Application of the alkaline comet assay in biodosimetry: assessment of in vivo DNA damage in human peripheral leukocytes after a gamma radiation incident

Pattern of chromosomal aberrations persisting over 30 years in a Chernobyl Nuclear Power Plant accident survivor: study using mFISH

The long-term in vivo cytogenetic effects of high-dose radiation exposure can be traced in accidentally irradiated persons, and particularly useful for developing strategies of monitoring and therapy of such patients, as well as for elucidating the fundamental aspects of hematopoiesis and radiobiology. Using 24-color fluorescent in situ hybridization (mFISH), we analysed the frequency and the spectrum of chromosomal aberrations (CA) in peripheral blood lymphocytes of the Chernobyl Nuclear Power Plant (NPP) accident victim 30, 31, 32 and 33 years after acute accidental exposure to high-dose gamma radiation of the whole body. Totally, 993 metaphase cells were analyzed (or 219, 272, 258, 244 cells each year), of which 297 were aberrant. Our study demonstrated a constant aberrant cell frequency at 28% in 2016-2018 years, while in 2019, a significant increase up to 35% occurred due to contribution of significantly elevated frequency of simple aberrations in the absence of evident recent genotoxic factors. Four clonal aberrations were detected, three of which persisted for more than one year at a frequency up to 2.5% of analyzed cells. The distribution of 731 breakpoints per individual chromosomes was nearly proportional to their physical length, excepting Chromosomes 13 and 20, which were significantly breakpoint-deficient compared to the genome median rate. Monitoring of the long-term effects on chromosomal instability caused by radiation exposure is important for understanding and predicting the long-term effects of ionizing radiation.

Application of Gamma Ray-Responsive Genes for Transcriptome-Based Phytodosimetry in Rice

Transcriptome-based dose–response curves were recently applied to the phytodosimetry of gamma radiation in a dicot plant, Arabidopsis thaliana, as an alternative biological assessment of genotoxicity using DNA damage response (DDR) genes. In the present study, we characterized gamma ray-responsive marker genes for transcriptome-based phytodosimetry in a monocot plant, rice (Oryza sativa L.), and compared different phytodosimetry models between rice and Arabidopsis using gamma-H2AX, comet, and quantitative transcriptomic assays. The transcriptome-based dose–response curves of four marker genes (OsGRG, OsMutS, OsRAD51, and OsRPA1) were reliably fitted to quadratic or exponential decay equations (r² > 0.99). However, the single or integrated dose–response curves of these genes were distinctive from the conventional models obtained by the gamma-H2AX or comet assays. In comparison, rice displayed a higher dose-dependency in the comet signal and OsRAD51 transcription, while the gamma-H2AX induction was more dose-dependent in Arabidopsis. The dose-dependent transcriptions of the selected gamma-ray-inducible marker genes, including OsGRG, OsMutS, OsRAD51, and OsRPA1 in rice and AtGRG, AtPARP1, AtRAD51, and AtRPA1E in Arabidopsis, were maintained similarly at different vegetative stages. These results suggested that the transcriptome-based phytodosimetry model should be further corrected with conventional genotoxicity- or DDR-based models despite the high reliability or dose-dependency of the model. In addition, the relative weighting of each gene in the integrated transcriptome-based dose–response model using multiple genes needs to be considered based on the trend and amplitude of the transcriptional change.

Effects of different mobile phone UMTS signals on DNA, apoptosis and oxidative stress in human lymphocytes

Different scientific reports suggested link between exposure to radiofrequency radiation (RF) from mobile communications and induction of reactive oxygen species (ROS) and DNA damage while other studies have not found such a link. However, the available studies are not directly comparable because they were performed at different parameters of exposure, including carrier frequency of RF signal, which was shown to be a critical for appearance of the RF effects. For the first time, we comparatively analyzed genotoxic effects of UMTS signals at different frequency channels used by 3G mobile phones (1923, 1947.47, and 1977 MHz). Genotoxicity was examined in human lymphocytes exposed to RF for 1 h and 3 h using complimentary endpoints such as induction of ROS by imaging flow cytometry, DNA damage by alkaline comet assay, mutations in TP53 gene by RSM assay, preleukemic fusion genes (PFG) by RT-qPCR, and apoptosis by flow cytometry. No effects of RF exposure on ROS, apoptosis, PFG, and mutations in TP53 gene were revealed regardless the UMTS frequency while inhibition of a bulk RNA expression was found. On the other hand, we found relatively small but statistically significant induction of DNA damage in dependence on UMTS frequency channel with maximal effect at 1977.0 MHz. Our data support a notion that each specific signal used in mobile communication should be tested in specially designed experiments to rule out that prolonged exposure to RF from mobile communication would induce genotoxic effects and affect the health of human population.

A Comet Assay for DNA Damage and Repair After Exposure to Carbon-Ion Beams or X-rays in Saccharomyces Cerevisiae

Ionizing radiation (IR) can result in serious genomic instability and genotoxicity by causing DNA damage. Carbon ion (CI) beams and X-rays are typical IRs and possess high-linear energy transfer (LET) and low-LET, respectively. In this article, a comet assay that was optimized by decreasing the electrophoresis time (8 minutes) and voltage (0.5 V/cm) was performed to elucidate and quantify the DNA damage induced by CI or X-rays radiation. Two quantitative methods for the comet assay, namely, comet score and olive tail moment, were compared, and the appropriate means and parameter values were selected for the present assay. The dose-effect relationship for CI or X-rays radiation and the DNA repair process were studied in yeast cells. These results showed that the quadratic function fitted the dose-effect relationship after CI or X-rays exposure, and the trend for the models fitted the dose-effect curves for various repair times was precisely described by the cubic function. A kinetics model was also creatively used to describe the process of DNA repair, and equations were calculated within repairable ranges that could be used to roughly evaluate the process and time necessary for DNA repair.

Transcriptome-based biological dosimetry of gamma radiation in Arabidopsis using DNA damage response genes

Plants are used as representative reference biota for the biological assessment of environmental risks such as ionizing radiation due to their immobility. This study proposed a faster, more economical, and more effective method than conventional cytogenetic methods for the biological dosimetry of ionizing radiation in plants (phytodosimetry). We compared various dose-response curves for the radiation-induced DNA damage response (DDR) in Arabidopsis thaliana after relatively "low-dose" gamma irradiation (3, 6, 12, 24, and 48 Gy) below tens of Gy using comet (or single-cell gel electrophoresis), gamma-H2AX, and transcriptomic assays of seven DDR genes (AGO2, BRCA1, GRG, PARP1, RAD17, RAD51, and RPA1E) using quantitative real time PCR. The DDR signal from the comet assay was saturated at 6 Gy, while the gamma-H2AX signal increased up to 48 Gy, following a linear-quadratic dose-response model. The transcriptional changes in the seven DDR genes were fitted to linear or supra-linear quadratic equations with significant dose-dependency. The dose-dependent transcriptional changes were maintained similarly until 24 h after irradiation. The integrated transcriptional dose-response model of AGO2, BRCA1, GRG, and PARP1 was very similar to that of gamma-H2AX, while the transcriptional changes in the BRCA1, GRG, and PARP1 DDR genes revealed significant dependency on the dose-rate, ecotype, and radiation dose. These results suggest that the transcriptome-based dose-response model fitted to a quadratic equation could be used practically for phytodosimetry instead of conventional cytogenetic models, such as the comet and gamma-H2AX assays. The effects of dose-rate and ecotype on the transcriptional changes of DDR genes should also be considered to improve the transcriptome-based phytodosimetry model.

Cytogenetic endpoints and Xenobiotic gene polymorphism in lymphocytes of hospital workers chronically exposed to ionizing radiation in Cardiology, Radiology and Orthopedic Laboratories

Ionizing radiation (IR) is known as a classical mutagen capable of inducing various kinds of stable and unstable chromosomal aberrations (CA) including the possibility of increasing the incidence of DNA damage. This study aims to assess occupationally induced CA in workers chronically exposed to low doses of IR in Radiology (RL), Cardiology (CL) and Orthopedic (OL) Laboratories in hospitals of Tamil Nadu. We performed the analysis of CA by trypsin G-banding, micronucleus (MN) assay, Comet assay and Xenobiotic-metabolizing gene polymorphisms (GSTM1, GSTT1 and GSTP1) in 56 exposed and 56 control subjects who were matched for gender and age (± 2 years). Higher degree of CA and MN frequencies were observed in exposed groups, especially in CL subjects compared to other exposed groups and controls (p<0.05). Higher frequency of DNA tail length and tail moment was observed in the CL exposed subjects compared to the RL and OL subjects. The frequencies of GSTM1 and GSTT1 null genotypes were 39.3 percent and 14.3 percent, respectively. No significant difference in allele frequencies between exposed subjects and controls were observed (p=0.0128). Using multiple linear regression analysis, statistical significance was determined for work duration and age for the CL, RL and OL workers and the examination of the possible impact by confounding factors showed few significant influences on the radiation exposure, as a specific biomarker. However, the findings from the present study suggest that, awareness should be created among the personnel exposed to radiations in hospital laboratories, highlighting the necessity of applying radiation protection principles against medical radiation exposure.

Evaluation of the comet assay for assessing the dose-response relationship of DNA damage induced by ionizing radiation

Dose- and time-response curves were combined to assess the potential of the comet assay in radiation biodosimetry. The neutral comet assay was used to detect DNA double-strand breaks in lymphocytes caused by γ-ray irradiation. A clear dose-response relationship with DNA double-strand breaks using the comet assay was found at different times after irradiation (p < 0.001). A time-response relationship was also found within 72 h after irradiation (p < 0.001). The curves for DNA double-strand breaks and DNA repair in vitro of human lymphocytes presented a nice model, and a smooth, three-dimensional plane model was obtained when the two curves were combined.

Cytogenetic abnormalities in lymphocytes from victims exposed to cobalt-60 radiation

The present study investigates cytogenetic damage in lymphocytes, derived from three victims who were unfortunately exposed to cobalt-60 (60Co) radiation (the 1999 accident occurred in a village in China's Henan province). Case A of the three victims was exposed to a higher dose of 60Co radiation than Cases B and C. The chromosomal aberrations, cytokinesis-block micronucleus (CBMN, the CBMN assay), and DNA double-strand breaks (DSBs, the comet assay) examined in this study are biomarkers for cytogenetic abnormalities. After the lymphocytes collected from the victims were cultured, the frequencies of dicentric chromosomes and rings (dic + r) and CBMN in the first mitotic division detected in the lymphocytes of Case A were found to be substantially higher than in Cases B and C. Similarly, the DNA-DSB level found in the peripheral blood collected from Case A was much higher than those of Cases B and C. These results suggest that an acutely enhanced induction of the 60Co-induced cytogenetic abnormality frequency in humans depends on the dose of 60Co radiation. This finding is supported by the data obtained using practical techniques to evaluate early lymphoid-tissue abnormalities induced after exposure to acute radiation.

DNA damage in hair root cells as a biomarker for gamma ray exposure

The purpose of the present research is to examine whether human hair root cells can be used for dose assessment after in vitro exposure to ionizing radiation. Hair root samples plucked from random head regions were collected from 5 healthy human subjects. Some of these hair samples were used as control and some were irradiated with 0.5-5Gy of gamma ray using a Cs-137 gamma irradiator at a dose rate of 0.14Gy/s. DNA damage (single-strand breaks) was determined in hair root cells of these samples using the comet assay technique. The comet assay parameters, tail length (TL) and tail moment (TM), showed a significant increase (p<.05) in single-strand DNA breaks in hair roots cells of the exposed samples compared to control. A linear dose-effect relationship was observed when tail moment or tail length was plotted against the log of the radiation dose. This research suggests a possible use of human hair root cell DNA damage as a biomarker especially for low dose radiation.

Radiation-induced biomarkers for the detection and assessment of absorbed radiation doses

Radiation incident involving living organisms is an uncommon but a very serious situation. The first step in medical management including triage is high-throughput assessment of the radiation dose received. Radiation exposure levels can be assessed from viability of cells, cellular organelles such as chromosome and different intermediate metabolites. Oxidative damages by ionizing radiation result in carcinogenesis, lowering of the immune response and, ultimately, damage to the hematopoietic system, gastrointestinal system and central nervous system. Biodosimetry is based on the measurement of the radiation-induced changes, which can correlate them with the absorbed dose. Radiation biomarkers such as chromosome aberration are most widely used. Serum enzymes such as serum amylase and diamine oxidase are the most promising biodosimeters. The level of gene expression and protein are also good biomarkers of radiation.

Primary DNA damage assessed with the comet assay and comparison to the absorbed dose of diagnostic X-rays in children

The aim of this work is to assess DNA damage in peripheral blood lymphocytes of children prior to and following airway X-ray examinations of the chest using the alkaline comet assay and to compare data with the measured absorbed dose. Twenty children with pulmonary diseases, between the ages of 5 and 14 years, are assessed. Absorbed dose measurements are conducted for posterior-anterior projection on the forehead, thyroid gland, gonads, chest, and back. Doses are measured using thermoluminescent and radiophotoluminescent dosimetry systems. Differences between tail lengths, tail intensity, and tail moments as well as for the long-tailed nuclei before and after exposures are statistically significant and are dependent on the individual. The results demonstrate the usefulness of the comet assay as a measure of X-ray damage to lymphocytes in a clinical setting. Doses measured with both dosimeters show satisfactory agreement (0.01 mSv) and are suitable for dosimetric measurements in X-ray diagnostics.

In vitro assessment of genotoxic effects of electric arc furnace dust on human lymphocytes using the alkaline comet assay

In vitro genotoxic effects of leachates of electric arc furnace dust (EAFD) on human peripheral lymphocytes, assessed prior and following the treatment with a strong alkaline solution were investigated using the alkaline comet assay. Prior and following the treatment, lymphocytes were incubated with leachate of EAFD for 6 and 24 hours at 37 degrees C. Negative controls were also included. Mean values of the tail lengths established in the samples treated with the leachate stemming from the original dust for 6 and 24 hours, were 15.70 microm and 16.78 microm, respectively, as compared to 12.33 microm found in the control sample. Slight, but significant increase in the tail length was also found with the dust treated with a strong alkaline solution (13.37 microm and 13.60 microm). In case of high heavy metal concentrations (the extract of the original furnace dust), the incubation period was revealed to be of significance as well. The obtained results lead to the conclusion that alkaline comet assay could be used as a rapid, sensitive and low-cost tool when assessing genotoxicity of various waste materials, such as leachates of the electric arc furnace dust.

Assessment of DNA sensitivity in peripheral blood leukocytes after occupational exposure to microwave radiation: the alkaline comet assay and chromatid breakage assay

DNA sensitivity in peripheral blood leukocytes of radar-facility workers daily exposed to microwave radiation and an unexposed control subjects was investigated. The study was carried out on clinically healthy male workers employed on radar equipment and antenna system service within a microwave field of 10 muW/cm(2)-20 mW/cm(2) with frequency range of 1,250-1,350 MHz. The control group consisted of subjects of similar age. The evaluation of DNA damage and sensitivity was performed using alkaline comet assay and chromatid breakage assay (bleomycin-sensitivity assay). The levels of DNA damage in exposed subjects determined by alkaline comet assay were increased compared to control group and showed inter-individual variations. After short exposure of cultured lymphocytes to bleomycin cells of subjects occupationally exposed to microwave (MW) radiation responded with high numbers of chromatid breaks. Almost three times higher number of bleomycin-induced chromatid breaks in cultured peripheral blood lymphocytes were determined in comparison with control group. The difference in break per cell (b/c) values recorded between smokers and non-smokers was statistically significant in the exposed group. Regression analyses showed significant positive correlation between the results obtained with two different methods. Considering the correlation coefficients, the number of metaphase with breaks was a better predictor of the comet assay parameters compared to b/c ratio. The best correlation was found between tail moment and number of chromatid with breaks. Our results indicate that MW radiation represents a potential DNA-damaging hazard using the alkaline comet assay and chromatid breakage assay as sensitive biomarkers of individual cancer susceptibility.