Is the loss of endothelial thrombomodulin involved in the mechanism of chronicity in late radiation enteropathy?

Abstract

Radiation enteropathy is characterized by locally elevated levels of inflammatory and fibrogenic cytokines. Microvascular injury may sustain these alterations through persistent local hypercoagulopathy, platelet aggregation, leukocyte adhesion and release of biologically active mediators. This study assessed the relationship of endothelial thrombomodulin (TM), a key regulator of the protein C anticoagulant pathway and marker of endothelial function, with transforming growth factor beta (TGF-beta) immunoreactivity and morphologic alterations in radiation enteropathy. Small bowel resection specimens from 9 patients with radiation enteropathy were analyzed by computerized quantitative immunohistochemistry using antibodies against TM, von Willebrand factor (vWF) and TGF-beta. Identical measurements were performed on intestinal resection specimens from otherwise healthy penetrating trauma victims and on archived small intestines. A previously validated image analysis technique was used to assess submucosal vessels for TM and vWF immunoreactivity, and the intestinal wall for total extracellular matrix-associated TGF-beta immunoreactivity. Specimens from irradiated patients showed prominent submucosal and subserosal thickening and fibrosis, and obliterative vasculopathy. Control specimens were histopathologically normal. Vascular density and vWF immunoreactivity were similar in radiation enteropathy patients and controls. The image-analysis techniques were highly reproducible, with correlation coefficients for repeated measurements ranging from 0.86 to 0.93. Radiation enteropathy specimens exhibited a highly significant reduction in the number and proportion of TM-positive submucosal vessels per unit area (P < 0.0001) and increased intestinal wall TGF-beta immunoreactivity (P = 0.002). These data support the theory that sustained endothelial dysfunction is involved in the molecular pathogenesis of radiation enteropathy, and point to TM as important in the chronic nature of radiation enteropathy and a potential target for prophylactic and therapeutic interventions.