EARLY ASSESSMENT OF APOPTOSIS IN ISOLATED ISLETS OF LANGERHANS1

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.

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.

Inactivation of p27kip1 Promoted Nonspecific Inflammation by Enhancing Macrophage Proliferation in Islet Transplantation

Islet transplantation suffers from low efficiency caused by nonspecific inflammation-induced graft loss after transplantation. This study reports increased islet loss and enhanced inflammatory response in p27-deficient mice (p27-/-) and proposes a possible mechanism. Compared with wild type, p27-/- mice showed more severe functional injury of islet, with increased serum levels of inflammatory cytokines IL-1 and TNF-α, inducing macrophage proliferation. Furthermore, the increased number, proapoptotic proteins, and nuclear factor-kappa b (NF-κB) phosphorylation status of the infiltrating macrophages were accompanied by increased TNF-α mRNA level of islet graft site in p27-/- mice. Moreover, in vitro, we found that macrophages were still activated and cocultured with islet and promoted islet loss even blocking the direct effect of TNF-α on islets. Malondialdehyde (MDA, an end product of lipid peroxidation) in islet and media were increased after cocultured with macrophages. p27 deficiency also increased macrophage proliferation and islet injury. Therefore, p27 inactivation promotes injury islet graft loss via the elevation of proliferation and inflammatory cytokines secretion in infiltrating macrophages which induced nonspecific inflammation independent of TNF-α/nuclear factor-kappa b pathway. This potentially represents a promising therapeutic target in improving islet graft survival.

The Effect of Donor Factors on Human Islet Yield and Their in Vivo Function

Background

A major problem in the islet field is the high selectivity exercised in accepting cadaveric pancreas for islet isolation. This practice is based on experience that indicates that islet yield and posttransplant function are related to donor demographics and injury mechanisms.

Objective

To examine factors influencing islets recovery and in vivo function with emphasis on donor-related factors.

Methods

Islets were isolated from 99 human donor pancreata, and islet yield was reported as islet equivalent per gram pancreatic tissue. Donor, procurement, and isolation factors were collected for each isolation and correlation statistics were performed between these variables and islet yield.

Results

Results indicated a differential effect of enzyme mixes on yield with 2 Collagenase P digestion most suitable for increased ischemic time ( R2 = 0.1; P < .08), Liberase with small donor pancreas size and elevated preprocurement glucose ( R2 = 0.15; P < .02), and Serva with female donors ( R2 = 0.17; P < .06). Islets from 29 isolations were further tested by transplantation under the kidney capsule of immune-deficient NOD-SCID mice. Although all 29 preparations had acceptable in vitro perfusion parameters indicating viability, only 19 functioned in vivo with serum levels of insulin >5 U/mL and C peptide >1.5 ng/mL. No significant differences in donor, procurement, and isolation factors were evident between the islet preparations that functioned in vivo and those that were nonfunctional.

Conclusions

These data demonstrate that although yield is affected by a variety of donor factors and enzyme mixes, these factors do not affect islet in vivo function.

Human Serum Versus Human Serum Albumin Supplementation in Human Islet Pretransplantation Culture: In Vitro and In Vivo Assessment

There is conflicting evidence favoring both the use of human serum (HS) and of human serum albumin (HSA) in human islet culture. We evaluated the effects of HS versus HSA supplementation on 1) in vitro β-cell viability and function and 2) in vivo islet graft revascularization, islet viability, β-cell death, and metabolic outcome after transplantation. Islets isolated from 14 cadaveric organ donors were cultured for 3 days in CMRL 1066 medium supplemented with HS or HSA. After 3 days in culture, β-cell apoptosis was lower in HS group (1.41 ± 0.27 vs. 2.38 ± 0.39%, p = 0.029), and the recovery of islets was 77 ± 11% and 54 ± 1% in HS- and HSA-cultured groups, respectively. Glucose-stimulated insulin secretion (GSIS) was higher in HS group (29.4, range 10.4-99.9, vs. 22.3, range 8.7-70.6, p = 0.031). In vivo viability and revascularization was determined in HS- and HSA-cultured islets transplanted into the anterior chamber of the eye of Balb/c mice (n = 14), and β-cell apoptosis in paraffin-embedded mouse eyes. Islet viability and β-cell apoptosis were similar in both groups. Revascularization was observed in one graft (HS group) on day 10 after transplantation. Islet function was determined in streptozotocin (STZ)-diabetic nude mice (n = 33) transplanted with 2,000 IEQs cultured with HS or HSA that showed similar blood glucose levels and percentage of normoglycemic animals over time. In conclusion, human islets cultured in medium supplemented with HS showed higher survival in vitro, as well as islet viability and function. The higher in vitro survival increased the number of islets available for transplantation. However, the beneficial effect on viability and function did not translate into an improved metabolic evolution when a similar number of HSA- and HS-cultured islets was transplanted.

Impact of islet size on pancreatic islet transplantation and potential interventions to improve outcome

Better results have been recently reported in clinical pancreatic islet transplantation (ITX) due mostly to improved isolation techniques and immunosuppression; however, some limitations still exist. It is known that following transplantation, 30% to 60% of the islets are lost. In our study, we have investigated 1) the role of size as a factor affecting islet engraftment and 2) potential procedural manipulations to increase the number of smaller functional islets that can be transplanted. C57/BL10 mice were used as donors and recipients in a syngeneic islet transplant model. Isolated islets were divided by size (large, >300 μm; medium 150-300 μm; small, <150 μm). Each size was transplanted in chemically induced diabetic mice as full (600 IEQ), suboptimal (400 IEQ), and marginal mass (200 IEQ). Control animals received all size islets. Engraftment was defined as reversal of diabetes by day 7 posttransplantation. When the superiority of smaller islets was observed, strategies of overdigestion and fragmentation were adopted during islet isolation in the attempt to reduce islet size and improve engraftment. Smaller islets were significantly superior in engraftment compared to medium, large, and control (all sizes) groups. This was more evident when marginal mass data were compared. In all masses, success decreased as islet size increased. Once islets were engrafted, functionality was not affected by size. When larger islets were fragmented, a significant decrease in islet functionality was observed. On the contrary, if pancreata were slightly overdigested, although not as successful as small naive islets, an increase in engraftment was observed when compared to the control group. In conclusion, smaller islets are superior in engraftment following islet transplantation. Fragmentation has a deleterious effect on islet engraftment. Islet isolations can be performed by reducing islet size with slight overdigestion, and it can be safely adopted to improve clinical outcome.

Proangiogenic hydrogels within macroporous scaffolds enhance islet engraftment in an extrahepatic site

The transplantation of allogeneic islets in recent clinical trials has shown substantial promise as a therapy for type 1 diabetes; however, long-term insulin independence remains inadequate. This has been largely attributed to the current intravascular, hepatic transplant site, which exposes islets to mechanical and inflammatory stresses. A highly macroporous scaffold, housed within an alternative transplant site, can support an ideal environment for islet transplantation by providing three-dimensional distribution of islets, while permitting the infiltration of host vasculature. In the present study, we sought to evaluate the synergistic effect of a proangiogenic hydrogel loaded within the void space of a macroporous poly(dimethylsiloxane) (PDMS) scaffold on islet engraftment. The fibrin-based proangiogenic hydrogel tested presents platelet derived growth factor (PDGF-BB), via a fibronectin (FN) fragment containing growth factor and major integrin binding sites in close proximity. The combination of the proangiogenic hydrogel with PDMS scaffolds resulted in a significant decrease in the time to normoglycemia for syngeneic mouse islet transplants. This benefit was associated with an observed increase in competent vessel branching, as well as mature intraislet vessels. Overall, the addition of the proangiogenic factor PDGF-BB, delivered via the FN fragment-functionalized hydrogel, positively influenced the efficiency of engraftment. These characteristics, along with its ease of retrieval, make this combination of a biostable macroporous scaffold and a degradable proangiogenic hydrogel a supportive structure for insulin-producing cells implanted in extrahepatic sites.

The effects of oral carvacrol treatment against H2O2 induced injury on isolated pancreas islet cells of rats

Pancreatic islet transplantation is an alternative treatment of insulin replacement therapy in diabetes mellitus, but the islets are exposed to many chemical, mechanical damages, and oxidative stress before transplantation. Carvacrol is a well-known essential oil for its antioxidant, antimicrobial, antifungal and antiinflammatory properties. The aim of this study was to investigate the possible protective effects of carvacrol against H 2O 2 induced cellular injury on isolated pancreas islets. After carvacrol (20, 40 and 80 mg/kg/day) treatment, the pancreas islets were isolated by enzyme digestion. The isolated islets were incubated within 0, 150 and 300 µM H 2O 2 containing medium at +4°C for 15 min. Then, the islets were examined with fluorescein diacetate and propidium iodide mixture stains for viability. A number of islets were stored for lipid peroxidation, protein oxidation and DNA fragmentation analysis. The cell viability ratio of Carvacrol 20 mg/kg/day group was increased in comparison to control and vehicle (DMSO) groups. Additionally, carvacrol application protected the cells from lipid peroxidation and protein oxidation induced by H 2O 2. H 2O 2 caused tissue injury and DNA fragmentation. There was only one DNA fragmentation band from islet cells of 20 mg/kg/day carvacrol treated group, however there were more than one bands from control and DMSO groups. In conclusion, carvacrol treatment ameliorates islet cell injury induced by H 2O 2. However, the dose of carvacrol is important and our results suggest that 20 mg/kg/day dose is more effective than doses of 40 or 80 mg/kg/day.

Inflammation-Mediated Regulation of MicroRNA Expression in Transplanted Pancreatic Islets

Nonspecific inflammation in the transplant microenvironment results in β-cell dysfunction and death influencing negatively graft outcome. MicroRNA (miRNA) expression and gene target regulation in transplanted islets are not yet well characterized. We evaluated the impact of inflammation on miRNA expression in transplanted rat islets. Islets exposed in vitro to proinflammatory cytokines and explanted syngeneic islet grafts were evaluated by miRNA arrays. A subset of 26 islet miRNAs was affected by inflammation both in vivo and in vitro. Induction of miRNAs was dependent on NF-κB, a pathway linked with cytokine-mediated islet cell death. RT-PCR confirmed expression of 8 miRNAs. The association between these miRNAs and mRNA target-predicting algorithms in genome-wide RNA studies of β-cell inflammation identified 238 potential miRNA gene targets. Several genes were ontologically associated with regulation of insulin signaling and secretion, diabetes, and islet physiology. One of the most activated miRNAs was miR-21. Overexpression of miR-21 in insulin-secreting MIN6 cells downregulated endogenous expression of the tumor suppressor Pdcd4 and of Pclo, a Ca²⁺ sensor protein involved in insulin secretion. Bioinformatics identified both as potential targets. The integrated analysis of miRNA and mRNA expression profiles revealed potential targets that may identify molecular targets for therapeutic interventions.

Importance of oestrogen receptors to preserve functional β-cell mass in diabetes

Protecting the functional mass of insulin-producing β cells of the pancreas is a major therapeutic challenge in patients with type 1 (T1DM) or type 2 diabetes mellitus (T2DM). The gonadal hormone 17β-oestradiol (E2) is involved in reproductive, bone, cardiovascular and neuronal physiology. In rodent models of T1DM and T2DM, treatment with E2 protects pancreatic β cells against oxidative stress, amyloid polypeptide toxicity, lipotoxicity and apoptosis. Three oestrogen receptors (ERs)--ERα, ERβ and the G protein-coupled ER (GPER)--have been identified in rodent and human β cells. Whereas activation of ERα enhances glucose-stimulated insulin biosynthesis, reduces islet toxic lipid accumulation and promotes β-cell survival from proapoptotic stimuli, activation of ERβ increases glucose-stimulated insulin secretion. However, activation of GPER protects β cells from apoptosis, raises glucose-stimulated insulin secretion and lipid homeostasis without affecting insulin biosynthesis. Oestrogens are also improving islet engraftment in rodent models of pancreatic islet transplantation. This Review describes developments in the role of ERs in islet insulin biosynthesis and secretion, lipid homeostasis and survival. Moreover, we discuss why and how enhancing ER action in β cells without the undesirable effect of general oestrogen therapy is a therapeutic avenue to preserve functional β-cell mass in patients with diabetes mellitus.

Improved intraportal islet transplantation outcome by systemic IKK-beta inhibition: NF-κB activity in pancreatic islets depends on oxygen availability

Intraportal islet transplantation suffers from low efficiency caused by substantial islet mass loss after transplantation. How this process is regulated is still unclear. Here, we show that NF-κB activation was detectable in islet grafts shortly after transplantation of porcine islets to diabetic NMRI nu/nu mice, and systemic NF-κB inhibition in transplanted animals significantly prolonged islet graft survival. Proinflammatory cytokines alone did not cause evident cell death in pancreatic islet within 24 h, while the combination of cytokines with hypoxia resulted in a strong induction of cell death that could be blocked dose-dependently by a selective IKK-β inhibitor. Under hypoxia, NF-κB activity impaired expression of antiapoptotic gene BCL-xL, c-FLIP and survivin. NF-κB activation in isolated islets was reduced by hypoxia in a time-dependent manner, accordingly, NF-κB activation in transplanted islets diminished by time. Our data indicate that, while NF-κB has an antiapoptotic role under normoxia, low oxygen conditions decrease its activity and transform it to a proapoptotic transcription factor in pancreatic islets. We conclude that NF-κB inhibition represents a potential strategy to improve islet transplantation efficiency.

AMP-activated protein kinase regulates glucagon secretion from mouse pancreatic alpha cells

AIM/HYPOTHESIS

AMP-activated protein kinase (AMPK), encoded by Prkaa genes, is emerging as a key regulator of overall energy homeostasis and the control of insulin secretion and action. We sought here to investigate the role of AMPK in controlling glucagon secretion from pancreatic islet alpha cells.

METHODS

AMPK activity was modulated in vitro in clonal alphaTC1-9 cells and isolated mouse pancreatic islets using pharmacological agents and adenoviruses encoding constitutively active or dominant negative forms of AMPK. Glucagon secretion was measured during static incubation by radioimmunoassay. AMPK activity was assessed by both direct phosphotransfer assay and by western (immuno-)blotting of the phosphorylated AMPK α subunits and the downstream target acetyl-CoA carboxylase 1. Intracellular free [Ca²(+)] was measured using Fura-Red.

RESULTS

Increasing glucose concentrations strongly inhibited AMPK activity in clonal pancreatic alpha cells. Forced increases in AMPK activity in alphaTC1-9 cells, achieved through the use of pharmacological agents including metformin, phenformin and A-769662, or via adenoviral transduction, resulted in stimulation of glucagon secretion at both low and high glucose concentrations, whereas AMPK inactivation inhibited both [Ca²(+)](i) increases and glucagon secretion at low glucose. Transduction of isolated mouse islets with an adenovirus encoding AMPK-CA under the control of the preproglucagon promoter increased glucagon secretion selectively at elevated glucose concentrations.

CONCLUSIONS/INTERPRETATION

AMPK is strongly regulated by glucose in pancreatic alpha cells, and increases in AMPK activity are sufficient and necessary for the stimulation of glucagon release in vitro. Modulation of AMPK activity in alpha cells may therefore provide a novel approach to controlling blood glucose concentrations.

Silencing inducible nitric oxide synthase protects rat pancreatic islet

OBJECTIVE

To investigate the effect of inducible nitric oxide synthase (iNOS) RNA interference on cytokine-induced injury of pancreatic islet in rats.

MATERIALS AND METHODS

Islets from Wistar rats were cultured in vitro and then randomly divided into five groups: group A, islets were cultured exclusively; group B, islets were transfected with negative control siRNA; group C, islets were transfected with iNOS siRNA; group D, islets were transfected with iNOS siRNA and then treated with TNF-alpha+IL-1beta; group E, islets were treated with TNF-alpha+IL-1beta. The expression of iNOS, Bax and Fas was determined by RT-PCR and Western blot. The viability of islet was examined by AO/EB staining and function was examined by glucose-stimulated insulin secretion (GSIS) assay.

RESULTS

The expression of iNOS and the promoting apoptosis gene Bax and Fas were significantly up-regulated by the induction of IL-1beta and TNF-alpha. Thus they led to apoptosis increase and the insulin secretion index decrease (1.87+/-0.31 vs 3.83+/-1.40, P<0.01). Silencing iNOS by RNAi prevented the up-regulation of Bax and Fas induced by cytokine, thus reduced apoptosis of islets and recovered the insulin secretion index (3.43+/-0.24 vs 1.87+/-0.31, P<0.01).

CONCLUSION

The apoptosis from cytokines to islets mediated by iNOS could be suppressed by RNA interference, which favors the survival and function of islets.

Islet assessment for transplantation

PURPOSE OF REVIEW

There is a critical need for meaningful viability and potency assays that characterize islet preparations for release prior to clinical islet cell transplantation. Development, testing, and validation of such assays have been the subject of intense investigation for the last decade. These efforts are reviewed, highlighting the most recent results while focusing on the most promising assays.

RECENT FINDINGS

Assays based on membrane integrity do not reflect true viability when applied to either intact islets or dispersed islet cells. Assays requiring disaggregation of intact islets into individual cells for assessment introduce additional problems of cell damage and loss. Assays evaluating mitochondrial function, specifically mitochondrial membrane potential, bioenergetic status, and cellular oxygen consumption rate, especially when conducted with intact islets, appear most promising in evaluating their quality prior to islet cell transplantation. Prospective, quantitative assays based on measurements of oxygen consumption rate with intact islets have been developed, validated, and their results correlated with transplant outcomes in the diabetic nude mouse bioassay.

CONCLUSION

More sensitive and reliable islet viability and potency tests have been recently developed and tested. Those evaluating mitochondrial function are most promising, correlate with transplant outcomes in mice, and are currently being evaluated in the clinical setting.

Suppressor of cytokine signaling-1 inhibits caspase activation and protects from cytokine-induced beta cell death

Pancreatic beta cell damage caused by proinflammatory cytokines interleukin-1beta (IL-1beta), interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha) is a key event in the pathogenesis of type 1 diabetes. The suppressor of cytokine signaling-1 (SOCS-1) blocks IFNgamma-induced signaling and prevents diabetes in the non-obese diabetic mouse. Here, we investigated if SOCS-1 overexpression in primary beta cells provides protection from cytokine-induced islet cell dysfunction and death. We demonstrate that SOCS-1 does not prevent increase in NO production and decrease in glucose-stimulated insulin secretion in the presence of IL-1beta, IFNgamma, TNFalpha. However, it decreases the activation of caspase-3, -8 and -9, and thereby, promotes a robust protection from cytokine-induced beta cell death. Our data suggest that SOCS-1 overexpression may not be sufficient in preventing all the biological activities of IFNgamma in beta cells. In summary, we show that interference with IFNgamma signal transduction pathways by SOCS-1 inhibits cytokine-stimulated pancreatic beta cell death.

Flow cytometric quantification of glucose-stimulated beta-cell metabolic flux can reveal impaired islet functional potency

The objective of this study was to develop a multiparametric flow cytometry assay to simultaneously quantify isolated pancreatic islet cell viability, apoptosis, and glucose-induced metabolic flux. INS-1 and rat islet beta-cells were stained with fluorescent probes for cell viability (ToPro3), apoptosis (Annexin V and VADFMK), and intracellular calcium (Ca2+(i)) (Fura Red), stimulated with glucose, and analyzed on a FACS Vantage flow cytometer. Glucose-induced metabolic activity was indicated by changes in Fura Red fluorescence and the autofluorescence of the pyridine [NAD(P)H] and flavin (FAD/FMN) nucleotides. Rat islets cultured under conditions of proinflammatory cytokine-induced oxidative stress were evaluated by flow cytometry and transplantation into diabetic mice. INS-1 and rat islet beta-cell health and metabolic activity were quantified in response to elevated glucose dose and inhibitors of glycolysis and mitochondrial function. Changes in metabolite fluorescence were converted to an area under the curve (AUC) value. Rat islets cultured under oxidative stress conditions showed decreased viability, increased apoptosis, and decreased glucose-induced metabolic activity indicated by reduced AUC for pyridine and flavin nucleotides and Ca2+(i). Reduced metabolite AUC measured by flow cytometry correlated with the inability to reverse diabetes in mice. Single cell flow cytometry can simultaneously quantify both overall islet cell health and beta-cell glucose responsiveness as indicators of functional potency.

Anti-inflammatory thalidomide improves islet grafts survival and functions in a xenogenic environment

Thalidomide possesses both anti-inflammatory and anti-angiogenic properties. This study investigates its potential application in islet transplantation with a xenogenic transplantation model. Transplantation was performed using C57Bl/6 mice and NMRI nu/nu mice as recipients of porcine islets. Moreover, islet graft vasculature and inflammation were investigated to identify the mechanisms of thalidomide action. In the immunocompetent environment of C57Bl/6 mice, a fast graft rejection was observed. The group treated with thalidomide 200 mg/kg BW per day achieved and maintained euglycemia in the complete observation period for 42 days. The treated mice had more functional islet graft mass with less leukocyte infiltration. The pro-inflammatory TNF-α and VEGF content in islet grafted kidneys was significantly lowered by the treatment. By comparison, thalidomide was not effective in improving graft survival in immunocompromised nude mice. It strongly inhibited the VEGF and TNF-α-induced endothelial proliferation of isolated pig islets in a dose dependent manner. The magnitude of thalidomide's inhibitory effect was nearly identical to the effect of VEGF- receptor 2 inhibitor SU416 and anti-TNF-receptor 1 neutralizing antibody, and was reversed by sphingosine-1-phosphate. In conclusion, the anti-inflammatory effect of thalidomide improved islet graft survival and function in a transplantation model with a maximum immune barrier.

Caspase-3 gene silencing for inhibiting apoptosis in insulinoma cells and human islets

Although islet transplantation has great potential to treat type I diabetes, most islet grafts do not function due to the host immune rejection, nonspecific inflammatory response and poor revascularization. Since caspase-3 plays a crucial role in apoptosis of transplanted islet cells, we used chemically synthesized small interfering RNAs (siRNAs) to silence caspase-3 in insulinoma (INS-1E) cells and human islets, and then determined whether caspase-3 gene silencing can prevent these cells from cytokine-induced apoptosis. Transfection of INS-1E cells and islets with siRNAs reduced caspase-3 transcripts by 50-67% and 50%, respectively. Additionally, apoptosis in transfected insulinoma cells was markedly inhibited. Since gene silencing did not last beyond two days, we converted potent siRNA into shRNA and constructed replication deficient adenoviral (Adv) vectors encoding these shRNAs driven by a U6 or H1 promoter. Compared to chemically synthesized siRNA, Adv-caspase-3-shRNA efficiently transduced islets, showed relatively higher and prolonged levels of gene silencing beyond five days, with higher gene silencing with a U6 promoter, and protected islets from cytokine-induced apoptosis. Finally, return to normoglycemia was achieved at 1 day post-transplantation of Adv-caspase-3-shRNA transduced islets under the kidney capsules of streptozotocin induced nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice and maintained beyond two weeks. Blood glucose levels returned to > or = 325 mg/dL upon removal of the islet graft-bearing kidney at 32 days after transplantation, confirming that transplanted islets were functional.

Advances in long-term islet culture: the Memphis experience

Long-term culture of human islets provides opportunity for improving results of islet transplantation. The techniques of long-term culture are reproducible and can result in improved function of the islet after transplantation into NOD-SCID mice. We have been able to cure streptozotocin-induced diabetes by islets cultured for more than 6 mo. Culture conditions play an important role in the success of the procedure. Culture success is dependent on the media type, additives, type of colloid or protein used, purity of the islets, and concentration and volume of the tissue. Cellular and structural changes occur over time in culture. These changes may explain the improved efficacy of the islet graft after short and intermediate culture periods. Further research into long-term culture of islets is necessary to fully explore the potential of the technique.

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.

Cobalt Protoporpyhrin Reduces Caspase-3,-7 Enzyme Activity in Neonatal Porcine Islets, But Does Not Inhibit Cell Death Induced by TNF-α

Apoptotic phenomena observed in vitro following isolation and following transplantation contribute significantly to islet graft loss. Strategies to reduce apoptosis of islet tissue prior to and posttransplantation may improve graft survival and function and reduce the amount of tissue necessary to achieve insulin independence. The expression of cytoprotective proteins is one such strategy that may prolong islet survival. In this light, heme-oxygenase 1 (HO-1) upregulation has been studied in both allo- and xenotransplantation models. In this study, the effect of HO-1 on apoptosis in neonatal porcine islet-like cell clusters (NPICC) was assessed. In in vitro assessments of NPICC apoptosis, NPICC showed a high sensitivity to apoptotic stimulation using a combination of TNF-α and cycloheximide. Stimulation with TNF-α alone was sufficient to induce reproducible apoptotic responses as demonstrated by caspase-3,-7 activation and subdiploid DNA analysis. Dose-dependent, high-level HO-1 protein expression was achieved following culture of NPICC in medium containing either cobalt protoporphyrin (CoPP) or cobalt mesoporphyrin (CoMP). CoPP treatment resulted in the reduction of caspase-3,-7 enzyme activity following TNF-α stimulation. However, such an effect was not associated with a reduction in the levels of cell death. Indeed, the inhibition of caspase enzyme activity resulted in decreased PARP-1 cleavage, which may lead to heightened levels of necrosis in treated NPICC cultures, possibly explaining the observed commitment of NPICC to the death pathway.

Increased albumin concentration reduces apoptosis and improves functionality of human islets

Providing sufficient islet mass is important for successful islet transplantation. Apoptosis plays a major role in post-isolation islet cell death, and prevention of apoptosis could improve transplant outcomes. The purpose of this study was to determine whether increased concentration of human albumin (HA) in pre-transplantation culture of human islets would reduce apoptosis. Human islets were cultured in CMRL with 1.5 or 5% of HA for 24 h and apoptosis was evaluated indirectly by measuring caspase 3 activity and tetramethylrhodamine-ethyl-ester (TMRE) in dissociated islets. Islet function and viability were evaluated. Islets cultured in higher albumin concentration presented with lower caspase 3 activity (43.9 +/- 3.9 vs. 67.4 +/- 11.1, p = 0.011), and had increased insulin secretory capacity (Stimulation index 3.76 +/- 0.91 vs 1.23 +/- 0.21, p = 0.023). We conclude that an increase in albumin concentration can prevent apoptosis in isolated human islets. These findings may have implications for islet transplant outcomes.

Inhibition of AMP-activated protein kinase protects pancreatic beta-cells from cytokine-mediated apoptosis and CD8+ T-cell-induced cytotoxicity

OBJECTIVE

Apoptotic destruction of insulin-producing pancreatic beta-cells is involved in the etiology of both type 1 and type 2 diabetes. AMP-activated protein kinase (AMPK) is a sensor of cellular energy charge whose sustained activation has recently been implicated in pancreatic beta-cell apoptosis and in islet cell death posttransplantation. Here, we examine the importance of beta-cell AMPK in cytokine-induced apoptosis and in the cytotoxic action of CD8(+) T-cells.

RESEARCH DESIGN AND METHODS

Clonal MIN6 beta-cells or CD1 mouse pancreatic islets were infected with recombinant adenoviruses encoding enhanced green fluorescent protein (eGFP/null), constitutively active AMPK (AMPK-CA), or dominant-negative AMPK (AMPK-DN) and exposed or not to tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma. Apoptosis was detected by monitoring the cleavage of caspase-3 and DNA fragmentation. The cytotoxic effect of CD8(+) purified T-cells was examined against pancreatic islets from NOD mice infected with either null or the AMPK-DN-expressing adenoviruses.

RESULTS

Exposure to cytokines, or expression of AMPK-CA, induced apoptosis in clonal MIN6 beta-cells and CD1 mouse pancreatic islets. By contrast, overexpression of AMPK-DN protected against the proapoptotic effect of these agents, in part by preventing decreases in cellular ATP, and lowered the cytotoxic effect of CD8(+) T-cells toward NOD mouse islets.

CONCLUSIONS

Inhibition of AMPK activity enhances islet survival in the face of assault by either cytokines or T-cells. AMPK may therefore represent an interesting therapeutic target to suppress immune-mediated beta-cell destruction and may increase the efficacy of islet allografts in type 1 diabetes.

In vitro and in vivo prevention of human CD8+ CTL-mediated xenocytotoxicity by pig c-FLIP expression in porcine endothelial cells

Overcoming cell-mediated immunity, especially of human CD8(+) CTLs, is important for the success of xenotransplantation. Our group has previously reported that the cytotoxicity of human CD8(+) CTLs against pig endothelial cells (PEC) is highly detrimental and mediated in major part by the Fas/FasL apoptotic pathway. Cellular FLICE inhibitory protein (c-FLIP) was originally identified as an inhibitor of death-receptor signaling through binding competition with caspase-8 for recruitment to Fas-associated via death domain (FADD). Two major c-FLIP variants result from alternative mRNA splicing: a short, 26-KDa protein (c-FLIP(S)) and a long, 55-KDa form (c-FLIP(L)). The cytoprotective effects of c-FLIP(S/L) in xenograft cells remain controversial. This study demonstrates that the overexpression of c-FLIP(S/L) genes markedly suppress human CD8(+) CTL-mediated xenocytotoxicity and, in addition, the cytoprotective effects of c-FLIP(L) appear to be significantly stronger than those of c-FLIP(S). Furthermore, to prove the prolonged effects of xenograft survival, PEC transfectants with c-FLIP(S/L) genes were transplanted under rat kidney capsules. Prolonged survival was elicited from FLIP(S/L) transfectants, whereas parental PEC was completely rejected through day 5, posttransplant. Thus, intracellular remodeling with the overexpression of c-FLIP(S/L) in xenograft cells may avoid innate cellular attacks against xenografts and facilitate long-term xenograft survival.

The application of low shear modeled microgravity to 3-D cell biology and tissue engineering

The practice of cell culture has been virtually unchanged for 100 years. Until recently, life scientists have had to content themselves with two-dimensional cell culture technology. Clearly, living creatures are not constructed in two dimensions and thus it has become widely recognized that in vitro culture systems must become three dimensional to correctly model in vivo biology. Attempts to modify conventional 2-D culture technology to accommodate 3-D cell growth such as embedding cells in extracellular matrix have demonstrated the superiority of concept. Nevertheless, there are serious drawbacks to this approach including limited mass transport and lack of scalability. Recently, a new cell culture technology developed at NASA to study the effects of microgravity on cells has emerged to solve many of the problems of 3-D cell culture. The technology, the Rotating Wall Vessel (RWV) is a single axis clinostat consisting of a fluid-filled, cylindrical, horizontally rotating culture vessel. Cells placed in this environment are suspended by the resolution of the gravitational, centrifugal and Coriolis forces with extremely low mechanical shear. These conditions, which have been called "low shear modeled microgravity", enable cells to assemble into tissue-like aggregates with high mass transport of nutrients, oxygen and wastes. Examples of the use of the RWV for basic cell biology research and tissue engineering applications are discussed.

Rapid loss of intraportally transplanted islets: an overview of pathophysiology and preventive strategies

Islets isolated from multiple pancreas donors are often necessary to achieve euglycemia in type 1 diabetic patients treated by islet allotransplantation. This increases the burden on the limited pool of donor organs. After infusion into the portal vein, a substantial percentage of islets are lost in the immediate post-transplant period through an inflammatory response termed the instant blood-mediated inflammatory reaction (IBMIR). IBMIR is equally, if not more of a problem after islet xenotransplantation, e.g., using pig islets in non-human primates. Coagulation, platelet aggregation, complement activation, and neutrophil and monocyte infiltration play roles in this reaction. IBMIR is potentially triggered by islet surface molecules, such as tissue factor and collagen residues that are normally not in direct contact with the blood. Also, stress during the islet isolation process results in the expression and production of several inflammatory mediators by the islets themselves. The potential mechanisms involved in this rapid graft loss and treatment options to reduce this loss are reviewed. Preventive strategies for IBMIR can include systemic treatment of the recipient, pre-conditioning of the isolated islets, or, in the case of xenotransplantation, genetic modification of the organ-source pig. Pre-conditioning of islets in culture by exposure to anti-inflammatory agents or by genetic modification harbors fewer risks of systemic complications in the recipient. The future of clinical islet transplantation will, at least in part, depend on the success of efforts made to reduce rapid graft loss, and thus allow islet transplantation to become a more efficient therapy by the use of single donors.

Cell-permeable pentapeptide V5 inhibits apoptosis and enhances insulin secretion, allowing experimental single-donor islet transplantation in mice

OBJECTIVE

Treatment of diabetic patients by pancreatic islet transplantation often requires the use of islets from two to four donors to produce insulin independence in a single recipient. Following isolation and transplantation, islets are susceptible to apoptosis, which limits their function and probably long-term islet graft survival.

RESEARCH DESIGN AND METHODS

To address this issue, we examined the effect of the cell-permeable apoptosis inhibitor pentapeptide Val-Pro-Met-Leu-Lys, V5, on pancreatic islets in a mouse model.

RESULTS

V5 treatment upregulated expression of anti-apoptotic proteins Bcl-2 and XIAP (X-linked inhibitor of apoptosis protein) by more than 3- and 11-fold and downregulated expression of apoptosis-inducing proteins Bax, Bad, and nuclear factor-kappaB-p65 by 10, 30, and nearly 50%, respectively. Treatment improved the recovered islet mass following collagenase digestion and isolation by 44% and in vitro glucose-responsive insulin secretion nearly fourfold. Following transplantation in streptozotocin-induced diabetic mice, 150 V5-treated islet equivalents functioned as well as 450 control untreated islet equivalents in normalizing blood glucose.

CONCLUSIONS

These studies indicate that inhibition of apoptosis by V5 significantly improves islet function following isolation and improves islet graft function following transplantation. Use of this reagent in clinical islet transplantation could have a dramatic impact on the number of patients that might benefit from this therapy and could affect long-term graft survival.

Regulation of pancreatic islet cell survival and replication by gamma-aminobutyric acid

AIMS/HYPOTHESIS

Pancreatic islets have evolved remarkable, though poorly understood mechanisms to modify beta cell mass when nutrient intake fluctuates or cells are damaged. We hypothesised that appropriate and timely adjustments in cell number occur because beta cells release proliferative signals to surrounding cells when stimulated by nutrients and 'bleed' these growth factors upon injury.

MATERIALS AND METHODS

In rat pancreatic islets, we measured DNA content, insulin content, insulin secretion after treatment, immunoblots of apoptotic proteins and the uptake of nucleoside analogues to assess the ability of gamma-aminobutyric acid (GABA), which is highly concentrated in beta cells, to act as a growth and survival factor. This focus is supported by work from others demonstrating that GABA increases cell proliferation in the developing nervous system, acts as a survival factor for differentiated neurons and, interestingly, protects plants under stress.

RESULTS

Our results show that DNA, insulin content and insulin secretion are higher in freshly isolated islets treated with GABA or GABA B receptor agonists. Exposure to GABA upregulated the anti-apoptotic protein B-cell chronic lymphocytic leukaemia XL and limited activation of caspase 3 in islets. The cellular proliferation rate in GABA-treated islets was twice that of untreated controls.

CONCLUSIONS/INTERPRETATION

We conclude that GABA serves diverse purposes in the islet, meeting a number of functional criteria to act as an endogenous co-regulator of beta cell mass.

Mitochondrial Targeting with Antioxidant Peptide SS-31 Prevents Mitochondrial Depolarization, Reduces Islet Cell Apoptosis, Increases Islet Cell Yield, and Improves Posttransplantation Function

Apoptotic cell death is a defined pathway for islet cell demise, and mitochondrial dysfunction contributes to islet cell apoptosis. The hypothesis that the novel peptide D-Arg-2', 6'-dimethyltyrosine-Lys-Phe-NH2 (SS-31), previously shown to target inner mitochondrial membrane and prevent oxidative damage of neuronal cells and other cell types, optimizes pancreatic islet isolation and improves posttransplantation function in recipients with diabetes was investigated. Herein is demonstrated that SS-31 readily penetrates intact mouse islets, preserves mitochondrial polarization, reduces islet cell apoptosis, and increases islet cell yield. Optimization of islet isolation is demonstrable after SS-31 pretreatment of islet (pancreas) donor mice and with the addition of SS-31 to reagents that are used in the isolation of mouse islets. The supplementation of in vitro culture medium with SS-31 reduced islet cell apoptosis and increased the viability of human islets, as ascertained by dual-parameter flow cytometry analysis. In a stringent marginal islet cell mass transplantation model (200 mouse islets transplanted under the renal capsule of syngeneic diabetic mice) and using islets that were derived from old mice (>24 wk), SS-31 treatment was associated with prompt and sustained normoglycemia, whereas the untreated islet graft recipients remained diabetic. Our data suggest a novel strategy to optimize islet isolation and reduce the need for multiple pancreata to achieve insulin independence in the recipient with type 1 diabetes. Because SS-31 was effective with "extended" islet donors, it is hypothesized that the antioxidant SS-31 may serve to increase the pool of eligible organ donors.

Detection of insulin mRNA in the peripheral blood after human islet transplantion predicts deterioration of metabolic control

Recent updates of the Edmonton trial have shown that insulin independence is progressively lost in approximately 90% of islet transplant recipients over the first 5 years. Early prediction of islet graft injury could prompt the implementation of strategies attempting to salvage the transplanted islets. We hypothesize that islet damage is associated with the release and detection of insulin mRNA in the circulating blood. Whole blood samples were prospectively taken from 19 patients with type 1 diabetes receiving 31 islet transplants, immediately prior to transplantation and at regular time-points thereafter. After RNA extraction, levels of insulin mRNA were determined by quantitative reverse tran-scriptase-polymerase chain reaction. All patients exhibited a primary peak of insulin mRNA immediately after transplantation, without correlation of duration and amplitude with graft size or outcome. Twenty-five subsequent peaks were observed during the follow-up of 17 transplantations. Fourteen secondary peaks (56%) were closely followed by events related to islet graft function. Duration and amplitude of peaks were higher when they heralded occurrence of an adverse event. Peaks of insulin mRNA can be detected and are often associated with alterations of islet graft function. These data suggest that insulin mRNA detection in the peripheral blood is a promising method for the prediction of islet graft damage.

Pancreatic islet transplantation for treating diabetes

Pancreatic islet transplantation is one of the options for treating diabetes and has been shown to improve the quality of life of severe diabetic patients. Since the Edmonton protocol was announced, islet transplantation have advanced considerably, including islet after kidney transplantation, utilisation of non-heart-beating donors, single-donor islet transplantation and living-donor islet transplantation. These advances were based on revised immunosuppression protocols, improved pancreas procurement and islet isolation methods, and enhanced islet engraftment. Further improvements are necessary to make islet transplantation a routine clinical treatment. To synergise efforts towards a cure for type 1 diabetes, a Diabetes Research Institute (DRI) Federation is currently being established to include leading diabetes research centres worldwide, including DRIs in Miami, Edmonton and Kyoto among others.

Integrin signaling via RGD peptides and anti-beta1 antibodies confers resistance to apoptosis in islets of Langerhans

Islet transplantation is associated with a high rate of early graft failure caused by early immune attack and poor functionality of islets. Apoptosis of islet cells appears soon after islet isolation and primarily involves the beta-cell. The purpose of this study was to determine the effect of ligation to extracellular matrix (ECM) proteins on survival of the islets of Langerhans following islet isolation. Islets that had been cultured for 24 h on collagen type I showed an islet survival of 59.7 +/- 8.7%, while islets that had been cultured on collagen type IV and laminin showed an islet survival of 88.6 +/- 10.3 and 94.3 +/- 5.6%, respectively. Islets that had been pretreated with anti-beta1 antibodies and argenin-glycin-aspartic acid (RGD) peptides showed a decrease in the level of apoptosis by a factor of 2.5 and 3.1, respectively, and an increase of phospho-Akt Ser 473 activity by a factor of 3.1 and 2.9, respectively, compared with untreated islets. When detached from their natural ECM surrounding in the pancreas, islet cells undergo apoptosis, unless islets are cultured on collagen IV or laminin or treated with anti-beta1 integrin antibodies or RGD peptides to mimic ECM ligation. These results indicate that inhibition of anoikis may offer opportunities to improve function and viability of islet cells.

Liver ischemia contributes to early islet failure following intraportal transplantation: benefits of liver ischemic-preconditioning

Early graft failure following intraportal islet transplantation (IPIT) represents a major obstacle for successful islet transplantation. Here, we examined the role of islet emboli in the induction of early graft failure and utilized a strategy of ischemic-preconditioning (IP) to prevent early islet destruction in a model of syngeneic IPIT in STZ-induced diabetic mice. Numerous focal areas of liver necrosis associated with the islet emboli were observed within 24 h post-IPIT. Pro-inflammatory cytokines, IL-1beta and IL-6, were significantly increased 3 h after IPIT, while TNF-alpha was elevated for up to 5 days post-IPIT. Caspase-3 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling positive cells were observed in the transplanted islets trapped in areas of necrotic liver at 3 h and 1 day post-IPIT. Hyperglycemia was corrected immediately following IPIT of 200 islets, but recurrence of hyperglycemia was observed within 14 days associated with a poor response to glucose challenge. IP, a procedure of pre-exposure of the liver to transient ischemia and reperfusion, protected the liver from embolism-induced ischemic injury and prevented early islet graft failure. These data suggest that islet embolism in the portal vein is a major cause of functional loss following IPIT that can be prevented by liver IP.

Transduction of pancreatic islets with pseudotyped adeno-associated virus: effect of viral capsid and genome conversion

BACKGROUND

Recombinant adeno-associated viral (rAAV) vectors currently show promise for islet gene therapy. In the presence of complementing AAV2 Rep proteins, AAV2 genomes can be packaged with other serotype capsids to assemble infectious virions. During transduction, the ssDNA to dsDNA conversion is one of the major rate-limiting steps that contribute to the slow onset of transgene expression.

METHODS

Using pseudotyping strategy, we produced double-stranded (dsAAV) and single-stranded (ssAAV) rAAV2 genomes carrying the GFP reporter gene packaged into AAV1, AAV2, and AAV5 capsids. The ability of cross-packaged AAV1, AAV2, and AAV5 at the same genome containing particle (gcp) concentration to transduce murine and human pancreatic islets was evaluated by GFP positive cell percentage. Transgenic expression was also determined by transplant transduced human islet into SCID mice.

RESULTS

Pseudotyped rAAV2/1 based vectors transduced murine islets at greater efficiency than either rAAV2/2 or rAAV2/5 vectors. For human islets transduction, the rAAV2/2 vector was more efficient than rAAV2/1 or rAAV2/5 vectors. rAAV2/2 transduced human islets more efficiently than murine islets, while rAAV2/1 transducted murine islets more efficiently than human islets. dsAAV, which do not require second strand synthesis and thus are potentially more efficient, evidenced 5 fold higher transduction ability than ssAAV vectors. Pseudotyped rAAV transduced islet grafts maintained normal function, expressed transgenic product persistently in vivo, and reversed diabetes.

CONCLUSIONS

The transduction efficiency of rAAV vectors was dependent on the cross-packaged capsid. The vector capsids permit species-specific transduction. For human islets, dsAAV2/2 vectors may be the most efficient vector for clinical development.

OP-142 Gene Expression Profile of Nonfunctional Human Pancreatic Islets: Predictors of Transplant Failure?

Islet culture has become a standard part of most successful protocols for clinical islet transplantation. To date, however, islets are transplanted based on crude measures of viability, purity and in vitro insulin production without adequate prior assessment of the potential for in vivo function. The purpose of this study was to define the gene expression profiles of human islets associated with in vivo function using a nonimmune NOD-scid mouse model. Human islets from eight isolations were maintained in culture for 7 to 14 days in Memphis serum-free media until transplanted. The RNA was extracted from 10,000 IEQ using RNASTAT-60. The gene expression profiles were analyzed using high-density Affymetrix U133A GeneChips and Genespring software. An aliquot of 2000 IEQ from each islet preparation was also transplanted into NOD-scid animals (n = 5) for in vivo function assessments. Islet function was assessed by measurements of human C-peptide at days 7 and 14 posttransplant. Human C-peptide levels were determined by radioimmunoassay. Gene analysis of nonfunction islets (4 of 8 islet preparations) showed high relative levels of expression of proinflammatory genes and low relative levels of genes directed toward insulin processing and secretion as well as islet integrity. Overexpression of hypoxia and proinflammatory genes may result in reduced insulin secretion and lead to islet destruction posttransplantation. Identifying and validating those genes could allow the development of a potency assay for human transplantation that would be very useful for screening human islet preparations before clinical transplant.

Measurement of apoptosis of intact human islets by confocal optical sectioning and stereologic analysis of YO-PRO-1-stained islets

Apoptosis is an established pathway for islet cell demise. Current protocols for assessment of islet cell apoptosis are time-consuming (as with terminal deoxynucleotide transferase-mediated dUTP nick-end labeling reaction) and involve disruption of the islet architecture (as with flow cytometry) or destruction of cell integrity (as with enzyme-linked immunosorbent assay). The membranes of apoptotic cells, but not those of live cells, are permeant to the DNA-intercalant dye YO-PRO-1. We report a novel methodology for the rapid quantification of apoptosis of human islets: confocal laser optical sectioning and stereologic analysis of intact human islets stained with YO-PRO-1 and Hoechst 33342. The advantages include (1) rapid quantification of apoptosis without disrupting islet architecture and (2) identification of significant heterogeneity in the extent of apoptosis among islets from the same isolate. Confocal laser scanning microscopy microscopic imaging of YO-PRO-1-stained islets may advance investigation of islet cell apoptosis and help develop islet parameters predictive of posttransplant function.

Cytokines activate caspase-3 in insulinoma cells of diabetes-prone NOD mice directly and via upregulation of Fas

In type 1 diabetes, autoimmune inflammation of pancreatic islets of Langerhans ('insulitis') results in destruction of insulin-producing beta cells. Cytokines released from islet-infiltrating mononuclear cells are known to be cytotoxic both directly and by upregulating Fas for FasL-induced apoptosis. To investigate the role of caspase-3, a major effector of apoptosis in beta-cell death, we asked whether cytokine- and/or FasL-induced apoptosis was associated with increased activity of caspase-3 in NIT-1 insulinoma cells and islets of autoimmune diabetes-prone NOD mice. Measurement of caspase-3 activity using a fluorogenic cleavage assay was validated in NOD mouse thymocytes undergoing dexamethasone (Dex)-induced apoptosis. For cytokine-induced apoptosis, NIT-1 cells or islets were exposed to IL-1 beta and IFN-gamma for 24 h. Caspase-3-like activity was increased 2.1+/-0.7 and 2.4+/-0.9-fold in lysates of cytokine-treated NIT-1 cells and NOD mouse islets, respectively. However, NIT-1 cells exhibited 2.1% (4.7 pg active caspase-3/microg protein) and islets 0.8% (1.9 pg active caspase-3/microg protein) of the active caspase-3 content observed in Dex-treated thymocytes (225.1 pg active caspase-3/microg protein). After 24 h cytokine-exposure, the percentage of Fas-positive NIT-1 cells increased from 1.4+/-1.1 to 29.7+/-11.6%. Addition of FasL for a further 3 h increased caspase-3-like activity an additional 1.8-fold in cytokine-treated NIT-1 cells. In summary, exposure of NOD mouse insulinoma cells or islets to IL-1 beta and IFN-gamma for 24 h induced caspase-3-like activity that, in the case of insulinoma cells at least, can be further enhanced by interaction of cytokine-induced Fas receptor with FasL. Compared to thymocytes, insulinoma cells and islets from NOD mice were characterised by low basal and cytokine-induced caspase-3 activity.

Delivery of Bcl-XL or its BH4 domain by protein transduction inhibits apoptosis in human islets

Viability of isolated islets is one of the main obstacles limiting islet transplantation success. It has been reported that overexpression of Bcl-2/Bcl-XL proteins enhances islet viability. To avoid potential complications associated with long-term expression of anti-apoptotic proteins, we investigated the possibility of delivering Bcl-XL or its anti-apoptotic domain BH4 to islets by protein transduction. Bcl-XL and BH4 molecules were fused to TAT/PTD, the 11-aa cell penetrating peptide from HIV-1 transactivating protein, generating TAT-Bcl-XL and TAT-BH4, respectively. Transduction efficiency was assessed by laser scanning confocal microscopy of live islets. Biological activity was tested as the ability to protect NIT-1 insulinoma cell line from death induced by staurosporine or serum deprivation. Spontaneous caspase activation in human islets and cytotoxicity caused by IL-1beta were significantly reduced in the presence of TAT-Bcl-XL and TAT-BH4. We conclude that both TAT proteins are biologically active after transduction and could be an asset in the improvement of islet viability.

Caspase-3 inhibitor prevents apoptosis of human islets immediately after isolation and improves islet graft function

OBJECTIVES

Apoptosis appears in islets after isolation, and it has a detrimental effect on the islet function. To improve the outcome of clinical islet transplantation, it is crucial to protect islets from apoptosis. The aim of this study was to determine whether a caspase-3 inhibitor (Z-DEVD-FMK) added to culture media protects islets from apoptosis and to compare the effects of fetal bovine serum (FBS) with human serum albumin (HSA) as a protein supplement in culture.

METHODS

Isolated human islets were cultured under 4 different conditions: 0.5% HSA (control), 0.5% HSA + 25 micromol/L Z-DEVD-FMK, 0.5% HSA + 100 micromol/L Z-DEVD-FMK and 10% FBS for 2 days. Next, 1000 IEQ islets precultured with 0.5% HSA and with or without 100 micromol/L Z-DEVD-FMK were transplanted to diabetic nude mice.

RESULTS

The islet yields were higher in Z-DEVD-FMK-treated groups, and the inhibitor prevented apoptosis dose dependently. The yield and insulin release were higher in FBS-treated group than in the control group, but FBS did not affect apoptosis. All 6 mice transplanted with islets pretreated with Z-DEVD-FMK, and 3 of 8 mice with control islets became normoglycemic posttransplantation.

CONCLUSION

Z-DEVD-FMK prevented apoptosis of isolated human islets and improved its function. FBS (10%) improved the islet yield and insulin secretion more than 0.5% HSA.

Neuropeptide Y promotes beta-cell replication via extracellular signal-regulated kinase activation

AIMS/HYPOTHESIS

Previous studies have shown that neuropeptide Y (NPY) gene expression and release are increased in hyperphagic ob/ob mice and diabetic rats. Therefore, we hypothesized that orexigenic agent, NPY, has the effect on the obesity and diabetes. To elucidate the relationship, we have studied the regulatory role of NPY on islet cells.

METHODS

Isolated islets were incubated with NPY or NPY Y1 receptor specific antagonist, BIBP3226. Proliferation, apoptosis, and Y1 receptor expression were identified by immunohistochemistry. We studied that ERK1/2 mediates the NPY pathway with PD98059 (MAP kinase inhibitor), wortmannin (phosphatidylinositol 3-kinase inhibitor), and BIM-1 (protein kinase C inhibitor). After NPY-treated islets were exposed to high glucose, insulin levels were detected.

RESULTS

beta-Cell replication was enhanced in a dose-dependent manner, but without any changes on the other cells in islet. NPY Y1 receptors were expressed on islet and NPY induced phosphorylation of ERK1/2 rapidly and transiently. PD98059 (MAPK kinase inhibitor) and BIM-1 (protein kinase C inhibitor) inhibited activation of ERK1/2 by NPY, but wortmannin (phosphatidylinositol 3-kinase inhibitor) did not. Exposure of NPY-treated islets to high glucose showed the decreasing trend of insulin secretion.

CONCLUSION/INTERPRETATION

Our data suggest that NPY promotes beta-cell replication via extracellular signal-regulated kinase activation and inhibits glucose-stimulated insulin secretion.

Detection of secretion from pancreatic islets using chemically modified electrodes

Secretion of insulin from pancreatic islets was monitored indirectly by detecting zinc. Anodic stripping voltammetric measurements of zinc were done on a bismuth-modified electrode. Comparison of the performance of bismuth-modified electrodes and mercury film electrodes showed that bismuth is an appropriate alternative for Zn detection. The bismuth-coated electrode was used to detect zinc in insulin samples and insulin secreted from pancreatic islets upon stimulation with high concentrations of K(+). Detection of zinc released from pancreatic islets was done in the culture medium without any further cleanup. This detection method can be used to monitor secretion from pancreatic islets in their native environment.

Changes in liver enzymes after clinical islet transplantation

BACKGROUND

Clinical islet transplantation (ITx) shows insulin independence with adequate metabolic control in patients with type 1 diabetes. The aim of this study was to characterize the pattern of elevation in liver enzymes observed after ITx and to investigate any correlation between these elevations and graft characteristics or graft functional outcome.

METHODS

Eighty-four consecutive ITx procedures were performed in 42 recipients. Liver function tests (LFT) were assessed during the first 40 days posttransplant. LFT elevated greater than or equal to 2.5 times above the upper limit of normal (ULN) were considered relevant.

RESULTS

In 54% of the transplants, the aspartate aminotransferase (AST) increased by more than 2.5 times above ULN. A 5-fold increase in AST was observed in 27% of the procedures. The highest AST levels were observed after the first ITx. AST for all transplants peaked at 7+/-0.5 days at a value of 162+/-23 U/L (P<0.001, compared with the pretransplant values). Changes in alanine aminotransferase were similar to AST. Alkaline phosphatase increased more than 2-fold above ULN in 12% of the procedures. LFT normalized in 90% of the recipients within 4 weeks posttransplant. The remaining 10% normalized within 2 months after ITx. Graft characteristics and graft function were not significantly different when comparing LFT with greater than 5-fold versus less than 2.5-fold increase above ULN. The mean bilirubin remained within the normal range.

CONCLUSIONS

After intraportal ITx, a significant increase in LFT levels was noticed in more than 50% of the procedures. These levels normalized spontaneously in 90% of the recipients within 4 weeks. No correlation between the increase in LFT and graft characteristics or graft function was found.

Human, nonhuman primate, and rat pancreatic islets express erythropoietin receptors

BACKGROUND

Erythropoietin (EPO) promotes survival in a variety of cells by mediating antiapoptotic signals through the EPO receptor (R). The authors examined pancreatic islets for the presence of EPO-R to determine whether these cells are protected by EPO from cytokine-induced apoptosis.

METHODS

Reverse-transcriptase polymerase chain reaction, immunohistology, and Western blots were used to establish the presence and localization of EPO-R on rat, nonhuman primate, and human islets. Islets were exposed to cytokines in the presence and absence of recombinant EPO and apoptosis was measured using a terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay followed by fluorescence-activated cell sorter analysis. Glucose stimulation indices were measured to assess the effect of EPO on islet function.

RESULTS

The presence of EPO-R was demonstrated on islets regardless of species. Recombinant EPO protected islets in culture from cytokine-induced apoptosis in a dose-dependent manner. Furthermore, the presence of EPO in the media does not adversely affect islet function.

CONCLUSIONS

This is the first demonstration that pancreatic islets express EPO-R and that EPO may prevent islet-cell apoptosis in culture. In vivo trials to evaluate the potential of long-term expression of EPO to augment islet survival in transplantation are underway.

Protection of islets by in situ peptide-mediated transduction of the Ikappa B kinase inhibitor Nemo-binding domain peptide

We have previously demonstrated that adenoviral gene transfer of the NF-kappaB inhibitor IkappaB to human islets results in protection from interleukin (IL)-1beta-mediated dysfunction and apoptosis. Here we report that human and mouse islets can be efficiently transduced by a cationic peptide transduction domain (PTD-5) without impairment of islet function. PTD mediated delivery of a peptide inhibitor of the IL-1beta-induced IkappaB kinase (IKK), derived from IKKbeta (NBD; Nemo-binding domain), and completely blocked the detrimental effects of IL-1beta on islet function and NF-kappaB activity, in a similar manner to Ad-IkappaB. We also demonstrate that mouse islets can be transduced in situ by infusion of the transduction peptide through the bile duct prior to isolation, resulting in 40% peptide transduction of the beta-cells. Delivery of the IKK inhibitor transduction fusion peptide (PTD-5-NBD) in situ to mouse islets resulted in improved islet function and viability after isolation. These results demonstrate the feasibility of using PTD-mediated delivery to transiently modify islets in situ to improve their viability and function during isolation, prior to transplantation.