Ischaemia is linked to inflammation and induction of angiogenesis in pancreatic islets

Emerging strategies to bypass transplant rejection via biomaterial-assisted immunoengineering: Insights from islets and beyond

Novel transplantation techniques are currently under development to preserve the function of impaired tissues or organs. While current technologies can enhance the survival of recipients, they have remained elusive to date due to graft rejection by undesired in vivo immune responses despite systemic prescription of immunosuppressants. The need for life-long immunomodulation and serious adverse effects of current medicines, the development of novel biomaterial-based immunoengineering strategies has attracted much attention lately. Immunomodulatory 3D platforms can alter immune responses locally and/or prevent transplant rejection through the protection of the graft from the attack of immune system. These new approaches aim to overcome the complexity of the long-term administration of systemic immunosuppressants, including the risks of infection, cancer incidence, and systemic toxicity. In addition, they can decrease the effective dose of the delivered drugs via direct delivery at the transplantation site. In this review, we comprehensively address the immune rejection mechanisms, followed by recent developments in biomaterial-based immunoengineering strategies to prolong transplant survival. We also compare the efficacy and safety of these new platforms with conventional agents. Finally, challenges and barriers for the clinical translation of the biomaterial-based immunoengineering transplants and prospects are discussed.

Cell Replacement Therapy for Type 1 Diabetes Patients: Potential Mechanisms Leading to Stem-Cell-Derived Pancreatic β-Cell Loss upon Transplant

Cell replacement therapy using stem-cell-derived insulin-producing β-like cells (sBCs) has been proposed as a practical cure for patients with type one diabetes (T1D). sBCs can correct diabetes in preclinical animal models, demonstrating the promise of this stem cell-based approach. However, in vivo studies have demonstrated that most sBCs, similarly to cadaveric human islets, are lost upon transplantation due to ischemia and other unknown mechanisms. Hence, there is a critical knowledge gap in the current field concerning the fate of sBCs upon engraftment. Here we review, discuss effects, and propose additional potential mechanisms that could contribute toward β-cell loss in vivo. We summarize and highlight some of the literature on phenotypic loss in β-cells under both steady, stressed, and diseased diabetic conditions. Specifically, we focus on β-cell death, dedifferentiation into progenitors, trans-differentiation into other hormone-expressing cells, and/or interconversion into less functional β-cell subtypes as potential mechanisms. While current cell replacement therapy efforts employing sBCs carry great promise as an abundant cell source, addressing the somewhat neglected aspect of β-cell loss in vivo will further accelerate sBC transplantation as a promising therapeutic modality that could significantly enhance the life quality of T1D patients.

Microvessels derived from hiPSCs are a novel source for angiogenesis and tissue regeneration

The establishment of effective vascularization represents a key challenge in regenerative medicine. Adequate sources of vascular cells and intact vessel fragments have not yet been explored. We herein examined the potential application of microvessels induced from hiPSCs for rapid angiogenesis and tissue regeneration. Microvessels were generated from human pluripotent stem cells (iMVs) under a defined induction protocol and compared with human adipose tissue-derived microvessels (ad-MVs) to illustrate the similarity and differences of the alternative source. Then, the therapeutic effect of iMVs was detected by transplantation in vivo. The renal ischemia-reperfusion model and skin damage model were applied to explore the potential effect of vascular cells derived from iMVs (iMVs-VCs). Besides, the subcutaneous transplantation model and muscle injury model were established to explore the ability of iMVs for angiogenesis and tissue regeneration. The results revealed that iMVs had remarkable similarities to natural blood vessels in structure and cellular composition, and were potent for vascular formation and self-organization. The infusion of iMVs-VCs promoted tissue repair in the renal and skin damage model through direct contribution to the reconstruction of blood vessels and modulation of the immune microenvironment. Moreover, the transplantation of intact iMVs could form a massive perfused blood vessel and promote muscle regeneration at the early stage. The infusion of iMVs-VCs could facilitate the reconstruction and regeneration of blood vessels and modulation of the immune microenvironment to restore structures and functions of damaged tissues. Meanwhile, the intact iMVs could rapidly form perfused vessels and promote muscle regeneration. With the advantages of abundant sources and high angiogenesis potency, iMVs could be a candidate source for vascularization units for regenerative medicine.

Is the IL1RA/IL1B Ratio a Suitable Biomarker for Subclinical Endometritis in Dairy Cows?

The adequate expression of cytokines is essential for the prevention and healing of bovine endometrial inflammation. This study investigated the intra-uterine concentration of the proinflammatory cytokine interleukin (IL)1B and its antagonist IL1RA in cows with and without subclinical endometritis (SE). Samples were taken from 37 uteri at the abattoir and 26 uteri in vivo. Uterine secretion samples were classified as showing no signs of SE (SEneg; polymorphonuclear neutrophil granulocyte (PMN) < 5%) or showing signs of SE (SEpos; PMN ≥ 5%). Concentrations and ratios for IL1B and IL1RA were measured using a commercial and a newly established AlphaLISA kit, respectively. In both groups, a higher concentration of IL1B was detected in the SEpos group compared with the SEneg group (abattoir: p = 0.027; in vivo p < 0.001). No significant differences were observed in the concentration of IL1RA (p > 0.05). In uterine secretion samples retrieved in vivo, a lower IL1RA/IL1B ratio was detected in the SEpos group compared with the SEneg group (p = 0.002). The results of this study highlight the important role of IL1B and IL1RA during endometritis and the potential of the IL1RA/IL1B ratio as a possible biomarker for SE.

The ischaemic preconditioning paradox and its implications for islet isolation from heart-beating and non heart-beating donors

The impact of ischaemia can severely damage procured donor organs for transplantation. The pancreas, and pancreatic islets in particular, is one of the most sensitive tissues towards hypoxia. The present study was aimed to assess the effect of hypoxic preconditioning (HP) performed ex-vivo in islets isolated from heart-beating donor (HBD) and non heart-beating donor (NHBD) rats. After HP purified islets were cultured for 24 h in hypoxia followed by islet characterisation. Post-culture islet yields were significantly lower in sham-treated NHBD than in HBD. This difference was reduced when NHBD islets were preconditioned. Similar results were observed regarding viability, apoptosis and in vitro function. Reactive oxygen species generation after hypoxic culture was significantly enhanced in sham-treated NHBD than in HBD islets. Again, this difference could be diminished through HP. qRT-PCR revealed that HP decreases pro-apoptotic genes but increases HIF-1 and VEGF. However, the extent of reduction and augmentation was always substantially higher in preconditioned NHBD than in HBD islets. Our findings indicate a lower benefit of HBD islets from HP than NHBD islets. The ischaemic preconditioning paradox suggests that HP should be primarily applied to islets from marginal donors. This observation needs evaluation in human islets.

Co-transplantation of Islets-Laden Microgels and Biodegradable O2-Generating Microspheres for Diabetes Treatment

Pancreatic islets transplantation is an optimal alternative to exogenous insulin injection for long-term effective type 1 diabetes treatment. However, direct islets transplantation without any protection can induce cell necrosis due to severe host immune rejection. Insufficient O₂ supply induced by the lack of capillary network at the early stage of islets transplantation is another critical constraint limiting islets survival and insulin-secretion function. In this paper, we design a novel co-transplantation system composed of islets-laden nanocomposite microgels and O₂-generating microspheres. In particular, nanocomposite microgels confer the encapsulated islets with simultaneous physical protection and chemical anti-inflammation/immunosuppression by covalently anchoring rapamycin-loaded cyclodextrin nanoparticles to microgel network. Meanwhile, O₂-generating microspheres prepared by blending inorganic peroxides in biodegradable polycaprolactone and polylactic acid can generate in situ O₂ gas and thus avoid hypoxia environment around transplanted islets. In vivo therapeutic effect of diabetic mice proves the reversion of the high blood glucose level back to normoglycemia and superior glucose tolerance for at least 90 days post co-transplantation. In brief, the localized drug and oxygen codelivery, as well as physical protection provided by our co-transplantation system, has the potential to overcome to a large extent the inflammatory, hypoxia, and host immune rejection after islets transplantation. This new strategy may have wider application in other cell replacement therapies.

Preservation of pancreas in the University of Wisconsin solution supplemented with AP39 reduces reactive oxygen species production and improves islet graft function

Ischemia-reperfusion injury (IRI) results in increased rates of delayed graft function and early graft loss. It has recently been reported that hydrogen sulfide (H₂ S) protects organ grafts against prolonged IRI. Here, we investigated whether the preservation of pancreas in University of Wisconsin (UW) solution supplemented with AP39, which is a mitochondrial-targeted H₂ S donor, protected pancreatic islets against IRI and improved islet function. Porcine pancreata were preserved in the UW solution with AP39 (UW + AP39) or the vehicle (UW) for 18 h, followed by islet isolation. The islet yields before and after purification were significantly higher in the UW + AP39 group than in the UW group. The islets isolated from the pancreas preserved in UW + AP39 exhibited significantly decreased levels of reactive oxygen species (ROS) production and a significantly increased mitochondrial membrane potential as compared to the islets isolated from the pancreas preserved in the vehicle. We found that the pancreas preserved in UW + AP39 improved the outcome of islet transplantation in streptozotocin-induced diabetic mice. These results suggest that the preservation of pancreas in UW + AP39 protects the islet grafts against IRI and could thus serve as a novel clinical strategy for improving islet transplantation outcomes.

The Role of Interleukin-1β in Destruction of Transplanted Islets

Islet transplantation is a promising β-cell replacement therapy for type 1 diabetes, which can reduce glucose lability and hypoglycemic episodes compared with standard insulin therapy. Despite the tremendous progress made in this field, challenges remain in terms of long-term successful transplant outcomes. The insulin independence rate remains low after islet transplantation from one donor pancreas. It has been reported that the islet-related inflammatory response is the main cause of early islet damage and graft loss after transplantation. The production of interleukin-1β (IL-1β) has considered to be one of the primary harmful inflammatory events during pancreatic procurement, islet isolation, and islet transplantation. Evidence suggests that the innate immune response is upregulated through the activity of Toll-like receptors and The NACHT Domain-Leucine-Rich Repeat and PYD-containing Protein 3 inflammasome, which are the starting points for a series of signaling events that drive excessive IL-1β production in islet transplantation. In this review, we show recent contributions to the advancement of knowledge of IL-1β in islet transplantation and discuss several strategies targeting IL-1β for improving islet engraftment.

Heterogeneity and neurovascular integration of intraportally transplanted islets revealed by 3-D mouse liver histology

Intraportal islet transplantation has been clinically applied for treatment of unstable type 1 diabetes. However, in the liver, systematic assessment of the dispersed islet grafts and the graft-hepatic integration remains difficult, even in animal models. This is due to the lack of global and in-depth analyses of the transplanted islets and their microenvironment. Here, we apply three-dimensional (3-D) mouse liver histology to investigate the islet graft microstructure, vasculature, and innervation. Streptozotocin-induced diabetic mice were used in syngeneic intraportal islet transplantation to achieve euglycemia. Optically cleared livers were prepared to enable 3-D morphological and quantitative analyses of the engrafted islets. 3-D image data reveal the clot- and plaque-like islet grafts in the liver: the former are derived from islet emboli and associated with ischemia, whereas the latter (minority) resemble the plaques on the walls of portal vessels (e.g., at the bifurcation) with mild, if any, perigraft tissue damage. Three weeks after transplantation, both types of grafts are revascularized, yet significantly more lymphatics are associated with the plaque- than clot-like grafts. Regarding the islet reinnervation, both types of grafts connect to the periportal nerve plexus and develop peri- and intragraft innervation. Specifically, the sympathetic axons and varicosities contact the α-cells, highlighting the graft-host neural integration. We present the heterogeneity of the intraportally transplanted islets and the graft-host neurovascular integration in mice. Our work provides the technical and morphological foundation for future high-definitional 3-D tissue and cellular analyses of human islet grafts in the liver.NEW & NOTEWORTHY Modern 3-D histology identifies the clot- and plaque-like islet grafts in the mouse liver, which otherwise cannot be distinguished with the standard microtome-based histology. The two types of grafts are similar in blood microvessel density and sympathetic reinnervation. Their differences, however, are their locations, severity of associated liver injury, and access to lymphatic vessels. Our work provides the technical and morphological foundation for future high-definitional 3-D tissue/cellular analyses of human islet grafts in the liver.

High Concentrations of Etanercept Reduce Human Islet Function and Integrity

Background

Most islet transplant groups worldwide routinely use the TNFα inhibitor Etanercept in their peri-transplant protocols. Surprisingly, there have been no published dose-response studies on the effects of Etanercept on human islets. Our study aimed to address this by treating cultured human islets with increasing concentrations of Etanercept.

Materials and Methods

Isolated human islets were cultured for 3–4 days in normoxic (21% oxygen) or in hypoxic (2% oxygen) atmosphere using Etanercept dissolved in a range of 2.5–40 µg/mL prior to islet characterisation.

Results

In normoxic atmosphere, it was found that 5 µg/mL is the most efficient dose to preserve islet morphological and functional integrity during culture. Increasing the dose to 10 µg/mL or more resulted in detrimental effects with respect to viability and glucose-stimulated insulin release. When human islets were cultured for 3 to 4 days in clinically relevant hypoxia and treated with 5 µg/mL Etanercept, post-culture islet survival (P < 0.001) and in vitro function (P < 0.01) were significantly improved. This correlated with a substantially reduced cytokine production (P < 0.05), improved mitochondrial function (P < 0.01), and reduced production of reactive oxygen species (P < 0.001) in hypoxia-exposed islets.

Conclusion

These findings suggest that the therapeutic window of Etanercept is very narrow and that this should be considered when optimising the dosage and route of Etanercept administration in islet-transplant recipients or when designing novel drug-delivering islet scaffolds.

Angiogenic biomaterials to promote therapeutic regeneration and investigate disease progression

The vasculature is a key component of the tissue microenvironment. Traditionally known for its role in providing nutrients and oxygen to surrounding cells, the vasculature is now also acknowledged to provide signaling cues that influence biological outcomes in regeneration and disease. These cues come from the cells that comprise vasculature, as well as the dynamic biophysical and biochemical properties of the surrounding extracellular matrix that accompany vascular development and remodeling. In this review, we illustrate the larger role of the vasculature in the context of regenerative biology and cancer progression. We describe cellular, biophysical, biochemical, and metabolic components of vascularized microenvironments. Moreover, we provide an overview of multidimensional angiogenic biomaterials that have been developed to promote therapeutic vascularization and regeneration, as well as to mimic elements of vascularized microenvironments as a means to uncover mechanisms by which vasculature influences cancer progression and therapy.

Enhancement of Subcutaneously Transplanted β Cell Survival Using 3D Stem Cell Spheroids with Proangiogenic and Prosurvival Potential

Islet transplantation has been demonstrated to be a promising therapy for type 1 diabetes mellitus. Although it is a minimally invasive operating procedure and provides easy access for graft monitoring, subcutaneous transplantation of the islet only has limited therapeutic outcomes, owing to the poor capacity of skin tissue to foster revascularization in a short period. Herein, 3D cell spheroids of clinically accessible umbilical cord blood mesenchymal stem cells and human umbilical vein endothelial cells are formed and employed for codelivery with β cells subcutaneously. The 3D stem cell spheroids, which can secrete multiple proangiogenic and prosurvival growth factors, induce robust angiogenesis and prevent β cell graft death, as indicated by the results of in vivo bioluminescent tracking and histological analysis. These experimental data highlight the efficacy of the 3D stem cell spheroids that are fabricated using translationally applicable cell types in promoting the survival and function of subcutaneously transplanted β cells.

Beneficial effects of the novel marine oxygen carrier M101 during cold preservation of rat and human pancreas

Ischaemia impairs organ quality during preservation in a time‐dependent manner, due to a lack of oxygen supply. Its impact on pancreas and islet transplantation outcome has been demonstrated by a correlation between cold ischaemia time and poor islet isolation efficiency. Our goal in the present study was to improve pancreas and islet quality using a novel natural oxygen carrier (M101, 2 g/L), which has been proven safe and efficient in other clinical applications, including kidney transplantation, and for several pre‐clinical transplantation models. When M101 was added to the preservation solution of rat pancreas during ischaemia, a decrease in oxidative stress (ROS), necrosis (HMGB1), and cellular stress pathway (p38 MAPK)activity was observed. Freshly isolated islets had improved function when M101 was injected in the pancreas. Additionally, human pancreases exposed to M101 for 3 hours had an increase in complex 1 mitochondrial activity, as well as activation of AKT activity, a cell survival marker. Insulin secretion was also up‐regulated for isolated islets. In summary, these results demonstrate a positive effect of the oxygen carrier M101 on rat and human pancreas during preservation, with an overall improvement in post‐isolation islet quality.

Micro/nanobubbles: Improving Pancreatic Islet Cell Survival for Transplantation

PURPOSE

The preservation of transplantable tissue is directly tied to and limited by the ischemia time. Micro/nanobubbles (MNBs) are miniature gaseous voids that allow for the oxygenation of tissue given their high oxygen-carrying capacity. One of the current limitations of islet cell transplantation for type 1 diabetes is poor islet survival, caused by hypoxia, after harvesting the cells from pancreata. As such, the purpose of this study was to elucidate whether MNBs, when added to standard culture medium, improve islet cell survival postharvest.

MATERIALS AND METHODS

Islet cells were harvested from Sprague-Dawley rat pancreas tissue via a standard collagenase digestion and gradient purification. To create the MNB solution, a shear-based generation system was used to produce both air- and oxygen-filled MNBs in standard Connaught Medical Research Laboratories (CMRL) medium. Four groups, consisting of 500 islet equivalents, were cultured with either the standard CMRL medium, macrobubble-CMRL, MNB (air)-CMRL, or MNB (O2)-CMRL, and they were incubated at 37°C. Each treatment solution was replenished 24 hours postincubation, and after 48 hours of culture, dithizone staining was used to determine the islet cell counts, and the viability was assessed using Calcein AM/propidium iodide staining.

RESULTS

Islet cells that were preserved in macrobubble-CMRL, MNB (air)-CMRL, and MNB (O2)-CMRL conditions showed an increased survival compared with those cultured with standard CMRL. The islet cells cultured in the MNB (air)-CMRL condition demonstrated the greatest cell survival compared with all other groups, including the pure oxygen-carrying MNBs. None of the MNB treatments significantly altered the viability of the islet cells compared to the control condition.

CONCLUSIONS

The addition of MNBs to culture medium offers an innovative approach for the oxygenation of transplantable tissue, such as islet cells. This study demonstrated that MNBs filled with air provided the most optimal addition to the islet cell culture medium for improving islet cell survival amongst the treatment groups we tested. Given these findings, we hypothesize that MNBs may also improve the oxygenation and survival of a variety of other tissues, including fat grafts from lipoaspirate, chronic wounds, and solid organs.

Adipose tissue-derived mesenchymal stem cells rescue the function of islets transplanted in sub-therapeutic numbers via their angiogenic properties

A significant proportion of islets are lost following transplantation due to hypoxia and inflammation. We hypothesize that adipose tissue-derived mesenchymal stem cells (AD-MSCs) can rescue a sub-therapeutic number of transplanted islets by helping them establish a new blood supply and reducing inflammation. Diabetic mice received syngeneic transplantation with 75 (minimal), 150 (sub-therapeutic), or 225 (therapeutic) islets, with or without 1 × 10⁶ mouse AD-MSCs. Fasting blood glucose (FBG) values were measured over 6 weeks with tissue samples collected for islet structure and morphology (H&E, insulin/glucagon staining). Histological and immunohistochemical analyses of islets were also performed at 2 weeks in animals transplanted with a sub-therapeutic number of islets, with and without AD-MSCs, to determine new blood vessel formation, the presence of pro-angiogenic factors facilitating revascularization, and the degree of inflammation. AD-MSCs had no beneficial effect on FBG values when co-transplanted with a minimal or therapeutic number of islets. However, AD-MSCs significantly reduced FBG values and restored glycemic control in diabetic animals transplanted with a sub-therapeutic number of islets. Islets co-transplanted with AD-MSCs preserved their native morphology and organization and exhibited less aggregation when compared to islets transplanted alone. In the sub-therapeutic group, AD-MSCs significantly increased islet revascularization and the expression of angiogenic factors including hepatocyte growth factor (HGF) and angiopoietin-1 (Ang-1) while also reducing inflammation. AD-MSCs can rescue the function of islets when transplanted in a sub-therapeutic number, for at least 6 weeks, via their ability to maintain islet architecture while concurrently facilitating islet revascularization and reducing inflammation.

Improved islet recovery and efficacy through co-culture and co-transplantation of islets with human adipose-derived mesenchymal stem cells

Islet transplantation is an established clinical procedure for select patients with type 1 diabetes and severe hypoglycemia to stabilize glycemic control. Post-transplant, substantial beta cell mass is lost, necessitating multiple donors to maintain euglycemia. A potential strategy to augment islet engraftment is the co-transplantation of islets with multipotent mesenchymal stem cells to capitalize upon their pro-angiogenic and anti-inflammatory properties. Herein, we examine the in vitro and in vivo effect of co-culturing murine islets with human adipose-derived mesenchymal stem cells (Ad-MSCs). Islets co-cultured with Ad-MSCs for 48 hours had decreased cell death, superior viability as measured by membrane integrity, improved glucose stimulated insulin secretion and reduced apoptosis compared to control islets. These observations were recapitulated with human islets, albeit tested in a limited capacity. Recipients of marginal mouse islet mass grafts, co-transplanted with Ad-MSCs without a co-culture period, did not reverse to normoglycemia as efficiently as islets alone. However, utilizing a 48-hour co-culture period, marginal mouse islets grafts with Ad-MSCs achieved a superior percent euglycemia rate when compared to islets cultured and transplanted alone. A co-culture period of human islets with human Ad-MSCs may have a clinical benefit improving engraftment outcomes.

Danggui Sini Decoction Protected Islet Endothelial Cell Survival from Hypoxic Damage via PI3K/Akt/eNOS Pathway

Danggui Sini decoction (DSD) is a traditional Chinese decoction, which is wildly applied and showed to be effective in ameliorating ischemia-related symptoms. However, the mechanisms of DSD action in ischemic damage remain to be fully clarified. Pancreatic islet endothelial cells are pivotal constituent of islet microvasculature, with high vulnerability to hypoxic injuries. Here, using MST1 cell, a pancreatic islet endothelial cell-line, as a model, we investigated the effects of DSD on hypoxia-stimulated endothelial cell lesions and its underlying mechanisms. We found that DSD-Containing Serum (DSD-CS), collected from DSD-treated rats, could efficiently protect MST1 survival and proliferation from Cobalt chloride (CoCl₂) induced damage, including cell viability, proliferation, and tube formation. Furthermore, DSD-CS restored the activity of PI3K/Akt/eNOS signaling inhibited by CoCl₂ in MST1 cells. The protective effect of DSD-CS could be blocked by the specific PI3K/Akt/eNOS inhibitor LY294002, suggesting that DSD-CS protection of MST1 cell survival from hypoxia was mediated by PI3K/Akt/eNOS pathway. In conclusion, DSD treatment protected MST1 survival from hypoxic injuries via PI3K/Akt/eNOS pathway, indicating its role in protecting microvascular endothelial cells.

Applications of particulate oxygen-generating substances (POGS) in the bioartificial pancreas

Type-1 Diabetes (T1D) is a devastating autoimmune disorder which results in the destruction of beta cells within the pancreas. A promising treatment strategy for T1D is the replacement of the lost beta cell mass through implantation of immune-isolated microencapsulated islets referred to as the bioartificial pancreas. The goal of this approach is to restore blood glucose regulation and prevent the long-term comorbidities of T1D without the need for immunosuppressants. A major requirement in the quest to achieve this goal is to address the oxygen needs of islet cells. Islets are highly metabolically active and require a significant amount of oxygen for normal function. During the process of isolation, microencapsulation, and processing prior to transplantation, the islets' oxygen supply is disrupted, and a large amount of islet cells are therefore lost due to extended hypoxia, thus creating a major barrier to clinical success with this treatment. In this work, we have investigated the oxygen generating compounds, sodium percarbonate (SPO) and calcium peroxide (CPO) as potential supplemental oxygen sources for islets during isolation and encapsulation before and immediately after transplantation. First, SPO particles were used as an oxygen source for islets during isolation. Secondly, silicone films containing SPO were used to provide supplemental oxygen to islets for up to 4 days in culture. Finally, CPO was used as an oxygen source for encapsulated cells by co-encapsulating CPO particles with islets in permselective alginate microspheres. These studies provide an important proof of concept for the utilization of these oxygen generating materials to prevent beta cell death caused by hypoxia.

Redox-Dependent Inflammation in Islet Transplantation Rejection

Type 1 diabetes is an autoimmune disease that results in the progressive destruction of insulin-producing pancreatic β-cells inside the islets of Langerhans. The loss of this vital population leaves patients with a lifelong dependency on exogenous insulin and puts them at risk for life-threatening complications. One method being investigated to help restore insulin independence in these patients is islet cell transplantation. However, challenges associated with transplant rejection and islet viability have prevented long-term β-cell function. Redox signaling and the production of reactive oxygen species (ROS) by recipient immune cells and transplanted islets themselves are key players in graft rejection. Therefore, dissipation of ROS generation is a viable intervention that can protect transplanted islets from immune-mediated destruction. Here, we will discuss the newly appreciated role of redox signaling and ROS synthesis during graft rejection as well as new strategies being tested for their efficacy in redox modulation during islet cell transplantation.

Insulin treatment restores islet microvascular vasomotion function in diabetic mice

BACKGROUND

The microcirculation plays an important role in the pathogenesis of diabetes and its complications. We hypothesized that pancreatic islet microvascular (PIM) vasomotion, as a parameter of pancreatic islet microcirculation function, is abnormal in diabetic mice and that insulin treatment may reverse this dysfunction.

METHODS

Mice were randomly assigned to non-diabetic control, untreated diabetic, and insulin-treated diabetic groups (n = 6 in each group). Separate groups of streptozotocin (STZ)-induced diabetic and high-fat diet-fed mice were used as a model of hyperglycemia. Insulin-treated diabetic mice were treated with 1-1.5 IU/day insulin for 1 week. Laser Doppler monitors were used to evaluate PIM vasomotion. Morphological and ultrastructural changes in islet endothelial cells were determined by immunohistochemistry and transmission electron microscopy. Glucagon, insulin, vascular endothelial growth factor (VEGF)-A, and platelet endothelial cell adhesion molecule (PECAM-1) expression was determined by immunohistochemistry and Western blotting.

RESULTS

In both untreated diabetic groups, the pancreatic islet microcirculation was unable to regulate PIM vasomotion. The rhythm of vasomotion was irregular, and the average blood perfusion, amplitude, frequency, and relative velocity of vasomotion were significantly lower than in non-diabetic controls. Insulin treatment restored the functional status of PIM vasomotion. In islet endothelial cells from both untreated diabetic groups, the mitochondria were swollen with disarrangement of the cristae, and the distribution of PECAM-1 was discontinuous. Insulin treatment significantly increased the reduced expression of PECAM-1 in both untreated diabetic groups and VEGF-A expression in untreated STZ-diabetic mice.

CONCLUSION

The results suggest that the functional status of PIM vasomotion is impaired in diabetic mice but can be restored by insulin.

Vasculogenic hydrogel enhances islet survival, engraftment, and function in leading extrahepatic sites

Islet transplantation is a promising alternative therapy for insulin-dependent patients, with the potential to eliminate life-threatening hypoglycemic episodes and secondary complications of long-term diabetes. However, widespread application of this therapy has been limited by inadequate graft function and longevity, in part due to the loss of up to 60% of the graft in the hostile intrahepatic transplant site. We report a proteolytically degradable synthetic hydrogel, functionalized with vasculogenic factors for localized delivery, engineered to deliver islet grafts to extrahepatic transplant sites via in situ gelation under physiological conditions. Hydrogels induced differences in vascularization and innate immune responses among subcutaneous, small bowel mesentery, and epididymal fat pad transplant sites with improved vascularization and reduced inflammation at the epididymal fat pad site. This biomaterial-based strategy improved the survival, engraftment, and function of a single pancreatic donor islet mass graft compared to the current clinical intraportal delivery technique. This biomaterial strategy has the potential to improve clinical outcomes in islet autotransplantation after pancreatectomy and reduce the burden on donor organ availability by maximizing graft survival in clinical islet transplantation for type 1 diabetes patients.

Physiologic Doses of Bilirubin Contribute to Tolerance of Islet Transplants by Suppressing the Innate Immune Response

Bilirubin has been recognized as a powerful cytoprotectant when used at physiologic doses and was recently shown to have immunomodulatory effects in islet allograft transplantation, conveying donor-specific tolerance in a murine model. We hypothesized that bilirubin, an antioxidant, acts to suppress the innate immune response to islet allografts through two mechanisms: 1) by suppressing graft release of damage-associated molecular patterns (DAMPs) and inflammatory cytokines, and 2) by producing a tolerogenic phenotype in antigen-presenting cells. Bilirubin was administered intraperitoneally before pancreatic procurement or was added to culture media after islet isolation in AJ mice. Islets were exposed to transplant-associated nutrient deprivation and hypoxia. Bilirubin significantly decreased islet cell death after isolation and hypoxic stress. Bilirubin supplementation of islet media also decreased the release of DAMPs (HMGB1), inflammatory cytokines (IL-1β and IL-6), and chemokines (MCP-1). Cytoprotection was mediated by the antioxidant effects of bilirubin. Treatment of macrophages with bilirubin induced a regulatory phenotype, with increased expression of PD-L1. Coculture of these macrophages with splenocytes led to expansion of Foxp3+ Tregs. In conclusion, exogenous bilirubin supplementation showed cytoprotective and antioxidant effects in a relevant model of islet isolation and hypoxic stress. Suppression of DAMP release, alterations in cytokine profiles, and tolerogenic effects on macrophages suggest that the use of this natural antioxidant may provide a method of preconditioning to improve outcomes after allograft transplantation.

Hormetic and regulatory effects of lipid peroxidation mediators in pancreatic beta cells

Nutrient sensing mechanisms of carbohydrates, amino acids and lipids operate distinct pathways that are essential for the adaptation to varying metabolic conditions. The role of nutrient-induced biosynthesis of hormones is paramount for attaining metabolic homeostasis in the organism. Nutrient overload attenuate key metabolic cellular functions and interfere with hormonal-regulated inter- and intra-organ communication, which may ultimately lead to metabolic derangements. Hyperglycemia and high levels of saturated free fatty acids induce excessive production of oxygen free radicals in tissues and cells. This phenomenon, which is accentuated in both type-1 and type-2 diabetic patients, has been associated with the development of impaired glucose tolerance and the etiology of peripheral complications. However, low levels of the same free radicals also induce hormetic responses that protect cells against deleterious effects of the same radicals. Of interest is the role of hydroxyl radicals in initiating peroxidation of polyunsaturated fatty acids (PUFA) and generation of α,β-unsaturated reactive 4-hydroxyalkenals that avidly form covalent adducts with nucleophilic moieties in proteins, phospholipids and nucleic acids. Numerous studies have linked the lipid peroxidation product 4-hydroxy-2E-nonenal (4-HNE) to different pathological and cytotoxic processes. Similarly, two other members of the family, 4-hydroxyl-2E-hexenal (4-HHE) and 4-hydroxy-2E,6Z-dodecadienal (4-HDDE), have also been identified as potential cytotoxic agents. It has been suggested that 4-HNE-induced modifications in macromolecules in cells may alter their cellular functions and modify signaling properties. Yet, it has also been acknowledged that these bioactive aldehydes also function as signaling molecules that directly modify cell functions in a hormetic fashion to enable cells adapt to various stressful stimuli. Recent studies have shown that 4-HNE and 4-HDDE, which activate peroxisome proliferator-activated receptor δ (PPARδ) in vascular endothelial cells and insulin secreting beta cells, promote such adaptive responses to ameliorate detrimental effects of high glucose and diabetes-like conditions. In addition, due to the electrophilic nature of these reactive aldehydes they form covalent adducts with electronegative moieties in proteins, phosphatidylethanolamine and nucleotides. Normally these non-enzymatic modifications are maintained below the cytotoxic range due to efficient cellular neutralization processes of 4-hydroxyalkenals. The major neutralizing enzymes include fatty aldehyde dehydrogenase (FALDH), aldose reductase (AR) and alcohol dehydrogenase (ADH), which transform the aldehyde to the corresponding carboxylic acid or alcohols, respectively, or by biding to the thiol group in glutathione (GSH) by the action of glutathione-S-transferase (GST). This review describes the hormetic and cytotoxic roles of oxygen free radicals and 4-hydroxyalkenals in beta cells exposed to nutritional challenges and the cellular mechanisms they employ to maintain their level at functional range below the cytotoxic threshold.

PD-L1 Deficiency within Islets Reduces Allograft Survival in Mice

Background

Islet transplantation may potentially cure type 1 diabetes mellitus (T1DM). However, immune rejection, especially that induced by the alloreactive T-cell response, remains a restraining factor for the long-term survival of grafted islets. Programmed death ligand-1 (PD-L1) is a negative costimulatory molecule. PD-L1 deficiency within the donor heart accelerates allograft rejection. Here, we investigate whether PD-L1 deficiency in donor islets reduces allograft survival time.

Methods

Glucose Stimulation Assays were performed to evaluate whether PD-L1 deficiency has detrimental effects on islet function. Islets isolated from PDL1-deficient mice or wild- type (WT) mice (C57BL/6j) were implanted beneath the renal capsule of streptozotocin (STZ)-induced diabetic BALB/c mice. Blood glucose levels and graft survival time after transplantation were monitored. Moreover, we analyzed the residual islets, infiltrating immune cells and alloreactive cells from the recipients.

Results

PD-L1 deficiency within islets does not affect islet function. However, islet PD-L1 deficiency increased allograft rejection and was associated with enhanced inflammatory cell infiltration and recipient T-cell alloreactivity.

Conclusions

This is the first report to demonstrate that PD-L1 deficiency accelerated islet allograft rejection and regulated recipient alloimmune responses.

Regenerative Therapy of Type 1 Diabetes Mellitus: From Pancreatic Islet Transplantation to Mesenchymal Stem Cells

Type 1 diabetes is an autoimmune disease resulting in the permanent destruction of pancreatic islets. Islet transplantation to portal vein provides an approach to compensate for loss of insulin producing cells. Clinical trials demonstrated that even partial islet graft function reduces severe hypoglycemic events in patients. However, therapeutic impact is restrained due to shortage of pancreas organ donors and instant inflammation occurring in the hepatic environment of the graft. We summarize on what is known about regenerative therapy in type 1 diabetes focusing on pancreatic islet transplantation and new avenues of cell substitution. Metabolic pathways and energy production of transplanted cells are required to be balanced and protection from inflammation in their intravascular bed is desired. Mesenchymal stem cells (MSCs) have anti-inflammatory features, and so they are interesting as a therapy for type 1 diabetes. Recently, they were reported to reduce hyperglycemia in diabetic rodents, and they were even discussed as being turned into endodermal or pancreatic progenitor cells. MSCs are recognized to meet the demand of an individual therapy not raising the concerns of embryonic or induced pluripotent stem cells for therapy.

Respective effects of oxygen and energy substrate deprivation on beta cell viability

Deficit in oxygen and energetic substrates delivery is a key factor in islet loss during islet transplantation. Permeability transition pore (PTP) is a mitochondrial channel involved in cell death. We have studied the respective effects of oxygen and energy substrate deprivation on beta cell viability as well as the involvement of oxidative stress and PTP opening. Energy substrate deprivation for 1h followed by incubation in normal conditions led to a cyclosporin A (CsA)-sensitive-PTP-opening in INS-1 cells and human islets. Such a procedure dramatically decreased INS-1 cells viability except when transient removal of energy substrates was performed in anoxia, in the presence of antioxidant N-acetylcysteine (NAC) or when CsA or metformin inhibited PTP opening. Superoxide production increased during removal of energy substrates and increased again when normal energy substrates were restored. NAC, anoxia or metformin prevented the two phases of oxidative stress while CsA prevented the second one only. Hypoxia or anoxia alone did not induce oxidative stress, PTP opening or cell death. In conclusion, energy substrate deprivation leads to an oxidative stress followed by PTP opening, triggering beta cell death. Pharmacological prevention of PTP opening during islet transplantation may be a suitable option to improve islet survival and graft success.

Engineered VEGF-releasing PEG-MAL hydrogel for pancreatic islet vascularization

Biofunctionalized polyethylene glycol maleimide (PEG-MAL) hydrogels were engineered as a platform to deliver pancreatic islets to the small bowel mesentery and promote graft vascularization. VEGF, a potent stimulator of angiogenesis, was incorporated into the hydrogel to be released in an on-demand manner through enzymatic degradation. PEG-MAL hydrogel enabled extended in vivo release of VEGF. Isolated rat islets encapsulated in PEG-MAL hydrogels remained viable in culture and secreted insulin. Islets encapsulated in PEG-MAL matrix and transplanted to the small bowel mesentery of healthy rats grafted to the host tissue and revascularized by 4 weeks. Addition of VEGF release to the PEG-MAL matrix greatly augmented the vascularization response. These results establish PEG-MAL engineered matrices as a vascular-inductive cell delivery vehicle and warrant their further investigation as islet transplantation vehicles in diabetic animal models.

Beneficial effect of insulin treatment on islet transplantation outcomes in Akita mice

Islet transplantation is a promising potential therapy for patients with type 1 diabetes. The outcome of islet transplantation depends on the transplantation of a sufficient amount of β-cell mass. However, the initial loss of islets after transplantation is problematic. We hypothesized the hyperglycemic status of the recipient may negatively affect graft survival. Therefore, in the present study, we evaluated the effect of insulin treatment on islet transplantation involving a suboptimal amount of islets in Akita mice, which is a diabetes model mouse with an Insulin 2 gene missense mutation. Fifty islets were transplanted under the left kidney capsule of the recipient mouse with or without insulin treatment. For insulin treatment, sustained-release insulin implants were implanted subcutaneously into recipient mice 2 weeks before transplantation and maintained for 4 weeks. Islet transplantation without insulin treatment did not reverse hyperglycemia. In contrast, the group that received transplants in combination with insulin treatment exhibited improved fasting blood glucose levels until 18 weeks after transplantation, even after insulin treatment was discontinued. The group that underwent islet transplantation in combination with insulin treatment had better glucose tolerance than the group that did not undergo insulin treatment. Insulin treatment improved graft survival from the acute phase (i.e., 1 day after transplantation) to the chronic phase (i.e., 18 weeks after transplantation). Islet apoptosis increased with increasing glucose concentration in the medium or blood in both the in vitro culture and in vivo transplantation experiments. Expression profile analysis of grafts indicated that genes related to immune response, chemotaxis, and inflammatory response were specifically upregulated when islets were transplanted into mice with hyperglycemia compared to those with normoglycemia. Thus, the results demonstrate that insulin treatment protects islets from the initial rapid loss that is usually observed after transplantation and positively affects the outcome of islet transplantation in Akita mice.

Maintenance of ischemic β cell viability through delivery of lipids and ATP by targeted liposomes

Islet transplantation is a promising treatment for type 1 diabetes, but despite the successes, existing challenges prevent widespread application. Ischemia, occurring during pancreas preservation and isolation, as well as after islet transplantation, decreases islet viability and function. We hypothesized that the liposomal delivery of adenosine triphosphate (ATP) could prevent the loss of cell viability during an ischemic insult. In this work we use a model β cell line, INS-1 to probe the liposome/cell interactions and examined the ability of liposomes functionalized with the fibronectin-mimetic peptide PR_b to facilitate the delivery of ATP to ischemic β cells. We demonstrate that PR_b increases the binding and internalization of liposomes to the β cells. Unexpectedly, when comparing the ability of PR_b liposomes with and without ATP to protect INS-1 cells from ischemia we found that both formulations increased cell survival. By probing the functional activity of ischemic cells treated with PR_b functionalized liposomes with and without ATP we find that both lipids and ATP play a role in maintaining cell metabolic activity after an ischemic insult and preventing cell necrosis. This approach may be beneficial for preventing ischemia related damage to islet cells, especially in the organ preservation stage.

Preculturing Islets With Adipose-Derived Mesenchymal Stromal Cells Is an Effective Strategy for Improving Transplantation Efficiency at the Clinically Preferred Intraportal Site

We have recently shown that preculturing islets with kidney-derived mesenchymal stromal cells (MSCs) improves transplantation outcome in streptozotocin-diabetic mice implanted with a minimal mass of islets beneath the kidney capsule. In the present study, we have extended our previous observations to investigate whether preculturing islets with MSCs can also be used to enhance islet function at the clinically used intraportal site. We have used MSCs derived from adipose tissue, which are more readily accessible than alternative sources in human subjects and can be expanded to clinically efficacious numbers, to preculture islets throughout this study. The in vivo efficacy of grafts consisting of islets precultured alone or with MSCs was tested using a syngeneic streptozotocin-diabetic minimal islet mass model at the clinically relevant intraportal site. Blood glucose concentrations were monitored for 1 month. The vascularization of islets precultured alone or with MSCs was investigated both in vitro and in vivo, using immunohistochemistry. Islet insulin content was measured by radioimmunoassay. The effect of preculturing islets with MSCs on islet function in vitro was investigated using static incubation assays. There was no beneficial angiogenic influence of MSC preculture, as demonstrated by the comparable vascularization of islets precultured alone or with MSCs, both in vitro after 3 days and in vivo 1 month after islet transplantation. However, the in vitro insulin secretory capacity of MSC precultured islets was superior to that of islets precultured alone. In vivo, this was associated with improved glycemia at 7, 14, 21, and 28 days posttransplantation, in recipients of MSC precultured islets compared to islets precultured alone. The area of individual islets within the graft-bearing liver was significantly higher in recipients of MSC precultured islets compared to islets precultured alone. Our experimental studies suggest that preculturing islets with MSCs represents a favorable strategy for improving the efficiency of clinical islet transplantation.

PEG-maleimide hydrogels for protein and cell delivery in regenerative medicine

Protein- and cell-based therapies represent highly promising strategies for regenerative medicine, immunotherapy, and oncology. However, these therapies are significantly limited by delivery considerations, particularly in terms of protein stability and dosing kinetics as well as cell survival, engraftment, and function. Hydrogels represent versatile and robust delivery vehicles for proteins and cells due to their high water content that retains protein biological activity, high cytocompatibility and minimal adverse host reactions, flexibility and tunability in terms of chemistry, structure, and polymerization format, ability to incorporate various biomolecules to convey biofunctionality, and opportunity for minimally invasive delivery as injectable carriers. This review highlights recent progress in the engineering of poly(ethylene glycol) hydrogels cross-linked using maleimide reactive groups for protein and cell delivery.

Diazoxide, a K(ATP) channel opener, prevents ischemia-reperfusion injury in rodent pancreatic islets

Diazoxide (DZ) is a pharmacological opener of ATP-sensitive K(+) channels that has been used for mimicking ischemic preconditioning and shows protection against ischemic damage. Here we investigated whether diazoxide supplementation to University of Wisconsin (UW) solution has cellular protection during islet isolation and improves in vivo islet transplant outcomes in a rodent ischemia model. C57/B6 mice pancreata were flushed with UW or UW + DZ solution and cold preserved for 6 or 10 h prior to islet isolation. Islet yield, in vitro and in vivo function, mitochondrial morphology, and apoptosis were evaluated. Significantly higher islet yields were observed in the UW + DZ group than in the UW group (237.5 ± 25.6 vs. 108.7 ± 49.3, p < 0.01). The islets from the UW + DZ group displayed a significantly higher glucose-induced insulin secretion (0.97 ng/ml ± 0.15 vs. 0.758 ng/ml ± 0.21, p = 0.009) and insulin content (60.96 ng/islet ± 13.94 vs. 42.09 ng/islet ± 8.15, p = 0.002). The DZ-treated islets had well-preserved mitochondrial morphology with superior responses of mitochondrial potentials, and calcium influx responded to glucose. A higher number of living cells and less late apoptotic cells were observed in the UW + DZ group (p < 0.05). Additionally, the islets from the UW + DZ group had a significantly higher cure rate and improved glucose tolerance. This study is the first to report mitoprotective effects of DZ for pancreas preservation and islet isolation. In the future, it will be necessary to further understand the underlying mechanism for the mitoprotection and to test this promising approach for pancreas preservation and the islet isolation process in nonhuman primates and ultimately humans.

Manufacturing porcine islets: culture at 22 °C has no advantage above culture at 37 °C: a gene expression evaluation

BACKGROUND

The manufacturing process of islets includes a culture step which was originally introduced to ease the logistics of procedures in preparing the graft and transplant recipient. It has been suggested that culture at room temperature has an advantage over culture at 37 °C, in part by reducing immunogenicity via preferential elimination of contaminating cells (such as passenger leukocytes) within islets. We investigated this using islets isolated from pancreata of adult pigs.

METHODS

Porcine islets were isolated from three donors and cultured at 37 °C for 1 day, and then under three different conditions: 37 °C for 6 days (condition A); 22 °C for 6 days (condition B); or 22 °C for 5 days followed by 37 °C for 1 day (condition C). Recovery was assessed by DNA measurement, viability by oxygen consumption rate normalized for DNA (OCR/DNA), and gene expression by RT-PCR for a series of 9 lymphocyte markers, 11 lymphokines and chemokines, and 14 apoptotic and stress markers.

RESULTS

Post-culture islet recoveries were similar for the three culture conditions. Average OCR/DNA values were 129-159 nmol/min·mgDNA before culture, and 259-291, 204-212, and 207-228 nmol/min·mgDNA, respectively, for culture under conditions A, B, and C, respectively. Irrespective of culture condition, examined gene expression in all three series of lymphocyte markers, lymphokines and chemokines, and apoptotic and stress markers manifested a statistically significant decrease upon culture for 7 days. This decrease was most dramatic for condition A: in particular, most of lymphocyte markers showed a >10-fold reduction and also six markers in the lymphokine and chemokine series; these reductions are consistent with the elimination of immune cells present within islets during culture. The reduction was less for apoptotic and stress markers. For culture under condition B, the reduction in gene expression was less, and culture under condition C resulted in gene expression levels similar to those under condition A: this indicates that 24 h at 37 °C is sufficient to re-equilibrate gene expression levels from those in islets cultured at 22 °C to those in islets cultured at 37 °C. Results were consistent among the preparations from the three donors.

CONCLUSIONS

Culture of porcine islets at 37 °C provides benefits over culture at 22 °C with respect to OCR/DNA outcomes and reduced expression of genes encoding lymphocyte markers, lymphokines and chemokines, and markers for apoptosis and stress.

Proangiogenic hydrogels within macroporous scaffolds enhance islet engraftment in an extrahepatic site

The transplantation of allogeneic islets in recent clinical trials has shown substantial promise as a therapy for type 1 diabetes; however, long-term insulin independence remains inadequate. This has been largely attributed to the current intravascular, hepatic transplant site, which exposes islets to mechanical and inflammatory stresses. A highly macroporous scaffold, housed within an alternative transplant site, can support an ideal environment for islet transplantation by providing three-dimensional distribution of islets, while permitting the infiltration of host vasculature. In the present study, we sought to evaluate the synergistic effect of a proangiogenic hydrogel loaded within the void space of a macroporous poly(dimethylsiloxane) (PDMS) scaffold on islet engraftment. The fibrin-based proangiogenic hydrogel tested presents platelet derived growth factor (PDGF-BB), via a fibronectin (FN) fragment containing growth factor and major integrin binding sites in close proximity. The combination of the proangiogenic hydrogel with PDMS scaffolds resulted in a significant decrease in the time to normoglycemia for syngeneic mouse islet transplants. This benefit was associated with an observed increase in competent vessel branching, as well as mature intraislet vessels. Overall, the addition of the proangiogenic factor PDGF-BB, delivered via the FN fragment-functionalized hydrogel, positively influenced the efficiency of engraftment. These characteristics, along with its ease of retrieval, make this combination of a biostable macroporous scaffold and a degradable proangiogenic hydrogel a supportive structure for insulin-producing cells implanted in extrahepatic sites.

Endogenous expression of B7-H4 improves long-term murine islet allograft survival

BACKGROUND

Allograft rejection is one of the main obstacles for islet transplantation. B7-H4 plays a key role in maintaining T-cell homeostasis by reducing T-cell proliferation and cytokine production. In this study, we investigated whether the endogenous expression of B7-H4 in β cells from B7-H4 transgenic mice enhances islet allograft survival.

METHODS

B7-H4 transgenic C57BL/6 (B6) mice (RIP.B7-H4) were developed by inserting the entire B7-H4 open reading frame under the rat insulin promoter (RIP). B7-H4 protein expression was examined by flow cytometric analysis and immunohistochemical staining. Islet allograft survival was investigated in streptozotocin-induced diabetic recipient BALB/c (H-2d) mice transplanted with 400 islets from RIP.B7-H4 (H-2b) mice under the kidney capsule. The recipient control group received islets from wild-type B6 donors.

RESULTS

B7-H4 protein was significantly up-regulated in isolated islets from RIP.B7-H4 compared with wild-type B6 mice (56%±23% vs. 3%±1.2%). B7-H4 was coexpressed with insulin, but not glucagon, suggesting that B7-H4 is expressed in a β-cell-specific manner. Recipient BALB/c mice transplanted with RIP.B7-H4 islets established euglycemia for 42.3±18.4 days (mean±SD; n=9) compared with controls at 23.1±7.8 days (mean±SD; n=12; P<0.004, log-rank test).

CONCLUSIONS

The endogenous expression of B7-H4 in donor β cells from transgenic mice prolongs islet allograft survival, confirming the negative role of B7-H4 in regulating alloreactive T-cell responses.

Poly(ethylene glycol) cross-linked hemoglobin with antioxidant enzymes protects pancreatic islets from hypoxic and free radical stress and extends islet functionality

The objective of this study was to investigate the efficiency of multifunctional poly(ethylene glycol)-based hemoglobin conjugates crosslinked with antioxidant enzymes for their ability to protect an oxygen carrier (hemoglobin) and insulin secreting islets from the combination of hypoxic and free radical stress under simulated transplantation conditions. In this study, RINm5F cells and isolated pancreatic islets were challenged with oxidants (H(2)O(2) or xanthine and xanthine oxidase) and incubated with conjugates (hemoglobin-hemoglobin or superoxide dismutase-catalase-hemoglobin) in normoxia (21% oxygen) or hypoxia (6% or 1% oxygen). Hemoglobin protection, intracellular free radical activity and cell viability in RINm5F cells measured by methemoglobin, dichlorofluorescein-diacetate, and (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay, respectively, showed that cells were better protected by conjugates containing antioxidant enzymes. Insulin secretion from islets and qualitative confocal evaluation of viability showed beta cells were protected by conjugates containing antioxidant enzymes when exposed to induced stress. Our study suggested that antioxidant enzymes play a significant role in hemoglobin protection and thus extended cell protection.

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.

Evolution of β-Cell Replacement Therapy in Diabetes Mellitus: Islet Cell Transplantation

Diabetes mellitus remains one of the leading causes of morbidity and mortality worldwide. According to the Centers for Disease Control and Prevention, approximately 23.6 million people in the United States are affected. Of these individuals, 5 to 10% have been diagnosed with Type 1 diabetes mellitus (T1DM), an autoimmune disease. Although it often appears in childhood, T1DM may manifest at any age, leading to significant morbidity and decreased quality of life. Since the 1960s, the surgical treatment for diabetes mellitus has evolved to become a viable alternative to insulin administration, beginning with pancreatic transplantation. While islet cell transplantation has emerged as another potential alternative, its role in the treatment of T1DM remains to be solidified as research continues to establish it as a truly viable alternative for achieving insulin independence. In this paper, the historical evolution, procurement, current status, benefits, risks, and ongoing research of islet cell transplantation are explored.

31-Phosphorus magnetic resonance spectroscopy for dynamic assessment of adenosine triphosphate levels in pancreas preserved by the two-layer method

Cold preservation injury influences islet graft function. Reliable tools for real-time assessment of pancreas viability before islet isolation are lacking. Phosphorus magnetic resonance spectroscopy ((31)P-MRS) was used immediately after organ harvest to study rat pancreases at 4 °C to 6 °C in five randomized preservation groups: Marshall's solution, static two-layer method (TLM), continuous TLM with oxygen perfused at 0.5 L/min, and static TLM or continuous TLM both the latter following 30 minutes of warm ischemia (WI). (31)P spectra were analyzed for phosphomonoesters, inorganic phosphate (Pi) and α-, β-and γ-nucleotide triphosphate. Intergroup rates of change of [γ-adenosine triphosphate (ATP)]/[Pi] and [β-ATP]/[Pi] throughout preservation period were significantly different. For continuous TLM there was an increase relative to baseline (0.043 (SD0.033) h(-1) and 0.029 (0.029) h(-1), respectively) but a decrease for both static TLM (-0.023 (0.016) h(-1) and 0.015 (0.026), P < .001 and < .05, respectively) and Marshall's (-0.049 (0.025) h(-1) and -0.036 (0.019) h(-1), respectively, both P < .001) with respect to continuous TLM. Rate of decrease was similar for the Marshall's and static TLM groups. [γ-ATP]/[Pi] and [β-ATP]/[Pi] increased with WI continuous TLM (0.008 [0.009] h(-1) and 0.007 [0.008] hr(-1), respectively) but decreased for WI static TLM (-0.018 (0.008) h(-1) and -0.014 (0.004) hr(-1), respectively, P < .001). (31)P-MRS is an effective tool for noninvasive assessment of pancreas bioenergetics. Continuous TLM preserves cellular bioenergetics and is superior to current non-perfluorocar bone based solutions for pancreas preservation.

Cell surface engineering with polyelectrolyte multilayer thin films

Layer-by-layer assembly of polyelectrolyte multilayer (PEM) films represents a bottom-up approach for re-engineering the molecular landscape of cell surfaces with spatially continuous and molecularly uniform ultrathin films. However, fabricating PEMs on viable cells has proven challenging owing to the high cytotoxicity of polycations. Here, we report the rational engineering of a new class of PEMs with modular biological functionality and tunable physicochemical properties which have been engineered to abrogate cytotoxicity. Specifically, we have discovered a subset of cationic copolymers that undergoes a conformational change, which mitigates membrane disruption and facilitates the deposition of PEMs on cell surfaces that are tailorable in composition, reactivity, thickness, and mechanical properties. Furthermore, we demonstrate the first successful in vivo application of PEM-engineered cells, which maintained viability and function upon transplantation and were used as carriers for in vivo delivery of PEMs containing biomolecular payloads. This new class of polymeric film and the design strategies developed herein establish an enabling technology for cell transplantation and other therapies based on engineered cells.

Creation of a prevascularized site for cell transplantation in rats

INTRODUCTION

Transplanted cells, especially islet cells, are likely to become apoptotic due to local hypoxia leading to graft dysfunction. Isolated pancreatic islet cells depend on the diffusion of oxygen from the surrounding tissue; therefore, access to sufficient oxygen supply is beneficial, particularly when microcapsules are used for immunoisolation in xenotransplantation. The aim of this study was to create a prevascularized site for cell transplantation in rats and test its effectiveness with microencapsulated HEK293 cells.

METHODS

The combination of implantation of a foam dressing, vacuum-assisted wound closure (foam+VAC) and hyperbaric oxygenation (HBO) was used in 40 Sprague-Dawley rats. Blood flow and vascular endothelial growth factor (VEGF) levels were determined. Sodium cellulose sulphate (SCS)-microencapsulated HEK293 cells were xenotransplanted into the foam dressing in rats pre-treated with HBO, and angiogenesis and apoptosis were assessed.

RESULTS

Vessel ingrowth and VEGF levels increased depending on the duration of HBO treatment. The area containing the foam was perfused significantly better in the experimental groups when compared to controls. Only a small amount of apoptosis occurs in SCS-microencapsulated HEK293 cells after xenotransplantation.

CONCLUSION

As ischemia-damaged cells are likely to undergo cell death or loose functionality due to hypoxia, therefore leading to graft dysfunction, the combination foam+VAC and HBO might be a promising method to create a prevascularized site to achieve better results in xenogeneic cell transplantation.

Diannexin decreases inflammatory cell infiltration into the islet graft, reduces β-cell apoptosis, and improves early graft function

BACKGROUND

A major unmet challenge is to reduce the islet mass needed for insulin independence in type 1 diabetic recipients after islet transplantation. The recombinant homodimer of human annexin V, diannexin, has completed a Phase II Clinical Trial in Kidney Transplantation (NCT00615966).

METHODS

We developed a marginal islet mass transplantation model (10-12 islets per gram of recipient body weight) and investigated whether diannexin prevents β-cell apoptosis and improves islet graft function. Diannexin was administered to islet cell donors shortly before pancreas harvest, added to isolation reagents, and infused into recipients at the time of transplantation and repeated daily until day 4.

RESULTS

In the syngeneic marginal islet mass transplantation model, the median time needed to achieve normoglycemia was reduced from 17.0 days among untreated controls to 3.5 days among diannexin-treated recipients (P=0.004). Histologic analysis of islet grafts harvested on day 3 posttransplantation revealed decreased macrophage (44.7%±9.8% vs. 19.2%±3.2%, P=0.007) and T-cell infiltration (25.9%±5.5% vs. 9.1%±1.1%, P=0.004), and a lower rate of islet cell apoptosis (20.5%±2.8% vs. 7.6%±2.3%, P=0.01) with diannexin treatment. Expression profiling of the islet grafts showed significantly lower levels of mRNA for the proapoptotic molecule Bid, but higher levels of interleukin-6, interferon-γ, and immunosuppressive cytokine interleukin-10.

CONCLUSIONS

Our findings demonstrate that diannexin improves the early function of marginal mass islet grafts, and its effects are associated with reductions in inflammatory cell infiltration and β-cell death by apoptosis after islet transplantation.

Transcriptional and post-transcriptional regulation of proangiogenic factors by the unfolded protein response

Background

Inadequate extracellular conditions can adversely affect the environment of the ER and impinge on the maturation of nascent proteins. The resultant accumulation of unfolded proteins activates a signal transduction pathway, known as the unfolded protein response, which serves primarily to protect the cell during stress and helps restore homeostasis to the ER.

Principal Findings

Microarray analysis of the unfolded protein response in a human medulloblastoma cell line treated with thapsigargin revealed that, in addition to known targets, a large number of proangiogenic factors were up-regulated. Real-Time PCR analyses confirmed that four of these factors, VEGFA, FGF2, angiogenin and IL8, were transcriptionally up-regulated in multiple cell lines by various ER stress inducers. Our studies on VEGFA regulation revealed that XBP-1(S), a UPR-inducible transcription factor, bound to two regions on the VEGFA promoter, and analysis of XBP-1 null mouse embryonic fibroblasts revealed that it contributes to VEGFA expression in response to ER stress. ATF4, another UPR-inducible transcription factor, also binds to the VEGFA gene, although its contribution to VEGFA transcription appeared to be fairly modest. We also found that VEGFA mRNA stability is increased in response to UPR activation, via activation of AMP kinase, demonstrating that increased mRNA levels occur at two regulatory points. In keeping with the mRNA levels, we found that VEGFA protein is secreted at levels as high as or higher than that achieved in response to hypoxia.

Conclusions and Significance

Our results indicate that the UPR plays a significant role in inducing positive regulators of angiogenesis. It also regulates VEGFA expression at transcriptional, post-transcriptional and post-translational levels and is likely to have widespread implications for promoting angiogenesis in response to normal physiological cues as well as in pathological conditions like cancer.

Elimination of negative feedback control mechanisms along the insulin signaling pathway improves beta-cell function under stress

OBJECTIVE

Cellular stress and proinflammatory cytokines induce phosphorylation of insulin receptor substrate (IRS) proteins at Ser sites that inhibit insulin and IGF-1 signaling. Here, we examined the role of Ser phosphorylation of IRS-2 in mediating the inhibitory effects of proinflammatory cytokines and cellular stress on beta-cell function.

RESEARCH DESIGN AND METHODS

Five potential inhibitory Ser sites located proximally to the P-Tyr binding domain of IRS-2 were mutated to Ala. These IRS-2 mutants, denoted IRS-2(5A), and their wild-type controls (IRS-2(WT)) were introduced into adenoviral constructs that were infected into Min6 cells or into cultured murine islets.

RESULTS

When expressed in cultured mouse islets, IRS-2(5A) was better than IRS-2(WT) in protecting beta-cells from apoptosis induced by a combination of IL-1beta, IFN-gamma, TNF-alpha, and Fas ligand. Cytokine-treated islets expressing IRS2(5A) secreted significantly more insulin in response to glucose than did islets expressing IRS-2(WT). This could be attributed to the higher transcription of Pdx1 in cytokine-treated islets that expressed IRS-2(5A). Accordingly, transplantation of 200 islets expressing IRS2(5A) into STZ-induced diabetic mice restored their ability to respond to a glucose load similar to naïve mice. In contrast, mice transplanted with islets expressing IRS2(WT) maintained sustained hyperglycemia 3 days after transplantation.

CONCLUSIONS

Elimination of a physiological negative feedback control mechanism along the insulin-signaling pathway that involves Ser/Thr phosphorylation of IRS-2 affords protection against the adverse effects of proinflammatory cytokines and improves beta-cell function under stress. Genetic approaches that promote IRS2(5A) expression in pancreatic beta-cells, therefore, could be considered a rational treatment against beta-cell failure after islet transplantation.

Biomolecular surface engineering of pancreatic islets with thrombomodulin

Islet transplantation has emerged as a promising treatment for Type 1 diabetes, but its clinical impact remains limited by early islet destruction mediated by prothrombotic and innate inflammatory responses elicited upon transplantation. Thrombomodulin (TM) acts as an important regulator of thrombosis and inflammation through its capacity to channel the catalytic activity of thrombin towards generation of activated protein C (APC), a potent anticoagulant and anti-inflammatory agent. We herein describe a novel biomolecular strategy for re-engineering the surface of pancreatic islets with TM. A biosynthetic approach was employed to generate recombinant human TM (rTM) bearing a C-terminal azide group, which facilitated site-specific biotinylation of rTM through Staudinger ligation. Murine pancreatic islets were covalently biotinylated through targeting of cell surface amines and aldehydes and both islet viability and the surface density of streptavidin were maximized through optimization of biotinylation conditions. rTM was immobilized on islet surfaces through streptavidin-biotin interactions, resulting in a nearly threefold increase in the catalytic capacity of islets to generate APC.