Human islet oxygen consumption rate and DNA measurements predict diabetes reversal in nude mice

Cold-induced FOXO1 nuclear transport aids cold survival and tissue storage

Cold-induced injuries severely limit opportunities and outcomes of hypothermic therapies and organ preservation, calling for better understanding of cold adaptation. Here, by surveying cold-altered chromatin accessibility and integrated CUT&Tag/RNA-seq analyses in human stem cells, we reveal forkhead box O1 (FOXO1) as a key transcription factor for autonomous cold adaptation. Accordingly, we find a nonconventional, temperature-sensitive FOXO1 transport mechanism involving the nuclear pore complex protein RANBP2, SUMO-modification of transporter proteins Importin-7 and Exportin-1, and a SUMO-interacting motif on FOXO1. Our conclusions are supported by cold survival experiments with human cell models and zebrafish larvae. Promoting FOXO1 nuclear entry by the Exportin-1 inhibitor KPT-330 enhances cold tolerance in pre-diabetic obese mice, and greatly prolongs the shelf-life of human and mouse pancreatic tissues and islets. Transplantation of mouse islets cold-stored for 14 days reestablishes normoglycemia in diabetic mice. Our findings uncover a regulatory network and potential therapeutic targets to boost spontaneous cold adaptation.

A static glucose-stimulated insulin secretion (sGSIS) assay that is significantly predictive of time to diabetes reversal in the human islet bioassay

INTRODUCTION

Static incubation (static glucose-stimulated insulin secretion, sGSIS) is a measure of islet secretory function. The Stimulation Index (SI; insulin produced in high glucose/insulin produced in low glucose) is currently used as a product release criterion of islet transplant potency.

RESEARCH DESIGN AND METHODS

Our hypothesis was that the Delta, insulin secreted in high glucose minus insulin secreted in low glucose, would be more predictive. To evaluate this hypothesis, sGSIS was performed on 32 consecutive human islet preparations, immobilizing the islets in a slurry of Sepharose beads to minimize mechanical perturbation. Simultaneous full-mass subrenal capsular transplants were performed in chemically induced diabetic immunodeficient mice. Logistic regression analysis was used to determine optimal cut-points for diabetes reversal time and the Fisher Exact Test was used to assess the ability of the Delta and the SI to accurately classify transplant outcomes. Receiver operating characteristic curve analysis was performed on cut-point grouped data, assessing the predictive power and optimal cut-point for each sGSIS potency metric. Finally, standard Kaplan-Meier-type survival analysis was conducted.

RESULTS

In the case of the sGSIS the Delta provided a superior islet potency metric relative to the SI.ConclusionsThe sGSIS Delta value is predicitive of time to diabetes reversal in the full mass human islet transplant bioassay.

Twenty years of islet-on-a-chip: microfluidic tools for dissecting islet metabolism and function

Pancreatic islets are metabolically active micron-sized tissues responsible for controlling blood glucose through the secretion of insulin and glucagon. A loss of functional islet mass results in type 1 and 2 diabetes. Islet-on-a-chip devices are powerful microfluidic tools used to trap and study living ex vivo human and murine pancreatic islets and potentially stem cell-derived islet organoids. Devices developed over the past twenty years offer the ability to treat islets with controlled and dynamic microenvironments to mimic in vivo conditions and facilitate diabetes research. In this review, we explore the various islet-on-a-chip devices used to immobilize islets, regulate the microenvironment, and dynamically detect islet metabolism and insulin secretion. We first describe and assess the various methods used to immobilize islets including chambers, dam-walls, and hydrodynamic traps. We subsequently describe the surrounding methods used to create glucose gradients, enhance the reaggregation of dispersed islets, and control the microenvironment of stem cell-derived islet organoids. We focus on the various methods used to measure insulin secretion including capillary electrophoresis, droplet microfluidics, off-chip ELISAs, and on-chip fluorescence anisotropy immunoassays. Additionally, we delve into the various multiparametric readouts (NAD(P)H, Ca2+-activity, and O2-consumption rate) achieved primarily by adopting a microscopy-compatible optical window into the devices. By critical assessment of these advancements, we aim to inspire the development of new devices by the microfluidics community and accelerate the adoption of islet-on-a-chip devices by the wider diabetes research and clinical communities.

Alpha-1 Antitrypsin Augmentation Therapy in Chronic Pancreatitis Patients Undergoing Total Pancreatectomy and Islet Autotransplantation: A Randomized, Controlled Study

Stress-induced islet graft loss during the peri-transplantation period reduces the efficacy of islet transplantation. In this prospective, randomized, double-blind clinical trial, we evaluated the safety and efficacy of 60 mg/kg human alpha-1 antitrypsin (AAT) or placebo infusion weekly for four doses beginning before surgery in chronic pancreatitis (CP) patients undergoing total pancreatectomy and islet autotransplantation (TP-IAT). Subjects were followed for 12 months post-TP-IAT. The dose of AAT was safe, as there was no difference in the types and severity of adverse events in participants from both groups. There were some biochemical signals of treatment effect with a higher oxygen consumption rate in AAT islets before transplantation and a lower serum C-peptide (an indicator of islet death) in the AAT group at 15 min after islet infusion. Findings per the statistical analysis plan using a modified intention to treat analysis showed no difference in the C-peptide area under the curve (AUC) following a mixed meal tolerance test at 12 months post-TP-IAT. There was no difference in the secondary and exploratory outcomes. Although AAT therapy did not show improvement in C-peptide AUC in this study, AAT therapy is safe in CP patients and there are experiences gained on optimal clinical trial design in this challenging disease.

Extracellular matrix inclusion in immunoisolating alginate-based microcapsules promotes longevity, reduces fibrosis, and supports function of islet allografts in vivo

Immunoisolation of pancreatic-islets in alginate-microcapsules is applied to treat diabetes. However, long-term islet function is limited, which might be due to damaged and lack of contact with pancreatic extracellular matrix (ECM) components. Herein we investigated the impact of collagen IV combined with laminin sequences, either RGD, LRE, or PDSGR, on graft-survival of microencapsulated bioluminescent islets in vivo. Collagen IV with RGD had the most pronounced effect. It enhanced after 8-week implantation in immune-incompetent mice the bioluminescence of allogeneic islets by 3.2-fold, oxygen consumption rate by 14.3-fold and glucose-induced insulin release by 9.6-fold. Transcriptomics demonstrated that ECM enhanced canonical pathways involving insulin-secretion and that it suppressed pathways related to inflammation and hypoxic stress. Also, 5.8-fold fewer capsules were affected by fibrosis. In a subsequent longevity study in immune-competent mice, microencapsulated allografts containing collagen IV and RGD had a 2.4-fold higher functionality in the first week after implantation and remained at least 2.1-fold higher during the study. Islets in microcapsules containing collagen IV and RGD survived 211 ± 24.1 days while controls survived 125 ± 19.7 days. Our findings provide in vivo evidence for the efficacy of supplementing immunoisolating devices with specific ECM components to enhance functionality and longevity of islet-grafts in vivo. STATEMENT OF SIGNIFICANCE: Limitations in duration of survival of immunoisolated pancreatic islet grafts is a major obstacle for application of the technology to treat diabetes. Accumulating evidence supports that incorporation of extracellular matrix (ECM) molecules in the capsules enhances longevity of pancreatic islets. After selection of the most efficacious laminin sequence in vitro, we show in vivo that inclusion of collagen IV and RGD in alginate-based microcapsules enhances survival, insulin secretion function, and mitochondrial function. It also suppresses fibrosis by lowering proinflammatory cytokines secretion. Moreover, transcriptomic analysis shows that ECM-inclusion promotes insulin-secretion related pathways and attenuates inflammation and hypoxic stress related pathways in islets. We show that inclusion of ECM in immunoisolating devices is a promising strategy to promote long-term survival of islet-grafts.

A predictive computational platform for optimizing the design of bioartificial pancreas devices

The delivery of encapsulated islets or stem cell-derived insulin-producing cells (i.e., bioartificial pancreas devices) may achieve a functional cure for type 1 diabetes, but their efficacy is limited by mass transport constraints. Modeling such constraints is thus desirable, but previous efforts invoke simplifications which limit the utility of their insights. Herein, we present a computational platform for investigating the therapeutic capacity of generic and user-programmable bioartificial pancreas devices, which accounts for highly influential stochastic properties including the size distribution and random localization of the cells. We first apply the platform in a study which finds that endogenous islet size distribution variance significantly influences device potency. Then we pursue optimizations, determining ideal device structures and estimates of the curative cell dose. Finally, we propose a new, device-specific islet equivalence conversion table, and develop a surrogate machine learning model, hosted on a web application, to rapidly produce these coefficients for user-defined devices.

Engineering Vascularized Islet Macroencapsulation Devices: An in vitro Platform to Study Oxygen Transport in Perfused Immobilized Pancreatic Beta Cell Cultures

Islet encapsulation devices serve to deliver pancreatic beta cells to type 1 diabetic patients without the need for chronic immunosuppression. However, clinical translation is hampered by mass transport limitations causing graft hypoxia. This is exacerbated in devices relying only on passive diffusion for oxygenation. Here, we describe the application of a cylindrical in vitro perfusion system to study oxygen effects on islet-like clusters immobilized in alginate hydrogel. Mouse insulinoma 6 islet-like clusters were generated using microwell plates and characterized with respect to size distribution, viability, and oxygen consumption rate to determine an appropriate seeding density for perfusion studies. Immobilized clusters were perfused through a central channel at different oxygen tensions. Analysis of histological staining indicated the distribution of viable clusters was severely limited to near the perfusion channel at low oxygen tensions, while the distribution was broadest at normoxia. The results agreed with a 3D computational model designed to simulate the oxygen distribution within the perfusion device. Further simulations were generated to predict device performance with human islets under in vitro and in vivo conditions. The combination of experimental and computational findings suggest that a multichannel perfusion strategy could support in vivo viability and function of a therapeutic islet dose.

Optimization of an O2-balanced bioartificial pancreas for type 1 diabetes using statistical design of experiment

A bioartificial pancreas (BAP) encapsulating high pancreatic islets concentration is a promising alternative for type 1 diabetes therapy. However, the main limitation of this approach is O₂ supply, especially until graft neovascularization. Here, we described a methodology to design an optimal O₂-balanced BAP using statistical design of experiment (DoE). A full factorial DoE was first performed to screen two O₂-technologies on their ability to preserve pseudo-islet viability and function under hypoxia and normoxia. Then, response surface methodology was used to define the optimal O₂-carrier and islet seeding concentrations to maximize the number of viable pseudo-islets in the BAP containing an O₂-generator under hypoxia. Monitoring of viability, function and maturation of neonatal pig islets for 15 days in vitro demonstrated the efficiency of the optimal O₂-balanced BAP. The findings should allow the design of a more realistic BAP for humans with high islets concentration by maintaining the O₂ balance in the device.

Pancreatic islet cryopreservation by vitrification achieves high viability, function, recovery and clinical scalability for transplantation

Pancreatic islet transplantation can cure diabetes but requires accessible, high-quality islets in sufficient quantities. Cryopreservation could solve islet supply chain challenges by enabling quality-controlled banking and pooling of donor islets. Unfortunately, cryopreservation has not succeeded in this objective, as it must simultaneously provide high recovery, viability, function and scalability. Here, we achieve this goal in mouse, porcine, human and human stem cell (SC)-derived beta cell (SC-beta) islets by comprehensive optimization of cryoprotectant agent (CPA) composition, CPA loading and unloading conditions and methods for vitrification and rewarming (VR). Post-VR islet viability, relative to control, was 90.5% for mouse, 92.1% for SC-beta, 87.2% for porcine and 87.4% for human islets, and it remained unchanged for at least 9 months of cryogenic storage. VR islets had normal macroscopic, microscopic, and ultrastructural morphology. Mitochondrial membrane potential and adenosine triphosphate (ATP) levels were slightly reduced, but all other measures of cellular respiration, including oxygen consumption rate (OCR) to produce ATP, were unchanged. VR islets had normal glucose-stimulated insulin secretion (GSIS) function in vitro and in vivo. Porcine and SC-beta islets made insulin in xenotransplant models, and mouse islets tested in a marginal mass syngeneic transplant model cured diabetes in 92% of recipients within 24–48 h after transplant. Excellent glycemic control was seen for 150 days. Finally, our approach processed 2,500 islets with >95% islets recovery at >89% post-thaw viability and can readily be scaled up for higher throughput. These results suggest that cryopreservation can now be used to supply needed islets for improved transplantation outcomes that cure diabetes.

Optimization of vitrification approaches substantially improves pancreatic islet cryopreservation for banking and boosts transplantation outcomes in diabetes.

Heme oxygenase-1 gene delivery for altering high mobility group box-1 protein in pancreatic islet

Pancreatic islet transplantation is a promising strategy for the treatment of type I diabetes. High-mobility group box-1 (HMGB1), highly expressed in islet cells, is a potent immune stimulator in immune rejection. Heme oxygenase-1 (HO1) gene therapy can modulate the release of HMGB1 by altering intracellular molecules for successful cell transplantation. After delivery of the heme oxygenase-1 (HO1) gene to islet cells using an adeno-associated viral vector (AAV), it was evaluated the changes in cytoplasmic Ca²⁺ ions and calcineurin activity as well as histone acetyltransferase (HAT) and Poly(ADP) ribose polymerase-1 (PARP-1). Inhibition of HMGB1 release was evaluated through altering these intracellular molecules. Then, after transplantation of HO1-transduced islets, the therapeutic effect of them was evaluated through measuring blood glucose level to diabetic mice and through immunohistochemical analysis. The transduced HO1 gene significantly inhibited HMGB1 release in islets that was under the cell damage by hypoxia exposure. It was confirmed that this result was initially due to the decrease in cytoplasmic Ca²⁺ ion concentration and calcineurin activity. In addition, the delivered HO1 gene simultaneously reduced the activity of HAT and PARP-1, which are involved in the translocation of HMGB1 from the nucleus to the cytoplasm. As a result, when the HO1 gene-transduced islets were transplanted into diabetic mice, the treatment efficiency of diabetes was effectively improved by increasing the survival rate of the islets. Collectively, these results suggest that HO1 gene transfer can be used for successful islet transplantation by altering the activity of intracellular signal molecules and reducing HMGB1 release.

Optical sensor arrays designed for guided manufacture of perfluorocarbon nanoemulsions with a non-synthetic stabilizer

Hydrophobic drugs are incorporated into oil-in-water nanoemulsions (OIW) either as new formulations or repurposed for intravenous delivery. Typically, these are manufactured through stepwise processes of sonication or high-pressure homogenization (HPH). The guiding criteria for most nanoemulsion manufacture are the size and homogeneity/polydispersity of the drug-laden particles with strict requirements for clinical injectables. To date, most formulation optimization is done through trial and error with stepwise sampling during processing utilizing dynamic light scattering (DLS), light obscuration sensing (LOS) or laser particle tracking (LPT) to assess manufacturing progress. The objective of this work was to develop and implement an in-line optical turbidity/nephelometry sensor array for the longitudinal in-process monitoring of nanoemulsion manufacture. A further objective was the use of this sensor array to rapidly optimize the manufacture of a sub-120 nm oxygen carrying perfluorocarbon nanoemulsion with a non-synthetic stabilizer. During processing, samples were taken for particle size measurement and further characterization. There was a significant correlation and agreement between particle size and sensor signal as well as improved process reproducibility through sensor-guided manufacture. Given the cost associated with nanoemulsion development and scale-up manufacture, our sensor arrays could be an invaluable tool for efficient and cost-effective drug development. Sensor-guided manufacturing was used to optimize oxygen-carrying nanoemulsions. These were tested, in vitro, for their ability to improve the viability of encapsulated endocrine clusters (mouse insulinoma, Min6) and to eliminate hypoxia due to oxygen mass transfer limitations. The nanomulsions significantly improved encapsulated cluster viability and reduced hypoxia within the microcapsule environment. STATEMENT OF SIGNIFICANCE: Nanoemulsions are rapidly becoming vehicles for the controlled release delivery of both hydrophilic and hydrophobic drugs given their large surface area for exchange. As work shifts from bench to large scale manufacturing, there is a critical need for technologies that can monitor and accumulate data during processing, particularly regarding the endpoint criteria of particle size and stability. To date, no such technology has been implemented in nanoemulsion manufacture. In this paper we develop and implement an optical sensor array for in-line nanoemulsion process monitoring and then use the array to optimize the development and manufacture of novel reproducible oxygen carrying nanoemulsions lacking synthetic surfactants.

A Multiparametric Assessment of Human Islets Predicts Transplant Outcomes in Diabetic Mice

Prior to transplantation into individuals with type 1 diabetes, in vitro assays are used to evaluate the quality, function and survival of isolated human islets. In addition to the assessments of these parameters in islet, they can be evaluated by multiparametric morphological scoring (0–10 points) and grading (A, B, C, D, and F) based on islet characteristics (shape, border, integrity, single cells, and diameter). However, correlation between the multiparametric assessment and transplantation outcome has not been fully elucidated. In this study, 55 human islet isolations were scored using this multiparametric assessment. The results were correlated with outcomes after transplantation into immunodeficient diabetic mice. In addition, the multiparametric assessment was compared with oxygen consumption rate of isolated islets as a potential prediction factor for successful transplantations. All islet batches were assessed and found to score: 9 points (n = 18, Grade A), 8 points (n = 19, Grade B), and 7 points (n = 18, Grade B). Islets that scored 9 (Grade A), scored 8 (Grade B) and scored 7 (Grade B) were transplanted into NOD/SCID mice and reversed diabetes in 81.2%, 59.4%, and 33.3% of animals, respectively (P < 0.0001). Islet scoring and grading correlated well with glycemic control post-transplantation (P < 0.0001) and reversal rate of diabetes (P < 0.05). Notably, islet scoring and grading showed stronger correlation with transplantation outcome compared to oxygen consumption rate. Taken together, a multiparametric assessment of isolated human islets was highly predictive of transplantation outcome in diabetic mice.

A bioinspired scaffold for rapid oxygenation of cell encapsulation systems

Inadequate oxygenation is a major challenge in cell encapsulation, a therapy which holds potential to treat many diseases including type I diabetes. In such systems, cellular oxygen (O2) delivery is limited to slow passive diffusion from transplantation sites through the poorly O2-soluble encapsulating matrix, usually a hydrogel. This constrains the maximum permitted distance between the encapsulated cells and host site to within a few hundred micrometers to ensure cellular function. Inspired by the natural gas-phase tracheal O2 delivery system of insects, we present herein the design of a biomimetic scaffold featuring internal continuous air channels endowed with 10,000-fold higher O2 diffusivity than hydrogels. We incorporate the scaffold into a bulk hydrogel containing cells, which facilitates rapid O2 transport through the whole system to cells several millimeters away from the device-host boundary. A computational model, validated by in vitro analysis, predicts that cells and islets maintain high viability even in a thick (6.6 mm) device. Finally, the therapeutic potential of the device is demonstrated through the correction of diabetes in immunocompetent mice using rat islets for over 6 months.

HLA-G1+ Expression in GGTA1KO Pigs Suppresses Human and Monkey Anti-Pig T, B and NK Cell Responses

The human leukocyte antigen G1 (HLA-G1), a non-classical class I major histocompatibility complex (MHC-I) protein, is a potent immunomodulatory molecule at the maternal/fetal interface and other environments to regulate the cellular immune response. We created GGTA1-/HLAG1+ pigs to explore their use as organ and cell donors that may extend xenograft survival and function in both preclinical nonhuman primate (NHP) models and future clinical trials. In the present study, HLA-G1 was expressed from the porcine ROSA26 locus by homology directed repair (HDR) mediated knock-in (KI) with simultaneous deletion of α-1-3-galactotransferase gene (GGTA1; GTKO) using the clustered regularly interspersed palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas9) gene-editing system. GTKO/HLAG1+ pigs showing immune inhibitory functions were generated through somatic cell nuclear transfer (SCNT). The presence of HLA-G1 at the ROSA26 locus and the deletion of GGTA1 were confirmed by next generation sequencing (NGS) and Sanger's sequencing. Fibroblasts from piglets, biopsies from transplantable organs, and islets were positive for HLA-G1 expression by confocal microscopy, flow cytometry, or q-PCR. The expression of cell surface HLA-G1 molecule associated with endogenous β2-microglobulin (β2m) was confirmed by staining genetically engineered cells with fluorescently labeled recombinant ILT2 protein. Fibroblasts obtained from GTKO/HLAG1+ pigs were shown to modulate the immune response by lowering IFN-γ production by T cells and proliferation of CD4+ and CD8+ T cells, B cells and natural killer (NK) cells, as well as by augmenting phosphorylation of Src homology region 2 domain-containing phosphatase-2 (SHP-2), which plays a central role in immune suppression. Islets isolated from GTKO/HLA-G1+ genetically engineered pigs and transplanted into streptozotocin-diabetic nude mice restored normoglycemia, suggesting that the expression of HLA-G1 did not interfere with their ability to reverse diabetes. The findings presented here suggest that the HLA-G1+ transgene can be stably expressed from the ROSA26 locus of non-fetal maternal tissue at the cell surface. By providing an immunomodulatory signal, expression of HLA-G1+ may extend survival of porcine pancreatic islet and organ xenografts.

Insulinoma-derived pseudo-islets for diabetes research

The islets of Langerhans of the pancreas are the primary endocrine organ responsible for regulating whole body glucose homeostasis. The use of isolated primary islets for research development and training requires organ resection, careful digestion, and isolation of the islets from nonendocrine tissue. This process is time consuming, expensive, and requires substantial expertise. For these reasons, we sought to develop a more rapidly obtainable and consistent model system with characteristic islet morphology and function that could be employed to train personnel and better inform experiments prior to using isolated rodent and human islets. Immortalized β cell lines reflect several aspects of primary β cells, but cell propagation in monolayer cell culture limits their usefulness in several areas of research, which depend on islet morphology and/or functional assessment. In this manuscript, we describe the propagation and characterization of insulinoma pseudo-islets (IPIs) from a rat insulinoma cell line INS832/3. IPIs were generated with an average diameter of 200 μm, consistent with general islet morphology. The rates of oxygen consumption and mitochondrial oxidation-reduction changes in response to glucose and metabolic modulators were similar to isolated rat islets. In addition, the dynamic insulin secretory patterns of IPIs were similar to primary rat islets. Thus, INS832/3-derived IPIs provide a valuable and convenient model for accelerating islet and diabetes research.

An immune regulatory 3D-printed alginate-pectin construct for immunoisolation of insulin producing β-cells

Different bioinks have been used to produce cell-laden alginate-based hydrogel constructs for cell replacement therapy but some of these approaches suffer from issues with print quality, long-term mechanical instability, and bioincompatibility. In this study, new alginate-based bioinks were developed to produce cell-laden grid-shaped hydrogel constructs with stable integrity and immunomodulating capacity. Integrity and printability were improved by including the co-block-polymer Pluronic F127 in alginate solutions. To reduce inflammatory responses, pectin with a low degree of methylation was included and tested for inhibition of Toll-Like Receptor 2/1 (TLR2/1) dimerization and activation and tissue responses under the skin of mice. The viscoelastic properties of alginate-Pluronic constructs were unaffected by pectin incorporation. The tested pectin protected printed insulin-producing MIN6 cells from inflammatory stress as evidenced by higher numbers of surviving cells within the pectin-containing construct following exposure to a cocktail of the pro-inflammatory cytokines namely, IL-1β, IFN-γ, and TNF-α. The results suggested that the cell-laden construct bioprinted with pectin-alginate-Pluronic bioink reduced tissue responses via inhibiting TLR2/1 and support insulin-producing β-cell survival under inflammatory stress. Our study provides a potential novel strategy to improve long-term survival of pancreatic islet grafts for Type 1 Diabetes (T1D) treatment.

High Fractions of Large Islets in Human Islet Preparations Detrimentally Affect Posttransplant Outcomes in Streptozotocin-Induced Diabetic Immunodeficient Mice

OBJECTIVES

The aim of this study was to determine whether the size of islets isolated from human donors-measured pretransplant-impacts transplantation outcomes in diabetic mice.

METHODS

Human islets (1200 islet equivalents) were transplanted into the kidney capsules of streptozotocin-induced diabetic immunodeficient mice. Data from a total of 174 mice that received islets from 45 isolations were analyzed to evaluate the correlation between pretransplant islet size and posttransplant diabetes reversal. Fluorescent images of islet clusters were used to categorize individual islets by size (small, 50-150 μm; medium, 150-250 μm; large, >250 μm), and the fractions of islets in each category were calculated.

RESULTS

The fraction of large islets negatively correlated with diabetes reversal rates. Mice that received islet grafts containing 0% to 5%, 5% to 10%, and more than 10% large islets had diabetes reversal rates of 75%, 61%, and 45%, respectively (P = 0.0112). Furthermore, mice that exhibited diabetes reversal received smaller fractions of large islets than mice that did not (5.5% vs 8.0%, P = 0.0003). Intriguingly, the fractions of medium and small islets did not correlate with diabetes reversal outcomes.

CONCLUSIONS

The fraction of large islets is a sensitive predictor of human islet transplantation outcomes in diabetic mice.

Nanotechnology Approaches to Modulate Immune Responses to Cell-based Therapies for Type 1 Diabetes

Islet transplantation is a promising curative treatment option for type 1 diabetes (T1D) as it can provide physiological blood glucose control. The widespread utilization of islet transplantation is limited due to systemic immunosuppression requirements, persisting graft immunodestruction, and poor islet engraftment. Traditional macro- and micropolymeric encapsulation strategies can alleviate the need for antirejection immunosuppression, yet the increased graft volume and diffusional distances imparted by these coatings can be detrimental to graft viability and glucose control. Additionally, systemic administration of pro-engraftment and antirejection therapeutics leaves patients vulnerable to adverse off-target side effects. Nanoscale engineering techniques can be used to immunocamouflage islets, modulate the transplant microenvironment, and provide localized pro-engraftment cues. In this review, we discuss the applications of nanotechnology to advance the clinical potential of islet transplantation, with a focus on cell surface engineering, bioactive functionalization, and use of nanoparticles in T1D cell-based treatments.

Optimizing beta cell function through mesenchymal stromal cell-mediated mitochondria transfer

Pretransplant islet culture is associated with the loss of islet cell mass and insulin secretory function. Insulin secretion from islet β‐cells is primarily controlled by mitochondrial ATP generation in response to elevations in extracellular glucose. Coculture of islets with mesenchymal stromal cells (MSCs) improves islet insulin secretory function in vitro, which correlates with superior islet graft function in vivo. This study aimed to determine whether the improved islet function is associated with mitochondrial transfer from MSCs to cocultured islets. We have demonstrated mitochondrial transfer from human adipose MSCs to human islet β‐cells in coculture. Fluorescence imaging showed that mitochondrial transfer occurs, at least partially, through tunneling nanotube (TNT)‐like structures. The extent of mitochondrial transfer to clinically relevant human islets was greater than that to experimental mouse islets. Human islets are subjected to more extreme cellular stressors than mouse islets, which may induce “danger signals” for MSCs, initiating the donation of MSC‐derived mitochondria to human islet β‐cells. Our observations of increased MSC‐mediated mitochondria transfer to hypoxia‐exposed mouse islets are consistent with this and suggest that MSCs are most effective in supporting the secretory function of compromised β‐cells. Ensuring optimal MSC‐derived mitochondria transfer in preculture and/or cotransplantation strategies could be used to maximize the therapeutic efficacy of MSCs, thus enabling the more widespread application of clinical islet transplantation.

Semi-Automated Assessment of Human Islet Viability Predicts Transplantation Outcomes in a Diabetic Mouse Model

In clinical and experimental human pancreatic islet transplantations, establishing pretransplant assessments that accurately predict transplantation outcomes is crucial. Conventional in vitro viability assessment that relies on manual counting of viable islets is a routine pretransplant assessment. However, this method does not correlate with transplantation outcomes; to improve the method, we recently introduced a semi-automated method using imaging software to objectively determine area-based viability. The goal of the present study was to correlate semi-automated viability assessment with posttransplantation outcomes of human islet transplantations in diabetic immunodeficient mice, the gold standard for in vivo functional assessment of isolated human islets. We collected data from 61 human islet isolations and 188 subsequent in vivo mouse transplantations. We assessed islet viability by fluorescein diacetate and propidium iodide staining using both the conventional and semi-automated method. Transplantations of 1,200 islet equivalents under the kidney capsule were performed in streptozotocin-induced diabetic immunodeficient mice. Among the pretransplant variables, including donor factors and post-isolation assessments, viability measured using the semi-automated method demonstrated a strong influence on in vivo islet transplantation outcomes in multivariate analysis. We calculated an optimized cutoff value (96.1%) for viability measured using the semi-automated method and showed a significant difference in diabetes reversal rate for islets with viability above this cutoff (77% reversal) vs. below this cutoff (49% reversal). We performed a detailed analysis to show that both the objective measurement and the improved area-based scoring system, which distinguished between small and large islets, were key features of the semi-automated method that allowed for precise evaluation of viability. Taken together, our results suggest that semi-automated viability assessment offers a promising alternative pretransplant assessment over conventional manual assessment to predict human islet transplantation outcomes.

Islet Harvest in Carbon Monoxide-Saturated Medium for Chronic Pancreatitis Patients Undergoing Islet Autotransplantation

Stresses encountered during human islet isolation lead to unavoidable β-cell death after transplantation. This reduces the chance of insulin independence in chronic pancreatitis patients undergoing total pancreatectomy and islet autotransplantation. We tested whether harvesting islets in carbon monoxide-saturated solutions is safe and can enhance islet survival and insulin independence after total pancreatectomy and islet autotransplantation. Chronic pancreatitis patients who consented to the study were randomized into carbon monoxide (islets harvested in a carbon monoxide-saturated medium) or control (islets harvested in a normal medium) groups. Islet yield, viability, oxygen consumption rate, β-cell death (measured by unmethylated insulin DNA), and serum cytokine levels were measured during the peri-transplantation period. Adverse events, metabolic phenotypes, and islet function were measured prior and at 6 months post-transplantation. No adverse events directly related to the infusion of carbon monoxide islets were observed. Carbon monoxide islets showed significantly higher viability before transplantation. Subjects receiving carbon monoxide islets had less β-cell death, decreased CCL23, and increased CXCL12 levels at 1 or 3 days post transplantation compared with controls. Three in 10 (30%) of the carbon monoxide subjects and none of the control subjects were insulin independent. This pilot trial showed for the first time that harvesting human islets in carbon monoxide-saturated solutions is safe for total pancreatectomy and islet autotransplantation patients.

Necrostatin-1 supplementation enhances young porcine islet maturation and in vitro function

BACKGROUND

Necroptosis has been demonstrated to be a primary mechanism of islet cell death. This study evaluated whether the supplementation of necrostatin-1 (Nec-1), a potent inhibitor of necroptosis, to islet culture media could improve the recovery, maturation, and function of pre-weaned porcine islets (PPIs).

METHODS

PPIs were isolated from pre-weaned Yorkshire piglets (8-15 days old) and either cultured in control islet culture media (n = 6) or supplemented with Nec-1 (100 µM, n = 5). On days 3 and 7 of culture, islets were assessed for recovery, insulin content, viability, cellular composition, GLUT2 expression in beta cells, differentiation of pancreatic endocrine progenitor cells, function, and oxygen consumption rate.

RESULTS

Nec-1 supplementation induced a 2-fold increase in the insulin content of PPIs on day 7 of culture. When compared to untreated islets, Nec-1 treatment doubled the beta- and alpha-cell composition and accelerated the development of delta cells. Additionally, beta cells of Nec-1-treated islets had a significant upregulation in GLUT2 expression. The enhanced development of major endocrine cells and GLUT2 expression after Nec-1 treatment subsequently led to a significant increase in the amount of insulin secreted in response to in vitro glucose challenge. Islet recovery, viability, and oxygen consumption rate were unaffected by Nec-1.

CONCLUSION

This study underlines the importance of necroptosis in islet cell death after isolation and demonstrates the novel effects of Nec-1 to increase islet insulin content, enhance pancreatic endocrine cell development, facilitate GLUT2 upregulation in beta cells, and augment insulin secretion. Nec-1 supplementation to culture media significantly improves islet quality prior to xenotransplantation.

Oxygen generating biomaterial improves the function and efficacy of beta cells within a macroencapsulation device

Tissue-engineered devices have the potential to significantly improve human health. A major impediment to the success of clinically scaled transplants, however, is insufficient oxygen transport, which leads to extensive cell death and dysfunction. To provide in situ supplementation of oxygen within a cellular implant, we developed a hydrolytically reactive oxygen generating material in the form of polydimethylsiloxane (PDMS) encapsulated solid calcium peroxide, termed OxySite. Herein, we demonstrate, for the first time, the successful implementation of this in situ oxygen-generating biomaterial to support elevated cellular function and efficacy of macroencapsulation devices for the treatment of type 1 diabetes. Under extreme hypoxic conditions, devices supplemented with OxySite exhibited substantially elevated beta cell and islet viability and function. Furthermore, the inclusion of OxySite within implanted macrodevices resulted in the significant improvement of graft efficacy and insulin production in a diabetic rodent model. Translating to human islets at elevated loading densities further validated the advantages of this material. This simple biomaterial-based approach for delivering a localized and controllable oxygen supply provides a broad and impactful platform for improving the therapeutic efficacy of cell-based approaches.

Mathematical predictions of oxygen availability in micro- and macro-encapsulated human and porcine pancreatic islets

Optimal function of immunoisolated islets requires adequate supply of oxygen to metabolically active insulin producing beta-cells. Using mathematical modeling, we investigated the influence of the pO₂ on islet insulin secretory capacity and evaluated conditions that could lead to the development of tissue anoxia, modeled for a 300 μm islet in a 500 μm microcapsule or a 500 μm planar, slab-shaped macrocapsule. The pO₂ was used to assess the part of islets that contributed to insulin secretion. Assuming a 500 μm macrocapsule with a 300 μm islet, with oxygen consumption rate (OCR) of 100-300 nmol min^-1 mg^-1 DNA, islets did not develop any necrotic core. The nonfunctional zone (with no insulin secretion if pO₂  < 0.1 mmHg) was 0.3% for human islets (OCR ~100 nmol/min/mg DNA) and 35% for porcine islets (OCR ~300 nmol/min/mg DNA). The OCR of the islet preparation is profoundly affected by islet size, with optimal size of <250 μm in diameter (human) or <150 μm (porcine). Our data suggest that microcapsules afford superior oxygen delivery to encapsulated islets than macrocapsules, and optimal islet function can be achieved by encapsulating multiple, small (<150 μm) islets with OCR of ~100 nmol min^-1 mg^-1 DNA (human islets) or ~200 nmol min^-1 mg^-1 DNA (porcine islets).

Improved recovery of human islets from young donor pancreases utilizing increased protease dose to collagenase for digesting peri-islet extracellular matrix

Human islet isolation from young donor pancreases (YDP) utilizing the current purified standard dose of collagenase-protease enzyme mixtures often results in the release of a high percentage of mantled islets. Mantled islets are those surrounded by exocrine tissue and are difficult to purify by density gradient centrifugation, leading to poor islet recovery. Based on difference in extracellular matrix, and total collagen content between YDP and old donor pancreas (ODP, > 35 Y) led us to compare results from islet isolation using increased collagenase combination (ICC) or increased protease combination (IPC), to the standard enzyme combination (SEC) in a "trisected" pancreas model to overcome the donor-to-donor variability. These results showed a reduced percentage of mantled islets (17% ± 7.5%) and higher postpurification islet recovery (83.8% ± 5.6%) with IPC. Furthermore, these results were confirmed in 13 consecutive whole pancreas islet isolations utilizing IPC from VitaCyte, Roche, or SERVA collagenase-protease enzyme mixtures. Results obtained from in vitro and in vivo islet functional assessment indicated that islets isolated using IPC retained normal islet morphology, insulin secretion, and the ability to reverse diabetes after transplantation in diabetic nude mice. This is the first report utilizing trisected pancreas to assess the effectiveness of different enzyme combinations to improve islet recovery from young donor pancreases.

Oxygenation strategies for encapsulated islet and beta cell transplants

Human allogeneic islet transplantation (ITx) is emerging as a promising treatment option for qualified patients with type 1 diabetes. However, widespread clinical application of allogeneic ITx is hindered by two critical barriers: the need for systemic immunosuppression and the limited supply of human islet tissue. Biocompatible, retrievable immunoisolation devices containing glucose-responsive insulin-secreting tissue may address both critical barriers by enabling the more effective and efficient use of allogeneic islets without immunosuppression in the near-term, and ultimately the use of a cell source with a virtually unlimited supply, such as human stem cell-derived β-cells or xenogeneic (porcine) islets with minimal or no immunosuppression. However, even though encapsulation methods have been developed and immunoprotection has been successfully tested in small and large animal models and to a limited extent in proof-of-concept clinical studies, the effective use of encapsulation approaches to convincingly and consistently treat diabetes in humans has yet to be demonstrated. There is increasing consensus that inadequate oxygen supply is a major factor limiting their clinical translation and routine implementation. Poor oxygenation negatively affects cell viability and β-cell function, and the problem is exacerbated with the high-density seeding required for reasonably-sized clinical encapsulation devices. Approaches for enhanced oxygen delivery to encapsulated tissues in implantable devices are therefore being actively developed and tested. This review summarizes fundamental aspects of islet microarchitecture and β-cell physiology as well as encapsulation approaches highlighting the need for adequate oxygenation; it also evaluates existing and emerging approaches for enhanced oxygen delivery to encapsulation devices, particularly with the advent of β-cell sources from stem cells that may enable the large-scale application of this approach.

Oxygen Perfusion (Persufflation) of Human Pancreata Enhances Insulin Secretion and Attenuates Islet Proinflammatory Signaling

BACKGROUND

All human islets used in research and for the clinical treatment of diabetes are subject to ischemic damage during pancreas procurement, preservation, and islet isolation. A major factor influencing islet function is exposure of pancreata to cold ischemia during unavoidable windows of preservation by static cold storage (SCS). Improved preservation methods may prevent this functional deterioration. In the present study, we investigated whether pancreas preservation by gaseous oxygen perfusion (persufflation) better preserved islet function versus SCS.

METHODS

Human pancreata were preserved by SCS or by persufflation in combination with SCS. Islets were subsequently isolated, and preparations in each group matched for SCS or total preservation time were compared using dynamic glucose-stimulated insulin secretion as a measure of β-cell function and RNA sequencing to elucidate transcriptomic changes.

RESULTS

Persufflated pancreata had reduced SCS time, which resulted in islets with higher glucose-stimulated insulin secretion compared to islets from SCS only pancreata. RNA sequencing of islets from persufflated pancreata identified reduced inflammatory and greater metabolic gene expression, consistent with expectations of reducing cold ischemic exposure. Portions of these transcriptional responses were not associated with time spent in SCS and were attributable to pancreatic reoxygenation. Furthermore, persufflation extended the total preservation time by 50% without any detectable decline in islet function or viability.

CONCLUSIONS

These data demonstrate that pancreas preservation by persufflation rather than SCS before islet isolation reduces inflammatory responses and promotes metabolic pathways in human islets, which results in improved β cell function.

In vitro characterization of neonatal, juvenile, and adult porcine islet oxygen demand, β-cell function, and transcriptomes

BACKGROUND

There is currently a shortage of human donor pancreata which limits the broad application of islet transplantation as a treatment for type 1 diabetes. Porcine islets have demonstrated potential as an alternative source, but a study evaluating islets from different donor ages under unified protocols has yet to be conducted.

METHODS

Neonatal porcine islets (NPI; 1-3 days), juvenile porcine islets (JPI; 18-21 days), and adult porcine islets (API; 2+ years) were compared in vitro, including assessments of oxygen consumption rate, membrane integrity determined by FDA/PI staining, β-cell proliferation, dynamic glucose-stimulated insulin secretion, and RNA sequencing.

RESULTS

Oxygen consumption rate normalized to DNA was not significantly different between ages. Membrane integrity was age dependent, and API had the highest percentage of intact cells. API also had the highest glucose-stimulated insulin secretion response during a dynamic insulin secretion assay and had 50-fold higher total insulin content compared to NPI and JPI. NPI and JPI had similar glucose responsiveness, β-cell percentage, and β-cell proliferation rate. Transcriptome analysis was consistent with physiological assessments. API transcriptomes were enriched for cellular metabolic and insulin secretory pathways, while NPI exhibited higher expression of genes associated with proliferation.

CONCLUSIONS

The oxygen demand, membrane integrity, β-cell function and proliferation, and transcriptomes of islets from API, JPI, and NPI provide a comprehensive physiological comparison for future studies. These assessments will inform the optimal application of each age of porcine islet to expand the availability of islet transplantation.

The Flaws and Future of Islet Volume Measurements

When working with isolated islet preparations, measuring the volume of tissue is not a trivial matter. Islets come in a large range of sizes and are often contaminated with exocrine tissue. Many factors complicate the procedure, and yet knowledge of the islet volume is essential for predicting the success of an islet transplant or comparing experimental groups in the laboratory. In 1990, Ricordi presented the islet equivalency (IEQ), defined as one IEQ equaling a single spherical islet of 150 μm in diameter. The method for estimating IEQ was developed by visualizing islets in a microscope, estimating their diameter in 50 μm categories and calculating a total volume for the preparation. Shortly after its introduction, the IEQ was adopted as the standard method for islet volume measurements. It has helped to advance research in the field by providing a useful tool improving the reproducibility of islet research and eventually the success of clinical islet transplants. However, the accuracy of the IEQ method has been questioned for years and many alternatives have been proposed, but none have been able to replace the widespread use of the IEQ. This article reviews the history of the IEQ, and discusses the benefits and failings of the measurement. A thorough evaluation of alternatives for estimating islet volume is provided along with the steps needed to uniformly move to an improved method of islet volume estimation. The lessons learned from islet researchers may serve as a guide for other fields of regenerative medicine as cell clusters become a more attractive therapeutic option.

Beta Cell Death by Cell-free DNA and Outcome After Clinical Islet Transplantation

BACKGROUND

Optimizing engraftment and early survival after clinical islet transplantation is critical to long-term function, but there are no reliable, quantifiable measures to assess beta cell death. Circulating cell-free DNA (cfDNA) derived from beta cells has been identified as a novel biomarker to detect cell loss and was recently validated in new-onset type 1 diabetes and in islet transplant patients.

METHODS

Herein we report beta cell cfDNA measurements after allotransplantation in 37 subjects and the correlation with clinical outcomes.

RESULTS

A distinctive peak of cfDNA was observed 1 hour after transplantation in 31 (83.8%) of 37 subjects. The presence and magnitude of this signal did not correlate with transplant outcome. The 1-hour signal represents dead beta cells carried over into the recipient after islet isolation and culture, combined with acute cell death post infusion. Beta cell cfDNA was also detected 24 hours posttransplant (8/37 subjects, 21.6%). This signal was associated with higher 1-month insulin requirements (P = 0.04), lower 1-month stimulated C-peptide levels (P = 0.01), and overall worse 3-month engraftment, by insulin independence (receiver operating characteristic-area under the curve = 0.70, P = 0.03) and beta 2 score (receiver operating characteristic-area under the curve = 0.77, P = 0.006).

CONCLUSIONS

cfDNA-based estimation of beta cell death 24 hours after islet allotransplantation correlates with clinical outcome and could predict early engraftment.

Characterization of Adipose Tissue Product Quality Using Measurements of Oxygen Consumption Rate

BACKGROUND

Fat grafting is a common procedure in plastic surgery but associated with unpredictable graft retention. Adipose tissue (AT) "product" quality is affected by the methods used for harvest, processing and transfer, which vary widely amongst surgeons. Currently, there is no method available to accurately assess the quality of AT.

OBJECTIVES

In this study, we present a novel method for the assessment of AT product quality through direct measurements of oxygen consumption rate (OCR). OCR has exhibited potential in predicting outcomes following pancreatic islet transplant. Our study aim was to reapportion existing technology for its use with AT preparations and to confirm that these measurements are feasible.

METHODS

OCR was successfully measured for en bloc and postprocessed AT using a stirred microchamber system. OCR was then normalized to DNA content (OCR/DNA), which represents the AT product quality.

RESULTS

Mean (±SE) OCR/DNA values for fresh en bloc and post-processed AT were 149.8 (± 9.1) and 61.1 (± 6.1) nmol/min/mg DNA, respectively. These preliminary data suggest that: (1) OCR and OCR/DNA measurements of AT harvested using conventional protocol are feasible; and (2) standard AT processing results in a decrease in overall AT product quality.

CONCLUSIONS

OCR measurements of AT using existing technology can be done and enables accurate, real-time, quantitative assessment of the quality of AT product prior to transfer. The availability and further validation of this type of assay could enable optimization of fat grafting protocol by providing a tool for the more detailed study of procedural variables that affect AT product quality.

Oxygen-permeable microwell device maintains islet mass and integrity during shipping

Islet transplantation is currently the only minimally invasive therapy available for patients with type 1 diabetes that can lead to insulin independence; however, it is limited to only a small number of patients. Although clinical procedures have improved in the isolation and culture of islets, a large number of islets are still lost in the pre-transplant period, limiting the success of this treatment. Moreover, current practice includes islets being prepared at specialized centers, which are sometimes remote to the transplant location. Thus, a critical point of intervention to maintain the quality and quantity of isolated islets is during transportation between isolation centers and the transplanting hospitals, during which 20-40% of functional islets can be lost. The current study investigated the use of an oxygen-permeable PDMS microwell device for long-distance transportation of isolated islets. We demonstrate that the microwell device protected islets from aggregation during transport, maintaining viability and average islet size during shipping.

Effect of the Zinc Oxide Nanoparticles and Thiamine for the Management of Diabetes in Alloxan-Induced Mice: a Stereological and Biochemical Study

This research was carried out to evaluate the antidiabetic effects of zinc oxide nanoparticles (ZnO NPs) and thiamine following experimental diabetes. Fifty-six 6-week-old female mice were used and divided into seven groups of eight animals. Diabetes was induced in fasted mice by using intraperitoneal (IP) injection of alloxan (180 mg/kg). Groups included (I) non-diabetic control, (II) thiamine (30 mg/l, IP), (III) alloxan-induced diabetic mice, (IV) diabetes + ZnO NPs (0.1 mg/kg IP), (V) diabetes + ZnO NPs (0.5 mg/kg IP), (VI) diabetes + ZnO NPs (0.1 mg/kg IP) + thiamine (30 mg/l, IP), and (VII) diabetes + ZnO NPs (0.5 mg/kg IP) + thiamine (30 mg/l, IP). Coincident with pancreas recovery, in diabetic treated mice (groups IV to VII), the mean islet volume, islets per square micrometer, and volume density of the pancreas had increased than in alloxan-induced diabetic mice. ZnO NPs and thiamine induced a decreasing blood glucose, lower serum triglyceride (TG), LDL, and total cholesterol (TC) levels in alloxan-induced diabetic mice treated with ZnO NPs and thiamine, simultaneously increasing HDL as well. In conclusion, ZnO NPs and thiamine are potent antidiabetic factors, and that, these compound supplementation possesses hypoglycemic properties and have effect on serum lipid parameters in diabetes mice.

Plasticity and Aggregation of Juvenile Porcine Islets in Modified Culture: Preliminary Observations

Diabetes is a major health problem worldwide, and there is substantial interest in developing xenogeneic islet transplantation as a potential treatment. The potential to relieve the demand on an inadequate supply of human pancreata is dependent upon the efficiency of techniques for isolating and culturing islets from the source pancreata. Porcine islets are favored for xenotransplantation, but mature pigs (>2 years) present logistic and economic challenges, and young pigs (3-6 months) have not yet proven to be an adequate source. In this study, islets were isolated from 20 juvenile porcine pancreata (~3 months; 25 kg Yorkshire pigs) immediately following procurement or after 24 h of hypothermic machine perfusion (HMP) preservation. The resulting islet preparations were characterized using a battery of tests during culture in silicone rubber membrane flasks. Islet biology assessment included oxygen consumption, insulin secretion, histopathology, and in vivo function. Islet yields were highest from HMP-preserved pancreata (2,242 ± 449 IEQ/g). All preparations comprised a high proportion (>90%) of small islets (<100 μm), and purity was on average 63 ± 6%. Morphologically, islets appeared as clusters on day 0, loosely disaggregated structures at day 1, and transitioned to aggregated structures comprising both exocrine and endocrine cells by day 6. Histopathology confirmed both insulin and glucagon staining in cultures and grafts excised after transplantation in mice. Nuclear staining (Ki-67) confirmed mitotic activity consistent with the observed plasticity of these structures. Metabolic integrity was demonstrated by oxygen consumption rates = 175 ± 16 nmol/min/mg DNA, and physiological function was intact by glucose stimulation after 6-8 days in culture. In vivo function was confirmed with blood glucose control achieved in nearly 50% (8/17) of transplants. Preparation and culture of juvenile porcine islets as a source for islet transplantation require specialized conditions. These immature islets undergo plasticity in culture and form fully functional multicellular structures. Further development of this method for culturing immature porcine islets is expected to generate small pancreatic tissue-derived organoids termed "pancreatites," as a therapeutic product from juvenile pigs for xenotransplantation and diabetes research.

Historical Perspectives and Current Challenges in Cell Microencapsulation

The principle of immunoisolation of cells is based on encapsulation of cells in immunoprotective but semipermeable membranes that protect cells from hazardous effects of the host immune system but allows ingress of nutrients and outgress of therapeutic molecules. The technology was introduced in 1933 but has only received its deserved attention for its therapeutic application for three decades now.In the past decade important advances have been made in creating capsules that provoke minimal or no inflammatory responses. There are however new emerging challenges. These challenges relate to optimal nutrition and oxygen supply as well as standardization and documentation of capsule properties.It is concluded that the proof of principle of applicability of encapsulated grafts for treatment of human disease has been demonstrated and merits optimism about its clinical potential. Further innovation requires a much more systematic approach in identifying crucial properties of capsules and cellular grafts to allow sound interpretations of the results.

Human islet xenotransplantation in rodents: A literature review of experimental model trends

Among the innovations for the treatment of type 1 diabetes, islet transplantation is a less invasive method of treatment, although it is still in development. One of the greatest barriers to this technique is the low number of pancreas donors and the low number of pancreases that are available for transplantation. Rodent models have been chosen in most studies of islet rejection and type 1 diabetes prevention to evaluate the quality and function of isolated human islets and to identify alternative solutions to the problem of islet scarcity. The purpose of this study is to conduct a review of islet xenotransplantation experiments from humans to rodents, to organize and analyze the parameters of these experiments, to describe trends in experimental modeling and to assess the viability of this procedure. In this study, we reviewed recently published research regarding islet xenotransplantation from humans to rodents, and we summarized the findings and organized the relevant data. The included studies were recent reports that involved xenotransplantation using human islets in a rodent model. We excluded the studies that related to isotransplantation, autotransplantation and allotransplantation. A total of 34 studies that related to xenotransplantation were selected for review based on their relevance and current data. Advances in the use of different graft sites may overcome autoimmunity and rejection after transplantation, which may solve the problem of the scarcity of islet donors in patients with type 1 diabetes.

Mitigating hypoxic stress on pancreatic islets via in situ oxygen generating biomaterial

A major obstacle in the survival and efficacy of tissue engineered transplants is inadequate oxygenation, whereby unsupportive oxygen tensions result in significant cellular dysfunction and death within the implant. In a previous report, we developed an innovative oxygen generating biomaterial, termed OxySite, to provide supportive in situ oxygenation to cells and prevent hypoxia-induced damage. Herein, we explored the capacity of this biomaterial to mitigate hypoxic stress in both rat and nonhuman primate pancreatic islets by decreasing cell death, supporting metabolic activity, sustaining aerobic metabolism, preserving glucose responsiveness, and decreasing the generation of inflammatory cytokines. Further, the impact of supplemental oxygenation on in vivo cell function was explored by the transplantation of islets previously co-cultured with OxySite into a diabetic rat model. Transplant outcomes revealed significant improvement in graft efficacy for OxySite-treated islets, when transplanted within an extrahepatic site. These results demonstrate the potency of the OxySite material to mitigate activation of detrimental hypoxia-induced pathways in islets during culture and highlights the importance of in situ oxygenation on resulting islet transplant outcomes.

Cell number per spheroid and electrical conductivity of nanowires influence the function of silicon nanowired human cardiac spheroids

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide an unlimited cell source to treat cardiovascular diseases, the leading cause of death worldwide. However, current hiPSC-CMs retain an immature phenotype that leads to difficulties for integration with adult myocardium after transplantation. To address this, we recently utilized electrically conductive silicon nanowires (e-SiNWs) to facilitate self-assembly of hiPSC-CMs to form nanowired hiPSC cardiac spheroids. Our previous results showed addition of e-SiNWs effectively enhanced the functions of the cardiac spheroids and improved the cellular maturation of hiPSC-CMs. Here, we examined two important factors that can affect functions of the nanowired hiPSC cardiac spheroids: (1) cell number per spheroid (i.e., size of the spheroids), and (2) the electrical conductivity of the e-SiNWs. To examine the first factor, we prepared hiPSC cardiac spheroids with four different sizes by varying cell number per spheroid (∼0.5k, ∼1k, ∼3k, ∼7k cells/spheroid). Spheroids with ∼3k cells/spheroid was found to maximize the beneficial effects of the 3D spheroid microenvironment. This result was explained with a semi-quantitative theory that considers two competing factors: 1) the improved 3D cell-cell adhesion, and 2) the reduced oxygen supply to the center of spheroids with the increase of cell number. Also, the critical role of electrical conductivity of silicon nanowires has been confirmed in improving tissue function of hiPSC cardiac spheroids. These results lay down a solid foundation to develop suitable nanowired hiPSC cardiac spheroids as an innovative cell delivery system to treat cardiovascular diseases.

STATEMENT OF SIGNIFICANCE

Cardiovascular disease is the leading cause of death and disability worldwide. Due to the limited regenerative capacity of adult human hearts, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have received significant attention because they provide a patient specific cell source to regenerate damaged hearts. Despite the progress, current human hiPSC-CMs retain an immature phenotype that leads to difficulties for integration with adult myocardium after transplantation. To address this, we recently utilized electrically conductive silicon nanowires (e-SiNWs) to facilitate self-assembly of hiPSC-CMs to form nanowired hiPSC cardiac spheroids. Our previous results showed addition of e-SiNWs effectively enhanced the functions of the cardiac spheroids and improved the cellular maturation of hiPSC-CMs. In this manuscript, we examined the effects of two important factors on the functions of nanowired hiPSC cardiac spheroids: (1) cell number per spheroid (i.e., size of the spheroids), and (2) the electrical conductivity of the e-SiNWs. The results from these studies will allow for the development of suitable nanowired hiPSC cardiac spheroids to effectively deliver hiPSC-CMs for heart repair.

Noninvasive assessment of tissue-engineered graft viability by oxygen-17 magnetic resonance spectroscopy

Transplantation of macroencapsulated tissue-engineered grafts (TEGs) is being investigated as a treatment for type 1 diabetes, but there is a critical need to measure TEG viability both in vitro and in vivo. Oxygen deficiency is the most critical issue preventing widespread implementation of TEG transplantation and delivery of supplemental oxygen (DSO) has been shown to enhance TEG survival and function in vivo. In this study, we demonstrate the first use of oxygen-17 magnetic resonance spectroscopy (¹⁷ O-MRS) to measure the oxygen consumption rate (OCR) of TEGs and show that in addition to providing therapeutic benefits to TEGs, DSO with ¹⁷ O₂ can also enable measurements of TEG viability. Macroencapsulated TEGs containing βTC3 murine insulinoma cells were prepared with three fractional viabilities and provided with ¹⁷ O₂ . Cellular metabolism of ¹⁷ O₂ into nascent mitochondrial water (H₂¹⁷ O) was monitored by ¹⁷ O-MRS and, from the measured data, OCR was calculated. For comparison, OCR was simultaneously measured on a separate, but equivalent sample of cells with a well-established stirred microchamber technique. OCR measured by ¹⁷ O-MRS agreed well with measurements made in the stirred microchamber device. These studies confirm that ¹⁷ O-MRS can quantify TEG viability noninvasively. Biotechnol. Bioeng. 2017;114: 1118-1121. © 2016 Wiley Periodicals, Inc.

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.

Continuous Quadrupole Magnetic Separation of Islets during Digestion Improves Purified Porcine Islet Viability

Islet transplantation (ITx) is an emerging and promising therapy for patients with uncontrolled type 1 diabetes. The islet isolation and purification processes require exposure to extended cold ischemia, warm-enzymatic digestion, mechanical agitation, and use of damaging chemicals for density gradient separation (DG), all of which reduce viable islet yield. In this paper, we describe initial proof-of-concept studies exploring quadrupole magnetic separation (QMS) of islets as an alternative to DG to reduce exposure to these harsh conditions. Three porcine pancreata were split into two parts, the splenic lobe (SPL) and the combined connecting/duodenal lobes (CDL), for paired digestions and purifications. Islets in the SPL were preferentially labeled using magnetic microparticles (MMPs) that lodge within the islet microvasculature when infused into the pancreas and were continuously separated from the exocrine tissue by QMS during the collection phase of the digestion process. Unlabeled islets from the CDL were purified by conventional DG. Islets purified by QMS exhibited significantly improved viability (measured by oxygen consumption rate per DNA, p < 0.03) and better morphology relative to control islets. Islet purification by QMS can reduce the detrimental effects of prolonged exposure to toxic enzymes and density gradient solutions and substantially improve islet viability after isolation.

Clinical Islet Isolation

The overarching success of islet transplantation relies on the success in the laboratory to isolate the islets. This chapter focuses on the processes of human islet cell isolation and the ways to optimally provide islet cells for transplantation. The major improvements in regards to the choice of enzyme type, way the digested pancreas tissue is handled to best separate islets from the acinar and surrounding tissues, the various methods of purification of the islets, their subsequent culture and quality assurance to improve outcomes to culminate in safe and effective islet transplantation will be discussed. After decades of improvements, islet cell isolation and transplantation now clearly offer a safe, effective and feasible therapeutic treatment option for an increasing number of patients suffering from type 1 diabetes specifically for those with severe hypoglycaemic unawareness.

Identifying Effective Enzyme Activity Targets for Recombinant Class I and Class II Collagenase for Successful Human Islet Isolation

Isolation following a good manufacturing practice-compliant, human islet product requires development of a robust islet isolation procedure where effective limits of key reagents are known. The enzymes used for islet isolation are critical but little is known about the doses of class I and class II collagenase required for successful islet isolation.

METHODS

We used a factorial approach to evaluate the effect of high and low target activities of recombinant class I (rC1) and class II (rC2) collagenase on human islet yield. Consequently, 4 different enzyme formulations with divergent C1:C2 collagenase mass ratios were assessed, each supplemented with the same dose of neutral protease. Both split pancreas and whole pancreas models were used to test enzyme targets (n = 20). Islet yield/g pancreas was compared with historical enzymes (n = 42).

RESULTS

Varying the Wunsch (rC2) and collagen degradation activity (CDA, rC1) target dose, and consequently the C1:C2 mass ratio, had no significant effect on tissue digestion. Digestions using higher doses of Wunsch and CDA resulted in comparable islet yields to those obtained with 60% and 50% of those activities, respectively. Factorial analysis revealed no significant main effect of Wunsch activity or CDA for any parameter measured. Aggregate results from 4 different collagenase formulations gave 44% higher islet yield (>5000 islet equivalents/g) in the body/tail of the pancreas (n = 12) when compared with those from the same segment using a standard natural collagenase/protease mixture (n = 6). Additionally, islet yields greater than 5000 islet equivalents/g pancreas were also obtained in whole human pancreas.

CONCLUSIONS

A broader C1:C2 ratio can be used for human islet isolation than has been used in the past. Recombinant collagenase is an effective replacement for the natural enzyme and we have determined that high islet yield can be obtained even with low doses of rC1:rC2, which is beneficial for the survival of islets.

Islet preparation purity is overestimated, and less pure fractions have lower post-culture viability before clinical allotransplantation

BACKGROUND

Replacement of β-cells with the use of isolated islet allotransplantation (IT) is an emerging therapy for type 1 diabetics with hypoglycemia unawareness. The current standard protocol calls for a 36-72-hour culture period before IT. We examined 13 clinical islet preparations with ≥2 purity fractions to determine the effect of culture on viability.

METHODS

After standard islet isolation and purification, pure islet fractions were placed at 37°C with 5% CO2 for 12-24 hours and subsequently moved to 22°C, whereas less pure fractions were cultured at 22°C for the entire duration. Culture density was targeted at a range of 100-200 islet equivalents (IEQ)/cm(2) adjusted for purity. Islets were assessed for purity (dithizone staining), quantity (pellet volume and DNA), and viability (oxygen consumption rate normalized to DNA content [OCR/DNA] and membrane integrity).

RESULTS

Results indicated that purity was overestimated, especially in less pure fractions. This was evidenced by significantly larger observed pellet sizes than expected and tissue amount as quantified with the use of a dsDNA assay when available. Less pure fractions showed significantly lower OCR/DNA and membrane integrity compared with pure. The difference in viability between the 2 purity fractions may be due to a variety of reasons, including hypoxia, nutrient deficiency, toxic metabolite accumulation, and/or proteolytic enzymes released by acinar tissue impurities that are not neutralized by human serum albumin in the culture media.

CONCLUSIONS

Current clinical islet culture protocols should be examined further, especially for less pure fractions, to ensure the maintenance of viability before transplantation. Even though relatively small, the difference in viability is important because the amount of dead or dying tissue introduced into recipients may be dramatically increased, especially with less pure preparations.