Implantation site-dependent dysfunction of transplanted pancreatic islets

Vascular niche of pancreatic islets

Pancreatic islets are highly vascularized micro-organs. Approximately 10% of an islet consists of blood vessels. The induction and maintenance of the islet vascular system depend on VEGF secreted from β-cells. VEGF is also critical for the phenotype of the islet vasculature by induction of a vast number of fenestrae. The islet vasculature serves the role of supplying the endocrine cells with oxygen and nutrients, but may also be important for proper glucose sensing of the cells, for paracrine support of endocrine function and growth, and for drainage of metabolites and secreted islet hormones into the systemic circulation. Emerging evidence suggests an important role of islet endothelial cells to maintain β-cell function and growth by secretion of molecules such as hepatocyte growth factor, thrombospondin-1 and laminins, thereby forming a vascular niche for the endocrine cells.

Increased CD4+CD25+Foxp3+ regulatory T cells in tolerance induced by portal venous injection

BACKGROUND

A portal vein injection (PVI) of allogeneic donor antigen is known to prolong the survival of a subsequently transplanted allograft; however, the underlying mechanism remains to be clarified.

METHODS

Irradiated C57BL/6 (B6) splenocytes were injected into BALB/c mice via the portal vein. Seven days after injection, the proportions of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells were determined in the blood, liver, and spleen. CD4(+) and CD8(+) T cells were isolated from BALB/c mice that received PVI of B6 splenocytes (PVI mice), adoptively transferred into recipient BALB/c mice 1 day before B6 or third-party C3H heart transplantation, and graft survival was compared. B6 or C3H heart allografts were implanted into anti-CD25 monoclonal antibody (mAb)-treated PVI and untreated PVI mice, and graft survivals were compared. The percentages of CD4(+)CD25(+)Foxp3(+) Treg, cytokine profiles, and ratios of apoptosis were determined in anti-CD25 mAb-treated PVI and untreated PVI mice.

RESULTS

PVI of allogeneic cells induced antigen-specific tolerance and increased the percentage of CD4(+)CD25(+)Foxp3(+) Treg. Adoptive transfer of CD4(+) T cells, but not CD8(+) T cells, from PVI mice prolonged B6 heart allograft survival. Depletion of CD4(+)CD25(+) T cells prevented the induction of tolerance and decreased the percentage of CD4(+)CD25(+)Foxp3(+) Treg in the CD3(+) T-cell pool, and thus was associated with decreased production of interleukin (IL)-4 and apoptosis of T cells.

CONCLUSION

Increased CD4(+)CD25(+)Foxp3(+) Treg play an important role in portal vein tolerance induction, at least partly via increasing the production of IL-4 and decreasing apoptosis of T cells.

Neurogenin3 is sufficient for transdetermination of hepatic progenitor cells into neo-islets in vivo but not transdifferentiation of hepatocytes

The transcription factor Neurogenin3 (Ngn3) is required for islet-cell type specification. Here, we show that hepatic gene transfer of Ngn3 transiently induces insulin in terminally differentiated hepatocytes but fails to transdifferentiate them, i.e., switch their lineage into islet cells. However, Ngn3 leads to long-term diabetes reversal in mice due to the emergence of periportal islet-like cell clusters. These neo-islets display glycemia-regulated insulin, beta-cell-specific transcripts, and an islet-specific transcription cascade, and they produce all four major islet hormones. They appear to arise from hepatic progenitor cells, most likely endoderm-derived oval cells. Thus, transfer of a single lineage-defining transcription factor, Ngn3, is sufficient to induce cell-lineage switching from a hepatic to an islet lineage in these progenitor cells, a process consistent with transdetermination, i.e, lineage switching in lineage-determined, but not terminally differentiated, cells. This paradigm of induced transdetermination of receptive progenitor cells in vivo may be generally applicable to therapeutic organogenesis for multiple diseases, including diabetes.

Low revascularization of human islets when experimentally transplanted into the liver

Previously, we have found that human islets experimentally transplanted beneath the kidney capsule have lower vascular density than native islets. This study aimed to investigate whether human islets experimentally transplanted into the liver are also poorly revascularized in the same manner as islets at the renal subcapsular site. Human islets were transplanted to nude mice. One month posttransplantation, the islet graft-bearing livers or kidneys were removed, formalin-fixed, and stained with the lectin Bandeiraea (Griffonia) simplicifolia (BS-1) to visualize endothelium. The vascular density in the intraportally transplanted human islets was found to be similarly low as in human islets transplanted beneath the kidney capsule. The intrahepatic human islets were coated with numerous vessels, but few vessels could be seen within the islets. Human islets transplanted intraportally into the liver become poorly revascularized. This could contribute to the loss of function in human islets transplanted into the liver over time.

Optimal implantation site for pancreatic islet transplantation

BACKGROUND

Since the first report of successful pancreatic islet transplantation to reverse hyperglycaemia in diabetic rodents, there has been great interest in determining the optimal site for implantation. Although the portal vein remains the most frequently used site clinically, it is not ideal. About half of the islets introduced into the liver die during or shortly after transplantation. Although many patients achieve insulin independence after portal vein infusion of islets, in the long term most resume insulin injections.

METHODS

This review considers possible sites and techniques of islet transplantation in small and large animal models, and in humans. Metabolic, immunological and technical aspects are discussed.

RESULTS AND CONCLUSION

Many groups have sought an alternative site that might offer improved engraftment and long-term survival, together with reduced procedure-related complications. The spleen, pancreas, kidney capsule, peritoneum and omental pouch have been explored. The advantages and disadvantages of various sites are discussed in order to define the most suitable for clinical use and to direct future research.

An update on preventive and regenerative therapies in diabetes mellitus

Type 1A (immune-mediated) and type 2 diabetes mellitus are two of the most common severe chronic illnesses, affecting over 230 million people worldwide with an estimated global prevalence of 5.1%. Although type 1 and type 2 diabetes differ greatly in modes of pathogenesis, these illnesses share a common pathology and consequences characterized by loss of functional beta-cell mass and subsequent dysregulation of carbohydrate and lipid metabolism. Since therapy for diabetes and the associated complications poses enormous public health and economic burdens, novel preventive and regenerative therapies have emerged in the past decade with the aim to preserve beta-cell mass and delay the onset of diabetes. The goal of this review is to provide a comprehensive overview of current efforts in the fight against diabetes, and attempts to document all strategies that have emerged in clinical studies within the past 25 years. First, strategies to identify individuals at risk, ranging from whole-genome scans to autoantibody screening, will be discussed. Second, novel approaches to prevent or delay the onset of disease will be covered. Particular focus is given on emerging strategies for individuals at risk for type 1 diabetes that target T-cell regulation and induction of tolerance, while new pharmaceutical concepts in combination with lifestyle interventions are discussed within the scope of type 2 diabetes prevention. Lastly, important efforts to halt disease progression with emphasis on beta-cell regeneration are presented.

Expression of human insulin gene wrapped with chitosan nanoparticles in NIH3T3 cells and diabetic rats

AIM

To study the expression of human insulin gene wrapped with chitosan nanoparticles in NIH3T3 cells and diabetic rats.

METHODS

pCMV.Ins, an expression plasmid of the human insulin gene, was constructed. In total, 100 microg pCMV.Ins wrapped with chitosan nanoparticles (chitosan-pCMV.Ins) was transfected to NIH3T3 cells and diabetes rats through lavage and coloclysis, respectively. The transfected cells were grown in Dulbecco's modified Eagle's medium, containing G418, for 72 h after transfection. The clones were selected and continued to grow in G418 medium for 24 d. The expression of human insulin was detected by immunohistochemistry. Human insulin in the culture medium of transfected cells was measured. Fasting blood glucose and plasma human insulin of diabetic rats were measured for 5 d after transfection. RT-PCR and Western blotting were performed to confirm the expression of the human insulin gene in diabetic rats.

RESULTS

Approximately 10% of NIH3T3 cells transfected by chitosan-pCMV.Ins expressed human insulin. Human insulin in the culture medium of NIH3T3 cells transfected by chitosan-pCMV.Ins significantly increased compared with that of the control group (P<0.01). Fasting blood glucose levels of the lavage group and the coloclysis group decreased significantly in 5 d (P<0.01) in comparison, while plasma insulin levels were much higher (P<0.01). The human insulin gene mRNA and human insulin were only detected in the lavage and the coloclysis groups.

CONCLUSION

The human insulin gene can be transfected and expressed successfully by chitosan- pCMV.Ins in NIH3T3 cells and diabetes rats, which indicates that chitosan is a promising, non-viral vector for gene expression.

Thrombosis and inflammation in intraportal islet transplantation: a review of pathophysiology and emerging therapeutics

With the inception of the Edmonton Protocol, intraportal islet transplantation (IPIT) has re-emerged as a promising cell-based therapy for type 1 diabetes. However, current clinical islet transplantation remains limited, in part, by the need to transplant islets from 2-4 donor organs, often through several separate infusions, to reverse diabetes in a single patient. Results from clinical islet transplantation and experimental animal models now indicate that the majority of transplanted islets are destroyed in the immediate post-transplant period, a process largely facilitated by deleterious inflammatory responses triggered by islet-derived procoagulant and proinflammatory mediators. Herein, mechanisms that underlie the pathophysiology of thrombosis and inflammation in IPIT are reviewed, and emerging approaches to improve islet engraftment through attenuation of inflammatory responses are discussed.

The Choice of Anatomical Site for Islet Transplantation

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

Resolving the conundrum of islet transplantation by linking metabolic dysregulation, inflammation, and immune regulation

Although type 1 diabetes cannot be prevented or reversed, replacement of insulin production by transplantation of the pancreas or pancreatic islets represents a definitive solution. At present, transplantation can restore euglycemia, but this restoration is short-lived, requires islets from multiple donors, and necessitates lifelong immunosuppression. An emerging paradigm in transplantation and autoimmunity indicates that systemic inflammation contributes to tissue injury while disrupting immune tolerance. We identify multiple barriers to successful islet transplantation, each of which either contributes to the inflammatory state or is augmented by it. To optimize islet transplantation for diabetes reversal, we suggest that targeting these interacting barriers and the accompanying inflammation may represent an improved approach to achieve successful clinical islet transplantation by enhancing islet survival, regeneration or neogenesis potential, and tolerance induction. Overall, we consider the proinflammatory effects of important technical, immunological, and metabolic barriers including: 1) islet isolation and transplantation, including selection of implantation site; 2) recurrent autoimmunity, alloimmune rejection, and unique features of the autoimmune-prone immune system; and 3) the deranged metabolism of the islet transplant recipient. Consideration of these themes reveals that each is interrelated to and exacerbated by the other and that this connection is mediated by a systemic inflammatory state. This inflammatory state may form the central barrier to successful islet transplantation. Overall, there remains substantial promise in islet transplantation with several avenues of ongoing promising research. This review focuses on interactions between the technical, immunological, and metabolic barriers that must be overcome to optimize the success of this important therapeutic approach.

Gene therapy for type 1 diabetes mellitus in rats by gastrointestinal administration of chitosan nanoparticles containing human insulin gene

AIM: To study the expression of human insulin gene in gastrointestinal tracts of diabetic rats.

METHODS: pCMV.Ins, an expression plasmid of the human insulin gene, wrapped with chitosan nanoparticles, was transfected to the diabetic rats through lavage and coloclysis, respectively. Fasting blood glucose and plasma insulin levels were measured for 7 d. Reverse transcription polymerase chain reaction (RT-PCR) analysis and Western blot analysis were performed to confirm the expression of human insulin gene.

RESULTS: Compared with the control group, the fasting blood glucose levels in the lavage and coloclysis groups were decreased significantly in 4 d (5.63 ± 0.48 mmol/L and 5.07 ± 0.37 mmol/L vs 22.12 ± 1.31 mmol/L, respectively, P < 0.01), while the plasma insulin levels were much higher (32.26 ± 1.81 &mgr;IU/mL and 32.79 ± 1.84 &mgr;IU/mL vs 14.23 ± 1.38 &mgr;IU/mL, respectively, P < 0.01). The human insulin gene mRNA and human insulin were only detected in the lavage and coloclysis groups.

CONCLUSION: Human insulin gene wrapped with chitosan nanoparticles can be successfully transfected to rats through gastrointestinal tract, indicating that chitosan is a promising non-viral vector.

Intrahepatic glucose flux as a mechanism for defective intrahepatic islet alpha-cell response to hypoglycemia

OBJECTIVE

Glucagon responses to hypoglycemia from islets transplanted in the liver are defective. To determine whether this defect is related to intrahepatic glycogen, islets from inbred Lewis rats were transplanted into the hepatic sinus (H group), peritoneal cavity (P group), omentum (O group), and kidney capsule (K group) of recipient Lewis rats previously rendered diabetic with streptozotocin (STZ).

RESEARCH DESIGN AND METHODS

Glucagon responses to hypoglycemia were obtained before and after transplantation under fed conditions and after fasting for 16 h and 48 h to deplete liver glycogen.

RESULTS

Glucagon (area under the curve) responses to hypoglycemia in the H group (8,839 +/- 1,988 pg/ml per 90 min) were significantly less than in normal rats (40,777 +/- 8,192; P < 0.01). Fasting significantly decreased hepatic glycogen levels. Glucagon responses in the H group were significantly larger after fasting (fed 8,839 +/- 1,988 vs. 16-h fasting 24,715 +/- 5,210 and 48-h fasting 29,639 +/- 4,550; P < 0.01). Glucagon response in the H group decreased after refeeding (48-h fasting 29,639 +/- 4,550 vs. refed 10,276 +/- 2,750; P < 0.01). There was no difference in glucagon response to hypoglycemia between the H and the normal control group after fasting for 48 h (H 29,639 +/- 4,550 vs. control 37,632 +/- 5,335; P = NS). No intragroup differences were observed in the P, O, and K groups, or normal control and STZ groups, when comparing fed or fasting states.

CONCLUSIONS

These data suggest that defective glucagon responses to hypoglycemia by intrahepatic islet alpha-cells is due to dominance of a suppressive signal caused by increased glucose flux and glucose levels within the liver secondary to increased glycogenolysis caused by systemic hypoglycemia.