Glucose control and long-term survival in biobreeding/Worcester rats after intraperitoneal implantation of hydrophilic macrobeads containing porcine islets without immunosuppression

Long-term efficacy and safety of porcine islet macrobeads in nonimmunosuppressed diabetic cynomolgus macaques

Although human islet transplantation has proven to provide clinical benefits, especially the near complete amelioration of hypoglycemia, the supply of human islets is limited and insufficient to meet the needs of all people that could benefit from islet transplantation. Porcine islets, secreting insulin nearly identical to that of human insulin, have been proposed as a viable supply of unlimited islets. Further, encapsulation of the porcine islets has been shown to reduce or eliminate the use of immunosuppressive therapy that would be required to prevent rejection of the foreign islet tissue. The goal of the current study was to determine the long-term safety and efficacy of agarose encapsulated porcine islets (macrobeads) in diabetic cynomolgus macaques, in a study emulating a proposed IND trial in which daily exogenous insulin therapy would be reduced by 50% with no loss of glucose regulation. Four of six animals implanted with macrobeads demonstrated ≥ 30% reduction in insulin requirements in year 1 of follow-up. Animals were followed for 2, 3.5, and 7.4 years with no serious adverse events, mortality or evidence of pathogen transmission. This study supports the continued pursuit of encapsulated porcine islet therapy as a promising treatment option for diabetes mellitus.

Cytocompatible cell encapsulation via hydrogel photopolymerization in microfluidic emulsion droplets

Encapsulating cells within biocompatible materials is a widely pursued and promising element of tissue engineering and cell-based therapies. Recently, extensive interest in microfluidic-enabled cell encapsulation has emerged as a strategy to structure hydrogels and establish custom cellular microenvironments. In particular, it has been shown that the microfluidic-enabled photoencapsulation of cells within PEG diacrylate (PEGDA)-based microparticles can be performed cytocompatibly within gas-permeable, nitrogen-jacketed polydimethylsiloxane microfluidic devices, which mitigate the oxygen inhibition of radical chain growth photopolymerization. Compared to bulk polymerization, in which cells are suspended in a static hydrogel-forming solution during gelation, encapsulating cells via microfluidic processing exposes cells to a host of potentially deleterious stresses such as fluidic shear rate, transient oxygen depletion, elevated pressures, and UV exposure. In this work, we systematically examine the effects of these factors on the viability of cells that have been microfluidically photoencapsulated in PEGDA. It was found that the fluidic shear rate during microdroplet formation did not have a direct effect on cell viability, but the flow rate ratio of oil to aqueous solution would impart harmful effects to cells when a critical threshold was exceeded. The effects of UV exposure time and intensity on cells, however, are more complex, as they contribute unequally to the cumulative rate of peroxy radical generation, which is strongly correlated with cell viability. A reaction-diffusion model has been developed to calculate the cumulative peroxy radical concentration over a range of UV light intensity and radiation times, which was used to gain further quantitative understanding of experimental results. Conclusions drawn from this work provide a comprehensive guide to mitigate the physical and biochemical damage imparted to cells during microfluidic photoencapsulation and expands the potential for this technique.

A comprehensive microbiological safety approach for agarose encapsulated porcine islets intended for clinical trials

BACKGROUND

The use of porcine islets to replace insulin-producing islet β-cells, destroyed during the diabetogenic disease process, presents distinct challenges if this option is to become a therapeutic reality for the treatment of type 1 diabetes. These challenges include a thorough evaluation of the microbiological safety of the islets. In this study, we describe a robust porcine islet-screening program that provides a high level of confidence in the microbiological safety of porcine islets suitable for clinical trials.

METHODS

A four-checkpoint program systematically screens the donor herd (Large White - Yorkshire × Landrace F1 hybrid animals), individual sentinel and pancreas donor animals and, critically, the islet macrobeads themselves. Molecular assays screen for more than 30 known viruses, while electron microscopy and in vitro studies are employed to screen for potential new or divergent (emergent) viruses.

RESULTS

Of 1207 monthly samples taken from random animals over a 2-year period, only a single positive result for Transmissible gastroenteritis virus was observed, demonstrating the high level of biosecurity maintained in the source herd. Given the lack of clinical signs, positive antibody titers for Porcine reproductive and respiratory syndrome virus, Porcine parvovirus, and Influenza A confirm the efficacy of the herd vaccination program. Porcine respiratory coronavirus was found to be present in the herd, as expected for domestic swine. Tissue homogenate samples from six sentinel and 11 donor animals, over the same 2-year period, were negative for the presence of viruses when co-cultured with six different cell lines from four species. The absence of adventitious viruses in separate islet macrobead preparations produced from 12 individual pancreas donor animals was confirmed using validated molecular (n = 32 viruses), in vitro culture (cells from four species), and transmission electron microscopy assays (200 cell profiles per donor animal) over the same 2-year period. There has been no evidence of viral transmission following the implantation of these same encapsulated and functional porcine islets into non-immunosuppressed diabetic cynomolgus macaques for up to 4 years. Isolated peripheral blood mononuclear cells from all time points were negative for PCV (Type 2), PLHV, PRRSV, PCMV, and PERV-A, PERV-B, and PERV-C by PCR analysis in all six recipient animals.

CONCLUSION

The four-checkpoint program is a robust and reliable method for characterization of the microbiological safety of encapsulated porcine islets intended for clinical trials.

First-in-Human Phase 1 Trial of Agarose Beads Containing Murine RENCA Cells in Advanced Solid Tumors

PURPOSE

Agarose macrobeads containing mouse renal adenocarcinoma cells (RMBs) release factors, suppressing the growth of cancer cells and prolonging survival in spontaneous or induced tumor animals, mediated, in part, by increased levels of myocyte-enhancing factor (MEF2D) via EGFR-and AKT-signaling pathways. The primary objective of this study was to determine the safety of RMBs in advanced, treatment-resistant metastatic cancers, and then its efficacy (survival), which is the secondary objective.

METHODS

Thirty-one patients underwent up to four intraperitoneal implantations of RMBs (8 or 16 macrobeads/kg) via laparoscopy in this single-arm trial (FDA BB-IND 10091; NCT 00283075). Serial physical examinations, laboratory testing, and PET-CT imaging were performed before and three months after each implant.

RESULTS

RMBs were well tolerated at both dose levels (mean 660.9 per implant). AEs were (Grade 1/2) with no treatment-related SAEs.

CONCLUSION

The data support the safety of RMB therapy in advanced-malignancy patients, and the preliminary evidence for their potential efficacy is encouraging. A Phase 2 efficacy trial is ongoing.

Oxygen-Purged Microfluidic Device to Enhance Cell Viability in Photopolymerized PEG Hydrogel Microparticles

Encapsulating cells within biocompatible materials is a widely used strategy for cell delivery and tissue engineering. While cells are commonly suspended within bulk hydrogel-forming solutions during gelation, substantial interest in the microfluidic fabrication of miniaturized cell encapsulation vehicles has more recently emerged. Here, we utilize multiphase microfluidics to encapsulate cells within photopolymerized picoliter-volume water-in-oil droplets at high production rates. The photoinitiated polymerization of polyethylene glycol diacrylate (PEGDA) is used to continuously produce solid particles from aqueous liquid drops containing cells and hydrogel forming solution. It is well understood that this photoinitiated addition reaction is inhibited by oxygen. In contrast to bulk polymerization in which ambient oxygen is rapidly and harmlessly consumed, allowing the polymerization reaction to proceed, photopolymerization within air permeable polydimethylsiloxane (PDMS) microfluidic devices allows oxygen to be replenished by diffusion as it is depleted. This sustained presence of oxygen and the consequential accumulation of peroxy radicals produce a dramatic effect upon both droplet polymerization and post-encapsulation cell viability. In this work we employ a nitrogen microjacketed microfluidic device to purge oxygen from flowing fluids during photopolymerization. By increasing the purging nitrogen pressure, oxygen concentration was attenuated, and increased post-encapsulation cell viability was achieved. A reaction-diffusion model was used to predict the cumulative intradroplet concentration of peroxy radicals, which corresponded directly to post-encapsulation cell viability. The nitrogen-jacketed microfluidic device presented here allows the droplet oxygen concentration to be finely tuned during cell encapsulation, leading to high post-encapsulation cell viability.

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.

Evolution of Islet Transplantation for the Last 30 Years

In this article, we will review the changes that have occurred in islet transplantation at the birth of Pancreas 30 years ago. The first attempts at β-cell replacement in humans, pancreas and islet transplantation, were performed in the 1960s and 1970s. Although pancreas transplantation has been an accepted treatment for severe labile diabetes predating the emergence of the journal, allogeneic islet transplantation remains experimental. Current investigations within islet transplantation focus to improve islet function after transplantation. Improving islet viability during isolation, exploring ways to increase engraftment, and protection from the host immune system are some of the goals of these investigative efforts. The major barriers to clinical islet transplantation are shortage of human pancreas, the need for immunosuppression, and the inadequacy of the islet isolation process. It is generally accepted that islet encapsulation is an immunoisolation tool with good potential to address the first 2 of those barriers. We have therefore devoted a major part of this review to the critical factors needed to make it a clinical reality. With improved islet isolation techniques and determination of the best site of engraftment as well as improved encapsulation techniques, we hope that islet transplantation could someday achieve routine clinical use.

Impact of the Type of Continuous Insulin Administration on Metabolism in a Diabetic Rat Model

Exogenous insulin is the only treatment available for type 1 diabetic patients and is mostly administered by subcutaneous (SC) injection in a basal and bolus scheme using insulin pens (injection) or pumps (preimplanted SC catheter). Some divergence exists between these two modes of administration, since pumps provide better glycaemic control compared to injections in humans. The aim of this study was to compare the impacts of two modes of insulin administration (single injections of long-acting insulin or pump delivery of rapid-acting insulin) at the same dosage (4 IU/200 g/day) on rat metabolism and tissues. The rat weight and blood glucose levels were measured periodically after treatment. Immunostaining for signs of oxidative stress and for macrophages was performed on the liver and omental tissues. The continuous insulin delivery by pumps restored normoglycaemia, which induced the reduction of both reactive oxygen species and macrophage infiltration into the liver and omentum. Injections controlled the glucose levels for only a short period of time and therefore tissue stress and inflammation were elevated. In conclusion, the insulin administration mode has a crucial impact on rat metabolic parameters, which has to be taken into account when studies are designed.

Effects of early and late diabetic neuropathy on sciatic nerve block duration and neurotoxicity in Zucker diabetic fatty rats

BACKGROUND

The neuropathy of type II diabetes mellitus (DM) is increasing in prevalence worldwide. We aimed to test the hypothesis that in a rodent model of type II DM, neuropathy would lead to increased neurotoxicity and block duration after lidocaine-induced sciatic nerve block when compared with control animals.

METHODS

Experiments were carried out in Zucker diabetic fatty rats aged 10 weeks (early diabetic) or 18 weeks (late diabetic, with or without insulin 3 units per day), and age-matched healthy controls. Left sciatic nerve block was performed using 0.2 ml lidocaine 2%. Nerve conduction velocity (NCV) and F-wave latency were used to quantify nerve function before, and 1 week after nerve block, after which sciatic nerves were used for neurohistopathology.

RESULTS

Early diabetic animals did not show increased signs of nerve dysfunction after nerve block. In late diabetic animals without insulin vs control animals, NCV was 34.8 (5.0) vs 41.1 (4.1) ms s(-1) (P<0.01), and F-wave latency was 7.7 (0.5) vs 7.0 (0.2) ms (P<0.01), respectively. Motor nerve block duration was prolonged in late diabetic animals, but neurotoxicity was not. Late diabetic animals receiving insulin showed intermediate results.

CONCLUSIONS

In a rodent type II DM model, nerves have increased sensitivity for short-acting local anaesthetics without adjuvants in vivo, as evidenced by prolonged block duration. This sensitivity appears to increase with the progression of neuropathy. Our results do not support the hypothesis that neuropathy due to type II DM increases the risk of nerve injury after nerve block.

Islet and stem cell encapsulation for clinical transplantation

Over the last decade, improvements in islet isolation techniques have made islet transplantation an option for a certain subset of patients with long-standing diabetes. Although islet transplants have shown improved graft function, adequate function beyond the second year has not yet been demonstrated, and patients still require immunosuppression to prevent rejection. Since allogeneic islet transplants have experienced some success, the next step is to improve graft function while eliminating the need for systemic immunosuppressive therapy. Biomaterial encapsulation offers a strategy to avoid the need for toxic immunosuppression while increasing the chances of graft function and survival. Encapsulation entails coating cells or tissue in a semipermeable biocompatible material that allows for the passage of nutrients, oxygen, and hormones while blocking immune cells and regulatory substances from recognizing and destroying the cell, thus avoiding the need for systemic immunosuppressive therapy. Despite advances in encapsulation technology, these developments have not yet been meaningfully translated into clinical islet transplantation, for which several factors are to blame, including graft hypoxia, host inflammatory response, fibrosis, improper choice of biomaterial type, lack of standard guidelines, and post-transplantation device failure. Several new approaches, such as the use of porcine islets, stem cells, development of prevascularized implants, islet nanocoating, and multilayer encapsulation, continue to generate intense scientific interest in this rapidly expanding field. This review provides a comprehensive update on islet and stem cell encapsulation as a treatment modality in type 1 diabetes, including a historical outlook as well as current and future research avenues.

Pravastatin improves glucose regulation and biocompatibility of agarose encapsulated porcine islets following transplantation into pancreatectomized dogs

The encapsulation of porcine islets is an attractive methodology for the treatment of Type I diabetes. In the current study, the use of pravastatin as a mild anti-inflammatory agent was investigated in pancreatectomized diabetic canines transplanted with porcine islets encapsulated in agarose-agarose macrobeads and given 80 mg/day of pravastatin (n = 3) while control animals did not receive pravastatin (n = 3). Control animals reached preimplant insulin requirements on days 18, 19, and 32. Pravastatin-treated animals reached preimplant insulin requirements on days 22, 27, and 50. Two animals from each group received a second macrobead implant: control animals remained insulin-free for 15 and 21 days (AUC = 3003 and 5078 mg/dL/24 hr days 1 to 15) and reached preimplant insulin requirements on days 62 and 131. Pravastatin treated animals remained insulin-free for 21 and 34 days (AUC = 1559 and 1903 mg/dL/24 hr days 1 to 15) and reached preimplant insulin requirements on days 38 and 192. Total incidence (83.3% versus 64.3%) and total severity (22.7 versus 18.3) of inflammation on tissue surfaces were higher in the control group at necropsy. These findings support pravastatin therapy in conjunction with the transplantation of encapsulated xenogeneic islets for the treatment of diabetes mellitus.

Enhancement of in vitro and in vivo function of agarose-encapsulated porcine islets by changes in the islet microenvironment

The transplantation of porcine islets of Langerhans to treat type 1 diabetes may provide a solution to the demand for insulin-producing cells. Porcine islets encapsulated in agarose-agarose macrobeads have been shown to function in nonimmunosuppressed xenogeneic models of both streptozotocin-induced and autoimmune type 1 diabetes. One advantage of agarose encapsulation is the ability to culture macrobeads for extended periods, permitting microbiological and functional assessment. Herein we describe optimization of the agarose matrix that results in improved islet function. Porcine islets (500 IEQs) from retired breeding sows were encapsulated in 1.5% SeaKem Gold (SG), 0.8% SG, or 0.8% Litex (Li) agarose, followed by an outer capsule of 5% SG agarose. Insulin production by the encapsulated islets exhibited an agarose-specific effect with 20% (0.8% SG) to 50% (0.8% Li) higher initial insulin production relative to 1.5% SG macrobeads. Insulin production was further increased by 40-50% from week 2 to week 12 in both agarose types at the 0.8% concentration, whereas islets encapsulated in 1.5% SG agarose increased insulin production by approximately 20%. Correspondingly, fewer macrobeads were required to restore normoglycemia in streptozotocin-induced diabetic female CD(SD) rats that received 0.8% Li (15 macrobeads) or 0.8% SG (17 macrobeads) as compared to 1.5% SG (19 macrobeads). Islet cell proliferation was also observed during the first 2 months postencapsulation, peaking at 4 weeks, where approximately 50% of islets contained proliferative cells, including β-cells, regardless of agarose type. These results illustrate the importance of optimizing the microenvironment of encapsulated islets to improve islet performance and advance the potential of islet xenotransplantation for the treatment of type 1 diabetes.

Hydrophilic agarose macrobead cultures select for outgrowth of carcinoma cell populations that can restrict tumor growth

Cancer cells and their associated tumors have long been considered to exhibit unregulated proliferation or growth. However, a substantial body of evidence indicates that tumor growth is subject to both positive and negative regulatory controls. Here, we describe a novel property of tumor growth regulation that is neither species nor tumor-type specific. This property, functionally a type of feedback control, is triggered by the encapsulation of neoplastic cells in a growth-restricting hydrogel composed of an agarose matrix with a second coating of agarose to form 6- to 8-mm diameter macrobeads. In a mouse cell model of renal adenocarcinoma (RENCA cells), this process resulted in selection for a stem cell-like subpopulation which together with at least one other cell subpopulation drove colony formation in the macrobeads. Cells in these colonies produced diffusible substances that markedly inhibited in vitro and in vivo proliferation of epithelial-derived tumor cells outside the macrobeads. RENCA cells in monolayer culture that were exposed to RENCA macrobead-conditioned media exhibited cell-cycle accumulation in S phase due to activation of a G(2)/M checkpoint. At least 10 proteins with known tumor suppression functions were identified by analysis of RENCA macrobead-conditioned media, the properties of which offer opportunities to further dissect the molecular basis for tumor growth control. More generally, macrobead culture may permit the isolation of cancer stem cells and other cells of the stem cell niche, perhaps providing strategies to define more effective biologically based clinical approaches to treat neoplastic disease.

Treatment of diabetes with encapsulated islets

Cell encapsulation has been proposed for the treatment of a wide variety of diseases since it allows for transplantation of cells in the absence of undesired immunosuppression. The technology has been proposed to be a solution for the treatment of diabetes since it potentially allows a mandatory minute-to-minute regulation of glucose levels without side-effects. Encapsulation is based on the principle that transplanted tissue is protected for the host immune system by a semipermeable capsule. Many different concepts of capsules have been tested. During the past two decades three major approaches of encapsulation have been studied. These include (i) intravascular macrocapsules, which are anastomosed to the vascular system as AV shunt, (ii) extravascular macrocapsules, which are mostly diffusion chambers transplanted at different sites and (iii) extravascular microcapsules transplanted in the peritoneal cavity. The advantages and pitfalls of the three approaches are discussed and compared in view of applicability in clinical islet transplantation.

Improved glucose regulation on a low carbohydrate diet in diabetic rats transplanted with macroencapsulated porcine islets

Islet xenografts from porcine donors can reverse diabetes in experimental animal models and may be an alternative to human islet transplantation. We have recently reported the ability of porcine islets encapsulated in a double layer of hydrophilic agarose to maintain in vitro functional ability for >6 months. Although beta-cells are capable of adapting their secretory capacity in response to glucose levels, evidence has shown that prolonged hyperglycemia can compromise this ability. The aim of the present study was to determine the effects of diet manipulation on the long-term regulation of blood glucose levels, and the preservation of functional islet in the macrobeads. Twenty-one streptozotocin-induced diabetic Wistar-Furth male rats were randomly assigned to two diets containing 64% carbohydrate (CHO) or 20% CHO. Groups of five to six animals assigned to either diet were implanted with either empty (EM) or porcine islet-containing macrobeads (PIM) and followed for 333 days. Observations included general condition, body weight, blood glucose, and food and water intakes. Monthly blood samples were collected for insulin and C-peptide analysis. The 20% CHO diet significantly lowered blood glucose values when compared with those of the 64% CHO groups for both the empty (14.94 +/- 0.41 vs. 16.26 +/- 0.42 mmol/L, respectively, p < 0.001) and islet macrobead recipients (12.88 +/- 0.39 vs. 15.57 +/-0.85 mmol/L, respectively, p <0.001). The different diets, however, had no statistically significant effects on the preservation of islet mass in the macrobead. Serum porcine C-peptide was detected throughout the experiment in animals receiving porcine islet macrobeads, regardless of diet. Diabetic rats fed a low carbohydrate level diet and transplanted with porcine islet macrobeads had improved total tissue glucose disposal and improved clinical parameters associated with diabetes.

Xenogeneic islet transplantation of microencapsulated porcine islets for therapy of type I diabetes: long-term normoglycemia in STZ-diabetic rats without immunosuppression

PURPOSE

Rejection and possible infection with porcine pathogens are obstacles in clinical xenogeneic transplantation of porcine pancreatic islets (PPI) to treat diabetic patients. A solution to this problem could be microencapsulation of the PPI. However, isolation and microencapsulation are highly demanding tasks with considerable risks of damaging the PPI. Thus, it is not surprising that the long-term function (>200 days) of microencapsulated PPI (mPPI), transplanted to diabetic rats, has been observed only in a few cases.

METHODS

Diabetes was induced in Wistar rats with streptozotozin (STZ 60 mg/kg body weight). Animals with consecutive blood glucose levels >300 mg/dl for more than 2 days were considered diabetic. PPI were isolated from brain-dead hybrid pigs (age 6-7 months or 2-3 years) using the Ricordi-technique and Liberase(PI). After in vitro culture PPI were microencapsulated with highly purified barium-alginate and 1,000 mPPI of 300-500 microm Ø were transplanted under the left kidney capsule and/or into the peritoneal cavity of STZ-diabetic rats (n = 15) without immunosuppression. Daily, later weekly, blood glucose level and body-weight were measured.

RESULTS

mPPI showed normal glucose tolerance in vitro and also in vivo. Normoglycemia occurred between day 1 and 15 after transplantation. Four mPPI grafts functioned for more than 230 days, the longest now for >550 days. Three rats are currently normoglycemic for >40 days. Six rats lost xenograft function after 12-20 days, due to inflammatory reactions at the site of the grafts. Two xenografts failed to induce normoglycemia, because the capsules did not contain enough viable PPI.

CONCLUSIONS

Microencapsulated xenogeneic islets can induce long term normoglycemia in rats without immunosuppression. However, very often the grafts fail to control the blood glucose level adequately. The reasons for these failures are currently under investigation. Nevertheless, our results are very promising and might lead the way towards preclinical trials in non-human primates.

Encapsulation of porcine islets permits extended culture time and insulin independence in spontaneously diabetic BB rats

The ability to culture porcine islets for extended times allows for both their functional assessment and the assurance of their microbiological safety prior to transplantation. We have previously shown that agarose-encapsulated porcine islets can be cultured for at least 24 weeks. In the current study, porcine islet agarose macrobeads cultured for up to 67 weeks were assessed for their ability to restore normoglycemia, respond to an intraperitoneal glucose challenge, maintain spontaneously diabetic BB rats free of insulin therapy for more than 6 months, and for their biocompatibility. Porcine islets were encapsulated in agarose macrobeads and subjected to weekly static perifusion assays for the assessment of insulin production. After in vitro culture for either 9, 40, or 67 weeks, 56-60 macrobeads were transplanted to each spontaneously diabetic BB rat. Transplanted rats were monitored daily for blood glucose levels. Glucose tolerance tests and assessments for porcine C-peptide were conducted at various intervals throughout the study. Normoglycemia (100-200 mg/dl) was initially restored in all islet transplanted rats. Moderate hyperglycemia (200-400 mg/dl) developed at around 30 days posttransplantation and continued throughout the study period of 201-202 days. Importantly, all rats that received encapsulated porcine islets continued to gain weight and were free of exogenous insulin therapy for the entire study. Porcine C-peptide (0.2-0.9 ng/ml) was detected in the serum of islet recipients throughout the study period. No differences were detected between recipient animals receiving islet macrobeads of various ages. These results demonstrate that the encapsulation of porcine islets in agarose macrobeads allows for extended culture periods and is an appropriate strategy for functional and microbiological assessment prior to clinical use.

PEG-based hydrogels as an in vitro encapsulation platform for testing controlled beta-cell microenvironments

An in vitro encapsulation platform for systematically testing the effects of microenvironmental parameters on encapsulated islets was developed. The base encapsulation matrix was a biocompatible hydrogel formed via the photoinitiated polymerization of dimethacrylated poly(ethylene glycol) (PEGDM). The resulting inert encapsulation matrix affords control over the biochemical and biophysical cellular microenvironment and the introduction of systematic changes to this environment. The compatibility of the PEG-based encapsulation platform with pancreatic beta-cells was first established using a murine beta-cell line, MIN6. When cell-cell contacts were introduced via aggregation of MIN6 beta-cells prior to encapsulation, MIN6 beta-cells remained viable within the PEG hydrogel platform throughout 3weeks of in vitro culture. Proliferating cells were observed within encapsulated MIN6 aggregates qualitatively with bromodeoxyuridine staining and quantitatively by measuring the DNA content of encapsulation samples with time. MIN6 beta-cells were encapsulated in hydrogels formed from three PEGDM macromers of varying molecular weights (M (n)=4,000, 8,000, 10,000g/mol), and the resulting differences in hydrogel crosslinking density, which influences transport properties, did not affect encapsulated beta-cell survival. Encapsulated MIN6 beta-cells transplanted into diabetic mice returned blood glucose levels to normal levels, indicating in vivo function. Finally, the compatibility of the PEG encapsulation system with freshly isolated islets was confirmed.

Survival of microencapsulated adult pig islets in mice in spite of an antibody response

The aim of this study was to assess the capacity of simple alginate capsules to protect adult pig islets in a model of xenotransplantation. Adult pig islets were microencapsulated in alginate, with either single alginate coats (SAC) or double alginate coats (DAC), and transplanted into the streptozotocin-induced diabetic B6AF1 mice. Normalization of glucose levels was associated with an improvement of the glucose clearance during intravenous glucose tolerance tests. After explantation, all mice became hyperglycemic, demonstrating the efficacy of the encapsulated pig islets. Explanted capsules were mainly free of fibrotic reaction and encapsulated islets were still functional, responding to glucose stimulation with a 10-fold increase in insulin secretion. However, a significant decrease in the insulin content and insulin responses to glucose was observed for encapsulated islets explanted from hyperglycemic mice. An immune response of both IgG and IgM subtypes was detectable after transplantation. Interestingly, there were more newly formed antibodies in the serum of mice transplanted with SAC capsules than in the serum of mice transplanted with DAC capsules. In conclusion, alginate capsules can prolong the survival of adult pig islets transplanted into diabetic mice for up to 190 days, even in the presence of an antibody response.

Macrophage depletion improves survival of porcine neonatal pancreatic cell clusters contained in alginate macrocapsules transplanted into rats

BACKGROUND

Macrophages can accumulate on the surface of empty and islet-containing alginate capsules, leading to loss of functional tissue. In this study, the effect of peritoneal macrophage depletion on the biocompatibility of alginate macrocapsules and function of macroencapsulated porcine neonatal pancreatic cell clusters (NPCCs) was investigated.

METHODS

Clodronate liposomes were injected into the peritoneal cavities of normoglycemic Lewis rats 5 and 2 days before the transplantation. Empty or NPCC-containing Ca-alginate poly L-lysine (PLL)-coated macrocapsules were transplanted into the peritoneal cavities of rats injected with either clodronate liposomes or saline. On days 7, 14 and 21, samples were evaluated by immunohistochemistry for cellular immune responses on the surface of the macrocapsules and for macrophage populations in omental tissue. To assess the function of macroencapsulated NPCCs, insulin secretory responses to glucose and theophylline were measured after capsule retrieval.

RESULTS

In saline-injected control groups, all of the empty and NPCC-containing macrocapsules were overgrown with macrophages, this being especially severe on NPCC-containing macrocapsules. In the clodronate liposomes-injected group, the majority of the empty macrocapsules were free of macrophage accumulation and the NPCC-containing macrocapsules were less overgrown than in control animals. Higher insulin responses to glucose and theophylline were observed in NPCCs retrieved from rats injected with clodronate liposomes.

CONCLUSION

We conclude that depletion of peritoneal macrophages with clodronate liposomes improve the survival of macroencapsulated NPCCs.

Encapsulation of pancreatic islets for transplantation in diabetes: the untouchable islets

The aim of encapsulation of pancreatic islets is to transplant in the absence of immunosuppression. It is based on the principle that transplanted tissue is protected from the host immune system by an artificial membrane. Encapsulation allows for application of insulin-secreting cells of animal or other surrogate sources, to overcome human islet shortage. The advantages and pitfalls of the approaches developed so far are discussed and compared, together with some recent progress, in view of applicability in clinical islet transplantation.

Alternatives to immunosuppressive drugs in human islet transplantation

Although intensive insulin therapy has resulted in improved metabolic control and decreases in the incidence of complications, the occurrence of severe hypoglycemia remains an issue, as does the continued potential for complications. Islet transplantation, a promising treatment for type I diabetes, has been shown to improve blood sugar levels and decrease or even abrogate the incidence of hypoglycemia. The lack of tissue availability and the toxic effects of immunosuppressants, however, limit the application of islet transplantation as a cure for diabetes. This article discusses possible alternatives to immunosuppressive drugs in human islet transplantations.

Peritoneal implantation of macroencapsulated porcine pancreatic islets in diabetic rats ameliorates severe hyperglycemia and prevents retraction and simplification of hippocampal dendrites

The hippocampus of rats with uncontrolled insulin-dependent diabetes undergoes retraction and simplification of apical dendrites of the CA3 pyramidal neurons and synaptic rearrangements within mossy fiber terminals that could alter hippocampal connectivity and function. The intraperitoneal implantation of hydrophilic agarose macrobeads containing porcine islets for 17 days in rats with streptozotocin-induced diabetes results in normalization of body weight gain, significant control of hyperglycemia and prevention of hippocampal dendritic remodeling, and therefore, provides an effective therapeutic option.