Explore Of Mitochondrial DNA Deletion As Radiation Biological Dosimeter

The study include two parts contents.Part1Influence of different types of rays and different cell radiosensitivity on mtDNA deletionsObjective To verify mtDNA deletion as a potential biological radiation dosimeter, it is necessary to study the relationship between mtDNA deletion and cell radiosensitivity and ray type. To study mtDNA deletions irradiated by different types of rays and mtDNA deletions of cells with different radiosensitivity irradiated by the same ray.Methods T lymphocyte Jurkat, Clone E6-1were cultured for72h after irradiated by y ray at the doses of0,0.1,0.5,2,5and10Gy, and irradiated by α-particle at the doses of0,0.1,0.2,0.5,1and2Gy. Hepatoma cells PLC and Hep3B were cultured for72h after irradiated by y ray at the doses of0,0.1,0.2,0.5,1,5and10Gy. Mitochondrial DNA4934bp and4977bp deletions before and after the irradiation were detected by real-time polymerase chain reaction after DNA were extracted.Results There were no obvious differences between expression of mtDNA4977bp deletions irradiated by low doses of y ray. Expression of mtDNA4977bp deletion showed a dose-response relationship. MtDNA4977bp deletion increased with doses. Compared to y ray, mtDNA4977bp deletion had higher level after irradiated by a particle at the dose of0.5Gy, difference was statistically significant (t=8.006, P<0.05).4934bp deletion increased with irradiation doses which were less than0.5Gy when irradiated by α-particle. But mtDNA4934bp deletion showed no apparent regularity after irradiated by y ray. When irradiated at the same doses, differences of mtDNA4934bp deletion between a-particle and y ray were not statistically significant. MtDNA4977bp deletion of Hep3B cell with higher radiosensitivity showed higher level than PLC cell with lower radiosensitivity at the doses of0.1,0.2and1Gy, t=5.98,7.163and3.039(P<0.05), the differences were statistically significant. But mtDNA4934bp deletion of cells with high radiosensitivity was not necessarily higher at the same radiation dose, and there was no obvious relationship between mtDNA4934bp deletion and cell radiosensitivity.Conclusion The type of rays should been taken into account for estimating exposure doses accurately. There was relationship between mtDNA4977bp deletion and radiosensitivity, which was not found between mtDNA4934bp deletion and radiosensitivity. Part2Time and dose effect relationship of the human peripheral blood mitochondrial DNA deletions induced by137Csγ rayObjective Ionizing radiation and chemicals can induce mtDNA deletion, but specificity, time-effect and dose-effect are still uncertain. We use real-time PCR to study the time and dose effect of the human peripheral blood mitochondrial DNA4934bp and4977bp deletion induced by137Csγ ray and provide theoretical basis on its implication in biological dosimetry.Methods The peripheral blood of five healthy adults were collected and irradiated with137Cs y-rays. The peripheral blood of one healthy adult was irradiated at the dose of5Gy and cultured for2,24,48and72h. The peripheral blood of other four healthy adults were cultured for2h after irradiated at the doses of0,0.5,1,2,5and10Gy. The peripheral blood mitochondrial DNA4934bp and4977bp deletions before and after the irradiation were detected by real-time polymerase chain reaction and gel electrophoresis. The dose-effect curves were fitted using Curve Expert1.4Software.Results Mitochondrial DNA4934bp and4977bp deletions induced by137Csγ ray increased after irradiating for2h, mtDNA4934bp deletion had comparative high level at2h and48h (t=10.782and8.966, P<0.05), and mtDNA4977bp deletion reached the highest level at48h (t=7.433, P<0.05). Mitochondrial DNA4934bp (t=2.895～8.105, P<0.05) and4977bp deletion (t=3.006～7.715, P<0.05) irradiated by0.5～10Gy137Csγ ray increased with increasing of irradiation dose in a dose-dependently manner. Mitochondrial DNA4977bp deletion was higher than4934bp deletion for those samples exposed with same dose of irradiation, especially at10Gy, the difference was more obvious (t=2.919, P<0.05), which suggested that4977bp deletion might be more sensitive than4934bp deletion at high dose. The dose-effect equation for4934bp deletion and4977bp deletion were Y1=1.178+0.1219D (R2=0.9269) and Y22=1.2578+0.1933D (R2=0.9016), respectively.Conclusion Mitochondrial DNA deletion was associated with radiation exposure, and it may be a available method for biological dose estimation and prognostic evaluation.