超高剂量率照射诱导质粒DNA链断裂损伤的研究

Ultra-high dose rate irradiation induced DNA strand break in plasmid DNA

目的对比分析超高剂量率(FLASH)和常规剂量率电子线照射在诱导DNA链断裂损伤中的作用,探讨FLASH效应是否与照射诱导的DNA链断裂损伤减少有关。方法在生理氧含量(4%)和空气氧含量(21%)条件下,对置于超纯水的pBR322质粒DNA分别实施FLASH(125 Gy/s)和常规(0.05 Gy/s)照射。通过琼脂糖凝胶电泳实验检测开环带DNA和线性带DNA发生情况。进一步应用自由基清除剂Samwirin A(SW)清除电离辐射产生的自由基,分析清除自由基对开环带DNA和线性带DNA形成的影响。最后,量化质粒DNA损伤并采用数学模型计算FLASH照射后产生开环带DNA和线性带DNA的相对生物效应(RBE)。结果生理氧含量下,FLASH和常规照射所诱导DNA链断裂损伤呈现出剂量依赖性。其中,超纯水中,FLASH照射诱导的线性带DNA生成率较常规照射显著降低(t=5.28、5.79、7.01、7.66,P<0.05)。采用SW预处理后,FLASH和常规照射后质粒DNA链断裂损伤差异无统计学意义(P>0.05)。当氧含量为21%时,FLASH照射与常规照射导致DNA损伤效应无差别,且均较生理氧含量时明显增加。此外,FLASH照射每Gy诱导线性带DNA和开环带DNA的损伤速率分别为常规照射的(2.78±0.03)和(1.85±0.17)倍。结论FLASH照射较常规照射减轻正常组织放射损伤主要与电离辐射后自由基产生有关,FLASH效应受氧含量的影响。

Objective To compare the effects on DNA strand break induced by ultra-high dose rate(FLASH)electron beam and conventional irradiation,and investigate whether FLASH effect was correlated with a reduction of radiation response.Methods Aqueous pBR322 plasmid was treated with FLASH(125 Gy/s)and conventional irradiation(0.05 Gy/s)under physioxia(4%O2)and normoxia(21%O2).Open circle DNA and linear DNA were detected by agarose gel electrophoresis,and the plasmid DNA damage was quantified with an established mathematical model to calculate the relative biological effect(RBE)of DNA damage.In some experiments,Samwirin A(SW)was applied to scavenge free radicals generated by ionizing radiation.Results Under physioxia,the yields of DNA strand breakage induced by both FLASH and conventional irradiation had a dose-dependent manner.FLASH irradiation could significantly decrease radiation-induced linear DNA compared with conventional irradiation(t=5.28,5.79,7.01,7.66,P<0.05).However,when the aqueous plasmid was pretreated with SW,there was no difference of DNA strand breakage between FLASH and conventional irradiation(P>0.05).Both of the yields of open circle DNA and linear DNA had no difference caused by FLASH and conventional radiotherapy at normoxia,but were significantly higher than those under physioxia.In addition,the yields of linear DNA and open circle DNA induced by FLASH irradiation per Gy were(2.78±0.03)and(1.85±0.17)times higher than those of conventional irradiation,respectively.Conclusions FLASH irradiation attenuated radiation-induced DNA damage since a low production yield of free radical in comparison with conventional irradiation,and hence the FLASH effect was correlated with oxygen content.