Intrathymic islet transplantation in the canine: I. Histological and functional evidence of autologous intrathymic islet engraftment and survival in pancreatectomized recipients

Brown Adipose Tissue: A Potential Site for Islet Transplantation

BACKGROUND

Islet transplantation is a promising treatment in patients with complicated diabetes. The ideal transplant site that can extend islet graft survival and reduce the required number of engrafted islets remains to be established.

METHODS

Donor islets were isolated from red fluorescent protein (RFP) mice and transplanted into interscapular brown adipose tissue (BAT) or unilateral inguinal white adipose tissue of age-matched diabetic RFP mice. Blood glucose and body weight of the mice were monitored, and vitality and function of ectopic RFP islets were detected by fluorescence imaging, histological examination, and intraperitoneal glucose tolerance test (GTT).

RESULTS

BAT enabled the marginal number of grafted islets (80 islets) to restore blood glucose, insulin level, and GTT to normal values in all diabetic recipient mice in the short term after graft, and maintained these values for 1 year at the end of the experiment. Importantly, in the short term after transplantation, abundant extra- and intraislet neovasculatures were observed in BAT, but not in white adipose tissue, which allowed the ectopic islets to retain typical architecture and morphology and contributed to the normal GTT. Moreover, the islet-engrafted BAT displayed normal structure and morphology without significant immunocyte infiltration, and the recipient mice also showed normal lipid levels in the blood.

CONCLUSIONS

BAT remarkably enhances the viability and biological function of the transplanted ectopic islets. Moreover, the anatomical location of BAT lends itself to biopsy, removal, and islet retransplantation, which strongly suggests the BAT as a potential desirable site for islet transplantation in basic and clinical research.

The Optimization of the Prevascularization Procedures for Improving Subcutaneous Islet Engraftment

BACKGROUND

Subcutaneous islet transplantation is associated with minimal invasiveness, but poor vascularization. Thus, the optimization of the prevascularization procedures is crucial for improving the outcomes. Although the effectiveness of basic fibroblast growth factor (bFGF) was reported, the optimal procedures remain unclear. We sought to optimize the prevascularization procedures including the use of a novel scaffold, recombinant peptide (RCP).

METHODS

Devices containing various amount of bFGF with/without heparin or RCP were implanted into the subcutaneous space of diabetic C57BL/6 mice. Syngeneic islets were transplanted into the prevascularized space. Blood glucose, intraperitoneal glucose tolerance, and immunohistochemistry were evaluated.

RESULTS

The cure rates in all the device groups irrespective of bFGF doses were considerably higher than in the nondevice group. The cure rate in the bFGF0 group was unexpectedly higher than that in the subcutaneous islet transplant alone group (the None group) (57.1% vs 28.6%). Glucose tolerance was ameliorated in the bFGF10(-), 10(+) and 15(-) groups. The number of von Willebrand factor-positive vessels in the bFGF10(+) group was significantly higher than that in the None and bFGF0 groups (P < 0.01). Taken together, the bFGF10(+) group was considered to have received optimized procedures. In a marginal graft model, the efficiency in the RCP group was better than that in the bFGF10(+) group, furthermore, comparable to that in the intraportal transplantation group. Unlike bFGF, no bleeding and effusion were observed in the RCP group.

CONCLUSIONS

These results suggest that optimizing biomaterials to induce efficient prevascularization could be a novel strategy for improving subcutaneous islet transplantation.

Tissue-engineering approaches in pancreatic islet transplantation

Pancreatic islet transplantation is a promising alternative to whole-pancreas transplantation as a treatment of type 1 diabetes mellitus. This technique has been extensively developed during the past few years, with the main purpose of minimizing the complications arising from the standard protocols used in organ transplantation. By using a variety of strategies used in tissue engineering and regenerative medicine, pancreatic islets have been successfully introduced in host patients with different outcomes in terms of islet survival and functionality, as well as the desired normoglycemic control. Here, we describe and discuss those strategies to transplant islets together with different scaffolds, in combination with various cell types and diffusible factors, and always with the aim of reducing host immune response and achieving islet survival, regardless of the site of transplantation.

The Spleen as an Optimal Site for Islet Transplantation and a Source of Mesenchymal Stem Cells

This review demonstrates the unique potential of the spleen as an optimal site for islet transplantation and as a source of mesenchymal stem cells. Islet transplantation is a cellular replacement therapy used to treat severe diabetes mellitus; however, its clinical outcome is currently unsatisfactory. Selection of the most appropriate transplantation site is a major factor affecting the clinical success of this therapy. The spleen has long been studied as a candidate site for islet transplantation. Its advantages include physiological insulin drainage and regulation of immunity, and it has recently also been shown to contribute to the regeneration of transplanted islets. However, the efficacy of transplantation in the spleen is lower than that of intraportal transplantation, which is the current representative method of clinical islet transplantation. Safer and more effective methods of islet transplantation need to be established to allow the spleen to be used for clinical transplantation. The spleen is also of interest as a mesenchymal stem cell reservoir. Splenic mesenchymal stem cells contribute to the repair of damaged tissue, and their infusion may thus be a promising therapy for autoimmune diseases, including type 1 diabetes mellitus and Sjogren’s syndrome.

An overview of the necessary thymic contributions to tolerance in transplantation

The thymus is important for the development of the immune system. However, aging leads to predictable involution of the thymus and immunodeficiency. These immunodeficiencies may be rectified with thymic rejuvenation. Atrophy of the thymus is governed by a complex interplay of molecular, cytokine and hormonal factors. Herein we review the interaction of these factors across age and how they may be targeted for thymic rejuvenation. We further discuss the growing pre-clinical evidence defining the necessary and sufficient contributions of the thymus to successful tolerance induction in transplantation.

Revascularization of transplanted pancreatic islets and role of the transplantation site

Since the initial reporting of the successful reversal of hyperglycemia through the transplantation of pancreatic islets, significant research efforts have been conducted in elucidating the process of revascularization and the influence of engraftment site on graft function and survival. During the isolation process the intrinsic islet vascular networks are destroyed, leading to impaired revascularization after transplant. As a result, in some cases a significant quantity of the beta cell mass transplanted dies acutely following the infusion into the portal vein, the most clinically used site of engraftment. Subsequently, despite the majority of patients achieving insulin independence after transplant, a proportion of them recommence small, supplemental exogenous insulin over time. Herein, this review considers the process of islet revascularization after transplant, its limiting factors, and potential strategies to improve this critical step. Furthermore, we provide a characterization of alternative transplant sites, analyzing the historical evolution and their role towards advancing transplant outcomes in both the experimental and clinical settings.

Animal models of diabetes mellitus for islet transplantation

Due to current improvements in techniques for islet isolation and transplantation and protocols for immunosuppressants, islet transplantation has become an effective treatment for severe diabetes patients. Many diabetic animal models have contributed to such improvements. In this paper, we focus on 3 types of models with different mechanisms for inducing diabetes mellitus (DM): models induced by drugs including streptozotocin (STZ), pancreatomized models, and spontaneous models due to autoimmunity. STZ-induced diabetes is one of the most commonly used experimental diabetic models and is employed using many specimens including rodents, pigs or monkeys. The management of STZ models is well established for islet studies. Pancreatomized models reveal different aspects compared to STZ-induced models in terms of loss of function in the increase and decrease of blood glucose and therefore are useful for evaluating the condition in total pancreatomized patients. Spontaneous models are useful for preclinical studies including the assessment of immunosuppressants because such models involve the same mechanisms as type 1 DM in the clinical setting. In conclusion, islet researchers should select suitable diabetic animal models according to the aim of the study.

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.

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.

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.

[Experimental pancreatic islet transplant into the genito-urinary tract simultaneous to kidney transplant]

INTRODUCTION AND OBJECTIVES

Simultaneous kidney and pancreas transplant is a good treatment for both renal and pancreas insufficiency. Experimental apply of genitourinary tract for pancreas implantation is reported in this work.

MATERIAL AND METHOD

Twenty animals aged as average 5.5 monts (SD 1.1) and an average weight of 53 kgr were submitted to this protocol. In the day 1 a left nephrectomy is completed and the graft is perfused with University of Wisconsin solution. A partial pancreatectomy is completed at following, isolation of pancreatic islets by colagenase enzymatic digestion. Islets are dryed with Ditizone and culptured for 24 hours at 37 degrees C and 5% CO2. Day-2 a right nephrectomy is performed and orthotopic renal autotransplant using the left kidney is completed. Pancreatic islets are transplanted in 4 different locations of the genitourinary tract: renal subcapsular space, bladder submucosae, testis parenchyma and vas deferens. Day-7, all the animals were sacrifized to complete pathological study.

RESULTS AND CONCLUSIONS

Viable islets were isolated in bladder submucosae and testis after transdeferential injection.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.