In Vitro Studies of Squalene‐Gusperimus Nanoparticles in Islet‐Containing Alginate Microcapsules to Regulate the Immune Response in the Immediate Posttransplant Period

Pancreatic stellate cells support human pancreatic β-cell viability in vitro and enhance survival of immunoisolated human islets exposed to cytokines

Pancreatic islet transplantation is proposed as a cure for type 1 diabetes mellitus (T1D). Despite its success in optimal regulation of glucose levels, limitations in longevity of islet grafts still require innovative solutions. Inflammatory stress post-transplantation and loss of extracellular matrix attribute to the limited β-cell survival. Pancreatic stellate cells (PSCs), identified as pancreatic-specific stromal cells, have the potential to play a crucial role in preserving islet survival. Our study aimed to determine the effects of PSCs co-cultured with human CM β-cells and human islets under inflammatory stress induced by a cytokine cocktail of IFN-γ, TNF-α and IL-1β. Transwell culture inserts were utilized to assess the paracrine impact of PSCs on β-cells, alongside co-cultures enabling direct interaction between PSCs and human islets. We found that co-culturing PSCs with human CM β-cells and human cadaveric islets had rescuing effects on cytokine-induced stress. Effects were different under normoglycemic and hyperglycemic conditions. PSCs were associated with upregulation of β-cell mitochondrial activity and suppression of inflammatory gene expression. The rescuing effects exist both in indirect and direct co-culture methods. Furthermore, we tested whether PSCs have rescuing effects on human islets in conventional alginate-based microcapsules and in composite microcapsules composed of alginate-pectin collagen type IV, laminin sequence RGD, Nec-1, and amino acid. PSCs partially prevented cytokine-induced stress in both systems, but beneficial effects were stronger in composite capsules. Our findings show novel effects of PSCs on islet health. Islets and PSCs coculturing or co-transplantation might mitigate the inflammation stress and improve islet transplantation outcomes.

A composite capsule strategy to support longevity of microencapsulated pancreatic β cells

Pancreatic islet microencapsulation allows transplantation of insulin producing cells in absence of systemic immunosuppression, but graft survival is still limited. In vivo studies have demonstrated that many islet-cells die in the immediate period after transplantation. Here we test whether intracapsular inclusion of ECM components (collagen IV and RGD) with necrostatin-1 (Nec-1), as well as amino acids (AA) have protective effects on islet survival. Also, the inclusion of pectin was tested as it enhances the mitochondrial health of β-cells. To enhance the longevity of encapsulated islets, we studied the impact of the incorporation of the mentioned components into the alginate-based microcapsules in vitro. The efficacy of the different composite microcapsules on MIN6 β-cell or human islet-cell survival and function, as well as suppression of DAMP-induced immune activation, were determined. Finally, we examined the mitochondrial dynamic genes. This was done in the absence and presence of a cytokine cocktail. Here, we found that composite microcapsules of APENAA improved insulin secretion and enhanced the mitochondrial activity of β-cells. Under cytokine exposure, they prevented the cytokine-induced decrease of mitochondrial activity as well as viability till day 5. The rescuing effects of the composite capsules were accompanied by alleviated mitochondrial dynamic gene expression. The composite capsule strategy of APENAA might support the longevity of microencapsulated β-cells by lowering susceptibility to inflammatory stress. Our data demonstrate that combining strategies to support β-cells by changing the intracapsular microenvironment might be an effective way to preserve islet graft longevity in the immediate period after transplantation.

Enhancing longevity of immunoisolated pancreatic islet grafts by modifying both the intracapsular and extracapsular environment

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease characterized by autoimmune destruction of pancreatic β cells. Transplantation of immunoisolated pancreatic islets might treat T1DM in the absence of chronic immunosuppression. Important advances have been made in the past decade as capsules can be produced that provoke minimal to no foreign body response after implantation. However, graft survival is still limited as islet dysfunction may occur due to chronic damage to islets during islet isolation, immune responses induced by inflammatory cells, and nutritional issues for encapsulated cells. This review summarizes the current challenges for promoting longevity of grafts. Possible strategies for improving islet graft longevity are also discussed, including supplementation of the intracapsular milieu with essential survival factors, promotion of vascularization and oxygenation near capsules, modulation of biomaterials, and co-transplantation of accessory cells. Current insight is that both the intracapsular as well as the extracapsular properties should be improved to achieve long-term survival of islet-tissue. Some of these approaches reproducibly induce normoglycemia for more than a year in rodents. Further development of the technology requires collective research efforts in material science, immunology, and endocrinology. STATEMENT OF SIGNIFICANCE: Islet immunoisolation allows for transplantation of insulin producing cells in absence of immunosuppression and might facilitate the use of xenogeneic cell sources or grafting of cells obtained from replenishable cell sources. However, a major challenge to date is to create a microenvironment that supports long-term graft survival. This review provides a comprehensive overview of the currently identified factors that have been demonstrated to be involved in either stimulating or reducing islet graft survival in immunoisolating devices and discussed current strategies to enhance the longevity of encapsulated islet grafts as treatment for type 1 diabetes. Although significant challenges remain, interdisciplinary collaboration across fields may overcome obstacles and facilitate the translation of encapsulated cell therapy from the laboratory to clinical application.

Species-dependent impact of immunosuppressive squalene-gusperimus nanoparticles and adipose-derived stem cells on isolated human and rat pancreatic islets

Transplantation of pancreatic islets is a promising approach to controlling glucose levels in type 1 diabetes mellitus (T1DM), but islet survival is still limited. To overcome this, islet co-culture with mesenchymal stromal cells (MSCs) together with safe immunosuppressive agents like squalene-gusperimus nanoparticles (Sq-GusNPs) may be applied. This could support islet survival and engraftment. Here, we studied how Sq-GusNPs and adipose-derived stem cells (ASCs) influence islets response under pro-inflammatory conditions. Through qRT-PCR, we studied the expression of specific genes at 24 hours in human and rat islets and ASCs in co-culture under indirect contact with or without treatment with Sq-GusNPs. We characterized how the response of islets and ASCs starts at molecular level before impaired viability or function is observed and how this response differs between species. Human islets and ASCs responses showed to be principally influenced by NF-κB activation, whereas rat islet and ASCs responses showed to be principally mediated by nitrosative stress. Rat islets showed tolerance to inflammatory conditions due to IL-1Ra secretion which was also observed in rat ASCs. Human islets induced the expression of cytokines and chemokines with pro-angiogenic, tissue repair, and anti-apoptotic properties in human ASCs under basal conditions. This expression was not inhibited by Sq-GusNPs. Our results showed a clear difference in the response elicited by human and rat islets and ASCs in front of an inflammatory stimulus and Sq-GusNPs. Our data support the use of ASCs and Sq-GusNP to facilitate engraftment of islets for T1DM treatment.