Evidence of Functional Impairment of Syngeneically Transplanted Mouse Pancreatic Islets Retrieved from the Liver

Abstract

A drawback in pancreatic islet transplantation is the large number of islets needed to obtain insulin independence in patients with diabetes. This most likely reflects extensive posttransplantation islet cell death and functional impairment of the remaining endocrine cells. We aimed to develop an experimental method to retrieve transplanted islets from the mouse liver, which would enable comparisons of transplanted and endogenous islets and provide valuable information on functional changes induced by intraportal transplantation. Transplanted islets were obtained by retrograde perfusion of the liver with collagenase. The identity of retrieved tissue as transplanted islets was confirmed by intravital staining, immunohistochemistry, and electron microscopy. The retrieved islets, irrespective of whether they had resided in diabetic or nondiabetic recipients, had a markedly lower insulin content and glucose-stimulated insulin release when compared with isolated endogenous islets. The glucose oxidation rate was also markedly lower in the retrieved islets, suggesting mitochondrial dysfunction. These disturbances in insulin content, insulin release, and glucose oxidation rate were not reversed by a few days of culture after retrieval. The results implicate changes in islet function after intraportal transplantation. Such dysfunction may contribute to the high number of islets needed for successful transplantation in diabetic individuals. Diabetes 53:948 -954, 2004 R ecent modifications in islet allotransplantation protocols, such as immunosuppressive treatment regimens without steroids and cyclosporine, as well as repeated transplantations to increase the implanted endocrine mass, have substantially increased the number of patients who achieve insulin independence (1-3). However, that two to three transplantations are usually needed to reverse hyperglycemia in humans suggests that the liver does not provide optimal conditions for engraftment. Indeed, although Ͼ85% of the normal islet mass (4) was transplanted when applying the Edmonton protocol, the insulin response to glucose in these patients was only ϳ20%, whereas the insulin response to arginine (ATP independent) was ϳ45% of that seen in healthy individuals (3,5). This suggests that islet cell death occurs in the immediate posttransplantation period (6,7) but may also indicate a functional impairment in the surviving endocrine cells.Experimental investigations (8 -11) on the endocrine function of intraportally transplanted islets have previously been performed by perfusion of whole rat livers containing transplanted islets. Even though this is an elegant approach, it does not enable functional comparisons to be made between endogenous and transplanted islets. Because the volume of the surviving islet mass is unknown, the contribution of islet death versus dysfunction of remaining islets to a poor insulin response is impossible to evaluate. Thus, to approach this problem of functional evaluation of intraportally implanted islets, we applied methods for enzymatic bre...

Improved vascular engraftment and function of autotransplanted pancreatic islets as a result of partial pancreatectomy in the mouse and rat

“…Interestingly, we recently observed that islets implanted into the kidney and the liver both have a decreased first phase of insulin release in response to glucose as compared with native islets [39]. This impaired insulin release in control islet grafts may reflect disturbances in the secretory machinery of beta cells [49,50]. It should be noted that islet endothelial cells can directly stimulate beta cell insulin secretion through paracrine effects [40].…”

Permanent Survival of Fully MHC-Mismatched Islet Allografts by Targeting a Single Chemokine Receptor Pathway

“…Clinically, islets are currently transplanted into the liver via the portal vein (27), although some data suggest this is far from an optimal site for engraftment (28,29). The current studies indicate that if donor DC or passenger leukocytes are unable to migrate to secondary lymphoid tissues as a result of lack of expression of CCR7 ligands, islet allografts are accepted long-term, whereas if these cells enter the vasculature rather than the lymphatic system they are able to home to the spleen and elicit standard allograft responses.…”

Beneficial Role of Pancreatic Microenvironment for Angiogenesis in Transplanted Pancreatic Islets

“…However, recipient blood vessels attracted to the islets rarely enter the endo-(38). It is possible that the observed findings of selective poor revascularization of heterotopic implants reflect the crine tissue in this setting (19,21). This suggests location of matrix or tissue-bound angiostatic factors within the inhibitory influences of such guidance proteins to foreign-organ endothelial cells.…”

“…Currently, extensive islet cell significant after correction. death occurs in the immediate posttransplantation period (2,3,10,11), as well as a functional impairment in the RESULTS surviving endocrine cells (16,21).Our previous studies have shown that heterotopically implanted islets become The YC-3.0 islets retained their EYFP expression and remained at least 6 months after intrapancreatic transpoorly revascularized. Similar results were obtained irrespective of whether the islets were implanted beneath plantation (two out of two animals).…”