Detailed protocol for evaluation of dynamic perifusion of human islets to assess β-cell function

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.

A scalable human islet 3D-culture platform maintains cell mass and function long-term for transplantation

Present-day islet culture methods provide short-term maintenance of cell viability and function, limiting access to islet transplantation. Attempts to lengthen culture intervals remain unsuccessful. A new method was developed to permit the long-term culture of islets. Human islets were embedded in polysaccharide 3D-hydrogel in cell culture inserts or gas-permeable chambers with serum-free CMRL 1066 supplemented media for up to 8 weeks. The long-term cultured islets maintained better morphology, cell mass, and viability at 4 weeks than islets in conventional suspension culture. In fact, islets cultured in the 3D-hydrogel retained β cell mass and function on par with freshly isolated islets in vitro and, when transplanted into diabetic mice, restored glucose balance similar to fresh islets. Using gas-permeable chambers, the 3D-hydrogel culture method was scaled up over 10-fold and maintained islet viability and function, although the cell mass recovery rate was 50%. Additional optimization of scale-up methods continues. If successful, this technology could afford flexibility and expand access to islet transplantation, especially single-donor islet-after-kidney transplantation.

Short-term function and immune-protection of microencapsulated adult porcine islets with alginate incorporating CXCL12 in healthy and diabetic non-human primates without systemic immune suppression: A pilot study

Replacement of insulin-producing pancreatic beta-cells by islet transplantation offers a functional cure for type-1 diabetes (T1D). We recently demonstrated that a clinical grade alginate micro-encapsulant incorporating the immune-repellent chemokine and pro-survival factor CXCL12 could protect and sustain the integrity and function of autologous islets in healthy non-human primates (NHPs) without systemic immune suppression. In this pilot study, we examined the impact of the CXCL12 micro encapsulant on the function and inflammatory and immune responses of xenogeneic islets transplanted into the omental tissue bilayer sac (OB; n = 4) and diabetic (n = 1) NHPs. Changes in the expression of cytokines after implantation were limited to 2-6-fold changes in blood, most of which did not persist over the first 4 weeks after implantation. Flow cytometry of PBMCs following transplantation showed minimal changes in IFNγ or TNFα expression on xenoantigen-specific CD4+  or CD8+  T cells compared to unstimulated cells, and these occurred mainly in the first 4 weeks. Microbeads were readily retrievable for assessment at day 90 and day 180 and at retrieval were without microscopic signs of degradation or foreign body responses (FBR). In vitro and immunohistochemistry studies of explanted microbeads indicated the presence of functional xenogeneic islets at day 30 post transplantation in all biopsied NHPs. These results from a small pilot study revealed that CXCL12-microencapsulated xenogeneic islets abrogate inflammatory and adaptive immune responses to the xenograft. This work paves the way toward future larger scale studies of the transplantation of alginate microbeads with CXCL12 and porcine or human stem cell-derived beta cells or allogeneic islets into diabetic NHPs without systemic immunosuppression.

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.

Smartphone-microfluidic fluorescence imaging system for studying islet physiology

Smartphone technology has been recently applied for biomedical image acquisition and data analysis due to its high-quality imaging capability, and flexibility to customize multi-purpose apps. In this work, we developed and characterized a smartphone-microfluidic fluorescence imaging system for studying the physiology of pancreatic islets. We further evaluated the system capability by performing real-time fluorescence imaging on mouse islets labeled with either chemical fluorescence dyes or genetically encoded fluorescent protein indicators (GEFPIs). Our results showed that the system was capable of analyzing key beta-cell insulin stimulator-release coupling factors in response to various stimuli with high-resolution dynamics. Furthermore, the integration of a microfluidics allowed high-resolution detection of insulin secretion at single islet level. When compared to conventional fluorescence microscopes and macro islet perifusion apparatus, the system has the advantages of low cost, portable, and easy to operate. With all of these features, we envision that this smartphone-microfluidic fluorescence imaging system can be applied to study islet physiology and clinical applications.

Chronic marijuana usage by human pancreas donors is associated with impaired islet function

We investigated the effect of chronic marijuana use, defined as 4 times weekly for more than 3 years, on human pancreatic islets. Pancreata from deceased donors who chronically used marijuana were compared to those from age, sex and ethnicity matched non-users. The islets from marijuana-users displayed reduced insulin secretion as compared to islets from non-users upon stimulation with high glucose (AUC, 3.41 ± 0.62 versus 5.14 ±0.47, p<0.05) and high glucose plus KCl (AUC, 4.48 ± 0.41 versus 7.69 ± 0.58, p<0.001). When human islets from chronic marijuana-users were transplanted into diabetic mice, the mean reversal rate of diabetes was 35% versus 77% in animals receiving islets from non-users (p<0.01). Immunofluorescent staining for cannabinoid receptor type 1 (CB1R) was shown to be colocalized with insulin and enhanced significantly in beta cells from marijuana-users vs. non-users (CB1R intensity/islet area, 14.95 ± 2.71 vs. 3.23 ± 0.87, p<0.001). In contrast, CB1R expression was not co-localized with glucagon or somatostatin. Furthermore, isolated islets from chronic marijuana-users appeared hypertrophic. In conclusion, excessive marijuana use affects islet endocrine phenotype and function in vitro and in vivo. Given the increasing use of marijuana, our results underline the importance of including lifestyle when evaluating human islets for transplantation or research.

The potential of the incorporated collagen microspheres in alginate hydrogel as an engineered three-dimensional microenvironment to attenuate apoptosis in human pancreatic islets

BACKGROUND

Tissue engineering is considered as a promising tool for remodeling the native cells microenvironment. In the present study, the effect of alginate hydrogel and collagen microspheres integrated with extracellular matrix components were evaluated in the decrement of apoptosis in human pancreatic islets.

MATERIALS/METHODS

For three-dimensional culture, the islets were encapsulated in collagen microspheres, containing laminin and collagen IV and embedded in alginate scaffold for one week. After that the islets were examined in terms of viability, apoptosis, genes and proteins expression including BAX, BCL2, active caspase-3, and insulin. Moreover, the islets function was evaluated through glucose-induced insulin and C-peptide secretion assay. In order to evaluate the structure of the scaffolds and the morphology of the pancreatic islets in three-dimensional microenvironments, we performed scanning electron microscopy.

RESULTS

Our findings showed that the designed hydrogel scaffolds significantly improved the islets viability using the reduction of activated caspase-3 and TUNEL positive cells.

CONCLUSIONS

The reconstruction of the destructed matrix with alginate hydrogels and collagen microspheres might be an effective step to promote the culture of the islets.

β-Cell pre-mir-21 induces dysfunction and loss of cellular identity by targeting transforming growth factor beta 2 (Tgfb2) and Smad family member 2 (Smad2) mRNAs

OBJECTIVE

β-cell microRNA-21 (miR-21) is increased by islet inflammatory stress but it decreases glucose-stimulated insulin secretion (GSIS). Thus, we sought to define the effects of miR-21 on β-cell function using in vitro and in vivo systems.

METHODS

We developed a tetracycline-on system of pre-miR-21 induction in clonal β-cells and human islets, along with transgenic zebrafish and mouse models of β-cell-specific pre-miR-21 overexpression.

RESULTS

β-cell miR-21 induction markedly reduced GSIS and led to reductions in transcription factors associated with β-cell identity and increased markers of dedifferentiation, which led us to hypothesize that miR-21 induces β-cell dysfunction by loss of cell identity. In silico analysis identified transforming growth factor-beta 2 (Tgfb2) and Smad family member 2 (Smad2) mRNAs as predicted miR-21 targets associated with the maintenance of β-cell identity. Tgfb2 and Smad2 were confirmed as direct miR-21 targets through RT-PCR, immunoblot, pulldown, and luciferase assays. In vivo zebrafish and mouse models exhibited glucose intolerance, decreased peak GSIS, decreased expression of β-cell identity markers, increased insulin and glucagon co-staining cells, and reduced Tgfb2 and Smad2 expression.

CONCLUSIONS

These findings implicate miR-21-mediated reduction of mRNAs specifying β-cell identity as a contributor to β-cell dysfunction by the loss of cellular differentiation.

Glucose Response by Stem Cell-Derived β Cells In Vitro Is Inhibited by a Bottleneck in Glycolysis

Stem cell-derived β (SC-β) cells could provide unlimited human β cells toward a curative diabetes treatment. Differentiation of SC-β cells yields transplantable islets that secrete insulin in response to glucose challenges. Following transplantation into mice, SC-β cell function is comparable to human islets, but the magnitude and consistency of response in vitro are less robust than observed in cadaveric islets. Here, we profile metabolism of SC-β cells and islets to quantify their capacity to sense glucose and identify reduced anaplerotic cycling in the mitochondria as the cause of reduced glucose-stimulated insulin secretion in SC-β cells. This activity can be rescued by challenging SC-β cells with intermediate metabolites from the TCA cycle and late but not early glycolysis, downstream of the enzymes glyceraldehyde 3-phosphate dehydrogenase and phosphoglycerate kinase. Bypassing this metabolic bottleneck results in a robust, bi-phasic insulin release in vitro that is identical in magnitude to functionally mature human islets.

Glucose-stimulated insulin secretion is deficient in stem cell-derived β (SC-β) cells in vitro. Davis et al. use metabolomic analysis to define a glycolytic bottleneck inhibiting glucose metabolism and sensing in SC-β cells. Cell-permeable intermediates bypass this bottleneck, as does transplantation in vivo, producing insulin secretion indistinguishable from human islets.

Functional analysis of islet cells in vitro, in situ, and in vivo

The islet of Langerhans contains at least five types of endocrine cells producing distinct hormones. In response to nutrient or neuronal stimulation, islet endocrine cells release biochemicals including peptide hormones to regulate metabolism and to control glucose homeostasis. It is now recognized that malfunction of islet cells, notably insufficient insulin release of β-cells and hypersecretion of glucagon from α-cells, represents a causal event leading to hyperglycemia and frank diabetes, a disease that is increasing at an alarming rate to reach an epidemic level worldwide. Understanding the mechanisms regulating stimulus-secretion coupling and investigating how islet β-cells maintain a robust secretory activity are important topics in islet biology and diabetes research. To facilitate such studies, a number of biological systems and assay platforms have been developed for the functional analysis of islet cells. These technologies have enabled detailed analyses of individual islets at the cellular level, either in vitro, in situ, or in vivo.

A Versatile Model of Microfluidic Perifusion System for the Evaluation of C-Peptide Secretion Profiles: Comparison Between Human Pancreatic Islets and HLSC-Derived Islet-Like Structures

A robust and easy-to-use tool for the ex vivo dynamic evaluation of pancreatic islet (PI) function is essential for further development of novel cell-based therapeutic approaches to treating diabetes. Here, we developed four different glucose perifusion protocols (GPPs) in a microfluidic perifusion system (MPS), based entirely on commercially available components. After validation, the GPPs were used to evaluate C-peptide secretion profiles of PIs derived from different donors (healthy, obese, and type 2 diabetic) and from human liver stem-cell-derived islet-like structures (HLSC-ILS). Using this device, we demonstrated that PIs derived from healthy donors displayed a physiological C-peptide secretion profile as characterized by the response to (a) different glucose concentrations, (b) consecutive pulses of high-glucose concentrations, (c) a glucose threshold ranging from 5–8 mM, and (d) a constant high-glucose perifusion in a biphasic manner. Moreover, we were able to detect a dysregulated secretion profile in PIs derived from both obese and type 2 diabetes mellitus (T2DM) donors. Finally, we also evaluated the kinetic secretion profiles of HLSC-ILS, demonstrating that, nonetheless, with a lower amplitude of secretion compared to PI derived from healthy donors, they were already glucose-responsive on day seven post-differentiation. In conclusion, we have provided evidence that our MPS is a versatile device and may represent a valuable tool to study insulin-producing cells in vitro.

Targeted Derivation of Organotypic Glucose- and GLP-1-Responsive β Cells Prior to Transplantation into Diabetic Recipients

Generation of functional β cells from pluripotent sources would accelerate diagnostic and therapeutic applications for diabetes research and therapy. However, it has been challenging to generate competent β cells with dynamic insulin-secretory capacity to glucose and incretin stimulations. We introduced transcription factors, critical for β-cell development and function, in differentiating human induced pluripotent stem cells (PSCs) and assessed the impact on the functionality of derived β-cell (psBC) progeny. A perifusion system revealed stepwise transduction of the PDX1, NEUROG3, and MAFA triad (PNM) enabled in vitro generation of psBCs with glucose and GLP-1 responsiveness within 3 weeks. PNM transduction upregulated genes associated with glucose sensing, insulin secretion, and β-cell maturation. In recipient diabetic mice, PNM-transduced psBCs showed glucose-responsive insulin secretion as early as 1 week post transplantation. Thus, enhanced pre-emptive β-cell specification of PSCs by PNM drives generation of glucose- and incretin-responsive psBCs in vitro, offering a competent tissue-primed biotherapy.

Acquisition of Dynamic Function in Human Stem Cell-Derived β Cells

Recent advances in human pluripotent stem cell (hPSC) differentiation protocols have generated insulin-producing cells resembling pancreatic β cells. While these stem cell-derived β (SC-β) cells are capable of undergoing glucose-stimulated insulin secretion (GSIS), insulin secretion per cell remains low compared with islets and cells lack dynamic insulin release. Herein, we report a differentiation strategy focused on modulating transforming growth factor β (TGF-β) signaling, controlling cellular cluster size, and using an enriched serum-free media to generate SC-β cells that express β cell markers and undergo GSIS with first- and second-phase dynamic insulin secretion. Transplantation of these cells into mice greatly improves glucose tolerance. These results reveal that specific time frames for inhibiting and permitting TGF-β signaling are required during SC-β cell differentiation to achieve dynamic function. The capacity of these cells to undergo GSIS with dynamic insulin release makes them a promising cell source for diabetes cellular therapy.

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Development of differentiation protocol to β-like cells with enhanced function

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TGF-β signaling promotes acquisition of dynamic function in maturing β-like cells

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Transplanted cells rapidly restore glucose tolerance in mice

Pancreatic β-Cell Rest Replenishes Insulin Secretory Capacity and Attenuates Diabetes in an Extreme Model of Obese Type 2 Diabetes

The onset of common obesity-linked type 2 diabetes (T2D) is marked by exhaustive failure of pancreatic β-cell functional mass to compensate for insulin resistance and increased metabolic demand, leading to uncontrolled hyperglycemia. Here, the β-cell-deficient obese hyperglycemic/hyperinsulinemic KS db/db mouse model was used to assess consequential effects on β-cell functional recovery by lowering glucose homeostasis and/or improving insulin sensitivity after treatment with thiazolidinedione therapy or glucagon-like peptide 1 receptor agonism alone or in combination with sodium/glucose cotransporter 2 inhibition (SGLT-2i). SGLT-2i combination therapies improved glucose homeostasis, independent of changes in body weight, resulting in a synergistic increase in pancreatic insulin content marked by significant recovery of the β-cell mature insulin secretory population but with limited changes in β-cell mass and no indication of β-cell dedifferentiation. Restoration of β-cell insulin secretory capacity also restored biphasic insulin secretion. These data emphasize that by therapeutically alleviating the demand for insulin in vivo, irrespective of weight loss, endogenous β-cells recover significant function that can contribute to attenuating diabetes. Thus, this study provides evidence that alleviation of metabolic demand on the β-cell, rather than targeting the β-cell itself, could be effective in delaying the progression of T2D.

Tissue Engineering Approaches in the Design of Healthy and Pathological In Vitro Tissue Models

In the tissue engineering (TE) paradigm, engineering and life sciences tools are combined to develop bioartificial substitutes for organs and tissues, which can in turn be applied in regenerative medicine, pharmaceutical, diagnostic, and basic research to elucidate fundamental aspects of cell functions in vivo or to identify mechanisms involved in aging processes and disease onset and progression. The complex three-dimensional (3D) microenvironment in which cells are organized in vivo allows the interaction between different cell types and between cells and the extracellular matrix, the composition of which varies as a function of the tissue, the degree of maturation, and health conditions. In this context, 3D in vitro models can more realistically reproduce a tissue or organ than two-dimensional (2D) models. Moreover, they can overcome the limitations of animal models and reduce the need for in vivo tests, according to the "3Rs" guiding principles for a more ethical research. The design of 3D engineered tissue models is currently in its development stage, showing high potential in overcoming the limitations of already available models. However, many issues are still opened, concerning the identification of the optimal scaffold-forming materials, cell source and biofabrication technology, and the best cell culture conditions (biochemical and physical cues) to finely replicate the native tissue and the surrounding environment. In the near future, 3D tissue-engineered models are expected to become useful tools in the preliminary testing and screening of drugs and therapies and in the investigation of the molecular mechanisms underpinning disease onset and progression. In this review, the application of TE principles to the design of in vitro 3D models will be surveyed, with a focus on the strengths and weaknesses of this emerging approach. In addition, a brief overview on the development of in vitro models of healthy and pathological bone, heart, pancreas, and liver will be presented.

Human CB1 Receptor Isoforms, present in Hepatocytes and β-cells, are Involved in Regulating Metabolism

Therapeutics aimed at blocking the cannabinoid 1 (CB1) receptor for treatment of obesity resulted in significant improvements in liver function, glucose uptake and pancreatic β-cell function independent of weight loss or CB1 receptor blockade in the brain, suggesting that peripherally-acting only CB1 receptor blockers may be useful therapeutic agents. Neuropsychiatric side effects and lack of tissue specificity precluded clinical use of first-generation, centrally acting CB1 receptor blockers. In this study we specifically analyzed the potential relevance to diabetes of human CB1 receptor isoforms in extraneural tissues involved in glucose metabolism. We identified an isoform of the human CB1 receptor (CB1b) that is highly expressed in β-cells and hepatocytes but not in the brain. Importantly, CB1b shows stronger affinity for the inverse agonist JD-5037 than for rimonabant compared to CB1 full length. Most relevant to the field, CB1b is a potent regulator of adenylyl cyclase activity in peripheral metabolic tissues. CB1b blockade by JD-5037 results in stronger adenylyl cyclase activation compared to rimonabant and it is a better enhancer of insulin secretion in β-cells. We propose this isoform as a principal pharmacological target for the treatment of metabolic disorders involving glucose metabolism.

Exenatide Treatment Alone Improves β-Cell Function in a Canine Model of Pre-Diabetes

Background

Exenatide’s effects on glucose metabolism have been studied extensively in diabetes but not in pre-diabetes.

Objective

We examined the chronic effects of exenatide alone on glucose metabolism in pre-diabetic canines.

Design and Methods

After 10 weeks of high-fat diet (HFD), adult dogs received one injection of streptozotocin (STZ, 18.5 mg/kg). After induction of pre-diabetes, while maintained on HFD, animals were randomized to receive either exenatide (n = 7) or placebo (n = 7) for 12 weeks. β-Cell function was calculated from the intravenous glucose tolerance test (IVGTT, expressed as the acute insulin response, AIR_G), the oral glucose tolerance test (OGTT, insulinogenic index) and the graded-hyperglycemic clamp (clamp insulinogenic index). Whole-body insulin sensitivity was assessed by the IVGTT. At the end of the study, pancreatic islets were isolated to assess β-cell function in vitro.

Results

OGTT: STZ caused an increase in glycemia at 120 min by 22.0% (interquartile range, IQR, 31.5%) (P = 0.011). IVGTT: This protocol also showed a reduction in glucose tolerance by 48.8% (IQR, 36.9%) (P = 0.002). AIR_G decreased by 54.0% (IQR, 40.7%) (P = 0.010), leading to mild fasting hyperglycemia (P = 0.039). Exenatide, compared with placebo, decreased body weight (P<0.001) without altering food intake, fasting glycemia, insulinemia, glycated hemoglobin A1c, or glucose tolerance. Exenatide, compared with placebo, increased both OGTT- (P = 0.040) and clamp-based insulinogenic indexes (P = 0.016), improved insulin secretion in vitro (P = 0.041), but had no noticeable effect on insulin sensitivity (P = 0.405).

Conclusions

In pre-diabetic canines, 12-week exenatide treatment improved β-cell function but not glucose tolerance or insulin sensitivity. These findings demonstrate partial beneficial metabolic effects of exenatide alone on an animal model of pre-diabetes.

Dynamics of glucose-induced insulin secretion in normal human islets

The biphasic pattern of glucose-induced insulin secretion is altered in type 2 diabetes. Impairment of the first phase is an early sign of β-cell dysfunction, but the underlying mechanisms are still unknown. Their identification through in vitro comparisons of islets from diabetic and control subjects requires characterization and quantification of the dynamics of insulin secretion by normal islets. When perifused normal human islets were stimulated with 15 mmol/l glucose (G15), the proinsulin/insulin ratio in secretory products rapidly and reversibly decreased (∼50%) and did not reaugment with time. Switching from prestimulatory G3 to G6-G30 induced biphasic insulin secretion with flat but sustained (2 h) second phases. Stimulation index reached 6.7- and 3.6-fold for the first and second phases induced by G10. Concentration dependency was similar for both phases, with half-maximal and maximal responses at G6.5 and G15, respectively. First-phase response to G15-G30 was diminished by short (30-60 min) prestimulation in G6 (vs. G3) and abolished by prestimulation in G8, whereas the second phase was unaffected. After 1-2 days of culture in G8 (instead of G5), islets were virtually unresponsive to G15. In both settings, a brief return to G3-G5 or transient omission of CaCl2 restored biphasic insulin secretion. Strikingly, tolbutamide and arginine evoked immediate insulin secretion in islets refractory to glucose. In conclusion, we quantitatively characterized the dynamics of glucose-induced insulin secretion in normal human islets and showed that slight elevation of prestimulatory glucose reversibly impairs the first phase, which supports the view that the similar impairment in type 2 diabetic patients might partially be a secondary phenomenon.

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.

Sodium levels of human pancreatic donors are a critical factor for determination of islet efficacy and survival

Organs from hypernatremia (elevated Na+) donors when used for transplantation have had dismal outcomes. However, islet isolation from hypernatremic donors for both transplantation and research applications has not yet been investigated. A retrospective analysis of in vivo and in vitro islet function studies was performed on islets isolated from hypernatremic (serum sodium levels≥160 meq/l) and normal control (serum sodium levels≤155 meq/l) donors. Twelve isolations from 32 hypernatremic and 53 isolations from 222 normal donors were randomly transplanted into diabetic NOD Scid mice. Sodium levels upon pancreas procurement were significantly elevated in the hypernatremia group (163.5±0.6 meq/l) compared with the normal control group (145.9±0.4 meq/l) (P<0.001). The postculture islet recovery rate was significantly lower in the hypernatremia (59.1±3.8%) group compared with the normal (73.6±1.8%) group (P=0.005). The duration of hypernatremia was inversely correlated with the recovery rate (r2=0.370, P<0.001). Furthermore, the percentage of successful graft function when transplanted into diabetic NOD Scid mice was significantly lower in the hypernatremia (42%) group compared with the normal control (85%) group (P<0.001). The ability to predict islet graft function posttransplantation using donor sodium levels and duration of hypernatremia was significant (ROC analysis, P=0.022 and 0.042, respectively). In conclusion, duration of donor hypernatremia is associated with reduced islet recovery postculture. The efficacy of islets from hypernatremia donors diminished when transplanted into diabetic recipients.

Development of in vitro 3D TissueFlex® islet model for diabetic drug efficacy testing

Increasing individuals diagnosed with type II diabetes pose a strong demand for the development of more effective anti-diabetic drugs. However, expensive, ethically controversial animal-based screening for anti-diabetic compounds is not always predictive of the human response. The use of in vitro cell-based models in research presents obviously ethical and cost advantages over in vivo models. This study was to develop an in vitro three-dimensional (3D) perfused culture model of islets (Islet TF) for maintaining viability and functionality longer for diabetic drug efficacy tests. Briefly fresh isolated rat islets were encapsulated in ultrapure alginate and the encapsulated islets were cultured in TissueFlex(®), a multiple, parallel perfused microbioreactor system for 7 days. The encapsulated islets cultured statically in cell culture plates (3D static) and islets cultured in suspension (2D) were used as the comparisons. In this study we demonstrate for the first time that Islet TF model can maintain the in vitro islet viability, and more importantly, the elevated functionality in terms of insulin release and dynamic responses over a 7-day culture period. The Islet TF displays a high sensitivity in responding to drugs and drug dosages over conventional 2D and 3D static models. Actual drug administration in clinics could be simulated using the developed Islet TF model, and the patterns of insulin release response to the tested drugs were in agreement with the data obtained in vivo. Islet TF could be a more predictive in vitro model for routine short- and long-term anti-diabetic drug efficacy testing.

Human islet cell isolation: the initial step in an islet transplanting program in Shiraz, Southern Iran

OBJECTIVES

Type 1 diabetes mellitus is an emerging epidemic worldwide and results from autoimmune destruction of insulin-producing β cells. Islet transplanting is a potential treatment for type 1 diabetes mellitus.

MATERIALS AND METHODS

The Shiraz Organ Transplant Center is a leading center for organ transplants, especially pancreatic transplants, in Iran. For this reason, we want to establish an islet transplanting program. Here, we briefly describe our experience with islet isolation on 6 pancreata from deceased donors. We discussed the necessary equipment required for this procedure, as well as the professionals needed and a specially planned facility.

RESULTS

Islet yield was ≤ 100 000 (islet equivalent), viability 40% to 45%, and the purity was 30% to 45%. We do not have a refrigerated COBE processor for purification; therefore, the yield was low. Our experience shows that we should improve things, so as to acquire more islets for developing clinical grade cell therapy.

CONCLUSIONS

Overall, isolation costs are high, and accessing a safer, more economic, and persistent source of material and reagents will improve this technique.