In vitro modulation of monocyte chemoattractant protein-1 release in human pancreatic islets

Engineering β Cell Replacement Therapies for Type 1 Diabetes: Biomaterial Advances and Considerations for Macroscale Constructs

While significant progress has been made in treatments for type 1 diabetes (T1D) based on exogenous insulin, transplantation of insulin-producing cells (islets or stem cell-derived β cells) remains a promising curative strategy. The current paradigm for T1D cell therapy is clinical islet transplantation (CIT)-the infusion of islets into the liver-although this therapeutic modality comes with its own limitations that deteriorate islet health. Biomaterials can be leveraged to actively address the limitations of CIT, including undesired host inflammatory and immune responses, lack of vascularization, hypoxia, and the absence of native islet extracellular matrix cues. Moreover, in efforts toward a clinically translatable T1D cell therapy, much research now focuses on developing biomaterial platforms at the macroscale, at which implanted platforms can be easily retrieved and monitored. In this review, we discuss how biomaterials have recently been harnessed for macroscale T1D β cell replacement therapies.

Chemokines and Their Receptors in Islet Allograft Rejection and as Targets for Tolerance Induction

Graft rejection is a major barrier to successful outcome of transplantation surgery. Islet transplantation introduces insulin secreting tissue into type 1 diabetes mellitus recipients, relieving patients from exogenous insulin injection. However, insulitis of grafted tissue and allograft rejection prevent long-term insulin independence. Leukocyte trafficking is necessary for the launch of successful immune responses to pathogen or allograft. Chemokines, small chemotactic cytokines, direct the migration of leukocytes through their interaction with chemokine receptors found on cell surfaces of immune cells. Unique receptor expression of leukocytes, and the specificity of chemokine secretion during various states of immune response, suggest that the extracellular chemokine milieu specifically homes certain leukocyte subsets. Thus, only those leukocytes required for the current immune task are attracted to the inflammatory site. Chemokine blockade, using antagonists and monoclonal antibodies directed against chemokine receptors, is an emerging and specific immunosuppressive strategy. Importantly, chemokine blockade may potentiate tolerance induction regimens to be used following transplantation surgery, and prevent the need for life-long immunosuppression of islet transplant recipients. Here, the role for chemokine blockade in islet transplant rejection and tolerance is reviewed.

DAMP production by human islets under low oxygen and nutrients in the presence or absence of an immunoisolating-capsule and necrostatin-1

In between the period of transplantation and revascularization, pancreatic islets are exposed to low-oxygen and low-nutrient conditions. In the present study we mimicked those conditions in vitro to study the involvement of different cell death processes, release of danger-associated molecular patterns (DAMP), and associated in vitro immune activation. Under low-oxygen and low-nutrient conditions, apoptosis, autophagy and necroptosis occur in human islets. Necroptosis is responsible for DAMP-release such as dsDNA, uric acid, and HMGB1. The sensors of the innate immune system able to recognize these DAMPs are mainly TLR, NOD receptors, and C-type lectins. By using cell-lines with a non-functional adaptor molecule MyD88, we were able to show that the islet-derived DAMPs signal mainly via TLR. Immunoisolation in immunoprotective membranes reduced DAMP release and immune activation via retention of the relative large DAMPs in the capsules. Another effective strategy was suppressing necroptosis using the inhibitor nec-1. Although the effect on cell-survival was minor, nec-1 was able to reduce the release of HMGB1 and its associated immune activation. Our data demonstrate that in the immediate post-transplant period islets release DAMPs that in vitro enhance responses of innate immune cells. DAMP release can be reduced in vitro by immunoisolation or intervention with nec-1.

Current status of islet cell transplantation

Despite substantial advances in islet isolation methods and immunosuppressive protocol, pancreatic islet cell transplantation remains an experimental procedure currently limited to the most severe cases of type 1 diabetes mellitus. The objectives of this treatment are to prevent severe hypoglycemic episodes in patients with hypoglycemia unawareness and to achieve a more physiological metabolic control. Insulin independence and long term-graft function with improvement of quality of life have been obtained in several international islet transplant centers. However, experimental trials of islet transplantation clearly highlighted several obstacles that remain to be overcome before the procedure could be proposed to a much larger patient population. This review provides a brief historical perspective of islet transplantation, islet isolation techniques, the transplant procedure, immunosuppressive therapy, and outlines current challenges and future directions in clinical islet transplantation.

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.

Curcumin inhibits in vitro MCP-1 release from mouse pancreatic islets

OBJECTIVES

Monocyte chemoattractant proteins (MCP-1) belongs to the CC family of chemokines secreted from islets of the pancreas, producing recruitment of inflammatory cells leading to an acute immune response with graft rejection in clinical transplantation. Expression and release of many inflammatory cytokines and chemokines, including MCP-1 is regulated by the nuclear factor (NF)-kappaB pathway. Curcumin is an NF-kappaB inhibitor with a variety of biological activities anti-inflammatory, antitumor, antioxidant, and antichemotactic effects. The aim of this study was to examine the effect of curcumin on in vitro MCP-1 release from pancreatic islets.

METHODS

Mouse pancreatic islets in 18-hour cultures were treated with 0 or 10 or 20 micromol/L curcumin and with LPS for an additional 24 hours. MCP-1 levels in culture supernates of islets with versus without curcumin treatment were measured by an ELISA assay.

RESULTS

We observed that curcumin at the concentration of 20 micromol/L significantly decreased MCP-1 release from mouse islets compared to the control group (P = .005). In addition at both of 10 micromol/L and 20 micromol/L curcumin concentrations there was a decreased level of MCP-1 released from LPS-treated versus control islets (P = .01).

Would blockage of cytokines improve the outcome of pancreatic islet transplantation?

It has been estimated that up to 60% of pancreatic islet tissue undergoes apoptosis within the first several days post-transplantation. This strongly suggests the involvement of an inflammatory event other than alloantigen-specific immune reaction following islet transplantation which contributes to partial destruction of grafts. Inflammatory cytokines including IL-1beta, TNF-alpha and IFN-gamma are implicated in the pancreatic islet beta-cell death and functional loss during autoimmune diabetes and also seem to be involved in early loss of islet mass in islet transplantation. Inflammatory cytokines and free oxygen radicals released in situ could cause apoptosis and the functional impairment of islets after islet transplantation and graft failure. It can be hypothesized that preventing destruction of transplanted islets using cytokine blockade could be helpful in improving islet transplantation outcome. Several approaches have been made based on this hypothesis to examine the effect of inflammatory blockade on the islets survival and functional islet mass. Further investigations are required to identify most efficient way for block of cytokine-induced damage in pancreatic islets transplantation.