Islet graft assessment in the Edmonton Protocol: implications for predicting long-term clinical outcome

Diabetes current and future translatable therapies

Diabetes is one of the major diseases and concerns of public health systems that affects over 200 million patients worldwide. It is estimated that 90% of these patients suffer from diabetes type 2, while 10% present diabetes type 1. This type of diabetes and certain types of diabetes type 2, are characterized by dysregulation of blood glycemic levels due to the total or partial depletion of insulin-secreting pancreatic β-cells. Different approaches have been proposed for long-term treatment of insulin-dependent patients; amongst them, cell-based approaches have been the subject of basic and clinical research since they allow blood glucose level sensing and in situ insulin secretion. The current gold standard for insulin-dependent patients is on-demand exogenous insulin application; cell-based therapies aim to remove this burden from the patient and caregivers. In recent years, protocols to isolate and implant pancreatic islets from diseased donors have been developed and tested in clinical trials. Nevertheless, the shortage of donors, along with the need of immunosuppressive companion therapies, have pushed researchers to focus their attention and efforts to overcome these disadvantages and develop alternative strategies. This review discusses current tested clinical approaches and future potential alternatives for diabetes type 1, and some diabetes type 2, insulin-dependent patients. Additionally, advantages and disadvantages of these discussed methods.

Pancreas and islet morphology in cystic fibrosis: clues to the etiology of cystic fibrosis-related diabetes

Cystic fibrosis (CF) is a multi-organ disease caused by loss-of-function mutations in CFTR (which encodes the CF transmembrane conductance regulator ion channel). Cystic fibrosis related diabetes (CFRD) occurs in 40-50% of adults with CF and is associated with significantly increased morbidity and mortality. CFRD arises from insufficient insulin release from β cells in the pancreatic islet, but the mechanisms underlying the loss of β cell function remain understudied. Widespread pathological changes in the CF pancreas provide clues to these mechanisms. The exocrine pancreas is the epicenter of pancreas pathology in CF, with ductal pathology being the initiating event. Loss of CFTR function results in ductal plugging and subsequent obliteration. This in turn leads to destruction of acinar cells, fibrosis and fatty replacement. Despite this adverse environment, islets remain relatively well preserved. However, islet composition and arrangement are abnormal, including a modest decrease in β cells and an increase in α, δ and γ cell abundance. The small amount of available data suggest that substantial loss of pancreatic/islet microvasculature, autonomic nerve fibers and intra-islet macrophages occur. Conversely, T-cell infiltration is increased and, in CFRD, islet amyloid deposition is a frequent occurrence. Together, these pathological changes clearly demonstrate that CF is a disease of the pancreas/islet microenvironment. Any or all of these changes are likely to have a dramatic effect on the β cell, which relies on positive signals from all of these neighboring cell types for its normal function and survival. A thorough characterization of the CF pancreas microenvironment is needed to develop better therapies to treat, and ultimately prevent CFRD.

Pancreatic Islet Viability Assessment Using Hyperspectral Imaging of Autofluorescence

Islets prepared for transplantation into type 1 diabetes patients are exposed to compromising intrinsic and extrinsic factors that contribute to early graft failure, necessitating repeated islet infusions for clinical insulin independence. A lack of reliable pre-transplant measures to determine islet viability severely limits the success of islet transplantation and will limit future beta cell replacement strategies. We applied hyperspectral fluorescent microscopy to determine whether we could non-invasively detect islet damage induced by oxidative stress, hypoxia, cytokine injury, and warm ischaemia, and so predict transplant outcomes in a mouse model. In assessing islet spectral signals for NAD(P)H, flavins, collagen-I, and cytochrome-C in intact islets, we distinguished islets compromised by oxidative stress (ROS) (AUC = 1.00), hypoxia (AUC = 0.69), cytokine exposure (AUC = 0.94), and warm ischaemia (AUC = 0.94) compared to islets harvested from pristine anaesthetised heart-beating mouse donors. Significantly, with unsupervised assessment we defined an autofluorescent score for ischaemic islets that accurately predicted the restoration of glucose control in diabetic recipients following transplantation. Similar results were obtained for islet single cell suspensions, suggesting translational utility in the context of emerging beta cell replacement strategies. These data show that the pre-transplant hyperspectral imaging of islet autofluorescence has promise for predicting islet viability and transplant success.

Advantages of the retroperitoneal retrocolic space as the transplant site for encapsulated xenogeneic islets

OBJECTIVE

Islet allotransplantation has demonstrated improved clinical outcomes using the hepatic portal vein as the standard infusion method. However, the current implantation site is not ideal due to the short-term thrombotic and long-term immune destruction. Meanwhile, the shortage of human organ donors further limits its application. To find a new strategy, we tested a new polymer combination for islet encapsulation and transplantation. Meanwhile, we explored a new site for xenogeneic islet transplantation in mice.

METHOD

We synthesized a hydrogel combining alginate plus poly-ethylene-imine (Alg/PEI) for the encapsulation of rat, neonatal porcine, and human islets. Transplantation was performed into the retroperitoneal retro-colic space of diabetic mice. Control mice received free islets under the kidney capsule or encapsulated islets into the peritoneum. The biochemical indexes were measured, and the transplanted islets were harvested for immunohistochemical staining of insulin and glucagon.

RESULTS

Mice receiving encapsulated rat, porcine and human islets transplanted into the retroperitoneal space maintained normoglycemia for a median of 275, 145.5, and 146 days, respectively. In contrast, encapsulated xenogeneic islets transplanted into the peritoneum, maintained function for a median of 61, 95.5, and 82 days, respectively. Meanwhile, xenogeneic islets transplanted free into the kidney capsule lost their function within 3 days after transplantation. Immunohistochemical staining of encapsulated rat, porcine and human islets, retrieved from the retroperitoneal space, allowed to distinguish morphological normal insulin expressing β- and glucagon expressing α-cells at 70, 60, and 100 days post-transplant, respectively.

CONCLUSION

Transplantation of Alg/PEI encapsulated xenogeneic islets into the retroperitoneal space provides a valuable new implantation strategy for the treatment of type 1 diabetes.

Automated pancreatic islet viability assessment for transplantation using bright-field deep morphological signature

Islets transplanted for type-1 diabetes have their viability reduced by warm ischemia, dimethyloxalylglycine (DMOG; hypoxia model), oxidative stress and cytokine injury. This results in frequent transplant failures and the major burden of patients having to undergo multiple rounds of treatment for insulin independence. Presently there is no reliable measure to assess islet preparation viability prior to clinical transplantation. We investigated deep morphological signatures (DMS) for detecting the exposure of islets to viability compromising insults from brightfield images. Accuracies ranged from 98 % to 68 % for; ROS damage, pro-inflammatory cytokines, warm ischemia and DMOG. When islets were disaggregated to single cells to enable higher throughput data collection, good accuracy was still obtained (83-71 %). Encapsulation of islets reduced accuracy for cytokine exposure, but it was still high (78 %). Unsupervised modelling of the DMS for islet preparations transplanted into a syngeneic mouse model was able to predict whether or not they would restore glucose control with 100 % accuracy. Our strategy for constructing DMS' is effective for the assessment of islet pre-transplant viability. If translated into the clinic, standard equipment could be used to prospectively identify non-functional islet preparations unable to contribute to the restoration of glucose control and reduce the burden of unsuccessful treatments.

Adhesion Characteristics of Human Pancreatic Islets, Duct Epithelial Cells, and Acinar Cells to a Polymer Scaffold

We reported in 2018 that among several extracellular matrices, fibronectin, type I collagen, type IV collagen, laminin I, fibrinogen, and bovine serum albumin, fibronectin is particularly useful for adhesion of porcine pancreatic tissue. Subsequently, we developed a technology that enables the chemical coating of the constituent motifs of fibronectin onto cell culture dishes. In this experiment, we used islets (purity ≥ 90%), duct epithelial cells (purity ≥ 60%), and acinar cells (purity ≥ 99%) isolated from human pancreas according to the Edmonton protocol published in 2000 and achieved adhesion to the constituent motifs of fibronectin. A solution including cGMP Prodo Islet Media was used as the assay solution. In islets, adhesion was enhanced with the constitutive motifs of fibronectin compared with uncoated islets. In the functional evaluation of islets, insulin mRNA expression and insulin secretion were enhanced by the constitutive motif of fibronectin compared with non-coated islets. The stimulation index was comparable between non-coated islets and fibronectin motifs. In duct epithelial cells, adhesion was mildly promoted by the fibronectin component compared with non-coated component, while in acinar cells, adhesion was inhibited by the fibronectin component compared with the non-coated component. These data suggest that the constitutive motifs of fibronectin are useful for the adhesion of islets and duct epithelial cells.

High bicarbonate concentration increases glucose-induced insulin secretion in pancreatic β-cells

Low serum bicarbonate is closely related to type 2 diabetes mellitus. However, the precise role of bicarbonate on glucose homeostasis and insulin secretion remains unknown. In this study, we investigated the effects of bicarbonate concentration on pancreatic β-cells. It was observed that the high bicarbonate concentration of the cell culture medium significantly increased the glucose-induced insulin secretion (GSIS) levels in mouse islets, MIN6, and the INS-1E β cells. MIN6 cells presented an impaired GSIS; the cells produced a lower bicarbonate concentration when co-cultured with Capan-1 than when with CFPAC-1. NBCe1, a major bicarbonate transporter was observed to block the increasing insulin secretions, which were promoted by a high concentration of bicarbonate. In addition, higher extracellular bicarbonate concentration significantly increased the intracellular cAMP level, pHi, and calcium concentration with a 16.7 mM of glucose stimulation. Further study demonstrated that a low concentration of extracellular bicarbonate significantly impaired the functioning of pancreatic β cells by reducing coupling Ca²⁺ influx, whose process may be modulated by NBCe1. Taken together, our results conclude that bicarbonate may serve as a novel target in diabetes prevention-related research.

Engineering islets from stem cells for advanced therapies of diabetes

Diabetes mellitus is a metabolic disorder that affects more than 460 million people worldwide. Type 1 diabetes (T1D) is caused by autoimmune destruction of β-cells, whereas type 2 diabetes (T2D) is caused by a hostile metabolic environment that leads to β-cell exhaustion and dysfunction. Currently, first-line medications treat the symptomatic insulin resistance and hyperglycaemia, but do not prevent the progressive decline of β-cell mass and function. Thus, advanced therapies need to be developed that either protect or regenerate endogenous β-cell mass early in disease progression or replace lost β-cells with stem cell-derived β-like cells or engineered islet-like clusters. In this Review, we discuss the state of the art of stem cell differentiation and islet engineering, reflect on current and future challenges in the area and highlight the potential for cell replacement therapies, disease modelling and drug development using these cells. These efforts in stem cell and regenerative medicine will lay the foundations for future biomedical breakthroughs and potentially curative treatments for diabetes.

Pancreatic β Cells Inhibit Glucagon Secretion from α Cells: An In Vitro Demonstration of α-β Cell Interaction

Interactions between endocrine α and β cells are critical to their secretory function in vivo. The interactions are highly regulated, although yet to be fully understood. In this study, we aim to assess the impact of α and β cell co-culture on hormone secretion. Mouse clonal cell lines α-TC6-1 (α cell line) and MIN-6 (β cell line) were cultured independently or in combination in a medium containing 5.5, 11.1, or 25 mM glucose, respectively. After 72 h, hormone release was measured using insulin and glucagon secretion assays, the cell distribution was visualized by inverted microscopy and an immunocytochemistry assay, and changes in gene expressions were assessed using the RT-PCR technique. The co-culture of the two cell lines caused a decrease in glucagon secretion from α-TC1-6 cells, while no effect on insulin secretion from MIN-6 cells was revealed. Both types of cells were randomly scattered throughout the culture flask, unlike in mice islets in vivo where β cells cluster in the core and α cells are localized at the periphery. During the α-β cell co-culture, the gene expression of glucagon (Gcg) decreased significantly. We conclude that islet β cells suppress glucagon secretion from α cells, apparently via direct cell-to-cell contact, of which the molecular mechanism needs further verification.

Optimal allogeneic islet dose for transplantation in insulin-dependent diabetic Macaca fascicularis monkeys

Many groups are working to improve the results of clinical allogeneic islet transplantation in a primate model. However, few studies have focused on the optimal islet dose for achieving normal glycemia without exogenous insulin after transplantation in primate models or on the relationship between rejection and islet amyloid polypeptide (IAPP) expression. We evaluated the dose (10,000, 20,000, and > 25,000 islet equivalents (IEQ)/kg) needed to achieve normal glycemia without exogenous insulin after transplantation using eleven cynomolgus monkeys, and we analyzed the characteristics exhibited in the islets after transplantation. 10,000 IEQ/kg (N = 2) failed to control blood glucose level, despite injection with the highest dose of exogenous insulin, and 20,000 IEQ/kg group (N = 5) achieved unstable control, with a high insulin requirement. However, 25,000 IEQ/kg (N = 4) achieved normal glycemia without exogenous insulin and maintained it for more than 60 days. Immunohistochemistry results from staining islets found in liver biopsies indicated that as the number of transplanted islets decreased, the amount of IAPP accumulation within the islets increased, which accelerated CD3⁺ T cell infiltration. In conclusion, the optimal transplantation dose for achieving a normal glycemia without exogenous insulin in our cynomolgus monkey model was > 25,000 IEQ/kg, and the accumulation of IAPP early after transplantation, which depends on the transplanted islet dose, can be considered one factor in rejection.

A Practical Guide to Rodent Islet Isolation and Assessment Revisited

Insufficient insulin secretion is a key component of both type 1 and type 2 diabetes. Since insulin is released by the islets of Langerhans, obtaining viable and functional islets is critical for research and transplantation. The effective and efficient isolation of these small islands of endocrine cells from the sea of exocrine tissue that is the rest of the pancreas is not necessarily simple or quick. Choosing and administering the digestive enzyme, separation of the islets from acinar tissue, and culture of islets are all things that must be considered. The purpose of this review is to provide a history of the development of islet isolation procedures and to serve as a practical guide to rodent islet research for newcomers to islet biology. We discuss key elements of mouse islet isolation including choosing collagenase, the digestion process, purification of islets using a density gradient, and islet culture conditions. In addition, this paper reviews techniques for assessing islet viability and function such as visual assessment, glucose-stimulated insulin secretion and intracellular calcium measurements. A detailed protocol is provided that describes a common method our laboratory uses to obtain viable and functional mouse islets for in vitro study. This review thus provides a strong foundation for successful procurement and purification of high-quality mouse islets for research purposes.

Use of Culture to Reach Metabolically Adequate Beta-cell Dose by Combining Donor Islet Cell Isolates for Transplantation in Type 1 Diabetes Patients

BACKGROUND

Clinical islet transplantation is generally conducted within 72 hours after isolating sufficient beta-cell mass. A preparation that does not meet the sufficient dose can be cultured until this is reached after combination with subsequent ones. This retrospective study examines whether metabolic outcome is influenced by culture duration.

METHODS

Forty type 1 diabetes recipients of intraportal islet cell grafts under antithymocyte globulin induction and mycophenolate mofetil-tacrolimus maintenance immunosuppression were analyzed. One subgroup (n = 10) was transplanted with preparations cultured for ≥96 hours; in the other subgroup (n = 30) grafts contained similar beta-cell numbers but included isolates that were cultured for a shorter duration. Both subgroups were compared by numbers with plasma C-peptide ≥0.5 ng/mL, low glycemic variability associated with C-peptide ≥1.0 ng/mL, and with insulin independence.

RESULTS

The subgroup with all cells cultured ≥96 hours exhibited longer C-peptide ≥0.5 ng/mL (103 versus 48 mo; P = 0.006), and more patients with low glycemic variability and C-peptide ≥1.0 ng/mL, at month 12 (9/10 versus 12/30; P = 0.005) and 24 (7/10 versus 6/30; P = 0.007). In addition, 9/10 became insulin-independent versus 15/30 (P = 0.03). Grafts with all cells cultured ≥96 hours did not contain more beta cells but a higher endocrine purity (49% versus 36%; P = 0.03). In multivariate analysis, longer culture duration and older recipient age were independently associated with longer graft function.

CONCLUSIONS

Human islet isolates with insufficient beta-cell mass for implantation within 72 hours can be cultured for 96 hours and longer to combine multiple preparations in order to reach the desired beta-cell dose and therefore result in a better metabolic benefit.

The Effect of Recovery Warm-up Time Following Cold Storage on the Dynamic Glucose-stimulated Insulin Secretion of Isolated Human Islets

Standardized islet characterization assays that can provide results in a timely manner are essential for successful islet cell transplantation. A critical component of islet cell quality is β-cell function, and perifusion-based assessments of dynamic glucose-stimulated insulin secretion (GSIS) are the most informative method to assess this, as they provide the most complex in vitro evaluation of GSIS. However, protocols used vary considerably among centers and investigators as they often use different low- and high-glucose concentrations, exposure-times, flow-rates, oxygen concentrations, islet numbers, analytical methods, measurement units, and instruments, which result in different readouts and make comparisons across platforms difficult. Additionally, the conditions of islet storage and shipment prior to assessment may also affect islet function. Establishing improved standardized protocols for perifusion GSIS assays should be an integral part of the ongoing effort to increase the rigor of human islet studies. Here, we performed detailed evaluation of GSIS of human islets using a fully automated multichannel perifusion instrument following various warm-up recovery times after cold storage that corresponds to current shipping conditions (8°C). We found that recovery times shorter than 18 h (overnight) resulted in impaired insulin secretion. While the effects were relatively moderate on second-phase insulin secretion, first-phase peaks were restored only following 18-h incubation. Hence, the biphasic profile of dynamic GSIS was considerably affected when islets were not allowed to recover for a sufficient time after being maintained in cold. Accordingly, while cold storage might improve islet cell survival during shipment and prolong the length of culture, functional assessments should be performed only after allowing for at least overnight recovery at physiological temperatures.

Therapeutic potential of mesenchymal stem cells in treating both types of diabetes mellitus and associated diseases

Diabetes mellitus is a common lifestyle disease which can be classified into type 1 diabetes mellitus and type 2 diabetes mellitus. While both result in hyperglycemia due to lack of insulin action and further associated chronic ailments, there is a marked distinction in the cause for each type due to which both require a different prophylaxis. As observed, type 1 diabetes is caused due to the autoimmune action of the body resulting in the destruction of pancreatic islet cells. On the other hand, type 2 diabetes is caused either due to insulin resistance of target cells or lack of insulin production as per physiological requirements. Attempts to cure the disease have been made by bringing drastic changes in the patients' lifestyle; parenteral administration of insulin; prescription of drugs such as biguanides, meglitinides, and amylin; pancreatic transplantation; and immunotherapy. While these attempts cause a certain degree of relief to the patient, none of these can cure diabetes mellitus. However, a new treatment strategy led by the discovery of mesenchymal stem cells and their unique immunomodulatory and multipotent properties has inspired therapies to treat diabetes by essentially reversing the conditions causing the disease. The current review aims to enumerate the role of various mesenchymal stem cells and the different approaches to treat both types of diabetes and its associated diseases as well.

Pancreas-on-a-Chip Technology for Transplantation Applications

PURPOSE OF REVIEW

Human pancreas-on-a-chip (PoC) technology is quickly advancing as a platform for complex in vitro modeling of islet physiology. This review summarizes the current progress and evaluates the possibility of using this technology for clinical islet transplantation.

RECENT FINDINGS

PoC microfluidic platforms have mainly shown proof of principle for long-term culturing of islets to study islet function in a standardized format. Advancement in microfluidic design by using imaging-compatible biomaterials and biosensor technology might provide a novel future tool for predicting islet transplantation outcome. Progress in combining islets with other tissue types gives a possibility to study diabetic interventions in a minimal equivalent in vitro environment. Although the field of PoC is still in its infancy, considerable progress in the development of functional systems has brought the technology on the verge of a general applicable tool that may be used to study islet quality and to replace animal testing in the development of diabetes interventions.

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.

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.

Endodermal differentiation of human induced pluripotent stem cells using simple dialysis culture system in suspension culture

A differentiation of human induced pluripotent stem cells (hiPSCs) into definitive endoderm linage is required for a preparation of metabolic organ derived cells. The differentiation consumed high-priced cytokines and small molecules, which have hampered the manufacturability of differentiated cells. Although the cytokines and small molecules are remained or cells produce the autocrine factors, daily culture medium change should be proceeded to remove toxic metabolites generated from cells. In this study, we developed a simple dialysis culture system to refine the medium during definitive endodermal differentiation. We demonstrated that dialysis culture prevented cell damage to remove lactate. The hiPSCs cultured with dialysis also differentiated similarly as usual differentiation without dialysis even if they were not supplied Activin A for latter culture days in the differentiation. With this dialysis culture system, hiPSCs were differentiated into endodermal lineage with medium refinement and recycling and autocrine factors as well as cytokines, which may lead to reduce differentiation cost.

A novel fast-slow model of diabetes progression: Insights into mechanisms of response to the interventions in the Diabetes Prevention Program

Several models for the long-term development of T2DM already exist, focusing on the dynamics of the interaction between glycemia, insulinemia and β-cell mass. Current models consider representative (fasting or daily average) glycemia and insulinemia as characterizing the compensation state of the subject at some instant in slow time. This implies that only these representative levels can be followed through time and that the role of fast glycemic oscillations is neglected. An improved model (DPM15) for the long-term progression of T2DM is proposed, introducing separate peripheral and hepatic (liver and kidney) insulin actions. The DPM15 model no longer uses near-equilibrium approximation to separate fast and slow time scales, but rather describes, at each step in slow time, a complete day in the life of the virtual subject in fast time. The model can thus represent both fasting and postprandial glycemic levels and describe the effect of interventions acting on insulin-enhanced tissue glucose disposal or on insulin-inhibited hepatic glucose output, as well as on insulin secretion and β-cell replicating ability. The model can simulate long-term variations of commonly used clinical indices (HOMA-B, HOMA-IR, insulinogenic index) as well as of Oral Glucose Tolerance or Euglycemic Hyperinsulinemic Clamp test results. The model has been calibrated against observational data from the Diabetes Prevention Program study: it shows good adaptation to observations as a function of very plausible values of the parameters describing the effect of such interventions as Placebo, Intensive LifeStyle and Metformin administration.

Concentration-Dependency and Time Profile of Insulin Secretion: Dynamic Perifusion Studies With Human and Murine Islets

The detailed characterization and quantification of the kinetics of glucose-stimulated insulin secretion (GSIS) by normal pancreatic islets is of considerable interest for characterizing β-cell dysfunction, assessing the quality of isolated islets, and improving the design of artificial pancreas devices. Here, we performed dynamic evaluation of GSIS by human and mouse islets at high temporal resolution (every minute) in response to different glucose steps using an automated multichannel perifusion instrument. In both species, insulin responses were biphasic (a transient first-phase peak followed by a sustained second-phase), and the amount of insulin released showed a sigmoid-type dependence on glucose concentration. However, compared to murine islets, human islets have (1) a less pronounced first-phase response, (2) a flat secretion rate during second-phase response, (3) a left-shifted concentration response (reaching half-maximal response at 7.9 ± 0.4 vs. 13.7 ± 0.6 mM), and (4) an ~3-fold lower maximal secretion rate (8.3 ± 2.3 vs. 23.9 ± 5.1 pg/min/islet at 30 mM glucose). These results can be used to establish a more informative protocol for the calculation of the stimulation index, which is widely used for islet assessment in both research and clinical applications, but without an accepted standard or clear evidence as to what low- to high-glucose steps can provide better characterization of islet function. Data obtained here suggest that human islet functionality might be best characterized with a dynamic stimulation index obtained with a glucose step from a low of 4-5 to a high of 14-17 mM (e.g., G4 → G16).

Pancreatic ductal cells may have a negative effect on human islet transplantation

AIM

To evaluate the effect of pancreatic ductal cells on experimental human islet transplantation.

MATERIALS AND METHODS

Isolated islets were additionally purified by handpicking. Ductal cells were purified by magnetic cell sorting and then clustered into ductal pancreatospheres (DPS). Islets, DPS, and islets + DPS (100 islets + 75 DPS, or 100 islets + 200 DPS) were cultured and glucose-stimulated insulin secretion, β-cell apoptosis, and gene expression was determined. Islets and islets + DPS preparations (800 islets + 600 DPS) were transplanted to streptozotocin-treated immunodeficient mice and glycemia, graft morphometry, and gene expression were determined.

RESULTS

Insulin stimulation index was higher in islets than in islets co-cultured with DPS (5.59 ± 0.93 vs 4.02 ± 0.46; p<0.05). IL1B and CXCL11 expression was higher in 100 islets + 200 DPS than in islets (p<0.01), and IL-1β was detected in supernatants collected from DPS and islets + DPS preparations, but not in islets. Hyperglycemia developed in 33% and 67% of mice transplanted with islets or with islets + DPS respectively. β-cell mass was 26% lower in islets + DPS than in islets grafts (p>0.05), and the ratio β-/endocrine non-β-cell mass was lower in islets + DPS grafts (islets: 2.05 ± 0.18, islets + DPS: 1.35 ± 0.15; p<0.01). IL1B and IL1RN expression was significantly higher in islets + DPS grafts.

CONCLUSIONS

Islet preparations enriched with ductal cells have a lower insulin stimulation index in vitro and achieved a worse metabolic outcome after transplantation. Inflammation may mediate the deleterious effects of ductal cells on islet cells.

Induction of Expandable Tissue-Specific Progenitor Cells from Human Pancreatic Tissue through Transient Expression of Defined Factors

We recently demonstrated the generation of mouse induced tissue-specific stem (iTS) cells through transient overexpression of reprogramming factors combined with tissue-specific selection. Here we induced expandable tissue-specific progenitor (iTP) cells from human pancreatic tissue through transient expression of genes encoding the reprogramming factors OCT4 (octamer-binding transcription factor 4), p53 small hairpin RNA (shRNA), SOX2 (sex-determining region Y-box 2), KLF4 (Kruppel-like factor 4), L-MYC, and LIN28. Transfection of episomal plasmid vectors into human pancreatic tissue efficiently generated iTP cells expressing genetic markers of endoderm and pancreatic progenitors. The iTP cells differentiated into insulin-producing cells more efficiently than human induced pluripotent stem cells (iPSCs). iTP cells continued to proliferate faster than pancreatic tissue cells until days 100-120 (passages 15-20). iTP cells subcutaneously inoculated into immunodeficient mice did not form teratomas. Genomic bisulfite nucleotide sequence analysis demonstrated that the OCT4 and NANOG promoters remained partially methylated in iTP cells. We compared the global gene expression profiles of iPSCs, iTP cells, and pancreatic cells (islets >80%). Microarray analyses revealed that the gene expression profiles of iTP cells were similar, but not identical, to those of iPSCs but different from those of pancreatic cells. The generation of human iTP cells may have important implications for the clinical application of stem/progenitor cells.

Influence of organ donor attributes and preparation characteristics on the dynamics of insulin secretion in isolated human islets

In vitro studies of human pancreatic islets are critical for understanding normal insulin secretion and its perturbations in diabetic β-cells, but the influence of islet preparation characteristics and organ donor attributes in such experiments is poorly documented. Preparations from normal donors were tested with a standardized protocol evaluating dynamic insulin secretion induced by glucose, tolbutamide, and cAMP (forskolin). Secretion rates, normalized to insulin content (fractional insulin secretion), were analyzed as a function of preparation and donor characteristics. Low purity (25-45%) of the preparation (n = 8) blunted the first phase of insulin secretion induced by glucose or tolbutamide and increased basal secretion, resulting in threefold lower stimulation index than in more pure (55-95%) preparations (n = 43). In these more pure preparations, cold ischemia time (1-13 h) before pancreas digestion did not impact insulin secretion. Islet size (estimated by the islet size index) did not influence the dynamics of secretion, but fractional insulin secretion rates were greater in large than small islets, and positively correlated with islet size. Age of the donors (20-68 years) had no influence on islet size and insulin content or on dynamics and amplitude of insulin secretion, which were also similar in islets from male and female donors. In contrast, islet size and islet insulin content (normalized for size), and basal or stimulated insulin secretion positively correlated with Body-Mass Index (19-33). These results contradict previous reports on the impact of donor age and islet size and point to possible confounding effects of donor BMI in insulin secretion studies with isolated human islets.

Type 1 Diabetes Mellitus reversal via implantation of magnetically purified microencapsulated pseudoislets

Microencapsulation of pancreatic islets for the treatment of Type I Diabetes Mellitus (T1DM) generates a high quantity of empty microcapsules, resulting in high therapeutic graft volumes that can enhance the host's immune response. We report a 3D printed microfluidic magnetic sorting device for microcapsules purification with the objective to reduce the number of empty microcapsules prior transplantation. In this study, INS1E pseudoislets were microencapsulated within alginate (A) and alginate-poly-L-lysine-alginate (APA) microcapsules and purified through the microfluidic device. APA microcapsules demonstrated higher mechanical integrity and stability than A microcapsules, showing better pseudoislets viability and biological function. Importantly, we obtained a reduction of the graft volume of 77.5% for A microcapsules and 78.6% for APA microcapsules. After subcutaneous implantation of induced diabetic Wistar rats with magnetically purified APA microencapsulated pseudoislets, blood glucose levels were restored into normoglycemia (<200 mg/dL) for almost 17 weeks. In conclusion, our described microfluidic magnetic sorting device represents a great alternative approach for the graft volume reduction of microencapsulated pseudoislets and its application in T1DM disease.

Characterization of induced tissue-specific stem cells from pancreas by a synthetic self-replicative RNA

Induced pluripotent stem (iPS) cells have significant implications for overcoming most of the ethical issues associated with embryonic stem (ES) cells. Furthermore, our recent study demonstrated the generation of induced tissue-specific stem (iTS) cells by transient overexpression of the reprogramming factors using a plasmid combined with tissue-specific selection. In this study, we were able to generate RNA-based iTS cells that utilize a single, synthetic, self-replicating VEE-RF RNA replicon expressing four reprogramming factors (OCT4, KLF4, SOX2, and GLIS1). A single VEE-RF RNA transfection into mouse pancreatic tissue resulted in efficient generation of iTS cells from pancreas (iTS-P cells) with genetic markers of endoderm and pancreatic progenitors and differentiation into insulin-producing cells more efficiently than ES cells. Subcutaneous transplantation of iTS-P cells into immunodeficient mice resulted in no teratoma formation. Bisulfite genomic sequencing demonstrated that the promoters of Oct4 and Nanog remained partially methylated in iTS-P cells. We compared the global gene-expression profiles of ES cells, iTS-P cells, and pancreatic islets. Microarray analyses confirmed that the iTS-P cells were similar but not identical to ES cells compared with islets. These data suggest that iTS-P cells are cells that inherit numerous components of epigenetic memory from pancreas cells and acquire self-renewal potential. The generation of iTS cells may have important implications for the clinical application of stem cells.

A Comparison of Pancreatic Islet Purification using Iodixanol with University of Wisconsin Solution and with Na-Lactobionate and Histidine Solution

Purification of pancreatic islets is an important step in islet isolation for islet transplantation. In this study, to investigate how a solution composed mainly of Na-lactobionate and histidine (HL) influences the purification of islets, iodixanol was added to a purified solution for porcine islet isolation. A solution (IU) made by adding iodixanol to University of Wisconsin solution and a solution (IHL) made by adding iodixanol to HL solution were used to evaluate the islet isolation performance. We noted no significant differences between the two purification methods with regard to the islet yield, survival rate or purity, score, or stimulation index. These results show that IHL solution is as useful as IU solution for islet purification.

Selective Osmotic Shock for Islet Isolation in the Cadaveric Canine Pancreas

Currently, islet isolation is performed using harsh collagenases that cause nonspecific injury to both islets and exocrine tissue, negatively affecting the outcome of cell transplantation. We evaluated a novel islet isolation protocol utilizing high concentrations of glucose to cause selective osmotic shock (SOS). Islets have a membrane glucose transporter that allows adaptation to changes in glucose concentrations while exocrine tissue can be selectively destroyed by these osmolar shifts. Canine pancreata were obtained within 15 min after euthanasia from animals ( n = 6) euthanized for reasons unrelated to this study. Each pancreas was divided into 4 segments that were randomized to receive 300 mOsm glucose for 20 min (group 1), 600 mOsm for 20 min (group 2), 300 mOsm for 40 min (group 3), or 600 mOsm for 40 min (group 4). Islet yield, purity, and viability were compared between groups. Mean ± standard error of the mean islet yield for groups 1 to 4 was 428 ± 159, 560 ± 257, 878 ± 443, and 990 ± 394 islet equivalents per gram, respectively. Purity ranged from 37% to 45% without the use of density gradient centrifugation and was not significantly different between groups. Islet cell viability was excellent overall (89%) and did not differ between treatment protocol. Islet function was best in groups treated with 300 mOsm of glucose (stimulation index [SI] = 3.3), suggesting that the lower concentration of glucose may be preferred for use in canine islet isolation. SOS provides a widely available means for researchers to isolate canine islets for use in islet transplantation or in studies of canine islet physiology.

Adhesion characteristics of porcine pancreatic islets and exocrine tissue to coating materials

Since the report of the Edmonton protocol in 2000, islet transplantation has been implemented worldwide, and xenotransplantation using porcine islets has also been reported. In addition, many basic experiments using pancreatic islets and exocrine tissue after isolation have been reported. Recently, exocrine cells have been found to be essential for inducing the differentiation of pancreatic islets. Therefore, the importance of the culture conditions for pancreatic tissue when conducting experiments using pancreatic tissue is also increasing. In this study, we focused on the coat material and examined the adhesive properties of porcine pancreatic islets and exocrine tissue after isolation. Porcine islet isolation was performed, and isolated islets (purity ≥95%) and exocrine tissue (purity ≥99%) were used to achieve adhesion to several extracellular matrixes, fibronectin, collagen type I, collagen type IV, laminin I, fibrinogen, and bovine serum albumin (BSA). DMEM with 0.5% FBS was used as the assay medium. For exocrine tissue, the adhesion was promoted in fibronectin, collagen type I, laminin I, and fibrinogen. The adhesive ability to fibronectin was more than twice that to BSA, while the adhesive ability to collagen type I, laminin I, and fibrinogen was less than twice that to BSA. For islets, the adhesive ability to fibronectin was weaker than that of exocrine tissue. Furthermore, the adhesion effect in fibronectin was obtained within 30 minutes and in medium containing little serum for both islets and exocrine tissues. These data suggest that fibronectin may be useful for the adhesion of pancreatic tissue.

Polymeric nano-shielded islets with heparin-polyethylene glycol in a non-human primate model

Intraportal pancreatic islet transplantation incurs huge cell losses during its early stages due to instant blood-mediated inflammatory reactions (IBMIRs), which may also drive regulation of the adaptive immune system. Therefore, a method that evades IBMIR will improve clinical islet transplantation. We used a layer-by-layer approach to shield non-human primate (NHP) islets with polyethylene glycol (nano-shielded islets, NSIs) and polyethylene glycol plus heparin (heparin nano-shielded islets; HNSIs). Islets ranging from 10,000 to 20,000 IEQ/kg body weight were transplanted into 19 cynomolgus monkeys (n = 4, control; n = 5, NSI; and n = 10, HNSI). The mean C-peptide positive graft survival times were 68.5, 64 and 108 days for the control, NSI and HNSI groups, respectively (P = 0.012). HNSI also reduced the factors responsible for IBMIR in vitro. Based on these data, HNSIs in conjunction with clinically established immunosuppressive drug regimens will result in superior outcomes compared to those achieved with the current protocol for clinical islet transplantation.

Purity of islet preparations and 5-year metabolic outcome of allogenic islet transplantation

In allogenic islet transplantation (IT), high purity of islet preparations and low contamination by nonislet cells are generally favored. The aim of the present study was to analyze the relation between the purity of transplanted preparations and graft function during 5 years post-IT. Twenty-four patients with type 1 diabetes, followed for 5 years after IT, were enrolled. Metabolic parameters and daily insulin requirements were compared between patients who received islet preparations with a mean purity <50% (LOW purity) or ≥50% (HIGH purity). We also analyzed blood levels of carbohydrate antigen 19-9 (CA 19-9)-a biomarker of pancreatic ductal cells-and glucagon, before and after IT. At 5 years, mean hemoglobin A1c (HbA1c levels) (P = .01) and daily insulin requirements (P = .03) were lower in the LOW purity group. Insulin independence was more frequent in the LOW purity group (P < .05). CA19-9 and glucagon levels increased post-IT (P < .0001) and were inversely correlated with the degree of purity. Overall, our results suggest that nonislet cells have a beneficial effect on long-term islet graft function, possibly through ductal-to-endocrine cell differentiation. ClinicalTrial.gov NCT00446264 and NCT01123187.

Mesenchymal stromal cells improve human islet function through released products and extracellular matrix

AIMS

The aims of the present study were (i) to determine whether the reported beneficial effects of mesenchymal stromal cells (MSCs) on mouse islet function extend to clinically relevant human tissues (islets and MSCs), enabling translation into improved protocols for clinical human islet transplantation; and (ii) to identify possible mechanisms through which human MSCs influence human islet function.

MATERIALS AND METHODS

Human islets were co-cultured with human adipose tissue-derived MSCs (hASCs) or pre-treated with its products - extracellular matrix (ECM) and annexin A1 (ANXA1). Mouse islets were pre-treated with mouse MSC-derived ECM. Islet insulin secretory function was assessed in vitro by radioimmunoassay. Quantitative RT-PCR was used to screen human adipMSCs for potential ligands of human islet G-protein-coupled receptors.

RESULTS

We show that co-culture with hASCs improves human islet secretory function in vitro, as measured by glucose-stimulated insulin secretion, confirming previous reports using rodent tissues. Furthermore, we demonstrate that these beneficial effects on islet function can be partly attributed to the MSC-derived products ECM and ANXA1.

CONCLUSIONS

Our results suggest that hASCs have the potential to improve the quality of human islets isolated for transplantation therapy of Type 1 diabetes. Furthermore, it may be possible to achieve improvements in human islet quality in a cell-free culture system by using the MSC-derived products ANXA1 and ECM.

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

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

The quest to make fully functional human pancreatic beta cells from embryonic stem cells: climbing a mountain in the clouds

The production of fully functional insulin-secreting cells to treat diabetes is a major goal of regenerative medicine. In this article, I review progress towards this goal over the last 15 years from the perspective of a beta cell biologist. I describe the current state-of-the-art, and speculate on the general approaches that will be required to identify and achieve our ultimate goal of producing functional beta cells. The need for deeper phenotyping of heterogeneous cultures of stem cell derived islet-like cells in parallel with a better understanding of the heterogeneity of the target cell type(s) is emphasised. This deep phenotyping should include high-throughput single-cell analysis, as well as comprehensive 'omics technologies to provide unbiased characterisation of cell products and human beta cells. There are justified calls for more detailed and well-powered studies of primary human pancreatic beta cell physiology, and I propose online databases of standardised human beta cell responses to physiological stimuli, including both functional and metabolomic/proteomic/transcriptomic profiles. With a concerted, community-wide effort, including both basic and applied scientists, beta cell replacement will become a clinical reality for patients with diabetes.

Bioengineering the Endocrine Pancreas: Intraomental Islet Transplantation Within a Biologic Resorbable Scaffold

Transplantation of pancreatic islets is a therapeutic option to preserve or restore β-cell function. Our study was aimed at developing a clinically applicable protocol for extrahepatic transplantation of pancreatic islets. The potency of islets implanted onto the omentum, using an in situ-generated adherent, resorbable plasma-thrombin biologic scaffold, was evaluated in diabetic rat and nonhuman primate (NHP) models. Intraomental islet engraftment in the biologic scaffold was confirmed by achievement of improved metabolic function and preservation of islet cytoarchitecture, with reconstitution of rich intrainsular vascular networks in both species. Long-term nonfasting normoglycemia and adequate glucose clearance (tolerance tests) were achieved in both intrahepatic and intraomental sites in rats. Intraomental graft recipients displayed lower levels of serum biomarkers of islet distress (e.g., acute serum insulin) and inflammation (e.g., leptin and α2-macroglobulin). Importantly, low-purity (30:70% endocrine:exocrine) syngeneic rat islet preparations displayed function equivalent to that of pure (>95% endocrine) preparations after intraomental biologic scaffold implantation. Moreover, the biologic scaffold sustained allogeneic islet engraftment in immunosuppressed recipients. Collectively, our feasibility/efficacy data, along with the simplicity of the procedure and the safety of the biologic scaffold components, represented sufficient preclinical testing to proceed to a pilot phase I/II clinical trial.

Pancreatic β Cell Mass Death

Type two diabetes (T2D) is a challenging metabolic disorder for which a cure has not yet been found. Its etiology is associated with several phenomena, including significant loss of insulin-producing, beta cell (β cell) mass via progressive programmed cell death and disrupted cellular autophagy. In diabetes, the etiology of β cell death and the role of mitochondria are complex and involve several layers of mechanisms. Understanding the dynamics of those mechanisms could permit researchers to develop an intervention for the progressive loss of β cells. Currently, diabetes research has shifted toward rejuvenation and plasticity technology and away from the simplified approach of hormonal compensation. Diabetes research is currently challenged by questions such as how to enhance cell survival, decrease apoptosis and replenish β cell mass in diabetic patients. In this review, we discuss evidence that β cell development and mass formation are guided by specific signaling systems, particularly hormones, transcription factors, and growth factors, all of which could be manipulated to enhance mass growth. There is also strong evidence that β cells are dynamically active cells, which, under specific conditions such as obesity, can increase in size and subsequently increase insulin secretion. In certain cases of aggressive or advanced forms of T2D, β cells become markedly impaired, and the only alternatives for maintaining glucose homeostasis are through partial or complete cell grafting (the Edmonton protocol). In these cases, the harvesting of an enriched population of viable β cells is required for transplantation. This task necessitates a deep understanding of the pharmacological agents that affect β cell survival, mass, and function. The aim of this review is to initiate discussion about the important signals in pancreatic β cell development and mass formation and to highlight the process by which cell death occurs in diabetes. This review also examines the attempts that have been made to recover or increase cell mass in diabetic patients by using various pharmacological agents.

β-Cell regeneration through the transdifferentiation of pancreatic cells: Pancreatic progenitor cells in the pancreas

Pancreatic progenitor cell research has been in the spotlight, as these cells have the potential to replace pancreatic β‐cells for the treatment of type 1 and 2 diabetic patients with the absence or reduction of pancreatic β‐cells. During the past few decades, the successful treatment of diabetes through transplantation of the whole pancreas or isolated islets has nearly been achieved. However, novel sources of pancreatic islets or insulin‐producing cells are required to provide sufficient amounts of donor tissues. To overcome this limitation, the use of pancreatic progenitor cells is gaining more attention. In particular, pancreatic exocrine cells, such as duct epithelial cells and acinar cells, are attractive candidates for β‐cell regeneration because of their differentiation potential and pancreatic lineage characteristics. It has been assumed that β‐cell neogenesis from pancreatic progenitor cells could occur in pancreatic ducts in the postnatal stage. Several studies have shown that insulin‐producing cells can arise in the duct tissue of the adult pancreas. Acinar cells also might have the potential to differentiate into insulin‐producing cells. The present review summarizes recent progress in research on the transdifferentiation of pancreatic exocrine cells into insulin‐producing cells, especially duct and acinar cells.

Sensing and Sensibility: Single-Islet-based Quality Control Assay of Cryopreserved Pancreatic Islets with Functionalized Hydrogel Microcapsules

Despite decades of research and clinical studies of islet transplantations, finding simple yet reliable islet quality assays that correlate accurately with in vivo potency is still a major challenge, especially for real-time and single-islet-based quality assessment. Herein, proof-of-concept studies of a cryopreserved microcapsule-based quality control assays are presented for single islets. Individual rat pancreatic islets and fluorescent oxygen-sensitive dye (FOSD) are encapsulated in alginate hydrogel microcapsules via a microfluidic device. To test the susceptibility of the microcapsules and the FOSD to cryopreservation, the islet microcapsules containing FOSD are cryopreserved and the islet functionalities (adenosine triphosphate, static insulin release measurement, and oxygen consumption rate) are assessed after freezing and thawing steps. The cryopreserved islet capsules with FOSD remain functional after encapsulation and freezing/thawing procedures, validating a simple yet reliable individual-islet-based quality control method for the entire islet processing procedure prior to transplantation. This work also demonstrates that the functionality of cryopreserved islets can be improved by introducing trehalose into the routinely used cryoprotectant dimethyl sulfoxide. The functionalized alginate hydrogel microcapsules with embedded FOSD and optimized cryopreservation protocol presented in this work serve as a versatile islet quality assay and offer tremendous promise for tackling existing challenges in islet transplantation procedures.

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.

Isolation and characterization of human islet stellate cells

BACKGROUND AND AIMS

We have previously demonstrated that islet stellate cells (ISCs) exhibiting a similar phenotype to classical pancreatic stellate cells (PSCs) could be isolated from rat islets, where they may contribute to islet fibrosis in type 2 diabetes mellitus (T2DM). This study was designed to determine whether human islets also contain ISC.

MATERIALS AND METHODS

Using standard explants techniques, human ISCs were enriched from freshly isolated human islets. Immunofluorescence visualization of markers for PSCs(α-smooth muscle actin;α-SMA), desmin, vimentin, glial fibrillary acidic protein (GFAP) was used to characterize the human ISC. Cell counting kit-8 (CCK-8) was used to assess the proliferation of ISC. The wound-healing assay and the transwell migration were used to assess the migration capacity of ISC. Immunofluorescence against collagen typesI (col-I), collagen typesIII (col-III) and fibronectin (FN) was performed to identify extracellular matrix (ECM) component synthesized by ISC. Adipogenic and osteogenic differentiation were tried to detected stem cell potential.

RESULTS

In culture, ISC with triangular shape grow out from human islets. The passaged ISC expressed α-SMA, desmin, vimentin, GFAP and was positive for col-I, col-III and FN. The proliferation and migration ability of ISC was significantly slower than those of PSC. And both the human PSC and ISC were able to differentiate in vitro into adipocyte- and osteoblast-like cells.

CONCLUSION

Similar to our previous rat experiment, the current study shows that human islets also contain ISC which is phenotypically similar but not identical to human PSC.

3-D imaging of islets in obesity: formation of the islet-duct complex and neurovascular remodeling in young hyperphagic mice

BACKGROUND

Obesity and insulin resistance lead to islet hyperplasia. However, how the islet remodeling influences the pancreatic environment and the associated neurovascular networks is largely unknown. The lack of information is primarily due to the difficulty of global visualization of the hyperplasic islet (>200 μm) and the neurovascular environment with high definition.

METHODS

We modulated the pancreatic optical property to achieve 3-dimensional (3-D) whole-islet histology and to integrate transmitted light microscopy (which provides the ground-truth tissue information) with confocal fluorescence imaging. The new optical and imaging conditions were used to globally examine the hyperplastic islets of the young (2 months) obese db/db and ob/ob mice, which otherwise cannot be easily portrayed by the standard microtome-based histology. The voxel-based islet micrographs were digitally processed for stereo projection and qualitative and quantitative analyses of the islet tissue networks.

RESULTS

Paired staining and imaging of the pancreatic islets, ducts and neurovascular networks reveal the unexpected formation of the 'neuro-insular-ductal complex' in the young obese mice. The complex consists of the peri- and/or intra-islet ducts and prominent peri-ductal sympathetic nerves; the latter contributes to a marked increase in islet sympathetic innervation. In vascular characterization, we identify a decreased perivascular density of the ob/ob islet pericytes, which adapt to ensheathing the dilated microvessels with hypertrophic processes.

CONCLUSIONS

Modulation of pancreatic optical property enables 3-D panoramic examination of islets in the young hyperphagic mice to reveal the formation of the islet-duct complex and neurovascular remodeling. On the basis of the morphological proximity of the remodeled tissue networks, we propose a reactive islet microenvironment consisting of the endocrine cells, ductal epithelium and neurovascular tissues in response to the metabolic challenge that is experienced early in life.

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.

Optimization and Scale-up Isolation and Culture of Neonatal Porcine Islets: Potential for Clinical Application

One challenge that must be overcome to allow transplantation of neonatal porcine islets (NPIs) to become a clinical reality is defining a reproducible and scalable protocol for the efficient preparation of therapeutic quantities of clinical grade NPIs. In our standard protocol, we routinely isolate NPIs from a maximum of four pancreases, requiring tissue culture in 16 Petri dishes (four per pancreas) in Ham's F10 and bovine serum albumin (BSA). We have now developed a scalable and technically simpler protocol that allows us to isolate NPIs from a minimum of 12 pancreases at a time by employing automated tissue chopping, collagenase digestion in a single vessel, and tissue culture/media changes in 75% fewer Petri dishes. For culture, BSA is replaced with human serum albumin and supplemented with Z-VAD-FMK general caspase inhibitor and a protease inhibitor cocktail. The caspase inhibitor was added to the media for only the first 90 min of culture. NPIs isolated using the scalable protocol had significantly more cellular insulin recovered (56.9 ± 1.4 µg) when compared to the standard protocol (15.0 ± 0.5 µg; p < 0.05). Compared to our standard protocol, recovery of β-cells (6.0 × 10(6) ± 0.2 vs. 10.0 × 10(6) ± 0.4; p < 0.05) and islet equivalents (35,135 ± 186 vs. 41,810 ± 226; p < 0.05) was significantly higher using the scalable protocol. During a static glucose stimulation assay, the SI of islets isolated by the standard protocol were significantly lower than the scale-up protocol (4.3 ± 0.2 vs. 5.5 ± 0.1; p < 0.05). Mice transplanted with NPIs using the scalable protocol had significantly lower blood glucose levels than the mice that receiving NPIs from the standard protocol (p < 0.01) and responded significantly better to a glucose tolerance test. Based on the above findings, this improved simpler scalable protocol is a significantly more efficient means for preparing therapeutic quantities of clinical grade NPIs.

Neurogenin 3 Expressing Cells in the Human Exocrine Pancreas Have the Capacity for Endocrine Cell Fate

Neurogenin 3 (NGN3) is necessary and sufficient for endocrine differentiation during pancreatic development and is expressed by a population of progenitor cells that give rise exclusively to hormone-secreting cells within islets. NGN3 protein can be detected in the adult rodent pancreas only following certain types of injury, when it is transiently expressed by exocrine cells undergoing reprogramming to an endocrine cell fate. Here, NGN3 protein can be detected in 2% of acinar and duct cells in living biopsies of histologically normal adult human pancreata and 10% in cadaveric biopsies of organ donor pancreata. The percentage and total number of NGN3+ cells increase during culture without evidence of proliferation or selective cell death. Isolation of highly purified and viable NGN3+ cell populations can be achieved based on coexpression of the cell surface glycoprotein CD133. Transcriptome and targeted expression analyses of isolated CD133+ / NGN3+ cells indicate that they are distinct from surrounding exocrine tissue with respect to expression phenotype and Notch signaling activity, but retain high level mRNA expression of genes indicative of acinar and duct cell function. NGN3+ cells have an mRNA expression profile that resembles that of mouse early endocrine progenitor cells. During in vitro differentiation, NGN3+ cells express genes in a pattern characteristic of endocrine development and result in cells that resemble beta cells on the basis of coexpression of insulin C-peptide, chromogranin A and pancreatic and duodenal homeobox 1. NGN3 expression in the adult human exocrine pancreas marks a dedifferentiating cell population with the capacity to take on an endocrine cell fate. These cells represent a potential source for the treatment of diabetes either through ex vivo manipulation, or in vivo by targeting mechanisms controlling their population size and endocrine cell fate commitment.

Plasma GAD65, a Marker for Early β-Cell Loss After Intraportal Islet Cell Transplantation in Diabetic Patients

CONTEXT AND OBJECTIVE

Intraportal islet transplantation can restore insulin production in type 1 diabetes patients, but its effect is subject to several interfering processes. To assess the influence of β-cell loss before and during engraftment, we searched for a real-time marker of β-cell destruction. Previous studies showed that 65-kDa isoform of glutamate decarboxylase (GAD65) is discharged by chemically damaged rat β-cells. We therefore examined the utility of the GAD65 assay to detect and quantify destruction of human β-cells in vitro and in vivo.

DESIGN AND PARTICIPANTS

A time-resolved fluorescence immunoassay was used to measure GAD65 discharge from β-cells after administration of toxins or after intraportal transplantation. The study in patients involved type 1 diabetes recipients of 56 implants.

RESULTS

GAD65 was discharged from cultured human β-cells between 4 and 24 hours after acute insult and proportional to the number of dying cells. It was also detected in plasma during the first 24 hours after intraportal transplantation of human islet cell grafts. Diabetic nude rat recipients without hyperglycemic correction exhibited higher plasma GAD65 levels than those with normalization. In type 1 diabetes recipients of grafts with 2-5 × 10(6) β-cells per kilogram of body weight, five of six with plasma GAD65 greater than 1 ng/mL failed to increase plasma C-peptide by greater than 0.5 ng/mL at posttransplant month 2, whereas five of six with undetectable plasma GAD 65 and 15 of 19 with intermediate levels did result in such increase.

CONCLUSION

Plasma GAD65 qualifies as a marker for early β-cell loss after intraportal transplantation. Further studies are needed to extend its clinical utility.

Human islet preparations distributed for research exhibit a variety of insulin-secretory profiles

Human islet research is providing new insights into human islet biology and diabetes, using islets isolated at multiple US centers from donors with varying characteristics. This creates challenges for understanding, interpreting, and integrating research findings from the many laboratories that use these islets. In what is, to our knowledge, the first standardized assessment of human islet preparations from multiple isolation centers, we measured insulin secretion from 202 preparations isolated at 15 centers over 11 years and noted five distinct patterns of insulin secretion. Approximately three quarters were appropriately responsive to stimuli, but one quarter were dysfunctional, with unstable basal insulin secretion and/or an impairment in stimulated insulin secretion. Importantly, the patterns of insulin secretion by responsive human islet preparations (stable Baseline and Fold stimulation of insulin secretion) isolated at different centers were similar and improved slightly over the years studied. When all preparations studied were considered, basal and stimulated insulin secretion did not correlate with isolation center, biological differences of the islet donor, or differences in isolation, such as Cold Ischemia Time. Dysfunctional islet preparations could not be predicted from the information provided by the isolation center and had altered expression of genes encoding components of the glucose-sensing pathway, but not of insulin production or cell death. These results indicate that insulin secretion by most preparations from multiple centers is similar but that in vitro responsiveness of human islets cannot be predicted, necessitating preexperimental human islet assessment. These results should be considered when one is designing, interpreting, and integrating experiments using human islets.

Development and Characterization of a Collagen-Based Matrix for Vascularization and Cell Delivery

Since the development of the Edmonton protocol, islet transplantation is increasingly encouraging as a treatment for type 1 diabetes. Strategies to ameliorate problems with the intraportal site include macroencapsulating the islets in diverse biomaterials. Characterization of these biomaterials is important to optimally tune the properties to support islets and promote vascularization. In this study, we characterize the cross-linker-dependent properties of collagen-based matrices containing chondroitin-6-sulfate, chitosan, and laminin, cross-linked with 7.5, 30, or 120 mM of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide. The swelling ratio was found to be significantly negatively correlated with increasing cross-linker concentrations (p<0.0001; R2=0.718). The matrix released insulin in a reproducible logarithmic manner (R2 of 0.99 for all concentrations), demonstrating cross-linker-dependent control of drug release. The matrices with the highest cross-linker concentrations resisted degradation by collagenase for longer than the lowest concentrations (58.13%±2.22% vs. 13.69%±7.67%; p<0.05). Scanning electron microscopy images of the matrices revealed that the matrices had uniform topography and porosity, indicating efficient cross-linking and incorporation of the polymer components. Matrices were transplanted subcutaneously in naive BALB/c mice, and the number and size of vessels were quantified using von Willebrand factor staining; matrices with higher cross-linking concentrations had significantly larger capillaries at every time point up to 4 weeks after transplantation compared to the lowest cross-linker concentration group. CD31 staining visualized the capillaries at each time point. Taken together, these data show that this collagen-based matrix is reproducible with cross-linking-dependent properties that can be optimized to support vascularization and islet function.