Increased transforming growth factor β (TGF-β) immunoreactivity is independently associated with chronic injury in both consequential and primary radiation enteropathy

Purpose : Radiation enteropathy is characterized by sustained increase in transforming growth factor β (TGF-β) immunoreactivity and connective tissue mast cell (CTMC) hyperplasia that may be responsible for progressive fibrosis and lead to clinical complications. We examined to what extent these chronic molecular and cellular phenomena are associated with acute mucosal breakdown (consequential injury) and/or direct (primary) radiation injury in late-responding compartments. Methods and Materials : Rat small intestine was exposed to 50.4 Gy x-irradiation given either over 18 days (2.8 Gy daily or 5.6 Gy every other day) or 9 days (2.8 Gy twice daily or 5.6 Gy daily). Intestinal complications were recorded and groups of animals were euthanized at 2 and 26 weeks to assess subacute and chronic injury. Histopathologic changes were assessed with a radiation injury scoring system (RIS), total TGF-β immunoreactivity was quantified with computerized image analysis, and CTMC hyperplasia was assessed' in toluidine bluestained sections. Results : TGF-β immunoreactivity and CTMC hyperplasia colocalized in areas of injury and were highly significantly correlated. Increased fraction size and decreased overall treatment time were associated with increased RIS ( p < 0.01 and p < 0.00001), increased TGF-β immunoreactivity ( p = 0.01 and p < 0.001), and degree of CTMC hyperplasia ( p = 0.01 and p < 0.001). Postradiation CTMC numbers increased across treatment groups from 2 to 26 weeks ( p < 0.01). TGF-β immunoreactivity was independently associated with chronic intestinal wall fibrosis ( p = 0.003). Conclusion : This in vivo study supports in vitro evidence linking increased TGF-β immunoreactivity and mast cell hyperplasia and strongly suggests their involvement in the molecular pathogenesis of both primary and consequential radiation enteropathy.