Combined Hydration and Antibiotics with Lisinopril to Mitigate Acute and Delayed High-dose Radiation Injuries to Multiple Organs

Development of a Radiation-induced Pulmonary Fibrosis Partial Body Irradiation Model in C57BL/6 Mice

With the current volatile geopolitical climate, the threat of nuclear assault is high. Exposure to ionizing radiation from either nuclear incidents or radiological accidents often lead to major harmful consequences to human health. Depending on the absorbed dose, the symptoms of the acute radiation syndrome and delayed effects of acute radiation exposure (DEARE) can appear within hours, weeks to months. The lung is a relatively radiosensitive organ with manifestation of radiation pneumonitis as an acute effect, followed by apparent fibrosis in weeks or even months. A recently developed, first-of-its-kind murine model for partial-body irradiation (PBI) injury, which can be used to test potential countermeasures against multi-organ damage such as gastrointestinal (GI) tract and lungs was used for irradiation, with 2.5% bone marrow spared (BM2.5-PBI) from radiation exposure. Long-term damage to lungs from radiation was evaluated using µ-CT scans, pulmonary function testing, histopathological parameters and molecular biomarkers. Pulmonary fibrosis was detected by ground glass opacity observed in µ-CT scans of male and female C57BL/6J mice 6-7 months after BM2.5-PBI. Lung mechanics assessments pertaining to peripheral airways suggested fibrotic lungs with stiffer parenchymal lung tissue and reduced inspiratory capacity in irradiated animals 6-7 months after BM2.5-PBI. Histopathological evaluation of the irradiated lungs revealed presence of focal and diffuse pleural, and parenchymal inflammatory and fibrotic lesions. Fibrosis was confirmed by elevated levels of collagen when compared to lungs of age-matched naïve mice. These findings were validated by findings of elevated levels of pro-fibrotic biomarkers and reduction in anti-inflammatory proteins. In conclusion, a long-term model for radiation-induced pulmonary fibrosis was established, and countermeasures could be screened in this model for survival and protection/mitigation or recovery from radiation-induced pulmonary damage.

2nd Window NIR Imaging of Radiation Injury Mitigation Provided by Reduced Notch-Dll4 Expression on Vasculature

PURPOSE

Vascular endothelium plays a central role in the pathogenesis of acute and chronic radiation injuries, yet the mechanisms which promote sustained endothelial dysfunction and contribute to late responding organ failure are unclear. We employed 2nd window (> 1100 nm emission) Near-Infrared (NIR) imaging using indocyanine green (ICG) to track and define the role of the notch ligand Delta-like ligand 4 (Dll4) in mediating vascular injury in two late-responding radiosensitive organs: the lung and kidney.

PROCEDURES

Consomic strains of female Salt Sensitive or SS (Dll4-high) and SS with 3rd chromosome inherited from Brown Norway, SS.BN3 (Dll4-low) rats at ages 11-12 weeks were used to demonstrate the impact of reduced Dll4 expression on long-term vascular integrity, renal function, and survival following high-dose 13 Gy partial body irradiation at 42- and 90 days post-radiation. 2nd window dynamic NIR fluorescence imaging with ICG was analyzed with physiology-based pharmacokinetic modeling and confirmed with assays of endothelial Dll4 expression to assess the role of endogenous Dll4 expression on radiation injury protection.

RESULTS

We show that SS.BN3 (Dll4-low) rats are relatively protected from vascular permeability disruption compared to the SS (Dll4-high) strain. We further demonstrated that SS.BN3 (Dll4-low) rats have reduced radiation induced loss of CD31+ vascular endothelial cells, and increased Dll4 vascular expression is correlated with vascular dysfunction.

CONCLUSIONS

Together, these data suggest Dll4 plays a key role in pathogenesis of radiation-induced vascular injury to the lung and kidney.

Radiation-induced multi-organ injury

PURPOSE

Natural history studies have been informative in dissecting radiation injury, isolating its effects, and compartmentalizing injury based on the extent of exposure and the elapsed time post-irradiation. Although radiation injury models are useful for investigating the mechanism of action in isolated subsyndromes and development of medical countermeasures (MCMs), it is clear that ionizing radiation exposure leads to multi-organ injury (MOI).

METHODS

The Radiation and Nuclear Countermeasures Program within the National Institute of Allergy and Infectious Diseases partnered with the Biomedical Advanced Research and Development Authority to convene a virtual two-day meeting titled 'Radiation-Induced Multi-Organ Injury' on June 7-8, 2022. Invited subject matter experts presented their research findings in MOI, including study of mechanisms and possible MCMs to address complex radiation-induced injuries.

RESULTS

This workshop report summarizes key information from each presentation and discussion by the speakers and audience participants.

CONCLUSIONS

Understanding the mechanisms that lead to radiation-induced MOI is critical to advancing candidate MCMs that could mitigate the injury and reduce associated morbidity and mortality. The observation that some of these mechanisms associated with MOI include systemic injuries, such as inflammation and vascular damage, suggests that MCMs that address systemic pathways could be effective against multiple organ systems.

Development of a Multi-Organ Radiation Injury Model with Precise Dosimetry with Focus on GI-ARS

The goal of this study was to establish a model of partial-body irradiation (PBI) sparing 2.5% of the bone marrow (BM2.5-PBI) that accurately recapitulates radiological/nuclear exposure scenarios. Here we have reported a model which produces gastrointestinal (GI) damage utilizing a clinical linear accelerator (LINAC) with precise dosimetry, which can be used to develop medical countermeasures (MCM) for GI acute radiation syndrome (ARS) under the FDA animal rule. The PBI model (1 hind leg spared) was developed in male and female C57BL/6 mice that received radiation doses ranging from 12-17 Gy with no supportive care. GI pathophysiology was assessed by crypt cell loss and correlated with peak lethality between days 4 and 10 after PBI. The radiation dose resulting in 50% mortality in 30 days (LD50/30) was determined by probit analysis. Differential blood cell counts in peripheral blood, colony forming units (CFU) in bone marrow, and sternal megakaryocytes were analyzed between days 1-30, to assess the extent of hematopoietic ARS (H-ARS) injury. Radiation-induced GI damage was also assessed by measuring: 1. bacterial load (16S rRNA) by RT-PCR on days 4 and 7 after PBI in liver, spleen and jejunum, 2. liposaccharide binding protein (LBP) levels in liver, and 3. fluorescein isothiocyanate (FITC)-dextran, E-selectin, sP-selectin, VEGF, FGF-2, MMP-9, citrulline, and serum amyloid A (SAA) levels in serum. The LD50/30 of male mice was 14.3 Gy (95% confidence interval 14.1-14.7 Gy) and of female mice was 14.5 Gy (95% confidence interval 14.3-14.7 Gy). Secondary endpoints included loss of viable crypts, higher bacterial loads in spleen and liver, higher LBP in liver, increased FITC-dextran and SAA levels, and decreased levels of citrulline and endothelial biomarkers in serum. The BM2.5-PBI model, developed for the first time with precise dosimetry, showed acute radiation-induced GI damage that is correlated with lethality, as well as a response to various markers of inflammation and vascular damage. Sex-specific differences were observed with respect to radiation dose response. Currently, no MCM is available as a mitigator for GI-ARS. This BM2.5-PBI mouse model can be regarded as the first high-throughput PBI model with precise dosimetry for developing MCMs for GI-ARS under the FDA animal rule.

Biological sex differences in renin angiotensin system enzymes ACE and ACE2 regulate normal tissue response to radiation injury

Introduction: In experimental animal models, biological sex-differences in the manifestation and severity of normal tissue radiation injury have been well-documented. Previously we demonstrated male and female rats have differential and highly reproducible responses to high-dose partial body irradiation (PBI) with male rats having greater susceptibility to both gastrointestinal acute radiation syndrome (GI-ARS) and radiation pneumonitis than female rats. Methods: In the current study, we have investigated whether differential expression of the renin-angiotensin system (RAS) enzymes angiotensin converting enzyme (ACE) and ACE2 contribute to the observed sex-related differences in radiation response. Results: During the period of symptomatic pneumonitis, the relative ratio of ACE to ACE2 (ACE/ACE2) protein in the whole lung was significantly increased by radiation in male rats alone. Systemic treatment with small molecule ACE2 agonist diminazene aceturate (DIZE) increased lung ACE2 activity and reduced morbidity during radiation pneumonitis in both sexes. Notably DIZE treatment also abrogated morbidity in male rats during GI-ARS. We then evaluated the contribution of the irradiated bone marrow (BM) compartment on lung immune cell infiltration and ACE imbalance during pneumonitis. Transplantation of bone marrow from irradiated donors increased both ACE-expressing myeloid cell infiltration and immune ACE activity in the lung during pneumonitis compared to non-irradiated donors. Discussion: Together, these data demonstrate radiation induces a sex-dependent imbalance in the renin-angiotensin system enzymes ACE and ACE2. Additionally, these data suggest a role for ACE-expressing myeloid cells in the pathogenesis of radiation pneumonitis. Finally, the observed sex-differences underscore the need for consideration of sex as a biological variable in the development of medical countermeasures for radiation exposure.

The progression of radiation injury in a Wistar rat model of partial body irradiation with ∼5% bone marrow shielding

PURPOSE

To describe the dose response relationship and natural history of radiation injury in the Wistar rat and it's suitability for use in medical countermeasures (MCM) testing.

MATERIALS & METHODS

In two separate studies, male and female rats were exposed to partial body irradiation (PBI) with 5% bone marrow sparing. Animals were X-ray irradiated from 7 to 12 Gy at 7-10 weeks of age. Acute radiation syndrome (ARS) survival at 30 days and delayed effects of acute radiation exposure (DEARE) survival at 182 days were assessed. Radiation effects were determined by clinical observations, body weights, hematology, clinical chemistry, magnetic resonance imaging of lung, whole-body plethysmography, and histopathology.

RESULTS

Rats developed canonical ARS responses of hematopoietic atrophy and gastrointestinal injury resulting in mortality at doses ≥8Gy in males and ≥8.5 Gy in females. DEARE mortality occurred at doses ≥8Gy for both sexes. Findings indicate lung, kidney, and/or liver injury, and persistent hematological dysregulation, revealing multi-organ injury as a DEARE.

CONCLUSION

The Wistar rat PBI model is suitable for testing MCMs against hematopoietic and gastrointestinal ARS. DEARE multi-organ injury occurred in both sexes irradiated with 8-9Gy, also suggesting suitability for polypharmacy studies addressing the combination of ARS and DEARE injury.

The delayed effects of acute radiation exposure (DEARE): characteristics, mechanisms, animal models, and promising medical countermeasures

PURPOSE

Terrorist use of nuclear weapons and radiation accidents put the human population at risk for exposure to life-threatening levels of radiation. Victims of lethal radiation exposure face potentially lethal acute injury, while survivors of the acute phase are plagued with chronic debilitating multi-organ injuries for years after exposure. Developing effective medical countermeasures (MCM) for the treatment of radiation exposure is an urgent need that relies heavily on studies conducted in reliable and well-characterized animal models according to the FDA Animal Rule. Although relevant animal models have been developed in several species and four MCM for treatment of the acute radiation syndrome are now FDA-approved, animal models for the delayed effects of acute radiation exposure (DEARE) have only recently been developed, and there are no licensed MCM for DEARE. Herein, we provide a review of the DEARE including key characteristics of the DEARE gleaned from human data as well as animal, mechanisms common to multi-organ DEARE, small and large animal models used to study the DEARE, and promising new or repurposed MCM under development for alleviation of the DEARE.

CONCLUSIONS

Intensification of research efforts and support focused on better understanding of mechanisms and natural history of DEARE are urgently needed. Such knowledge provides the necessary first steps toward the design and development of MCM that effectively alleviate the life-debilitating consequences of the DEARE for the benefit of humankind worldwide.

Biomarkers to Predict Lethal Radiation Injury to the Rat Lung

Currently, there are no biomarkers to predict lethal lung injury by radiation. Since it is not ethical to irradiate humans, animal models must be used to identify biomarkers. Injury to the female WAG/RijCmcr rat has been well-characterized after exposure to eight doses of whole thorax irradiation: 0-, 5-, 10-, 11-, 12-, 13-, 14- and 15-Gy. End points such as SPECT imaging of the lung using molecular probes, measurement of circulating blood cells and specific miRNA have been shown to change after radiation. Our goal was to use these changes to predict lethal lung injury in the rat model, 2 weeks post-irradiation, before any symptoms manifest and after which a countermeasure can be given to enhance survival. SPECT imaging with 99mTc-MAA identified a decrease in perfusion in the lung after irradiation. A decrease in circulating white blood cells and an increase in five specific miRNAs in whole blood were also tested. Univariate analyses were then conducted on the combined dataset. The results indicated that a combination of percent change in lymphocytes and monocytes, as well as pulmonary perfusion volume could predict survival from radiation to the lungs with 88.5% accuracy (95% confidence intervals of 77.8, 95.3) with a p-value of < 0.0001 versus no information rate. This study is one of the first to report a set of minimally invasive endpoints to predict lethal radiation injury in female rats. Lung-specific injury can be visualized by 99mTc-MAA as early as 2 weeks after radiation.

Where are the medical countermeasures against the ARS and DEARE? A current topic relative to an animal model research platform, radiation exposure context, the acute and delayed effects of acute exposure, and the FDA animal rule

PURPOSE

A question echoed by the National Biodefense Science Board (NBSB) in 2010, remains a reasonable question in 2023; 'Where are the Countermeasures?'. A critical path for development of medical countermeasures (MCM) against acute, radiation-induced organ-specific injury within the acute radiation syndrome (ARS) and the delayed effects of acute radiation exposure (DEARE) requires the recognition of problems and solutions inherent in the path to FDA approval under the Animal Rule. Keep Rule number one in mind, It's not easy.

CONSIDERATIONS

The current topic herein is focused on defining the nonhuman primate model(s) for efficient MCM development relative to consideration of prompt and delayed exposure in the context of the nuclear scenario. The rhesus macaque is a predictive model for human exposure of partial-body irradiation with marginal bone marrow sparing that allows definition of the multiple organ injury in the acute radiation syndrome (ARS) and the delayed effects of acute radiation exposure (DEARE). The continued definition of natural history is required to delineate an associative or causal interaction within the concurrent multi-organ injury characteristic of the ARS and DEARE. A more efficient development of organ specific MCM for both pre-exposure and post-exposure prophylaxis to include acute radiation-induced combined injury requires closing critical gaps in knowledge and urgent support to rectify the national shortage of nonhuman primates. The rhesus macaque is a validated, predictive model of the human response to prompt and delayed radiation exposure, medical management and MCM treatment. A rational approach to further development of the cynomolgus macaque as a comparable model is urgently required for continued development of MCM for FDA approval.

CONCLUSION

It is imperative to examine the key variables relative to animal model development and validation, The pharmacokinetics, pharmacodynamics and exposure profiles, of candidate MCM relative to route, administration schedule and optimal efficacy define the fully effective dose. The conduct of adequate and well-controlled pivotal efficacy studies as well as safety and toxicity studies support approval under the FDA Animal Rule and label definition for human use.

Analysis of the urinary metabolic profiles in irradiated rats treated with Activated Protein C (APC), a potential mitigator of radiation toxicity

PURPOSE

The goal of the current study was to identify longitudinal changes in urinary metabolites following IR exposure and to determine potential alleviation of radiation toxicities by administration of recombinant APC formulations.

MATERIALS AND METHODS

Female adult WAG/RijCmcr rats were irradiated with 13.0 Gy leg-out partial body X-rays; longitudinally collected urine samples were subject to LC-MS based metabolomic profiling. Sub-cohorts of rats were treated with three variants of recombinant APC namely, rat wildtype (WT) APC, rat 3K3A mutant form of APC, and human WT APC as two bolus injections at 24 and 48 hours post IR.

RESULTS

Radiation induced robust changes in the urinary profiles leading to oxidative stress, severe dyslipidemia, and altered biosynthesis of PUFAs, glycerophospholipids, sphingolipids, and steroids. Alterations were observed in multiple metabolic pathways related to energy metabolism, nucleotide biosynthesis and metabolism that were indicative of disrupted mitochondrial function and DNA damage. On the other hand, sub-cohorts of rats that were treated with rat wildtype-APC showed alleviation of radiation toxicities, in part, at the 90-day time point, while rat 3K3A-APC showed partial alleviation of radiation induced metabolic alterations 14 days after irradiation.

CONCLUSIONS

Taken together, these results show that augmenting the Protein C pathway and activity via administration of recombinant APC may be an effective approach for mitigation of radiation induced normal tissue toxicity.

IPW-5371 mitigates the delayed effects of acute radiation exposure in WAG/RijCmcr rats when started 15 days after PBI with bone marrow sparing

PURPOSE

To test IPW-5371 for the mitigation of the delayed effects of acute radiation exposure (DEARE). Survivors of acute radiation exposure are at risk for developing delayed multi-organ toxicities; however, there are no FDA-approved medical countermeasures (MCM) to mitigate DEARE.

METHODS

WAG/RijCmcr female rat model of partial-body irradiation (PBI), by shielding part of one hind leg, was used to test IPW-5371 (7 and 20 mg kg-1 d-1) for mitigation of lung and kidney DEARE when started 15 d after PBI. Rats were fed known amounts of IPW-5371 using a syringe, instead of delivery by daily oral gavage, sparing exacerbation of esophageal injury by radiation. The primary endpoint, all-cause morbidity was assessed over 215 d. Secondary endpoints: body weight, breathing rate and blood urea nitrogen were also assessed.

RESULTS

IPW-5371 enhanced survival (primary endpoint) as well as attenuated secondary endpoints of lung and kidney injuries by radiation.

CONCLUSION

To provide a window for dosimetry and triage, as well as avoid oral delivery during the acute radiation syndrome (ARS), the drug regimen was started at 15 d after 13.5 Gy PBI. The experimental design to test mitigation of DEARE was customized for translation in humans, using an animal model of radiation that was designed to simulate a radiologic attack or accident. The results support advanced development of IPW-5371 to mitigate lethal lung and kidney injuries after irradiation of multiple organs.

Combined angiotensin-converting enzyme and aminopeptidase inhibition for treatment of experimental ventilator-induced lung injury in mice

Introduction: Ventilator-induced lung injury (VILI) may aggravate critical illness. Although angiotensin-converting enzyme (ACE) inhibition has beneficial effects in ventilator-induced lung injury, its clinical application is impeded by concomitant hypotension. We hypothesized that the aminopeptidase inhibitor ALT-00 may oppose the hypotension induced by an angiotensin-converting enzyme inhibitor, and that this combination would activate the alternative renin-angiotensin system (RAS) axis to counteract ventilator-induced lung injury. Methods: In separate experiments, C57BL/6 mice were mechanically ventilated with low (LVT, 6 mL/kg) and high tidal volumes (HVT, 30 mL/kg) for 4 h or remained unventilated (sham). High tidal volume-ventilated mice were treated with lisinopril (0.15 μg/kg/min) ± ALT-00 at 2.7, 10 or 100 μg/kg/min. Blood pressure was recorded at baseline and after 4 h. Lung histology was evaluated for ventilator-induced lung injury and the angiotensin (Ang) metabolite profile in plasma (equilibrium levels of Ang I, Ang II, Ang III, Ang IV, Ang 1-7, and Ang 1-5) was measured with liquid chromatography tandem mass spectrometry at the end of the experiment. Angiotensin concentration-based markers for renin, angiotensin-converting enzyme and alternative renin-angiotensin system activities were calculated. Results: High tidal volume-ventilated mice treated with lisinopril showed a significant drop in the mean arterial pressure at 4 h compared to baseline, which was prevented by adding ALT-00 at 10 and 100 μg/kg/min. Ang I, Ang II and Ang 1-7 plasma equilibrium levels were elevated in the high tidal volumes group versus the sham group. Lisinopril reduced Ang II and slightly increased Ang I and Ang 1-7 levels versus the untreated high tidal volumes group. Adding ALT-00 at 10 and 100 μg/kg/min increased Ang I and Ang 1-7 levels versus the high tidal volume group, and partly prevented the downregulation of Ang II levels caused by lisinopril. The histological lung injury score was higher in the high tidal volume group versus the sham and low tidal volume groups, and was attenuated by lisinopril ± ALT-00 at all dose levels. Conclusion: Combined angiotensin-converting enzyme plus aminopeptidase inhibition prevented systemic hypotension and maintained the protective effect of lisinopril. In this study, a combination of lisinopril and ALT-00 at 10 μg/kg/min appeared to be the optimal approach, which may represent a promising strategy to counteract ventilator-induced lung injury that merits further exploration.

Animal Care in Radiation Medical Countermeasures Studies

Animal models are necessary to demonstrate the efficacy of medical countermeasures (MCM) to mitigate/treat acute radiation syndrome and the delayed effects of acute radiation exposure and develop biodosimetry signatures for use in triage and to guide medical management. The use of animal models in radiation research allows for the simulation of the biological effects of exposure in humans. Robust and well-controlled animal studies provide a platform to address basic mechanistic and safety questions that cannot be conducted in humans. The U.S. Department of Health and Human Services has tasked the National Institute of Allergy and Infectious Diseases (NIAID) with identifying and funding early- through advanced-stage MCM development for radiation-induced injuries; and advancement of biodosimetry platforms and exploration of biomarkers for triage, definitive dose, and predictive purposes. Some of these NIAID-funded projects may transition to the Biomedical Advanced Research and Development Authority (BARDA), a component of the Office of the Assistant Secretary for Preparedness and Response in the U.S. Department of Health and Human Services, which is tasked with the advanced development of MCMs to include pharmacokinetic, exposure, and safety assessments in humans. Guided by the U.S. Food and Drug Administration's (FDA) Animal Rule, both NIAID and BARDA work closely with researchers to advance product and device development, setting them on a course for eventual licensure/approval/clearance of their approaches by the FDA. In August 2020, NIAID partnered with BARDA to conduct a workshop to discuss currently accepted animal care protocols and examine aspects of animal models that can influence outcomes of studies to explore MCM efficacy for potential harmonization. This report provides an overview of the two-day workshop, which includes a series of special topic presentations followed by panel discussions with subject-matter experts from academia, industry partners, and select governmental agencies.

Angiotensin converting enzyme (ACE) inhibitors as radiation countermeasures for long-duration space flights

Angiotensin converting enzyme (ACE) inhibitors are effective countermeasures to chronic radiation injuries in rodent models, and there is evidence for similar effects in humans. In rodent models ACE inhibitors are effective mitigators of radiation injury to kidney, lung, central nervous system (CNS) and skin, even when started weeks after irradiation. In humans, the best data for their efficacy as radiation countermeasures comes from retrospective studies of injuries in radiotherapy patients. We propose that ACE inhibitors, at doses approved for human use for other indications, could be used to reduce the risk of chronic radiation injuries from deep-space exploration. Because of the potential interaction of ACE inhibitors and microgravity (due to effects of ACE inhibitors on fluid balance) use might be restricted to post-exposure when/if radiation exposures reached a danger level. A major unresolved issue for this approach is the sparse evidence for the efficacy of ACE inhibitors after low-dose-rate exposure and/or for high-LET radiations (as would occur on long-duration space flights). A second issue is that the lack of a clear mechanism of action of the ACE inhibitors as mitigators makes obtaining an appropriate label under the Food and Drug Administration Animal Rule difficult.

Vascular regression in the kidney: changes in 3D vessel structure with time post-irradiation

Though angiogenesis has been investigated in depth, vascular regression and rarefaction remain poorly understood. Regression of renal vasculature accompanies many pathological states such as diabetes, hypertension, atherosclerosis, and radiotherapy. Radiation decreases microvessel density in multiple organs, though the mechanism is not known. By using a whole animal (rat) model with a single dose of partial body irradiation to the kidney, changes in the volume of renal vasculature were recorded at two time points, 60 and 90 days after exposure. Next, a novel vascular and metabolic imaging (VMI) technique was used to computationally assess 3D vessel diameter, volume, branch depth, and density over multiple levels of branching down to 70 µm. Four groups of rats were studied, of which two groups received a single dose of 12.5 Gy X-rays. The kidneys were harvested after 60 or 90 days from one irradiated and one non-irradiated group at each time point. Measurements of the 3D vasculature showed that by day-90 post-radiation, when renal function is known to deteriorate, total vessel volume, vessel density, maximum branch depth, and the number of terminal points in the kidneys decreased by 55%, 57%, 28%, and 53%, respectively. Decreases in the same parameters were not statistically significant at 60 days post-irradiation. Smaller vessels with internal diameters of 70-450 µm as well as large vessels of diameter 451-850 µm, both decreased by 90 days post-radiation. Vascular regression in the lungs of the same strain of irradiated rats has been reported to occur before 60 days supporting the hypothesis that this process is regulated in an organ-specific manner and occurs by a concurrent decrease in luminal diameters of small as well as large blood vessels.

Mitigation of Multi-Organ Radiation Injury with ACE2 Agonist Diminazene Aceturate

The renin-angiotensin system (RAS) is known to regulate the pathogenesis of radiation-induced injury as inhibitors of the RAS enzyme angiotensin converting enzyme (ACE) have established function as mitigators of multi-organ radiation injury. To further elucidate the role of RAS signaling during both the acute and delayed syndromes of radiation exposure, we have evaluated whether pharmacologic modulation of alternate RAS enzyme angiotensin converting enzyme 2 (ACE2) reduces the pathogenesis of multi-organ radiation-induced injuries. Here, we demonstrate pharmacologic ACE2 activation with the small molecule ACE2 agonist diminazene aceturate (DIZE) improves survival in rat models of both hematologic acute radiation syndrome (H-ARS) and multi-organ delayed effects of acute radiation exposure (DEARE). In the H-ARS model, DIZE treatment increased 30-day survival by 30% compared to vehicle control rats after a LD50/30 total-body irradiation (TBI) dose of 7.75 Gy. In the mitigation of DEARE, ACE2 agonism with DIZE increased median survival by 30 days, reduced breathing rate, and reduced blood urea nitrogen (BUN) levels compared to control rats after partial-body irradiation (PBI) of 13.5 Gy. DIZE treatment was observed to have systemic effects which may explain the multi-organ benefits observed including mobilization of hematopoietic progenitors to the circulation and a reduction in plasma TGF-beta levels. These data suggest the ACE2 enzyme plays a critical role in the RAS-mediated pathogenesis of radiation injury and may be a potential therapeutic target for the development of medical countermeasures for acute radiation exposure.

Medical management of acute radiation syndrome

Acute radiation syndrome (ARS) is a clinical syndrome involving four organ systems, resulting in the hematopoietic syndrome (HS), gastrointestinal subsyndrome (GIS), neurovascular subsyndrome (NVS) and cutaneous subsyndrome (CS). Since few healthcare providers have seen an ARS case, evidence-based recommendations are needed to guide medical management in a mass casualty scenario. The authors reviewed recommendations from evidence-based and narrative reviews by expert consultants to the World Health Organisation (WHO), a subsequent review of published HS cases, and infectious disease guidelines for management of febrile neutropenia. The WHO Consultancy applied a rigorous grading system to evaluate treatment strategies described in published ARS cases as of 2009, strategies to manage HS in unirradiated persons, results of ARS studies in animal models of ARS, and recommendations of prior expert panels. Major findings for HS were (a) no randomised controlled studies have been performed, (b) data are restricted by the lack of comparator groups, and (c) reports of countermeasures for management of injury to non-hematopoietic organs are often incomplete. Strength of recommendations ranged from strong to weak. Countermeasures of potential benefit include cytokines and for a subgroup of HS patients, hematopoietic stem cell transplantation. These recommendations did not change in a subsequent analysis of HS cases. Recommendations also included fluoroquinolones, bowel decontamination, serotonin receptor antagonists, loperamide and enteral nutrition for GIS; supportive care for NVS; and topical steroids, antihistamines and antibiotics, and surgical excision/grafting for CS. Also reviewed are critical care management guidelines, the role of mesenchymal stem cells for CS, the potential of a platelet-stimulating cytokine for HS, and the author's approach to clinical management of microbial infections associated with ARS based on published guidelines of infectious disease experts. Today's management of HS is supported by evidence-based guidelines. Management of non-HS subsyndromes is supported by a narrative review of the literature and recommendations of infectious disease societies.

Lisinopril Mitigates Radiation-Induced Mitochondrial Defects in Rat Heart and Blood Cells

The genetic bases and disparate responses to radiotherapy are poorly understood, especially for cardiotoxicity resulting from treatment of thoracic tumors. Preclinical animal models such as the Dahl salt-sensitive (SS) rat can serve as a surrogate model for salt-sensitive low renin hypertension, common to African Americans, where aldosterone contributes to hypertension-related alterations of peripheral vascular and renal vascular function. Brown Norway (BN) rats, in comparison, are a normotensive control group, while consomic SSBN6 with substitution of rat chromosome 6 (homologous to human chromosome 14) on an SS background manifests cardioprotection and mitochondrial preservation to SS rats after injury. In this study, 2 groups from each of the 3 rat strains had their hearts irradiated (8 Gy X 5 fractions). One irradiated group was treated with the ACE-inhibitor lisinopril, and a separate group in each strain served as nonirradiated controls. Radiation reduced cardiac end diastolic volume by 9-11% and increased thickness of the interventricular septum (11-16%) and left ventricular posterior wall (14-15%) in all 3 strains (5-10 rats/group) after 120 days. Lisinopril mitigated the increase in posterior wall thickness. Mitochondrial function was measured by the Seahorse Cell Mitochondrial Stress test in peripheral blood mononuclear cells (PBMC) at 90 days. Radiation did not alter mitochondrial respiration in PBMC from BN or SSBN6. However, maximal mitochondrial respiration and spare capacity were reduced by radiation in PBMC from SS rats (p=0.016 and 0.002 respectively, 9-10 rats/group) and this effect was mitigated by lisinopril (p=0.04 and 0.023 respectively, 9-10 rats/group). Taken together, these results indicate injury to the heart by radiation in all 3 strains of rats, although the SS rats had greater susceptibility for mitochondrial dysfunction. Lisinopril mitigated injury independent of genetic background.

The Interplay among Radiation Therapy, Antibiotics and the Microbiota: Impact on Cancer Treatment Outcomes

Radiation therapy has been used for more than a century, either alone or in combination with other therapeutic modalities, to treat most types of cancer. On average, radiation therapy is included in the treatment plans for over 50% of all cancer patients, and it is estimated to contribute to about 40% of curative protocols, a success rate that may reach 90%, or higher, for certain tumor types, particularly on patients diagnosed at early disease stages. A growing body of research provides solid support for the existence of bidirectional interaction between radiation exposure and the human microbiota. Radiation treatment causes quantitative and qualitative changes in the gut microbiota composition, often leading to an increased abundance of potentially hazardous or pathogenic microbes and a concomitant decrease in commensal bacteria. In turn, the resulting dysbiotic microbiota becomes an important contributor to worsen the adverse events caused in patients by the inflammatory process triggered by the radiation treatment and a significant determinant of the radiation therapy anti-tumor effectiveness. Antibiotics, which are frequently included as prophylactic agents in cancer treatment protocols to prevent patient infections, may affect the radiation/microbiota interaction through mechanisms involving both their antimicrobial activity, as a mediator of microbiota imbalances, and their dual capacity to act as pro- or anti-tumorigenic effectors and, consequently, as critical determinants of radiation therapy outcomes. In this scenario, it becomes important to introduce the use of probiotics and/or other agents that may stabilize the healthy microbiota before patients are exposed to radiation. Ultimately, newly developed methodologies may facilitate performing personalized microbiota screenings on patients before radiation therapy as an accurate way to identify which antibiotics may be used, if needed, and to inform the overall treatment planning. This review examines currently available data on these issues from the perspective of improving radiation therapy outcomes.

Pharmacological ACE-inhibition Mitigates Radiation-Induced Pneumonitis by Suppressing ACE-expressing Lung Myeloid Cells

PURPOSE

Radiation-induced lung injury is a major dose-limiting toxicity for thoracic radiotherapy patients. In experimental models, treatment with angiotensin converting enzyme (ACE) inhibitors mitigates radiation pneumonitis; however, the mechanism of action is not well understood. Here, we evaluate the direct role of ACE inhibition on lung immune cells.

METHODS AND MATERIALS

ACE expression and activity were determined in the lung immune cell compartment of irradiated adult rats following either high dose fractionated radiation therapy (RT) to the right lung (5 fractions x 9 Gy) or a single dose of 13.5 Gy partial body irradiation (PBI). Mitigation of radiation-induced pneumonitis with the ACE-inhibitor lisinopril was evaluated in the 13.5 Gy rat PBI model. During pneumonitis, we characterized inflammation and immune cell content in the lungs and bronchoalveolar lavage fluid (BALF). In vitro mechanistic studies were performed using primary human monocytes and the human monocytic THP-1 cell line.

RESULTS

In both the PBI and fractionated RT models, radiation increased ACE activity in lung immune cells. Treatment with lisinopril improved survival during radiation pneumonitis (p=0.0004). Lisinopril abrogated radiation-induced increases in BALF MCP-1 (CCL2) and MIP-1α cytokine levels (p < 0.0001). Treatment with lisinopril reduced both ACE expression (p=0.006) and frequency of CD45⁺CD11b⁺ lung myeloid cells (p=0.004). In vitro, radiation injury acutely increased ACE activity (p=0.045) and reactive oxygen species (ROS) generation (p=0.004) in human monocytes, whereas treatment with lisinopril blocked radiation-induced increases in both ACE and ROS. Interestingly, radiation-induced ROS generation was blocked by pharmacological inhibition of either NADPH oxidase 2 (NOX2) (p=0.012) or the type 1 angiotensin receptor (AGTR1) (p=0.013).

CONCLUSIONS

These data demonstrate radiation-induced ACE activation within the immune compartment promotes the pathogenesis of radiation pneumonitis, while ACE inhibition suppresses activation of pro-inflammatory immune cell subsets. Mechanistically, our in vitro data demonstrate radiation directly activates the ACE/AGTR1 pathway in immune cells and promotes generation of ROS via Nox2.

Molecular Changes in miRNA in Irradiated Rat Kidneys: Role of miR-34a and its Vascular Targets in the Notch Pathway

The mechanism(s) of vascular regression in adult organs remains an unexplored gap. Irradiation to the kidney results in vascular regression and renal failure. The goal of this work was to determine molecular mechanism(s) of radiation-induced vascular regression and its mitigation by the drug lisinopril. Female WAG/RijCmcr rats received either 13 Gy X-ray irradiation, sparing one leg, or no irradiation, the latter serving as age-matched controls. Some irradiated animals received lisinopril. Kidney miRNA-seq was performed 35 days postirradiation, before symptoms of nephropathy. MicroRNA expression profiles were compared with data from humans. MicroRNA targets were predicted using TargetScan and confirmed by qRT-PCR and Western blot. Renal vascular endothelial cell density was evaluated at 100 days to confirm vascular regression. The normal rat kidney microRNA profile resembled that of humans. MiR-34a was increased >7-fold and emerged as the predominant rat microRNA altered by radiation. Expression of Jagged1, a ligand in the Notch pathway of vascular development and a target of miR-34a-5p was decreased by radiation but not in irradiated rats receiving lisinopril. Radiation decreased endothelial cells in the kidneys at 100 days, confirming vascular regression. In conclusion, the results of this study showed that radiation greatly increased miRNA34-a in rat kidneys, while lisinopril mitigated radiation-induced decrease of the Notch ligand, Jagged1, a molecular target of miRNA34-a.

Recent advances in medical countermeasure development against acute radiation exposure based on the US FDA animal rule

Recent advances in medical countermeasures (MCMs) has been dependent on the Food and Drug Administration (FDA) animal rule (AR) and the final guidance document provided for industry on product development. The criteria outlined therein establish the path for approval under the AR. The guidance document, along with the funding and requirements from the federal agencies provided the basic considerations for animal model development in assessing radiation effects and efficacy against the potential lethal effects of acute radiation injury and the delayed effects of acute exposure. Animal models, essential for determining MCM efficacy, were developed and validated to assess organ-specific, potentially lethal, radiation effects against the gastrointestinal (GI) and hematopoietic acute radiation syndrome (H-ARS), and radiation-induced delayed effects to lung and associated comorbidities of prolonged immune suppression, GI, kidney and heart injury. Partial-body irradiation models where marginal bone marrow was spared resulted in the ability to evaluate the concomitant evolution of multiple organ injury in the acute and delayed effects in survivors of acute radiation exposure. There are no MCMs for prophylaxis against the major sequelae of the ARS or the delayed effects of acute exposure. Also lacking are MCMs that will mitigate the GI ARS consequent to potentially lethal exposure from a terrorist event or major radiation accident. Additionally, the gap in countermeasures for prophylaxis may extend to mixed neutron/gamma radiation if current modelling predicts prompt exposure from an improvised nuclear device. However, progress in the field of MCM development has been made due to federal and corporate funding, clarification of the critical criteria for efficacy within the FDA AR and the concomitant development and validation of additional animal models. These models provided for a strategic and tactical approach to determine radiation effects and MCM efficacy.

Meeting Report: A Poly-Pharmacy Approach to Mitigate Acute Radiation Syndrome

The National Institute of Allergy and Infectious Diseases, Radiation and Nuclear Countermeasures Program, was tasked by the United States Congress and the U.S. Department of Health and Human Services to identify and fund early-to-mid-stage development of medical countermeasures (MCMs) to treat radiation-induced injuries. In developing MCMs to treat various sub-syndromes (e.g., hematopoietic, gastrointestinal, lung), it is important to investigate whether a poly-pharmacy approach (i.e., drug cocktails) can provide additive benefits to mitigate injuries arising from the acute radiation syndrome (ARS). In addition, potential drug-drug interactions must be examined. For this reason, a workshop was held, which centered on understanding the current state of research investigating poly-pharmacy approaches to treat radiation injuries. The first session set the stage with an introduction to the concept of operations or support available for the response to a nuclear incident, as this is the key to any emergency response, including MCM availability and distribution. The second session followed the natural history of ARS in both humans and animal models to underscore the complexity of ARS and why a poly-pharmacy approach may be necessary. The third session featured talks from investigators conducting current MCM poly-pharmacy research. The meeting closed with a focus on regulatory considerations for the development of poly-pharmacy approaches or combination treatments for ARS.

Rat Models of Partial-body Irradiation with Bone Marrow-sparing (Leg-out PBI) Designed for FDA Approval of Countermeasures for Mitigation of Acute and Delayed Injuries by Radiation

ABSTRACT

The goal of this study was to develop rat models of partial body irradiation with bone-marrow sparing (leg-out PBI) to test medical countermeasures (MCM) of both acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE) under the FDA animal rule. The leg-out PBI models were developed in female and male WAG/RijCmcr rats at doses of 12.5-14.5 Gy. Rats received supportive care consisting of fluids and antibiotics. Gastrointestinal ARS (GI-ARS) was assessed by lethality to d 7 and diarrhea scoring to d 10. Differential blood counts were analyzed between d 1-42 for the natural history of hematopoietic ARS (H-ARS). Lethality and breathing intervals (BI) were measured between d 28-110 to assess delayed injury to the lung (L-DEARE). Kidney injury (K-DEARE) was evaluated by measuring elevation of blood urea nitrogen (BUN) between d 90-180. The LD50/30, including both lethality from GI-ARS and H-ARS, for female and male rats are 14.0 Gy and 13.5 Gy, respectively, while the LD50/7 for only GI-ARS are 14.3 Gy and 13.6 Gy, respectively. The all-cause mortalities, including ARS and L-DEARE, through 120 d (LD50/120) are 13.5 Gy and 12.9 Gy, respectively. Secondary end points confirmed occurrence of four distinct sequelae representing GI, hematopoietic, lung, and kidney toxicities after leg-out PBI. Adult rat models of leg-out PBI showed the acute and long-term sequelae of radiation damage that has been reported in human radiation exposure case studies. Sex-specific differences were observed in the DRR between females and males. These rat models are among the most useful for the development and approval of countermeasures for mitigation of radiation injuries under the FDA animal rule.

A Trans-Agency Workshop on the Pathophysiology of Radiation-Induced Lung Injury

Research and development of medical countermeasures (MCMs) for radiation-induced lung injury relies on the availability of animal models with well-characterized pathophysiology, allowing effective bridging to humans. To develop useful animal models, it is important to understand the clinical condition, advantages and limitations of individual models, and how to properly apply these models to demonstrate MCM efficacy. On March 20, 2019, a meeting sponsored by the Radiation and Nuclear Countermeasures Program (RNCP) within the National Institute of Allergy and Infectious Diseases (NIAID) brought together medical, scientific and regulatory communities, including academic and industry subject matter experts, and government stakeholders from the Food and Drug Administration (FDA) and the Biomedical Advanced Research and Development Authority (BARDA), to identify critical research gaps, discuss current clinical practices for various forms of pulmonary damage, and consider available animal models for radiation-induced lung injury.

Identifying Candidate Biomarkers of Ionizing Radiation in Human Pulmonary Microvascular Lumens Using Microfluidics-A Pilot Study

The microvasculature system is critical for the delivery and removal of key nutrients and waste products and is significantly damaged by ionizing radiation. Single-cell capillaries and microvasculature structures are the primary cause of circulatory dysfunction, one that results in morbidities leading to progressive tissue and organ failure and premature death. Identifying tissue-specific biomarkers that are predictive of the extent of tissue and organ damage will aid in developing medical countermeasures for treating individuals exposed to ionizing radiation. In this pilot study, we developed and tested a 17 µL human-derived microvascular microfluidic lumen for identifying candidate biomarkers of ionizing radiation exposure. Through mass-spectrometry-based proteomics, we detected 35 proteins that may be candidate early biomarkers of ionizing radiation exposure. This pilot study demonstrates the feasibility of using humanized microfluidic and organ-on-a-chip systems for biomarker discovery studies. A more elaborate study of sufficient statistical power is needed to identify candidate biomarkers and test medical countermeasures of ionizing radiation.

3D Optical Cryo-Imaging Method: A Novel Approach to Quantify Renal Mitochondrial Bioenergetics Dysfunction

Mitochondrial dysfunction contributes to various injuries and diseases. A mechanistic understanding of how dysfunctional mitochondria modulates metabolism is of paramount importance. Three-dimensional (3D) optical cryo-imager is a custom-designed device that can quantify the volumetric bioenergetics of organs in small animal models. The instrument captures the autofluorescence of bioenergetics indices (NADH and FAD) from tissues at cryogenic temperature. The quantified redox ratio (NADH/FAD) is used as an optical indicator of mitochondrial redox state.

Three-dimensional vascular and metabolic imaging using inverted autofluorescence

SIGNIFICANCE

Three-dimensional (3D) vascular and metabolic imaging (VMI) of whole organs in rodents provides critical and important (patho)physiological information in studying animal models of vascular network.

AIM

Autofluorescence metabolic imaging has been used to evaluate mitochondrial metabolites such as nicotinamide adenine dinucleotide (NADH) and flavine adenine dinucleotide (FAD). Leveraging these autofluorescence images of whole organs of rodents, we have developed a 3D vascular segmentation technique to delineate the anatomy of the vasculature as well as mitochondrial metabolic distribution.

APPROACH

By measuring fluorescence from naturally occurring mitochondrial metabolites combined with light-absorbing properties of hemoglobin, we detected the 3D structure of the vascular tree of rodent lungs, kidneys, hearts, and livers using VMI. For lung VMI, an exogenous fluorescent dye was injected into the trachea for inflation and to separate the airways, confirming no overlap between the segmented vessels and airways.

RESULTS

The kidney vasculature from genetically engineered rats expressing endothelial-specific red fluorescent protein TdTomato confirmed a significant overlap with VMI. This approach abided by the "minimum work" hypothesis of the vascular network fitting to Murray's law. Finally, the vascular segmentation approach confirmed the vascular regression in rats, induced by ionizing radiation.

CONCLUSIONS

Simultaneous vascular and metabolic information extracted from the VMI provides quantitative diagnostic markers without the confounding effects of vascular stains, fillers, or contrast agents.

Long-acting PGE2 and Lisinopril Mitigate H-ARS

Thrombocytopenia is a major complication in hematopoietic-acute radiation syndrome (H-ARS) that increases the risk of mortality from uncontrolled hemorrhage. There is a great demand for new therapies to improve survival and mitigate bleeding in H-ARS. Thrombopoiesis requires interactions between megakaryocytes (MKs) and endothelial cells. 16, 16-dimethyl prostaglandin E2 (dmPGE2), a longer-acting analogue of PGE2, promotes hematopoietic recovery after total-body irradiation (TBI), and various angiotensin-converting enzyme (ACE) inhibitors mitigate endothelial injury after radiation exposure. Here, we tested a combination therapy of dmPGE2 and lisinopril to mitigate thrombocytopenia in murine models of H-ARS following TBI. After 7.75 Gy TBI, dmPGE2 and lisinopril each increased survival relative to vehicle controls. Importantly, combined dmPGE2 and lisinopril therapy enhanced survival greater than either individual agent. Studies performed after 4 Gy TBI revealed reduced numbers of marrow MKs and circulating platelets. In addition, sublethal TBI induced abnormalities both in MK maturation and in in vitro and in vivo platelet function. dmPGE2, alone and in combination with lisinopril, improved recovery of marrow MKs and peripheral platelets. Finally, sublethal TBI transiently reduced the number of marrow Lin-CD45-CD31+Sca-1- sinusoidal endothelial cells, while combined dmPGE2 and lisinopril treatment, but not single-agent treatment, accelerated their recovery. Taken together, these data support the concept that combined dmPGE2 and lisinopril therapy improves thrombocytopenia and survival by promoting recovery of the MK lineage, as well as the MK niche, in the setting of H-ARS.

Acute Radiation-Induced Hematopoietic Depletion Does Not Alter the Onset or Severity of Pneumonitis in Mice

Survival from partial-body irradiation (PBI) may be limited by the development of the late lung injury response of pneumonitis. Herein we investigated the hypothesis that acute hematopoietic depletion alters the onset and severity of lung disease in a mouse model. To establish depletion, C3H/HeJ mice received 8 Gy PBI with shielding of only the tibiae, ankles and feet. One week after irradiation, blood lymphocyte and neutrophil counts were each significantly reduced (P < 0.04) in these mice compared to levels in untreated controls or in mice receiving 16 Gy to the whole thorax only. All 8 Gy PBI mice survived to the experimental end point of 16 weeks postirradiation. To determine whether the hematopoietic depletion affects lung disease, groups of mice received 8 Gy PBI plus 8 Gy whole-thorax irradiation (total lung dose of 16 Gy) or 16 Gy whole-thorax irradiation only. The weight loss, survival to onset of respiratory distress (P = 0.17) and pneumonitis score (P = 0.96) of mice that received 8 Gy PBI plus 8 Gy whole-thorax irradiation were not significantly different from those of mice receiving 16 Gy whole-thorax irradiation only. Mice in respiratory distress from PBI plus whole-thorax irradiation had significantly reduced (P = 0.02) blood monocyte counts compared to levels in distressed, whole-thorax irradiated mice, and symptomatic pneumonitis was associated with increased blood neutrophil counts (P = 0.04) relative to measures from irradiated, non-distressed mice. In conclusion, survivable acute hematopoietic depletion by partial-body irradiation did not alter the onset or severity of lethal pneumonitis in the C3H/HeJ mouse model.

Acute Radiation Syndrome and the Microbiome: Impact and Review

Study of the human microbiota has been a centuries-long endeavor, but since the inception of the National Institutes of Health (NIH) Human Microbiome Project in 2007, research has greatly expanded, including the space involving radiation injury. As acute radiation syndrome (ARS) is multisystemic, the microbiome niches across all areas of the body may be affected. This review highlights advances in radiation research examining the effect of irradiation on the microbiome and its potential use as a target for medical countermeasures or biodosimetry approaches, or as a medical countermeasure itself. The authors also address animal model considerations for designing studies, and the potential to use the microbiome as a biomarker to assess radiation exposure and predict outcome. Recent research has shown that the microbiome holds enormous potential for mitigation of radiation injury, in the context of both radiotherapy and radiological/nuclear public health emergencies. Gaps still exist, but the field is moving forward with much promise.

Polypharmacy to Mitigate Acute and Delayed Radiation Syndromes

There is a need for countermeasures to mitigate lethal acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE). In WAG/RijCmcr rats, ARS occurs by 30-days following total body irradiation (TBI), and manifests as potentially lethal gastrointestinal (GI) and hematopoietic (H-ARS) toxicities after >12.5 and >7 Gy, respectively. DEARE, which includes potentially lethal lung and kidney injuries, is observed after partial body irradiation >12.5 Gy, with one hind limb shielded (leg-out PBI). The goal of this study is to enhance survival from ARS and DEARE by polypharmacy, since no monotherapy has demonstrated efficacy to mitigate both sets of injuries. For mitigation of ARS following 7.5 Gy TBI, a combination of three hematopoietic growth factors (polyethylene glycol (PEG) human granulocyte colony-stimulating factor (hG-CSF), PEG murine granulocyte-macrophage-CSF (mGM-CSF), and PEG human Interleukin (hIL)-11), which have shown survival efficacy in murine models of H-ARS were tested. This triple combination (TC) enhanced survival by 30-days from ∼25% to >60%. The TC was then combined with proven medical countermeasures for GI-ARS and DEARE, namely enrofloxacin, saline and the angiotensin converting enzyme inhibitor, lisinopril. This combination of ARS and DEARE mitigators improved survival from GI-ARS, H-ARS, and DEARE after 7.5 Gy TBI or 13 Gy PBI. Circulating blood cell recovery as well as lung and kidney function were also improved by TC + lisinopril. Taken together these results demonstrate an efficacious polypharmacy to mitigate radiation-induced ARS and DEARE in rats.

Radiation Increases Bioavailability of Lisinopril, a Mitigator of Radiation-Induced Toxicities

There are no FDA-approved drugs to mitigate the delayed effects of radiation exposure that may occur after a radiological attack or nuclear accident. To date, angiotensin-converting enzyme inhibitors are one of the most successful candidates for mitigation of hematopoietic, lung, kidney, and brain injuries in rodent models and may mitigate delayed radiation injuries after radiotherapy. Rat models of partial body irradiation sparing part of one hind leg (leg-out PBI) have been developed to simultaneously expose multiple organs to high doses of ionizing radiation and avoid lethal hematological toxicity to study the late effects of radiation. Exposures between 9 and 14 Gy damage the gut and bone marrow (acute radiation syndrome), followed by delayed injuries to the lung, heart, and kidney. The goal of the current study is to compare the pharmacokinetics (PK) of a lead angiotensin converting enzyme (ACE) inhibitor, lisinopril, in irradiated vs. nonirradiated rats, as a step toward licensure by the FDA.

Methods: Female WAG/RijCmcr rats were irradiated with 12.5–13 Gy leg-out PBI. At day 35 after irradiation, during a latent period for injury, irradiated and nonirradiated siblings received a single gavage (0.3 mg, 0.6 mg) or intravenous injection (0.06 mg) of lisinopril. Plasma, urine, lung, liver and kidney levels of lisinopril were measured at different times. PK modeling (R package) was performed to track distribution of lisinopril in different compartments.

Results: A two-compartment (central plasma and periphery) PK model best fit lisinopril measurements, with two additional components, the gavage and urine. The absorption and renal clearance rates were similar between nonirradiated and irradiated animals (respectively: ratios 0.883, p = 0.527; 0.943, p = 0.605). Inter-compartmental clearance (from plasma to periphery) for the irradiated rats was lower than for the nonirradiated rats (ratio 0.615, p = 0.003), while the bioavailability of the drug was 33% higher (ratio = 1.326, p < 0.001).

Interpretation: Since receptors for lisinopril are present in endothelial cells lining blood vessels, and radiation induces vascular regression, it is possible that less lisinopril remains bound in irradiated rats, increasing circulating levels of the drug. However, this study cannot rule out changes in total amount of lisinopril absorbed or excreted long-term, after irradiation in rats.

A rapid dynamic in vivo near-infrared fluorescence imaging assay to track lung vascular permeability after acute radiation injury

To develop a dynamic in vivo near-infrared (NIR) fluorescence imaging assay to quantify sequential changes in lung vascular permeability-surface area product (PS) in rodents. Dynamic NIR imaging methods for determining lung vascular permeability-surface area product were developed and tested on non-irradiated and 13 Gy irradiated rats with/without treatment with lisinopril, a radiation mitigator. A physiologically-based pharmacokinetic (PBPK) model of indocyanine green (ICG) pulmonary disposition was applied to in vivo imaging data and PS was estimated. In vivo results were validated by five accepted assays: ex vivo perfused lung imaging, endothelial filtration coefficient (Kf) measurement, pulmonary vascular resistance measurement, Evan's blue dye uptake, and histopathology. A PBPK model-derived measure of lung vascular permeability-surface area product increased from 2.60 ± 0.40 [CL: 2.42-2.78] mL/min in the non-irradiated group to 6.94 ± 8.25 [CL: 3.56-10.31] mL/min in 13 Gy group after 42 days. Lisinopril treatment lowered PS in the 13 Gy group to 4.76 ± 6.17 [CL: 2.12-7.40] mL/min. A much higher up to 5× change in PS values was observed in rats exhibiting severe radiation injury. Ex vivo K_f (mL/min/cm H₂O/g dry lung weight), a measure of pulmonary vascular permeability, showed similar trends in lungs of irradiated rats (0.164 ± 0.081 [CL: 0.11-0.22]) as compared to non-irradiated controls (0.022 ± 0.003 [CL: 0.019-0.025]), with reduction to 0.070 ± 0.035 [CL: 0.045-0.096] for irradiated rats treated with lisinopril. Similar trends were observed for ex vivo pulmonary vascular resistance, Evan's blue uptake, and histopathology. Our results suggest that whole body dynamic NIR fluorescence imaging can replace current assays, which are all terminal. The imaging accurately tracks changes in PS and changes in lung interstitial transport in vivo in response to radiation injury.

Commonalities Between COVID-19 and Radiation Injury

As the multi-systemic components of COVID-19 emerge, parallel etiologies can be drawn between SARS-CoV-2 infection and radiation injuries. While some SARS-CoV-2-infected individuals present as asymptomatic, others exhibit mild symptoms that may include fever, cough, chills, and unusual symptoms like loss of taste and smell and reddening in the extremities (e.g., "COVID toes," suggestive of microvessel damage). Still others alarm healthcare providers with extreme and rapid onset of high-risk indicators of mortality that include acute respiratory distress syndrome (ARDS), multi-organ hypercoagulation, hypoxia and cardiovascular damage. Researchers are quickly refocusing their science to address this enigmatic virus that seems to unveil itself in new ways without discrimination. As investigators begin to identify early markers of disease, identification of common threads with other pathologies may provide some clues. Interestingly, years of research in the field of radiation biology documents the complex multiorgan nature of another disease state that occurs after exposure to high doses of radiation: the acute radiation syndrome (ARS). Inflammation is a key common player in COVID-19 and ARS, and drives the multi-system damage that dramatically alters biological homeostasis. Both conditions initiate a cytokine storm, with similar pro-inflammatory molecules increased and other anti-inflammatory molecules decreased. These changes manifest in a variety of ways, with a demonstrably higher health impact in patients having underlying medical conditions. The potentially dramatic human impact of ARS has guided the science that has identified many biomarkers of radiation exposure, established medical management strategies for ARS, and led to the development of medical countermeasures for use in the event of a radiation public health emergency. These efforts can now be leveraged to help elucidate mechanisms of action of COVID-19 injuries. Furthermore, this intersection between COVID-19 and ARS may point to approaches that could accelerate the discovery of treatments for both.

Fate of Hematopoiesis During Aging. What Do We Really Know, and What are its Implications?

There is an ongoing shift in demographics such that older persons will outnumber young persons in the coming years, and with it age-associated tissue attrition and increased diseases and disorders. There has been increased information on the association of the aging process with dysregulation of hematopoietic stem (HSC) and progenitor (HPC) cells, and hematopoiesis. This review provides an extensive up-to date summary on the literature of aged hematopoiesis and HSCs placed in context of potential artifacts of the collection and processing procedure, that may not be totally representative of the status of HSCs in their in vivo bone marrow microenvironment, and what the implications of this are for understanding aged hematopoiesis. This review covers a number of interactive areas, many of which have not been adequately explored. There are still many unknowns and mechanistic insights to be elucidated to better understand effects of aging on the hematopoietic system, efforts that will take multidisciplinary approaches, and that could lead to means to ameliorate at least some of the dysregulation of HSCs and HPCs associated with the aging process. Graphical Abstract.

Proteomic Evaluation of the Natural History of the Acute Radiation Syndrome of the Gastrointestinal Tract in a Non-human Primate Model of Partial-body Irradiation with Minimal Bone Marrow Sparing Includes Dysregulation of the Retinoid Pathway

Exposure to ionizing radiation results in injuries of the hematopoietic, gastrointestinal, and respiratory systems, which are the leading causes responsible for morbidity and mortality. Gastrointestinal injury occurs as an acute radiation syndrome. To help inform on the natural history of the radiation-induced injury of the partial body irradiation model, we quantitatively profiled the proteome of jejunum from non-human primates following 12 Gy partial body irradiation with 2.5% bone marrow sparing over a time period of 3 wk. Jejunum was analyzed by liquid chromatography-tandem mass spectrometry, and pathway and gene ontology analysis were performed. A total of 3,245 unique proteins were quantified out of more than 3,700 proteins identified in this study. Also a total of 289 proteins of the quantified proteins showed significant and consistent responses across at least three time points post-irradiation, of which 263 proteins showed strong upregulations while 26 proteins showed downregulations. Bioinformatic analysis suggests significant pathway and upstream regulator perturbations post-high dose irradiation and shed light on underlying mechanisms of radiation damage. Canonical pathways altered by radiation included GP6 signaling pathway, acute phase response signaling, LXR/RXR activation, and intrinsic prothrombin activation pathway. Additionally, we observed dysregulation of proteins of the retinoid pathway and retinoic acid, an active metabolite of vitamin A, as quantified by liquid chromatography-tandem mass spectrometry. Correlation of changes in protein abundance with a well-characterized histological endpoint, corrected crypt number, was used to evaluate biomarker potential. These data further define the natural history of the gastrointestinal acute radiation syndrome in a non-human primate model of partial body irradiation with minimal bone marrow sparing.

Immune Reconstitution and Thymic Involution in the Acute and Delayed Hematopoietic Radiation Syndromes

Lymphoid lineage recovery and involution after exposure to potentially lethal doses of ionizing radiation have not been well defined, especially the long-term effects in aged survivors and with regard to male/female differences. To examine these questions, male and female C57BL/6 mice were exposed to lethal radiation at 12 wk of age in a model of the Hematopoietic-Acute Radiation Syndrome, and bone marrow, thymus, spleen, and peripheral blood examined up to 24 mo of age for the lymphopoietic delayed effects of acute radiation exposure. Aged mice showed myeloid skewing and incomplete lymphocyte recovery in all lymphoid tissues. Spleen and peripheral blood both exhibited a monophasic recovery pattern, while thymus demonstrated a biphasic pattern. Naïve T cells in blood and spleen and all subsets of thymocytes were decreased in aged irradiated mice compared to age-matched non-irradiated controls. Of interest, irradiated males experienced significantly improved reconstitution of thymocyte subsets and peripheral blood elements compared to females. Bone marrow from aged irradiated survivors was significantly deficient in the primitive lymphoid-primed multipotent progenitors and common lymphoid progenitors, which were only 8-10% of levels in aged-matched non-irradiated controls. Taken together, these analyses define significant age- and sex-related deficiencies at all levels of lymphopoiesis throughout the lifespan of survivors of the Hematopoietic-Acute Radiation Syndrome and may provide a murine model suitable for assessing the efficacy of potential medical countermeasures and therapeutic strategies to alleviate the severe immune suppression that occurs after radiation exposure.

Acute Radiation-induced Lung Injury in the Non-human Primate: A Review and Comparison of Mortality and Co-morbidities Using Models of Partial-body Irradiation with Marginal Bone Marrow Sparing and Whole Thorax Lung Irradiation

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 of radiation-induced lung injury. Herein, a literature review of published studies showing the evolution of lethal lung injury characteristic of the delayed effects of acute radiation exposure between the two significantly different exposure protocols, whole thorax lung irradiation and partial-body irradiation with bone marrow sparing in the nonhuman primate, is provided. The selection of published data was made from the open literature. The primary studies conducted at two research sites benefitted from the similarity of major variables; namely, both sites used rhesus macaques of approximate age and body weight and radiation exposure by LINAC-derived 6 MV photons at dose rates of 0.80 Gy min and 1.00 Gy min delivered to the midline tissue via bilateral, anterior/posterior, posterior/anterior geometry. An advantage relative to sex difference resulted from the use of male and female macaques by the Maryland and the Washington sites, respectively. Subject-based medical management was used for all macaques. The primary studies (6) provided adequate data to establish dose response relationships within 180 d for the radiation-induced lung injury consequent to whole thorax lung irradiation (male vs. female) and partial-body irradiation with bone marrow sparing exposure protocols (male). The dose response relationships established by probit analyses vs. linear dose relationships were characterized by two main parameters or dependent variables, a slope and LD50/180. Respective LD50/180 values for the primary studies that used whole thorax lung irradiation for respective male and female nonhuman primates were 10.24 Gy [9.87, 10.52] (n = 76, male) and 10.28 Gy [9.68, 10.92] (n = 40, female) at two different research sites. The respective slopes were steep at 1.73 [0.841, 2.604] and 1.15 [0.65, 1.65] probits per linear dose. The LD50/180 value and slope derived from the dose response relationships for the partial-body irradiation with bone marrow sparing exposure was 9.94 Gy [9.35, 10.29] (n = 87) and 1.21 [0.70, 1.73] probits per linear dose. A secondary study (1) provided data on limited control cohort of nonhuman primates exposed to whole thorax lung irradiation. The data supported the incidence of clinical, radiographic, and histological indices of the dose-dependent lung injury in the nonhuman primates. Tertiary studies (6) provided data derived from collaboration with the noted primary and secondary studies on control cohorts of nonhuman primates exposed to whole thorax lung irradiation and partial-body irradiation with bone marrow sparing exposure. These studies provided a summary of histological evidence of fibrosis, inflammation and reactive/proliferative changes in pneumonocytes characteristic of lung injury and data on biomarkers for radiation-induced lung injury based on matrix-assisted laser desorption ionization-mass spectrometry imaging and gene expression approaches. The available database in young rhesus macaques exposed to whole thorax lung irradiation or partial-body irradiation with bone marrow sparing using 6 MV LINAC-derived radiation with medical management showed that the dose response relationships were equivalent relative to the primary endpoint all-cause mortality. Additionally, the latency, incidence, severity, and progression of the clinical, radiographic, and histological indices of lung injury were comparable. However, the differences between the exposure protocols are remarkable relative to the demonstrated time course between the multiple organ injury of the acute radiation syndrome and that of the delayed effects of acute radiation exposure, respectively.

Wound Trauma Exacerbates Acute, but not Delayed, Effects of Radiation in Rats: Mitigation by Lisinopril

The goal of this study is to understand and mitigate the effects of wounds on acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE), for preparedness against a radiological attack or accident. Combined injuries from concomitant trauma and radiation are likely in these scenarios. Either exacerbation or mitigation of radiation damage by wound trauma has been previously reported in preclinical studies. Female WAG/RijCmcr rats received 13 Gy X-rays, with partial-body shielding of one leg. Within 2 h, irradiated rats and non-irradiated controls were given full-thickness skin wounds with or without lisinopril, started orally 7 days after irradiation. Morbidity, skin wound area, breathing interval and blood urea nitrogen were measured up to 160 days post-irradiation to independently evaluate wound trauma and DEARE. Wounding exacerbated morbidity in irradiated rats between 5 and 14 days post-irradiation (during the ARS phase), and irradiation delayed wound healing. Wounding did not alter delayed morbidities from radiation pneumonitis or nephropathy after 30 days post-irradiation. Lisinopril did not mitigate wound healing, but markedly decreased morbidity during DEARE from 31 through 160 days. The results derived from this unique model of combined injuries suggest different molecular mechanisms of injury and healing of ARS and DEARE after radiation exposure.

The efficacy and safety of amifostine for the acute radiation syndrome

Introduction: A radiation countermeasure that can be used prior to radiation exposure to protect the population from the harmful effects of radiation exposure remains a major unmet medical need and is recognized as an important area for research. Despite substantial advances in the research and development for finding nontoxic, safe, and effective prophylactic countermeasures for the acute radiation syndrome (ARS), no such agent has been approved by the United States Food and Drug Administration (FDA). Area covered: Despite the progress made to improve the effectiveness of amifostine as a radioprotector for ARS, none of the strategies have resolved the issue of its toxicity/side effects. Thus, the FDA has approved amifostine for limited clinical indications, but not for non-clinical uses. This article reviews recent strategies and progress that have been made to move forward this potentially useful countermeasure for ARS. Expert opinion: Although the recent investigations have been promising for fielding safe and effective radiation countermeasures, additional work is needed to improve and advance drug design and delivery strategies to get FDA approval for broadened, non-clinical use of amifostine during a radiological/nuclear scenario.

Saving normal tissues - a goal for the ages

Almost since the earliest utilization of ionizing radiation, many within the radiation community have worked toward either preventing (i.e. protecting) normal tissues from unwanted radiation injury or rescuing them from the downstream consequences of exposure. However, despite over a century of such investigations, only incremental gains have been made toward this goal and, with certainty, no outright panacea having been found. In celebration of the 60th anniversary of the International Journal of Radiation Biology and to chronicle the efforts that have been made to date, we undertook a non-rigorous survey of the articles published by normal tissue researchers in this area, using those that have appeared in the aforementioned journal as a road map. Three 'snapshots' of publications on normal tissue countermeasures were taken: the earliest (1959-1963) and most recent (2013-2018) 5-year of issues, as well as a 5-year intermediate span (1987-1991). Limiting the survey solely to articles appearing within International Journal of Radiation Biology likely reduced the number of translational studies interrogated given the basic science tenor of this particular publication. In addition, by taking 'snapshots' rather than considering the entire breadth of the journal's history in this field, important papers that were published during the interim periods were omitted, for which we apologize. Nonetheless, since the journal's inception, we observed that, during the chosen periods, the majority of studies undertaken in the field of normal tissue countermeasures, whether investigating radiation protectants, mitigators or treatments, have focused on agents that interfere with the physical, chemical and/or biological effects known to occur during the acute period following whole body/high single dose exposures. This relatively narrow approach to the reduction of normal tissue effects, especially those that can take months, if not years, to develop, seems to contradict our growing understanding of the progressive complexities of the microenvironmental disruption that follows the initial radiation injury. Given the analytical tools now at our disposal and the enormous benefits that may be reaped in terms of improving patient outcomes, as well as the potential for offering countermeasures to those affected by accidental or mass casualty exposures, it appears time to broaden our approaches to developing normal tissue countermeasures. We have no doubt that the contributors and readership of the International Journal of Radiation Biology will continue to contribute to this effort for the foreseeable future.

Optical Metabolic Imaging for Assessment of Radiation-Induced Injury to Rat Kidney and Mitigation by Lisinopril

The kidney is one of the most radiosensitive organs; it is the primary dose-limiting organ in radiotherapies for upper abdominal cancers. The role of mitochondrial redox state in the development and treatment of renal radiation injury, however, remains ill-defined. This study utilizes 3D optical cryo-imaging to quantify renal mitochondrial bioenergetics dysfunction after 13 Gy leg-out partial body irradiation (PBI). Furthermore, the mitigating effects of lisinopril (lisino), an anti-hypertensive angiotensin converting enzyme inhibitor, is assessed in renal radiation-induced injuries. Around day 150 post-irradiation, kidneys are harvested for cryo-imaging. The 3D images of the metabolic indices (NADH, nicotinamide adenine dinucleotide, and FAD, flavin adenine dinucleotide) are acquired, and the mitochondrial redox states of the irradiated and irradiated + lisino kidneys are quantified by calculating the volumetric mean redox ratio (NADH/FAD). PBI oxidized renal mitochondrial redox state by 78%. The kidneys from the irradiated + lisino rats showed mitigation of mitochondrial redox state by 93% compared to the PBI group. The study provides evidence for an altered bioenergetics and energy metabolism in the rat model of irradiation-induced kidney damage. In addition, the results suggest that lisinopril mitigates irradiation damage by attenuating the oxidation of mitochondria leading to increase redox ratio.

Effects of Diet on Late Radiation Injuries in Rats

It has been speculated that the addition of antioxidants to diet could act as either radioprotectors or as mitigators of radiation injury. In preparation for studies of the mitigation efficacy of antioxidants, rats were placed on a modified version of AIN-76A, the diet typically used in such studies. This AIN-76A diet is refined and has no synthetic antioxidants or isoflavones. Compared to the natural-ingredient Teklad 8904 diet used in previous studies, use of the AIN-76A diet from 1-18 wk after irradiation significantly reduced injury in a radiation nephropathy model. A confirmation study included an additional arm in which the AIN-76A diet was started 2 wk prior to irradiation; again, the switch to AIN-76A postirradiation mitigated radiation nephropathy (p < 0.001), but switching to the AIN-76A diet preirradiation had no effect (p > 0.2). The two diets do not differ in salt content, but the AIN-76A diet is somewhat lower in protein (18% vs. 24%). The protein source (primarily soy in Teklad 8904 vs. casein in AIN-76A) might explain the effects. However, replacing the casein in AIN-76A with soy did not change the mitigation efficacy of the diet (p > 0.2 for comparison of the different AIN-76A diets). A similar study in a rat radiation pneumonitis model also suggested mitigation by postirradiation use of AIN-76A, although the effect was not statistically significant (p = 0.07). In conclusion, base diet alone can have biologically significant effects on organ radiosensitivity, but the mechanistic basis for the effect and its dependence of timing relative to irradiation are unclear.

Cardiac Remodeling and Reversible Pulmonary Hypertension During Pneumonitis in Rats after 13-Gy Partial-Body Irradiation with Minimal Bone Marrow Sparing: Effect of Lisinopril

Total-body irradiation causes acute and delayed toxicity to hematopoietic, pulmonary, cardiac, gastrointestinal, renal, and other organ systems. Angiotensin-converting enzyme inhibitors mitigate many of the delayed injuries to these systems. The purpose of this study was to define echocardiographic features in rats at two times after irradiation, the first before lethal radiation pneumonitis (50 d) and the second after recovery from pneumonitis but before lethal radiation nephropathy (100 d), and to determine the actions of the angiotensin-converting enzyme inhibitor lisinopril. Four groups of female WAG/RijCmcr rats at 11-12 wk of age were studied: nonirradiated, nonirradiated plus lisinopril, 13-Gy partial-body irradiation sparing one hind leg (leg-out partial-body irradiation), and 13-Gy leg-out partial-body irradiation plus lisinopril. Lisinopril was started 7 d after radiation. Echocardiograms were obtained at 50 and 100 d, and cardiac histology was assessed after 100 d. Irradiation without lisinopril demonstrated echocardiographic transient pulmonary hypertension by 50 d which was largely resolved by 100 d in survivors. Irradiated rats given lisinopril showed no increase in pulmonary artery pressures at 50 d but exhibited left ventricular remodeling. By 100 d these rats showed some signs of pulmonary hypertension. Lisinopril alone had no impact on echocardiographic end points at either time point in nonirradiated rats. Mild increases in mast cells and fibrosis in the heart were observed after 100 d following 13-Gy leg-out partial-body irradiation. These data demonstrate irradiation-induced pulmonary hypertension which was reversed in survivors of pneumonitis. Lisinopril modified cardiovascular remodeling to enhance survival in this model from 41% to 86% (p = 0.0013).

Delayed Effects of Acute Radiation Exposure (Deare) in Juvenile and Old Rats: Mitigation by Lisinopril

Our goal is to develop lisinopril as a mitigator of delayed effects of acute radiation exposure in the National Institute of Allergy and Infectious Diseases program for radiation countermeasures. Published studies demonstrated mitigation of delayed effects of acute radiation exposure by lisinopril in adult rats. However, juvenile or old rats beyond their reproductive lifespans have never been tested. Since no preclinical models of delayed effects of acute radiation exposure were available in these special populations, appropriate rat models were developed to test lisinopril after irradiation. Juvenile (42-d-old, prepubertal) female and male WAG/RijCmcr (Wistar) rats were given 13-Gy partial-body irradiation with only part of one hind limb shielded. Lethality from lung injury between 39-58 d and radiation nephropathy between 106-114 d were recorded. All irradiated-only juvenile rats were morbid from delayed effects of acute radiation exposure by 114 d, while lisinopril (24 mg m d) started 7 d after irradiation and continued improved survival to 88% (p = 0.0015, n ≥ 8/group). Old rats (>483-d-old, reproductively senescent) were irradiated with 13-Gy partial-body irradiation keeping part of one leg shielded and additionally shielding the head in some animals. Irradiated old females developed lethal nephropathy, and all became morbid by 170 d after irradiation, though no rats displayed lethal radiation pneumonitis. Similar results were observed for irradiated geriatric males, though 33% of rats remained alive at 180 d after irradiation. Lisinopril mitigated radiation nephropathy in old rats of both sexes. Finally, comparison of delayed effects of acute radiation exposure between irradiated juvenile, adult, and old rats showed younger rats were more sensitive to delayed effects of acute radiation exposure with earlier manifestation of injuries to some organs.

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.