Introduction: Graft cold storage and subsequent reperfusion during small bowel transplantation result in various degrees of mucosal injury ranging from mild edema to extensive mucosal loss. Mucosal barrier impairment favors bacterial translocation and fluid loss and raises nutritional challenges. Moreover, injured enterocytes can produce and release proinflammatory mediators and upregulate various epitopes towards an inflammatory phenotype. We studied the process of mucosal injury and repair during the early period after intestinal transplantation from a histological and molecular standpoint.

Methods: Three months old, Sprague Dawley male rats were used as donors and recipients. Donor intestines were perfused and stored in saline for 3 hours, then transplanted heterotopically using microvascular anastomoses. Small bowel graft segments were obtained after preservation, and at 20 minutes, 12 hours and 24 hours after reperfusion. Histology studies (Chiu score, Goblet cell count, morphometry, immunohistochemistry) and ddPCR for tight junctions (tricellulin, claudin-3), apoptosis (Bax, Bcl-2) and inflammation (IL-6, ICAM-1, TLR-4, TLR-9) were performed.

Results: Cold storage lead to extensive epithelial detachment (corresponding to Chiu grade 3) and reperfusion lead to extensive villus loss (about 50 % of the initial villus length, Chiu grade 5). Goblet cells showed a significant reduction (p<0.01). All these parameters ceased to differ significantly compared to normal intestines after 24 hours of reperfusion. However the villi appeared shorter and broader than in normal intestines and total mucosal voljme was reduced. Bax, Bcl-2, IL-6, ICAM-1 and TLR4 mRNA levels were lower after 24 hours compared with immediately after reperfusion. mRNA for tight junction proteins tricelllulin and claudin-3 remained lower than in normal intestines.

Discussion: The current data suggest that early mucosal recovery after intestinal transplantation is mainly due to cell migration and lamina propria remodeling rather than enterocyte proliferation. This rapid phenomenon seems to be accompanied by a local downregulation of the inflammatory response. The very rapid recovery of the rat intestine following moderate/severe reperfusion injury needs to be considered when designing intestinal transplant experiments and choosing sampling and end points.