Improved functional survival of human islets of Langerhans in three-dimensional matrix culture

Transporting cells over several days without dry-ice

This paper describes a simple, hazard-free and inexpensive procedure that allows researchers to send cultured cells across the globe at ambient temperatures. The method enables transit of up to 2 weeks without compromising cell recovery. Its use will assist collaborators in distant laboratories to exchange cells without using dry-ice.

Summary: An easy dry-ice-free method of sending cultured cells across the globe at ambient temperatures.

Electrospun Nanofibers for Diabetes: Tissue Engineering and Cell-Based Therapies

Diabetes mellitus is an autoimmune disease which causes loss of insulin secretion producing hyperglycemia by promoting progressive destruction of pancreatic β cells. An ideal therapeutic approach to manage diabetes mellitus is pancreatic β cells replacement. The aim of this review article was to evaluate the role of nanofibrous scaffolds and stem cells in the treatment of diabetes mellitus. Various studies have pointed out that application of electrospun biomaterials has considerably attracted researchers in the field of tissue engineering. The principles of cell therapy for diabetes have been reviewed in the first part of this article, while the usability of tissue engineering as a new therapeutic approach is discussed in the second part.

Tissue-Engineered Pancreatic Islets: Culturing Rat Islets in the Chitosan Sponge

Subcutaneous islet transplantation has become an attractive modality. With development of tissue-engineering techniques, it is possible to rectify the disadvantage of poor blood supply in the subcutaneous site by reconstruction of the capillary network. According to reports, the Chitosan sponge (CS) could be used for reconstruction of in vitro capillary-like network and could be used in artificial skin equivalent. In this study, we cultured the islets in CS for future application. CSs, having 200–500 μm pore size, were prepared by freeze-drying method. Rat islets were isolated from the pancreas of Lewis rats (10 weeks old, 280–300 g, male) by collagenase digestion followed by discontinuous dextran gradient centrifugation method. Each 20 islets were seeded equally into the CSs and were cultured for 62 days with various culture media such as RPMI-1640, Dulbecco's modified Eagle's medium (DMEM), and Eagle's MEM. They contained 10% fetal bovine serum (FBS) and 5 ml/L antibiotic-antimycotic mixed stock solution in the culture dishes. Insulin concentration both inside and outside of the islet-seeded CS was measured during culture. Changes in the morphology of islets were also observed in this study. Freshly isolated islets had a loose appearance with an irregular border, and most were seen as a single islet. Occasionally a cluster, consisting of 2–4 islets ranging mainly from 150 to 250 μm in diameter, was observed. Islets cultured in the CSs in different culture media retained initial morphology, which had well-delineated smooth borders for at least 53 days. The insulin release behavior of islets cultured in the CS showed constant secretory capacities for 49 days. After that they exhibited a rapid and definitive decline from the initial insulin release. Until this stage, insulin concentration in the CS was well maintained. The properties were dependent on culture medium used and insulin diffusion released from islets. This experiment is a new study model for establishment of islet culture in a three-dimensional matrix. Also extension of this observation will provide new insights for islet transplantation at the subcutaneous site by a tissue-engineering approach.

Survival and Function of Islets during Culture

Cell and tissue culture techniques have improved considerably since the first attempts to maintain explants of animal tissue in vitro. The two major developments that have allowed these improvements are the ability to produce continuous cell lines, thus allowing reproducible results to be obtained, and the definition of media for different cell types, thereby reducing the need for supplements of serum and other extraneous extracts. The requirements of islets in culture have been more difficult to define, largely because islets do not proliferate in culture and proliferation rate cannot therefore be used to measure the suitability of the medium. Further difficulties arise because islets are highly metabolically active “mini-organelles.” Although many studies have been undertaken to try and optimize media for the culture islets of Langerhans, the media most commonly used are commercially available media developed for other cell types. There remains ample scope for further refinement of the composition of islet culture media, with the possibility of different media for islets from different species.

Islet product characteristics and factors related to successful human islet transplantation from the Collaborative Islet Transplant Registry (CITR) 1999-2010

The Collaborative Islet Transplant Registry (CITR) collects data on clinical islet isolations and transplants. This retrospective report analyzed 1017 islet isolation procedures performed for 537 recipients of allogeneic clinical islet transplantation in 1999-2010. This study describes changes in donor and islet isolation variables by era and factors associated with quantity and quality of final islet products. Donor body weight and BMI increased significantly over the period (p<0.001). Islet yield measures have improved with time including islet equivalent (IEQ)/particle ratio and IEQs infused. The average dose of islets infused significantly increased in the era of 2007-2010 when compared to 1999-2002 (445.4±156.8 vs. 421.3±155.4×0(3) IEQ; p<0.05). Islet purity and total number of β cells significantly improved over the study period (p<0.01 and <0.05, respectively). Otherwise, the quality of clinical islets has remained consistently very high through this period, and differs substantially from nonclinical islets. In multivariate analysis of all recipient, donor and islet factors, and medical management factors, the only islet product characteristic that correlated with clinical outcomes was total IEQs infused. This analysis shows improvements in both quantity and some quality criteria of clinical islets produced over 1999-2010, and these parallel improvements in clinical outcomes over the same period.

Tissue engineering approaches to cell-based type 1 diabetes therapy

Type 1 diabetes mellitus is an autoimmune disease resulting from the destruction of insulin-producing pancreatic β-cells. Cell-based therapies, involving the transplantation of functional β-cells into diabetic patients, have been explored as a potential long-term treatment for this condition; however, success is limited. A tissue engineering approach of culturing insulin-producing cells with extracellular matrix (ECM) molecules in three-dimensional (3D) constructs has the potential to enhance the efficacy of cell-based therapies for diabetes. When cultured in 3D environments, insulin-producing cells are often more viable and secrete more insulin than those in two dimensions. The addition of ECM molecules to the culture environments, depending on the specific type of molecule, can further enhance the viability and insulin secretion. This review addresses the different cell sources that can be utilized as β-cell replacements, the essential ECM molecules for the survival of these cells, and the 3D culture techniques that have been used to benefit cell function.

Therapeutic cell encapsulation techniques and applications in diabetes

The encapsulation of therapeutic cells permits the implantation of allogeneic and xenogeneic cells for the regulation of certain physiological processes damaged by the death or senescence of host tissues. The encapsulation of pancreatic cells for the treatment of diabetes is emphasized; however, many of the techniques are applicable to a wide array of mammalian cell applications. The summary of both established and novel encapsulation techniques, clinical trials, and commercial product developments highlights the metered but steady pace of therapeutic cell encapsulation towards implementation.

Development of in vitro 3D TissueFlex® islet model for diabetic drug efficacy testing

Increasing individuals diagnosed with type II diabetes pose a strong demand for the development of more effective anti-diabetic drugs. However, expensive, ethically controversial animal-based screening for anti-diabetic compounds is not always predictive of the human response. The use of in vitro cell-based models in research presents obviously ethical and cost advantages over in vivo models. This study was to develop an in vitro three-dimensional (3D) perfused culture model of islets (Islet TF) for maintaining viability and functionality longer for diabetic drug efficacy tests. Briefly fresh isolated rat islets were encapsulated in ultrapure alginate and the encapsulated islets were cultured in TissueFlex(®), a multiple, parallel perfused microbioreactor system for 7 days. The encapsulated islets cultured statically in cell culture plates (3D static) and islets cultured in suspension (2D) were used as the comparisons. In this study we demonstrate for the first time that Islet TF model can maintain the in vitro islet viability, and more importantly, the elevated functionality in terms of insulin release and dynamic responses over a 7-day culture period. The Islet TF displays a high sensitivity in responding to drugs and drug dosages over conventional 2D and 3D static models. Actual drug administration in clinics could be simulated using the developed Islet TF model, and the patterns of insulin release response to the tested drugs were in agreement with the data obtained in vivo. Islet TF could be a more predictive in vitro model for routine short- and long-term anti-diabetic drug efficacy testing.

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

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

Enhanced function of pancreatic islets co-encapsulated with ECM proteins and mesenchymal stromal cells in a silk hydrogel

Pancreatic islet encapsulation within biosynthetic materials has had limited clinical success due to loss of islet function and cell death. As an alternative encapsulation material, a silk-based scaffold was developed to reestablish the islet microenvironment lost during cell isolation. Islets were encapsulated with ECM proteins (laminin and collagen IV) and mesenchymal stromal cells (MSCs), known to have immunomodulatory properties or to enhance islet cell graft survival and function. After a 7 day in vitro encapsulation, islets remained viable and maintained insulin secretion in response to glucose stimulation. Islets encapsulated with collagen IV, or laminin had increased insulin secretion at day 2 and day 7, respectively. A 3.2-fold synergistic improvement in islet insulin secretion was observed when islets were co-encapsulated with MSCs and ECM proteins. Furthermore, encapsulated islets had increased gene expression of functional genes; insulin I, insulin II, glucagon, somatostatin, and PDX-1, and lower expression of the de-differentiation genes cytokeratin 19 and vimentin compared to non-encapsulated cells. This work demonstrates that encapsulation in silk with both MSCs and ECM proteins enhances islet function and with further development may have potential as a suitable platform for islet delivery in vivo.

Perfluorocarbon Emulsions Prevent Hypoxia of Pancreatic β-Cells

As oxygen carriers, perfluorocarbon emulsions might be useful to decrease hypoxia of pancreatic islets before transplantation. However, their hydrophobicity prevents their homogenisation in culture medium. To increase the surface of contact between islets and Perfluorooctyl bromide (PFOB), and consequently oxygen delivery, we tested effect of a PFOB emulsion in culture medium on β-cell lines and rat pancreatic islets. RINm5F β-cell line or pancreatic rat islets were incubated for 3 days in the presence of PFOB emulsion in media (3.5% w/v). Preoxygenation of the medium was performed before culture. Cell viability was assessed by apoptotic markers (Bax and Bcl-2) and by staining (fluoresceine diacetate and propidium iodide). β-Cell functionality was determined by insulin release during a glucose stimulation test and. Hypoxia markers, HIF-1α and VEGF, were studied at days 1 and 3 using RT-PCR, Western blotting, and ELISA. PFOB emulsions preserved viability and functionality of RINm5F cells with a decrease of HIF-1α and VEGF expression. Islets viability was preserved during 3 days of culture. Secretion of VEGF was higher in untreated control (0.09 ± 0.041 μg VEGF/mg total protein) than in PFOB emulsion incubated islets (0.02 ± 0.19 μg VEGF/mg total protein, n = 4, p < 0.05) at day 1. At day 3, VEGF secretion was increased as compared to day 1 in control (0.23 ± 0.04 μg VEGF/mg total protein) but it was imbalance by the presence of PFOB emulsion (0.09 ± 0.03 μg VEGF/mg total protein, n = 5, p < 0.05). While insulin secretion was maintained in response to a glucose stimulation test until day 3 when islets were incubated in the presence of PFOB emulsion preoxygenated (0.81 ± 0.16 at day 1 vs. 0.75 ± 0.24 at day 3), the ability to secrete insulin in the presence of high glucose concentration was lost in islets controls (0.51 ± 0.18 at day 1 vs. 0.21 ± 0.13 at day 3). Atmospheric oxygen delivery by PFOB emulsion might be sufficient to decrease islets hypoxia. However, to improve islets functionality, overoxygenation is needed. Finally, maintenance of islet viability and functionality for several days after isolation could improve the outcome of islets transplantation.

Preservation of pancreatic islets in cold UW solution before transplantation

Culture of islets prior to transplantation needs to be revisited for maintaining functional islet capacity. This study was conducted to compare cold UW (University of Wisconsin) preservation with conventional culture based on insulin secretory capacity in vitro and in vivo. Islets isolated from Wistar rats were either cultured for 24 h at 37°C in RPMI1640 medium or DMEM containing various concentrations of glucose or preserved for the same period in UW solution or in DMEM solution at 4°C. The islet yield in UW group, but not in other groups, was maintained as comparable with that of fresh islets. Insulin secretory capacity in response to glucose was maintained only in the islets of UW group, but not in other groups. SCID mice given 300 IEQ islets of UW group showed gradual restoration of normoglycemia as found in the mice given freshly isolated islets. Meanwhile, those mice given cultured islets for 24 h at 37°C in RPMI1640 medium showed rapid decrease of blood glucose levels on day 1 followed by relatively elevated levels on day 2, suggesting unstable insulin secretory capacity of islets.   Morphological staining with anti-HMGB1 (high mobility group B1) antibody revealed central damage of islets in all culture groups regardless of glucose concentration and in islets of cold DMEM group, whereas those in the UW group were quite intact. These results suggest that cold preservation in UW solution is simple and beneficial in protecting islets morphologically and functionally before transplantation.

Low-temperature preservation of isolated islets is superior to conventional islet culture before islet transplantation

BACKGROUND

Although culturing islets before transplantation provides flexibility for evaluation of isolated islets and pretreatment of patients, it is well-known that isolated islets deteriorate rapidly in culture. In this study, we evaluated optimal temperature for culture/preservation of isolated human islets before transplantation.

METHODS

Isolated islets were cultured or preserved for 48 hr in the following culture/preservation conditions: preservation at 4 degrees C in University of Wisconsin solution and culture at 22 degrees C or 37 degrees C in culture medium.

RESULTS

Islet morphology after 4 degrees C preservation was similar to that of fresh islets, whereas islet diameter after 37 degrees C or 22 degrees C culture was smaller than that of fresh islets. Islet yield significantly decreased at higher temperatures (24% loss in 37 degrees C culture and 19% loss in 22 degrees C culture, but <5% loss in 4 degrees C preservation). Cultured/preserved islets were transplanted into diabetic nude mice. The attainability of posttransplantation normoglycemia was significantly higher in the 4 degrees C preservation group than in 22 degrees C and 37 degrees C culture groups.

CONCLUSION

Preservation of isolated islets at 4 degrees C improves the outcome of islet transplantation more efficiently than preservation at 22 degrees C or 37 degrees C. Based on these data, we have performed short-time cold storage of isolated islets instead of culturing for current clinical islet transplantation.

Plasma-fibroblast gel as scaffold for islet transplantation

The transplant of pancreatic islets into the liver can restore normal blood glucose levels in patients with type I diabetes. However, long-term results have indicated that the site and method of transplantation still need to be optimized to improve islet engraftment. This study was designed to assess the efficiency of the use of clotted blood plasma containing fibroblasts ("plasma-fibroblast gel") as a scaffold for subcutaneous islet transplantation in diabetic athymic mice. Islets embedded in the plasma-fibroblast gel were able to resolve hyperglycemia in transplanted mice, restoring normoglycemia over a 60-day period and allowing gradual body weight recovery. Glucose clearances were significantly improved when compared to those recorded in diabetic animals and similar to those observed in the control group (free islets transplanted beneath the kidney capsule). Histological evaluation revealed functional islets within a subcutaneous tissue rich in collagen fibers that was well vascularized, with blood vessels observed around and inside the islets. These findings suggest that this approach could be used as an alternative option for the treatment of type I diabetes in human clinical practice.

Sustained insulin secretory response in human islets co-cultured with pancreatic duct-derived epithelial cells within a rotational cell culture system

AIMS/HYPOTHESIS

Loss of the trophic support provided by surrounding non-endocrine pancreatic cell populations underlies the decline in beta cell mass and insulin secretory function observed in human islets following isolation and culture. This study sought to determine whether restoration of regulatory influences mediated by ductal epithelial cells promotes sustained beta cell function in vitro.

METHODS

Human islets were isolated according to existing protocols. Ductal epithelial cells were harvested from the exocrine tissue remaining after islet isolation, expanded in monolayer culture and characterised using fluorescence immunocytochemistry. The two cell types were co-cultured under conventional static culture conditions or within a rotational cell culture system. The effect of co-culture on islet structural integrity, beta cell mass and insulin secretory capacity was observed for 10 days following isolation.

RESULTS

Human islets maintained under conventional culture conditions exhibited a characteristic loss in structural integrity and functional viability as indicated by a diminution of glucose responsiveness. By contrast, co-culture of islets with ductal epithelial cells led to preserved islet morphology and sustained beta cell function, most evident in co-cultures held within the rotational cell culture system, which showed a significantly (p < 0.05) greater insulin secretory response to elevated glucose compared with control islets. Similarly, insulin/protein ratio data suggested that the presence of ductal epithelial cells is beneficial for the maintenance of beta cell mass.

CONCLUSIONS/INTERPRETATION

The data indicate a supportive role for ductal epithelial cells in islet viability. Further characterisation of the regulatory influences may lead to novel strategies to improve long-term beta cell function both in vitro and following islet transplantation.

c-Jun N-terminal kinase 1 is deleterious to the function and survival of murine pancreatic islets

AIMS/HYPOTHESIS

Inhibition of c-jun N-terminal kinase (JNK) favours pancreatic islet function and survival. Since two JNK isoforms are present in the pancreas (JNK1 and JNK2), we addressed their specific roles in experimental islet transplantation.

METHODS

C57BL/6J (wild-type [WT]), Jnk1 (also known as Mapk8)(-/-) and Jnk2 (also known as Mapk9)(-/-) mice were used as donor/recipients in a syngeneic islet transplantation model. Islet cell composition, function, viability, production of cytokines and of vascular endothelial growth factor (VEGF) were also studied in vitro.

RESULTS

Jnk1 ( -/- ) islets secreted more insulin in response to glucose and were more resistant to cytokine-induced cell death compared with WT and Jnk2 (-/-) islets (p < 0.01). Cytokines reduced VEGF production in WT and Jnk2 (-/-) but not Jnk1 ( -/- ) islets; VEGF blockade restored Jnk1 ( -/- ) islet susceptibility to cytokine-induced cell death. Transplantation of Jnk1 ( -/- ) or WT islets into WT recipients made diabetic had similar outcomes. However, Jnk1 ( -/- ) recipients of WT islets had shorter time to diabetes reversal (17 vs 55 days in WT, p = 0.033), while none of the Jnk2 (-/-) recipients had diabetes reversal (0% vs 71% in WT, p = 0.0003). Co-culture of WT islets with macrophages from each strain revealed a discordant cytokine production.

CONCLUSIONS/INTERPRETATION

We have shown a deleterious effect of JNK2 deficiency on islet graft outcome, most likely related to JNK1 activation, suggesting that specific JNK1 blockade may be superior to general JNK inhibition, particularly when administered to transplant recipients.

Risk factors for islet loss during culture prior to transplantation

Culturing islets can add great flexibility to a clinical islet transplant program. However, a reduction in the islet mass has been frequently observed during culture and its degree varies. The aim of this study was to identify the risk factors associated with a significant islet loss during culture. One-hundred and four islet preparations cultured in an attempt to use for transplantation constituted this study. After culture for 20 h (median), islet yield significantly decreased from 363 309 +/- 12 647 to 313 035 +/- 10 862 islet equivalent yield (IE) (mean +/- SE), accompanied by a reduction in packed tissue volume from 3.9 +/- 0.1 to 3.0 +/- 0.1 ml and islet index (IE/islet particle count) from 1.20 +/- 0.04 to 1.05 +/- 0.04. Culture did not markedly alter islet purity or percent of trapped islet. Morphology score and viability were significantly improved after culture. Of 104 islet preparations, 37 suffered a substantial islet loss (> 20%) over culture. Factors significantly associated with risk of islet loss identified by univariate analysis were longer cold ischemia time, two-layer method (TLM) preservation, lower islet purity, and higher islet index. Multivariate analysis revealed that independent predictors of islet loss were higher islet index and the use of TLM. This study provides novel information on the link between donor- isolation factors and islet loss during culture.

Reestablishment of microenvironment is necessary to maintain in vitro and in vivo human islet function

Islet transplantation is associated with an elevated rate of early graft failure. The isolation process leads to structural and functional abnormalities. The reestablishment of the cell-matrix relationship is important to modulate the survival and function of islets. Thus, we evaluated the effect of human fibronectin (hFN) and self-assembling peptide nanofiber (SAPNF) in the ability to support islet function in vitro and after transplantation into streptozotocin (STZ)-induced diabetic severe combined immunodeficiency (SCID) mice. Human isolated islets were cultured with hFN or SAPNF for 7 days. Their ability to maintain insulin production/glucose responsiveness over time was evaluated. Islets embedded in hFN, SAPNF, or alone were transplanted into STZ-induced diabetic SCID mice. Islet grafts were removed after 14 days to evaluate insulin content, insulin expression, and apoptosis. SAPNF-entrapped islets maintained satisfactory morphology/viability and capability of glucose-dependent insulin secretion for over 7 days, whereas islets cultured in hFN underwent widespread deterioration. In vivo grafts containing human islets in SAPNF showed remarkably higher insulin content and expression when compared with human islets in hFn or alone. RT-PCR revealed lower caspase-3 expression in SAPNF islets grafts. These studies indicate that the reestablishment of the cell-matrix interactions by a synthetic matrix in the immediate postisolation period is a useful tool to maintain islet functions in vitro and in vivo.

Beneficial Effect of the Nonpeptidyl Low Molecular Weight Radical Scavenger IAC on Cultured Human Islet Function

We examined a possible protective effect of the nonpeptidyl low molecular weight radical scavenger IAC [bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)decanedioate di-hydrochloride] on isolated human islet cells against isolation and culture oxidative stress. Islets isolated from pancreases of nondiabetic multiorgan donors by collagenase digestion were purified by density gradient centrifugation. After the isolation, islets were either exposed or not exposed for 7 days to 10 μmol/L IAC. We found that IAC markedly reduced oxidative stress and ameliorated islets function. These results suggest that the use of IAC could be an interesting pharmacological approach for the treatment of the islets before transplantation.

Human albumin preserves islet mass and function better than whole serum during pretransplantation islet culture

OBJECTIVE

Human islet transplant protocols frequently include a brief period of islet culture before transplantation. Some investigators have suggested that medium supplementation with human serum might quench collagenase activity and provide better culture conditions when compared with human albumin. We studied the effect of whole serum on islet count, islet equivalence, insulin secretion, and DNA content in human islets.

METHODS

Adult human islets isolated from a single pancreas with purity >50% were cultured in identical 150 islet equivalent samples at 37 degrees C using CMRL 1066-based islet medium (Mediatech) supplemented with either 0.5% human albumin or 10% human AB serum. Prior to culture and after 3 days, islets were assessed in vitro using dithizone staining (n = 4), insulin release after static glucose stimulation (n = 8), and DNA content (n = 8).

RESULTS

After 3 days, islet mass (defined by the number of islets and islet equivalents counted after dithizone staining) was better preserved in islets cultured in 0.5% human albumin. Although the stimulation index and total DNA content were similar between groups, islets cultured in human albumin demonstrated greater absolute insulin secretion (p = .02) and insulin secretion per cell (p = .02).

CONCLUSIONS

When used to supplement CMRL 1066-based islet culture medium, human albumin preserves islet mass and secretory capacity better than whole human serum. Human serum offers no advantage in islet preservation or function.

Inhibition of c-jun N terminal kinase (JNK) improves functional beta cell mass in human islets and leads to AKT and glycogen synthase kinase-3 (GSK-3) phosphorylation

AIMS/HYPOTHESIS

Activation of c-jun N-terminal kinase (JNK) has been described in islet isolation and engraftment, making JNK a key target in islet transplantation. The objective of this study was to investigate if JNK inhibition with a cell-permeable TAT peptide inhibitor (L-JNKI) protects functional beta cell mass in human islets and affects AKT and its substrates in islet cells.

METHODS

The effect of L-JNKI (10 micromol/l) on islet count, mitochondrial membrane potential, glucose-stimulated insulin release and phosphorylation of both AKT and its substrates, as well as on reversal of diabetes in immunodeficient diabetic Nu/Nu mice was studied.

RESULTS

In vitro, L-JNKI reduced the islet loss in culture and protected from cell death caused by acute cytokine exposure. In vivo, treatment of freshly isolated human islets and diabetic Nu/Nu mice recipients of such islets resulted in improved functional beta cell mass. We showed that L-JNKI activates AKT and downregulates glycogen synthase kinase-3 beta (GSK-3B) in human islets exposed to cytokines, while other AKT substrates were unaffected, suggesting that a specific AKT/GSK-3B regulation by L-JNKI may represent one of its mechanisms of cytoprotection.

CONCLUSIONS/INTERPRETATION

In conclusion, we have demonstrated that targeting JNK in human pancreatic islets results in improved functional beta cell mass and in the regulation of AKT/GSK3B activity.

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

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

Insulin secretion from pancreatic islets in fibrin glue clots at different fibrinogen and thrombin concentrations

BACKGROUND

Fibrin glue has proven to be a good delivery system for cell transplantation but the factors that influence the fibrin-cell relationships are not well understood. The purpose of this study was to assess the effect of different concentrations of fibrin glue components (thrombin and fibrinogen) on the function of pancreatic islets.

METHOD

Islets were isolated from rat pancreata and combined with 6 different fibrin glue formulations. Each islet sample was incubated sequentially with RPMI containing low and high glucose, and culture supernatants were harvested for insulin determination using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The control group (no fibrin glue) and group 3 (with thrombin 50 U/mL and fibrinogen 10 mg/mL) had the highest insulin secretion in response to glucose stimulation. These were followed by groups 5 and 4 with 2.6 and 1.8 stimulation indexes, respectively. Group 2 (with thrombin 50 U/mL and fibrinogen 5 mg/mL) and group 6 (commercial kit with thrombin 250 U/mL and fibrinogen 75-115 mg/mL) had the lowest insulin response after glucose stimulation.

CONCLUSION

This study demonstrates that different fibrin glue formulations significantly impact pancreatic islets function. In the future, when using fibrin glue as a carrier for pancreatic islet transplantation, lower concentrations of fibrinogen and thrombin are recommended to obtain more viable and functional grafts.

Influence of heme oxygenase-1 gene transfer on the viability and function of rat islets in in vitro culture

AIM: To investigate the influence of heme oxygenase-1 (HO-1) gene transfer on the viability and function of cultured rat islets in vitro.

METHODS: Islets were isolated from the pancreata of Sprague-Dawley rats by intraductal collagenase digestion, and purified by discontinuous Ficoll density gradient centrifugation. Purified rat islets were transfected with adenoviral vectors containing human HO-1 gene (Ad-HO-1) or enhanced green fluorescent protein gene (Ad-EGFP), and then cultured for seven days. Transfection was confirmed by fluorescence microscopy and Western blot. Islet viability was evaluated by acridine orange/ propidium iodide fluorescent staining. Glucose-stimulated insulin release was detected using insulin radioimmunoassay kits and was used to assess the function of islets. Stimulation index (SI) was calculated by dividing the insulin release upon high glucose stimulation by the insulin release upon low glucose stimulation.

RESULTS: After seven days culture, the viability of cultured rat islets decreased significantly (92% ± 6% vs 52% ± 13%, P < 0.05), and glucose-stimulated insulin release also decreased significantly (6.47 ± 0.55 mIU/L/30IEQ vs 4.57 ± 0.40 mIU/L/30IEQ, 14.93 ± 1.17 mIU/L/30IEQ vs 9.63 ± 0.71 mIU/L/30IEQ, P < 0.05). Transfection of rat islets with adenoviral vectors at an MOI of 20 was efficient, and did not impair islet function. At 7 d post-transfection, the viability of Ad-HO-1 transfected islets was higher than that of control islets (71% ± 15% vs 52% ± 13%, P < 0.05). There was no significant difference in insulin release upon low glucose stimulation (2.8 mmol/L) among Ad-HO-1 transfected group, Ad-EGFP transfected group, and control group (P > 0.05), while when stimulated by high glucose (16.7 mmol/L) solution, insulin release in Ad-HO-1 transfected group was significantly higher than that in Ad-EGFP transfected group and control group, respectively (12.50 ± 2.17 mIU/L/30IEQ vs 8.87 ± 0.65 mIU/L/30IEQ; 12.50 ± 2.17 mIU/L/30IEQ vs 9.63 ± 0.71 mIU/L/30IEQ, P < 0.05). The SI of Ad-HO-1 transfected group was also significantly higher than that of Ad-EGFP transfected group and control group, respectively (2.21 ± 0.02 vs 2.08 ± 0.05; 2.21 ± 0.02 vs 2.11 ± 0.03, P < 0.05).

CONCLUSION: The viability and function of rat islets decrease over time in in vitro culture, and heme oxygenase-1 gene transfer could improve the viability and function of cultured rat islets.

Pretransplant islet culture: a comparison of four serum-free media using a murine model of islet transplantation

INTRODUCTION

Human islet transplant protocols frequently incorporate a brief period of islet culture before transplantation. The optimal medium for pretransplant islet culture is unknown.

METHODS

We compared four serum-free media formulated for human islets: Miami (MM1), Memphis (M-SFM), Edmonton (EDM), and hCell OCZEM-SF/AF (hCell). Islets isolated from a single human pancreas with purity >80% were cultured in 2500-islet-equivalent (IE) fractions using the media listed. After 7 days, each 2500-IE fraction was grafted under the kidney capsule of a streptozocin-diabetic rag1 mouse (n = 4 per group). Mice were evaluated with serum glucose monitoring, stimulated C-peptide release, and glucose tolerance tests. Islet fractions transplanted immediately after isolation (n = 4 mice) served as controls. In vitro islet function was assessed on days 0 and 3 and included insulin release (after static glucose stimulation), total cellular C-peptide content, cell count, and viability.

RESULTS

Glucose control was improved in all cohorts of mice after transplant, but only islet grafts cultured in MM1 were statistically indistinguishable from fresh islets. MM1- and hCell-cultured islet grafts showed improved glucose tolerance compared with fresh islets; C-peptide release was similar among the four cohorts. In vitro, only islets cultured in MM1 had similar stimulation index to fresh islets, whereas only hCell- and MM1-cultured islets demonstrated recovery of C-peptide content and insulin release.

CONCLUSIONS

Media choice before transplant can influence islet quality, even when culture periods are short. Miami MM1 and hCell media may provide better islet protection than alternative media.

Rescue purification maximizes the use of human islet preparations for transplantation

The relative inefficiency of the islet purification process may hamper obtaining enough islets for transplantation even with adequate pre-purification counts. In this study, we determined the effect of an additional purification step on total islet yields and pancreas utilization at our center. Twenty-five pancreata were processed using the automated method followed by continuous gradient purification (CGP), and the less pure islet fractions were subjected to additional rescue gradient purification (RGP). CGP and RGP islets were combined and transplanted into patients with type 1 diabetes. CGP and RGP islets showed no significant differences in cell viability, insulin secretion in vitro and function when transplanted into chemically diabetic mice. Mean RGP contribution to the final preparation was 27.9 +/- 19.9%. In 12 of 25 preparations, CGP yielded <5000 IEQ/kg of recipient body weight, and inclusion of RGP islets to the final preparation allowed to obtain the minimal islet number required for transplantation. Transplanted islets resulted in sustained C-peptide production, HbA1(C) normalization and insulin-independence or reduced insulin requirements. Taken together, our data suggest that RGP islets are comparable in terms of viability and potency to CGP islets. RGP may be of assistance in maximizing the number of islet preparations successfully used in transplant protocols.

A novel approach to increase human islet cell mass while preserving beta-cell function

Human islet expansion in monolayer culture leads to loss of function and senescence. By maintaining the 3-D configuration of islets in fibrin gels, it is feasible to expand beta-cells in response to hepatocyte growth factor (HGF) while preserving physiologic glucose responsiveness both in vitro and in vivo after transplantation into nude mice. Islets were cultured free floating with or without growth factors and nicotinamide and in fibrin gels with the same conditions. Proliferation was observed only in islets cultured in fibrin gels and the cocktail; total insulin increased by threefold, with a concomitant increase in beta-cell mass by morphometry. Insulin release after glucose challenge was also preserved. Islets in fibrin gels gave rise in vivo to large grafts rich in insulin and glucagon, and grafts from free-floating islets were smaller with fewer endocrine cells. Circulating human C-peptide levels were higher than in the mice receiving free-floating islets. In summary, fibrin allows for HGF-mediated cell proliferation while preserving glucose responsiveness in an environment that preserves cell-cell contacts. Limited islet ex vivo expansion under these conditions may improve recipient-donor tissue ratios to equal the functional results of whole-organ transplants.

Improving function and survival of porcine islet xenografts using microencapsulation and culture preconditioning

INTRODUCTION AND AIMS

Porcine pancreatic islets have been difficult to preserve because isolated porcine islets tend to disaggregate to single cells and lose function under culture conditions. In the current study, the influence of agarose microencapsulation on the maintenance of the number and function of islets in culture preservations and the effect of culture preconditioning of microencapsulated porcine islets on xenogenic transplantation were investigated.

METHODOLOGY

Porcine islets were isolated and then microencapsulated in 5% agarose membrane. The percentage of naked and microencapsulated islets remaining in the culture preservations was assessed. The effect of microencapsulation and culture on secretory function was investigated in vitro. The survival of overnight-cultured and 7-days-cultured microencapsulated islets in xenogenic transplantations was examined.

RESULTS

A good percentage of microencapsulated islets remained in the culture preservations. They could maintain good secretory functions in vitro after 7 days of culture. In addition, we observed a significant prolongation of mean islet survival by culture preconditioning.

CONCLUSIONS

The present findings suggest that microencapsulation is one of the useful preserving methods for maintenance of the number and function of cultured isolated porcine islets. Moreover, culture preconditioning is effective for improving islet survival and might be a good option leading to clinical success.

Improved in vivo pancreatic islet function after prolonged in vitro islet culture

BACKGROUND

Difficulties with recovering and preserving pancreatic islets have hampered progress in islet transplantation. In previous in vitro studies, our laboratory successfully demonstrated that using serum-free medium for prolonged pancreatic islet culture allows postculture recovery ratios greater than those obtained with standard media with sustained in vitro islet function. The goal of this study was to determine whether culturing of islets in a modified serum-free medium (M-SFM) would sustain function in vivo.

METHODS

Islets were isolated from pancreata procured from 12 cadaveric organ donors and cultured in the M-SFM for up to 2 months, cryopreserved at -70 degrees C within 1-3 days of isolation for 2 months, or placed in short-term culture (3-5 days) before their transplantation under the kidney capsule of nonobese diabetic-severe combined immunodeficient mice (n=4-7 per group/time point). In vivo islet function was assessed by measuring the production of human insulin and C-peptide over a period of 3-15 months.

RESULTS

After extended culture of islets in M-SFM for 1 or 2 months, transplanted islets maintained their viability, and in some instances in vivo function improved when compared with short-term cultured islets transplanted from the same preparation (P<0.01). Improvement was particularly evident for islets cultured for 1 month. Furthermore, when compared with cryopreserved preparations, early function (postoperative day 7) of islets from 1-month culture preparations was statistically better (P<0.05). Prolonged culture in M-SFM had no significant impact on long-term function, inasmuch as cultured islets functioned for more than 120 days.

CONCLUSION

These data demonstrate that prolonged islet culture in M-SFM sustained viability and function, and in some instances had a positive effect on in vivo islet function, particularly in the 1-month cultures. No negative effect on long-term in vivo function was demonstrated in this study. Confirmation in clinical models utilizing extended (1-2 months) islet culture in M-SFM could significantly enhance islet transplantation by allowing the identification of best-matched recipients, pretransplantation recipient conditioning, and possible pretransplantation islet modifications to promote engraftment and prolonged graft function.

Porcine neonatal pancreatic cell clusters in tissue culture: benefits of serum and immobilization in alginate hydrogel

Porcine neonatal pancreatic cell clusters (NPCCs) may be a suitable source of insulin producing tissue for transplantation in diabetic patients. The possible beneficial effect of serum on maturation of NPCCs in vitro is difficult to achieve because of cell clumping, which can be avoided by immobilization in alginate hydrogel matrix. Collagenase treated pancreata, cultured for 4 days, formed NPCCs that were embedded in alginate cross-linked with CaCl2 and cultured in modified Ham's F10 medium with 10% fetal calf serum (FCS) for 10 days. NPCCs cultured as suspension in F10+ with 0.5% bovine serum albumin or with 10% FCS were used as control. To prevent the aggregation when cultured with serum, NPCCs were kept as a very diluted suspension. At the beginning and end of the culture, samples were taken for insulin and DNA content and immunostained for beta and non-beta cells. The culture of NPCCs immobilized in alginate resulted with 3-fold increase in insulin content and 9-fold increase in insulin/DNA ratio. Histology revealed evident increase of number of insulin- and other hormone-positive cells compared with the control. Even though 2 weeks in culture resulted in impaired glucose-induced insulin release, the amount of insulin secreted by clusters cultured in the presence of serum was 4-fold higher than in serum-free conditions. After transplantation, NPCCs retrieved from alginate reversed hyperglycemia similarly to NPCCs cultured in standard conditions. In conclusion, this study shows the feasibility of in vitro immobilization of NPCCs in alginate three-dimensional matrix, allowing cell clusters to be cultured at least two times higher density compared with culture in suspension.

Characterization of integrin expression in islets isolated from hamster, canine, porcine, and human pancreas

The reasons for the failure of clinical islet transplantation remain obscure. Islet isolation, however, exposes the islet to variety of cellular stresses, including disruption of the cell-matrix relationship, an event associated with apoptosis. The cell-matrix relationship is characterized by an interaction between cell surface integrin receptors and matrix molecules of the surrounding basement membrane (BM). The purpose of this study was to characterize integrin expression and the distribution of the peri-insular BM in human, porcine, canine, and hamster pancreas, and after routine islet isolation. Whereas islets in the porcine pancreas do not have a demonstrable BM, islets in the human, canine, and hamster pancreas have an almost continuous BM with very little direct exocrine to endocrine cell-cell contact. After islet isolation, the BM was destroyed, only to be reestablished during the period of culture. In the pancreas of all four species, integrin alpha3 was expressed only on islet cells, and integrin alpha5 was present on islet cells as well as on acinar, centroacinar, and duct cells. Integrin alphaV was detected only in human and canine pancreas. Integrin beta1 was demonstrated only in the human pancreas. In isolated islets, integrin alpha3, alpha5, and alphaV expression decreased during the culture period and the intensity of the staining was observed to be coincident with the distribution of the BM. In summary, this is the first report of integrin expression in hamster, canine, porcine, and human islets. After islet isolation, the altered islet cell-matrix relationship is reflected both in the decrease in integrin expression and in the destruction of the peri-insular BM. These profound changes will need to be considered as the process of islet isolation for transplantation is refined. (J Histochem Cytochem 47:499-506, 1999)

Microfabricated immunoisolating biocapsules

A microfabricated silicon-based biocapsule for the immunoisolation of cell transplants is presented. The biocapsule-forming process employs bulk micromachining to define cell-containing chambers within single crystalline silicon wafers. These chambers interface with the surrounding biological environment through polycrystalline silicon filter membranes. The membranes are surface micromachined to present a high density of uniform pores, thus affording sufficient permeability to oxygen, glucose, and insulin. The pore dimensions, as small as 20 nm, are designed to impede the passage of immune molecules and graft-borne viruses. The underlying filter-membrane nanotechnology has been successfully applied in controlled cell culture systems (Ferrari et al., 1995), and is under study for viral elimination in plasma fractionation protocols. Here we report the encouraging results of in vitro experiments investigating the biocompatibility of the microfabricated biocapsule, and demonstrate that encapsulated rat neonatal pancreatic islets significantly outlive and outperform controls in terms of insulin-secretion capability over periods of several weeks. These results appear to warrant further investigations on the potential of cell xenografts encapsulated within microfabricated, immunoisolating environments for the treatment of insulin-dependent diabetes.

Long-term preservation of islets of Langerhans in hydrophilic macrobeads

Several obstacles have hindered the successful transplantation of islets of Langerhans to human patients in efforts to cure type I diabetes mellitus. One problem is the necessity for short- and long-term storage of islets after isolation and before transplantation. Current long-term storage methods, such as incubation in a physiological medium and cryopreservation, are suboptimal, resulting in significant loss of viable islet mass or function. Better storage methods are needed. In this study we examined the long-term storage of rat islets in macrobeads composed of agarose and collagen. Islets isolated from Wistar-Furth rats were placed into macrobeads (1000 islets/macrobead) and maintained in culture for periods of up to 189 days at 37 degrees C. Insulin released from the cultured macrobeads remained constant for periods of at least 154 days. In one group, insulin release was 1050 mU/24 hr/4 beads on day 3 and 1040 mU/24 hr/4 beads on day 154. In another group, insuling release was 1305 Xenotransplantation of Wistar Furth islet macrobeads, stored for 10 to 112 days at 37 degrees C, degrees C into 42 B6AF/1 mice with streptozotocin-induced diabetes resulted in a return to euglycemia in the recipients within 24 hr. Thereafter, euglycemia was maintained for more than 100 days in 32/42 of the recipients, and removal of the macrobeads caused a return to hyperglycemia within 48 hr in all animals. In addition, a group of 7 mice receiving macrobeads containing 1000 islets stored for 84 days had normal glucose tolerance tests (compared with those of 7 nontreated, nontransplanted mice with streptozotocin-induced diabetes and 7 normal mice), demonstrating that the islets in the macrobeads were functioning as they would in an intact pancreas. Finally, 5 macrobeads transplanted after initial storage of 112 days, removed from the first recipient after 100 days or more, stored again for 4 days in vitro, and retransplanted into 5 other diabetic mice also restored and maintained euglycemia for at least 45 days. Our results indicate that collagen-agarose macrobeads are capable of preserving rat pancreatic islets for extended periods without loss of in vitro insulin release capability or ability to achieve and maintain euglycemia in vivo. As such they should be useful for human islet transplantation efforts.

Survival and function of islets during culture

Cell and tissue culture techniques have improved considerably since the first attempts to maintain explants of animal tissue in vitro. The two major developments that have allowed these improvements are the ability to produce continuous cell lines, thus allowing reproducible results to be obtained, and the definition of media for different cell types, thereby reducing the need for supplements of serum and other extraneous extracts. The requirements of islets in culture have been more difficult to define, largely because islets do not proliferate in culture and proliferation rate cannot therefore be used to measure the suitability of the medium. Further difficulties arise because islets are highly metabolically active "mini-organelles." Although many studies have been undertaken to try and optimize media for the culture islets of Langerhans, the media most commonly used are commercially available media developed for other cell types. There remains ample scope for further refinement of the composition of islet culture media, with the possibility of different media for islets from different species.