDTC+IR).Each group consists of 7 rats.1 Radiation: Rats in Irradiation group and PDTC+ Irradiation group were subjected to local heart irradiation(2.0 x 2.0 cm size of the radiation field,the depth of 1.5 cm)with a single fraction of 20.0 Gy(at a dose rate of 1.8Gy/min)from a precise type medical high-energy linear accelerator producing6 MV X-ray.2 PDTC treatment: PDTC dose is calculated on the basis of body weight(120mg/kg).PDTC were injected intraperitonally 30 min prior to radiation exposure in PDTC + Irradiation group,then PDTC was given regularly once a day until the 14 th day,whereas Control group and Irradiation group were given the same volume of normal saline daily.3 Histopathological evaluation: Alterations of morphological structure of myocardial cell,fibroblast or interstitial tissues were examined by HE staining and the distribution of collagen fiber was analyzed by Masson staining,which can be used assess myocardial fibrosis.4 Biochemical assays in rat cardiac tissues: The protein expression levels of NF-? B members P50 and P65,hypoxia-inducible factor 1 ?(HIF-1 ?),connective tissue growth factor(CTGF),as well as collagen type ?(COL-1),were quantitatively analyzed by Western blot.The mRNA expression levels ofthe above factors were determined by Quantitative Real-time PCR(qPCR).Results:1 Histopathological evaluation:(1)HE staining from paraffin section:Irradiation induced significantly myocardial edema,derangement,some myocardial cells rupture and nucleus mild contraction,staining deepened,a small profiled nucleus,visible myocardial interstitial inflammatory cell infiltration accompanied by increased fibroblast.Treatment with PDTC to some extent improved damages as mentioned above.(2)Masson's trichrome staining: All the collagen fiber was stained as blue-green.Collagen fibers in Irradiation group are widely distributed at the interstitial tissue and increased significantly compared with the control group.Normal myocardial cell have a tendency to be replaced.As a result of quantitative analysis,radiation induced a significant increase in collagen volume fraction(CVF)(P<0.05),but such a deposition of collagen was reduced by PDTC treatment(P<0.05).2 Western blot and qPCR analysis:(1)The expression of P50?P65 and HIF-1 ? was increased by irradiation in both protein and mRNA levers(P <0.05 for both)by irradiation and were decreased after treatment with PDTC(P<0.05 for both).(2)The expression of CTGF were increased by irradiation in both protein and mRNA levers(P < 0.05 for both),but there is only a general tendency that were decreased after treatment with PDTC(P>0.05 for both).(3)Irradiation resulted in the upregulation of COL-1 in both protein and mRNA levers(P < 0.05 for both)and was decreased after treatment with PDTC in protein lever(P < 0.05),but in mRNA lever it was just showing a declining tendency after treatment with PDTC(P>0.05).Conclusions:1 Radiation exposure can cause myocardial cell inflammation,activate the pathway of inflammatory response.Pathological tissue slice observation showed visible myocardial cell edema,cell interstitial inflammatory cells infiltration.2 Radiation can induce myocardial fibrosis in the early days,pathological tissue slice observation showed regulation of fibroblast and collagen fiber.3 Radiation exposure can cause the upregulation of HIF-1?,CTGF both in protein and mRNA levers,which may be associated with myocardial inflammation and fibrosis.4 PDTC can inhibit excessive activation of NF-?B inflammatory pathway,reducing radioactive myocardial inflammation and fibrosis,and resulted the decrease of HIF-1 ?,suggesting that RIHD at early stage is able to be improved to some extent by inhibition of inflammation and HIF-1 ?transcription.