Article Commentary: Pancreatic Islet Transplantation: An Update

Retrovirally Transferred Genes Inhibit Apoptosis in an Insulin-Secreting Cell Line: Implications for Islet Transplantation

The transplantation of pancreatic islets for the treatment of type I diabetes is hindered by the enormous loss of cells due to early apoptotic events. Genetic engineering of islets with cytoprotective genes is an important strategy aimed to enhance the survival of these cells in the transplant setting. The present study was designed to evaluate and compare the effects of five genes on a cell line derived from insulin-producing β-cells, NIT-1. Cells were transduced using a Maloney murine leukemia virus (MLV) vector coding for yellow fluorescent protein (YFP) and for one of the following antiapoptotic genes: cFLIP, FADD-DN, BcL-2, PI-9, and ICAM-2. These genes were able to protect NIT-1 cells from cytokine-induced apoptosis to varying degrees ranging from no protection to significant protection equivalent to an optimal dose of a chemical caspase inhibitor. The data demonstrate that cFLIP, FADD-DN, and PI-9 are significantly more effective in protecting NIT-1 cells than BcL-2 and ICAM-2. Additionally, the data show that despite its weak in vitro inhibition of caspase-3, PI-9 affords significant protection against TNF-α-induced apoptosis in these cells. These genes may be ideal candidates to augment islet survival following transplantation.

Polyphenol, an Extract of Green Tea, Increases Culture Recovery Rates of Isolated Islets from Nonhuman Primate Pancreata and Marginal Grade Human Pancreata

Investigations indicate that an extract of green tea, polyphenol, can significantly increase the culture survival rate of rat islets without deteriorating their functionality. In this study, we examined the effect of adding polyphenol to islets isolated from human pancreata and nonhuman primate pancreata. Islets were isolated from human pancreata that did not meet criteria for clinical transplantation (n = 6) and from nonhuman primate pancreata (n = 5). The islets were cultured in CMRL-1066 + 10% FCS with the addition of 0, 30, 60, 125, 250, or 500 μg/ml of polyphenol. After 24 or 48 h of culture, islet yield, viability, purity, morphology, and stimulation index was assessed. RT-PCR and Western blot analysis were also performed to assess the expression levels of the apoptotic related genes, Bcl-2 and BAX. After 24 h of culture, islet yields were significantly higher in cultures supplemented with 30–250 μg/ml of polyphenol than in cultures without polyphenol. After 48 h of culture, significant differences in islet numbers were observed with polyphenol concentrations of 125 μg/ml (p < 0.01) and 250 μg/ml (p < 0.01). However, no significant differences were noted in islet viability, purity, morphology, and stimulation index at each time point with or without polyphenol. RT-PCR and Western blot analysis of the islets indicated that Bcl-2 levels increased by 2.5-fold and BAX levels decreased by twofold in cultures supplemented with polyphenol. This resulted in BAX/Bcl-2 ratios that were lower in polyphenol-supplemented cultures than with control cultures. Polyphenol increases culture recovery rates by precluding islet apoptosis.

Polyvinyl Pyrrolidone: A Novel Cryoprotectant in Islet Cell Cryopreservation

The present study was performed on the basis of the hypothesis that the low molecular weight (MW) compounds, DMSO and glycerol, permeate the cell and interact hydrophobically with intracellular proteins, thereby perturbing the cytoskeletal architecture of frozen cells and diminishing islet cell integrity and function. Isolated rat islets were cultured overnight (18–24 h) at 37°C in RPMI medium supplemented with 10% fetal calf serum and 1% mixture of penicillin/streptomycin. Using a programmable temperature controller, samples of precounted islets were then frozen under liquid nitrogen, in the presence of either 2 M DMSO (MW = 0.078 kDa), 3 M glycerol (MW = 0.092 kDa), 5% polyethylene glycol (PEG, MW = 20 kDa), or 10% polyvinylpyrrolidone (PVP, MW = 40 kDa), and stored at −80°C for 1 week. Following thawing and overnight (18–24 h) culture, intact islet recovery was determined by islet counting after dithizone staining. Islet function was assessed by determination of glucose-stimulated insulin secretion in perifusion experiments with Krebs-Ringer bicarbonate buffer, pH 7.4, containing either basal (3.3 mM) or high (16.7 mM) glucose concentrations. The assessment of islet recovery and function of all cryopreserved samples was performed only after thawing and overnight culture (18–24 h) of islets. The mean ± SEM percent intact islet recovery was higher with PVP compared with DMSO (82 ± 4.6 vs. 62.7 ± 3.1%, respectively, p < 0.005, n = 9). Furthermore, the glucose stimulation index of insulin secretion by islets taken from samples frozen with PEG and PVP, after thawing and overnight culture, was comparable to that of freshly isolated islets, in contrast to DMSO and glycerol. There was no significant difference in intact islet recovery and function between samples frozen with PVP and those frozen with PEG. Samples frozen with DMSO and glycerol had similar results in islet recovery and function. These data show that PVP is a new and potent cryoprotectant for islet cell freezing.

Survey of Apoptosis After Hypothermic Storage of a Pancreatic β-Cell Line

Insulin-dependent diabetes mellitus is one of the leading causes of death world wide. Donor-derived pancreas and islet of Langerhans transplantation are potential cures, however, postmortem ischemia impacts islet quality. The murine βt3 cell line was used as a model to study apoptosis after hypothermic storage by comparing Unisol™ with Belzer's machine perfusion solution (BMPS) and the University of Wisconsin (UW) solution. The objective was to determine which of these solutions provided the best support for βt3 cells and which solution demonstrated the least amount of apoptotic activity. Several apoptosis markers were measured that included the translocation of phosphatidylserine, caspase activity, and the formation of DNA laddering. In addition, metabolic activity and membrane integrity were also measured. The results demonstrated that the three solutions behaved similarly during overnight cold storage at 4°C. However, Unisol was consistently better than UW solution and BMPS, demonstrating better cell viability and recovery, and lower levels of apoptotic activity when all three parameters were measured. These results demonstrated that apoptosis plays an important role in the survival of cells and tissues during cold storage. Development of solutions to help prevent or decrease the levels of apoptosis after cold storage will likely improve overall cell and tissue recovery and survival in a clinical setting.

Development of pancreas storage solutions: Initial screening of cytoprotective supplements for β-cell survival and metabolic status after hypothermic storage

Insulin-dependent diabetes mellitus is one of the leading causes of death world-wide. Donor-derived pancreas and Islet of Langerhans transplantation are potential cures; however, postmortem ischemia impacts islet quality. The murine βt3 cell line was employed as a model to study cell viability and proliferation after hypothermic storage by comparing Belzer's Machine Perfusion Solution with Unisol™ Solution. The objective was to determine which of these solutions provided the best base line support for βt3 cells and to screen potential cytoprotective additives to the solutions. Initial βt3 cell viability was similar in the two storage solutions; however, better proliferation was observed after storage in Unisol Solution. The caspase inhibitor, Q-VD-OPH, and α-tocopherol improved viability in both storage solutions, suggesting that apoptotic pathways may be responsible for cell death during hypothermic storage of βt3 cells. Analysis of apoptosis markers, caspase activity, and DNA laddering showed a reduction in apoptosis when these additives were included. The effects of Q-VD-OPH and α-tocopherol were also synergistic when employed together during either hypothermic exposure, post-hypothermic physiologic incubation, or combinations of hypothermic exposure and physiologic incubation. These results suggest that both supplements should be included in pancreas hypothermic storage solutions and in islet culture media during post-isolation culture prior to transplantation.

Immuno-isolation of pancreatic islet allografts using pegylated nanotherapy leads to long-term normoglycemia in full MHC mismatch recipient mice

Two major hurdles need to be surmounted for cell therapy for diabetes: (i) allo-immune rejection of grafted pancreatic islets, or stem/precursor cell-derived insulin-secreting cells; and (ii) continuing auto-immunity against the diabetogenic endogenous target antigen. Nanotherapeutics offer a novel approach to overcome these problems and here we ask if creation of “stealth” islets encapsulated within a thin cage of pegylated material of 100–200 nanometers thick provides a viable option for islet transplantation. The aims of this study were to test islet viability and functionality following encapsulation within the pegylated cage, and functional efficacy in vivo in terms of graft-derived control of normoglycemia in diabetic mice. We first demonstrated that pegylation of the islet surface, plus or minus nanoparticles, improved long-term islet viability in vitro compared to non-pegylated (naked) control islets. Moreover, pegylation of the islets with nanoparticles was compatible with glucose-stimulated insulin secretion and insulin biogenesis. We next looked for functionality of the created “stealth” DBA/2 (H-2^d) islets in vivo by comparing glycemic profiles across 4 groups of streptozotozin-induced diabetic C57BL/6 (H-2^b) recipients of (i) naked islets; (ii) pegylated islets; (iii) pegylated islets with nanoparticles (empty); and (iv) pegylated islets with nanoparticles loaded with a cargo of leukemia inhibitory factor (LIF), a factor both promotes adaptive immune tolerance and regulates pancreatic β cell mass. Without any other treatment, normoglycemia was lost after 17 d (+/−7.5 d) in control group. In striking contrast, recipients in groups (ii), (iii), and (iv) showed long-term (>100 d) normoglycemia involving 30%; 43%, and 57% of the recipients in each respective group. In conclusion, construction of “stealth” islets by pegylation-based nanotherapeutics not only supports islet structure and function, but also effectively isolates the islets from immune-mediated destruction. The added value of nanoparticles to deliver immune modulators plus growth factors such as LIF expands the potential of this novel therapeutic approach to cell therapy for diabetes.

Microvesicles derived from endothelial progenitor cells enhance neoangiogenesis of human pancreatic islets

The efficacy of islet transplantation is limited by poor graft vascularization. We herein demonstrated that microvesicles (MVs) released from endothelial progenitor cells (EPCs) enhanced human islet vascularization. After incorporation into islet endothelium and β-cells, EPC-derived MVs favored insulin secretion, survival, and revascularization of islets transplanted in SCID mice. MVs induced in vitro islet endothelial cell proliferation, migration, resistance to apoptosis, and organization in vessel-like structures. Moreover, MVs partially overcame the antiangiogenic effect of rapamycin and inhibited endothelial-leukocyte interaction via L-selectin and CD40. MVs were previously shown to contain defined patterns of mRNAs. Here we demonstrated that MVs carried the proangiogenic miR-126 and miR-296 microRNAs (miRNAs). MVs pretreated with RNase or derived from Dicer knocked-down EPCs showed a reduced angiogenic effect. In addition, MVs overcame the antiangiogenic effect of the specific antagomiRs of miR-126 and miR-296, suggesting a relevant contribution of miRNAs delivered by MVs to islet endothelium. Microarray analysis of MV-stimulated islet endothelium indicated the upregulation of mRNAs coding for factors involved in endothelial proliferation, differentiation, and angiogenesis. In addition, MVs induced the activation of the PI3K-Akt and eNOS signaling pathways in islet endothelium. These results suggest that MVs activate an angiogenic program in islet endothelium that may sustain revascularization and β-cell function.

Mesenchymal Stromal Cells as a Therapeutic Strategy to Support Islet Transplantation in Type 1 Diabetes Mellitus

Type 1 diabetes is an autoimmune disorder that leads to destruction of pancreatic β islet cells and is a growing global health issue. While insulin replacement remains the standard therapy for type 1 diabetes, exogenous insulin does not mimic the physiology of insulin secretion. Transplantation of pancreatic islets has the potential to cure this disease; however, there are several major limitations to widespread implementation of islet transplants. The use of mesenchymal stromal cells (MSCs) in the treatment of type 1 diabetes has been investigated as an adjunct therapy during islet graft administration to prevent initial islet loss and promote engraftment and revascularization of islets. In this review we will discuss the results of recent MSC studies in animal models of diabetes with a focus on islet transplantation and explore the potential for these findings to be extended to clinical use for the treatment of type 1 diabetes.

A Meta-Analysis for Comparison of the Two-Layer and University of Wisconsin Pancreas Preservation Methods in Islet Transplantation

Conflicting results have been reported on the effectiveness of the two-layer method (TLM) compared with the University of Wisconsin (UW) method for preserving pancreata. The objective of this study was to compile the evidence for or against any difference in human islet yield and viability between these two. PubMed (January 2000 to May 2008) and Cochran Library searches were performed and 17 studies were included for the meta-analysis. Data on donor characteristics, preservation time, and outcomes were abstracted. Studies were subgrouped based on how TLM was used (UW + TLM or TLM alone), on mean cold ischemic time (CIT) (>20 h or <20 h), and on whether special chemical was used (yes or no). Meta-analysis of all studies and subgroups was performed and the pooled standardized mean differences (SMD) with 95% confidence intervals (CI) were reported. Overall, the use of TLM significantly increased islet yield [SMD, 0.74 (0.44–1.04)] and viability [SMD, 0.63 (0.14–1.12)]. The beneficial effects of TLM on islet yield were more evident when TLM was used following UW storage or when prolonged CIT was used. TLM used alone, shorter CIT, and no chemical use all resulted in similar islet viability between TLM and UW groups. Beneficial effects of TLM on islet viability were demonstrated only when TLM was used following UW storage, or with prolonged CIT, or with chemical use. In conclusion, the TLM was beneficial for prolonged pancreas preservation before human islet isolation; however, benefit of the TLM for short-term preservation was not clear.

Homogeneous insulin and C-Peptide sensors for rapid assessment of insulin and C-peptide secretion by the islets

OBJECTIVE

Glucose-stimulated islet insulin or C-peptide secretion experiments are a fundamental tool for studying and assessing islet function. The goal of this work was to develop Ab-based fluorescent homogenous sensors that would allow rapid, inexpensive, near-instantaneous determinations of insulin and C-peptide levels in biological samples.

RESEARCH DESIGN AND METHODS

Our approach was to use molecular pincer design (Heyduk et al., Anal Chem 2008;80:5152-5159) in which a pair of antibodies recognizing nonoverlapping epitopes of the target are modified with short fluorochrome-labeled complementary oligonucleotides and are used to generate a fluorescence energy transfer (FRET) signal in the presence of insulin or C-peptide.

RESULTS

The sensors were capable of detecting insulin and C-peptide with high specificity and with picomolar concentration detection limits in times as short as 20 min. Insulin and C-peptide levels determined with the FRET sensors showed outstanding correlation with determinations performed under the same conditions with enzyme-linked immunosorbent assay. Most importantly, the sensors were capable of rapid and accurate determinations of insulin and C-peptide secreted from human or rodent islets, verifying their applicability for rapid assessment of islet function.

CONCLUSIONS

The homogeneous, rapid, and uncomplicated nature of insulin and C-peptide FRET sensors allows rapid assessment of β-cell function and could enable point-of-care determinations of insulin and C-peptide.

Review of vitreous islet cryopreservation: Some practical issues and their resolution

Transplantation of pancreatic islets for the treatment of diabetes mellitus is widely anticipated to eventually provide a cure once a means for preventing rejection is found without reliance upon global immunosuppression. Long-term storage of islets is crucial for the organization of transplantation, islet banking, tissue matching, organ sharing, immuno-manipulation and multiple donor transplantation. Existing methods of cryopreservation involving freezing are known to be suboptimal providing only about 50% survival. The development of techniques for ice-free cryopreservation of mammalian tissues using both natural and synthetic ice blocking molecules, and the process of vitrification (formation of a glass as opposed to crystalline ice) has been a focus of research during recent years. These approaches have established in other tissues that vitrification can markedly improve survival by circumventing ice-induced injury. Here we review some of the underlying issues that impact the vitrification approach to islet cryopreservation and describe some initial studies to apply these new technologies to the long-term storage of pancreatic islets. These studies were designed to optimize both the pre-vitrification hypothermic exposure conditions using newly developed media and to compare new techniques for ice-free cryopreservation with conventional freezing protocols. Some practical constraints and feasible resolutions are discussed. Eventually the optimized techniques will be applied to clinical allografts and xenografts or genetically-modified islets designed to overcome immune responses in the diabetic host.

Comparison of the portal vein and kidney subcapsule as sites for primate islet autotransplantation

To date, the portal vein has been the primary site for clinical islet transplantation. Despite success, potential complications such as portal vein thrombosis still exist. The kidney subcapsule has been used successfully in rodent models of islet transplantation. We hypothesized that the kidney subcapsule as a site for islet transplantation in the nonhuman primate model would be as effective as the portal vein. Diabetes was induced in the primate Macaca fascicularis via a total pancreatectomy. Animals were kept under anesthesia during the isolation procedure. Islet isolation was performed using intraductal infusion with Liberase HI and mechanical digestion in the Ricordi chamber, and were purified using a continuous Ficoll gradient. Purified islets were autotransplanted either into the portal vein (n = 6) or the left kidney subcapsule (n = 5) of pancreatectomized animals. Intravenous glucose tolerance tests were performed prior to pancreatectomy and 10 days following transplantation. Three animals underwent pancreatectomy and served as diabetic controls. Of the six animals receiving islets in the portal vein, one developed portal vein thrombosis. All remaining autotransplanted animals in this group remained normoglycemic with glucose-induced insulin secretion that was not different from that prior to pancreatectomy. Of the five animals undergoing transplantation into the kidney subcapsule, only one maintained normoglycemia and elicited insulin secretion in response to glucose stimulation. The other four animals remained hyperglycemic. We conclude that the portal vein is superior to the kidney subcapsule as a site for islet transplantation in nonhuman primates 10 days posttransplantation.

Effect of alginate composition and gelling cation on micro-bead swelling

PURPOSE

The purpose of this study was to determine the roles of alginate composition and gelling cations on bead swelling, which affects its durability.

METHOD

Using a 2-channel droplet generator, microspheres were generated with 1.5% solutions of low viscosity high-mannuronic acid (LVM), medium viscosity high-mannuronic acid (MVM), low viscosity high-guluronic acid (LVG) and medium viscosity high-guluronic acid (MVG) alginate. They were gelled by cross-linking with 1.1% solution of either BaCl2 or CaCl2. The diameters of the micro-beads were measured and recorded on day 0. The micro-beads were subsequently washed and incubated in saline at 37 degrees C for 2 weeks with size assessment every 2 days. The data were normalized by calculation of the percentage change from control (day 0) for all groups of micro-beads.

RESULTS

Diameters of all beads were between 550 and 700 microm on day 0. Viscosity had no effect on swelling of Ba++- and Ca++-alginate micro-beads. Ca++-alginate micro-beads were more prone to swelling than the corresponding Ba++-alginate beads. High G-Ba++ beads had only a modest increase in size over time, in contrast to the high M-Ba++.

CONCLUSION

Alginate composition and the gelling cation have significant effects on bead swelling.

Effect of alginate composition and gelling cation on microbead swelling

PURPOSE

The purpose of this study was to determine the roles of alginate composition and gelling cations on bead swelling, which affects its durability.

METHOD

Using a 2-channel droplet generator, microspheres were generated with 1.5% solutions of low viscosity high-mannuronic acid (LVM), medium viscosity high-mannuronic acid (MVM), low viscosity high-guluronic acid (LVG) and medium viscosity high-guluronic acid (MVG) alginate. They were gelled by cross-linking with 1.1% solution of either BaCl2 or CaCl2. The diameters of the microbeads were measured and recorded on day 0. The microbeads were subsequently washed and incubated in saline at 37 degrees C for 2 weeks with size assessment every 2 days. The data were normalized by calculation of the percentage change from control (day 0) for all groups of microbeads.

RESULTS

Diameters of all beads were between 550-700 microns on day 0. Viscosity had no effect on swelling of Ba++- and Ca++-alginate microbeads. Ca++-alginate microbeads were more prone to swelling than the corresponding Ba++-alginate beads. High G-Ba++ beads had only a modest increase in size over time, in contrast to the high M-Ba++.

CONCLUSION

Alginate composition and the gelling cation have significant effects on bead swelling.

Magnetic resonance imaging of gadolinium-labeled pancreatic islets for experimental transplantation

New imaging techniques that couple anatomical resolution to sensitivity may greatly contribute to improving islet transplantation. In the present work, a report is given of the direct detection of islets by magnetic resonance imaging (MRI) after ex vivo cell labeling with the MRI T(1) contrast agent GdHPDO3A. Experiments on mouse and human islets demonstrated well-tolerated uptake of GdHPDO3A, based on morphology, viability, glucose-dependent insulin response and apoptosis/toxicity gene array profile. GdHPDO3A loading was sufficient for in vitro MRI cell detection. In vivo isotransplanted mouse islets into the kidney capsule and xenotransplanted human islets within the mouse liver were detected. Imaging specificity was supported by the absence of signal in unlabeled islet transplants, its persistence upon using fat-suppression MRI protocols and the colocalization with the transplanted islets. In conclusion, direct islet imaging with high spatial and contrast resolution after labeling with GdHPDO3A is demonstrated, allowing visualization of kidney subcapsular mouse islet grafts and intrahepatic human islet xenografts.

Tetracycline-regulated expression of VEGF-A in beta cells induces angiogenesis: improvement of engraftment following transplantation

Early revascularization of pancreatic islet cells after transplantation is crucial for engraftment, and it has been suggested that vascular endothelial growth factor-A (VEGF-A) plays a significant role in this process. Although VEGF gene therapy can improve angiogenesis, uncontrolled VEGF secretion can lead to vascular tumor formation. Here we have explored the role of temporal VEGF expression, controlled by a tetracycline (TC)-regulated promoter, on revascularization and engraftment of genetically modified beta cells following transplantation. To this end, we modified the CDM3D beta cell line using a lentiviral vector to promote secretion of VEGF-A either in a TC-regulated (TET cells) or a constitutive (PGK cells) manner. VEGF secretion, angiogenesis, cell proliferation, and stimulated insulin secretion were assessed in vitro. VEGF secretion was increased in TET and PGK cells, and VEGF delivery resulted in angiogenesis, whereas addition of TC inhibited these processes. Insulin secretion by the three cell types was similar. We used a syngeneic mouse model of transplantation to assess the effects of this controlled VEGF expression in vivo. Time to normoglycemia, intraperitoneal glucose tolerance test, graft vascular density, and cellular mass were evaluated. Increased expression of VEGF resulted in significantly better revascularization and engraftment after transplantation when compared to control cells. In vivo, there was a significant increase in vascular density in grafted TET and PGK cells versus control cells. Moreover, the time for diabetic mice to return to normoglycemia and the stimulated plasma glucose clearance were also significantly accelerated in mice transplanted with TET and PGK cells when compared to control cells. VEGF was only needed during the first 2-3 weeks after transplantation; when removed, normoglycemia and graft vascularization were maintained. TC-treated mice grafted with TC-treated cells failed to restore normoglycemia. This approach allowed us to switch off VEGF secretion when the desired effects had been achieved. TC-regulated temporal expression of VEGF using a gene therapy approach presents a novel way to improve early revascularization and engraftment after islet cell transplantation.

Antiangiogenic and immunomodulatory effects of rapamycin on islet endothelium: relevance for islet transplantation

Donor intra-islet endothelial cells contribute to neovascularization after transplantation. Several factors may interfere with this process and ultimately influence islet engraftment. Rapamycin, a central immunosuppressant in islet transplantation, is an mTOR inhibitor that has been shown to inhibit cancer angiogenesis. The aim of this study was to evaluate the effects of rapamycin on islet endothelium. Rapamycin inhibited the outgrowth of endothelial cells from freshly purified human islets and the formation of capillary-like structures in vitro and in vivo after subcutaneous injection within Matrigel plugs into SCID mice. Rapamycin decreased migration, proliferation and angiogenic properties of human and mouse islet-derived endothelial cell lines with appearance of apoptosis. The expression of angiogenesis-related factors VEGF, alphaVbeta3 integrin and thrombospondin-1 on islet endothelium was altered in the presence of rapamycin. On the other hand, rapamycin decreased the surface expression of molecules involved in immune processes such as ICAM-1 and CD40 and reduced the adhesion of T cells to islet endothelium. Our results suggest that rapamycin exerts dual effects on islet endothelium inducing a simultaneous inhibition of angiogenesis and a down-regulation of receptors involved in lymphocyte adhesion and activation.

Effective islet isolation method with extremely high islet yields from adult pigs

Achieving good islet isolation is one of the most important factors for successful islet transplantation. Porcine pancreas is suitable for islet isolation research due to its anatomical and physiological similarities to human pancreas. In this study, we evaluated a new porcine islet isolation method designed to maximize islet yield and compared it with our previous open pan method and the standard method using a Ricordi chamber (Ricordi method). We performed 15 porcine islet isolations, five each with the new method, the open pan method, and the Ricordi method. The new method features several important improvements. Pancreata remain uncut and are kept intact during collagenase intraductal injection, a large filtration chamber to handle whole pancreata, low concentration of collagenase (Liberase HI) for digestion, and large plastic containers for large-scale islet purification. All isolated islets were assessed for yield, purity, viability and in vitro function. Islets isolated with this new method were transplanted under the kidney capsules of SCID mice with chemically induced diabetes for in vivo functional assessment (n = 8). With the new method, we obtained on average more than 1,000,000 islet equivalents (IE) (1,236,266 +/- 213,486 IE) (mean +/- SE) before purification and 800,000 IE (879,815 +/- 222,729 IE) after purification from one adult pig. Islet yield per pancreas was significantly higher compared with our previous open pan method (30,666 +/- 11,532 IE, p < 0.01) and the Ricordi method (317,073 +/- 86,093 IE, p < 0.05). All mice, transplanted with 1000 islets from the new method, returned to normoglycemia within 4 days after transplantation. Our new method makes it possible to obtain extremely high porcine islet yield with good function. It should produce useful information for human islet isolation and transplantation, and might be applied to single donor clinical xenogeneic transplantation.

Platelet-Activating Factor Synthesis and Response on Pancreatic Islet Endothelial Cells: Relevance for Islet Transplantation

BACKGROUND

Recent data suggest that donor intraislet endothelial cells may survive islet transplantation and participate to the events that influence islet engraftment. However, the mechanisms that regulate islet endothelial behavior in this setting are poorly known.

METHODS

We obtained immortalized human (hIECs) and mouse (mIECs) islet endothelial cells by transfection with SV40-T-large antigen and studied the synthesis and response to Platelet-activating factor (PAF), a multipotent phospholipid that acts as endothelial mediator of both inflammation and angiogenesis.

RESULTS

HIECs showed typical endothelial markers such as expression of vWF, CD31, and CD105, uptake of acetylated-LDL and binding to ULE-A lectin. Moreover, they expressed nestin, the PAF-receptor and possess surface fenestrations and in vitro angiogenic ability of forming tubular structures on Matrigel. Likewise, mIECs showed expression of vWF, CD31, nestin, PAF-receptor and CD105, and uptake of acetylated-LDL. HIECs and mIECs rapidly produced PAF under stimulation with thrombin in a dose-dependent way. Exogenous PAF or thrombin-induced PAF synthesis increased leukocyte adhesion to hIECS and mIECs and cell motility of both endothelial cell lines. Moreover, PAF or thrombin-induced PAF synthesis accelerated in vitro formation of vessel-like tubular structures when hIECs are seeded on Matrigel. Notably, gene-microarray analysis detected up-regulation of beta3 integrin gene on hIECs stimulated with PAF, that was confirmed at the protein level.

CONCLUSIONS

Based on the novel development of immortalized islet endothelium, these results suggest that PAF may have a dual role that links inflammation to angiogenesis in the early events of islet transplantation.

Effect of microcapsule composition and short-term immunosuppression on intraportal biocompatibility

With higher nutrient and oxygen supply and close contact to blood, the portal vein is a possible alternative to the peritoneal cavity for transplantation of encapsulated cells. Data regarding intraportal biocompatibility of microcapsules are lacking. Microcapsules were built from five alginate types differing in their molar mass and mannuronic/guluronic acid ratios by complex formation with divalent cations (barium or calcium) or mixtures of divalent cations and polycations. They were injected in the portal vein of rats, and cellular and fibrotic pericapsular infiltration thickness was measured 3 and 7 days after implantation. Overgrowth was characterized using various stainings or immunohistochemistry (hematoxylin and eosin, Giemsa, ED-1 for monocyte/macrophage, alpha-actin for myofibroblasts, CD31 for endothelial cells). The impact of short-term immunosuppression (gadolinium-chloride IV 20 mg/kg/day on days--1 and 4 as well as 10 days of rapamycin PO 1 mg/kg/day, tacrolimus PO 3 mg/kg/day, or combinations of rapamycin/tacrolimus or gadolinium/tacrolimus) was further assessed 3, 7, and 42 days after implantation. Overall, overgrowth increased from day 3 to day 7 (p < 0.05). Three and 7 days after implantation, polycation-containing microcapsules induced more reaction than microbeads (p < 0.0001 and p < 0.01). Considering polycation-free beads, barium-alginate induced the weakest reaction. Biocompatibility of microbeads was independent of mannuronic/guluronic acid ratio and molar mass of the alginate. Infiltration was mainly a monocyte/macrophage-rich foreign body reaction, but an eosinophil-containing immunoallergic reaction was also observed. Short-term immunosuppression significantly reduced infiltration in all conditions and up to 42 days after implantation. Biocompatibility after intraportal infusion was best for barium-alginate microbeads and poorest for polycation-containing microcapsules. Short- and long-term overgrowth could be significantly reduced by short-term immunosuppression.

Assessment of human pancreatic islet architecture and composition by laser scanning confocal microscopy

The recent success of pancreatic islet transplantation has generated considerable enthusiasm. To better understand the quality and characteristics of human islets used for transplantation, we performed detailed analysis of islet architecture and composition using confocal laser scanning microscopy. Human islets from six separate isolations provided by three different islet isolation centers were compared with isolated mouse and non-human primate islets. As expected from histological sections of murine pancreas, in isolated murine islets alpha and delta cells resided at the periphery of the beta-cell core. However, human islets were markedly different in that alpha, beta, and delta cells were dispersed throughout the islet. This pattern of cell distribution was present in all human islet preparations and islets of various sizes and was also seen in histological sections of human pancreas. The architecture of isolated non-human primate islets was very similar to that of human islets. Using an image analysis program, we calculated the volume of alpha, beta, and delta cells. In contrast to murine islets, we found that populations of islet cell types varied considerably in human islets. The results indicate that human islets not only are quite heterogeneous in terms of cell composition but also have a substantially different architecture from widely studied murine islets.

Establishing an islet transplantation program in a developing country

Diabetes is an emerging epidemic throughout the world. In our city alone, there are approximately 25,000 known diabetics (5% to 10% type 1) among a total population of 1.7 million inhabitants, and the incidence is increasing among all age groups. Islet transplantation is a potential treatment for type 1 diabetes mellitus. For this reason, we intended to establish an islet transplantation program. This required competent and well-trained professionals, a specially planned facility adhering to rigid regulations regarding safety and sterility, and a detailed study of the ethical laws and rules involving transplantation. In this article, we describe the process including any difficulties or barriers encountered due to limited resources in a developing country. We also describe all stages of personnel training and the necessary equipment and work area of a similar specialized center following the guidelines of the Brazilian National Agency for Health Care. Finally, we discuss our expectations for the initial phase of our islet transplantation program.

The use of multiparametric monitoring during islet cell isolation and culture: a potential tool for in-process corrections of critical physiological factors

Variables such as pH, pCO2, and PO2 have been established in the literature as critical factors that could affect the outcome of the islet cell processing and, therefore, the quality of the cells that could be transplanted. This report describes a highly accurate continuous multiparametric monitoring system and its evaluation for continuous monitoring of physiological variables during critical steps of the islet isolation procedure as well as during in vitro culture of the insulin-producing cells. Close monitoring of these variables could be of assistance to improve the outcome of islet cell processing, allowing to identify as soon as possible problems that could be corrected during the procedure, as well as during in vitro preservation, or shipment to remote sites.

Gene expression profiling of cultured human islet preparations

The expression of functional and regulatory genes by islet cells is a key determinant for the success of islet transplantation. The aim of this study is twofold: first, to characterize the cluster of genes expressed in human islet isolations; and second, to validate the capability of gene array technology to assess with accuracy the expression of various transcripts. RNA from isolated islet preparations obtained from three independent donors was converted to cDNA and then transcribed to cRNA. Individual cRNA preparations were then hybridized to U133A microarrays carrying approximately 23,000 genes, and analyzed using GeneSpring (SiliconGenetics, Redwood City, CA) software. Real-time reverse transcription-polymerase chain reaction was performed to validate results obtained by microarray analysis. Microarray analysis identified the expression of about 7,000 genes transcribed in cultured human islet preparations. Enzymes represented the most abundant class of genes identified, followed by nuclear binding proteins, signal transduction molecules, transport proteins, and growth factor receptors and their ligands. Real-time polymerase chain reaction confirmed the identification of various islet-specific genes detected by microarray analysis, but also showed that such genes as pancreatic duodenal homeobox 1 protein and glucagon-like peptide 1 receptor, which were not detected by gene array, can be readily identified and quantified. In addition, gene array produced a suboptimal quantification of genes expressed in large amounts by islet cells. Indeed, the abundance of mRNA for insulin when compared with the level of somatostatin mRNA was not as different as one would have predicated based on the classic knowledge of islet physiology. Gene array analysis appears to be a valuable tool to obtain preliminary information of genes expressed by a given tissue. The expression levels of transcripts expressed in very low or very high quantities need to be confirmed by an independent technique.

The bag method for islet cell infusion

As islet cell transplantation gains increasing interest following results published by the Edmonton group, results that have been successfully reproduced by several centers nationwide and abroad, the need of guidelines to standardize the procedure becomes highly important. We detail the key steps of the infusion procedure utilizing a closed gravity fed bag system utilized at our institution since 1990, which consists of a 600-ml transfer bag and a 150-ml rinse bag connected via sterile tubing. The use of gravity allows for a control rate of infusion as well as providing a safety mechanism through natural reduction of flow that parallels any increase in portal pressure, therefore allowing the operator to prevent precipitous pressure rises. Reports on significant rise in portal pressures during islet cell infusion as well as portal vein thrombosis have been published. Infusion at these centers was carried out using a syringe method. Using our technique, portal vein thrombosis (partial or complete) was not detected in any of the infusions performed at our institution. This method may be of assistance to minimize some of the observed complications associated with islet transplant procedures and has now been adapted by most centers performing clinical islet transplantation.

Influence of pancreas preservation on human islet isolation outcomes: impact of the two-layer method

BACKGROUND

Human pancreas preservation for islet transplantation holds additional challenges and considerations compared with whole pancreas transplantation. The purpose of this study was to clarify the limitations of the University of Wisconsin (UW) solution and the potentials of the two-layer method (TLM) for pancreas preservation before human islet isolation.

METHODS

We retrospectively evaluated human islet isolation records between January 2001 and February 2003. One hundred forty-two human pancreata were procured from cadaveric donors and preserved by means of the UW solution (n=112) or TLM (n=30). Human islet isolations were performed using a standard protocol and assessed by islet recovery and in vitro function of islets.

RESULTS

Eight to ten hours of cold ischemia in the UW solution is a critical point for successful islet isolations. It is difficult to recover a sufficient number of viable islets for transplantation from human pancreata with more than 10 hours of cold storage in the UW solution. The overall islet recovery in the TLM group was significantly higher than in the UW group. With 10 to 16 hours of cold storage, the success rates of islet isolations remained at 62% in the TLM group but decreased to 22% in the UW group. Transplanted islets in the TLM group worked well in the recipients.

CONCLUSIONS

There are time limitations for using the UW solution for pancreas preservation before human islet isolation. The TLM is a potential method to prolong the optimal cold storage time for successful islet isolations.

Intraislet endothelial cells contribute to revascularization of transplanted pancreatic islets

Pancreatic islet transplantation is an emerging therapy for type 1 diabetes. To survive and function, transplanted islets must revascularize because islet isolation severs arterial and venous connections; the current paradigm is that islet revascularization originates from the transplant recipient. Because isolated islets retain intraislet endothelial cells, we determined whether these endothelial cells contribute to the revascularization using a murine model with tagged endothelial cells (lacZ knock-in to Flk-1/VEGFR2 gene) and using transplanted human islets. At 3-5 weeks after transplantation beneath the renal capsule, we found that islets were revascularized and that the transplant recipient vasculature indeed contributed to the revascularization process. Using the lacZ-tagged endothelial cell model, we found that intraislet endothelial cells not only survived after transplantation but became a functional part of revascularized islet graft. A similar contribution of intraislet endothelial cells was also seen with human islets transplanted into an immunodeficient mouse model. In the murine model, individual blood vessels within the islet graft consisted of donor or recipient endothelial cells or were a chimera of donor and recipient endothelial cells, indicating that both sources of endothelial cells contribute to the new vasculature. These observations suggest that interventions to activate, amplify, or sustain intraislet endothelial cells before and after transplantation may facilitate islet revascularization, enhance islet survival, and improve islet transplantation.