Abstract
AimThe 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 [131I]NaI. In this approach, we tried to mimic ex vivo the irradiation of patient blood in the first hours after radioiodine therapy.Material and methodsBlood 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 [131I]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).ResultsThirty-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−1, which is in good agreement with data obtained from external irradiation with γ- or X-rays.ConclusionThis 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 131I exposure is comparable to that of external irradiation with γ- or X-rays.
Highlights
As stated in a recent position paper of the European Association of Nuclear Medicine (EANM) [1], studying the induction and repair of radiation-induced DNA damage is of high interest for clinical applications of ionizing radiation as it may differ in comparison to external beam radiotherapy
European Journal of Nuclear Medicine and Molecular Imaging the damage sensor 53BP1 to the surrounding chromatin domain [8, 9] where it co-localizes with γ-H2AX [10] to form microscopically visible foci. 53BP1 recruitment influences DNA damage repair pathway choice and contributes to the repair of double-strand breaks (DSBs) in heterochromatin [11, 12]
This is in line with studies of the DNA damage focus assay by Horn et al [21] and Mariotti et al [22], who discovered that the number of radiation-induced foci (RIF) per cell decreases over time with the onset of DNA repair and follows a biexponential function
Summary
As stated in a recent position paper of the European Association of Nuclear Medicine (EANM) [1], studying the induction and repair of radiation-induced DNA damage is of high interest for clinical applications of ionizing radiation as it may differ in comparison to external beam radiotherapy (e.g. see [2,3,4]).For the detection of DNA double-strand breaks (DSBs) in the low-dose range, the biomarkers γ-H2AX and 53BP1 are widely used. As stated in a recent position paper of the European Association of Nuclear Medicine (EANM) [1], studying the induction and repair of radiation-induced DNA damage is of high interest for clinical applications of ionizing radiation as it may differ in comparison to external beam radiotherapy (e.g. see [2,3,4]). European Journal of Nuclear Medicine and Molecular Imaging the damage sensor 53BP1 to the surrounding chromatin domain [8, 9] where it co-localizes with γ-H2AX [10] to form microscopically visible foci. DSB foci disappear by 53BP1 dissociation and γ-H2AX dephosphorylation after DSB repair has been completed [11, 16]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: European Journal of Nuclear Medicine and Molecular Imaging
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
