Pancreatic islet transplantation

Islet transplantation: overcoming the organ shortage

BACKGROUND

Type 1 diabetes mellitus (T1D) is a condition resulting from autoimmune destruction of pancreatic β cells, leading patients to require lifelong insulin therapy, which, most often, does not avoid the most common complications of this disease. Transplantation of isolated pancreatic islets from heart-beating organ donors is a promising alternative treatment for T1D, however, this approach is severely limited by the shortage of pancreata maintained under adequate conditions.

METHODS

In order to analyze whether and how this problem could be overcome, we undertook a retrospective study from January 2007 to January 2010, evaluating the profile of brain-dead human pancreas donors offered to our Cell and Molecular Therapy NUCEL Center ( www.usp.br/nucel ) and the basis for organ refusal.

RESULTS

During this time period, 558 pancreata were offered by the São Paulo State Transplantation Central, 512 of which were refused and 46 were accepted for islet isolation and transplantation. Due to the elevated number of refused organs, we decided to analyze the main reasons for refusal in order to evaluate the possibility of improving the organ acceptance rate. The data indicate that hyperglycemia, technical issues, age, positive serology and hyperamylasemia are the top five main causes for declination of a pancreas offer.

CONCLUSIONS

This study underlines the main reasons to decline a pancreas offer in Sao Paulo-Brazil and provides some guidance to ameliorate the rate of eligible pancreas donors, aiming at improving the islet isolation and transplantation outcome.

TRIAL REGISTRATION

Protocol CAPPesq number 0742/02/CONEP 9230.

Clinical applications of pluripotent stem cells and their derivatives: current status and future perspectives

Pluripotent stem cells (PSCs) can differentiate into specific cell types and thus hold great promise in regenerative medicine to treat certain diseases. Hence, several studies have been performed harnessing their salutary properties in regenerative medicine. Despite several challenges associated with the clinical applications of PSCs, worldwide efforts are harnessing their potential in the regeneration of damaged tissues. Several clinical trials have been performed using PSCs or their derivatives. However, the delay in publishing the data obtained in the trials has led to a lack of awareness about their outcomes, resulting in apprehension about cellular therapies. Here, the authors review the published papers containing data from recent clinical trials done with PSCs. PSC-derived extracellular vesicles hold great potential in regenerative therapy. Since published papers containing the data obtained in clinical trials on PSC-derived extracellular vesicles are not available yet, the authors have reviewed some of the pre-clinical work done with them.

Integrating Additive Manufacturing Techniques to Improve Cell-Based Implants for the Treatment of Type 1 Diabetes

The increasing global prevalence of endocrine diseases like type 1 diabetes mellitus (T1DM) elevates the need for cellular replacement approaches, which can potentially enhance therapeutic durability and outcomes. Central to any cell therapy is the design of delivery systems that support cell survival and integration. In T1DM, well-established fabrication methods have created a wide range of implants, ranging from 3D macro-scale scaffolds to nano-scale coatings. These traditional methods, however, are often challenged by their inherent limitations in reproducible and discrete fabrication, particularly when scaling to the clinic. Additive manufacturing (AM) techniques provide a means to address these challenges by delivering improved control over construct geometry and microscale component placement. While still early in development in the context of T1DM cellular transplantation, the integration of AM approaches serves to improve nutrient material transport, vascularization efficiency, and the accuracy of cell, matrix, and local therapeutic placement. This review highlights current methods in T1DM cellular transplantation and the potential of AM approaches to overcome these limitations. In addition, emerging AM technologies and their broader application to cell-based therapy are discussed.

Cotransplant With Pancreatic Islet Homogenate Improved Survival and Long-Term Efficacy of Islet Transplant in Streptozotocin-Diabetic Rats

OBJECTIVES

Pancreatic islet transplant is suggested as a promising treatment option in diabetes, but the number of viable and functional islets and the long-term efficacy of transplanted islets have not been satisfactory. Islet isolation leads to destruction of the extracellular matrix and loss of trophic support of islets, which reduces their survival and function. Reconstruction of islet microenvironment with biomaterials may preserve islet survival and graft efficacy. Accordingly, we investigated the effects of pancreatic islet homogenate on islet quality and graft outcomes in diabetic rats.

MATERIALS AND METHODS

Islets were isolated from the pancreas of Sprague Dawley rats and were cultured with or without pancreatic islet homogenate. Before transplant, viability, insulin content, and insulin released from cultured islets were assessed. Islets were then transplanted into subcapsular space of diabetic rat kidney. Transplant outcomes were evaluated by plasma glucose and insulin levels, glucose tolerance tests, and stress oxidative markers.

RESULTS

Viability and insulin release in the pancreatic islet homogenate-treated islets were significantly higher than that in the control islets. After transplant of islets, recipient rats with pancreatic islet homogenate showed significant decreases in blood glucose and malondialdehyde levels and increases in superoxide dismutase activity and plasma insulin levels.

CONCLUSIONS

Islet treatment with pancreatic islet homogenate could improve islet survival and transplant function and outcomes. Oxidative stress reduction might be a secondary beneficial effect of improved quality of treated islets.

Engineering a macroporous oxygen-generating scaffold for enhancing islet cell transplantation within an extrahepatic site

Insufficient oxygenation is a serious issue arising within cell-based implants, as the hypoxic period between implantation and vascularization of the graft is largely unavoidable. In situ oxygen supplementation at the implant site should significantly mitigate hypoxia-induced cell death and dysfunction, as well as improve transplant efficacy, particularly for highly metabolically active cells such as pancreatic islets. One promising approach is the use of an oxygen generating material created through the encapsulation of calcium peroxide within polydimethylsiloxane (PDMS), termed OxySite. In this study, OxySite microbeads were incorporated within a macroporous PDMS scaffold to create a single, streamlined, oxygen generating macroporous scaffold. The resulting OxySite scaffold generated sufficient local oxygenation for up to 20 days, with nontoxic levels of reaction intermediates or by-products. The benefit of local oxygen release on transplant efficacy was investigated in a diabetic Lewis rat syngeneic transplantation model using a clinically relevant islet dosage (10,000 IEQ/kg BW) with different isolation purities (80%, 90%, and 99%). Impure islet preparations containing pancreatic non-islet cells, which are common in the clinical setting, permit examination of the effect of increased overall oxygen demand. Our transplantation outcomes showed that elevating the oxygen demand of the graft with decreasing isolation purity resulted in decreased graft efficacy for control implants, while the integration of OxySite significantly mitigated this impact and resulted in improved graft outcomes. Results highlight the superior clinical translational potential of these off-the-shelf OxySite scaffolds, where islet purity and the overall oxygen demands of implants are increased and highly variable. The oxygen-generating porous scaffold further provides a broad platform for enhancing the survival and efficacy of cellular implants for numerous other applications. STATEMENT OF SIGNIFICANCE: Hypoxia is a serious issue within tissue engineered implants. To address this challenge, we developed a distinct macroporous scaffold platform containing oxygen-generating microbeads. This oxygen-generating scaffold showed the potential to support clinically relevant cell dosages for islet transplantation, leading to improved treatment efficacy. This platform can also be used to mitigate hypoxia for other biomedical applications.

Recent progress in pancreatic islet cell therapy

Human pluripotent stem cells (PSCs), including human embryonic stem cells and induced pluripotent stem cells, are promising cell sources in regenerating pancreatic islets through in vitro directed differentiation. Recent progress in this research field has made it possible to generate glucose-responsive pancreatic islet cells from PSCs. Single-cell RNA sequencing techniques have been applied to analyze PSC-derived endocrine beta-cells, which are then compared with human islets. This has led to the identification of novel signaling pathways and molecules involved in lineage commitment during pancreatic differentiation and maturation processes. Single-cell transcriptomics are also used to construct a detailed map of in vivo endocrine differentiation of developing mouse embryos to study pancreatic islet development. Mimicking those occurring in vivo, it was reported that differentiating PSCs can generate similar islet cell structures, while metabolomics analysis highlighted key components involved in PSC-derived pancreatic islet cell function, providing information for the improvement of in vitro pancreatic maturation procedures. In addition, cell transplantation into diabetic animal models, together with the cell delivery system, is studied to ensure the therapeutic potentials of PSC-derived pancreatic islet cells. Combined with gene-editing technology, the engineered mutation-corrected PSC lines originated from diabetes patients could be differentiated into functional pancreatic islet cells, suggesting possible autologous cell therapy in the future. These PSC-derived pancreatic islet cells are a potential tool for studies of disease modeling and drug testing. Herein, we outlined the directed differentiation procedures of PSC-derived pancreatic islet cells, novel findings through transcriptome and metabolome studies, and recent progress in disease modeling.

Microelectrode Array based Functional Testing of Pancreatic Islet Cells

Electrophysiological techniques to characterize the functionality of islets of Langerhans have been limited to short-term, one-time recordings such as a patch clamp recording. We describe the use of microelectrode arrays (MEAs) to better understand the electrophysiology of dissociated islet cells in response to glucose in a real-time, non-invasive method over prolonged culture periods. Human islets were dissociated into singular cells and seeded onto MEA, which were cultured for up to 7 days. Immunofluorescent imaging revealed that several cellular subtypes of islets; β, δ, and γ cells were present after dissociation. At days 1, 3, 5, and 7 of culture, MEA recordings captured higher electrical activities of islet cells under 16.7 mM glucose (high glucose) than 1.1 mM glucose (low glucose) conditions. The fraction of the plateau phase (FOPP), which is the fraction of time with spiking activity recorded using the MEA, consistently showed distinguishably greater percentages of spiking activity with high glucose compared to the low glucose for all culture days. In parallel, glucose stimulated insulin secretion was measured revealing a diminished insulin response after day 3 of culture. Additionally, MEA spiking profiles were similar to the time course of insulin response when glucose concentration is switched from 1.1 to 16.7 mM. Our analyses suggest that extracellular recordings of dissociated islet cells using MEA is an effective approach to rapidly assess islet functionality, and could supplement standard assays such as glucose stimulate insulin response.

Translational assessment of a genetic engineering methodology to improve islet function for transplantation

Background

The functional quality of insulin-secreting islet beta cells is a major factor determining the outcome of clinical transplantations for diabetes. It is therefore of importance to develop methodological strategies aiming at optimizing islet cell function prior to transplantation. In this study we propose a synthetic biology approach to genetically engineer cellular signalling pathways in islet cells.

Methods

We established a novel procedure to modify islet beta cell function by combining adenovirus-mediated transduction with reaggregation of islet cells into pseudoislets. As a proof-of-concept for the genetic engineering of islets prior to transplantation, this methodology was applied to increase the expression of the V1b receptor specifically in insulin-secreting beta cells. The functional outcomes were assessed in vitro and in vivo following transplantation into the anterior chamber of the eye.

Findings

Pseudoislets produced from mouse dissociated islet cells displayed basic functions similar to intact native islets in terms of glucose induced intracellular signalling and insulin release, and after transplantation were properly vascularized and contributed to blood glucose homeostasis. The synthetic amplification of the V1b receptor signalling in beta cells successfully modulated pseudoislet function in vitro. Finally, in vivo responses of these pseudoislet grafts to vasopressin allowed evaluation of the potential benefits of this approach in regenerative medicine.

Interpretation

These results are promising first steps towards the generation of high-quality islets and suggest synthetic biology as an important tool in future clinical islet transplantations. Moreover, the presented methodology might serve as a useful research strategy to dissect cellular signalling mechanisms of relevance for optimal islet function.

Decellularized pancreas as a native extracellular matrix scaffold for pancreatic islet seeding and culture

Diabetes mellitus involves the loss of function and/or absolute numbers of insulin-producing β cells in pancreatic islets. Islet transplantation is currently being investigated as a potential cure, and advances in tissue engineering methods can be used to improve pancreatic islets survival and functionality. Transplanted islets experience anoikis, hypoxia, and inflammation-mediated immune response, leading to early damage and subsequent failure of the graft. Recent development in tissue engineering enables the use of decellularized organs as scaffolds for cell therapies. Decellularized pancreas could be a suitable scaffold as it can retain the native extracellular matrix and vasculature. In this study, mouse pancreata were decellularized by perfusion using 0.5% sodium dodecyl sulfate. Different characterizations revealed that the resulting matrix was free of cells and retained part of the pancreas extracellular matrix including the vasculature and its internal elastic basal lamina, the ducts with their basal membrane, and the glycosaminoglycan and collagen structures. Islets were infused into the ductal system of decellularized pancreata, and glucose-stimulated insulin secretion results confirmed their functionality after 48 hr. Also, recellularizing the decellularized pancreas with green fluorescent protein-tagged INS-1 cells and culturing the system over 120 days confirmed the biocompatibility and non-toxic nature of the scaffold. Green fluorescent protein-tagged INS-1 cells formed pseudoislets that were, over time, budding out of the decellularized pancreata. Decellularized pancreatic scaffolds seeded with endocrine pancreatic tissue could be a potential bioengineered organ for transplantation.

Human pancreatic islet transplantation: an update and description of the establishment of a pancreatic islet isolation laboratory

Type 1 diabetes mellitus (T1DM) is associated with chronic complications that lead to high morbidity and mortality rates in young adults of productive age. Intensive insulin therapy has been able to reduce the likelihood of the development of chronic diabetes complications. However, this treatment is still associated with an increased incidence of hypoglycemia. In patients with "brittle T1DM", who have severe hypoglycemia without adrenergic symptoms (hypoglycemia unawareness), islet transplantation may be a therapeutic option to restore both insulin secretion and hypoglycemic perception. The Edmonton group demonstrated that most patients who received islet infusions from more than one donor and were treated with steroid-free immunosuppressive drugs displayed a considerable decline in the initial insulin independence rates at eight years following the transplantation, but showed permanent C-peptide secretion, which facilitated glycemic control and protected patients against hypoglycemic episodes. Recently, data published by the Collaborative Islet Transplant Registry (CITR) has revealed that approximately 50% of the patients who undergo islet transplantation are insulin independent after a 3-year follow-up. Therefore, islet transplantation is able to successfully decrease plasma glucose and HbA1c levels, the occurrence of severe hypoglycemia, and improve patient quality of life. The goal of this paper was to review the human islet isolation and transplantation processes, and to describe the establishment of a human islet isolation laboratory at the Endocrine Division of the Hospital de Clínicas de Porto Alegre - Rio Grande do Sul, Brazil.

The immunosuppressive role of adenosine A2A receptors in ischemia reperfusion injury and islet transplantation

Activation of adenosine A2A receptors (A2AR) reduces inflammation by generally inhibiting the activation of pro-inflammatory cells, decreasing endothelial adhesion molecule expression and reducing the release of proinflammatory cytokine mediators. Numerous preclinical studies using selective A2AR agonists, antagonists, A2AR knockout as well as chimeric mice have suggested the therapeutic potential of A2AR agonists for the treatment of ischemia reperfusion injury (IRI) and autoimmune diseases. This review summarizes the immunosuppressive actions of A2AR agonists in murine IRI models of liver, kidney, heart, lung and CNS, and gives details on the cellular effects of A2AR activation in neutrophils, macrophages, dendritic cells, natural killer cells, NKT cells, T effector cells and CD4+CD25+FoxP3+ T regulatory cells. This is discussed in the context of cytokine mediators involved in inflammatory cascades. Whilst the role of adenosine receptor agonists in various models of autoimmune disease has been well-documented, very little information is available regarding the role of A2AR activation in type 1 diabetes mellitus (T1DM). An overview of the pathogenesis of T1DM as well as early islet graft rejection in the immediate peri-transplantation period offers insight regarding the use of A2AR agonists as a beneficial intervention in clinical islet transplantation, promoting islet graft survival, minimizing early islet loss and reducing the number of islets required for successful transplantation, thereby increasing the availability of this procedure to a greater number of recipients. In summary, the use of A2AR agonists as a clinical intervention in IRI and as an adjunct to clinical immunesuppressive regimen in islet transplantation is highlighted.

The functional and molecular characterisation of human embryonic stem cell-derived insulin-positive cells compared with adult pancreatic beta cells

AIMS/HYPOTHESIS

Using a novel directed differentiation protocol, we recently generated up to 25% insulin-producing cells from human embryonic stem cells (hESCs) (insulin(+) cells). At this juncture, it was important to functionally and molecularly characterise these hESC-derived insulin(+) cells and identify key differences and similarities between them and primary beta cells.

METHODS

We used a new reporter hESC line with green fluorescent protein (GFP) cDNA targeted to the INS locus by homologous recombination (INS (GFP/w)) and an untargeted hESC line (HES2). INS (GFP/w) allowed efficient identification and purification of GFP-producing (INS:GFP(+)) cells. Insulin(+) cells were examined for key features of adult beta cells using microarray, quantitative PCR, secretion assays, imaging and electrophysiology.

RESULTS

Immunofluorescent staining showed complete co-localisation of insulin with GFP; however, cells were often multihormonal, many with granules containing insulin and glucagon. Electrophysiological recordings revealed variable K(ATP) and voltage-gated Ca(2+) channel activity, and reduced glucose-induced cytosolic Ca(2+) uptake. This translated into defective glucose-stimulated insulin secretion but, intriguingly, appropriate glucagon responses. Gene profiling revealed differences in global gene expression between INS:GFP(+) cells and adult human islets; however, INS:GFP(+) cells had remarkably similar expression of endocrine-lineage transcription factors and genes involved in glucose sensing and exocytosis.

CONCLUSIONS/INTERPRETATION

INS:GFP(+) cells can be purified from differentiated hESCs, providing a superior source of insulin-producing cells. Genomic analyses revealed that INS:GFP(+) cells collectively resemble immature endocrine cells. However, insulin(+) cells were heterogeneous, a fact that translated into important functional differences within this population. The information gained from this study may now be used to generate new iterations of functioning beta cells that can be purified for transplant.

Recognition and killing of human and murine pancreatic beta cells by the NK receptor NKp46

Type 1 diabetes is an incurable disease that is currently treated by insulin injections or in rare cases by islet transplantation. We have recently shown that NKp46, a major killer receptor expressed by NK cells, recognizes an unknown ligand expressed by β cells and that in the absence of NKp46, or when its activity is blocked, diabetes development is inhibited. In this study, we investigate whether NKp46 is involved in the killing of human β cells that are intended to be used for transplantation, and we also thoroughly characterize the interaction between NKp46 and its human and mouse β cell ligands. We show that human β cells express an unknown ligand for NKp46 and are killed in an NKp46-dependent manner. We further demonstrate that the expression of the NKp46 ligand is detected on human β cells already at the embryonic stage and that it appears on murine β cells only following birth. Because the NKp46 ligand is detected on healthy β cells, we wondered why type 1 diabetes does not develop in all individuals and show that NK cells are absent from the vicinity of islets of healthy mice and are detected in situ in proximity with β cells in NOD mice. We also investigate the molecular mechanisms controlling NKp46 interactions with its β cell ligand and demonstrate that the recognition is confined to the membrane proximal domain and stalk region of NKp46 and that two glycosylated residues of NKp46, Thr(125) and Asn(216), are critical for this recognition.

Hemoglobin conjugates with antioxidant enzymes (hemoglobin-superoxide dismutase-catalase) via poly(ethylene glycol) crosslinker for protection of pancreatic beta RINm5F cells in hypoxia

A low p50 hemoglobin (Hb) (p50 indicates O(2) tension at which Hb is half-saturated)-based oxygen carrier conjugated to antioxidant enzymes via dicarboxymethylated poly(ethylene glycol) (PEG) linker may have the beneficial effect in protecting pancreatic beta cells from severe hypoxia at transplantation sites. In this study, the oxygen dissociation curves, Hill plots, Bohr Effect, and oxygen content of Hb conjugates were measured. The protective effect due to incubation of Hb-conjugates (Hb/PEG molar ratio 1:10) with pancreatic beta cells (RINm5F) against hypoxia (6%, 3%, and 1% oxygen) was evaluated by an MTT assay and confocal microscopy. Quantitatively, Hb conjugates with antioxidant enzymes offered statistically significant protection (p<0.01, increased viability ∼80%) from hypoxia compared to control cells in 1% oxygen environment. Confocal images also showed that the low p50 Hb conjugates with antioxidants protected RINm5F cells from hypoxia.