The Pig as the Donor of Pancreatic Islets for Men

The islet size to oxygen consumption ratio reliably predicts reversal of diabetes posttransplant

β-Cell replacement therapy by either whole-organ pancreas or islets of Langerhans transplantation can restore carbohydrate control to diabetic patients and reduces complications associated with the disease. One of the variables inherent in islet transplantation is the isolation of functional islets from donor pancreata. Islet isolations fail to consistently produce good-quality functional islets. A rapid pretransplant assay to determine posttransplant function of islets would be an invaluable tool. We have tested the novel hypothesis that modified oxygen consumption rates (OCR), standardized to DNA quantity (nmol/min-mg DNA), would serve as a pretransplant assessment of the metabolic potency of the islets postisolation. This study compares the ability of current in vitro assays to predict in vivo restoration of normoglycemia in a diabetic nude mouse posttransplantation of adult pig islets. There is known to be a diversity of islet sizes within each preparation. This parameter has not heretofore been effectively considered a critical factor in islet engraftment. Our results suggest a surprising finding that islet size influences the probability of restoring carbohydrate control. Based on this observation, we thus developed a novel predictor of islet graft function that combines the effects of both islet OCR and size. When OCR was divided by the islet index (size), a highly significant predictor of graft function was established (p = 0.0002, n = 75). Furthermore, when OCR/islet index values exceeded 70.0 nmol/min-mg DNA/islet index, an effective threshold of diabetes reversal was observed. This assay can be performed with as few as 1,000 islet equivalents (IEQ) and conducted in less than 60 min. Our data suggest that, using this novel method to assess islet cell function prior to transplantation, OCR/islet index thresholds provide a valuable tool in identifying which islet preparations are most likely to restore glycemic control posttransplant.

Stem cell-based treatments for Type 1 diabetes mellitus: bone marrow, embryonic, hepatic, pancreatic and induced pluripotent stem cells

Type 1 diabetes mellitus--characterized by the permanent destruction of insulin-secreting β-cells--is responsive to cell-based treatments that replace lost β-cell populations. The current gold standard of pancreas transplantation provides only temporary independence from exogenous insulin and is fraught with complications, including increased mortality. Stem cells offer a number of theoretical advantages over current therapies. Our review will focus on the development of treatments involving tissue stem cells from bone marrow, liver and pancreatic cells, as well as the potential use of embryonic and induced pluripotent stem cells for Type 1 diabetes therapy. While the body of research involving stem cells is at once promising and inconsistent, bone marrow-derived mesenchymal stem cell transplantation seems to offer the most compelling evidence of efficacy. These cells have been demonstrated to increase endogenous insulin production, while partially mitigating the autoimmune destruction of newly formed β-cells. However, recently successful experiments involving induced pluripotent stem cells could quickly move them into the foreground of therapeutic research. We address the limitations encountered by present research and look toward the future of stem cell treatments for Type 1 diabetes.

The Choice of Anatomical Site for Islet Transplantation

Islet transplantation into the portal vein is the current clinical practice. However, it has now been recognized that this implantation site has several characteristics that can hamper islet engraftment and survival, such as low oxygen tension, an active innate immune system, and the provocation of an inflammatory response (IBMIR). These factors result in the loss of many transplanted islets, mainly during the first hours or days after transplantation, which could in part explain the necessity for the transplantation of islets from multiple pancreas donors to cure type 1 diabetes. This increases the burden on the limited pool of donor organs. Therefore, an alternative anatomical site for islet transplantation that offers maximum engraftment, efficacious use of produced insulin, and maximum patient safety is urgently needed. In this review, the experience with alternative sites for islet implantation in clinical and experimental models is discussed. Subcutaneous transplantation guarantees maximum patient safety and has become clinically applicable. Future improvements could be achieved with innovative designs for devices to induce neovascularization and protect the islets from cellular rejection. However, other sites, such as the omentum, offer drainage of produced insulin into the portal vein for direct utilization in the liver. The use of pigs would not only overcome the shortage of transplantable islets, but genetic modification could result in the expression of human genes, such as complement regulatory or “anticoagulation” genes in the islets to overcome some site-specific disadvantages. Eventually, the liver will most likely be replaced by a site that allows long-term survival of islets from a single donor to reverse type 1 diabetes.