AT, Raavi V, Easwaramoorthy V, Murugaiyan P, Perumal V. Enhanced γ-H2AX Foci Frequency and Altered Gene Expression in Participants Exposed to Ionizing Radiation During I-131 Nuclear Medicine Procedures

Purpose

Ionizing radiation-based technologies are extensively used in the diagnosis and treatment of diseases. While utilizing the technologies, exposure to a certain amount of radiation is unavoidable. Data can be obtained from participants who received radiation during medical imaging and therapeutic purposes to predict the effects of low-dose radiation.

Methods

To understand the effects of low-dose radiation, participants (n = 22) who received radioactive I-131 for scan/therapy were used as a model in this study. Blood samples were drawn pre- and post-administration of I-131. Biological effects were measured using markers of DNA damage (γ-H2AX, micronucleus (MN), and chromosomal aberrations (CA)) and response to damage through gene expression changes (ATM, CDKN1A, DDB2, FDXR, and PCNA) in blood samples.

Results

Mean frequency of γ-H2AX foci in pre-samples was 0.28 ± 0.16, and post-samples were 1.03 ± 0.60. γ-H2AX foci frequency obtained from post-samples showed significant (p < 0.0001) and a heterogeneous increase in all the participants (received I-131 for scan/therapy) when compared to pre-samples. A significant increase (p < 0.0001) in MN and CA frequency was also observed in participants who received the I-131 therapy. Gene expression analysis indicates that all genes (ATM, CDKN1A, DDB2, FDXR, and PCNA) were altered in post-samples, although with varying degrees, suggesting that the cellular responses to DNA damage, such as damage repair, cell cycle regulation to aid in repair and apoptosis are increased, which priority is given to repair, followed by apoptosis.

Conclusion

The results of this study indicate that the participants who received I-131 (low doses of β- and γ-radiation) can produce substantial biological effects.

Baseline micronucleus frequencies and 60Co cytokinesis-block micronucleus assay dose-response curve for biodosimetry in Vietnam

This study aims to establish baseline micronucleus (MN) frequencies from various populations of residents in Vietnam and develop a 60Co dose-response curve for the cytokinesis-block micronucleus (CBMN) assay. Blood samples were exposed in vitro to a 60Co source at a dose rate of 275 mGy per min in a range of 0.1 to 4.0 Gy. MN background frequencies were 4.5 ± 3.2, 7.3 ± 4.6, 7.0 ± 3.8 and 13.1 ± 6.7 in 1000 binucleated (BN) cells for 96 healthy donors, 22 male radiation workers and 12 breast cancer patients, respectively. Blood samples from three healthy donors were used to generate the MN dose-response curve: y = C + (0.0496 ± 0.0069)D + (0.0143 ± 0.0026)D2. This curve was verified through an inter-laboratory comparison (RENEB ILC 2021). Our findings highlight the significance of the CBMN assay as an additional essential tool for biodosimetry in Vietnam.

Establishment of in vitro Calibration Curve for 60Co-γ-rays Induced Phospho-53BP1 Foci, Rapid Biodosimetry and Initial Triage, and Comparative Evaluations With γH2AX and Cytogenetic Assays

A rapid and reliable method for biodosimetry of populations exposed to ionizing radiation in the event of an incident or accident is crucial for initial triage and medical attention. DNA-double strand breaks (DSBs) are indicative of radiation exposure, and DSB-repair proteins (53BP1, γH2AX, ATM, etc.) are considered sensitive markers of DSB quantification. Phospho-53BP1 and γH2AX immunofluorescence technique serves as a sensitive, reliable, and reproducible tool for the detection and quantification of DSB-repair proteins, which can be used for biological dose estimations. In this study, dose-response curves were generated for ⁶⁰Co-γ-rays induced phospho-53 Binding Protein 1 (phospho-53BP1) foci at 1, 2, 4, 8, 16, and 24 h, post-irradiation for a dose range of 0.05–4 Gy using fluorescence microscopy. Following ISO recommendations, minimum detection limits (MDLs) were estimated to be 16, 18, 25, 40, 50, and 75 mGy for dose-response curves generated at 1, 2, 4, 8, 16, and 24 h post-irradiation. Colocalization and correlation of phospho-53BP1 and γH2AX were also measured in irradiated peripheral blood lymphocytes (PBLs) to gain dual confirmation. Comparative evaluation of the established curve was made by γH2AX-immunofluorescence, dicentric chromosome assay (DCA), and reciprocal translocation (RT) assays by reconstructing the dose of 6 dose-blinded samples. Coefficients of respective in-house established dose-response curves were employed to reconstruct the blind doses. Estimated doses were within the variation of 4.124%. For lower doses (0.052 Gy), phospho-53BP1 and γH2AX assays gave closer estimates with the variation of −4.1 to + 9% in comparison to cytogenetic assays, where variations were −8.5 to 24%. For higher doses (3 and 4 Gy), both the cytogenetic and immunofluorescence (phospho-53BP1 and γH2AX), assays gave comparable close estimates, with −11.3 to + 14.3% and −10.3 to −13.7%, variations, respectively.

Telomere fragility in radiology workers occupationally exposed to low doses of ionising radiation

Ionising radiation damages DNA directly and indirectly through increased production of reactive oxygen species. Although telomeres have been reported as indicators of radiosensitivity, their maintenance in response to occupational exposure to low radiation doses is still a matter of debate. In this work we aimed to investigate telomere length and structure in hospital workers occupationally exposed to X-rays and to relate these findings to oxidation of biomolecules and chromosome aberrations. Blood samples of exposed participants and matching controls were taken during periodical check-ups. Chromosome aberrations and telomere length and structure were analysed in peripheral blood lymphocytes using Q-FISH, whereas oxidative stress parameters [pro/antioxidant balance (PAB), lipid peroxidation, and 8-oxo-dG] were measured in plasma samples. Based on the CA findings we divided the exposed group into two subgroups, of which one had chromosome aberrations in the first division metaphases and the other did not. There was no significant difference in telomere length between any of the groups. However, both subgroups showed significantly higher rate of fragile telomeres and higher lipid peroxidation product and 8-oxo-dG levels than controls. The rate of fragile telomeres significantly correlated with plasma levels of 8-oxo-dG, which suggests that continuous exposure to low radiation doses induces oxidative base damage of guanine resulting in telomere fragility.

Comparative analysis of physical doses and biomarker changes in subjects underwent Computed Tomography, Positron Emission Tomography-Computed Tomography, and interventional procedures

Even though the medical uses of ionizing radiation are well-acknowledged globally as vital tools for the improvement of human health, they also symbolize the major man-made sources of radiation exposure to the population. Estimation of absorbed dose and biological changes after radiation-based imaging might help to better understand the effects of low dose radiation. Because of this, we measured the Entrance Surface Dose (ESD) at different anatomical locations using Lithium tetraborate doped with manganese (Li₂B₄O₇: Mn), recorded Dose Length Product (DLP) and Dose Area Product (DAP), analyzed Chromosomal Aberration (CA), Micronucleus (MN), gamma-H2AX (γ-H2AX), and p53^ser15 proteins in the blood lymphocytes of patients (n = 267) underwent Computed Tomography (CT), Positron Emission Tomography-CT (PET/CT), and interventional procedures and healthy volunteers (n = 19). The DLP and effective doses obtained from PET/CT procedures were significantly higher (p < 0.05) when compared to CT. Fluoroscopic time and DAP were significantly higher (p < 0.05) in therapeutic compared to diagnostic interventional procedures. All the anatomical locations registered a significant amount of ESD, the ESD obtained from CT and interventional procedures were significantly (p < 0.05) higher when compared to PET/CT. Fluoroscopic time did not correlate with the ESD (eye, head, thyroid, and shoulder; R² = 0.03). CA frequency after PET/CT was significantly higher (p < 0.001) when compared to CT and interventional procedures. MN frequency was significantly higher in 24-hs (p < 0.001) post-interventional procedure compared to 2-hs. The mean ± SD of mean fluorescence intensity of γ-H2AX and p53^ser15 obtained from all subjects underwent PET/CT and interventional procedures did not show a significant difference (p > 0.05) between pre- and post-procedure. However, the relative fluorescence intensity of γ-H2AX and p53^ser15 was >1 in 58.5 % and 65.8 % of subjects respectively. Large inter-individual variation and lack of correlation between physical dose and biomarkers suggest the need for robust dosimetry with a large sample size to understand the health effects of low dose radiation.