Assessment of total- and partial-body irradiation in a baboon model: preliminary results of a kinetic study including clinical, physical, and biological parameters

High variability in short and long-term recovery kinetic of blood cell count and blood chemistry in a partial body irradiation mouse model

PURPOSE

In the aftermath of a nuclear disaster or accident, survivors will suffer from radiation-induced normal tissue damage. Recovery after radiation exposure is dictated by several factors, one of which is degree of shielding at time of exposure. This study aims to characterize the short and late term changes in kinetics and magnitude of pancytopenia and blood chemistry in a model of heterogeneous radiation exposure, or partial body irradiation (PBI), compared to whole body irradiation (WBI).

MATERIALS AND METHODS

Male C57BL/6 mice, 8-10 weeks of age, were WBI at 6 different doses (6, 6.1. 6.15, 6.2, 6.5, and 7.5 Gy) to establish the LD50. To determine the effect of shielding on blood cell counts and chemistry, animals were either WBI at 6 Gy (LD2230) or 6 Gy PBI with one leg shielding (LD030). Complete blood counts and chemistry were measured at 1, 5-, 10-, 20-, 30- and 120-days post-irradiation.

RESULTS AND CONCLUSIONS

Irradiated animals had significant depletion of white blood cells, red blood cells and platelets up to 10 days post-irradiation. Separation between PBI and WBI were observed at 10- and 20-days post-irradiation at which point PBI animals showed sign of recovery while overall cell count remains depleted in WBI animals up to 30 days post-irradiation. In addition, significant changes were found in parameters indicative of hematopoietic injury including hemoglobin count, hematocrit count and white blood cell population. Significant changes were observed in kidney function with changes to blood urea nitrogen and calcium concentration at 5-days post-irradiation. At 10-days post-irradiation. liver function changes differentiated WBI from PBI animals. Long-term, irradiated animal's chemistry values and many blood counts were not significantly different from Sham. In conclusion, partial shielding ensured complete survival and demonstrated a different recovery kinetics of blood and chemistry parameters after irradiation compared to survivors of whole body irradiation and no single hemopoietic parameter was able to consistently differentiate irradiated from Sham animals. This seems to indicate that there is no single robust hemopoietic parameter to differentiate those exposed from those who were not due to the inherent variability in individual responses. Furthermore, there were no significant long-term effects on these blood parameters between survivors of WBI and PBI except that shielding accelerated recovery.

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.

Electrical Signal Initiates Kinetic Assembly of Collagen to Construct Optically Transparent and Geometry Customized Artificial Cornea Substitutes

Corneal transplantation is an effective treatment for reconstructing injured corneas but is very limited due to insufficient donors, which has led to a growing demand for development of artificial corneal substitutes (ACSs). Collagen is a potential building block for ACS fabrication, whereas technically there are limited capabilities to control the collagen assembly for creating highly transparent collagen ACSs. Here, we report an electro-assembly technique to kinetically control collagen assembly on the nanoscale that allows the yielding collagen ACSs with structure determined superior optics. Structurally, the kinetically electro-assembled collagen (KEA-Col) is composed of partially aligned microfibrils (∼10 nm in diameter) with compacted lamellar organization. Optical analysis reveals that such microstructure is directly responsible for its optimal light transmittance by reducing light scattering. Moreover, this method allows the creation of complex three-dimensional geometries and thus is convenient to customize collagen ACSs with specific curvatures to meet refractive power requirements. Available properties (e.g., optics and mechanics) of cross-linked KEA-Cols were studied to meet the clinical requirement as ACSs, and in vitro tests further proved their beneficial characteristics of cell growth and migration. An in vivo study established a rabbit lamellar keratectomy corneal wound model and demonstrated the customized collagen ACSs can adapt to the defective cornea and support epithelial healing as well as stroma integration and reconstruction with lower immunoreaction compared with commercial xenografts, which suggests its promising application prospects. More broadly, this work illustrates the potential for enlisting electrical signals to mediate collagen's assembly and microstructure organization for specific structural functionalization for regenerative medicine.

Early molecular markers for retrospective biodosimetry and prediction of acute health effects

Radiation-induced biological changes occurring within hours and days after irradiation can be potentially used for either exposure reconstruction (retrospective dosimetry) or the prediction of consecutively occurring acute or chronic health effects. The advantage of molecular protein or gene expression (GE) (mRNA) marker lies in their capability for early (1-3 days after irradiation), high-throughput and point-of-care diagnosis, required for the prediction of the acute radiation syndrome (ARS) in radiological or nuclear scenarios. These molecular marker in most cases respond differently regarding exposure characteristics such as e.g. radiation quality, dose, dose rate and most importantly over time. Changes over time are in particular challenging and demand certain strategies to deal with. With this review, we provide an overview and will focus on already identified and used mRNA GE and protein markers of the peripheral blood related to the ARS. These molecules are examined in light of 'ideal' characteristics of a biomarkers (e.g. easy accessible, early response, signal persistency) and the validation degree. Finally, we present strategies on the use of these markers considering challenges as their variation over time and future developments regarding e.g. origin of samples, point of care and high-throughput diagnosis.

Early Biomarkers Associated with P53 Signaling for Acute Radiation Injury

Accurate dose assessment within 1 day or even 12 h after exposure through current methods of dose estimation remains a challenge, in response to a large number of casualties caused by nuclear or radiation accidents. P53 signaling pathway plays an important role in DNA damage repair and cell apoptosis induced by ionizing radiation. The changes of radiation-induced P53 related genes in the early stage of ionizing radiation should compensate for the deficiency of lymphocyte decline and γ-H2AX analysis as novel biomarkers of radiation damage. Bioinformatic analysis was performed on previous data to find candidate genes from human peripheral blood irradiated in vitro. The expression levels of candidate genes were detected by RT-PCR. The expressions of screened DDB2, AEN, TRIAP1, and TRAF4 were stable in healthy population, but significantly up-regulated by radiation, with time specificity and dose dependence in 2–24 h after irradiation. They are early indicators for medical treatment in acute radiation injury. Their effective combination could achieve a more accurate dose assessment for large-scale wounded patients within 24 h post exposure. The effective combination of p53-related genes DDB2, AEN, TRIAP1, and TRAF4 is a novel biodosimetry for a large number of people exposed to acute nuclear accidents.

Chromosome aberration dynamics in breast cancer patients treated with radiotherapy: Implications for radiation biodosimetry

Although radiological accidents often result in partial-body radiation exposure, most biodosimetry studies focus on estimating whole-body exposure doses. We have evaluated time-dependent changes in chromosomal aberrations before, during, and after localized fractionated radiotherapy. Twelve patients with carcinoma in situ of the breast who underwent identical adjuvant radiation therapy (50 Gy in 25 fractions) were included in the study. Lymphocytes were collected from patients before, during, and after radiotherapy, to measure chromosome aberrations, such as dicentric chromosomes and translocations. Chromosome aberrations were then used to calculate whole- and partial-body biological absorbed doses of radiation. Dicentric chromosome frequencies in all study participants increased during radiotherapy (p < 0.05 in Kruskal-Wallis test). Increases of translocation frequencies during radiotherapy were observed in seven of the twelve patients. The increased levels of dicentric chromosomes and translocations persisted throughout our 1-year follow-up, and evidence of partial-body exposure (such as Papworth's U-value > 1.96) was observed more than 1 year after radiotherapy. We found that cytogenetic biomarkers reflected partial-body fractionated radiation exposure more than 1 year post-exposure. Our findings suggest that chromosome aberrations can be used to estimate biological absorbed radiation doses and can inform medical intervention for individuals suspected of fractionated or partial-body radiation exposure.

BABOON RADIATION QUALITY (MIXED-FIELD NEUTRON AND GAMMA, GAMMA ALONE) DOSE-RESPONSE MODEL SYSTEMS: ASSESSMENT OF H-ARS SEVERITY USING HAEMATOLOGIC BIOMARKERS

Results from archived (1986 and 1996) experiments were used to establish a baboon radiation-quality dose-response database with haematology biomarker time-course data following exposure to mixed-fields (i.e. neutron to gamma ratio: 5.5; dose: 0-8 Gy) and 60Co gamma-ray exposures (0-15 Gy). Time-course (i.e. 0-40 d) haematology changes for relevant blood-cell types for both mixed-field (neutron to gamma ratio = 5.5) and gamma ray alone were compared and models developed that showed significant differences using the maximum likehood ratio test. A consensus METREPOL-like haematology ARS (H-ARS) severity scoring system for baboons was established using these results. The data for mixed-field and the gamma only cohorts appeared similar, and so the cohorts were pooled into a single consensus H-ARS severity scoring system. These findings provide proof-of-concept for the use of a METREPOL H-ARS severity scoring system following mixed-field and gamma exposures.

Differentiation of Heterogeneous Radiation Exposure Using Hematology and Blood Chemistry

In the aftermath of a nuclear incident, survivors will suffer the deleterious effects from acute radiation exposure. The majority of those affected would have received heterogeneous radiation exposure, reflected in hematological metrics and blood chemistry. Here, we investigated the acute and long-term changes in kinetics and magnitude of pancytopenia and blood chemistry in rats irradiated using varying degrees of body shielding. We hypothesized that, although a single blood count may not be able to differentiate the degree of radiation exposure, a combination of measurements from complete blood cell counts (CBCs) and blood chemistry tests is able to do so. Male Sprague Dawley rats, 8-10 weeks of age, received single-dose 7.5 Gy (160 kVp, 25 mA, 1.16 Gy/min) whole-body irradiation (WBI, LD_100/30) or partial-body irradiation (PBI), as follows: one leg shielded (1LS, LD_0/30), two legs shielded (2LS, LD_0/30) or the upper half of the body shielded (UHS, LD_0/30). Animal morbidity and weights were measured. Blood was drawn at 1, 5, 10, 20 and 30 days postirradiation (n = 4-11). For kidney and liver function measurements, CBC and blood chemistry analyses were performed. WBI animals on average survived 9 ± 0.4 days postirradiation. In contrast, all PBI animals survived the 30-day study period. CBC analysis revealed that both white blood cell (WBC) and platelet counts were most affected after irradiation. While WBC counts were significantly lower in all irradiated groups on days 1, 5 and 10, platelets were only significantly lower on days 5 and 10 postirradiation. In addition, on day 5 postirradiation both WBC and platelet counts were able to differentiate WBI (non-survivors) from PBI 2LS and UHS animals (survivors). Using four blood parameters (platelets, percentage lymphocytes, percentage neutrophils and percentage monocytes) on day 5 after 7.5 Gy irradiation and a linear discrimination analysis (LDA), we were able to predict the degree of body exposure in animals with a 95.8% accuracy. Alkaline phosphatase (ALP) was significantly lower in all groups on days 5 and 10 postirradiation compared to baseline. Furthermore, ALP was significantly higher in the UHS than WBI animals. The AST:ALT ratio was significantly higher than baseline in all irradiated groups on day 1 postirradiation. In conclusion, four CBC parameters, on day 5 after receiving a 7.5 Gy dose of radiation, can be employed in a LDA to differentiate various degrees of exposure (shielding). The characterization presented in this work paves the way for further studies in differences caused by heterogeneous body exposure to radiation and a new metric for biodosimetry.

Efficacy of Neulasta or Neupogen on H-ARS and GI-ARS Mortality and Hematopoietic Recovery in Nonhuman Primates After 10-Gy Irradiation With 2.5% Bone Marrow Sparing

A nonhuman primate model of acute, partial-body, high-dose irradiation with minimal (2.5%) bone marrow sparing was used to assess endogenous gastrointestinal and hematopoietic recovery and the ability of Neulasta (pegylated granulocyte colony-stimulating factor) or Neupogen (granulocyte colony-stimulating factor) to enhance recovery from myelosuppression when administered at an increased interval between exposure and initiation of treatment. A secondary objective was to assess the effect of Neulasta or Neupogen on mortality and morbidity due to the hematopoietic acute radiation syndrome and concomitant gastrointestinal acute radiation syndrome. Nonhuman primates were exposed to 10.0 Gy, 6 MV, linear accelerator-derived photons delivered at 0.80 Gy min. All nonhuman primates received subject-based medical management. Nonhuman primates were dosed daily with control article (5% dextrose in water), initiated on day 1 postexposure; Neulasta (300 μg kg), administered on days 1, 8, and 15 or days 3, 10, and 17 postexposure; or Neupogen (10 μg kg), administered daily postexposure following its initiation on day 1 or day 3 until neutrophil recovery (absolute neutrophil count ≥1,000 cells μL for 3 consecutive days). Mortality in the irradiated cohorts suggested that administration of Neulasta or Neupogen on either schedule did not affect mortality due to gastrointestinal acute radiation syndrome or mitigate mortality due to hematopoietic acute radiation syndrome (plus gastrointestinal damage). Following 10.0 Gy partial-body irradiation with 2.5% bone marrow sparing, the mean duration of neutropenia (absolute neutrophil count <500 cells μL) was 22.4 d in the control cohort vs. 13.0 and 15.3 d in the Neulasta day 1, 8, 15 and day 3, 10, 17 cohorts, relative to 16.2 and 17.4 d in the Neupogen cohorts initiated on day 1 and day 3, respectively. The absolute neutrophil count nadirs were 48 cells μL in the controls; 117 cells μL and 40 cells μL in the Neulasta days 1, 8, and 15 or days 3, 10, and 17 cohorts, respectively; and 75 cells μL and 37 cells μL in the Neupogen day 1 and day 3 cohorts, respectively. Therefore, the earlier administration of Neulasta or Neupogen was more effective in this model of marginal 2.5% bone marrow sparing. The approximate 2.5% bone marrow sparing may approach the threshold for efficacy of the lineage-specific medical countermeasure. The partial-body irradiation with 2.5% bone marrow sparing model can be used to assess medical countermeasure efficacy in the context of the concomitant gastrointestinal and hematopoietic acute radiation syndrome sequelae.

The Gastrointestinal Subsyndrome of the Acute Radiation Syndrome in Rhesus Macaques: A Systematic Review of the Lethal Dose-response Relationship With and Without Medical Management

Well-characterized animal models that mimic the human response to potentially lethal doses of radiation are required to assess the efficacy of medical countermeasures under the criteria of the US Food and Drug Administration's Animal Rule. Development of a model for the gastrointestinal acute radiation syndrome requires knowledge of the radiation dose-response relationship and time course of mortality and morbidity across the acute and prolonged gastrointestinal radiation syndrome. The nonhuman primate, rhesus macaque, is a relevant animal model that has been used to determine the efficacy of medical countermeasures to mitigate major signs of morbidity and mortality relative to the hematopoietic acute radiation syndrome, gastrointestinal acute radiation syndrome, and lung injury. It can be used to assess the natural history of gastrointestinal damage, concurrent multiple organ injury, and aspects of the mechanism of action for acute radiation exposure and treatment. A systematic review of relevant studies that determined the dose-response relationship for the gastrointestinal acute and prolonged radiation syndrome in the rhesus macaque relative to radiation dose, quality, dose rate, exposure uniformity, and use of medical management has never been performed.

The Time Course of Radiation-induced Lung Injury in a Nonhuman Primate Model of Partial-body Irradiation With Minimal Bone Marrow Sparing: Clinical and Radiographic Evidence and the Effect of Neupogen Administration

The primary objectives of two companion manuscripts were to assess the natural history of delayed radiation-induced lung injury in a nonhuman primate model of acute high-dose, partial-body irradiation with 5% bone marrow sparing, to include the clinical, radiographic, and histopathological evidence and the effect of Neupogen administration on the morbidity and mortality. Nonhuman primates were exposed to 10.0 or 11.0 Gy with 6 MV linac-derived photons at approximately 0.80 Gy min. All nonhuman primates received subject-based, medical management. Subsets of nonhuman primates were administered Neupogen (10 μg kg) starting on day 1, day 3, or day 5 until recovery (absolute neutrophil count ≥ 1,000 cells μL for three consecutive days). Mortality due to multiple organ injury at 180 d study duration: Mortality at 180 d post either 10.0 Gy or 11.0 Gy was the consequence of concurrent injury due to the acute radiation syndrome (gastrointestinal and hematological) and delayed radiation-induced lung injury. The 180-d all-cause mortality observed in the control cohorts at 10.0 Gy (53%) or 11.0 Gy (86%) did not vary from cohorts that received Neupogen at any administration schedule. Mortality ranged from 43-50% (10 Gy) to 75-100% (11.0 Gy) in the Neupogen-treated cohorts. The study, however, was not powered to detect statistical significant differences between mortality in the control and Neupogen-treated cohorts. Clinical and radiographic evidence of radiation-induced lung injury: The mean nonsedated respiratory rate in the control cohorts exposed to 10 or 11 Gy increased from a baseline value of 37 breaths min to >60 breaths min within 103 d and 94 d postexposure, and the incidence of nonsedated respiratory rate > 80 breaths min was 50% and 70%, respectively. The mean duration of latency to development of clinical pneumonitis and/or fibrosis (nonsedated respiratory rate > 80 breaths min) was not significantly different between the 10.0-Gy or 11.0 Gy-cohorts (range 100-107 d). Neupogen (granulocyte colony-stimulating factor) administration had no apparent effect of the latency, incidence, or severity of nonsedated respiratory rate within either radiation dose or administration schedule. Computed tomography scans were obtained and images were analyzed for evidence of lung injury, e.g., pneumonitis and/or fibrosis, pleural and pericardial effusion. A quantitative, semiautomated method was developed based on differences in radiodensity (Hounsfield units) and lung morphology to extract the volume of pneumonitis/fibrosis and pleural effusion as indexed against total lung at each time point obtained. At both irradiation doses, 100% of the nonhuman primates surviving acute radiation syndrome manifested radiographic evidence of radiation-induced lung injury as pneumonitis and/or fibrosis. There was no apparent effect of Neupogen administration on the latency, incidence, severity, or progression of pneumonitis/fibrosis:total lung volume or pleural effusion:total lung volume at either exposure. A comparative review of the data illustrated the concomitant time course of increased mortality, nonsedated respiratory rate, and pneumonitis/fibrosis:total lung volume and pleural effusion:total lung volume consequent to 10.0-Gy or 11.0-Gy partial-body irradiation with 5% bone marrow sparing. All key parameters proceeded from a latent period of approximately 60 d followed by an increase in all three indices of clinical and radiographic evidence of radiation-induced lung injury within the next 60 d to 120 d postexposure. The subsequent time course and longitudinal analysis was influenced by the persistent progression of radiation-induced lung injury, administration of dexamethasone, and loss of nonhuman primates due to lethality. Companion paper: Lung and Heart Injury in a Nonhuman Primate Model of Partial-body Irradiation With Minimal Bone Marrow Sparing: Histopathological Evidence of Lung and Heart Injury (Parker et al. 2019): Note that the computed tomography-based radiodensity data do not permit differentiation of pneumonitis and fibrosis. The companion paper employed Masson's trichrome, collagen 1, and selected staining to identify the key time and incidence parameters relative to excessive collagen deposition indicative of fibrosis and associated histopathology in the lung. This histological database provided valuable longitudinal analysis in support of the clinical and radiographic evidence associated with the time course of radiation-induced lung injury.

WAG/RijCmcr rat models for injuries to multiple organs by single high dose ionizing radiation: similarities to nonhuman primates (NHP)

Purpose: Defined animal models are needed to pursue the FDA Animal Rule for approval of medical countermeasure for radiation injuries. This study compares WAG/RijCmcr rat and nonhuman primate (NHP) models for acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE).Materials and methods: Irradiation models include total body irradiation, partial body irradiation with bone marrow sparing and whole thorax lung irradiations. Organ-specific sequelae of radiation injuries were compared using dose-response relationships.Results and conclusions: Rats and NHP manifest similar organ dysfunctions after radiation, starting with acute gastrointestinal (GI-ARS) and hematopoietic (H-ARS) syndromes followed by lung, heart and kidney toxicities. Humans also manifest these sequelae. Latencies for injury were earlier in rats than in NHP. After whole thorax lung irradiations (WTLI) up to 13 Gy, there was recovery of lung function from pneumonitis in rats. This has not been evaluated in NHP. The latency, incidence, severity and progression of radiation pneumonitis was not influenced by early multi-organ injury from ARS in rats or NHP. Rats developed more severe radiation nephropathy than NHP, and also progressed more rapidly. Dosimetry, anesthesia, environment, supportive care, euthanasia criteria etc., may account for the alterations in radiation sensitivity observed between species.

Use of Proteomic and Hematology Biomarkers for Prediction of Hematopoietic Acute Radiation Syndrome Severity in Baboon Radiation Models

Use of plasma proteomic and hematological biomarkers represents a promising approach to provide useful diagnostic information for assessment of the severity of hematopoietic acute radiation syndrome. Eighteen baboons were evaluated in a radiation model that underwent total-body and partial-body irradiations at doses of Co gamma rays from 2.5 to 15 Gy at dose rates of 6.25 cGy min and 32 cGy min. Hematopoietic acute radiation syndrome severity levels determined by an analysis of blood count changes measured up to 60 d after irradiation were used to gauge overall hematopoietic acute radiation syndrome severity classifications. A panel of protein biomarkers was measured on plasma samples collected at 0 to 28 d after exposure using electrochemiluminescence-detection technology. The database was split into two distinct groups (i.e., "calibration," n = 11; "validation," n = 7). The calibration database was used in an initial stepwise regression multivariate model-fitting approach followed by down selection of biomarkers for identification of subpanels of hematopoietic acute radiation syndrome-responsive biomarkers for three time windows (i.e., 0-2 d, 2-7 d, 7-28 d). Model 1 (0-2 d) includes log C-reactive protein (p < 0.0001), log interleukin-13 (p < 0.0054), and procalcitonin (p < 0.0316) biomarkers; model 2 (2-7 d) includes log CD27 (p < 0.0001), log FMS-related tyrosine kinase 3 ligand (p < 0.0001), log serum amyloid A (p < 0.0007), and log interleukin-6 (p < 0.0002); and model 3 (7-28 d) includes log CD27 (p < 0.0012), log serum amyloid A (p < 0.0002), log erythropoietin (p < 0.0001), and log CD177 (p < 0.0001). The predicted risk of radiation injury categorization values, representing the hematopoietic acute radiation syndrome severity outcome for the three models, produced least squares multiple regression fit confidences of R = 0.73, 0.82, and 0.75, respectively. The resultant algorithms support the proof of concept that plasma proteomic biomarkers can supplement clinical signs and symptoms to assess hematopoietic acute radiation syndrome risk severity.

[Biomarkers of radiation-induced DNA repair processes]

The identification of DNA repair biomarkers is of paramount importance. Indeed, it is the first step in the process of modulating radiosensitivity and radioresistance. Unlike tools of detection and measurement of DNA damage, DNA repair biomarkers highlight the variations of DNA damage responses, depending on the dose and the dose rate. The aim of the present review is to describe the main biomarkers of radiation-induced DNA repair. We will focus on double strand breaks (DSB), because of their major role in radiation-induced cell death. The most important DNA repair biomarkers are DNA damage signaling proteins, with ATM, DNA-PKcs, 53BP1 and γ-H2AX. They can be analyzed either using immunostaining, or using lived cell imaging. However, to date, these techniques are still time and money consuming. The development of "omics" technologies should lead the way to new (and usable in daily routine) DNA repair biomarkers.

Nonhuman primates as models for the discovery and development of radiation countermeasures

INTRODUCTION

Despite significant scientific advances over the past six decades toward the development of safe and effective radiation countermeasures for humans using animal models, only two pharmaceutical agents have been approved by United States Food and Drug Administration (US FDA) for hematopoietic acute radiation syndrome (H-ARS). Additional research efforts are needed to further develop large animal models for improving the prediction of clinical safety and effectiveness of radiation countermeasures for ARS and delayed effects of acute radiation exposure (DEARE) in humans. Area covered: The authors review the suitability of animal models for the development of radiation countermeasures for ARS following the FDA Animal Rule with a special focus on nonhuman primate (NHP) models of ARS. There are seven centers in the United States currently conducting studies with irradiated NHPs, with the majority of studies being conducted with rhesus monkeys. Expert opinion: The NHP model is considered the gold standard animal model for drug development and approval by the FDA. The lack of suitable substitutes for NHP models for predicting response in humans serves as a bottleneck for the development of radiation countermeasures. Additional large animal models need to be characterized to support the development and FDA-approval of new radiation countermeasures.

A biosafety evaluation of synchrotron radiation X-ray to skin and bone marrow: single dose irradiation study of rats and macaques

PURPOSE

Very limited experimental data is available regarding the safe dosages related to synchrotron radiation (SR) procedures. We used young rats and macaques to address bone marrow and skin tolerance to various doses of synchrotron radiation.

METHODS

Rats were subjected to 0, 0.5, 2.5, 5, 25 or 100 Gy local SR X-ray irradiation at left hind limb. Rat blood samples were analyzed at 2-90 days after irradiation. The SR X-ray irradiated skin and tibia were sectioned for morphological examination. For non-human primate study, three male macaques were subjected to 0.5 or 2.5 Gy SR X-ray on crus. Skin responses of macaques were observed.

RESULTS

All rats that received SR X-ray irradiation doses greater than 2.5 Gy experienced hair loss and bone-growth inhibition, which were accompanied by decreased number of follicles, thickened epidermal layer, and decreased density of bone marrow cells (p < 0.05). Macaque skin could tolerate 0.5 Gy SR X-ray but showed significant hair loss when the dose was raised above 2.5 Gy.

CONCLUSION

The safety threshold doses of SR X-ray for rat skin, bone marrow and macaque skin are between 0.5 and 2.5 Gy. Our study provided essential information regarding the biosafety of SR X-ray irradiation.

Soluble Vascular Endothelial Cadherin as a New Biomarker of Irradiation in Highly Irradiated Baboons with Bone Marrow Protection

Vascular endothelial cadherin is the main component of adherens junctions enabling cohesion of the endothelial monolayer in vessels. The extracellular part of vascular endothelial cadherin (VE-cadherin) can be cleaved, releasing soluble fragments in blood (sVE-cadherin). In some diseases with endothelial dysfunction, a correlation between increased blood sVE-cadherin levels and disease state has been proposed. Irradiation is known to induce endothelial damage, but new serum biomarkers are needed to evaluate endothelial damage after irradiation. Here, the authors investigated whether sVE-cadherin may be an interesting biomarker of irradiation in highly irradiated baboons with bone marrow protection. sVE-cadherin was detected in the plasma of young as well as old baboons. Plasma sVE-cadherin levels significantly decrease a few days after irradiation but recover in the late time after irradiation. Kinetic analysis of plasma sVE-cadherin levels suggests a correlation with white blood cell counts in both the acute phase of irradiation and during hematopoietic recovery, suggesting that plasma sVE-cadherin levels may be partly linked to the disappearance and recovery of white blood cells. Interestingly, after hematopoietic recovery was completed, sVE-cadherin levels were found to exceed control values, suggesting that plasma sVE-cadherin may represent a new biomarker of endothelial damage or neovascularization in the late time after irradiation.

Use of biomarkers for assessing radiation injury and efficacy of countermeasures

Several candidate drugs for acute radiation syndrome (ARS) have been identified that have low toxicity and significant radioprotective and radiomitigative efficacy. Inasmuch as exposing healthy human volunteers to injurious levels of radiation is unethical, development and approval of new radiation countermeasures for ARS are therefore presently based on animal studies and Phase I safety study in healthy volunteers. The Animal Efficacy Rule, which underlies the Food and Drug Administration approval pathway, requires a sound understanding of the mechanisms of injury, drug efficacy, and efficacy biomarkers. In this context, it is important to identify biomarkers for radiation injury and drug efficacy that can extrapolate animal efficacy results, and can be used to convert drug doses deduced from animal studies to those that can be efficacious when used in humans. Here, we summarize the progress of studies to identify candidate biomarkers for the extent of radiation injury and for evaluation of countermeasure efficacy.

The Effect of Radiation Dose and Variation in Neupogen® Initiation Schedule on the Mitigation of Myelosuppression during the Concomitant GI-ARS and H-ARS in a Nonhuman Primate Model of High-dose Exposure with Marrow Sparing

A nonhuman primate (NHP) model of acute high-dose, partial-body irradiation with 5% bone marrow (PBI/BM5) sparing was used to assess the effect of Neupogen® [granulocyte colony stimulating factor (G-CSF)] to mitigate the associated myelosuppression when administered at an increasing interval between exposure and initiation of treatment. A secondary objective was to assess the effect of Neupogen® on the mortality or morbidity of the hematopoietic (H)- acute radiation syndrome (ARS) and concurrent acute gastrointestinal radiation syndrome (GI-ARS). NHP were exposed to 10.0 or 11.0 Gy with 6 MV LINAC-derived photons at approximately 0.80 Gy min. All NHP received medical management. NHP were dosed daily with control article (5% dextrose in water) initiated on day 1 post-exposure or Neupogen® (10 μg kg) initiated on day 1, day 3, or day 5 until recovery [absolute neutrophil count (ANC) ≥ 1,000 cells μL for three consecutive days]. Mortality in both the 10.0 Gy and 11.0 Gy cohorts suggested that early administration of Neupogen® at day 1 post exposure may affect acute GI-ARS mortality, while Neupogen® appeared to mitigate mortality due to the H-ARS. However, the study was not powered to detect statistically significant differences in survival. The ability of Neupogen® to stimulate granulopoiesis was assessed by evaluating key parameters for ANC recovery: the depth of nadir, duration of neutropenia (ANC < 500 cells μL) and recovery time to ANC ≥ 1,000 cells μL. Following 10.0 Gy PBI/BM5, the mean duration of neutropenia was 11.6 d in the control cohort vs. 3.5 d and 4.6 d in the day 1 and day 3 Neupogen® cohorts, respectively. The respective ANC nadirs were 94 cells μL, 220 cells μL, and 243 cells μL for the control and day 1 and day 3 Neupogen® cohorts. Following 11.0 Gy PBI/BM5, the duration of neutropenia was 10.9 d in the control cohort vs. 2.8 d, 3.8 d, and 4.5 d in the day 1, day 3, and day 5 Neupogen® cohorts, respectively. The respective ANC nadirs for the control and day 1, day 3, and day 5 Neupogen® cohorts were 131 cells μL, 292 cells μL, 236 cells μL, and 217 cells μL, respectively. Therefore, the acceleration of granulopoiesis by Neupogen® in this model is independent of the time interval between radiation exposure and treatment initiation up to 5 d post-exposure. The PBI/BM5 model can be used to assess medical countermeasure efficacy in the context of the concurrent GI- and H-ARS.

The Hematopoietic Syndrome of the Acute Radiation Syndrome in Rhesus Macaques: A Systematic Review of the Lethal Dose Response Relationship

Well characterized animal models that mimic the human response to potentially lethal doses of radiation are required to assess the efficacy of medical countermeasures under the criteria of the U.S. Food and Drug Administration "animal rule." Development of a model requires the determination of the radiation dose response relationship and time course of mortality and morbidity across the hematopoietic acute radiation syndrome. The nonhuman primate, rhesus macaque, is a relevant animal model that may be used to determine the efficacy of medical countermeasures to mitigate major signs of morbidity and mortality at selected lethal doses of total body irradiation. A systematic review of relevant studies that determined the dose response relationship for the hematopoietic acute radiation syndrome in the rhesus macaque relative to radiation quality, dose rate, and exposure uniformity has never been performed. The selection of data cohorts was made from the following sources: Ovid Medline (1957-present), PubMed (1954-present), AGRICOLA (1976-present), Web of Science (1954-present), and U.S. HHS REPORT (2002 to present). The following terms were used: Rhesus, total body-irradiation, total body x irradiation, TBI, irradiation, gamma radiation, hematopoiesis, LD50/60, Macaca mulatta, whole-body irradiation, nonhuman primate, NHP, monkey, primates, hematopoietic radiation syndrome, mortality, and nuclear radiation. The reference lists of all studies, published and unpublished, were reviewed for additional studies. The total number of hits across all search sites was 3,001. There were a number of referenced, unpublished, non-peer reviewed government reports that were unavailable for review. Fifteen studies, 11 primary (n = 863) and four secondary (n = 153) studies [n = 1,016 total nonhuman primates (NHP), rhesus Macaca mulatta] were evaluated to provide an informative and consistent review. The dose response relationships (DRRs) were determined for uniform or non-uniform total body irradiation (TBI) with 250 kVp or 2 MeV x radiation, Co gamma radiation and reactor- and nuclear weapon-derived mixed gamma: neutron-radiation, delivered at various dose rates from a total body, bilateral, rotational, or unilateral exposure aspect. The DRRs established by a probit analysis vs. linear dose relationship were characterized by two main parameters or dependent variables: a slope and LD50/30. Respective LD50/30 values for studies that used 250 kVp x radiation (five primary studies combined, n = 338), 2 MeV x radiation, Co gamma radiation, and steady-state reactor-derived mixed gamma:neutron radiation for total body uniform exposures were 521 rad [498, 542], 671 rad [632, 715], 644 rad [613, 678], and 385 rad [357, 413]. The respective slopes were steep and ranged from 0.738 to 1.316. The DRR, LD50/30 values and slopes were also determined for total body, non-uniform, unilateral, pulse-rate exposures of mixed gamma:neutron radiation derived at reactor and nuclear weapon detonations. The LD50/30 values were, respectively, 395 rad [337, 432] and 412 rad [359, 460]. Secondary data sets of limited studies that did not describe a DRR were used to support the mid-to-high lethal dose range for the H-ARS and the threshold dose range for the concurrent acute GI ARS. The available evidence provided a reliable and extensive database that characterized the DRR for the H-ARS in young rhesus macaques exposed to 250 kVp uniform total body x radiation without the benefit of medical management. A less substantial but consistent database demonstrated the DRR for total body exposure of differing radiation quality, dose rate and non-uniform exposure. The DRR for the H-ARS is characterized by steep slopes and relative LD50/30 values that reflect the radiation quality, exposure aspect, and dose rate over a range in time from 1954-2012.

Total Body Irradiation in the "Hematopoietic" Dose Range Induces Substantial Intestinal Injury in Non-Human Primates

The non-human primate has been a useful model for studies of human acute radiation syndrome (ARS). However, to date structural changes in various parts of the intestine after total body irradiation (TBI) have not been systematically studied in this model. Here we report on our current study of TBI-induced intestinal structural injury in the non-human primate after doses typically associated with hematopoietic ARS. Twenty-four non-human primates were divided into three groups: sham-irradiated control group; and total body cobalt-60 (60Co) 6.7 Gy gamma-irradiated group; and total body 60Co 7.4 Gy gamma-irradiated group. After animals were euthanized at day 4, 7 and 12 postirradiation, sections of small intestine (duodenum, proximal jejunum, distal jejunum and ileum) were collected and fixed in 10% formalin. The intestinal mucosal surface length, villus height and crypt depths were assessed by computer-assisted image analysis. Plasma citrulline levels were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Total bone marrow cells were counted and hematopoietic stem/progenitor cells in bone marrow were analyzed by flow cytometer. Histopathologically, all segments exhibited conspicuous disappearance of plicae circulares and prominent atrophy of crypts and villi. Intestinal mucosal surface length was significantly decreased in all intestinal segments on day 4, 7 and 12 after irradiation (P < 0.02-P < 0.001). Villus height was significantly reduced in all segments on day 4 and 7 (P = 0.02-0.005), whereas it had recovered by day 12 (P > 0.05). Crypt depth was also significantly reduced in all segments on day 4, 7 and 12 after irradiation (P < 0.04-P < 0.001). Plasma citrulline levels were dramatically reduced after irradiation, consistent with intestinal mucosal injury. Both 6.7 and 7.4 Gy TBI reduced total number of bone marrow cells. And further analysis showed that the number and function of CD45(+)CD34(+) hematopoietic stem/progenitors in bone marrow decreased significantly. In summary, TBI in the hematopoietic ARS dose range induces substantial intestinal injury in all segments of the small bowel. These findings underscore the importance of maintaining the mucosal barrier that separates the gut microbiome from the body's interior after TBI.

Revisiting Biomarkers of Total-Body and Partial-Body Exposure in a Baboon Model of Irradiation

In case of a mass casualty radiation event, there is a need to distinguish total-body irradiation (TBI) and partial-body irradiation (PBI) to concentrate overwhelmed medical resources to the individuals that would develop an acute radiation syndrome (ARS) and need hematologic support (i.e., mostly TBI victims). To improve the identification and medical care of TBI versus PBI individuals, reliable biomarkers of exposure could be very useful. To investigate this issue, pairs of baboons (n = 18) were exposed to different situations of TBI and PBI corresponding to an equivalent of either 5 Gy ⁶⁰Co gamma irradiation (5 Gy TBI; 7.5 Gy left hemibody/2.5 right hemibody TBI; 5.55 Gy 90% PBI; 6.25 Gy 80% PBI; 10 Gy 50% PBI, 15 Gy 30% PBI) or 2.5 Gy (2.5 Gy TBI; 5 Gy 50% PBI). More than fifty parameters were evaluated before and after irradiation at several time points up to 200 days. A partial least square discriminant analysis showed a good distinction of TBI from PBI situations that were equivalent to 5 Gy. Furthermore, all the animals were pooled in two groups, TBI (n = 6) and PBI (n = 12), for comparison using a logistic regression and a non parametric statistical test. Nine plasmatic biochemical markers and most of hematological parameters turned out to discriminate between TBI and PBI animals during the prodromal phase and the manifest illness phase. The most significant biomarkers were aspartate aminotransferase, creatine kinase, lactico dehydrogenase, urea, Flt3-ligand, iron, C-reactive protein, absolute neutrophil count and neutrophil-to-lymphocyte ratio for the early period, and Flt3-ligand, iron, platelet count, hemoglobin, monocyte count, absolute neutrophil count and neutrophil-to-lymphocyte ratio for the ARS phase. These results suggest that heterogeneity could be distinguished within a range of 2.5 to 5 Gy TBI.

Further biodosimetry investigations using murine partial-body irradiation model

This study evaluates both the effects of physical restraint and use of candidate biomarkers in a CD2F1 male mouse partial-body irradiation model for biological dosimetry diagnostic assays. Mice were irradiated (6-Gy, 250-kVp X ray) to 3/3rd (total body), 2/3rd (gut and torso), 1/3rd (gut only) and 0/3rd (sham) of total body. Blood was sampled for haematology and blood plasma proteomic biomarkers at 1 and 2 d after exposure. Increases in the body fraction exposed showed progressive decreases in lymphocyte counts and increases in the neutrophil-to-lymphocyte ratios with no significant differences in the neutrophil and platelet counts. The radioresponse for plasma biomarker Flt3L showed proportional increases; however, G-CSF and SAA levels exhibited dramatic and non-proportional increases in levels. Physical restraint at 1 d post-exposure increased lymphocyte counts and SAA, decreased neutrophil-to-lymphocyte ratio and Flt3L and showed no effects on neutrophil and platelet counts or G-CSF.

Useful radiation dose biomarkers for early identification of partial-body exposures

Although less urgent than the physical injuries caused by an unexpected nuclear and radiological (NR) event, radiation damages can be treated more effectively if the intensity and extent of the exposure are evaluated rapidly. In this work, the authors followed within the first 7 d after exposure a few early biomarkers that could be easily deployable (simple and fast sampling and analysis) to determine their potential in distinguishing a total body irradiation (TBI) from a dose-equivalent partial exposure. A plausible accident scenario was created for this study by exposing unilaterally nonhuman primates of body mass comparable to humans to 5 Gy, to either the whole body or to part of it. Using logistic regression analysis, it was shown that both a combination of three parameters together [absolute neutrophil count; monocyte count on the first day; and C-reactive protein (CRP) 5 d after exposure] or CRP 7 d after irradiation completely separated the partial exposures from the TBIs. A quasi-complete separation using receiver-operator characteristic (ROC) was observed for neutrophil count to lymphocyte count ratio during the first day after exposure.

Significance of bioindicators to predict survival in irradiated minipigs

The minipig is emerging as a potential alternative non-rodent animal model. Several biological markers (e.g., blood counts, laboratory parameters, and clinical signs) have been proposed for rapid triage of radiation victims. Here, the authors focus on the significance of bio-indicators for prediction of survivors after irradiation and compare it with human data; the relationship between these biomarkers and radiation dose is not part of this study. Male Göttingen minipigs (age 4-5 mo, weight 9-10 kg) were irradiated (or sham-irradiated) bilaterally with gamma-photons (⁶⁰Co, 0.5-0.6 Gy min⁻¹) in the dose range of 1.6-12 Gy. Peripheral blood cell counts, laboratory parameters, and clinical symptoms were collected up to 10 d after irradiation and analyzed using logistic regression analysis and calculating ROC curves. In moribund pigs, parameters such as decreased lymphocyte/granulocyte counts, increased C-reactive protein, alkaline phosphatase values, as well as increased citrulline values and body temperature, significantly (p < 0.002 up to p < 0.0001) discriminated non-survivors from survivors with high precision (ROC > 0.8). However, most predictive within the first 3 d after exposure was a combination of decreased lymphocyte counts and increased body temperature observed as early as 3 h after radiation exposure (ROC: 0.93-0.96, p < 0.0001). Sham-irradiated animals (corresponding to "worried wells") could be easily discriminated from dying pigs, thus pointing to the diagnostic significance of this analysis. These data corroborate with earlier findings performed on human radiation victims suffering from severe hematological syndrome and provide further evidence for the suitability of the minipig model as a potential alternative non-rodent animal model.

Identification and quantitation of biomarkers for radiation-induced injury via mass spectrometry

Biomarker identification and validation for radiation exposure is a rapidly expanding field encompassing the need for well defined animal models and advanced analytical techniques. The resources within the consortium, Medical Countermeasures Against Radiological Threats (MCART), provide a unique opportunity for accessing well defined animal models that simulate the key sequelae of the acute radiation syndrome and the delayed effects of acute radiation exposure. Likewise, the use of mass spectrometry-based analytical techniques for biomarker discovery and validation enables a robust analytical platform that is amenable to a variety of sample matrices and considered the benchmark for biomolecular identification and quantitation. Herein, the authors demonstrate the use of two targeted mass spectrometry approaches to link established MCART animal models to identified metabolite biomarkers. Circulating citrulline concentration was correlated to gross histological gastrointestinal tissue damage, and retinoic acid production in lung tissue was established to be reduced at early and late time points post high dose irradiation. Going forward, the use of mass spectrometry-based metabolomics coupled to well defined animal models provides the unique opportunity for comprehensive biomarker discovery.