Co-encapsulation of bioengineered IGF-II-producing cells and pancreatic islets: effect on beta-cell survival

A gelatin hydrogel nonwoven fabric improves outcomes of subcutaneous islet transplantation

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

An Overview of Engineered Hydrogel-Based Biomaterials for Improved β-Cell Survival and Insulin Secretion

Islet transplantation provides a promising strategy in treating type 1 diabetes as an autoimmune disease, in which damaged β-cells are replaced with new islets in a minimally invasive procedure. Although islet transplantation avoids the complications associated with whole pancreas transplantations, its clinical applications maintain significant drawbacks, including long-term immunosuppression, a lack of compatible donors, and blood-mediated inflammatory responses. Biomaterial-assisted islet transplantation is an emerging technology that embeds desired cells into biomaterials, which are then directly transplanted into the patient, overcoming the aforementioned challenges. Among various biomaterials, hydrogels are the preferred biomaterial of choice in these transplants due to their ECM-like structure and tunable properties. This review aims to present a comprehensive overview of hydrogel-based biomaterials that are engineered for encapsulation of insulin-secreting cells, focusing on new hydrogel design and modification strategies to improve β-cell viability, decrease inflammatory responses, and enhance insulin secretion. We will discuss the current status of clinical studies using therapeutic bioengineering hydrogels in insulin release and prospective approaches.

Prevascularization-free Primary Subcutaneous Transplantation of Xenogeneic Islets Coencapsulated With Hepatocyte Growth Factor

Subcutaneous pouch is a potential site for islet transplantation. However, insufficient oxygen supply remains challenging. Pretreatment of neovascularization using basic fibroblast growth factor can solve this, but it needs 2× operations. We developed a device that contains rat islets in chitosan gel packed in a bag made of highly biocompatible ethylene vinyl alcohol copolymer porous membrane. This study investigated whether coencapsulation of hepatocyte growth factor (HGF) with islets in the device enables novel method of prevascularization-free primary subcutaneous transplantation.

METHODS

In vitro experiments examined slow release of HGF from the chitosan gel and islet-protection effect of HGF against hypoxia. In the latter, rat islets with/without HGF (200 ng/mL) was cultured in 1% oxygen. In in vivo experiment, fabricated device with/without HGF (10 μg/device) containing rat islets was primarily transplanted to streptozotocin-induced diabetic mice subcutaneously.

RESULTS

In vitro experiments showed sustained release of HGF for 28 d and alleviating effect of HGF on cell death and glucose-responsive insulin release after hypoxic culture. Islet + HGF mice, but not islet-alone mice, showed decreased nonfasting blood glucose and regained body weight after transplantation. In intraperitoneal glucose tolerance test, islet + HGF mice exhibited decreased fasting blood glucose (200 ± 55 mg/dL) and good blood glucose disappearance rate (K value) (0.817 ± 0.101) comparing to normal mice (123 ± 28 mg/dL and 1.074 ± 0.374, respectively). However, in islet-alone mice, fasting blood glucose was high (365 ± 172 mg/dL) and K value was indeterminable. Serum insulin in islet + HGF mice (1.58 ± 0.94 μg/L) was close to normal mice (1.66 ± 0.55 μg/L), whereas those in islet-alone mice (0.279 ± 0.076 μg/L) and diabetic mice (0.165 ± 0.079 μg/L) were low. Immunohistochemical examination showed intact insulin- and glucagon-positive islets in retrieved devices with HGF, but no intact islet was found in the device without HGF.

CONCLUSIONS

HGF could enhance islet survival in hypoxia and enhance in vivo function of encapsulated islets after primary subcutaneous transplantation.

Encapsulated Islet Transplantation: Where Do We Stand?

Transplantation of pancreatic islets encapsulated within immuno-protective microcapsules is a strategy that has the potential to overcome graft rejection without the need for toxic immunosuppressive medication. However, despite promising preclinical studies, clinical trials using encapsulated islets have lacked long-term efficacy, and although generally considered clinically safe, have not been encouraging overall. One of the major factors limiting the long-term function of encapsulated islets is the host's immunological reaction to the transplanted graft which is often manifested as pericapsular fibrotic overgrowth (PFO). PFO forms a barrier on the capsule surface that prevents the ingress of oxygen and nutrients leading to islet cell starvation, hypoxia and death. The mechanism of PFO formation is still not elucidated fully and studies using a pig model have tried to understand the host immune response to empty alginate microcapsules. In this review, the varied strategies to overcome or reduce PFO are discussed, including alginate purification, altering microcapsule geometry, modifying alginate chemical composition, co-encapsulation with immunomodulatory cells, administration of pharmacological agents, and alternative transplantation sites. Nanoencapsulation technologies, such as conformal and layer-by-layer coating technologies, as well as nanofiber, thin-film nanoporous devices, and silicone based NanoGland devices are also addressed. Finally, this review outlines recent progress in imaging technologies to track encapsulated cells, as well as promising perspectives concerning the production of insulin-producing cells from stem cells for encapsulation.

Applications of Cell Microencapsulation

The goal of this chapter is to provide an overview of the different purposes for which the cell microencapsulation technology can be used. These include immunoisolation of non-autologous cells used for cell therapy; immobilization of cells for localized (targeted) delivery of therapeutic products to ablate, repair, or regenerate tissue; simultaneous delivery of multiple therapeutic agents in cell therapy; spatial compartmentalization of cells in complex tissue engineering; expansion of cells in culture; and production of different probiotics and metabolites for industrial applications. For each of these applications, specific examples are provided to illustrate how the microencapsulation technology can be utilized to achieve the purpose. However, successful use of the cell microencapsulation technology for whatever purpose will ultimately depend upon careful consideration for the choice of the encapsulating polymers, the method of fabrication (cross-linking) of the microbeads, which affects the permselectivity, the biocompatibility and the mechanical strength of the microbeads as well as environmental parameters such as temperature, humidity, osmotic pressure, and storage solutions.The various applications discussed in this chapter are illustrated in the different chapters of this book and where appropriate relevant images of the microencapsulation products are provided. It is hoped that this outline of the different applications of cell microencapsulation would provide a good platform for tissue engineers, scientists, and clinicians to design novel tissue constructs and products for therapeutic and industrial applications.

Evolution of Islet Transplantation for the Last 30 Years

In this article, we will review the changes that have occurred in islet transplantation at the birth of Pancreas 30 years ago. The first attempts at β-cell replacement in humans, pancreas and islet transplantation, were performed in the 1960s and 1970s. Although pancreas transplantation has been an accepted treatment for severe labile diabetes predating the emergence of the journal, allogeneic islet transplantation remains experimental. Current investigations within islet transplantation focus to improve islet function after transplantation. Improving islet viability during isolation, exploring ways to increase engraftment, and protection from the host immune system are some of the goals of these investigative efforts. The major barriers to clinical islet transplantation are shortage of human pancreas, the need for immunosuppression, and the inadequacy of the islet isolation process. It is generally accepted that islet encapsulation is an immunoisolation tool with good potential to address the first 2 of those barriers. We have therefore devoted a major part of this review to the critical factors needed to make it a clinical reality. With improved islet isolation techniques and determination of the best site of engraftment as well as improved encapsulation techniques, we hope that islet transplantation could someday achieve routine clinical use.

Using mass spectrometry to detect, differentiate, and semiquantitate closely related peptide hormones in complex milieu: measurement of IGF-II and vesiculin

The search for an islet β-cell growth factor has been a key objective in recent diabetes research, because the ability to regenerate and/or protect the functioning β-cell population in patients could result in a great advancement for diabetes treatment. IGF-I and IGF-II are known to play crucial roles in fetal growth and prenatal development, and there is growing evidence that IGF-II increases β-cell proliferation and survival in vitro and in vivo. A search for the source of IGF-II-like immunoreactivity in isolated β-cell secretory granules from the murine cell line βTC6-F7 revealed a novel 2-chain IGF-II-derived peptide, which we named vesiculin and which has been shown to be a full insulin agonist. Here, we present a liquid chromatography-tandem mass spectrometry method that enables selective detection and semiquantitation of the highly related IGF-II and vesiculin molecules. We have used this method to measure these 2 peptides in conditioned media from 2 β-cell lines, produced under increasing glucose concentrations. This technique detected both IGF-II and vesiculin in media conditioned by MIN6 and βTC6-F7 cells at levels in the range of 0 to 6 μM (total insulin, 80-450 μM) and revealed a glucose-stimulated increase in insulin, IGF-II, and vesiculin. IGF-II was detected in adult human and neonatal mouse serum in high levels, but vesiculin was not present. The methodology we present herein has utility for detecting and differentiating active peptides that are highly related and of low abundance.

IGF2: an endocrine hormone to improve islet transplant survival

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

Bisphenol A enhances kisspeptin neurons in anteroventral periventricular nucleus of female mice

Bisphenol-A (BPA), an environmental estrogen, adversely affects female reproductive health. However, the underlying mechanisms remain largely unknown. We found that oral administration (p.o.) of BPA (20  μg/kg) to adult female mice at proestrus, but not at estrus or diestrus, significantly increased the levels of plasma E₂, LH and FSH, and Gnrh mRNA within 6  h. The administration of BPA at proestrus, but not at diestrus, could elevate the levels of Kiss1 mRNA and kisspeptin protein in anteroventral periventricular nucleus (AVPV) within 6  h. In contrast, the level of Kiss1 mRNA in arcuate nucleus (ARC) was hardly altered by BPA administration. In addition, at proestrus, a single injection (i.c.v.) of BPA dose-dependently enhanced the AVPV-kisspeptin expression within 6  h, this was sensitive to E₂ depletion by ovariectomy and an estrogen receptor α (ERα) antagonist. Similarly, the injection of BPA (i.c.v.) at proestrus could elevate the levels of plasma E₂, LH, and Gnrh mRNA within 6  h in a dose-dependent manner, which was blocked by antagonists of GPR54 or ERα. Injection of BPA (i.c.v.) at proestrus failed to alter the timing and peak concentration of LH-surge generation. In ovariectomized mice, the application of E₂ induced a dose-dependent increase in the AVPV-Kiss1 mRNA level, indicating 'E₂-induced positive feedback', which was enhanced by BPA injection (i.c.v.). The levels of Erα (Esr1) and Erβ (Esr2) mRNAs in AVPV and ARC did not differ significantly between vehicle-and BPA-treated groups. This study provides in vivo evidence that exposure of adult female mice to a low dose of BPA disrupts the hypothalamic-pituitary-gonadal reproductive endocrine system through enhancing AVPV-kisspeptin expression and release.

Insulin-like growth factor-II and insulin-like growth factor binding protein-2 prospectively predict longitudinal elevation of HDL-cholesterol in type 2 diabetes

INTRODUCTION

Associations of insulin-like growth factor-II (IGF-II) and insulin-like growth factor binding protein-2 (IGFBP-2) with cardiovascular risk have been inadequately studied. We hypothesized that IGF-II and IGFBP-2 associate with longitudinal trends in lipid profiles in type 2 diabetes patients.

SUBJECTS AND METHODS

Four hundred and eighty nine subjects with type 2 diabetes (age 27-87 years) from the Salford Diabetes Cohort were studied. Longitudinal clinical information was extracted for an eight-year period (2002-2009) from an integrated electronic dataset of primary care and hospital data.

RESULTS

There were 294 male subjects and mean age was 62.9 years. At baseline, IGF-II concentration was 602 ng/mL. HDL cholesterol at baseline was associated with log-IGF-II concentration in a model adjusted for age, gender, baseline body-mass index (BMI), estimated glomerular filtration rate (eGFR) and lipid-lowering therapy. IGFBP-1 and IGFBP-2 were associated with high HDL-cholesterol. A higher circulating IGF-II concentration at baseline was also associated with longitudinal increase in HDL-cholesterol in mixed-effects regression analyses independent of IGF-I, IGFBP-1, IGFBP-2, IGFBP-3, age, gender, eGFR, BMI and lipid-lowering therapy. Log-transformed baseline concentrations of IGFBP-1 and IGFBP-2 were also associated with longitudinal elevation in HDL-cholesterol. No association was observed for IGF-II or IGFBP-2 with longitudinal LDL cholesterol trends.

CONCLUSION

Our analyses based on 'real world' data demonstrate that higher baseline IGF-II and IGFBP-2 predict increased HDL concentration over time, implicating IGF-II in modulation of circulating HDL-cholesterol concentrations.

Alginate hydrogel as a potential alternative to hyaluronic acid as submucosal injection material

BACKGROUND

Sodium alginate is currently used in medical products, including drugs and cosmetic materials. It can also be used as a submucosal injection material due to its excellent water retention ability. Alginate with a high water retention ability is called alginate hydrogel (AH). The aim of this study was to investigate the usefulness of AH as a submucosal injection material.

METHODS

To investigate the optimal viscosity of AH as a submucosal injection material, we observed the changes in submucosal height from the initial submucosal height in the stomachs of six miniature pigs for each injection material tested (0.3 % AH, 0.5 % hyaluronic acid, glycerol). All submucosal heights were compared serially over time (3, 5, 10, 20, and 30 min). Both immediate and 1-week delayed tissue reactions were investigated endoscopically in the same living pigs. Histological analyses were performed after the animals had been sacrificed.

RESULTS

In a preliminary study, we determined that 0.3 % sodium alginate mixed with BaCl2 (400 μl) was the optimal viscosity of AH as an injection material. Our comparison of submucosal height changes over time showed that there was a significant decrease in submucosal height just 3 min following the injection of hyaluronic acid and glycerol, but that following the injection of AH a significant decrease in submucosal height was observed only after 10 min (p < 0.05). The histological analyses revealed that there were mild capillary dilations with congestion and mild fibrotic changes with some lymphocytic infiltration at the AH injection site.

CONCLUSION

Alginate hydrogel demonstrated long-lasting maintenance of submucosal elevation, safety, and cost-effectiveness in a pig model, which makes it a potential alternative to hyaluronic acid.

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.

Delivering bioactive molecules as instructive cues to engineered tissues

INTRODUCTION

Growth factors and other bioactive molecules play a crucial role in the creation of functional engineered tissues from dissociated cells.

AREAS COVERED

This review discusses the delivery of bioactive molecules - particularly growth factors - to affect cellular function in the context of tissue engineering. We discuss the primary biological themes that are addressed by delivering bioactives, the types of molecules that are to be delivered, the major materials used in producing scaffolds and/or drug delivery systems, and the principal drug delivery strategies.

EXPERT OPINION

Drug delivery systems have allowed the sustained release of bioactive molecules to engineered tissues, with marked effects on tissue function. Sophisticated drug delivery techniques will allow precise recapitulation of developmental milestones by providing temporally distinct patterns of release of multiple bioactives. High-resolution patterning techniques will allow tissue constructs to be designed with precisely defined areas where bioactives can act. New biological discoveries, just as the development of small molecules with potent effects on cell differentiation, will likely have a marked impact on the field.

Maintaining functional islets through encapsulation in an injectable saccharide-peptide hydrogel

Islet transplantation offers a promising treatment for type 1 diabetes (T1D). However, a major hurdle in this treatment is the rapid loss of functional islets during culture and after transplantation. The liver site, currently utilized for transplantation, is suboptimal for achieving long-term insulin independence due to a rapid islet loss followed by a chronic decline in islet function after transplantation. Herein, we report a synthetic saccharide-peptide (SP) hydrogel that allows suspending islets in liquid and injecting for in situ polymerization without forming islet clumps, indicating its potential in extrahepatic islet transplantation. In vitro, rat islets in SP hydrogel maintained a 3D structure and high glucose-stimulated insulin release similar to that observed in freshly isolated islets for 4 weeks, while control islets cultured in suspension lost their 3D structure and insulin release responses by 2 weeks. Biocompatibility of SP hydrogel was shown by the absence of cytokine mRNA activation in peripheral blood mononuclear cells (PBMCs) exposed to hydrogel in vitro and by the absence of cellular infiltrates in and around the hydrogel implanted subcutaneously. Syngeneic Lewis rat islets transplanted in SP hydrogel in various extrahepatic sites stained strongly for insulin, and more effectively reversed diabetes than unencapsulated islets when transplanted in an omental pocket. In conclusion, the SP hydrogel is non-cytotoxic and supports normal islet structure and function both in vitro and in vivo. Specifically, the ability of the hydrogel to separate individual islets after transplantation is important for maintaining their function in vivo. This important property, combined with the versatility and biocompatibility, makes our SP hydrogel a promising synthetic scaffold that can facilitate transplantation of organized heterogeneous cells to preserve their micro-structure and function.

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

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

Current status of immunomodulatory and cellular therapies in preclinical and clinical islet transplantation

Clinical islet transplantation is a β-cell replacement strategy that represents a possible definitive intervention for patients with type 1 diabetes, offering substantial benefits in terms of lowering daily insulin requirements and reducing incidences of debilitating hypoglycemic episodes and unawareness. Despite impressive advances in this field, a limiting supply of islets, inadequate means for preventing islet rejection, and the deleterious diabetogenic and nephrotoxic side effects associated with chronic immunosuppressive therapy preclude its wide-spread applicability. Islet transplantation however allows a window of opportunity for attempting various therapeutic manipulations of islets prior to transplantation aimed at achieving superior transplant outcomes. In this paper, we will focus on the current status of various immunosuppressive and cellular therapies that promote graft function and survival in preclinical and clinical islet transplantation with special emphasis on the tolerance-inducing capacity of regulatory T cells as well as the β-cells regenerative capacity of stem cells.