The RABiT: high-throughput technology for assessing global DSB repair

Artificial Intelligence in Andrology: From Semen Analysis to Image Diagnostics

Artificial intelligence (AI) in medicine has gained a lot of momentum in the last decades and has been applied to various fields of medicine. Advances in computer science, medical informatics, robotics, and the need for personalized medicine have facilitated the role of AI in modern healthcare. Similarly, as in other fields, AI applications, such as machine learning, artificial neural networks, and deep learning, have shown great potential in andrology and reproductive medicine. AI-based tools are poised to become valuable assets with abilities to support and aid in diagnosing and treating male infertility, and in improving the accuracy of patient care. These automated, AI-based predictions may offer consistency and efficiency in terms of time and cost in infertility research and clinical management. In andrology and reproductive medicine, AI has been used for objective sperm, oocyte, and embryo selection, prediction of surgical outcomes, cost-effective assessment, development of robotic surgery, and clinical decision-making systems. In the future, better integration and implementation of AI into medicine will undoubtedly lead to pioneering evidence-based breakthroughs and the reshaping of andrology and reproductive medicine.

Assessment of Micronuclei Frequency in the Peripheral Blood of Adult and Pediatric Patients Receiving Fractionated Total Body Irradiation

The cytokinesis-block micronucleus (CBMN) assay is an established method for assessing chromosome damage in human peripheral blood lymphocytes resulting from exposure to genotoxic agents such as ionizing radiation. The objective of this study was to measure cytogenetic DNA damage and hematology parameters in vivo based on MN frequency in peripheral blood lymphocytes (PBLs) from adult and pediatric leukemia patients undergoing hematopoietic stem cell transplantation preceded by total body irradiation (TBI) as part of the conditioning regimen. CBMN assay cultures were prepared from fresh blood samples collected before and at 4 and 24 h after the start of TBI, corresponding to doses of 1.25 Gy and 3.75 Gy, respectively. For both age groups, there was a significant increase in MN yields with increasing dose (p < 0.05) and dose-dependent decrease in the nuclear division index (NDI; p < 0.0001). In the pre-radiotherapy samples, there was a significantly higher NDI measured in the pediatric cohort compared to the adult due to an increase in the percentage of tri- and quadri-nucleated cells scored. Complete blood counts with differential recorded before and after TBI at the 24-h time point showed a rapid increase in neutrophil (p = 0.0001) and decrease in lymphocyte (p = 0.0006) counts, resulting in a highly elevated neutrophil-to-lymphocyte ratio (NLR) of 14.45 ± 1.85 after 3.75 Gy TBI (pre-exposure = 4.62 ± 0.49), indicating a strong systemic inflammatory response. Correlation of the hematological cell subset counts with cytogenetic damage, indicated that only the lymphocyte subset survival fraction (after TBI compared with before TBI) showed a negative correlation with increasing MN frequency from 0 to 1.25 Gy (r = -0.931; p = 0.007). Further, the data presented here indicate that the combination of CBMN assay endpoints (MN frequency and NDI values) and hematology parameters could be used to assess cytogenetic damage and early hematopoietic injury in the peripheral blood of leukemia patients, 24 h after TBI exposure.

Paper-Based Vertical Flow Immunoassay for the Point-of-Care Multiplex Detection of Radiation Dosimetry Genes

In a nuclear or radiological incident, first responders must quickly and accurately measure radiation exposure among civilians as medical countermeasures are radiation dose-dependent and time-sensitive. Although several approaches have been explored to measure absorbed radiation dose, there is an important need to develop point-of-care (POC) bioassay devices that can be used immediately to triage thousands of individuals potentially exposed to radiation. Here we present a proof-of-concept study showing the use of a paper-based vertical flow immunoassay (VFI) to detect radiation dosimetry genes. Using labeled primers during amplification and a multiplex membrane, our results showed that the nucleic acid VFI can simultaneously detect two biodosimetry genes, CDKN1A and DDB2, as well as one housekeeping gene MRPS5. The assay demonstrated good linearity and precision with an inter- and intra-assay coefficient of variance <20% and <10%, respectively. Moreover, the assay showed its ability to discriminate non-irradiated controls (0 Gy) from irradiated samples (1 + 2 Gy) with an overall sensitivity of 62.5% and specificity of 100% (AUC = 0.8672, 95% CI: 0.723-1.000; p = 0.004). Interestingly, the gene combination also showed a dose-dependent response for 0, 1, and 2 Gy, similar to data obtained by real-time PCR benchmark. These preliminary results suggest that a VFI platform can be used to detect simultaneously multiple genes that can be then quantified, thus offering a new approach for a POC biodosimetry assay that could be rapidly deployed on-site to test a large population and help triage and medical management after radiological event.

Improved prediction of breast cancer risk based on phenotypic DNA damage repair capacity in peripheral blood B cells

Background

Standard Breast Cancer (BC) risk prediction models based only on epidemiologic factors generally have quite poor performance, and there have been a number of risk scores proposed to improve them, such as AI-based mammographic information, polygenic risk scores and pathogenic variants. Even with these additions BC risk prediction performance is still at best moderate. In that decreased DNA repair capacity (DRC) is a major risk factor for development of cancer, we investigated the potential to improve BC risk prediction models by including a measured phenotypic DRC assay.

Methods

Using blood samples from the Breast Cancer Family Registry we assessed the performance of phenotypic markers of DRC in 46 matched pairs of individuals, one from each pair with BC (with blood drawn before BC diagnosis) and the other from controls matched by age and time since blood draw. We assessed DRC in thawed cryopreserved peripheral blood mononuclear cells (PBMCs) by measuring γ-H2AX yields (a marker for DNA double-strand breaks) at multiple times from 1 to 20 hrs after a radiation challenge. The studies were performed using surface markers to discriminate between different PBMC subtypes.

Results

The parameter F res , the residual damage signal in PBMC B cells at 20 hrs post challenge, was the strongest predictor of breast cancer with an AUC (Area Under receiver-operator Curve) of 0.89 [95% Confidence Interval: 0.84-0.93] and a BC status prediction accuracy of 0.80. To illustrate the combined use of a phenotypic predictor with standard BC predictors, we combined F res in B cells with age at blood draw, and found that the combination resulted in significantly greater BC predictive power (AUC of 0.97 [95% CI: 0.94-0.99]), an increase of 13 percentage points over age alone.

Conclusions

If replicated in larger studies, these results suggest that inclusion of a fingerstick-based phenotypic DRC blood test has the potential to markedly improve BC risk prediction.

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.

Classifier Spot Count Optimization of Automated Fluorescent Slide Scanning System

Purpose: Ionizing radiation induced foci (IRIF) known also as DNA repair foci represent the most sensitive endpoint for assessing DNA double strand breaks (DSB). IRIF are usually visualized and enumerated with the aid of fluorescence microscopy using antibodies to γH2AX and 53BP1. Although several approaches and software packages were developed for the quantification of IRIF, not one of them was commonly accepted and inter-laboratory variability in the outputs was reported. In this study, the sensitization of Metafer software to counting also small appearing IRIF was validated.

Materials and Methods: Human lymphocytes were γ-irradiated at a dose of 2 Gy. The cells were fixed at 0.5, 1, 2, and 18 hours post-irradiation, permeabilized and IRIF were immunostained using appropriate antibodies. Cell images were acquired with the automatic Metafer system. Radiation-induced γH2AX and 53BP1 foci were enumerated using either manual counting (JCountPro program) or the Metafer software (after its classifier optimization has been done) and compared. The statistical analysis was performed using One-way ANOVA.

Results: The enumeration of 53BP1, γH2AX foci manually by JCountPro did not statistically significantly differ from the automatic one performed with the optimized Metafer classifier. A detailed step-by-step protocol of this successful optimization is described in this study.

Conclusions: We concluded that the Metafer software after the optimization was efficient in objectively enumerating IRIF, having a potential for usage in clinics and molecular epidemiology.

Quantification of histone H2AX phosphorylation in white blood cells induced by ex vivo gamma irradiation of whole blood by both flow cytometry and foci counting as a dose estimation in rapid triage

A quick, reliable, and reproducible biological assay to distinguish individuals with possible life-threatening risk following radiological or nuclear incidents remains a quest in biodosimetry. In this paper, we examined the use of a γ-H2AX assay as an early dose estimation for rapid triage based on both flow cytometry and image analyses. In the experiment, whole blood from 11 donors was irradiated ex vivo inside a water phantom by gamma rays from Co-60 at 0.51 Gy/min. After the lysis of red blood cells, the white blood cells were collected for immunofluorescence labeling of γ-H2AX, CD45, and nuclear stained for signal collection and visualization. Analysis by flow cytometry showed that the relative γ-H2AX intensities of lymphocytes and granulocytes increased linearly with absorbed doses from 0 to 6 Gy with a large variation among individuals observed above 2 Gy. The relative γ-H2AX intensities of lymphocytes assessed by two different laboratories were highly correlated (ICC = 0.979). Using confocal microscopic images, γ-H2AX foci were observed to be discretely distributed inside the nuclei and to increase proportionally with doses from 0 to 2 Gy, whereas large plagues of merged foci appeared at 4 and 6 Gy, resulting in the saturation of foci counts above 4 Gy. The number of total foci per cell as well as the number of foci per plane were significantly different at 0 vs 1 and 2 vs 4 Gy doses (p < 0.01). Blind tests at 0.5 Gy and 1 Gy doses showed that dose estimation by flow cytometry had a mean absolute difference of less than 0.5 Gy from the actual value. In conclusion, while flow cytometry can provide a dose estimation with an uncertainty of 0.5 Gy at doses ≤ 1 Gy, foci counting can identify merged foci that are prominent at doses ≥ 4 Gy.

DNA double-strand break repair in cancer: A path to achieving precision medicine

The assessment of DNA damage can be a significant diagnostic for precision medicine. DNA double strand break (DSBs) pathways in cancer are the primary targets in a majority of anticancer therapies, yet the molecular vulnerabilities that underlie each tumor can vary widely making the application of precision medicine challenging. Identifying and understanding these interindividual vulnerabilities enables the design of targeted DSB inhibitors along with evolving precision medicine approaches to selectively kill cancer cells with minimal side effects. A major challenge however, is defining exactly how to target unique differences in DSB repair pathway mechanisms. This review comprises a brief overview of the DSB repair mechanisms in cancer and includes results obtained with revolutionary advances such as CRISPR/Cas9 and machine learning/artificial intelligence, which are rapidly advancing not only our understanding of determinants of DSB repair choice, but also how it can be used to advance precision medicine. Scientific innovation in the methods used to diagnose and treat cancer is converging with advances in basic science and translational research. This revolution will continue to be a critical driver of precision medicine that will enable precise targeting of unique individual mechanisms. This review aims to lay the foundation for achieving this goal.

Evaluation of DNA double-strand break repair capacity in human cells: Critical overview of current functional methods

DNA double-strand breaks (DSBs) are highly deleterious lesions, responsible for mutagenesis, chromosomal translocation or cell death. DSB repair (DSBR) is therefore a critical part of the DNA damage response (DDR) to restore molecular and genomic integrity. In humans, this process is achieved through different pathways with various outcomes. The balance between DSB repair activities varies depending on cell types, tissues or individuals. Over the years, several methods have been developed to study variations in DSBR capacity. Here, we mainly focus on functional techniques, which provide dynamic information regarding global DSB repair proficiency or the activity of specific pathways. These methods rely on two kinds of approaches. Indirect techniques, such as pulse field gel electrophoresis (PFGE), the comet assay and immunofluorescence (IF), measure DSB repair capacity by quantifying the time-dependent decrease in DSB levels after exposure to a DNA-damaging agent. On the other hand, cell-free assays and reporter-based methods directly track the repair of an artificial DNA substrate. Each approach has intrinsic advantages and limitations and despite considerable efforts, there is currently no ideal method to quantify DSBR capacity. All techniques provide different information and can be regarded as complementary, but some studies report conflicting results. Parameters such as the type of biological material, the required equipment or the cost of analysis may also limit available options. Improving currently available methods measuring DSBR capacity would be a major step forward and we present direct applications in mechanistic studies, drug development, human biomonitoring and personalized medicine, where DSBR analysis may improve the identification of patients eligible for chemo- and radiotherapy.

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.

Fluorescence Sheds Light on DNA Damage, DNA Repair, and Mutations

DNA damage can lead to carcinogenic mutations and toxicity that promotes diseases. Therefore, having rapid assays to quantify DNA damage, DNA repair, mutations, and cytotoxicity is broadly relevant to health. For example, DNA damage assays can be used to screen chemicals for genotoxicity, and knowledge about DNA repair capacity has applications in precision prevention and in personalized medicine. Furthermore, knowledge of mutation frequency has predictive power for downstream cancer, and assays for cytotoxicity can predict deleterious health effects. Tests for all of these purposes have been rendered faster and more effective via adoption of fluorescent readouts. Here, we provide an overview of established and emerging cell-based assays that exploit fluorescence for studies of DNA damage and its consequences.

Comparison of inexperienced operators and experts in γH2A.X and 53BP1 foci assay for high-throughput biodosimetry approaches in a mass casualty incident

PURPOSE

In case of population exposure by ionizing radiation, a fast and reliable dose assessment of exposed and non-exposed individuals is crucial important. In initial triage, physicians have to take fast decisions whom to treat with adequate medical care. In addition, worries about significant exposure can be taken away from hundreds to thousands non- or low exposed individuals. Studies have shown that the γH2A.X radiation-induced foci assay is a promising test for fast triage decisions. However, in a large-scale scenario most biodosimetry laboratories will quickly reach their capacity limit. The aim of this study was to evaluate the benefit of inexperienced experimenters to speed up the foci assay and manual foci scoring.

MATERIALS AND METHODS

The participants of two training courses performed the radiation-induced foci assay (γH2A.X) under the guidance of experts and scored foci (γH2A.X and 53BP1) on sham-irradiated and irradiated blood samples (0.05-1.5 Gy). The outcome of laboratory experiments and manual foci scoring by 26 operators with basic experience in laboratory work was statistically analyzed in comparison to the results from experts.

RESULTS

Inexperienced operators prepared slides with significant dose-effects (0, 0.1 and 1.0 Gy) for semi-automatic microscopic analyses. Manual foci scoring by inexperienced scorer resulted in a dose-effect curve for γH2A.X, 53BP1 and co-localized foci. In addition, inexperienced scorers were able to distinguish low irradiation doses from unirradiated cells. While 53BP1 foci scoring was in accordance to the expert counting, differences between beginners and expert increased for γH2A.X or co-localized foci.

CONCLUSIONS

In case of a large-scale radiation event, inexperienced staff is useful to support laboratories in slide preparation for semi-automatic foci counting as well as γH2A.X and 53BP1 manual foci scoring for triage-mode biodosimetry. Slides can be clearly classified in the non-, low- or high-exposed category.

DNA damage response in peripheral mouse blood leukocytes in vivo after variable, low-dose rate exposure

Environmental contamination and ingestion of the radionuclide Cesium-137 (137Cs) is a large concern in fallout from a nuclear reactor accident or improvised nuclear device, and highlights the need to develop biological assays for low-dose rate, internal emitter radiation. To mimic low-dose rates attributable to fallout, we have developed a VAriable Dose-rate External 137Cs irradiatoR (VADER), which can provide arbitrarily varying and progressive low-dose rate irradiations in the range of 0.1-1.2 Gy/day, while circumventing the complexities of dealing with radioactively contaminated biomaterials. We investigated the kinetics of mouse peripheral leukocytes DNA damage response in vivo after variable, low-dose rate 137Cs exposure. C57BL/6 mice were placed in the VADER over 7 days with total accumulated dose up to 2.7 Gy. Peripheral blood response including the leukocyte depletion, apoptosis as well as its signal protein p53 and DNA repair biomarker γ-H2AX was measured. The results illustrated that blood leukocyte numbers had significantly dropped by day 7. P53 levels peaked at day 2 (total dose = 0.91 Gy) and then declined; whereas, γ-H2AX fluorescence intensity (MFI) and foci number generally increased with accumulated dose and peaked at day 5 (total dose = 2.08 Gy). ROC curve analysis for γ-H2AX provided a good discrimination of accumulated dose < 2 Gy and ≥ 2 Gy, highlighting the potential of γ-H2AX MFI as a biomarker for dosimetry in a protracted, environmental exposure scenario.

Effect of dose and dose rate on temporal γ-H2AX kinetics in mouse blood and spleen mononuclear cells in vivo following Cesium-137 administration

Background

Cesium-137 (¹³⁷Cs) is one of the major and most clinically relevant radionuclides of concern in a radiological dispersal device, “dirty bomb” scenario as well as in nuclear accidents and detonations. In this exposure scenario, a significant amount of soluble radionuclide(s) may be dispersed into the atmosphere as a component of fallout. The objectives of the present study were to investigate the effect of protracted ¹³⁷Cs radionuclide exposures on DNA damage in mouse blood and spleen mononuclear cells (MNCs) in vivo using the γ-H2AX biomarker, and to develop a mathematical formalism for these processes.

Results

C57BL/6 mice were injected with a range of ¹³⁷CsCl activities (5.74, 6.66, 7.65 and 9.28 MBq) to achieve total-body committed doses of ~ 4 Gy at Days 3, 5, 7, and 14. Close to 50% of ¹³⁷Cs was excreted by day 5, leading to a slower rate of decay for the remaining time of the study; ¹³⁷Cs excretion kinetics were independent of activity level within the tested range, and the absorbed radiation dose was determined by injected activity and time after injection. Measurements of γ-H2AX fluorescence in blood and spleen MNCs at each time point were used to develop a new biodosimetric mathematical formalism to estimate injected activity based on γ-H2AX fluorescence and time after injection. The formalism performed reasonably well on blood data at 2–5 days after injection: Pearson and Spearman’s correlation coefficients between actual and predicted activity values were 0.857 (p = 0.00659) and 0.929 (p = 0.00223), respectively.

Conclusions

Despite the complicated nature of the studied biological system and the time-dependent changes in radiation dose and dose rate due to radionuclide excretion and other processes, we have used the γ-H2AX repair kinetics to develop a mathematical formalism, which can relatively accurately predict injected ¹³⁷Cs activity 2–5 days after initial exposure. To determine the assay’s usefulness to predict retrospective absorbed dose for medical triage, further studies are required to validate the sensitivity and accuracy of the γ-H2AX response after protracted exposures.

Electronic supplementary material

The online version of this article (10.1186/s12860-019-0195-2) contains supplementary material, which is available to authorized users.

Automated Triage Radiation Biodosimetry: Integrating Imaging Flow Cytometry with High-Throughput Robotics to Perform the Cytokinesis-Block Micronucleus Assay

The cytokinesis-block micronucleus (CBMN) assay has become a fully-validated and standardized method for radiation biodosimetry. The assay is typically performed using microscopy, which is labor intensive, time consuming and impractical after a large-scale radiological/nuclear event. Imaging flow cytometry (IFC), which combines the statistical power of traditional flow cytometry with the sensitivity and specificity of microscopy, has been recently used to perform the CBMN assay. Since this technology is capable of automated sample acquisition and multi-file analysis, we have integrated IFC into our Rapid Automated Biodosimetry Technology (RABiT-II). Assay development and optimization studies were designed to increase the yield of binucleated cells (BNCs), and improve data acquisition and analysis templates to increase the speed and accuracy of image analysis. Human peripheral blood samples were exposed ex vivo with up to 4 Gy of c rays at a dose rate of 0.73 Gy/min. After irradiation, samples were transferred to microtubes (total volume of 1 ml including blood and media) and organized into a standard 8 × 12 plate format. Sample processing methods were modified by increasing the blood-to-media ratio, adding hypotonic solution prior to cell fixation and optimizing nuclear DRAQ5 staining, leading to an increase of 81% in BNC yield. Modification of the imaging processing algorithms within IFC software also improved BNC and MN identification, and reduced the average time of image analysis by 78%. Finally, 50 ll of irradiated whole blood was cultured with 200 ll of media in 96-well plates. All sample processing steps were performed automatically using the RABiT-II cell: :explorer robotic system adopting the optimized IFC-CBMN assay protocol. The results presented here detail a novel, high-throughput RABiT-IFC CBMN assay that possesses the potential to increase capacity for triage biodosimetry during a large-scale radiological/nuclear event.

RABiT-II: A Fully-Automated Micronucleus Assay System with Shortened Time to Result

In this work, we describe a fully automated cytokinesis-block micronucleus (CBMN) assay with a significantly shortened time to result, motivated by the need for rapid high-throughput biodosimetric estimation of radiation doses from small-volume human blood samples. The Rapid Automated Biodosimetry Tool (RABiT-II) currently consists of two commercial automated systems: a PerkinElmer cell::explorer Workstation and a GE Healthcare IN Cell Analyzer 2000 Imager. Blood samples (30 μl) from eight healthy volunteers were gamma-ray irradiated ex vivo with 0 (control), 0.5, 1.5, 2.5, 3.5 or 4.5 Gy and processed with full automation in 96-well plates on the RABiT-II system. The total cell culture time was 54 h and total assay time was 3 days. DAPI-stained fixed samples were imaged on an IN Cell Analyzer 2000 with fully-automated image analysis using the GE Healthcare IN Cell Developer Toolbox version 1.9. A CBMN dose-response calibration curve was established, after which the capability of the system to predict known doses was assessed. Various radiation doses for irradiated samples from two donors were estimated within 20% of the true dose (±0.5 Gy below 2 Gy) in 97% of the samples, with the doses in some 5 Gy irradiated samples being underestimated by up to 25%. In summary, the findings from this work demonstrate that the accelerated CBMN assay can be automated in a high-throughput format, using commercial biotech robotic systems, in 96-well plates, providing a rapid and reliable bioassay for radiation exposure.

Pharmacological approach to increasing the retention of radiation-induced γ-H2AX foci using phosphatase inhibitors: significance in radiation biodosimetry

In a scenario of accidental mass radiation exposure transportation and analysis of samples may take some time, resulting in loss of biomarker information over this period. The present study aims to use phosphatase inhibitors for longer retention of focal signals to adopt γ-H2AX as a biodosimetric biomarker for the management of early triage. Peripheral blood lymphocytes isolated from healthy individuals were irradiated in vitro with x-rays and γ-H2AX foci were analysed using fluorescent microscopy and flow cytometric methods. Further, the effect of protein phosphatase 2A inhibitors such as calyculin A, fostriecin and okadiac acid on the retention of foci was studied. Fluorescent microscopy was found to be a more sensitive method than flow cytometry. Calyculin A showed significant retention of focal signals at 6 h with 1.5-fold increased retention compared to radiation alone; this may prove beneficial in early triage management because of a better dose approximation.

Towards precision prevention: Technologies for identifying healthy individuals with high risk of disease

The rise of advanced technologies for characterizing human populations at the molecular level, from sequence to function, is shifting disease prevention paradigms toward personalized strategies. Because minimization of adverse outcomes is a key driver for treatment decisions for diseased populations, developing personalized therapy strategies represent an important dimension of both precision medicine and personalized prevention. In this commentary, we highlight recently developed enabling technologies in the field of DNA damage, DNA repair, and mutagenesis. We propose that omics approaches and functional assays can be integrated into population studies that fuse basic, translational and clinical research with commercial expertise in order to accelerate personalized prevention and treatment of cancer and other diseases linked to aberrant responses to DNA damage. This collaborative approach is generally applicable to efforts to develop data-driven, individualized prevention and treatment strategies for other diseases. We also recommend strategies for maximizing the use of biological samples for epidemiological studies, and for applying emerging technologies to clinical applications.

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.

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.

Validation of JCountPro software for efficient assessment of ionizing radiation-induced foci in human lymphocytes

PURPOSE

Ionizing radiation-induced foci (IRIF) known also as DNA repair foci represent the most sensitive and specific assay for assessing DNA double-strand break (DSB). IRIF are usually visualized and enumerated with the aid of fluorescence microscopy using antibodies to phosphorylated γH2AX and 53BP1. Although several approaches and software packages were developed for quantification of IRIF, not one of them was commonly accepted and inter-laboratory variability in the outputs was reported. In this study, JCountPro software was validated for IRIF enumeration in two independent laboratories.

MATERIALS AND METHODS

Human lymphocytes were γ-irradiated at doses of 0, 2, 5, 10 and 50 cGy. The cells were fixed, permeabilized and IRIF were immunostained using appropriate antibodies. Cell images were acquired with automatic Metafer system. Endogenous and radiation-induced γH2AX and 53BP1 foci were enumerated using JCountPro. This analysis was performed from the same cell galleries by the researchers from two laboratories. Yield of foci was analyzed by either arithmetic mean (AM) value (foci/cell) or principal average (PA) derived from the approximation of foci distribution with Poisson statistics. Statistical analysis was performed using factorial ANOVA.

RESULTS

Enumeration of 53BP1, γH2AX and co-localized 53BP1/γH2AX foci by JCountPro was essentially the same between laboratories. IRIF were detected at all doses and linear dose response was obtained in the studied dose range. PA values from Poisson distribution fitted the data better as compared to AM values and were more powerful and sensitive for IRIF analysis than the AM values. All JCountPro data were confirmed by visual focus enumeration.

CONCLUSIONS

We concluded that the JCountPro software was efficient in objectively enumerating IRIF regardless of an individual researcher's bias and has a potential for usage in clinics and molecular epidemiology.

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

Gamma-H2AX (γ-H2AX) assay is a marker to measure double-strand breaks in the deoxyribonucleic acid. Variables such as age, oxidative stress, temperature, genetic factors and inter-individual variation have been reported to influence the baseline γ-H2AX focus levels. Therefore, knowledge on baseline frequency of γ-H2AX foci in a targeted population would facilitate reliable radiation triage and dose estimation. The objective of the present study was to establish the baseline data using blood samples from healthy volunteers (n = 130) differing in age, occupation and lifestyle as well as from occupationally exposed health workers (n = 20). The γ-H2AX focus assay was performed using epifluorescence microscopy. In vitro dose-response curve for γ-H2AX foci was constructed in blood samples (n = 3) exposed to X-rays (30 min post-exposure). The mean γ-H2AX focus frequency obtained in healthy volunteers was 0.042 ± 0.001 and showed an age-related increase (p < 0.001). Significantly higher (p < 0.005) focus frequencies were observed in health workers (0.066 ± 0.005) than in healthy volunteers. A sub-group analysis did not show a significant (p > 0.1) difference in γ-H2AX focus frequency among sexes. Blood exposed in vitro to X-rays showed dose-dependent increase in γ-H2AX foci frequency (Y = 0.1902 ± 0.1363 + 2.9020 ± 0.3240 * D). Baseline frequency of γ-H2AX foci obtained from different age groups showed a significant (p < 0.01) influence on the dose-response coefficients. The overall results demonstrated that the γ-H2AX assay can be used as a reliable biomarker for radiation triage and estimating the radiation absorbed dose by considering variables such as age, occupation and lifestyle factors.

Mean frequency and relative fluorescence intensity measurement of γ-H2AX foci dose response in PBL exposed to γ-irradiation: An inter- and intra-laboratory comparison and its relevance for radiation triage

Measurement of γ-H2AX protein changes in the peripheral blood lymphocytes (PBL) of individuals exposed to ionizing radiation is a simple, sensitive, and rapid assay for radiation triage and early marker of dose estimation. The qualitative and quantitative measurements of the protein changes were examined using flow cytometry and microscopy. Whole blood and isolated lymphocytes were exposed in vitro between 0.1 and 5 Gy doses of (60) Co γ-radiation at a dose rate of 1 Gy/min. Radiation induced γ-H2AX foci frequency (n = 3) and relative fluorescence intensity (n = 7) in PBL was measured at 0.5 and 2 hrs postexposure. The observed dose response for γ-H2AX foci frequency at both time points, for whole blood and isolated lymphocytes did not show any significant (P > 0.05) differences. However, when compared with γ-H2AX foci frequency scored manually (microscopy), the semiautomated analysis (captured images) showed a better correlation (r(2) = 0.918) than that obtained with automated (Metafer) scoring (r(2) = 0.690). It is noteworthy to mention that, the γ-H2AX foci frequency quantified using microscopy showed a dose dependent increase up to 2 Gy and the relative fluorescence intensity (RFI) measured with flow cytometry revealed an increase up to 5 Gy in the PBL exposed in vitro. Moreover, a better correlation was observed between the γ-H2AX foci frequency obtained by manual scoring and RFI (r(2) = 0.910). Kinetic studies showed that the γ-H2AX foci remain more or less unchanged up to 4 hrs and reduces gradually over 48 hrs of postexposure at 37°C. Further, inter and intra-laboratory comparisons showed consistency in the scoring of γ-H2AX foci frequency by manual and semiautomated scoring. The overall results suggest that measurement of γ-H2AX (microscopy and flow cytometry) should be employed within 4 to 6 hrs for a reliable dosimetry either by sharing the work load between the laboratories or investing more manpower; however, triage can be possible even up to 48 hrs of postirradiation.

γ-H2AX Kinetic Profile in Mouse Lymphocytes Exposed to the Internal Emitters Cesium-137 and Strontium-90

In the event of a dirty bomb scenario or an industrial nuclear accident, a significant dose of volatile radionuclides such as 137Cs and 90Sr may be dispersed into the atmosphere as a component of fallout and inhaled or ingested by hundreds and thousands of people. To study the effects of prolonged exposure to ingested radionuclides, we have performed long-term (30 day) internal-emitter mouse irradiations using soluble-injected 137CsCl and 90SrCl2 radioisotopes. The effect of ionizing radiation on the induction and repair of DNA double strand breaks (DSBs) in peripheral mouse lymphocytes in vivo was determined using the γ-H2AX biodosimetry marker. Using a serial sacrifice experimental design, whole-body radiation absorbed doses for 137Cs (0 to 10 Gy) and 90Sr (0 to 49 Gy) were delivered over 30 days following exposure to each radionuclide. The committed absorbed doses of the two internal emitters as a function of time post exposure were calculated based on their retention parameters and their derived dose coefficients for each specific sacrifice time. In order to measure the kinetic profile for γ-H2AX, peripheral blood samples were drawn at 5 specific timed dose points over the 30-day study period and the total γ-H2AX nuclear fluorescence per lymphocyte was determined using image analysis software. A key finding was that a significant γ-H2AX signal was observed in vivo several weeks after a single radionuclide exposure. A mechanistically-motivated model was used to analyze the temporal kinetics of γ-H2AX fluorescence. Exposure to either radionuclide showed two peaks of γ-H2AX: one within the first week, which may represent the death of mature, differentiated lymphocytes, and the second at approximately three weeks, which may represent the production of new lymphocytes from damaged progenitor cells. The complexity of the observed responses to internal irradiation is likely caused by the interplay between continual production and repair of DNA damage, cell cycle effects and apoptosis.

Radiation signature on exposed cells: Relevance in dose estimation

The radiation is considered as a double edged sword, as its beneficial and detrimental effects have been demonstrated. The potential benefits are being exploited to its maximum by adopting safe handling of radionuclide stipulated by the regulatory agencies. While the occupational workers are monitored by personnel monitoring devices, for general publics, it is not a regular practice. However, it can be achieved by using biomarkers with a potential for the radiation triage and medical management. An ideal biomarker to adopt in those situations should be rapid, specific, sensitive, reproducible, and able to categorize the nature of exposure and could provide a reliable dose estimation irrespective of the time of the exposures. Since cytogenetic markers shown to have many advantages relatively than other markers, the origins of various chromosomal abnormalities induced by ionizing radiations along with dose-response curves generated in the laboratory are presented. Current status of the gold standard dicentric chromosome assay, micronucleus assay, translocation measurement by fluorescence in-situ hybridization and an emerging protein marker the γ-H2AX assay are discussed with our laboratory data. With the wide choice of methods, an appropriate assay can be employed based on the net.

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

Biodosimetry is an essential tool for providing timely assessments of radiation exposure. For a large mass-casualty event involving exposure to ionizing radiation, it is of utmost importance to rapidly provide dose information for medical treatment. The well-established cytokinesis-block micronucleus (CBMN) assay is a validated method for biodosimetry. However, the need for an accelerated sample processing is required for the CBMN assay to be a suitable population triage tool. We report here on the development of a high-throughput and miniaturized version of the CMBN assay for accelerated sample processing.

An automated imaging system for radiation biodosimetry

We describe here an automated imaging system developed at the Center for High Throughput Minimally Invasive Radiation Biodosimetry. The imaging system is built around a fast, sensitive sCMOS camera and rapid switchable LED light source. It features complete automation of all the steps of the imaging process and contains built-in feedback loops to ensure proper operation. The imaging system is intended as a back end to the RABiT-a robotic platform for radiation biodosimetry. It is intended to automate image acquisition and analysis for four biodosimetry assays for which we have developed automated protocols: The Cytokinesis Blocked Micronucleus assay, the γ-H2AX assay, the Dicentric assay (using PNA or FISH probes) and the RABiT-BAND assay.

High throughput measurement of γH2AX DSB repair kinetics in a healthy human population

The Columbia University RABiT (Rapid Automated Biodosimetry Tool) quantifies DNA damage using fingerstick volumes of blood. One RABiT protocol quantifies the total γ-H2AX fluorescence per nucleus, a measure of DNA double strand breaks (DSB) by an immunofluorescent assay at a single time point. Using the recently extended RABiT system, that assays the γ-H2AX repair kinetics at multiple time points, the present small scale study followed its kinetics post irradiation at 0.5 h, 2 h, 4 h, 7 h and 24 h in lymphocytes from 94 healthy adults. The lymphocytes were irradiated ex vivo with 4 Gy γ rays using an external Cs-137 source. The effect of age, gender, race, ethnicity, alcohol use on the endogenous and post irradiation total γ-H2AX protein yields at various time points were statistically analyzed. The endogenous γ-H2AX levels were influenced by age, race and alcohol use within Hispanics. In response to radiation, induction of γ-H2AX yields at 0.5 h and peak formation at 2 h were independent of age, gender, ethnicity except for race and alcohol use that delayed the peak to 4 h time point. Despite the shift in the peak observed, the γ-H2AX yields reached close to baseline at 24 h for all groups. Age and race affected the rate of progression of the DSB repair soon after the yields reached maximum. Finally we show a positive correlation between endogenous γ-H2AX levels with radiation induced γ-H2AX yields (RIY) (r=0.257, P=0.02) and a negative correlation with residuals (r=-0.521, P=<0.0001). A positive correlation was also observed between RIY and DNA repair rate (r=0.634, P<0.0001). Our findings suggest age, race, ethnicity and alcohol use influence DSB γ-H2AX repair kinetics as measured by RABiT immunofluorescent assay.

Effect of dose rate on residual γ-H2AX levels and frequency of micronuclei in X-irradiated mouse lymphocytes

The biological risks associated with low-dose-rate (LDR) radiation exposures are not yet well defined. To assess the risk related to DNA damage, we compared the yields of two established biodosimetry end points, γ-H2AX and micronuclei (MNi), in peripheral mouse blood lymphocytes after prolonged in vivo exposure to LDR X rays (0.31 cGy/min) vs. acute high-dose-rate (HDR) exposure (1.03 Gy/min). C57BL/6 mice were total-body irradiated with 320 kVP X rays with doses of 0, 1.1, 2.2 and 4.45 Gy. Residual levels of total γ-H2AX fluorescence in lymphocytes isolated 24 h after the start of irradiation were assessed using indirect immunofluorescence methods. The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was used to determine apoptotic cell frequency in lymphocytes sampled at 24 h. Curve fitting analysis suggested that the dose response for γ-H2AX yields after acute exposures could be described by a linear dependence. In contrast, a linear-quadratic dose-response shape was more appropriate for LDR exposure (perhaps reflecting differences in repair time after different LDR doses). Dose-rate sparing effects (P < 0.05) were observed at doses ≤2.2 Gy, such that the acute dose γ-H2AX and TUNEL-positive cell yields were significantly larger than the equivalent LDR yields. At the 4.45 Gy dose there was no difference in γ-H2AX expression between the two dose rates, whereas there was a two- to threefold increase in apoptosis in the LDR samples compared to the equivalent 4.45 Gy acute dose. Micronuclei yields were measured at 24 h and 7 days using the in vitro cytokinesis-blocked micronucleus (CBMN) assay. The results showed that MNi yields increased up to 2.2 Gy with no further increase at 4.45 Gy and with no detectable dose-rate effect across the dose range 24 h or 7 days post exposure. In conclusion, the γ-H2AX biomarker showed higher sensitivity to measure dose-rate effects after low-dose LDR X rays compared to MNi formation; however, confounding factors such as variable repair times post exposure, increased cell killing and cell cycle block likely contributed to the yields of MNi with accumulating doses of ionizing radiation.