Department of Nuclear Medicine, University of Würzburg, Würzburg, Germany.
Bundeswehr Institute of Radiobiology affiliated to the University of Ulm, Munich, Germany.
Eur J Nucl Med Mol Imaging. 2022 Apr;49(5):1447-1455. doi: 10.1007/s00259-021-05605-8. Epub 2021 Nov 13.
The aim of this study was to provide a systematic approach to characterize DNA damage induction and repair in isolated peripheral blood mononuclear cells (PBMCs) after internal ex vivo irradiation with [I]NaI. In this approach, we tried to mimic ex vivo the irradiation of patient blood in the first hours after radioiodine therapy.
Blood of 33 patients of two centres was collected immediately before radioiodine therapy of differentiated thyroid cancer (DTC) and split into two samples. One sample served as non-irradiated control. The second sample was exposed to ionizing radiation by adding 1 ml of [I]NaI solution to 7 ml of blood, followed by incubation at 37 °C for 1 h. PBMCs of both samples were isolated, split in three parts each and (i) fixed in 70% ethanol and stored at - 20 °C directly (0 h) after irradiation, (ii) after 4 h and (iii) 24 h after irradiation and culture in RPMI medium. After immunofluorescence staining microscopically visible co-localizing γ-H2AX + 53BP1 foci were scored in 100 cells per sample as biomarkers for radiation-induced double-strand breaks (DSBs).
Thirty-two of 33 blood samples could be analysed. The mean absorbed dose to the blood in all irradiated samples was 50.1 ± 2.3 mGy. For all time points (0 h, 4 h, 24 h), the average number of γ-H2AX + 53BP1 foci per cell was significantly different when compared to baseline and the other time points. The average number of radiation-induced foci (RIF) per cell after irradiation was 0.72 ± 0.16 at t = 0 h, 0.26 ± 0.09 at t = 4 h and 0.04 ± 0.09 at t = 24 h. A monoexponential fit of the mean values of the three time points provided a decay rate of 0.25 ± 0.05 h, which is in good agreement with data obtained from external irradiation with γ- or X-rays.
This study provides novel data about the ex vivo DSB repair in internally irradiated PBMCs of patients before radionuclide therapy. Our findings show, in a large patient sample, that efficient repair occurs after internal irradiation with 50 mGy absorbed dose, and that the induction and repair rate after I exposure is comparable to that of external irradiation with γ- or X-rays.
本研究旨在提供一种系统的方法来描述内部离体照射[I]NaI 后分离的外周血单个核细胞（PBMC）中的 DNA 损伤诱导和修复。在这种方法中，我们试图模拟放射性碘治疗后患者血液的离体照射。
来自两个中心的 33 名患者的血液在分化型甲状腺癌（DTC）的放射性碘治疗前立即采集，并分为两份样本。一份样本作为未照射对照。将第二份样本暴露于电离辐射，向 7ml 血液中加入 1ml [I]NaI 溶液，然后在 37°C 孵育 1 小时。两份样本的 PBMC 均被分离，每份样本分为三份，（i）直接在照射后（0 小时）固定在 70%乙醇中并储存在-20°C 下，（ii）在 4 小时后，以及（iii）在 24 小时后，在 RPMI 培养基中培养。在显微镜下用免疫荧光染色后，对每个样本的 100 个细胞中肉眼可见的共定位 γ-H2AX+53BP1 焦点进行评分，作为辐射诱导的双链断裂（DSB）的生物标志物。
33 个血样中有 32 个可以分析。所有照射样本的血液平均吸收剂量为 50.1±2.3mGy。所有时间点（0 小时、4 小时、24 小时）的细胞中 γ-H2AX+53BP1 焦点的平均数量与基线和其他时间点均有显著差异。照射后细胞中辐射诱导焦点（RIF）的平均数量在 t=0 小时时为 0.72±0.16，在 t=4 小时时为 0.26±0.09，在 t=24 小时时为 0.04±0.09。三个时间点的平均值的单指数拟合提供了 0.25±0.05h 的衰减率，这与γ或 X 射线外照射获得的数据非常吻合。
本研究提供了关于放射性碘治疗前患者体内照射后 PBMC 中离体 DSB 修复的新数据。我们的发现表明，在一个大的患者样本中，在吸收剂量为 50mGy 的内照射后，有效的修复发生了，并且 I 暴露后的诱导和修复率与γ或 X 射线的外照射相当。
