Morphological changes of isolated rat pancreatic islets: a structural, ultrastructural and morphometric study

The role of lutein-rich purple sweet potato leaf extract on the amelioration of diabetic retinopathy in streptozotocin-induced Sprague-Dawley rats

The objective of this study is to access the effect of purple sweet potato leaf (PSPL) extract on diabetic retinopathy (DR) of streptozotocin (STZ)-induced male Sprague-Dawley (SD) rats. In this study, rats were injected intraperitoneally with a single dose of 60 mg/kg STZ, and diabetes was confirmed on day 7. Rats were further divided into a few groups, which were then orally administered with one of the following treatments: 25 mg/kg of gliclazide (D25G), 200 mg/kg of PSPL extract (DT 200), and 400 mg/kg of PSPL extract (DT 400). However, the normal control (NS) and control group for diabetic (DNS) were given normal saline (NS) for 12 weeks. The results show that the treated group demonstrated a reduction in serum oral glucose tolerance test (OGTT) levels of DT 200 and DT 400, and an increase in the serum and retinal insulin levels, and restored oxidative stress markers in serum and retina on week 12. The PSPL extract exhibited protective effects in maintaining the kidney, liver, retina, and pancreas architecture in 400 mg/kg compared to the 200 mg/kg treated group and D25G, thereby restoring fully transparent lenses in diabetes-induced rats. In conclusion, 400 mg/kg PSPL is the most effective dose for the amelioration of STZ-induced DR pathology in male SD rats.

Determinants and dynamics of pancreatic islet architecture

The islets of Langerhans are highly organized structures that have species-specific, three-dimensional tissue architecture. Islet architecture is critical for proper hormone secretion in response to nutritional stimuli. Islet architecture is disrupted in all types of diabetes mellitus and in cadaveric islets for transplantation during isolation, culture, and perfusion, limiting patient outcomes. Moreover, recapitulating native islet architecture remains a key challenge for in vitro generation of islets from stem cells. In this review, we discuss work that has led to the current understanding of determinants of pancreatic islet architecture, and how this architecture is maintained or disrupted during tissue remodeling in response to normal and pathological metabolic changes. We further discuss both empirical and modeling data that highlight the importance of islet architecture for islet function.

Pancreas Preservation with a Neutrophil Elastase Inhibitor, Alvelestat, Contributes to Improvement of Porcine Islet Isolation and Transplantation

For pancreatic islet transplantation, pancreas procurement, preservation, and islet isolation destroy cellular and non-cellular components and activate components such as resident neutrophils, which play an important role in the impairment of islet survival. It has been reported that inhibitors of neutrophil elastase (NE), such as sivelestat and α1-antitrypsin, could contribute to improvement of islet isolation and transplantation. In this study, we investigated whether pancreatic preservation with alvelestat, a novel NE inhibitor, improves porcine islet yield and function. Porcine pancreata were preserved with or without 5 μM alvelestat for 18 h, and islet isolation was performed. The islet yields before and after purification were significantly higher in the alvelestat (+) group than in the alvelestat (−) group. After islet transplantation into streptozotocin-induced diabetic mice, blood glucose levels reached the normoglycemic range in 55% and 5% of diabetic mice in the alvelestat (+) and alvelestat (−) groups, respectively. These results suggest that pancreas preservation with alvelestat improves islet yield and graft function and could thus serve as a novel clinical strategy for improving the outcome of islet transplantation.

Physiological and Histological Changes in Pancreatic Gland Associated with Ageing in Local Rabbits in Iraq

The pancreas is a pear-shaped flat organ resembling the letter L, and yellowish to pink in color. This organ is of medical significance since it is associated with two life-threatening diseases including diabetes mellitus and pancreatic cancer. This study was conducted on male rabbits which were assigned into 3 age groups (6-month-old, 1-year-old, and 3-year-old rabbits). Physiological and histological changes of the pancreas were studied in the adopted age groups. The physiological aspect and the histological structure of the pancreas were also studied by the analysis of the level of pancreatic gland hormones and hormonal changes. Based on the results, there were significant differences in the concentration of pancreatic gland hormones. Insulin level in the second study group was more than that in the first and third groups, while the highest concentration of blood sugar (glucose) was observed in the third group, compared to the first and second. Although the basic structure of the pancreas was similar in all samples, changes were observed in the tissue structure of the pancreas throughout the process of aging. By the increase of age (from 1 to 3 years old), Langerhans islets increased in size, contained alpha and beta cells that were surrounded by a loose connective tissue in the third stage. Moreover, no significant difference was observed in the diameters of cells that produced enzymes at all stages of life. Physiological and histological changes indicated that age plays a role in the function and structure of the pancreas gland during different stages of life. In addition, this study indicated that the hormonal variability of the pancreas is closely related to the histological composition of gland components. Therefore, further studies on the role of factors, such as gender, different breeds, or environmental conditions seem to be necessary and may provide more information on factors that may affect the effectiveness and activity of the pancreas gland.

Fabrication of functional rat pseudo-islets after cryopreservation of pancreatic islets or dispersed islet cells

Dispersed single cells from pancreatic islets can configure the three-dimensional islet-like architecture (pseudo-islets) with insulin secretion potential and controllable size through their aggregation property. The present study was designed to investigate whether cryopreservation of islets or islet cells can contribute to the efficient pseudo-islet fabrication in the rat model. In control group (CT), islet single cells were prepared by trypsin digestion of 50-400-µm ø fresh control islets, and then cultured for 3 days in the U-bottom microwell to fabricate pseudo-islets. In vitrification-warming group (VW), islet single cells were prepared from postwarm islets cryopreserved by vitrification on nylon mesh device, and then cultured for 3 days. In freezing group (FR), islet single cells originated from fresh islets were subjected to a conventional Bicell® freezing, and postthaw cells were cultured for 3 days. To generate 1 islet equivalent pseudo-islets (150 µm ø) by the sphere culture, 1250 CT cells, 1250 VW cells, and 1500 FR cells were seeded to each microwell. The viability of the pseudo-islets was comparable among the three groups (93.9%-96.9%). Furthermore, the insulin secretion assay showed that those pseudo-islets responded sufficiently to the high glucose stimulation. Immunostaining for insulin and glucagon showed that the endocrine cell arrangement of those pseudo-islets is similar to that of native and isolated islets. These islets/pseudo-islets had the β-cells in core and the α-cells in mantle, which was typical characteristic of the rodent islets. However, some clusters of α-cells were observed inside the FR pseudo-islets. Interestingly, the VW pseudo-islets had significantly fewer α-cells than the CT or FR pseudo-islets. These results suggest that the sphere culture of islet cells is useful tool to generate the pseudo-islets with the customized size and normal functionality, even after islet cryopreservation.

Recruited fibroblasts reconstitute the peri-islet membrane: a longitudinal imaging study of human islet grafting and revascularisation

AIMS/HYPOTHESIS

Rapid and adequate islet revascularisation and restoration of the islet-extracellular matrix (ECM) interaction are significant factors influencing islet survival and function of the transplanted islets in individuals with type 1 diabetes. Because the ECM encapsulating the islets is degraded during islet isolation, understanding the process of revascularisation and engraftment after transplantation is essential and needs further investigation.

METHODS

Here we apply a longitudinal and high-resolution imaging approach to investigate the dynamics of the pancreatic islet engraftment process up to 11 months after transplantation. Human and mouse islet grafts were inserted into the anterior chamber of the mouse eye, using a NOD.ROSA-tomato.Rag2^-/- or B6.ROSA-tomato host allowing the investigation of the expansion of host vs donor cells and the contribution of host cells to aspects such as promoting the encapsulation and vascularisation of the graft.

RESULTS

A fibroblast-like stromal cell population of host origin rapidly migrates to ensheath the transplanted islet and aid in the formation of a basement membrane-like structure. Moreover, we show that the vessel network, while reconstituted by host endothelial cells, still retains the overall architecture of the donor islets.

CONCLUSIONS/INTERPRETATION

In this transplantation situation the fibroblast-like stromal cells appear to take over as main producers of ECM or act as a scaffold for other ECM-producing cells to reconstitute a peri-islet-like basement membrane. This may have implications for our understanding of long-term graft rejection and for the design of novel strategies to interfere with this process.

Generation of Human Stem Cell-Derived Pancreatic Organoids (POs) for Regenerative Medicine

Insulin-dependent diabetes mellitus or type 1 diabetes mellitus (T1DM) is an auto-immune condition characterized by the loss of pancreatic β-cells. The curative approach for highly selected patients is the pancreas or the pancreatic islet transplantation. Nevertheless, these options are limited by a growing shortage of donor organs and by the requirement of immunosuppression.Xenotransplantation of porcine islets has been extensively investigated. Nevertheless, the strong xenoimmunity and the risk of transmission of porcine endogenous retroviruses, have limited their application in clinic. Generation of β-like cells from stem cells is one of the most promising strategies in regenerative medicine. Embryonic, and more recently, adult stem cells are currently the most promising cell sources exploited to generate functional β-cells in vitro. A number of studies demonstrated that stem cells could generate functional pancreatic organoids (POs), able to restore normoglycemia when implanted in different preclinical diabetic models. Nevertheless, a gradual loss of function and cell dead are commonly detected when POs are transplanted in immunocompetent animals. So far, the main issue to be solved is the post-transplanted islet loss, due to the host immune attack. To avoid this hurdle, nanotechnology has provided a number of polymers currently under investigation for islet micro and macro-encapsulation. These new approaches, besides conferring PO immune protection, are able to supply oxygen and nutrients and to preserve PO morphology and long-term viability.Herein, we summarize the current knowledge on bioengineered POs and the stem cell differentiation platforms. We also discuss the in vitro strategies used to generate functional POs, and the protocols currently used to confer immune-protection against the host immune attack (micro- and macro-encapsulation). In addition, the most relevant ongoing clinical trials, and the most relevant hurdles met to move towards clinical application are revised.

Endocrine cell type sorting and mature architecture in the islets of Langerhans require expression of Roundabout receptors in β cells

Pancreatic islets of Langerhans display characteristic spatial architecture of their endocrine cell types. This architecture is critical for cell-cell communication and coordinated hormone secretion. Islet architecture is disrupted in type-2 diabetes. Moreover, the generation of architecturally correct islets in vitro remains a challenge in regenerative approaches to type-1 diabetes. Although the characteristic islet architecture is well documented, the mechanisms controlling its formation remain obscure. Here, we report that correct endocrine cell type sorting and the formation of mature islet architecture require the expression of Roundabout (Robo) receptors in β cells. Mice with whole-body deletion of Robo1 and conditional deletion of Robo2 either in all endocrine cells or selectively in β cells show complete loss of endocrine cell type sorting, highlighting the importance of β cells as the primary organizer of islet architecture. Conditional deletion of Robo in mature β cells subsequent to islet formation results in a similar phenotype. Finally, we provide evidence to suggest that the loss of islet architecture in Robo KO mice is not due to β cell transdifferentiation, cell death or loss of β cell differentiation or maturation.

Fully Automated Islet Cell Counter (ICC) for the Assessment of Islet Mass, Purity, and Size Distribution by Digital Image Analysis

For isolated pancreatic islet cell preparations, it is important to be able to reliably assess their mass and quality, and for clinical applications, it is part of the regulatory requirement. Accurate assessment, however, is difficult because islets are spheroid-like cell aggregates of different sizes (<50 to 500 μm) resulting in possible thousandfold differences between the mass contribution of individual particles. The current standard manual counting method that uses size-based group classification is known to be error prone and operator dependent. Digital image analysis (DIA)-based methods can provide less subjective, more reproducible, and better-documented islet cell mass (IEQ) estimates; however, so far, none has become widely accepted or used. Here we present results obtained using a compact, self-contained islet cell counter (ICC3) that includes both the hardware and software needed for automated islet counting and requires minimal operator training and input; hence, it can be easily adapted at any center and could provide a convenient standardized cGMP-compliant IEQ assessment. Using cross-validated sample counting, we found that for most human islet cell preparations, ICC3 provides islet mass (IEQ) estimates that correlate well with those obtained by trained operators using the current manual SOP method ( r² = 0.78, slope = 1.02). Variability and reproducibility are also improved compared to the manual method, and most of the remaining variability (CV = 8.9%) results from the rearrangement of the islet particles due to movement of the sample between counts. Characterization of the size distribution is also important, and the present digitally collected data allow more detailed analysis and coverage of a wider size range. We found again that for human islet cell preparations, a Weibull distribution function provides good description of the particle size.

Enzyme Development for Human Islet Isolation: Five Decades of Progress or Stagnation?

In comparison to procedures used for the separation of individual cell types from other organs, the process of human pancreatic islet isolation aims to digest the pancreatic exocrine matrix completely without dispersing the individual cells within the endocrine cell cluster. This objective is unique within the field of tissue separation, and outlines the challenge of islet isolation to balance two opposing priorities. Although significant progress has been made in the characterization and production of enzyme blends for islet isolation, there are still numerous areas which require improvement. The ultimate goal of enzyme production, namely the routine production of a consistent and standardized enzyme blend, has still not been realized. This seems to be mainly the result of a lack of detailed knowledge regarding the structure of the pancreatic extracellular matrix and the synergistic interplay between collagenase and different supplementary proteases during the degradation of the extracellular matrix. Furthermore, the activation of intrinsic proteolytic enzymes produced by the pancreatic acinar cells, also impacts on the chance of a successful outcome of human islet isolation. This overview discusses the challenges of pancreatic enzymatic digestion during human islet isolation, and outlines the developments in this field over the past 5 decades.

An optimized protocol for purification of functional islets of Langerhans

Islets of Langerhans and β-cell isolation constitute routinely used cell models for diabetic research, and refining islet isolation protocols and cell quality assessment is a high priority. Numerous protocols have been published describing isolate of islets, but often rigorous and systematic assessment of their integrity is lacking. Herein, we propose a new protocol for optimal generation of islets. Pancreases from mice and rats were excised and digested using a low-activity collagenase solution and islets were then purified by a series of sedimentations and a Percoll gradient. Islets were maintained in culture for 5 days, during which viability, pro/antiapoptotic, and islet-specific genes, glucose-stimulated calcium entry, glucose uptake, and insulin secretion were assessed. The commonly used islet isolation technique by collagenase injection through the common bile duct (CBD) was also performed and compared with the present approach. This new protocol produced islets that retained a healthy status as demonstrated by the yield of stable living cells. Furthermore, calcium oscillation, glucose uptake, and insulin secretion remained intact in the islet cultures. This was reproducible when many rodent species were used, and neither sex nor age affected the cells behavior. When compared with the CBD technique, islet physiology was similar. Finally, this approach was used to uncover new ion channel candidates implicated in insulin secretion. In conclusion, this study outlines an efficient protocol for islet preparation that may support research into new therapeutic targets in diabetes research.

Composition and organization of the pancreatic extracellular matrix by combined methods of immunohistochemistry, proteomics and scanning electron microscopy

The epidemic expansion of diabetes is a major concern of public health. A promising treatment is the transplantation of islets of Langerhans isolated from the whole pancreas but the yields of islets isolation and the rates of successful engraftments still have to be improved to make this therapy effective. The extracellular matrix (ECM) of the pancreatic tissue is partially lost during the isolation process and a comprehensive knowledge of the pancreatic ECM composition and organization could identify targets to improve islets isolation and transplantation or highlight new therapeutics for pancreatic diseases. The organization, composition and three-dimensional architecture of the pancreatic ECM were analysed in mouse and pig by three different techniques. Laminin α-4 and β-2 chains are localized by immunohistochemistry in the exocrine tissue and inside islets of mouse pancreas but not around islets that are surrounded by an ECM made of collagen type IV and type V. Collagen type I, III, and VI were identified by proteomics as specific constituents of the pig pancreatic ECM along with the low-abundance isoforms α3(IV) α4(IV) α5(IV) and α1(V) α2(V) α3(V) of collagen type IV and type V respectively. The three-dimensional ECM architecture is analysed on decellularized mouse pancreas by scanning electron microscopy and is organized in honeycomb structures made of thin ECM fibers assembled in thicker bundles. The combination of immunohistochemistry, proteomics and scanning electron microscopy gives complementary perspective on the pancreatic ECM composition and organization. It represents a valuable toolbox for deeper investigations of ECMs and proposes clues in tissue engineering of the pancreas.

Imaging of Hydrogel Microsphere Structure and Foreign Body Response Based on Endogenous X-Ray Phase Contrast

Transplantation of functional islets encapsulated in stable biomaterials has the potential to cure Type I diabetes. However, the success of these materials requires the ability to quantitatively evaluate their stability. Imaging techniques that enable monitoring of biomaterial performance are critical to further development in the field. X-ray phase-contrast (XPC) imaging is an emerging class of X-ray techniques that have shown significant promise for imaging biomaterial and soft tissue structures. In this study, XPC imaging techniques are shown to enable three dimensional (3D) imaging and evaluation of islet volume, alginate hydrogel structure, and local soft tissue features ex vivo. Rat islets were encapsulated in sterile ultrapurified alginate systems produced using a high-throughput microfluidic system. The encapsulated islets were implanted in omentum pouches created in a rodent model of type 1 diabetes. Microbeads were imaged with XPC imaging before implantation and as whole tissue samples after explantation from the animals. XPC microcomputed tomography (μCT) was performed with systems using tube-based and synchrotron X-ray sources. Islets could be identified within alginate beads and the islet volume was quantified in the synchrotron-based μCT volumes. Omental adipose tissue could be distinguished from inflammatory regions resulting from implanted beads in harvested samples with both XPC imaging techniques. Individual beads and the local encapsulation response were observed and quantified using quantitative measurements, which showed good agreement with histology. The 3D structure of the microbeads could be characterized with XPC imaging and failed beads could also be identified. These results point to the substantial potential of XPC imaging as a tool for imaging biomaterials in small animal models and deliver a critical step toward in vivo imaging.

Continuous Quadrupole Magnetic Separation of Islets during Digestion Improves Purified Porcine Islet Viability

Islet transplantation (ITx) is an emerging and promising therapy for patients with uncontrolled type 1 diabetes. The islet isolation and purification processes require exposure to extended cold ischemia, warm-enzymatic digestion, mechanical agitation, and use of damaging chemicals for density gradient separation (DG), all of which reduce viable islet yield. In this paper, we describe initial proof-of-concept studies exploring quadrupole magnetic separation (QMS) of islets as an alternative to DG to reduce exposure to these harsh conditions. Three porcine pancreata were split into two parts, the splenic lobe (SPL) and the combined connecting/duodenal lobes (CDL), for paired digestions and purifications. Islets in the SPL were preferentially labeled using magnetic microparticles (MMPs) that lodge within the islet microvasculature when infused into the pancreas and were continuously separated from the exocrine tissue by QMS during the collection phase of the digestion process. Unlabeled islets from the CDL were purified by conventional DG. Islets purified by QMS exhibited significantly improved viability (measured by oxygen consumption rate per DNA, p < 0.03) and better morphology relative to control islets. Islet purification by QMS can reduce the detrimental effects of prolonged exposure to toxic enzymes and density gradient solutions and substantially improve islet viability after isolation.

High Seeding Density Induces Local Hypoxia and Triggers a Proinflammatory Response in Isolated Human Islets

Hypoxia is the main threat to morphological and functional integrity of isolated pancreatic islets. Lack of oxygen seems to be of particular importance for functionality of encapsulated islets. The present study was initiated as an experimental model for the environment experienced by human islets in a confined space present during culture, shipment, and in an implanted macrodevice. Quadruplicate aliquots of isolated human islets (n = 12) were cultured for 24 h at 37°C under normoxic conditions using 24-well plates equipped with 8-µm pore size filter inserts and filled with islet aliquots adjusted to obtain a seeding density of 75, 150, 300, or 600 IEQ/cm(2). After culture viability, glucose-stimulated insulin release, DNA content as well as Bax and Bcl-2 gene expression were measured. Culture supernatants were collected to determine production of VEGF and MCP-1. Viability correlated inversely with IEQ seeding density (r = -0.71, p < 0.001), while the correlation of VEGF and MCP-1 secretion with seeding density was positive (r = 0.78, p < 0.001; r = 0.54, p < 0.001). Decreased viability corresponded with a significant increase in the Bax/Bcl-2 mRNA ratio at 300 and 600 IEQ/cm(2) and with a sigificantly reduced glucose-stimulated insulin secretion and insulin content compared to 75 or 150 IEQ/cm(2) (p < 0.01). The present study demonstrates that the seeding density is inversely correlated with islet viability and in vitro function. This is associated with a significant increase in VEGF and MCP-1 release suggesting a hypoxic and proinflammatory islet microenvironment.

Ultrastructural Analysis of In Vivo Hypoglycemiant Effect of Two Polyoxometalates in Rats with Streptozotocin-Induced Diabetes

Two polyoxometalates (POMs), synthesized through a self-assembling method, were used in the treatment of streptozotocin (STZ)-induced diabetic rats. One of these nanocompounds [tris(vanadyl)-substituted tungsto-antimonate(III)-anions—POM1] was previously described in the literature, whereas the second [tris-butyltin-21-tungsto-9-antimonate(III)-anions—POM2], was prepared by us based on our original formula. In rats with STZ-induced diabetes treated with POMs (up to a cumulative dose of 4 mg/kg bodyweight at the end of the treatments), statistically significant reduced levels of blood glucose were measured after 3 weeks, as compared with the diabetic control groups (DCGs). Ultrastructural analysis of pancreatic β-cells (including the mean diameter of secretory vesicles and of their insulin granules) in the treated diabetic rats proved the POMs contribute to limitation of cellular degeneration triggered by STZ, as well as to the presence of increased amounts of insulin-containing vesicles as compared with the DCG. The two POMs also showed hepatoprotective properties when ultrastructural aspects of hepatocytes in the experimental groups of rats were studied. Based on our in vivo studies, we concluded that the two POMs tested achieved hypoglycemiant effects by preventing STZ-triggered apoptosis of pancreatic β-cells and stimulation of insulin synthesis.

Portal Venous Oxygen Persufflation of the Donation after Cardiac Death pancreas in a rat model is superior to static cold storage and hypothermic machine perfusion

Success of clinical pancreatic islet transplantation depends on the mass of viable islets transplanted and the proportion of transplanted islets that survive early ischaemia reperfusion injury. Novel pancreas preservation techniques to improve islet preservation and viability can increase the utilization of donation after cardiac death donor pancreases for islet transplantation. Rat pancreases were retrieved after 30 min of warm ischaemia and preserved by static cold storage, hypothermic machine perfusion or retrograde portal venous oxygen persufflation for 6 h. They underwent collagenase digestion and density gradient separation to isolate islets. The yield, viability, morphology were compared. In vitro function of isolated islets was compared using glucose stimulated insulin secretion test. Portal venous oxygen persufflation improved the islet yield, viability and morphology as compared to static cold storage. The percentage of pancreases with good in vitro function (stimulation index > 1.0) was also higher after oxygen persufflation as compared to static cold storage. Retrograde portal venous oxygen persufflation of donation after cardiac death donor rat pancreases has the potential to improve islet yield.

Impact of islet size on pancreatic islet transplantation and potential interventions to improve outcome

Better results have been recently reported in clinical pancreatic islet transplantation (ITX) due mostly to improved isolation techniques and immunosuppression; however, some limitations still exist. It is known that following transplantation, 30% to 60% of the islets are lost. In our study, we have investigated 1) the role of size as a factor affecting islet engraftment and 2) potential procedural manipulations to increase the number of smaller functional islets that can be transplanted. C57/BL10 mice were used as donors and recipients in a syngeneic islet transplant model. Isolated islets were divided by size (large, >300 μm; medium 150-300 μm; small, <150 μm). Each size was transplanted in chemically induced diabetic mice as full (600 IEQ), suboptimal (400 IEQ), and marginal mass (200 IEQ). Control animals received all size islets. Engraftment was defined as reversal of diabetes by day 7 posttransplantation. When the superiority of smaller islets was observed, strategies of overdigestion and fragmentation were adopted during islet isolation in the attempt to reduce islet size and improve engraftment. Smaller islets were significantly superior in engraftment compared to medium, large, and control (all sizes) groups. This was more evident when marginal mass data were compared. In all masses, success decreased as islet size increased. Once islets were engrafted, functionality was not affected by size. When larger islets were fragmented, a significant decrease in islet functionality was observed. On the contrary, if pancreata were slightly overdigested, although not as successful as small naive islets, an increase in engraftment was observed when compared to the control group. In conclusion, smaller islets are superior in engraftment following islet transplantation. Fragmentation has a deleterious effect on islet engraftment. Islet isolations can be performed by reducing islet size with slight overdigestion, and it can be safely adopted to improve clinical outcome.

A model to evaluate toxic factors influencing islets during collagenase digestion: the role of serine protease inhibitor in the protection of islets

The recovery of all of the islets contained in a pancreas is the goal of islet isolation for transplantation. This study reveals an environment that injures the isolated islets during digestion and proposes a new model for optimal islet isolation. Islets were isolated from Wistar rat pancreases by stationary collagenase digestion while the digestion time was varied at 15, 30, 60, and 120 min. The digested pancreas and islets were analyzed histologically and adenosine nucleotides were measured. Overnight cultured islets (40 islets) were cocultured for 30 min with the supernatants obtained from pancreatic collagenase digestion at different digestion periods in order to assess the toxic environment. The peak yields of islets were obtained at 30 min of digestion. The histological study of digested pancreas showed that the exocrine cells lost their cellular integrity at 120 min of digestion, but the islet cells were left intact. Accordingly, the ATP levels of the pancreatic tissue decreased during the digestion period. The coculture experiment demonstrated that the islets cultured with the supernatants from the collagenase digestion showed digestion time-dependent disruption of the cellular integrity of islets in accordance with a rapid decrease of ATP levels in the islets. The addition of serine protease inhibitors into this coculture clearly showed protection of islets, which maintained high ATP levels in association with intact membrane integrity as assessed by AO/PI staining. Morphological deterioration of islets as well as a marked ATP decrease was evident in the entire digested pancreas as well as in islets cocultured in the supernatants from the collagenase digestion. Various factors toxic to the islets can therefore be analyzed in future experiments using this coculture model for obtaining a good yield of viable islets.

Significant improvement in islet yield and survival with modified ET-Kyoto solution: ET-Kyoto/Neutrophil elastase inhibitor

Although islet transplantation can achieve insulin independence in patients with type 1 diabetes, sufficient number of islets derived from two or more donors is usually required to achieve normoglycemia. Activated neutrophils and neutrophil elastase (NE), which is released from these neutrophils, can directly cause injury in islet grafts. We hypothesized that inhibition of NE improves islet isolation and islet allograft survival. We tested our hypothesis by examining the effects of modified ET-Kyoto solution supplemented with sivelestat, a NE inhibitor (S-Kyoto solution), on islet yield and viability in islet isolation and the effect of intraperitoneally injected sivelestat on islet graft survival in a mouse allotransplant model. NE and proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-6 increased markedly at the end of warm digestion during islet isolation and exhibited direct cytotoxic activity against the islets causing their apoptosis. The use of S-Kyoto solution significantly improved islet yield and viability. Furthermore, treatment with sivelestat resulted in significant prolongation of islet allograft survival in recipient mice. Furthermore, serum levels of IL-6 and TNF-α at 1 and 2 weeks posttransplantation were significantly higher in islet recipients than before transplantation. Our results indicated that NE released from activated neutrophils negatively affects islet survival and that its suppression both in vitro and in vivo improved islet yield and prolonged islet graft survival. The results suggest that inhibition of NE activity could be potentially useful in islet transplantation for patients with type 1 diabetes mellitus.

Simplified method to isolate highly pure canine pancreatic islets

OBJECTIVES

The canine model has been used extensively to improve the human pancreatic islet isolation technique. At the functional level, dog islets show high similarity to human islets and thus can be a helpful tool for islet research. We describe and compare 2 manual isolation methods, M1 (initial) and M2 (modified), and analyze the variables associated with the outcomes, including islet yield, purity, and glucose-stimulated insulin secretion (GSIS).

METHODS

Male mongrel dogs were used in the study. M2 (n = 7) included higher collagenase concentration, shorter digestion time, faster shaking speed, colder purification temperature, and higher differential density gradient than M1 (n = 7).

RESULTS

Islet yield was similar between methods (3111.0 ± 309.1 and 3155.8 ± 644.5 islets/g, M1 and M2, respectively; P = 0.951). Pancreas weight and purity together were directly associated with the yield (adjusted R(2) = 0.61; P = 0.002). Purity was considerably improved with M2 (96.7% ± 1.2% vs 75.0% ± 6.3%; P = 0.006). M2 improved GSIS (P = 0.021). Independently, digestion time was inversely associated with GSIS.

CONCLUSIONS

We describe an isolation method (M2) to obtain a highly pure yield of dog islets with adequate β-cell glucose responsiveness. The isolation variables associated with the outcomes in our canine model confirm previous reports in other species, including humans.

Pancreatic ultrastructural enhancement due to telmisartan plus sitagliptin treatment in diet-induced obese C57BL/6 mice

OBJECTIVE

We sought to evaluate the effects of telmisartan, sitagliptin, or their combination on pancreatic ultrastructural alterations in high-fat-fed C57BL/6 mice.

METHODS

Three-month-old C57BL/6 mice were fed with standard chow (SC, 10% lipids) or high-fat diet (HF, 60% lipids) during 10 weeks to induce obesity and its comorbidities. After this period, treatment began (lasted 6 weeks), and the HF group was divided into 4 subgroups: untreated HF, HF plus telmisartan (5 mg/kg per day), HF plus sitagliptin (1.1 g/kg per day), and HF plus telmisartan plus sitagliptin. Drugs were mixed with diet. Biochemical analyses, radioimmunoassay, immunofluorescence, stereology, and transmission electron microscopy were performed to assess pancreatic remodeling.

RESULTS

Overweight, hyperinsulinemia, hyperglycemia, and dyslipidemia were found in the HF group, but these outcomes were controlled by the different treatments. Untreated HF animals also showed alterations concerning distribution of α/β cell followed by large and numerous lipid droplets within pancreas. Telmisartan and sitagliptin as monotherapy alleviated these findings, and a complete reversal of pancreatic steatosis was observed after treating with the combination of the 2 drugs.

CONCLUSIONS

AT1 receptor blockade, partial peroxisome proliferator-activated receptor gamma activation, and extended incretin action emerge as feasible strategies to control pancreatic steatosis and avoid progression of pancreatic diseases due to lipotoxicity.

Islet-like cell aggregates generated from human adipose tissue derived stem cells ameliorate experimental diabetes in mice

Background

Type 1 Diabetes Mellitus is caused by auto immune destruction of insulin producing beta cells in the pancreas. Currently available treatments include transplantation of isolated islets from donor pancreas to the patient. However, this method is limited by inadequate means of immuno-suppression to prevent islet rejection and importantly, limited supply of islets for transplantation. Autologous adult stem cells are now considered for cell replacement therapy in diabetes as it has the potential to generate neo-islets which are genetically part of the treated individual. Adopting methods of islet encapsulation in immuno-isolatory devices would eliminate the need for immuno-suppressants.

Methodology/Principal Findings

In the present study we explore the potential of human adipose tissue derived adult stem cells (h-ASCs) to differentiate into functional islet like cell aggregates (ICAs). Our stage specific differentiation protocol permit the conversion of mesodermic h-ASCs to definitive endoderm (Hnf3β, TCF2 and Sox17) and to PDX1, Ngn3, NeuroD, Pax4 positive pancreatic endoderm which further matures in vitro to secrete insulin. These ICAs are shown to produce human C-peptide in a glucose dependent manner exhibiting in-vitro functionality. Transplantation of mature ICAs, packed in immuno-isolatory biocompatible capsules to STZ induced diabetic mice restored near normoglycemia within 3–4 weeks. The detection of human C-peptide, 1155±165 pM in blood serum of experimental mice demonstrate the efficacy of our differentiation approach.

Conclusions

h-ASC is an ideal population of personal stem cells for cell replacement therapy, given that they are abundant, easily available and autologous in origin. Our findings present evidence that h-ASCs could be induced to differentiate into physiologically competent functional islet like cell aggregates, which may provide as a source of alternative islets for cell replacement therapy in type 1 diabetes.

Co-transplantation of mesenchymal stem cells maintains islet organisation and morphology in mice

AIMS/HYPOTHESIS

Recent studies have shown that mesenchymal stem cells (MSCs) secrete several factors that improve survival and function of transplanted islets. Implantation of islets beneath the kidney capsule results in morphological changes, due to interactions of the graft with the host, thus impairing islet function. We co-transplanted MSCs with islets to determine their effects on the remodelling process and studied graft function in a mouse model of minimal islet mass.

METHODS

Islets were syngeneically transplanted, either alone or with kidney-derived MSCs, underneath the kidney capsule of streptozotocin-induced diabetic C57Bl/6 mice. Blood glucose levels were monitored and intraperitoneal glucose tolerance tests carried out. Hormone contents of grafts and pancreas were assessed by radioimmunoassay. Graft morphology and vascularisation were evaluated by immunohistochemistry.

RESULTS

MSCs improved the capacity of islet grafts to reverse hyperglycaemia, with 92% of mice co-transplanted with MSCs reverting to normoglycaemia, compared with 42% of those transplanted with islets alone. Average blood glucose concentrations were lower throughout the 1 month monitoring period in MSC co-transplanted mice. MSCs did not alter graft hormone content. Islets co-transplanted with MSCs maintained a morphology that more closely resembled that of islets in the endogenous pancreas, both in terms of size, and of endocrine and endothelial cell distribution. Vascular engraftment was superior in MSC co-transplanted mice, as shown by increased endothelial cell numbers within the endocrine tissue.

CONCLUSIONS/INTERPRETATION

Co-transplantation of islets with MSCs had a profound impact on the remodelling process, maintaining islet organisation and improving islet revascularisation. MSCs also improved the capacity of islets to reverse hyperglycaemia.

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.

Functional MRI characterization of isolated human islet activation

The noninvasive assessment of pancreatic islets would be an invaluable tool in advancing the treatment of type I diabetes and in understanding its pathophysiology. As shown previously in rodents, manganese-enhanced MRI (MEMRI) can be successfully used to quantify β-cell function. In this study, we successfully applied this technique to isolated human pancreatic islets in both a static and, more significantly, MRI-compatible perfusion set-up. Unlike rodent islets, which produced a significant increase in the signal-to-noise ratio (SNR) when treated with 25 µM MnCl(2) or less, human islets demonstrated significant manganese uptake when exposed to an extracellular concentration of 50 µM MnCl(2). Nonspecific passive manganese uptake was present and quantified in a 15% SNR increase over the control group. However, glucose-induced manganese uptake caused an SNR increase equal to 45% over nonactivated islets. This corresponds to a statistically significant decrease in the T(1) relaxation time from 1501 ms for untreated islets to 1362 ms following passive uptake, and to 861 ms following glucose stimulation. As expected, no manganese cytotoxicity was measured, as shown by normal insulin secretion profiles. These data confirm the viability of MEMRI to assess isolated human islet functionality in vitro, and this technique shows promise for the monitoring of their performance in vivo following transplantation.

Generation of pancreatic hormone-expressing islet-like cell aggregates from murine adipose tissue-derived stem cells

The success of cell replacement therapy for diabetes depends on the availability and generation of an adequate number of islets, preferably from an autologous origin. Stem cells are now being probed for the generation of physiologically competent, insulin-producing cells. In this investigation, we explored the potential of adipose tissue-derived stem cells (ASCs) to differentiate into pancreatic hormone-expressing islet-like cell aggregates (ICAs). We initiated ASC culture from epididymal fat pads of Swiss albino mice to obtain mesenchymal cells, murine epididymal (mE)-ASCs. Subsequent single-cell cloning resulted in a homogeneous cell population with a CD29(+)CD44(+)Sca-1(+) surface antigen expression profile. We formulated a 10-day differentiation protocol to generate insulin-expressing ICAs from mE-ASCs by progressively changing the differentiation cocktail on day 1, day 3, and day 5. Our stage-specific approach successfully differentiated mesodermic mE-ASCs into definitive endoderm (cells expressing Sox17, Foxa2, GATA-4, and cytokeratin [CK]-19), then into pancreatic endoderm (cells expressing pancreatic and duodenal homeobox [PDX]-1, Ngn3, NeuroD, Pax4, and glucose transporter 2), and finally into cells expressing pancreatic hormones (insulin, glucagon, somatostatin). Fluorescence-activated cell sorting analysis showed that day 5 ICAs contained 64.84% +/- 7.03% PDX-1(+) cells, and in day 10 mature ICAs, 48.17% +/- 3% of cells expressed C-peptide. Day 10 ICAs released C-peptide in a glucose-dependent manner, exhibiting in vitro functionality. Electron microscopy of day 10 ICAs revealed the presence of numerous secretory granules within the cell cytoplasm. Calcium alginate-encapsulated day 10 ICAs (1,000-1,200), when transplanted i.p. into streptozotocin-induced diabetic mice, restored normoglycemia within 2 weeks. The data presented here demonstrate the feasibility of using ASCs as a source of autologous stem cells to differentiate into the pancreatic lineage.

Improved, low-cost methods for pancreatic islet purification in rats

OBJECTIVE

Density gradient separation of islets from exocrine tissue is usually performed using Ficoll. However, this reagent significantly increases the cost of isolation. The aim of the present study was to investigate the effects on islet preparations of purification methods using Lymphoprep and Iodixanol (OptiPrep) density gradients.

METHODS

Pancreata were procured from 46 Wistar rats, loaded with collagenase V (Sigma), and mechanically dissociated using standard procedures. After the digestion phase, the islets purified by 3 methods-Ficoll, Lymphoprep, and Iodixanol (OptiPrep)-were assessed for yields, purity, morphology, and in vitro function.

RESULT

We expressed the yields as islet equivalents (IEQ, diameter standardizing to 150 microm), showing no significant differences. Compared with the Ficoll group, the purity was significantly higher in the Lymphoprep (P = .005) and Iodixanol (OptiPrep) groups (P = .011). While the viability was >90% in all 3 groups, the viability in the Lymphoprep Group and OptiPrep groups was significantly higher than that of the Ficoll group (P < .001). In vitro islet function did not differ among the 3 experimental groups.

CONCLUSION

Lymphoprep and Iodixanol were as effective as Ficoll in terms of islet yield and in vitro function. High-purity and high-viability islet cells were obtained using improved Lymphoprep-based or Iodixanol (OptiPrep)-based density gradient methods, potential low-cost substitutes for Ficoll.

Quantitative assessment of islet cell products: estimating the accuracy of the existing protocol and accounting for islet size distribution

The ability to consistently and reliably assess the total number and the size distribution of isolated pancreatic islet cells from a small sample is of crucial relevance for the adequate characterization of islet cell preparations used for research or transplantation purposes. Here, data from a large number of isolations were used to establish a continuous probability density function describing the size distribution of human pancreatic islets. This function was then used to generate a polymeric microsphere mixture with a composition resembling those of isolated islets, which, in turn, was used to quantitatively assess the accuracy, reliability, and operator-dependent variability of the currently utilized manual standard procedure of quantification of islet cell preparation. Furthermore, on the basis of the best fit probability density function, which corresponds to a Weibull distribution, a slightly modified scale of islet equivalent number (IEQ) conversion factors is proposed that incorporates the size distribution of islets and accounts for the decreasing probability of finding larger islets within each size group. Compared to the current calculation method, these factors introduce a 4-8% downward correction of the total IEQ estimate, but they reflect a statistically more accurate contribution of differently sized islets.

Bioengineering of a functional sheet of islet cells for the treatment of diabetes mellitus

The present study was designed to establish a novel tissue engineering approach for diabetes mellitus (DM) by fabricating a tissue sheet composed of pancreatic islet cells for in vivo transplantation. Pancreatic islet cell suspensions were obtained from Lewis rats, and plated onto temperature-responsive culture dishes coated with extracellular matrix (ECM) proteins. After the cells reached confluency, islet cells cultured on laminin-5 coated dishes were successfully harvested as a uniformly spread tissue sheet by lowering the culture temperature to 20 degrees C for 20 min. The functional activity of the islet cell sheets was confirmed by histological examination and Insulin secretion assay prior to in vivo transplantation. Histological examination revealed that the harvested islet cell sheet was comprised of insulin- (76%) and glucagon- (19%) positive cells, respectively. In vivo functionality of the islet cell sheet was maintained even 7 days after transplantation into the subcutaneous space of Lewis rats. The present study describes an approach to generate a functional sheet of pancreatic islet cells on laminin-5 coated temperature-responsive dishes, which can be subsequently transplanted in vivo. This study serves as the foundation for the creation of a novel cell-based therapy for DM to provide patients an alternative method.

FEM-based oxygen consumption and cell viability models for avascular pancreatic islets

BACKGROUND

The function and viability of cultured, transplanted, or encapsulated pancreatic islets is often limited by hypoxia because these islets have lost their vasculature during the isolation process and have to rely on gradient-driven passive diffusion, which cannot provide adequate oxygen transport. Pancreatic islets (islets of Langerhans) are particularly susceptible due to their relatively large size, large metabolic demand, and increased sensitivity to hypoxia. Here, finite element method (FEM) based multiphysics models are explored to describe oxygen transport and cell viability in avascular islets both in static and in moving culture media.

METHODS

Two- and three-dimensional models were built in COMSOL Multiphysics using the convection and diffusion as well as the incompressible Navier-Stokes fluid dynamics application modes. Oxygen consumption was assumed to follow Michaelis-Menten-type kinetics and to cease when local concentrations fell below a critical threshold; in a dynamic model, it was also allowed to increase with increasing glucose concentration.

RESULTS

Partial differential equation (PDE) based exploratory cellular-level oxygen consumption and cell viability models incorporating physiologically realistic assumptions have been implemented for fully scaled cell culture geometries with 100, 150, and 200 microm diameter islets as representative. Calculated oxygen concentrations and intra-islet regions likely to suffer from hypoxia-related necrosis obtained for traditional flask-type cultures, oxygen-permeable silicone-rubber membrane bottom cultures, and perifusion chambers with flowing media and varying incoming glucose levels are presented in detail illustrated with corresponding colour-coded figures and animations.

CONCLUSION

Results of the computational models are, as a first estimate, in good quantitative agreement with existing experimental evidence, and they confirm that during culture, hypoxia is often a problem for non-vascularised islet and can lead to considerable cell death (necrosis), especially in the core region of larger islets. Such models are of considerable interest to improve the function and viability of cultured, transplanted, or encapsulated islets. The present implementation allows convenient extension to true multiphysics applications that solve coupled physics phenomena such as diffusion and consumption with convection due to flowing or moving media.

Revascularization and remodelling of pancreatic islets grafted under the kidney capsule

The revascularization and the structural changes resulting from interactions between the graft and the host were investigated in transplanted pancreatic islets under the kidney capsule. Islets were isolated from mice pancreata and transplanted in syngeneic diabetic animals. Graft-bearing kidneys were collected on different days post-transplant and processed for light microscopy, immunohistochemistry and transmission electron microscopy. A numerical analysis was performed in order to compare the percentage number of the different types of cells in native islets and at different time points after the transplant. Recipient animals reversed diabetes within 4 days. An intraperitoneal glucose tolerance test was performed to determine islet functionality under stressful conditions. During the initial few days post-transplant, the islets showed peculiar shapes and the graft tended to aggregate along the vessels. Starting at days 4-7 post-transplant, islets were revascularized from vessels connected to both the cortical and the capsular vascular network of the kidney. From day 7-14 post-transplant, the vessels progressively appeared more similar in features and size to those of in situ pancreatic islets. Both the percentage number of the different cell types and the distribution of Alpha, Beta and Delta cells inside the graft were significantly different as compared with intact islets, demonstrating quantitative and structural changes after the engraftment. No concomitant proliferation of Beta cells was detected using a bromodeoxyuridin staining method. Despite the fact that quick revascularization preserved a large mass of tissue, the remodelling process of the graft and the newly formed vascularization led to a different organization of the endocrine tissue as compared with intact in situ islets. This constitutes the morphological basis for alterations of the normal intercellular interactions and may explain the altered secretory cell function often observed in transplant.