Assessment of Intracellular Insulin Content during All Steps of Human Islet Isolation Procedure

Traditional and emerging strategies using hepatocytes for pancreatic regenerative medicine

Although pancreas and islet cell transplantation are the only ways to prevent the late complications of insulin-dependent diabetes, a shortage of donors is a major obstacle to tissue and organ transplantation. Stem cell therapy is an effective treatment for diabetes and other pancreatic-related diseases, which can be achieved by inducing their differentiation into insulin-secreting cells. The liver is considered an ideal source of pancreatic cells due to its similar developmental origin and strong regenerative ability as the pancreas. This article reviews the traditional and emerging strategies using hepatocytes for pancreatic regenerative medicine and evaluates their advantages and challenges. Gene reprogramming and chemical reprogramming technologies are traditional strategies with potential to improve the efficiency and specificity of cell reprogramming and promote the transformation of hepatocytes into islet cells. At the same time, organoid technology, as an emerging strategy, has received extensive attention. Biomaterials provide a three-dimensional culture microenvironment for cells, which helps improve cell survival and differentiation efficiency. In addition, clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing technology has brought new opportunities and challenges to the development of organoid technology.

EndoC-βH5 cells are storable and ready-to-use human pancreatic beta cells with physiological insulin secretion

OBJECTIVES

Readily accessible human pancreatic beta cells that are functionally close to primary adult beta cells are a crucial model to better understand human beta cell physiology and develop new treatments for diabetes. We here report the characterization of EndoC-βH5 cells, the latest in the EndoC-βH cell family.

METHODS

EndoC-βH5 cells were generated by integrative gene transfer of immortalizing transgenes hTERT and SV40 large T along with Herpes Simplex Virus-1 thymidine kinase into human fetal pancreas. Immortalizing transgenes were removed after amplification using CRE activation and remaining non-excized cells eliminated using ganciclovir. Resulting cells were distributed as ready to use EndoC-βH5 cells. We performed transcriptome, immunological and extensive functional assays.

RESULTS

Ready to use EndoC-βH5 cells display highly efficient glucose dependent insulin secretion. A robust 10-fold insulin secretion index was observed and reproduced in four independent laboratories across Europe. EndoC-βH5 cells secrete insulin in a dynamic manner in response to glucose and secretion is further potentiated by GIP and GLP-1 analogs. RNA-seq confirmed abundant expression of beta cell transcription factors and functional markers, including incretin receptors. Cytokines induce a gene expression signature of inflammatory pathways and antigen processing and presentation. Finally, modified HLA-A2 expressing EndoC-βH5 cells elicit specific A2-alloreactive CD8 T cell activation.

CONCLUSIONS

EndoC-βH5 cells represent a unique storable and ready to use human pancreatic beta cell model with highly robust and reproducible features. Such cells are thus relevant for the study of beta cell function, screening and validation of new drugs, and development of disease models.

Pancreatic Islet Purification from Large Mammals and Humans Using a COBE 2991 Cell Processor versus Large Plastic Bottles

The islet purification step in clinical islet isolation is important for minimizing the risks associated with intraportal infusion. Continuous density gradient with a COBE 2991 cell processor is commonly used for clinical islet purification. However, the high shear force involved in the purification method using the COBE 2991 cell processor causes mechanical damage to the islets. We and other groups have shown human/porcine islet purification using large cylindrical plastic bottles. Shear stress can be minimized or eliminated using large cylindrical plastic bottles because the bottles do not have a narrow segment and no centrifugation is required during tissue loading and the collection processes of islet purification. This review describes current advances in islet purification from large mammals and humans using a COBE 2991 cell processor versus large cylindrical plastic bottles.

A direct look at the dysfunction and pathology of the β cells in human type 2 diabetes

β cells uniquely produce and secrete insulin under the control of several, integrated signals, to maintain blood glucose concentrations within a narrow physiological interval. β cell failure is key to the onset and progression of type 2 diabetes, due to impaired function and reduced mass. In this review we focus on several features of human β cell dysfunction and pathology in type 2 diabetes, as revealed by direct assessment of isolated islet traits and examination of pancreatic tissue from organ donors, surgical samples or autoptic specimens. Insulin secretion defects and pathology findings are discussed in relation to some of the major underlying mechanisms, to also provide clues for conceiving better prevention and treatment of type 2 diabetes by targeting the pancreatic β cells.

Quantifying the Effects of Different Neutral Proteases on Human Islet Integrity

Efficient islet release from the pancreas requires the combination of collagenase, neutral protease (cNP), or thermolysin (TL). Recently, it has been shown that clostripain (CP) may also contribute to efficient islet release from the human pancreas. The aim of this study was to evaluate the impact of these proteases on human islet integrity in a prospective approach. Islets were isolated from the pancreas of 10 brain-dead human organ donors. Purified islets were precultured for 3 to 4 d at 37 °C to ensure that preparations were cleared of predamaged islets, and only integral islets were subjected to 90 min of incubation at 37 °C in Hank’s balanced salt solution supplemented with cNP, TL, or CP. The protease concentrations were calculated for a pancreas of 100 g trimmed weight utilizing 120 dimethyl-casein units of cNP, 70,000 caseinase units of TL, or 200 benzoyl-l-arginine-ethyl-ester units of CP (1×). These activities were then increased both 5× and 10×. After subsequent 24-h culture in enzyme-free culture medium, treated islets were assessed and normalized to sham-treated controls. Compared with controls and CP, islet yield was significantly reduced by using the 5× activity of cNP and TL, inducing also fragmentation and DNA release. Viability significantly decreased not until adding the 1× activity of cNP, 5× activity of TL, or 10× activity of CP. Although mitochondrial function was significantly lowered by 1× cNP and 5× TL, CP did not affect mitochondria at any concentration. cNP- and TL-incubated islets significantly lost intracellular insulin already at 1× activity, while the 10× activity of CP had to be added to observe a similar effect. cNP and TL have a similar toxic potency regarding islet integrity. CP also induces adverse effects on islets, but the toxic threshold is generally higher. We hypothesize that CP can serve as supplementary protease to minimize cNP or TL activity for efficient pancreas digestion.

Comparison of Clostripain and Neutral Protease as Supplementary Enzymes for Human Islet Isolation

Although human islet transplantation has been established as valid and safe treatment for patients with type 1 diabetes, the utilization rates of human pancreases for clinical islet transplantation are still limited and substantially determined by the quality and composition of collagenase blends. While function and integrity of collagenase has been extensively investigated, information is still lacking about the most suitable supplementary neutral proteases. The present study compared islet isolation outcome after pancreas digestion by means of collagenase used alone or supplemented with either neutral protease (NP), clostripain (CP), or both proteases. Decent amounts of islet equivalents (IEQ) were isolated using collagenase alone (3090 ± 550 IEQ/g), or in combination with NP (2340 ± 450 IEQ/g) or CP (2740 ± 280 IEQ/g). Nevertheless, the proportion of undigested tissue was higher after using collagenase alone (21.1 ± 1.1%, P < 0.05) compared with addition of NP (13.3 ± 2.2%) or CP plus NP (13.7 ± 2.6%). Likewise, the percentage of embedded islets was highest using collagenase only (13 ± 2%) and lowest adding NP plus CP (4 ± 1%, P < 0.01). The latter combination resulted in lowest post-culture overall survival (42.7 ± 3.9%), while highest survival was observed after supplementation with CP (74.5 ± 4.8%, P < 0.01). An insulin response toward glucose challenge was present in all experimental groups, but the stimulation index was significantly decreased using collagenase plus NP (2.0 ± 0.12) compared with supplementation with CP (3.16 ± 0.4, P < 0.001). This study demonstrates for the first time that it is possible to isolate significant numbers of human islets combining collagenase only with CP. The supplementation with CP is an effective means to substantially reduce NP activity, which significantly decreases survival and viability after culture. This will facilitate the manufacturing of enzyme blends with less harmful characteristics.

Secretagogin is increased in plasma from type 2 diabetes patients and potentially reflects stress and islet dysfunction

Beta cell dysfunction accompanies and drives the progression of type 2 diabetes mellitus (T2D), but there are few clinical biomarkers available to assess islet cell stress in humans. Secretagogin, a protein enriched in pancreatic islets, demonstrates protective effects on beta cell function in animals. However, its potential as a circulating biomarker released from human beta cells and islets has not been studied. In this study primary human islets, beta cells and plasma samples were used to explore secretion and expression of secretagogin in relation to the T2D pathology. Secretagogin was abundantly and specifically expressed and secreted from human islets. Furthermore, T2D patients had an elevated plasma level of secretagogin compared with matched healthy controls, which was confirmed in plasma of diabetic mice transplanted with human islets. Additionally, the plasma secretagogin level of the human cohort had an inverse correlation to clinical assessments of beta cell function. To explore the mechanism of secretagogin release in vitro, human beta cells (EndoC-βH1) were exposed to elevated glucose or cellular stress-inducing agents. Secretagogin was not released in parallel with glucose stimulated insulin release, but was markedly elevated in response to endoplasmic reticulum stressors and cytokines. These findings indicate that secretagogin is a potential novel biomarker, reflecting stress and islet cell dysfunction in T2D patients.

Adenovirus-Mediated Expression of the Anticoagulant Hirudin in Human Islets: A Tool to Make the Islets Biocompatible to Blood

Human islets induce an injurious clotting reaction at the time of transplantation. A potential strategy to counteract this reaction would be to allow the islets to express hirudin, a protein with direct anticoagulative activity. Human islets were transduced with an adenoviral vector encoding hirudin, an empty corresponding vector, or left untreated. Islet culture supernatants were analyzed for hirudin using an ELISA, a chromogenic substrate assay based on the thrombin-binding properties of hirudin and in a whole blood viscosimetry assay. Immunohistochemical evaluation and determination of hirudin content revealed an abundant expression of hirudin after transduction. Hirudin content in transduced islets was in the range of the insulin content levels. A delay in human whole blood clotting time could be observed after addition of supernatants taken from islet cultures expressing hirudin. However, transduced islets showed an impaired glucose-stimulated insulin release, but could readily be retrieved 6 weeks after transplantation to athymic mice. A marked expression and secretion of hirudin with functional capacity can be induced in human islets using an adenoviral vector. The impairment in glucose-stimulated insulin release in hirudin-secreting islets, compared to controls, indicates that the additional protein synthesis affects the functional capacity of the islets.

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

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

Comparison of Neutral Proteases and Collagenase Class I as Essential Enzymes for Human Islet Isolation

Efficient islet isolation requires synergistic interaction between collagenase class I (CI) and class II (CII). The CI degradation alters the ratio between CI and CII and is responsible for batch-to-batch variations. This study compares the role of neutral protease (NP) plus clostripain (CP) with CI as essential enzymes for human islet isolation.

METHODS

Human islets were isolated using 4 different enzyme mixtures composed of CII plus either intact (CI-115) or degraded CI (CI-100). Blends were administered either with or without NP/CP. Purified islets were cultured for 3 to 4 days before islet quality assessment.

RESULTS

Whereas using intact CI-115 without NP/CP did not significantly reduce islet yield (3429 ± 631 vs 3087 ± 970 islet equivalent/g, nonsignificant), administration of degraded CI-100 without NP/CP decreased islet yield from 3501 ± 580 to 1312 ± 244 islet equivalent/g (P < 0.01), doubled the amount of undigested tissue from 11.8 ± 1.6 to 24.4 ± 1.2% (P < 0.01) and triplicated the percentage of trapped islets from 7.7 ± 2.8 to 22.5 ± 3.6% (P < 0.05). Islet yield did not vary between supplemented CI-115 and CI-100, but was increased using CI-115 when NP/CP was omitted (P < 0.05). A trend toward higher viability and increased secretory insulin response was noted in both CI-100 and CI-115 when NP/CP was not added.

CONCLUSIONS

This study suggests that NP/CP can compensate reduced CI activity. Future attempts to optimize enzyme blends should consider the possibility to increase the proportion of collagenase CI to reduce the need for potentially harmful NPs.

Type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is an expanding global health problem, closely linked to the epidemic of obesity. Individuals with T2DM are at high risk for both microvascular complications (including retinopathy, nephropathy and neuropathy) and macrovascular complications (such as cardiovascular comorbidities), owing to hyperglycaemia and individual components of the insulin resistance (metabolic) syndrome. Environmental factors (for example, obesity, an unhealthy diet and physical inactivity) and genetic factors contribute to the multiple pathophysiological disturbances that are responsible for impaired glucose homeostasis in T2DM. Insulin resistance and impaired insulin secretion remain the core defects in T2DM, but at least six other pathophysiological abnormalities contribute to the dysregulation of glucose metabolism. The multiple pathogenetic disturbances present in T2DM dictate that multiple antidiabetic agents, used in combination, will be required to maintain normoglycaemia. The treatment must not only be effective and safe but also improve the quality of life. Several novel medications are in development, but the greatest need is for agents that enhance insulin sensitivity, halt the progressive pancreatic β-cell failure that is characteristic of T2DM and prevent or reverse the microvascular complications. For an illustrated summary of this Primer, visit: http://go.nature.com/V2eGfN.

Influence of in vitro and in vivo oxygen modulation on β cell differentiation from human embryonic stem cells

The possibility of using human embryonic stem (hES) cell-derived β cells as an alternative to cadaveric islets for the treatment of type 1 diabetes is now widely acknowledged. However, current differentiation methods consistently fail to generate meaningful numbers of mature, functional β cells. In order to address this issue, we set out to explore the role of oxygen modulation in the maturation of pancreatic progenitor (PP) cells differentiated from hES cells. We have previously determined that oxygenation is a powerful driver of murine PP differentiation along the endocrine lineage of the pancreas. We hypothesized that targeting physiological oxygen partial pressure (pO2) levels seen in mature islets would help the differentiation of PP cells along the β-cell lineage. This hypothesis was tested both in vivo (by exposing PP-transplanted immunodeficient mice to a daily hyperbaric oxygen regimen) and in vitro (by allowing PP cells to mature in a perfluorocarbon-based culture device designed to carefully adjust pO2 to a desired range). Our results show that oxygen modulation does indeed contribute to enhanced maturation of PP cells, as evidenced by improved engraftment, segregation of α and β cells, body weight maintenance, and rate of diabetes reversal in vivo, and by elevated expression of pancreatic endocrine makers, β-cell differentiation yield, and insulin production in vitro. Our studies confirm the importance of oxygen modulation as a key variable to consider in the design of β-cell differentiation protocols and open the door to future strategies for the transplantation of fully mature β cells.

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

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

A subset of human pancreatic beta cells express functional CD14 receptors: a signaling pathway for beta cell-related glycolipids, sulfatide and β-galactosylceramide

BACKGROUND

T1DM is a T-cell-mediated autoimmune disease targeting insulin-producing beta-cells. Multiple factors may contribute to the development of T1DM. Among these, the metabolic state of beta-cells and pro-inflammatory cytokines, produced by infiltrating immune cells, have been implicated in the precipitation of T1DM.

METHODS AND RESULTS

In this study, confocal immunofluorescence microscopy of human pancreata revealed a distinct subset of beta-cells expressing the innate LPS co-receptor CD14. Human islets expressed fully functional CD14 as LPS stimulation led to a dose-dependent secretion of tumour necrosis factor (TNFα), interleukin (IL)-1β and IL-8, which were substantially inhibited by a blocking anti-CD14 mAb. In addition, LPS stimulation impaired the glucose-mediated insulin secretion in rat islets. β-GalCer and sulfatide, glycolipids that are related to insulin processing and secretion, are possibly interacting with the CD14 receptor complex. β-GalCer had an LPS-like, serum- and CD14-dependent effect on the induction of pro-inflammatory cytokines in a human monocyte cell line. In contrast, the LPS-mediated cytokine production was inhibited by sulfatide. Human islets also responded to β-GalCer (10 µg/mL) by secreting TNFα, IL-1β and IL-8, whereas sulfatide partly inhibited the effect of LPS.

CONCLUSIONS

A subset of human beta-cells expresses functional CD14 receptor and thus is able to recognize both exogenous bacterial (LPS) as well as endogenous ligands (e.g. glycolipids of beta-cell origin). The CD14 expression on a subset of human beta-cells may play a role in the innate surveillance of the endocrine environment but may also contribute to innate immune mechanisms in the early stages of beta-cell aggression.

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

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

Positron emission tomography in clinical islet transplantation

The fate of islets in clinical transplantation is unclear. To elude on this positron emission tomography combined with computed tomography (PET/CT) was performed for 60 min during islet transplantation in five patients receiving six transplants. A fraction of the islets (23%) were labeled with 18F-fluorodeoxyglucose ([(18)F]FDG) and carefully mixed with unlabeled islets just prior to intraportal transplantation. The peak radioactivity concentration in the liver was found at 19 min after start of islet infusion and corresponded to only 75% of what was expected, indicating that islets are lost during the transplantation procedure. No accumulation of radioactivity was found in the lungs. A nonphysiological peak of C-peptide was found in plasma during and immediately after transplantation in all subjects. Distribution in the liver was heterogeneous with wide variations in location and concentration. Islets found in areas with concentrations of >400 IEQ/cc liver tissue varied between 1% and 32% of the graft in different subjects. No side effects attributed to the PET/CT procedure were found. Clinical outcome in all patients was comparable to that previously observed indicating that the [(18)F]FDG labeling procedure did not harm the islets. The technique has potential to be used to assess approaches to enhance islet survival and engraftment in clinical transplantation.

Large-scale comparison of Liberase HI and collagenase NB1 utilized for human islet isolation

For more than a decade Liberase HI was commonly used as the standard enzyme blend for clinical human islet isolation until enforced replacement by collagenase NB1 (NB1). This change resulted initially in a reduction in islet isolation outcome and transplant activities worldwide. This retrospective study was initiated to compare the efficiency of NB1 premium grade with Liberase in 197 human islet isolations. All pancreata were processed between January 2006 and June 2008 utilizing the same procedures for isolation and quality assessment except the administration of preselected lots of either Liberase (n = 101) or NB1 (n = 96). Utilizing Liberase, significantly more digested tissue and purified islet yield was produced compared to NB1. In contrast, the use of NB1 was associated with significantly higher purity and glucose stimulation index during dynamic perifusion. The expression of proinflammatory markers was almost identical except tissue factor expression, which was higher after utilization of Liberase. No difference was found in the percentage of pancreata fulfilling the criteria for clinical islet transplantation. The results suggest that Liberase is more efficient for pancreas dissociation than collagenase NB1 but seems to be more harmful to exocrine cells and islet tissue.

Isolating human islets of Langerhans causes loss of decay accelerating factor (CD55) on beta-cells

It has previously been reported that human decay accelerating factor (DAF; CD55) is not expressed on cells isolated from human islets. We have investigated if this absence is caused by the islet isolation procedure and/or the single cell isolation technique. We focused on loss of DAF expression on beta-cells within the intact islet and on isolated individual beta-cells. We established that DAF was expressed in islets and on beta-cells prior to isolation by in situ analysis in the intact pancreas. In situ immunohistochemistry (IHC) was used to examine DAF expression on human pancreatic islets and isolated islets. A reverse transcriptase-polymerase chain reaction (RT-PCR) specific for human DAF mRNA was developed to measure mRNA levels in situ in islets within the intact pancreas, isolated islets, and purified beta-cells. beta-Cells were purified by fluorescence-activated cell sorting. DAF protein expression on these purified cells was measured using flow cytometry. Expression of DAF protein was present on the islets, including beta-cells within the human pancreas; however, comparative data from IHC and flow cytometry revealed the absence of DAF protein on beta-cells in both isolated islets and single cell preparations. Furthermore, compared to mRNA levels detected by in situ RT-PCR in the intact pancreas and in human HEK 293 cells, isolated islets, and purified human beta-cells showed downregulation of DAF mRNA. mRNA was detectable in both of these preparations by RT-PCR; levels were lower following both the islet isolation process (53%) and single cell preparation (a further 62%) compared to HEK 293 controls. Human islet allotransplantation might be more successful if either de novo transfer of DAF onto the isolated islets or novel techniques for islet isolation preserving DAF could be developed.

Human islet separation utilizing a closed automated purification system

A central step within the human islet isolation process is the separation of islets from contaminating exocrine tissue utilizing linear, continuous density gradients manufactured by means of manually controlled standard gradient makers (SGM). The present study was performed to develop a closed, automated purification system (APS) that customizes density gradient profiles aiming to standardize and optimize human islet purification. Digested human pancreata were pooled, split evenly, and incubated in UW solution according to our standard protocol (n = 11). Continuous density gradient centrifugation was performed in parallel in two refrigerated COBE 2991 cell separators loaded with light (1.076 g/ml) and heavy (1.097 g/ml) Ficoll utilizing either an SGM or two computer-controlled pumps connected to Ficoll-containing bags. Quality control included islet equivalent (IE) yield, purity, in vitro function, and islet cytokine expression. Gradient profiles demonstrated that the APS readily customizes linear and nonlinear gradients. In comparison to the SGM, the APS recovered a higher percentage of the expected volume of continuous gradients (90.0 +/- 1.1% vs. 98.2 +/- 2.0%, p < 0.05). Islet yield (120,468 +/- 15,970 vs. 114,570 +/- 15,313 IE, NS) and purity (51.7 +/- 4.8% vs. 54.4 +/- 4.9%, NS) were nearly identical utilizing the SGM or APS. Decreased MCP-1, IL-6, and IL-8 expression indicated that APS-purified islets were possibly exposed to less proinflammatory stress. Compared to standard procedures, similar success and gentle continuous density gradient separation of human islets is feasible utilizing the APS. The APS facilitates the standardization of this complex procedure according to cGMP standards.

Local expression of B7-H4 by recombinant adenovirus transduction in mouse islets prolongs allograft survival

BACKGROUND

Allogeneic pancreatic islet transplantation has the potential to cure type 1 diabetes. One of the barriers to islet transplantation is the alloreactive T-cell response between donors and recipients. Costimulatory molecules, which play a major role in the regulation of the immune response to antigens during graft rejection, may be used to inhibit allograft destruction. B7-H4 is one such member in the costimulatory family, which has established negative regulatory function of T-cell responses.

METHODS

To determine whether local expression of B7-H4 protein can protect beta cells from damage in islet allotransplantation, we have constructed a recombinant adenovirus expressing a B7-H4 complementary deoxyribonucleic acid (Ad-B7-H4). To study the in vivo effects of B7-H4 expression on islet graft survival, adenovirus-transduced islets from donor Balb/c mice were transplanted into streptozotocin-diabetic C57BL/6 mice (n=12).

RESULTS

Expression of B7-H4 in islets by Ad-B7-H4 transduction at an optimized condition did not inhibit glucose-stimulated insulin secretion of the treated islets. The recipient mice transplanted with Ad-B7-H4-transduced islets established euglycemia for a longer time (mean 56.5 days), compared with control mice transplanted with Ad-LacZ-transduced islets (mean 14.5 days, [n=12, P<0.001]). Splenocytes isolated from the recipients of Ad-B7-H4-transduced islets showed hyporesponsiveness to alloantigenic stimulation, compared with control recipients. CD45 and insulin staining of the graft transplanted with Ad-B7-H4-transduced islets indicated the preservation of beta cells and decrease of infiltrating immune cells.

CONCLUSIONS

Local expression of B7-H4 prolongs islet allograft survival in vivo, suggesting translational potential for beta-cell replacement with reduced immune injury.

Subcellular protein extraction from human pancreatic cancer tissues

Proteins are the major class of effector molecules in cellular systems. For the identification of functional differences between normal and diseased tissues, a reliable analysis of their protein content is essential. Reproducible isolation and fractionation of intact proteins are important in this respect, but their complexity in structure and concentration, their close interaction, and their instability represent major challenges. For protein isolation in tissues, the breakdown of cell-cell and cell-matrix connections within a tissue without affecting protein quality is a critical factor. We compared different processes for a compartmental protein preparation from pancreatic tissue, one of the most challenging tissues for protein isolation because of its high protease content. Success of the different procedures varied greatly. Based on a scheme of tissue-slicing and subsequent cell isolation, we established a reliable workflow for the fractional extraction of cytosolic proteins, membrane and organelle proteins, nuclear proteins, and cytoskeletal filaments. The tissue slices also allow for a representative confirmation of individual samples' cellular status by histochemical processes, and a proper separation or mixing of cellular material from across a tumor if required.

H2O2-induced Ca2+ influx and its inhibition by N-(p-amylcinnamoyl) anthranilic acid in the beta-cells: involvement of TRPM2 channels

Type 2 melastatin-related transient receptor potential channel (TRPM2), a member of the melastatin-related TRP (transient receptor potential) subfamily is a Ca(2+)-permeable channel activated by hydrogen peroxide (H(2)O(2)). We have investigated the role of TRPM2 channels in mediating the H(2)O(2)-induced increase in the cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) in insulin-secreting cells. In fura-2 loaded INS-1E cells, a widely used model of beta-cells, and in human beta-cells, H(2)O(2) increased [Ca(2+)](i), in the presence of 3 mM glucose, by inducing Ca(2+) influx across the plasma membrane. H(2)O(2)-induced Ca(2+) influx was not blocked by nimodipine, a blocker of the L-type voltage-gated Ca(2+) channels nor by 2-aminoethoxydiphenyl borate, a blocker of several TRP channels and store-operated channels, but it was completely blocked by N-(p-amylcinnamoyl)anthranilic acid (ACA), a potent inhibitor of TRPM2. Adenosine diphosphate phosphate ribose, a specific activator of TRPM2 channel and H(2)O(2), induced inward cation currents that were blocked by ACA. Western blot using antibodies directed to the epitopes on the N-terminal and on the C-terminal parts of TRPM2 identified the full length TRPM2 (TRPM2-L), and the C-terminally truncated TRPM2 (TRPM2-S) in human islets. We conclude that functional TRPM2 channels mediate H(2)O(2)-induced Ca(2+) entry in beta-cells, a process potently inhibited by ACA.

The importance of tryptic-like activity in purified enzyme blends for efficient islet isolation

BACKGROUND

The isolation of islets from the human pancreas critically depends on an efficient enzyme blend. Previous studies have solely focused on the presence of collagenase and neutral protease/thermolysin. Despite improved characterization of these components, the lot-related variability in efficacy still persists suggesting that additional so far disregarded enzymes are required for efficient islet cleavage.

METHODS

Varying activities of a tryptic-like enzyme were identified within collagenase NB1 lots, which were selected according to a matched ratio between tryptic-like and collagenase activity (TLA-ratio). Rat and human pancreata were processed with current standard procedures.

RESULTS

Increasing the TLA-ratio from 1.3% to 10% reduced pancreas dissociation time in rats by 50% without affecting islet yield, viability, or posttransplant function in diabetic nude mice. Enhancing the TLA-ratio from 1.3% to 12.6% for human pancreas processing resulted in a significant reduction of recirculation time and increased incrementally human islet yield without affecting purity, in vitro function or recovery after culture. Optimized pancreas digestion correlated with a higher percentage of islet preparations fulfilling quality criteria for clinical transplantation.

CONCLUSIONS

We conclude that TLA is an effective component that should be included in moderate amounts in enzyme blends for human islet isolation to optimize the efficiency and minimize the lot-related variability.

Formation of composite endothelial cell-mesenchymal stem cell islets: a novel approach to promote islet revascularization

OBJECTIVE

Mesenchymal stem cells (MSCs) contribute to endothelial cell (EC) migration by producing proteases, thereby paving the way into the tissues for ECs. MSCs were added to our previously described composite EC islets as a potential means to improve their capacity for islet angiogenesis.

RESEARCH DESIGN AND METHODS

Human islets were coated with primary human bone marrow-derived MSCs and dermal microvascular ECs. The capacity of ECs, with or without MSCs, to adhere to and grow into human islets was analyzed. The survival and functionality of these composite islets were evaluated in a dynamic perifusion assay, and their capacity for angiogenesis in vitro was assessed in a three-dimensional fibrin gel assay.

RESULTS

ECs proliferated after culture in MSC-conditioned medium, and MSCs improved the EC coverage threefold compared with EC islets alone. Islet survival in vitro and the functionality of the composite islets after culture were equal to those of control islets. The EC-MSC islets showed a twofold increase in total sprout formation compared with EC islets, and vascular sprouts emanating from the EC-MSC-islet surface showed migration of ECs into the islets and also into the surrounding matrix, either alone or in concert with MSCs.

CONCLUSIONS

EC proliferation, sprout formation, and ingrowth of ECs into the islets were enhanced by MSCs. The use of composite EC-MSC islets may have beneficial effects on revascularization and immune regulation. The technique presented allows for pretreatment of donor islets with recipient-derived ECs and MSCs as a means of improving islet engraftment.

No beneficial effect of two-layer storage compared with UW-storage on human islet isolation and transplantation

BACKGROUND

Shipment of pancreata between distant centers is frequently associated with prolonged cold ischemia time (CIT) that leads to poorer outcomes for islet transplantation. Clinical pilot trials have indicated that oxygenation of explanted human pancreata utilizing the two-layer method (TLM) allows the use of marginal donor pancreata for islet transplantation. The present study aimed to clarify whether TLM enhances the ischemic tolerance of human pancreata.

METHODS

We analyzed retrospectively the outcome of 200 human islet isolations performed after TLM preservation or storage in University of Wisconsin solution (UWS).

RESULTS

Donor characteristics and digestion parameters did not vary significantly between TLM-preserved and UWS-stored pancreata. No differences were observed between experimental groups with regard to islet yield, purity, or dynamic glucose stimulation index after either short or prolonged CIT. However, CIT and stimulation index were negatively correlated in each experimental group. The isolation outcome in donors aged > or =60 years was not increased after TLM preservation when compared to UWS storage. No effect was observed regarding islet posttransplant function in recipients with established kidney grafts.

CONCLUSIONS

The present study suggests that the ischemic tolerance of human pancreata cannot be extended by TLM preservation. In addition, TLM does not seem to improve the isolation outcome for pancreata from elderly donors.

Generation of insulin-producing cells from human bone marrow mesenchymal stem cells by genetic manipulation

Beta cell replacement is a promising approach for treatment of type 1 diabetes; however, it is limited by a shortage of pancreas donors. The pluripotent MSC in adult bone marrow (BM) offer an attractive source of stem cells for generation of surrogate beta cells. BM-MSC can be obtained with relative ease from each patient, allowing potential circumvention of allograft rejection. Here, we report a procedure for expansion of BM-MSC in vitro and their differentiation into insulin-producing cells. The pancreatic duodenal homeobox 1 (Pdx1) gene was expressed in BM-MSC from 14 human donors, and the extent of differentiation of these cells toward the beta-cell phenotype was evaluated. RNA and protein analyses documented the activation of expression of all four islet hormones. However, the cells lacked expression of NEUROD1, a key transcription factor in differentiated beta cells. A significant insulin content, as well as glucose-stimulated insulin release, were demonstrated in vitro. Cell transplantation into streptozotocin-diabetic immunodeficient mice resulted in further differentiation, including induction of NEUROD1, and reduction of hyperglycemia. These findings were reproducible in BM-MSC from 9 of 14 donors of both sexes, ages 19-62. These results suggest a therapeutic potential for PDX1-expressing BM-MSC in beta-cell replacement in patients with type 1 diabetes.

Glucose-dependent expansion of pancreatic beta-cells by the protein p8 in vitro and in vivo

p8 protein expression is known to be upregulated in the exocrine pancreas during acute pancreatitis. Own previous work revealed glucose-dependent p8 expression also in endocrine pancreatic beta-cells. Here we demonstrate that glucose-induced INS-1 beta-cell expansion is preceded by p8 protein expression. Moreover, isopropylthiogalactoside (IPTG)-induced p8 overexpression in INS-1 beta-cells (p8-INS-1) enhances cell proliferation and expansion in the presence of glucose only. Although beta-cell-related gene expression (PDX-1, proinsulin I, GLUT2, glucokinase, amylin) and function (insulin content and secretion) are slightly reduced during p8 overexpression, removal of IPTG reverses beta-cell function within 24 h to normal levels. In addition, insulin secretion of p8-INS-1 beta-cells in response to 0-25 mM glucose is not altered by preceding p8-induced beta-cell expansion. Adenovirally transduced p8 overexpression in primary human pancreatic islets increases proliferation, expansion, and cumulative insulin secretion in vitro. Transplantation of mock-transduced control islets under the kidney capsule of immunosuppressed streptozotocin-diabetic mice reduces blood glucose and increases human C-peptide serum concentrations to stable levels after 3 days. In contrast, transplantation of equal numbers of p8-transduced islets results in a continuous decrease of blood glucose and increase of human C-peptide beyond 3 days, indicating p8-induced expansion of transplanted human beta-cells in vivo. This is underlined by a doubling of insulin content in kidneys containing p8-transduced islet grafts explanted on day 9. These results establish p8 as a novel molecular mediator of glucose-induced pancreatic beta-cell expansion in vitro and in vivo and support the notion of existing beta-cell replication in the adult organism.

Neutrophilic granulocytes are the predominant cell type infiltrating pancreatic islets in contact with ABO-compatible blood

The poor outcome of intraportal islet transplantation may be explained by the instant blood-mediated inflammatory reaction (IBMIR), characterized by islet entrapment in blood clots, leucocyte infiltration and disruption of islet morphology. Here we employ a newly developed in vitro system to identify the blood cells involved in this process. Islets were mixed with ABO-compatible blood in heparinized tubes and incubated for various times up to 6 h. Clots were analysed immunohistochemically for detection of platelets (CD41a), leucocytes/lymphocytes (CD11b), granulocytes (CD16, lysozyme), neutrophilic granulocytes (neutrophil elastase), eosinophilic granulocytes (NaCN + H(2)O(2)), macrophages (CD68), dendritic cells (CD209/DC-SIGN), B cells (CD20) and T cells (CD4, CD8). Platelets were rapidly deposited around the islets in contact with the blood, reaching a maximum by 30 min. The first neutrophilic granulocytes appeared in the islets after 15 min, increased at 1 h and peaked at 2 h. Small numbers of macrophages were found infiltrating the islets already after 5 min, with a slight increase over time. However, control stainings of cultured islets and pancreas biopsies identified these cells as being largely of donor origin. No T cells, B cells, dendritic cells or eosinophilic granulocytes were detected during the 6 h observation time. Neutrophilic granulocytes were identified as the main infiltrating blood cell in islets exposed to blood, implying that these cells play a key role in clinical islet transplantation. Because islets are known to be exquisitely susceptible to oxidative stress, development of drugs targeting neutrophilic cytotoxicity could markedly improve the outcome of islet transplantation.

Protein profiling of human pancreatic islets by two-dimensional gel electrophoresis and mass spectrometry

Completion of the human genome sequence has provided scientists with powerful resources with which to explore the molecular events associated with disease states such as diabetes. Understanding the relative levels of expression of gene products, especially of proteins, and their post-translational modifications will be critical. However, though the pancreatic islets play a key role in glucose homeostasis, global protein expression data in human are decidedly lacking. We here report the two-dimensional protein map and database of human pancreatic islets. A high level of reproducibility was obtained among the gels and a total of 744 protein spots were detected. We have successfully identified 130 spots corresponding to 66 different protein entries and generated a reference map of human islets. The functionally characterized proteins include enzymes, chaperones, cellular structural proteins, cellular defense proteins, signaling molecules, and transport proteins. A number of proteins identified in this study (e.g., annexin A2, elongation factor 1-alpha 2, histone H2B.a/g/k, heat shock protein 90 beta, heat shock 27 kDa protein, cyclophilin B, peroxiredoxin 4, cytokeratins 7, 18, and 19) have not been previously described in the database of mouse pancreatic islets. In addition, altered expression of several proteins, like GRP78, GRP94, PDI, calreticulin, annexin, cytokeratins, profilin, heat shock proteins, and ORP150 have been associated with the development of diabetes. The data presented in this study provides a first-draft reference map of the human islet proteome, that will pave the way for further proteome analysis of pancreatic islets in both healthy and diabetic individuals, generating insights into the pathophysiology of this condition.

Differentiation of human liver-derived, insulin-producing cells toward the beta-cell phenotype

beta-Cell transplantation is viewed as a cure for type 1 diabetes; however, it is limited by the number of pancreas donors. Human stem cells offer the promise of an abundant source of insulin-producing cells, given the existence of methods for manipulating their differentiation. We have previously demonstrated that the expression of the beta-cell transcription factor pancreatic duodenal homeobox 1 (PDX-1) in human fetal liver cells activates multiple aspects of the beta-cell phenotype. These cells, termed FH-B-TPN cells, produce insulin, release insulin in response to physiological glucose levels, and replace beta-cell function in diabetic immunodeficient mice. However, they deviate from the normal beta-cell phenotype by the lack of expression of a number of beta-cell genes, the expression of non-beta-cell genes, and a lower insulin content. Here we aimed to promote differentiation of FH-B-TPN cells toward the beta-cell phenotype using soluble factors. Cells cultured with activin A in serum-free medium upregulated expression of NeuroD and Nkx2.2 and downregulated paired box homeotic gene 6 (PAX-6). Glucokinase and prohormone convertase 1/3 were also upregulated, whereas pancreatic polypeptide and glucagon as well as liver markers were downregulated. Insulin content was increased by up to 33-fold, to approximately 60% of the insulin content of normal beta-cells. The cells were shown to contain human C-peptide and release insulin in response to physiological glucose levels. Cell transplantation into immunodeficient diabetic mice resulted in the restoration of stable euglycemia. The cells continued to express insulin in vivo, and no cell replication was detected. Thus, the manipulation of culture conditions induced a significant and stable differentiation of FH-B-TPN cells toward the beta-cell phenotype, making them excellent candidates for beta-cell replacement in type 1 diabetes.

The Rap-B-Raf signalling pathway is activated by glucose and glucagon-like peptide-1 in human islet cells

AIMS/HYPOTHESIS

Glucose and glucagon-like peptide-1 have been shown to activate extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase in beta cells. We examined the contributions of the small GTPases Rap and Ras and the serine-threonine kinases B-Raf and Raf-1 to the activation of these kinases in human islet cells.

METHODS

The expression of Rap, Ras, B-Raf and Raf-1 in human islets was examined by immunohistochemistry and immunoblotting. Human islets were incubated in glucose at concentrations of 2.5 and 15 mmol/l and were stimulated with 10 nmol/l glucagon-like peptide-1. The activation of ERK and Raf kinases was examined by phosphorylation-specific antibodies and immuno-complexed kinase assays. The activation of Rap and Ras was determined by pull-down assays. Stimulation of phosphoinositide 3-kinase was detected by immuno-complexed lipid kinase assays.

RESULTS

Extracellular-regulated kinase and protein kinase B (a downstream target of phosphoinositide 3-kinase) were activated in islets stimulated with glucose and glucagon-like peptide-1. In these islets, the Rap-B-Raf signalling pathway was activated preferentially compared with Ras and Raf-1, and activated Rap and B-Raf mediated ERK stimulation in kinase assays in vitro. In addition, Rap rather than Ras mediated activation of phosphoinositide 3-kinase in islets stimulated with glucose and glucagon-like peptide-1.

CONCLUSIONS/INTERPRETATION

In human islet cells, glucose and glucagon-like peptide-1 activate the Rap and B-Raf signalling module, which mediates ERK activation in assays in vitro. Rap also activates phosphoinositide 3-kinase, delineating central roles for Rap and B-Raf as therapeutic targets for beta cell growth in diabetes mellitus.

Vascular endothelial growth factor increases functional beta-cell mass by improvement of angiogenesis of isolated human and murine pancreatic islets

BACKGROUND

Blood flow is impaired in islet transplants, but there is conflicting evidence on improving the outcome by promoting vascularization. We previously reported that islet endothelial cells (EC) possess significant angiogenic capacity.

METHODS

To further address this issue, we studied human islets in culture under hypoxic conditions. Moreover, we used a transgene mouse model with human vascular endothelial growth factor (VEGF) production in beta-cells under the control of the rat insulin promoter (RIP) to stimulate islet EC proliferation.

RESULTS

Subsequent to a hypoxic stimulus, islets responded with specific expression patterns of VEGF and fibroblast growth factor; however, this was not sufficient to prevent the decay of islet EC. VEGF release of RIP-VEGF transgenic islets was controlled by glucose and resulted in the formation of sprouts. When transplanted to the kidney capsule of diabetic mice, RIP-VEGF islets significantly enhanced microvascular density and functional blood flow to the graft compared with controls.

CONCLUSIONS

Optimized angiogenesis of islet transplants resulted in greater availability of insulin caused by beta-cell proliferation and a significantly higher percentage (90% versus 20%) of mice cured from diabetes.

Current status of clinical islet transplantation

Islet transplantation is currently being explored as a treatment for patients with type 1 diabetes. At present, the number of patients becoming insulin-independent is rapidly increasing world-wide applying the transplantation protocol originally described by the group in Edmonton. A hallmark in this procedure is repeated infusions of islets obtained from 2 to 4 donors until normoglycemia is achieved. In order to establish islet transplantation as a widely accepted treatment modality, and make tolerance induction regimes applicable, it is essential that the donor:recipient ratio is brought down to 1:1. A conceivable strategy to achieve this goal in clinical islet transplantation is discussed.

Tissue factor produced by the endocrine cells of the islets of Langerhans is associated with a negative outcome of clinical islet transplantation

There are strong indications that only a small fraction of grafts successfully engraft in clinical islet transplantation. One explanation may be the instant blood-mediated inflammatory reaction (IBMIR) elicited by tissue factor, which is produced by the endocrine cells. In the present study, we show that islets intended for islet transplantation produce tissue factor in both the transmembrane and the alternatively spliced form and that the membrane-bound form is released as microparticles often associated with both insulin and glucagon granules. A low-molecular mass factor VIIa (FVIIa) inhibitor that indirectly blocks both forms of tissue factor was shown in vitro to be a promising drug to eliminate the IBMIR. Thrombin-antithrombin complex (TAT) and FVIIa-antithrombin complex (FVIIa-AT) were measured in nine patients who together received 20 infusions of isolated human islets. Both the TAT and FVIIa-AT complexes increased rapidly within 15-60 min after infusion. When the initial TAT and FVIIa-AT levels were plotted against the increase in C-peptide concentration after 7 days, patients with an initially strong IBMIR showed no significant increase in insulin synthesis after 7 days. In conclusion, tissue factor present in both the islets and the culture medium and elicits IBMIR, which affects the function of the transplanted islets.

The development of new density gradient media for purifying human islets and islet-quality assessments

Successful islet transplantation is dependent on the quality and quantity of islets infused. Islets are purified on density gradients, but procedures currently used have limited capacity for pancreatic digests, islet yield, and viability. We aimed to improve islet purification with a modified gradient medium. Biocoll was diluted in University of Wisconsin solution to create linear density gradients of 1.065 to 1.095 g/mL. Properties of islets purified from 22 human pancreas digests with modified medium were compared with 15 preparations using standard medium. The modification increased the capacity of gradients for pancreatic digests from 20 to 60 mL, islet yield increased from 218,000 to 435,318 per isolation, and viability increased from 65.4% to 92.1%. Islet fractions contained greater than 95% of recovered insulin. Islets showed good physiologic responses to secretagogues and restored normoglycemia in streptozotocin-induced diabetic severe combined immunodeficiency disease mice. The new medium enhances yield, purity, and viability of human islet preparations for clinical islet transplantation.

Nicotinamide inhibits tissue factor expression in isolated human pancreatic islets: implications for clinical islet transplantation1

BACKGROUND

Islet-produced tissue factor (TF) triggers an adverse clotting reaction, the instant blood-mediated inflammatory reaction (IBMIR), providing a likely explanation for the need of tissue from multiple donors in clinical islet transplantation. In this study, the authors investigated whether compounds previously shown to affect TF and macrophage chemoattractant protein (MCP)-1 expression in monocytes and endothelial cells have the same effect in human islet cells.

METHODS

Islets were cultured in the presence of l-arginine, cyclosporine A, enalapril, or nicotinamide for 48 hr, after which the TF content and MCP-1 expression were assessed. The effect of nicotinamide on IBMIR was evaluated by exposing the treated islets to fresh human ABO-compatible blood in an in vitro loop model.

RESULTS

Nicotinamide was the only compound that significantly reduced both TF and MCP-1. This reduction was dose-dependent. The level of MCP-1 was strongly correlated with TF expression (r2=0.98). In addition, the level of TF was also correlated with the ability of the islets to initiate IBMIR (r2=0.94).

CONCLUSIONS

TF and MCP-1 expression in human islets can be decreased by adding nicotinamide to the culture medium. These observations indicate that the adverse effects of IBMIR in clinical islet transplantation could be reduced without endangering the recipient using antithrombotic drugs.

Inflammatory mediators expressed in human islets of Langerhans: implications for islet transplantation

Expression of immune modulating mediators in human Islets of Langerhans could have important implications for development of autoimmunity in type 1 diabetes and influence the outcome of clinical islet transplantation. Islets obtained from five donors were analyzed at various times after isolation using cDNA array technology. The Atlas Human Cytokine/Receptor and Hematology/Immunology nylon membranes representing 268 genes and 406, respectively, were used and the relative expression of each gene analyzed. Of the 51 gene products identified, high mRNA expression of MCP-1, MIF, VEGF, and thymosin beta-10 was detected in all islet samples. IL-8, IL-1-beta, IL-5R, and INF-gamma antagonist were expressed in islets cultured for 2 days. IL-2R was expressed in islets cultured for more than 6 days. In conclusion, several inflammatory mediators were expressed in isolated islets, particularly at an early stage after isolation, indicating that a few days of culture could be beneficial for the outcome of islet transplantation.

Successful human islet isolation utilizing recombinant collagenase

The enzymatic dissociation of acinar tissue by collagenase is a substantial step in the isolation of pancreatic islets. Although essential collagenase components have been purified, the variability in the activity of different batches limits long-term reproducibility of isolation success. The utilization of purified recombinant proteases would solve this problem. In the present study, pancreases from multiorgan donors were dissociated by means of digestion-filtration using either Liberase HI (n = 51) or a recombinant collagenase blend (n = 25). No significant differences were found regarding islet yield before and after purification, the percent of exocrine-attached islets, and final purity. However, the ratio between islet equivalents and islet numbers indicated a lesser fragmentation in islets isolated with recombinant collagenase (P < 0.01). In contrast, viability was slightly higher in islets isolated with Liberase (92.3 +/- 0.8 vs. 85.6 +/- 2.9%; P < 0.05). Insulin release during static glucose incubation was not different between experimental groups. Islet transplantation into diabetic nude mice resulted in sustained normoglycemia in either group until the graft was removed. These results demonstrated that viable human islets can be isolated using recombinant collagenase. Final optimization of this enzyme blend would offer continuous reproducibility of isolation success.

Adenovirus-mediated expression of human CD55 or CD59 protects adult porcine islets from complement-mediated cell lysis by human serum

BACKGROUND

Protection against complement activation may reduce acute islet damage in pig-to-human islet xenotransplantation. Expression of the human complement regulatory proteins decay-accelerating factor (DAF, CD55) or CD59 was induced on intact adult porcine islets (APIs) by adenoviral transduction. The functional capacity of the transgenes was examined in vitro after exposure to fresh human serum.

METHODS

Intact APIs were transduced with adenoviral vectors Ad.hDAF or Ad.hCD59 or a control vector. After 3 days, the islets were trypsin dissociated to a single-cell suspension. A cytotoxicity assay was performed in which the islet cells were incubated with human complement active AB serum. Flow cytometry and immunohistochemistry were used to evaluate transgene expression.

RESULTS

APIs could be transduced to express hDAF or hCD59. Flow cytometry analysis of islet single cells revealed that only a fraction of the cells expressed the transgene; immunohistochemical staining of transduced islets demonstrated that mainly cells located in the periphery of the islets were expressing the protein. Cells from nontransduced islets or islets expressing the control protein were sensitive to lysis in human sera (66+/-4.0% and 73+/-3.7% cytotoxicity, respectively). Single cells from islets transduced with hDAF and hCD59 were partially protected from lysis. Islet cells expressing hCD59 were slightly less sensitive to lysis (33+/-3.3%) than cells expressing hDAF (45+/-3.5%).

CONCLUSIONS

These data show that intact pig islets can be transduced to express human regulators of complement activation on the surface and that pig islet cells expressing hDAF or hCD59 are less sensitive to complement-mediated lysis.

Production of tissue factor by pancreatic islet cells as a trigger of detrimental thrombotic reactions in clinical islet transplantation

BACKGROUND

Intraportal transplantation of pancreatic islets offers improved glycaemic control and insulin independence in type 1 diabetes mellitus, but intraportal thrombosis remains a possible complication. The thrombotic reaction may explain why graft loss occurs and islets from more than one donor are needed, since contact between human islets and ABO-compatible blood in vitro triggers a thrombotic reaction that damages the islets. We investigated the possible mechanism and treatment of such thrombotic reactions.

METHODS

Coagulation activation and islet damage were monitored in four patients undergoing clinical islet transplantation according to a modified Edmonton protocol. Expression of tissue factor (TF) in the islet preparations was investigated by immunohistochemistry, immunoprecipitation, electron microscopy, and RT-PCR. To assess TF activity in purified islets, human islets were mixed with non-anticoagulated ABO-compatible blood in tubing loops coated with heparin.

FINDINGS

Coagulation activation and subsequent release of insulin were found consistently after clinical islet transplantation, even in the absence of signs of intraportal thrombosis. The endocrine, but not the exocrine, cells of the pancreas were found to synthesise and secrete active TF. The clotting reaction triggered by pancreatic islets in vitro could be abrogated by blocking the active site of TF with specific antibodies or site-inactivated factor VIIa, a candidate drug for inhibition of TF activity in vivo.

INTERPRETATION

Blockade of TF represents a new therapeutic approach that might increase the success of islet transplantation in patients with type 1 diabetes, in terms of both the risk of intraportal thrombosis and the need for islets from more than one donor.

Islet filtration: a simple and rapid new purification procedure that avoids ficoll and improves islet mass and function

Islet isolation is a time-consuming process. Islet yields vary, and previous in vitro studies suggest that Ficoll may be an islet toxin. Here, we describe an alternative, Ficoll-free method to purify murine islets by filtration through a cell strainer. Collagenase digestion of pancreata was carried out using standard procedures. The pancreatic digest was divided into aliquots and purified either by Ficoll or by filtration. Following filtration, islets were intact and separated from nondigested tissue. Purity was similar to that achieved using Ficoll. However, purification by filtration was faster, increased islet yield, and resulted in higher insulin secretion in vitro. Moreover, when syngeneic diabetic hosts were transplanted with a marginal islet mass, islets purified by filtration restored normoglycemia significantly faster than those isolated by Ficoll. This suggests that Ficoll exposure negatively impacts islet function. In conclusion, islet filtration is a simple and rapid procedure for purification of islets that demonstrate improved functional mass.

Inhibition of thrombin abrogates the instant blood-mediated inflammatory reaction triggered by isolated human islets: possible application of the thrombin inhibitor melagatran in clinical islet transplantation

A thrombotic/inflammatory reaction is elicited when isolated islets of Langerhans come in contact with ABO-compatible blood. The detrimental effects of this instant blood-mediated inflammatory reaction (IBMIR) provide a reasonable explanation for the observation that an unexpectedly high number of islets, from several donors, are needed to produce normoglycemia in transplant patients with type 1 diabetes. In this study, the hypothesis that a specific thrombin inhibitor, Melagatran, could reduce IBMIR in an in vitro model in which human islets are exposed to ABO-compatible blood was tested. The administration of Melagatran abrogated IBMIR dose-dependently. Islets exposed to blood, in the absence or presence of 0.4 micromol/l Melagatran, exhibited a loss of integrity and were found to be trapped in macroscopic clots containing platelets and CD11b(+) leukocytes. At concentrations from 1 to 10 micromol/l, Melagatran inhibited both coagulation and complement activation. Also, platelet and leukocyte activation and consumption were decreased. Islet morphology was maintained with almost no platelets adhering to the surface, and infiltration by CD11b(+) leukocytes was considerably reduced. In conclusion, Melagatran significantly reduced IBMIR in this model system. This protective effect indicates that thrombin plays a pivotal role in IBMIR and suggests that thrombin inhibition can improve the outcome of clinical islet transplantation.

Expression of complement regulatory proteins on islets of Langerhans: a comparison between human islets and islets isolated from normal and hDAF transgenic pigs

BACKGROUND

The expression of regulators of complement activity (RCAs) on islet cells may be of great importance for protecting them against complement-mediated lysis in the immediate posttransplant period after intraportal islet transplantation. We examined porcine and human islet cells for expression of RCA. We also examined to what extent human decay accelerating factor (hDAF) is expressed on adult and fetal islet cells isolated from hDAF transgenic (TG) pigs having a high transgene expression on endothelial cells. Moreover, the susceptibility of the various types of cells to lysis in human serum and blood was investigated.

METHODS

Adult human islets (n=5), normal adult and fetal porcine islets (n=9 and n=8, respectively), and islets from adult and fetal hDAF TG pigs (n=5 and n=6, respectively) were examined. With islet single-cell suspensions and flow cytometry, adult human islet cells were examined for expression of hDAF (CD55), hCD59, and human membrane cofactor protein (hMCP; CD46), while porcine islet cells were examined for expression of pCD59 and pMCP. Islet cells from hDAF TG pigs were also examined for hDAF expression. Porcine peripheral blood lymphocytes, normal and hDAF TG porcine endothelial cell lines, a human endothelial cell line, and the human cell line U937 served as controls. Islet cytotoxicity was assayed after incubation of the islet cells with fresh human serum. Furthermore, adult islets from normal control pigs and hDAF TG pigs were exposed to fresh human blood in vitro for 60 min, and the inflammatory reaction elicited was compared between the different types of islets.

RESULTS

All human islet cell preparations expressed hCD59, two of five expressed hMCP, but none expressed hDAF. Porcine islet cells expressed both pCD59 and pMCP. Normal adult porcine islet cells exposed to fresh human serum resulted in 74+/-5.4% cell lysis (mean+/-SEM, n=16). In comparison, only 1.3+/-2.8% (n=20, P<0.001) of human islet cells were lysed in the human serum. One islet cell preparation from an hDAF TG pig expressed small amounts of hDAF. This preparation from hDAF TG pigs bound significantly less C3c than did normal control islets (mean fluorescence ratio 16+/-2.2 and 58+/-4.3, respectively; P=0.046) and were partially protected from cell lysis in fresh human serum (47+/-10% and 78+/-18% cell lysis, respectively; P=0.046). The other four preparations from hDAF TG pigs were negative for hDAF and were equally susceptible to lysis as normal control islets. All fetal pancreatic islet cells from hDAF TG pigs analyzed were negative for hDAF expression. When exposed to fresh human blood in vitro, adult and fetal islets from hDAF TG pigs elicited equally strong inflammatory changes as did the normal control islets. The inflammatory changes were characterized by activation of the complement and coagulation systems, resulting in islet damage with "dumping" of insulin into the blood.

CONCLUSIONS

Porcine and human islet cells express species-restricted complement regulatory proteins, with the human islet cells expressing mainly hCD59. A low expression of hDAF was detected on islet cells from one of five hDAF TG pigs. These islet cells displayed reduced islet cell cytotoxicity in fresh human serum. We conclude that protection from complement-mediated lysis will be important in the context of intraportal pig-to-human islet transplantation, and expression of a human RCA on islet cells should be beneficial in this context.

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

BACKGROUND

Primary nonfunction resulting in immediate graft loss is responsible for the failure of a large number of islet transplants. Evidence is accumulating to single out endotoxin contamination of the various reagents needed for islet isolation as a major cause of early graft loss.

METHODS

Islets isolated with endotoxin-containing (400 endotoxin units/ml) collagenase type V and "endotoxin-free" (3.1 endotoxin units/ml) Liberase were compared. Graft function was assessed using a syngeneic murine model of marginal islet mass transplantation. Pro-inflammatory cytokine production by islets was measured by ELISA in culture supernatants, and quantitative reverse transcriptase-PCR. Islet cell apoptosis was measured using the annexin assay.

RESULTS

Graft function was significantly delayed when islets were isolated with endotoxin-containing collagenase. Addition of endotoxin to the Liberase solution similarly delayed graft function. After 18 hr in culture, collagenase-isolated islets released higher amounts of proinflammatory cytokines compared with Liberase-isolated islets (interleukin-6: 2,185+/-1,174 pg/ml vs. 520+/-201 pg/ml; tumor necrosis factor-alpha: 304+/-298 pg/ml vs. 0; IL-1beta: 12.5 pg/ml+/-12.5 vs. 0). This observation correlated with higher cytokine mRNA expression in collagenase-isolated islets. The percentage of apoptotic islet cells immediately after isolation was 17.2%+/-9.4 in collagenase-isolated islets and 7.1%+/-2.1 in Liberase-isolated islets.

CONCLUSIONS

We propose that endotoxin contamination is the primum movens of a chain of events that involves intra-islet cytokine production and release and islet cell apoptosis, and endotoxin contamination can ultimately lead to primary nonfunction in vivo. This emphasizes the fact that using endotoxin-free reagents during isolation is a key factor for successful islet transplantation.

Non-heart-beating organ donors: a potential source of islets for transplantation?

BACKGROUND

The shortage of organ donors relative to the number of patients on transplant waiting lists has led to a renewed interest in the use of non-heart-beating (NHB) organ donors in many centers. The lack of donors is also a problem for islet transplantation. The disparity between donor organs and potential recipients is further exacerbated by the requirement to transplant a large number of islets to increase the chance of success and the high level of variability in islet isolation yield. Non-heart-beating (NHB) donors have not previously been assessed as a source of islets for transplantation, and it is unknown what affects the additional factor of warm ischemic injury associated with NHB organs may have on the success of islet isolation.

METHODS

This study assesses the yield and function of islets from NHB donors and compares the results with islets obtained from heart-beating brain-dead (HB) donors.

RESULTS

There were no differences in the yield of islets per gram of pancreas, 1788 (0-4620) NHB vs. 1580 (26-2544) HB (median, range). The secretory function was also similar in both groups, with stimulation indices of 0.71-3.49 for NHB vs. 0.30-3.57 for HB (overall range). There was no correlation between islet yield and warm ischemia time in the NHB donor group.

CONCLUSIONS

In conclusion, the study has demonstrated that it is possible to isolate large numbers of islets from NHB donor pancreata and that, where NHB donor programs exist, these could provide a significant addition to the number of potentially transplantable islets.