Large animal models in intestinal transplantation

The pig as a preclinical model for intestinal ischemia-reperfusion and transplantation studies

Small bowel transplantation has become an established procedure for treatment of irreversible intestinal failure. In this procedure, primary ischemia and reperfusion is inevitable and will lead to some level of tissue injury. Both clinical and experimental data demonstrate that events occurring at the time of transplantation, called ischemia reperfusion injury (IRI), may have deleterious short- and long-term effects, manifesting as increased episodes of acute rejection and chronic allograft dysfunction. Recently, the acute phase of IRI has been increasingly viewed as part of the innate immune response to the lack of vascular perfusion and oxygen. Research on intestinal IRI that aims to understand its mechanisms and the means to reduce its impact on morbidity and mortality related to intestinal transplantations is considered important because a link has been suggested between innate immunity, adaptive immune responses and organ regeneration, and thus long-term graft function. This article provides an overview of porcine models commonly used to study intestinal reperfusion injury and to evaluate intestinal transplant protocols. It also updates the current knowledge obtained from this model, establishing the pig as a reference standard in intestinal transplantation research.

Surgical technique for combined intestine-auxiliary liver transplantation in rats: development of a new microsurgical model

Combined liver-intestine transplantation is an evolving procedure, and auxiliary liver transplantation has several advantages over standard orthotopic liver transplantation. We present a new model of combined intestine-auxiliary liver transplantation in rats. Total small bowel and 60% liver were harvested en bloc. An aortic segment that contained the celiac axis and superior mesenteric artery ensured blood supply to the graft. Venous drainage of the grafted intestine was achieved via the intact portal vein of the graft. The infrahepatic vena cava was cut at different levels during the modification period and at the oblique level of the left renal vein in consecutive series. Revascularization was accomplished by end-to-side anastomosis of the aorta and of the infrahepatic vena cava. The recipient small bowel was resected and the intestine continuity restored by anastomosis. Total operation time averaged 130 min. The overall survival rate of 3 months in the consecutive series was 80% (16/20). Exploratory laparatomy and histologic study in 3 rats on 90 days after transplantation revealed normal and viable grafts. Liver function was normal and both grafted liver and intestine showed normal histologic architectures in 5 rats observed for 12 months after transplantation. The present model is reproducible and allows preclinical research on several aspects of experimental combined intestine-auxiliary liver transplantation.

Small bowel transplantation

The development of small bowel transplantation has long been hindered by the immunological and infectious barriers peculiar to the small bowel. Gradual progress has been achieved during the past decade with the use of tacrolimus and the availability of better anti-infection prophylaxis. The current status of small bowel transplantation as a life-saving option for patients failing on total parenteral nutrition and those who have developed irreversible liver failure is undisputed. Small bowel transplantation can be performed as either an intestine-only graft or as part of a composite graft with the liver and, on occasion, other organs. The various techniques of donor and recipient operations are relatively standardized. Despite the progress made, the most common causes of death and graft loss continue to be sepsis, rejection, and lymphomas. Further progress can be achieved by development of more effective immunosuppressive and immunomodulatory strategies. The role of inducing chimerism by adjuvant donor-specific bone marrow transfusions to promote graft tolerance is uncertain. Until the mortality and graft losses are further reduced, the role of small bowel transplantation will be limited to a salvage procedure for failure of total parenteral nutrition rather than a primary treatment of intestinal failure.