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...

In previous studies we have shown that apparently normal human islets, transplanted under the renal capsule of nude mice, frequently and rapidly develop amyloid deposits derived from the -cell hormone islet amyloid polypeptide (IAPP). In the present study, we show for the first time that human islets, transplanted into the liver or spleen of nude mice, also develop islet amyloid rapidly. Ultrastructural studies of such islets showed that the first aggregation of IAPP takes place within thecells and that extracellular deposits show up later in the amyloid formation process. We also found that the amount of amyloid formed in human islet grafts placed under the kidney capsule increased with extended (26 weeks) observation time. Moreover, prolonged in vitro culture (14 days) prior to the implantation under the renal capsule seemed to enhance the formation of amyloid in the grafted islets. Since aggregated IAPP has been shown to be toxic to -cells, the finding of amyloid deposits in transplanted islets offers a possible explanation to the frequent loss of function of islets transplanted into diabetic patients.

The vascular density is decreased in islets implanted to cure diabetic recipients. No improvement occurs in transplanted islets after 1 month posttransplantation.

The transplantation of microencapsulated islets may allow reversal of hyperglycemia in the absence of immunosuppression. Poly-L-lysine (PLL) on capsules may potentiate the fibrotic reaction against implanted capsules. The aims of this study were to investigate how the biocompatibility of such capsules affects their function in vivo and to compare their efficacy relative to naked islets after intraperitoneal transplantation to nude or immune competent mice. Alloxan-diabetic C57BL/6 wild-type or nude (nu/nu) mice were transplanted with naked BALB/c islets, empty capsules, or microencapsulated BALB/c islets. Three types of capsules were used, one containing a high guluronic acid (G) alginate and PLL, one with a high mannuronic acid (M) alginate and PLL, and one high M alginate capsule with no PLL. Hyperglycemia in nude mice was reversed after transplantation of naked islets or islets encapsulated in a capsule containing high M alginate. Nude mice transplanted with islets encapsulated in the high G capsules showed only a transient reversal of hyperglycemia. In an allogeneic system, naked BALB/c islets were rejected by day 10 after transplantation, whereas the islets encapsulated in high M capsules continued to function for at least a month. When PLL was excluded from the capsules, the grafts functioned for up to 8 weeks. Islets microencapsulated in high G alginate capsules fail to reverse hyperglycemia for more than a few days in nude mice. However, islets in high M alginate capsules can reverse hyperglycemia in nude and immune competent mice. Islets microencapsulated in PLL-free high M alginate capsules function for 8 weeks in immune competent mice.