Valizadeh M, Shirazi A, Izadi P, Tavakkoly Bazzaz J, Rezaeejam H
Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran.
Department of Medical Genetics, Tehran University of Medical Sciences, Tehran, Iran.
J Biomed Phys Eng. 2017 Mar 1;7(1):27-36. eCollection 2017 Mar.
After radiation therapy (RT), some health hazards including DNA damages may occur where melatonin can play a protective role due to free radical generation. On the other hand, serious accidental overexposures may occur during RT due to nuclear accidents which necessitate the need for study on exposure to high-dose radiations during treatments.
The aim of this study was to study the expression level of two genes in non-homologous end joining (NHEJ) pathways named Xrcc4 and Xrcc6 (Ku70) in order to examine the effect of melatonin on repair of DNA double-strand breaks (BSBs) caused by 8Gy ionizing radiation.
One hundred eight male Wistar rats were irradiated with a whole body gamma radiation dose of 8Gy with or without melatonin pretreatments. They were divided into six different groups of control, 100 mg/kg melatonin alone, 8Gy irradiation alone, vehicle alone, vehicle plus 8Gy irradiation and 100 mg/kg melatonin plus 8Gy irradiation. Peripheral blood samples were collected at 8, 24 and 48 h after irradiation. Ku70 and Xrcc4 gene expression were evaluated by real-time quantitative polymerase chain reaction (qPCR) technique and analyzed by one-way ANOVA test.
Expression of Ku70 and Xrcc4 genes normalized against Hprt gene showed significant difference in melatonin plus irradiation group at 8h compared to the control group (p<0.05). At 24h post irradiation, gene expression changes were significantly upregulated in irradiation-alone group as well as melatonin plus irradiation group (p<0.05). No significant change was found in any groups compared to control group at 48 h time point.
We concluded that, by increasing expression level of Ku70 and Xrcc4 genes, 100 mg/kg melatonin administration 8 and 24 h before 8 Gyionizing radiation can significantly affect the repair of DNA DSBs in NHEJ pathway.
放射治疗（RT）后，可能会出现包括DNA损伤在内的一些健康危害，而褪黑素由于能产生自由基，可能起到保护作用。另一方面，放疗期间可能因核事故发生严重的意外过度暴露，这使得有必要研究治疗期间高剂量辐射暴露的情况。
本研究旨在研究非同源末端连接（NHEJ）途径中两个名为Xrcc4和Xrcc6（Ku70）的基因的表达水平，以检验褪黑素对8Gy电离辐射所致DNA双链断裂（DSBs）修复的影响。
108只雄性Wistar大鼠接受全身8Gyγ射线照射，照射前分别给予或不给予褪黑素预处理。它们被分为六个不同的组：对照组、单独给予100mg/kg褪黑素组、单独8Gy照射组、单独给予赋形剂组、赋形剂加8Gy照射组和100mg/kg褪黑素加8Gy照射组。照射后8、24和48小时采集外周血样本。通过实时定量聚合酶链反应（qPCR）技术评估Ku70和Xrcc4基因表达，并通过单因素方差分析进行分析。
与对照组相比，在8小时时，以Hprt基因为对照进行标准化后的Ku70和Xrcc4基因表达在褪黑素加照射组有显著差异（p<0.05）。照射后24小时，单独照射组以及褪黑素加照射组的基因表达变化显著上调（p<0.05）。在48小时时间点，与对照组相比，任何组均未发现显著变化。
我们得出结论，在8Gy电离辐射前8小时和24小时给予100mg/kg褪黑素，通过增加Ku70和Xrcc4基因的表达水平，可显著影响NHEJ途径中DNA DSBs的修复。
