Establishing a Mouse Model for Radiation Induced Esophagitis

To establish mouse models of radiation-induced esophagitis with fractionated irradiation using BALB/c or C57Bl/6 mice. Thoracic irradiation at 0, 8, 12, or 15 Gy was given daily for 5 days by 320 kV X-ray irradiator to 6-week-old male BALB/c (n = 4∼5 per group) or C57Bl/6 mice (n = 4 per group). Changes in the body weight and daily food intake were assessed for both strains of mice. At day 11, BALB/c esophagus was harvested and examined for the following assays: 1) histology by H&E staining; 2) cytokine array; 3) fluorescence-activated cell sorting (FACS) analysis by using Annexin V and propidium iodide (PI); and 4) quantitative real time-PCR (qRT-PCR) analysis. We observed that fractionated irradiation produced a significant body weight reduction in Balb/c mice (20% by 12 Gy × 5 and 30% by 15 Gy × 5). In contrast, C57Bl/6 mice seemed to be more resistant to fractionation irradiation as they exhibited little change in the body weight. As food intake in Balb/c mice was also significantly decreased at these doses compared to the control mice (P < .05 for 12 Gy × 5 and P < 0.01 for 15 Gy × 5), dose of 12 Gy × 5 were selected for all assays. Histopathology of irradiated Balb/c mice showed erosive epithelium, mucosal detachment, and leukocyte infiltration. Florescence-activated cell sorting analysis confirmed that irradiated esophagus had increased number of apoptotic cells, as evidenced by Annexin V and PI double positivity. We found that cytokines for C5/C5a, Timp-1 (tissue-inhibitor of metalloproteinases-1), Ccl2/Mcp-1 (monocyte chemoattractant protein-1), and IL-16 (interleukin-16) were increased in the irradiated esophagus compared to non-irradiated esophagus; qRT-PCR analyses revealed that Timp-1 as well as other genes involved in extracellular matrix remodeling including Pai-1 (plasminogen activator inhibitor-1), Gm-csf (granulocyte macrophage-colony stimulating factor), Vegf (vascular endothelial growth factor), and Sdf-1 (stromal-derived factor-1) were increased; whereas, Egf (epidermal growth factor), a potent mitogen for epithelial cells, was significantly decreased in the esophagus of irradiated mice. We established that BALB/c mice were more sensitive to fractionated irradiation than C57Bl/6 mice for developing symptoms reflecting radiation-induced esophagitis. In BALB/c mice, 12 Gy × 5 regimen seem to be the best schedule producing a significant reduction in the body weight and food intake, and histopathologic features similar to human esophagitis. Increased RNA transcripts for extracellular remodeling and cytokines indicate an active dynamics of tissue remodeling in the irradiated esophagus. Decreased Egf expression in the irradiated esophagus suggests that EGF may be a potential therapeutic strategy to treat radiation-induced esophagitis, and we are currently investigating this strategy.