Elevation of vascular endothelial growth factor production and its effect on revascularization and function of graft islets in diabetic rats

Harnessing cellular therapeutics for type 1 diabetes mellitus: progress, challenges, and the road ahead

Type 1 diabetes mellitus (T1DM) is a growing global health concern that affects approximately 8.5 million individuals worldwide. T1DM is characterized by an autoimmune destruction of pancreatic β cells, leading to a disruption in glucose homeostasis. Therapeutic intervention for T1DM requires a complex regimen of glycaemic monitoring and the administration of exogenous insulin to regulate blood glucose levels. Advances in continuous glucose monitoring and algorithm-driven insulin delivery devices have improved the quality of life of patients. Despite this, mimicking islet function and complex physiological feedback remains challenging. Pancreatic islet transplantation represents a potential functional cure for T1DM but is hindered by donor scarcity, variability in harvested cells, aggressive immunosuppressive regimens and suboptimal clinical outcomes. Current research is directed towards generating alternative cell sources, improving transplantation methods, and enhancing cell survival without chronic immunosuppression. This Review maps the progress in cell replacement therapies for T1DM and outlines the remaining challenges and future directions. We explore the state-of-the-art strategies for generating replenishable β cells, cell delivery technologies and local targeted immune modulation. Finally, we highlight relevant animal models and the regulatory aspects for advancing these technologies towards clinical deployment.

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Combinatorial islet protective therapeutic approaches in β-cell transplantation: Rationally designed solutions using a target product profile

While progress has been made in the development of islet cell transplantation (ICT) as a viable alternative to the use of exogenous insulin therapy in the treatment of type 1 diabetes, it has not yet achieved its full potential in clinical studies. Ideally, ICT would enable lifelong maintenance of euglycemia without the need for exogenous insulin, blood glucose monitoring or systemic immune suppression. To achieve such an optimal result, therapeutic approaches should simultaneously promote long-term islet viability, functionality, and localized immune protection. In practice, however, these factors are typically tackled individually. Furthermore, while the requirements of optimal ICT are implicitly acknowledged across numerous publications, the literature contains few comprehensive articulations of the target product profile (TPP) for an optimal ICT product, including key characteristics of safety and efficacy. This review aims to provide a novel TPP for ICT and presents promising tried and untried combinatorial approaches that could be used to achieve the target product profile. We also highlight regulatory barriers to the development and adoption of ICT, particularly in the United States, where ICT is only approved for use in academic clinical trials and is not reimbursed by insurance carriers. Overall, this review argues that the clear definition of a TPP in addition to the use of combinatorial approaches could help to overcome the clinical barriers to the widespread adoption of ICT for the treatment of type 1 diabetes.

Effect of bone-shaped nanotube-hydrogel drug delivery system for enhanced osseointegration

Anodic titanium dioxide nanotubes (TNT) have a range of beneficial theranostic properties. However, a lack of effective osseointegration is a problem frequently associated with the titanium dental implant surface. Here, we investigated whether bone-shaped nanotube titanium implants could enhance osseointegration via promoting initial release of vascular endothelial growth factor 165 (VEGF165) and dual release of recombinant human bone morphogenetic protein-2 (rhBMP-2). Thus, we generated cylindrical-shaped nanotubes (TNT1) and bone-shaped nanotubes (TNT2) through voltage-varying and time-varying electrochemical anodization methods, respectively. Additionally, we prepared rhBMP-2-loaded cylindrical-shaped nanotubes/VEGF165-loaded hydrogel (TNT-F1) and rhBMP-2-loaded bone-shaped nanotubes/VEGF165-loaded hydrogel (TNT-F2) drug delivery systems. We evaluated the characteristics and release kinetics of the drug delivery systems, and then analyzed the cytocompatibility and osteogenic differentiation of these specimens with mesenchymal stem cells (MSCs) in vitro. Finally, we utilized a rat femur defect model to test the bone formation capacity of nanotube-hydrogel drug delivery system in vivo. Among these different nanotubes structures, the bone-shaped one was the optimum structure for growth factor release.

Chemokines and their receptors: predictors of the therapeutic potential of mesenchymal stromal cells

Multipotent mesenchymal stromal cells (MSCs) are promising cellular therapeutics for the treatment of inflammatory and degenerative disorders due to their anti-inflammatory, immunomodulatory and regenerative potentials. MSCs can be sourced from a variety of tissues within the body, but bone marrow is the most frequently used starting material for clinical use. The chemokine family contains many regulators of inflammation, cellular function and cellular migration-all critical factors in understanding the potential potency of a novel cellular therapeutic. In this review, we focus on expression of chemokine receptors and chemokine ligands by MSCs isolated from different tissues. We discuss the differential migratory, angiogenetic and immunomodulatory potential to understand the role that tissue source of MSC may play within a clinical context. Furthermore, this is strongly associated with leukocyte recruitment, immunomodulatory potential and T cell inhibition potential and we hypothesize that chemokine profiling can be used to predict the in vivo therapeutic potential of MSCs isolated from new sources and compare them to BM MSCs.

Cell Therapy for Type 1 Diabetes: Current and Future Strategies

PURPOSE OF THE REVIEW

Type 1 diabetes (T1D) is defined by an autoimmune destruction of insulin producing β-cells located in the endocrine part of the pancreas, the islets of Langerhans. As exogenous insulin administration fails at preventing severe complications associated with this disease, cell replacement therapies are being considered as a means to treat T1D. The purpose of this manuscript is to review the challenges associated with current strategies and discuss the potential of stem cell therapy for the treatment of T1D.

RECENT FINDINGS

The most prominent therapy offered to T1D patients is exogenous insulin administration which, despite formulations improvement, remains a suboptimal treatment, due to the frequency of injections and the issues associated with precise dosing. As immunotherapy approaches have remained unsuccessful, the only cure for T1D is transplantation of donor-derived pancreas or islets. However, donor scarcity, graft loss, and immune response to the foreign tissue are issues challenging this approach and limiting the number of patients who can benefit from such treatments. In this review, we discuss the causes of T1D and the shortcomings of the current treatments. Furthermore, we summarize the cutting edge research that aims to tackle the current challenges in reaching a quality-controlled product with long-term effects, with a focus on regenerative medicine approaches using human pluripotent stem cells.

Glial cell-line derived neurotrophic factor protects human islets from nutrient deprivation and endoplasmic reticulum stress induced apoptosis

One of the key limitations to successful human islet transplantation is loss of islets due to stress responses pre- and post-transplantation. Nutrient deprivation and ER stress have been identified as important mechanisms leading to apoptosis. Glial Cell-line Derived Neurotrophic Factor (GDNF) has recently been found to promote islet survival after isolation. However, whether GDNF could rescue human islets from nutrient deprivation and ER stress-mediated apoptosis is unknown. Herein, by mimicking those conditions in vitro, we have shown that GDNF significantly improved glucose stimulated insulin secretion, reduced apoptosis and proinsulin:insulin ratio in nutrient deprived human islets. Furthermore, GDNF alleviated thapsigargin-induced ER stress evidenced by reduced expressions of IRE1α and BiP and consequently apoptosis. Importantly, this was associated with an increase in phosphorylation of PI3K/AKT and GSK3B signaling pathway. Transplantation of ER stressed human islets pre-treated with GDNF under kidney capsule of diabetic mice resulted in reduced expressions of IRE1α and BiP in human islet grafts with improved grafts function shown by higher levels of human C-peptide post-transplantation. We suggest that GDNF has protective and anti-apoptotic effects on nutrient deprived and ER stress activated human islets and could play a significant role in rescuing human islets from stress responses.

Pro-angiogenic Role of Insulin: From Physiology to Pathology

The underlying molecular mechanisms involve in the regulation of the angiogenic process by insulin are not well understood. In this review article, we aim to describe the role of insulin and insulin receptor activation on the control of angiogenesis and how these mechanisms can be deregulated in human diseases. Functional expression of insulin receptors and their signaling pathways has been described on endothelial cells and pericytes, both of the main cells involved in vessel formation and maturation. Consequently, insulin has been shown to regulate endothelial cell migration, proliferation, and in vitro tubular structure formation through binding to its receptors and activation of intracellular phosphorylation cascades. Furthermore, insulin-mediated pro-angiogenic state is potentiated by generation of vascular growth factors, such as the vascular endothelial growth factor, produced by endothelial cells. Additionally, diseases such as insulin resistance, obesity, diabetes, and cancer may be associated with the deregulation of insulin-mediated angiogenesis. Despite this knowledge, the underlying molecular mechanisms need to be elucidated in order to provide new insights into the role of insulin on angiogenesis.

Human multipotent adult progenitor cells enhance islet function and revascularisation when co-transplanted as a composite pellet in a mouse model of diabetes

AIMS/HYPOTHESIS

Hypoxia in the initial days after islet transplantation leads to considerable loss of islet mass and contributes to disappointing outcomes in the clinical setting. The aim of the present study was to investigate whether co-transplantation of human non-endothelial bone marrow-derived multipotent adult progenitor cells (MAPCs), which are non-immunogenic and can secrete angiogenic growth factors during the initial days after implantation, could improve islet engraftment and survival.

METHODS

Islets (150) were co-transplanted, with or without human MAPCs (2.5 × 10⁵) as separate or composite pellets, under the kidney capsule of syngeneic alloxan-induced diabetic C57BL/6 mice. Blood glucose levels were frequently monitored and IPGTTs were carried out. Grafts and serum were harvested at 2 and 5 weeks after transplantation to assess outcome.

RESULTS

Human MAPCs produced high amounts of angiogenic growth factors, including vascular endothelial growth factor, in vitro and in vivo, as demonstrated by the induction of neo-angiogenesis in the chorioallantoic membrane assay. Islet-human MAPC co-transplantation as a composite pellet significantly improved the outcome of islet transplantation as measured by the initial glycaemic control, diabetes reversal rate, glucose tolerance and serum C-peptide concentration compared with the outcome following transplantation of islets alone. Histologically, a higher blood vessel area and density in addition to a higher vessel/islet ratio were detected in recipients of islet-human MAPC composites.

CONCLUSIONS/INTERPRETATION

The present data suggest that co-transplantation of mouse pancreatic islets with human MAPCs, which secrete high amounts of angiogenic growth factors, enhance islet graft revascularisation and subsequently improve islet graft function.

Advances in Local Drug Release and Scaffolding Design to Enhance Cell Therapy for Diabetes

Islet transplant is a curative treatment for insulin-dependent diabetes. However, challenges, including poor tissue survival and a lack of efficient engraftment, must be overcome. An encapsulating or scaffolding material can act as a vehicle for agents carefully chosen for the islet transplant application. From open porous scaffolds to spherical capsules and conformal coatings, greater immune protection is often accompanied by greater distances to microvasculature. Generating a local oxygen supply from the implant material or encouraging vessel growth through the release of local factors can create an oxygenated engraftment site. Intricately related to the vascularization response, inflammatory interaction with the cell supporting implant is a long-standing hurdle to material-based islet transplant. Modulation of the immune responses to the islets as well as the material itself must be considered. To match the post-transplant complexity, the release rate can be tuned to orchestrate temporal responses. Material degradation properties can be utilized in passive approaches or external stimuli and biological cues in active approaches. A combination of multiple carefully chosen factors delivered in an agent-specialized manner is considered by this review to improve the long-term function of islets transplanted in scaffolding and encapsulating materials.

VEGF-conjugated alginate hydrogel prompt angiogenesis and improve pancreatic islet engraftment and function in type 1 diabetes

Type 1 diabetes was a life-long disease that affected numerous people around the world. Insulin therapy has its limitations that may involve hyperglycemia and heavy burden of patient by repeated dose. Islet transplantation emerged as a promising approach to reach periodical reverse of diabetes, however, transplanted islets suffer from foreign body reaction and lack of nutrition and oxygen supply, especially in the blood-vessel-shortage subcutaneous site which was preferred by patient and surgeon. In this study, we designed and synthesized a vascular endothelial growth factor (VEGF) conjugated alginate material to encapsulate the transplanted islets via 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) reaction, and successful conjugation was confirmed by Nuclear Magnetic Resonance H1 spectrum. The best VEGF concentration (100ng/ml) was determined by the combined studies of the mechanical property and endothelial cell growth assay. In vivo study, conjugated VEGF on alginate exhibited sustained promoting angiogenesis property after subcutaneous transplantation by histology study and islets encapsulated in this material achieved long term therapeutic effect (up to 50days) in the diabetic mice model. In conclusion, this study establishes a simple biomaterial strategy for islet transplantation to enhance islet survival and function, which could be a feasible therapeutic alternative for type 1 diabetes.

Engineered VEGF-releasing PEG-MAL hydrogel for pancreatic islet vascularization

Biofunctionalized polyethylene glycol maleimide (PEG-MAL) hydrogels were engineered as a platform to deliver pancreatic islets to the small bowel mesentery and promote graft vascularization. VEGF, a potent stimulator of angiogenesis, was incorporated into the hydrogel to be released in an on-demand manner through enzymatic degradation. PEG-MAL hydrogel enabled extended in vivo release of VEGF. Isolated rat islets encapsulated in PEG-MAL hydrogels remained viable in culture and secreted insulin. Islets encapsulated in PEG-MAL matrix and transplanted to the small bowel mesentery of healthy rats grafted to the host tissue and revascularized by 4 weeks. Addition of VEGF release to the PEG-MAL matrix greatly augmented the vascularization response. These results establish PEG-MAL engineered matrices as a vascular-inductive cell delivery vehicle and warrant their further investigation as islet transplantation vehicles in diabetic animal models.

Inducible VEGF expression by human embryonic stem cell-derived mesenchymal stromal cells reduces the minimal islet mass required to reverse diabetes

Islet transplantation has been hampered by loss of function due to poor revascularization. We hypothesize that co-transplantation of islets with human embryonic stem cell-derived mesenchymal stromal cells that conditionally overexpress VEGF (hESC-MSC:VEGF) may augment islet revascularization and reduce the minimal islet mass required to reverse diabetes in mice. HESC-MSCs were transduced by recombinant lentiviruses that allowed conditional (Dox-regulated) overexpression of VEGF.

HESC-MSC

VEGF were characterized by tube formation assay. After co-transplantation of hESC-MSC:VEGF with murine islets in collagen-fibrin hydrogel in the omental pouch of diabetic nude mice, we measured blood glucose, body weight, glucose tolerance and serum C-peptide. As control, islets were transplanted alone or with non-transduced hESC-MSCs. Next, we compared functional parameters of 400 islets alone versus 200 islets co-transplanted with hESC-MSC:VEGF. As control, 200 islets were transplanted alone. Metabolic function of islets transplanted with hESC-MSC:VEGF significantly improved, accompanied by superior graft revascularization, compared with control groups. Transplantation of 200 islets with hESC-MSC:VEGF showed superior function over 400 islets alone. We conclude that co-transplantation of islets with VEGF-expressing hESC-MSCs allowed for at least a 50% reduction in minimal islet mass required to reverse diabetes in mice. This approach may contribute to alleviate the need for multiple donor organs per patient.

A silk-based encapsulation platform for pancreatic islet transplantation improves islet function in vivo

The success of pancreatic islet (PI) transplantation is challenged by PI functional damage during the peritransplantation period. A silk-based encapsulation platform including mesenchymal stromal cells (MSCs) was evaluated for islet cell delivery in vivo. Islet equivalents (IEQs) were transplanted into the epididymal fat pads of mice with streptozotocin-induced diabetes. Three PI combinations were tested: (A) co-encapsulated in silk with MSCs; (b) encapsulated in silk alone; or (c) pelleted. Blood glucose levels were monitored and intraperitoneal glucose tolerance test (IPGTT) was performed upon return to euglycaemia. Grafts were removed for histology and cytokine content analysis. Mice with PI grafts in silk showed a prompt return to euglycaemia. IPGTT was significantly improved with PI in silk with MSCs, compared to PI in silk alone or pelleted. Both Th₁ and Th₂ cytokines were increased in PI grafts in silk, but Th₁ cytokines were decreased significantly with PI and MSC co-encapsulation. Histological analysis showed osteogenesis and chondrogenesis in the silk grafts containing MSCs. Future studies will evaluate MSC stability and function in vivo and improve silk biocompatibility for applications in islet transplantation. Copyright © 2015 John Wiley & Sons, Ltd.

PEG-maleimide hydrogels for protein and cell delivery in regenerative medicine

Protein- and cell-based therapies represent highly promising strategies for regenerative medicine, immunotherapy, and oncology. However, these therapies are significantly limited by delivery considerations, particularly in terms of protein stability and dosing kinetics as well as cell survival, engraftment, and function. Hydrogels represent versatile and robust delivery vehicles for proteins and cells due to their high water content that retains protein biological activity, high cytocompatibility and minimal adverse host reactions, flexibility and tunability in terms of chemistry, structure, and polymerization format, ability to incorporate various biomolecules to convey biofunctionality, and opportunity for minimally invasive delivery as injectable carriers. This review highlights recent progress in the engineering of poly(ethylene glycol) hydrogels cross-linked using maleimide reactive groups for protein and cell delivery.

Small islets transplantation superiority to large ones: implications from islet microcirculation and revascularization

Pancreatic islet transplantation is a promising therapy to regain glycemic control in diabetic patients. The selection of ideal grafts is the basis to guarantee short-term effectivity and longevity of the transplanted islets. Contradictory to the traditional notion, recent findings implied the superiority of small islets for better transplantation outcomes rather than the large and intact ones. However, the mechanisms remain to be elucidated. Recent evidences emphasized the major impact of microcirculation on islet β -cell mass and function. And potentials in islet graft revascularization are crucial for their survival and preserved function in the recipient. In this study, we verified the distinct histological phenotype and functionality of small islets versus large ones both in vitro and in vivo. With efforts to exploring the differences in microcirculation and revascularization of islet grafts, we further evaluated local expressions of angiotensin and vascular endothelial growth factor A (VEGF-A) at different levels. Our findings reveal that, apart from the higher density of insulin-producing β -cells, small islets express less angiotensin and more angiotrophic VEGF-A. We therefore hypothesized a logical explanation of the small islet superiority for transplantation outcome from the aspects of facilitated microcirculation and revascularization intrinsically in small islets.

The endocrine role between β cells and intra-islet endothelial cells

The islets of Langerhans is the endocrine function region of pancreas, which exist in five cell types. The majority of endocrine cells are insulin-secreting β cells, mixed up with glucagon-secreting α-cells. The islets of Langerhans are highly vascularized, and the capillary network around the islet is about five times denser than that in the exocrine tissues. It guarantees endocrine cells adequately contact with the capillary networks. Above mentioned is the basis of deep study the interaction between β cells and capillary. Increasing number of studies contribute to the consensus that endothelial cells have positive effects in the islet microenvironment. Endothelial cells can act as endocrine cells which release many active substances, such as hepatocyte growth factors (HGF), thrombospondin-1(TSP-1), laminins, and collagens by means of different molecule pathways, inducing β cells differentiation, proliferation, survivor, and insulin release next to the vessels. Apart from the effect of endothelial cells on β cells by paracrine fashion, the islets can utilize VEGF-A, angiopoietin-1 and insulin signaling to increase the interaction with endothelial cells. As the endocrine role of endothelial cells to β cells, it may be a novel target to stimulate β cells regeneration, promote vascularization post islet transplantation strategy in the treatment of diabetes mellitus.

Bioengineered sites for islet cell transplantation

Although islet transplantation has demonstrated its potential use in treating type 1 diabetes, this remains limited by the need for daily immunosuppression. Islet encapsulation was then proposed with a view to avoiding any immunosuppressive regimen and related side effects. In order to obtain a standard clinical procedure in terms of safety and reproducibility, two important factors have to be taken into account: the encapsulation design (which determines the graft volume) and the implantation site. Indeed, the implantation site should meet certain requirements: (1) its space must be large enough for the volume of transplanted tissues; (2) there must be proximity to abundant vascularization with a good oxygen supply; (3) there must be real-time access to physiologically representative blood glucose levels; (4) there must be easy access for implantation and the reversibility of the procedure (for safety); and finally, (5) the site should have minimal early inflammatory reaction and promote long-term survival. The aim of this article is to review possible preclinical/clinical implantation sites (in comparison with free islets) for encapsulated islet transplantation as a function of the encapsulation design: macro/microcapsules and conformal coating.

Vasculogenic bio-synthetic hydrogel for enhancement of pancreatic islet engraftment and function in type 1 diabetes

Type 1 diabetes (T1DM) affects one in every 400 children and adolescents in the US. Due to the limitations of exogenous insulin therapy and whole pancreas transplantation, pancreatic islet transplantation has emerged as a promising therapy for T1DM. However, this therapy is severely limited by donor islet availability and poor islet engraftment and function. We engineered an injectable bio-synthetic, polyethylene glycol-maleimide hydrogel to enhance vascularization and engraftment of transplanted pancreatic islets in a mouse model of T1DM. Controlled presentation of VEGF-A and cell-adhesive peptides within this engineered material significantly improved the vascularization and function of islets delivered to the small bowel mesentery, a metabolically relevant site for insulin release. Diabetic mice receiving islets transplanted in proteolytically degradable hydrogels incorporating VEGF-A exhibited complete reversal of diabetic hyperglycemia with a 40% reduction in the number of islets required. Furthermore, hydrogel-delivered islets significantly improved weight gain, regulation of a glucose challenge, and intra-islet vascularization and engraftment compared to the clinical standard of islet infusion through the hepatic portal vein. This study establishes a simple biomaterial strategy for islet transplantation to promote enhanced islet engraftment and function.

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.

Harnessing the immunomodulatory and tissue repair properties of mesenchymal stem cells to restore β cell function

Islet cell transplantation has therapeutic potential to cure type 1 diabetes (T1D), which is characterized by autoimmune-mediated destruction of insulin-producing β cells. However, current success rates are limited by long-term decline in islet graft function resulting partially from poor revascularization and immune destruction. Mesenchymal stem cells (MSCs) have the potential to enhance islet transplantation and prevent disease progression by a multifaceted approach. MSCs have been shown to be effective at inhibiting inflammatory-mediated immune responses and at promoting tissue regeneration. The immunomodulatory and tissue repairing properties of MSCs may benefit β cell regeneration in the context of T1D. This review will elucidate how MSCs can minimize β cell damage by providing survival signals and simultaneously modulate the immune response by inhibiting activation, and proliferation of several immune cell types. In addition, MSCs can enhance islet graft revascularization, maintaining long-term β cell viability and function.

Pluripotent stem cell-derived pancreatic β-cells: potential for regenerative medicine in diabetes

Diabetes mellitus, which affects 346 million people, is one of the leading causes of death worldwide. Pancreatic β-cells, existing in the islets of Langerhans, play central roles in the progression of diabetes. An efficient strategy to produce functional pancreatic β-cells is important for both transplantation therapy and disease modeling of diabetes. Human pluripotent stem cells, including human embryonic stem cells and induced pluripotent stem cells, provide unlimited starting materials to generate differentiated cells for regenerative studies. Significant progress has been made in human embryonic/induced pluripotent stem cell differentiation in the last several years. However, efficient generation of mature pancreatic β-cells with complete functional capabilities has not yet been accomplished. Here, we review recent successes as well as the technical and theoretical challenges in the use of pluripotent stem cell-derived pancreatic β-cells for disease modeling and replacement therapy of diabetes.

Mussel-inspired immobilization of vascular endothelial growth factor (VEGF) for enhanced endothelialization of vascular grafts

Most polymeric vascular prosthetic materials have low patency rate for replacement of small diameter vessels (<5 mm), mainly due to failure to generate healthy endothelium. In this study, we present polydopamine-mediated immobilization of growth factors on the surface of polymeric materials as a versatile tool to modify surface characteristics of vascular grafts potentially for accelerated endothelialization. Polydopamine was deposited on the surface of biocompatible poly(L-lactide-co-ε-caprolactone) (PLCL) elastomer, on which vascular endothelial growth factor (VEGF) was subsequently immobilized by simple dipping. Surface characteristics and composition were investigated by using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Immobilization of VEGF on the polydopamine-deposited PLCL films was effective (19.8 ± 0.4 and 197.4 ± 19.7 ng/cm(2) for DPv20 and DPv200 films, respectively), and biotin-mediated labeling of immobilized VEGF revealed that the fluorescence intensity increased as a function of the concentration of VEGF solution. The effect of VEGF on adhesion of HUVECs was marginal, which may have been masked by polydopamine layer that also enhanced cell adhesion. However, VEGF-immobilized substrate significantly enhanced proliferation of HUVECs for over 7 days of in vitro culture and also improved their migration. In addition, immobilized VEGF supported robust cell to cell interactions with strong expression of CD 31 marker. The same process was effective for immobilization of basic fibroblast growth factor, demonstrating the robustness of polydopamine layer for secondary ligation of growth factors as a simple and novel surface modification strategy for vascular graft materials.

Mesenchymal stem cells and islet cotransplantation in diabetic rats: improved islet graft revascularization and function by human adipose tissue-derived stem cells preconditioned with natural molecules

Hypoxia plays an important role in limiting the engraftment, survival, and function of intrahepatically transplanted islets. Mesenchymal stem cells (MSCs) were recently used in animal models of islet transplantation not only to reduce allograft rejection but also to promote revascularization. Among different possible origins, adipose tissue represents a novel and good source of MSCs. Moreover, the capability of adipose tissue-derived stem cells (ASCs) to improve islet graft revascularization was recently reported after hybrid transplantation in mice. Within this context, we have previously shown that hyaluronan esters of butyric and retinoic acids can significantly enhance the rescuing potential of human MSCs (hMSCs). Here we evaluated whether ex vivo preconditioning of human ASCs (hASCs) with a mixture of hyaluronic (HA), butyric (BU), and retinoic (RA) acids may result in optimization of graft revascularization after islet/stem cell intrahepatic cotransplantation in syngeneic diabetic rats. We demonstrated that hASCs exposed to the mixture of molecules are able to increase the secretion of vascular endothelial growth factor (VEGF) as well as the transcription of angiogenic genes, including VEGF, KDR (kinase insert domain receptor), and hepatocyte growth factor (HGF). Rats transplanted with islets cocultured with preconditioned hASCs exhibited a better glycemic control than rats transplanted with an equal volume of islets and control hASCs. Cotransplantation with preconditioned hASCs was also associated with enhanced islet revascularization in vivo, as highlighted by graft morphological analysis. The observed increase in islet graft revascularization and function suggests that our method of stem cell preconditioning may represent a novel strategy to remarkably improve the efficacy of islets-hMSCs cotransplantation.

Maternal protein malnutrition does not impair insulin secretion from pancreatic islets of offspring after transplantation into diabetic rats

Pancreatic islets from adult rats whose mothers were protein restricted during lactation undersecrete insulin. The current work analyzes whether this secretory dysfunction can be improved when the pancreatic islets are grafted into hyperglycemic diabetic rats. Two groups of rats were used: the adult offspring from dams that received a low protein diet (4%) during the initial 2/3 of lactation (LP) and, as a control, the adult offspring from dams that consumed a normal protein diet (23%) during the entire period of lactation (NP). Islets from NP- and LP-rats were transplanted into diabetic recipient rats, which were generated by streptozotocin treatment. The islets were transplanted via the portal vein under anesthesia. The fed blood glucose levels were monitored during the 4 days post-transplantation. Transplanted islets from LP-rats (T LP) decreased the fed glucose levels of diabetic rats 34% (21.37±0.24 mM, p<0.05); however, the levels still remained 2-fold higher than those of the sham-operated controls (6.88±0.39 mM, p<0.05). Grafts with NP-islets (T NP) produced the same effect as the LP-islets in diabetic rats. The high fasting blood glucose levels of diabetic rats were improved by the transplantations. Islet grafts from both rat groups recovered 50% of the retroperitoneal fat mass of the diabetic rats (0.55±0.08 g/100 g of body weight for T NP and 0.56±0.07 g/100 g of body weight for T LP, p<0.05). Because pancreatic islets from both the NP- and LP-rats were able to regulate fasting blood glucose concentrations in hyperglycemic rats, we propose that the altered function of pancreatic islets from LP-rats is not permanent.

Islet transplantation in rodents. Do encapsulated islets really work?

CONTEXT

Diabetes mellitus type I affects around 240 million people in the world and only in the USA 7.8% of the population. It has been estimated that the costs of its complications account for 5% to 10% of the total healthcare spending around the world. According to World Health Organization, 300 million people are expected to develop diabetes mellitus by the year 2025. The pancreatic islet transplantation is expected to be less invasive than a pancreas transplant, which is currently the most commonly used approach.

OBJECTIVES

To compare the encapsulated and free islet transplantation in rodents looking at sites of islet implantation, number of injected islets, viability and immunosuppression.

METHODS

A literature search was conducted using MEDLINE/PUBMED and SCIELO with terms about islet transplantation in the rodent from 2000 to 2010. We found 2,636 articles but only 56 articles from 2000 to 2010 were selected.

RESULTS

In these 56 articles used, 34% were encapsulated and 66% were nonencapsulated islets. Analyzing both types of islets transplantation, the majority of the encapsulated islets were implanted into the peritoneal cavity and the nonencapsulated islets into the liver, through the portal vein. In addition, the great advantage of the peritoneal cavity as the site of islet transplantation is its blood supply. Both vascular endothelial cells and vascular endothelial growth factor were used to stimulate angiogenesis of the islet grafts, increasing the vascularization rapidly after implantation. It also has been proven that there is influence of the capsules, since the larger the capsule more chances there are of central necrosis. In some articles, the use of immunosuppression demonstrated to increase the life expectancy of the graft.

CONCLUSION

While significant progress has been made in the islets transplantation field, many obstacles remain to be overcome. Microencapsulation provides a means to transplant islets without immunosuppressive agents and may enable the performance of xenotransplantation. The use of alternative donor sources, fewer islets per capsule and the appropriate deployment location, such as the peritoneal cavity, may give a future perspective to the application of immunoprotective capsules and viability in clinical practice. A variety of strategies, such as genetic engineering, co-encapsulation, improvement in oxygen supply or the establishment of hypoxia resistance will also improve the islet transplantation performance. It remains to be determined which combination of strategies with encapsulation can fulfill the promise of establishing a simple and safe transplantation as a cure for diabetes.

Bone marrow-derived mesenchymal stem cells enhance cryopreserved trachea allograft epithelium regeneration and vascular endothelial growth factor expression

BACKGROUND

Epithelium regeneration and revascularization of tracheal implants are challenging issues to be solved in tracheal transplantation research. Bone marrow-derived mesenchymal stem cells (BMSCs) can migrate to the damaged tissue and promote functional restoration. Here, we applied intravenous transplantation of BMSCs combined with a cryopreserved allograft to investigate the role of BMSCs in enhancing implant survival, tracheal epithelium regeneration and revascularization.

METHODS

After transplantation with cryopreserved allografts, PKH-26 labeled 3 to 5 passage BMSCs were injected into recipient rats through the tail vein. Rats in the control groups were injected with a comparable amount of phosphate-buffered saline. We observed the histology of the tracheal allograft and measured vascular endothelial growth factor (VEGF) protein levels in the epithelium to evaluate the effect of BMSCs on epithelium regeneration and revascularization.

RESULTS

Histologic observation of the rats from the BMSCs injection groups showed that the tracheal lumen was covered by pseudostriated ciliated columnar epithelium. The cartilage structure was intact. There were no signs of denaturation or necrosis. PKH-26 labeled BMSCs migrated to the implant site and exhibited red fluorescence, with the brightest red fluorescence at the anastomotic site. VEGF protein levels in the allograft epithelium of the BMSCs injection group were higher than the levels in the phosphate-buffered saline injection group.

CONCLUSIONS

Our results indicate that given systemic administration, BMSCs may enhance epithelium regeneration and revascularization by upregulating VEGF expression.

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.

Improvement of Rat Islet Viability during Transplantation: Validation of Pharmacological Approach to Induce VEGF Overexpression

Delayed and insufficient revascularization during islet transplantation deprives islets of oxygen and nutrients, resulting in graft failure. Vascular endothelial growth factor (VEGF) could play a critical role in islet revascularization. We aimed to develop pharmacological strategies for VEGF overexpression in pancreatic islets using the iron chelator deferoxamine (DFO), thus avoiding obstacles or safety risks associated with gene therapy. Rat pancreatic islets were infected in vivo using an adenovirus (ADE) encoding human VEGF gene (4.108 pfu/pancreas) or were incubated in the presence of DFO (10 μmol/L). In vitro viability, functionality, and the secretion of VEGF were evaluated in islets 1 and 3 days after treatment. Infected islets or islets incubated with DFO were transplanted into the liver of syngenic diabetic rats and the graft efficiency was estimated in vivo by measuring body weight, glycemia, C-peptide secretion, and animal survival over a period of 2 months. DFO induced transient VEGF overexpression over 3 days, whereas infection with ADE resulted in prolonged VEGF overexpression lasting 14 days; however, this was toxic and decreased islet viability and functionality. The in vivo study showed a decrease in rat deaths after the transplantation of islets treated with DFO or ADE compared with the sham and control group. ADE treatment improved body weight and C-peptide levels. Gene therapy and DFO improved metabolic control in diabetic rats after transplantation, but this effect was limited in the presence of DFO. The pharmacological approach is an interesting strategy for improving graft efficiency during transplantation, but this approach needs to be improved with drugs that are more specific.

Creation of a prevascularized site for cell transplantation in rats

INTRODUCTION

Transplanted cells, especially islet cells, are likely to become apoptotic due to local hypoxia leading to graft dysfunction. Isolated pancreatic islet cells depend on the diffusion of oxygen from the surrounding tissue; therefore, access to sufficient oxygen supply is beneficial, particularly when microcapsules are used for immunoisolation in xenotransplantation. The aim of this study was to create a prevascularized site for cell transplantation in rats and test its effectiveness with microencapsulated HEK293 cells.

METHODS

The combination of implantation of a foam dressing, vacuum-assisted wound closure (foam+VAC) and hyperbaric oxygenation (HBO) was used in 40 Sprague-Dawley rats. Blood flow and vascular endothelial growth factor (VEGF) levels were determined. Sodium cellulose sulphate (SCS)-microencapsulated HEK293 cells were xenotransplanted into the foam dressing in rats pre-treated with HBO, and angiogenesis and apoptosis were assessed.

RESULTS

Vessel ingrowth and VEGF levels increased depending on the duration of HBO treatment. The area containing the foam was perfused significantly better in the experimental groups when compared to controls. Only a small amount of apoptosis occurs in SCS-microencapsulated HEK293 cells after xenotransplantation.

CONCLUSION

As ischemia-damaged cells are likely to undergo cell death or loose functionality due to hypoxia, therefore leading to graft dysfunction, the combination foam+VAC and HBO might be a promising method to create a prevascularized site to achieve better results in xenogeneic cell transplantation.

Effect of hypoxia-inducible VEGF gene expression on revascularization and graft function in mouse islet transplantation

For gene transfer strategies to improve islet engraftment, vascular endothelial growth factor (VEGF) expression should be regulated in a way that matches the transient nature of revascularization with simultaneously avoiding undesirable effects of overexpression. The aim of this study was to investigate the effects of hypoxia-inducible VEGF gene transfer using the RTP801 promoter on islet grafts. We implanted pSV-hVEGF transfected, pRTP801-hVEGF transfected or nontransfected mouse islets under the kidney capsule of streptozotocin-induced diabetic syngeneic mice. Human VEGF immunostaining of day 3 grafts revealed that the pRTP801-hVEGF transfected group had higher hVEGF expression compared with the pSV-hVEGF transfected group. BS-1 staining of day 3 grafts from the pRTP801-hVEGF transfected group showed the highest vascular density, which was comparable with day 6 grafts from the nontransfected group. In 360 islet equivalent (IEQ)-transplantation which reverted hyperglycemia in all mice, the area under the curve of glucose levels during intraperitoneal glucose tolerance test 7 weeks post-transplant was lower in mice transplanted with pRTP801-hVEGF transfected grafts compared with mice transplanted with nontransfected grafts. In 220 IEQ-transplantations, diabetic mice transplanted with pRTP801-hVEGF islets became normoglycemic more rapidly compared with mice transplanted with pSV-hVEGF or nontransfected islets, and diabetes reversal rate after 50 days was 90%, 68%, and 50%, respectively. In conclusion, our results indicate that regulated overexpression of hVEGF in a hypoxia-inducible manner enhances islet vascular engraftment and preserves islet function overtime in transplants.

Engineering more than a cell: vascularization strategies in tissue engineering

Host integration and performance of engineered tissues have been severely limited by the lack of robust strategies to generate patent vascularization and tissue perfusion. This review highlights a selection of exciting developments in vascularization approaches for tissue engineering research. Current strategies for vascularization in tissue engineering are related to growth factor signaling and delivery, cell transplantation, bioactive smart matrix materials, and directed fabrication. Application of these techniques to in vivo models has resulted in a number of robust host vascular responses, especially with synergistic and engineered bioactive systems. The future outlook of the field includes refinement and development of new technologies for vascularization and combining these techniques with functional repair models for metabolically active tissues and relevant disease states.

Trophic molecules derived from human mesenchymal stem cells enhance survival, function, and angiogenesis of isolated islets after transplantation

BACKGROUND

Mesenchymal stem cells (MSCs), also known as multipotent progenitor cells, release several factors that support cell survival and enhance wound healing. We hypothesized that MSC-secreted molecules would induce a trophic effect in pancreatic islet culture conditions.

METHODS

Pancreatic islets were co-cultured with MSCs, and ADP/ATP ratios, glucose stimulated insulin secretion (GSIS), and DNA fragmentation were evaluated to measure islet quality and viability in vitro. The induction of signal molecules related to the control of survival, function, and angiogenesis was also analyzed. Cell quality assays, DNA fragmentation assays, and islet transplantation into streptozotocin-induced diabetic mice were performed using MSC-conditioned medium (CM)-cultured islets. Furthermore, we identified soluble molecules within MSC-CM.

RESULTS

Islets co-cultured with MSCs demonstrated lower ADP/ATP ratios, and higher GSIS indexes and viability. Furthermore, co-cultured islets revealed higher levels of anti-apoptotic signal molecules (X-linked inhibitor of apoptosis protein, Bcl-xL, Bcl-2, and heat shock protein-32) and demonstrated increased vascular endothelial growth factor receptor 2 and Tie-2 mRNA expression and increased levels of phosphorylated Tie-2 and focal adhesion kinase protein. Islets cultured in MSC-CM demonstrated lower ADP/ATP ratios, less apoptosis, and a higher GSIS indexes. Diabetic mice that received islet transplants (200 islet equivalent) cultured in MSC-CM for 48 hr demonstrated significantly lower blood glucose levels and enhanced blood vessel formation. In addition, interleukin-6, interleukin-8, vascular endothelial growth factor-A, hepatocyte growth factor, and transforming growth factor-beta were detected at significant levels in MSC-CM.

CONCLUSIONS

These results suggest that the trophic factors secreted by human MSCs enhance islet survival and function after transplantation.

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.

Influence of human allogenic bone marrow and cord blood-derived mesenchymal stem cell secreting trophic factors on ATP (adenosine-5'-triphosphate)/ADP (adenosine-5'-diphosphate) ratio and insulin secretory function of isolated human islets from cadaveric donor

Successful islet transplantation (ITx) is not only dependent on the number of islets, but also their quality, including viability, metabolic activity, and function. Islet quality decreases during cultivation after the isolation procedure. To overcome this obstacle, we established the practice of islet and mesenchymal stem cells (MSCs) coculture. This coculture condition improved the ATP (adenosine-5'-triphosphate)/ADP (adenosine-5'-diphosphate) ratio and insulin secretory function in vitro. It is believed that the enhancement of islet quality in islet-MSCs cocultures may be caused by the secretion of active agents by MSCs. Herein we have shown that interleukin-6 (IL-6), vascular endothelial growth factor-A (VEGF-A), hepatocyte growth factor (HGF), and transforming growth factor-beta (TGF-beta) were significantly increased as measured by enzyme-linked immunosorbent assay (ELISA) in MSCs-cultured medium, factors that have been shown to improve the survival, function, and angiogenesis/revascularization of islets. These results indicated that the quality of human islets was enhanced by trophic molecules secreted by MSCs, which influence the intracellular islet ATP content and insulin secretory function.

Effect of renin angiotensin system blockade on the islet microvessel density of diabetic rats and its relationship with islet function

To investigate the effects of rennin angiotensin system blockade on the microvessel density in islets of diabetic rats and its relationship with islet function, diabetes model was created by feeding of high-caloric laboratory chow plus intraperitoneal injection of a small dose of streptozotocin (30 mg/kg). After 8 weeks intervention with perindopril (AE, n=10) or valsartan (AR, n=10), the islet function of the animals was evaluated by intravenous insulin release test (IVIRT). The pancreases were immunohistochemically stained to analyze the content of insulin and vascular endothelial growth factor (VEGF) in the islets. The microvessel density (MVD) of islets was detected by counting CD34 positive cells. The hypoxia inducible factor (HIF)-1alpha mRNA expression in the islets was detected by RT-PCR. Compared with normal control group (NC, n=10), the area under the curve for insulin from 0 to 30 min (AUCI(0-30)) of diabetes group (DM, n=8) was decreased by 66.3%; the insulin relative concentration (IRC) of betacell was decreased significantly; the relative content of VEGF was increased obviously [(-4.21+/-0.13) vs (-4.06+/-0.29)]; MVD in islets was decreased by 71.4%; the relative expression of HIF-1alpha mRNA was increased by 1.19 times (all P<0.01). Compared with DM group, the AUCI(0-30) of AE and AR group was increased by 44.6% and 34.9% respectively; IRC was also increased significantly; the relative content of VEGF was decreased by 21.2% and 21.7% respectively; MVD was increased by 62.5% and 75.0% respectively; the relative expression of HIF-1alpha was decreased by 27.2% and 29.0% respectively (all P<0.01 or P<0.05). There were no significant differences in the said indexes between group AE and AR. It is concluded that the blockade of RAS may ameliorate islets function of diabetic rats by increasing the MVD in islets.

Adenoviral infection or deferoxamine? Two approaches to overexpress VEGF in beta-cell lines

Rapid and adequate revascularization of transplanted islets is important for their survival and function during transplantation. Vascular endothelial growth factor (VEGF) could play a critical role with respect to islet revascularization. The aim of this study was to compare two strategies that are used to overexpress VEGF in beta-cells: (1) gene therapy through adenoviral infection and (2) a pharmacological approach using deferoxamine (DFO). beta-Cell lines from rat insulinoma (RINm5F) were either infected using an adenovirus encoding the gene of human VEGF 165 or incubated with DFO. One day after treatment, the viability of RINm5F cells was preserved with 10 micromol/L of DFO (103.95 +/- 5.66% toward control; n = 4). In addition, adenoviral infection maintained the viability of cells for all the concentrations used. In both treatments, overexpression of VEGF was in a comparable level. Finally, the ratio of Bax/Bcl-2 indicated that the apoptosis increased in infected beta-cells whereas treatment with DFO seems to be antiapoptotic. Our results suggest that the use of DFO could be a realistic approach to improve the vascularization of islets during transplantation.

Angiogenic and lymphangiogenic microvessel density in recurrent pleomorphic adenoma

BACKGROUND

Recurrent pleomorphic adenoma (RPA) is an uncommon and challenging disease. The aim of this study was to determine if there is a difference between RPA and the pleomorphic adenoma (PA) without recurrence related to tumor blood and lymphatic vascularization. Moreover, we compared the microvessel density (MVD) between cell-rich areas (predominance of epithelial cells) and cell-poor areas (predominance of myxoid and chondroid areas) of the stroma of PA and RPA. In addition, immunohistochemical staining for the Ki-67 antigen was conducted simultaneously to evaluate cell proliferation in PA and RPA.

METHODS

A total of 19 cases of PA and 24 cases of RPA, blood, and lymphatic vessels were analyzed by immunohistochemical technique using the antibodies CD34, CD105, D2-40, and Ki-67.

RESULTS

Comparing no recurrent with recurrent tumor, no significant difference was found in terms of lymphatic vessel density, MVD, and proliferation index. When MVD and proliferation index were compared with different areas in cellular composition (cell-rich and cell-poor areas), there was a significant difference in PA, as well as in RPA.

CONCLUSION

This study shows that although RPA presents more aggressive clinical behavior than PA, there is no difference between tumor blood and lymphatic vascularization, suggesting that there is no correlation between vascularity and risk of recurrence. Furthermore, vascularized stroma in PA, as well as RPA, depends on the proportion of the cellular composition.

The omentum: anatomical, metabolic, and surgical aspects

INTRODUCTION

The omentum is acknowledged to have diverse functions in the pathophysiology of intra-abdominal disease. Its angiogenic properties act as a natural defense mechanism in peritonitis and intra-abdominal sepsis. With advancing technology the omentum is revealing itself as a new player in the field of molecular surgery with special reference to cancer, obesity and tissue reconstruction.

MATERIALS AND METHODS

This article reviews the existing and potential surgical applications of the omentum.

Islet cell transplantation

PURPOSE OF REVIEW

The transplantation of human islets has come a long way since the first diabetic person became insulin independent in 1989. The advent of a steroid-free immunosuppressive protocol in 2000 resulted in most recipients becoming insulin independent and remaining so for a year. However, beta-cell function declines thereafter. Strategies to enhance the islet mass transplanted and preserve beta-cell function are necessary.

RECENT FINDINGS

This review covers recent advances in determining the selection of appropriate enzymes for islet isolation, use of pancreases from heart-dead donors and techniques for predicting the functional capacity of isolated islets prior to transplantation. Changing the transplantation site away from the liver, where many islets are destroyed by an inflammatory process, is reviewed, and the possibility of seeding islets onto three-dimensional biodegradable scaffolds discussed. A method of preventing apoptosis of the beta cells prior to transplantation is detailed, as is the beneficial effect of using exenatide, after transplantation. Novel techniques to image islets are discussed, and this requires the labelling of the islets prior to implantation. Enhancing the vascularization of islets is shown to enhance functional outcomes. Encapsulation of the islets should obviate the need for using antirejection drugs, and it may be possible to expand beta cells in vitro.

SUMMARY

The above strategies are likely to enhance the outcomes of clinical islet transplants.