A C57L/J Mouse Model of the Delayed Effects of Acute Radiation Exposure in the Context of Evolving Multi-Organ Dysfunction and Failure after Total-Body Irradiation with 2.5% Bone Marrow Sparing

Abstract

The objective of the current study was to establish a mouse model of acute radiation syndrome (ARS) after total-body irradiation with 2.5% bone marrow sparing (TBI/BM2.5) that progressed to the delayed effects of acute radiation exposure, specifically pneumonitis and/or pulmonary fibrosis (DEARE-lung), in animals surviving longer than 60 days. Two hundred age and sex matched C57L/J mice were assigned to one of six arms to receive a dose of 9.5 to 13.25 Gy of 320 kV X-ray TBI/BM2.5. A sham-irradiated cohort was included as an age- and sex-matched control. Blood was sampled from the facial vein prior to irradiation and on days 5, 10, 15, 20, 25, and 30 postirradiation for hematology. Respiratory function was monitored at regular intervals throughout the in-life phase. Animals with respiratory dysfunction were administered a single 12-day tapered regimen of dexamethasone, allometrically scaled from a similar regimen in the non-human primate. All animals were monitored daily for up to 224 days postirradiation for signs of organ dysfunction and morbidity/mortality. At euthanasia due to criteria or at the study endpoint, wet lung weights were recorded, and blood sampled for hematology and serum chemistry. The left lung, heart, spleen, small and large intestine, and kidneys were processed for histopathology. A dose-response curve with the estimated lethal dose for 10–99% of animals with 95% confidence intervals was established. The median survival time was significantly prolonged in males as compared to females across the 10.25 to 12.5 Gy dose range. Animal sex played a significant role in overall survival, with males 50% less likely to expire prior to the study endpoint compared to females. All animals developed pancytopenia within the first one- to two-weeks after TBI/BM2.5 followed by a progressive recovery through day 30. Fourteen percent of animals expired during the first 30-days postirradiation due to ARS (e.g., myelosuppression, gastrointestinal tissue abnormalities), with most deaths occurring prior to day 15. Microscopic findings show the presence of radiation pneumonitis as early as day 57. At time points later than day 70, pneumonitis was consistently present in the lungs of mice and the severity was comparable across radiation dose arms. Pulmonary fibrosis was first noted at day 64 but was not consistently present and stable in severity until after day 70. Fibrosis was comparable across radiation dose arms. In conclusion, this study established a multiple organ injury mouse model that progresses through the ARS phase to DEARE-lung, characterized by respiratory dysfunction, and microscopic abnormalities consistent with radiation pneumonitis/fibrosis. The model provides a platform for future development of medical countermeasures for approval and licensure by the U.S. Food and Drug Administration under the animal rule regulatory pathway.

Delayed effects of radiation exposure in a C57L/J mouse model of partial body irradiation with ~2.5% bone marrow shielding

“…Chronic kidney disease following irradiation develops clinically, and both PBI rat ( 23 ) and PBI NHP ( 20 ) models develop K-DEARE either concurrent to, or following, L-DEARE. In the C57L/J mouse model described herein, there is a lack of evidence for the development of K-DEARE, and this is consistent with the similar C57L/J model developed by Gibbs et al ( 10 ). Histopathology findings of were primarily of minimal tubule degeneration.…”

“…In the PBI L/J model presented here, hematopoietic atrophy and gastrointestinal necrosis are clearly observed in the hematology values and histopathology tissues collected from ARS moribund mice (Figure 6B). These are welldocumented, deterministic events common to PBI resulting in Hand GI-ARS for both the C57BL6 (21), and C57 L/J (10).…”

“…The acute radiation response in the PBI BM2.5 C57L/J mouse model shows many characteristics common to TBI and PBI models of H- and GI-ARS in other strains of mice, in rats, and non-human primates. Leukocytopenia just days after irradiation is a common finding in TBI C57BL6 mice ( 16 ) and rhesus macaques ( 17 ), PBI C57BL6 ( 18 ), and C57 L/J ( 10 ) mice, Wistar rats ( 15 ) and rhesus macaques ( 19 , 20 ). In the PBI L/J model presented here, hematopoietic atrophy and gastrointestinal necrosis are clearly observed in the hematology values and histopathology tissues collected from ARS moribund mice ( Figure 6B ).…”

“…The objective of this manuscript is to describe the natural history of radiation injury in C57L/J mice and generate probit estimates for lethality after PBI. The C57L/J strain is of interest because it has been shown to reliably develop L-DEARE following PBI with bone marrow sparing ( 10 ), TBI + whole thorax lung irradiation (WTLI) ( 11 ), and in the WTLI only ( 12 ) model, using exposures that do not result in a high degree of ARS associated mortality. Furthermore, earlier studies have shown that the L/J strain reflects the pathological features of human radiation lung injury to a greater degree than mouse strains such as the C57BL6/J, C3H, CBA, C57BR/J, BALB/c, and A/J ( 12 – 14 ).…”

High Doses of Radiation Cause Cochlear Immunological Stress and Sensorineural Hearing Loss

“…By day 10, some of the mice had lost more than 30 percent of their body weight and showed signs of multiple organ failure, such as navicular abscesses, coarse hair, sunken eyeballs, and erratic gait. The severity of systemic adverse reactions may be related to animal susceptibility to radiation and individual differences [19].…”