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

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