High Seeding Density Induces Local Hypoxia and Triggers a Proinflammatory Response in Isolated Human Islets

Perlecan: An Islet Basement Membrane Protein with Protective Anti-Inflammatory Characteristics

Throughout the isolation process, human islets are subjected to destruction of the islet basement membrane (BM) and reduced oxygen supply. Reconstruction of the BM represents an option to improve islet function and survival post-transplant and may particularly be relevant for islet encapsulation devices and scaffolds. In the present study, we assessed whether Perlecan, used alone or combined with the BM proteins (BMPs) Collagen-IV and Laminin-521, has the ability to protect isolated human islets from hypoxia-induced damage. Islets isolated from the pancreas of seven different organ donors were cultured for 4-5 days at 2% oxygen in plain CMRL (sham-treated controls) or in CMRL supplemented with BMPs used either alone or in combination. Postculture, islets were characterized regarding survival, in vitro function and production of chemokines and reactive oxygen species (ROS). Individually added BMPs significantly doubled islet survival and increased in vitro function. Combining BMPs did not provide a synergistic effect. Among the tested BMPs, Perlecan demonstrated the significantly strongest inhibitory effect on chemokine and ROS production when compared with sham-treatment (p < 0.001). Perlecan may be useful to improve islet survival prior to and after transplantation. Its anti-inflammatory potency should be considered to optimise encapsulation and scaffolds to protect isolated human islets post-transplant.

Solubilized Pancreatic Extracellular Matrix from Juvenile Pigs Protects Isolated Human Islets from Hypoxia-Induced Damage: A Viable Option for Clinical Islet Transplantation

The pancreatic extracellular matrix (ECM) is an enormously complex construct. Previous studies underline the challenges to identify the optimal combinations and ratios of individual ECM proteins for promoting survival and function of isolated and transplanted islets. This study aimed on assessing the efficiency of solubilized natural ECM extracted from juvenile pigs, an unlimited donor source. Isolated human islets were cultured under a hypoxic atmosphere (2% oxygen) in media supplemented with either solubilized porcine pancreatic ECM (ppECM) or a mixture of human ECM proteins composed of collagen-IV, laminin-521, and nidogen-1 (hEPM). Control islets were cultured under identical conditions without ECM-compounds. Reactive oxygen species production increased three-fold in controls but was reduced by hEPM or ppECM. Early apoptosis remained on preculture levels when islets were treated with hEPM or ppECM. Preculture viability was preserved when hEPM or ppECM was administered. Whilst controls failed to respond to glucose challenge, treatment with hEPM or ppECM preserved the physiological insulin response. In summary, overall survival was significantly highest in ppECM-treated islets. This study presents a new approach to protect human islets from hypoxia-induced damage by supplementing media with ppECM extracted from an unlimited donor source. The findings may also serve as starting point for a novel encapsulation technique to protect isolated human islets.

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

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

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

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

Basement membrane proteins improve human islet survival in hypoxia: Implications for islet inflammation

Enzymatic digestion of the pancreas during islet isolation is associated with disintegration of the islet basement membrane (IBM) that can cause reduction of functional and morphological islet integrity. Attempts to re-establish IBM by coating the surface of culture vessels with various IBM proteins (IBMP) have resulted in loss of islet phenotype and function. This study investigated the capability of Collagen-IV, Laminin-521 and Nidogen-1, utilised as single or combined media supplements, to protect human islets cultured in hypoxia. When individually supplemented to media, all IBMP significantly improved islet survival and in-vitro function, finally resulting in as much as a two-fold increase of islet overall survival. In contrast, combining IBMP enhanced the production of chemokines and reactive oxygen species diminishing all positive effects of individually added IBMP. This impact was concentration-dependent and concerned nearly all parameters of islet integrity. Predictive extrapolation of these findings to data from 116 processed human pancreases suggests that more than 90% of suboptimal pancreases could be rescued for clinical islet transplantation increasing the number of transplantable preparations from actual 25 to 40 when adding Nidogen-1 to pretransplant culture. This study suggests that media supplementation with essential IBMP protects human islets from hypoxia. Amongst those, certain IBMP may be incompatible when combined or applied at higher concentrations. STATEMENT OF SIGNIFICANCE: Pancreatic islet transplantation is a minimally-invasive treatment that can reverse type 1 diabetes in certain patients. It involves infusing of insulin-producing cell-clusters (islets) from donor pancreases. Unfortunately, islet extraction is associated with damage of the islet basement membrane (IBM) causing reduced islet function and cell death. Attempts to re-establish the IBM by coating the surface of culture vessels with IBM proteins (IBMP) have been unsuccessful. Instead, we dissolved the most relevant IBM components Collagen-IV, Laminin-521 and Nidogen-1 in media routinely used for clinical islet culture and transplantation. We found human islet survival and function was substantially improved by IBMP, particularly Nidogen-1, when exposed to a hypoxic environment as found in vivo. We also investigated IBMP combinations. Our present findings have important clinical implications.

High Concentrations of Etanercept Reduce Human Islet Function and Integrity

Background

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

Materials and Methods

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

Results

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

Conclusion

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

Automation, Monitoring, and Standardization of Cell Product Manufacturing

Although regenerative medicine products are at the forefront of scientific research, technological innovation, and clinical translation, their reproducibility and large-scale production are compromised by automation, monitoring, and standardization issues. To overcome these limitations, new technologies at software (e.g., algorithms and artificial intelligence models, combined with imaging software and machine learning techniques) and hardware (e.g., automated liquid handling, automated cell expansion bioreactor systems, automated colony-forming unit counting and characterization units, and scalable cell culture plates) level are under intense investigation. Automation, monitoring and standardization should be considered at the early stages of the developmental cycle of cell products to deliver more robust and effective therapies and treatment plans to the bedside, reducing healthcare expenditure and improving services and patient care.

Safety and function of a new pre-vascularized bioartificial pancreas in an allogeneic rat model

Cell encapsulation could overcome limitations of free islets transplantation but is currently limited by inefficient cells immune protection and hypoxia. As a response to these challenges, we tested in vitro and in vivo the safety and efficacy of a new macroencapsulation device named MailPan^®. Membranes of MailPan^® device were tested in vitro in static conditions. Its bio-integration and level of oxygenation was assessed after implantation in non-diabetic rats. Immune protection properties were also assessed in rat with injection in the device of allogeneic islets with incompatible Major Histocompatibility Complex. Finally, function was assessed in diabetic rats with a Beta cell line injected in MailPan^®. In vitro, membranes of the device showed high permeability to glucose, insulin, and rejected IgG. In rat, the device displayed good bio-integration, efficient vascularization, and satisfactory oxygenation (>5%), while positron emission tomography (PET)-scan and angiography also highlighted rapid exchanges between blood circulation and the MailPan^®. The device showed its immune protection properties by preventing formation, by the rat recipient, of antibodies against encapsulated allogenic islets. Injection of a rat beta cell line into the device normalized fasting glycemia of diabetic rat with retrieval of viable cell clusters after 2 months. These data suggest that MailPan^® constitutes a promising encapsulation device for widespread use of cell therapy for type 1 diabetes.

Hypoxia-Induced Damage in Human Islets Is Reduced With the Use of Mesenchymal Stem Cell-Preconditioned Medium

BACKGROUND

Mesenchymal stem cells (MSCs) are protective for islets when cotransplanted in a hypoxic environment. However, the risk of neoplasia is increased when MSCs are transplanted into immunosuppressed patients. This initial study aimed to investigate whether the production of protective factors from MSC can be stimulated by different culture conditions to benefit human islets cultured in hypoxia.

METHODS

MSC were isolated from human adipose tissue and cultured for 2 days in supplemented Minimum Essential Media α (MEMα) and 21% (21%-MEMα) or 1% oxygen (1%-MEMα). Native MEMα served as control. After MSC harvesting, cell-depleted media were frozen at -20°C until use for human islet culture in 2% oxygen for 72-96 hours before islet characterization. Data were normalized to control islets cultured in native MEMα and 2% oxygen (mean ± SEM).

RESULTS

After culture in 21%- or 1%-MEMα, islet recovery increased to 117 ± 12% (NS) and 138 ± 12% (P < .05), respectively. Viability did not change after culture in native MEMα (59 ± 2%), 21%-MEMα (59 ± 3%), or 1%-MEMα (61 ± 3%). Compared with control samples, the glucose stimulation index was increased after culture in 21%-MEMα (P < .05) or 1%-MEMα (P < .05). Overall survival was higher in 1%-MEMα (143 ± 14%) than in 21%-MEMα (119 ± 14%; NS) or native MEMα (P < .05).

CONCLUSIONS

This study demonstrates that MSC-preconditioned MEMα increases survival and in vitro function of hypoxic human islets. These findings indicate that hypoxic MSCs seem to produce factors that improve survival of islets suffering from hypoxia.

Impact of Oxygen on Pancreatic Islet Survival

Pancreatic islet transplantation is a promising treatment option for individuals with type 1 diabetes; however, maintaining islet function after transplantation remains a large challenge. Multiple factors, including hypoxia associated events, trigger pretransplant and posttransplant loss of islet function. In fact, islets are easily damaged in hypoxic conditions before transplantation including the preparation steps of pancreas procurement, islet isolation, and culture. Furthermore, after transplantation, islets are also exposed to the hypoxic environment of the transplant site until they are vascularized and engrafted. Because islets are exposed to such drastic environmental changes, protective measures are important to maintain islet viability and function. Many studies have demonstrated that the prevention of hypoxia contributes to maintaining islet quality. In this review, we summarize the latest oxygen-related islet physiology, including computational simulation. Furthermore, we review recent advances in oxygen-associated treatment options used as part of the transplant process, including up-to-date oxygen generating biomaterials as well as a classical oxygen inhalation therapy.

Effect of Etanercept Concentration on Human Islet Integrity

BACKGROUND

Etanercept is widely used as an antiinflammatory drug to improve engraftment after intraportal islet transplantation. In contrast to other immunosuppressive agents, very little is known about detrimental effects of etanercept on islets. The aim of this pilot study was to define the toxic range of etanercept.

METHODS

Human islets isolated from 8 donors were cultured for 4-5 days at 37°C in culture medium supplemented with etanercept at concentrations from 2.5 to 40 μg/mL, corresponding to potential in vivo levels within the portal vein. After culture, islet equivalent (IEQ) yield, fragmentation index (islet number/IEQ), purity, viability, and stimulated insulin release (2 vs 20 mmol/L) were assessed and normalized to islets before culture.

RESULTS

Yield (73 ± 8%) and viability (91 ± 4%) were highest with 5 μg/mL etanercept. Islet loss was evident when etanercept was ≥10 μg/mL (55 ± 7%; P < .05 vs control). Fragmentation (154 ± 34%; P < .05) was markedly increased and viability (81 ± 4%, P < .05) markedly decreased with etanercept >10 μg/mL. The accumulation of cell debris at concentrations ≥20 μg/mL resulted in a significant reduction of islet purity (84 ± 3%; P < .05). Etanercept did not interfere with stimulated insulin secretion at concentrations ≤10 μg/mL. The maximum stimulation index was noted at 2.5 μg/mL (1.8 ± 0.1).

CONCLUSIONS

Etanercept is tolerated by isolated human islets at concentrations <10 μg/mL. Our data suggest that the tight range between benefit and toxicity should be considered for dosage and administration of etanercept.

Clinical Islet Isolation

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