A tripartite anoikis-like mechanism causes early isolated islet apoptosis

3D evaluation of the extracellular matrix of hypoxic pancreatic islets using light sheet fluorescence microscopy

Pancreatic islet transplantation is a promising treatment for type 1 diabetes, but the survival and function of transplanted islets are hindered by the loss of extracellular matrix (ECM) during islet isolation and by low oxygenation upon implantation. This study aimed to evaluate the impact of hypoxia on ECM using a cutting-edge imaging approach based on tissue clearing and 3D microscopy. Human and rat islets were cultured under normoxic (O2 21%) or hypoxic (O2 1%) conditions. Immunofluorescence staining targeting insulin, glucagon, CA9 (a hypoxia marker), ECM proteins (collagen 4, fibronectin, laminin), and E-cadherin (intercellular adhesion protein) was performed on fixed whole islets. The cleared islets were imaged using Light Sheet Fluorescence Microscopy (LSFM) and digitally analyzed. The volumetric analysis of target proteins did not show significant differences in abundance between the experimental groups. However, 3D projections revealed distinct morphological features that differentiated normoxic and hypoxic islets. Under normoxic conditions, ECM could be found throughout the islets. Hypoxic islets exhibited areas of scattered nuclei and central clusters of ECM proteins, indicating central necrosis. E-cadherin was absent in these areas. Our results, demonstrating a diminution of islets' functional mass in hypoxia, align with the functional decline observed in transplanted islets experiencing low oxygenation after grafting. This study provides a methodology combining tissue clearing, multiplex immunofluorescence, Light Sheet Fluorescence Microscopy, and digital image analysis to investigate pancreatic islet morphology. This 3D approach allowed us to highlight ECM organizational changes during hypoxia from a morphological perspective.

Advances and challenges of the cell-based therapies among diabetic patients

Diabetes mellitus is a significant global public health challenge, with a rising prevalence and associated morbidity and mortality. Cell therapy has evolved over time and holds great potential in diabetes treatment. In the present review, we discussed the recent progresses in cell-based therapies for diabetes that provides an overview of islet and stem cell transplantation technologies used in clinical settings, highlighting their strengths and limitations. We also discussed immunomodulatory strategies employed in cell therapies. Therefore, this review highlights key progresses that pave the way to design transformative treatments to improve the life quality among diabetic patients.

Trimetazidine Preconditioning Potentiates the Effect of Mesenchymal Stem Cells Secretome on the Preservation of Rat Pancreatic Islet Survival and Function In Vitro

Islet transplantation offers improved glycemic control in individuals with type 1 diabetes mellitus. However, in vitro islet culture is associated with islet apoptosis and eventually will lose their functionality prior to transplantation. In this study, we examined the effects of mesenchymal stem cells (MSCs) secretome preconditioned with diazoxide (DZ) and trimetazidine (TMZ) on rat islet cells during pre-transplant culture. With and without preconditioned hAD-MSCs' concentrated conditioned media (CCM) were added to the culture medium containing rat islets every 12 h for 24 and 48 h, after testing for selected cytokine concentrations (interleukin (IL)-4, IL-6, IL-13). Insulin content, glucose-stimulated insulin secretion, islet cell apoptosis, and mRNA expression of pro-apoptotic (BAX, BAK-1, and PUMA) and anti-apoptotic factors (BCL-2, BCL-xL, and XIAP) in rat islets were assessed after 24 and 48 h of culture. The protein level of IL-6 and IL-4 was significantly higher in TMZ-MSC-CM compared to MSC-non-CM. In rat isolated islets, normalized secreted insulin in the presence of 16.7 mM glucose was significantly higher in treated islet groups compared to control islets at both 24 and 48 h cultivation. Also, the percentage of apoptotic islet cells TMZ-MSC-CCM-treated islets was significantly lower compared to MSC-CM and MSC-CCM-treated islets in both 24 and 48 h cultivation. Consistent with the number of apoptotic cells, after 24 h culture, the expression of BCL-2 and BCL-xL genes in the control islets was lower than all treatment islet groups and in 48 h was lower than only TMZ-MSC-CM-treated islets. Also, the expression of the XIAP gene in control islets was significantly lower compared to the TMZ-MSC-CCM-treated islets at both at 24 and 48 h. In addition, mRNA level of the BAX gene in TMZ-MSC-CCM-treated islets was significantly lower compared to other groups at 48 h. Our findings revealed that TMZ proved to be more effective than DZ and could enhance the potential of hAD-MSCs-CM to improve the function and viability of islets prior to transplantation.

Simple Complexity: Incorporating Bioinspired Delivery Machinery within Self-Assembled Peptide Biogels

Bioinspired self-assembly is a bottom-up strategy enabling biologically sophisticated nanostructured biogels that can mimic natural tissue. Self-assembling peptides (SAPs), carefully designed, form signal-rich supramolecular nanostructures that intertwine to form a hydrogel material that can be used for a range of cell and tissue engineering scaffolds. Using the tools of nature, they are a versatile framework for the supply and presentation of important biological factors. Recent developments have shown promise for many applications such as therapeutic gene, drug and cell delivery and yet are stable enough for large-scale tissue engineering. This is due to their excellent programmability—features can be incorporated for innate biocompatibility, biodegradability, synthetic feasibility, biological functionality and responsiveness to external stimuli. SAPs can be used independently or combined with other (macro)molecules to recapitulate surprisingly complex biological functions in a simple framework. It is easy to accomplish localized delivery, since they can be injected and can deliver targeted and sustained effects. In this review, we discuss the categories of SAPs, applications for gene and drug delivery, and their inherent design challenges. We highlight selected applications from the literature and make suggestions to advance the field with SAPs as a simple, yet smart delivery platform for emerging BioMedTech applications.

No Time to Die-How Islets Meet Their Demise in Transplantation

Islet transplantation represents an effective treatment for patients with type 1 diabetes mellitus (T1DM) and severe hypoglycaemia unawareness, capable of circumventing impaired counterregulatory pathways that no longer provide protection against low blood glucose levels. The additional beneficial effect of normalizing metabolic glycaemic control is the minimisation of further complications related to T1DM and insulin administration. However, patients require allogeneic islets from up to three donors, and the long-term insulin independence is inferior to that achieved with solid organ (whole pancreas) transplantation. This is likely due to the fragility of islets caused by the isolation process, innate immune responses following portal infusion, auto- and allo-immune-mediated destruction and β-cell exhaustion following transplantation. This review covers the specific challenges related to islet vulnerability and dysfunction that affect long-term cell survival following transplantation.

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.

A human pancreatic ECM hydrogel optimized for 3-D modeling of the islet microenvironment

Extracellular matrix (ECM) plays a multitude of roles, including supporting cells through structural and biochemical interactions. ECM is damaged in the process of isolating human islets for clinical transplantation and basic research. A platform in which islets can be cultured in contact with natural pancreatic ECM is desirable to better understand and support islet health, and to recapitulate the native islet environment. Our study demonstrates the derivation of a practical and durable hydrogel from decellularized human pancreas that supports human islet survival and function. Islets embedded in this hydrogel show increased glucose- and KCl-stimulated insulin secretion, and improved mitochondrial function compared to islets cultured without pancreatic matrix. In extended culture, hydrogel co-culture significantly reduced levels of apoptosis compared to suspension culture and preserved controlled glucose-responsive function. Isolated islets displayed altered endocrine and non-endocrine cell arrangement compared to in situ islets; hydrogel preserved an islet architecture more similar to that observed in situ. RNA sequencing confirmed that gene expression differences between islets cultured in suspension and hydrogel largely fell within gene ontology terms related to extracellular signaling and adhesion. Natural pancreatic ECM improves the survival and physiology of isolated human islets.

Degradable methacrylic acid-based synthetic hydrogel for subcutaneous islet transplantation

Islet transplantation is a promising regenerative therapy that would reduce the dependence of type 1 diabetic patients on insulin injections. However, islet transplantation is not yet widely available, in part because there is no ideal transplant site. The subcutaneous space has been highlighted as a promising transplant site, but it does not have the vasculature required to support an islet graft. In this study we demonstrate that islets engraft in the subcutaneous space when injected in an inherently vascularizing, degradable methacrylic acid-polyethylene glycol (MAA-PEG) hydrogel; no vascularizing cells or growth factors were required. In streptozotocin-induced diabetic mice, injection of 600 rodent islet equivalents in MAA-PEG hydrogels was sufficient to reverse diabetes for 70 days; a PEG gel without MAA had no benefit. MAA-PEG hydrogel scaffolds degraded over the course of a week and were replaced by a host-derived, vascularized, innervated matrix that supported subcutaneous islets. The survival of islet grafts through the inflammatory events of subcutaneous transplantation, hydrogel degradation, and islet revascularization underscore the benefits of the MAA biomaterial. Our findings establish the MAA-PEG hydrogel as a platform for subcutaneous islet transplantation.

Decellularized Matrix Bioscaffolds: Implementation of Native Microenvironment in Pancreatic Tissue Engineering

ABSTRACT

Type 1 diabetes is an autoimmune disease, and its incidence is usually estimated in the range of 5% to 10%. Currently, the administration of exogenous insulin is the standard of care therapy. However, this therapy is not effective in some patients who may develop some chronic complications. Islet transplantation into the liver is another therapy with promising outcomes; however, the long-term efficacy of this therapeutic option is limited to a small number of patients. Because native extracellular matrix (ECM) components provide a suitable microenvironment for islet functions, engineering a 3-dimensional construct that recapitulates the native pancreatic environment could address these obstacles. Many attempts have been conducted to mimic an in vivo microenvironment to increase the survival of islets or islet-like clusters. With the advent of decellularization technology, it is possible to use a native ECM in organ engineering. Pancreatic decellularized bioscaffold provides proper cell-cell and cell-ECM interactions and retains growth factors that are critical in the determination of cell fate within a native organ. This review summarizes the current knowledge of decellularized matrix technology and addresses its possible limitations before use in the clinic.

Rebuilding a better home for transplanted islets

Diabetes can be treated with β cell replacement therapy, where a patient is transplanted with cadaveric human islets to restore glycemic control. Despite this being an effective treatment, the process of isolating islets from the pancreas requires collagenase digestion which disrupts the islet extracellular matrix (ECM) and activates anoikis-mediated apoptosis. To improve islet survival in culture and after transplantation, the islet microenvironment may be enhanced with the addition of ECM components which are lost during isolation. Furthermore, novel β cell replacement strategies, such as stem cell-derived beta cell (SCβC) treatments or alternative transplant sites and devices, could benefit from a better understanding of how β cells interact with ECM. In this mini-review, we discuss the current understanding of the pancreas and islet ECM composition and review decellularization approaches to generate a native pancreatic ECM scaffold for use in both islet and SCβC culture and transplantation.

Extracellular matrix scaffold and hydrogel derived from decellularized and delipidized human pancreas

Extracellular matrix (ECM) plays an important developmental role by regulating cell behaviour through structural and biochemical stimulation. Tissue-specific ECM, attained through decellularization, has been proposed in several strategies for tissue and organ replacement. Decellularization of animal pancreata has been reported, but the same methods applied to human pancreas are less effective due to higher lipid content. Moreover, ECM-derived hydrogels can be obtained from many decellularized tissues, but methods have not been reported to obtain human pancreas-derived hydrogel. Using novel decellularization methods with human pancreas we produced an acellular, 3D biological scaffold (hP-ECM) and hydrogel (hP-HG) amenable to tissue culture, transplantation and proteomic applications. The inclusion of a homogenization step in the decellularization protocol significantly improved lipid removal and gelation capability of the resulting ECM, which was capable of gelation at 37 °C in vitro and in vivo, and is cytocompatible with a variety of cell types and islet-like tissues in vitro. Overall, this study demonstrates the characterisation of a novel protocol for the decellularization and delipidization of human pancreatic tissue for the production of acellular ECM and ECM hydrogel suitable for cell culture and transplantation applications. We also report a list of 120 proteins present within the human pancreatic matrisome.

Tetrahydrocurcumin Enhances Islet Cell Function and Attenuates Apoptosis in Mouse Islets

BACKGROUND

The transplantation of isolated pancreatic islets is a promising treatment for diabetes. Curcumin has been used for its pharmacologic effects, such as antidiabetic and anti-inflammatory activities. Tetrahydrocurcumin (THC), one of the major metabolites of curcumin, has been reported to have antioxidant and anti-inflammatory activities. This study examines the hypothesis that preoperative THC treatment can attenuate ischemic damage and apoptosis before islet transplantation.

METHODS

Islets isolated from Balb/c mice were randomly divided into 2 groups and cultured in medium supplemented with or without THC. In vitro islet viability and function were assessed. After treatment with a cytokine cocktail consisting of tumor necrosis factor-α, interferon-β, and interleukin-1β, islet cell viability, function, and apoptotic status were determined. Proteins related to apoptosis were analyzed using INS-1 cell after streptozocin treatment.

RESULTS

There was no difference in cell viability between the 2 groups. Islets cultured in the medium supplemented with THC showed 1.3-fold higher glucose-induced insulin secretion than the islets cultured in the medium without THC. After treatment with a cytokine cocktail, glucose-induced insulin release, and NO of the islets were significantly improved in THC-treated islets compared with islets not treated with THC. Apoptosis was significantly decreased, and B-cell lymphoma-2 was elevated in the THC-treated group. The streptozocin-treated INS-1 cell produced significantly higher levels of and B-cell lymphoma-2-associated X protein, caspase-3, and caspase-9 than INS-1 treated with THC.

CONCLUSIONS

These results suggest that preoperative THC administration enhances islet function before transplantation and attenuates the cytokine-induced damage associated with apoptosis.

Effectiveness of bioengineered islet cell sheets for the treatment of diabetes mellitus

BACKGROUND

The present study aimed to evaluate whether bioengineered mouse islet cell sheets can be used for the treatment of diabetes mellitus.

METHODS

Isolated mouse pancreatic islets were dispersed, and cells were plated on temperature-responsive culture plates coated with iMatrix-551. On day 3 of culture, the sheets were detached from the plates and used for further analysis or transplantation. The following parameters were assessed: (1) morphology, (2) expression of β-cell-specific transcription factors and other islet-related proteins, (3) methylation level of the pancreatic duodenal homeobox-1 (Pdx-1) promoter, as determined by bisulfite sequencing, and (4) levels of serum glucose after transplantation of one or two islet cell sheets into the abdominal cavity of streptozotocin-induced diabetic severe combined immunodeficiency mice.

RESULTS

From each mouse, we recovered approximately 233.3 ± 12.5 islets and 1.4 ± 0.1 × 10⁵ cells after dispersion. We estimate that approximately 68.2% of the cells were lost during dispersion. The viability of recovered single cells was 91.3 ± 0.9%. The engineered islet cell sheets were stable, but the messenger RNA levels of various β-cell-specific transcription factors were significantly lower than those of primary islets, whereas Pdx-1 promoter methylation and the expression of NeuroD, Pdx-1, and glucagon proteins were similar between sheets and islets. Moreover, transplantation of islet cell sheets did not revert serum hyperglycemia in any of the recipient mice.

CONCLUSIONS

Engineering effective islet cell sheets require further research efforts, as the currently produced sheets remain functionally inferior compared with primary islets.

Porcine Islet Graft Function is Affected by Pretreatment with a Caspase-3 Inhibitor

During the isolation procedure and after transplantation islets are subjected to numerous variables associated with the induction of apoptosis. The present study investigated the effect of transient pretreatment with caspase inhibitors on function and survival of transplanted pig islets. Isolated porcine islets (3000 IEQ) were incubated overnight in 200 μM of the caspase-3 inhibitor DEVD-CMK prior to transplantation into diabetic nude mice. Glucose-stimulated insulin release of pretreated islets was assessed during static incubation. DEVD-CMK successfully prevented the expression of capase-3 and DFF as demonstrated in heat-shocked pig islets. Nevertheless, transient pretreatment of freshly isolated pig islets with DEVD-CMK resulted in a significantly decreased final graft function of 50.0% (n = 16) compared to 85.7% (n = 14) in control islets (p < 0.05). Glucose-stimulated insulin release of porcine islets (n = 6) was not significantly effected by overnight culture with DEVD-CMK. Morphological assessment revealed that this caspase-3 inhibitor significantly increased the percentage of necrosis to a small, but nevertheless significant, extent in comparison to control islets (p < 0.05). The study demonstrates that short-time pretreatment with the caspase-3 inhibitor DEVD-CMK reduces the capacity of transplanted porcine islets to restore normoglycemia in diabetic nude mice.

Bio-synthetic materials for immunomodulation of islet transplants

Clinical islet transplantation is an effective therapy in restoring physiological glycemic control in type 1 diabetics. However, allogeneic islets derived from cadaveric sources elicit immune responses that result in acute and chronic islet destruction. To prevent immune destruction of islets, transplant recipients require lifelong delivery of immunosuppressive drugs, which are associated with debilitating side effects. Biomaterial-based strategies to eliminate the need for immunosuppressive drugs are an emerging therapy for improving islet transplantation. In this context, two main approaches have been used: 1) encapsulation of islets to prevent infiltration and contact of immune cells, and 2) local release of immunomodulatory molecules from biomaterial systems that suppress local immunity. Synthetic biomaterials provide excellent control over material properties, molecule presentation, and therapeutic release, and thus, are an emerging platform for immunomodulation to facilitate islet transplantation. This review highlights various synthetic biomaterial-based strategies for preventing immune rejection of islet allografts.

Key Matrix Proteins Within the Pancreatic Islet Basement Membrane Are Differentially Digested During Human Islet Isolation

Clinical islet transplantation achieves insulin independence in selected patients, yet current methods for extracting islets from their surrounding pancreatic matrix are suboptimal. The islet basement membrane (BM) influences islet function and survival and is a critical marker of islet integrity following rodent islet isolation. No studies have investigated the impact of islet isolation on BM integrity in human islets, which have a unique duplex structure. To address this, samples were taken from 27 clinical human islet isolations (donor age 41-59, BMI 26-38, cold ischemic time < 10 h). Collagen IV, pan-laminin, perlecan and laminin-α5 in the islet BM were significantly digested by enzyme treatment. In isolated islets, laminin-α5 (found in both layers of the duplex BM) and perlecan were lost entirely, with no restoration evident during culture. Collagen IV and pan-laminin were present in the disorganized BM of isolated islets, yet a significant reduction in pan-laminin was seen during the initial 24 h culture period. Islet cytotoxicity increased during culture. Therefore, the human islet BM is substantially disrupted during the islet isolation procedure. Islet function and survival may be compromised as a consequence of an incomplete islet BM, which has implications for islet survival and transplanted graft longevity.

The impact of cell surface PEGylation and short-course immunotherapy on islet graft survival in an allogeneic murine model

Islet transplantation is a promising therapy for Type 1 diabetes mellitus; however, host inflammatory and immune responses lead to islet dysfunction and destruction, despite potent systemic immunosuppression. Grafting of poly(ethylene glycol) (PEG) to the periphery of cells or tissues can mitigate inflammation and immune recognition via generation of a steric barrier. Herein, we sought to evaluate the complementary impact of islet PEGylation with a short-course immunotherapy on the survival of fully-MHC mismatched islet allografts (DBA/2 islets into diabetic C57BL/6J recipients). Anti-Lymphocyte Function-associated Antigen 1 (LFA-1) antibody was selected as a complementary, transient, systemic immune monotherapy. Islets were PEGylated via an optimized protocol, with resulting islets exhibiting robust cell viability and function. Following transplantation, a significant subset of diabetic animals receiving PEGylated islets (60%) or anti-LFA-1 antibody (50%) exhibited long-term (>100d) normoglycemia. The combinatorial approach proved synergistic, with 78% of the grafts exhibiting euglycemia long-term. Additional studies examining graft cellular infiltrates at early time points characterized the local impact of the transplant protocol on graft survival. Results illustrate the capacity of a simple polymer grafting approach to impart significant immunoprotective effects via modulation of the local transplant environment, while short-term immunotherapy serves to complement this effect.

STATEMENT OF SIGNIFICANCE

We believe this study is important and of interest to the biomaterials and transplant community for several reasons: 1) it provides an optimized protocol for the PEGylation of islets, with minimal impact on the coated islets, which can be easily translated for clinical applications; 2) this optimized protocol demonstrates the benefits of islet PEGylation in providing modest immunosuppression in a murine model; 3) this work demonstrates the combinatory impact of PEGylation with short-course immunotherapy (via LFA-1 blockage), illustrating the capacity of PEGylation to complement existing immunotherapy; and 4) it suggests macrophage phenotype shifting as the potential mechanism for this observed benefit.

Red Ginseng Administration Before Islet Isolation Attenuates Apoptosis and Improves Islet Function and Transplant Outcome in a Syngeneic Mouse Marginal Islet Mass Model

BACKGROUND

Transplantation of isolated islets is a promising treatment for diabetes. Red ginseng (RG) is steamed ginseng and has been reported to enhance insulin secretion-stimulating and anti-apoptotic activities in pancreatic β-cells. In this study, we examined the hypothesis that pre-operative RG treatment enhances islet cell function and anti-apoptosis and investigated whether RG improves islet engraftment by transplant of a marginal mass of syngeneic islets pretreated with RG in diabetic mice.

METHODS

Balb/c mice were randomly divided into 2 groups, and 1 group was administered RG (400 mg/kg/day orally) for 7 days before islet isolation. In vitro islet viability and function were assessed. After cytokine treatment, cell viability, function, and apoptosis of islet cells were analyzed. Furthermore, we studied the effects of RG in a syngeneic islet graft model. A marginal mass of syngeneic mouse islets was transplanted into diabetic hosts.

RESULTS

Islet pretreatment with RG showed 1.4-fold higher glucose-induced insulin secretion than did control islets. RG pretreatment upregulated B-cell lymphoma 2 (Bcl-2) expression and downregulated Bcl-associated X protein (BAX), caspase-3, and inducible nitric oxide synthase (iNOS) expression. Glucose-induced insulin release, NO, and apoptosis were significantly improved in RG-pretreated islets compared with cytokine-treated islets. RG-pretreated mice exhibited improved marginal mass islet graft survival compared with controls.

CONCLUSIONS

These results suggest that pre-operative RG administration enhanced islet function before transplantation and attenuated cytokine-induced damage associated with apoptosis. These studies indicate that inhibition of apoptosis by RG significantly improved islet cell and graft function after isolation and transplantation, respectively.

Macroporous biohybrid cryogels for co-housing pancreatic islets with mesenchymal stromal cells

Intrahepatic transplantation of allogeneic pancreatic islets offers a promising therapy for type 1 diabetes. However, long-term insulin independency is often not achieved due to severe islet loss shortly after transplantation. To improve islet survival and function, extrahepatic biomaterial-assisted transplantation of pancreatic islets to alternative sites has been suggested. Herein, we present macroporous, star-shaped poly(ethylene glycol) (starPEG)-heparin cryogel scaffolds, covalently modified with adhesion peptides, for the housing of pancreatic islets in three-dimensional (3D) co-culture with adherent mesenchymal stromal cells (MSC) as accessory cells. The implantable biohybrid scaffolds provide efficient transport properties, mechanical protection, and a supportive extracellular environment as a desirable niche for the islets. MSC colonized the cryogel scaffolds and produced extracellular matrix proteins that are important components of the natural islet microenvironment known to facilitate matrix-cell interactions and to prevent cellular stress. Islets survived the seeding procedure into the cryogel scaffolds and secreted insulin after glucose stimulation in vitro. In a rodent model, intact islets and MSC could be visualized within the scaffolds seven days after subcutaneous transplantation. Overall, this demonstrates the potential of customized macroporous starPEG-heparin cryogel scaffolds in combination with MSC to serve as a multifunctional islet supportive carrier for transplantation applications.

STATEMENT OF SIGNIFICANCE

Diabetes results in the insufficient production of insulin by the pancreatic β-cells in the islets of Langerhans. Transplantation of pancreatic islets offers valuable options for treating the disease; however, many transplanted islets often do not survive the transplantation or die shortly thereafter. Co-transplanted, supporting cells and biomaterials can be instrumental for improving islet survival, function and protection from the immune system. In the present study, islet supportive hydrogel sponges were explored for the co-transplantation of islets and mesenchymal stromal cells. Survival and continued function of the supported islets were demonstrated in vitro. The in vivo feasibility of the approach was shown by transplantation in a mouse model.

Oxygenation of the Intraportally Transplanted Pancreatic Islet

Intraportal islet transplantation (IT) is not widely utilized as a treatment for type 1 diabetes. Oxygenation of the intraportally transplanted islet has not been studied extensively. We present a diffusion-reaction model that predicts the presence of an anoxic core and a larger partly functional core within intraportally transplanted islets. Four variables were studied: islet diameter, islet fractional viability, external oxygen partial pressure (P) (in surrounding portal blood), and presence or absence of a thrombus on the islet surface. Results indicate that an islet with average size and fractional viability exhibits an anoxic volume fraction (AVF) of 14% and a function loss of 72% at a low external P. Thrombus formation increased AVF to 30% and function loss to 92%, suggesting that the effect of thrombosis may be substantial. External P and islet diameter accounted for the greatest overall impact on AVF and loss of function. At our institutions, large human alloislets (>200 μm diameter) account for ~20% of total islet number but ~70% of total islet volume; since most of the total transplanted islet volume is accounted for by large islets, most of the intraportal islet cells are likely to be anoxic and not fully functional.

Improving pancreatic islet in vitro functionality and transplantation efficiency by using heparin mimetic peptide nanofiber gels

Pancreatic islet transplantation is a promising treatment for type 1 diabetes. However, viability and functionality of the islets after transplantation are limited due to loss of integrity and destruction of blood vessel networks. Thus, it is important to provide a proper mechanically and biologically supportive environment for enhancing both in vitro islet culture and transplantation efficiency. Here, we demonstrate that heparin mimetic peptide amphiphile (HM-PA) nanofibrous network is a promising platform for these purposes. The islets cultured with peptide nanofiber gel containing growth factors exhibited a similar glucose stimulation index as that of the freshly isolated islets even after 7 days. After transplantation of islets to STZ-induced diabetic rats, 28 day-long monitoring displayed that islets that were transplanted in HM-PA nanofiber gels maintained better blood glucose levels at normal levels compared to the only islet transplantation group. In addition, intraperitoneal glucose tolerance test revealed that animals that were transplanted with islets within peptide gels showed a similar pattern with the healthy control group. Histological assessment showed that islets transplanted within peptide nanofiber gels demonstrated better islet integrity due to increased blood vessel density. This work demonstrates that using the HM-PA nanofiber gel platform enhances the islets function and islet transplantation efficiency both in vitro and in vivo.

Fabrication of three-dimensional bioplotted hydrogel scaffolds for islets of Langerhans transplantation

In clinical islet transplantation, allogeneic islets of Langerhans are transplanted into the portal vein of patients with type 1 diabetes, enabling the restoration of normoglycemia. After intra-hepatic transplantation several factors are involved in the decay in islet mass and function mainly caused by an immediate blood mediated inflammatory response, lack of vascularization, and allo- and autoimmunity. Bioengineered scaffolds can potentially provide an alternative extra-hepatic transplantation site for islets by improving nutrient diffusion and blood supply to the scaffold. This would ultimately result in enhanced islet viability and functionality compared to conventional intra portal transplantation. In this regard, the biomaterial choice, the three-dimensional (3D) shape and scaffold porosity are key parameters for an optimal construct design and, ultimately, transplantation outcome. We used 3D bioplotting for the fabrication of a 3D alginate-based porous scaffold as an extra-hepatic islet delivery system. In 3D-plotted alginate scaffolds the surface to volume ratio, and thus oxygen and nutrient transport, is increased compared to conventional bulk hydrogels. Several alginate mixtures have been tested for INS1E β-cell viability. Alginate/gelatin mixtures resulted in high plotting performances, and satisfactory handling properties. INS1E β-cells, human and mouse islets were successfully embedded in 3D-plotted constructs without affecting their morphology and viability, while preventing their aggregation. 3D plotted scaffolds could help in creating an alternative extra-hepatic transplantation site. In contrast to microcapsule embedding, in 3D plotted scaffold islets are confined in one location and blood vessels can grow into the pores of the construct, in closer contact to the embedded tissue. Once revascularization has occurred, the functionality is fully restored upon degradation of the scaffold.

Therapeutic Potential of Laminin–Biodritin Microcapsules for Type 1 Diabetes Mellitus

Pancreatic islet microencapsulation constitutes an attractive therapy for type 1 diabetes mellitus; however, long-term β-cell function remains a major problem. Loss of extracellular matrix interactions during islet isolation dramatically affects β-cell viability. We have previously shown beneficial effects of laminin (LN) in human islet cultures. Herein, we investigated whether LN could improve the outcome of transplantation after islet microencapsulation in Biodritin, an alginate-based material. To test LN-Biodritin stability, microcapsules were subjected to different types of in vitro stress. Focusing on biocompatibility, empty microcapsules were coincubated with the RAW 264.7 macrophage cell line for up to 24 h, and empty beads were implanted IP in mice and retrieved for analyses after 7 and 30 days. Upon culturing for 48 h, mRNA, protein levels, and caspase 3 activity were evaluated in islets microencapsulated with LN-Biodritin. Mice rendered diabetic by streptozotocin injection were transplanted with microencapsulated islets, followed by assessment of body weight, glycemia, and graft function (evaluated by OGTT). Graft efficiency was observed upon microencapsulated islet explantation. The results obtained showed that LN-Biodritin microcapsules were as stable and biocompatible as Biodritin. Modulation of mRNA and protein levels suggested protection against apoptosis and islet stress. Mice transplanted with LN-Biodritin microencapsulated islets presented a better outcome at 198 days postsurgery. Graft explantation led animals to hyperglycemia. In conclusion, LN-Biodritin constitutes a very promising biomaterial for islet transplantation.

Assessment of tissue-engineered islet graft viability by fluorine magnetic resonance spectroscopy

INTRODUCTION

Despite significant progress in the last decade, islet transplantation remains an experimental therapy for a limited number of patients with type 1 diabetes. Tissue-engineered approaches may provide promising alternatives to the current clinical protocol and would benefit greatly from concurrent development of graft quality assessment techniques. This study was designed to evaluate whether viability of tissue-engineered islet grafts can be assessed using fluorine magnetic resonance spectroscopy ((19)F-MRS), by the noninvasive measurement of oxygen partial pressure (pO(2)) and the subsequent calculation of islet oxygen consumption rate (OCR).

METHODS

Scaffolds composed of porcine plasma were seeded with human islets and perfluorodecalin. Each graft was covered with the same volume of culture media in a Petri dish. Four scaffolds were seeded with various numbers (0-8000) of islet equivalents (IE) aliquoted from the same preparation. After randomizing run order, grafts were examined by (19)F-MRS at 37°C using a 5T spectrometer and a single-loop surface coil placed underneath. A standard inversion recovery sequence was used to obtain characteristic (19)F spin-lattice relaxation times (T1), which were converted to steady-state average pO(2) estimates using a previously determined linear calibration (R(2) = 1.000). Each condition was assessed using replicate (19)F-MRS measurements (n = 6-8).

RESULTS

Grafts exhibited IE dose-dependent increases in T1 and decreases in pO(2) estimates. From the difference between scaffold pO(2) estimates and ambient pO(2), the islet preparation OCR was calculated to be 95 ± 12 (mean ± standard error of the mean) nmol/(min·mg DNA) using theoretical modeling. This value compared well with OCR values measured using established methods for human islet preparations.

CONCLUSIONS

(19)F-MRS can be used for noninvasive pre- and possibly posttransplant assessment of tissue-engineered islet graft viability by estimating the amount of viable, oxygen-consuming tissue in a scaffold.

Intraportal islet oxygenation

Islet transplantation (IT) is a promising therapy for the treatment of diabetes. The large number of islets required to achieve insulin independence limit its cost-effectiveness and the number of patients who can be treated. It is believed that >50% of islets are lost in the immediate post-IT period. Poor oxygenation in the early post-IT period is recognized as a possible reason for islet loss and dysfunction but has not been extensively studied. Several key variables affect oxygenation in this setting, including (1) local oxygen partial pressure (pO(2)), (2) islet oxygen consumption, (3) islet size (diameter, D), and (4) presence or absence of thrombosis on the islet surface. We discuss implications of oxygen-limiting conditions on intraportal islet viability and function. Of the 4 key variables, the islet size appears to be the most important determinant of the anoxic and nonfunctional islet volume fractions. Similarly, the effect of thrombus formation on the islet surface may be substantial. At the University of Minnesota, average size distribution data from clinical alloislet preparations (n = 10) indicate that >150-µm D islets account for only ~30% of the total islet number, but >85% of the total islet volume. This suggests that improved oxygen supply to the islets may have a profound impact on islet survivability and function since most of the β-cell volume is within large islets which are most susceptible to oxygen-limiting conditions. The assumption that the liver is a suitable islet transplant site from the standpoint of oxygenation should be reconsidered.

Improved physiological properties of gravity-enforced reassembled rat and human pancreatic pseudo-islets

Previously we demonstrated the superiority of small islets vs large islets in terms of function and survival after transplantation, and we generated reaggregated rat islets (pseudo-islets) of standardized small dimensions by the hanging-drop culture method (HDCM). The aim of this study was to generate human pseudo-islets by HDCM and to evaluate and compare the physiological properties of rat and human pseudo-islets. Isolated rat and human islets were dissociated into single cells and incubated for 6-14 days by HDCM. Newly formed pseudo-islets were analysed for dimensions, morphology, glucose-stimulated insulin secretion (GSIS) and total insulin content. The morphology of reaggregated human islets was similar to that of native islets, while rat pseudo-islets had a reduced content of α and δ cells. GSIS of small rat and human pseudo-islets (250 cells) was increased up to 4.0-fold (p < 0.01) and 2.5-fold (p < 0.001), respectively, when compared to their native counterparts. Human pseudo-islets showed a more pronounced first-phase insulin secretion as compared to intact islets. GSIS was inversely correlated to islet size, and small islets (250 cells) contained up to six-fold more insulin/cell than large islets (1500 cells). Tissue loss with this new technology could be reduced to 49.2 ± 1.5% in rat islets, as compared to the starting amount. With HDCM, pseudo-islets of standardized size with similar cellular composition and improved biological function can be generated, which compensates for tissue loss during production. Transplantation of small pseudo-islets may represent an attractive strategy to improve graft survival and function, due to better oxygen and nutrient supply during the phase of revascularization. Copyright © 2014 John Wiley & Sons, Ltd.

On the TRAIL of obesity and diabetes

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been extensively studied for its preferential ability to induce apoptosis of cancer cells. Beyond the cytotoxic capacity of TRAIL, new physiological and pathological roles for TRAIL have been identified, and there is now growing evidence supporting its involvement in the development of obesity and diabetes. This review summarizes the most recent findings associating TRAIL with obesity and diabetes in both humans and experimental settings. We also present and discuss some of the reported controversies behind TRAIL signaling and function. Understanding TRAIL mechanism(s) in vivo and its involvement in disease may lead to novel strategies to combat the growing pandemic of obesity and diabetes worldwide.

Correction of diabetes mellitus by transplanting minimal mass of syngeneic islets into vascularized small intestinal segment

Transplantation of mature islets into portal vein has been most effective thus far, although attrition of transplanted islets constitutes a major limitation, and alternative approaches are required. We analyzed the mechanisms by which islets engrafted, vascularized and functioned over the long term in the small intestinal submucosa. To determine engraftment, survival and function, 350 syngenic islets were transplanted into either intestinal segments or portal vein of diabetic rats. Islet reorganization, vascularization and function were analyzed by histological analysis, RT-PCR analysis as well as glycemic control over up to 1 year. Transplantation of syngeneic islets in marginal numbers successfully restored normoglycemia in diabetic rats. Transplantation of semi-pure islet preparation did not impair their engraftment, vascularization and function. Islets were morphologically intact and expressed insulin as well as glucagon over the year. Expression of angiogenic genes permitted revascularization of transplanted islets. We identified the expression of transcription factors required for maintenance of beta cells. These studies demonstrated that marginal mass of transplanted islets was sufficient to restore euglycemia in streptozotocin-treated rats. These superior results were obtained despite use of an impure preparation of islets in animals with small intestinal segment. Our findings will help advance new horizons for cell therapy in patients with diabetes.

Collagen IV-modified scaffolds improve islet survival and function and reduce time to euglycemia

Islet transplantation on extracellular matrix (ECM) protein-modified biodegradable microporous poly(lactide-co-glycolide) scaffolds is a potential curative treatment for type 1 diabetes mellitus (T1DM). Collagen IV-modified scaffolds, relative to control scaffolds, significantly decreased the time required to restore euglycemia from 17 to 3 days. We investigated the processes by which collagen IV-modified scaffolds enhanced islet function and mediated early restoration of euglycemia post-transplantation. We characterized the effect of collagen IV-modified scaffolds on islet survival, metabolism, and insulin secretion in vitro and early- and intermediate-term islet mass and vascular density post-transplantation and correlated these with early restoration of euglycemia in a syngeneic mouse model. Control scaffolds maintained native islet morphologies and architectures as well as collagen IV-modified scaffolds in vivo. The islet size and vascular density increased, while β-cell proliferation decreased from day 16 to 113 post-transplantation. Collagen IV-modified scaffolds promoted islet cell viability and decreased early-stage apoptosis in islet cells in vitro-phenomena that coincided with enhanced islet metabolic function and glucose-stimulated insulin secretion. These findings suggest that collagen IV-modified scaffolds promote the early restoration of euglycemia post-transplantation by enhancing islet metabolism and glucose-stimulated insulin secretion. These studies of ECM proteins, in particular collagen IV, and islet function provide key insights for the engineering of a microenvironment that would serve as a platform for enhancing islet transplantation as a viable clinical therapy for T1DM.

Engineering a local microenvironment for pancreatic islet replacement

Intraportal islet transplantation has emerged as a promising treatment for type 1 diabetes mellitus (T1DM). Nevertheless, long-term efficacy has been limited to a marginal number of patients. Outcomes have been restricted, in part, by challenges associated with the transplant site, poor vascularization, and disruption of the native islet architecture during the isolation process. Engineering a biomaterial platform that recapitulates critical components of the pancreatic environment can serve to address these hurdles. This review highlights the challenges and opportunities in engineering 3D niches for islets, specifically: the importance of site selection; the application of scaffold functionalization to present bioactive motifs; and the development of technologies for enhancing implant nutritional profiles. The potential of these novel approaches to improve islet engraftment and duration of function is discussed.

Porcine pancreas extracellular matrix as a platform for endocrine pancreas bioengineering

Emergent technologies of regenerative medicine have the potential to overcome the limitations of organ transplantation by supplying tissues and organs bioengineered in the laboratory. Pancreas bioengineering requires a scaffold that approximates the biochemical, spatial and vascular relationships of the native extracellular matrix (ECM). We describe the generation of a whole organ, three-dimensional pancreas scaffold using acellular porcine pancreas. Imaging studies confirm that our protocol effectively removes cellular material while preserving ECM proteins and the native vascular tree. The scaffold was seeded with human stem cells and porcine pancreatic islets, demonstrating that the decellularized pancreas can support cellular adhesion and maintenance of cell functions. These findings advance the field of regenerative medicine towards the development of a fully functional, bioengineered pancreas capable of establishing and sustaining euglycemia and may be used for transplantation to cure diabetes mellitus.

Pancreatic islet basement membrane loss and remodeling after mouse islet isolation and transplantation: impact for allograft rejection

The isolation of islets by collagenase digestion can cause damage and impact the efficiency of islet engraftment and function. In this study, we assessed the basement membranes (BMs) of mouse pancreatic islets as a molecular biomarker for islet integrity, damage after isolation, and islet repair in vitro as well as in the absence or presence of an immune response after transplantation. Immunofluorescence staining of BM matrix proteins and the endothelial cell marker platelet endothelial cell adhesion molecule-1 (PECAM-1) was performed on pancreatic islets in situ, isolated islets, islets cultured for 4 days, and islet grafts at 3-10 days posttransplantation. Flow cytometry was used to investigate the expression of BM matrix proteins in isolated islet β-cells. The islet BM, consisting of collagen type IV and components of Engelbreth-Holm-Swarm (EHS) tumor laminin 111, laminin α2, nidogen-2, and perlecan in pancreatic islets in situ, was completely lost during islet isolation. It was not reestablished during culture for 4 days. Peri- and intraislet BM restoration was identified after islet isotransplantation and coincided with the migration pattern of PECAM-1(+) vascular endothelial cells (VECs). After islet allotransplantation, the restoration of VEC-derived peri-islet BMs was initiated but did not lead to the formation of the intraislet vasculature. Instead, an abnormally enlarged peri-islet vasculature developed, coinciding with islet allograft rejection. The islet BM is a sensitive biomarker of islet damage resulting from enzymatic isolation and of islet repair after transplantation. After transplantation, remodeling of both peri- and intraislet BMs restores β-cell-matrix attachment, a recognized requirement for β-cell survival, for isografts but not for allografts. Preventing isolation-induced islet BM damage would be expected to preserve the intrinsic barrier function of islet BMs, thereby influencing both the effector mechanisms required for allograft rejection and the antirejection strategies needed for allograft survival.

In situ application of hydrogel-type fibrin-islet composite optimized for rapid glycemic control by subcutaneous xenogeneic porcine islet transplantation

Maximum engraftment of transplanted islets is essential for the clinical application of a subcutaneous site. Significant barriers to the current approaches are associated with their low effectiveness, complexity and unproven biosafety. Here, we evaluated and optimized a fibrin-islet composite for effective glycemic control in a subcutaneous site whose environment is highly hypoxic due to low vascularization potential. In the setting of xenogeneic porcine islet transplantation into the subcutaneous space of a diabetic mouse, the in vivo islet functions were greatly affected by the concentrations of fibrinogen and thrombin. The optimized hydrogel-type fibrin remarkably reduced the marginal islet mass to approximately one tenth that of islets without fibrin. This marginal islet mass was comparable to that in the setting of the subcapsular space of the kidney, which is a highly vascularized organ. Highly vascularized structures were generated inside and on the outer surface of the grafts. A hydrogel-type fibrin-islet composite established early diabetic control within an average of 3.4days after the transplantation. In the mechanistic studies, fibrin promoted local angiogenesis, enhanced islet viability and prevented fragmentation of islets into single cells. In conclusion, in situ application of hydrogel-type fibrin-islet composite may be a promising modality in the clinical success of subcutaneous islet transplantation.

Novel Positive-Charged Nanoparticles for Efficient Magnetic Resonance Imaging of Islet Transplantation

Significant graft loss immediately after islet transplantation occurs due to immunological and nonimmunological events. Magnetic resonance imaging (MRI) is an attractive potential tool for monitoring islet mass in vivo. Although an efficient uptake of MRI contrast agent is required for islet cell labeling, commercially available magnetic nanoparticles are not efficiently transduced into cells. In this study, we developed six kinds of novel magnetic iron oxide nanoparticles, which are electrically charged by cationic end-group substitution of dextran. Each of the nanoparticles consisted of a small monocrystalline, superparamagnetic iron oxide core that is stabilized by a cross-linked aminated dextran coating to improve stability. We also used three different commercially available nanoparticles for controls. The labeling efficiency of the novel nanoparticles was evaluated, and the feasibility of the imaging by MRI was assessed. The positive-charged nanoparticles were transduced into a β-cell line, MIN6 cells, but not three commercially available nanoparticles. MRI showed a marked decrease in signal intensity on T1- and T2-weighted images at the site of the labeled cells in vitro. These data suggest that novel positive-charged nanoparticles could be useful MRI contrast agents to monitor islet mass after transplantation.

Significant improvement in islet yield and survival with modified ET-Kyoto solution: ET-Kyoto/Neutrophil elastase inhibitor

Although islet transplantation can achieve insulin independence in patients with type 1 diabetes, sufficient number of islets derived from two or more donors is usually required to achieve normoglycemia. Activated neutrophils and neutrophil elastase (NE), which is released from these neutrophils, can directly cause injury in islet grafts. We hypothesized that inhibition of NE improves islet isolation and islet allograft survival. We tested our hypothesis by examining the effects of modified ET-Kyoto solution supplemented with sivelestat, a NE inhibitor (S-Kyoto solution), on islet yield and viability in islet isolation and the effect of intraperitoneally injected sivelestat on islet graft survival in a mouse allotransplant model. NE and proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-6 increased markedly at the end of warm digestion during islet isolation and exhibited direct cytotoxic activity against the islets causing their apoptosis. The use of S-Kyoto solution significantly improved islet yield and viability. Furthermore, treatment with sivelestat resulted in significant prolongation of islet allograft survival in recipient mice. Furthermore, serum levels of IL-6 and TNF-α at 1 and 2 weeks posttransplantation were significantly higher in islet recipients than before transplantation. Our results indicated that NE released from activated neutrophils negatively affects islet survival and that its suppression both in vitro and in vivo improved islet yield and prolonged islet graft survival. The results suggest that inhibition of NE activity could be potentially useful in islet transplantation for patients with type 1 diabetes mellitus.

Reversal of diabetes by the creation of neo-islet tissues into a subcutaneous site using islet cell sheets

BACKGROUND

There remains a paucity of therapeutic approaches to completely treat diabetes mellitus. This study was designed to develop a dispersed islet cell-based tissue engineering approach to engineer functional neo-islet tissues in the absence of traditional bioabsorbable scaffold matrices.

METHODS

Specialized coated plastic dishes were prepared by covalently immobilizing a temperature-responsive polymer, poly(N-isopropylacrylamide), onto the plastic followed by coating with laminin-5. Dispersed rat islet cells were plated on the laminin-5-poly(N-isopropylacrylamide) dishes. After 2 days of culturing, islet cells were harvested as a uniformly connected tissue sheet by lowering the culture temperature from 37°C to 20°C for 30 min. Two harvested islet cell sheets were transplanted into the subcutaneous space of streptozotocin-induced diabetic severe combined immunodeficiency (SCID) mice to engineer neo-islet tissues in vivo. Therapeutic effects were investigated after the tissue engineering procedures.

RESULTS

In all of the diabetic SCID mice transplanted with the islet sheets, serum hyperglycemia was successfully reverted to a steady normoglycemic level. The recipient SCID mice demonstrated positive for serum rat C-peptide and elevated serum insulin levels. Moreover, the islet cell sheet-transplanted SCID mice demonstrated rapid glucose clearance and return of serum glucose levels after intraperitoneal glucose tolerance test. Histological examination revealed that the transplanted islet cell sheets were structured as flat clusters of islet tissues in which an active vascular network manifested within and surrounding the newly formed tissues.

CONCLUSIONS

This study describes a new proof-of-concept therapeutic approach to engineer functional neo-islet tissues for the treatment of type 1 diabetes mellitus.

Hyperoxia during colon surgery is associated with a reduction of xanthine oxidase activity and oxidative stress in colonic mucosa

BACKGROUND

Gut manipulation during surgery may induce local oxidative stress. Supplemental inspired oxygen increases arterial and tissue oxygen partial pressures. This study examined whether a 0.80 fraction of inspired oxygen (FiO(2)) attenuates the oxidative stress, reducing xanthine oxidase (XO) activity in colonic mucosa as a possible mechanism during colon surgery.

METHODS

Twenty-four cancer patients who underwent elective colon resection were randomly assigned to either 0.30 FiO(2) or 0.80 FiO(2) during surgery. Malondialdehyde (MDA) and oxidized glutathione (GSSG) levels were measured in blood plasma. We also determined the enzymatic activities of XO and xanthine dehydrogenase (XDH) in the colonic mucosa after resection of the piece of colon.

RESULTS

Oxygen partial pressure in arterial blood was higher in the 0.80 FiO(2) group than in the 0.30 FiO(2) group (P<0.001). MDA and GSSG levels measured in blood plasma as well as MDA measured in colonic mucosa were lower in the 0.80 FiO(2) group than in the 0.30 FiO(2) group. Otherwise, XO enzymatic activity and XO/(XO+XDH) ratio in colonic mucosa were lower in the 0.80 FiO(2) group than in the 0.30 FiO(2) group.

CONCLUSIONS

XO may be a major source of reactive oxygen species in patients during colon surgery. Inspiring 0.80 oxygen during colon surgery increases arterial partial pressure and this treatment was associated with reduced XO activity and levels of oxidative stress in colonic mucosa.

Islet transplantation: factors in short-term islet survival

Islet transplantation has the potential to cure type 1 diabetes. In recent years, the proportion of patients achieving initial insulin independence has improved, but longer term outcomes remain poor compared to those for whole pancreas transplants. This review article will discuss factors affecting islet yield and viability leading up to transplantation and in the immediate post-transplant period.

Edaravone, a free radical scavenger, promotes engraftment of intraportally transplanted islet cells

OBJECTIVES

Pancreatic islet transplantation requires multiple transplants to achieve insulin independence. Only one third of the islet mass is stably engrafted; one of the causes of which is ascribed to oxidative stress. We confirmed the hypothesis that administration of edaravone, a free radical scavenger, in the early posttransplantation period promotes islet cell engraftment.

METHODS

Islet isograft from a single donor was intraportally transplanted into streptozotocin-diabetic F344 rats, and intravenous edaravone (3 mg/kg) was administered immediately and 24 hours after the transplantation. Plasma glucose concentrations were monitored for 28 days. Serum insulin levels were obtained on the second week. Morphologic studies were performed on insulin-immunostained and TUNEL-stained sections of the recipient liver.

RESULTS

In the edaravone-treated group, hyperglycemia was ameliorated, and 50% of rats achieved normoglycemia (<200 mg/dL). All rats in the control group remained hyperglycemic (>400 mg/dL). Insulin secretion of the edaravone-treated group was superior to the controls. Morphologically, the number and size of the islet β cells of the edaravone-treated group were larger than those of the controls. The number of TUNEL-positive cells in each islet of the edaravone-treated group were fewer than those of the controls.

CONCLUSIONS

In streptozotocin-diabetic rats, edaravone administration in the early posttransplantation period promotes engraftment of intraportally transplanted islet cells.

Use of integrin-linked kinase to extend function of encapsulated pancreatic tissue

We have studied the impact of overexpression of an intracellular signaling protein, integrin-linked kinase (ILK), on the survival and function of encapsulated islet tissue used for the treatment of type 1 diabetes. The dimensions of the encapsulated tissue can impact the stresses placed on the tissue and ILK overexpression shows the ability to extend function of dissociated cells as well as intact islets. These results suggest that lost cell-extracellular matrix interactions in cell encapsulation systems can lead to decreased insulin secretion and ILK signaling is a target to overcome this phenomenon.

Donor pretreatment with DHMEQ improves islet transplantation

BACKGROUND

Currently, pancreatic islet transplantation to achieve normoglycemia in insulin-dependent diabetes mellitus (IDDM) requires two or more donors. This may be due to the inability to transplant functionally preserved and viable islets after isolation. Islets have already been subjected to various harmful stresses during the isolation process leading to apoptosis. One of the intracellular signaling pathways, the transcription factor nuclear factor-kappaB (NF-kappaB)-related pathway, is relevant to the mechanism of beta-cell apoptosis in isolated islets. We attempted to prevent islet apoptosis during isolation by a novel NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ).

MATERIALS AND METHODS

DHMEQ was injected intraperitoneally into donor mice 2 h prior to isolation. NF-kappaB activation, the functioning of isolated islets, apoptosis after isolation, and cytokine- and apoptosis-related genes were analyzed. After 160 equivalents of islets were transplanted into diabetic mice, graft survival and function were evaluated.

RESULTS

Intra-islet NF-kappaB was activated immediately after isolation, and DHMEQ inhibited NF-kappaB activation without deterioration of islet function. DHMEQ significantly prevented apoptosis by inhibiting caspase 3/7 activities and down-regulated Bax, a pro-apoptotic gene. Donor pretreatment with DHMEQ significantly improved engraftment in syngeneic islet transplantation in mice, thus preserving insulin contents in the graft liver, as assessed by functional and histologic analyses.

CONCLUSIONS

DHMEQ is a promising agent in islet transplantation because it protects islets from apoptosis during isolation stress. Donor pretreatment with DHMEQ can significantly affect the success of islet engraftment.

Islet assessment for transplantation

PURPOSE OF REVIEW

There is a critical need for meaningful viability and potency assays that characterize islet preparations for release prior to clinical islet cell transplantation. Development, testing, and validation of such assays have been the subject of intense investigation for the last decade. These efforts are reviewed, highlighting the most recent results while focusing on the most promising assays.

RECENT FINDINGS

Assays based on membrane integrity do not reflect true viability when applied to either intact islets or dispersed islet cells. Assays requiring disaggregation of intact islets into individual cells for assessment introduce additional problems of cell damage and loss. Assays evaluating mitochondrial function, specifically mitochondrial membrane potential, bioenergetic status, and cellular oxygen consumption rate, especially when conducted with intact islets, appear most promising in evaluating their quality prior to islet cell transplantation. Prospective, quantitative assays based on measurements of oxygen consumption rate with intact islets have been developed, validated, and their results correlated with transplant outcomes in the diabetic nude mouse bioassay.

CONCLUSION

More sensitive and reliable islet viability and potency tests have been recently developed and tested. Those evaluating mitochondrial function are most promising, correlate with transplant outcomes in mice, and are currently being evaluated in the clinical setting.

Extracellular matrix in pancreatic islets: relevance to scaffold design and transplantation

Intrahepatic islet transplantation provides a potentially more benign alternative to pancreatic transplantation. However, islet transplants are associated with limited engraftment potential. This inefficiency is likely at least partially attributable to the isolation process, which removes islets from their native environment. Isolation not only disrupts the internal vascularization and innervation of islets, but also fundamentally changes interactions between islet cells and macromolecules of the extracellular matrix (ECM). Signaling interactions between islet cells and ECM are known to regulate multiple aspects of islet physiology, including survival, proliferation, and insulin secretion. Although it is highly likely that disruptions to these interactions during isolation significantly affect transplant outcomes, the true implications of these conditions are not well understood. The following article reviews current understandings and uncertainties in islet-ECM interactions and explains their potential impact on posttransplant engraftment. Topics covered include matrix and receptor compositions in native islets, effects of isolation and culture on islet-ECM interactions, and potential for postisolation restoration of islet-ECM interactions. Greater understanding in these areas may help to reduce isolation and transplantation stresses and improve islet engraftment.

Cell-matrix interactions improve beta-cell survival and insulin secretion in three-dimensional culture

Controlled matrix interactions were presented to pancreatic beta-cells in three-dimensional culture within poly(ethylene glycol) hydrogels. Dispersed MIN6 beta-cells were encapsulated in gel environments containing the following entrapped extracellular matrix (ECM) proteins: collagen type I, collagen type IV, fibrinogen, fibronectin, laminin, and vitronectin. In ECM-containing gels, beta-cell survival was significantly better than in gels without ECM over 10 days. Correspondingly, apoptosis in encapsulated beta-cells was less in the presence of each matrix protein, suggesting the ability of individual matrix interactions to prevent matrix signaling-related apoptosis (anoikis). MIN6 beta-cells cultured in gels containing collagen type IV or laminin secreted more insulin in response to glucose stimulation than beta-cells in all other experimental conditions. Variations in collagen type IV or laminin concentration between 10 microg/mL and 250 microg/mL did not affect insulin secretion. Finally, beta-cell function in hydrogels presenting both collagen type IV and laminin revealed synergistic interactions. With a total protein concentration of 100 microg/mL, three gel compositions of varying ratios of collagen type IV to laminin (25:75, 50:50, and 75:25) were tested. In the presence of 25 microg/mL of collagen type IV and 75 microg/mL of laminin, beta-cell insulin secretion was greater than with laminin or collagen type IV individually. These results demonstrate that specific, rationally designed extracellular environments promote isolated beta-cell survival and function.

Pancreas preservation for pancreas and islet transplantation

PURPOSE OF REVIEW

To summarize advances and limitations in pancreas procurement and preservation for pancreas and islet transplantation, and review advances in islet protection and preservation.

RECENT FINDINGS

Pancreases procured after cardiac death, with in-situ regional organ cooling, have been successfully used for islet transplantation. Colloid-free Celsior and histidine-tryptophan-ketoglutarate preservation solutions are comparable to University of Wisconsin solution when used for cold storage before pancreas transplantation. Colloid-free preservation solutions are inferior to University of Wisconsin solution for pancreas preservation prior to islet isolation and transplantation. Clinical reports on pancreas transplants suggest that the two-layer method may not offer significant benefits over cold storage with the University of Wisconsin solution: improved oxygenation may depend on the graft size; benefits in experimental models may not translate to human organs. Improvements in islet yield and quality occurred from pancreases treated with inhibitors of stress-induced apoptosis during procurement, storage, isolation or culture desirable before islet isolation and transplantation and may improve islet yield and quality. Methods for real-time, noninvasive assessment of pancreas quality during preservation have been implemented and objective islet-potency assays have been developed and validated. These innovations should contribute to objective evaluation and establishment of improved pancreas-preservation and islet-isolation strategies.

SUMMARY

Cold storage may be adequate for preservation before pancreas transplants, but insufficient when pancreases are processed for islets or when expanded donors are used. Supplementation of cold-storage solutions with cytoprotective agents and perfusion may improve pancreas and islet transplant outcomes.

Extracellular matrix protein-coated scaffolds promote the reversal of diabetes after extrahepatic islet transplantation

BACKGROUND

The survival and function of transplanted pancreatic islets is limited, owing in part to disruption of islet-matrix attachments during the isolation procedure. Using polymer scaffolds as a platform for islet transplantation, we investigated the hypothesis that replacement of key extracellular matrix components known to surround islets in vivo would improve graft function at an extrahepatic implantation site.

METHODS

Microporous polymer scaffolds fabricated from copolymers of lactide and glycolide were adsorbed with collagen IV, fibronectin, laminin-332 or serum proteins before seeding with 125 mouse islets. Islet-seeded scaffolds were then implanted onto the epididymal fat pad of syngeneic mice with streptozotocin-induced diabetes. Nonfasting glucose levels, weight gain, response to glucose challenges, and histology were used to assess graft function for 10 months after transplantation.

RESULTS

Mice transplanted with islets seeded onto scaffolds adsorbed with collagen IV achieved euglycemia fastest and their response to glucose challenge was similar to normal mice. Fibronectin and laminin similarly promoted euglycemia, yet required more time than collagen IV and less time than serum. Histopathological assessment of retrieved grafts demonstrated that coating scaffolds with specific extracellular matrix proteins increased total islet area in the sections and vessel density within the transplanted islets, relative to controls.

CONCLUSIONS

Extracellular matrix proteins adsorbed to microporous scaffolds can enhance the function of transplanted islets, with collagen IV maximizing graft function relative to the other proteins tested. These scaffolds enable the creation of well-defined microenvironments that promote graft efficacy at extrahepatic sites.