Superiority of small islets in human islet transplantation

Illuminating the complete ß-cell mass of the human pancreas- signifying a new view on the islets of Langerhans

Pancreatic islets of Langerhans play a pivotal role in regulating blood glucose homeostasis, but critical information regarding their mass, distribution and composition is lacking within a whole organ context. Here, we apply a 3D imaging pipeline to generate a complete account of the insulin-producing islets throughout the human pancreas at a microscopic resolution and within a maintained spatial 3D context. These data show that human islets are far more heterogenous than previously accounted for with regards to their size distribution and cellular make up. By deep tissue 3D imaging, this in-depth study demonstrates that 50% of the human insulin-expressing islets are virtually devoid of glucagon-producing α-cells, an observation with significant implications for both experimental and clinical research.

Donor- and isolation-related predictive factors of in vitro secretory function of cultured human islets

Background and aims

Human islet preparations designated for research exhibit diverse insulin-secretory profiles. This study aims to assess the impact of donor- and isolation-related factors on in vitro islet secretory function.

Methods

A retrospective analysis of 46 isolations from 23 pancreata discarded for clinical transplantation was conducted. In vitro islet secretory function tests were performed on Day 1 and Day 7 of culture. Linear mixed-effects models (LMMs) were employed to investigate the relationships between various predictors characterizing the patient and donor characteristics as well as the isolation effectiveness and two functional outcomes including the islet stimulation index (SI) and area under the insulin curve (AUC). Fixed effects were introduced to represent the main effects of each predictor, and backward elimination was utilized to select the most significant fixed effects for the final model. Interaction effects between the timepoint (Day 7 vs. Day 1) and the predictors were also evaluated to assess whether predictors were associated with the temporal evolution of SI and AUC. Fold-change (Fc) values associated with each predictor were obtained by exponentiating the corresponding coefficients of the models, which were built on log-transformed outcomes.

Results

Analysis using LMMs revealed that donor body mass index (BMI) (Fc = 0.961, 95% CI = 0.927-0.996, p = 0.05), donor gender (female vs. male, Fc = 0.702, 95% CI = 0.524-0.942, p = 0.04), and donor hypertension (Fc = 0.623, 95% CI = 0.466-0.832, p= <0.01) were significantly and independently associated with SI. Moreover, donor gender (Fc = 0.512, 95% CI = 0.302-0.864, p = 0.02), donor cause of death (cerebrovascular accident vs. cardiac arrest, Fc = 2.129, 95% CI = 0.915-4.946, p = 0.09; trauma vs. cardiac arrest, Fc = 2.129, 95% CI = 1.112-7.106, p = 0.04), pancreas weight (Fc = 1.01, 95% CI = 1.001-1.019, p = 0.03), and islet equivalent (IEQ)/mg (Fc = 1.277, 95% CI = 1.088-1.510, p ≤ 0.01) were significantly and independently associated with AUC. There was no predictor significantly associated with the temporal evolution between Day 1 and Day 7 for both SI and AUC outcomes.

Conclusion

This study identified donor- and isolation-related factors influencing in vitro islet secretory function. Further investigations are essential to validate the applicability of these results in clinical practice.

Biomaterial-assisted strategies to improve islet graft revascularization and transplant outcomes

Islet transplantation holds significant promise as a curative approach for type 1 diabetes (T1D). However, the transition of islet transplantation from the experimental phase to widespread clinical implementation has not occurred yet. One major hurdle in this field is the challenge of insufficient vascularization and subsequent early loss of transplanted islets, especially in non-intraportal transplantation sites. The establishment of a fully functional vascular system following transplantation is crucial for the survival and secretion function of islet grafts. This vascular network not only ensures the delivery of oxygen and nutrients, but also plays a critical role in insulin release and the timely removal of metabolic waste from the grafts. This review summarizes recent advances in effective strategies to improve graft revascularization and enhance islet survival. These advancements include the local release and regulation of angiogenic factors (e.g., vascular endothelial growth factor, VEGF), co-transplantation of vascular fragments, and pre-vascularization of the graft site. These innovative approaches pave the way for the development of effective islet transplantation therapies for individuals with T1D.

On Chip Sorting of Stem Cell-Derived β Cell Clusters Using Traveling Surface Acoustic Waves

There is a critical need for sorting complex materials, such as pancreatic islets of Langerhans, exocrine acinar tissues, and embryoid bodies. These materials are cell clusters, which have highly heterogeneous physical properties (such as size, shape, morphology, and deformability). Selecting such materials on the basis of specific properties can improve clinical outcomes and help advance biomedical research. In this work, we focused on sorting one such complex material, human stem cell-derived β cell clusters (SC-β cell clusters), by size. For this purpose, we developed a microfluidic device in which an image detection system was coupled to an actuation mechanism based on traveling surface acoustic waves (TSAWs). SC-β cell clusters of varying size (∼100-500 μm in diameter) were passed through the sorting device. Inside the device, the size of each cluster was estimated from their bright-field images. After size identification, larger clusters, relative to the cutoff size for separation, were selectively actuated using TSAW pulses. As a result of this selective actuation, smaller and larger clusters exited the device from different outlets. At the current sample dilutions, the experimental sorting efficiency ranged between 78% and 90% for a separation cutoff size of 250 μm, yielding sorting throughputs of up to 0.2 SC-β cell clusters/s using our proof-of-concept design. The biocompatibility of this sorting technique was also established, as no difference in SC-β cell cluster viability due to TSAW pulse usage was found. We conclude the proof-of-concept sorting work by discussing a few ways to optimize sorting of SC-β cell clusters for potentially higher sorting efficiency and throughput. This sorting technique can potentially help in achieving a better distribution of islets for clinical islet transplantation (a potential cure for type 1 diabetes). Additionally, the use of this technique for sorting islets can help in characterizing islet biophysical properties by size and selecting suitable islets for improved islet cryopreservation.

Preventive Effect of Molecular Iodine in Pancreatic Disorders from Hypothyroid Rabbits

Pancreatic alterations such as inflammation and insulin resistance accompany hypothyroidism. Molecular iodine (I2) exerts antioxidant and differentiation actions in several tissues, and the pancreas is an iodine-uptake tissue. We analyzed the effect of two oral I2 doses on pancreatic disorders in a model of hypothyroidism for 30 days. Adult female rabbits were divided into the following groups: control, moderate oral dose of I2 (0.2 mg/kg, M-I2), high oral dose of I2 (2.0 mg/kg, H-I2), oral dose of methimazole (MMI; 10 mg/kg), MMI + M-I2,, and MMI + H-I2. Moderate or high I2 supplementation did not modify circulating metabolites or pancreatic morphology. The MMI group showed reductions of circulating thyroxine (T4) and triiodothyronine (T3), moderate glucose increments, and significant increases in cholesterol and low-density lipoproteins. Acinar fibrosis, high insulin content, lipoperoxidation, and overexpression of GLUT4 were observed in the pancreas of this group. M-I2 supplementation normalized the T4 and cholesterol, but T3 remained low. Pancreatic alterations were prevented, and nuclear factor erythroid-2-related factor-2 (Nrf2), antioxidant enzymes, and peroxisome proliferator-activated receptor gamma (PPARG) maintained their basal values. In MMI + H-I2, hypothyroidism was avoided, but pancreatic alterations and low PPARG expression remained. In conclusion, M-I2 supplementation reestablishes thyronine synthesis and diminishes pancreatic alterations, possibly related to Nrf2 and PPARG activation.

Three Dimensional Models of Endocrine Organs and Target Tissues Regulated by the Endocrine System

Immortalized cell lines originating from tumors and cultured in monolayers in vitro display consistent behavior and response, and generate reproducible results across laboratories. However, for certain endpoints, these cell lines behave quite differently from the original solid tumors. Thereby, the homogeneity of immortalized cell lines and two-dimensionality of monolayer cultures deters from the development of new therapies and translatability of results to the more complex situation in vivo. Organoids originating from tissue biopsies and spheroids from cell lines mimic the heterogeneous and multidimensional characteristics of tumor cells in 3D structures in vitro. Thus, they have the advantage of recapitulating the more complex tissue architecture of solid tumors. In this review, we discuss recent efforts in basic and preclinical cancer research to establish methods to generate organoids/spheroids and living biobanks from endocrine tissues and target organs under endocrine control while striving to achieve solutions in personalized medicine.

Unlocking the post-transplant microenvironment for successful islet function and survival

Islet transplantation (IT) offers the potential to restore euglycemia for patients with type 1 diabetes mellitus (T1DM). Despite improvements in islet isolation techniques and immunosuppressive regimes, outcomes remain suboptimal with UK five-year graft survivals (5YGS) of 55% and most patients still requiring exogenous insulin after multiple islet infusions. Native islets have a significant non-endocrine component with dense extra-cellular matrix (ECM), important for islet development, cell survival and function. Collagenase isolation necessarily disrupts this complex islet microenvironment, leaving islets devoid of a supporting framework and increasing vulnerability of transplanted islets. Following portal venous transplantation, a liver injury response is potentially induced, which typically results in inflammation and ECM deposition from liver specific myofibroblasts. The impact of this response may have important impact on islet survival and function. A fibroblast response and ECM deposition at the kidney capsule and eye chamber alongside other implantation sites have been shown to be beneficial for survival and function. Investigating the implantation site microenvironment and the interactions of transplanted islets with ECM proteins may reveal therapeutic interventions to improve IT and stem-cell derived beta-cell therapy.

Sustained heterologous gene expression in pancreatic islet organoids using adeno-associated virus serotype 8

Genetic modification of pancreatic islet organoids, assembled in vitro prior to transplantation is an emerging alternative to direct in vivo genetic manipulations for a number of clinical and research applications. We have previously shown that dispersion of islet cells followed by re-aggregation into islet organoids, or pseudoislets, allows for efficient transduction with viral vectors, while maintaining physiological functions of native islets. Among viruses currently used for genetic manipulations, adeno-associated viruses (AAVs) have the most attractive safety profile making them suitable for gene therapy applications. Studies reporting on pseudoislet transduction with AAVs are, however, lacking. Here, we have characterized in detail the performance of AAV serotype 8 in transduction of islet cells during pseudoislet formation in comparison with human adenovirus type 5 (AdV5). We have assessed such parameters as transduction efficiency, expression kinetics, and endocrine cell tropism of AAV8 alone or in combination with AdV5. Data provided within our study may serve as a reference point for future functional studies using AAVs for gene transfer to islet cell organoids and will facilitate further development of engineered pseudoislets of superior quality suitable for clinical transplantation.

Continuous vs. discontinuous purification of isolated human islets: functional and morphological comparison

Background

The COBE 2991 cell processor, commonly used for pancreatic islet isolation, is no longer distributed in Europe, leading to a search for alternative purification procedures with equivalent efficacy. The aim of this study was to evaluate the efficacy of an alternative method based on the discontinuous purification of islets.

Methods

The conventional isolation procedure using a standard continuous islet purification with COBE 2991 of n = 4 human pancreas was compared to n = 8 procedures using a discontinuous purification with a "bottle" method from donors of similar characteristics. Islet equivalents, purity, and dynamic glucose-stimulated insulin secretion were evaluated.

Results

A similar islet yield was obtained using continuous vs. discontinuous purification methods (76,292.5 ± 40,550.44 vs. 79,625 ± 41,484.46 islet equivalents, p = 0.89). Islets from both groups had similar purity (78.75% ± 19.73% vs. 55% ± 18.16%, p = 0.08) and functionality both in terms of stimulation index (3.31 ± 0.83 vs. 5.58 ± 3.38, p = 0.22) and insulin secretion (1.26 ± 0.83 vs. 1.53 ± 1.40 mean AUC, p = 0.73). Moreover, the size of the islets was significantly larger in the discontinuous vs. continuous purification group (19.2% ± 10.3% vs. 45.4% ± 18.8% of islets less than 100 µm, p = 0.0097 and 23.7% ± 5.3% vs. 15.6% ± 5.8% of 200-250 µm islet size, p = 0.03).

Conclusion

Compared to the conventional purification procedure, discontinuous purification with a bottle method shows similar results with regard to isolation yield and islet secretory function. Furthermore, this alternative technique allows for obtaining larger islets.

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

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

Comparative Study of Two Common In Vitro Models for the Pancreatic Islet with MIN6

BACKGROUND

Islet transplantation is currently considered the most promising method for treating insulin-dependent diabetes. The two most-studied artificial islets are alginate-encapsulated β cells or β cell spheroids. As three-dimensional (3D) models, both artificial islets have better insulin secretory functions and transplantation efficiencies than cells in two-dimensional (2D) monolayer culture. However, the effects of these two methods have not been compared yet. Therefore, in this study, cells from the mouse islet β cell line Min6 were constructed as scaffold-free spheroids or alginate-encapsulated dispersed cells.

METHODS

MIN6 cell spheroids were prepared by using Agarose-base microwell arrays. The insulin secretion level was determined by mouse insulin ELISA kit, and the gene and protein expression status of the MIN6 were performed by Quantitative polymerase chain reaction and immunoblot, respectively.

RESULTS

Both 3D cultures effectively promoted the proliferation and glucose-stimulated insulin release (GSIS) of MIN6 cells compared to 2D adherent cells. Furthermore, 1% alginate-encapsulated MIN6 cells demonstrated more significant effects than the spheroids. In general, three pancreatic genes were expressed at higher levels in response to the 3D culture than to the 2D culture, and pancreatic/duodenal homeobox-1 (PDX1) expression was higher in the cells encapsulated in 1% alginate than that in the spheroids. A western blot analysis showed that 1% alginate-encapsulated MIN6 cells activated the phosphoinositide 3-kinase (PI3K)/serine/threonine protein kinase (AKT)/forkhead transcription factor FKHR (FoxO1) pathway more than the spheroids, 0.5% alginate-, or 2% alginate-encapsulated cells did. The 3D MIN6 culture, therefore, showed improved effects compared to the 2D culture, and the 1% alginate-encapsulated MIN6 cells exhibited better effects than the spheroids. The upregulation of PDX1 expression through the activation of the PI3K/AKT/FoxO1 pathway may mediate the improved cell proliferation and GSIS in 1% alginate-encapsulated MIN6 cells.

CONCLUSION

This study may contribute to the construction of in vitro culture systems for pancreatic islets to meet clinical requirements.

Formation of Re-Aggregated Neonatal Porcine Islet Clusters Improves In Vitro Function and Transplantation Outcome

Neonatal porcine islet-like cell clusters (NPICCs) are a promising source for islet cell transplantation. Excellent islet quality is important to achieve a cure for type 1 diabetes. We investigated formation of cell clusters from dispersed NPICCs on microwell cell culture plates, evaluated the composition of re-aggregated porcine islets (REPIs) and compared in vivo function by transplantation into diabetic NOD-SCID IL2rγ-/- (NSG) mice with native NPICCs. Dissociation of NPICCs into single cells and re-aggregation resulted in the formation of uniform REPI clusters. A higher prevalence of normoglycemia was observed in diabetic NSG mice after transplantation with a limited number (n = 1500) of REPIs (85.7%) versus NPICCs (n = 1500) (33.3%) (p < 0.05). Transplanted REPIs and NPICCs displayed a similar architecture of endocrine and endothelial cells. Intraperitoneal glucose tolerance tests revealed an improved beta cell function after transplantation of 1500 REPIs (AUC glucose 0-120 min 6260 ± 305.3) as compared to transplantation of 3000 native NPICCs (AUC glucose 0-120 min 8073 ± 536.2) (p < 0.01). Re-aggregation of single cells from dissociated NPICCs generates cell clusters with excellent functionality and improved in vivo function as compared to native NPICCs.

Generation of Insulin-Producing Multicellular Organoids

Clinical islet transplantation (CIT) is an established noninvasive treatment for type I diabetes (T1D) and has demonstrated improved glycemic control, preventing the occurrence of severe hypoglycemia. However, CIT has several limitations, such as the need for multiple donors, lifelong immunosuppression, and suboptimal long-term graft function. Most of the transplanted islets are lost due to inflammation, ischemic damage, and delayed revascularization.Generation of organoids have gained increasing interest in regenerative medicine in recent years. In the context of beta-cell replacement, it offers a possibility to address limitations of CIT by allowing to produce uniform organoids from single or multiple cell types facilitating revascularization and anti-inflammatory and/or immunomodulatory protection. We have previously generated multicellular insulin-secreting organoids composed of islet cells and the human amniotic epithelial cells (hAECs). These 3D insulin-secreting structures demonstrated improved viability and function both in vitro and in vivo. Here we detail a stepwise methodology to generate insulin-secreting organoids using two different methods. In addition, quality assessment in vitro tests are also described.

From islet of Langerhans transplantation to the bioartificial pancreas

Type 1 diabetes is a disease resulting from autoimmune destruction of the insulin-producing beta cells in the pancreas. When type 1 diabetes develops into severe secondary complications, in particular end-stage nephropathy, or life-threatening severe hypoglycemia, the best therapeutic approach is pancreas transplantation, or more recently transplantation of the pancreatic islets of Langerhans. Islet transplantation is a cell therapy procedure, that is minimally invasive and has a low morbidity, but does not display the same rate of functional success as the more invasive pancreas transplantation because of suboptimal engraftment and survival. Another issue is that pancreas or islet transplantation (collectively known as beta cell replacement therapy) is limited by the shortage of organ donors and by the need for lifelong immunosuppression to prevent immune rejection and recurrence of autoimmunity. A bioartificial pancreas is a construct made of functional, insulin-producing tissue, embedded in an anti-inflammatory, immunomodulatory microenvironment and encapsulated in a perm-selective membrane allowing glucose sensing and insulin release, but isolating from attacks by cells of the immune system. A successful bioartificial pancreas would address the issues of engraftment, survival and rejection. Inclusion of unlimited sources of insulin-producing cells, such as xenogeneic porcine islets or stem cell-derived beta cells would further solve the problem of organ shortage. This article reviews the current status of clinical islet transplantation, the strategies aiming at developing a bioartificial pancreas, the clinical trials conducted in the field and the perspectives for further progress.

Microwell culture platform maintains viability and mass of human pancreatic islets

Background

Transplantation of the human pancreatic islets is a promising approach for specific types of diabetes to improve glycemic control. Although effective, there are several issues that limit the clinical expansion of this treatment, including difficulty in maintaining the quality and quantity of isolated human islets prior to transplantation. During the culture, we frequently observe the multiple islets fusing together into large constructs, in which hypoxia-induced cell damage significantly reduces their viability and mass. In this study, we introduce the microwell platform optimized for the human islets to prevent unsolicited fusion, thus maintaining their viability and mass in long-term cultures.

Method

Human islets are heterogeneous in size; therefore, two different-sized microwells were prepared in a 35 mm-dish format: 140 µm × 300 µm-microwells for <160 µm-islets and 200 µm × 370 µm-microwells for >160 µm-islets. Human islets (2,000 islet equivalent) were filtered through a 160 µm-mesh to prepare two size categories for subsequent two week-cultures in each microwell dish. Conventional flat-bottomed 35 mm-dishes were used for non-filtered islets (2,000 islet equivalent/2 dishes). Post-cultured islets are collected to combine in each condition (microwells and flat) for the comparisons in viability, islet mass, morphology, function and metabolism. Islets from three donors were independently tested.

Results

The microwell platform prevented islet fusion during culture compared to conventional flat bottom dishes, which improved human islet viability and mass. Islet viability and mass on the microwells were well-maintained and comparable to those in pre-culture, while flat bottom dishes significantly reduced islet viability and mass in two weeks. Morphology assessed by histology, insulin-secreting function and metabolism by oxygen consumption did not exhibit the statistical significance among the three different conditions.

Conclusion

Microwell-bottomed dishes maintained viability and mass of human islets for two weeks, which is significantly improved when compared to the conventional flat-bottomed dishes.

Anionic polymers amplify electrokinetic perfusion through extracellular matrices

Electrical stimulation (ES) promotes healing of chronic epidermal wounds and delays degeneration of articular cartilage. Despite electrotherapeutic treatment of these non-excitable tissues, the mechanisms by which ES promotes repair are unknown. We hypothesize that a beneficial role of ES is dependent on electrokinetic perfusion in the extracellular space and that it mimics the effects of interstitial flow. In vivo, the extracellular space contains mixtures of extracellular proteins and negatively charged glycosaminoglycans and proteoglycans surrounding cells. While these anionic macromolecules promote water retention and increase mechanical support under compression, in the presence of ES they should also enhance electro-osmotic flow (EOF) to a greater extent than proteins alone. To test this hypothesis, we compare EOF rates between artificial matrices of gelatin (denatured collagen) with matrices of gelatin mixed with anionic polymers to mimic endogenous charged macromolecules. We report that addition of anionic polymers amplifies EOF and that a matrix comprised of 0.5% polyacrylate and 1.5% gelatin generates EOF with similar rates to those reported in cartilage. The enhanced EOF reduces mortality of cells at lower applied voltage compared to gelatin matrices alone. We also use modeling to describe the range of thermal changes that occur during these electrokinetic experiments and during electrokinetic perfusion of soft tissues. We conclude that the negative charge density of native extracellular matrices promotes electrokinetic perfusion during electrical therapies in soft tissues and may promote survival of artificial tissues and organs prior to vascularization and during transplantation.

Innovative multidimensional models in a high-throughput-format for different cell types of endocrine origin

The adrenal gland provides an important function by integrating neuronal, immune, vascular, metabolic and endocrine signals under a common organ capsule. It is the central organ of the stress response system and has been implicated in numerous stress-related disorders. While for other diseases, regeneration of healthy organ tissue has been aimed at such approaches are lacking for endocrine diseases - with the exception of type-I-diabetes. Moreover, adrenal tumor formation is very common, however, appropriate high-throughput applications reflecting the high heterogeneity and furthermore relevant 3D-structures in vitro are still widely lacking. Recently, we have initiated the development of standardized multidimensional models of a variety of endocrine cell/tissue sources in a new multiwell-format. Firstly, we confirmed common applicability for pancreatic pseudo-islets. Next, we translated applicability for spheroid establishment to adrenocortical cell lines as well as patient material to establish spheroids from malignant, but also benign adrenal tumors. We aimed furthermore at the development of bovine derived healthy adrenal organoids and were able to establish steroidogenic active organoids containing both, cells of cortical and medullary origin. Overall, we hope to open new avenues for basic research, endocrine cancer and adrenal tissue-replacement-therapies as we demonstrate potential for innovative mechanistic insights and personalized medicine in endocrine (tumor)-biology.

Therapeutic Effects of Insulin-Producing Human Umbilical Cord-Derived Mesenchymal Stem Cells in a Type 1 Diabetes Mouse Model

In patients with type 1 diabetes (T1D), compromised pancreatic β-cell functions are compensated through daily insulin injections or the transplantation of pancreatic tissue or islet cells. However, both approaches are associated with specific challenges. The transplantation of mesenchymal stem cells (MSCs) represents a potential alternative, as MSCs have tissue-forming capacity and can be isolated from various tissues. The human umbilical cord (hUC) is a good source of freely available MSCs, which can be collected through pain-free, non-invasive methods subject to minimal ethical concerns. We sought to develop a method for the in vitro generation of insulin-producing cells (IPCs) using MSCs. We examined the potential therapeutic uses and efficacy of IPCs generated from hUC-derived MSCs (hUC-IPCs) and human adipose tissue (hAD)-derived MSCs (hAD-IPCs) through in vitro experiments and streptozotocin (STZ)-induced C57BL/6 T1D mouse models. We discovered that compared to hAD-IPCs, hUC-IPCs exhibited a superior insulin secretion capacity. Therefore, hUC-IPCs were selected as candidates for T1D cell therapy in mice. Fasting glucose and intraperitoneal glucose tolerance test levels were lower in hUC-IPC-transplanted mice than in T1D control mice and hAD-IPC-transplanted mice. Our findings support the potential use of MSCs for the treatment of T1D.

S. C, L. D, M. G, S. P, R. L. L, C. A. H. Engineering Vascularized Islet Macroencapsulation Devices: An in vitro Platform to Study Oxygen Transport in Perfused Immobilized Pancreatic Beta Cell Cultures

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

Microwell bag culture for large-scale production of homogeneous islet-like clusters

Pluripotent stem-cell derived cells can be used for type I diabetes treatment, but we require at least 10⁵–10⁶ islet-like clusters per patient. Although thousands of uniform cell clusters can be produced using a conventional microwell plate, numerous obstacles need to be overcome for its clinical use. In this study, we aimed to develop a novel bag culture method for the production of uniform cell clusters on a large scale (10⁵–10⁶ clusters). We prepared small-scale culture bags (< 10⁵ clusters) with microwells at the bottom and optimized the conditions for producing uniform-sized clusters in the bag using undifferentiated induced pluripotent stem cells (iPSCs). Subsequently, we verified the suitability of the bag culture method using iPSC-derived pancreatic islet cells (iPICs) and successfully demonstrate the production of 6.5 × 10⁵ uniform iPIC clusters using a large-scale bag. In addition, we simplified the pre- and post-process of the culture—a degassing process before cell seeding and a cluster harvesting process. In conclusion, compared with conventional methods, the cluster production method using bags exhibits improved scalability, sterility, and operability for both clinical and research use.

The response of three-dimensional pancreatic alpha and beta cell co-cultures to oxidative stress

The pancreatic islets of Langerhans have low endogenous antioxidant levels and are thus especially sensitive to oxidative stress, which is known to influence cell survival and behaviour. As bioengineered islets are gaining interest for therapeutic purposes, it is important to understand how their composition can be optimized to diminish oxidative stress. We investigated how the ratio of the two main islet cell types (alpha and beta cells) and their culture in three-dimensional aggregates could protect against oxidative stress. Monolayer and aggregate cultures were established by seeding the alphaTC1 (alpha) and INS1E (beta) cell lines in varying ratios, and hydrogen peroxide was applied to induce oxidative stress. Viability, oxidative stress, and the level of the antioxidant glutathione were measured. Both aggregation and an increasing prevalence of INS1E cells in the co-cultures conferred greater resistance to cell death induced by oxidative stress. Increasing the prevalence of INS1E cells also decreased the number of alphaTC1 cells experiencing oxidative stress in the monolayer culture. In 3D aggregates, culturing the alphaTC1 and INS1E cells in a ratio of 50:50 prevented oxidative stress in both cell types. Together, the results of this study lead to new insight into how modulating the composition and dimensionality of a co-culture can influence the oxidative stress levels experienced by the cells.

Maternal Hypothyroidism in Rats Reduces Placental Lactogen, Lowers Insulin Levels, and Causes Glucose Intolerance

Hypothyroidism increases the incidence of gestational diabetes mellitus (GDM) but the mechanisms responsible are unknown. This study aimed to assess the pathophysiological mechanisms by which hypothyroidism leads to glucose intolerance in pregnancy. Hypothyroidism was induced in female Sprague-Dawley rats by adding methimazole (MMI) to drinking water at moderate (MOD, MMI at 0.005% w/v) and severe (SEV, MMI at 0.02% w/v) doses from 1 week before pregnancy and throughout gestation. A nonpregnant cohort received the same dose for the same duration but were not mated. On gestational day 16 (GD16), or nonpregnant day 16 (NP16), animals were subjected to an intraperitoneal glucose tolerance test. Tissues and blood samples were collected 4 days later. Hypothyroidism induced a diabetic-like phenotype by GD16 in pregnant females only. Pregnant MOD and SEV females had reduced fasting plasma insulin, less insulin following a glucose load, and altered expression of genes involved in insulin signaling within skeletal muscle and adipose tissue. Hypothyroidism reduced rat placental lactogen concentrations, which was accompanied by reduced percentage β-cell cross-sectional area (CSA) relative to total pancreas CSA, and a reduced number of large β-cell clusters in the SEV hypothyroid group. Plasma triglycerides and free fatty acids were reduced by hypothyroidism in pregnant rats, as was the expression of genes that regulate lipid homeostasis. Hypothyroidism in pregnant rats results in a diabetic-like phenotype that is likely mediated by impaired β-cell expansion in pregnancy. This pregnancy-specific phenomenon is likely due to reduced placental lactogen secretion.

[Generating pancreatic islets organoids: Langerhanoids]

The extension of islet transplantation to a wider number of Type 1 diabetic patients is compromised by the scarcity of donors, the reduced ex vivo survival of pancreatic islets and the use of immunosuppressive treatments. Islets of Langerhans isolated from brain-dead donors are currently the only cell source for transplantation. Thus, it is crucial to find an alternative and an abundant source of functional insulin secreting cells not only for clinical use but also for the development of research dedicated to the screening of drugs and to the development of new therapeutic targets. Several groups around the world, including ours, develop 3D culture models as Langerhanoids that closely mimick human pancreatic islets physiology. In this review, we describe recent advances to mimic the pancreatic niche (extracellular matrix, vascularization, microfluidics) allowing better functionality of Langerhanoids.

Bio-Engineering of Pre-Vascularized Islet Organoids for the Treatment of Type 1 Diabetes

Lack of rapid revascularization and inflammatory attacks at the site of transplantation contribute to impaired islet engraftment and suboptimal metabolic control after clinical islet transplantation. In order to overcome these limitations and enhance engraftment and revascularization, we have generated and transplanted pre-vascularized insulin-secreting organoids composed of rat islet cells, human amniotic epithelial cells (hAECs), and human umbilical vein endothelial cells (HUVECs). Our study demonstrates that pre-vascularized islet organoids exhibit enhanced in vitro function compared to native islets, and, most importantly, better engraftment and improved vascularization in vivo in a murine model. This is mainly due to cross-talk between hAECs, HUVECs and islet cells, mediated by the upregulation of genes promoting angiogenesis (vegf-a) and β cell function (glp-1r, pdx1). The possibility of adding a selected source of endothelial cells for the neo-vascularization of insulin-scereting grafts may also allow implementation of β cell replacement therapies in more favourable transplantation sites than the liver.

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.

A 3D bioprinted hybrid encapsulation system for delivery of human pluripotent stem cell-derived pancreatic islet-like aggregates

Islet transplantation is a promising treatment for type 1 diabetes. However, treatment failure can result from loss of functional cells associated with cell dispersion, low viability, and severe immune response. To overcome these limitations, various islet encapsulation approaches have been introduced. Among them, macroencapsulation offers the advantages of delivering and retrieving a large volume of islets in one system. In this study, we developed a hybrid encapsulation system composed of a macroporous polymer capsule with stagger-type membrane and assemblable structure, and a nanoporous decellularized extracellular matrix (dECM) hydrogel containing pancreatic islet-like aggregates using 3D bioprinting technique. The outer part (macroporous polymer capsule) was designed to have an interconnected porous architecture, which allows insulin-producingβ-cells encapsulated in the hybrid encapsulation system to maintain their cellular behaviors, including viability, cell proliferation, and insulin-producing function. The inner part (nanoporous dECM hydrogel), composed of the 3D biofabricated pancreatic islet-like aggregates, was simultaneously placed into the macroporous polymer capsule in one step. The developed hybrid encapsulation system exhibited biocompatibilityin vitroandin vivoin terms of M1 macrophage polarization. Furthermore, by controlling the printing parameters, we generated islet-like aggregates, improving cell viability and functionality. Moreover, the 3D bioprinted pancreatic islet-like aggregates exhibited structural maturation and functional enhancement associated with intercellular interaction occurring at theβ-cell edges. In addition, we also investigated the therapeutic potential of a hybrid encapsulation system by integrating human pluripotent stem cell-derived insulin-producing cells, which are promising to overcome the donor shortage problem. In summary, these results demonstrated that the 3D bioprinting approach facilitates the fabrication of a hybrid islet encapsulation system with multiple materials and potentially improves the clinical outcomes by driving structural maturation and functional improvement of cells.

Clinical use of donation after circulatory death pancreas for islet transplantation

Due to a shortage of donation after brain death (DBD) organs, donation after circulatory death (DCD) is increasingly performed. In the field of islet transplantation, there is uncertainty regarding the suitability of DCD pancreas in terms of islet yield and function after islet isolation. The aim of this study was to investigate the potential use of DCD pancreas for islet transplantation. Islet isolation procedures from 126 category 3 DCD and 258 DBD pancreas were performed in a 9-year period. Islet yield after isolation was significantly lower for DCD compared to DBD pancreas (395 515 islet equivalents [IEQ] and 480 017 IEQ, respectively; p = .003). The decrease in IEQ during 2 days of culture was not different between the two groups. Warm ischemia time was not related to DCD islet yield. In vitro insulin secretion after a glucose challenge was similar between DCD and DBD islets. After islet transplantation, DCD islet graft recipients had similar graft function (AUC C-peptide) during mixed meal tolerance tests and Igls score compared to DBD graft recipients. In conclusion, DCD islets can be considered for clinical islet transplantation.

Vascepa protects against high-fat diet-induced glucose intolerance, insulin resistance, and impaired β-cell function

Omega-3 fatty acid prescription drugs, Vascepa (≥96% eicosapentaenoic acid [EPA] ethyl ester) and Lovaza (46.5% EPA and 37.5% docosahexaenoic acid ethyl ester) are known therapeutic regimens to treat hypertriglyceridemia. However, their impact on glucose homeostasis, progression to type 2 diabetes, and pancreatic beta cell function are not well understood. In the present study, mice were treated with Vascepa or Lovaza for one week prior to six weeks of high-fat diet feeding. Vascepa but not Lovaza led to reduced insulin resistance, reduced fasting insulin and glucose, and improved glucose intolerance. Vascepa improved beta cell function, reduced liver triglycerides with enhanced expression of hepatic fatty acid oxidation genes, and altered microbiota composition. Vascepa has protective effects on diet-induced insulin resistance and glucose intolerance in mice.

Process parameter development for the scaled generation of stem cell-derived pancreatic endocrine cells

Diabetes is a debilitating disease characterized by high blood glucose levels. The global prevalence of this disease has been projected to reach 700 million adults by the year 2045. Type 1 diabetes represents about 10% of the reported cases of diabetes. Although islet transplantation can be a highly effective method to treat type 1 diabetes, its widespread application is limited by the paucity of cadaveric donor islets. The use of pluripotent stem cells as an unlimited cell source to generate insulin‐producing cells for implant is a promising alternative for treating diabetes. However, to be clinically relevant, it is necessary to manufacture these stem cell‐derived cells at sufficient scales. Significant advances have been made in differentiation protocols used to generate stem cell‐derived cells capable of reversing diabetes in animal models and for testing in clinical trials. We discuss the potential of both stem cell‐derived pancreatic progenitors and more matured insulin‐producing cells to treat diabetes. We discuss the need for rigorous bioprocess parameter optimization and identify some critical process parameters and strategies that may influence the critical quality attributes of the cells with the goal of facilitating scalable manufacturing of human pluripotent stem cell‐derived pancreatic endocrine cells.

Design Considerations for Macroencapsulation Devices for Stem Cell Derived Islets for the Treatment of Type 1 Diabetes

Stem cell derived insulin producing cells or islets have shown promise in reversing Type 1 Diabetes (T1D), yet successful transplantation currently necessitates long-term modulation with immunosuppressant drugs. An alternative approach to avoiding this immune response is to utilize an islet macroencapsulation device, where islets are incorporated into a selectively permeable membrane that can protect the transplanted cells from acute host response, whilst enabling delivery of insulin. These macroencapsulation systems have to meet a number of stringent and challenging design criteria in order to achieve the ultimate goal of reversing T1D. In this progress report, the design considerations and functional requirements of macroencapsulation systems are reviewed, specifically for stem-cell derived islets (SC-islets), highlighting distinct design parameters. Additionally, a perspective on the future for macroencapsulation systems is given, and how incorporating continuous sensing and closed-loop feedback can be transformative in advancing toward an autonomous biohybrid artificial pancreas.

Engineering of Primary Pancreatic Islet Cell Spheroids for Three-dimensional Culture or Transplantation: A Methodological Comparative Study

Three-dimensional (3D) cell culture by engineering spheroids has gained increasing attention in recent years because of the potential advantages of such systems over conventional two-dimensional (2D) tissue culture. Benefits include the ability of 3D to provide a more physiologically relevant environment, for the generation of uniform, size-controlled spheroids with organ-like microarchitecture and morphology. In recent years, different techniques have been described for the generation of cellular spheroids. Here, we have compared the efficiency of four different methods of islet cell aggregation. Rat pancreatic islets were dissociated into single cells before reaggregation. Spheroids were generated either by (i) self-aggregation in nonadherent petri dishes, (ii) in 3D hanging drop culture, (iii) in agarose microwell plates or (iv) using the Sphericalplate 5D™. Generated spheroids consisted of 250 cells, except for the self-aggregation method, where the number of cells per spheroid cannot be controlled. Cell function and morphology were assessed by glucose stimulated insulin secretion (GSIS) test and histology, respectively. The quantity of material, labor intensity, and time necessary for spheroid production were compared between the different techniques. Results were also compared with native islets. Native islets and self-aggregated spheroids showed an important heterogeneity in terms of size and shape and were larger than spheroids generated with the other methods. Spheroids generated in hanging drops, in the Sphericalplate 5D™, and in agarose microwell plates were homogeneous, with well-defined round shape and a mean diameter of 90 µm. GSIS results showed improved insulin secretion in response to glucose in comparison with native islets and self-aggregated spheroids. Spheroids can be generated using different techniques and each of them present advantages and inconveniences. For islet cell aggregation, we recommend, based on our results, to use the hanging drop technique, the agarose microwell plates, or the Sphericalplate 5D™ depending on the experiments, the latter being the only option available for large-scale spheroids production.

Hypothermic oxygenated machine perfusion of the human pancreas for clinical islet isolation: a prospective feasibility study

Due to an increasing scarcity of pancreases with optimal donor characteristics, islet isolation centers utilize pancreases from extended criteria donors, such as from donation after circulatory death (DCD) donors, which are particularly susceptible to prolonged cold ischemia time (CIT). We hypothesized that hypothermic machine perfusion (HMP) can safely increase CIT. Five human DCD pancreases were subjected to 6 h of oxygenated HMP. Perfusion parameters, apoptosis, and edema were measured prior to islet isolation. Five human DBD pancreases were evaluated after static cold storage (SCS). Islet viability, and in vitro and in vivo functionality in diabetic mice were analyzed. Islets were isolated from HMP pancreases after 13.4 h [12.9–14.5] CIT and after 9.2 h [6.5–12.5] CIT from SCS pancreases. Histological analysis of the pancreatic tissue showed that HMP did not induce edema nor apoptosis. Islets maintained >90% viable during culture, and an appropriate in vitro and in vivo function in mice was demonstrated after HMP. The current study design does not permit to demonstrate that oxygenated HMP allows for cold ischemia extension; however, the successful isolation of functional islets from discarded human DCD pancreases after performing 6 h of oxygenated HMP indicates that oxygenated HMP may be a useful technology for better preservation of pancreases.

Superporous agarose scaffolds for encapsulation of adult human islets and human stem-cell-derived β cells for intravascular bioartificial pancreas applications

Type 1 diabetic patients with severe hypoglycemia unawareness have benefitted from cellular therapies, such as pancreas or islet transplantation; however, donor shortage and the need for immunosuppression limits widespread clinical application. We previously developed an intravascular bioartificial pancreas (iBAP) using silicon nanopore membranes (SNM) for immunoprotection. To ensure ample nutrient delivery, the iBAP will need a cell scaffold with high hydraulic permeability to provide mechanical support and maintain islet viability and function. Here, we examine the feasibility of superporous agarose (SPA) as a potential cell scaffold in the iBAP. SPA exhibits 66-fold greater hydraulic permeability than the SNM along with a short (<10 μm) diffusion distance to the nearest islet. SPA also supports short-term functionality of both encapsulated human islets and stem-cell-derived enriched β-clusters in a convection-based system, demonstrated by high viability (>95%) and biphasic insulin responses to dynamic glucose stimulus. These findings suggest that the SPA scaffold will not limit nutrient delivery in a convection-based bioartificial pancreas and merits continued investigation.

Comparison of islet isolation result and clinical applicability according to GMP-grade collagenase enzyme blend in adult porcine islet isolation and culture

Background

Porcine islet xenotransplantation is a promising treatment for type 1 diabetes as an alternative to human pancreatic islet transplantation and long‐term insulin therapy. Several research groups have explored porcine islets as an alternative to the inconsistent and chronic shortage of pancreases from human organ donors. Studies have confirmed successful transplant of porcine islets into non‐human primate models of diabetes; however, in most cases, they require more than one adult porcine donor to achieve sufficient viable islet mass for sustained function. The importance of GMP‐grade reagents includes the following: specific enzymes utilized in the pancreatic isolation process were identified as a key factor in successful human clinical islet transplantation trials using cadaveric islets. As xenotransplantation clinical research progresses, isolation reagents and digestion enzymes play a key role in the consistency of the product and ultimately the outcome of the islet xenotransplant. In this study, we evaluated several commercially available enzyme blends that have been used for islet isolation. We evaluated their impact on islet isolation yield and subsequent islet function as part of our plan to bring xenotransplantation into clinical xenotransplantation trials.

Methods

Adult porcine islets were isolated from 16 to 17‐month‐old Yucatan miniature pigs following standard rapid procurement. Pigs weighed on average 48.71 ± 2.85 kg, and the produced pancreases were 39.51 ± 1.80 grams (mean ± SEM). After ductal cannulation, we evaluated both GMP‐grade enzymes (Collagenase AF‐1 GMP grade and Liberase MTF C/T GMP grade) and compared with standard non‐GMP enzyme blend (Collagenase P). Islet quality control assessments including islet yield, islet size (IEQ), membrane integrity (acridine orange/propidium iodide), and functional viability (GSIS) were evaluated in triplicate on day 1 post‐islet isolation culture.

Results

Islet yield was highest in the group of adult pigs where Collagenase AF‐1 GMP grade was utilized. The mean islet yield was 16 586 ± 1391 IEQ/g vs 8302 ± 986 IEQ/g from pancreases isolated using unpurified crude Collagenase P. The mean islet size was higher in Collagenase AF‐1 GMP grade with neutral protease than in Collagenase P and Liberase MTF C/T GMP grade. We observed no significant difference between the experimental groups, but in vitro islet function after overnight tissue culture was significantly higher in Collagenase AF‐1 GMP grade with neutral protease and Liberase MTF C/T GMP grade than the crude control enzyme group. As expected, the GMP‐grade enzyme has significantly lower endotoxin levels than the crude control enzyme group when measured.

Conclusions

This study validates the importance of using specifically blended GMP grade for adult pig islet isolation for xenotransplantation trials and the ability to isolate a sufficient number of viable islets from one adult pig to provide a sufficient number for islets for a clinical islet transplantation. GMP‐grade enzymes are highly efficient in increasing islet yield, size, viability, and function at a lower and acceptable endotoxin level. Ongoing research transplants these islets into animal models of diabetes to validate in vivo function. Also, these defined and reproducible techniques using GMP‐grade enzymes allow for continuance of our plan to advance to xenotransplantation of isolated pig islets for the treatment of type 1 diabetes.

Islet Transplantation in the Lung via Endoscopic Aerosolization: Investigation of Feasibility, Islet Cluster Cell Vitality, and Structural Integrity

Aerosolized drug delivery has recently attracted much attention as a possible new tool for the delivery of complex nanoparticles. This study aims to investigate whether catheter-based aerosolization of islets via endobronchial systems is a feasible option in islet transplantation. Besides investigating the feasibility of islet aerosolization, we also examined cluster cell vitality and structural integrity of the islets following aerosolization. Using an ex vivo postmortem swine model, porcine pancreatic islets were isolated and aerosolized with an endoscopic spray catheter. Following aerosolization, islet cell vitality and function were assessed via Calcein AM and propidium iodide as well as insulin production after glucose exposure. In the final step, the overall feasibility of the procedure and structural integrity of cells were analyzed and evaluated with respect to clinical applicability. No significant difference was detected in the viability of control islets (90.67 ± 2.19) vs aerosolized islets (90.68 ± 1.20). Similarly, there was no significant difference in control islets (1.62 ± 0.086) vs aerosolized islets (1.42 ± 0.11) regarding insulin release after stimulation. Indocyanine green marked islets were transplanted into the lung without major difficulty. Histological analysis confirmed retained structural integrity and predominant location in the alveolar cavity. Our ex vivo data suggest that catheter-based aerosolized islet cell delivery is a promising tool for the application of cell clusters. According to our data, islet cell clusters delivery is feasible from a mechanical and physical perspective. Moreover, cell vitality and structural integrity remain largely unaffected following aerosolization. These preliminary results are encouraging and represent a first step toward endoscopically assisted islet cell implantation in the lung.

Heterogeneous toroidal spiral particles for islet encapsulation

Transplantable cell encapsulation systems present a promising approach to deliver a therapeutic solution from hormone-producing cells for the treatment of endocrine diseases like type 1 diabetes. However, the development of a broadly effective and safe transplantation system has been challenging. While some current micro-sized capsules have been optimized for adequate nutrient and metabolic transport, they lack the robustness and retrievability for the clinical safety translation that macro-devices may offer. An existing challenge to be addressed in the current macro-devices is their configuration which may lead to unsatisfactory mass transfer. Here, we design and characterize a millimeter-size particle system of poly-ethylene glycol (PEG) featuring internal toroidal spiral channels, called toroidal spiral particles (TSPs). The characteristic internal structure of the TSPs allows for large encapsulation capacity and large surface area available to all the encapsulated cell mass for effective molecular diffusion. The polymeric matrix renders the particle flexible yet robust for safe transplantation and retrieval. We demonstrate the feasibility of fabricating these particles with various polymer compositions, while optimizing their mechanical properties as well as glucose and insulin permeability. Encapsulation of islets of Langerhans is achieved with high loading capacity (∼160 IEQ per TSP) and excellent cell viability. TSP-encapsulated islets showed similar glucose-stimulated insulin secretion to the naked islets. Preliminary biocompatibility of the TSPs on naïve C57BL/6 mice shows minimal inflammatory response after 4-week transplantation into the intraperitoneal (IP) space. Long-term therapeutic efficacy of encapsulated islets needs to be confirmed in diabetic rodent models in the future, while determining minimal mass required to reverse diabetes. However, we believe from the in vitro favorable results and the TSPs' unique design that TSPs may provide a safe, effective method to transplant and retrieve therapeutic cells for type 1 diabetes treatment and may also be applicable for other cell therapies.

The Efficacy of the Hepatocyte Spheroids for Hepatocyte Transplantation

The safety and short-term efficacy of hepatocyte transplantation (HCTx) have been widely proven. However, issues such as reduced viability and/or function of hepatocytes, insufficient engraftment, and lack of a long-term effect have to be overcome for widespread application of HCTx. In this study, we evaluated hepatocyte spheroids (HSs), formed by self-aggregation of hepatocytes, as an alternative to hepatocytes in single-cell suspension. Hepatocytes were isolated from C57BL/6 J mice liver using a three-step collagenase perfusion technique and HSs were formed by the hanging drop method. After the spheroids formation, the HSs showed significantly higher mRNA expression of albumin, ornithine transcarbamylase, glucose-6-phosphate, alpha-1-antitrypsin, low density lipoprotein receptor, coagulation factors, and apolipoprotein E (ApoE) than 2 dimensional (2D)-cultured hepatocytes (p < 0.05). Albumin production by HSs was significantly higher than that by 2D-cultured hepatocytes (9.5 ± 2.5 vs 3.5 ± 1.8 μg/dL, p < 0.05). The HSs, but not single hepatocytes, maintained viability and albumin mRNA expression in suspension (92.0 ± 2.8% and 1.03 ± 0.09 at 6 h). HSs (3.6 × 10⁶ cells) or isolated hepatocytes (fSH, 3.6 × 10⁶ cells) were transplanted into the liver of ApoE knockout (KO-/-) mice via the portal vein. Following transplantation, serum ApoE concentration (ng/mL) of HS-transplanted mice (1w: 63.1 ± 56.7, 4w: 17.0 ± 10.9) was higher than that of fSH-transplanted mice (1 w: 33.4 ± 13.0, 4w: 13.7 ± 9.6). In both groups, the mRNA levels of pro-inflammatory cytokines (IL-6, IL-1β, TNF-α, MCP-1, and MIP-1β) were upregulated in the liver following transplantation; however, no significant differences were observed. Pathologically, transplanted HSs were observed as flat cell clusters in contact with the portal vein wall on day 7. Additionally, ApoE positive cells were observed in the liver parenchyma distant from the portal vein on day 28. Our results indicate that HS is a promising alternative to single hepatocytes and can be applied for HCTx.

In vivovascularization and islet function in a microwell device for pancreatic islet transplantation

Islet encapsulation in membrane-based devices could allow for transplantation of donor islet tissue in the absence of immunosuppression. To achieve long-term survival of islets, the device should allow rapid exchange of essential nutrients and be vascularized to guarantee continued support of islet function. Recently, we have proposed a membrane-based macroencapsulation device consisting of a microwell membrane for islet separation covered by a micropatterned membrane lid. The device can prevent islet aggregation and support functional islet survivalin vitro. Here, based on previous modeling studies, we develop an improved device with smaller microwell dimensions, decreased spacing between the microwells and reduced membrane thickness and investigate its performancein vitroandin vivo. This improved device allows for encapsulating higher islet numbers without islet aggregation and by applying anin vivoimaging system we demonstrate very good perfusion of the device when implanted intraperitoneally in mice. Besides, when it is implanted subcutaneously in mice, islet viability is maintained and a vascular network in close proximity to the device is developed. All these important findings demonstrate the potential of this device for islet transplantation.

Glucose-induced insulin secretion in isolated human islets: Does it truly reflect β-cell function in vivo?

BACKGROUND

Diabetes always involves variable degrees of β-cell demise and malfunction leading to insufficient insulin secretion. Besides clinical investigations, many research projects used rodent islets to study various facets of β-cell pathophysiology. Their important contributions laid the foundations of steadily increasing numbers of experimental studies resorting to isolated human islets.

SCOPE OF REVIEW

This review, based on an analysis of data published over 60 years of clinical investigations and results of more recent studies in isolated islets, addresses a question of translational nature. Does the information obtained in vitro with human islets fit with our knowledge of insulin secretion in man? The aims are not to discuss specificities of pathways controlling secretion but to compare qualitative and quantitative features of glucose-induced insulin secretion in isolated human islets and in living human subjects.

MAJOR CONCLUSIONS

Much of the information gathered in vitro can reliably be translated to the in vivo situation. There is a fairly good, though not complete, qualitative and quantitative coherence between insulin secretion rates measured in vivo and in vitro during stimulation with physiological glucose concentrations, but the concordance fades out under extreme conditions. Perplexing discrepancies also exist between insulin secretion in subjects with Type 2 diabetes and their islets studied in vitro, in particular concerning the kinetics. Future projects should ascertain that the experimental conditions are close to physiological and do not alter the function of normal and diabetic islets.

Bioengineered Islet Cell Transplantation

Purpose of Review

β cell replacement via whole pancreas or islet transplantation has greatly evolved for the cure of type 1 diabetes. Both these strategies are however still affected by several limitations. Pancreas bioengineering holds the potential to overcome these hurdles aiming to repair and regenerate β cell compartment. In this review, we detail the state-of-the-art and recent progress in the bioengineering field applied to diabetes research.

Recent Findings

The primary target of pancreatic bioengineering is to manufacture a construct supporting insulin activity in vivo. Scaffold-base technique, 3D bioprinting, macro-devices, insulin-secreting organoids, and pancreas-on-chip represent the most promising technologies for pancreatic bioengineering.

Summary

There are several factors affecting the clinical application of these technologies, and studies reported so far are encouraging but need to be optimized. Nevertheless pancreas bioengineering is evolving very quickly and its combination with stem cell research developments can only accelerate this trend.

Peritoneal dissolved oxygen and function of encapsulated adult porcine islets transplanted in streptozotocin diabetic mice

BACKGROUND

Alginate-encapsulated islet xenografts have restored normoglycemia in diabetic animals for various periods of time. Plausible mechanisms of graft failure in vivo include immune rejection and hypoxia. We sought to understand the effects of encapsulated adult porcine islet (API) dosage on the peritoneal dissolved oxygen (DO) level in correlation to the achieved glycemic regulation in diabetic mice.

METHODS

Adult porcine islets encapsulated in barium alginate were transplanted intraperitoneally in streptozotocin diabetic BALB/c mice at 6000 and 4000 islet equivalents (IEQ) and in normal mice at 500 IEQ; APIs encapsulated in calcium alginate were transplanted at 6000 IEQ in diabetic mice. In all cases, cell-free barium alginate capsules containing a perfluorocarbon emulsion were co-implanted for DO measurements using ¹⁹ F NMR spectroscopy. Blood glucose levels and peritoneal DO were measured over 60 days or until graft failure. Explanted capsules were evaluated microscopically and histologically.

RESULTS

Both barium and calcium alginate-encapsulated APIs at 6000 IEQ reversed diabetes until day 60; barium alginate-encapsulated APIs at 4000 IEQ also reversed diabetes but with a higher failure rate. Transplanted APIs significantly reduced the peritoneal DO, approximately in a dose-dependent manner. The number of viable islets and the insulin content per capsule decreased over time. Capsules retrieved from normoglycemic mice exhibited minimal host cell adherence.

CONCLUSIONS

Transplantation of encapsulated APIs can reduce peritoneal DO to severely hypoxic levels. Although normoglycemia could be maintained within the study period, the DO levels suggest that hypoxia is a factor contributing to loss of islet viability and insulin secretion with time in mice.

Deciphering the Complex Communication Networks That Orchestrate Pancreatic Islet Function

Pancreatic islets are clusters of hormone-secreting endocrine cells that rely on intricate cell-cell communication mechanisms for proper function. The importance of multicellular cooperation in islet cell physiology was first noted nearly 30 years ago in seminal studies showing that hormone secretion from endocrine cell types is diminished when these cells are dispersed. These studies showed that reestablishing cellular contacts in so-called pseudoislets caused endocrine cells to regain hormone secretory function. This not only demonstrated that cooperation between islet cells is highly synergistic but also gave birth to the field of pancreatic islet organoids. Here we review recent advances related to the mechanisms of islet cell cross talk. We first describe new developments that revise current notions about purinergic and GABA signaling in islets. Then we comment on novel multicellular imaging studies that are revealing emergent properties of islet communication networks. We finish by highlighting and discussing recent synthetic approaches that use islet organoids of varied cellular composition to interrogate intraislet signaling mechanisms. This reverse engineering of islets not only will shed light on the mechanisms of intraislet signaling and define communication networks but also may guide efforts aimed at restoring islet function and β-cell mass in diabetes.

3D perfusion culture of mouse insulinoma in macro-porous scaffolds enhanced insulin production response

To address the remaining issue of poor cell immobilization and insufficient mass transfer in scaffold-based tissue engineering approach for future islet transplantation, we employed a macro-porous poly-l-lactide (PLLA) scaffold immobilizing mouse insulinoma cells and studied its function toward an implantable pancreatic tissue in 7-day perfusion culture. The murine pancreatic β cells could be immobilized in the PLLA scaffold at a high density of 10⁷ cells per cm³ close to the estimated range in normal pancreas. The perfusion culture promoted the 3D cellular organization as observed with live/dead staining and histological staining. The insulin production was significantly enhanced in comparison with static 2D culture and 3D rotational suspension culture by two and six folds, respectively (p < 0.001). As enhanced insulin response was only observed where both the perfusion and 3D cellular organization were present, this could represent important elements in engineering a functional bioartificial pancreas.

3D quantification of changes in pancreatic islets in mouse models of diabetes type I and II

Diabetes is characterized by rising levels of blood glucose and is often associated with a progressive loss of insulin-producing beta cells. Recent studies have demonstrated that it is possible to regenerate new beta cells through proliferation of existing beta cells or trans-differentiation of other cell types into beta cells, raising hope that diabetes can be cured through restoration of functional beta cell mass. Efficient quantification of beta cell mass and islet characteristics is needed to enhance drug discovery for diabetes. Here, we report a 3D quantitative imaging platform for unbiased evaluation of changes in islets in mouse models of type I and II diabetes. To determine whether the method can detect pharmacologically induced changes in beta cell volume, mice were treated for 14 days with either vehicle or the insulin receptor antagonist S961 (2.4 nmol/day) using osmotic minipumps. Mice treated with S961 displayed increased blood glucose and insulin levels. Light-sheet imaging of insulin and Ki67 (also known as Mki67)-immunostained pancreata revealed a 43% increase in beta cell volume and 21% increase in islet number. S961 treatment resulted in an increase in islets positive for the cell proliferation marker Ki67, suggesting that proliferation of existing beta cells underlies the expansion of total beta cell volume. Using light-sheet imaging of a non-obese diabetic mouse model of type I diabetes, we also characterized the infiltration of CD45 (also known as PTPRC)-labeled leukocytes in islets. At 14 weeks, 40% of the small islets, but more than 80% of large islets, showed leukocyte infiltration. These results demonstrate how quantitative light-sheet imaging can capture changes in individual islets to help pharmacological research in diabetes.

Fluorescence lifetime metabolic mapping of hypoxia-induced damage in pancreatic pseudo-islets

Pancreatic islet isolation from donor pancreases is an essential step for the transplantation of insulin-secreting β-cells as a therapy to treat type 1 diabetes mellitus. This process however damages islet basement membranes, which can lead to islet dysfunction or death. Posttransplantation, islets are further stressed by a hypoxic environment and immune reactions that cause poor engraftment and graft failure. The current standards to assess islet quality before transplantation are destructive procedures, performed on a small islet population that does not reflect the heterogeneity of large isolated islet batches. In this study, we incorporated fluorescence lifetime imaging microscopy (FLIM) into a pancreas-on-chip system to establish a protocol to noninvasively assess the viability and functionality of pancreatic β-cells in a three-dimensional in vitro model (= pseudo-islets). We demonstrate how (pre-) hypoxic β-cell-composed pseudo-islets can be discriminated from healthy functional pseudo-islets according to their FLIM-based metabolic profiles. The use of FLIM during the pretransplantation pancreatic islet selection process has the potential to improve the outcome of β-cell islet transplantation.

Spheroid Fabrication Using Concave Microwells Enhances the Differentiation Efficacy and Function of Insulin-Producing Cells via Cytoskeletal Changes

Pancreatic islet transplantation is the fundamental treatment for insulin-dependent diabetes; however, donor shortage is a major hurdle in its use as a standard treatment. Accordingly, differentiated insulin-producing cells (DIPCs) are being developed as a new islet source. Differentiation efficiency could be enhanced if the spheroid structure of the natural islets could be recapitulated. Here, we fabricated DIPC spheroids using concave microwells, which enabled large-scale production of spheroids of the desired size. We prepared DIPCs from human liver cells by trans-differentiation using transcription factor gene transduction. Islet-related gene expression and insulin secretion levels were higher in spheroids compared to those in single-cell DIPCs, whereas actin–myosin interactions significantly decreased. We verified actin–myosin-dependent insulin expression in single-cell DIPCs by using actin–myosin interaction inhibitors. Upon transplanting cells into the kidney capsule of diabetic mouse, blood glucose levels decreased to 200 mg/dL in spheroid-transplanted mice but not in single cell-transplanted mice. Spheroid-transplanted mice showed high engraftment efficiency in in vivo fluorescence imaging. These results demonstrated that spheroids fabricated using concave microwells enhanced the engraftment and functions of DIPCs via actin–myosin-mediated cytoskeletal changes. Our strategy potentially extends the clinical application of DIPCs for improved differentiation, glycemic control, and transplantation efficiency of islets.

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.

Collagen and Endothelial Cell Coculture Improves β-Cell Functionality and Rescues Pancreatic Extracellular Matrix

The use of biomaterials and biomaterial functionalization is a promising approach to support pancreatic islet viability posttransplantation in an effort to reduce insulin dependence for patients afflicted with diabetes mellitus type 1. Extracellular matrix (ECM) proteins are known to impact numerous reparative functions in the body. Assessing how endogenously expressed pancreatic ECM proteins are affected by posttransplant-like hypoxic conditions may provide significant insights toward the development of tissue-engineered therapeutic strategies to positively influence β-cell survival, proliferation, and functionality. Here, we investigated the expression of three relevant groups of pancreatic ECM proteins in human native tissue, including basement membrane (BM) proteins (collagen type 4 [COL4], laminins [LAM]), proteoglycans (decorin [DCN], nidogen-1 [NID1]), and fibril-forming proteins (fibronectin [FN], collagen type 1 [COL1]). In an in vitro hypoxia model, we identified that ECM proteins were differently affected by hypoxic conditions, contributing to an overall loss of β-cell functionality. The use of a COL1 hydrogel as carrier material demonstrated a protective effect on β-cells mitigating the effect of hypoxia on proteoglycans as well as fibril-forming protein expression, supporting β-cell functionality in hypoxia. We further showed that providing endothelial cells (ECs) into the COL1 hydrogel improves β-cell response as well as the expression of relevant BM proteins. Our data show that β-cells benefit from a microenvironment composed of structure-providing COL1 with the incorporation of ECs to withstand the harsh conditions of hypoxia. Such hydrogels support β-cell survival and can serve as an initial source of ECM proteins to allow cell engraftment while preserving cell functionality posttransplantation. Impact statement Expression analysis identifies hypoxia-induced pathological changes in extracellular matrix (ECM) homeostasis as potential targets to support β-cell transplants by encapsulation in biomaterials for the treatment of diabetes mellitus. A collagen-1 hydrogel is shown to attenuate the effect of hypoxia on β-cells and their ECM expression. The functionalization of the hydrogel with endothelial cells increases the β-cell response to glucose and rescues essential basement membrane proteins.

Integration of Islet/Beta-Cell Transplants with Host Tissue Using Biomaterial Platforms

Cell-based therapies are emerging for type I diabetes mellitus (T1D), an autoimmune disease characterized by the destruction of insulin-producing pancreatic β-cells, as a means to provide long-term restoration of glycemic control. Biomaterial scaffolds provide an opportunity to enhance the manufacturing and transplantation of islets or stem cell-derived β-cells. In contrast to encapsulation strategies that prevent host contact with the graft, recent approaches aim to integrate the transplant with the host to facilitate glucose sensing and insulin distribution, while also needing to modulate the immune response. Scaffolds can provide a supportive niche for cells either during the manufacturing process or following transplantation at extrahepatic sites. Scaffolds are being functionalized to deliver oxygen, angiogenic, anti-inflammatory, or trophic factors, and may facilitate cotransplantation of cells that can enhance engraftment or modulate immune responses. This local engineering of the transplant environment can complement systemic approaches for maximizing β-cell function or modulating immune responses leading to rejection. This review discusses the various scaffold platforms and design parameters that have been identified for the manufacture of human pluripotent stem cell-derived β-cells, and the transplantation of islets/β-cells to maintain normal blood glucose levels.