Radiation-Induced Esophagitis In Vivo and In Vitro Reveals That Epidermal Growth Factor Is a Potential Candidate for Therapeutic Intervention Strategy

Abstract

To establish and characterize radiation-induced esophagitis (RIE) invivo and invitro. Fractionated thoracic irradiation at 0, 8, 12, or 15Gy was given daily for 5days to Balb/c or C57Bl/6 mice. Changes in body weight gain and daily food intake were assessed. At the end of the study, we removed the esophagus and examined histology by hematoxylin and eosin staining, immune cell infiltration and apoptosis by fluorescence-activated cell sorting, and gene expression changes by quantitative real-time polymerase chain reaction. Het-1A human esophageal epithelial cells were irradiated at 6Gy, treated with recombinant human growth factors, and examined for gene expression changes, apoptosis, proliferation, and signal transduction pathways. We observed that irradiation at 12Gy or 15Gy per fraction produced significant reduction in body weight and decreased food intake in Balb/c mice but not as much in C57Bl/6 mice. Further analyses of Balb/c mice irradiated at 12Gy/fraction revealed attenuated epithelium, inflamed mucosa, and increased numbers of infiltrating CD4+ helper Tcells and apoptotic cells. Moreover, we found that expression of tissue inhibitor for metalloproteinase-1, plasminogen activator inhibitor-1, granulocyte macrophage-colony stimulating factor, vascular endothelial growth factor, and stromal-derived factor-1 were increased, whereas epidermal growth factor (EGF) was decreased. Irradiated Het-1A cells similarly showed a significant decrease in expression of EGF and connective tissue growth factor (CTGF). Treatment of EGF but not CTGF partially protected Het-1A cells from radiation-induced apoptosis and revealed phosphorylation of EGFR, AKT, and ERK signaling pathways. We established a mouse model of RIE in Balb/c mice with 12Gy×5 fractions, which showed reduced body weight gain, food intake, and histopathologic features similar to those of human esophagitis. Decreased EGF expression in the irradiated esophagus suggests that EGF may be a potential therapeutic intervention strategy to treat RIE.