Murine Radiation-Induced Stomach Pathology from Whole Thoracic Irradiation

PurposeRadiation-induced lung injury is a common side effect in the treatment of lung and breast cancers. There is a large focus in the field on leveraging mouse models of radiation-induced lung injury to find novel treatments for the condition. While attempting to irradiate mouse lungs for purposes of creating a radiation-induced pulmonary fibrosis model, noticeable declines in health were observed at much earlier time points than recorded for lung pathology. This was later attributed to stomach pathology observed in CT images and ex vivo dissection.MethodsFor this study, we used longitudinal microCT to characterize male C57Bl/6 mice irradiated with a single dose of 20 Gy to the whole thoracic area delivered by an X-Rad cabinet irradiator. CT was performed with respiratory gating at 2 to 4 week timepoints to construct a timeline of pathology leading up to fibrosis and quantify severity of fibrosis afterwards. However, a mouse imaged at the 10 week timepoint showed evidence of stomach distention. These mice were sacrificed and their stomachs removed. Histology was performed on the stomachs using H&E staining.ResultsOn the CT images, we observed a large, spherical volume of hypointense signal, caudal to the lungs (Figure 1). This correlated with a distended stomach caused by constipation and gas build-up within the stomach. Statistical analysis showed 81% of mice (n=105) died prematurely after irradiation and before significant development of pulmonary fibrosis. Mice sacrificed and dissected showed unpassed bolus as contents of the stomach, and histology showed cell necrosis of the stomach walls.ConclusionThe histology indicated an inability for food to be digested and moved into the small intestine. This lead to a blockage and ensuing stomach distention. Given the severity of the pathology’s consequences, it lead to the mouse’s imminent mortality inhibiting the efficacy of the study. Future studies need to consider careful placement of shields or any beam contouring devices to ensure protection of the stomach given its higher radiosensitivity in contrast to the lungs.

A modified bioassay for heat-stable Escherichia coli enterotoxin

Infant mice were injected orally with preparations containing Escherichia coli heat-stable enterotoxin (ST) and Evans blue dye, and incubated at 22 °C. With enterotoxin-positive samples, the stomach was distended and contained essentially all of the dye. With enterotoxin-negative samples, the stomach remained normal in size and the dye passed freely into the intestines. The time required to obtain the maximum ratio of gut weight to body weight varied from 30 to 90 min and was dependent upon the concentration of enterotoxin. Heat-labile enterotoxin (LT) had no effect during this period.Based on these findings, the mouse incubation time was reduced from 4 h to 90 min, and the heating of test samples was retained only for confirmation of ST. The location of the dye and stomach distention served as an indicator of positive responses to ST. Incubation of the mice at room temperature (22 °C) was found satisfactory.