Assessing the applicability of FISH-based prematurely condensed dicentric chromosome assay in triage biodosimetry

Chromosome length ratio as a biomarker of DNA damage in cells exposed to high dose ionizing radiation

The premature chromosome condensation (PCC) assay is considered as complementary bio-dosimetry tool for chromosome aberration assay and the PCC assay can be used to estimate high dose exposure. Though the PCC ring is considered as prospective biomarker, chromosome length ratio (ratio of longest and shortest chromosome length in PCC spreads) of chemically induced PCC is shown to be very good indicator of ionizing radiation. In view of this, an in-vitro study has been performed using PCC assay to suggest chromosome length ratio (LR) as potential bio-dosimeter induced by high dose ionizing radiation. Blood samples were collected from healthy subjects (n = 3) after prior consent and irradiated to ten different doses ranging between 0 and 20 Gy using 6 MV LINAC X-rays with dose rate of 5.6 Gy/min. Irradiated lymphocytes were cultured and calyculin induced PCC spreads were prepared. PCC spreads were captured using image analysis system and chromosome lengths were measured using open-source ImageJ software. For each dose, LR for 50 chromosome spreads were computed and mean LR value was calculated. LR varies between 6.0 ± 0.08 and 23.6 ± 0.55 for the dose range between 2 and 20 Gy. The dose response curve for LR was observed to be linear with y = 1.02x + 3.36, R² = 0.97. Linear dose response relationship obtained in the present study confirms the prospective use of LR measurement. This study is first of its kind to examine chromosome length ratio as a biomarker of DNA damage in cells exposed to high dose X-ray exposure.

Comparing Lymphocyte Radiosensitivity of Prostate Cancer Patients with Healthy Donors Using Micronuclei and Chemical Premature Chromosome Condensation Tests

Background:

Cytogenetic tests are usually used for diagnosing predisposed individuals to cancer by determining their lymphocyte radiosensitivity.

Objective:

To determine the potential role of radiosensitivity in predisposition of prostate cancer by comparing lymphocyte radiosensitivity of prostate cancer patients with healthy donors.

Materials and Methods:

In this experimental study, the blood samples of 10 prostate cancer patients and 10 healthy donors were irradiated to 0.25, 0.5, 1, 2, 4 and 6 Gy ionizing radiation produced by a 6MV Linac. One sample of each group receiving no radiation was regarded as the background. The micronuclei (MN) and chemical premature chromosome condensation (PCC) cytogenetic tests were performed on all samples and the numbers of MN and PCC rings were scored. Dose-response curves were plotted for both healthy and cancerous groups with two tests.

Results:

There was a significant difference between the numbers of MN within each group due to different levels of radiation doses. There was also a significant difference between the two groups in all identical doses, with the exception of 6 Gy. The chemical PCC test indicated a significant difference between the scored PCC rings in each group at doses higher than 0.25 Gy. However, no differences were noted between the healthy donors and prostate cancer patients receiving the same level of doses.

Conclusion:

MN test can be considered as a reliable indicator of predisposition of prostate cancer. On the other hand, the chemical PCC test could not differentiate between healthy donors and prostate cancer patients at the dose range examined in this study.

Use of human lymphocyte G0 PCCs to detect intra- and inter-chromosomal aberrations for early radiation biodosimetry and retrospective assessment of radiation-induced effects

A sensitive biodosimetry tool is required for rapid individualized dose estimation and risk assessment in the case of radiological or nuclear mass casualty scenarios to prioritize exposed humans for immediate medical countermeasures to reduce radiation related injuries or morbidity risks. Unlike the conventional Dicentric Chromosome Assay (DCA), which takes about 3–4 days for radiation dose estimation, cell fusion mediated Premature Chromosome Condensation (PCC) technique in G0 lymphocytes can be rapidly performed for radiation dose assessment within 6–8 hrs of sample receipt by alleviating the need for ex vivo lymphocyte proliferation for 48 hrs. Despite this advantage, the PCC technique has not yet been fully exploited for radiation biodosimetry. Realizing the advantage of G0 PCC technique that can be instantaneously applied to unstimulated lymphocytes, we evaluated the utility of G0 PCC technique in detecting ionizing radiation (IR) induced stable and unstable chromosomal aberrations for biodosimetry purposes. Our study demonstrates that PCC coupled with mFISH and mBAND techniques can efficiently detect both numerical and structural chromosome aberrations at the intra- and inter-chromosomal levels in unstimulated T- and B-lymphocytes. Collectively, we demonstrate that the G0 PCC technique has the potential for development as a biodosimetry tool for detecting unstable chromosome aberrations (chromosome fragments and dicentric chromosomes) for early radiation dose estimation and stable chromosome exchange events (translocations) for retrospective monitoring of individualized health risks in unstimulated lymphocytes.

Delineating the Effects of Ionizing Radiation on Erythropoietic Lineage-Implications for Radiation Biodosimetry

The overall lethality/morbidity of ionizing radiation exposure involves multiple forms of inhibitory or cytotoxic effects that may manifest in different tissues with a varying dose and time response. One of the major systemic effects leading to lethality of radiation includes its suppressive effect on hematopoiesis, which could be observed even at doses as low as 1-2 Gy, whereas effects on gastrointestinal and nervous systems appear at relatively higher doses in the same order. This article reviews the effects of radiation on the three distinct stages of erythropoiesis-formation of erythroid progenitor cells, differentiation of erythroid precursor cells, and terminal maturation. During these stepwise developmental processes, erythroid progenitor cells undergo rapid expansion to form terminally differentiated red blood cells that are continuously replenished from bone marrow into the circulating peripheral blood stream. Cellular radiation response depends upon many factors such as cell lineage, rate of proliferation, and differentiation status. Therefore, we discuss radiation-induced alterations during the progenitor, precursor, and terminal maturation stages and the implications thereof. Since biomarkers of ionizing radiation exposure in human populations are of great interest for assessing normal tissue injury as well as for biodosimetry in the event of accidental or incidental radiation exposures, we also highlight blood-based biomarkers that have potential utility for medical management.

Prophasing interphase chromatin for assessing genetic damages-The evolution, applications and the future prospects

Premature chromosome condensation (PCC) involves induction of near-chromosome-like morphology to interphase chromatin. Experimental induction of PCC was achieved by somatic cell hybridization (SCH), an approach which evolved into a chemical-induction process. PCC presents most probably the only way in which cytogenetic assessment of damages can be analyzed in special situations such as availability of limited numbers of sample cells and for cells which have lost their ability to divide. Initial experiments on PCC were reported in late 1960s and the technique has evolved into one with wide range of applications owing to its increased efficiency in detecting primary DNA damages. Biodosimetry remains as the primary area which utilizes PCC technique to the maximum efficiency with several multiple-groups participating in collaborative exercises for biodosimetric applications. However, in spite of the advantages that the technique offers, it is yet to reach its full potential. This is due to the inherent limitations of the manner in which PCC is induced currently; by the somatic cell hybridization and chemical-induction processes. An approach which combines these two would sure help in taking PCC to its highest potential as the preferred technique for assessment of primary DNA damages. We present the chronological events of evolution of the PCC technique along with its applications. Also, the limitations of the technique along with the suggestions for further refinement of the PCC technique are discussed.

Construction of Calibration Curve for Premature Chromosome Condensation Assay for Dose Assessment

Cytogenetic dosimetry plays an important role in the triage and medical management of affected people in radiological incidents/accidents. Cytogenetic biodosimetry uses different methods to estimate the absorbed dose in the exposed individuals, and each approach has its advantages and disadvantages. Premature chromosome condensation (PCC) assay presents several advantages that hopefully fulfill the gaps identified in the other cytogenetic methods. To introduce this technique into the panel of other cytogenetic methods, a calibration curve for PCC after γ-irradiation was generated for our laboratory.

Biodosimetry for High-Dose Exposures Based on Dicentric Analysis in Lymphocytes Released from the G2-Block by Caffeine

High-dose assessments using the conventional dicentric assay are essentially restricted to doses up to 5 Gy and only to lymphocytes that succeed to proceed to first post-exposure mitosis. Since G2-checkpoint activation facilitates DNA damage recognition and arrest of damaged cells, caffeine is used to release G2-blocked lymphocytes overcoming the mitotic index and dicentric yield saturation problems, enabling thus dicentric analysis even at high-dose exposures. Using the fluorescence in situ hybridization technique with telomere and centromere peptide nucleic acid probes, the released lymphocytes, identified as metaphases with decondensed chromosomes following 1.5 h caffeine treatment, show increased yield of dicentrics compared to that obtained in lymphocytes that reach metaphase without G2-checkpoint abrogation by caffeine. Here, a 3-h caffeine/colcemid co-treatment before harvesting at 55 h post-exposure is used so that the dicentric analysis using Giemsa staining is based predominantly on lymphocytes released from the G2-block, increasing thus dicentric yield and enabling construction of a dose-response calibration curve with improved precision of high-dose estimates.

Dose assessment intercomparisons within the RENEB network using G0-lymphocyte prematurely condensed chromosomes (PCC assay)

PURPOSE

Dose assessment intercomparisons within the RENEB network were performed for triage biodosimetry analyzing G₀-lymphocyte PCC for harmonization, standardization and optimization of the PCC assay.

MATERIALS AND METHODS

Comparative analysis among different partners for dose assessment included shipment of PCC-slides and captured images to construct dose-response curves for up to 6 Gy γ-rays. Accident simulation exercises were performed to assess the suitability of the PCC assay by detecting speed of analysis and minimum number of cells required for categorization of potentially exposed individuals.

RESULTS

Calibration data based on Giemsa-stained fragments in excess of 46 PCC were obtained by different partners using galleries of PCC images for each dose-point. Mean values derived from all scores yielded a linear dose-response with approximately 4 excess-fragments/cell/Gy. To unify scoring criteria, exercises were carried out using coded PCC-slides and/or coded irradiated blood samples. Analysis of samples received 24 h post-exposure was successfully performed using Giemsa staining (1 excess-fragment/cell/Gy) or centromere/telomere FISH-staining for dicentrics.

CONCLUSIONS

Dose assessments by RENEB partners using appropriate calibration curves were mostly in good agreement. The PCC assay is quick and reliable for whole- or partial-body triage biodosimetry by scoring excess-fragments or dicentrics in G₀-lymphocytes. Particularly, analysis of Giemsa-stained excess PCC-fragments is simple, inexpensive and its automation could increase throughput and scoring objectivity of the PCC assay.

Review of Cytogenetic analysis of restoration workers for Fukushima Daiichi nuclear power station accident

Japan faced with the nuclear accident of the Fukushima Daiichi Nuclear Power Station (NPS) caused by the combined disaster of the Great East Japan Earthquake and the subsequent tsunamis on 11 March 2011. National Institute of Radiological Sciences received all nuclear workers who were engaged in emergency response tasks at the NPS and suspected of being overexposed to acute radiation. Biological dosimetry by dicentric chromosome assay was helpful for medical triage and management of the workers.

Utilization of cytogenetic biomarkers as a tool for assessment of radiation injury and evaluation of radiomodulatory effects of various medicinal plants - a review

Systematic biological measurement of “cytogenetic endpoints” has helped phenomenally in assessment of risks associated with radiation exposure. There has been a surge in recent times for the usage of radioactive materials in health care, agriculture, industrial, and nuclear power sectors. The likelihood of radiation exposure from accidental or occupational means is always higher in an overburdened ecosystem that is continuously challenged to meet the population demands. Risks associated with radiation exposure in this era of modern industrial growth are minimal as international regulations for maintaining the safety standards are stringent and strictly adhered to, however, a recent disaster like “Fukushima” impels us to think beyond. The major objective of radiobiology is the development of an orally effective radio-modifier that provides protection from radiation exposure. Once available for mass usage, these compounds will not only be useful for providing selective protection against accidental and occupational radiation exposure but also help to permit use of higher doses of radiation during treatment of various malignancies curtailing unwarranted adverse effects imposed on normal tissues. Bio-active compounds isolated from natural sources enriched with antioxidants possess unique immune-modulating properties, thus providing a double edged benefit over synthetic radioprotectors. We aim to provide here a comprehensive overview of the various agents originating from plant sources that portrayed promising radioprotection in various experimental models with special emphasis on studies that used cytogenetic biomarkers. The agents will include crude extracts of various medicinal plants, purified fractions, and herbal preparations.

Triage biodosimetry using centromeric/telomeric PNA probes and Giemsa staining to score dicentrics or excess fragments in non-stimulated lymphocyte prematurely condensed chromosomes

The frequency of dicentric chromosomes in human peripheral blood lymphocytes at metaphase is considered as the "gold-standard" method for biological dosimetry and, presently, it is the most widely used for dose assessment. Yet, it needs lymphocyte stimulation and a 2-day culture, failing the requirement of rapid dose estimation, which is a high priority in radiation emergency medicine and triage biodosimetry. In the present work, we assess the applicability of cell fusion mediated premature chromosome condensation (PCC) methodology, which enables the analysis of radiation-induced chromosomal aberrations directly in non-stimulated G0-lymphocytes, without the 2-day culture delay. Despite its advantages, quantification of an exposure by means of the PCC-method is not currently widely used, mainly because Giemsa-staining of interphase G0-lymphocyte chromosomes facilitates the analysis of fragments and rings, but not of dicentrics. To overcome this shortcoming, the PCC-method is combined with fluorescence in situ hybridization (FISH), using simultaneously centromeric/telomeric peptide nucleic acid (PNA)-probes. This new approach enables an accurate analysis of dicentric and centric ring chromosomes, which are formed within 8h post irradiation and will, therefore, be present in the blood sample by the time it arrives for dose estimation. For triage biodosimetry, a dose response curve for up to 10Gy was constructed and compared to that obtained using conventional metaphase analysis with Giemsa or centromeric/telomeric PNA-probes in metaphase. Since FISH is labor intensive, a simple PCC-method scoring Giemsa-stained fragments in excess of 46 was also assessed as an even more rapid approach for triage biodosimetry. First, we studied the rejoining kinetics of fragments and constructed a dose-response curve for 24h repair time. Then, its applicability was assessed for four different doses and compared with the PCC-method using centromeric/telomeric PNA-probes, through the evaluation of speed of analysis and minimum number of cells required for dose estimation and categorization of exposed individuals.