Accelerated hematopoietic syndrome after radiation doses bridging hematopoietic (H-ARS) and gastrointestinal (GI-ARS) acute radiation syndrome: early hematological changes and systemic inflammatory response syndrome in minipig

Ferroptosis, Inflammation, and Microbiome Alterations in the Intestine in the Göttingen Minipig Model of Hematopoietic-Acute Radiation Syndrome

Hematopoietic acute radiation syndrome (H-ARS) involves injury to multiple organ systems following total body irradiation (TBI). Our laboratory demonstrated that captopril, an angiotensin-converting enzyme inhibitor, mitigates H-ARS in Göttingen minipigs, with improved survival and hematopoietic recovery, as well as the suppression of acute inflammation. However, the effects of captopril on the gastrointestinal (GI) system after TBI are not well known. We used a Göttingen minipig H-ARS model to investigate captopril's effects on the GI following TBI (60Co 1.79 or 1.80 Gy, 0.42-0.48 Gy/min), with endpoints at 6 or 35 days. The vehicle or captopril (0.96 mg/kg) was administered orally twice daily for 12 days, starting 4 h post-irradiation. Ilea were harvested for histological, protein, and RNA analyses. TBI increased congestion and mucosa erosion and hemorrhage, which were modulated by captopril. GPX-4 and SLC7A11 were downregulated post-irradiation, consistent with ferroptosis at 6 and 35 days post-irradiation in all groups. Interestingly, p21/waf1 increased at 6 days in vehicle-treated but not captopril-treated animals. An RT-qPCR analysis showed that radiation increased the gene expression of inflammatory cytokines IL1B, TNFA, CCL2, IL18, and CXCL8, and the inflammasome component NLRP3. Captopril suppressed radiation-induced IL1B and TNFA. Rectal microbiome analysis showed that 1 day of captopril treatment with radiation decreased overall diversity, with increased Proteobacteria phyla and Escherichia genera. By 6 days, captopril increased the relative abundance of Enterococcus, previously associated with improved H-ARS survival in mice. Our data suggest that captopril mitigates senescence, some inflammation, and microbiome alterations, but not ferroptosis markers in the intestine following TBI.

Considerations of Medical Preparedness to Assess and Treat Various Populations During a Radiation Public Health Emergency

During a radiological or nuclear public health emergency, given the heterogeneity of civilian populations, it is incumbent on medical response planners to understand and prepare for a potentially high degree of interindividual variability in the biological effects of radiation exposure. A part of advanced planning should include a comprehensive approach, in which the range of possible human responses in relation to the type of radiation expected from an incident has been thoughtfully considered. Although there are several reports addressing the radiation response for special populations (as compared to the standard 18-45-year-old male), the current review surveys published literature to assess the level of consideration given to differences in acute radiation responses in certain sub-groups. The authors attempt to bring clarity to the complex nature of human biology in the context of radiation to facilitate a path forward for radiation medical countermeasure (MCM) development that may be appropriate and effective in special populations. Consequently, the focus is on the medical (as opposed to logistical) aspects of preparedness and response. Populations identified for consideration include obstetric, pediatric, geriatric, males, females, individuals of different race/ethnicity, and people with comorbidities. Relevant animal models, biomarkers of radiation injury, and MCMs are highlighted, in addition to underscoring gaps in knowledge and the need for consistent and early inclusion of these populations in research. The inclusion of special populations in preclinical and clinical studies is essential to address shortcomings and is an important consideration for radiation public health emergency response planning. Pursuing this goal will benefit the population at large by considering those at greatest risk of health consequences after a radiological or nuclear mass casualty incident.

"Radio-Protective Effect of Aminocaproic Acid in Human Spermatozoa"

BACKGROUND

The negative effects of ionizing radiation on organs and the reproductive system are well known and documented. Exposure to gamma radiation can lead to oligospermia, azoospermia and DNA damage. Up to date, there is no effective pharmaceutical compound for protecting the male reproductive system and sperm.

OBJECTIVE

This study aimed at investigating the ability of Ɛ-aminocaproic acid (EACA) to prevent the damage of human spermatozoa and DNA induced by ionizing radiation.

MATERIALS AND METHODS

Sperm samples were obtained from healthy volunteers (35 men; 31.50 ± 7.34 years old). There were 4 experimental groups: 1) control group (CG), 2) group exposed to maximal radiation dose 67.88 mGy (RMAX), 3) low-dose radiation (minimal) 22.62 mGy (RMIN), and 4) group treated with radiation (67.88 mGy) and EACA (dose 50 ng/ml). Sperm motility, viability, and DNA damage were assessed.

RESULTS

We observed a significant decrease in total sperm motility of the RMAX group compared to CG (p < 0.05). Sperm viability in the RMAX group was also reduced in comparison to the control (p < 0.05). A significant increase in DNA fragmentation was detected in the RMAX group. The results demonstrated that the treatment of sperm with EACA led to a decrease in the fragmentation of the sperm DNA (compared to the RMAX group) (p < 0.05).

CONCLUSION

The results indicate that EACA effectively protects human spermatozoa from DNA damage induced by ionizing radiation. Treatment of spermatozoa with EACA led to the preservation of cell motility, viability, and DNA integrity upon radiation exposure.

Effects of captopril against radiation injuries in the Göttingen minipig model of hematopoietic-acute radiation syndrome

Our laboratory has demonstrated that captopril, an angiotensin converting enzyme inhibitor, mitigates hematopoietic injury following total body irradiation in mice. Improved survival in mice is correlated with improved recovery of mature blood cells and bone marrow, reduction of radiation-induced inflammation, and suppression of radiation coagulopathy. Here we investigated the effects of captopril treatment against radiation injuries in the Göttingen mini pig model of Hematopoietic-Acute Radiation Syndrome (H-ARS). Minipigs were given captopril orally (0.96 mg/kg) twice daily for 12 days following total body irradiation (⁶⁰Co 1.79 Gy, 0.42–0.48 Gy/min). Blood was drawn over a time course following irradiation, and tissue samples were collected at euthanasia (32–35 days post-irradiation). We observed improved survival with captopril treatment, with survival rates of 62.5% in vehicle treated and 87.5% in captopril treated group. Additionally, captopril significantly improved recovery of peripheral blood mononuclear cells, and a trend toward improvement in recovery of red blood cells and platelets. Captopril significantly reduced radiation-induced expression of cytokines erythropoietin and granulocyte-macrophage colony-stimulating factor and suppressed radiation-induced acute-phase inflammatory response cytokine serum amyloid protein A. Using quantitative-RT-PCR to monitor bone marrow recovery, we observed significant suppression of radiation-induced expression of redox stress genes and improved hematopoietic cytokine expression. Our findings suggest that captopril activities in the Göttingen minipig model of hematopoietic-acute radiation syndrome reflect findings in the murine model.

Celebrating 60 Years of Accomplishments of the Armed Forces Radiobiology Research Institute1

Chartered by the U.S. Congress in 1961, the Armed Forces Radiobiology Research Institute (AFRRI) is a Joint Department of Defense (DoD) entity with the mission of carrying out the Medical Radiological Defense Research Program in support of our military forces around the globe. In the last 60 years, the investigators at AFRRI have conducted exploratory and developmental research with broad application to the field of radiation sciences. As the only DoD facility dedicated to radiation research, AFRRI's Medical Radiobiology Advisory Team provides deployable medical and radiobiological subject matter expertise, advising commanders in the response to a U.S. nuclear weapon incident and other nuclear or radiological material incidents. AFRRI received the DoD Joint Meritorious Unit Award on February 17, 2004, for its exceptionally meritorious achievements from September 11, 2001 to June 20, 2003, in response to acts of terrorism and nuclear/radiological threats at home and abroad. In August 2009, the American Nuclear Society designated the institute a nuclear historic landmark as the U.S.'s primary source of medical nuclear and radiological research, preparedness and training. Since then, research has continued, and core areas of study include prevention, assessment and treatment of radiological injuries that may occur from exposure to a wide range of doses (low to high). AFRRI collaborates with other government entities, academic institutions, civilian laboratories and other countries to research the biological effects of ionizing radiation. Notable early research contributions were the establishment of dose limits for major acute radiation syndromes in primates, applicable to human exposures, followed by the subsequent evolution of radiobiology concepts, particularly the importance of immune collapse and combined injury. In this century, the program has been essential in the development and validation of prophylactic and therapeutic drugs, such as Amifostine, Neupogen®, Neulasta®, Nplate® and Leukine®, all of which are used to prevent and treat radiation injuries. Moreover, AFRRI has helped develop rapid, high-precision, biodosimetry tools ranging from novel assays to software decision support. New drug candidates and biological dose assessment technologies are currently being developed. Such efforts are supported by unique and unmatched radiation sources and generators that allow for comprehensive analyses across the various types and qualities of radiation. These include but are not limited to both 60Co facilities, a TRIGA® reactor providing variable mixed neutron and γ-ray fields, a clinical linear accelerator, and a small animal radiation research platform with low-energy photons. There are five major research areas at AFRRI that encompass the prevention, assessment and treatment of injuries resulting from the effects of ionizing radiation: 1. biodosimetry; 2. low-level and low-dose-rate radiation; 3. internal contamination and metal toxicity; 4. radiation combined injury; and 5. radiation medical countermeasures. These research areas are bolstered by an educational component to broadcast and increase awareness of the medical effects of ionizing radiation, in the mass-casualty scenario after a nuclear detonation or radiological accidents. This work provides a description of the military medical operations as well as the radiation facilities and capabilities present at AFRRI, followed by a review and discussion of each of the research areas.

Quantifying the influences of radiation therapy on deformability of human red blood cells by dual-beam optical tweezers

Radiation therapy is widely used as a treatment tool for malignancies. However, radiation-related complications are still unavoidable risks for off-target cells. Little is known about radiation therapy's possible effects on mechanical features of the off-target cells such as human red blood cells (RBCs). RBCs are nucleus-free circulating cells that can deform without losing functionality in healthy conditions. Thus, to evaluate in vitro effects of radiation therapy on the healthy plasma membrane of cells, RBCs were selected as a primary test model. RBCs were exposed to clinically prescribed radiotherapy doses of 2 Gy, 12 Gy and, 25 Gy, and each radiotherapy dose group was compared to a non-irradiated group. Cells were characterized by stretching using dual-beam optical tweezers and compared using the resulting deformability index. The group receiving the highest radiation dose was found statistically distinguishable from the control group (DI_0Gy = 0.33 ± 0.08), and revealed the highest deformability index (DI_25Gy = 0.38 ± 0.11, p = 0.0068), while no significant differences were found for 2 Gy (DI_2Gy = 0.33 ± 0.08, p = 0.9) and 12 Gy (DI_12Gy = 0.31 ± 0.09, p = 0.2) dose groups. Based on these findings, we conclude that radiotherapy exposure may alter the deformability of red blood cells depending on the dose amount, and measurement of deformability index by dual-beam optical tweezers can serve as a sensitive biomarker to probe responses of cells to the radiotherapy.

Little is known about radiation therapy's possible effects on mechanical features of off-target cells such as human red blood cells. Here, irradiated human red blood cells were stretched using dual-beam optical tweezers and compared using the resulting deformability index.

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.

Morphological and functional impairment in the gut in a partial body irradiation minipig model of GI-ARS

Purpose: Göttingen minipig (G-MP) displays classic gastrointestinal acute radiation syndrome (GI-ARS) following total body irradiation (TBI) at GI doses which are lethal by 10-14 days. In collaboration with BARDA, we are developing a hemi-body/partial body irradiation (PBI) model by exposing only the abdomen and lower extremities to study GI structure/function impairment, natural history of injury and recovery, as well as correlative biomarkers out to 30 days.Materials and methods: Twenty-four G-MP were exposed to either 12 or 16 Gy (LINAC Elekta); head, forelimbs, and thorax were outside the irradiation field, sparing ∼50% of the bone marrow. Animals were followed for 30 days with euthanasia scheduled at pre-set intervals to study the time course of GI injury and recovery. Hematological profiles, clinical symptoms, gross- and histo-pathology including markers of proliferation and apoptosis in the small intestines, gut function parameters (food tolerance, digestion, absorption, citrulline production), and levels of two biomarkers, CRP and IGF-1, were evaluated.Results: PBI at 16 Gy yielded higher lethality than 12 Gy. Unlike TBI, PBI did not cause severe pancytopenia or external hemorrhage, as expected, and allowed to focus the injury on GI organs while sparing the radiation sensitive heart and lung. Compromised animals showed inactivity, anorexia, vomiting, diarrhea, and weight loss. Histology revealed that in 12 Gy irradiated animals, lesions recovered overtime. In 16 Gy irradiated animals, lesions were more pronounced and persistent. BrdU and Ki67 labelling demonstrated dose-dependent loss of crypts and subsequent mucosal ulceration which recovered over time. Minimal apoptosis was observed at both doses. Reductions in food tolerance, digestion, absorption, and citrulline production were time and dose-dependent. Loss of citrulline reached a nadir between 6-12 days and then recovered partially. CRP and IGF-1 were upregulated following PBI at GI doses.Conclusions: This lower hemi-body irradiation model allowed for extended survival at GI-specific ARS doses and development of a well-controlled GI syndrome with minimal hematopoietic injury or confounding mortality from cardiopulmonary damage. A dose-dependent impairment in the intestinal structure resulted in overall decreased gut functionality followed by a partial recovery. However, while the structure appeared to be recovered, not all functionality was attained. PBI induced systemic inflammation and altered the IGF-1 hormone indicating that these can be used as biomarkers in the minipig even under partial body conditions. This PBI model aligns with other minipig models under BARDA's large animal consortium to test medical countermeasure efficacy against a less complex GI-specific ARS injury.

Neulasta Regimen for the Hematopoietic Acute Radiation Syndrome: Effects Beyond Neutrophil Recovery

PURPOSE

Understanding the physiopathology underlying the acute radiation syndrome (ARS) and the mechanism of action of drugs known to ameliorate ARS is expected to help identify novel countermeasure candidates and improve the outcome for victims exposed to radiation. Granulocyte colony-stimulating factor (G-CSF) has been approved by the US Food and Drug Administration for treatment of hematopoietic ARS (H-ARS) because of its ability to alleviate myelosuppression. Besides its role in hematopoiesis, G-CSF is known to protect the cardiovascular and neurologic systems, to attenuate vascular injury and cardiac toxicity, to preserve gap junction function, and to modulate inflammation and oxidative stress. Here, we characterized the protective effects of G-CSF beyond neutrophil recovery in minipigs exposed to H-ARS doses.

METHODS AND MATERIALS

Twenty male Göttingen minipigs were exposed to total body, acute ionizing radiation. Animals received either pegylated G-CSF (Neulasta) or dextrose at days 1 and 8 after irradiation. Survival was monitored over a 45-day period.

RESULTS

Neulasta decreased mortality compared with the control, reduced nadir and duration of neutropenia, and lowered prevalence of organ hemorrhage and frank bleeding episodes. Neulasta also increased plasma concentration of IGF-1 hormone, activated the cardiovascular protective IGF-1R/PI3K/Akt/eNOS/NO pathway, and enhanced membrane expression of VE-cadherin in the heart, improving vascular tone and barrier function. Expression of the acute phase protein CRP, a mediator of cardiovascular diseases and a negative regulator of the IGF-1 pathway, was also induced but at much lower extent compared with IGF-1. Activity of catalase and superoxide dismutase (SOD-1) was only marginally affected, whereas activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase was downregulated.

CONCLUSIONS

In addition to a neutrophilic effect, amelioration of endothelial homeostasis and barrier function and reduction in NADPH oxidase contribute to the beneficial effects of Neulasta for the treatment of H-ARS.

Characterization and Etiology of Swollen Muzzles in Irradiated Mice

Several investigators performing bone marrow transplantation studies have previously reported sporadic increases in mortality that were associated with pronounced swelling in the face, head and neck of mice. Over the past few years, we and others have noted an increasing number of experiments in which mice that have received total-body irradiation (TBI) or partial-body irradiation (PBI) develop swollen muzzles, drastic thickening of the upper lip and redness, bruising and/or swelling around the nose and muzzle and sometimes over the top of the head. We refer to this rapid and extreme swelling after irradiation as swollen muzzle syndrome (SMS). The development of SMS postirradiation is associated with morbidity that occurs earlier than would be expected from the traditional hematopoietic acute radiation syndrome (H-ARS), and has impeded studies in several laboratories attempting to evaluate medical countermeasures (MCM) against radiation. However, little has been done to characterize this somewhat unpredictable radiation effect. To investigate the cause and etiology of SMS, data from three different laboratories collected over a seven-year period from 100 MCM 30-day survival studies using mice from different vendors were retrospectively analyzed to determine the time of onset, progression and incidence of SMS in male and female mice exposed to various doses of ionizing radiation. An additional study compared incidence and etiology of SMS in mice from two different vendors (identified as vendors A and B) after exposure to the LD_50/30 (X rays). Mice presenting with SMS, as well as non-SMS (irradiated) control mice, were necropsied to determine microbial status of the blood, heart, spleen, liver, kidney and muzzle tissue. Only mice from vendor A (20%) developed SMS. While the number of bacterial species isolated from various tissues of SMS and non-SMS mice was not different, the number of tissues positive for bacteria was significantly greater in SMS mice. At least one tissue in 83% of SMS mice from vendor A tested positive for Streptococcus agalactiae [group B beta Streptococcus (GBS)], compared to 25% of non-SMS mice from vendor A, and 0% of non-SMS mice from vendor B. In addition, all mice from vendor A with SMS had at least one tissue with >10⁴ CFU/g, with GBS as the predominant bacterium, compared to only 25% of non-SMS mice from vendor A, and 0% of non-SMS mice from vendor B. The incidence and magnitude of GBS growth in cultures correlated with the onset of SMS; the earliest and heaviest infections occurred in mice presenting with SMS on days 5-6 postirradiation. The majority of SMS mice (5 out of 6) had positive blood cultures, with the same bacterial strain isolated from other tissues, suggesting systemic translocation via the bloodstream. We propose that testing of mice and the identification of the microorganisms frequently associated with SMS may provide guidance for selection of antimicrobials for use by other investigators in studies evaluating potential MCM, and for the ordering, handling and care of immunodeficient mice or mice that are to be rendered immunodeficient after acute irradiation.

Pilot Study of Radiation-induced Gastrointestinal Injury in a Hemi-body Shielded Göttingen Minipig Model

Development of medical countermeasures (MCMs) for gastrointestinal (GI) injury following acute radiation exposure requires well-characterized models that can assess not only survival but also secondary endpoints, including structural and functional characteristics of GI damage and recovery that ultimately contribute to long-term survival. The authors conducted a pilot study in a hemi-body shielded Göttingen minipig model of radiation-induced GI injury that enables radiation damage to the GI tract to be evaluated and reduces the potential for hemorrhage and/or damage in other more sensitive organ systems. With shielding of the head, chest, and front legs, radiation dose levels of 14 Gy were required to see significant GI-related morbidity, while dose levels of 16 Gy resulted in significant mortality by day 45 post-irradiation. Periodic scheduled necropsies showed significant reduction in and slow recovery of intestinal crypt count at 14 and 16 Gy. Intestinal proliferative activity was initially increased and then gradually decreased over the course of the study. Histological evidence of marked inflammatory infiltrates was noted in the GI tract at day 5, while collagen deposition, indicative of fibrosis, was observed as early as day 15, peaking at day 30. The radiation dose-responsive indicators of GI damage identified in this model (i.e., intestinal crypt count and proliferative activity) may serve as useful endpoints for evaluation of the efficacy of potential MCMs.

Expanded Characterization of a Hemi-Body Shielded Göttingen Minipig Model of Radiation-induced Gastrointestinal Injury Incorporating Oral Dosing Procedures

In collaboration with the Biomedical Advanced Research and Development Authority (BARDA), the authors recently conducted a pilot study in a hemi-body shielded model of radiation-induced gastrointestinal (GI) injury in Göttingen minipigs following exposure to radiation dose levels between 8-16 Gy. Herein, the impact of oral dosing procedures is assessed, as well as the specific causes of death in animals exposed to radiation doses of 14 and 16 Gy (n = 64; 32 male, 32 female, between 6 and 8 mo of age). Oral dosing using a 2-tablet placebo system comprised of both immediate release and enteric-coated tablets starting 24 h post-irradiation resulted in inhibited gastric emptying of the enteric-coated tablets, which were found to be retained in the stomach and/or regurgitated. This finding appears to be species-specific, as similar findings have not been reported for other large animal species (e.g., non-human primates). Mortality was primarily dictated by decreased activity, body weight loss (>35%), and/or respiratory distress, despite shielding of the lung. The cause of respiratory distress in animals that were pre-terminally euthanized varied according to the timing of death, with interstitial inflammation and extensive fibrosis observed >20 days post-irradiation. Kidney damage was also identified in most animals after day 10. Changes in the GI tract were consistent with previous studies and included collagen deposition/fibrosis. Observations of inflammatory infiltrates and interstitial inflammation/fibrosis in both shielded and unshielded organs support a strong secondary inflammatory syndrome post-irradiation.

Surface-enhanced Raman spectroscopy competitive binding biosensor development utilizing surface modification of silver nanocubes and a citrulline aptamer

A point-of-care (PoC) device with the ability to detect biomarkers at low concentrations in bodily fluids would have an enormous potential for medical diagnostics outside the central laboratory. One method to monitor analytes at low concentrations is by using surface-enhanced Raman spectroscopy (SERS). In this preliminary study toward using SERS for PoC biosensing, the surface of colloidal silver (Ag) nanocubes has been modified to test the feasibility of a competitive binding SERS assay utilizing aptamers against citrulline. Specifically, Ag nanocubes were functionalized with mercaptobenzoic acid, as well as a heterobifunctional polyethylene glycol linker that forms an amide bond with the amino acid citrulline. After the functionalization, the nanocubes were characterized by zeta-potential, transmission electron microscopy images, ultraviolet/visible spectroscopy, and by SERS. The citrulline aptamers were developed and tested using backscattering interferometry. The data show that our surface modification method does work and that the functionalized nanoparticles can be detected using SERS down to a 24.5 picomolar level. Last, we used microscale thermophoresis to show that the aptamers bind to citrulline with at least a 50 times stronger affinity than other amino acids. Download PDF SAVE FOR LATER

MODELING H-ARS USING HEMATOLOGICAL PARAMETERS: A COMPARISON BETWEEN THE NON-HUMAN PRIMATE AND MINIPIG

Multiple hematological biomarkers (i.e. complete blood counts and serum chemistry parameters) were used in a multivariate linear-regression fit to create predictive algorithms for estimating the severity of hematopoietic acute radiation syndrome (H-ARS) using two different species (i.e. Göttingen Minipig and non-human primate (NHP) (Macacca mulatta)). Biomarker data were analyzed prior to irradiation and between 1-60 days (minipig) and 1-30 days (NHP) after irradiation exposures of 1.6-3.5 Gy (minipig) and 6.5 Gy (NHP) ⁶⁰Co gamma ray doses at 0.5-0.6 Gy min^-1 and 0.4 Gy min^-1, respectively. Fitted radiation risk and injury categorization (RRIC) values and RRIC prediction percent accuracies were compared between the two models. Both models estimated H-ARS severity with over 80% overall predictive power and with receiver operating characteristic curve area values of 0.884 and 0.825. These results based on two animal radiation models support the concept for the use of a hematopoietic-based algorithm for predicting the risk of H-ARS in humans.

Citrulline as a Biomarker for Gastrointestinal-Acute Radiation Syndrome: Species Differences and Experimental Condition Effects

Animal models of hematopoietic and gastrointestinal acute radiation syndromes (ARS) have been characterized to develop medical countermeasures. Acute radiation-induced decrease of intestinal absorptive function has been correlated to a decrease in the number of intestinal crypt cells resulting from apoptosis and enterocyte mass reduction. Citrulline, a noncoded amino acid, is produced almost exclusively by the enterocytes of the small intestine. Citrullinemia has been identified as a simple, sensitive and suitable biomarker for radiation-induced injury associated with gastrointestinal ARS (GI-ARS). Here we discuss the effect of radiation on plasma citrulline levels in three different species, C57BL/6 mice, Göttingen minipigs and rhesus nonhuman primates (NHPs), measured by liquid chromatography tandem mass spectrometry (LC-MS/MS). The effects of experimental study conditions such as feeding and anesthesia were also examined on plasma citrulline levels in the NHPs. Both the mice and Göttingen minipigs were partial-body irradiated (PBI) with doses from 13-17 Gy and 8-16 Gy, respectively, whereas NHPs were total-body irradiated (TBI) with doses from 6.72-13 Gy. Blood samples were taken at different time points and plasma citrulline levels were measured in the three species at baseline and after irradiation. Basal plasma citrulline concentrations (mean ± SEM) in mice and minipigs were 57.8 ± 2.8 μM and 63.1 ± 2.1 μM, respectively. NHPs showed a basal plasma citrulline concentration of 32.6 ± 0.7 μM, very similar to that of humans (∼40 μM). Plasma citrulline progressively decreased after irradiation, reaching nadir values between day 3.5 and 7. The onset of citrulline recovery was observed earlier at lower radiation doses, while only partial citrulline recovery was noted at higher radiation doses in minipigs and NHPs, complete recovery was noted in mice at all doses. Plasma citrulline levels in NHPs anesthetized with ketamine and acepromazine significantly decreased by 35.5% (P = 0.0017), compared to unanesthetized NHPs. In the postprandial state, citrulline concentrations in NHPs were slightly but significantly decreased by 12.2% (P = 0.0287). These results suggest that plasma citrulline is affected by experimental conditions such as anesthesia and feeding.

Citrulline as a Biomarker in the Murine Total-Body Irradiation Model: Correlation of Circulating and Tissue Citrulline to Small Intestine Epithelial Histopathology

The use of plasma citrulline as a biomarker for gastrointestinal acute radiation syndrome via exposure to total-body irradiation in a murine model was investigated. The radiation exposure covered lethal, mid-lethal, and sub-lethal gastrointestinal acute radiation syndrome. Plasma citrulline profiles were generated over the first 6 d following total-body irradiation exposure of 6-15 Gy. In addition, plasma citrulline was comprehensively evaluated in the context of matching small intestine citrulline and histopathology. Higher plasma citrulline was significantly associated with lower irradiation doses over the first 6 d following the irradiation insult. Furthermore, higher plasma citrulline was significantly associated with higher crypt survival. The correlation of the plasma citrulline to crypt survival was more robust for higher irradiation doses and for later time points. The data suggested plasma citrulline was most informative for reflecting gastrointestinal injury resulting from exposure to 9-15 Gy total-body irradiation covering time-points 2-5 d post the irradiation insult.

Erythrocyte stiffness during morphological remodeling induced by carbon ion radiation

The adverse effect induced by carbon ion radiation (CIR) is still an unavoidable hazard to the treatment object. Thus, evaluation of its adverse effects on the body is a critical problem with respect to radiation therapy. We aimed to investigate the change between the configuration and mechanical properties of erythrocytes induced by radiation and found differences in both the configuration and the mechanical properties with involving in morphological remodeling process. Syrian hamsters were subjected to whole-body irradiation with carbon ion beams (1, 2, 4, and 6 Gy) or X-rays (2, 4, 6, and 12 Gy) for 3, 14 and 28 days. Erythrocytes in peripheral blood and bone marrow were collected for cytomorphological analysis. The mechanical properties of the erythrocytes were determined using atomic force microscopy, and the expression of the cytoskeletal protein spectrin-α1 was analyzed via western blotting. The results showed that dynamic changes were evident in erythrocytes exposed to different doses of carbon ion beams compared with X-rays and the control (0 Gy). The magnitude of impairment of the cell number and cellular morphology manifested the subtle variation according to the irradiation dose. In particular, the differences in the size, shape and mechanical properties of the erythrocytes were well exhibited. Furthermore, immunoblot data showed that the expression of the cytoskeletal protein spectrin-α1 was changed after irradiation, and there was a common pattern among its substantive characteristics in the irradiated group. Based on these findings, the present study concluded that CIR could induce a change in mechanical properties during morphological remodeling of erythrocytes. According to the unique characteristics of the biomechanical categories, we deduce that changes in cytomorphology and mechanical properties can be measured to evaluate the adverse effects generated by tumor radiotherapy. Additionally, for the first time, the current study provides a new strategy for enhancing the assessment of the curative effects and safety of clinical radiotherapy, as well as reducing adverse effects.