Late Effects of Total-Body Gamma Irradiation on Cardiac Structure and Function in Male Rhesus Macaques

A Novel TGFβ Receptor Inhibitor, IPW-5371, Prevents Diet-induced Hepatic Steatosis and Insulin Resistance in Irradiated Mice

As the number of cancer survivors increases and the risk of accidental radiation exposure rises, there is a pressing need to characterize the delayed effects of radiation exposure and develop medical countermeasures. Radiation has been shown to damage adipose progenitor cells and increase liver fibrosis, such that it predisposes patients to developing metabolic-associated fatty liver disease (MAFLD) and insulin resistance. The risk of developing these conditions is compounded by the global rise of diets rich in carbohydrates and fats. Radiation persistently increases the signaling cascade of transforming growth factor β (TGFβ), leading to heightened fibrosis as characteristic of the delayed effects of radiation exposure. We investigate here a potential radiation medical countermeasure, IPW-5371, a small molecule inhibitor of TGFβRI kinase (ALK5). We found that mice exposed to sub-lethal whole-body irradiation and chronic Western diet consumption but treated with IPW-5371 had a similar body weight, food consumption, and fat mass compared to control mice exposed to radiation. The IPW-5371 treated mice maintained lower fibrosis and fat accumulation in the liver, were more responsive to insulin and had lower circulating triglycerides and better muscle endurance. Future studies are needed to verify the improvement by IPW-5371 on the structure and function of other metabolically active tissues such as adipose and skeletal muscle, but these data demonstrate that IPW-5371 protects liver and whole-body health in rodents exposed to radiation and a Western diet, and there may be promise in using IPW-5371 to prevent the development of MAFLD.

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.

Resilience, aging, and response to radiation exposure (RARRE) in nonhuman primates: a resource review

The Wake Forest nonhuman primate (NHP) Radiation Late Effects Cohort (RLEC) is a unique and irreplaceable population of aging NHP radiation survivors which serves the nation's need to understand the late effects of radiation exposure. Over the past 16 years, Wake Forest has evaluated > 250 previously irradiated rhesus macaques (Macaca mulatta) that were exposed to single total body irradiation (IR) doses of 1.14-8.5 Gy or to partial body exposures of up to 10 Gy (5% bone marrow sparing) or 10.75 Gy (whole thorax). Though primarily used to examine IR effects on disease-specific processes or to develop radiation countermeasures, this resource provides insights on resilience across physiologic systems and its relationship with biological aging. Exposure to IR has well documented deleterious effects on health, but the late effects of IR are highly variable. Some animals exhibit multimorbidity and accumulated health deficits, whereas others remain relatively resilient years after exposure to total body IR. This provides an opportunity to evaluate biological aging at the nexus of resilient/vulnerable responses to a stressor. Consideration of inter-individual differences in response to this stressor can inform individualized strategies to manage late effects of radiation exposure, and provide insight into mechanisms underlying systemic resilience and aging. The utility of this cohort for age-related research questions was summarized at the 2022 Trans-NIH Geroscience Interest Group's Workshop on Animal Models for Geroscience. We present a brief review of radiation injury and its relationship to aging and resilience in NHPs with a focus on the RLEC.

Immune Dysfunction from Radiation Exposure

Exposure to ionizing radiation causes acute damage and loss of bone marrow and peripheral immune cells that can result in high mortality due to reduced resistance to infections and hemorrhage. Besides these acute effects, tissue damage from radiation can trigger inflammatory responses, leading to progressive and chronic tissue damage by radiation-induced loss of immune cell types that are required for resolving tissue injuries. Understanding the mechanisms involved in radiation-induced immune system injury and repair will provide new insights for developing medical countermeasures that help restore immune homeostasis. For these reasons, The Radiation and Nuclear Countermeasures Program (RNCP) and the Basic Immunology Branch (BIB) under the Division of Allergy, Immunology, and Transplantation (DAIT) within the National Institute of Allergy and Infectious Diseases (NIAID) convened a two-day workshop, along with partners from the Biomedical Advanced Research and Development Authority (BARDA), and the Radiation Injury Treatment Network (RITN). This workshop, titled "Immune Dysfunction from Radiation Exposure," was held virtually on September 9-10, 2020; this Commentary provides a high-level overview of what was discussed at the meeting.

Immune Dysfunction from Radiation Exposure

The hematopoietic system is highly sensitive to ionizing radiation. Damage to the immune system may result in opportunistic infections and hemorrhage, which could lead to mortality. Inflammation triggered by tissue damage can also lead to additional local or widespread tissue damage. The immune system is responsible for tissue repair and restoration, which is made more challenging when it is in the process of self-recovery. Because of these challenges, the Radiation and Nuclear Countermeasures Program (RNCP) and the Basic Immunology Branch (BIB) under the Division of Allergy, Immunology, and Transplantation (DAIT) within the National Institute of Allergy and Infectious Diseases (NIAID), along with partners from the Biomedical Advanced Research and Development Authority (BARDA), and the Radiation Injury Treatment Network (RITN) sponsored a two-day meeting titled Immune Dysfunction from Radiation Exposure held on September 9-10, 2020. The intent was to discuss the manifestations and mechanisms of radiation-induced immune dysfunction in people and animals, identify knowledge gaps, and discuss possible treatments to restore immune function and enhance tissue repair after irradiation.

The NIAID/RNCP Biodosimetry Program: An Overview

Established in 2004, the Radiation and Nuclear Countermeasures Program (RNCP), within the National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health has the central mission to advance medical countermeasure mitigators/therapeutics, and biomarkers and technologies to assess, triage, and inform medical management of patients experiencing acute radiation syndrome and/or the delayed effects of acute radiation exposure. The RNCP biodosimetry mission space encompasses: (1) basic research to elucidate novel approaches for rapid and accurate assessment of radiation exposure, (2) studies to support advanced development for US Food and Drug Administration (FDA) clearance of promising triage or treatment devices/approaches, (3) characterization of biomarkers and/or assays to determine degree of tissue or organ dose that can predict outcome of radiation injuries (i.e., organ failure, morbidity, and/or mortality), and (4) outreach efforts to facilitate interactions with researchers developing cutting edge biodosimetry approaches. Thus far, no biodosimetry device has been FDA cleared for use during a radiological/nuclear incident. At NIAID, advancement of radiation biomarkers and biodosimetry approaches is facilitated by a variety of funding mechanisms (grants, contracts, cooperative and interagency agreements, and Small Business Innovation Research awards), with the objective of advancing devices and assays toward clearance, as outlined in the FDA's Radiation Biodosimetry Medical Countermeasure Devices Guidance. The ultimate goal of the RNCP biodosimetry program is to develop and establish accurate and reliable biodosimetry tools that will improve radiation preparedness and ultimately save lives during a radiological or nuclear incident.

Assessment of Blood Pressure in Irradiated Rhesus Macaques (Macaca mulatta)

There is increasing evidence that circulatory disease incidence and mortality is associated with radiation exposure. Wake Forest School of Medicine is home to a unique cohort of total-body irradiated macaques, some with evidence of vascular end-organ disease in the brain, kidney and heart. Because there is a link between high blood pressure and vascular disease in all these sites, we undertook a retrospective study to evaluate blood pressure and radiation in this cohort of animals. In this work, we utilized a cohort of nonhuman primates (rhesus macaques, Macaca mulatta) long-term survivors of high-dose total-body irradiation (1.1-8.5 Gy, N = 129) and controls (N = 37) to evaluate the effects of radiation on blood pressure and obesity. Subjects were between 3 and 22 years of age (median 9 years). Blood pressure (BP) was measured 1-14 years postirradiation (median 4 years). Subjects were sedated with a combination of ketamine HCl (15 mg/kg body weight, IM) and midazolam (0.1 mg/kg body weight, IM) and systolic, diastolic, and mean arterial pressures were measured using a high definition oscillometer. Obesity was defined by dual energy X-ray absorptiometry as a body fat percentage >35%. Statistical analysis of the collected data indicated significant increases in blood pressure with increasing age and obesity. However, radiation did not significantly alter blood pressure in irradiated animals relative to controls, radiation dose, or age of irradiation.

Delayed effects of radiation in adipose tissue reflect progenitor damage and not cellular senescence

The pathogenesis of many age-related diseases is linked to cellular senescence, a state of inflammation-inducing, irreversible cell cycle arrest. The consequences and mechanisms of age-associated cellular senescence are often studied using in vivo models of radiation exposure. However, it is unknown whether radiation induces persistent senescence, like that observed in ageing. We performed analogous studies in mice and monkeys, where young mice and rhesus macaques received sub-lethal doses of ionizing radiation and were observed for ~ 15% of their expected lifespan. Assessments of 8-hydroxy-2' -deoxyguanosine (8-OHdG), senescence-associated beta-galactosidase (SAβ-gal), and p16Ink4a and p21 were performed on mitotic and post-mitotic tissues - liver and adipose tissue - 6 months and 3 years post-exposure for the mice and monkeys, respectively. No elevations in 8-OHdG, SA-βgal staining, or p16 Ink4a or p21 gene or protein expression were found in mouse and monkey liver or adipose tissue compared to control animals. Despite no evidence of senescence, progenitor cell dysfunction persisted after radiation exposure, as indicated by lower in situ CD34+ adipose cells (p = 0.03), and deficient adipose stromal vascular cell proliferation (p < 0.05) and differentiation (p = 0.04) ex vivo. Our investigation cautions that employing radiation to study senescence-related processes should be limited to the acute post-exposure period and that stem cell damage likely underpins the dysfunction associated with delayed effects of radiation.

Quantitative Assessment and Comparative Analysis of Longitudinal Lung CT Scans of Chest-Irradiated Nonhuman Primates

Computed tomography (CT) imaging has been used to diagnose radiation-induced lung injury for decades. However, histogram-based quantitative tools have rarely been applied to assess lung abnormality due to radiation-induced lung injury (RILI). Here, we used first-order summary statistics to derive and assess threshold measures extracted from whole lung histograms of CT radiodensity in rhesus macaques. For the present study, CT scans of animals exposed to 10 Gy of whole thorax irradiation were utilized from a previous study spanning 2-9 months postirradiation. These animals were grouped into survivors and non-survivors based on their clinical and experimental endpoints. We quantified the change in lung attenuation after irradiation relative to baseline using three density parameters; average lung density (ALD), percent change in hyper-dense lung volume (PCHV), hyperdense volume as a percent of total volume (PCHV/TV) at 2-month intervals and compared each parameter between the two irradiated groups (non-survivors and survivors). We also correlated our results with histological findings. All the three indices (ALD, PCHV, PCHV/TV) obtained from density histograms showed a significant increase in lung injury in non-survivors relative to survivors, with PCHV relatively more sensitive to detect early RILI changes. We observed a significant positive correlation between histologic pneumonitis scores and each of the three CT measurements, indicating that CT density is useful as a surrogate for histologic disease severity in RILI. CT-based three density parameters, ALD, PCHV, PCHV/TV, may serve as surrogates for likely histopathology patterns in future studies of RILI disease progression.

Preclinical models of radiation-induced cardiac toxicity: Potential mechanisms and biomarkers

Radiation therapy (RT) is an important modality in cancer treatment with >50% of cancer patients undergoing RT for curative or palliative intent. In patients with breast, lung, and esophageal cancer, as well as mediastinal malignancies, incidental RT dose to heart or vascular structures has been linked to the development of Radiation-Induced Heart Disease (RIHD) which manifests as ischemic heart disease, cardiomyopathy, cardiac dysfunction, and heart failure. Despite the remarkable progress in the delivery of radiotherapy treatment, off-target cardiac toxicities are unavoidable. One of the best-studied pathological consequences of incidental exposure of the heart to RT is collagen deposition and fibrosis, leading to the development of radiation-induced myocardial fibrosis (RIMF). However, the pathogenesis of RIMF is still largely unknown. Moreover, there are no available clinical approaches to reverse RIMF once it occurs and it continues to impair the quality of life of long-term cancer survivors. Hence, there is an increasing need for more clinically relevant preclinical models to elucidate the molecular and cellular mechanisms involved in the development of RIMF. This review offers an insight into the existing preclinical models to study RIHD and the suggested mechanisms of RIMF, as well as available multi-modality treatments and outcomes. Moreover, we summarize the valuable detection methods of RIHD/RIMF, and the clinical use of sensitive radiographic and circulating biomarkers.

Total-Body Irradiation Is Associated With Increased Incidence of Mesenchymal Neoplasia in a Radiation Late Effects Cohort of Rhesus Macaques (Macaca mulatta)

PURPOSE

Cancer is a severe delayed effect of acute radiation exposure. Total-body irradiation has been associated with an increased risk of solid cancer and leukemia in Japanese atomic bomb survivors, and secondary malignancies, such as sarcoma, are a serious consequence of cancer radiation therapy. The radiation late effects cohort (RLEC) of rhesus macaques (Macaca mulatta) is a unique resource of more than 200 animals for studying the long-term consequences of total-body irradiation in an animal model that closely resembles humans at the genetic and physiologic levels.

METHODS AND MATERIALS

Using clinical records, clinical imaging, histopathology, and immunohistochemistry, this retrospective study characterized the incidence of neoplasia in the RLEC.

RESULTS

Since 2007, 61 neoplasms in 44 of 239 irradiated animals were documented (18.4% of the irradiated population). Only 1 neoplasm was diagnosed among the 51 nonirradiated controls of the RLEC (2.0%). The most common malignancies in the RLEC were sarcomas (38.3% of diagnoses), which are rare neoplasms in nonirradiated macaques. The most common sarcomas included malignant nerve sheath tumors and malignant glomus tumors. Carcinomas were less common (19.7% of diagnoses), and consisted primarily of renal cell and hepatocellular carcinomas. Neoplasia occurred in most major body systems, with the skin and subcutis being the most common site (40%). RNA analysis showed similarities in transcriptional profiles between RLEC and human malignant nerve sheath tumors.

CONCLUSIONS

This study indicates that total-body irradiation is associated with an increased incidence of neoplasia years following irradiation, at more than double the incidence described in aging, nonirradiated animals, and promotes tumor histotypes that are rarely observed in nonirradiated, aging rhesus macaques.

Age effects on radiation response: summary of a recent symposium and future perspectives

One of the principal uncertainties when estimating population risk of late effects from epidemiological data is that few radiation-exposed cohorts have been followed up to extinction. Therefore, the relative risk model has often been used to estimate radiation-associated risk and to extrapolate risk to the end of life. Epidemiological studies provide evidence that children are generally at higher risk of cancer induction than adults for a given radiation dose. However, the strength of evidence varies by cancer site and questions remain about site-specific age at exposure patterns. For solid cancers, there is a large body of evidence that excess relative risk (ERR) diminishes with increasing age at exposure. This pattern of risk is observed in the Life Span Study (LSS) as well as in other radiation-exposed populations for overall solid cancer incidence and mortality and for most site-specific solid cancers. However, there are some disparities by endpoint in the degree of variation of ERR with exposure age, with some sites (e.g., colon, lung) in the LSS incidence data showing no variation, or even increasing ERR with increasing age at exposure. The pattern of variation of excess absolute risk (EAR) with age at exposure is often similar, with EAR for solid cancers or solid cancer mortality decreasing with increasing age at exposure in the LSS. We shall review the human data from the Japanese LSS cohort, and a variety of other epidemiological data sets, including a review of types of medical diagnostic exposures, also some radiobiological animal data, all bearing on the issue of variations of radiation late-effects risk with age at exposure and with attained age. The paper includes a summary of several oral presentations given in a Symposium on "Age effects on radiation response" as part of the 67th Annual Meeting of the Radiation Research Society, held virtually on 3-6 October 2021.

Hypertension promotes microbial translocation and dysbiotic shifts in the fecal microbiome of nonhuman primates

Accumulating evidence indicates a link between gut barrier dysfunction and hypertension. However, it is unclear whether hypertension causes gut barrier dysfunction or vice versa and whether the gut microbiome plays a role. To understand this relationship, we first cross-sectionally examined 153 nonhuman primates [NHPs; Chlorocebus aethiops sabaeus; mean age, 16 ± 0.4 yr; 129 (84.3%) females] for cardiometabolic risk factors and gut barrier function biomarkers. This analysis identified blood pressure and age as specific factors that independently associated with microbial translocation. We then longitudinally tracked male, age-matched spontaneously hypertensive NHPs (Macaca mulatta) to normotensives (n = 16), mean age of 5.8 ± 0.5 yr, to confirm hypertension-related gut barrier dysfunction and to explore the role of microbiome by comparing groups at baseline, 12, and 27 mo. Collectively, hypertensive animals in both studies showed evidence of gut barrier dysfunction (i.e., microbial translocation), as indicated by higher plasma levels of lipopolysaccharide-binding protein (LBP)-1, when compared with normotensive animals. Furthermore, plasma LBP-1 levels were correlated with diastolic blood pressure, independent of age and other health markers, suggesting specificity of the effect of hypertension on microbial translocation. In over 2 yr of longitudinal assessment, hypertensive animals had escalating plasma levels of LBP-1 and greater bacterial gene expression in mesenteric lymph nodes compared with normotensive animals, confirming microbes translocated across the intestinal barrier. Concomitantly, we identified distinct shifts in the gut microbial signature of hypertensive versus normotensive animals at 12 and 27 mo. These results suggest that hypertension contributes to microbial translocation in the gut and eventually unhealthy shifts in the gut microbiome, possibly contributing to poor health outcomes, providing further impetus for the management of hypertension.NEW & NOTEWORTHY Hypertension specifically had detrimental effects on microbial translocation when age and metabolic syndrome criteria were evaluated as drivers of cardiovascular disease in a relevant nonhuman primate model. Intestinal barrier function exponentially decayed over time with chronic hypertension, and microbial translocation was confirmed by detection of more microbial genes in regional draining lymph nodes. Chronic hypertension resulted in fecal microbial dysbiosis and elevations of the biomarker NT-proBNP. This study provides insights on the barrier dysfunction, dysbiosis, and hypertension in controlled studies of nonhuman primates. Our study includes a longitudinal component comparing naturally occurring hypertensive to normotensive primates to confirm microbial translocation and dysbiotic microbiome development. Hypertension is an underappreciated driver of subclinical endotoxemia that can drive chronic inflammatory diseases.

SAMiRNA Targeting Amphiregulin Alleviate Total-Body-Irradiation-Induced Renal Fibrosis

Fibrosis is a serious unintended side effect of radiation therapy. In this study, we aimed to investigate whether amphiregulin (AREG) plays a critical role in fibrosis development after total-body irradiation (TBI). We found that the expression of AREG and fibrotic markers, such as α-smooth muscle actin (α-SMA) and collagen type I alpha 1 (COL1α1), was elevated in the kidneys of 6 Gy TBI mice. Expression of AREG and α-SMA was mainly elevated in the proximal and distal tubules of the kidney in response to TBI, which was confirmed by immunofluorescence staining. Knockdown of Areg mRNA using self-assembled-micelle inhibitory RNA (SAMiRNA) significantly reduced the expression of fibrotic markers, including α-SMA and COL1α1, and inflammatory regulators. Finally, intravenous injections of SAMiRNA targeting mouse Areg mRNA (SAMiRNA-mAREG) diminished radiation-induced collagen accumulation in the renal cortex and medulla. Taken together, the results of the present study suggest that blocking of AREG signaling via SAMiRNA-mAREG treatment could be a promising therapeutic approach to alleviate radiation-induced kidney fibrosis.

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.

Multi-omic Analysis of Non-human Primate Heart after Partial-body Radiation with Minimal Bone Marrow Sparing

ABSTRACT

High-dose radiation exposure results in hematopoietic and gastrointestinal acute radiation syndromes followed by delayed effects of acute radiation exposure, which encompasses multiple organs, including heart, kidney, and lung. Here we sought to further characterize the natural history of radiation-induced heart injury via determination of differential protein and metabolite expression in the heart. We quantitatively profiled the proteome and metabolome of left and right ventricle from non-human primates following 12 Gy partial body irradiation with 2.5% bone marrow sparing over a time period of 3 wk. Global proteome profiling identified more than 2,200 unique proteins, with 220 and 286 in the left and right ventricles, respectively, showing significant responses across at least three time points compared to baseline levels. High-throughput targeted metabolomics analyzed a total of 229 metabolites and metabolite combinations, with 18 and 22 in the left and right ventricles, respectively, showing significant responses compared to baseline levels. Bioinformatic analysis performed on metabolomic and proteomic data revealed pathways related to inflammation, energy metabolism, and myocardial remodeling were dysregulated. Additionally, we observed dysregulation of the retinoid homeostasis pathway, including significant post-radiation decreases in retinoic acid, an active metabolite of vitamin A. Significant differences between left and right ventricles in the pathology of radiation-induced injury were identified. This multi-omic study characterizes the natural history and molecular mechanisms of radiation-induced heart injury in NHP exposed to PBI with minimal bone marrow sparing.

Scientific research and product development in the United States to address injuries from a radiation public health emergency

The USA has experienced one large-scale nuclear incident in its history. Lessons learned during the Three-Mile Island nuclear accident provided government planners with insight into property damage resulting from a low-level release of radiation, and an awareness concerning how to prepare for future occurrences. However, if there is an incident resulting from detonation of an improvised nuclear device or state-sponsored device/weapon, resulting casualties and the need for medical treatment could overwhelm the nation's public health system. After the Cold War ended, government investments in radiation preparedness declined; however, the attacks on 9/11 led to re-establishment of research programs to plan for the possibility of a nuclear incident. Funding began in earnest in 2004, to address unmet research needs for radiation biomarkers, devices and products to triage and treat potentially large numbers of injured civilians. There are many biodosimetry approaches and medical countermeasures (MCMs) under study and in advanced development, including those to address radiation-induced injuries to organ systems including bone marrow, the gastrointestinal (GI) tract, lungs, skin, vasculature and kidneys. Biomarkers of interest in determining level of radiation exposure and susceptibility of injury include cytogenetic changes, 'omics' technologies and other approaches. Four drugs have been approved by the US Food and Drug Administration (FDA) for the treatment of acute radiation syndrome (ARS), with other licensures being sought; however, there are still no cleared devices to identify radiation-exposed individuals in need of treatment. Although many breakthroughs have been made in the efforts to expand availability of medical products, there is still work to be done.

Models for Translational Proton Radiobiology-From Bench to Bedside and Back

The number of proton therapy centers worldwide are increasing steadily, with more than two million cancer patients treated so far. Despite this development, pending questions on proton radiobiology still call for basic and translational preclinical research. Open issues are the on-going discussion on an energy-dependent varying proton RBE (relative biological effectiveness), a better characterization of normal tissue side effects and combination treatments with drugs originally developed for photon therapy. At the same time, novel possibilities arise, such as radioimmunotherapy, and new proton therapy schemata, such as FLASH irradiation and proton mini-beams. The study of those aspects demands for radiobiological models at different stages along the translational chain, allowing the investigation of mechanisms from the molecular level to whole organisms. Focusing on the challenges and specifics of proton research, this review summarizes the different available models, ranging from in vitro systems to animal studies of increasing complexity as well as complementing in silico approaches.

Analysis of lncRNA-miRNA-mRNA expression pattern in heart tissue after total body radiation in a mouse model

Background

Radiation therapy is integral to effective thoracic cancer treatments, but its application is limited by sensitivity of critical organs such as the heart. The impacts of acute radiation-induced damage and its chronic effects on normal heart cells are highly relevant in radiotherapy with increasing lifespans of patients. Biomarkers for normal tissue damage after radiation exposure, whether accidental or therapeutic, are being studied as indicators of both acute and delayed effects. Recent research has highlighted the potential importance of RNAs, including messenger RNAs (mRNAs), microRNAs (miRNAs), and long non-coding RNAs (lncRNAs) as biomarkers to assess radiation damage. Understanding changes in mRNA and non-coding RNA expression will elucidate biological pathway changes after radiation.

Methods

To identify significant expression changes in mRNAs, lncRNAs, and miRNAs, we performed whole transcriptome microarray analysis of mouse heart tissue at 48 h after whole-body irradiation with 1, 2, 4, 8, and 12 Gray (Gy). We also validated changes in specific lncRNAs through RT-qPCR. Ingenuity Pathway Analysis (IPA) was used to identify pathways associated with gene expression changes.

Results

We observed sustained increases in lncRNAs and mRNAs, across all doses of radiation. Alas2, Aplnr, and Cxc3r1 were the most significantly downregulated mRNAs across all doses. Among the significantly upregulated mRNAs were cell-cycle arrest biomarkers Gdf15, Cdkn1a, and Ckap2. Additionally, IPA identified significant changes in gene expression relevant to senescence, apoptosis, hemoglobin synthesis, inflammation, and metabolism. LncRNAs Abhd11os, Pvt1, Trp53cor1, and Dino showed increased expression with increasing doses of radiation. We did not observe any miRNAs with sustained up- or downregulation across all doses, but miR-149-3p, miR-6538, miR-8101, miR-7118-5p, miR-211-3p, and miR-3960 were significantly upregulated after 12 Gy.

Conclusions

Radiation-induced RNA expression changes may be predictive of normal tissue toxicities and may indicate targetable pathways for radiation countermeasure development and improved radiotherapy treatment plans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02998-w.

Nonhuman primate models in the study of spaceflight stressors: Past contributions and future directions

Studies in rodents suggest that exposure to distinct spaceflight stressors (e.g., space radiation, isolation/confinement, microgravity) may have a profound impact on an astronaut's ability to perform both simple and complex tasks related to neurocognitive performance, central nervous system (CNS) and vestibular/sensorimotor function. However, limited information is currently available on how combined exposure to the spaceflight stressors will impact CNS-related neurocognitive and neurobiological function in-flight and, as well, terrestrial risk of manifesting neurodegenerative conditions when astronauts return to earth. This information gap has significantly hindered our ability to realistically estimate spaceflight hazard risk to the CNS associated with deep space exploration. Notwithstanding a significant body of work with rodents, there have been very few direct investigations of the impact of these spaceflight stressors in combination and, to our knowledge, no such investigations using nonhuman primate (NHP) animal models. In view of the widely-recognized translational value of NHP data in advancing biomedical discoveries, this research deficiency limits our understanding regarding the impact of individual and combined spaceflight stressors on CNS-related neurobiological function. In this review, we address this knowledge gap by conducting a systematic and comprehensive evaluation of existing research on the impact of exposure to spaceflight stressors on NHP CNS-related function. This review is structured to: a) provide an overarching view of the past contributions of NHPs to spaceflight research as well as the strengths, limitations, and translational value of NHP research in its own right and within the existing context of NASA-relevant rodent research; b) highlight specific conclusions based on the published literature and areas needed for future endeavors; c) describe critical research gaps and priorities in NHP research to facilitate NASA's efforts to bridge the key knowledge gaps that currently exist in translating rodent data to humans; and d) provide a roadmap of recommendations for NASA regarding the availability, validity, strengths, and limitations of various NHP models for future targeted research.

Sex-dependent effects of genetic upregulation of activated protein C on delayed effects of acute radiation exposure in the mouse heart, small intestine, and skin

Accidental exposure to ionizing radiation may lead to delayed effects of acute radiation exposure (DEARE) in many organ systems. Activated protein C (APC) is a known mitigator of the acute radiation syndrome. To examine the role of APC in DEARE, we used a transgenic mouse model with 2- to 3-fold increased plasma levels of APC (high in APC, APCHi). Male and female APCHi mice and wild-type littermates were exposed to 9.5 Gy γ-rays with their hind-legs (bone marrow) shielded from radiation to allow long-term survival. At 3 and 6 months after irradiation, cardiac function was measured with ultrasonography. At 3 months, radiation increased cardiac dimensions in APCHi males, while decreases were seen in wild-type females. At this early time point, APCHi mice of both sexes were more susceptible to radiation-induced changes in systolic function compared to wild-types. At 6 months, a decrease in systolic function was mainly seen in male mice of both genotypes. At 6 months, specimens of heart, small intestine and dorsal skin were collected for tissue analysis. Female APCHi mice showed the most severe radiation-induced deposition of cardiac collagens but were protected against a radiation-induced loss of microvascular density. Both male and female APCHi mice were protected against a radiation induced upregulation of toll-like receptor 4 in the heart, but this did not translate into a clear protection against immune cell infiltration. In the small intestine, the APCHi genotype had no effect on an increase in the number of myeloperoxidase positive cells (seen mostly in females) or an increase in the expression of T-cell marker CD2 (males). Lastly, both male and female APCHi mice were protected against radiation-induced epidermal thickening and increase in 3-nitrotyrosine positive keratinocytes. In conclusion, prolonged high levels of APC in a transgenic mouse model had little effects on indicators of DEARE in the heart, small intestine and skin, with some differential effects in male compared to female mice.

Review of Current Healthcare Waste Management Methods and Their Effect on Global Health

Healthcare is a rapidly growing industry as medical treatments become more sophisticated, more in demand due to increasing incidence of chronic disease and more widely available worldwide. This booming industry is also creating more waste than ever before and, as such, there is a growing need to treat and dispose of this waste. Healthcare waste (HCW) disposal includes a multitude of disposal methods, including incineration, landfilling and chemical treatments. These rudimentary methods and their growing use present their own problems that negatively impact both the environment and, in turn, damage public health, thus contributing to a global healthcare crisis. The aim of this review was to examine the current HCW disposal methods in place and the harmful effects they have on the environment and on public health. The findings accumulated in this review demonstrate a heavy reliance on basic, low tech HCW disposal techniques and uncovered the negative impacts of these methods. There is a notable lack of employment of "greener" HCW disposal methods on a largescale due to cost, access and feasibility. Despite innovations in HCW disposal, there is no scalable, global green solution at present. Further, the review highlights that global health consequences of HCW disposal methods often differ depending on how developed the country is.

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.

Non-Human Primates Receiving High-Dose Total-Body Irradiation are at Risk of Developing Cerebrovascular Injury Years Postirradiation

Nuclear accidents and acts of terrorism have the potential to expose thousands of people to high-dose total-body iradiation (TBI). Those who survive the acute radiation syndrome are at risk of developing chronic, degenerative radiation-induced injuries [delayed effects of acute radiation (DEARE)] that may negatively affect quality of life. A growing body of literature suggests that the brain may be vulnerable to radiation injury at survivable doses, yet the long-term consequences of high-dose TBI on the adult brain are unclear. Herein we report the occurrence of lesions consistent with cerebrovascular injury, detected by susceptibility-weighted magnetic resonance imaging (MRI), in a cohort of non-human primate [(NHP); rhesus macaque, Macaca mulatta] long-term survivors of high-dose TBI (1.1-8.5 Gy). Animals were monitored longitudinally with brain MRI (approximately once every three years). Susceptibility-weighted images (SWI) were reviewed for hypointensities (cerebral microbleeds and/or focal necrosis). SWI hypointensities were noted in 13% of irradiated NHP; lesions were not observed in control animals. A prior history of exposure was correlated with an increased risk of developing a lesion detectable by MRI (P = 0.003). Twelve of 16 animals had at least one brain lesion present at the time of the first MRI evaluation; a subset of animals (n = 7) developed new lesions during the surveillance period (3.7-11.3 years postirradiation). Lesions occurred with a predilection for white matter and the gray-white matter junction. The majority of animals with lesions had one to three SWI hypointensities, but some animals had multifocal disease (n = 2). Histopathologic evaluation of deceased animals within the cohort (n = 3) revealed malformation of the cerebral vasculature and remodeling of the blood vessel walls. There was no association between comorbid diabetes mellitus or hypertension with SWI lesion status. These data suggest that long-term TBI survivors may be at risk of developing cerebrovascular injury years after irradiation.

Protective effect of trimetazidine in radiation-induced cardiac fibrosis in mice

Radiation-induced heart damage is a serious side effect caused by radiotherapy, especially during the treatment of cancer near the chest. Trimetazidine is effective at reducing inflammation in the heart, but how it affects radiation-induced cardiac fibrosis (RICF) is unknown. To investigate the potential effect and molecular mechanism, we designed this project with a C57BL6 male mouse model supposing trimetazidine could inhibit RICF in mice. During the experiment, mice were randomly divided into six groups including a control group (Con), radiation-damaged model group (Mod) and four experimental groups receiving low-dose (10 mg/kg/day) or high-dose (20 mg/kg/day) trimetazidine before or after radiation treatment. Apart from the control group, all mice chests were exposed to 6 MV X-rays at a single dose of 20 Gy to induce RICF, and tissue analysis was done at 8 weeks after irradiation. Fibroblast or interstitial tissues and cardiac fibrosis-like characteristics were determined using haematoxylin and eosin and Masson staining, which can be used to assess myocardial fibrosis. Immunohistochemical analysis and RT-PCR were used to determine gene expression and study the molecular mechanism. As a result, this study suggests that trimetazidine inhibits RICF by reducing gene expression related to myocyte apoptosis and fibrosis formation, i.e. connective tissue growth factor (CTGF), transforming growth factor (TGF)-β1, smad2 and smad3. In conclusion, by regulating the CTGF/TGF-β1/Smad pathway, trimetazidine could be a prospective drug for clinical treatment of RICF.

Advances in Preclinical Research Models of Radiation-Induced Cardiac Toxicity

Radiation therapy (RT) is an important component of cancer therapy, with >50% of cancer patients receiving RT. As the number of cancer survivors increases, the short- and long-term side effects of cancer therapy are of growing concern. Side effects of RT for thoracic tumors, notably cardiac and pulmonary toxicities, can cause morbidity and mortality in long-term cancer survivors. An understanding of the biological pathways and mechanisms involved in normal tissue toxicity from RT will improve future cancer treatments by reducing the risk of long-term side effects. Many of these mechanistic studies are performed in animal models of radiation exposure. In this area of research, the use of small animal image-guided RT with treatment planning systems that allow more accurate dose determination has the potential to revolutionize knowledge of clinically relevant tumor and normal tissue radiobiology. However, there are still a number of challenges to overcome to optimize such radiation delivery, including dose verification and calibration, determination of doses received by adjacent normal tissues that can affect outcomes, and motion management and identifying variation in doses due to animal heterogeneity. In addition, recent studies have begun to determine how animal strain and sex affect normal tissue radiation injuries. This review article discusses the known and potential benefits and caveats of newer technologies and methods used for small animal radiation delivery, as well as how the choice of animal models, including variables such as species, strain, and age, can alter the severity of cardiac radiation toxicities and impact their clinical relevance.

Transcriptional Profiling of Non-Human Primate Lymphoid Organ Responses to Total-Body Irradiation

The global threat of exposure to radiation and its subsequent outcomes require the development of effective strategies to mitigate immune cell injury. In this study we explored transcriptional and immunophenotypic characteristics of lymphoid organs of a non-human primate model after total-body irradiation (TBI). Fifteen middle-aged adult, ovariectomized, female cynomolgus macaques received a single dose of 0, 2 or 5 Gy gamma radiation. Thymus, spleen and lymph node from three controls and 2 Gy (n = 2) and 5 Gy (n = 2) exposed animals were assessed for molecular responses to TBI through microarray-based transcriptional profiling at day 5 postirradiation, and cellular changes through immunohistochemical (IHC) characterization of markers for B and T lymphocytes and macrophages across all 15 animals at time points up to 6 months postirradiation. Irradiated macaques developed acute hematopoietic syndrome. Analysis of array data at day 5 postirradiation identified transcripts with ≥2-fold difference from control and a false discovery rate (FDR) of Padj < 0.05 in lymph node (n = 666), spleen (n = 493) and thymus (n=3,014). Increasing stringency of the FDR to P < 0.001 reduced the number of genes to 71 for spleen and 379 for thymus. IHC and gene expression data demonstrated that irradiated animals had reduced numbers of T and B lymphocytes along with relative elevations of macrophages. Transcriptional analysis revealed unique patterns in primary and secondary lymphoid organs of cynomolgus macaques. Among the many differentially regulated transcripts, upregulation of noncoding RNAs [MIR34A for spleen and thymus and NEAT1 (NCRNA00084) for thymus] showed potential as biomarkers of radiation injury and targets for mitigating the effects of radiation-induced hematopoietic syndrome-impaired lymphoid reconstitution.

Monocyte Polarization is Altered by Total-Body Irradiation in Male Rhesus Macaques: Implications for Delayed Effects of Acute Radiation Exposure

Radiation-induced fibrosis (RIF) is a common delayed effect of acute ionizing radiation exposure (DEARE) affecting diverse tissues including the heart, lungs, liver and skin, leading to reduced tissue function and increased morbidity. Monocytes, which may be classified into classical (CD14⁺⁺, CD16^-), intermediate (CD14⁺⁺, CD16⁺) and non-classical (CD14^+/low, CD16⁺⁺) subtypes in humans and non-human primates (NHPs), and monocyte-derived macrophages may play an integral role in the pathogenesis of RIF. We tested the hypothesis that moderate to high levels of total-body exposure to radiation would alter monocyte polarization and produce phenotypes that could promote multi-organ fibrosis in a wellestablished NHP model of DEARE. Subjects were 16 young adult male rhesus macaques, ten of which were exposed to high-energy, 4 Gy X-ray total-body irradiation (TBI) and six that received sham irradiation (control). Total monocytes assessed by complete blood counts were 89% depleted in TBI animals by day 9 postirradiation (P < 0.05), but recovered by day 30 postirradiation and did not differ from control levels thereafter. Monocytes were isolated from peripheral blood mononuclear cells (PBMCs) and sorted into classical, intermediate and non-classical subsets using fluorescence-activated cell sorting (FACS) prior to and at 6 months post-TBI. At 6 months postirradiation, monocyte polarization shifted towards lower classical (92% → 86%) and higher intermediate (7% → 12%) and non-classical monocyte subsets (0.6% → 2%) (all P < 0.05) in TBI animals compared to baseline. No change in monocyte subsets was observed in control animals. Transcriptional profiles in classical and intermediate monocyte subsets were assessed using RNAseq. Classical monocyte gene expression did not change significantly over time or differ cross-sectionally between TBI and control groups. In contrast, significant numbers of differentially expressed genes (DEGs) were detected in intermediate monocyte comparisons between the TBI animals and all animals at baseline (304 DEGs), and in the TBI versus control animals at 6 months postirradiation (67 DEGs). Intermediate monocytes also differed between baseline and 6 months in control animals (147 DEGs). Pathway analysis was used to identify genes within significant canonical pathways, yielding 52 DEGs that were specific to irradiated intermediate monocytes. These DEGs and significant canonical pathways were associated with pro-fibrotic and anti-inflammatory signaling pathways that have been noted to induce M2 macrophage polarization. These findings support the hypothesis that TBI may alter monocyte programming and polarization towards a profibrotic phenotype, providing a novel target opportunity for therapies to inhibit or prevent RIF.

Huangqi Shengmai Yin Protects against Radiation-Induced Cardiac Fibrosis Injury by Regulating the TGF-β1/Smads and MMPs

Background

Radiation-induced heart damage is considered to be a progressive process of fibrosis. Emerging evidence has indicated that the Smads and matrix metalloproteinases (MMPs)/tissue inhibitors of MMPs (TIMP) may be involved in radiation-induced cardiac fibrosis (RICF) by regulating the activation of TGF-β1 signaling pathway. Based on this, the present study was undertaken to characterize the effect of Huangqi Shengmai Yin (HSY) on RICF in a rat model.

Methods

Precardiac region of rats was irradiated with 25 Gy X-rays, and their myocardial pathology scores in terms of injury and collagen volume fraction (CVF) and the expression levels of fibrotic molecules were detected.

Results

The pathology scores and CVF in myocardial tissue increased after irradiation, and the expression of TGF-β1, Col1, and Col3 increased. This change indicated that such irradiation promoted the fibrosis damage in rat hearts. The damage was accompanied by an increase in the expression of Smad 2, Smad3, Smad4, and MMP14 and a decrease in the expression of Smad 7 and TIMP1. Administration of HSY weakened the RICF by decreasing pathology score and CVF and decreased the expression of TGF-β1, Col1, and Col3 in irradiated rat hearts. In addition, Smad2, Smad3, Smad4, and MMP14 were downregulated, while Smad 7 and TIMP1 were upregulated during intervention with HSY.

Conclusions

The involvement of the TGF-β1/Smads and MMPs/TIMP system in RICF was confirmed. This study demonstrated, for the first time, that HSY attenuates the effects of RICF in a rat model. The effect HSY was found to be closely related to the TGF-β1/Smads signaling pathway and MMPs system. These results suggest that HSY is a prospective drug for clinical treatment of RICF.

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

Male rhesus macaques were subjected to partial-body irradiation at 10, 11, or 12 Gy with 5% bone marrow protection. Animals were euthanized when dictated by prospectively determined clinical parameters or at approximately 180 d following irradiation. Histological sections of lung and heart were stained with hematoxylin and eosin as well as a battery of histochemical and immunohistochemical stains. Histopathological alterations in the lung were centered on fibrosis, inflammation, and reactive/proliferative changes in pneumocytes. These changes were noted in animals necropsied after approximately 85-100 d postirradiation and extending through the observation period. Interstitial and pleural fibrosis demonstrated by Masson's trichrome staining were associated with increased alpha smooth muscle actin and collagen 1 immunohistochemical staining. Areas of interstitial fibrosis had reduced microvascular density with CD31 immunohistochemical staining. Accumulations of CD163- and CD206-positive alveolar macrophages were present in areas of interstitial fibrosis. Unidentified cells termed "myxoid" cells in alveolar walls had histochemical and immunohistochemical staining characteristics of epithelial-, endothelial-, or pericyte-mesenchymal transition states that were developing myofibroblast features. Distinctive focal or multifocal alveolar-bronchiolar hyperplasia had microscopic features of preneoplastic proliferation. Delayed radiation-associated changes in the heart consisted primarily of myocardial fibrosis, with rare histological evidence of myofiber degeneration.

White Matter is the Predilection Site of Late-Delayed Radiation-Induced Brain Injury in Non-Human Primates

Fractionated whole-brain irradiation for the treatment of intracranial neoplasia causes progressive neurodegeneration and neuroinflammation. The long-term consequences of single-fraction high-dose irradiation to the brain are unknown. To assess the late effects of brain irradiation we compared transcriptomic gene expression profiles from nonhuman primates (NHP; rhesus macaques Macaca mulatta) receiving single-fraction total-body irradiation (TBI; n = 5, 6.75-8.05 Gy, 6-9 years prior to necropsy) to those receiving fractionated whole-brain irradiation (fWBI; n = 5, 40 Gy, 8 × 5 Gy fractions; 12 months prior to necropsy) and control comparators (n = 5). Gene expression profiles from the dorsolateral prefrontal cortex (DLPFC), hippocampus (HC) and deep white matter (WM; centrum semiovale) were compared. Stratified analyses by treatment and region revealed that radiation-induced transcriptomic alterations were most prominent in animals receiving fWBI, and primarily affected white matter in both TBI and fWBI groups. Unsupervised canonical and ontologic analysis revealed that TBI or fWBI animals demonstrated shared patterns of injury, including white matter neuroinflammation, increased expression of complement factors and T-cell activation. Both irradiated groups also showed evidence of impaired glutamatergic neurotransmission and signal transduction within white matter, but not within the dorsolateral prefrontal cortex or hippocampus. Signaling pathways and structural elements involved in extracellular matrix (ECM) deposition and remodeling were noted within the white matter of animals receiving fWBI, but not of those receiving TBI. These findings indicate that those animals receiving TBI are susceptible to neurological injury similar to that observed after fWBI, and these changes persist for years postirradiation. Transcriptomic profiling reaffirmed that macrophage/microglial-mediated neuroinflammation is present in radiation-induced brain injury (RIBI), and our data provide novel evidence that the complement system may contribute to the pathogenesis of RIBI. Finally, these data challenge the assumption that the hippocampus is the predilection site of injury in RIBI, and indicate that impaired glutamatergic neurotransmission may occur in white matter injury.

The effects of Radix Angelica Sinensis and Radix Hedysari ultrafiltration extract on X-irradiation-induced myocardial fibrosis in rats

Radix Angelica Sinensis and Radix Hedysari are traditional Chinese medicines that are used for preventing and treating various diseases. This study aimed to investigate the effect and possible underlying mechanisms of Radix Angelica Sinensis and Radix Hedysari ultrafiltration extract (RAS-RH) on X-irradiation-induced cardiac fibrosis in rats. Our data demonstrated that (a) a single dose of total body irradiation (TBI) at 8 Gy resulted in cardiac fibrosis, whereas the control hearts exhibited less collagen and fibrosis. RAS-RH mitigated these morphological injuries. (b) TBI resulted in an increase in the serum levels of transforming growth factor β1 (TGF-β1) and troponin-I (TnI). RAS-RH inhibited the release of TBI-induced serum TGF-β1 and the TnI levels. (c) TBI inhibited the apoptosis of primary rat cardiac fibroblasts, whereas RAS-RH induced the apoptosis of primary rat cardiac fibroblasts after X- irradiation. (d) TBI resulted in an increase in the expression of osteopontin (OPN), c-fos, c-jun, miRNA-21 and collagen1α (COL1α) in primary rat cardiac fibroblasts, and RAS-RH mitigated the TBI-induced increased expression of OPN, c-jun, miRNA-21 and COL1α. In conclusion, these results demonstrate that RAS-RH exerts antifibrotic effects possibly through inducing the apoptosis of fibroblasts, inhibiting the release of serum TGF-β1, reducing the levels of serum TnI and reducing the expression of OPN, c-jun, miRNA-21 and COL1α. Therefore, RAS-RH may potentially be developed as a medical countermeasure for the mitigation of radiation-induced myocardial fibrosis.

The Aftermath of Surviving Acute Radiation Hematopoietic Syndrome and its Mitigation

Intensive research is underway to find new agents that can successfully mitigate the acute effects of radiation exposure. This is primarily in response to potential counterthreats of radiological terrorism and nuclear accidents but there is some hope that they might also be of value for cancer patients treated with radiation therapy. Research into mitigation countermeasures typically employs classic animal models of acute radiation syndromes (ARS) that develop after whole-body irradiation (WBI). While agents are available that successfully mitigate ARS when given after radiation exposure, their success raises questions as to whether they simply delay lethality or unmask potentially lethal radiation pathologies that may appear later in time. Life shortening is a well-known consequence of WBI in humans and experimental animals, but it is not often examined in a mitigation setting and its causes, other than cancer, are not well-defined. This is in large part because delayed effects of acute radiation exposure (DEARE) do not follow the strict time-dose phenomena associated with ARS and present as a diverse range of symptoms and pathologies with low mortality rates that can be evaluated only with the use of large cohorts of subjects, as in this study. Here, we describe chronically increased mortality rates up to 660 days in large numbers of mice given LD_70/30 doses of WBI. Systemic myeloid cell activation after WBI persists in some mice and is associated with late immunophenotypic changes and hematopoietic imbalance. Histopathological changes are largely of a chronic inflammatory nature and variable incidence, as are the clinical symptoms, including late diarrhea that correlates temporally with changes in the content of the microbiome. We also describe the acute and long-term consequences of mitigating hematopoietic ARS (H-ARS) lethality after LD_70/30 doses of WBI in multiple cohorts of mice treated uniformly with radiation mitigators that have a common 4-nitro-phenylsulfonamide (NPS) pharmacophore. Effective NPS mitigators dramatically decrease ARS mortality. There is slightly increased subacute mortality, but the rate of late mortalities is slowed, allowing some mice to live a normal life span, which is not the case for WBI controls. The study has broad relevance to radiation late effects and their potential mitigation and epitomizes the complex interaction between radiation-damaged tissues and immune homeostasis.

Impact of Ionizing Radiation on the Cardiovascular System: A Review

Radiation therapy has become one of the main forms of treatment for various types of cancers. Cancer patients previously treated with high doses of radiation are at a greater risk to develop cardiovascular complications later in life. The heart can receive varying doses of radiation depending on the type of therapy and can even reach doses in the range of 17 Gy. Multiple studies have highlighted the role of oxidative stress and inflammation in radiation-induced cardiovascular damage. Doses of ionizing radiation below 200 mGy, however, have been shown to have beneficial effects in some experimental models of radiation-induced damage, but low-dose effects in the heart is still debated. Low-dose radiation may promote heart health and reduce damage from oxidative stress and inflammation, however there are few studies focusing on the impact of low-dose radiation on the heart. In this review, we summarize recent studies from animal models and human data focusing on the effects and mechanism(s) of action of radiation-induced damage to the heart, as well as the effects of high and low doses of radiation and dose rates.

Changes in microvascular density differentiate metabolic health outcomes in monkeys with prior radiation exposure and subsequent skeletal muscle ECM remodeling

Radiation exposure accelerates the onset of age-related diseases such as diabetes, cardiovascular disease, and neoplasia and, thus, lends insight into in vivo mechanisms common to these disorders. Fibrosis and extracellular matrix (ECM) remodeling, which occur with aging and overnutrition and following irradiation, are risk factors for development of type 2 diabetes mellitus. We previously demonstrated an increased incidence of skeletal muscle insulin resistance and type 2 diabetes mellitus in monkeys that had been exposed to whole body irradiation 5-9 yr prior. We hypothesized that irradiation-induced fibrosis alters muscle architecture, predisposing irradiated animals to insulin resistance and overt diabetes. Rhesus macaques (Macaca mulatta, n = 7-8/group) grouped as nonirradiated age-matched controls (Non-Rad-CTL), irradiated nondiabetic monkeys (Rad-CTL), and irradiated monkeys that subsequently developed diabetes (Rad-DM) were compared. Prior radiation exposure resulted in persistent skeletal muscle ECM changes, including a relative overabundance of collagen IV and a trend toward increased transforming growth factor-β1. Preservation of microvascular markers differentiated the irradiated diabetic and nondiabetic groups. Microvascular density and plasma nitrate and heat shock protein 90 levels were lower in Rad-DM than Rad-CTL. These results are consistent with a protective effect of abundant microvasculature in maintaining glycemic control within radiation-induced fibrotic muscle.

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.

Loss of immune homeostasis dictates SHIV rebound after stem-cell transplantation

The conditioning regimen used as part of the Berlin patient's hematopoietic cell transplant likely contributed to his eradication of HIV infection. We studied the impact of conditioning in simian-human immunodeficiency virus-infected (SHIV-infected) macaques suppressed by combination antiretroviral therapy (cART). The conditioning regimen resulted in a dramatic, but incomplete depletion of CD4⁺ and CD8⁺ T cells and CD20⁺ B cells, increased T cell activation and exhaustion, and a significant loss of SHIV-specific Abs. The disrupted T cell homeostasis and markers of microbial translocation positively correlated with an increased viral rebound after cART interruption. Quantitative viral outgrowth and Tat/rev-induced limiting dilution assays showed that the size of the latent SHIV reservoir did not correlate with viral rebound. These findings identify perturbations of the immune system as a mechanism for the failure of autologous transplantation to eradicate HIV. Thus, transplantation strategies may be improved by incorporating immune modulators to prevent disrupted homeostasis, and gene therapy to protect transplanted cells.

NLRP3 inflammasome activation mediates radiation-induced pyroptosis in bone marrow-derived macrophages

A limit to the clinical benefit of radiotherapy is not an incapacity to eliminate tumor cells but rather a limit on its capacity to do so without destroying normal tissue and inducing inflammation. Recent evidence reveals that the inflammasome is essential for mediating radiation-induced cell and tissue damage. In this study, using primary cultured bone marrow-derived macrophages (BMDM) and a mouse radiation model, we explored the role of NLRP3 inflammasome activation and the secondary pyroptosis underlying radiation-induced immune cell death. We observed an increasing proportion of pyroptosis and elevating Caspase-1 activation in 10 and 20 Gy radiation groups. Nlrp3 knock out significantly diminished the quantity of cleaved-Caspase-1 (p10) and IL-1β as well as the proportion of pyroptosis. Additionally, in vivo research shows that 9.5 Gy of radiation promotes Caspase-1 activation in marginal zone cells and induces death in mice, both of which can be significantly inhibited by knocking out Nlrp3. Thus, based on these findings, we conclude that the NLRP3 inflammasome activation mediates radiation-induced pyroptosis in BMDMs. Targeting NLRP3 inflammasome and pyroptosis may serve as effective strategies to diminish injury caused by radiation.

Effects of ionizing radiation on the heart

This article provides an overview of studies addressing effects of ionizing radiation on the heart. Clinical studies have identified early and late manifestations of radiation-induced heart disease, a side effect of radiation therapy to tumors in the chest when all or part of the heart is situated in the radiation field. Studies in preclinical animal models have contributed to our understanding of the mechanisms by which radiation may injure the heart. More recent observations in human subjects suggest that ionizing radiation may have cardiovascular effects at lower doses than was previously thought. This has led to examinations of low-dose photons and low-dose charged particle irradiation in animal models. Lastly, studies have started to identify non-invasive methods for detection of cardiac radiation injury and interventions that may prevent or mitigate these adverse effects. Altogether, this ongoing research should increase our knowledge of biological mechanisms of cardiovascular radiation injury, identify non-invasive biomarkers for early detection, and potential interventions that may prevent or mitigate these adverse effects.