Adhesion of pancreatic beta cells to biopolymer films

Cryopreservation and post-thaw characterization of dissociated human islet cells

The objective of this study is to optimize the cryopreservation of dissociated islet cells and obtain functional cells that can be used in single-cell transcriptome studies on the pathology and treatment of diabetes. Using an iterative graded freezing approach we obtained viable cells after cooling in 10% dimethyl sulfoxide and 6% hydroxyethyl starch at 1°C/min to -40°C, storage in liquid nitrogen, rapid thaw, and removal of cryoprotectants by serial dilution. The expression of epithelial cell adhesion molecule declined immediately after thaw, but recovered after overnight incubation, while that of an endocrine cell marker (HPi2) remained high after cryopreservation. Patch-clamp electrophysiology revealed differences in channel activities and exocytosis of various islet cell types; however, exocytotic responses, and the biophysical properties of voltage-gated Na+ and Ca2+ channels, are sustained after cryopreservation. Single-cell RNA sequencing indicates that overall transcriptome and crucial exocytosis genes are comparable between fresh and cryopreserved dispersed human islet cells. Thus, we report an optimized procedure for cryopreserving dispersed islet cells that maintained their membrane integrity, along with their molecular and functional phenotypes. Our findings will not only provide a ready source of cells for investigating cellular mechanisms in diabetes but also for bio-engineering pseudo-islets and islet sheets for modeling studies and potential transplant applications.

Soft materials as biological and artificial membranes

The past few decades have seen emerging growth in the field of soft materials for synthetic biology. This review focuses on soft materials involved in biological and artificial membranes. The biological membranes discussed here are mainly those involved in the structure and function of cells and organelles. As building blocks in medicine, non-native membranes including nanocarriers (NCs), especially liposomes and DQAsomes, and polymeric membranes for scaffolds are constructed from amphiphilic combinations of lipids, proteins, and carbohydrates. Artificial membranes can be prepared using synthetic, soft materials and molecules and then incorporated into structures through self-organization to form micelles or niosomes. The modification of artificial membranes can be realized using traditional chemical methods such as click reactions to target the delivery of NCs and control the release of therapeutics. The biomembrane, a lamellar structure inlaid with ion channels, receptors, lipid rafts, enzymes, and other functional units, separates cells and organelles from the environment. An active domain inserted into the membrane and organelles for energy conversion and cellular communication can target disease by changing the membrane's composition, structure, and fluidity and affecting the on/off status of the membrane gates. The biological membrane targets analyzing pathological mechanisms and curing complex diseases, which inspires us to create NCs with artificial membranes.

Natural Polymeric Scaffolds for Tissue Engineering Applications

Natural polymeric scaffolds can be used for tissue engineering applications such as cell delivery and cell-free supporting of native tissues. This is because of their desirable properties such as; high biocompatibility, tunable mechanical strength and conductivity, large surface area, porous- and extracellular matrix (ECM)-mimicked structures. Specifically, their less toxicity and biocompatibility makes them suitable for several tissue engineering applications. For these reasons, several biopolymeric scaffolds are currently being explored for numerous tissue engineering applications. To date, research on the nature, chemistry, and properties of nanocomposite biopolymers are been reported, while the need for a comprehensive research note on more tissue engineering application of these biopolymers remains. As a result, this present study comprehensively reviews the development of common natural biopolymers as scaffolds for tissue engineering applications such as cartilage tissue engineering, cornea repairs, osteochondral defect repairs, and nerve regeneration. More so, the implications of research findings for further studies are presented, while the impact of research advances on future research and other specific recommendations are added as well.

A novel hydrogel scaffold contained bioactive glass nanowhisker (BGnW) for osteogenic differentiation of human mesenchymal stem cells (hMSCs) in vitro

Employing hydrogels as an alternative strategy for repairing bone defects has received great attention in bone tissue engineering. In this study, hydrogel scaffold based on collagen, gelatin, and glutaraldehyde was combined with bioactive glass nanowhiskers (BGnW) to differentiate human mesenchymal stem cells (hMSCs) into the osteogenic lineage and inducing biomineralization. Pure Gel-Glu-Col and bioactive glass nanowhiskers were used as control throughout the paper. Chemical, physical and morphological characteristics of the nanocomposite scaffold were assessed meticulously using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), porosity measurement, water uptake ability, tensile test, and scanning electron microscopy (SEM). To determine the cytotoxicity and cell viability of the hydrogel, MTT assay and Acridine orange (AO) staining were performed. hMSCs seeded on Gel-Glu-Col/BGnW were then incubated with osteogenic differentiation media for 14 days. Biomineralization assays (alkaline phosphatase (ALP) activity, calcium content assay, von Kossa, and Alizarin red staining) were carried out, and osteogenic genes and protein markers were examined using real time-PCR and immunocytochemistry. Results showed that the components of the hydrogel were properly integrated. The mechanical property of hydrogel was enhanced following the addition of BGnW. Cell viability assays confirmed the biocompatibility of the scaffold and increasing the proliferation after incorporating BGnW into pure Ge1-Glu-Col. Our nanocomposite maintained an enhanced ability of biomineralization as compared to its pure counterparts. Molecular investigations revealed an elevated level of osteogenic markers as compared to Ge1-Glu-Col and BGnW. All in all, Gel-Glu-Col/BGnW seems to be a potential candidate for the regeneration of bone tissue.

Gelatin: sources, preparation and application in food and biomedicine

Gelatin is a proteinaceous substance composed of all the essential amino acids (except tryptophan) and derived from collagen using a hydrolysis technique. Hydrogels and modified composites based on gelatin are widely used in the food industry, biomedicine, pharmaceutical industry and food packaging materials due to their biocompatibility, biodegradability, nonimmunogenicity and ability to stimulate cell adhesion and proliferation. Gelatin can absorb 5-10 times its weight of water and is the main ingredient of hard and soft capsules in pharmaceutical industry. It melts above 30°C and easily releases biologically active compounds, nutrients and drugs in human gastrointestinal tract. In addition, gelatin contains arginine-glycine-asparagine RGD-sequences in the polymer structure and contributes to various functions such as antioxidant, anti-hypertensive, anti-microbial, tissue regeneration, wound healing, enhances bone formation and anti-cancer therapy. This article reports a brief overview of gelatin sources, gelatin preparation processes and its physico-chemical properties, as well as advances in the preparation of gelatin-based composite materials and hydrogels for tissue engineering, drug delivery, wound dressings, active packaging using various cross-linking techniques.

Tissue Response to Subcutaneous Infusion Catheter

Insulin infusion pump, continuous glucose monitoring (CGM), and insulin infusion set (IIS) have been developed to be increasingly feasible for people with type 1 diabetes (T1D). Several recently approved CGMs are transitioning from 7-day to 10-day wear time without the need for fingerprick recalibration. Nevertheless, studies and improvements on IIS, a critical part of insulin pump therapy, have been limited. In particular, the recommended wear time of IIS is still 2-3 days, which can hardly match the current duration of CGM for potential closed-loop system development. It is generally believed that both the inserted catheter and the subsequent infused insulin drug could induce particular subcutaneous tissue response and skin-related complications at the infusion site. In certain cases, poor glycaemic control, increased risk of hypoglycemia, and serious cosmetic impact on people with diabetes were observed. Skin complication has also been attributed as an important factor resulting users to discontinue insulin pump therapy. This article provides the rare systematic review of IIS induced subcutaneous tissue responses and skin complications, including the impacts from the inserted catheters, the subcutaneous infused insulin, and the adhesive or tape used to immobilize the catheter. The FDA's recommendation for the frequency of IIS change was further discussed. Future studies on this topic are required to further understand the IIS-related problems, and future strategies could be developed accordingly to significantly reduce the incidence of these problems, extend the wear time, and increase the acceptance of insulin pump based therapy.

Ocular anti-inflammatory activity of prednisolone acetate loaded chitosan-deoxycholate self-assembled nanoparticles

Background and purpose: Conventional topical ophthalmic aqueous solutions and suspensions are often associated with low bioavailability and high administration frequency, pulsatile dose and poor exposure to certain ocular parts. The aim of this study was to develop an ophthalmic nanoparticles loaded gel, for delivering prednisolone acetate (PA), to increase dosing accuracy, bioavailability, and accordingly, efficiency of PA in treating inflammatory ocular diseases. Methods: A novel formulation of self-assembled nanoparticles was prepared by the complexation of chitosan (CS) and, the counter-ion, sodium deoxycholate (SD), loaded with the poorly-water-soluble PA. Particle size, zeta potential, encapsulation efficiency (EE) and drug loading content (LC) of prepared nanoparticles were assessed. Moreover, the nanoparticles were characterized using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). Drug release and eye anti-inflammatory potential of the prepared novel formulation was investigated. Results: Mean particle size of the nanoparticles have dropped from 976 nm ±43 (PDI 1.285) to 480 nm ±28 (PDI 1.396) when the ratio of CS-SD was decreased. The incorporation of 0.1-0.3% of polyvinyl alcohol (PVA), in the preparation stages, resulted in smaller nanoparticles: 462 nm ±19 (PDI 0.942) and 321 nm ±22 (PDI 0.454) respectively. DSC and FTIR results demonstrated the interaction between CS and SD, however, no interactions were detected between PA and CS or SD. Drug release of PA as received, in simulated tears fluid (pH 7.4), showed a twofold increase (reaching an average of 98.6% in 24 hours) when incorporated into an optimized nanoparticle gel formulation (1:5 CS-SD). Conclusion: The anti-inflammatory effect of PA nanoparticles loaded gel on female guinea pig eyes was significantly superior to that of the micronized drug loaded gel (P < 0.05).

Nanoparticle Based Treatment for Cardiovascular Diseases

Nanotechnology has gained increased attention for delivering therapeutic agents effectively to the cardiovascular system. Heart targeted nanocarrier based drug delivery is a new, effective and efficacious approach for treating various cardiac related disorders such as atherosclerosis, hypertension, and myocardial infarction. Nanocarrier based drug delivery system circumvents the problems associated with conventional drug delivery systems, including their nonspecificity, severe side effects and damage to the normal cells. Modification of physicochemical properties of nanocarriers such as size, shape and surface modifications can immensely alter its invivo pharmacokinetic and pharmacodynamic data and will provide better treatment strategy. Several nanocarriers such as lipid, phospholipid nanoparticles have been developed for delivering drugs to the target sites within the heart. This review summarizes and increases the understanding of the advanced nanosized drug delivery systems for treating cardiovascular disorders with the promising use of nanotechnology.

Polymeric Scaffolds for Pancreatic Tissue Engineering: A Review

In recent years, there has been an alarming increase in the incidence of diabetes, with one in every eleven individuals worldwide suffering from this debilitating disease. As the available treatment options fail to reduce disease progression, novel avenues such as the bioartificial pancreas are being given serious consideration. In the past decade, the research focus has shifted towards the field of tissue engineering, which helps to design biological substitutes for repair and replacement of non-functional or damaged organs. Scaffolds constitute an integral part of tissue engineering; they have been shown to mimic the native extracellular matrix, thereby supporting cell viability and proliferation. This review offers a novel compilation of the recent advances in polymeric scaffolds, which are used for pancreatic tissue engineering. Furthermore, in this article, the design strategies for bioartificial pancreatic constructs and their future applications in cell-based therapy are discussed.

Systematic review of islet cryopreservation

Pancreatic islet transplantation is being extensively researched as an alternative treatment for type 1 diabetic patients. This treatment is currently limited by temporal mismatch, between the availability of pancreas and isolated islets from deceased organ donor, and the recipient's need for freshly isolated islets. To solve this issue, cryopreservation of islets may offer the potential to bank islets for transplant on demand. Cryopreservation, however, introduces an overwhelmingly harsh environment to the ever-so-fragile islets. After exposure to the freezing and thawing, islets are usually either apoptotic, non-functional, or non-viable. Several studies have proposed various techniques that could lead to increased cell survival and function following a deep freeze. The purpose of this article is to critically review the techniques of islet cryopreservation, with the goal of highlighting optimization parameters that can lead to the most viable and functional islet upon recovery and/or transplant.

Integration of mesenchymal stem cells into islet cell spheroids improves long-term viability, but not islet function

Pancreatic islets, especially the large islets (> 150µm in diameter) have poor survival rates in culture. Co-culturing with mesenchymal stem cells (MSCs) has been shown to improve islet survival and function. However, most co-culture studies have been comprised of MSC surrounding islets in the media. The purpose of this study was to determine whether islet survival and function was improved when the 2 populations of cells were intermingled with each other in a defined geometry. Hybrid spheroids containing 25, 50 or 75 or 90% islets cells with appropriate numbers of MSCs were created along with spheroids comprised of only islet cells or only MSCs. Spheroids were tested for yield, viability, diameter, cellular composition, and glucose-stimulated insulin secretion. The 25% islet/75% MSC group created the fewest spheroids, with the poorest survival and insulin secretion and the largest diameter. The remaining groups were highly viable with average diameters under 80µm at formation. However, the hybrid spheroid groups preferred to cluster in islet-only spheroids. The 50, 75 and 90% islet cell groups had excellent long-term survival with 90-95% viability at 2 weeks in culture, compared with the islet only group that were below 80% viability. The glucose-stimulated insulin secretion was not statistically different for the 50, 75, or 90 groups when exposed to 2.4, 16.8, or 22.4 mM glucose. Only the spheroids with 25% islet cells had a statistically lower levels of insulin release, and the 100% had statistically higher levels at 22.4 mM glucose and in response to secretagogue. Thus, imbedded co-culture improved long-term viability, but failed to enhance glucose-stimulated insulin secretion in vitro.

Fabricating upconversion fluorescent nanoparticles modified substrate for dynamical control of cancer cells and pathogenic bacteria

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted widespread interests in the field of biomedicine because of their unique upconverting capability by converting near infrared (NIR) excitation to visible or ultraviolet (UV) emission. Here, we developed a novel UCNP-based substrate for dynamic capture and release of cancer cells and pathogenic bacteria under NIR-control. The UCNPs harvest NIR light and convert it to ultraviolet light, which subsequently result in the cleavage of photoresponsive linker (PR linker) from the substrate, and on demand allows the release of a captured cell. The results show that after seeding cells for 5 h, the cells were efficiently captured on the surface of the substrate and ˜89.4% of the originally captured S. aureus was released from the surface after exposure to 2 W/cm² NIR light for 30 min, and ˜92.1% of HepG2 cells. These findings provide a unique platform for exploring an entirely new application field for this promising luminescent nanomaterial.

Long-term cryopreservation of reaggregated pancreatic islets resulting in successful transplantation in rats

Preservation of pancreatic islets for long-term storage of islets used for transplantation or research has long been a goal. Unfortunately, few studies on long-term islet cryopreservation (1 month and longer) have reported positive outcomes in terms of islet yield, survival and function. In general, single cells have been shown to tolerate the cryopreservation procedure better than tissues/multicellular structures like islets. Thus, we optimized a method to cryopreserve single islet cells and, after thawing, reaggregated them into islet spheroids. Cryopreserved (CP) single human islet cells formed spheroids efficiently within 3-5 days after thawing. Approximately 79% of islet cells were recovered following the single-cell cryopreservation protocol. Viability after long-term cryopreservation (4 weeks or more) was significantly higher in the CP islet cell spheroids (97.4 ± 0.4%) compared to CP native islets (14.6 ± 0.4%). Moreover, CP islet cell spheroids had excellent viability even after weeks in culture (88.5 ± 1.6%). Metabolic activity was 4-5 times higher in CP islet cell spheroids than CP native islets at 24 and 48 h after thawing. Diabetic rats transplanted with CP islet cell spheroids were normoglycemic for 10 months, identical to diabetic rats transplanted with fresh islets. However, the animals receiving fresh islets required a higher volume of transplanted tissue to achieve normoglycemia compared to those transplanted with CP islet cell spheroids. By cryopreserving single cells instead of intact islets, we achieved highly viable and functional islets after thawing that required lower tissue volumes to reverse diabetes in rats.

Hyaluronic Acid/Collagen Hydrogel as an Alternative to Alginate for Long-Term Immunoprotected Islet Transplantation<sup/>

Alginate has long been the material of choice for immunoprotection of islets due to its low cost and ability to easily form microspheres. Unfortunately, this seaweed-derived material is notoriously prone to fibrotic overgrowth in vivo, resulting in premature graft failure. The purpose of this study was to test an alternative, hyaluronic acid (HA-COL), for in vitro function, viability, and allogeneic islet transplant outcomes in diabetic rats. In vitro studies indicated that the HA-COL gel had diffusion characteristics that would allow small molecules such as glucose and insulin to enter and exit the gel, whereas larger molecules (70 and 500 kDa dextrans) were impeded from diffusing past the gel edge in 24 h. Islets encapsulated in HA-COL hydrogel showed significantly improved in vitro viability over unencapsulated islets and retained their morphology and glucose sensitivity for 28 days. When unencapsulated allogeneic islet transplants were administered to the omentum of outbred rats, they initially were normoglycemic, but by 11 days returned to hyperglycemia. Immunohistological examination of the grafts and surrounding tissue indicated strong graft rejection. By comparison, when using the same outbred strain of rats, allogeneic transplantation of islets within the HA-COL gel reversed long-term diabetes and prevented graft rejection in all animals. Animals were sacrificed at 40, 52, 64, and 80 weeks for evaluation, and all were non-diabetic at sacrifice. Explanted grafts revealed viable islets in the transplant site as well as intact hydrogel, with little or no evidence of fibrotic overgrowth or cellular rejection. The results of these studies demonstrate great potential for HA-COL hydrogel as an alternative to sodium alginate for long-term immunoprotected islet transplantation.

Reciprocal interaction among gasotransmitters in isolated pancreatic β-cells

We aimed to elucidate the interplay among the three well-known gas molecules, nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S), and their effects on intracellular Ca(2+) concentration ([Ca(2+)]i) and insulin secretion in rat pancreatic β-cells. Immunofluorescence studies demonstrated the expression of constitutive enzymes that are responsible for the production of NO, CO and H2S. CO and H2S increased NO production as indicated by the increase in diaminofluorescein-2 triazole fluorescence. NO and CO induced an elevation in the sulfane sulfur pool and concomitantly H2S production. The NO- and CO-induced H2S production was partially inhibited by hypotaurine, an H2S scavenger. NO and H2S produced CO production as revealed by a myoglobin assay. A calmodulin antagonist in the absence of extracellular Ca(2+) significantly attenuated NO and H2S production. NO and CO induced a [Ca(2+)]i increase mainly via Ca(2+) release from internal stores; however, H2S induced a [Ca(2+)]i increase via the influx of extracellular Ca(2+). NO dose-dependently stimulated basal insulin release but CO dose-dependently inhibited it. H2S showed an insignificant effect on basal insulin secretion from freshly isolated pancreatic islets. Herein, we address for the first time the reciprocal and synergistic relation among gasotransmitters with diverse effects on basal insulin secretion that regulate β-cells functions and homeostasis.

Advances in self-assembled chitosan nanomaterials for drug delivery

Nanomaterials based on chitosan have emerged as promising carriers of therapeutic agents for drug delivery due to good biocompatibility, biodegradability, and low toxicity. Chitosan originated nanocarriers have been prepared by mini-emulsion, chemical or ionic gelation, coacervation/precipitation, and spray-drying methods. As alternatives to these traditional fabrication methods, self-assembled chitosan nanomaterials show significant advantages and have received growing scientific attention in recent years. Self-assembly is a spontaneous process by which organized structures with particular functions and properties could be obtained without additional complicated processing or modification steps. In this review, we focus on recent progress in the design, fabrication and physicochemical aspects of chitosan-based self-assembled nanomaterials. Their applications in drug delivery of different therapeutic agents are also discussed in details.

Bioactive and porous-structured nanocomposite microspheres effective for cell delivery: a feasibility study for bone tissue engineering

A novel nanocomposite microspherical cell-carrier system was developed to populate stem cells and to stimulate their osteogenesis for bone tissue engineering.

Emerging nanostructured materials for musculoskeletal tissue engineering

This review summarizes the recent developments in the preparation and applications of nanostructured materials for musculoskeletal tissue engineering.

Quality of Air-Transported Human Islets for Single Islet Cell Preparations

In new generation medical therapies for type 1 diabetes mellitus (DM), cell-based approaches using pancreatic islets have attracted significant attention worldwide. In particular, dispersed islet cells obtained from isolated pancreatic islets have been a valuable source in the cell biology and tissue engineering fields. Our experimental approach to the development of new islet-based DM therapies consisted of creating a monolithic islet cell sheet format using dispersed islet cells. In this experiment, we explored the potential of internationally transporting human islets from Alberta, Canada to Tokyo, Japan and obtaining viable dispersed islet cells. A total of 34 batches of isolated and purified human islets were transported using a commercial air courier service. Prior to shipping, the human islets had been in culture for 0-108 h at the University of Alberta. The transportation period from Alberta to Tokyo was 2-5 days. The transported human islet cells were enzymatically dispersed as single cells in Tokyo. The number of single islet cells decreased as the number of transportation days increased. In contrast, cell viability was maintained regardless of the number of transportation days. The preshipment culture time had no effect on the number or viability of single cells dispersed in Tokyo. When dispersed single islet cells were plated on laminin-5-coated temperature-responsive polymer-grafted culture dishes, the cells showed favorable attachment followed by extension as a monolithic format. The present study demonstrated that long-distance transported human islets are a viable cell source for experiments utilizing dispersed human islet cells.

A replacement for islet equivalents with improved reliability and validity

Islet equivalent (IE), the standard estimate of isolated islet volume, is an essential measure to determine the amount of transplanted islet tissue in the clinic and is used in research laboratories to normalize results, yet it is based on the false assumption that all islets are spherical. Here, we developed and tested a new easy-to-use method to quantify islet volume with greater accuracy. Isolated rat islets were dissociated into single cells, and the total cell number per islet was determined by using computer-assisted cytometry. Based on the cell number per islet, we created a regression model to convert islet diameter to cell number with a high R2 value (0.8) and good validity and reliability with the same model applicable to young and old rats and males or females. Conventional IE measurements overestimated the tissue volume of islets. To compare results obtained using IE or our new method, we compared Glut2 protein levels determined by Western Blot and proinsulin content via ELISA between small (diameter≤100 μm) and large (diameter≥200 μm) islets. When normalized by IE, large islets showed significantly lower Glut2 level and proinsulin content. However, when normalized by cell number, large and small islets had no difference in Glut2 levels, but large islets contained more proinsulin. In conclusion, normalizing islet volume by IE overestimated the tissue volume, which may lead to erroneous results. Normalizing by cell number is a more accurate method to quantify tissue amounts used in islet transplantation and research.

Hybrid hydroxyapatite nanoparticle colloidal gels are injectable fillers for bone tissue engineering

Injectable bone fillers have emerged as an alternative to the invasive surgery often required to treat bone defects. Current bone fillers may benefit from improvements in dynamic properties such as shear thinning during injection and recovery of material stiffness after placement. Negatively charged inorganic hydroxyapatite (HAp) nanoparticles (NPs) were assembled with positively charged organic poly(d,l-lactic-co-glycolic acid) (PLGA) NPs to create a cohesive colloidal gel. This material is held together by electrostatic forces that may be disrupted by shear to facilitate extrusion, molding, or injection. Scanning electron micrographs of the dried colloidal gels showed a well-organized, three-dimensional porous structure. Rheology tests revealed that certain colloidal gels could recover after being sheared. Human umbilical cord mesenchymal stem cells were also highly viable when seeded on the colloidal gels. HAp/PLGA NP colloidal gels offer an attractive scheme for injectable filling and regeneration of bone tissue.

Otubain 2 is a novel promoter of beta cell survival as revealed by siRNA high-throughput screens of human pancreatic islets

AIMS/HYPOTHESIS

Pro-inflammatory cytokines induce death of beta cells and hamper engraftment of transplanted islet mass. Our aim was to reveal novel genes involved in this process, as a platform for innovative therapeutic approaches.

METHODS

Small interfering RNA (siRNA) high-throughput screening (HTS) of primary human islets was employed to identify novel genes involved in cytokine-induced beta cell apoptosis. Dispersed human islets from nine human donors, treated with a combination of TNF-α, IL-1β and IFN-γ were transfected with ∼730 different siRNAs. Caspase-3/7 activity was measured, results were analysed and potential anti- and pro-apoptotic genes were identified.

RESULTS

Dispersed human pancreatic islets appeared to be suitable targets for performance of siRNA HTS. Using this methodology we found a number of potential pro- and anti-apoptotic target hits that have not been previously associated with pancreatic beta cell death. One such hit was the de-ubiquitinating enzyme otubain 2 (OTUB2). OTUB2 knockdown increased caspase-3/7 activity in MIN6 cells and primary human islets and inhibited insulin secretion and increased nuclear factor-κB (NF-κB) activity both under basal conditions and following cytokine treatment.

CONCLUSIONS

Use of dispersed human islets provides a new platform for functional HTS in a highly physiological system. Employing this technique enabled the identification of OTUB2 as a novel promoter of viability and insulin secretion in human beta cells. OTUB2 acts through the inhibition of NF-κB signalling, which is deleterious to beta cell survival. siRNA screens of human islets may therefore identify new targets, such as OTUB2, for therapeutic intervention in type 1 diabetes and islet transplantation.

Effects of Arg-Gly-Asp-modified elastin-like polypeptide on pseudoislet formation via up-regulation of cell adhesion molecules and extracellular matrix proteins

Extracellular matrix (ECM) plays an important role in controlling the β-cell morphology, survival and insulin secretary functions. An RGD-modified elastin-like polypeptide (RGD-ELP), TGPG[VGRGD(VGVPG)(6)](20)WPC, has been reported previously as a bioactive matrix. In this study, to investigate whether RGD-ELP affects β-cell growth characteristics and insulin secretion, β-TC6 cells were cultured on the RGD-ELP coatings prepared via thermally induced phase transition. On RGD-ELP, β-TC6 cells clustered into an islet-like architecture with high cell viability. Throughout 7days' culture, the proliferation rate of the cells within a pseudoislet was similar to that of monolayer culture. Under high glucose (25mM), β-TC6 pseudoislets showed up-regulated insulin gene expression and exhibited glucose-stimulated insulin secretion. Importantly, the mRNA and protein abundances of cell adhesion molecules (CAM) E-cadherin and connexin-36 were much higher in pseudoislets than in monolayer cells. The siRNA-mediated inhibition of E-cadherin or connexin-36 expression severely limited pseudoislet formation. In addition, the mRNA levels of collagen types I and IV, fibronectin and laminin were significantly elevated in pseudoislets. The results suggest that RGD-ELP promotes pseudoislet formation via up-regulation of the CAM and ECM components. The functional roles of RGD-ELP are discussed in respect of its molecular composition.

Size-related assessment on viability and insulin secretion of caprine islets in vitro

BACKGROUND

The successful isolation, purification, and culture of caprine islets has recently been reported. The present study shows arange of size distribution in caprine islet diameter from 50 to 250 μm, in which 80% of the total islet yield was comprised of small islets.

METHODS

Caprine islets were isolated and purified. Islets were handpicked and the diameter of the islets was recorded using light microscopy. Viablility of the islets was analyzed by confocal microscopy. Insulin secretion assay was carried out and analyzed by ELISA.

RESULTS

When tested at 48 h after isolation, these small islets were 29.3% more viable compared to the large-sized islets. Large islets showed a high ratio (P < 0.01) of central core necrosis (29.5% ± 1.92) whilst no significant core death was observed in small islets (2.33% ± 0.59). The annexin assay demonstrated 5.21% ± 0.97 and 7.34% ± 0.78 apoptotic death for small and large islets, respectively. During static incubation, small islets released 2.89-fold (1.39 ± 0.2 ng/IE) higher insulin level under low glucose induction (3.3 mm) and simultaneously 2.92-fold (2.95 ± 0.33 ng/IE) more insulin under high glucose condition (16.7 mm) in comparison to large islets at the same islet equivalents (P < 0.05).

CONCLUSION

The present findings evidenced the superior quality of smaller caprine islets compared to larger ones under an optimized basal maintenance condition. As it is equally important to preserve the quality of larger caprine islets, this work warrants further investigation on special culture conditions to support these islets.

Reduction of diffusion barriers in isolated rat islets improves survival, but not insulin secretion or transplantation outcome

For people with type 1 diabetes and severe hypoglycemic unawareness, islet transplants offer hope for improving the quality of life. However, islet cell death occurs quickly during or after transplantation, requiring large quantities of islets per transplant. The purpose of this study was to determine whether poor function demonstrated in large islets was a result of diffusion barriers and if removing those barriers could improve function and transplantation outcomes. Islets were isolated from male DA rats and measured for cell viability, islet survival, glucose diffusion and insulin secretion. Modeling of diffusion barriers was completed using dynamic partial differential equations for a sphere. Core cell death occurred in 100% of the large islets (diameter >150 µm), resulting in poor survival within 7 days after isolation. In contrast, small islets (diameter <100 µm) exhibited good survival rates in culture (91%). Glucose diffusion into islets was tracked with 2-NBDG; 4.2 µm/min in small islets and 2.8 µm/min in large islets. 2-NBDG never permeated to the core cells of islets larger than 150 µm diameter. Reducing the diffusion barrier in large islets improved their immediate and long-term viability in culture. However, reduction of the diffusion barrier in large islets failed to improve their inferior in vitro insulin secretion compared to small islets, and did not return glucose control to diabetic animals following transplantation. Thus, diffusion barriers lead to low viability and poor survival for large islets, but are not solely responsible for the inferior insulin secretion or poor transplantation outcomes of large versus small islets.

Islet transplantation: factors in short-term islet survival

Islet transplantation has the potential to cure type 1 diabetes. In recent years, the proportion of patients achieving initial insulin independence has improved, but longer term outcomes remain poor compared to those for whole pancreas transplants. This review article will discuss factors affecting islet yield and viability leading up to transplantation and in the immediate post-transplant period.

The use of biomaterials in islet transplantation

Pancreatic islet transplantation is a therapeutic option to replace destroyed β cells in autoimmune diabetes. Islets are transplanted into the liver via the portal vein; however, inflammation, the required immunosuppression, and lack of vasculature decrease early islet viability and function. Therefore, the use of accessory therapy and biomaterials to protect islets and improve islet function has definite therapeutic potential. Here we review the application of niche accessory cells and factors, as well as the use of biomaterials as carriers or capsules, for pancreatic islet transplantation.

Exercise increases insulin content and basal secretion in pancreatic islets in type 1 diabetic mice

Exercise appears to improve glycemic control for people with type 1 diabetes (T1D). However, the mechanism responsible for this improvement is unknown. We hypothesized that exercise has a direct effect on the insulin-producing islets. Eight-week-old mice were divided into four groups: sedentary diabetic, exercised diabetic, sedentary control, and exercised control. The exercised groups participated in voluntary wheel running for 6 weeks. When compared to the control groups, the islet density, islet diameter, and β-cell proportion per islet were significantly lower in both sedentary and exercised diabetic groups and these alterations were not improved with exercise. The total insulin content and insulin secretion were significantly lower in sedentary diabetics compared to controls. Exercise significantly improved insulin content and insulin secretion in islets in basal conditions. Thus, some improvements in exercise-induced glycemic control in T1D mice may be due to enhancement of insulin content and secretion in islets.

PLGA-chitosan/PLGA-alginate nanoparticle blends as biodegradable colloidal gels for seeding human umbilical cord mesenchymal stem cells

The natural polymers chitosan and alginate represent an attractive material choice for biodegradable inplants. These were used as coating materials to make positively and negatively charged PLGA nanoparticles, respectively. After blending at total solids concentration >10% wt/vol, these oppositely charged nanoparticles yielded a cohesive colloidal gel. Electrostatic forces between oppositely charged nanoparticles produced a stable 3D porous network that may be extruded or molded to the desired shape. This high concentration colloidal system demonstrated shear-thinning behavior due to the disruption of interparticle interactions. Once the external force was removed, the cohesive property of the colloidal gel was recovered. Scanning electron micrographs of dried colloidal networks revealed an organized, 3D microporous structure. Rheological studies were employed to probe the differences in plasticity and shear sensitivity of colloidal gels. Viability tests of hUCMSCs seeded on the colloidal gels also demonstrated the negligible cytotoxicity of the materials. All the results indicated the potential application of the biodegradable colloidal gels as an injectable scaffold in tissue engineering and drug release.

Low insulin content of large islet population is present in situ and in isolated islets

The existence of morphologically distinct populations of islets in the pancreas was described over 60 years ago. Unfortunately, little attention has been paid to possible functional differences between islet subpopulations until recently. We demonstrated that one population, the small islets, were superior to large islets in a number of functional aspects. However, that work did not determine whether these differences were inherent, or whether they arose because of the challenge of isolation procedures. Nor, were there data to explain the differences in insulin secretion. We utilized immunohistochemistry, immunofluorescence, ELISA, and transmission electron microscopy to compare the unique characteristics found in isolated rat islet populations in situ and after isolation. Insulin secretion of small isolated islets was significantly higher compared to large islets, which correlated with higher insulin content/area in small islets (in situ), a higher density of insulin secretory granules, and greater insulin content/volume in isolated islets. Specifically, the core b-cells of the large islets contained less insulin/cell with a lower insulin granule density than peripheral b-cells. When insulin secretion was normalized for total insulin content, large and small islets released the same percentage of total insulin. Small islets had a higher density of cells/area than large islets in vitro and in situ. The data provide a possible explanation for the inferior insulin secretion from large islets, as they have a lower total cell density and the b-cells of the core contain less insulin/cell.