Local radiotherapy of exposed murine small bowel: apoptosis and inflammation

Abstract

Background: Preoperative radiotherapy of the pelvic abdomen presents with complications mostly affecting the small bowel. The aim of this study was to define the features of early radiation-induced injury on small bowel.

Methods: 54 mice were divided into two groups (36 irradiated and 18 sham irradiated). Animals were placed on a special frame and (in the radiated group) the exteriorized segment of ileum was subjected to a single absorbed dose of 19 or 38 Gy radiation using 6 MV high energy photons. Specimens were collected for histology, immunohistochemistry (IHC) and ELISA analysis after 2, 24 and 48 hours. Venous blood was collected for systemic leucocyte count in a Burker chamber.

Results: Histology demonstrated progressive infiltration of inflammatory cells with cryptitis and increased apoptosis. MIP-2 (macrophage inflammatory protein) concentration was significantly increased in irradiated animals up to 48 hours. No significant differences were observed in IL-10 (interleukin) and TNF-alpha (tumour necrosis factor) levels. IHC with CD45 showed a significant increase at 2 hours of infiltrating leucocytes and lymphocytes after irradiation followed by progressive decrease with time. Caspase-3 expression increased significantly in a dose dependent trend in both irradiated groups up to 48 hours.

Conclusion: Acute small bowel injury caused by local irradiation is characterised by increased apoptosis of crypt epithelial cells and by lymphocyte infiltration of the underlying tissue. The severity of histological changes tends to be dose dependent and may affect the course of tissue damage.

Figure 1

Cross section of intestinal wall 48 hrs after 19 Gy irradiation. An increase in apoptosis (A), intraepithelial granulocytes (B) and lymphocytes (C) was observed. The slides were stained with hematoxylin and eosin for histological evaluation under light microscopy, which was done by the pathologist in a blinded fashion.

Figure 2

Cross section of intestinal wall 48 hrs after 38 Gy irradiation. An increase in apoptosis (A), intraepithelial granulocytes (B) and lymphocytes (C) was observed with degenerative epithelium and granulocyte exudate in the lumen (between the villi and even in the crypts, suggesting cryptitis). The slides were stained with hematoxylin and eosin for histological evaluation under light microscopy, which was done by the pathologist in a blinded fashion.

Figure 3

Caspase-3 positive stained cells in small bowel tissue comparing sham and different doses of radiation within each time point. * denotes p < 0.05 compared to sham group, # denotes p < 0.05 compared to 19 Gy group.

Figure 4

CD45 positive stained cells in small bowel tissue comparing sham and different doses of radiation within each time point. * denotes p < 0.05 compared to sham group, # denotes p < 0.05 compared to 19 Gy group.

Figure 5

MIP-2 concentration in small bowel tissue comparing sham and different doses of radiation within each time point. * denotes p < 0.05 compared to sham group, # denotes p < 0.05 compared to 19 Gy group.