Insulin-like growth factor II allows prolonged blood glucose normalization with a reduced islet cell mass transplantation

A Gelatin Hydrogel Nonwoven Fabric Enhances Subcutaneous Islet Engraftment in Rats

Although subcutaneous islet transplantation has many advantages, the subcutaneous space is poor in vessels and transplant efficiency is still low in animal models, except in mice. Subcutaneous islet transplantation using a two-step approach has been proposed, in which a favorable cavity is first prepared using various materials, followed by islet transplantation into the preformed cavity. We previously reported the efficacy of pretreatment using gelatin hydrogel nonwoven fabric (GHNF), and the length of the pretreatment period influenced the results in a mouse model. We investigated whether the preimplantation of GHNF could improve the subcutaneous islet transplantation outcomes in a rat model. GHNF sheets sandwiching a silicone spacer (GHNF group) and silicone spacers without GHNF sheets (control group) were implanted into the subcutaneous space of recipients three weeks before islet transplantation, and diabetes was induced seven days before islet transplantation. Syngeneic islets were transplanted into the space where the silicone spacer was removed. Blood glucose levels, glucose tolerance, immunohistochemistry, and neovascularization were evaluated. The GHNF group showed significantly better blood glucose changes than the control group (p < 0.01). The cure rate was significantly higher in the GHNF group (p < 0.05). The number of vWF-positive vessels was significantly higher in the GHNF group (p < 0.01), and lectin angiography showed the same tendency (p < 0.05). The expression of laminin and collagen III around the transplanted islets was also higher in the GHNF group (p < 0.01). GHNF pretreatment was effective in a rat model, and the main mechanisms might be neovascularization and compensation of the extracellular matrices.

A gelatin hydrogel nonwoven fabric improves outcomes of subcutaneous islet transplantation

Subcutaneous islet transplantation is a promising treatment for severe diabetes; however, poor engraftment hinders its prevalence. We previously reported that a recombinant peptide (RCP) enhances subcutaneous islet engraftment. However, it is impractical for clinical use because RCP must be removed when transplanting islets. We herein investigated whether a novel bioabsorbable gelatin hydrogel nonwoven fabric (GHNF) could improve subcutaneous islet engraftment. A silicon spacer with or without GHNF was implanted into the subcutaneous space of diabetic mice. Syngeneic islets were transplanted into the pretreated space or intraportally (Ipo group). Blood glucose, intraperitoneal glucose tolerance, immunohistochemistry, CT angiography and gene expression were evaluated. The cure rate and glucose tolerance of the GHNF group were significantly better than in the control and Ipo groups (p < 0.01, p < 0.05, respectively). In the GHNF group, a limited increase of vWF-positive vessels was detected in the islet capsule, whereas laminin (p < 0.05), collagen III and IV were considerably enhanced. TaqMan arrays revealed a significant upregulation of 19 target genes (including insulin-like growth factor-2) in the pretreated space. GHNF markedly improved the subcutaneous islet transplantation outcomes, likely due to ECM compensation and protection of islet function by various growth factors, rather than enhanced neovascularization.

Bioprinting an Artificial Pancreas for Type 1 Diabetes

PURPOSE OF REVIEW

Pancreatic islet cell transplantation is currently the only curative cell therapy for type 1 diabetes mellitus. However, its potential to treat many more patients is limited by several challenges. The emergence of 3D bioprinting technology from recent advances in 3D printing, biomaterials, and cell biology has provided the means to overcome these challenges.

RECENT FINDINGS

3D bioprinting allows for the precise fabrication of complex 3D architectures containing spatially distributed cells, biomaterials (bioink), and bioactive factors. Different strategies to capitalize on this ability have been investigated for the 3D bioprinting of pancreatic islets. In particular, with co-axial bioprinting technology, the co-printability of islets with supporting cells such as endothelial progenitor cells and regulatory T cells, which have been shown to accelerate revascularization of islets and improve the outcome of various transplantations, respectively, has been achieved. 3D bioprinting of islets for generation of an artificial pancreas is a newly emerging field of study with a vast potential to improve islet transplantation.

IGF2: an endocrine hormone to improve islet transplant survival

In the week following pancreatic islet transplantation, up to 50% of transplanted islets are lost due to apoptotic cell death triggered by hypoxic and pro-inflammatory cytokine-mediated cell stress. Thus, therapeutic approaches designed to protect islet cells from apoptosis could significantly improve islet transplant success. IGF2 is an anti-apoptotic endocrine protein that inhibits apoptotic cell death through the mitochondrial (intrinsic pathway) or via antagonising activation of pro-inflammatory cytokine signalling (extrinsic pathway), in doing so IGF2 has emerged as a promising therapeutic molecule to improve islet survival in the immediate post-transplant period. The development of novel biomaterials coated with IGF2 is a promising strategy to achieve this. This review examines the mechanisms mediating islet cell apoptosis in the peri- and post-transplant period and aims to identify the utility of IGF2 to promote islet survival and enhance long-term insulin independence rates within the setting of clinical islet transplantation.

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.

Insulin-Like growth factor-II (IGF-II) prevents proinflammatory cytokine-induced apoptosis and significantly improves islet survival after transplantation

BACKGROUND

The early loss of functional islet mass (50-70%) due to apoptosis after clinical transplantation contributes to islet allograft failure. Insulin-like growth factor (IGF)-II is an antiapoptotic protein that is highly expressed in β-cells during development but rapidly decreases in postnatal life.

METHODS

We used an adenoviral (Ad) vector to overexpress IGF-II in isolated rat islets and investigated its antiapoptotic action against exogenous cytokines interleukin-1β- and interferon-γ-induced islet cell death in vitro. Using an immunocompromised marginal mass islet transplant model, the ability of Ad-IGF-II-transduced rat islets to restore euglycemia in nonobese diabetic/severe combined immunodeficient diabetic recipients was assessed.

RESULTS

Ad-IGF-II transduction did not affect islet viability or function. Ad-IGF-II cytokine-treated islets exhibited decreased cell death (40% ± 2.8%) versus Ad-GFP and untransduced control islets (63.2% ± 2.5% and 53.6% ± 2.3%, respectively). Ad-IGF-II overexpression during cytokine treatment resulted in a marked reduction in terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive apoptotic cells (8.3% ± 1.4%) versus Ad-GFP control (41% ± 4.2%) and untransduced control islets (46.5% ± 6.2%). Western blot analysis confirmed that IGF-II inhibits apoptosis via activation of the phosphatidylinositol 3-kinase/Akt signaling pathway. Transplantation of IGF-II overexpressing islets under the kidney capsule of diabetic mice restored euglycemia in 77.8% of recipients compared with 18.2% and 47.5% of Ad-GFP and untransduced control islet recipients, respectively (P<0.05, log-rank [Mantel-Cox] test).

CONCLUSIONS

Antiapoptotic IGF-II decreases apoptosis in vitro and significantly improved islet transplant outcomes in vivo. Antiapoptotic gene transfer is a potentially powerful tool to improve islet survival after transplantation.

From cell culture to a cure: pancreatic β-cell replacement strategies for diabetes mellitus

Numerous advances have been made in pancreatic β-cell replacement therapies for diabetes mellitus. While these therapies provide a positive impact and possible cure for the individual recipient, access is limited by availability of donor tissues. The derivation of pluripotent stem cells using efficient differentiation technologies has resulted in the generation of insulin-producing cells with characteristics similar to islet β-cells. Experimental transplantation studies have shown that these cells are capable of reducing hyperglycemia in short-term assays. Novel methodologies that facilitate the neogenesis of β-cells from endogenous hepatic or pancreatic tissue sources are also being investigated as a β-cell replacement strategy. Further research is necessary to protect these transplanted or regenerated cells from diabetic autoimmune pathology.

Encapsulation of protein microfiber networks supporting pancreatic islets

Networks of discrete, genipin-crosslinked gelatin microfibers enveloping pancreatic islets were incorporated within barium alginate microcapsules. This novel technique enabled encapsulation of cellular aggregates in a spherical fibrous matrix <300 μm in diameter. Microfibers were produced by vortex-drawn extrusion within an alginate support matrix. Optimization culminated in a hydrated fiber diameter of 22.3 ± 0.4 μm, a significant reduction relative to that available through current gelatin microfiber spinning techniques, while making the process more reliable and less labor intensive. Microfibers were encapsulated at 40 vol % within 294 ± 4 μm 1.6% barium alginate microparticles by electrostatic-mediated dropwise extrusion. Pancreatic islets extracted from Sprague Dawley rats were encapsulated within the microparticles and analyzed over 21 days. Acridine orange and propidium iodide fluorescent viability staining and light microscopy indicated a significant increase in viability for islets within the fiber-embedded particles relative to fiber-free controls at days 7, 14, and 21. The fiber-embedded system also promoted cellular aggregate cohesion, reducing the incidence of dispersed islet morphologies within the capsules from 31 to 8% at day 21. Further enquiry into benefits of islet encapsulation within a protein fiber network will be the subject of future investigation.

Increased β-cell replication and β-cell mass regeneration in syngeneically transplanted rat islets overexpressing insulin-like growth factor II

Insulin-like growth factor II (IGF2) is a growth-promoting peptide that increases β-cell proliferation and survival. The aim of the study was to determine the effect of IGF2 overexpression on β-cell mass in transplanted islets. Islets infected with adenovirus encoding for IGF2 (Ad-IGF2 group), for luciferase (Ad-Luc control group), or with uninfected islets (control group) were syngeneically transplanted to streptozotocin-diabetic Lewis rats. Eight hundred islets, a minimal mass model to restore normoglycemia, or 500 islets, a clearly insufficient mass, were transplanted. Rats transplanted with 800 Ad-IGF2 islets showed a better metabolic evolution than control groups. As expected, rats transplanted with 500 Ad-IGF2 or control islets maintained similar hyperglycemia throughout the study, ensuring comparable metabolic conditions among both groups. β-Cell replication was higher in Ad-IGF2 group than in control group on days 3 [1.45% (IQR: 0.26) vs. 0.58% (IQR: 0.18), p = 0.006], 10 [1.58% (IQR: 1.40) vs. 0.90% (IQR: 0.61), p = 0.035], and 28 [1.35% (IQR: 0.35) vs. 0.64% (IQR: 0.28), p = 0.004] after transplantation. β-Cell mass was similarly reduced on day 3 after transplantation in Ad-IGF2 and control group [0.36 mg (IQR: 0.26) vs. 0.38 mg (IQR: 0.19)], it increased on day 10, and on day 28 it was higher in Ad-IGF2 than in control group [0.63 mg (IQR: 0.38) vs. 0.42 mg (IQR: 0.31), p = 0.008]. Apoptosis was similarly increased in Ad-IGF2 and control islets after transplantation. No differences in insulin secretion were found between Ad-IGF2 and uninfected control islets. In summary, IGF2 overexpression in transplanted islets increased β-cell replication, induced the regeneration of the transplanted β-cell mass, and had a beneficial effect on the metabolic outcome reducing the β-cell mass needed to achieve normoglycemia.

Pancreatic islet-specific overexpression of Reg3β protein induced the expression of pro-islet genes and protected the mice against streptozotocin-induced diabetes mellitus

Reg family proteins have been implicated in islet β-cell proliferation, survival, and regeneration. The expression of Reg3β (pancreatitis-associated protein) is highly induced in experimental diabetes and acute pancreatitis, but its precise role has not been established. Through knockout studies, this protein was shown to be mitogenic, antiapoptotic, and anti-inflammatory in the liver and pancreatic acinars. To test whether it can promote islet cell growth or survival against experimental damage, we developed β-cell-specific overexpression using rat insulin I promoter, evaluated the changes in normal islet function, gene expression profile, and the response to streptozotocin-induced diabetes. Significant and specific overexpression of Reg3β was achieved in the pancreatic islets of RIP-I/Reg3β mice, which exhibited normal islet histology, β-cell mass, and in vivo and in vitro insulin secretion in response to high glucose yet were slightly hyperglycemic and low in islet GLUT2 level. Upon streptozotocin treatment, in contrast to wild-type littermates that became hyperglycemic in 3 days and lost 15% of their weight, RIP-I/Reg3β mice were significantly protected from hyperglycemia and weight loss. To identify specific targets affected by Reg3β overexpression, a whole genome DNA microarray on islet RNA isolated from the transgenic mice revealed more than 45 genes significantly either up- or downregulated. Among them, islet-protective osteopontin/SPP1 and acute responsive nuclear protein p8/NUPR1 were significantly induced, a result further confirmed by real-time PCR, Western blots, and immunohistochemistry. Our results suggest that Reg3β is unlikely an islet growth factor but a putative protector that prevents streptozotocin-induced damage by inducing the expression of specific genes.

Direct effect of alginate purification on the survival of islets immobilized in alginate-based microcapsules

Alginate purification has been shown to decrease the host immune response to implanted alginate-based microcapsules, but the direct effect of contaminants on islet cell survival remains unknown. Wistar rat islets were immobilized in calcium alginate beads made with crude vs. purified alginate and then incubated in CMRL culture medium. Islet survival was evaluated at 1, 4, 7, 14 and 27 days post-encapsulation. Islet viability was investigated using a dual staining assay (propidium iodide and orange acridine). The islet cell necrosis and the proportion of apoptotic cells were quantified under optical microscopy and with a TUNEL assay, respectively. Islets immobilized in purified alginate were more viable, and had fewer necrotic centers, a smaller area of central necrosis and a lower number of apoptotic cells. At day 14 and 27 post-encapsulation, respectively, 48% and 23% of islets were viable with purified alginate vs. 18% and 8% with crude alginate (p<0.05). At day 14, the surface area of central necrosis and the number of necrotic islets were more important with the impure alginate (65% vs. 45% and 73% vs. 53%, respectively; p<0.05). We conclude that alginate purification improves the survival of islets that are immobilized in alginate-based microcapsules. These findings indicate that caution should be taken in the interpretation of in vivo experiments, as the results could be explained by either a direct effect on islet survival or a modification of the host reaction, or both. Moreover, it suggests that the effect on islet viability should be assessed during the development of biomaterials for cell encapsulation.

Overexpression of Reg3alpha increases cell growth and the levels of cyclin D1 and CDK4 in insulinoma cells

Regenerating gene (Reg) family protein Reg3alpha is normally expressed in pancreatic acinar and endocrine cells. In order to explore its effect on islet beta-cell replication, insulinoma MIN6 cells were stably transfected with murine Reg3alpha cDNA. Determined using real-time PCR and Western blots, the levels of Reg3alpha mRNA and protein in Reg3alpha-transfected clones were increased 10- and 6-fold, respectively. Western blots also revealed that the protein was released into the culture medium, consistent with an endocrine effect. In MTT cell proliferation assay, Reg3alpha-overexpressing cells exhibited a 2-fold increase in the rate of cell growth. In order to investigate the intracellular mechanism, we studied cell cycle regulatory proteins. In Reg3alpha-expressing cells, we detected 2.2- and 2.5-fold increased levels of cyclin D1 and CDK4, respectively, which paralleled a 1.8-fold increase in the rate of Akt phosphorylation. It is established that beta-cell replication is associated with increased cyclin D1 and CDK4 levels; deficiency in CDK4 or cyclin D2 results in reduced beta-cell mass and diabetes. Our results suggest that Reg3alpha stimulates beta-cell replication, by activating Akt kinase and increasing the levels of cyclin D1/CDK4.

Characterization of pancreatic ductal cells in human islet preparations

Substantial amounts of nonendocrine cells are implanted as part of human islet grafts, and a possible influence of nonendocrine cells on clinical islet transplantation outcome has been postulated. There are currently no product release criteria specific for nonendocrine cells due to lack of available methods. The aims of this study were to develop a method for the evaluation of pancreatic ductal cells (PDCs) for clinical islet transplantation and to characterize them regarding phenotype, viability, and function. We assessed 161 human islet preparations using laser scanning cytometry (LSC/iCys) for phenotypic analysis of nonendocrine cells and flow cytometry (FACS) for PDC viability. PDC and beta-cells obtained from different density fractions during the islet cell purification were compared in terms of viability. Furthermore, we examined PDC ability to produce proinflammatory cytokines/chemokines, vascular endothelial growth factor (VEGF) and tissue factor (TF) relevant to islet graft outcome. Phenotypic analysis by LSC/iCys indicated that single staining for CK19 or CA19-9 was not enough for identifying PDCs, and that double staining for amylase and CK19 or CA19-9 allowed for quantitative evaluation of acinar cells and PDC content in human islet preparation. PDC showed a significantly higher viability than beta-cells (PDC vs beta-cell: 75.5+/-13.9 and 62.7+/-18.7%; P<0.0001). Although beta-cell viability was independent of its density, that of PDCs was higher as the density from which they were recovered increased. There was no correlation between PDCs and beta-cell viability (R(2)=0.0078). PDCs sorted from high-density fractions produced significantly higher amounts of proinflammatory mediators and VEGF, but not TF. We conclude that PDCs isolated from different fractions had different viability and functions. The precise characterization and assessment of these cells in addition to beta-cells in human islet cell products may be of assistance in understanding their contribution to islet engraftment and in developing strategies to enhance islet graft function.

Does IGF-I stimulate pancreatic islet cell growth?

Both IGF-I and its receptor (IGF-IR) are specifically expressed in various cell types of the endocrine pancreas. IGF-I has long been considered a growth factor for islet cells as it induces DNA synthesis in a glucose-dependent manner, prevents Fas-mediated autoimmune beta-cell destruction and delays onset of diabetes in non-obese diabetic (NOD) mice. Islet-specific IGF-I overexpression promotes islet cell regeneration in diabetic mice. However, in the last few years, results from most gene-targeted mice have challenged this view. For instance, combined inactivation of insulin receptor and IGF-IR or IGF-I and IGF-II genes in early embryos results in no defect on islet cell development; islet beta-cell-specific inactivation of IGF-IR gene causes no change in beta-cell mass; liver- and pancreatic-specific IGF-I gene deficiency (LID and PID mice) suggests that IGF-I exerts an inhibitory effect on islet cell growth albeit indirectly through controlling growth hormone release or expression of Reg family genes. These results need to be evaluated with potential gene redundancy, model limitations, indirect effects and ligand-receptor cross-activations within the insulin/IGF family. Although IGF-I causes islet beta-cell proliferation and neogenesis directly, what occur in normal physiology, pathophysiology or during development of an organism might be different. Locally produced and systemic IGF-I does not seem to play a positive role in islet cell growth. Rather, it is probably a negative regulator through controlling growth hormone and insulin release, hyperglycemia, or Reg gene expression. These results complicate the perspective of an IGF-I therapy for beta-cell loss.

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

OBJECTIVE

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Activation of the Reg family genes by pancreatic-specific IGF-I gene deficiency and after streptozotocin-induced diabetes in mouse pancreas

We have recently reported that Pdx1-Cre-mediated whole pancreas inactivation of IGF-I gene [in pancreatic-specific IGF-I gene-deficient (PID) mice] results in increased beta-cell mass and significant protection against both type 1 and type 2 diabetes. Because the phenotype is unlikely a direct consequence of IGF-I deficiency, the present study was designed to explore possible activation of proislet factors in PID mice by using a whole genome DNA microarray. As a result, multiple members of the Reg family genes (Reg2, -3alpha, and -3beta, previously not known to promote islet cell growth) were significantly upregulated in the pancreas. This finding was subsequently confirmed by Northern blot and/or real-time PCR, which exhibited 2- to 8-fold increases in the levels of these mRNAs. Interestingly, these Reg family genes were also activated after streptozotocin-induced beta-cell damage and diabetes (wild-type T1D mice) when islet cells were undergoing regeneration. Immunohistochemistry revealed increased Reg proteins in exocrine as well as endocrine pancreas and suggested their potential role in beta-cell neogenesis in PID or T1D mice. Previously, other Reg proteins (Reg1 and islet neogenesis-associated protein) have been shown to promote islet cell replication and neogenesis. These uncharacterized Reg proteins may play a similar but more potent role, not only in normal islet cell growth in PID mice, but also in islet cell regeneration after T1D.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.

Morphological and ultrastructural features of human islet grafts performed in diabetic nude mice

Islet transplantation is a new therapeutic approach to type 1 diabetes mellitus. However, in several patients insulin levels are not restored and the glycemic control is inadequate. To clarify the cause of graft failure, the authors investigated with light and electron microscopy some human islet grafts before and after transplantation under the kidney capsule of streptozotocin-induced diabetic nude mice. In isolated islets, both pre- and post-transplantation, the endocrine component was scarcely represented, the beta/alpha cell ratio was reduced, and beta cells showed degenerative aspects such as apoptosis, immature secretory granules, and amylin fibrils deposition. The authors conclude that islet graft failure may be due to an insufficient beta cell mass related to their distress probably caused by anoxia and/or overstimulation.

Physicochemical model of alginate–poly-l-lysine microcapsules defined at the micrometric/nanometric scale using ATR-FTIR, XPS, and ToF-SIMS

Alginate-poly-L-lysine-alginate (APA) microcapsules are currently being investigated as a means to immuno-isolate transplanted cells, but their biocompatibility is limited. In this study, we verified the hypothesis that poly-L-lysine (PLL), which is immunogenic when unbound, is exposed at the APA microcapsule surface. To do so, we analysed the microcapsule membrane at the micrometric/nanometric scale using attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The results indicate that PLL and alginate molecules interact within the membrane. PLL exists in considerable amounts near the surface, contributing to the majority of the carbon within the outermost 100 Angstroms of the membrane. PLL was also detected at the true surface (the outermost monolayer) of the microcapsules. The exposure of PLL does not appear to result from defects in the outer alginate coating. This physicochemical model of APA microcapsules could explain their immunogenicity and will play an important role in the optimization of the microcapsule design.

Inflammatory response to peritoneal implantation of alginate–poly-l-lysine microcapsules

A thorough understanding of the mechanisms involved in the host reaction to alginate-poly-L-lysine microcapsules (HRM) is important to design methods for the evaluation, selection, and development of biocompatible biomaterials and microcapsules or treatments to control this reaction. The objective of this study was to identify those immune cells and cytokines involved in the pathogenesis of the HRM. The total and differential cell counts were evaluated, and the mRNA expression of TNF-alpha, IL-1beta, IL-6 and TGF-beta1 was measured in peritoneal washings at 3, 17, 48, 96 and 168 h after saline or microcapsule injections. Neutrophil number and IL-1beta and IL-6 m-RNA expression presented an early transient increase, with no differences between saline and microcapsule injections, suggesting a reaction to the procedure. Macrophages, lymphocytes and TNF-alpha were significantly more activated over a longer period of time, after microcapsule implantation than saline injection. They are likely involved in transforming the reaction into a chronic inflammatory process. TGF-beta1 and IL-1beta presented a late (day 7) significant increase after microcapsule but not saline injections. They are likely involved in transforming the reaction into a fibrogenic process. These results suggest that macrophages, lymphocytes, TNF-alpha, IL-1beta and TGF-beta1 play a role in the pathogenesis of the HRM.

Microencapsulation of living cells in semi-permeable membranes with covalently cross-linked layers

Microencapsulation in semi-permeable membranes protects transplanted cells against immune destruction. Microcapsule strength is critical. We describe a method to microencapsulate living cells in alginate-poly-L-lysine (PLL)-alginate membranes with covalent links between adjacent layers of microcapsule membranes, while preserving the desired membrane molecular weight cut-off (MWCO) and microencapsulated cell viability. A heterobifunctional photoactivatable cross-linker, N-5-azido-2-nitrobenzoyloxysuccinimide (ANB-NOS) was used. The N-hydroxysuccinimide ester group of ANB-NOS was covalently linked to PLL. Islets of Langerhans were immobilized in alginate beads, incubated in PLL-ANB-NOS and again in alginate. Upon illumination with UVA, covalent links were created between the phenyl azide residue of ANB-NOS and alginate from both the core bead and the outer coating. Covalently linked microcapsules remained intact after 3 years in a strong alkaline buffer (pH 12), whereas standard microcapsules disappeared within 45 s in the same solution. A standardized mechanical stress broke 22-fold more standard than covalently linked microcapsules. The MWCO and microencapsulated cell viability were similar with standard and covalently linked microcapsules. These microcapsules, extremely resistant to chemical and mechanical stresses, will be useful in numerous applications.

Pancreatic-specific inactivation of IGF-I gene causes enlarged pancreatic islets and significant resistance to diabetes

The dogma that IGF-I stimulates pancreatic islet growth has been challenged by combinational targeting of IGF or IGF-IR (IGF receptor) genes as well as beta-cell-specific IGF-IR gene deficiency, which caused no defect in islet cell growth. To assess the physiological role of locally produced IGF-I, we have developed pancreatic-specific IGF-I gene deficiency (PID) by crossing Pdx1-Cre and IGF-I/loxP mice. PID mice are normal except for decreased blood glucose level and a 2.3-fold enlarged islet cell mass. When challenged with low doses of streptozotocin, control mice developed hyperglycemia after 6 days that was maintained at high levels for at least 2 months. In contrast, PID mice only exhibited marginal hyperglycemia after 12 days, maintained throughout the experiment. Fifteen days after streptozotocin, PID mice demonstrated significantly higher levels of insulin production. Furthermore, streptozotocin-induced beta-cell apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL] assay) was significantly prevented in PID mice. Finally, PID mice exhibited a delayed onset of type 2 diabetes induced by a high-fat diet, accompanied by super enlarged pancreatic islets, increased insulin mRNA levels, and preserved sensitivity to insulin. Our results suggest that locally produced IGF-I within the pancreas inhibits islet cell growth; its deficiency provides a protective environment to the beta-cells and potential in combating diabetes.

Elevated vascular endothelial growth factor production in islets improves islet graft vascularization

Successful islet transplantation depends on the infusion of sufficiently large quantities of islets, of which only approximately 30% become stably engrafted. Rapid and adequate revascularization of transplanted islets is important for islet survival and function. Delayed and insufficient revascularization can deprive islets of oxygen and nutrients, resulting in islet cell death and early graft failure. To improve islet revascularization, we delivered human vascular endothelial growth factor (VEGF) cDNA to murine islets, followed by transplantation under the renal capsule in diabetic mice. Diabetic animals receiving a marginal mass of 300 islets that were pretransduced with a VEGF vector exhibited near normoglycemia. In contrast, diabetic mice receiving an equivalent number of islets that were transduced with a control vector remained hyperglycemic. Immunohistochemistry with anti-insulin and anti-CD31 antibodies revealed a relatively higher insulin content and greater degree of microvasculature in the VEGF vector-transduced islet grafts, which correlated with significantly improved blood glucose profiles and enhanced insulin secretion in response to glucose challenge in this group of diabetic recipient mice. These results demonstrate that VEGF production in islets stimulates graft angiogenesis and enhances islet revascularization. This mechanism might be explored as a novel strategy to accelerate islet revascularization and improve long-term survival of functional islet mass posttransplantation.