Endotoxin-mediated delayed islet graft function is associated with increased intra-islet cytokine production and islet cell apoptosis

Optimization of Follicle Isolation for Bioengineering of Human Artificial Ovary

Background: A functional artificial ovary is a promising strategy to recover fertility and restore endocrine function in cancer patients. The aim of this study is to optimize the follicle isolation protocol for cryopreserved human ovarian tissues. Methods: Each of the cryopreserved human ovarian cortex pieces (OCPs) from 10 patients was cut into two equal parts and randomly distributed into two treatment groups. Group 1: OCPs digested with Tumor Dissociation Enzyme (TDE); Group 2: OCPs digested with Liberase Dispase High (DH). The efficiency of both groups were evaluated in terms of yield, viability, morphology, and a short-term in vitro culture (IVC) in alginate scaffolds. Results: The TDE can isolate more primordial follicles and smaller diameter of follicles than Liberase DH. The TDE also enabled the isolation of more bright red follicles, higher percent of viable follicles, more morphologically normal follicles, and lower oxidative stress levels compared with Liberase DH. After eight days of IVC, follicles in the TDE group had a higher growth rate from Day 0 to Day 8, and higher viability on Day 8 than the Liberase DH Group. Conclusion: The TDE can be considered an alternative to Liberase DH, enables the isolation of a higher number of healthy follicles from human OCPs, and improves follicle survival after IVC in contrast to Liberase DH.

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.

A Practical Guide to Rodent Islet Isolation and Assessment Revisited

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

Prevention of Autoimmune Diabetes in NOD Mice by Dimethyl Fumarate

Oxidative stress plays critical roles in the pathogenesis of diabetes. This study tested the hypothesis that by protecting β-cells against oxidative stress and inflammation, an Nrf2 activator, dimethyl fumarate (DMF), may prevent or delay the onset of type 1 diabetes in non-obese diabetic (NOD) mice. Firstly, islet isolation was conducted to confirm the antioxidative effects of DMF oral administration on islet cells. Secondly, in a spontaneous diabetes model, DMF (25 mg/kg) was fed to mice once daily starting at the age of 8 weeks up to the age of 22 weeks. In a cyclophosphamide-induced accelerated diabetes model, DMF (25 mg/kg) was fed to mice twice daily for 2 weeks. In the islet isolation study, DMF administration improved the isolation yield, attenuated oxidative stress and enhanced GCLC and NQO1 expression in the islets. In the spontaneous model, DMF significantly reduced the onset of diabetes compared to the control group (25% vs. 54.2%). In the accelerated model, DMF reduced the onset of diabetes from 58.3% to 16.7%. The insulitis score in the islets of the DMF treatment group (1.6 ± 0.32) was significantly lower than in the control group (3.47 ± 0.21). The serum IL-1α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-9, IL-12p70, IFN-γ, TNF-α, MCP-1 and CXCL16 levels in the DMF-treated group were lower than in the control group. In conclusion, DMF may protect islet cells and reduce the incidence of autoimmune diabetes in NOD mice by attenuating insulitis and proinflammatory cytokine production.

Optimization of Porcine Ovarian Follicle Isolation Methods for Better Developmental Potential

In the present study, we present a comparative analysis among the outputs of porcine follicle isolation using either mechanical technique alone or in combination with enzymes, proposing an optimized protocol useful for all further applications related to follicle in vitro growth and reproductive tissue engineering. The porcine follicles were isolated using mechanical technique alone (hand blender and scalpels) or in combination with collagenase or Liberase Dispase High (DH) at different doses applying different protocols. Finally, the number, morphology, and stage of isolated follicles were compared between the protocols. Moreover, the follicle viability (live/dead assay) and morphology (rhodamine phalloidin and 4',6-diamidino-2-phenylindole staining and scanning electron microscopy analysis) were evaluated after 10 days of culture. We found an optimum protocol for intact follicle isolation using the mechanical technique in combination with enzymes at a concentration of 0.5 mg/mL. However, the number of total isolated follicles and primordial follicles was significantly higher when collagenase was used compared to Liberase DH (p < 0.05), while Liberase DH could isolate a significantly higher percentage of preantral follicles. After 10 days of culture, the morphology and health status of follicles were statistically higher when Liberase DH was used in comparison with collagenase. Moreover, on the follicles extracted with Liberase DH, it was possible to observe theca cells covering part of the follicle surface. In conclusion, we demonstrated that the intact primary or secondary follicles could not be obtained using only mechanical methods, which led to the isolation of denuded oocytes and dramatically damaged follicles. We concluded that the collagenase-based follicle isolation could negatively affect the morphology and developmental potential of the follicles. Moreover, the incubation of ovarian cortex tissues with Liberase DH solution is an optimized protocol for porcine ovarian follicle isolation with developmental competence. Impact statement Isolation and in vitro maturation of follicles can pave the way for activities on reproductive tissue engineering (REPROTEN) and developing an artificial ovary. In this regard, the standardization and optimization of the extraction methods are pivotal for the design of experiment of follicle in vitro growth. In the present study, we provided a comparative analysis among the outputs of porcine follicle isolation using either mechanical technique alone or in combination with collagenase or Liberase DH, proposing an optimized protocol useful for all further applications related to follicles' in vitro growth and REPROTEN.

Immunomodulation Followed by Antigen-Specific Treg Infusion Controls Islet Autoimmunity

Optimal immune-based therapies for type 1 diabetes (T1D) should restore self-tolerance without inducing chronic immunosuppression. CD4⁺Foxp3⁺ regulatory T cells (T_regs) are a key cell population capable of facilitating durable immune tolerance. However, clinical trials with expanded T_regs in T1D and solid-organ transplant recipients are limited by poor T_reg engraftment without host manipulation. We showed that T_reg engraftment and therapeutic benefit in nonautoimmune models required ablative host conditioning. Here, we evaluated T_reg engraftment and therapeutic efficacy in the nonobese diabetic (NOD) mouse model of autoimmune diabetes using nonablative, combinatorial regimens involving the anti-CD3 (αCD3), cyclophosphamide (CyP), and IAC (IL-2/JES6-1) antibody complex. We demonstrate that αCD3 alone induced substantial T-cell depletion, impacting both conventional T cells (T_conv) and T_regs, subsequently followed by more rapid rebound of T_regs Despite robust depletion of host T_conv and host T_regs, donor T_regs failed to engraft even with interleukin-2 (IL-2) support. A single dose of CyP after αCD3 depleted rebounding host T_regs and resulted in a 43-fold increase in donor T_reg engraftment, yet polyclonal donor T_regs failed to reverse diabetes. However, infusion of autoantigen-specific T_regs after αCD3 alone resulted in robust T_reg engraftment within the islets and induced remission in all mice. This novel combinatorial therapy promotes engraftment of autoantigen-specific donor T_regs and controls islet autoimmunity without long-term immunosuppression.

3-D physiomimetic extracellular matrix hydrogels provide a supportive microenvironment for rodent and human islet culture

Organ-on-a-chip platforms serve as cost-efficient testbeds for screening pharmaceutical agents, mimicking natural physiology, and studying disease. In the field of diabetes, the development of an islet-on-a-chip platform would have broad implications in understanding disease pathology and discovering potential therapies. Islet microphysiological systems are limited, however, by their poor cell survival and function in culture. A key factor that has been implicated in this decline is the disruption of islet-matrix interactions following isolation. Herein, we sought to recapitulate the in vivo peri-islet niche using decellularized extracellular matrix (ECM) hydrogels. Sourcing from porcine bladder, lung, and pancreas tissues, 3-D ECM hydrogels were generated, characterized, and validated using both rodent and human pancreatic islets. Optimized decellularization protocols resulted in hydrogels with distinctive viscoelastic properties that correlated to their matrix composition. The in situ 3-D encapsulation of human or rat islets within ECM hydrogels resulted in improved functional stability over standard culture conditions. Islet composition and morphology were also altered, with enhanced retention of islet-resident endothelial cells and the formation of cord-like structures or sprouts emerging from the islet spheroid. These supportive 3-D physiomimetic ECM hydrogels can be leveraged within microfluidic platforms for the long-term culture of islets.

Automated, High-Throughput Assays for Evaluation of Human Pancreatic Islet Function

An important challenge in pancreatic islet transplantation in association with type 1 diabetes is to define automatic high-throughput assays for evaluation of human islet function. The physiological techniques presently used are amenable to small-scale experimental samples and produce descriptive results. The postgenomic era provides an opportunity to analyze biological processes on a larger scale, but the transition to high-throughput technologies is still a challenge. As a first step to implement high-throughput assays for the study of human islet function, we have developed two methodologies: multiple automated perifusion to determine islet hormone secretion and high-throughput kinetic imaging to examine islet cellular responses. Both technologies use fully automated devices that allow performing simultaneous experiments on multiple islet preparations. Our results illustrate that these technologies can be applied to study the functional status and explore the pharmacological profiles of islet cells. These methodologies will enable functional characterization of human islet preparations before transplantation and thereby provide the basis for the establishment of predictive tests for β-cell potency.

Amelioration of Diabetes in Mice after Single-Donor Islet Transplantation Using the Controlled Release of Gelatinized FGF-2

Fibroblast growth factor (FGF)-2 has been recognized to be a key element involved in angiogenesis and a putative factor involved in stem cell-mediated islet regeneration. However, the usefulness of FGF-2 in an islet transplantation setting has not yet been explored. We therefore evaluated the effect of FGF-2 on both islet culture and islet transplantation. Isolated islets were cultured in the presence of 100 ng/ml FGF-2 for a week and then the glucose-responding insulin secretion and insulin contents were measured. Gelatinized FGF-2 (100 ng), which allowed the controlled release of FGF-2, was used for islet transplantation of streptozotocin-induced diabetic mice. Islets (150 IEQ), obtained from a single donor, mixed with gelatinized FGF-2, were transplanted into the subrenal capsule of the mice and the animals were observed for 30 days. Revascularization around the islet grafts was examined. The blood glucose levels were measured and the intraperitoneal glucose tolerance test (IPGTT) was performed. The supplementation of FGF-2 maintained proper insulin secretion and insulin contents in an in vitro culture. The use of gelatinized FGF-2 facilitated revascularization and favorable islet engraftment, thus resulting in an amelioration of the blood glucose levels in diabetic mice. The utilization of FGF-2 showed increased contents of insulin in the islet grafts and revealed a similar pattern as that of normal healthy mice in IPGTT. In contrast, the transplantation of islets without FGF-2 supplementation showed poor revascularization and failed to control the blood glucose levels in the diabetic mice.

Delivery of TAT/PTD-Fused Proteins/Peptides to Islets via Pancreatic Duct

Delivering cytoprotective proteins/peptides into pancreata prior to islet isolation through protein transduction (PT) is a novel strategy to enhance the yield of viable transplantable islets. Previous work has shown that the protein transduction domain PTD-5 efficiently transduced islets via the pancreatic duct. TAT/PTD is a well-characterized PTD with the capability to cross even the hemato–encephalic barrier. In this study, we investigated the utilization of the 11-aa TAT protein transduction domain (TAT/PTD) to deliver peptides or proteins of different sizes ranging from 1.2 to 120 kDa, as the TAT/PTD and TAT/PTD-BH4 peptide, or the TAT/PTD–β-galactosidase fusion protein, into islets through the pancreatic duct. Using flow cytometry analysis we found that TAT/PTD derivatives transduced practically 100% of the islet cell population. Moreover, confocal laser scanning microscopy in live, nonfixed islets confirmed these results assessing transduction of TAT/PTD molecules into intact nondisaggregated islets. TAT–β-galactosidase peptide conjugated to FITC was not compartment selective, as both cytoplasmic and nucleic cellular compartments were positively stained. Furthermore, TAT–β-galactosidase peptide delivery was highly effective, as even cells located in the inner core region of the islets were transduced. Finally, transduced TAT–β-galactosidase fusion protein was biologically active after islet isolation and manipulation, and islet insulin secretion capability was not compromised by peptide transduction. These findings suggest that the transduction of chimeric TAT/PTD proteins can represent an efficient tool of molecular delivery independent of the size, to enhance or modify a specific phenotype at the nuclei or cytoplasmic level.

Effect of Pretransplant Preconditioning by Whole Body Hyperthermia on Islet Graft Survival

Previous observations in heat-shocked pig islets revealed the ambivalent character of the stress response simultaneously inducing processes of protection and apoptosis. To clarify whether the proapoptotic character of the stress response is reduced in heat-exposed islets still embedded in their native environment, hyperthermia was performed in the present study either as whole body hyperthermia (WBH) prior to pancreas resection or as in vitro heat shock (HS) after isolation. HS (42°C/45 min) was induced in donors 12 h before isolation (WBH, n = 32) or in freshly isolated islets prior to 12 h of culture at 37°C (in vitro HS, n = 25). Islets continuously incubated at 37°C served as controls (n = 34). Proinflammatory treatment was performed with H2O2, DETA-NO, or a combination of IL-1β, TNF-α, and IFN-γ. Quality assessment included islet yield, viability staining, static glucose incubation, and nude mouse transplantation. WBH was significantly less effective than in vitro HS to induce HSP70 overexpression and to increase islet resistance against inflammatory mediators. Although characterized by an unaltered Bax to Bcl-2 ratio, islets subjected to WBH partially failed to restore sustained normoglycemia in diabetic nude mice. The inflammatory response observed in the pancreas of WBH-treated rats was associated with significantly reduced viability that seems to have a higher predictive value for posttransplant outcome compared to islet in vitro function or mitochondrial activity. In contrast, in vitro HS significantly decreased transcript levels of Bcl-2, but did not affect posttransplant function compared to sham-treated islets. These findings suggest that WBH is primarily associated with increased necrosis as a secondary tissue type-specific effect of pancreas damage while in vitro HS mainly induces apoptosis.

Comparison of Size, Viability, and Function of Fetal Pig Islet-Like Cell Clusters after Digestion Using Collagenase or Liberase

Liberase is a highly purified blend of collagenases that has been specifically developed to eliminate the numerous problems associated with the conventional use of crude collagenase when isolating islet-like cell clusters (ICCs) from pancreases of different species. The influence of Liberase on yield, size, viability, and function of ICCs has been documented when this enzyme was used to digest adult but not fetal pancreases. In this study, we compared the effects of collagenase and Liberase on fetal pig ICCs. A total of eight fetal pig pancreas digestions were analyzed. Fetuses were obtained from Large White Landrace pigs of gestational age 80 ± 2.1 days. The pancreases were digested with either 3 mg/ml collagenase P or 1.2 mg/ml Liberase HI. The time taken to digest the pancreas was shorter for collagenase when compared with Liberase (22 ± 2 vs. 31 ± 2 min). The size of ICCs was similar for both collagenase (83 ± 0.5 μm) and Liberase (79 ± 0.4 μm) as was the number of ICCs produced per pancreas (7653 ± 1297 vs. 8101 ± 1177). Viability, as assessed using fluorescent markers, was slightly greater for Liberase (79 ± 1% vs. 76 ± 1%, p < 0.05). Responsiveness to β-cell stimulus (20 mM KCl) was similar for both methods of isolation, as was the insulin content of the ICCs, both in vitro and at 1 month after transplantation of 1500 ICCs beneath the renal capsule of immunoincompetent mice. Despite the high content of endotoxins in collagenase, the above results show that this enzyme was equally as efficient as Liberase in isolating functional ICCs from fetal pig pancreas.

Enzyme Development for Human Islet Isolation: Five Decades of Progress or Stagnation?

In comparison to procedures used for the separation of individual cell types from other organs, the process of human pancreatic islet isolation aims to digest the pancreatic exocrine matrix completely without dispersing the individual cells within the endocrine cell cluster. This objective is unique within the field of tissue separation, and outlines the challenge of islet isolation to balance two opposing priorities. Although significant progress has been made in the characterization and production of enzyme blends for islet isolation, there are still numerous areas which require improvement. The ultimate goal of enzyme production, namely the routine production of a consistent and standardized enzyme blend, has still not been realized. This seems to be mainly the result of a lack of detailed knowledge regarding the structure of the pancreatic extracellular matrix and the synergistic interplay between collagenase and different supplementary proteases during the degradation of the extracellular matrix. Furthermore, the activation of intrinsic proteolytic enzymes produced by the pancreatic acinar cells, also impacts on the chance of a successful outcome of human islet isolation. This overview discusses the challenges of pancreatic enzymatic digestion during human islet isolation, and outlines the developments in this field over the past 5 decades.

Silicon nanopore membrane (SNM) for islet encapsulation and immunoisolation under convective transport

Problems associated with islet transplantation for Type 1 Diabetes (T1D) such as shortage of donor cells, use of immunosuppressive drugs remain as major challenges. Immune isolation using encapsulation may circumvent the use of immunosuppressants and prolong the longevity of transplanted islets. The encapsulating membrane must block the passage of host’s immune components while providing sufficient exchange of glucose, insulin and other small molecules. We report the development and characterization of a new generation of semipermeable ultrafiltration membrane, the silicon nanopore membrane (SNM), designed with approximately 7 nm-wide slit-pores to provide middle molecule selectivity by limiting passage of pro-inflammatory cytokines. Moreover, the use of convective transport with a pressure differential across the SNM overcomes the mass transfer limitations associated with diffusion through nanometer-scale pores. The SNM exhibited a hydraulic permeability of 130 ml/hr/m²/mmHg, which is more than 3 fold greater than existing polymer membranes. Analysis of sieving coefficients revealed 80% reduction in cytokines passage through SNM under convective transport. SNM protected encapsulated islets from infiltrating cytokines and retained islet viability over 6 hours and remained responsive to changes in glucose levels unlike non-encapsulated controls. Together, these data demonstrate the novel membrane exhibiting unprecedented hydraulic permeability and immune-protection for islet transplantation therapy.

Isolation and Flow Cytometric Analysis of Immune Cells from the Ischemic Mouse Brain

Ischemic stroke initiates a robust inflammatory response that starts in the intravascular compartment and involves rapid activation of brain resident cells. A key mechanism of this inflammatory response is the migration of circulating immune cells to the ischemic brain facilitated by chemokine release and increased endothelial adhesion molecule expression. Brain-invading leukocytes are well-known contributing to early-stage secondary ischemic injury, but their significance for the termination of inflammation and later brain repair has only recently been noticed.

Here, a simple protocol for the efficient isolation of immune cells from the ischemic mouse brain is provided. After transcardial perfusion, brain hemispheres are dissected and mechanically dissociated. Enzymatic digestion with Liberase is followed by density gradient (such as Percoll) centrifugation to remove myelin and cell debris. One major advantage of this protocol is the single-layer density gradient procedure which does not require time-consuming preparation of gradients and can be reliably performed. The approach yields highly reproducible cell counts per brain hemisphere and allows for measuring several flow cytometry panels in one biological replicate. Phenotypic characterization and quantification of brain-invading leukocytes after experimental stroke may contribute to a better understanding of their multifaceted roles in ischemic injury and repair.

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

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.

Insulin signaling: implications for podocyte biology in diabetic kidney disease

PURPOSE OF REVIEW

Several key elements of the insulin signaling cascade contribute to podocyte function and survival. While it was initially thought that the consequences of altered insulin signaling to podocyte function was strictly related to altered glucose uptake, it has become clear that upstream signaling events involved in cell survival, lipid metabolism or nutrient sensing and modulated by insulin are strong independent contributors to podocyte function.

RECENT FINDINGS

Akt2, the major isoform of Akt activated following cellular insulin stimulation, protects against the progression of renal disease in nephron-deficient mice, and podocyte-specific deletion of Akt2 results in a more rapid progression of experimental glomerular disease. In diabetes, podocyte mammalian target of rapamycin activation clearly contributes to podocyte injury and regulated autophagy. Furthermore, podocyte-specific glucose transporter type 4 (GLUT4) deficiency protects podocytes by preventing mammalian target of rapamycin signaling independently of glucose uptake. Finally, intracellular lipids have been recently recognized as major modulators of podocyte insulin signaling and as a new therapeutic target.

SUMMARY

The identification of new contributors to podocyte insulin signaling is of extreme translational value as it may lead to new drug development strategies for diabetic kidney disease, as well as for other proteinuric kidney diseases.

Nonenzymatic Cryogenic Isolation of Therapeutic Cells: Novel Approach for Enzyme-Free Isolation of Pancreatic Islets Using In Situ Cryopreservation of Islets and Concurrent Selective Freeze Destruction of Acinar Tissue

Cell-based therapies, which all involve processes for procurement and reimplantation of living cells, currently rely upon expensive, inconsistent, and even toxic enzyme digestion processes. A prime example is the preparation of isolated pancreatic islets for the treatment of type 1 diabetes by transplantation. To avoid the inherent pitfalls of these enzymatic methods, we have conceptualized an alternative approach based on the hypothesis that cryobiological techniques can be used for differential freeze destruction of the pancreas (Px) to release islets that are selectively cryopreserved in situ. Pancreata were procured from juvenile pigs using approved procedures. The concept of cryoisolation is based on differential processing of the pancreas in five stages: 1) infiltrating islets in situ preferentially with a cryoprotectant (CPA) cocktail via antegrade perfusion of the major arteries; 2) retrograde ductal infusion of water to distend the acinar; 3) freezing the entire Px solid to lt; −160°C for storage in liquid nitrogen; 4) mechanically crushing and pulverizing the frozen Px into small fragments; 5) thawing the frozen fragments, filtering, and washing to remove the CPA. Finally, the filtered effluent (cryoisolate) was stained with dithizone for identification of intact islets and with Syto 13/PI for fluorescence viability testing and glucose-stimulated insulin release assessment. As predicted, the cryoisolate contained small fragments of residual tissue comprising an amorphous mass of acinar tissue with largely intact and viable (>90%) embedded islets. Islets were typically larger (range 50–500 μm diameter) than their counterparts isolated from juvenile pigs using conventional enzyme digestion techniques. Functionally, the islets from replicate cryoisolates responded to a glucose challenge with a mean stimulation index = 3.3 ± 0.7. An enzyme-free method of islet isolation relying on in situ cryopreservation of islets with simultaneous freeze destruction of acinar tissue is feasible and proposed as a new and novel method that avoids the problems associated with conventional collagenase digestion methods.

Follicles of various maturation stages react differently to enzymatic isolation: a comparison of different isolation protocols

Isolation of human follicles is based on digestion of the tissue by combinations of enzymes. Follicle vitality and morphology are often based on the analysis of pooled follicles of different maturation stages. Information is therefore lacking on the effect of the isolation protocol to individual follicles of different maturation stages. A study was conducted using five protocols combining different enzymes and varying concentrations. Isolated follicles were classified according to their maturation stages, counted and characterized for vitality, morphology, early apoptosis and organization of transzonal projections. No statistical differences were found between the protocols when outcome parameters were analysed on a pool of follicles regardless of their maturation status. Differences were observed in quality when the follicles were analysed separately according to their maturation status. Combining morphologic characteristics and vitality, both Liberase DH and Liberase TM combined with collagenase IV were better at isolating high-quality primordial follicles, compared with collagenase IV. No statistical difference between the isolation protocols was found for primary follicles. If only high-quality isolated secondary follicles are needed, collagenase IV is found to be most advantageous. Follicles of different maturation stages react differently when enzymatic isolation protocols are compared.

Real-time immune cell interactions in target tissue during autoimmune-induced damage and graft tolerance

Real-time imaging studies are reshaping immunological paradigms, but a visual framework is lacking for self-antigen-specific T cells at the effector phase in target tissues. To address this issue, we conducted intravital, longitudinal imaging analyses of cellular behavior in nonlymphoid target tissues to illustrate some key aspects of T cell biology. We used mouse models of T cell-mediated damage and protection of pancreatic islet grafts. Both CD4(+) and CD8(+) effector T (Teff) lymphocytes directly engaged target cells. Strikingly, juxtaposed β cells lacking specific antigens were not subject to bystander destruction but grew substantially in days, likely by replication. In target tissue, Foxp3(+) regulatory T (Treg) cells persistently contacted Teff cells with or without involvement of CD11c(+) dendritic cells, an observation conciliating with the in vitro "trademark" of Treg function, contact-dependent suppression. This study illustrates tolerance induction by contact-based immune cell interaction in target tissues and highlights potentials of tissue regeneration under antigenic incognito in inflammatory settings.

Anti-caspase-3 preconditioning increases proinsulin secretion and deteriorates posttransplant function of isolated human islets

Human islet isolation is associated with adverse conditions inducing apoptosis and necrosis. The aim of the present study was to assess whether antiapoptotic preconditioning can improve in vitro and posttransplant function of isolated human islets. A dose-finding study demonstrated that 200 μmol/L of the caspase-3 inhibitor Ac-DEVD-CMK was most efficient to reduce the expression of activated caspase-3 in isolated human islets exposed to severe heat shock. Ac-DEVD-CMK-pretreated or sham-treated islets were transplanted into immunocompetent or immunodeficient diabetic mice and subjected to static glucose incubation to measure insulin and proinsulin secretion. Antiapoptotic pretreatment significantly deteriorated graft function resulting in elevated nonfasting serum glucose when compared to sham-treated islets transplanted into diabetic nude mice (p < 0.01) and into immunocompetent mice (p < 0.05). Ac-DEVD-CMK pretreatment did not significantly change basal and glucose-stimulated insulin release compared to sham-treated human islets but increased the proinsulin release at high glucose concentrations (20 mM) thus reducing the insulin-to-proinsulin ratio in preconditioned islets (p < 0.05). This study demonstrates that the caspase-3 inhibitor Ac-DEVD-CMK interferes with proinsulin conversion in preconditioned islets reducing their potency to cure diabetic mice. The mechanism behind this phenomenon is unclear so far but may be related to the ketone CMK linked to the Ac-DEVD molecule. Further studies are required to identify biocompatible caspase inhibitors suitable for islet preconditioning.

Electrofusion of mesenchymal stem cells and islet cells for diabetes therapy: a rat model

Islet transplantation is a minimally invasive treatment for severe diabetes. However, it often requires multiple donors to accomplish insulin-independence and the long-term results are not yet satisfying. Therefore, novel ways to overcome these problems have been explored. Isolated islets are fragile and susceptible to pro-apoptotic factors and poorly proliferative. In contrast, mesenchymal stem cells (MSCs) are highly proliferative, anti-apoptotic and pluripotent to differentiate toward various cell types, promote angiogenesis and modulate inflammation, thereby studied as an enhancer of islet function and engraftment. Electrofusion is an efficient method of cell fusion and nuclear reprogramming occurs in hybrid cells between different cell types. Therefore, we hypothesized that electrofusion between MSC and islet cells may yield robust islet cells for diabetes therapy. We establish a method of electrofusion between dispersed islet cells and MSCs in rats. The fusion cells maintained glucose-responsive insulin release for 20 days in vitro. Renal subcapsular transplantation of fusion cells prepared from suboptimal islet mass (1,000 islets) that did not correct hyperglycemia even if co-transplanted with MSCs, caused slow but consistent lowering of blood glucose with significant weight gain within the observation period in streptozotocin-induced diabetic rats. In the fusion cells between rat islet cells and mouse MSCs, RT-PCR showed new expression of both rat MSC-related genes and mouse β-cell-related genes, indicating bidirectional reprogramming of both β-cell and MSCs nuclei. Moreover, decreased caspase3 expression and new expression of Ki-67 in the islet cell nuclei suggested alleviated apoptosis and gain of proliferative capability, respectively. These results show that electrofusion between MSCs and islet cells yield special cells with β-cell function and robustness of MSCs and seems feasible for novel therapeutic strategy for diabetes mellitus.

Clinical islet isolation outcomes with a highly purified neutral protease for pancreas dissociation

BACKGROUND

Pancreas dissociation is a critical initial component of the islet isolation procedure and introduces high variability based on factors including the enzyme type, specificity and potency. Product refinement and alterations to the application strategies have improved isolation outcomes over time; however, islet utilization from donor organs remains low. In this study we evaluate a low endotoxin-high activity grade neutral protease in clinical islet isolation.

MATERIALS AND METHODS

The use of a non-collagenolytic enzyme, either thermolysin or high active neutral protease, was randomized in clinical islet isolations to evaluate efficacy. Additionally a retrospective comparison to neutral protease NB was conducted.

RESULTS

The thermolysin group had lower trapped islet population and increased purity and post-culture islet mass in comparison to high active grade neutral protease. Comparison of neutral protease NB GMP grade to high active neutral protease displayed no measurable difference in islet mass or viability and transplantation outcomes at 1 mo post-transplant were favorable for both groups.

CONCLUSIONS

High activity neutral protease can generate clinical grade islets and may prove beneficial to islet function and viability based on a reduced endotoxin load but dosing of neutral protease requires ongoing optimization.

Islet isolation from adult designated pathogen-free pigs: use of the newer bovine nervous tissue-free enzymes and a revised donor selection strategy would improve the islet graft function

BACKGROUND

In clinical trials using adult porcine islet products, islets should be isolated from the designated pathogen-free (DPF) pigs under the current good manufacturing practice (GMP) regulations. Our previous studies suggested that male DPF pigs are better donors than retired breeder pigs and histomorphometrical parameters of donor pancreas predict the porcine islet quality. We aimed to investigate whether the use of the newer bovine nervous tissue-free enzymes and a revised donor selection strategy could improve the islet graft function in the context of islet isolation with DPF pigs.

METHODS

Using 30 DPF pigs within a closed herd, we compared the islet yield of porcine islets isolated with Liberase PI (n = 11, as a historical control group), Liberase MTF C/T, which is a GMP-grade enzyme (n = 12), and CIzyme collagenase MA/BP protease (n = 7). We analyzed the relationship between the diabetes reversal rate of recipient NOD/SCID mice (n = 75) and histomorphometric parameters of each donor pancreas as well as donor characteristics.

RESULTS

Proportion of islets larger than 200 μm from the biopsied donor pancreas (P = 0.006) better predicted islet yield than age (P = 0.760) or body weight (P = 0.371) of donor. The proportion of islets larger than 200 μm from the biopsied donor pancreas was not related to the sex of the donor miniature pig (P = 0.358). The islet yield obtained with the three enzymes did not differ, even after stratification of the donor with the histomorphometric parameters of the biopsied donor pancreas and the sex of donor. The use of the newer bovine nervous tissue-free enzymes (P < 0.001), a higher proportion of large islets in donor pancreas (P = 0.006), and a male sex of the donor (P = 0.025) were independent predictors of earlier diabetes reversal.

CONCLUSIONS

Use of the newer bovine nervous tissue-free enzymes including a GMP-grade enzyme resulted in better islet quality than that of islet isolated using Liberase PI. To obtain high-quality islet from DPF pigs, the donor should be male pig and histomorphometrical parameters from donor pancreas should be considered.

Evidence of endoplasmic reticulum stress mediating cell death in transplanted human islets

A key limitation to the success of islet transplantation is islet cell exhaustion and cell death during islet isolation and following transplantation. Endoplasmic reticulum (ER) stress has been identified as an important mechanism in the development of β-cell dysfunction, cell death, and diabetes. This study investigated the role of ER stress in islet loss during human islet isolation and posttransplantation in a diabetic athymic mouse model. Islets were isolated from human organ donor pancreata using intraductal enzymatic dissociation and continuous density gradient purification. ER stress mediators were assessed by Western blot and by RT-PCR. Caspase-3 activity was quantified by a bioluminescent peptide cleavage assay. Normal and streptozotocin-treated diabetic nude mice were transplanted with 2,000 IEQ of human islets under the kidney capsule and the grafts were harvested 3 or 28 days after transplantation. The grafts were analyzed for the presence for ER stress signals by immunohistochemistry. Isolated islets demonstrated higher levels of ER chaperone Bip, ER stress mediators eIF2α, ATF, spliced XBP-1, and CHOP, and also ER stress-associated apoptotic signals like JNK, caspase-3/7, and cleaved PARP. Donor pancreatic tissue did not show expression of any of these ER stress mediators. After transplantation, low expression of only protective ER stress mediators was evident in the grafts from the normal recipients. In contrast, both protective and apoptotic ER stress mediators were highly expressed in the grafts of hyperglycemic mice. ER stress mediators were induced during islet isolation and may contribute to islet apoptosis and cell death. Islet isolation activates ER stress and apoptotic pathways in isolated islets. Hyperglycemia may prolong this ER stress signal in engrafted islets, converting the protective aspects of the ER stress response to a proapoptotic response and thus contribute to deterioration of β-cell function and survival.

Donor islet endothelial cells in pancreatic islet revascularization

OBJECTIVE

Freshly isolated pancreatic islets contain, in contrast to cultured islets, intraislet endothelial cells (ECs), which can contribute to the formation of functional blood vessels after transplantation. We have characterized how donor islet endothelial cells (DIECs) may contribute to the revascularization rate, vascular density, and endocrine graft function after transplantation of freshly isolated and cultured islets.

RESEARCH DESIGN AND METHODS

Freshly isolated and cultured islets were transplanted under the kidney capsule and into the anterior chamber of the eye. Intravital laser scanning microscopy was used to monitor the revascularization process and DIECs in intact grafts. The grafts' metabolic function was examined by reversal of diabetes, and the ultrastructural morphology by transmission electron microscopy.

RESULTS

DIECs significantly contributed to the vasculature of fresh islet grafts, assessed up to 5 months after transplantation, but were hardly detected in cultured islet grafts. Early participation of DIECs in the revascularization process correlated with a higher revascularization rate of freshly isolated islets compared with cultured islets. However, after complete revascularization, the vascular density was similar in the two groups, and host ECs gained morphological features resembling the endogenous islet vasculature. Surprisingly, grafts originating from cultured islets reversed diabetes more rapidly than those originating from fresh islets.

CONCLUSIONS

In summary, DIECs contributed to the revascularization of fresh, but not cultured, islets by participating in early processes of vessel formation and persisting in the vasculature over long periods of time. However, the DIECs did not increase the vascular density or improve the endocrine function of the grafts.

Evaluation of viable β-cell mass is useful for selecting collagenase for human islet isolation: comparison of collagenase NB1 and liberase HI

The selection of enzyme blend is critical for the success of human islet isolations. Liberase HI collagenase (Roche) was introduced in the 1990s and had been widely used for clinical islet transplantation. More recently, a blend collagenase NB1 has been rendered available. The aim of this study was to evaluate the isolation outcomes and islet quality comparing human islet cells processed using NB1 and Liberase HI. A total of 90 isolations processed using NB1 (n = 40) or Liberase HI (n = 50) was retrospectively analyzed. Islet yield, function in vitro and in vivo, cellular (including β-cell-specific) viability and content, as well as isolation-related factors were compared. No significant differences in donor-related factors were found between the groups. There were also no significant differences in islet yields (NB1 vs. Liberase: 263,389 ± 21,550 vs. 324,256 ± 27,192 IEQ; p = n.s., respectively). The pancreata processed with NB1 showed a significantly longer digestion time (18.6 ± 0.7 vs. 14.5 ± 0.5 min, p < 0.01), lower β-cell viability (54.3 ± 3.4% vs. 72.0 ± 2.1%, p < 0.01), β-cell mass (93,671 ± 11,150 vs. 148,961 ± 12,812 IEQ, p < 0.01), and viable β-cell mass (47,317 ± 6,486 vs. 106,631 ± 10,228 VβIEQ, p < 0.01) than Liberase HI. In addition, islets obtained with Liberase showed significantly better graft function in in vivo assessment of islet potency. The utilization of collagenase NB1 in human islet isolation was associated with significantly lower β-cell viability, mass, and islet potency in vivo in our series when compared to Liberase HI, even though there was no significant difference in islet yields between the groups. Evaluation of viable β-cell mass contained in human islet preparations will be useful for selecting enzyme blends.

A novel method for quantitative monitoring of transplanted islets of langerhans by positive contrast magnetic resonance imaging

The Automatic Quantitative Ultrashort Echo Time imaging (AQUTE) protocol for serial MRI allows quantitative in vivo monitoring of iron labeled pancreatic islets of Langerhans transplanted into the liver, quantifying graft implantation and persistence in a rodent model. Rats (n = 14), transplanted with iron oxide loaded cells (0-4000 islet equivalents, IEQ), were imaged using a 3D radial ultrashort echo time difference technique (dUTE) on a Siemens MAGNETOM 3T clinical scanner up to 5 months postsurgery. In vivo 3D dUTE images gave positive contrast from labeled cells, suppressing liver signal and small vessels, allowing automatic quantification. Position of labeled islet clusters was consistent over time and quantification of hyperintense pixels correlated with the number of injected IEQs (R² = 0.898, p < 0.0001), and showed persistence over time (5 months posttransplantation). Automatic quantification was superior to standard imaging and manual counting methods, due to the uniform suppressed background and high contrast, resulting in significant timesavings, reproducibility and ease of quantification. Three-dimensional coverage of the whole liver in the absence of cardiac/respiratory artifact provided further improvement over conventional imaging. This imaging protocol reliably quantifies transplanted islet mass and has high translational potential to clinical studies of transplanted pancreatic islets.

Highly purified versus filtered crude collagenase: comparable human islet isolation outcomes

This study was designed to retrospectively compare the impact of crude Sigma V collagenase (Sigma V, n = 52) with high-purified Serva NB1 collagenase (Serva NB1, n = 42) on human islet isolation outcomes. A three-step filtration was applied to the crude Sigma V to remove endotoxin contamination and impurities; in addition, this process was used as a lot prescreening tool. Isolation outcomes were determined by digestion efficacy, islet yields, purity, viability, glucose-stimulated insulin release, and endotoxin content. The digestion efficacy between Sigma V and Serva NB1 was statistically significant (Sigma V: 64.71% vs. Serva NB1: 69.71%, p = 0.0014). However, the islet yields were similar (Sigma V: 23422.58 vs. Serva NB1: 271097 IEq, p = 0.23) between groups. There was no significant purity difference observed in fractions with purities greater than 75%. Viability (Sigma V: 93.3% vs. Serva NB1: 94.8%, p = 0.061) and stimulation indexes (Sigma V: 3.41 vs. Serva NB1: 2.74, p = 0.187) were also similar between the two groups. The impact of cold ischemia and age on the isolation outcome in the Sigma V group was comparable to the Serva NB1 group. The endotoxin content of the final products in the filtered Sigma V group was significantly less than that in the high-purified Serva NB1 group (0.022 vs. 0.052 EU/ml, p = 0.003). Additionally, in the Sigma V group there was minimal lot to lot variation and no significant loss of enzymatic activity after filtration. These findings indicate that the use of Sigma V or other crude enzyme blends for research pancreata is warranted to reduce isolation costs and increase the amount of islets available for critical islet research. These findings also validate the need for a systematic enzyme analysis to resolve these inconsistencies in overall enzyme quality once and for all.

CC Chemokine receptor 5 deficiency does not prevent local immune responses to adenovirus vector in islet transplant recipients

BACKGROUND

CC chemokine receptor 5 (CCR5) plays an important role in mediating inflammation. We examined the effect of CCR5 on the immune response to adenovirus vectors and graft function in islet transplant model.

MATERIALS AND METHODS

Syngeneic wild-type (WT) or CCR5-deficient (KO) mouse islets transduced with adenovirus encoding β-gal were transplanted under the renal capsule. After transplant, blood glucose, glucose tolerance, graft cellular infiltration, transgene and chemokine/receptor expression, and systemic anti-adenoviral/-β-gal immune response were evaluated.

RESULTS

Diabetes was reversed in 1 d in both WT and KO untransduced recipients, while islets transduced with adenovirus failed to reverse diabetes until 10 d post-transplant in WT recipients or even longer (>15 d) in KO recipients (P < 0.05). A profound infiltration of CD4(+), CD8(+) cells and macrophages was observed in both WT and KO transduced grafts at 25 d. Though transgene expression was significantly reduced, insulin and β-gal expression persisted over 3 mo. Glucose tolerance was impaired in all grafts in KO recipients compared with untransduced grafts in WT recipients at 25 d post-transplant, but was equivalent at 3 mo. Early expression of CCR2 mRNA was increased in transduced grafts in both WT and KO recipients. No systemic antivector immunity was demonstrated in any recipient group.

CONCLUSIONS

Transduction of islets with adenovirus causes significant local inflammation in islet grafts and impairs early graft function in CCR5-deficient recipients, but long-term graft function is preserved. Thus, CCR5 absence does not prevent the local immune response to adenovirus transduction, and vector-associated graft dysfunction is not mediated by CCR5.

Edaravone, a free radical scavenger, promotes engraftment of intraportally transplanted islet cells

OBJECTIVES

Pancreatic islet transplantation requires multiple transplants to achieve insulin independence. Only one third of the islet mass is stably engrafted; one of the causes of which is ascribed to oxidative stress. We confirmed the hypothesis that administration of edaravone, a free radical scavenger, in the early posttransplantation period promotes islet cell engraftment.

METHODS

Islet isograft from a single donor was intraportally transplanted into streptozotocin-diabetic F344 rats, and intravenous edaravone (3 mg/kg) was administered immediately and 24 hours after the transplantation. Plasma glucose concentrations were monitored for 28 days. Serum insulin levels were obtained on the second week. Morphologic studies were performed on insulin-immunostained and TUNEL-stained sections of the recipient liver.

RESULTS

In the edaravone-treated group, hyperglycemia was ameliorated, and 50% of rats achieved normoglycemia (<200 mg/dL). All rats in the control group remained hyperglycemic (>400 mg/dL). Insulin secretion of the edaravone-treated group was superior to the controls. Morphologically, the number and size of the islet β cells of the edaravone-treated group were larger than those of the controls. The number of TUNEL-positive cells in each islet of the edaravone-treated group were fewer than those of the controls.

CONCLUSIONS

In streptozotocin-diabetic rats, edaravone administration in the early posttransplantation period promotes engraftment of intraportally transplanted islet cells.

The sequential combination of a JNK inhibitor and simvastatin protects porcine islets from peritransplant apoptosis and inflammation

Intraductal administration of a c-Jun NH(2)-terminal kinase (JNK) inhibitor enhances islet viability. However, its role in reducing the inflammatory response in islets is unknown. It is also unknown whether a JNK inhibitor could act in synergy with statins. We examined if the sequential combination of a JNK inhibitor and simvastatin would reduce islet inflammation and improve islet viability. We performed porcine islet isolation with or without intraductal administration of SP600125, a JNK inhibitor. This was followed by culture medium supplementation with either nicotinamide alone or nicotinamide plus simvastatin. We assessed the viability of islets by flow cytometry, islet loss during overnight culture, graft function in NOD/SCID mice, and expression of inflammation-related genes in islets. The sequential combination of a JNK inhibitor and simvastatin increased the β-cell viability index of porcine islets cultured overnight (p = 0.015) as well as islet viability as assessed by a DNA binding dye staining (p = 0.011). The combination of a JNK inhibitor and simvastatin significantly increased the islet survival rate (p = 0.027) when the histomorphometry of donor pancreas indicated a large islet proportion of greater than 50.55%. When we transplanted the same islet mass per recipient for each group, there was no difference in overall islet graft function. Intraductal administration of JNK inhibitor significantly suppressed mRNA expression levels of interleukin-1β (IL-1β), interferon-γ, tumor necrosis factor-α, IL-6, IL-8, and macrophage chemoattractant protein-1. It also decreased the concentration of IL-1β (p = 0.040) and IL-8 (p = 0.023) in the culture supernatant. In conclusion, the sequential combination of a JNK inhibitor and simvastatin protected porcine islets from peritransplant apoptosis. Inhibition of JNK reduced the inflammatory response and could be considered an alternative target for suppression of porcine islet inflammation.

Islet-expressed TLR2 and TLR4 sense injury and mediate early graft failure after transplantation

Although islet transplantation is an effective treatment for Type 1 diabetes, primary engraftment failure contributes to suboptimal outcomes. We tested the hypothesis that islet isolation and transplantation activate innate immunity through TLR expressed on islets. Murine islets constitutively express TLR2 and TLR4, and TLR activation with peptidoglycan or LPS upregulates islet production of cytokines and chemokines. Following transplantation into streptozotocin-induced diabetic, syngeneic mice, islets exposed to LPS or peptidoglycan had primary graft failure with intra- and peri-islet mononuclear cell inflammation. The use of knockout mice showed that recipient CD8(+) T cells caused engraftment failure and did so in the absence of islet-derived DC. To mimic physiological islet injury, islets were transplanted with exocrine debris. Transplantation of TLR2/4(-/-) islets reduced proinflammatory cytokine production and improved islet survival. Stressed islets released the alarmin high-mobility group box protein 1 (HMGB1) and recombinant HMGB1 (rHMGB1) induced NFkB activation. NFkB activation was prevented in the absence of both TLR2 and TLR4. rHMGB1 pretreatment also prevented primary engraftment through a TLR2/4-dependent pathway. Our results show that islet graft failure can be initiated by TLR2 and TLR4 signaling and suggest that HMGB1 is one likely early mediator. Subsequent downstream signaling results in intra-islet inflammation followed by T-cell-mediated graft destruction.

Antiproinflammatory effects of iodixanol (OptiPrep)-based density gradient purification on human islet preparations

Islet isolation and purification using a continuous density gradient may reduce the volume of tissue necessary for implantation into patients, therefore minimizing the risks associated with intraportal infusion in islet transplantation. On the other hand, the purification procedure might result in a decreased number of islets recovered due to various stresses such as exposure to cytokine/chemokine. While a Ficoll-based density gradient has been widely used in purification for clinical trials, purification with iodixanol (OptiPrep) has been recently reported in islet transplant series with successful clinical outcomes. The aim of the current study was to compare the effects of the purification method using OptiPrep-based and Ficoll-based density gradients. Human islet isolations were performed using a modified automated method. After the digestion phase, pre-purification digests were divided into two groups and purified using a semiautomated cell processor with either a continuous Ficoll- or OptiPrep-based density gradient. The quantity, purity, viability, and cellular composition of islet preparations from each group were assessed. Cytokine/chemokine and tissue factor production from islet preparations after 48-h culture were also measured. Although islet purity, post-purification IEQ, islet recovery rate, FDA/PI, and fractional β-cell viability were comparable, β-cell mass after 48-h culture significantly improved in the OptiPrep group when compared to the Ficoll group. The production of cytokine/chemokine including IL-1β, TNF-α, IFN-γ, IL-6, IL-8, MIP-1β, MCP-1, and RANTES but not tissue factor from the OptiPrep group was significantly lower during 48-h culture after isolation. Each preparation contained the similar number of ductal cells and macrophages. Endotoxin level in both gradient medium was also comparable. The purification method using OptiPrep gradient media significantly reduced cytokine/chemokine production but not tissue factor from human islet preparations and improved β-cell survival during pretransplant culture. Our results suggest that the purification method using OptiPrep gradient media may be of assistance in increasing successful islet transplantation.

TLR4 mediates early graft failure after intraportal islet transplantation

We have previously shown that islet emboli in the portal vein block blood flow and induce local inflammatory reaction, resulting in functional loss of islet grafts following intraportal transplantation. This study was designed to test whether Toll-like receptor (TLR) activation mediates early islet graft failure. Syngeneic islet grafts were transplanted into chemically induced diabetic mice, and TLR deficient mice were used as donors and/or recipients of islet grafts. Islet viability, proinflammatory cytokines, high-mobility group box-1 (HMGB1) and NF-kappaB activation were analyzed by bioluminesce imaging (BLI), quantitative RT-PCR (qRT-PCR) and histology. Early islet graft failure was observed in mice with intraportal islet engrafts with increased proinflammatory cytokines, HMGB1 expression, NF-kappaB activation, caspase-3 and TUNEL positive cells. Deficiency of TLR4 in donor, but not in recipient, inhibited NF-kappaB activation, reduced proinflammatory cytokines and improved viability of islet grafts. Blockade of HMGB1 with anti-HMGB1 monoclonal antibody (mAb, 2g7) inhibited inflammatory reactions, as evidenced by reduced TNFalpha and IL-1ss production, and improved islet viability. We conclude that TLR4 activation mediates early graft failure following intraportal islet transplantation. Inhibition of TLR4 activation represents a novel strategy to attenuate early graft failure following intraportal islet transplantation.

[Cytoprotective effect of low-dose tacrolimus on islets of Langerhans in cultures subjected to stimulation by acute rejection cytokines]

INTRODUCTION

The improvement in pancreatic islet transplantation results is due to immunosuppression protocols that include, among others, low-dose tacrolimus. Both anti-inflammatory and anti-oxidant effects of tacrolimus could be useful in preventing primary rejection.

AIM

To evaluate in vitro islet low-dose tacrolimus response after pro-inflammatory stimulation.

MATERIAL AND METHODS

Isolated rat islets were cultured in RPMI medium in the presence of IL-1 (50 UI/mL) plus IF-gamma (1000 UI/mL) and tacrolimus (5 ng/mL). The 24 h production of lipoperoxide (LPO) and nitric oxide (NO) were measured as oxidative stress markers. Determination of apoptosis markers (nucleosome content and Bcl-2) was also performed.

RESULTS

Oxidative stress (LPO 10.1+/-1.16 pmol/islet x 24; NO 19.1+/-3.28 pmol/isletx24 h) and apoptosis (nucleosome 0.24+/-0.04 UI/islet; Bcl-2 0.69+/-0.212 UI/islet) markers showed a very significant increase after cytokine stimulation (p<0.01). Both effects improved by adding tacrolimus to the medium. Protective effect was complete when lipoperoxide (1.58 pmol/isletx24 h), nitric oxide (9.81 pmol/isletx24 h) and Bcl-2 (1.37+/-0.23 UI/islet) were determined.

CONCLUSION

In vitro cytoprotective effect of low-dose tacrolimus on isolated rat islets decreases both oxidative stress and apoptosis markers after stimulation of pro-inflammatory mediators.

Islet allograft rejection is independent of toll-like receptor signaling in mice

BACKGROUND

Islet transplantation is a promising therapy for type 1 diabetes; however, most islet grafts fail within 5 years. Innate immunity has been suggested to play a role in islet allograft rejection, potentially mediated by toll-like receptors (TLRs), a class of innate immune receptors. Lack of TLR4, in particular, has been reported to improve allograft survival. Therefore, we hypothesized that TLRs may be involved in islet allograft rejection, and that deletion of TLR4 may improve islet graft survival.

METHODS

Islets were isolated from C57BL/10ScNJ (Tlr4(-/-)) and C57BL/10 (wild-type [WT]) animals and transplanted into Balb/cJ recipients with streptozotocin-induced diabetes. Blood glucose levels were used to determine graft viability and immunostaining to assess graft morphology and immune cell infiltration. The roles of the TLR4 adaptor molecules MyD88 and TLR adaptor molecule 1 (Ticam-1) were assessed using islets isolated from mice lacking MyD88 (MyD88(-/-)), Ticam-1 (Ticam-1(-/-)), or the combined double knockout (MyD88(-/-)/Ticam-1(-/-)).

RESULTS

Contrary to our hypothesis, Tlr4(-/-) and WT islet allografts had similar failure rates; grafts failed at 23.2+/-1.2 and 24.5+/-1.5 days posttransplant, respectively (P=NS). Syngeneic grafts of Tlr4(-/-) and WT islets maintained normoglycemia for up to 10 weeks posttransplant, indicating that failure of Tlr4(-/-) islet allografts could not be attributed to an intrinsic defect in Tlr4(-/-) islets. Similarly, islet allotransplants from MyD88(-/-), Ticam-1(-/-), and MyD88(-/-)/Ticam-1(-/-) donors did not have improved allograft survival compared with WT controls.

CONCLUSIONS

These findings indicate that islet allograft rejection in mice is independent of TLR4 and the TLR adaptor molecules MyD88 and Ticam-1, speaking against an essential role for TLR signaling in islet allograft rejection.

Islet isolation for clinical transplantation

Islet transplantation is emerging as a viable treatment option for selected patients with type 1 diabetes. Following the initial report in 2000 from Edmonton of insulin independence in seven out of seven consecutive recipients, there has been a huge expansion in clinical islet transplantation. The challenge we now face is the apparent decline in graft function over time. Isolating high-quality human islets which survive and function for a longer period will no doubt contribute to further improvement in long-term clinical outcome. This chapter reviews the selection of appropriate donors for islet isolation and transplantation, describes each step during islet isolation, and discusses the scope for further improvements.

Antiapoptotic effect of tacrolimus on cytokine-challenged human islets

Our goal was to investigate whether previously related antiapoptotic and anti-inflammatory effects of tacrolimus could be useful in protecting human islets cultured in the presence of several proinflammatory mediators. Human islets obtained from cadaveric donors after intraductal infusion with collagenase, mechanical digestion, and continuous Ficoll gradient purification were cultured in RPMI-1640 medium for 24 h. Escherichia coli lipopolysaccharide (10 microg/ml) or interleukin-1 (50 UI/ml) + gamma-IF (1000 UI/ml) and low-dose tacroliumus (5 ng/ml) were added. Homogenized samples (300 IE) from five different donors where assigned to four different experimental groups (control, treatment, cytokines, and cytokines + treatment). To evaluate islet damage and apoptotic response, nucleosome content, Bcl-2 protein levels, caspase-3, -8, and -9 levels, and insulin concentration were measured. Also, TNF-alpha and IL-6 levels where assessed as indicators of the inflammatory response. All proapoptotic markers, TNF-alpha, and IL-6 levels were augmented after both LPS and cytokine stimulation. Tacrolimus reduced significantly all of them and restored baseline values of nucleosome and caspase-9 in both experiments and Bcl-2 and caspase-3 when IL-1 + gamma-IF was added. Twenty-four-hour insulin concentration diminished when LPS or IL-1 + gamma-IF were present. Tacrolimus treatment restored insulin levels in both experiments. These results suggest that in vitro apoptotic events and media insulin concentration decrease after proinflammatory stimulation can be reverted using low-dose tacrolimus.

Impact of pancreatic cold preservation on rat islet recovery and function

BACKGROUND

Islet transplantation success depends on the number and quality of islets transplanted. This study aimed at exploring the molecular mechanisms associated with cold pancreas preservation and their impact on islet cell survival and function.

METHODS

Rat pancreata were stored in cold University of Wisconsin preservation solution for short (3 hr; control) or long (18 hr) cold ischemia times (CIT).

RESULTS

Pancreata exposed to long CIT yielded lower islet numbers and showed reduced cellular viability; isolated islets displayed higher levels of phosphorylated stress-activated protein kinase (c-jun N-terminal Kinase and Mitogen-Activated Protein Kinase-p38), and chemokine (C-C) ligand-3, and lower levels of vascular endothelial growth factor, interleukins (IL)-9 and IL-10. Islets obtained from long-CIT pancreata were functionally impaired after transplantation. Differential proteomic expression in pancreatic tissue after CIT included increased eukaryotic translation elongation factor-1-alpha-1 (apoptosis related) and reduced Clade-B (serine protease inhibitor).

CONCLUSIONS

Our study indicates that cold ischemia stimulates inflammatory pathways (chemokine (c-c)ligand-3, phosphorylation of c-jun N-terminal Kinase and mitogen-activated protein kinase-p38, and eukaryotic translation elongation factor-1-alpha-1) and decreases repair/cytoprotective pathways (IL-10, vascular endothelial growth factor, and Clade-B), all of which may negatively affect the quality and mass of islets obtained from a donor pancreas.

Thrombomodulin improves early outcomes after intraportal islet transplantation

Primary islet nonfunction due to an instant blood mediated inflammatory reaction (IBMIR) leads to an increase in donor islet mass required to achieve euglycemia. In the presence of thrombin, thrombomodulin generates activated protein C (APC), which limits procoagulant and proinflammatory responses. In this study, we postulated that liposomal formulations of thrombomodulin (lipo-TM), due to its propensity for preferential uptake in the liver, would enhance intraportal engraftment of allogeneic islets by inhibiting the IBMIR. Diabetic C57BL/6J mice underwent intraportal transplantation with B10.BR murine islets. In the absence of treatment, conversion to euglycemia was observed among 29% of mice receiving 250 allo-islets. In contrast, a single infusion of lipo-TM led to euglycemia in 83% of recipients (p = 0.0019). Fibrin deposition (p < 0.0001), neutrophil infiltration (p < 0.0001), as well as expression TNF-alpha and IL-beta (p < 0.03) were significantly reduced. Significantly, thrombotic responses mediated by human islets in contact with human blood were also reduced by this approach. Lipo-TM improves the engraftment of allogeneic islets through a reduction in local thrombotic and inflammatory processes. As an enzyme-based pharmacotherapeutic, this strategy offers the potential for local generation of APC at the site of islet infusion, during the initial period of elevated thrombin production.

Quality control for clinical islet transplantation: organ procurement and preservation, the islet processing facility, isolation, and potency tests

Pancreatic islet transplantation has become one of the ideal treatments for patients with type 1 diabetes mellitus due to improvements in isolation techniques and immunosuppression regimens. In order to ensure the safety and rights of patients, isolated islets need to meet the criteria for regulation as both a biological product and a drug product. For the constant success of transplantation, therefore, all investigators involved in clinical islet transplantation must strive to ensure the safety, purity, and potency of islets in all the phases of clinical islet isolation and transplantation. In this review, we summarize the quality control for clinical islet isolation and transplantation, and the latest topics of pre-transplant islet assessment.

Riboflavin inhibits IL-6 expression and p38 activation in islet cells

Riboflavin is a water-soluble vitamin that reduces the production of proinflammatory mediators and oxygen radicals. Because islet beta-cells are very sensitive to oxidative stress and to cytokines, we investigated the possible cytoprotective effects of riboflavin on insulinoma NIT-1 cells and on isolated rodent islets. NIT-1 cells and islets cultured in the presence or absence of 10 microM riboflavin were studied at baseline and after exposure to cytokines (TNF-alpha, IL-1beta, INF-gamma). Riboflavin treatment did not affect islet cell viability as assessed by flow cytometry for caspases activation. However, riboflavin prevented the cytokine-induced increase in IL-6 mRNA expression and p38 phosphorylation analyzed by real-time PCR and immunoassay, respectively. In summary, nontoxic doses of riboflavin prevent cytokines-induced p38 phosphorylation and IL-6 upregulation in islet cells. This observation, together with the safety profile of riboflavin in the clinical setting, makes it an appealing agent for islet cytoprotection in islet transplantation protocols.

Sustained reversal of diabetes following islet transplantation to striated musculature in the rat

BACKGROUND

There is an increasing emphasis in the islet transplant community on the development of alternative sites for islet implantation. Striated musculature constitutes a potential alternative, which has been successfully employed in autotransplantation of parathyroid glands for decades. In the present study, a technique for intramuscular islet transplantation was developed and compared with intraportal islet transplantation in a syngeneic rat model.

MATERIALS AND METHODS

Lewis rats were used. Pancreata were digested using Liberase. Islets were either transplanted into m. biceps femoris in a pearls-on-a-string fashion or intraportally, and the ability to reverse diabetes was compared. Eight weeks after transplantation an IVGTT was performed. Real-time quantitative RT-PCR was employed on muscle biopsies to investigate mRNA levels of cytokines in response to the transplant procedure. Explanted livers, muscles, and pancreata were harvested at the end of the experiment for histopathological analyses.

RESULTS

2000 IEQ repeatedly cured diabetic rats at the intraportal site, while 4000 IEQ was required at the intramuscular site. Time to reversal of diabetes, post-transplant weight development, and IVGTT curves did not differ between the groups. Normoglycemia was sustainable to the end of the study (>100 days) for all animals. The transplant procedure upregulated pro-inflammatory cytokines (IL-6 and IL-8) in striated muscle, and peri-islet fibrosis was observed in intramuscular grafts.

CONCLUSIONS

Islet transplantation into striated musculature is feasible; however, in its present form the intramuscular site is less efficient compared with the liver in rats. The intramuscular site allows manipulation of the graft and implantation site prior to transplantation and may therefore have implications for islet transplantation in humans.

Noninvasive high-resolution in vivo imaging of cell biology in the anterior chamber of the mouse eye

There is clearly a demand for an experimental platform that enables cell biology to be studied in intact vascularized and innervated tissue in vivo. This platform should allow observations of cells noninvasively and longitudinally at single-cell resolution. For this purpose, we use the anterior chamber of the mouse eye in combination with laser scanning microscopy (LSM). Tissue transplanted to the anterior chamber of the eye is rapidly vascularized, innervated and regains function. After transplantation, LSM through the cornea allows repetitive and noninvasive in vivo imaging at cellular resolution. Morphology, vascularization, cell function and cell survival are monitored longitudinally using fluorescent proteins and dyes. We have used this system to study pancreatic islets, but the platform can easily be adapted for studying a variety of tissues and additional biological parameters. Transplantation to the anterior chamber of the eye takes 25 min, and in vivo imaging 1-5 h, depending on the features monitored.

Thrombosis and inflammation in intraportal islet transplantation: a review of pathophysiology and emerging therapeutics

With the inception of the Edmonton Protocol, intraportal islet transplantation (IPIT) has re-emerged as a promising cell-based therapy for type 1 diabetes. However, current clinical islet transplantation remains limited, in part, by the need to transplant islets from 2-4 donor organs, often through several separate infusions, to reverse diabetes in a single patient. Results from clinical islet transplantation and experimental animal models now indicate that the majority of transplanted islets are destroyed in the immediate post-transplant period, a process largely facilitated by deleterious inflammatory responses triggered by islet-derived procoagulant and proinflammatory mediators. Herein, mechanisms that underlie the pathophysiology of thrombosis and inflammation in IPIT are reviewed, and emerging approaches to improve islet engraftment through attenuation of inflammatory responses are discussed.