Alginate/polyaminoacidic coherent microcapsules for pancreatic islet graft immunoisolation in diabetic recipients

Revolutionizing pancreatic islet organoid transplants: Improving engraftment and exploring future frontiers

Type-1 Diabetes Mellitus (T1DM) manifests due to pancreatic beta cell destruction, causing insulin deficiency and hyperglycaemia. Current therapies are inadequate for brittle diabetics, necessitating pancreatic islet transplants, which however, introduces its own set of challenges such as paucity of donors, rigorous immunosuppression and autoimmune rejection. Organoid technology represents a significant stride in the field of regenerative medicine and bypasses donor-based approaches. Hence this article focuses on strategies enhancing the in vivo engraftment of islet organoids (IOs), namely vascularization, encapsulation, immune evasion, alternative extra-hepatic transplant sites and 3D bioprinting. Hypoxia-induced necrosis and delayed revascularization attenuate organoid viability and functional capacity, alleviated by the integration of diverse cell types e.g., human amniotic epithelial cells (hAECs) and human umbilical vein endothelial cells (HUVECs) to boost vascularization. Encapsulation with biocompatible materials and genetic modifications counters immune damage, while extra-hepatic sites avoid surgical complications and immediate blood-mediated inflammatory reactions (IBMIR). Customizable 3D bioprinting may help augment the viability and functionality of IOs. While the clinical translation of IOs faces hurdles, preliminary results show promise. This article underscores the importance of addressing challenges in IO transplantation to advance their use in treating type 1 diabetes effectively.

Review of Advanced Hydrogel-Based Cell Encapsulation Systems for Insulin Delivery in Type 1 Diabetes Mellitus

: Type 1 Diabetes Mellitus (T1DM) is characterized by the autoimmune destruction of β-cells in the pancreatic islets. In this regard, islet transplantation aims for the replacement of the damaged β-cells through minimally invasive surgical procedures, thereby being the most suitable strategy to cure T1DM. Unfortunately, this procedure still has limitations for its widespread clinical application, including the need for long-term immunosuppression, the lack of pancreas donors and the loss of a large percentage of islets after transplantation. To overcome the aforementioned issues, islets can be encapsulated within hydrogel-like biomaterials to diminish the loss of islets, to protect the islets resulting in a reduction or elimination of immunosuppression and to enable the use of other insulin-producing cell sources. This review aims to provide an update on the different hydrogel-based encapsulation strategies of insulin-producing cells, highlighting the advantages and drawbacks for a successful clinical application.

Polymeric nano-shielded islets with heparin-polyethylene glycol in a non-human primate model

Intraportal pancreatic islet transplantation incurs huge cell losses during its early stages due to instant blood-mediated inflammatory reactions (IBMIRs), which may also drive regulation of the adaptive immune system. Therefore, a method that evades IBMIR will improve clinical islet transplantation. We used a layer-by-layer approach to shield non-human primate (NHP) islets with polyethylene glycol (nano-shielded islets, NSIs) and polyethylene glycol plus heparin (heparin nano-shielded islets; HNSIs). Islets ranging from 10,000 to 20,000 IEQ/kg body weight were transplanted into 19 cynomolgus monkeys (n = 4, control; n = 5, NSI; and n = 10, HNSI). The mean C-peptide positive graft survival times were 68.5, 64 and 108 days for the control, NSI and HNSI groups, respectively (P = 0.012). HNSI also reduced the factors responsible for IBMIR in vitro. Based on these data, HNSIs in conjunction with clinically established immunosuppressive drug regimens will result in superior outcomes compared to those achieved with the current protocol for clinical islet transplantation.

A new scaffold containing small intestinal submucosa and mesenchymal stem cells improves pancreatic islet function and survival in vitro and in vivo

It is unknown whether a scaffold containing both small intestinal submucosa (SIS) and mesenchymal stem cells (MSCs) for transplantation may improve pancreatic islet function and survival. In this study, we examined the effects of a SIS-MSC scaffold on islet function and survival in vitro and in vivo. MSCs and pancreatic islets were isolated from Sprague-Dawley rats, and SIS was isolated from Bamei pigs. The islets were apportioned among 3 experimental groups as follows: SIS-islets, SIS-MSC-islets and control-islets. In vitro, islet function was measured by a glucose-stimulated insulin secretion test; cytokines in cultured supernatants were assessed by enzyme-linked immunosorbent assay; and gene expression was analyzed by reverse transcription-quantitative PCR. In vivo, islet transplantation was performed in rats, and graft function and survival were monitored by measuring the blood glucose levels. In vitro, the SIS-MSC scaffold was associated with improved islet viability and enhanced insulin secretion compared with the controls, as well as with the increased the expression of insulin 1 (Ins1), pancreatic and duodenal homeobox 1 (Pdx1), platelet endothelial cell adhesion molecule 1 [Pecam1; also known as cluster of differentiation 31 (CD31)] and vascular endothelial growth factor A (Vegfa) in the islets, increased growth factor secretion, and decreased tumor necrosis factor (TNF) secretion. In vivo, the SIS-MSC scaffold was associated with improved islet function and graft survival compared with the SIS and control groups. On the whole, our findings demonstrate that the SIS-MSC scaffold significantly improved pancreatic islet function and survival in vitro and in vivo. This improvement may be associated with the upregulation of insulin expression, the improvement of islet microcirculation and the secretion of cytokines.

Conformal polymer coatings for pancreatic islets transplantation

The aim of this work was to improve an aqueous two-phase system methodology for fabrication of coherent microcapsules. Simulated microgravity was investigated as tool to improve the cell cluster morphology in order to increase the overall quality of conformal polymer coatings, while the application of two concentric alginate layers and the use of barium instead of calcium as gelling ion was evaluated. Simulated microgravity enabled improvement of neonatal porcine cell cluster sphericity however the freely floating cells, originated during incubation and often found on the capsule surface, raised immunological concerns. Overall, these technical changes translated into improving quality of microcapsules, in terms of either morphologic aspects or the membrane's functional performance. Preparation procedure did not seem to adversely affect viability of the embodied cells. Moreover, the employed alginates high biocompatibility, per se, would promote a good encapsulated cell engraftment. Minimization of last generation microcapsule's size, made of highly purified alginates, represents a further advance on the new horizons of cell therapy for the treatment of a wide variety of chronic disorders, including insulin-dependent diabetes mellitus.

The use of biomaterials in islet transplantation

Pancreatic islet transplantation is a therapeutic option to replace destroyed β cells in autoimmune diabetes. Islets are transplanted into the liver via the portal vein; however, inflammation, the required immunosuppression, and lack of vasculature decrease early islet viability and function. Therefore, the use of accessory therapy and biomaterials to protect islets and improve islet function has definite therapeutic potential. Here we review the application of niche accessory cells and factors, as well as the use of biomaterials as carriers or capsules, for pancreatic islet transplantation.

Encapsulation of pancreatic islets within nano-thin functional polyethylene glycol coatings for enhanced insulin secretion

Covalent attachment of polymers to cells and tissues could be used to solve a variety of problems associated with cellular therapies. Insulin-dependent diabetes mellitus is a disease resulting from the autoimmune destruction of the beta cells of the islets of Langerhans in the pancreas. Transplantation of islets into diabetic patients is an attractive form of treatment, provided that the islets could be protected from the host's immune system to prevent graft rejection, and smaller numbers of islets transplanted in smaller volumes could be sufficient to reverse diabetes. Therefore, a need exists to develop islet encapsulation strategies that minimize transplant volume. In this study, we demonstrate the formation of nano-thin, poly(ethylene glycol) (PEG)-rich functional conformal coatings on individual islets via layer-by-layer assembly technique. The surface of the islets is modified with biotin-PEG-N-hydroxysuccinimide (NHS), and the islets are further covered by streptavidin (SA) and biotin-PEG-peptide conjugates using the layer-by-layer method. An insulinotropic ligand, glucagon-like peptide-1 (GLP-1), is conjugated to biotin-PEG-NHS. The insulinotropic effect of GLP-1 is investigated through layer-by-layer encapsulation of islets using the biotin-PEG-GLP-1 conjugate. The effect of islet surface modification using the biotin-PEG-GLP-1 conjugate on insulin secretion in response to glucose challenge is compared via static incubation and dynamic perifusion assays. The results show that islets coated with the functional PEG conjugate are capable of secreting more insulin in response to high glucose levels compared to control islets. Finally, the presence of SA is confirmed by indirect fluorescent staining with SA-Cy3, and the presence of PEG-peptide on the surface of the islets after treatment with biotin-PEG-GLP-1 is confirmed by indirect fluorescent staining with biotin-PEG-fluorescein isothiocyanate (FITC) and separately with an anti-GLP-1 antibody. This work demonstrates the feasibility of treating pancreatic islets with reactive polymeric segments and provides the foundation for a novel means of potential immunoisolation. With this technique, it may be possible to encapsulate and/or modify islets before portal vein transplantation and reduce transplantation volume significantly, and promote islet viability and insulin secretion due to the presence of insulinotropic peptides on the islet surface. Layer-by-layer self-assembly of PEG-GLP-1 offers a unique approach to islet encapsulation to stimulate insulin secretion in response to high glucose levels.

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.

Layer-by-layer assembly of a conformal nanothin PEG coating for intraportal islet transplantation

Encapsulation of cells and tissue offers a rational approach for attenuating deleterious host responses toward transplanted cells, but a need exists to develop cell encapsulation strategies that minimize transplant volume. In this report, we describe the formation of nanothin, PEG-rich conformal coatings on individual pancreatic islets via layer-by-layer self-assembly of poly( l-lysine)- g-poly(ethylene glycol)(biotin) (PPB) and streptavidin (SA). Through control of grafting ratio, PPB could be rendered nontoxic and facilitated growth of PPB/SA multilayer thin films that conformed to the heterogeneous islet surface. (PPB/SA) 8 multilayer films could be assembled without loss of islet viability or function, and coated islets performed comparably to untreated controls in vivo in a murine model of allogenic intraportal islet transplantation.

Challenges and emerging technologies in the immunoisolation of cells and tissues

Protection of transplanted cells from the host immune system using immunoisolation technology will be important in realizing the full potential of cell-based therapeutics. Microencapsulation of cells and cell aggregates has been the most widely explored immunoisolation strategy, but widespread clinical application of this technology has been limited, in part, by inadequate transport of nutrients, deleterious innate inflammatory responses, and immune recognition of encapsulated cells via indirect antigen presentation pathways. To reduce mass transport limitations and decrease void volume, recent efforts have focused on developing conformal coatings of micron and submicron scale on individual cells or cell aggregates. Additionally, anti-inflammatory and immunomodulatory capabilities are being integrated into immunoisolation devices to generate bioactive barriers that locally modulate host responses to encapsulated cells. Continued exploration of emerging paradigms governed by the inherent challenges associated with immunoisolation will be critical to actualizing the clinical potential of cell-based therapeutics.

Optimized parameters for microencapsulation of pancreatic islet cells: an in vitro study clueing on islet graft immunoprotection in type 1 diabetes mellitus

Alginate (AG)-based microcapsules may provide a selective permeable and biocompatible physical barrier to prevent islet graft (TX)-directed immune destruction. However, extent of the achieved immunoprotection will continue to be variable and unpredictable until the role of the individual mechanisms involved with TX-related inflammatory cell and immune reactivity are clarified. Macrophages (M) are believed to play a pivotal role in controlling the host/TX interaction and its consequences. We then have studied the effects of isolated rat M and their secretory products on allogeneic islets enveloped in variably sized and configured microcapsules, within in vitro mixed islet-M cocultures. In particular, we aimed to determine the sequence of immune or not immune specific cascade of early events that derive from such on interaction. One of the specific aims was to assess whether the membrane's physical intactness and conversely its even minimal rupture, along with the microcapsules' size (i.e., large vs. small) would significantly impact M reactivity and, thereby, the encapsulated islet viability and function. Special care was taken to evaluate extent of the elicited reactivity by meticulously monitoring cytokine, N2 derivative, and other proinflammatory protein curve profiles during the early M activation process. The study has preliminarily shown that, for equally formulated microcapsules, the capsular size and membrane's morphologic thoroughness are key to prevent M reactivity and possibly avoid the intracapsular islet cell damage. While elucidation of pathways involved with the encapsulated islet TX-directed host's responsiveness actually is in progress, it has clearly emerged that microcapsules should comply with well-defined physical properties and formulation specifications in order to obviate the primum movens of the inflammatory reaction process.

Nanoporous microsystems for islet cell replacement

The inadequacy of conventional insulin therapy for the treatment of Type I diabetes has stimulated research on several therapeutic alternatives, including insulin pumps and controlled release systems for insulin. One of the most physiological alternatives to insulin injections is the transplantation of insulin-secreting cells. It is the beta cells of the islets that secrete insulin in response to increasing blood glucose concentrations. Ideally, transplantation of such cells (allografts or xenografts) could restore normoglycemia. However, as with most tissue or cellular transplants, the cellular grafts, particularly xenografts, are subjected to immunorejection in the absence of chronic immunosuppression. Thus, it is of great interest to develop new technologies that may be used for islet cell replacement. This research proposal describes a new approach to cellular delivery based on micro- and nanotechnology. Utilizing this approach, nanoporous biocapsules are bulk and surface micromachined to present uniform and well-controlled pore sizes as small as 7 nm, tailored surface chemistries, and precise microarchitectures, in order to provide immunoisolating microenvironments for cells. Such a design may overcome some of the limitations associated with conventional encapsulation and delivery technologies, including chemical instabilities, material degradation or fracture, and broad membrane pore sizes.

Alginate microcapsules for pancreatic islet cell graft immunoprotection: struggle and progress towards the final cure for type 1 diabetes mellitus

Lights and shadows have been associated with the use of alginate/polyaminoacidic microcapsules for transplantation of pancreatic islet cells for the therapy of diabetes mellitus, with no recipient pharmacological immunosuppression. In fact, preliminary success in rodents has generally not matched the results achieved in diabetic higher mammals. The restricted availability of cadaveric human donor organs/tissue, coupled to regulatory hurdles in the use of microcapsules in patients, has significantly delayed the progress of microencapsulated islet grafts into pilot clinical trials. While the basic formulation of microcapsules from the author's laboratory, originally comprised of an alginate gel (AG) core, a double poly-L-ornithine (PLO) coat and an outer AG coat, has virtually remained unchanged, highly purified 'clinical grade' AG has been introduced in order to try to surmount regulatory restrictions. In parallel, novel insulin-producing cell types have been employed to fill the capsules, with particular regard to non-human tissue, such as adult and, more recently, neonatal porcine islets. In particular, using neonatal porcine islets enveloped in AG-PLO microcapsules, hyperglycaemia has been corrected in several diabetic animal models. Should standardisation and optimisation problems associated with both AG procurement and other membrane physical-chemical fabrication parameters be surmounted, microcapsules containing either human or, possibly, pig islets, could be close to approval for Phase I human clinical trials.

Mitogenic Effects of Brazilian Arthropod Venom on Isolated Islet Beta Cells: In Vitro Morphologic Ultrastructural and Functional Studies

Background

One of the major pitfalls associated with use of isolated adult islets of Langerhans’ cells is their minimal mitotic capacity. Consequently, maintenance of a steady viable islet cell mass is very difficult. To explore how to enhance beta-cell mitogenesis, we have examined the effects of venom fractions extracted from a Brazilian scorpion on morphologic and functional beta-cell patterns. The venom was previously known to induce nesidioblastosis-like effects with chronic hypoglycemia and pancreatitis in animal models.

Methods

Venom fractions purified from Tityus bahiensis were incubated with batches of isolated rat islets, while a morphologic examination, glucose-stimulated insulin release, insulin content, and insulin messenger ribonucleic acid (mRNA) were carried out early during incubation. On fixation and double fluorescence immunolabeling (rhodamine for anti-insulin monoclonal antibodies; fluorescein for anti-5-bromodeoxyuridine), the preparations were imaged by confocal laser microscopy (CLM) for morphometric quantification of the mitoses. Insulin recovery and mRNA were also assessed at 21 days of culture.

Results

Under CLM examination, the beta-cell mitotic rate significantly rose from 1 to 12.8% for the venom-exposed islets. At day 7, insulin release and content were significantly lower for the venom-exposed than the control islets. However, at day 21 of culture, insulin release in response to static incubation with glucose and insulin mRNA from the venom-exposed islets was higher than controls ( p < .05).

Conclusions

Incubation with the scorpion venom induced a rapid and significant increase in the beta-cell proliferation not associated with a short-term increase in insulin secretion. The latter fully resumed and overcame controls later in culture, possibly after completion of the beta-cell expansion process.

Development of cellulose sulfate-based polyelectrolyte complex microcapsules for medical applications

Microencapsulation, as a tool for immunoisolation for allogenic or xenogenic implants, is a rapidly growing field. However most of the approaches are based on alginate/polylysine capsules, despite this system's obvious disadvantages such as its pyrogenicity. Here we report a different encapsulation system based on sodium cellulose sulfate and polydiallyldimethyl ammonium chloride for the encapsulation of mammalian cells. We have characterized this system regarding capsule formation, strength and size of the capsules as well as viability of the cells after encapsulation. In addition, we demonstrate the efficacy of these capsules as a "microfactory" in vitro and in vivo. Using encapsulated hybridoma cells we were able to demonstrate long-term release of antibodies up to four months in vivo. In another application we could show the therapeutic relevance of encapsulated genetically modified cells as an in vivo activation center for cytostatic drugs during tumor therapy.