Islet transplantation outcomes in mice are better with fresh islets and exendin-4 treatment

Liraglutide Protects Pancreatic Islet From Ischemic Injury by Reducing Oxidative Stress and Activating Akt Signaling During Cold Preservation to Improve Islet Transplantation Outcomes

BACKGROUND

Islet transplantation is a promising therapy for patients with type 1 diabetes. However, ischemic injury to the donor islets during cold preservation leads to reduced islet quality and compromises transplant outcome. Several studies imply that liraglutide, a glucagon-like peptide-1 receptor agonist, has a positive effect on promoting islet survival, but its impact on islet cold-ischemic injury remains unexplored. Therefore, the aim of this study was to investigate whether liraglutide can improve islet transplantation efficacy by inhibiting cold-ischemic injury and to explore the underlying mechanisms.

METHODS

Liraglutide was applied in a mouse pancreas preservation model and a human islets cold-preservation model, and islet viability, function, oxidative stress levels were evaluated. Furthermore, islet transplantation was performed in a syngeneic mouse model and a human-to-nude mouse islet xenotransplantation model.

RESULTS

The supplementation of liraglutide in preservation solution improved islet viability, function, and reduced cell apoptosis. Liraglutide inhibited the oxidative stress of cold-preserved pancreas or islets through upregulating the antioxidant enzyme glutathione levels, inhibiting reactive oxygen species accumulation, and maintaining the mitochondrial membrane integrity, which is associated with the activation of Akt signaling. Furthermore, the addition of liraglutide during cold preservation of donor pancreas or donor islets significantly improved the subsequent transplant outcomes in both syngeneic mouse islet transplantation model and human-to-nude mouse islet xenotransplantation model.

CONCLUSIONS

Liraglutide protects islets from cold ischemia-related oxidative stress during preservation and hence improved islet transplantation outcomes, and this protective effect of liraglutide in islets is associated with the activation of Akt signaling.

Global trends and focuses of GLP-1RA in renal disease: a bibliometric analysis and visualization from 2005 to 2022

Glucagon-like peptide 1 receptor agonist (GLP-1RA) is a new class of glucose-lowing agents with the kidney benefit effect. This paper aims at finding the current state and hotspots of the research on GLP-1RA in kidney disease by using bibliometric methodologies and visualization maps to analyze publications and provide the direction for future studies on that topic. Literature information was obtained by retrieving the WoSCC database. Then, software like Microsoft Excel, VOSviewer, and CiteSpace was used to analyze and process obtained data. Bibliometric analysis and visualization of nations, authors, organizations, journals, keywords, and references were also done by VOSviewer and CiteSpace. A total of 991 publications written by 4747 authors from 1637 organizations in 75 countries on GLP-1RA in renal disease in Web of Science Core Collection were retrieved. The number of publications and citations kept growing from 2015 to 2022. The USA, Univ Copenhagen, and Rossing Peter are the leading country, organization, and author on this topic, respectively. All literature was published in 346 journals, and DIABETES OBESITY & METABOLISM is the journal with the most contributions. Meanwhile, most references are from DIABETES CARE. "Cardiovascular outcome" is the most frequent keyword in the total publications, and the reference cited most times is "Liraglutide and Cardiovascular Outcomes in Type 2 Diabetes" by Marso SP. The topic of GLP-1RA in renal disease has attracted more and more attention all over the world. Existing studies are mainly about clinical use in patients with diabetes, and studies on the mechanism are lacking.

Use of Culture to Reach Metabolically Adequate Beta-cell Dose by Combining Donor Islet Cell Isolates for Transplantation in Type 1 Diabetes Patients

BACKGROUND

Clinical islet transplantation is generally conducted within 72 hours after isolating sufficient beta-cell mass. A preparation that does not meet the sufficient dose can be cultured until this is reached after combination with subsequent ones. This retrospective study examines whether metabolic outcome is influenced by culture duration.

METHODS

Forty type 1 diabetes recipients of intraportal islet cell grafts under antithymocyte globulin induction and mycophenolate mofetil-tacrolimus maintenance immunosuppression were analyzed. One subgroup (n = 10) was transplanted with preparations cultured for ≥96 hours; in the other subgroup (n = 30) grafts contained similar beta-cell numbers but included isolates that were cultured for a shorter duration. Both subgroups were compared by numbers with plasma C-peptide ≥0.5 ng/mL, low glycemic variability associated with C-peptide ≥1.0 ng/mL, and with insulin independence.

RESULTS

The subgroup with all cells cultured ≥96 hours exhibited longer C-peptide ≥0.5 ng/mL (103 versus 48 mo; P = 0.006), and more patients with low glycemic variability and C-peptide ≥1.0 ng/mL, at month 12 (9/10 versus 12/30; P = 0.005) and 24 (7/10 versus 6/30; P = 0.007). In addition, 9/10 became insulin-independent versus 15/30 (P = 0.03). Grafts with all cells cultured ≥96 hours did not contain more beta cells but a higher endocrine purity (49% versus 36%; P = 0.03). In multivariate analysis, longer culture duration and older recipient age were independently associated with longer graft function.

CONCLUSIONS

Human islet isolates with insufficient beta-cell mass for implantation within 72 hours can be cultured for 96 hours and longer to combine multiple preparations in order to reach the desired beta-cell dose and therefore result in a better metabolic benefit.

Darbepoetin-α increases the blood volume flow in transplanted pancreatic islets in mice

AIMS

The minimal-invasive transplantation of pancreatic islets is a promising approach to treat diabetes mellitus type 1. However, islet transplantation is still hampered by the insufficient process of graft revascularization, leading to a poor clinical outcome. Accordingly, the identification of novel compounds, which accelerate and improve the revascularization of transplanted islets, is of great clinical interest. Previous studies have shown that darbepoetin (DPO)-α, a long lasting analogue of erythropoietin, is capable of promoting angiogenesis. Hence, we investigated in this study whether DPO improves the revascularization of transplanted islets.

METHODS

Islets were isolated from green fluorescent protein-positive FVB/N donor mice and transplanted into dorsal skinfold chambers of FVB/N wild-type animals, which were treated with DPO low dose (2.5 µg/kg), DPO high dose (10 µg/kg) or vehicle (control). The revascularization was assessed by repetitive intravital fluorescence microscopy over an observation period of 14 days. Subsequently, the cellular composition of the grafts was analyzed by immunohistochemistry.

RESULTS

The present study shows that neither low- nor high-dose DPO treatment accelerates the revascularization of free pancreatic islet grafts. However, high-dose DPO treatment increased the blood volume flow of the transplanted islet.

CONCLUSIONS

These findings demonstrated that DPO treatment does not affect the revascularization of transplanted islets. However, the glycoprotein increases the blood volume flow of the grafts, which results in an improved microvascular function and may facilitate successful transplantation.

Assessing Islet Transplantation Outcome in Mice

Islet transplantation is a potential treatment for Type 1 diabetes; however, improvements need to be made before it could become clinically widely available. In preclinical studies, the mouse is often used to model islet transplantation, with most studies aiming to improve transplantation outcome by manipulating the islets prior to transplantation or by treating the recipient mouse. Here, we describe the process of islet transplantation in the mouse, including how one can make the mouse diabetic, isolate donor islets, and transplant the islets into two different sites. Finally, we discuss how to assess the outcome of the transplantation in order to determine whether the experimental intervention has been beneficial.

Apolipoprotein E is a pancreatic extracellular factor that maintains mature β-cell gene expression

The in vivo microenvironment of tissues provides myriad unique signals to cells. Thus, following isolation, many cell types change in culture, often preserving some but not all of their in vivo characteristics in culture. At least some of the in vivo microenvironment may be mimicked by providing specific cues to cultured cells. Here, we show that after isolation and during maintenance in culture, adherent rat islets reduce expression of key β-cell transcription factors necessary for β-cell function and that soluble pancreatic decellularized matrix (DCM) can enhance β-cell gene expression. Following chromatographic fractionation of pancreatic DCM, we performed proteomics to identify soluble factors that can maintain β-cell stability and function. We identified Apolipoprotein E (ApoE) as an extracellular protein that significantly increased the expression of key β-cell genes. The ApoE effect on beta cells was mediated at least in part through the JAK/STAT signaling pathway. Together, these results reveal a role for ApoE as an extracellular factor that can maintain the mature β-cell gene expression profile.

Sitagliptin Treatment After Total Pancreatectomy With Islet Autotransplantation: A Randomized, Placebo-Controlled Study

Insulin independence after total pancreatectomy and islet autotransplant (TPIAT) for chronic pancreatitis is limited by a high rate of postprocedure beta cell apoptosis. Endogenous glucagon-like peptide-1 and glucose-dependent insulinotropic peptide, which are increased by dipeptidyl peptidase 4 inhibitor therapy (sitagliptin) may protect against beta cell apoptosis. To determine the effect of sitagliptin after TPIAT, 83 adult TPIAT recipients were randomized to receive sitagliptin (n = 54) or placebo (n = 29) for 12 months after TPIAT. At 12 and 18 months after TPIAT, participants were assessed for insulin independence; metabolic testing was performed with mixed meal tolerance testing and frequent sample intravenous glucose tolerance testing. Insulin independence did not differ between the sitagliptin and placebo groups at 12 months (42% vs. 45%, p = 0.82) or 18 months (36% vs. 44%, p = 0.48). At 12 months, insulin dose was 9.0 (standard error 1.7) units/day and 7.9 (2.2) units/day in the sitagliptin and placebo groups, respectively (p = 0.67) and at 18 months 10.3 (1.9) and 7.1 (2.6) units/day, respectively (p = 0.32). Hemoglobin A_1c levels and insulin secretory measures were similar in the two groups, as were adverse events. In conclusion, sitagliptin could be safely administered but did not improve metabolic outcomes after TPIAT.

Imatinib prevents beta cell death in vitro but does not improve islet transplantation outcome

Introduction Improving islet transplantation outcome could not only bring benefits to individual patients but also widen the patient pool to which this life-changing treatment is available. Imatinib has previously been shown to protect beta cells from apoptosis in a variety of in vitro and in vivo models. The aim of this study was to investigate whether imatinib could be used to improve islet transplantation outcome. Methods Islets were isolated from C57Bl/6 mice and pre-cultured with imatinib prior to exposure to streptozotocin and cytokines in vitro. Cell viability and glucose-induced insulin secretion were measured. For transplantation experiments, islets were pre-cultured with imatinib for either 72 h or 24 h prior to transplantation into streptozotocin-diabetic C57Bl/6 mice. In one experimental series mice were also administered imatinib after islet transplantation. Results Imatinib partially protected islets from beta cell death in vitro. However, pre-culturing islets in imatinib or administering the drug to the mice in the days following islet transplantation did not improve blood glucose concentrations more than control-cultured islets. Conclusion Although imatinib protected against beta cell death from cytokines and streptozotocin in vitro, it did not significantly improve syngeneic islet transplantation outcome.

Clinical Islet Isolation

The overarching success of islet transplantation relies on the success in the laboratory to isolate the islets. This chapter focuses on the processes of human islet cell isolation and the ways to optimally provide islet cells for transplantation. The major improvements in regards to the choice of enzyme type, way the digested pancreas tissue is handled to best separate islets from the acinar and surrounding tissues, the various methods of purification of the islets, their subsequent culture and quality assurance to improve outcomes to culminate in safe and effective islet transplantation will be discussed. After decades of improvements, islet cell isolation and transplantation now clearly offer a safe, effective and feasible therapeutic treatment option for an increasing number of patients suffering from type 1 diabetes specifically for those with severe hypoglycaemic unawareness.

The effects of exendin-4 treatment on graft failure: an animal study using a novel re-vascularized minimal human islet transplant model

Islet transplantation has become a viable clinical treatment, but is still compromised by long-term graft failure. Exendin-4, a glucagon-like peptide 1 receptor agonist, has in clinical studies been shown to improve insulin secretion in islet transplanted patients. However, little is known about the effect of exendin-4 on other metabolic parameters. We therefore aimed to determine what influence exendin-4 would have on revascularized minimal human islet grafts in a state of graft failure in terms of glucose metabolism, body weight, lipid levels and graft survival. Introducing the bilateral, subcapsular islet transplantation model, we first transplanted diabetic mice with a murine graft under the left kidney capsule sufficient to restore normoglycemia. After a convalescent period, we performed a second transplantation under the right kidney capsule with a minimal human islet graft and allowed for a second recovery. We then performed a left-sided nephrectomy, and immediately started treatment with exendin-4 with a low (20μg/kg/day) or high (200μg/kg/day) dose, or saline subcutaneously twice daily for 15 days. Blood was sampled, blood glucose and body weight monitored. The transplanted human islet grafts were collected at study end point and analyzed. We found that exendin-4 exerts its effect on failing human islet grafts in a bell-shaped dose-response curve. Both doses of exendin-4 equally and significantly reduced blood glucose. Glucagon-like peptide 1 (GLP-1), C-peptide and pro-insulin were conversely increased. In the course of the treatment, body weight and cholesterol levels were not affected. However, immunohistochemistry revealed an increase in beta cell nuclei count and reduced TUNEL staining only in the group treated with a low dose of exendin-4 compared to the high dose and control. Collectively, these results suggest that exendin-4 has a potential rescue effect on failing, revascularized human islets in terms of lowering blood glucose, maintaining beta cell numbers, and improving metabolic parameters during hyperglycemic stress.

Enhancing human islet transplantation by localized release of trophic factors from PLG scaffolds

Islet transplantation represents a potential cure for type 1 diabetes, yet the clinical approach of intrahepatic delivery is limited by the microenvironment. Microporous scaffolds enable extrahepatic transplantation, and the microenvironment can be designed to enhance islet engraftment and function. We investigated localized trophic factor delivery in a xenogeneic human islet to mouse model of islet transplantation. Double emulsion microspheres containing exendin-4 (Ex4) or insulin-like growth factor-1 (IGF-1) were incorporated into a layered scaffold design consisting of porous outer layers for islet transplantation and a center layer for sustained factor release. Protein encapsulation and release were dependent on both the polymer concentration and the identity of the protein. Proteins retained bioactivity upon release from scaffolds in vitro. A minimal human islet mass transplanted on Ex4-releasing scaffolds demonstrated significant improvement and prolongation of graft function relative to blank scaffolds carrying no protein, and the release profile significantly impacted the duration over which the graft functioned. Ex4-releasing scaffolds enabled better glycemic control in animals subjected to an intraperitoneal glucose tolerance test. Scaffolds releasing IGF-1 lowered blood glucose levels, yet the reduction was insufficient to achieve euglycemia. Ex4-delivering scaffolds provide an extrahepatic transplantation site for modulating the islet microenvironment to enhance islet function posttransplant.

Preculturing Islets With Adipose-Derived Mesenchymal Stromal Cells Is an Effective Strategy for Improving Transplantation Efficiency at the Clinically Preferred Intraportal Site

We have recently shown that preculturing islets with kidney-derived mesenchymal stromal cells (MSCs) improves transplantation outcome in streptozotocin-diabetic mice implanted with a minimal mass of islets beneath the kidney capsule. In the present study, we have extended our previous observations to investigate whether preculturing islets with MSCs can also be used to enhance islet function at the clinically used intraportal site. We have used MSCs derived from adipose tissue, which are more readily accessible than alternative sources in human subjects and can be expanded to clinically efficacious numbers, to preculture islets throughout this study. The in vivo efficacy of grafts consisting of islets precultured alone or with MSCs was tested using a syngeneic streptozotocin-diabetic minimal islet mass model at the clinically relevant intraportal site. Blood glucose concentrations were monitored for 1 month. The vascularization of islets precultured alone or with MSCs was investigated both in vitro and in vivo, using immunohistochemistry. Islet insulin content was measured by radioimmunoassay. The effect of preculturing islets with MSCs on islet function in vitro was investigated using static incubation assays. There was no beneficial angiogenic influence of MSC preculture, as demonstrated by the comparable vascularization of islets precultured alone or with MSCs, both in vitro after 3 days and in vivo 1 month after islet transplantation. However, the in vitro insulin secretory capacity of MSC precultured islets was superior to that of islets precultured alone. In vivo, this was associated with improved glycemia at 7, 14, 21, and 28 days posttransplantation, in recipients of MSC precultured islets compared to islets precultured alone. The area of individual islets within the graft-bearing liver was significantly higher in recipients of MSC precultured islets compared to islets precultured alone. Our experimental studies suggest that preculturing islets with MSCs represents a favorable strategy for improving the efficiency of clinical islet transplantation.

Inflammatory response in islet transplantation

Islet cell transplantation is a promising beta cell replacement therapy for patients with brittle type 1 diabetes as well as refractory chronic pancreatitis. Despite the vast advancements made in this field, challenges still remain in achieving high frequency and long-term successful transplant outcomes. Here we review recent advances in understanding the role of inflammation in islet transplantation and development of strategies to prevent damage to islets from inflammation. The inflammatory response associated with islets has been recognized as the primary cause of early damage to islets and graft loss after transplantation. Details on cell signaling pathways in islets triggered by cytokines and harmful inflammatory events during pancreas procurement, pancreas preservation, islet isolation, and islet infusion are presented. Robust control of pre- and peritransplant islet inflammation could improve posttransplant islet survival and in turn enhance the benefits of islet cell transplantation for patients who are insulin dependent. We discuss several potent anti-inflammatory strategies that show promise for improving islet engraftment. Further understanding of molecular mechanisms involved in the inflammatory response will provide the basis for developing potent therapeutic strategies for enhancing the quality and success of islet transplantation.

Effects of Dipeptidyl Peptidase-4 Inhibition with MK-0431 on Syngeneic Mouse Islet Transplantation

Dipeptidyl peptidase (DPP)-4 inhibitors increase circulating levels of glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide which may promote β-cell proliferation and survival. This study tested if DPP-4 inhibition with MK-0431 is beneficial for diabetic mice syngeneically transplanted with a marginal number of islets. We syngeneically transplanted 150 C57BL/6 mouse islets under the kidney capsule of each streptozotocin-diabetic mouse and then treated recipients with (n = 21) or without (n = 17) MK-0431 (30 mg/kg/day, po) for 6 weeks. After islet transplantation, blood glucose levels decreased in both MK-0431-treated and control groups. However, the blood glucose and area under the curve of the intraperitoneal glucose tolerance test at 2, 4, and 6 weeks were not significantly different between MK-0431-treated mice and controls. During 6 weeks, both groups exhibited increased body weights over time. However, the weight between two groups did not differ throughout the study period. At 6 weeks after transplantation, the graft beta-cell mass (0.024 ± 0.005 versus 0.023 ± 0.007 mg, P = 0.8793) and insulin content (140 ± 48 versus 231 ± 63 ng, P = 0.2939) were comparable in the MK-0431-treated group and controls. Our results indicate posttransplant DPP-4 inhibition with MK-0431 in the diabetic recipient with a marginal number of islets is not beneficial to transplantation outcome or islet grafts.

Use of glucagon-like peptide-1 agonists to improve islet graft performance

Human islet transplantation is an effective and promising therapy for type I diabetes. However, long-term insulin independence is both difficult to achieve and inconsistent. De novo or early administration of incretin-based drugs is being explored for improving islet engraftment. In addition to its glucose-dependent insulinotropic effects, incretins also lower postprandial glucose excursion by inhibiting glucagon secretion, delaying gastric emptying, and can protect beta-cell function. Incretin therapy has so far proven clinically safe and tolerable with little hypoglycemic risk. The present review aims to highlight the new frontiers in research involving incretins from both in vitro and in vivo animal studies in the field of islet transplant. It also provides an overview of the current clinical status of incretin usage in islet transplantation in the management of type I diabetes.

Anti-inflammatory strategies to enhance islet engraftment and survival

Early innate inflammatory reaction strongly affects islet engraftment and survival after intrahepatic transplantation. This early immune response is triggered by ischemia-reperfusion injury and instant blood mediated inflammatory reaction (IBMIR) occurring hours and days after islet infusion. Evidence in both mouse model and in human counterpart suggest the involvement of coagulation, complement system, and proinflammatory chemokines/cytokines. Identification and targeting of pathway(s), playing a role as "master regulator(s)" in post-transplant detrimental inflammatory events, is now mandatory to improve islet transplantation success. This review will focus on inflammatory pathway(s) differentially modulated by islet isolation and mainly associated with the early post-transplant events. Moreover, we will take into account anti-inflammatory strategies that have been tested at 2 levels: on the graft, ex vivo, during islet culture (i.e., donor) and/or on the graft site, in vivo, early after islet infusion (i.e., recipient).

Endothelial progenitor cells enhance islet engraftment, influence β-cell function, and modulate islet connexin 36 expression

The success of pancreatic islet transplantation is limited by delayed engraftment and suboptimal function in the longer term. Endothelial progenitor cells (EPCs) represent a potential cellular therapy that may improve the engraftment of transplanted pancreatic islets. In addition, EPCs may directly affect the function of pancreatic β-cells. The objective of this study was to examine the ability of EPCs to enhance pancreatic islet transplantation in a murine syngeneic marginal mass transplant model and to examine the mechanisms through which this occurs. We found that cotransplanted EPCs improved the cure rate and initial glycemic control of transplanted islets. Gene expression data indicate that EPCs, or their soluble products, modulate the expression of the β-cell surface molecule connexin 36 and affect glucose-stimulated insulin release in vitro. In conclusion, EPCs are a promising candidate for improving outcomes in islet transplantation, and their mechanisms of action warrant further study.

Pharmacology, physiology, and mechanisms of incretin hormone action

Incretin peptides, principally GLP-1 and GIP, regulate islet hormone secretion, glucose concentrations, lipid metabolism, gut motility, appetite and body weight, and immune function, providing a scientific basis for utilizing incretin-based therapies in the treatment of type 2 diabetes. Activation of GLP-1 and GIP receptors also leads to nonglycemic effects in multiple tissues, through direct actions on tissues expressing incretin receptors and indirect mechanisms mediated through neuronal and endocrine pathways. Here we contrast the pharmacology and physiology of incretin hormones and review recent advances in mechanisms coupling incretin receptor signaling to pleiotropic metabolic actions in preclinical studies. We discuss whether mechanisms identified in preclinical studies have potential translational relevance for the treatment of human disease and highlight controversies and uncertainties in incretin biology that require resolution in future studies.

Preventing p38 MAPK-mediated MafA degradation ameliorates β-cell dysfunction under oxidative stress

The reduction in the expression of glucose-responsive insulin gene transcription factor MafA accompanies the development of β-cell dysfunction under oxidative stress/diabetic milieu. Humans with type 2 diabetes have reduced MafA expression, and thus preventing this reduction could overcome β-cell dysfunction and diabetes. We previously showed that p38 MAPK, but not glycogen synthase kinase 3 (GSK3), is a major regulator of MafA degradation under oxidative stress. Here, we examined the mechanisms of this degradation and whether preventing MafA degradation under oxidative stress will overcome β-cell dysfunction. We show that under oxidative and nonoxidative conditions p38 MAPK directly binds to MafA and triggers MafA degradation via ubiquitin proteasomal pathway. However, unlike nonoxidative conditions, MafA degradation under oxidative stress depended on p38 MAPK-mediated phosphorylation at threonine (T) 134, and not T57. Furthermore the expression of alanine (A) 134-MafA, but not A57-MafA, reduced the oxidative stress-mediated loss of glucose-stimulated insulin secretion, which was independent of p38 MAPK action on protein kinase D, a regulator of insulin secretion. Interestingly, the expression of proteasomal activator PA28γ that degrades GSK3-phosphorylated (including T57) MafA was reduced under oxidative stress, explaining the dominance of p38 MAPK over the GSK3 pathway in regulating MafA stability under oxidative stress. These results identify two distinct pathways mediating p38 MAPK-dependent MafA degradation under oxidative and nonoxidative conditions and show that inhibiting MafA degradation under oxidative stress ameliorates β-cell dysfunction and could lead to novel therapies for diabetes.

Exendin-4 protects hypoxic islets from oxidative stress and improves islet transplantation outcome

Oxidative stress produced during pancreatic islet isolation leads to significant β-cell damage. Homeostatic cytokines secreted subsequently to islet transplantation damage β-cells by generating oxygen free radicals. In this study, exendin-4, a glucagon-like peptide-1 analog improved islet transplantation outcome by increasing the survival of diabetic recipient mice from 58% to 100%. We hypothesized that this beneficial effect was due to the ability of exendin-4 to reduce oxidative stress. Further experiments showed that it significantly reduced the apoptotic rate of cultured β-cells subjected to hypoxia or to IL-1β. Reduction of apoptotic events was confirmed in pancreatic islet grafts of exendin-4-treated mice. Exendin-4 enhanced Akt phosphorylation of β-cells and insulin released from them. It even augmented insulin secretion from islets cultivated at hypoxic conditions. Exposure to hypoxia led to a decrease in the activation of Akt, which was reversed when β-cells were pretreated with exendin-4. Moreover, exendin-4 increased the activity of redox enzymes in a hypoxia-treated β-cell line and reduced reactive oxygen species production in isolated pancreatic islets. Recovery from diabetes in mice transplanted with hypoxic islets was more efficient when they received exendin-4. In conclusion, exendin-4 rescued islets from oxidative stress caused by hypoxia or due to cytokine exposure. It improved the outcome of syngenic and xenogenic islet transplantation.

Maintenance of islet morphology is beneficial for transplantation outcome in diabetic mice

We have previously shown that co-transplantation of islets and Mesenchymal Stem Cells (MSCs) improves islet graft function and revascularisation, which was associated with the maintenance of normal islet morphology. The aim of the current study was to determine whether maintaining islet morphology in the absence of additional islet-helper cells would improve transplantation outcome in diabetic mice. Islets were isolated from C57BL/6 mice. Recipient streptozotocin-diabetic C57BL/6 mice were transplanted with a minimal mass of 150 islets as a single pellet or islets that were either manually dispersed or dispersed within a matrigel plug beneath the kidney capsule. Blood glucose concentrations were monitored for one month. Islet graft morphology and vascularisation were analysed by histology. Islets dispersed either alone or within matrigel plugs maintained near normal morphology, in contrast to pelleted islets, where individual islets fused to form large endocrine aggregates. The vascularisation of manually dispersed islets and islets dispersed within matrigel plugs was increased relative to respective control pelleted islet grafts. After one month 1/6 mice transplanted with pelleted islets cured compared to 5/6 mice transplanted with manually dispersed islets. The curative capacity of islets dispersed in matrigel was also better than that of pelleted islets (5/8 islet-matrigel implanted mice vs. 1/7 mice transplanted with pelleted islets cured by one month). Therefore, this study demonstrates that the maintenance of islet morphology is associated with improved graft function and revascularisation in diabetic mice.

Diabetes Mellitus: New Challenges and Innovative Therapies

Diabetes is a common chronic disease affecting an estimated 285 million adults worldwide. The rising incidence of diabetes, metabolic syndrome, and subsequent vascular diseases is a major public health problem in industrialized countries. This chapter summarizes current pharmacological approaches to treat diabetes mellitus and focuses on novel therapies for diabetes mellitus that are under development.

There is great potential for developing a new generation of therapeutics that offer better control of diabetes, its co-morbidities and its complications. Preclinical results are discussed for new approaches including AMPK activation, the FGF21 target, cell therapy approaches, adiponectin mimetics and novel insulin formulations. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications.

In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality of life in the near future.

Fresh islets are more effective for islet transplantation than cultured islets

For clinical islet transplantation, isolated islets deteriorate rapidly in culture, although culturing islets prior to transplantation provides flexibility for evaluation of isolated islets and pretreatment of patients. In the present study, we compared human fresh islets to cultured islets with in vitro and in vivo assays. After culture for 24, 48, and 72 h, islet yield significantly decreased from 2,000 to 1,738 ± 26 (13% loss), 1,525 ± 30 (24% loss), or 1,298 ± 18 IEQ (35% loss), respectively. The ATP contents were significantly higher in the 6-h cultured group (near fresh group) than in 48-h culture groups. The stimulation index was relatively higher in the 6-h cultured group than in 48-h cultured group. Human islets with or without culture were transplanted into diabetic nude mice. The attainability of posttransplantation normoglycemia was significantly higher in fresh group than in the culture groups. Intraperitoneal glucose tolerance testing (IPGTT) showed that the blood glucose levels of mice transplanted with fresh islets were significantly lower than with cultured islets at 30, 60, 90, and 120 min after injection. These data suggest that human islet transplantation without culture could avoid the deterioration of islets during culture and improve the outcome of islet transplantation. Based on these data, we have transplanted fresh islets without culture for our current clinical islet transplantation protocol.

Exendin-4 increases the expression of hypoxia-inducible factor-1α in rat islets and preserves the endocrine cell volume of both free and macroencapsulated islet grafts

In this study, we evaluated the effects of exendin-4 on free and encapsulated islet grafts in a rodent model. We also investigated the role of a transcription factor, hypoxia-inducible factor-1 (HIF-1), in mediating the beneficial effects of exendin-4. Diabetic athymic mice were transplanted with free rat islets under the kidney capsule or with macroencapsulated rat islets SC with or without exendin-4, islet preculture (exendin-4 0.1 nM for 20 h), and/or recipient treatment (IP 100 ng/day, day 0-7). The mice were followed for 4 weeks and the graft function and β-cell volume were evaluated. The effects of exendin-4 on islet HIF-1α mRNA and protein expression and on ATP content in a rat insulinoma cell line (INS-1E) were also examined. Preculture with exendin-4 followed by recipient treatment improved the outcome of both free (73% graft function vs. 26% in controls, p = 0.03) and macroencapsulated islet grafts (100% vs. 25% in controls, p = 0.02). In macroencapsulated grafts, the exendin-4-treated group had significantly larger endocrine volume, less graft necrosis, and more blood vessels around the capsule. In rat islets cultured with exendin-4, HIF-1α mRNA and protein expression were significantly enhanced. ATP content was increased in exendin-4-treated INS-1E cells under hypoxic conditions. The improved functional outcome after transplantation of a marginal islet mass with a brief initial treatment with exendin-4 is related to a larger surviving endocrine cell volume. Exendin-4 may improve islet graft resistance to hypoxia during the peritransplant period by increasing the expression of HIF-1α.

Markedly decreased blood perfusion of pancreatic islets transplanted intraportally into the liver: disruption of islet integrity necessary for islet revascularization

Experimental studies indicate low revascularization of intraportally transplanted islets. This study aimed to quantify, for the first time, the blood perfusion of intrahepatically transplanted islets and elucidate necessary factors for proper islet graft revascularization at this site. Yellow chameleon protein 3.0 islets expressing fluorescent protein in all cells were transplanted. Graft blood perfusion was determined by microspheres. The vascular density and relative contribution of donor blood vessels in revascularization was evaluated using islets expressing green fluorescent protein under the Tie-2 promoter. Blood perfusion of intrahepatic islets was as a mean only 5% of that of native islets at 1-month posttransplantation. However, there was a marked heterogeneity where blood perfusion was less decreased in islets transplanted without prior culture and in many cases restored in islets with disrupted integrity. Analysis of vascular density showed that distorted islets were well revascularized, whereas islets still intact at 1-month posttransplantation were almost avascular. Few donor endothelial cells were observed in the new islet vasculature. The very low blood perfusion of intraportally transplanted islets is likely to predispose for ischemia and hamper islet function. Since donor endothelial cells do not expand posttransplantation, disruption of islet integrity is necessary for revascularization to occur by recipient blood vessels.

Chemical methods to induce Beta-cell proliferation

Pancreatic beta-cell regeneration, for example, by inducing proliferation, remains an important goal in developing effective treatments for diabetes. However, beta cells have mainly been considered quiescent. This "static" view has recently been challenged by observations of relevant physiological conditions in which metabolic stress is compensated by an increase in beta-cell mass. Understanding the molecular mechanisms underlining these process could open the possibility of developing novel small molecules to increase beta-cell mass. Several cellular cell-cycle and signaling proteins provide attractive targets for high throughput screening, and recent advances in cell culture have enabled phenotypic screening for small molecule-induced beta-cell proliferation. We present here an overview of the current trends involving small-molecule approaches to induce beta-cell regeneration by proliferation.

Recent progress in pancreatic islet transplantation

Diabetes mellitus remains a major burden. More than 200 million people are affected worldwide, which represents 6% of the world’s population. Type 1 diabetes mellitus is an autoimmune disease, which induces the permanent destruction of the β-cells of the pancreatic islets of Langerhans. Although intensive insulin therapy has proven effective to delay and sometimes prevent the progression of complications such as nephropathy, neuropathy or retinopathy, it is difficult to achieve and maintain long term in most subjects. The successes achieved over the last few decades by the transplantation of whole pancreas and isolated islets suggest that diabetes can be cured by the replenishment of deficient β cells. However, islet transplantation efforts have various limitations, including the limited supply of donor pancreata, the paucity of experienced islet isolation teams, side effects of immunosuppressants and poor long term results. The purpose of this article is to review the recent progress in clinical islet transplantation for the treatment of diabetes and to describe the recent progress on pancreatic stem/progenitor cell research, which has opened up several possibilities for the development of new treatments for diabetes.

Islets transplanted in immunoisolation devices: a review of the progress and the challenges that remain

The concept of using an immunoisolation device to facilitate the transplantation of islets without the need for immunosuppression has been around for more than 50 yr. Significant progress has been made in developing suitable materials that satisfy the need for biocompatibility, durability, and permselectivity. However, the search is ongoing for a device that allows sufficient oxygen transfer while maintaining a barrier to immune cells and preventing rejection of the transplanted tissue. Separating the islets from the rich blood supply in the native pancreas takes its toll. The immunoisolated islets commonly suffer from hypoxia and necrosis, which in turn triggers a host immune response. Efforts have been made to improve the supply of nutrients by using proangiogenic factors to augment the development of a vascular supply in the transplant site, by using small islet cell aggregates to reduce the barrier to diffusion of oxygen, or by creating scaffolds that are in close proximity to a vascular network such as the omental blood supply. Even if these efforts are successful, the shortage of donor islet tissue available for transplantation remains a major problem. To this end, a search for a renewable source of insulin-producing cells is ongoing; whether these will come from adult or embryonic stem cells or xenogeneic sources remains to be seen. Herein we will review the above issues and chart the progress made with various immunoisolation devices in small and large animal models and the small number of clinical trials carried out to date.

Donor islet endothelial cells in pancreatic islet revascularization

OBJECTIVE

Freshly isolated pancreatic islets contain, in contrast to cultured islets, intraislet endothelial cells (ECs), which can contribute to the formation of functional blood vessels after transplantation. We have characterized how donor islet endothelial cells (DIECs) may contribute to the revascularization rate, vascular density, and endocrine graft function after transplantation of freshly isolated and cultured islets.

RESEARCH DESIGN AND METHODS

Freshly isolated and cultured islets were transplanted under the kidney capsule and into the anterior chamber of the eye. Intravital laser scanning microscopy was used to monitor the revascularization process and DIECs in intact grafts. The grafts' metabolic function was examined by reversal of diabetes, and the ultrastructural morphology by transmission electron microscopy.

RESULTS

DIECs significantly contributed to the vasculature of fresh islet grafts, assessed up to 5 months after transplantation, but were hardly detected in cultured islet grafts. Early participation of DIECs in the revascularization process correlated with a higher revascularization rate of freshly isolated islets compared with cultured islets. However, after complete revascularization, the vascular density was similar in the two groups, and host ECs gained morphological features resembling the endogenous islet vasculature. Surprisingly, grafts originating from cultured islets reversed diabetes more rapidly than those originating from fresh islets.

CONCLUSIONS

In summary, DIECs contributed to the revascularization of fresh, but not cultured, islets by participating in early processes of vessel formation and persisting in the vasculature over long periods of time. However, the DIECs did not increase the vascular density or improve the endocrine function of the grafts.

Calcium/calmodulin-dependent kinase IV controls glucose-induced Irs2 expression in mouse beta cells via activation of cAMP response element-binding protein

AIMS/HYPOTHESIS

Irs2, which is upregulated by glucose, is important for beta cell plasticity. Cyclic AMP response element-binding protein (CREB) stimulates beta cell Irs2 expression and is a major calcium/calmodulin-dependent kinase (CaMK)(IV) target in neurons. We therefore hypothesised that CaMK(IV) mediates glucose-induced Irs2 expression in beta cells via CREB activation.

METHODS

The functions of CaMK(IV) and CREB were investigated in MIN6 beta cells and mouse islets using the CaMK inhibitor KN62, the calcium chelator bapta-(AM) and the voltage-dependent calcium channel inhibitor nifedipine. Small interfering RNAs were used to silence endogenous CaMK(IV) production and expression vectors to overproduce constitutively active and dominant negative forms of CaMK(IV) and CREB. Irs1 and Irs2 expression were determined by quantitative PCR and Western blotting, and the role of CREB was also investigated by assessing its phosphorylation on serine 133.

RESULTS

Increasing the glucose concentration from 2.5 to 25 mmol/l stimulated CREB phosphorylation on serine 133 and specifically stimulated Irs2 but not Irs1 expression. Similarly, overproduction of a constitutively active form of CaMK(IV) promoted sustained CREB phosphorylation and a significant increase in Irs2 but not Irs1 expression. In contrast, these stimulatory effects of glucose were all suppressed by overproducing an inactive CaMK(IV) mutant. Inhibition of glucose-induced calcium influx with nifedipine or chelation of intracellular calcium with bapta-(AM), as well as silencing of CaMK(IV) or inhibition of its activity with KN62 resulted in similar observations. Finally, overproduction of a dominant negative form of CREB completely suppressed glucose and CaMK(IV) stimulation of Irs2 expression.

CONCLUSIONS/INTERPRETATION

Our results suggest that the Ca(2+)/CaMK(IV)/CREB cascade plays a critical role in the regulation of Irs2 expression in beta cells.

Comparison of fresh and cultured islets from human and porcine pancreata. Transplant Proc. 2010;42:2084-2086. [PMID: 20692414 DOI: 10.1016/j.transproceed.2010.05.098]

INTRODUCTION

For clinical islet transplantation, many centers have recently introduced of human islet cultures prior to transplantation. They provide flexibility to evaluate isolated islets and pretreat patients. However, isolated islets deteriorate rapidly in culture. In the present study, we compared fresh human and porcine islets with cultured islets for c-Jun NH(2)-terminal kinase (JNK) activity.

MATERIALS AND METHODS

Islet isolations from human and porcine pancreata were performed using the standard Ricordi technique with a modified Edmonton protocol. Isolated islets cultured for 24 hours at 37 degrees C with 5% CO(2) in culture medium were evaluated for counts and JNK activity.

RESULTS

After 24 hours of culture, the percentages of surviving islets were 86.9% for human and 47.3% for porcine sources. JNK activity in isolated islets declined to a low baseline level after 24-hour culture.

CONCLUSION

Both human and porcine islets deteriorated rapidly in 24-hour cultures, although the in vitro conditions did not induce JNK activation.

FGF-21 enhances islet engraftment in mouse syngeneic islet transplantation model

To clarify the effect of fibroblast growth factor-21 (FGF-21) on islet transplantation, a suboptimal number of islets were transplanted into streptozotocin (STZ)-induced diabetic mice with or without FGF-21 treatment. Three-day treatment with FGF-21 contributed to restoration of normoglycemia by suppressing islet graft loss. The FGF-21-treated mice showed lower glycemic levels despite similar insulin content in the graft than that in untreated mice on day 3, indicating that FGF-21 not only has a cytoprotective effect but also decreases β-cell load by increasing insulin sensitivity. These results suggest that FGF-21 may be useful as a treatment to improve islet engraftment rates in clinical islet transplantation.

Brain Death in Combination with Warm Ischemic Stress during Isolation Procedures Induces the Expression of Crucial Inflammatory Mediators in the Isolated Islets

Tissue factor (TF) and monocyte chemoattractant protein-1 (MCP-1) expressed on the islets have been identified as the main trigger of the instant blood-mediated inflammatory reaction (IBMIR) in islet transplantation. Because the key steps that directly induce TF and MCP-1 remain to be determined, we focused on the influence of brain death (BD) on TF and MCP-1 expression in the pancreatic tissues and isolated islets using a rodent model. TF and MCP-1 mRNA levels in the pancreatic tissues were similar between the BD and the control group. However, TF and MCP-1 mRNA in the fresh islets of the BD group were significantly higher than that of the control group ( p < 0.01). BD may thus be suggested to be of great importance as an initiator of TF and MCP-1 induction in the isolated islets. Furthermore, the upregulation of crucial inflammatory mediators induced by BD could be exacerbated by warm ischemic damage during digestion procedures. In the present study, the islet yield and purity were affected by BD. However, almost no influences were observed with respect to islet viability, indicating that the expression of inflammatory mediators rather than islet viability is more susceptible to BD. According to the change in time course of TF and MCP-1 expression in the isolated islets, the selected time point for islet infusion in current clinical islet transplantation was thus shown to be at its worst level, at least with respect to the damage caused by BD and ischemic stress. In conclusion, BD in combination with warm ischemic stress during isolation procedures induces a high expression of TF and MCP-1 in the isolated islets. In order to reduce the expression of crucial inflammatory mediators in the islet grafts, the management of the pancreas from brain-dead donors with early anti-inflammatory treatments is thus warranted.

Upgrading pretransplant human islet culture technology requires human serum combined with media renewal

BACKGROUND.: The original Edmonton protocol used fresh islets, but for obvious logistic advantages most transplant centers have implemented pretransplant culture in human albumin. The aim of this study was to improve current pretransplant human islet culture techniques. METHODS.: Clinical-grade purified human islets from a total of 24 donors were directly resuspended after isolation in CMRL 1066-based media at 37 degrees C, and media additions and renewal were tested. At days 1 and 5 of culture, in vitro quality controls included islet viability, insulin content and function, apoptosis, and in vivo islet potency assay in nude mice. RESULTS.: Replacing human albumin with human AB serum improved 1- and 5-day preservation of islet function and viability which was further enhanced with antioxidant Stem Ease, leading to the iCulture medium (enriched CMRL: pyruvate, zinc sulfate, insulin, transferrin, selenium, 2.5% human AB serum and Stem Ease). Major damage occurs in the first day of culture and frequent media renewal (25% vol/hr) in this period further improved viability, apoptosis, islet recovery, and function in vitro and in vivo, compared with only changing medium after overnight culture. CONCLUSIONS.: The described human islet culture technique (iCulture medium+renewal) seems to be the best choice for clinical human islet culture when short (1 day) or long (5 days) periods are used. Media choice and dilution play a major role in the function and survival of human islets in culture.

Glucagon-like peptide-1 receptor signalling selectively regulates murine lymphocyte proliferation and maintenance of peripheral regulatory T cells

AIMS/HYPOTHESIS

Glucagon-like peptide-1 receptor (GLP-1R) agonists improve glucose control in animals and humans with type 1 diabetes. However, there is little information on the role of the GLP-1R in the immune system. We studied the role of the GLP-1R in immune function in wild-type (WT) and nonobese diabetic (NOD) and Glp1r-/- mice.

METHODS

Glp1r mRNA expression was examined in sorted immune subpopulations by RT-PCR. The effects of GLP-1R activation were assessed on cAMP production and proliferation, migration and survival of primary immune cells from WT and NOD mice. The ability of primary cells from Glp1r-/- mice to proliferate, migrate or survive apoptosis was determined. Immunophenotyping studies were performed to assess the frequency of immune subpopulations in Glp1r-/- mice.

RESULTS

Ex vivo activation of the GLP-1R resulted in a modest but significant elevation of cAMP in primary thymocytes and splenocytes from both WT and NOD mice. GLP-1R activation did not increase proliferation of primary thymocytes, splenocytes or peripheral lymph node cells. In contrast, Glp1r-/- thymocytes exhibited a hypoproliferative response, whilst peripheral Glp1r-/- lymphocytes were hyperproliferative in response to mitogenic stimulation. Activation or loss of GLP-1R signalling did not modify apoptosis or chemotaxis in primary lymphocytes. Male Glp1r-/- mice exhibited a significantly lower percentage of peripheral regulatory T cells, although no differences were observed in the numbers of CD4+ and CD8+ T cells and B cells in the spleen and lymph nodes of Glp1r-/- mice.

CONCLUSIONS/INTERPRETATION

These studies establish that GLP-1R signalling may regulate lymphocyte proliferation and maintenance of peripheral regulatory T cells.

Diabetes mellitus: new challenges and innovative therapies

Diabetes mellitus is a widespread disease prevalence and incidence of which increases worldwide. The introduction of insulin therapy represented a major breakthrough in type 1 diabetes; however, frequent hyper- and hypoglycemia seriously affects the quality of life of these patients. New therapeutic approaches, such as whole pancreas transplant or pancreatic islet transplant, stem cell, gene therapy and islets encapsulation are discussed in this review. Regarding type 2 diabetes, therapy has been based on drugs that stimulate insulin secretion (sulphonylureas and rapid-acting secretagogues), reduce hepatic glucose production (biguanides), delay digestion and absorption of intestinal carbohydrate (alpha-glucosidase inhibitors) or improve insulin action (thiazolidinediones). This review is also focused on the newer therapeutically approaches such as incretin-based therapies, bariatric surgery, stem cells and other emerging therapies that promise to further extend the options available. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Some of these therapies rely on genetic modification of non-differentiated cells to express pancreatic endocrine developmental factors, promoting differentiation of non-endocrine cells into β-cells, enabling synthesis and secretion of insulin in a glucose-regulated manner. Alternative therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications. In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality-life and allow personalized therapy-planning in the near future.

Liraglutide, a long-acting human glucagon-like peptide 1 analogue, improves human islet survival in culture

The culture of human islets is associated with approximately 10-20% islet loss, occasionally preventing transplantation. Preconditioning of the islets to improve postculture yields would be of immediate benefit, with the potential to increase both the number of transplanted patients and their metabolic reserve. In this study, the effect of liraglutide, a long-acting human glucagon-like peptide 1 analogue, on cultured human islets was examined. Culture with liraglutide (1 micromol/l) was associated with a preservation of islet mass (significantly more islets at 24 and 48 h, compared to control; P < or = 0.05 at 24 and 48 h) and with the presence of larger islets (P < or = 0.05 at 48 h). These observations were supported by reduced apoptosis rates after 24 h of treatment. We also demonstrated that human islet engraftment is improved in C57Bl/6-RAG(-/-) mice treated with liraglutide 200 microg/kg sc twice daily (P < or = 0.05), suggesting that liraglutide should be continued after transplantation. Overall, these data demonstrate the beneficial effect of liraglutide on cultured human islets, preserving islet mass. They support the design of clinical studies looking at the effect of liraglutide in clinical islet transplantation.

Low-temperature preservation of isolated islets is superior to conventional islet culture before islet transplantation

BACKGROUND

Although culturing islets before transplantation provides flexibility for evaluation of isolated islets and pretreatment of patients, it is well-known that isolated islets deteriorate rapidly in culture. In this study, we evaluated optimal temperature for culture/preservation of isolated human islets before transplantation.

METHODS

Isolated islets were cultured or preserved for 48 hr in the following culture/preservation conditions: preservation at 4 degrees C in University of Wisconsin solution and culture at 22 degrees C or 37 degrees C in culture medium.

RESULTS

Islet morphology after 4 degrees C preservation was similar to that of fresh islets, whereas islet diameter after 37 degrees C or 22 degrees C culture was smaller than that of fresh islets. Islet yield significantly decreased at higher temperatures (24% loss in 37 degrees C culture and 19% loss in 22 degrees C culture, but <5% loss in 4 degrees C preservation). Cultured/preserved islets were transplanted into diabetic nude mice. The attainability of posttransplantation normoglycemia was significantly higher in the 4 degrees C preservation group than in 22 degrees C and 37 degrees C culture groups.

CONCLUSION

Preservation of isolated islets at 4 degrees C improves the outcome of islet transplantation more efficiently than preservation at 22 degrees C or 37 degrees C. Based on these data, we have performed short-time cold storage of isolated islets instead of culturing for current clinical islet transplantation.

Islet isolation for clinical transplantation

Islet transplantation is emerging as a viable treatment option for selected patients with type 1 diabetes. Following the initial report in 2000 from Edmonton of insulin independence in seven out of seven consecutive recipients, there has been a huge expansion in clinical islet transplantation. The challenge we now face is the apparent decline in graft function over time. Isolating high-quality human islets which survive and function for a longer period will no doubt contribute to further improvement in long-term clinical outcome. This chapter reviews the selection of appropriate donors for islet isolation and transplantation, describes each step during islet isolation, and discusses the scope for further improvements.

Pancreatic islet transplantation

BACKGROUND

No formulation of exogenous insulin available to date has yet been able to mimic the physiological nictemeral rhythms of this hormone, and despite all engineering advancements, the theoretical proposal of developing a mechanical replacement for pancreatic beta cell still has not been reached. Thus, the replacement of beta cells through pancreas and pancreatic islet transplantation are the only concrete alternatives for re-establishing the endogenous insulin secretion in type 1 diabetic patients. Since only 1 to 1.5% of the pancreatic mass corresponds to endocrine tissue, pancreatic islets transplantation arises as a natural alternative. Data from the International Islet Transplant Registry (ITR) from 1983 to December 2000 document a total of 493 transplants performed around the world, with progressively worse rates of post-transplant insulin independence. In 2000, the "Edmonton Protocol" introduced several modifications to the transplantation procedure, such as the use of a steroid-free immunosuppression regimen and transplantation of a mean islet mass of 11,000 islet equivalents per kilogram, which significantly improved 1-year outcomes. Although the results of a 5-year follow-up in 65 patients demonstrated improvement in glycemic instability in a significant portion of them, only 7.5% of the patients have reached insulin independence, indicating the need of further advances in the preservation of the function of transplanted islet. In addition to the scarcity of organs available for transplantation, islets transplantation still faces major challenges, specially those related to cell loss during the process of islet isolation and the losses related to the graft site, apoptosis, allorejection, autoimmunity, and immunosuppression. The main strategies to optimize islet transplantation aim at improving all these aspects.

CONCLUSION

Human islet transplantation should be regarded as an intervention that can decrease the frequency of severe hypoglycemic episodes and improve glycemic control in selected patient for whom benefits of 4-5 years duration would be very valuable. Its limitations, however, indicate that the procedure in its current format is not suitable for all patients with type 1 diabetes.

p38 MAPK is a major regulator of MafA protein stability under oxidative stress

Mammalian MafA/RIPE3b1 is an important glucose-responsive transcription factor that regulates function, maturation, and survival of beta-cells. Increased expression of MafA results in improved glucose-stimulated insulin secretion and beta-cell function. Because MafA is a highly phosphorylated protein, we examined whether regulating activity of protein kinases can increase MafA expression by enhancing its stability. We demonstrate that MafA protein stability in MIN6 cells and isolated mouse islets is regulated by both p38 MAPK and glycogen synthase kinase 3. Inhibiting p38 MAPK enhanced MafA stability in cells grown under both low and high concentrations of glucose. We also show that the N-terminal domain of MafA plays a major role in p38 MAPK-mediated degradation; simultaneous mutation of both threonines 57 and 134 into alanines in MafA was sufficient to prevent this degradation. Under oxidative stress, a condition detrimental to beta-cell function, a decrease in MafA stability was associated with a concomitant increase in active p38 MAPK. Interestingly, inhibiting p38 MAPK but not glycogen synthase kinase 3 prevented oxidative stress-dependent degradation of MafA. These results suggest that the p38 MAPK pathway may represent a common mechanism for regulating MafA levels under oxidative stress and basal and stimulatory glucose concentrations. Therefore, preventing p38 MAPK-mediated degradation of MafA represents a novel approach to improve beta-cell function.

The current status of islet transplantation and its perspectives

Transplantation of human pancreatic isolated islets can restore beta-cell function but it requires chronic immunosuppression. The outcome of islet transplantation mainly depends on both the quality of islet preparations, and the survival of the graft. The quality of islet preparations can be evaluated by the results of isolation, which determines the chance to achieve insulin independence. The survival of islet grafts is reflected by the amount of engrafted functional tissue that maintains metabolic control. Immunosuppressive therapy prevents the immunological rejection of grafts, but impairs their function and impedes their regenerative capacity. Therefore, the selection of high quality islet preparations and the reduction of toxic effects of immunosuppressive regimens might dramatically improve the outcomes. The application of stem cell therapy in islet transplantation may contribute to a better understanding of the mechanisms responsible for tissue homeostasis and immune tolerance. Xenogeneic islets may serve as an unlimited source if immune tolerance can be achieved. This may be a strategy to enable a substantial improvement in function while overcoming potentially deleterious risks.

Risk factors for islet loss during culture prior to transplantation

Culturing islets can add great flexibility to a clinical islet transplant program. However, a reduction in the islet mass has been frequently observed during culture and its degree varies. The aim of this study was to identify the risk factors associated with a significant islet loss during culture. One-hundred and four islet preparations cultured in an attempt to use for transplantation constituted this study. After culture for 20 h (median), islet yield significantly decreased from 363 309 +/- 12 647 to 313 035 +/- 10 862 islet equivalent yield (IE) (mean +/- SE), accompanied by a reduction in packed tissue volume from 3.9 +/- 0.1 to 3.0 +/- 0.1 ml and islet index (IE/islet particle count) from 1.20 +/- 0.04 to 1.05 +/- 0.04. Culture did not markedly alter islet purity or percent of trapped islet. Morphology score and viability were significantly improved after culture. Of 104 islet preparations, 37 suffered a substantial islet loss (> 20%) over culture. Factors significantly associated with risk of islet loss identified by univariate analysis were longer cold ischemia time, two-layer method (TLM) preservation, lower islet purity, and higher islet index. Multivariate analysis revealed that independent predictors of islet loss were higher islet index and the use of TLM. This study provides novel information on the link between donor- isolation factors and islet loss during culture.

Exendin-4 treatment expands graft beta-cell mass in diabetic mice transplanted with a marginal number of fresh islets

Exendin-4 stimulates insulin secretion, suppresses glucagons secretion, increases beta-cell replication and neogenesis, and reduces beta-cell apoptosis. However, it has been shown that posttransplant exendin-4 treatment did not improve glucose homeostasis in diabetic mice transplanted with a large number of freshly isolated islets. The aim of this study was to test if exendin-4 is beneficial for hyperglycemic recipients with a marginal number of fresh islets. We transplanted 150 C57BL/6 mouse islets under the kidney capsule of inbred streptozotocin-diabetic mice, and then treated the recipients with and without exendin-4 for 6 weeks. Before and after transplantation, recipients' blood glucose, body weight, and intraperitoneal glucose tolerance test were measured. At 6 weeks, the grafts were removed to determine beta-cell mass. Blood glucose levels in both groups decreased progressively after transplantation, and the exendin-4-treated group had had lower blood glucose than controls since day 3. By 6 weeks, euglycemia was achieved more in mice treated with exendin-4 than in controls (100% vs. 62.5%, p = 0.018). The time to obtain normoglycemia was shorter in the exendin-4-treated group than in controls (12 +/- 8 vs. 29 +/- 13 days, p < 0.001). Blood glucose at 6 weeks was 123 +/- 18 and 170 +/- 62 mg/dl in the exendin-4-treated group and controls, respectively (p = 0.008). Additionally, the exendin-4-treated group had better glucose tolerance than controls at 2 and 4 weeks (p <0.02). However, both groups exhibited increased body weight over time, and weight changes did not significantly differ between the two groups throughout the study period. At 6 weeks after transplantation, grafts in the exendin-4-treated group were more prominent and contained more insulin-stained cells than those of controls. They had 2.3-fold beta-cell mass of the graft compared with controls (0.30 +/- 0.11 vs. 0.13 +/- 0.03 mg, p = 0.012). These results indicate posttransplant exendin-4 treatment in the diabetic recipient with a marginal number of fresh islets expands graft beta-cell mass and improves transplantation outcome.