Caspase inhibitor therapy enhances marginal mass islet graft survival and preserves long-term function in islet transplantation

Synthesis of siRNA-Conjugated Dextran-Coated Iron Oxide Nanoparticles for Islet Protection During Transplantation and Noninvasive Imaging

Pancreatic islet transplantation (Tx) has a lifesaving potential for type 1 diabetes (T1D) patients. Islet damage during and after transplantation is one of the major reasons hampering its wide clinical application. Inability to monitor transplanted islets also severely limits our understanding of mechanisms regarding declining graft function after transplantation. Our team has proposed to use magnetic nanoparticles conjugated to siRNA (MN-siRNA) to label islets prior to transplantation with two goals in mind: to protect them from damage by silencing harmful genes and to monitor them after transplantation using noninvasive magnetic resonance imaging (MRI). This manuscript provides a step-by-step protocol for the synthesis and characterization of MN-siRNA probes.

A long way to go: caspase inhibitors in clinical use

Caspases are an evolutionary conserved family of cysteine-dependent proteases that are involved in many vital cellular processes including apoptosis, proliferation, differentiation and inflammatory response. Dysregulation of caspase-mediated apoptosis and inflammation has been linked to the pathogenesis of various diseases such as inflammatory diseases, neurological disorders, metabolic diseases, and cancer. Multiple caspase inhibitors have been designed and synthesized as a potential therapeutic tool for the treatment of cell death-related pathologies. However, only a few have progressed to clinical trials because of the consistent challenges faced amongst the different types of caspase inhibitors used for the treatment of the various pathologies, namely an inadequate efficacy, poor target specificity, or adverse side effects. Importantly, a large proportion of this failure lies in the lack of understanding various caspase functions. To overcome the current challenges, further studies on understanding caspase function in a disease model is a fundamental requirement to effectively develop their inhibitors as a treatment for the different pathologies. Therefore, the present review focuses on the descriptive properties and characteristics of caspase inhibitors known to date, and their therapeutic application in animal and clinical studies. In addition, a brief discussion on the achievements, and current challenges faced, are presented in support to providing more perspectives for further development of successful therapeutic caspase inhibitors for various diseases.

Protection of Pancreatic Islets Using Theranostic Silencing Nanoparticles in a Baboon Model of Islet Transplantation

The long-term success of pancreatic islet transplantation (Tx) as a cure for type 1 diabetes remains limited. Islet loss after Tx related to apoptosis, inflammation, and other factors continues to limit Tx efficacy. In this project, we demonstrate a novel approach aimed at protecting islets before Tx in nonhuman primates (NHPs) (baboons) by silencing a gene (caspase-3) responsible for induction of apoptosis. This was done using siRNA (siCas-3) conjugated to magnetic nanoparticles (MNs). In addition to serving as carriers for siCas-3, these nanoparticles also act as reporters for MRI, so islets labeled with MN-siCas-3 can be monitored in vivo after Tx. In vitro studies showed the antiapoptotic effect of MN-siCas-3 on islets in culture, resulting in minimal islet loss. For in vivo studies, donor baboon islets were labeled with MN-siCas-3 and infused into recipient diabetic subjects. A dramatic reduction in insulin requirements was observed in animals transplanted with even a marginal number of labeled islets compared with controls. By demonstrating the protective effect of MN-siCas-3 in the challenging NHP model, this study proposes a novel strategy to minimize the number of donor islets required from either cadaveric or living donors.

Nucleic acid-based theranostics in type 1 diabetes

Application of RNAi interference for type 1 diabetes (T1D) therapy bears tremendous potential. This review will discuss vehicles for oligonucleotide delivery, imaging modalities used for delivery monitoring, therapeutic targets, and different theranostic strategies that can be applied for T1D treatment.

Pan-caspase inhibitor F573 mitigates liver ischemia reperfusion injury in a murine model

Background

Liver ischemia reperfusion injury (IRI) remains a challenge in liver transplantation. A number of compounds have previously demonstrated efficacy in mitigating IRI. Herein, we applied three specific additive strategies to a mouse IRI screening model to determine their relative potencies in reducing such injury, with a view to future testing in a large animal and clinical ex situ normothermic perfusion setting: 1) F573, a pan-caspase inhibitor, 2) anti-inflammatory anakinra and etanrecept and 3) BMX-001, a mimetic of superoxide dismutase.

Methods

A non-lethal liver ischemia model in mice was used. Additives in the treatment groups were given at fixed time points before induction of injury, compared to a vehicle group that received no therapeutic treatment. Mice were recovered for 6 hours following the ischemic insult, at which point blood and tissue samples were obtained. Plasma was processed for transaminase levels. Whole liver tissue samples were processed for histology, markers of apoptosis, oxidative stress, and cytokine levels.

Results

In an in vivo murine IRI model, the F573 treatment group demonstrated statistically lower alanine aminotransferase (ALT) levels (p = 0.01), less evidence of apoptosis (p = 0.03), and lower cytokine levels compared to vehicle. The etanercept with anakinra treatment group demonstrated significantly lower cytokine levels. The BMX-001 group demonstrated significantly decreased apoptosis (p = 0.01) evident on TUNEL staining.

Conclusions

The administration of pan-caspase inhibitor F573 in a murine in vivo model likely mitigates liver IRI based on decreased markers of cellular injury, decreased evidence of apoptosis, and improved cytokine profiles. Anakinra with etanercept, and BMX-001 did not demonstrate convincing efficacy at reducing IRI in this model, and likely need further optimization. The positive findings set rational groundwork for future translational studies of applying F573 during normothermic ex situ liver perfusion, with the aim of improving the quality of marginal grafts.

Evaluation of Z-VAD-FMK as an anti-apoptotic drug to prevent granulosa cell apoptosis and follicular death after human ovarian tissue transplantation

PURPOSE

To evaluate the efficiency of ovarian tissue treatment with Z-VAD-FMK, a broad-spectrum caspase inhibitor, to prevent follicle loss induced by ischemia/reperfusion injury after transplantation.

METHODS

In vitro, granulosa cells were exposed to hypoxic conditions, reproducing early ischemia after ovarian tissue transplantation, and treated with Z-VAD-FMK (50 μM). In vivo, cryopreserved human ovarian fragments (n = 39) were embedded in a collagen matrix containing or not Z-VAD-FMK (50 μM) and xenotransplanted on SCID mice ovaries for 3 days or 3 weeks.

RESULTS

In vitro, Z-VAD-FMK maintained the metabolic activity of granulosa cells, reduced HGL5 cell death, and decreased PARP cleavage. In vivo, no improvement of follicular pool and global tissue preservation was observed with Z-VAD-FMK in ovarian tissue recovered 3-days post-grafting. Conversely, after 3 weeks of transplantation, the primary follicular density was higher in fragments treated with Z-VAD-FMK. This improvement was associated with a decreased percentage of apoptosis in the tissue.

CONCLUSIONS

In situ administration of Z-VAD-FMK slightly improves primary follicular preservation and reduces global apoptosis after 3 weeks of transplantation. Data presented herein will help to guide further researches towards a combined approach targeting multiple cell death pathways, angiogenesis stimulation, and follicular recruitment inhibition.

Anti-Inflammatory Strategies in Intrahepatic Islet Transplantation: A Comparative Study in Preclinical Models

BACKGROUND

The identification of pathway(s) playing a pivotal role in peritransplant detrimental inflammatory events represents the crucial step toward a better management and outcome of pancreatic islet transplanted patients. Recently, we selected the CXCR1/2 inhibition as a relevant strategy in enhancing pancreatic islet survival after transplantation.

METHODS

Here, the most clinically used anti-inflammatory compounds (IL1-receptor antagonist, steroids, and TNF-α inhibitor) alone or in combination with a CXCR1/2 inhibitor were evaluated in their ability to improve engraftment or delay graft rejection. To rule out bias related to transplantation site, we used well-established preclinical syngeneic (250 C57BL/6 equivalent islets in C57BL/6) and allogeneic (400 Balb/c equivalent islets in C57BL6) intrahepatic islet transplantation platforms.

RESULTS

In mice, we confirmed that targeting the CXCR1/2 pathway is crucial in preserving islet function and improving engraftment. In the allogeneic setting, CXCR1/2 inhibitor alone could reduce the overall recruitment of transplant-induced leukocytes and significantly prolong the time to graft rejection both as a single agent and in combination with immunosuppression. No other anti-inflammatory compounds tested (IL1-receptor antagonist, steroids, and TNF-α inhibitor) alone or in combination with CXCR1/2 inhibitor improve islet engraftment and significantly delay graft rejection in the presence of MMF + FK-506 immunosuppressive treatment.

CONCLUSIONS

These findings indicate that only the CXCR1/2-mediated axis plays a crucial role in controlling the islet damage and should be a target for intervention to improve the efficiency of islet transplantation.

Regulated Cell Death Seen through the Lens of Islet Transplantation

Clinical islet transplantation effectively restores euglycemia and corrects glycosylated hemoglobin in labile type 1 diabetes mellitus (T1DM). Despite marked improvements in islet transplantation outcomes, acute islet cell death remains a substantial obstacle that compromises long-term engraftment outcomes. Multiple organ donors are routinely required to achieve insulin independence. Therapeutic agents that ameliorate cell death and/or control injury-related inflammatory cascades offer potential to improve islet transplant success. Apoptotic cell death has been identified as a major contributor to cellular demise and therapeutic strategies that subvert initiation and consequences of apoptotic cell death have shown promise in pre-clinical models. Indeed, in numerous pathologies and diseases apoptosis has been the most extensively described form of regulated cell death. However, recent identification of novel, alternative regulated cell death pathways in other disease states and solid organ transplantation suggest that these additional pathways may also have substantial relevance in islet transplantation. These regulated, non-apoptotic cell death pathways exhibit distinct biochemical characteristics but have yet to be fully characterized within islet transplantation. We review herein the various regulated cell death pathways and highlight their relative potential contributions to islet viability, engraftment failure and islet dysfunction.

Ferroptosis-inducing agents compromise in vitro human islet viability and function

Human islet transplantation has been hampered by donor cell death associated with the islet preparation procedure before transplantation. Regulated necrosis pathways are biochemically and morphologically distinct from apoptosis. Recently, ferroptosis was identified as a non-apoptotic form of iron-dependent regulated necrosis implicated in various pathological conditions. Mediators of islet oxidative stress, including glutathione peroxidase-4 (GPX4), have been identified as inhibitors of ferroptosis, and mechanisms that affect GPX4 function can impact islet function and viability. Ferroptosis has not been investigated directly in human islets, and its relevance in islet transplantation remains unknown. Herein, we sought to determine whether in vitro human islet viability and function is compromised in the presence of two distinct ferroptosis-inducing agents (FIA), erastin or RSL3, and whether these effects could be rescued with ferroptosis inhibitors, ferrostatin-1 (Fer-1), or desferrioxamine (DFO). Viability, as assessed by lactate dehydrogenase (LDH) release, revealed significant death in erastin- and RSL3-treated islets, 20.3% ± 3.8 and 24.4% ± 2.5, 24 h post culture, respectively. These effects were ameliorated in islets pre-treated with Fer-1 or the iron chelator, desferrioxamine (DFO). Stimulation index, a marker of islet function revealed a significant reduction in function in erastin-treated islets (control 1.97 ± 0.13 vs. 50 μM erastin 1.32 ± 0.1) (p < 0.05). Fer-1 and DFO pre-treatment alone did not augment islet viability or function. Pre-treatment of islets with erastin or Fer-1 did not impact in vivo engraftment in an immunodeficient mouse transplant model. Our data reveal that islets are indeed susceptible to ferroptosis in vitro, and induction of this novel cell death modality leads to compromised islet function, which can be recoverable in the presence of the ferroptosis inhibitors. The in vivo impact of this pathway in islet transplantation remains elusive given the constraints of our study, but warrants continued investigation.

Engraftment Site and Effectiveness of the Pan-Caspase Inhibitor F573 to Improve Engraftment in Mouse and Human Islet Transplantation in Mice

BACKGROUND

Islet transplantation is an effective therapy in type 1 diabetes and recalcitrant hypoglycemia. However, there is an ongoing need to circumvent islet loss posttransplant. We explore herein the potential of the pan-caspase inhibitor F573 to mitigate early apoptosis-mediated islet death within portal and extrahepatic portal sites in mice.

METHODS

Mouse or human islets were cultured in standard media ±100 μM F573 and subsequently assessed for viability and apoptosis via terminal deoxynucleotidyl transferase dUTP nick end labeling staining and caspase-3 activation. Diabetic mice were transplanted with syngeneic islets placed under the kidney capsule (KC) or into the subcutaneous deviceless (DL) site at a marginal islet dose (150 islets), or into the portal vein (PV) at a full dose (500 islets). Human islets were transplanted under the KC of diabetic immunodeficient mice at a marginal dose (500 islet equivalents). Islets were cultured in the presence of F573, and F573 was administered subcutaneously on days 0 to 5 posttransplant. Control mice were transplanted with nontreated islets and were injected with saline. Graft function was measured by nonfasting blood glucose and glucose tolerance testing.

RESULTS

F573 markedly reduced human and mouse islet apoptosis after in vitro culture (P < 0.05 and P < 0.05, respectively). Furthermore, F573 improved human islet function when transplanted under the KC (P < 0.05); whereas F573 did not enhance murine islet marginal KC transplants. Conversely, F573 significantly improved mouse islet engraftment in the PV and DL site (P < 0.05 and P < 0.05, respectively).

CONCLUSIONS

The pan-caspase inhibitor F573 markedly reduces human and mouse islet apoptosis and improves engraftment most effectively in the portal and DL subcutaneous sites.

Anti-inflammatory strategies to enhance islet engraftment and survival

Early innate inflammatory reaction strongly affects islet engraftment and survival after intrahepatic transplantation. This early immune response is triggered by ischemia-reperfusion injury and instant blood mediated inflammatory reaction (IBMIR) occurring hours and days after islet infusion. Evidence in both mouse model and in human counterpart suggest the involvement of coagulation, complement system, and proinflammatory chemokines/cytokines. Identification and targeting of pathway(s), playing a role as "master regulator(s)" in post-transplant detrimental inflammatory events, is now mandatory to improve islet transplantation success. This review will focus on inflammatory pathway(s) differentially modulated by islet isolation and mainly associated with the early post-transplant events. Moreover, we will take into account anti-inflammatory strategies that have been tested at 2 levels: on the graft, ex vivo, during islet culture (i.e., donor) and/or on the graft site, in vivo, early after islet infusion (i.e., recipient).

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.

Embedding islet in a liquid scaffold increases islet viability and function

INTRODUCTION

Islet transplantation is a promising strategy to restore efficient insulin regulation in type 1 diabetes mellitus patients. However, shortage of islet donors, poor islet survival and toxicity of immunosuppressants often reduce the graft functional lifetime.

METHODS

We previously showed that a fibroblast populated-collagen matrix (CM) significantly improved engrafted islet viability/function. However, this composite was prone to gradual biodegradation and contraction. Moreover, to avoid use of systemic immunosuppressants, we proposed the use of a local immunosuppressive enzyme, indoleamine-2,3-dioxygenase (IDO). We developed a novel bioengineered crosslinked CM (CCM) to provide optimal matrix biomimetic. Viability and insulin secretory function of islets embedded within fibroblast populated CCM (FP-CCM) was evaluated in vitro and in vivo. IDO expression was transduced in fibroblasts by a lentiviral vector carrying IDO gene and islet viability was evaluated in the presence and absence of IDO producing cells.

RESULTS

Islet survival/function markedly improved within FP-CCM. Furthermore, our data shows that local lentiviral induction of IDO delivered by FP-CCM is nontoxic to the embedded islets.

CONCLUSIONS

This promising finding offers a new approach to improving islet transplant outcome.

Maintenance of islet morphology is beneficial for transplantation outcome in diabetic mice

We have previously shown that co-transplantation of islets and Mesenchymal Stem Cells (MSCs) improves islet graft function and revascularisation, which was associated with the maintenance of normal islet morphology. The aim of the current study was to determine whether maintaining islet morphology in the absence of additional islet-helper cells would improve transplantation outcome in diabetic mice. Islets were isolated from C57BL/6 mice. Recipient streptozotocin-diabetic C57BL/6 mice were transplanted with a minimal mass of 150 islets as a single pellet or islets that were either manually dispersed or dispersed within a matrigel plug beneath the kidney capsule. Blood glucose concentrations were monitored for one month. Islet graft morphology and vascularisation were analysed by histology. Islets dispersed either alone or within matrigel plugs maintained near normal morphology, in contrast to pelleted islets, where individual islets fused to form large endocrine aggregates. The vascularisation of manually dispersed islets and islets dispersed within matrigel plugs was increased relative to respective control pelleted islet grafts. After one month 1/6 mice transplanted with pelleted islets cured compared to 5/6 mice transplanted with manually dispersed islets. The curative capacity of islets dispersed in matrigel was also better than that of pelleted islets (5/8 islet-matrigel implanted mice vs. 1/7 mice transplanted with pelleted islets cured by one month). Therefore, this study demonstrates that the maintenance of islet morphology is associated with improved graft function and revascularisation in diabetic mice.

Inhibition of nuclear factor-κB activation in pancreatic β-cells has a protective effect on allogeneic pancreatic islet graft survival

Pancreatic islet transplantation, a treatment for type 1 diabetes, has met significant challenges, as a substantial fraction of the islet mass fails to engraft, partly due to death by apoptosis in the peri- and post-transplantation periods. Previous evidence has suggested that NF-κB activation is involved in cytokine-mediated β-cell apoptosis and regulates the expression of pro-inflammatory and chemokine genes. We therefore sought to explore the effects of β-cell-specific inhibition of NF-κB activation as a means of cytoprotection in an allogeneic model of islet transplantation. To this end, we used islets isolated from the ToI-β transgenic mouse, where NF-κB signalling can specifically and conditionally be inhibited in β-cells by expressing an inducible and non-degradable form of IκBα regulated by the tet-on system. Our results show that β-cell-specific blockade of NF-κB led to a prolonged islet graft survival, with a relative higher preservation of the engrafted endocrine tissue and reduced inflammation. Importantly, a longer delay in allograft rejection was achieved when mice were systemically treated with the proteasome inhibitor, Bortezomib. Our findings emphasize the contribution of NF-κB activation in the allograft rejection process, and suggest an involvement of the CXCL10/IP-10 chemokine. Furthermore, we suggest a potential, readily available therapeutic agent that may temper this process.

Diabetes Mellitus: New Challenges and Innovative Therapies

Diabetes is a common chronic disease affecting an estimated 285 million adults worldwide. The rising incidence of diabetes, metabolic syndrome, and subsequent vascular diseases is a major public health problem in industrialized countries. This chapter summarizes current pharmacological approaches to treat diabetes mellitus and focuses on novel therapies for diabetes mellitus that are under development.

There is great potential for developing a new generation of therapeutics that offer better control of diabetes, its co-morbidities and its complications. Preclinical results are discussed for new approaches including AMPK activation, the FGF21 target, cell therapy approaches, adiponectin mimetics and novel insulin formulations. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications.

In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality of life in the near future.

mTORC1 and mTORC2 regulate insulin secretion through Akt in INS-1 cells

Regulated associated protein of mTOR (Raptor) and rapamycin-insensitive companion of mTOR (rictor) are two proteins that delineate two different mTOR complexes, mTORC1 and mTORC2 respectively. Recent studies demonstrated the role of rictor in the development and function of β-cells. mTORC1 has long been known to impact β-cell function and development. However, most of the studies evaluating its role used either drug treatment (i.e. rapamycin) or modification of expression of proteins known to modulate its activity, and the direct role of raptor in insulin secretion is unclear. In this study, using siRNA, we investigated the role of raptor and rictor in insulin secretion and production in INS-1 cells and the possible cross talk between their respective complexes, mTORC1 and mTORC2. Reduced expression of raptor is associated with increased glucose-stimulated insulin secretion and intracellular insulin content. Downregulation of rictor expression leads to impaired insulin secretion without affecting insulin content and is able to correct the increased insulin secretion mediated by raptor siRNA. Using dominant-negative or constitutively active forms of Akt, we demonstrate that the effect of both raptor and rictor is mediated through alteration of Akt signaling. Our finding shed new light on the mechanism of control of insulin secretion and production by the mTOR, and they provide evidence for antagonistic effect of raptor and rictor on insulin secretion in response to glucose by modulating the activity of Akt, whereas only raptor is able to control insulin biosynthesis.

Islet transplantation in type 1 diabetes: ongoing challenges, refined procedures, and long-term outcome

Remarkable progress has been made in islet transplantation over a span of 40 years. Once just an experimental curiosity in mice, this therapy has moved forward, and can now provide robust therapy for highly selected patients with type 1 diabetes (T1D), refractory to stabilization by other means. This progress could not have occurred without extensive dynamic international collaboration. Currently, 1,085 patients have undergone islet transplantation at 40 international sites since the Edmonton Protocol was reported in 2000 (752 allografts, 333 autografts), according to the Collaborative Islet Transplant Registry. The long-term results of islet transplantation in selected centers now match registry data of pancreas-alone transplantation, with 6 sites reporting five-year insulin independence rates ≥50%. Islet transplantation has been criticized for the use of multiple donor pancreas organs, but progress has also occurred in single-donor success, with 10 sites reporting increased single-donor engraftment. The next wave of innovative clinical trial interventions will address instant blood-mediated inflammatory reaction (IBMIR), apoptosis, and inflammation, and will translate into further marked improvements in single-donor success. Effective control of auto- and alloimmunity is the key to long-term islet function, and high-resolution cellular and antibody-based assays will add considerable precision to this process. Advances in immunosuppression, with new antibody-based targeting of costimulatory blockade and other T-B cellular signaling, will have further profound impact on the safety record of immunotherapy. Clinical trials will move forward shortly to test out new human stem cell derived islets, and in parallel trials will move forward, testing pig islets for compatibility in patients. Induction of immunological tolerance to self-islet antigens and to allografts is a difficult challenge, but potentially within our grasp.

Alpha 1-antitrypsin reduces inflammation and enhances mouse pancreatic islet transplant survival

The promise of islet cell transplantation cannot be fully realized in the absence of improvements in engraftment of resilient islets. The marginal mass of islets surviving the serial peritransplant insults may lead to exhaustion and thereby contribute to an unacceptably high rate of intermediate and long-term graft loss. Hence, we have studied the effects of treatment with alpha 1-antitrypsin (AAT) in a syngeneic nonautoimmune islet graft model. A marginal number of syngeneic mouse islets were transplanted into nonautoimmune diabetic hosts and islet function was analyzed in control and AAT treated hosts. In untreated controls, marginal mass islet transplants did not restore euglycemia. Outcomes were dramatically improved by short-term AAT treatment. Transcriptional profiling identified 1,184 differentially expressed transcripts in AAT-treated hosts at 3 d posttransplantation. Systems-biology-based analysis revealed AAT down-regulated regulatory hubs formed by inflammation-related molecules (e.g., TNF-α, NF-κB). The conclusions yielded by the systems-biology analysis were rigorously confirmed by QRT-PCR and immunohistology. These data suggest that short-term AAT treatment of human islet transplant recipients may be worthy of a clinical trial.

Caspase inhibitor IDN6556 facilitates marginal mass islet engraftment in a porcine islet autotransplant model

BACKGROUND

Large numbers of islets are lost in the early phase after clinical islet transplantation, through apoptosis, necrosis, or innate inflammatory injury. We previously demonstrated the efficacy of a series of caspase inhibitors in mouse models on islet engraftment through reduction in early posttransplant apoptosis. We studied IDN6556, a caspase inhibitor with a first-pass effect, in a large animal (pig) intraportal marginal mass islet autotransplant model.

METHODS

Total pancreatectomy and marginal mass islet autotransplantation were carried out in Yucatan miniature swine to explore the effects of IDN6556 on islet engraftment. Pigs were treated with IDN6556 at a dose of 20 mg/kg orally twice daily (n=7) or phosphate-buffered saline control (n=6) orally for 7 days, and blood glucose was monitored for 1 month. Glucose tolerance and acute insulin release were determined at 1 month.

RESULTS

There were no differences in islet procurement, isolation, or islet functional parameters between the two groups. Pigs receiving IDN6556 had lower fasting blood glucose level after transplantation and a higher percentage (100% vs. 33.3%) showed fasting blood glucose levels less than 11 mM. This translated into an enhanced metabolic reserve and acute insulin release for pigs in the treatment group.

CONCLUSIONS

IDN6556 led to enhanced islet engraftment in this large animal islet transplant model. Although this study has limitations including a short interval of study (1 month) and the use of unpurified islets, the results justify early clinical trials of IDN6556 in islet transplantation.

Implication of mitochondrial cytoprotection in human islet isolation and transplantation

Islet transplantation is a promising therapy for type 1 diabetes mellitus; however, success rates in achieving both short- and long-term insulin independence are not consistent, due in part to inconsistent islet quality and quantity caused by the complex nature and multistep process of islet isolation and transplantation. Since the introduction of the Edmonton Protocol in 2000, more attention has been placed on preserving mitochondrial function as increasing evidences suggest that impaired mitochondrial integrity can adversely affect clinical outcomes. Some recent studies have demonstrated that it is possible to achieve islet cytoprotection by maintaining mitochondrial function and subsequently to improve islet transplantation outcomes. However, the benefits of mitoprotection in many cases are controversial and the underlying mechanisms are unclear. This article summarizes the recent progress associated with mitochondrial cytoprotection in each step of the islet isolation and transplantation process, as well as islet potency and viability assays based on the measurement of mitochondrial integrity. In addition, we briefly discuss immunosuppression side effects on islet graft function and how transplant site selection affects islet engraftment and clinical outcomes.

Human islets express a marked proinflammatory molecular signature prior to transplantation

In the context of islet transplantation, experimental models show that induction of islet intrinsic NF-κB-dependent proinflammatory genes can contribute to islet graft rejection. Isolation of human islets triggers activation of the NF-κB and mitogen-activated kinase (MAPK) stress response pathways. However, the downstream NF-κB target genes induced in human islets during the isolation process are poorly described. Therefore, in this study, using microarray, bioinformatic, and RTqPCR approaches, we determined the pattern of genes expressed by a set of 14 human islet preparations. We found that isolated human islets express a panel of genes reminiscent of cells undergoing a marked NF-κB-dependent proinflammatory response. Expressed genes included matrix metallopeptidase 1 (MMP1) and fibronectin 1 (FN1), factors involved in tissue remodeling, adhesion, and cell migration; inflammatory cytokines IL-1β and IL-8; genes regulating cell survival including A20 and ATF3; and notably high expression of a set of chemokines that would favor neutrophil and monocyte recruitment including CXCL2, CCL2, CXCL12, CXCL1, CXCL6, and CCL28. Of note, the inflammatory profile of isolated human islets was maintained after transplantation into RAG(-/-) recipients. Thus, human islets can provide a reservoir of NF-κB-dependent inflammatory factors that have the potential to contribute to the anti-islet-graft immune response. To test this hypothesis, we extracted rodent islets under optimal conditions, forced activation of NF-κB, and transplanted them into allogenic recipients. These NF-κB activated islets not only expressed the same chemokine profile observed in human islets but also struggled to maintain normoglycemia posttransplantation. Further, NF-κB-activated islets were rejected with a faster tempo as compared to non-NF-κB-activated rodent islets. Thus, isolated human islets can make cell autonomous contributions to the ensuing allograft response by elaborating inflammatory factors that contribute to their own demise. These data highlight the potential importance of islet intrinsic proinflammatory responses as targets for therapeutic intervention.

Exendin-4 increases the expression of hypoxia-inducible factor-1α in rat islets and preserves the endocrine cell volume of both free and macroencapsulated islet grafts

In this study, we evaluated the effects of exendin-4 on free and encapsulated islet grafts in a rodent model. We also investigated the role of a transcription factor, hypoxia-inducible factor-1 (HIF-1), in mediating the beneficial effects of exendin-4. Diabetic athymic mice were transplanted with free rat islets under the kidney capsule or with macroencapsulated rat islets SC with or without exendin-4, islet preculture (exendin-4 0.1 nM for 20 h), and/or recipient treatment (IP 100 ng/day, day 0-7). The mice were followed for 4 weeks and the graft function and β-cell volume were evaluated. The effects of exendin-4 on islet HIF-1α mRNA and protein expression and on ATP content in a rat insulinoma cell line (INS-1E) were also examined. Preculture with exendin-4 followed by recipient treatment improved the outcome of both free (73% graft function vs. 26% in controls, p = 0.03) and macroencapsulated islet grafts (100% vs. 25% in controls, p = 0.02). In macroencapsulated grafts, the exendin-4-treated group had significantly larger endocrine volume, less graft necrosis, and more blood vessels around the capsule. In rat islets cultured with exendin-4, HIF-1α mRNA and protein expression were significantly enhanced. ATP content was increased in exendin-4-treated INS-1E cells under hypoxic conditions. The improved functional outcome after transplantation of a marginal islet mass with a brief initial treatment with exendin-4 is related to a larger surviving endocrine cell volume. Exendin-4 may improve islet graft resistance to hypoxia during the peritransplant period by increasing the expression of HIF-1α.

Evolution of β-Cell Replacement Therapy in Diabetes Mellitus: Islet Cell Transplantation

Diabetes mellitus remains one of the leading causes of morbidity and mortality worldwide. According to the Centers for Disease Control and Prevention, approximately 23.6 million people in the United States are affected. Of these individuals, 5 to 10% have been diagnosed with Type 1 diabetes mellitus (T1DM), an autoimmune disease. Although it often appears in childhood, T1DM may manifest at any age, leading to significant morbidity and decreased quality of life. Since the 1960s, the surgical treatment for diabetes mellitus has evolved to become a viable alternative to insulin administration, beginning with pancreatic transplantation. While islet cell transplantation has emerged as another potential alternative, its role in the treatment of T1DM remains to be solidified as research continues to establish it as a truly viable alternative for achieving insulin independence. In this paper, the historical evolution, procurement, current status, benefits, risks, and ongoing research of islet cell transplantation are explored.

The caspase inhibitor IDN-6556 (PF3491390) improves marginal mass engraftment after islet transplantation in mice

BACKGROUND

Islet transplantation has become a viable option for selected type 1 diabetic patients; however, a significant portion need to return to exogenous insulin. The predominant factors include impaired islet engraftment and early islet loss. Caspase inhibition is a potent way to improve islet engraftment, but all tested compounds so far have not been clinically relevant. IDN-6556 (PF3491390) has already been used clinically and can be delivered orally with high portal vein concentrations.

METHODS

Mice were given a marginal mass islet graft of either mouse or human islets and treated with either IDN-6556 (10 or 20 mg/kg ip bid) or vehicle and followed for diabetes reversal. At 1 month post-transplant, mice were subjected to a glucose tolerance test and an assessment of graft mass. In separate experiments, human islets were cultured with IDN-6556 or vehicle to assess for islet survival and viability.

RESULTS

In both syngeneic mouse islets and human islets transplanted into immunodeficient mice, IDN-6556 (20 mg/kg) given for 7 days post-transplant led to a significantly enhanced rate of diabetes reversal as compared to vehicle. In addition, mice receiving caspase inhibitor displayed improved glucose tolerance and graft survival at the 1-month point. We also found protective effects in vitro for islet viability and marked reduction in apoptosis in vivo.

CONCLUSION

Taken together, these results demonstrate the effectiveness of caspase inhibition with IDN-6556 on islet transplantation and in particular islet engraftment and survival.

Fibroblast populated collagen matrix promotes islet survival and reduces the number of islets required for diabetes reversal

Islet transplantation represents a viable treatment for type 1 diabetes. However, due to loss of substantial mass of islets early after transplantation, islets from two or more donors are required to achieve insulin independence. Islet-extracellular matrix disengagement, which occurs during islet isolation process, leads to subsequent islet cell apoptosis and is an important contributing factor to early islet loss. In this study, we developed a fibroblast populated collagen matrix (FPCM) as a novel scaffold to improve islet cell viability and function post-transplantation. FPCM was developed by embedding fibroblasts within type-I collagen and used as scaffold for islet grafts. Viability and insulin secretory function of islets embedded within FPCM was evaluated in vitro and in a syngeneic murine islet transplantation model. Islets embedded within acellular matrix or naked islets were used as control. Islet cell survival and function was markedly improved particularly after embedding within FPCM. The composite scaffold significantly promoted islet isograft survival and reduced the critical islet mass required for diabetes reversal by half (from 200 to 100 islets per recipient). Fibroblast embedded within FPCM produced fibronectin and growth factors and induced islet cell proliferation. No evidence of fibroblast over-growth within composite grafts was noticed. These results confirm that FPCM significantly promotes islet viability and functionality, enhances engraftment of islet grafts and decreases the critical islet mass needed to reverse hyperglycemia. This promising finding offers a new approach to reducing the number of islet donors per recipient and improving islet transplant outcome.

Expression of pro- and antiapoptotic molecules of the Bcl-2 family in human islets postisolation

Human islets are subjected to a number of stresses before and during their isolation that may influence their survival and engraftment after transplantation. Apoptosis is likely to be activated in response to these stresses. Apoptosis due to intrinsic stresses is regulated by pro- and antiapoptotic members of the Bcl-2 family. While the role of the Bcl-2 family in apoptosis of rodent islets is becoming increasingly understood, little is known about which of these molecules are expressed or required for apoptosis of human islets. This study investigated the expression of the Bcl-2 family of molecules in isolated human islets. RNA and protein lysates were extracted from human islets immediately postisolation. At the same time, standard quality control assays including viability staining and β-cell content were performed on each islet preparation. Microarrays, RT-PCR, and Western blotting were performed on islet RNA and protein. The prosurvival molecules Bcl-xl and Mcl-1, but not Bcl-2, were highly expressed. The multidomain proapoptotic effector molecule Bax was expressed at higher levels than Bak. Proapoptotic BH3-only molecules were expressed at low levels, with Bid being the most abundant. The proapoptotic molecules BNIP3, BNIP3L, and Beclin-1 were all highly expressed, indicating exposure of islets to oxygen and nutrient deprivation during isolation. Our data provide a comprehensive analysis of expression levels of pro- and antiapoptotic Bcl-2 family members in isolated human islets. Knowledge of which molecules are expressed will guide future research to understand the apoptotic pathways activated during isolation or after transplantation. This is crucial for the design of methods to achieve improved transplantation outcomes.

Influence of microenvironment on engraftment of transplanted β-cells

Pancreatic islet transplantation into the liver provides a possibility to treat selected patients with brittle type 1 diabetes mellitus. However, massive early β-cell death increases the number of islets needed to restore glucose homeostasis. Moreover, late dysfunction and death contribute to the poor long-term results of islet transplantation on insulin independence. Studies in recent years have identified early and late challenges for transplanted pancreatic islets, including an instant blood-mediated inflammatory reaction when exposing human islets to the blood microenvironment in the portal vein and the low oxygenated milieu of islets transplanted into the liver. Poor revascularization of remaining intact islets combined with severe changes in the gene expression of islets transplanted into the liver contributes to late dysfunction. Strategies to overcome these hurdles have been developed, and some of these interventions are now even tested in clinical trials providing a hope to improve results in clinical islet transplantation. In parallel, experimental and clinical studies have, based on the identified problems with the liver site, evaluated the possibility of change of implantation organ in order to improve the results. Site-specific differences clearly exist in the engraftment of transplanted islets, and a more thorough characterization of alternative locations is needed. New strategies with modifications of islet microenvironment with cells and growth factors adhered to the islet surface or in a surrounding matrix could be designed to intervene with site-specific hurdles and provide possibilities to improve future results of islet transplantation.

Novel culture technique involving an histone deacetylase inhibitor reduces the marginal islet mass to correct streptozotocin-induced diabetes

Islet transplantation is limited by the difficulties in isolating the pancreatic islets from the cadaveric donor and maintaining them in culture. To increase islet viability and function after isolation, here we present a novel culture technique involving an histone deacetylase inhibitor (HDACi) to rejuvenate the isolated islets. Pancreatic islets were isolated from Sprague-Dawley (SD) rats and one group (FIs; freshly isolated islets) was used after overnight culture and the other group (RIs; rejuvenated islet) was subjected to rejuvenation culture procedure, which is composed of three discrete steps including degranulation, chromatin remodeling, and regranulation. FIs and RIs were compared with regard to intracellular insulin content, glucose-stimulated insulin secretion (GSIS) capacity, gene expression profile, viability and apoptosis rate under oxidative stresses, and the engraftment efficacy in the xenogeneic islet transplantation models. RIs have been shown to have 1.9 ± 0.28- and 1.7 ± 0.31-fold greater intracellular insulin content and GSIS capacity, respectively, than FIs. HDACi increased overall histone acetylation levels, with inducing increased expression of many genes including insulin 1, insulin 2, GLUT2, and Ogg1. This enhanced islet capacity resulted in more resistance against oxidative stresses and increase of the engraftment efficacy shown by reduction of twofold marginal mass of islets in xenogeneic transplantation model. In conclusion, a novel rejuvenating culture technique using HDACi as chromatin remodeling agents improved the function and viability of the freshly isolated islets, contributing to the reduction of islet mass for the control of hyperglycemia in islet transplantation.

Combined small interfering RNA therapy and in vivo magnetic resonance imaging in islet transplantation

OBJECTIVE

Recent advances in human islet transplantation are hampered by significant graft loss shortly after transplantation and inability to follow islet fate directly. Both issues were addressed by utilizing a dual-purpose therapy/imaging small interfering RNA (siRNA)-nanoparticle probe targeting apoptotic-related gene caspase-3. We expect that treatment with the probe would result in significantly better survival of transplanted islets, which could be monitored by in vivo magnetic resonance imaging (MRI).

RESEARCH DESIGN AND METHODS

We synthesized a probe consisting of therapeutic (siRNA to human caspase-3) and imaging (magnetic iron oxide nanoparticles, MN) moieties. In vitro testing of the probe included serum starvation of the islets followed by treatment with the probe. Caspase-3 gene silencing and protein expression were determined by RT-PCR and Western blot, respectively. In vivo studies included serial MRI of NOD-SCID mice transplanted with MN-small interfering (si)Caspase-3-labeled human islets under the left kidney capsule and MN-treated islets under the right kidney capsule.

RESULTS

Treatment with MN-siCaspase-3 probe resulted in decrease of mRNA and protein expression in serum-starved islets compared with controls. In vivo MRI showed that there were significant differences in the relative volume change between MN-siCaspase-3-treated grafts and MN-labeled grafts. Histology revealed decreased caspase-3 expression and cell apoptosis in MN-siCaspase-3-treated grafts compared with the control side.

CONCLUSIONS

Our data show the feasibility of combining siRNA therapy and in vivo monitoring of transplanted islets in mice. We observed a protective effect of MN-siCaspase-3 in treated islets both in vitro and in vivo. This study could potentially aid in increasing the success of clinical islet transplantation.

ORF3 of porcine circovirus 2 enhances the in vitro and in vivo spread of the of the virus

The ORF3 protein of the pathogenic porcine circovirus 2 (PCV2) causes apoptosis of the virus-infected cells. In PCV2-infected piglets, ORF3 induces B and CD4 T lymphocyte depletion and lymphoid organ destruction and the ORF3-deficient PCV2 is attenuated in its pathogenicity (Virology, 383 (2009), 338). In addition to its role in causing the apoptosis of the immune cells, characteristic of the PCV2 infection associated disease conditions, the ORF3 also plays a role in the systemic dissemination of the PCV2 infection. Our experiments here show that ORF3 expedites the spread of the virus by inducing the early release of the virus from the infected cells. Further, in PCV2-infected mice, the ORF3-induced apoptosis also aids in recruiting macrophages to phagocytize the infected apoptotic cells leading to the systemic dissemination of the infection. The apoptotic activity of the ORF3 of PCV2 hence lends advantage to the spread of the virus.

Caspase activation is not required for villous cytotrophoblast fusion into syncytiotrophoblasts

The villous trophoblast renews itself by fusion of individual stem cells (cytotrophoblasts, CT) with a functional syncytium (syncytiotrophoblast, ST). The literature indicates that fusion occurs with limited activation (proteolytic cleavage) of caspase-8 in CT and is inhibited either by blocking caspase-8 synthesis or inhibiting activation with a caspase-8-specific inhibitor, zIETD. We challenge part of this evidence: inhibition of differentiation with caspase-8 inhibitors. Br-cAMP-stimulated differentiation of isolated CT into multinucleated syncytia in culture is not blocked with three different low molecular weight inhibitors of caspase-8: broad caspase inhibitors zVAD-fmk and qVD-OPh and the caspase-8-specific inhibitor zIETD-fmk. Syncytialization was determined by desmoplakin staining of intracellular boundaries surrounding >2 nuclei and by diffusion within fused cells of long-lived cytoplasmic staining from half of original CT to the unstained half. Differentiation of isolated CT into hCGβ-secreting syncytiotrophoblast was also not blocked by the inhibitors nor was upregulation of hCGβ secretion blocked in ST-stripped and regenerated 5 day explant cultures. The ratio of CT to ST nuclei present was also not changed in explant cultures by caspase inhibitors. The effectiveness of caspase inhibitors was demonstrated by their ability to completely block TNFα-induced apoptosis. We conclude that activation of caspases in general, and caspase-8 in particular, is not required for villous CT differentiation into ST. However, another role of intact caspase-8 (proform) in CT differentiation remains possible.

Caspase inhibitor ZVAD-fmk facilitates engraftment of donor hematopoietic stem cells in intra-bone marrow-bone marrow transplantation

When bone marrow transplantation (BMT) is carried out, survival of the donor hematopoietic stem cells is crucial to maintain donor hematopoiesis in the recipients. We have shown that intra-bone marrow-bone marrow transplantation (IBM-BMT) can induce the rapid recovery of donor hematopoiesis and allow a reduction in radiation doses as a pretreatment for BMT. If IBM-BMT methodology can be further improved, BMT could be carried out more safely and more easily. In this experiment, we attempted to suppress apoptosis of donor hematopoietic cells using a caspase inhibitor, ZVAD-fmk, upon IBM-BMT in mouse allogeneic IBM-BMT. IBM-BMT with ZVAD-fmk induced superior engraftment of donor hematopoietic cells and greater numbers of day-12 colony-forming units of spleen (CFU-S) than IBM-BMT without ZVAD-fmk upon allogeneic BMT (C57BL/6 into BALB/c mice). ZVAD-fmk slightly suppressed apoptosis of whole BMCs, whereas it significantly suppressed apoptosis of c-kit+/Sca-1+/lineage(-) cells (KSL cells) in vitro. These results suggest that ZVAD-fmk can suppress apoptosis of hematopoietic stem cells and/or immature progenitor cells of the donor bone marrow cells, thereby accelerating the donor hematopoiesis.

Prediction of marginal mass required for successful islet transplantation

Islet quality assessment methods for predicting diabetes reversal (DR) following transplantation are needed. We investigated two islet parameters, oxygen consumption rate (OCR) and OCR per DNA content, to predict transplantation outcome and explored the impact of islet quality on marginal islet mass for DR. Outcomes in immunosuppressed diabetic mice were evaluated by transplanting mixtures of healthy and purposely damaged rat islets for systematic variation of OCR/DNA over a wide range. The probability of DR increased with increasing transplanted OCR and OCR/DNA. On coordinates of OCR versus OCR/DNA, data fell into regions in which DR occurred in all, some, or none of the animals with a sharp threshold of around 150-nmol/min mg DNA. A model incorporating both parameters predicted transplantation outcome with sensitivity and specificity of 93% and 94%, respectively. Marginal mass was not constant, depended on OCR/DNA, and increased from 2,800 to over 100,000 islet equivalents/kg body weight as OCR/DNA decreased. We conclude that measurements of OCR and OCR/DNA are useful for predicting transplantation outcome in this model system, and OCR/DNA can be used to estimate the marginal mass required for reversing diabetes. Because human clinical islet preparations in a previous study had OCR/DNA.

Caspase inhibitor therapy synergizes with costimulation blockade to promote indefinite islet allograft survival

OBJECTIVE

Costimulation blockade has emerged as a selective nontoxic maintenance therapy in transplantation. However, these drugs must be combined with other immunomodulatory agents to ensure long-term graft survival.

RESEARCH DESIGN AND METHODS

Recent work has demonstrated that caspase inhibitor therapy (EP1013) prevents engraftment phase islet loss and markedly reduces the islet mass required to reverse diabetes. The "danger" hypothesis suggests that reduction in graft apoptosis should reduce the threshold for immunosuppression and increase the possibility for tolerance induction. Thus, the impact of combination of EP1013 treatment with costimulation blockade (CTLA4-Ig) was investigated in this study.

RESULTS

Islet allografts were completed in fully major histocompatibility complex (MHC)-mismatched mice (Balb/C to B6). When animals received vehicle or EP1013, there was no difference in graft survival. CTLA4-Ig resulted in prolonged graft survival in 40% of the animals, whereas EP1013+CLTA4-Ig resulted in a significant increase in graft survival (91% >180 days; P = 0.01). Ex vivo analysis revealed that animals receiving EP1013 or EP1013+CTLA4-Ig had a reduced frequency of alloreactive interferon (IFN)-gamma-secreting T-cells and an increased frequency of intragraft Foxp3(+) Treg cells. Alloantibody assays indicated that treatment with EP1013 or CTLA4-Ig prevented allosensitization.

CONCLUSIONS

This study suggests that addition of caspase inhibitor therapy to costimulation blockade will improve clinical transplantation by minimizing immune stimulation and thus reduce the requirement for long-term immunosuppressive therapy. The approach also prevents allosensitization, which may be an important component of chronic graft loss in clinical transplantation.

Executioners of apoptosis in pancreatic {beta}-cells: not just for cell death

Pancreatic beta-cell mass is dynamic and is regulated by beta-cell proliferation, neogenesis, and apoptosis. Under physiological conditions, apoptosis is tightly regulated with a slow, net rise in beta-cell mass over time. Excessive beta-cell apoptosis is an important contributor to both type 1 and type 2 diabetes development. Therefore, much effort has been given recently to better understand the mechanisms of apoptosis that occur both during physiological homeostasis and during the course of both types of diabetes. Caspases are the executioners of apoptosis that ultimately result in cell suicide. In mammals, there are 14 caspases, of which many participate in the apoptotic pathways. Genetic mouse models have been important tools for elucidation of the specific apoptotic pathways that play an essential role in beta-cell apoptosis under physiological and pathological conditions. This review focuses on the diverse roles of each of the specific caspases and their regulators, unveiling both the classical apoptotic roles as well as emerging nonapoptotic roles.

Diabetes mellitus: new challenges and innovative therapies

Diabetes mellitus is a widespread disease prevalence and incidence of which increases worldwide. The introduction of insulin therapy represented a major breakthrough in type 1 diabetes; however, frequent hyper- and hypoglycemia seriously affects the quality of life of these patients. New therapeutic approaches, such as whole pancreas transplant or pancreatic islet transplant, stem cell, gene therapy and islets encapsulation are discussed in this review. Regarding type 2 diabetes, therapy has been based on drugs that stimulate insulin secretion (sulphonylureas and rapid-acting secretagogues), reduce hepatic glucose production (biguanides), delay digestion and absorption of intestinal carbohydrate (alpha-glucosidase inhibitors) or improve insulin action (thiazolidinediones). This review is also focused on the newer therapeutically approaches such as incretin-based therapies, bariatric surgery, stem cells and other emerging therapies that promise to further extend the options available. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Some of these therapies rely on genetic modification of non-differentiated cells to express pancreatic endocrine developmental factors, promoting differentiation of non-endocrine cells into β-cells, enabling synthesis and secretion of insulin in a glucose-regulated manner. Alternative therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications. In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality-life and allow personalized therapy-planning in the near future.

Beta cell apoptosis in diabetes

Apoptosis of beta cells is a feature of both type 1 and type 2 diabetes as well as loss of islets after transplantation. In type 1 diabetes, beta cells are destroyed by immunological mechanisms. In type 2 diabetes abnormal levels of metabolic factors contribute to beta cell failure and subsequent apoptosis. Loss of beta cells after islet transplantation is due to many factors including the stress associated with islet isolation, primary graft non-function and allogeneic graft rejection. Irrespective of the exact mediators, highly conserved intracellular pathways of apoptosis are triggered. This review will outline the molecular mediators of beta cell apoptosis and the intracellular pathways activated.

Polyglycolic Acid-islet grafts improve blood glucose and insulin concentrations in rats with induced diabetes

Pancreatic islet transplantation is a promising therapeutic treatment for type 1 diabetes mellitus. In the present study, we cocultured islets with or without a polyglycolic acid (PGA) fibrous scaffold for 5 days and transplanted the PGA-islet grafts into the leg muscles of Wistar rats with streptozotocin-induced diabetes; controls were injected with saline. The results showed that the blood glucose concentrations of the group given islets embedded with the PGA scaffold were lower than those without the scaffold or controls. On the other hand, the insulin content of the PGA-islet group was higher at all 5 time points compared with the insulin contents of the other 2 groups. After transplantation, many islets in the PGA-islet grafts showed normal morphology (as seen under the scanning electron microscope) and were surrounded by red blood cells. A fibrous extracellular matrix was visible around the PGA-islet grafts. These results demonstrated that PGA-islet grafts improved blood glucose and insulin concentrations in rats with induced diabetes.

Pancreatic islet transplantation

BACKGROUND

No formulation of exogenous insulin available to date has yet been able to mimic the physiological nictemeral rhythms of this hormone, and despite all engineering advancements, the theoretical proposal of developing a mechanical replacement for pancreatic beta cell still has not been reached. Thus, the replacement of beta cells through pancreas and pancreatic islet transplantation are the only concrete alternatives for re-establishing the endogenous insulin secretion in type 1 diabetic patients. Since only 1 to 1.5% of the pancreatic mass corresponds to endocrine tissue, pancreatic islets transplantation arises as a natural alternative. Data from the International Islet Transplant Registry (ITR) from 1983 to December 2000 document a total of 493 transplants performed around the world, with progressively worse rates of post-transplant insulin independence. In 2000, the "Edmonton Protocol" introduced several modifications to the transplantation procedure, such as the use of a steroid-free immunosuppression regimen and transplantation of a mean islet mass of 11,000 islet equivalents per kilogram, which significantly improved 1-year outcomes. Although the results of a 5-year follow-up in 65 patients demonstrated improvement in glycemic instability in a significant portion of them, only 7.5% of the patients have reached insulin independence, indicating the need of further advances in the preservation of the function of transplanted islet. In addition to the scarcity of organs available for transplantation, islets transplantation still faces major challenges, specially those related to cell loss during the process of islet isolation and the losses related to the graft site, apoptosis, allorejection, autoimmunity, and immunosuppression. The main strategies to optimize islet transplantation aim at improving all these aspects.

CONCLUSION

Human islet transplantation should be regarded as an intervention that can decrease the frequency of severe hypoglycemic episodes and improve glycemic control in selected patient for whom benefits of 4-5 years duration would be very valuable. Its limitations, however, indicate that the procedure in its current format is not suitable for all patients with type 1 diabetes.

A fibrin gel carrier system for islet transplantation into kidney subcapsule

Islet transplantation is a promising therapeutic option for type 1 diabetes, and actively performed in the clinic as well as in the animal experiments. For the rodent experiments, islet transplantation into kidney subcapsule is widely used to assess islet quality, however, it is often difficult to do using a polyethylene tubing and fine needle because of inherent dead volume of needle and stickiness of the tubing to islets. This problem makes it difficult to interpret the physiological response to different islet doses. Here, we developed a simple fibrin gel carrier system for islet transplantation into kidney subcapsule and utilized it to determine the marginal islet mass sufficient for correction of hyperglycemia in diabetic nude mice.

IL-1beta receptor blockade protects islets against pro-inflammatory cytokine induced necrosis and apoptosis

Pro-inflammatory cytokines (PIC) impair islet viability and function by activating inflammatory pathways that induce both necrosis and apoptosis. The aim of this study was to utilize an in vitro rat islet model to evaluate the efficacy of a clinically approved IL-1 receptor antagonist (Anakinra) in blocking PIC induced islet impairment. Isolated rat islets were cultured for 48 h +/- PIC (IL-1beta, IFNgamma, and TNFalpha) and +/-IL-1ra then assayed for cellular integrity by flow cytometry, MAPK phosphorylation by proteome array, and gene expression by RT-PCR. Nitric oxide (NO) release into the culture media was measured by Griess reaction. Islet functional potency was tested by glucose stimulated insulin secretion (GSIS) and by transplantation into streptozotocin-induced diabetic NOD.scid mice. Rat islets cultured with PIC upregulated genes for NOS2a, COX2, IL6, IL1b, TNFa, and HMOX1. IL-1ra prevented the PIC induced upregulation of all of these genes except for TNFa. Inhibition of PIC induced iNOS by NG-monomethyl-L-arginine (NMMA) only blocked the increased expression of HMOX1. IL-1ra completely abrogated the effects of PIC with respect to NO production, necrosis, apoptosis, mitochondrial dysfunction, GSIS, and in vivo potency. IL-1ra was not effective at preventing the induction of necrosis or apoptosis by exogenous NO. These data demonstrate that Anakinra is an effective agent to inhibit the activation of IL-1beta dependent inflammatory pathways in cultured rat islets and support the extension of its application to human islets in vitro and potentially as a post transplant therapy.

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

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

Human beta-cell precursors mature into functional insulin-producing cells in an immunoisolation device: implications for diabetes cell therapies

BACKGROUND

Islet transplantation is limited by the need for chronic immunosuppression and the paucity of donor tissue. As new sources of human beta-cells are developed (e.g., stem cell-derived tissue), transplanting them in a durable device could obviate the need for immunosuppression, while also protecting the patient from any risk of tumorigenicity. Here, we studied (1) the survival and function of encapsulated human beta-cells and their progenitors and (2) the engraftment of encapsulated murine beta-cells in allo- and autoimmune settings.

METHODS

Human islets and human fetal pancreatic islet-like cell clusters were encapsulated in polytetrafluorethylene devices (TheraCyte) and transplanted into immunodeficient mice. Graft survival and function was measured by immunohistochemistry, circulating human C-peptide levels, and blood glucose levels. Bioluminescent imaging was used to monitor encapsulated neonatal murine islets.

RESULTS

Encapsulated human islet-like cell clusters survived, replicated, and acquired a level of glucose responsive insulin secretion sufficient to ameliorate hyperglycemia in diabetic mice. Bioluminescent imaging of encapsulated murine neonatal islets revealed a dynamic process of cell death followed by regrowth, resulting in robust long-term allograft survival. Further, in the non-obese diabetic (NOD) mouse model of type I diabetes, encapsulated primary beta-cells ameliorated diabetes without stimulating a detectable T-cell response.

CONCLUSIONS

We demonstrate for the first time that human beta-cells function is compatible with encapsulation in a durable, immunoprotective device. Moreover, our study suggests that encapsulation of beta-cells before terminal differentiation will be a successful approach for new cell-based therapies for diabetes, such as those derived from stem cells.

Porcine marginal mass islet autografts resist metabolic failure over time and are enhanced by early treatment with liraglutide

Although insulin independence is maintained in most islet recipients at 1 yr after transplant, extended follow-up has revealed that many patients will eventually require insulin therapy. Previous studies have shown that islet autografts are prone to chronic failure in large animals and humans, suggesting that nonimmunological events contribute to islet graft functional decay. Early intervention with therapies that promote graft stability should provide a measurable benefit over time. In this study, the efficacy of the long-acting glucagon-like peptide-1 analog liraglutide was explored in a porcine marginal mass islet autograft transplant model. Incubation with liraglutide enhanced porcine islet survival and function after prolonged culture. Most vehicle-treated (83%) and liraglutide-treated (80%) animals became insulin independent after islet autotransplantation. Although liraglutide therapy did not improve insulin independence rates or blood glucose levels after transplant, a significant increase in insulin secretion and acute-phase insulin response was observed in treated animals. Surprisingly, no evidence for deterioration of graft function was observed in any of the transplanted animals over more than 18 months of follow-up despite significant weight gain; in fact, an enhanced response to glucose developed over time even in control animals. Histological analysis showed that intraportally transplanted islets remained highly insulin positive, retained alpha-cells, and did not form amyloid deposits. This study demonstrates that marginal mass porcine islet autografts have stable long-term function, even in the presence of an increasing metabolic demand. These results are discrepant with previous large animal studies and suggest that porcine islets may be resistant to metabolic failure.

The role of macrophage migration inhibitory factor in mouse islet transplantation

BACKGROUND

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine produced by many tissues including pancreatic beta-cells.

METHODS

This study investigates the impact of MIF on islet transplantation using MIF knock-out (MIFko) mice.

RESULTS

Early islet function, assessed with a syngeneic marginal islet mass transplant model, was enhanced when using MIFko islets (P<0.05 compared with wild-type [WT] controls). This result was supported by increased in vitro resistance of MIFko islets to apoptosis (terminal deoxynucleotide tranferase-mediated dUTP nick-end labeling assay), and by improved glucose metabolism (lower blood glucose levels, reduced glucose areas under curve and higher insulin release during intraperitoneal glucose challenges, and in vitro in the absence of MIF, P<0.01). The beneficial impact of MIFko islets was insufficient to delay allogeneic islet rejection. However, the rejection of WT islet allografts was marginally delayed in MIFko recipients by 6 days when compared with WT recipient (P<0.05). This effect is supported by the lower activity of MIF-deficient macrophages, assessed in vitro and in vivo by cotransplantation of islet/macrophages. Leukocyte infiltration of the graft and donor-specific lymphocyte activity (mixed lymphocyte reaction, interferon gamma ELISPOT) were similar in both groups.

CONCLUSION

These data indicate that targeting MIF has the potential to improve early function after syngeneic islet transplantation, but has only a marginal impact on allogeneic rejection.

Optimal implantation site for pancreatic islet transplantation

BACKGROUND

Since the first report of successful pancreatic islet transplantation to reverse hyperglycaemia in diabetic rodents, there has been great interest in determining the optimal site for implantation. Although the portal vein remains the most frequently used site clinically, it is not ideal. About half of the islets introduced into the liver die during or shortly after transplantation. Although many patients achieve insulin independence after portal vein infusion of islets, in the long term most resume insulin injections.

METHODS

This review considers possible sites and techniques of islet transplantation in small and large animal models, and in humans. Metabolic, immunological and technical aspects are discussed.

RESULTS AND CONCLUSION

Many groups have sought an alternative site that might offer improved engraftment and long-term survival, together with reduced procedure-related complications. The spleen, pancreas, kidney capsule, peritoneum and omental pouch have been explored. The advantages and disadvantages of various sites are discussed in order to define the most suitable for clinical use and to direct future research.

Protection of human pancreatic islets using a lentiviral vector expressing two genes: cFLIP and GFP

Pancreatic islet transplantation can provide insulin independence to diabetic patients. However, apoptosis of islets often leads to early graft failure. Genetic engineering with protective gene(s) can improve the viability of these cells. Here we show successful transduction of human islets with a feline immunodeficiency virus (FIV) vector expressing both a cytoprotective (cFLIP) gene and the green fluorescent protein (GFP). Despite using low virus titers to maximize safety, transduced islets expressed both genes, resulting in improved beta-cell metabolic activity and viability. Although only approximately 10% of total islet cells were transduced, the significant viability advantages suggest a "barrier" effect in which protecting the periphery of the islet shields the core. These results provide the first demonstration that a lentiviral vector can express two genes in islets. Furthermore, the engineered islets are resistant to a variety of apoptotic stimuli, suggesting the potential of this approach in enhancing the viability of transplanted cells.