Effect of the Diabetic State on Islet Engraftment and Function in a Large Animal Model of Islet-Kidney Transplantation.

In islet transplantation, in addition to immunologic and ischemic factors, the diabetic/hyperglycemic state of the recipient has been proposed, although not yet validated, as a possible cause of islet toxicity, contributing to islet loss during the engraftment period. Using a miniature swine model of islet transplantation, we have now assessed the effect of a persistent state of hyperglycemia on islet engraftment and subsequent function. An islet-kidney (IK) model previously described by our laboratory was utilized.

Assessing the effect of immunosuppression on engraftment of pancreatic islets.

Background: In addition to ischemia and immunologic factors, immunosuppressive drugs have been suggested as a possible contributing factor to the loss of functional islets after allogeneic islet cell transplantation. Using our previously described islet-kidney (IK) transplantation model in miniature swine, we studied whether an islet-toxic triple-drug immunosuppressive regimen (cyclosporine+azathioprine+prednisone) affects the islet engraftment process and thus long-term islet function.

Methods: Donor animals underwent partial pancreatectomy, autologous islet preparation, and injection of these islets under the autologous kidney capsule to prepare an IK.

Quantitative analysis of cell composition and purity of human pancreatic islet preparations.

Despite improvements in outcomes for human islet transplantation, characterization of islet preparations remains poorly defined. This study used both light microscopy (LM) and electron microscopy (EM) to characterize 33 islet preparations used for clinical transplants. EM allowed an accurate identification and quantification of cell types with measured cell number fractions (mean±s.

Activation of pancreatic-duct-derived progenitor cells during pancreas regeneration in adult rats.

The adult pancreas has considerable capacity to regenerate in response to injury. We hypothesized that after partial pancreatectomy (Px) in adult rats, pancreatic-duct cells serve as a source of regeneration by undergoing a reproducible dedifferentiation and redifferentiation. We support this hypothesis by the detection of an early loss of the ductal differentiation marker Hnf6 in the mature ducts, followed by the transient appearance of areas composed of proliferating ductules, called foci of regeneration, which subsequently form new pancreatic lobes.

In vivo imaging of autologous islet grafts in the liver and under the kidney capsule in non-human primates.

Objective: As islet transplantation begins to show promise as a clinical method, there is a critical need for reliable, noninvasive techniques to monitor islet graft survival. Previous work in our laboratory has shown that human islets labeled with a superparamagnetic iron oxide contrast agent and transplanted into mice could be detected by magnetic resonance imaging (MRI). The potential translation of these findings to the clinical situation requires validation of our methodology in a non-human primate model, which we have now carried out in baboons (Papio hamadryas) and reported here.

Pig islet xenograft rejection in a mouse model with an established human immune system.

Background: Xenotransplantation from pigs provides a potential solution to the severe shortage of human pancreata, but strong immunological rejection prevents its clinical application. A better understanding of the human immune response to pig islets would help develop effective strategies for preventing graft rejection.

Methods: We assessed pig islet rejection by human immune cells in humanized mice with a functional human immune system.

Direct and indirect effects of insulin on hepatic glucose production in diabetic depancreatized dogs during euglycemia.

Insulin suppresses glucose production (GP) via both extrahepatic (indirect) and hepatic (direct) effects. We have shown that the direct effect, undetectable in moderately hyperglycemic diabetic dogs, is restored by insulin-induced euglycemia. The first aim of the present study was to determine whether euglycemia per se, and not the excess insulin needed to obtain it, restores the direct effect of insulin on GP.

Oleate-induced decrease in hepatocyte insulin binding is mediated by PKC-delta.

We have previously shown that free fatty acids (FFA) impair hepatic insulin extraction in vivo and thus generate hyperinsulinemia, a suspected risk factor for atherosclerosis and cancer. Hepatic insulin extraction is a receptor-mediated event, which is initiated by hepatocyte insulin binding. In the present study, we investigated the effect of FFA on insulin binding in freshly isolated rat hepatocytes maintained at 10 mM glucose.

Bilirubin can induce tolerance to islet allografts.

Induction of heme oxygenase-1 (HO-1) expression in recipients of allogeneic islets can lead to long-term survival (>100 d) of those islets. We tested whether administration of bilirubin would substitute for the beneficial effects of HO-1 expression in islet transplantation. Administering bilirubin to the recipient (B6AF1) or incubating islets in a bilirubin-containing solution ex vivo led to long-term survival of allogeneic islets in a significant percentage of cases.

Long-term normoglycemia in rats receiving transplants with encapsulated islets.

Background: To follow up on previously successful transplantation of encapsulated islets in mice, the present study was performed in rats to determine the effects of several factors, including alginate composition and concentration of cross-linking agent and capsule size on the effectiveness of encapsulated islets.

Methods: Highly purified alginate of either high guluronic acid or high mannuronic acid (M) with low endotoxin content was used. Regular-size (0.

A simple and cost-effective method for the isolation of islets from nonhuman primates.

Recent advances in islet cell transplantation have led to insulin independence in a majority of islet transplant recipients. However, there exists a need to overcome the shortage of donor tissue and the necessity for life-long immunosuppression. Preclinical studies in large animal models are necessary to evaluate the safety and efficacy of alternative approaches for clinical islet transplantation.

Exercise induces hypoglycemia in rats with islet transplantation.

Recently, islet transplantation in patients with type 1 diabetes has had greater success than in the past, but the important question of whether the kinetics of islet secretion are able to accommodate the metabolic demands of special conditions such as exercise remains unanswered. Syngeneic rat islets (4,000 islet equivalents/rat) were transplanted into the liver, kidney, and peritoneal cavity (encapsulated or nonencapsulated) of rats with streptozocin-induced diabetes. Normoglycemic transplanted rats and age-matched controls were subjected to 30 min of moderate exercise on a treadmill 5 weeks after transplantation.

Genetic engineering of a suboptimal islet graft with A20 preserves beta cell mass and function.

Transplantation of an excessive number of islets of Langerhans (two to four pancreata per recipient) into patients with type I diabetes is required to restore euglycemia. Hypoxia, nutrient deprivation, local inflammation, and the beta cell inflammatory response (up-regulation of NF-kappaB-dependent genes such as inos) result in beta cell destruction in the early post-transplantation period. Genetic engineering of islets with anti-inflammatory and antiapoptotic genes may prevent beta cell loss and primary nonfunction.

Insulin inhibits glucose production by a direct effect in diabetic depancreatized dogs during euglycemia.

In our previous studies in nondiabetic dogs and humans, insulin suppressed glucose production (GP) by both an indirect extrahepatic and a direct hepatic effect. However, insulin had no direct effect on GP in diabetic depancreatized dogs under conditions of moderate hyperglycemia. The present study was designed to investigate whether insulin can inhibit GP by a direct effect in this model under conditions of euglycemia.