Clinical islet transplant--state of the art

Polyphenol, an Extract of Green Tea, Increases Culture Recovery Rates of Isolated Islets from Nonhuman Primate Pancreata and Marginal Grade Human Pancreata

Investigations indicate that an extract of green tea, polyphenol, can significantly increase the culture survival rate of rat islets without deteriorating their functionality. In this study, we examined the effect of adding polyphenol to islets isolated from human pancreata and nonhuman primate pancreata. Islets were isolated from human pancreata that did not meet criteria for clinical transplantation (n = 6) and from nonhuman primate pancreata (n = 5). The islets were cultured in CMRL-1066 + 10% FCS with the addition of 0, 30, 60, 125, 250, or 500 μg/ml of polyphenol. After 24 or 48 h of culture, islet yield, viability, purity, morphology, and stimulation index was assessed. RT-PCR and Western blot analysis were also performed to assess the expression levels of the apoptotic related genes, Bcl-2 and BAX. After 24 h of culture, islet yields were significantly higher in cultures supplemented with 30–250 μg/ml of polyphenol than in cultures without polyphenol. After 48 h of culture, significant differences in islet numbers were observed with polyphenol concentrations of 125 μg/ml (p < 0.01) and 250 μg/ml (p < 0.01). However, no significant differences were noted in islet viability, purity, morphology, and stimulation index at each time point with or without polyphenol. RT-PCR and Western blot analysis of the islets indicated that Bcl-2 levels increased by 2.5-fold and BAX levels decreased by twofold in cultures supplemented with polyphenol. This resulted in BAX/Bcl-2 ratios that were lower in polyphenol-supplemented cultures than with control cultures. Polyphenol increases culture recovery rates by precluding islet apoptosis.

MRI-sensitive contrast agent with anticoagulant activity for surface camouflage of transplanted pancreatic islets

Pancreatic islet implantation in the liver is a promising approach for diabetes therapy. However, 70% of the islet mass fails to be engrafted in the liver due to the instant blood-mediated inflammatory reactions (IBMIR) resulting from direct contact between islet cells and the bloodstream. To overcome this issue, direct monitoring is very important for establishing prognosis after islet cell therapy. Here we established a new type of MR contrast agent with anticoagulant activity via heparin-immobilized superparamagnetic iron oxide (HSPIO). The HSPIO was chemically conjugated onto islet surface ex vivo without damage of their viability and functionality. The conjugated HSPIO nanoparticles onto islet surface could attenuate IBMIR in vitro and in vivo. The HSPIO-conjugated islets could cure the blood glucose levels of diabetes animals after implantation. In addition, the HSPIO nanoparticles were well maintained on the transplanted islets for a long time during modulation of inflammation. Also, they allowed for stable visualization of the implanted islet cells for more than 150 days without reduction of the MRI signal. Furthermore, when HSPIO itself was intraportally injected, it was rapidly eliminated without accumulation in the liver, suggesting that HSPIO nanoparticles could only track the immobilized islet. Collectively, this HSPIO nanoparticle having MRI sensitivity and anticoagulant activity could be utilized for successful islet implantation.

Polymer Chemistry in Diabetes Treatment by Encapsulated Islets of Langerhans: Review to 2006

Polymeric materials have been successfully used in numerous medical applications because of their diverse properties. For example, development of a bioartificial pancreas remains a challenge for polymer chemistry. Polymers, as a form of various encapsulation device, have been proposed for designing the semipermeable membrane capable of long-term immunoprotection of transplanted islets of Langerhans, which regulate the blood glucose level in a diabetic patient. This review describes the current situation in the field, discussing aspects of material selection, encapsulation devices, and encapsulation protocols. Problems and unanswered questions are emphasized to illustrate why clinical therapies with encapsulated islets have not been realized, despite intense activity over the past 15 years. The review was prepared with the goal to address professionals in the field as well as the broad polymer community to help in overcoming final barriers to the clinical phase for transplantation of islets of Langerhans encapsulated in a polymeric membrane.

3,5,3'-Triiodo-L-thyronine enhances the differentiation of a human pancreatic duct cell line (hPANC-1) towards a beta-cell-Like phenotype

The thyroid hormone, 3,5,3'-Triiodo-L-thyronine (T3), is essential for growth, differentiation, and regulation of metabolic functions in multicellular organisms, although the specific mechanisms of this control are still unknown. In this study, treatment of a human pancreatic duct cell line (hPANC-1) with T3 blocks cell growth by an increase of cells in G(0)/G(1) cell cycle phase and enhances morphological and functional changes as indicated by the marked increase in the synthesis of insulin and the parallel decrease of the ductal differentiation marker cytokeratin19. Expression analysis of some of the genes regulating pancreatic beta-cell differentiation revealed a time-dependent increase in insulin and glut2 mRNA levels in response to T3. As last step of the acquisition of a beta-cell-like phenotype, we present evidence that thyroid hormones are able to increase the release of insulin into the culture medium. In conclusion, our results suggest, for the first time, that thyroid hormones induce cell cycle perturbations and play an important role in the process of transdifferentiation of a human pancreatic duct line (hPANC-1) into pancreatic-beta-cell-like cells. These findings have important implications in cell-therapy based treatment of diabetes and may provide important insights in the designing of novel therapeutic agents to restore normal glycemia in subjects with diabetes.

Islet replacement vs. regeneration: hope or hype?

Type 1 diabetes is caused by autoimmune destruction of pancreatic islet beta-cells. Management of this disease is burdensome both to the individual and society, costing over 100 billion US dollars annually. Shortage of pancreatic tissue, together with a lifetime requirement of immunosuppressive drugs to prevent rejection and recurrent disease, remain as major hurdles yet to be overcome prior to widespread applicability. Stem cells, with their potential of developing into pancreatic beta-cells, appear to be the best prospect for overcoming the islet shortage. Current investigation, however (both embryonic and adult stem cells), is still in the preliminary stage and several more years remain before they can potentially be used in the clinical setting. Procedures that reduce in vitro manipulation of cells and allow stem cells to develop into islets in vivo are crucial. Furthermore, the regeneration of existing islets is a distinct possibility. Simplistically, it might be hypothesized that down-regulation of autoimmunity may give the pancreas the breathing space to regenerate islets. Supplementation with factors known to induce beta-cell replication and neogenesis might further augment the regenerative processes. Clearly, islet-regeneration research will soon match the level of interest currently focused on in vitro stem cell-based approaches.

Hybrid pancreatic tissue substitute consisting of recombinant insulin-secreting cells and glucose-responsive material

Insulin-dependent diabetes is a serious pathological condition, currently treated by blood glucose monitoring and daily insulin injections, which, however, do not prevent long-term complications. A tissue-engineered pancreatic substitute has the potential to provide a more physiologic, less invasive, and potentially less costly treatment of the disease. A major issue in developing such a substitute is the cells being used. Nonpancreatic cells, retrieved from the same patient and genetically engineered to secrete insulin constitutively or with some glucose responsiveness, offer the significant advantages of being immune-acceptable and relaxing the tissue availability limitations, which exist with islets from cadaveric donors. These cells, however, do not have insulin secretion dynamics appropriate for restoration of euglycemia in higher animals and, eventually, humans. In this study, we present the concept of a hybrid pancreatic substitute consisting of such cells sequestered in a material exhibiting glucose-dependent changes of its permeability to insulin. A Concanavalin A-glycogen material sandwiched between two polycarbonate membranes and exhibiting glucose-dependent sol-gel transformations was used. Rates of insulin transport through this material in gel and sol forms were characterized for both FITC-labeled insulin in solution and insulin secreted by betaTC3 mouse insulinoma cells. Effective diffusivities through sol were found to be up to 3.5-fold higher than through the gel state of the material. A mathematical model of a hybrid construct was formulated and analyzed to simulate the secretory behavior in response to step ups and downs in the surrounding glucose concentration. The experimental and modeling studies indicate that a hybrid pancreatic substitute consisting of constitutively secreting cells and glucose-responsive material has the potential to provide a more physiologic regulation of insulin release than the cells by themselves or in an inert material.

In vitro-generation of surrogate islets from adult stem cells

Type 1 diabetes is one of the more costly chronic diseases of children and adolescents throughout North America and Europe, exhibiting an average estimated prevalence rate of nearly 0.2%. It occurs in genetically predisposed individuals when the immune system attacks and destroys specifically the insulin-producing beta cells of the pancreatic islets of Langerhans. While routine insulin therapy can provide diabetic patients with their daily insulin requirements, non-compliance and undetected hyperglycemic excursions often lead to subsequent long-term microvascular and macrovascular complications. The only real cure for type 1 diabetes is replacement of the beta cell mass, currently being accomplished through ecto-pancreatic transplantation and islet implantation. Both of these procedures suffer from a chronic shortage of available donor tissue in comparison to the number of potential recipients. To circumvent this need, three alternative approaches are being intensively investigated: (1) the production of surrogate cells by genetically modifying non-endocrine cells to secrete insulin in response to glucose challenge; (2) the trans-differentiation of non-endocrine stem/progenitor cells or mature cells to glucose-responsive adult tissue; and (3) the regulated differentiation of islet stem/progenitor cells to produce large numbers of mature, functional islets. In recent years, each of these approaches has made impressive advances, leading to the most important question, 'how soon will this new science be available to the patient?' In the present review, we discuss some of the recent advances, focusing primarily on the differentiation of islet stem cells to functional endocrine pancreas that may form the basis for future treatment.

Detection of secretion from pancreatic islets using chemically modified electrodes

Secretion of insulin from pancreatic islets was monitored indirectly by detecting zinc. Anodic stripping voltammetric measurements of zinc were done on a bismuth-modified electrode. Comparison of the performance of bismuth-modified electrodes and mercury film electrodes showed that bismuth is an appropriate alternative for Zn detection. The bismuth-coated electrode was used to detect zinc in insulin samples and insulin secreted from pancreatic islets upon stimulation with high concentrations of K(+). Detection of zinc released from pancreatic islets was done in the culture medium without any further cleanup. This detection method can be used to monitor secretion from pancreatic islets in their native environment.

Islet transplant: an option for childhood diabetes?

Careful assessment of the safety and efficacy of islet transplantation should guide the selection process of a small number of children with type 1 diabetes who may be eligible for the procedure--some of whom are already receiving immunosuppression because of a previous transplant, others who are scheduled to receive de novo islet alone transplantation because of a life threatening risk of hypoglycemia. The outcomes of these initial investigations are predicted to shape the future boundaries of islet transplantation, diabetes, and transplantation.

Development and characterization of simulant pancreatic islets

Insulin is stored in pancreatic islets as a zinc-insulin complex, and stimulating the islets results in the release of insulin and zinc. Simulant pancreatic islet beads have been developed using agarose beads (50-250 micro m diameter) derivatized with iminodiacetic acid that have been loaded with zinc. A qualitative comparison of the simulant beads with pancreatic islets has been made by staining with dithizone and a zinc-binding fluorescent dye, TSQ. The binding capacity of simulant beads was determined to be 34 micro mol Zn(2+)/g of dried beads using anodic stripping voltammetry. Hydrochloric acid was used to release zinc from beads to mimic the secretion of insulin from pancreatic islets and a release profile was established. The simulant beads can be used to optimize the islet isolation process and reduce the use of real islets in method development.

Malonyl-CoA signaling, lipid partitioning, and glucolipotoxicity: role in beta-cell adaptation and failure in the etiology of diabetes

Beta-cells possess inherent mechanisms to adapt to overnutrition and the prevailing concentrations of glucose, fatty acids, and other fuels to maintain glucose homeostasis. However, this is balanced by potentially harmful actions of the same nutrients. Both glucose and fatty acids may cause good/adaptive or evil/toxic actions on the beta-cell, depending on their concentrations and the time during which they are elevated. Chronic high glucose dramatically influences beta-cell lipid metabolism via substrate availability, changes in the activity and expression of enzymes of glucose and lipid metabolism, and modifications in the expression level of key transcription factors. We discuss here the emerging view that beta-cell "glucotoxicity" is in part indirectly caused by "lipotoxicity," and that beta-cell abnormalities will become particularly apparent when both glucose and circulating fatty acids are high. We support the concept that elevated glucose and fatty acids synergize in causing toxicity in islets and other organs, a process that may be instrumental in the pleiotropic defects associated with the metabolic syndrome and type 1 and type 2 diabetes. The mechanisms by which hyperglycemia and hyperlipidemia alter insulin secretion are discussed and a model of beta-cell "glucolipotoxicity" that implicates alterations in beta-cell malonyl-CoA concentrations; peroxisome proliferator-activated receptor-alpha and -gamma and sterol regulatory element binding protein-1c expression; and lipid partitioning is proposed.