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

MICROBIOME AND INFLAMMASOME ALTERATIONS FOUND DURING RADIATION DOSE FINDING IN A SINCLAIR MINIPIG MODEL OF GASTROINTESTINAL ACUTE RADIATION SYNDROME

ABSTRACT

Both abdominal radiotherapy and a nuclear event can result in gastrointestinal symptoms, including acute radiation syndrome (GI-ARS). GI-ARS is characterized by compromised intestinal barrier integrity increasing the risk for infectious complications. Physiologically relevant animal models are crucial for elucidating host responses and therapeutic targets. We aimed to determine the radiation dose requirements for creating GI-ARS in the Sinclair minipig. Male, sexually mature swine were randomly divided into sham (n = 6) and three lower hemibody radiation dosage groups of 8, 10, and 12 Gy (n = 5/group) delivered using linear accelerator-derived x-rays (1.9 Gy/min). Animals were monitored for GI-ARS symptoms for 14 days with rectal swab and blood collection at days 0-3, 7, 10, and 14 followed by necropsy for western blotting and histology. Dose-dependent increases in weight loss, diarrhea severity, and mortality (log-rank test, P = 0.041) were seen. Villi length was significantly reduced in all irradiated animals compared to controls ( P < 0.001). Serum citrulline decreased and bacterial translocation increased after irradiation compared to controls. Increased NLRP3 levels in post-mortem jejunum were seen ( P = 0.0043) as well as increased IL-1β levels in the 12 Gy group ( P = 0.041). Radiation dose and survival were associated with significant gut microbial community shifts in beta diversity. Moreover, decedents had increased Porphyromonas, Campylobacter, Bacteroides , Parvimonas , and decreased Fusobacterium and decreased Aerococcus, Lactobacillus, Prevotella, and Streptococcus . Our novel Sinclair minipig model showed dose-dependent clinical symptoms of GI-ARS. These findings provide invaluable insights into the intricate interplay between GI-ARS, intestinal inflammation, and gut microbiota alterations offering potential targets for therapeutic and diagnostic interventions after radiation exposure.

Acute Radiation Syndrome and the Microbiome: Impact and Review

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

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.