A strategy for the engineering of insulin producing cells with a broad spectrum of defense properties

ECM-enriched alginate hydrogels for bioartificial pancreas: an ideal niche to improve insulin secretion and diabetic glucose profile

INTRODUCTION

The success of a bioartificial pancreas crucially depends on ameliorating encapsulated beta cells survival and function. By mimicking the cellular in vivo niche, the aim of this study was to develop a novel model for beta cells encapsulation capable of establishing an appropriate microenvironment that supports interactions between cells and extracellular matrix (ECM) components.

METHODS

ECM components (Arg-Gly-Asp, abbreviated as RGD) were chemically incorporated in alginate hydrogels (alginate-RGD). After encapsulation, INS-1E beta cells outcome was analyzed in vitro and after their implantation in an animal model of diabetes.

RESULTS

Our alginate-RGD model demonstrated to be a good in vitro niche for supporting beta cells viability, proliferation, and activity, namely by improving the key feature of insulin secretion. RGD peptides promoted cell-matrix interactions, enhanced endogenous ECM components expression, and favored the assembly of individual cells into multicellular spheroids, an essential configuration for proper beta cell functioning. In vivo, our pivotal model for diabetes treatment exhibited an improved glycemic profile of type 2 diabetic rats, where insulin secreted from encapsulated cells was more efficiently used.

CONCLUSIONS

We were able to successfully introduce a novel valuable function in an old ally in biomedical applications, the alginate. The proposed alginate-RGD model stands out as a promising approach to improve beta cells survival and function, increasing the success of this therapeutic strategy, which might greatly improve the quality of life of an increasing number of diabetic patients worldwide.

Oxygenation strategies for encapsulated islet and beta cell transplants

Human allogeneic islet transplantation (ITx) is emerging as a promising treatment option for qualified patients with type 1 diabetes. However, widespread clinical application of allogeneic ITx is hindered by two critical barriers: the need for systemic immunosuppression and the limited supply of human islet tissue. Biocompatible, retrievable immunoisolation devices containing glucose-responsive insulin-secreting tissue may address both critical barriers by enabling the more effective and efficient use of allogeneic islets without immunosuppression in the near-term, and ultimately the use of a cell source with a virtually unlimited supply, such as human stem cell-derived β-cells or xenogeneic (porcine) islets with minimal or no immunosuppression. However, even though encapsulation methods have been developed and immunoprotection has been successfully tested in small and large animal models and to a limited extent in proof-of-concept clinical studies, the effective use of encapsulation approaches to convincingly and consistently treat diabetes in humans has yet to be demonstrated. There is increasing consensus that inadequate oxygen supply is a major factor limiting their clinical translation and routine implementation. Poor oxygenation negatively affects cell viability and β-cell function, and the problem is exacerbated with the high-density seeding required for reasonably-sized clinical encapsulation devices. Approaches for enhanced oxygen delivery to encapsulated tissues in implantable devices are therefore being actively developed and tested. This review summarizes fundamental aspects of islet microarchitecture and β-cell physiology as well as encapsulation approaches highlighting the need for adequate oxygenation; it also evaluates existing and emerging approaches for enhanced oxygen delivery to encapsulation devices, particularly with the advent of β-cell sources from stem cells that may enable the large-scale application of this approach.

Nanotechnology in cell replacement therapies for type 1 diabetes

Islet transplantation is a promising long-term, compliance-free, complication-preventing treatment for type 1 diabetes. However, islet transplantation is currently limited to a narrow set of patients due to the shortage of donor islets and side effects from immunosuppression. Encapsulating cells in an immunoisolating membrane can allow for their transplantation without the need for immunosuppression. Alternatively, "open" systems may improve islet health and function by allowing vascular ingrowth at clinically attractive sites. Many processes that enable graft success in both approaches occur at the nanoscale level-in this review we thus consider nanotechnology in cell replacement therapies for type 1 diabetes. A variety of biomaterial-based strategies at the nanometer range have emerged to promote immune-isolation or modulation, proangiogenic, or insulinotropic effects. Additionally, coating islets with nano-thin polymer films has burgeoned as an islet protection modality. Materials approaches that utilize nanoscale features manipulate biology at the molecular scale, offering unique solutions to the enduring challenges of islet transplantation.

The emerging field of pancreatic tissue engineering: A systematic review and evidence map of scaffold materials and scaffolding techniques for insulin-secreting cells

A bioartificial endocrine pancreas is proposed as a future alternative to current treatment options. Patients with insulin-secretion deficiency might benefit. This is the first systematic review that provides an overview of scaffold materials and techniques for insulin-secreting cells or cells to be differentiated into insulin-secreting cells. An electronic literature survey was conducted in PubMed/MEDLINE and Web of Science, limited to the past 10 years. A total of 197 articles investigating 60 different materials met the inclusion criteria. The extracted data on materials, cell types, study design, and transplantation sites were plotted into two evidence gap maps. Integral parts of the tissue engineering network such as fabrication technique, extracellular matrix, vascularization, immunoprotection, suitable transplantation sites, and the use of stem cells are highlighted. This systematic review provides an evidence-based structure for future studies. Accumulating evidence shows that scaffold-based tissue engineering can enhance the viability and function or differentiation of insulin-secreting cells both in vitro and in vivo.

Islet encapsulation

Review of emerging advances and persisting challenges in the engineering and translation of islet encapsulation technologies.

Pancreatic Islet Survival and Engraftment Is Promoted by Culture on Functionalized Spider Silk Matrices

Transplantation of pancreatic islets is one approach for treatment of diabetes, however, hampered by the low availability of viable islets. Islet isolation leads to disruption of the environment surrounding the endocrine cells, which contributes to eventual cell death. The reestablishment of this environment is vital, why we herein investigated the possibility of using recombinant spider silk to support islets in vitro after isolation. The spider silk protein 4RepCT was formulated into three different formats; 2D-film, fiber mesh and 3D-foam, in order to provide a matrix that can give the islets physical support in vitro. Moreover, cell-binding motifs from laminin were incorporated into the silk protein in order to create matrices that mimic the natural cell environment. Pancreatic mouse islets were thoroughly analyzed for adherence, necrosis and function after in vitro maintenance on the silk matrices. To investigate their suitability for transplantation, we utilized an eye model which allows in vivo imaging of engraftment. Interestingly, islets that had been maintained on silk foam during in vitro culture showed improved revascularization. This coincided with the observation of preserved islet architecture with endothelial cells present after in vitro culture on silk foam. Selected matrices were further evaluated for long-term preservation of human islets. Matrices with the cell-binding motif RGD improved human islet maintenance (from 36% to 79%) with preserved islets architecture and function for over 3 months in vitro. The islets established cell-matrix contacts and formed vessel-like structures along the silk. Moreover, RGD matrices promoted formation of new, insulin-positive islet-like clusters that were connected to the original islets via endothelial cells. On silk matrices with islets from younger donors (<35 year), the amount of newly formed islet-like clusters found after 1 month in culture were almost double compared to the initial number of islets added.

Oxygen supply to encapsulated therapeutic cells

Therapeutic cells encapsulated in immunobarrier devices have promise for treatment of a variety of human diseases without immunosuppression. The absence of sufficient oxygen supply to maintain viability and function of encapsulated tissue has been the most critical impediment to progress. Within the framework of oxygen supply limitations, we review the major issues related to development of these devices, primarily in the context of encapsulated islets of Langerhans for treating diabetes, including device designs and materials, supply of tissue, protection from immune rejection, and maintenance of cell viability and function. We describe various defensive measures investigated to enhance survival of transplanted tissue, and we review the diverse approaches to enhancement of oxygen transport to encapsulated tissue, including manipulation of diffusion distances and oxygen permeability of materials, induction of neovascularization with angiogenic factors and vascularizing membranes, and methods for increasing the oxygen concentration adjacent to encapsulated tissue so as to exceed that in the microvasculature. Recent developments, particularly in this latter area, suggest that the field is ready for clinical trials of encapsulated therapeutic cells to treat diabetes.

Induction of beta-cell resistance to hypoxia and technologies for oxygen delivery to transplanted pancreatic islets

Hypoxia is believed to be a crucial factor involved in cell adaptation to environmental stress. Islet transplantation, especially with immunoisolated islets, interrupts vascular connections, resulting in the substantially decreased delivery of oxygen and nutrients to islet cells. Insulin-producing pancreatic beta cells are known to be highly susceptible to oxygen deficiency. Such susceptibility to hypoxia is believed to be one of the main causes of beta-cell death in the post-transplantation period. Different strategies have been developed for the protection of beta cells against hypoxic injury and for oxygen delivery to transplanted islets. The enhancement of beta-cell defense properties against hypoxia has been achieved using various techniques such as gene transfection, drug supplementation, co-culturing with stem cells and cell selection. Technologies for oxygen delivery to transplanted islets include local neovascularization of subcutaneous sites, electrochemical and photosynthetic oxygen generation, oxygen refuelling of bio-artificial pancreas and whole body oxygenation by using hyperbaric therapy. Progress in the field of oxygen technologies for islet transplantation requires a multidisciplinary approach to explore and optimize the interaction between components of the biological system and different technological processes. This review article focuses mainly on the recently developed strategies for oxygenation and protection from hypoxic injury - to achieve stable and long-term normoglycaemia in diabetic patients with transplanted pancreatic islets.

Different susceptibility of rat pancreatic alpha and beta cells to hypoxia

Insulin-producing beta cells are known to be highly susceptible to hypoxia, which is a major factor in their destruction after pancreatic islet transplantation. However, whether the glucagon-producing pancreatic islet alpha cells are sensitive to hypoxia is not known. Our objective was to compare the sensitivity of alpha and beta cells to hypoxia. Isolated rat pancreatic islets were exposed to hypoxia (1% oxygen, 94% N(2), 5% CO(2)) for 3 days. The viability of the alpha and beta cells, as well as the stimulus-specific secretion of glucagon and insulin, was evaluated. A quantitative analysis of the proportion of beta to alpha cells indicated that, under normoxic conditions, islet cells were composed mainly of beta cells (87 ± 3%) with only 13 ± 3% alpha cells. Instead, hypoxia treatment significantly increased the proportion of alpha cells (40 ± 13%) and decreased the proportion of beta cells to 60 ± 13%. Using the fluorescent TUNEL assay we found that only a few percent of beta cells and alpha cells were apoptotic in normoxia. In contrast, hypoxia induced an abundance of apoptotic beta cells (61 ± 22%) and had no effect on the level of apoptosis in alpha cells. In conclusion, this study demonstrates that hypoxia results in severe functional abnormality in both beta and alpha cells while alpha cells display significantly decreased rate of apoptosis compared to intensive apoptotic injury of beta cells. These findings have implications for the understanding of the possible role of hypoxia in the pathophysiology of diabetes.

Pig-to-nonhuman primates pancreatic islet xenotransplantation: an overview

The therapy of type 1 diabetes is an open challenging problem. The restoration of normoglycemia and insulin independence in immunosuppressed type 1 diabetic recipients of islet allotransplantation has shown the potential of a cell-based diabetes therapy. Even if successful, this approach poses a problem of scarce tissue supply. Xenotransplantation can be the answer to this limited donor availability and, among possible candidate tissues for xenotransplantation, porcine islets are the closest to a future clinical application. Xenotransplantation, with pigs as donors, offers the possibility of using healthy, living, and genetically modified islets from pathogen-free animals available in unlimited number of islets. Several studies in the pig-to-nonhuman primate model demonstrated the feasibility of successful preclinical islet xenotransplantation and have provided insights into the critical events and possible mechanisms of immune recognition and rejection of xenogeneic islet grafts. Particularly promising results in the achievement of prolonged insulin independence were obtained with newly developed, genetically modified pigs islets able to produce immunoregulatory products, using different implantation sites, and new immunotherapeutic strategies. Nonetheless, further efforts are needed to generate additional safety and efficacy data in nonhuman primate models to safely translate these findings into the clinic.