Integration of new biological and physical retrospective dosimetry methods into EU emergency response plans : joint RENEB and EURADOS inter-laboratory comparisons

Purpose: RENEB, 'Realising the European Network of Biodosimetry and Physical Retrospective Dosimetry,' is a network for research and emergency response mutual assistance in biodosimetry within the EU. Within this extremely active network, a number of new dosimetry methods have recently been proposed or developed. There is a requirement to test and/or validate these candidate techniques and inter-comparison exercises are a well-established method for such validation. Materials and methods: The authors present details of inter-comparisons of four such new methods: dicentric chromosome analysis including telomere and centromere staining; the gene expression assay carried out in whole blood; Raman spectroscopy on blood lymphocytes, and detection of radiation induced thermoluminescent signals in glass screens taken from mobile phones. Results: In general the results show good agreement between the laboratories and methods within the expected levels of uncertainty, and thus demonstrate that there is a lot of potential for each of the candidate techniques. Conclusions: Further work is required before the new methods can be included within the suite of reliable dosimetry methods for use by RENEB partners and others in routine and emergency response scenarios

Characterization of cell cycle perturbances after exposure to I-123-iododeoxyuridine

Introduction: Due to the numerous short-range electrons ejected during a single decay of an Auger electron emitter (AEE), the biological effectiveness of AEE depends strongly on intracellular location. DNA-associated AEE possess the highest biological effectiveness per decay and are presumed to cause complex DNA lesions and cell cycle perturbances. The main goal of the study was to determine the average number of decay per cell necessary to induce a pronounced G2/M-arrest in human T-lymphoma Jurkat cells.Material & Methods: Synchronized Jurkat cells were exposed to I-123-iododeoxyuridine (I-123-UdR, 1-50 kBq/ml) for 20 h and co-labeled with 5-ethynyl-2'-deoxyuridine (EdU). Cell cycle was subsequently analyzed by flowcytometry (FACSCanto II, FACSDiva software, BD). General cellular uptake and DNA-incorporation of I-123-UdR in isolated DNA (DNeasy Blood & Tissue Kit; QIAGEN) was determined by gamma-counting (Perkin Elmer). Results: The percentage of G2/M-cells which are labeled with EdU increased 20 h after exposure to I-123-UdR/EdU from 26% in the control to 57%, 66% and 63% at 111, 417 and 3255 accumulated decays per cell, respectively. Simultaneously, the percentages of post-mitotic G1-cells which are fully labeled with EdU decreased from 38% in the control to 10%, 1% and 3% at 111, 417 and 3255 accumulated decays per cell, respectively. Approximately 93% of the cells were labeled with I-123-UdR/EdU after 20 h of exposure whilst ~ 90% of the I-123-UdR activity was located in the DNA. Conclusions: On average one decay every ~180 seconds of I-123 occurring in the genome of a Jurkat cell induces a massive G2/M-arrest. This coincides very well with observations in I-125-UdR exposed SCL-II cells, showing massive and persistent G2/M-arrest at similar decay rates. Decay rates as low as one decay every 12 minutes per genome induce massive but transient G2/M-arrest suggesting different damage levels for induction and escape of the G2/M arrest in human cells.Funded by Bundesministerium für Bildung und Forschung (BMBF), Project No.: 02NUK005

A comparative study on the cyto- and genotoxicity of the Auger electron emitter I-123- and I-125 in-vitro

The Auger effect is not yet fully understood in respect to the deposited energy as well as to the dose rate. Therefore, we studied the Auger electron emitter (AEE) I-123 and I-125 which are characterized by a different half-life (13.2 h vs. 59.4 d) and by different average numbers of Auger electrons emitted per decay (ratio I-123/I-125 ~ 1:2). The biological response in mammalian cells labelled with various activity concentrations of 5-(123)iodine-2'-deoxyuridine (I-123-UdR) and (5-(125)iodine-2'-deoxyuridine (I-125-UdR) was thoroughly investigated to further elucidate the biological effectiveness of these particular electron emitters. SCL-II cells were synchronized in G1-cell cycle phase, subsequently labelled with I-123- respectively I-125-UdR and the cellular uptake and DNA incorporation of I-UdR was determined. Chromatin damage was quantified by the alkaline Comet assay, apoptosis induction assessed by the Annexin V/PI assay employing flow cytometry and micronucleus formation was quantified using the Cytochalasin-B micronucleus assay at various times post-labelling. Cs-137 γ-rays served as reference radiation.I-125-UdR caused pronounced apoptosis when compared to !-123-UdR. Micronucleus induction and chromatin damage was very similar for both radionuclides. Both AEE caused a pronounced and long-lasting G2/M cell cycle arrest. On average one decay of I-125 every 120 seconds in the DNA of a single cell is sufficient to induce a permanent G2/M cell cycle arrest in SCL-II cells.Albeit of a lower dose rate, I-125-UdR is more cytotoxic in comparison with I-123-UdR.Funded by Bundesministerium für Umwelt, Natur und Reaktorsicherheit (BMU), Bundesamt für Strahlenschutz; Project No.: 3608S0300

Analysis of Iodine-125-induced chromosome aberrations

DNA-associated Auger-electron emitters (AEE) induce cellular damage leading to high-LET type cell survival curves and possess enhanced relative biological effectiveness. Moreover, DNA dsb induced by 125I-deoxyuridine (125I-UdR) decays are claimed to be very complex. To elucidate the assumed genotoxic potential, chromosome aberrations were analyzed in 125I-UdR-exposed human peripheral blood lymphocytes (PBL).After 18 h labeling with 125I-UdR the cell cycle distribution is severely disturbed. Furthermore, 40% of PBL are fully labelled and 20% show a moderate uptake. Primarily chromatid-type aberrations are induced. PBL reveal a very broad dose-dependent response spectrum: equal numbers of cells have either no aberration, or display a moderate aberration level. Few cells exhibit a high aberration score (> 10 aberrations). A dose-dependent increase of aberrations is measured in the range of 0.2 to 2 Gy, followed by a plateau between 2 and 4.5 Gy. The data indicate that even the lowest dose of 0.2 Gy leads to a 4.5-fold increase of aberrations in PBL compared to the controls. Furthermore, a dose-dependent increase of cell death is observed.125I-UdR has a very strong genotoxic capacity in human PBL even at very low doses of about 0.2 Gy. Efficiently labeled cells display a prolonged cell cycle compared to moderate labeled cells and cell death contributes substantially to the desynchronisation of the cell cycle. It can be concluded that every fourth intracellular 125I decay give rise to a single chromosome aberration

Study On The Radiotoxicity Of The Auger Electron Emitter Technetium-99m In Functional Rat Thyroid Cells

Introduction: Because of its favorable half-life (6.02 hours) and distinct characteristic gamma-ray line, Technetium-99m (Tc-99m) is the most widespread radionuclide in nuclear medicine. Additionally, this nuclide emits low energetic, short-range Auger electrons which can deposit large amounts of energy in a rather small volume in the immediate vicinity of the decay site. When located in close proximity to the DNA, the biological effects caused by Auger emitters are severe and comparable to high-LET radiation. This poses the question towards an increased relative biological effectiveness (RBE) of the Auger electron emitter Tc-99m. To assess the potential impact of Tc-99m-Pertechnetate on cellular level, DNA double-strand breaks (gammaH2AX assay) and cell killing (colony forming assay) was investigated after extracellular and intracellular localization of Tc-99m in the functional rat thyroid cell line, FRTL-5 and effects were compared to high dose-rate external uniform γ-irradiation (Cs-137; 0.7 Gy/min).Material and methods: FRTL-5 cells were ex-posed to 25, 50 and 75 MBq Tc-99m pertechne-tate. Extracellular localization of Tc-99m was achieved by inhibiting the Sodium-Iodide Sym-porter (NIS) with sodium perchlorate (SP). Standard Colony Forming Assay was employed. GammaH2AX staining was achieved using a mouse anti-phospho H2AX antibody (Clone JBW301, Invitrogen). External high dose-rate γ-irradiation was performed with a Cs-137 source (GammaCell 40). Cell number and Tc-99m uptake was determined in each individual experiment (CASY® Schärfe System; Gamma Counter, Wallace 3" PerkinElmer). Dosimetry at cellular level was based on cell size and point kernel calculations using electron spectra provided and published by Pomplun et al. 2006 [1].Results: A rapid cellular uptake of Tc-99m in FRTL-5 cells was observed. Inhibtion of NIS re-stricted the uptake efficiently. However, no complete inhibition of uptake was observed. GammaH2AX-foci induction was somewhat higher per dose unit when Tc-99m was located intracellular. Tc-99m induced more prominent cell killing when located intracellular as compared to extracellular localization per decay. However, per dose unit no significant differences were observed (Figure 1). Compared to high dose rate external γ-irradiation GammaH2AX-foci induction as well as cell killing was much weaker after Tc-99m-exposure as already published for cell killing and micronucleus induction in SCL-II cells by Kriehuber et al., 2004 [2]. SP treatment itself had no influence on cytotoxic damage.Conclusions: No significant effect on cell killing due to the localization (intra- vs extracellular) of Tc-99m was observed per unit dose ruling out any Auger electron-associated enhanced cytotoxicity for Tc-99m pertechnetate. The cytotoxic effect of Tc-99m and GammaH2AX-foci induction is much weaker when compared to external high dose rate γ-exposure, which is most likely explained by the low dose rate of the Tc-99m exposure. Figure 1. Cell survival of FRTL-5 cells as measured in the colony forming assay. Survival fraction (SF) as a function of cellular radiation dose revealed no significant differences in cell survival between cells with (filled diamonds) and without (open diamonds) Tc-99m uptake. External homogenous high dose-rate γ-irradiation (Cs-137 exposure, dose rate 0.7 Gy/min, circles) was 4 to 7 times more efficient in cell killing when compared to Tc-99m exposed cells (diamonds).References: 1. Estimation of a radiation weighting factor for 99mTc (E. Pomplun et al.), Radiat. Prot. Dosimetry 122, 80-81 (2006)2. Study on cell survial, induction of apoptosis and micronucleus formation in SCL-II cells after exposure to the Auger electron emitter (99m)Tc (R. Kriehuber et al.), Int. J Radiat. Biol. 80, 875-880 (2004

Corrigendum to 'Chromosome aberrations induced by the Auger electron emitter (125)I' [Mut. Res.-Genet. Toxicol. Environ. Mutagen. 793 (2015) 64-70].

The authors regret that a mistake occurred in Section 4.2.3 of the discussion, in the summary (Section 5) and in the abstract, when comparing their own results with data from the literature (Yasui 2004; Sedelnikova et al., 2002). The argumentation that every 125I-induced dsb is converted into a chromosome aberration is wrong. We made an incorrect calculation when correlating the decays per cell with the resulting chromosome aberrations. After reconsideration, our data (based on nine experiments) indicate that it takes on average 250 decays to induce one chromosome aberration (CA). Thus, the comparison of our CA data with the DSB data from Yasui [18] and Sedelnikova et al. [17] seems to be not adequate anymore. The authors would like to apologise for any inconvenience caused