Development of a High-Throughput and Miniaturized Cytokinesis-Block Micronucleus Assay for Use as a Biological Dosimetry Population Triage Tool

Improving radiation dosimetry with an automated micronucleus scoring system: correction of automated scoring errors

Radiation dose estimations performed by automated counting of micronuclei (MN) have been studied for their utility for triage following large-scale radiological incidents; although speed is essential, it also is essential to estimate radiation doses as accurately as possible for long-term epidemiological follow-up. Our goal in this study was to evaluate and improve the performance of automated MN counting for biodosimetry using the cytokinesis-block micronucleus (CBMN) assay. We measured false detection rates and used them to improve the accuracy of dosimetry. The average false-positive rate for binucleated cells was 1.14%; average false-positive and -negative MN rates were 1.03% and 3.50%, respectively. Detection errors seemed to be correlated with radiation dose. Correction of errors by visual inspection of images used for automated counting, called the semi-automated and manual scoring method, increased accuracy of dose estimation. Our findings suggest that dose assessment of the automated MN scoring system can be improved by subsequent error correction, which could be useful for performing biodosimetry on large numbers of people rapidly, accurately, and efficiently.

Longitudinal multi-omic changes in the transcriptome and proteome of peripheral blood cells after a 4 Gy total body radiation dose to Rhesus macaques

BACKGROUND

Non-human primates, such as Rhesus macaques, are a powerful model for studies of the cellular and physiological effects of radiation, development of radiation biodosimetry, and for understanding the impact of radiation on human health. Here, we study the effects of 4 Gy total body irradiation (TBI) at the molecular level out to 28 days and at the cytogenetic level out to 56 days after exposure. We combine the global transcriptomic and proteomic responses in peripheral whole blood to assess the impact of acute TBI exposure at extended times post irradiation.

RESULTS

The overall mRNA response in the first week reflects a strong inflammatory reaction, infection response with neutrophil and platelet activation. At 1 week, cell cycle arrest and re-entry processes were enriched among mRNA changes, oncogene-induced senescence and MAPK signaling among the proteome changes. Influenza life cycle and infection pathways initiated earlier in mRNA and are reflected among the proteomic changes during the first week. Transcription factor proteins SRC, TGFβ and NFATC2 were immediately induced at 1 day after irradiation with increased transcriptional activity as predicted by mRNA changes persisting up to 1 week. Cell counts revealed a mild / moderate hematopoietic acute radiation syndrome (H-ARS) reaction to irradiation with expected lymphopenia, neutropenia and thrombocytopenia that resolved within 30 days. Measurements of micronuclei per binucleated cell levels in cytokinesis-blocked T-lymphocytes remained high in the range 0.27-0.33 up to 28 days and declined to 0.1 by day 56.

CONCLUSIONS

Overall, we show that the TBI 4 Gy dose in NHPs induces many cellular changes that persist up to 1 month after exposure, consistent with damage, death, and repopulation of blood cells.

A machine learning method for improving the accuracy of radiation biodosimetry by combining data from the dicentric chromosomes and micronucleus assays

A large-scale malicious or accidental radiological event can expose vast numbers of people to ionizing radiation. The dicentric chromosome (DCA) and cytokinesis-block micronucleus (CBMN) assays are well-established biodosimetry methods for estimating individual absorbed doses after radiation exposure. Here we used machine learning (ML) to test the hypothesis that combining automated DCA and CBMN assays will improve dose reconstruction accuracy, compared with using either cytogenetic assay alone. We analyzed 1349 blood sample aliquots from 155 donors of different ages (3-69 years) and sexes (49.1% males), ex vivo irradiated with 0-8 Gy at dose rates from 0.08 Gy/day to ≥ 600 Gy/s. We compared the performances of several state-of-the-art ensemble ML methods and found that random forest generated the best results, with R² for actual vs. reconstructed doses on a testing data subset = 0.845, and mean absolute error = 0.628 Gy. The most important predictor variables were CBMN and DCA frequencies, and age. Removing CBMN or DCA data from the model significantly increased squared errors on testing data (p-values 3.4 × 10^-8 and 1.1 × 10^-6, respectively). These findings demonstrate the promising potential of combining CBMN and DCA assay data to reconstruct radiation doses in realistic scenarios of heterogeneous populations exposed to a mass-casualty radiological event.

Optimisation of an automated high-throughput micronucleus (HiTMiN) assay to measure genotoxicity of environmental contaminants

Anthropogenic contaminants can have a variety of adverse effects on exposed organisms, including genotoxicity in the form of DNA damage. One of the most commonly used methods to evaluate genotoxicity in exposed organisms is the micronucleus (MN) assay. It provides an efficient assessment of chromosomal impairment due to either chromosomal rupture or mis-segregation during mitosis. However, evaluating chromosomal damage in the MN assay through manual microscopy is a highly time-consuming and somewhat subjective process. High-throughput evaluation with automated image analysis could reduce subjectivity and increase accuracy and throughput. In this study, we optimised and streamlined the HiTMiN assay, adapting the MN assay to a miniaturised, 96-well plate format with reduced steps, and applied it to both primary cells from green turtle fibroblasts (GT12s-p) and a freshwater fish hepatoma cell line (PLHC-1). Image analysis using both commercial (Columbus) and freely available (CellProfiler) software automated the scoring of MN, with improved precision and drastically reduced time compared to manual scoring and other available protocols. The assay was validated through exposure to two inorganic (chromium and cobalt) and one organic (the herbicide metolachlor) compounds, which are genotoxicants of concern in the marine environment. All compounds tested induced MN formation below cytotoxic concentrations. The HiTMiN assay presented here greatly increases the suitability of the MN assay as a quick, affordable, sensitive and accurate assay to measure genotoxicity of environmental samples in different cell lines.

NIH Policies and Regulatory Pathways to U.S. FDA licensure: Strategies to Inform Advancement of Radiation Medical Countermeasures and Biodosimetry Devices

The Radiation and Nuclear Countermeasures Program within the National Institute of Allergy and Infectious Diseases (NIAID), is tasked with the mandate of identifying biodosimetry tests to assess exposure and medical countermeasures (MCMs) to mitigate/treat injuries to individuals exposed to significant doses of ionizing radiation from a radiological/nuclear incident, hosted. To fulfill this mandate, the Radiation and Nuclear Countermeasures Program (RNCP), hosted a workshop in 2018 workshop entitled "Policies and Regulatory Pathways to U.S. FDA licensure: Radiation Countermeasures and Biodosimetry Devices." The purpose of the meeting was to facilitate the advancement of MCMs and biodosimetry devices by assessing the research devices and animal models used in preclinical studies; government policies on reproducibility, rigor and robustness; regulatory considerations for MCMs and biodosimetry devices; and lessons learned from sponsors of early stage MCM or biodosimetry devices. Meeting presentations were followed by a NIAID-led, open discussion among academic investigators, industry researchers and U.S. government representatives.

CytoRADx: A High-Throughput, Standardized Biodosimetry Diagnostic System Based on the Cytokinesis-Block Micronucleus Assay

In a large-scale catastrophe, such as a nuclear detonation in a major city, it will be crucial to accurately diagnose large numbers of people to direct scarce medical resources to those in greatest need. Currently no FDA-cleared tests are available to diagnose radiation exposures, which can lead to complex, life-threatening injuries. To address this gap, we have achieved substantial advancements in radiation biodosimetry through refinement and adaptation of the cytokinesis-block micronucleus (CBMN) assay as a high throughput, quantitative diagnostic test. The classical CBMN approach, which quantifies micronuclei (MN) resulting from DNA damage, suffers from considerable time and expert labor requirements, in addition to a lack of universal methodology across laboratories. We have developed the CytoRADx™ System to address these drawbacks by implementing a standardized reagent kit, optimized assay protocol, fully automated microscopy and image analysis, and integrated dose prediction. These enhancements allow the CytoRADx System to obtain high-throughput, standardized results without specialized labor or laboratory-specific calibration curves. The CytoRADx System has been optimized for use with both humans and non-human primates (NHP) to quantify radiation dose-dependent formation of micronuclei in lymphocytes, observed using whole blood samples. Cell nuclei and resulting MN are fluorescently stained and preserved on durable microscope slides using materials provided in the kit. Up to 1,000 slides per day are subsequently scanned using the commercially based RADxScan™ Imager with customized software, which automatically quantifies the cellular features and calculates the radiation dose. Using less than 1 mL of blood, irradiated ex vivo, our system has demonstrated accurate and precise measurement of exposures from 0 to 8 Gy (90% of results within 1 Gy of delivered dose). These results were obtained from 636 human samples (24 distinct donors) and 445 NHP samples (30 distinct subjects). The system demonstrated comparable results during in vivo studies, including an investigation of 43 NHPs receiving single-dose total-body irradiation. System performance is repeatable across laboratories, operators, and instruments. Results are also statistically similar across diverse populations, considering various demographics, common medications, medical conditions, and acute injuries associated with radiological disasters. Dose calculations are stable over time as well, providing reproducible results for at least 28 days postirradiation, and for blood specimens collected and stored at room temperature for at least 72 h. The CytoRADx System provides significant advancements in the field of biodosimetry that will enable accurate diagnoses across diverse populations in large-scale emergency scenarios. In addition, our technological enhancements to the well-established CBMN assay provide a pathway for future diagnostic applications, such as toxicology and oncology.

Automated Cytogenetic Biodosimetry at Population-Scale

The dicentric chromosome (DC) assay accurately quantifies exposure to radiation; however, manual and semi-automated assignment of DCs has limited its use for a potential large-scale radiation incident. The Automated Dicentric Chromosome Identifier and Dose Estimator (ADCI) software automates unattended DC detection and determines radiation exposures, fulfilling IAEA criteria for triage biodosimetry. This study evaluates the throughput of high-performance ADCI (ADCI-HT) to stratify exposures of populations in 15 simulated population scale radiation exposures. ADCI-HT streamlines dose estimation using a supercomputer by optimal hierarchical scheduling of DC detection for varying numbers of samples and metaphase cell images in parallel on multiple processors. We evaluated processing times and accuracy of estimated exposures across census-defined populations. Image processing of 1744 samples on 16,384 CPUs required 1 h 11 min 23 s and radiation dose estimation based on DC frequencies required 32 sec. Processing of 40,000 samples at 10 exposures from five laboratories required 25 h and met IAEA criteria (dose estimates were within 0.5 Gy; median = 0.07). Geostatistically interpolated radiation exposure contours of simulated nuclear incidents were defined by samples exposed to clinically relevant exposure levels (1 and 2 Gy). Analysis of all exposed individuals with ADCI-HT required 0.6–7.4 days, depending on the population density of the simulation.

Machine learning methodology for high throughput personalized neutron dose reconstruction in mixed neutron + photon exposures

We implemented machine learning in the radiation biodosimetry field to quantitatively reconstruct neutron doses in mixed neutron + photon exposures, which are expected in improvised nuclear device detonations. Such individualized reconstructions are crucial for triage and treatment because neutrons are more biologically damaging than photons. We used a high-throughput micronucleus assay with automated scanning/imaging on lymphocytes from human blood ex-vivo irradiated with 44 different combinations of 0-4 Gy neutrons and 0-15 Gy photons (542 blood samples), which include reanalysis of past experiments. We developed several metrics that describe micronuclei/cell probability distributions in binucleated cells, and used them as predictors in random forest (RF) and XGboost machine learning analyses to reconstruct the neutron dose in each sample. The probability of "overfitting" was minimized by training both algorithms with repeated cross-validation on a randomly-selected subset of the data, and measuring performance on the rest. RF achieved the best performance. Mean R² for actual vs. reconstructed neutron doses over 300 random training/testing splits was 0.869 (range 0.761 to 0.919) and root mean squared error was 0.239 (0.195 to 0.351) Gy. These results demonstrate the promising potential of machine learning to reconstruct the neutron dose component in clinically-relevant complex radiation exposure scenarios.

Retinol palmitate against toxicogenic damages of antineoplastic drugs on normal and tumor cells

The lack of tissue selectivity of anticancer drugs generates intense collateral and adverse effects of cancer patients, making the incorporation of vitamins or micronutrients into the diet of individuals to reduce side or adverse effects of antineoplastics. The study aimed to evaluate the effects of retinol palmitate (RP) on the toxicogenic damages induced by cyclophosphamide (CPA), doxorubicin (DOX) and its association with the AC protocol (CPA + DOX), in Sarcoma 180 (S-180) tumor cell line, using the micronuclei test with a block of cytokinesis (CBMN); and in non-tumor cells derived from Mus musculus using the comet assay. The results suggest that CPA, DOX and AC protocol induced significant toxicogenic damages (P < 0.05) on the S-180 cells by induction of micronuclei, cytoplasmic bridges, nuclear buds, apoptosis, and cell necrosis, proving their antitumor effects, and significant damage (P < 0.001) to the genetic material of peripheral blood cells of healthy mice, proving the genotoxic potential of these drugs. However, RP modulated the toxicogenic effects of antineoplastic tested both in the CBMN test (P < 0.05), at the concentrations of 1, 10 and 100 IU/mL; as in the comet assay (P < 0.001) at the concentration of 100 IU/kg for the index and frequency of genotoxic damage. The accumulated results suggest that RP reduced the action of antineoplastics in non-tumor cells as well as the cytotoxic, mutagenic, and cell death in neoplastic cells.

Cytogenetically-based biodosimetry after high doses of radiation

Dosimetry is an important tool for triage and treatment planning following any radiation exposure accident, and biological dosimetry, which estimates exposure dose using a biological parameter, is a practical means of determining the specific dose an individual receives. The cytokinesis-blocked micronucleus assay (CBMN) is an established biodosimetric tool to measure chromosomal damage in mitogen-stimulated human lymphocytes. The CBMN method is especially valuable for biodosimetry in triage situations thanks to simplicity in scoring and adaptability to high-throughput automated sample processing systems. While this technique produces dose-response data which fit very well to a linear-quadratic model for exposures to low linear energy transfer (LET) radiation and for doses up for 5 Gy, limitations to the accuracy of this method arise at larger doses. Accuracy at higher doses is limited by the number of cells reaching mitosis. Whereas it would be expected that the yield of micronuclei increases with the dose, in many experiments it has been shown to actually decrease when normalized over the total number of cells. This variation from a monotonically increasing dose response poses a limitation for retrospective dose reconstruction. In this study we modified the standard CBMN assay to increase its accuracy following exposures to higher doses of photons or a mixed neutron-photon beam. The assay is modified either through inhibitions of the G2/M and spindle checkpoints with the addition of caffeine and/or ZM447439 (an Aurora kinase inhibitor), respectively to the blood cultures at select times during the assay. Our results showed that caffeine addition improved assay performance for photon up to 10 Gy. This was achieved by extending the assay time from the typical 70 h to just 74 h. Compared to micronuclei yields without inhibitors, addition of caffeine and ZM447439 resulted in improved accuracy in the detection of micronuclei yields up to 10 Gy from photons and 4 Gy of mixed neutrons-photons. When the dose-effect curves were fitted to take into account the turnover phenomenon observed at higher doses, best fitting was achieved when the combination of both inhibitors was used. These techniques permit reliable dose reconstruction after high doses of radiation with a method that can be adapted to high-throughput automated sample processing systems.

A High Throughput Approach to Reconstruct Partial-Body and Neutron Radiation Exposures on an Individual Basis

Biodosimetry-based individualized reconstruction of complex irradiation scenarios (partial-body shielding and/or neutron + photon mixtures) can improve treatment decisions after mass-casualty radiation-related incidents. We used a high-throughput micronucleus assay with automated scanning and imaging software on ex-vivo irradiated human lymphocytes to: a) reconstruct partial-body and/or neutron exposure, and b) estimate separately the photon and neutron doses in a mixed exposure. The mechanistic background is that, compared with total-body photon irradiations, neutrons produce more heavily-damaged lymphocytes with multiple micronuclei/binucleated cell, whereas partial-body exposures produce fewer such lymphocytes. To utilize these differences for biodosimetry, we developed metrics that describe micronuclei distributions in binucleated cells and serve as predictors in machine learning or parametric analyses of the following scenarios: (A) Homogeneous gamma-irradiation, mimicking total-body exposures, vs. mixtures of irradiated blood with unirradiated blood, mimicking partial-body exposures. (B) X rays vs. various neutron + photon mixtures. The results showed high accuracies of scenario and dose reconstructions. Specifically, receiver operating characteristic curve areas (AUC) for sample classification by exposure type reached 0.931 and 0.916 in scenarios A and B, respectively. R² for actual vs. reconstructed doses in these scenarios reached 0.87 and 0.77, respectively. These encouraging findings demonstrate a proof-of-principle for the proposed approach of high-throughput reconstruction of clinically-relevant complex radiation exposure scenarios.

THE ROLE OF RADIOACTIVE METHODS IN THE DIAGNOSTIC TYPE OF HYDRONEPHROSIS IN CLEAN-UP WORKERS OF CHORNOBYL ACCIDENT

RATIONALE

Since the introduction of radionuclide research methods into clinical practice, they occupy an importantplace in the diagnosis of hydronephrosis and, at the same time, sufficiently objective, sensitive and atraumaticmethods of investigation.

OBJECTIVE

On the basis of retrospective data, to investigate the diagnostic role of radionuclide renography (RRG)and the method of indirect radionuclide renangiography (IRAG) in clean-up workers of Chornobyl accident withhydronephrosis.

MATERIALS AND METHODS

A total of 257 patients with hydronephrosis (140 women and 117 men) aged 15 to 77 yearswere examined by the RRG and the IRAG. The RRG technique consists of intravenous administration of a solution of131I-hypurane (2.5 kBq/kg) and continuous registration for 20 minutes of the level of radioactivity above the kid-neys with the help of sensors of the renograph UR 1-1. The IRAG was conducted for 30-45 seconds with exposure1 frame per second after intravenous administration of a solution of 99mTc-pentatech (2 MBq/kg).

RESULTS

The results of the radionuclide study of the hemodynamics of patients with different stages ofhydronephrosis made it possible to draw a conclusion regarding the expediency of taking into account the condi-tion of the cup-pelvic system in the preoperative period, as well as the parameters of the arterial and venous circu-lation.

CONCLUSIONS

Combined use of X-ray and radionuclide methods allows establishing the cause and consequences ofhydronephrosis, to develop a rational treatment plan. RRG and IRAG are reliable methods of dynamic control in post-operative observation of clean-up workers of Chornobyl accident with hydronephrosis.

DEVELOPMENT OF A MINIATURIZED VERSION OF DICENTRIC CHROMOSOME ASSAY TOOL FOR RADIOLOGICAL TRIAGE

Use of ionizing radiation (IR) in various industrial, medical and other applications can potentially increase the risk of medical, occupational or accidental human exposure. Additionally, in the event of a radiological or nuclear (R/N) incident, several tens of hundreds and thousands of people are likely to be exposed to IR. IR causes serious health effects including mortality from acute radiation syndrome and therefore it is imperative to determine the absorbed radiation dose, which will enable physicians in making an appropriate clinical 'life-saving' decision. The 'Dicentric Chromosome Assay (DCA)' is the gold standard for estimating the absorbed radiation dose but its performance is time consuming and laborious. Further, timely evaluation of dicentric chromosomes (DCs) for dose estimation in a large number of samples provides a bottleneck because of a limited number of trained personnel and a prolonged time for manual analysis. To circumvent some of these technical issues, we developed and optimized a miniaturized high throughput version of DCA (mini-DCA) in a 96-microtube matrix with bar-coded 1.4 ml tubes to enable the processing of a large number of samples. To increase the speed of DC analysis for radiation dose estimation, a semi-automated scoring was optimized using the Metafer DCScore algorithm. The accuracy of mini-DCA in dose estimation was verified and validated though comparison with conventional DCA performed in 15 ml conical tubes. The mini-DCA considerably reduced the sample processing time by a factor of 4 when compared to the conventional DCA. Further, the radiation doses estimated by mini-DCA using the triage mode of scoring (50 cells or 30 DCs) were similar to that of conventional DCA using 300-500 cells. The mini-DCA coupled with semi-automated DC scoring not only reduced the sample processing and analysis times by a factor of 4 but also enabled the processing of a large number of samples at once. Our mini-DCA method, once automated for high throughput robotic platforms, will be an effective radiological triage tool for mass casualty incidents.

EXPRESSION OF BIOLOGICAL MARKERS INDUCED BY IONIZING RADIATION AT THE LATE PERIOD AFTER EXPOSURE IN A WIDE RANGE OF DOSES

OBJECTIVE

To study radiation induced biological markers of the late period after exposure.

SUBJECTS AND METHODS

A study was performed in 235 Chornobyl accident male clean-up workers exposed in 1986-1987 (doses of external exposure: (M ± SD: 419.48 ± 654.60; range 0.10-3,500 mSv); age 58,34 ± 6,57 years. Controlgroup included 45 non-exposed subjects (mean age: 50.60 ± 5.37 (M ± SD). Gene expression was performed by RT-PCR on 7900HT Analyzer using TLDA for BCL2, CDKN2A, CLSTN2, GSTM1, IFNG, IL1B, MCF2L, SERPINB9, STAT3, TERF1, TERF2,TERT, TNF, TP53, CCND1 genes. Relative telomere length (RTL) was analysed by flow-FISH; immune cell subsets,γ-H2AХ and CyclinD1 expression by flow cytometry.

RESULTS

A statistically significant and dose-dependent decrease in expression of the BCL2, SERPINB9, CDKN2A, andSTAT3 genes was demonstrated in parallel to a dose-dependent overexpression of MCF2L and upregulation of TP53 (upto 100 mSv). IL1B expression was the highest in exposed to doses from 0.1 to 100 mSv with a negative correlationbetween at IL1B expression and CD19+3-, CD3-HLA-DR+, CD4+8- cell counts and CD4+/CD8+ ratio. Hyperexpression ofTNF gene in doses above 100 mSv to 1,000 mSv was shown, and in higher doses a combination of TNF downregula-tion with increase in IFNG gene expression were demonstrated with correlations with numbers of CD3+16+56+ andCD25+ lymphocytes and inhibition of expression CLSTN2. An increased expression of γ-H2AХ and Cyclin D1 corre-lated to radiation dose, telomere shortening to age and concommittant pathology.

CONCLUSIONS

Cellular immunity, gene expression, telomere length, intracellular protein parameters are shown to beamong perspective biological markers at a late period after radiation exposure.

The first in vivo multiparametric comparison of different radiation exposure biomarkers in human blood

The increasing risk of acute large-scale radiological/nuclear exposures of population underlines the necessity of developing new, rapid and high throughput biodosimetric tools for estimation of received dose and initial triage. We aimed to compare the induction and persistence of different radiation exposure biomarkers in human peripheral blood in vivo. Blood samples of patients with indicated radiotherapy (RT) undergoing partial body irradiation (PBI) were obtained soon before the first treatment and then after 24 h, 48 h, and 5 weeks; i.e. after 1, 2, and 25 fractionated RT procedures. We collected circulating peripheral blood from ten patients with tumor of endometrium (1.8 Gy per fraction) and eight patients with tumor of head and neck (2.0–2.121 Gy per fraction). Incidence of dicentrics and micronuclei was monitored as well as determination of apoptosis and the transcription level of selected radiation-responsive genes. Since mitochondrial DNA (mtDNA) has been reported to be a potential indicator of radiation damage in vitro, we also assessed mtDNA content and deletions by novel multiplex quantitative PCR. Cytogenetic data confirmed linear dose-dependent increase in dicentrics (p < 0.01) and micronuclei (p < 0.001) in peripheral blood mononuclear cells after PBI. Significant up-regulations of five previously identified transcriptional biomarkers of radiation exposure (PHPT1, CCNG1, CDKN1A, GADD45, and SESN1) were also found (p < 0.01). No statistical change in mtDNA deletion levels was detected; however, our data indicate that the total mtDNA content decreased with increasing number of RT fractions. Interestingly, the number of micronuclei appears to correlate with late radiation toxicity (r² = 0.9025) in endometrial patients suggesting the possibility of predicting the severity of RT-related toxicity by monitoring this parameter. Overall, these data represent, to our best knowledge, the first study providing a multiparametric comparison of radiation biomarkers in human blood in vivo, which have potential for improving biological dosimetry.

RABiT-II: Implementation of a High-Throughput Micronucleus Biodosimetry Assay on Commercial Biotech Robotic Systems

We demonstrate the use of high-throughput biodosimetry platforms based on commercial high-throughput/high-content screening robotic systems. The cytokinesis-block micronucleus (CBMN) assay, using only 20 μl whole blood from a fingerstick, was implemented on a PerkinElmer cell::explorer and General Electric IN Cell Analyzer 2000. On average 500 binucleated cells per sample were detected by our FluorQuantMN software. A calibration curve was generated in the radiation dose range up to 5.0 Gy using the data from 8 donors and 48,083 binucleated cells in total. The study described here demonstrates that high-throughput radiation biodosimetry is practical using current commercial high-throughput/high-content screening robotic systems, which can be readily programmed to perform and analyze robotics-optimized cytogenetic assays. Application to other commercial high-throughput/high-content screening systems beyond the ones used in this study is clearly practical. This approach will allow much wider access to high-throughput biodosimetric screening for large-scale radiological incidents than is currently available.

Biomarkers of Ionizing Radiation Exposure: A Multiparametric Approach

Humans are exposed to ionizing radiation not only through background radiation but also through the ubiquitous presence of devices and sources that generate radiation. With the expanded use of radiation in day-to-day life, the chances of accidents or misuse only increase. Therefore, a thorough understanding of the dynamic effects of radiation exposure on biological entities is necessary. The biological effects of radiation exposure on human cells depend on much variability such as level of exposure, dose rate, and the physiological state of the cells. During potential scenarios of a large-scale radiological event which results in mass casualties, dose estimates are essential to assign medical attention according to individual needs. Many attempts have been made to identify biomarkers which can be used for high throughput biodosimetry screening. In this study, we compare the results of different biodosimetry methods on the same irradiated cells to assess the suitability of current biomarkers and push forward the idea of employing a multiparametric approach to achieve an accurate dose and risk estimation.

THE DECADE OF THE RABiT (2005-15)

The RABiT (Rapid Automated Biodosimetry Tool) is a dedicated Robotic platform for the automation of cytogenetics-based biodosimetry assays. The RABiT was developed to fulfill the critical requirement for triage following a mass radiological or nuclear event. Starting from well-characterized and accepted assays we developed a custom robotic platform to automate them. We present here a brief historical overview of the RABiT program at Columbia University from its inception in 2005 until the RABiT was dismantled at the end of 2015. The main focus of this paper is to demonstrate how the biological assays drove development of the custom robotic systems and in turn new advances in commercial robotic platforms inspired small modifications in the assays to allow replacing customized robotics with 'off the shelf' systems. Currently, a second-generation, RABiT II, system at Columbia University, consisting of a PerkinElmer cell::explorer, was programmed to perform the RABiT assays and is undergoing testing and optimization studies.

Methemoglobin-Based Biological Dose Assessment for Human Blood

Methemoglobin is an oxidative form of hemoglobin in erythrocytes. The authors' aim was to develop a new biological dosimeter based on a methemoglobin assay. Methemoglobin in peripheral blood (of females or males) that was exposed to a Co source (0.20 Gy min) was quantified using an enzyme-linked immunosorbent assay. The dose range was 0.5-8.0 Gy. In a time-course experiment, the time points 0, 0.02, 1, 2, 3, 7, 15, 21, and 30 d after 4-Gy irradiation of heparinized peripheral blood were used. Methemoglobin levels in a lysed erythrocyte pellet from the irradiated blood of females and males increased with the increasing dose. Methemoglobin levels in female blood irradiated with γ-doses more than 4 Gy were significantly higher than those in male samples at the same doses. Two dose-response relations were fitted to the straight line: one is with the correlation coefficient of 0.98 for females, and the other is with the correlation coefficient of 0.99 for males. The lower limit of dose assessment based on methemoglobin is about 1 Gy. Methemoglobin levels in blood as a result of auto-oxidation increase after 7-d storage at -20 °C. The upregulation of methemoglobin induced by γ-radiation persists for ∼3 d. The absorbed doses that were estimated using the two dose-response relations were close to the actual doses. The results suggest that methemoglobin can be used as a rapid and accurate biological dosimeter for early assessment of absorbed γ-dose in human blood.

Accelerator-Based Biological Irradiation Facility Simulating Neutron Exposure from an Improvised Nuclear Device

We describe here an accelerator-based neutron irradiation facility, intended to expose blood or small animals to neutron fields mimicking those from an improvised nuclear device at relevant distances from the epicenter. Neutrons are generated by a mixed proton/deuteron beam on a thick beryllium target, generating a broad spectrum of neutron energies that match those estimated for the Hiroshima bomb at 1.5 km from ground zero. This spectrum, dominated by neutron energies between 0.2 and 9 MeV, is significantly different from the standard reactor fission spectrum, as the initial bomb spectrum changes when the neutrons are transported through air. The neutron and gamma dose rates were measured using a custom tissue-equivalent gas ionization chamber and a compensated Geiger-Mueller dosimeter, respectively. Neutron spectra were evaluated by unfolding measurements using a proton-recoil proportional counter and a liquid scintillator detector. As an illustration of the potential use of this facility we present micronucleus yields in single divided, cytokinesis-blocked human peripheral lymphocytes up to 1.5 Gy demonstrating 3- to 5-fold enhancement over equivalent X-ray doses. This facility is currently in routine use, irradiating both mice and human blood samples for evaluation of neutron-specific biodosimetry assays. Future studies will focus on dose reconstruction in realistic mixed neutron/photon fields.