We describe a new technique for microencapsulation with high-mannuronic acid (high-M) alginate crosslinked with BaCl 2 without a traditional permselective component, which allows the production of biocompatible capsules that allow prolonged survival of syngeneic and allogeneic transplanted islets in diabetic BALB/c and NOD mice for >350 days. The normalization of the glycemia in the transplanted mice was associated with normal glucose profiles in response to intravenous glucose tolerance tests. After explantation of the capsules, all mice became hyperglycemic, demonstrating the efficacy of the encapsulated islets. The retrieved capsules were free of cellular overgrowth and islets responded to glucose stimulation with a 5-to 10-fold increase of insulin secretion. Transfer of splenocytes isolated from transplanted NOD mice to NOD/SCID mice adoptively transferred diabetes, indicating that NOD recipients maintained islet-specific autoimmunity. In conclusion, we have developed a simple technique for microencapsulation that prolongs islet survival without immunosuppression, providing complete protection against allorejection and the recurrence of autoimmune diabetes. Diabetes 50: 1698 -1705, 2001 I slet transplantation represents an important alternative for the treatment of type 1 diabetes but still requires immunosuppressive agents with their serious side effects (1). One approach to avoid such treatment is to protect islets from the host's immune system with a semipermeable, biocompatible membrane (2,3). Transplantation of islets contained in alginate-poly-L-lysine (PLL) capsules was first described by Lim and Sun (4). Numerous studies have shown successful reversal of diabetes by transplantation of islets enclosed in alginate-PLL capsules in streptozotocin-induced animals (5-9). However, limited success has been reported in spontaneously diabetic NOD mice, a model of autoimmune diabetes (10 -13). Various factors have been implicated in the failure of encapsulated islets. A cellular reaction surrounding the capsules has often been observed, which could lead to depletion of oxygen and nutrients (14) or production of toxic cytokines (15). This accumulation of cells could be due to an immune response to the contained islets or to bioincompatibility of the capsular materials (16,17). Failure might also be attributed to problems with ␤-cell viability in the capsules (18).Protection of porcine islets remains a goal of encapsulation, but xenografts might be more difficult to protect than allografts, as suggested by studies performed with permeable polymer membranes (19,20). This concept is important because of the improved prospects for obtaining an abundant supply of human ␤-cells from precursor cells (21,22). The goal of this study was to determine whether stable biocompatible alginate microcapsules without a permselective component, such as PLL or polyethylene-glycol, would be able to protect mouse islets against allorejection and autoimmunity. RESEARCH DESIGN AND METHODSIslet isolation. Islets were isolated from ma...

The insulin receptor substrate 2 (Irs2) branch of the insulin/insulin-like growth factor-signaling cascade prevents diabetes in mice because it promotes ␤ cell replication, function, and survival, especially during metabolic stress. Because exendin-4 (Ex4), a long acting glucagon-like peptide 1 receptor agonist, has similar effects upon ␤ cells in rodents and humans, we investigated whether Irs2 signaling was required for Ex4 action in isolated ␤ cells and in Irs2 ؊/؊ mice. Ex4 increased cAMP levels in human islets and Min6 cells, which promoted Irs2 expression and stimulated Akt phosphorylation. In wild type mice Ex4 administered continuously for 28 days increased ␤ cell mass 2-fold. By contrast, Ex4 failed to arrest the progressive ␤ cell loss in Irs2 ؊/؊ mice, which culminated in fatal diabetes; however, Ex4 delayed the progression of diabetes by 3 weeks by promoting insulin secretion from the remaining islets. We conclude that some short term therapeutic effects of glucagon-like peptide 1 receptor agonists can be independent of Irs2, but its long term effects upon ␤ cell growth and survival are mediated by the Irs2 branch of the insulin/insulin-like growth factor signaling cascade.Diabetes mellitus is a complex disorder that arises from various causes, including dysregulated glucose sensing and impaired insulin secretion (maturity-onset diabetes of youth, MODY), autoimmune-mediated ␤ cell destruction (type 1), or insufficient compensation for peripheral insulin resistance (type 2) (1). Type 2 diabetes is the most prevalent form. It usually occurs at middle age and afflicts more than 30 million people over the age of 65 but is appearing with greater frequency in children and adolescents (2). Dysregulated insulin signaling exacerbated by chronic hyperglycemia promotes a cohort of systemic disorders, including dyslipidemia, hypertension, cardiovascular disease, and female infertility (3, 4). The search for strategies to promote ␤ cell function and regeneration has lead to the discovery that glucagon-like peptide-1 (GLP1) 2 receptor agonists increase insulin biosynthesis and secretion from ␤ cells, inhibit glucagon secretion from ␣-cells, and promote peripheral insulin sensitivity and satiety in type 2 diabetics (5-9). During a meal, GLP1 is secreted into the circulation from L cells located in the intestine (10); however, GLP1 is quickly inactivated by circulating dipeptidyl-peptidase IV, which diminishing its usefulness as an injectable therapeutic. Compounds that inhibit dipeptidyl-peptidase IV or GLP1 homologs like exendin-4 (Ex4) that are not degraded by dipeptidyl-peptidase IV display improved therapeutic efficacy (11-16). Administration of Ex4 to rodents or humans with type 2 diabetes increases first-phase insulin secretion and increases ␤ cell mass, which can compensate for peripheral insulin resistance (8,9,17,18). Recently, a synthetic Ex4 called Exenatide (Byetta, Amylin/Lily) has gained Food and Drug Administration approval as an injectable treatment for type 2 diabetes (15). Because Exenatide is the...

Despite improvements in outcomes for human islet transplantation, characterization of islet preparations remains poorly defined. This study used both light (LM) and electron microscopy (EM) to characterize 33 islet preparations used for clinical transplants. EM allowed accurate identification and quantification of cell types with measured cell number fractions (mean ± SEM) 35.6 ± 2.1% β-cells, 12.6 ± 1.0% non-β-islet cells, (48.3 ± 2.6% total islet cells), 22.7 ± 1.5% duct cells, and 25.3 ± 1.8% acinar cells. Of the islet cells, 73.6 ± 1.7% were β cells. For comparison to the literature, estimates of cell number fraction, cell volume, and extracellular volume were combined to convert number fraction data to volume fractions applicable to cells, islets, and the entire preparation. The mathematical framework for this conversion was developed. By volume, β cells were 86.5 ± 1.1% of the total islet cell volume and 61.2 ± 0.8% of intact islets (including the extracellular volume), which is similar to that of islets in the pancreas. Our estimates gave 1560 ± 20 cells in an islet equivalent (volume of 150-μm diameter sphere), of which 1140 ± 15 were β cells. To test if LM analysis of the same tissue samples could provide reasonable estimates of purity of the islet preparations, volume fraction islet tissue was measured on thin sections available from 27 of the clinical preparations by point counting morphometrics. Islet purity (islet volume fraction) of individual preparations determined by LM and EM analysis correlated linearly with excellent agreement (R2 = 0.95). However, islet purity by conventional dithizone staining was substantially higher with a 20-30% overestimation. Thus, both EM and LM provide accurate methods to determine the cell composition of human islets preparations and can help us understand many of the discrepancies of islet composition in the literature.

To test whether pancreatic duct cells are in vitro progenitors, they were purified from dispersed islet-depleted human pancreatic tissue using CA19-9 antibody. The purified fraction was almost entirely CK19؉ with no insulin ؉ cells, whereas the unpurified cells (crude duct) were 56% CK19 W hereas islet transplantation is an effective and beneficial treatment for type 1 diabetes, its application is limited by the shortage of islets. A possible solution is to generate insulin-producing cells from adult stem/progenitor cells of the pancreas. In vivo new ␤-cells are generated through replication of preexisting ␤-cells and neogenesis, the latter from differentiation of non-hormone-expressing progenitor cells (1-8). Putative adult stem/progenitor cells from mouse pancreas have been expanded clonally and after manipulation were found to express low levels of insulin and other pancreatic markers (9,10). While these findings are provocative, it has not yet been shown that such cells can become fully functional ␤-cells (11).Our group reported that islet-like structures, which secrete insulin in response to glucose, could be generated from islet-depleted pancreatic tissue remaining after human islet isolation (12). These findings were confirmed and extended by Otonkoski and colleagues (13). The cell of origin has been suspected to be ductal in origin but has not been conclusively shown. Additionally, three other groups (14 -16) have reported that putative progenitor cells, which arose from human islet preparations, could be expanded through many passages and then be manipulated to reexpress islet hormones at low levels. Gershengorn et al. (16), Habener and colleagues (14,17) and Efrat and colleagues (18) have suggested that the expanding cells are ␤-cells that have undergone epithelial-mesenchymal transition, no longer express insulin, and have great capacity for expansion. However, even the purest human islet preparations are not pure islet cells but contain many contaminating duct, acinar, and connective tissue cells. Olson and colleagues (15) showed that serpinginous cells expressing vimentin and nestin had no islet hormones during expansion but acquired low levels of islet markers after manipulation of culture conditions. Similar cells were initially suggested to be the preexisting nestinpositive cells found in the islets and in the ductal stroma (17). All of these studies have raised the possibility of generating new islet cells in vitro from human pancreatic tissue, but in each case the cell of origin has not been identified; thus, it is not clear whether ␤-cells actually undergo such a transition.The purpose of this study is to test whether highly purified human adult pancreatic duct cells can differentiate in vitro into insulin-producing cells. To this end, extremely pure duct preparations were obtained following immunomagnetic sorting with CA19-9 antibody. The affinity purification step is highly selective for pancreatic duct epithelial cells and is performed immediately after islet purification. Our method is qu...

Differentiation and maturation of porcine neonatal pancreatic cell clusters (NPCCs) microencapsulated in barium alginate were assessed after transplantation into immunocompetent mice. Microencapsulated NPCCs were transplanted into the peritoneal cavity of streptozocin-induced diabetic B6AF1 mice (n ‫؍‬ 32). The microcapsules were removed at 2, 6, and 20 weeks and examined for cellular overgrowth, insulin content, and insulin secretory responses to glucose and glucose with theophylline. The differentiation, maturation, and proliferation of the ␤-cells in the NPCCs were assessed by immunohistochemistry. Blood glucose levels were normalized in 81% of the animals that received a transplant and remained normal until termination of the experiments at 20 weeks. Hyperglycemic blood glucose levels after explantation of the capsules confirmed the function of the encapsulated NPCCs. Insulin content of the encapsulated NPCCs was increased 10-fold at 20 weeks after transplantation compared with pretransplantation levels. A 3.2-fold increase of the ratio of the ␤-cell area to the total cellular area was observed at 20 weeks, demonstrating the maturation of NPCCs into ␤-cells. A s a result of recent progress (1), there is increased interest in islet transplantation as a potential therapy for type 1 diabetes. However, two major barriers must be overcome before islet transplantation can be provided for more patients: 1) the limited availability of human pancreatic tissue and 2) the need for permanent immunosuppression to prevent graft rejection and autoimmunity (2). Xenogeneic islets from pigs and cows (3-5) have been considered as potential sources of islets for transplantation. Many factors favor the use of pigs: the similar structure of porcine and human insulin, the comparable glucose levels, and that both pigs and humans are omnivores. Islet cells can be isolated in large numbers from adult (6 -9) or neonatal pigs (10,11). However, adult pig islets have proved to be difficult to isolate and tend to fare poorly in tissue culture, which has limited their use. Neonatal pancreatic cell clusters (NPCCs) contain a high proportion of islet precursor cells, can be maintained in culture, and differentiate into ␤-cells after transplantation (11). Naked (10,12) or microencapsulated NPCCs (13) have been shown to restore normoglycemia after transplantation into streptozotocin (STZ)-diabetic nude mice.The concept of a bioartificial pancreas, consisting of islets enclosed within immunobarrier membranes, provides a potential way to overcome the need for immunosuppression. Our group recently developed a promising encapsulation method that uses highly purified alginate cross-linked with BaCl 2 , without a separate permselective barrier, which protects islets against allorejection and autoimmunity (14). The aims of this study were to assess the protective capacity of simple barium-alginate capsules in a xenotransplantation model of NPCCs transplanted into STZ-induced diabetic immunocompetent mice and then to evaluate the growth, maturation, a...

Context: Human ␤-cell gene profiling is a powerful tool for understanding ␤-cell biology in normal and pathological conditions. Assessment is complicated when isolated islets are studied because of contamination by non-␤-cells and the trauma of the isolation procedure. Objective:The objective was to use laser capture microdissection (LCM) of human ␤-cells from pancreases of cadaver donors and compare their gene expression with that of handpicked isolated islets.Design: Endogenous autofluorescence of ␤-cells facilitated procurement of purified ␤-cell tissue from frozen pancreatic sections with LCM. Gene expression profiles of three microdissected ␤-cell samples and three isolated islet preparations were obtained. The array data were normalized using DNA-Chip Analyzer software (Harvard School of Public Health, Boston, MA), and the lower confidence bound evaluated differentially expressed genes. Real-time PCR was performed on selected acinar genes and on the duct cell markers, carbonic anhydrase II and keratin 19. Results:Endogenous autofluorescence facilitates the microdissection of ␤-cell rich tissue in human pancreas. When compared with array profiles of purified ␤-cell tissue, with lower confidence bound set at 1.2, there were 4560 genes up-regulated and 1226 genes down-regulated in the isolated islets. Among the genes up-regulated in isolated islets were pancreatic acinar and duct genes, chemokine genes, and genes associated with hypoxia, apoptosis, and stress. Quantitative RT-PCR confirmed the differential expression of acinar gene transcripts and the duct marker carbonic anhydrase II in isolated islets. Conclusion

These results indicate that regular-size alginate capsules do less well in rats than in our previous experiments with mice. Smaller capsules made of alginate cross-linked with barium appear to provide better stability and may be a useful strategy for use in larger recipients.

Aims/hypothesis Islet transplantation is a promising treatment for type 1 diabetes but is hampered by a shortage of donor human tissue and early failure. Research on islet-cell transplantation includes finding new sources of cells and immunoisolation to protect from immune assault and tumorigenic potential. Small islet-cell aggregates were studied to determine if their survival and function were superior to intact islets within microcapsules because of reduced oxygen transport limitation and inflammatory mediators. Methods Islet-cell aggregates were generated by dispersing rat islets into single cells and allowing them to re-aggregate in culture. Rat islets and islet-cell aggregates were encapsulated in barium alginate capsules and studied when cultured in low (0.5% or 2%) or normal (20%) oxygen, or transplanted into mice. Results Encapsulated islet-cell aggregates were able to survive and function better than intact islets in terms of oxygen-consumption rate, nuclei counts, insulin-to-DNA ratio, and glucose-stimulated insulin secretion. They also had reduced expression of pro-inflammatory genes. Islet-cell aggregates showed reduced tissue necrosis in an immunodeficient transplant model and a much greater proportion of diabetic xenogeneic transplant recipients receiving islet-cell aggregates (tissue volume of only 85 islet equivalents) had reversal of hyperglycaemia than recipients receiving intact islets. Conclusions/interpretation These aggregates were superior to intact islets in terms of survival and function in low-oxygen culture and during transplantation and are likely to provide more efficient utilisation of islet tissue, a finding of importance for the future of cell therapy for diabetes.