Facilitating physiologic self-regeneration: a step beyond islet cell replacement

Comparative gene expression analysis of stemness between periodontal ligament and umbilical cord tissues in humans

Background/purpose

Due to their regenerative potential, periodontal ligament (PDL) and umbilical cord (UBC) tissues are an attractive potential mesenchymal stem cells (MSCs) source. This study compared the expression patterns of genes related to stemness between fresh PDL and UBC tissues.

Materials and methods

PDL tissues were collected from 38 permanent premolars extracted for orthodontic purposes, and UBC tissues were obtained from three newborns. Each sample was immediately frozen to prevent RNA degradation. cDNA microarray analysis, quantitative real-time polymerase chain reaction (PCR), and immunohistochemical staining were performed. Gene expression patterns associated with dental stemness (DS) and induced pluripotent stemness (iPS) were compared between PDL and UBC tissues.

Results

In the cDNA microarray analyses, the expressions of most iPS genes were greater in the PDL than in the UBC. Meanwhile, the expressions of most DS genes were greater in the UBC than in the PDL. Quantitative real-time PCR analyses showed that the expression levels of matrix metallopeptidase 13 (MMP13), ADAM metallopeptidase domain 22 (ADAM22), vascular cell adhesion protein 1 (VCAM1), and kruppel-like factor 4 (KLF4) genes were greater in the PDL than in the UBC, while the expressions of melanoma cell adhesion molecule (MCAM) and activated leukocyte cell adhesion molecule (ALCAM) were greater in the UBC than in the PDL.

Conclusion

These results suggest that UBC and PDL tissues showed slightly different expression patterns of genes related to stemness, which warrants further investigation to use these tissues for future regeneration and implantation therapies.

Targeted Ablation of Pancreatic β Cells in Medaka

The pancreas plays important roles in the regulation of blood glucose, and is a well-studied organ in mammals because its dysfunction causes serious disorders, such as diabetes mellitus. However, mammals have the limited capacity for tissue regeneration in their organs, including pancreas. Fish may be an attractive model for regeneration studies, as fish exhibit a greater capacity for regeneration than do mammals. To elucidate the regenerative capacity of pancreatic β cells in medaka, we generated transgenic lines, in which β cells can be specifically ablated using the nitroreductase (NTR)/metronidazole (Mtz) system. We examined β-cell regeneration at embryonic-larval stages after specific ablation of β cells, and found that medaka rapidly regenerate β cells. Furthermore, we found that teleost-specific secondary islet have a unique feature in that their size increases in response to β-cell ablation in principal islets.

Mechanisms of action of islet neogenesis-associated protein: comparison of the full-length recombinant protein and a bioactive peptide

Islet neogenesis-associated protein (INGAP) was discovered in the partially duct-obstructed hamster pancreas as a factor inducing formation of new duct-associated islets. A bioactive portion of INGAP, INGAP(104-118) peptide (INGAP-P), has been shown to have neogenic and insulin-potentiating activity in numerous studies, including recent phase 2 clinical trials that demonstrated improved glucose homeostasis in both type 1 and type 2 diabetic patients. Aiming to improve INGAP-P efficacy and to understand its mechanism of action, we cloned the full-length protein (rINGAP) and compared the signaling events induced by the protein and the peptide in RIN-m5F cells that respond to INGAP with an increase in proliferation. Here, we show that, although both rINGAP and INGAP-P signal via the Ras/Raf/ERK pathway, rINGAP is at least 100 times more efficient on a molar basis than INGAP-P. For either ligand, ERK1/2 activation appears to be pertussis toxin sensitive, suggesting involvement of a G protein-coupled receptor(s). However, there are clear differences between the peptide and the protein in interactions with the cell surface and in the downstream signaling. We demonstrate that fluorescent-labeled rINGAP is characterized by clustering on the membrane and by slow internalization (≤5 h), whereas INGAP-P does not cluster and is internalized within minutes. Signaling by rINGAP appears to involve Src, in contrast to INGAP-P, which appears to activate Akt in addition to the Ras/Raf/ERK1/2 pathway. Thus our data suggest that interactions of INGAP with the cell surface are important to consider for further development of INGAP as a pharmacotherapy for diabetes.

Cellular and physiological mechanisms of new-onset diabetes mellitus after solid organ transplantation

New-onset diabetes after transplantation is recognized as one of the metabolic consequences which may increase the risk of morbidity and mortality after solid organ transplantation. The pathophysiology of new-onset diabetes after transplantation has not been clearly defined and may resemble that of Type 2 diabetes, characterized by predominantly insulin resistance or defective insulin secretion, or both. This review aims to summarize the current state of knowledge regarding the prevalence, consequences, pathogenesis, and management of new-onset diabetes after transplantation, with a major focus on the possible mechanisms involved in the pathogenesis of the disorder. The aetiology of new-onset diabetes after transplantation is multifactorial, with diabetogenic immunosuppressive drugs playing a major role. Multiple cellular and physiologic mechanisms are involved in the process. Selection of an appropriate maintenance immunosuppressive regimen should involve balancing the risk of patient and graft survival vs. the potential for new-onset diabetes after transplantation.

Differences in self-peptide binding between T1D-related susceptible and protective DR4 subtypes

HLA-DR0401, 0403 and 0405 are associated with variable T1D susceptibilities when linked with a common HLA-DQ8 (DQA1∗0301/DQB1∗0302). It is unknown how the modest differences within the peptide binding regions of DR4 subtypes lead to distinct autoimmune risks. Since all Class II HLA molecules share the same intracellular compartments during biosynthesis, it is possible that DQ and DR compete with one another to bind and present antigenic peptides. As such, it is reasonable to hypothesize that a strong DR4 self-peptide binder down-modulates DQ8 epitope presentation more than a weak one. In this study, we first examined the binding of the peptides derived from two putative beta-cell autoantigens - GAD65 and insulin. Protective DR0403 bound similar number of self-peptides as susceptible DR0401 while highly susceptible DR0405 bound substantially less self-peptides than rest two molecules. Kinetic assays were used to further compare the stability of peptide:DR complexes formed between DR0401, 0403 and selected GAD65 peptides, which also bound DQ8. Two peptides with naturally processed DQ8 epitopes bound protective DR0403 with longer half-life and lower dissociation rate than susceptible DR0401, confirming DR0403 as a better peptide competitor than DR0401. The distinguishing peptide binding features of DR0401, DR0403, and DR0405 highlighted in this study help to explain the hierarchy of genetic associations between T1D and these DR4 subtypes. The enhanced peptide competition of DR0403 leads to a down-modulation of DQ8 epitope presentation, as compared to weak competitors such as DR0401 and DR0405, and therefore contributes to disease protection.

β-cell regeneration: the pancreatic intrinsic faculty

Type I diabetes (T1D) patients rely on cumbersome chronic injections of insulin, making the development of alternate durable treatments a priority. The ability of the pancreas to generate new β-cells has been described in experimental diabetes models and, importantly, in infants with T1D. Here we discuss recent advances in identifying the origin of new β-cells after pancreatic injury, with and without inflammation, revealing a surprising degree of cell plasticity in the mature pancreas. In particular, the inducible selective near-total destruction of β-cells in healthy adult mice uncovers the intrinsic capacity of differentiated pancreatic cells to spontaneously reprogram to produce insulin. This opens new therapeutic possibilities because it implies that β-cells can differentiate endogenously, in depleted adults, from heterologous origins.

Liganded thyroid hormone receptor-alpha enhances proliferation of pancreatic beta-cells

Failure of the functional pancreatic beta-cell mass to expand in response to increased metabolic demand is a hallmark of type 2 diabetes. Lineage tracing studies indicate that replication of existing beta-cells is important for beta-cell proliferation in adult animals. In rat pancreatic beta-cell lines (RIN5F), treatment with 100 nM thyroid hormone (triiodothyronine, T(3)) enhances cell proliferation. This result suggests that T(3) is required for beta-cell proliferation or replication. To identify the role of thyroid hormone receptor alpha (TR(alpha)) in the processes of beta-cell growth and cell cycle regulation, we constructed a recombinant adenovirus vector, AdTR(alpha). Infection with AdTR(alpha) to RIN5F cells increased the expression of cyclin D1 mRNA and protein. Overexpression of the cyclin D1 protein in AdTR(alpha)-infected cells led to activation of the cyclin D1/cyclin-dependent kinase/retinoblastoma protein/E2F pathway, along with cell cycle progression and cell proliferation following treatment with 100 nM T(3). Conversely, lowering cellular cyclin D1 by small interfering RNA knockdown in AdTR(alpha)-infected cells led to down-regulation of the cyclin D1/CDK/Rb/E2F pathway and inhibited cell proliferation. Furthermore, in immunodeficient mice with streptozotocin-induced diabetes, intrapancreatic injection of AdTR(alpha) led to the restoration of islet function and to an increase in the beta-cell mass. These results support the hypothesis that liganded TR(alpha) plays a critical role in beta-cell replication and in expansion of the beta-cell mass during postnatal development. Thus, liganded TR(alpha) may be a target for therapeutic strategies that can induce the expansion and regeneration of beta-cells.

Embryonic stem cell transplantation correlates with endogenous neurogenin 3 expression and pancreas regeneration in streptozotocin-injured mice

Pancreatic beta cell regeneration remains poorly understood, yet stimulation of adult beta cell neogenesis could lead to therapies for type 1 and type 2 diabetes. We studied the effect of embryonic stem (ES) cell transplantation on pancreas regeneration following beta cell injury. Female Balb/c nude mice were treated with streptozotocin to induce hyperglycemia and received an ES cell transplant 24 hr later beneath the renal capsule. Transplantation of ES cells prevented hyperglycemia in a subset of mice, maintaining euglycemia and mild glucose tolerance up to 5 weeks. Pancreata of euglycemic mice showed histological evidence of beta cell regeneration and expression of pancreas and duodenum transcription factor-1 (PDX-1) and neurogenin 3 (Ngn3) in ductal epithelium. Cell tracing analysis indicated that significant beta cell neogenesis from progenitor cells occurred between 2 to 3 weeks following injury in ES cell-transplanted mice but not in sham-transplanted animals. Significantly, whereas pancreas-localized ES cells or their derivatives were adjacent to sites of regeneration, neogenic pancreatic epithelia, including Ngn3+ cells, were endogenous. In conclusion, transplanted ES cells can migrate to the injured pancreas. Transplantation is associated with enhanced endogenous regeneration characterized by expression of Ngn3 and increased beta cell differentiation from endogenous progenitor cells.

Toward a cure for type 1 diabetes mellitus: diabetes-suppressive dendritic cells and beyond

Insulin has been the gold standard therapy for diabetes since its discovery and commercial availability. It remains the only pharmacologic therapy for type 1 diabetes (T1D), an autoimmune disease in which autoreactive T cells specifically kill the insulin-producing beta cells. Nevertheless, not even molecularly produced insulin administered four or five times per day can provide a physiologic regulation able to prevent the complications that account for the morbidity and mortality of diabetic patients. Also, insulin does not eliminate the T1D hallmark: beta-cell-specific autoimmunity. In other words, insulin is not a 'cure'. A successful cure must meet the following criteria: (i) it must either replace or maintain the functional integrity of the natural, insulin-producing tissue, the endocrine islets of Langerhans' and, more specifically, the insulin-producing beta cells; (ii) it must, at least, control the autoimmunity or eliminate it altogether; and (iii) it must be easy to apply to a large number of patients. Criterion 1 has been partially realized by allogeneic islet transplantation. Criterion 2 has been partially realized using monoclonal antibodies specific for T-cell surface proteins. Criterion 3 has yet to be realized, given that most of the novel therapies are currently quasi-patient-specific. Herein, we outline the current status of non-insulin-based therapies for T1D, with a focus on cell-based immunomodulation which we propose can achieve all three criteria illustrated above.

Beta-cell replacement and regeneration: Strategies of cell-based therapy for type 1 diabetes mellitus

Pancreatic islet transplantation has demonstrated that long-term insulin independence may be achieved in patients suffering from diabetes mellitus type 1. However, because of limited availability of islet tissue, new sources of insulin producing cells that are responsive to glucose are required. Development of pancreatic beta-cell lines from rodent or human origin has progressed slowly in recent years. Current experiments for ex vivo expansion of beta cells and in vitro differentiation of embryonic and adult stem cells into insulin producing beta-cell phenotypes led to promising results. Nevertheless, the cells generated to date lack important characteristics of mature beta cells and generally display reduced insulin secretion and loss of proliferative capacity. Therefore, much better understanding of the mechanisms that regulate expansion and differentiation of stem/progenitor cells is necessary. Here, we review recent advances in the identification of potential cellular sources, and the development of strategies to regenerate or fabricate insulin producing and glucose sensing cells that might enable future cell-based therapies of diabetes mellitus type 1.

Cellular therapies for type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a disease that results from the selective autoimmune destruction of insulin-producing beta-cells. This disease process lends itself to cellular therapy because of the single cell nature of insulin production. Murine models have provided opportunities for the study of cellular therapies for the treatment of diabetes, including the investigation of islet transplantation, and also the possibility of stem cell therapies and islet regeneration. Studies in islet transplantation have included both allo- and xeno-transplantation and have allowed for the study of new approaches for the reversal of autoimmunity and achieving immune tolerance. Stem cells from hematopoietic sources such as bone marrow and fetal cord blood, as well as from the pancreas, intestine, liver, and spleen promise either new sources of islets or may function as stimulators of islet regeneration. This review will summarize the various cellular interventions investigated as potential treatments of T1DM.

Increased islet neogenesis without increased islet mass precedes autoimmune attack in diabetes-prone rats

We reported previously that young BioBreeding diabetes-prone (BBdp) rats display increased neogenic extra-islet insulin+ clusters (EICs, <4 insulin+ cells) without an increase in beta-cell mass. Therefore, we investigated the possibility that abnormal islet expansion occurs in BBdp rats before the appearance of islet inflammation. Islet expansion was analyzed in pancreata from 14 to 45 day BBdp and control (BioBreeding control, BBc) rats using immunohistochemistry, morphometry, laser capture microdissection and reverse transcriptase-PCR. mRNA expression for Neurogenin-3, a developmental marker of endocrine progenitors, was three-fold greater in EIC of weanling BBdp and BBc rats compared with islet cells. With increasing age (14-30 days), Neurogenin-3 expression decreased in EIC and increased in islets. In BBdp rats, EIC number and beta-cell proliferation within EIC was greater compared with BBc animals; apoptosis did not differ. The area of small and medium islets in BBdp rats was greater than BBc rats between 14 and 30 days, but this did not result in increased total islet area or beta-cell mass. In addition, the number and area of very large islets was low at 45 days. The frequency of proliferating beta-cells decreased with increasing islet size in BBdp but was constant in BBc rats. Cell cycle analysis of islets revealed more G1 cells and fewer G2 cells in BBdp rats. The ratio of cyclinD2/Cdkn1a, genes that respectively promote or inhibit cell cycle progression, was decreased in BBdp islets. These results suggest that despite increased islet neogenesis, the capacity for islet expansion in diabetes-prone rats is compromised possibly due to decreased proliferative capacity with increasing islet size associated with a partial block at the G1/S cell cycle boundary in islet cells.

Recovery from diabetes in mice by beta cell regeneration

The mechanisms that regulate pancreatic beta cell mass are poorly understood. While autoimmune and pharmacological destruction of insulin-producing beta cells is often irreversible, adult beta cell mass does fluctuate in response to physiological cues including pregnancy and insulin resistance. This plasticity points to the possibility of harnessing the regenerative capacity of the beta cell to treat diabetes. We developed a transgenic mouse model to study the dynamics of beta cell regeneration from a diabetic state. Following doxycycline administration, transgenic mice expressed diphtheria toxin in beta cells, resulting in apoptosis of 70%-80% of beta cells, destruction of islet architecture, and diabetes. Withdrawal of doxycycline resulted in a spontaneous normalization of blood glucose levels and islet architecture and a significant regeneration of beta cell mass with no apparent toxicity of transient hyperglycemia. Lineage tracing analysis indicated that enhanced proliferation of surviving beta cells played the major role in regeneration. Surprisingly, treatment with Sirolimus and Tacrolimus, immunosuppressants used in the Edmonton protocol for human islet transplantation, inhibited beta cell regeneration and prevented the normalization of glucose homeostasis. These results suggest that regenerative therapy for type 1 diabetes may be achieved if autoimmunity is halted using regeneration-compatible drugs.

Specific inhibition of autoimmune T cell transmigration contributes to beta cell functionality and insulin synthesis in non-obese diabetic (NOD) mice

Human diabetes mellitus (IDDM; type I diabetes) is a T cell-mediated disease that is closely modeled in non-obese diabetic (NOD) mice. The pathogenesis of IDDM involves the transmigration of autoimmune T cells into the pancreatic islets and the subsequent destruction of insulin-producing beta cells. Therapeutic interventions leading to beta cell regeneration and the reversal of established IDDM are exceedingly limited. We report here that specific inhibition of T cell intra-islet transmigration by using a small molecule proteinase inhibitor restores beta cell functionality, increases insulin-producing beta cell mass, and alleviates the severity of IDDM in acutely diabetic NOD mice. As a result, acutely diabetic NOD mice do not require insulin injections for survival for a significant time period, thus providing a promising clue to effect IDDM reversal in humans. The extensive morphometric analyses and the measurements of both the C-peptide blood levels and the proinsulin mRNA levels in the islets support our conclusions. Diabetes transfer experiments suggest that the inhibitor specifically represses the T cell transmigration and homing processes as opposed to causing immunosuppression. Overall, our data provide a rationale for the pharmacological control of the T cell transmigration step in human IDDM.

Isolation outcome and functional characteristics of young and adult pig pancreatic islets for transplantation studies

INTRODUCTION

Pig islets have been proposed as an alternative to human islets for clinical use, but their use is limited by rejection. The availability of genetically modified pigs devoid of alpha1,3-galactosyltransferase might provide islets more suitable for xenotransplantation. To limit the costs involved in the logistics and health care of pigs for clinical xenotransplantation, we have studied whether younger, rather than older, pigs that are typically preferred can be used as islet donors.

METHODS

We utilized pancreases from Yorkshire and White Landrace wild-type pigs and alpha1,3-galactosyltransferase gene-knockout pigs of three main different age and size groups: (i) <6 months, (ii) 6 to 12 months, and (iii) >2 yr of age, inclusive of retired breeders. We compared isolation yield and in vitro and in vivo function of islet cells obtained from these groups.

RESULTS

Islets from adult pigs (>2 yr) offered not only higher islet yields, but retained the ability to preserve intact morphology during the isolation process and culture, in association with high functional properties after transplantation. Following isolation, islet cells from young (<6 m) and young-adult (6 to 12 m) pigs dissociated into small aggregates and single cells, and exhibited inferior functional properties than adult islets both in vitro and in vivo.

CONCLUSIONS

These data support the conclusion that, in view of the large number of islets needed to maintain normoglycemia after xenotransplantation, organ-source pigs need to reach adult age (>2 yr) before being considered optimal islet donors, in spite of the higher costs involved.

Pronounced cytosolic aggregation of cellular prion protein in pancreatic beta-cells in response to hyperglycemia

Cellular prion protein (PrP(C)), an N-linked glycoprotein, is expressed in a variety of tissues, but its functions remain unclear. PrP(C) is abundantly expressed in the endocrine pancreas, which regulates blood glucose homeostasis. Therefore, we investigated whether the expression of PrP(C) was altered in islets of Langerhans in a model of spontaneous type 1 diabetes, the diabetes-prone BioBreeding (BBdp) rat and a model of beta-cell adaptation to hyperglycemia, the chronic glucose-infused Sprague Dawley rat. Pancreatic sections from animals aged 7-100 days were stained immunohistochemically and evaluated using light, fluorescence and confocal microscopy. PrP(C) was ubiquitously expressed in all four major endocrine cell types within islets. Surprisingly, cytosolic inclusions containing PrP(C) were identified exclusively in a subpopulation of insulin-producing beta-cells. The inclusions exhibited different molecular characteristics from the PrP aggregates previously described in vitro in neurons. The frequency of beta-cells with PrP(C) inclusions increased with age and was threefold greater in diabetes-prone rats than in controls at 100 days. Cytosolic PrP(C) expression in beta-cells was suppressed whereas the number and size of PrP(C) inclusions markedly increased in response to hyperglycemia during the first 2 days of continuous glucose infusion in Sprague Dawley rats. In summary, this is the first report describing in vivo cytosolic PrP(C) aggregation. These unique PrP(C) inclusions were beta-cell specific, more frequent in diabetes-prone animals, and responded to hyperglycemia in glucose-infused Sprague Dawley rats. These data suggest a potential dysfunction in beta-cells of diabetes-prone rats, and point to new avenues for the study of diabetes pathogenesis.

Targeted ablation of beta cells in the embryonic zebrafish pancreas using E. coli nitroreductase

In order to generate a zebrafish model of beta cell regeneration, we have expressed an Escherichia coli gene called nfsB in the beta cells of embryonic zebrafish. This bacterial gene encodes a nitroreductase (NTR) enzyme, which can convert prodrugs such as metronidazole (Met) to cytotoxins. By fusing nfsB to mCherry, we can simultaneously render beta cells susceptible to prodrug and visualize Met dependent cell ablation. We show that the neighboring alpha and delta cells are unaffected by prodrug treatment and that ablation is beta cell specific. Following drug removal and 36h of recovery, beta cells regenerate. Using ptf1a morphants, it is clear that this beta cell recovery occurs independently of the presence of the exocrine pancreas. Also, by using photoconvertible Kaede to cell lineage trace and BrdU incorporation to label proliferation, we investigate mechanisms for beta regeneration. Therefore, we have developed a unique resource for the study of beta cell regeneration in a living vertebrate organism, which will provide the opportunity to conduct large-scale screens for pharmacological and genetic modifiers of beta cell regeneration.

Modulatory role of DR4- to DQ8-restricted CD4 T-cell responses and type 1 diabetes susceptibility

This study addressed an important biological question, namely how certain HLA molecules modulate the disease risk conferred by other HLA molecules. The HLA molecules under investigation were HLA-DQ8 and -DR4, the two most prevalent HLA class II alleles found in Caucasian type 1 diabetic patients. A panel of human GAD (hGAD65)-specific CD4 T-cell lines and hybridomas was generated to serve as detection reagents for evaluating the peptide occupancy of DQ8 and DR4. Results indicated that DQ8 and DR4 (0401) were able to bind the same hGAD65 peptides. The coexpression of DR4 (0401) diminished DQ8-restricted T-cell responses. In addition, we also demonstrated that the diminished T-cell response varied according to the specific DRB1*04 alleles. Taken together, this study provides evidence that DR4 is able to modulate DQ8-restricted T-cell responses, possibly by competing for peptides. Given that DQ8 is a primary genetic determinant of type 1 diabetes, the decreased DQ8-restricted CD4 T-cell activity due to peptide competition may be the mechanism explaining the modulation effect of DR4 to type 1 diabetes susceptibility.

Rehabilitation of adaptive immunity and regeneration of beta cells

Type 1 Diabetes (T1D) is an autoimmune disease resulting from the destruction of pancreatic insulin-producing beta cells that most frequently occurs in genetically predisposed children. Recent observations illustrating the regenerative capability of the endocrine pancreas in addition to advances in stem cell and gene therapy technologies enable the exploration of alternatives to allogeneic islet transplantation. Living-cell-mediated approaches can abrogate autoimmunity and the consequent destruction of beta cells without the need for immunosuppressive drugs. Such approaches can be used as a foundation for new protocols that more easily translate to the clinical setting. The twin goals of controlling autoimmune disease and promoting stable regeneration of insulin-producing beta cells should be considered the cornerstones of the successful development of a cure for this chronic disease.

Induction of diabetes in cynomolgus monkeys with high-dose streptozotocin: adverse effects and early responses

OBJECTIVES

Streptozotocin (STZ) has been widely used to induce diabetes in nonhuman primates, although it has been found difficult to achieve complete diabetes without serious adverse effects. We have investigated different types and dosages of STZ to find a way to safely induce complete diabetes in cynomolgus monkeys.

METHODS

After adequate hydration, 10 monkeys received STZ. Five monkeys received conventional STZ (Sigma) at a dosage of 1250 mg/m ("high dose"; n = 4) or 60 mg/kg ("low dose"; n = 1; Group 1). Five monkeys received Zanosar STZ (Sicor Pharmaceuticals, Irvine, CA) at 150 mg/kg (high dose; n = 5; Group 2).

RESULTS

High-dose Group 1 monkeys became completely diabetic (n = 4), but a protein-losing nephropathy was observed in 3 of the 4 monkeys. The monkey that received 60 mg/kg STZ failed to become fully diabetic (C-peptide, > 1.86 ng/mL). Group 2 (high-dose Zanosar-treated) monkeys became completely diabetic but with no apparent adverse effects. A triphasic blood glucose response to STZ was documented in all the high-dose STZ-treated monkeys. Low-dose STZ failed to result in a triphasic response.

CONCLUSIONS

(1) High-dose Zanosar STZ induced diabetes safely in cynomolgus monkeys without adverse effects. (2) A triphasic blood glucose response suggested the complete induction of diabetes.

Suitability of human juvenile pancreatic islets for clinical use

AIMS/HYPOTHESIS

The limited availability of deceased donor pancreases suitable for pancreas and islet transplantation calls for a broader utilisation of donor tissue for transplantation purposes. Young donors, representing, fortunately, a minor but significant pool of individuals, have been largely under-employed, mainly because of anatomical and functional incompatibilities with potential recipients. For islet transplantation, the isolation of pancreatic islets from young donors rarely occurs, because of technical problems. As a result of the peculiar characteristics of young donor pancreases, the standard isolation procedure does not allow efficient separation of the islets from the surrounding exocrine tissue, and favours the generation of mantled islets. Nonetheless, young donor islets offer high qualitative and clinically appealing characteristics.

SUBJECTS AND METHODS

We standardised a modified methodology to obtain purified and mantle-free human islets from young donors. This method principally involves efficient delivery of isolation enzyme with reduced mechanical disruption of the pancreas combined with additional filtration steps.

RESULTS

We were able to obtain purified and mantle-free human islets from donors as young as 6 months of age with good morphological and functional properties. The good qualitative characteristics of the islets, evidenced in vitro, were proven in vivo, as they were qualitatively superior to islets of older donors in transplantation studies.

CONCLUSIONS/INTERPRETATION

This study justifies the utilisation of islets derived from young donors for islet transplantation.

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.