Frequency of gamma H2AX foci in healthy volunteers and health workers occupationally exposed to X-irradiation and its relevance in biological dosimetry

Candidate Gene Expression in Regional Population and Its Relevance for Radiation Triage

Quantification of gene expression signatures has been substantiated as a potential and rapid marker for radiation triage and biodosimetry during nuclear emergencies. Similar to the established biodosimetry assays, the gene expression assay has drawbacks such as being highly dynamic and transient, not specific to ionizing radiation, and also influenced by confounding factors such as gender, health status, lifestyle, and inflammation. In view of that, prior knowledge of baseline expression of certain candidate genes in a population could complement the discrimination of the unexposed from the exposed individuals without the need for individual pre-exposure controls. We intended to establish a baseline expression of reported radiation-responsive genes such as CDKN1A, DDB2, FDXR, and PCNA in the blood samples of healthy human participants and then compare it with diabetic/hypertension participants (as a chronic inflammatory condition) drawn from south Indian population. Further, we have examined the appropriateness of the assay for radiation triage-like situations; i.e., the expression profiles of those genes were examined in the participants who underwent X-ray-based medical imaging. Acute inflammation induced by lipopolysaccharide exposure in the blood significantly increased the fold expression of those genes (p < 0.0001) compared to the control. Whereas the basal expression level of those genes among the participants with the inflammatory condition is marginally higher than those observed in the healthy participants; despite the excess, the fold increase in those genes between the groups did not differ significantly. Consistent with the inflammatory participants, the basal expression level of those genes in the blood sample of participants who received X-radiation during neuro-interventional and computed tomography imaging is marginally higher than those observed in the pre-exposure of respective groups. Nevertheless, the fold increase in those genes did not differ significantly as the fold change fell within the two folds. Thus, overall results suggest that the utility of CDKN1A, DDB2, FDXR, and PCNA gene expression for radiation triage specific after very low-dose radiation exposure needs to be interpreted with caution for a much more reliable triage.

Non-linear dose response of DNA double strand breaks in response to chronic low dose radiation in individuals from high level natural radiation areas of Kerala coast

BACKGROUND

The human population living in high level natural radiation areas (HLNRAs) of Kerala coast provide unique opportunities to study the biological effects of low dose and low dose rate ionizing radiation below 100 mGy. The level of radiation in this area varies from < 1.0 to 45 mGy/year. The areas with ≤ 1.50 mGy/year are considered as normal level natural radiation areas (NLNRA) and > 1.50 mGy/year, as high level natural radiation areas (HLNRA). The present study evaluated dose response relationship between DNA double strand breaks (DSBs) and background radiation dose in individuals residing in Kerala coast. Venous blood samples were collected from 200 individuals belonging to NLNRA (n = 50) and four dose groups of HLNRA; 1.51-5.0 mGy/year (n = 50), 5.01-10.0 mGy/year (n = 30), 10.01-15.0 mGy/year (n = 33), > 15.0 mGy/year (n = 37) with written informed consent. The mean dose of NLNRA and four HLNRA dose groups studied are 1.21 ± 0.21 (range: 0.57-1.49), 3.02 ± 0.95 (range: 1.57-4.93), 7.43 ± 1.48 (range: 5.01-9.75), 12.22 ± 1.47 (range: 10.21-14.99), 21.64 ± 6.28 (range: 15.26-39.88) mGy/year, respectively. DNA DSBs were quantified using γH2AX as a marker, where foci were counted per cell using fluorescence microscopy.

RESULTS

Our results revealed that the frequency of γH2AX foci per cell was 0.090 ± 0.051 and 0.096 ± 0.051, respectively in NLNRA and HLNRA individuals, which were not significantly different (t₁₉₈ = 0.33; P = 0.739). The frequency of γH2AX foci was observed to be 0.090 ± 0.051, 0.096 ± 0.051, 0.076 ± 0.036, 0.087 ± 0.042, 0.108 ± 0.046 per cell, respectively in different dose groups of ≤ 1.50, 1.51-5.0, 5.01-10.0, 10.01-15.0, > 15.0mGy/year (ANOVA, F_4,195 = 2.18, P = 0.072) and suggested non-linearity in dose response. The frequency of γH2AX foci was observed to be 0.098 ± 0.042, 0.078 ± 0.037, 0.084 ± 0.042, 0.099 ± 0.058, 0.097 ± 0.06 and 0.114 ± 0.033 per cell in the age groups of ≤ 29, 30-34, 35-39, 40-44, 45-49 and ≥ 50 years, respectively (ANOVA, F_5,194 = 2.17, P = 0.059), which suggested marginal influence of age on the baseline of DSBs. Personal habits such as smoking (No v/s Yes: 0.092 ± 0.047 v/s 0.093 ± 0.048, t₁₉₈ = 0.13; P = 0.895) and drinking alcohol (No v/s Yes: 0.096 ± 0.052 v/s 0.091 ± 0.045, t₁₉₈ = 0.62; P = 0.538) did not show any influence on DSBs in the population.

CONCLUSION

The present study did not show any increase in DSBs in different dose groups of HLNRA compared to NLNRA, however, it suggested a non-linear dose response between DNA DSBs and chronic low dose radiation.

Radiobiological risks following dentomaxillofacial imaging: should we be concerned?

OBJECTIVES

This review aimed to present studies that prospectively investigated biological effects in patients following diagnostic dentomaxillofacial radiology (DMFR).

METHODS

Literature was systematically searched to retrieve all studies assessing radiobiological effects of using X-ray imaging in the dentomaxillofacial area, with reference to radiobiological outcomes for other imaging modalities and fields.

RESULTS

There is a lot of variability in the reported radiobiological assessment methods and radiation dose measures, making comparisons of radiobiological studies challenging. Most radiological DMFR studies are focusing on genotoxicity and cytotoxicity, data for 2D dentomaxillofacial radiographs, albeit with some methodological weakness biasing the results. For CBCT, available evidence is limited and few studies include comparative data on both adults and children.

CONCLUSIONS

In the future, one will have to strive towards patient-specific measures by considering age, gender and other individual radiation sensitivity-related factors. Ultimately, future radioprotection strategies should build further on the concept of personalized medicine, with patient-specific optimization of the imaging protocol, based on radiobiological variables.

Biomarkers of Genotoxicity in Medical Workers Exposed to Low-Dose Ionizing Radiation: Systematic Review and Meta-Analyses

Medical staff represent the largest group of workers occupationally exposed to ionizing radiation (IR). Chronic exposure to low-dose IR may result in DNA damage and genotoxicity associated with increased risk of cancer. This review aims to identify the genotoxicity biomarkers that are the most elevated in IR-exposed vs. unexposed health workers. A systematic review of the literature was performed to retrieve relevant studies with various biomarkers of genotoxicity. Subsequent meta-analyses produced a pooled effect size for several endpoints. The search procedure yielded 65 studies. Chromosome aberrations (CA) and micronuclei (MN) frequencies were significantly different between IR-exposed and unexposed workers (θ_pooled = 3.19, 95% CI 1.46–4.93; and θ_pooled = 1.41, 95% CI 0.97–1.86, for total aberrant cells and MN frequencies, respectively), which was not the case for ring chromosomes and nucleoplasmic bridges. Although less frequently used, stable translocations, sister chromatid exchanges (SCE) and comet assay endpoints were also statistically different between IR-exposed and unexposed workers. This review confirms the relevance of CA and MN as genotoxicity biomarkers that are consistently elevated in IR-exposed vs. unexposed workers. Other endpoints are strong candidates but require further studies to validate their usefulness. The integration of the identified biomarkers in future prospective epidemiological studies is encouraged.

Use of Biological Dosimetry for Monitoring Medical Workers Occupationally Exposed to Ionizing Radiation

Medical workers are the largest group exposed to man-made sources of ionizing radiation. The annual doses received by medical workers have decreased over the last several decades, however for some applications, like fluoroscopically guided procedures, the occupational doses still remain relatively high. Studies show that for some procedures the operator and staff still use insufficient protective and dosimetric equipment, which might cause an underestimation of medical exposures. Physical dosimetry methods are a staple for estimating occupational exposures, although due to the inconsistent use of protection measures, an alternative method such as biological dosimetry might complement the physical methods to achieve a more complete picture. Such methods were used to detect exposures to doses as low as 0.1 mSv/year, and could be useful for a more accurate assessment of genotoxic effects of ionizing radiation in medical workers. Biological dosimetry is usually based on the measurement of the effects present in peripheral blood lymphocytes. Although some methods, such as chromosome aberration scoring or micronucleus assay, show promising results, currently there is no one method recognized as most suitable for dosimetric application in the case of chronic, low-dose exposures. In this review we decided to evaluate different methods used for biological dosimetry in assessment of occupational exposures of medical workers.

Potential application of γ-H2AX as a biodosimetry tool for radiation triage

Radiation triage and biological dosimetry are two initial steps in the medical management of exposed individuals following radiological accidents. Well established biodosimetry methods such as the dicentric (DC) assay, micronucleus (MN) assay, and fluorescence in-situ hybridization (FISH) translocation assay (for residual damage) have been used for this purpose for several decades. Recent advances in scoring methodology and networking among established laboratories have increased triage capacity; however, these methods still have limitations in analysing large sample numbers, particularly because of the ∼ 48 h minimum culture time required prior to analysis. Hence, there is a need for simple, and high throughput markers to identify exposed individuals in case of radiological/nuclear emergencies. In recent years, a few markers were identified, one being phosphorylated histone 2AX (γ-H2AX), which measured a nuclear foci or nuclear staining intensity that was found to be suitable for triage. Measurement of γ-H2AX foci formed at and around the sites of DNA double-strand breaks is a rapid and sensitive biodosimetry method which does not require culturing and is thus promising for the analysis of a large number of samples. In this review, we have summarized the recent developments of γ-H2AX assay in radiation triage and biodosimetry, focusing chiefly on: i) the importance of baseline frequency and reported values among different laboratories, ii) the influence of known and unknown variables on dose estimation, iii) quality assurance such as inter-laboratory comparison between scorers and scoring methods, and iv) current limitations and potential for future development.

Preliminary quantitative evaluation of radiation-induced DNA damage in peripheral blood lymphocytes after cardiac dual-isotope imaging

DNA double-strand breaks (DSBs) of peripheral blood lymphocyte were prospectively assessed in 9 patients who were injected with ²⁰¹Tl-chloride and ¹²³I-beta-methyl-p-iodophenyl-pentadecanoic acid in dual-isotope imaging. Phosphorylated H2AX (γH2AX) was used as a biomarker for detecting DSBs, and the mean number of γH2AX foci per cell was measured microscopically. Mean γH2AX foci before administration of radiopharmaceuticals and at 3, 6, and 24 h following administration were 0.22 ± 0.34, 0.10 ± 0.14, 0.59 ± 0.46, and 0.52 ± 0.40, respectively (p = n.s. for all combinations).

Measurement of γ-H2AX foci, miRNA-101, and gene expression as a means to quantify radiation-absorbed dose in cancer patients who had undergone radiotherapy

Radiological accidents and nuclear terrorism pose an increased threat to members of the public who, following such an event, would need to be assessed for medical care by fast triage. Assay methods such as chromosome aberrations (CA), cytokinesis-block micronucleus (CBMN) and fluorescence in situ hybridization (FISH) techniques have been well established for dose estimation and their potential for handling more samples has also been proved with automation. However, culturing of lymphocytes is an inevitable step, which limits the potential of these markers for triage. In vitro analysis of gamma-H2AX (γ-H2AX), gene and microRNA (miRNA) markers do not require culturing of lymphocytes, and as such have been suggested as attractive tools for triage. Despite studies reporting in vitro dose-response curves, limited evidence is available evaluating the suitability of these assays in real situations. In this study, we have measured the absorbed dose using γ-H2AX, gene (GADD45A, FDXR, and CDKN1A) and miRNA-101 expression in blood samples of cancer patients (n = 20) who had undergone partial-body radiotherapy and compared with the derived equivalent whole-body doses (EWBD). The obtained results from all patients showed a significant (p < 0.05) increase of γ-H2AX foci in post-irradiated as compared to pre-irradiated samples. Moreover, estimated doses using γ-H2AX foci showed a correlation with the derived EWBD (r² = 0.60, p = 0.0003) and was also shown to be dependent on the irradiated body volume. Consistent with γ-H2AX foci frequency, an increase in fold change expression of genes and miRNA-101 was observed. However, the estimated dose significantly varied among the subjects and showed poor correlation (r² = 0.09, 0.04, 0.01 and 0.03 for GADD45A, FDXR, CDKN1A and miRNA-101, respectively) with EWBD. The overall results suggest that the established in vitro γ-H2AX assay is suitable for the detection of radiation exposure and can also provide an estimate of the dose in in vivo irradiated samples. The genes and miRNA-101 markers showed increased expression; nevertheless, there is a need for further improvements to measure doses accurately using these markers.