Mannogalactoglucan from mushrooms protects pancreatic islets via restoring UPR and promotes insulin secretion in TIDM mice

Type 1 diabetes mellitus(T1DM) lacks insulin secretion due to autoimmune deficiency of pancreaticβ-cells.Protecting pancreatic islets and enhancing insulin secretion has been therapeutic approaches.Mannogalactoglucan is the main type of polysaccharide from natural mushroom,which has potential medicinal prospects.Nevertheless,the antidiabetic property of mannogalactoglucan in T1DM has not been fully elucidated.In this study,we obtained the neutral fraction of alkali-soluble Armillaria mellea polysaccharide(AAMP-N) with the structure of mannogalactoglucan from the fruiting body of A.mellea and investigated the potential therapeutic value of AAMP-N in T1DM.We demonstrated that AAMP-N lowered blood glucose and improved diabetes symptoms in T1DM mice.AAMP-N activated unfolded protein response(UPR) signaling pathway to maintain ER protein folding homeostasis and promote insulin secretion in vivo.Besides that,AAMP-N promoted insulin synthesis via upregulating the expression of transcription factors,increased Ca^(2+) signals to stimulate intracellular insulin secretory vesicle transport via activating calcium/calmodulin-dependent kinase Ⅱ(CamkⅡ) and cAMP/PKA signals,and enhanced insulin secretory vesicle fusion with the plasma membrane via vesicle-associated membrane protein 2(VAMP2).Collectively,these studies demonstrated that the therapeutic potential of AAMP-N on pancreatic islets function,indicating that mannogalactoglucan could be natural nutraceutical used for the treatment of T1DM.

Fentanyl inhibits glucose-stimulated insulin release from β-cells in rat pancreatic islets

AIM： TO explore the effects of fentanyl on insulin release from freshly isolated rat pancreatic islets in static culture. METHODS： Islets were isolated from the pancreas of mature Sprague Dawley rats by common bile duct intraductal collagenase V digestion and were purified by discontinuous Ficoll density gradient centrifugation. The islets were divided into four groups according to the fentanyl concentration： control group （0 ng/mL）, group I （0.3 ng/mL）, group I （3.0 ng/mL）, and group III （30 ng/mL）. In each group, the islets were co-cultured for 48 h with drugs under static conditions with fentanyl alone, fentanyl ＋ 0.1 μg/mL naloxone or fentanyl ＋ 1.0 μg/mL naloxone. Cell viability was assessed by the MTT assay. Insulin release in response to low and high concentrations （2.8 mmol/L and 16.7 mmol/L, respectively） of glucose was investigated and electron microscopy morphological assessment was performed. RESULTS： Low- and high-glucose-stimulated insulin release in the control group was significantly higher than in groups I and II （62.33 ± 9.67 μIU vs 47.75 ± 8.47 μIU, 39.67 ± 6.18 μIU and 125.5 ± 22.04 μIU vs 96.17 ± 14.17 μIU, 75.17 ± 13.57 μIU, respectively, P 〈 0.01） and was lowest in group III （P 〈 0.01）. After adding 1 μg/mL naloxone, insulin release in groups II and II was not different from the control group. Electron microscopy studies showed that the islets were damaged by 30 ng/ml fentanyl. CONCLUSION： Fentanyl inhibited glucose-stimulated insulin release from rat islets, which could be prevented by naloxone. Higher concentrations of fentanyl significantly damaged β-cells of rat islets.

Encapsulated islets transplantation: Past, present and future

Islet transplantation could become an ideal treatment for severe diabetes to prevent hypoglycemia shock and irreversible diabetic complications, once some of the major and unresolved obstacles are overcome, including limited donor supplies and side effects caused by permanent immunosuppressant use. Approximately 30 years ago, some groups succeeded in improving the blood glucose of diabetic animals by transplanting encapsulated islets with semi-permeable membranes consisting of polymer. A semi-permeable membrane protects both the inner islets from mechanical stress and the recipient’s immune system (both cellular and humoral immunities), while allowing bidirectional diffusion of nutrients, oxygen, glucose, hormones and wastes, i.e., immune-isolation. This device, which enables immune-isolation, is called encapsulated islets or bio-artificial pancreas. Encapsulation with a semipermeable membrane can provide some advantages: (1) this device protects transplanted cells from the recipient’s immunity even if the xenogeneic islets (from large animals such as pig) or insulin-producing cells are derived from cells that have the potential for differentiation (some kinds of stem cells). In other words, the encapsulation technique can resolve the problem of limited donor supplies; and (2) encapsulation can reduce or prevent chronic administration of immunosuppressants and, therefore, important side effects otherwise induced by immunosuppressants. And now, many novel encapsulated islet systems have been developed and are being prepared for testing in a clinical setting.

Adult islets cultured in collagen gel transdifferentiate into duct-like cells

AIM: To establish a model of islet-ductal cell transdifferen-tiation to identify the transdifferentiated cells. METHODS: Collagen was extracted from rat tail at first. Purified rat islets were divided into three groups, embedded in collagen gel and incubated respectively in DMEM/F12 alone (control group), DMEM/F12 plus epidermal growth factor (EGF), DMEM/F12 plus EGF and cholera toxin (CT). Transdifferentiation was proved by microscopy, RT-PCR, immunohistochemistry and RIA. RESULTS: Islets embedded in collagen gel plus EGF and CT were cystically transformed and could express new gene cytokeratin 19 while still maintaining the expression of insulin and Pdx-1 genes. Immunohistochemistry demonstrated that the protein of cytokeratin 19 was only expressed in the third group. The insulin content secreted by islets in the third group decreased significantly during the transdiffe-rentiation. CONCLUSION: CT is a crucial factor for the islet-ductal cell transdifferentiation.

Survival of encapsulated islets: More than a membrane story

At present, proven clinical treatments but no cures are available for diabetes, a global epidemic with a huge economic burden. Transplantation of islets ofLangerhans by their infusion into vascularized organs is an experimental clinical protocol, the first approach to attain cure. However, it is associated with lifelong use of immunosuppressants. To overcome the need for immunosuppression, islets are encapsulated and separated from the host immune system by a permselective membrane. The lead material for this application is alginate which was tested in many animal models and a few clinical trials. This review discusses all aspects related to the function of transplanted encapsulated islets such as the basic requirements from a permselective membrane(e.g., allowable hydrodynamic radii, implications of the thickness of the membrane and relative electrical charge). Another aspect involves adequate oxygen supply, which is essential for survival/performance of transplanted islets, especially when using large retrievable macrocapsules implanted in poorly oxygenated sites like the subcutis. Notably, islets can survive under low oxygen tension and are physiologically active at > 40 Torr. Surprisingly, when densely crowded, islets are fully functional under hyperoxic pressure of up to 500 Torr(> 300% of atmospheric oxygen tension). The review also addresses an additional category of requirements for optimal performance of transplanted islets, named auxiliary technologies. These include control of inflammation, apoptosis, angiogenesis, and the intra-capsular environment. The review highlights that curing diabetes with a functional bio-artificial pancreas requires optimizing all of these aspects, and that significant advances have already been made in many of them.

Regenerative medicine of pancreatic islets

The pancreas became one of the first objects of regenerative medicine,since other possibilities of dealing with the pancreatic endocrine insufficiency were clearly exhausted.The number of people living with diabetes mellitus is currently approaching half a billion,hence the crucial relevance of new methods to stimulate regeneration of the insulin-secretingβ-cells of the islets of Langerhans.Natural restrictions on the islet regeneration are very tight;nevertheless,the islets are capable of physiological regeneration viaβ-cell self-replication,direct differentiation of multipotent progenitor cells and spontaneousα-toβ-orδ-toβ-cell conversion(trans-differentiation).The existing preclinical models ofβ-cell dysfunction or ablation(induced surgically,chemically or genetically)have significantly expanded our understanding of reparative regeneration of the islets and possible ways of its stimulation.The ultimate goal,sufficient level of functional activity ofβ-cells or their substitutes can be achieved by two prospective broad strategies:β-cell replacement andβ-cell regeneration.The“regeneration”strategy aims to maintain a preserved population ofβ-cells through in situ exposure to biologically active substances that improveβ-cell survival,replication and insulin secretion,or to evoke the intrinsic adaptive mechanisms triggering the spontaneous non-β-toβ-cell conversion.The“replacement”strategy implies transplantation ofβ-cells(as non-disintegrated pancreatic material or isolated donor islets)orβ-like cells obtained ex vivo from progenitors or mature somatic cells(for example,hepatocytes orα-cells)under the action of small-molecule inducers or by genetic modification.We believe that the huge volume of experimental and clinical studies will finally allow a safe and effective solution to a seemingly simple goal-restoration of the functionally activeβ-cells,the innermost hope of millions of people globally.

Macro-or microencapsulation of pig islets to cure type 1 diabetes

Although allogeneic islet transplantation can successfully cure type 1 diabetes,it has limited applicability.For example,organs are in short supply;several human pancreas donors are often needed to treat one diabetic recipient;the intrahepatic site may not be the most appropriate site for islet implantation;and immunosuppressive regimens,which are associated with side effects,are often required to prolong survival of the islet graft.An alternative source of insulinproducing cells would therefore be of major interest.Pigs represent a possible alternative source of beta cells.Grafting of pig islets may appear difficult because of the immunologic species barrier,but pig islets have been shown to function in primates for at least 6 mo with clinically incompatible immunosuppression.Therefore,a bioartificial pancreas made of encapsulated pig islets may resolve issues associated with islet allotransplantation.Although several groups have shown that encapsulated pig islets are functional in small-animal models,less is known about the use of bioartificial pancreases in large-animal models.In this review,we summarize current knowledge of encapsulated pig islets,to determine obstacles to implantation in humans and possible solutions to overcome these obstacles.

Intracerebral xenotransplantation of semipermeable membrane- encapsuled pancreatic islets

AIM： To identify the decreasing effect of xenotransplantion in combination with privileged sites on rejection and death of biological semipermeable membrane-（BSM） encapsulated implanted islets. METHODS： After the BSM experiment in vitro, BSM- encapsulated SD rat＇s islet-like cell clusters （ICCs） were xenotransplanted into normal dog＇s brain. Morphological changes were observed under light and transmission electron microscope. The islets and apoptosis of implanted B cells were identified by insulin-TONEL double staining. RESULTS： The BSM used in our study had a favorable permeability, some degree of rigidity, lighter foreign body reaction and toxicity. The grafts consisted of epithelioid cells and loose connective tissue. Severe infiltration of inflammatory cells was not observed. The implanted ICCs were identified 2 mo later and showed typical apoptosis. CONCLUSION： BSM xenotransplantation in combination with the privileged site can inhibit the rejection of implanted heterogeneous ICCs, and death of implanted heterogeneous B cells is associated with apoptosis. 2005 The WJG Press and Elsevier Inc. All rights reserved.

Prevention of core cell damage in isolated islets of Langerhans by low temperature preconditioning

AIM: To study the core cell damage in isolated islets of Langerhans and its prevention by low temperature preconditioning (26 ℃).METHODS: Islets were cultured at 37 ℃ for 7-14 d after isolation, and then at 26 ℃ for 2, 4 and 7 d before additional culture at 37 ℃ for another 7 d. Core cell damage in the isolated islets was monitored by video-microscopy and analyzed quantitatively by use of a computer-assisted image analysis system. The analysis included daily measurement of the diameter and the area of the isolated islets and the area of the core cell damage that developed in those islets over time during culture. Histology and TdT-mediated dUTP-biotin nick end labeling (TUNEL) assay were used to characterize the cell damage and to monitor islet function.RESULTS: Microscopic analysis showed that during the 7 to 14 d of culture at 37 ℃, core cell damage occurred in the larger islets with diameters ＞200 μm, which included both necrotic and apoptotic cell death. Low temperature (26 ℃) culture could prevent core cell damage of isolated islets. The 7-d culture procedure at 26 ℃ could inhibit most of the core cell (excluding diameters＞300 μm) damages when the islets were re-warmed at 37 ℃.CONCLUSION: Our results indicate that core cell damage within isolated islets of Langerhans correlates with the size of islets. Low temperature (26 ℃) culture can prevent core cell damage in isolated islets, and successfully precondition these islets for incubation at 37 ℃. These novel findings may help to understand the pathophysiology of early loss of islet tissue after transplantation, and may provide a new strategy to improve graft function in the clinical setting of islet transplantation.

AN EFFICIENT METHOD FOR ISOLATION AND PURIFICATION OF THE PANCREATIC ISLETS

On the base of the one step, operator independent method which was set up by Christophe A.E., the pancreas was infused with cold University of Wisconsin(UW) solution for the preservation, digested by the collagenase P, circuited with HBSS+5%fetal calf serum(FCS)+10mmol/L Hepes solution, and separated with the stainless steel mesh. The number of the collected islets were 400000～1800000 per pancreas, i.e. about 12150/g pancreas. After purification, the recovery was 350000～1700000 per pancreas, i.e. about 10250/g pancreas, the recovery rate was above 80%, and the purity of the final preparation was above 95%. The insulin secretion in the response to the high concentration glucose (22 mmol/L) stimulation was apparently different on the 1,3,5 day of the cultural islets, which the high level of insulin was three times the low level (5.5 mmol/L) on the 5th day, and the insulin level of the double stimulation under perfusion conditions is apparently higher than low glucose. The result demonstrated that the purified islets were functionally alive. Histological studies also show that the shape of islets are complete, and the β cell was specially stained by the dithizone (DTZ). The Trypan Blue staining had shown the living cell was above 90%. In conclusion, the new method was highly practical and yielded higher concentration of active pancreatic islets.

Study of the immunoisolating effects of barium-alginate microencapsu lation on rat islets allograft survival

Objective: To evaluate the immunoisola ti ng effects of barium-alginate microencapsulation on islets allograft survival. Methods: The nonmicroencapsulated and microencapsulated islets w ere transplanted under the kidney capsule or intraperitoneally into Wistar rat w ith STZ-induced diabetes. The blood glucose and insulin secretion of grafts wer e observed. Graft function was tested by oral glucose tolerance test (OGTT). Results: ①Five diabetic rats became normoglycemic for 48 to 72 h after microencapsulated islets transplantation. The survival of transplanted i slets was on an average of 6 W. ②The normalization of the glycemia and insulin in the transplanted rats was associated with normal glucose and insulin profiles in response to OGTT. Conclusion: Microencapsulation with barium -alginate membrane can prolong islet survival and protect islets against allore jection.

Glucose-stimulated insulin secretion in isolated pancreatic islets: Multiphysics FEM model calculations compared to results of perifusion experiments with human islets

Because insulin released by the β-cells of pancreatic islets is the main regulator of glucose levels, the quantitative modeling of their glucose-stimulated insulin secretion is of obvious interest not only to improve our understanding of the processes involved, but also to allow better assessment of β -cell function in diabetic patients or islet transplant recipients as well as the development of improved artificial or bioartificial pancreas devices. We have recently developed a general, local concentrations-based multiphysics computational model of insulin secretion in avascular pancreatic islets that can be used to calculate insulin secretion for arbitrary geometries of cultured, perifused, transplanted, or encapsulated islets in response to various glucose profiles. Here, experimental results obtained from two different dynamic glucose-stimulated insulin release (GSIR) perifusion studies performed by us following standard procedures are compared to those calculated by the model. Such perifusion studies allow the quantitative assessment of insulin release kinetics under fully controllable experimental conditions of varying external concentrations of glucose, oxygen, or other compounds of interest, and can provide an informative assessment of islet quality and function. The time-profile of the insulin secretion calculated by the model was in good agree- ment with the experimental results obtained with isolated human islets. Detailed spatial distributions of glucose, oxygen, and insulin were calculated and are presented to provide a quantitative visualization of various important aspects of the insulin secretion dynamics in perifused islets.

Bone marrow increases human islets insulin positive cells in co-culture: quantification with flow cytometry

We have previously demonstrated that allogeneic human bone marrow (BM) supports human islet function and longevity in vitro. We hypothesize that BM supporting human islets may include to increase β-cell in cultured islets. In this study, we developed a method to quantify insulin-producing β cells from cultured islets by using immunofluorescent staining and flow cytometry analysis to explore this possibility. The results show that human islets cocultured with BM for 39 days contained a significantly higher number of insulin-positive β cells (42.3% ± 4.5%) compared to the islet-only cultures (1.15% ± 0.78%), and increased insulin release levels evaluated by ELISA is consistent with increased β cells in same culture condition. Human islet culture with BM significantly increase β-cells while islet only culture lost β-cells in same culture period supports the possibility of BM increasing β-cells in cultured islets.

Study on Delaunay Triangulation with the Islets Constraints

Aiming at Delaunay triangulation with islets constrains in terrain simulation. A general Delaunay triangulation algorithm for constrained data set with islets is proposed. The algorithm firstly constructs Constrained Delaunay Triangulation with constraint polygons which are inner boundary of islets, then according to topological relations within edge, surface, arc segment, applies bidirectional search to find the triangle in islet, lastly it carries on certain corresponding processing to complete the Delaunay triangulation algorithm with islets. The analyses show the algorithm simple, fast speed. The algorithm can be used in 3-D terrain vision.

On Damped Wave Diffusion of Oxygen in Pancreatic Islets: Parabolic and Hyperbolic Models

Damped wave diffusion effects during oxygen transport in islets of Langerhans is studied. Simultaneous reaction and diffusion models were developed. The asymptotic limits of first and zeroth order in Michaelis and Menten kinetics was used in the study. Parabolic Fick diffusion and hyperbolic damped wave diffusion were studied separately. Method of relativistic transformation was used in order to obtain the solution for the hyperbolic model. Model solutions was used to obtain mass inertial times. Convective boundary condition was used. Sharma number (mass) may be used in evaluating the importance of the damped wave diffusion process in relation to other processes such as convection, Fick steady diffusion in the given application. Four regimes can be identified in the solution of hyperbolic damped wave diffusion model. These are;1) Zero Transfer Inertial Regime, 0 0≤τ≤τinertia;2) Rising Regime during times greater than inertial regime and less than at the wave front, Xp > τ, 3) at Wave front , τ = Xp;4) Falling Regime in open Interval, of times greater than at the wave front, τ > Xp. Method of superposition of steady state concentration and transient concentration used in both solutions of parabolic and hyperbolic models. Expression for steady state concentration developed. Closed form analytic model solutions developed in asymptotic limits of Michaelis and Menten kinetic at zeroth order and first order. Expression for Penetration Length Derived-Hypoxia Explained. Expression for Inertial Lag Time Derived. Solution was obtained by the method of separation of variables for transient for parabolic model and by the method of relativistic transformation for hyperbolic models. The concentration profile was expressed as a sum of steadty state and transient parts.

Characterization of Islets from Chronic Calcific Pancreatitis Patients of Tropical Region with Distinct Phenotype

Background and Objective: Islet autotransplantation is performed to preserve endocrine function in patients undergoing pancreatic resections for painful chronic pancreatitis. We characterized islets isolated from chronic pancreatitis patients (CP) of tropical region. Patients and Methods: Pancreatic tissues were obtained from CP patients with and without diabetes undergoing pancreatic resections (n = 35) and brain-dead multi organ donors (n = 6;considered as controls). Islets isolated were assessed for yield, purity, viability and in vitro islet function (Glucose stimulated insulin release, GSIR) as per standard protocols. Results: Islets from CP patients without diabetes were similar to controls in yield (control 4120 - 6100 IE/g, CP 3550 - 5660 IE/g), purity (control 78% ± 12%, CP 70% ± 8.2%) and viability (control 85% ± 8%, CP 81% ± 10%) and islets from CP patients with diabetes showed decreases in yield (3002 - 2300 IE/g), purity (61% ± 16%) and viability (62% ± 21%). Islets measuring 50 - 200 μ were similar in abundance in controls (94.74% ± 3.2%) and CP patients with and without diabetes, 86.31% ± 4.9%, 91.03% ± 3.8%. GSIR of islets from CP patients and controls were similar at 5.5 mM glucose (2.8 - 3.1 μU/ml). However, GSIR at 16.5 mM glucose was decreased in CP patients (control 18.5 ± 0.6, CP without diabetes 11.8 ± 0.3, CP with diabetes 4.3 ± 0.3 μU/ml). Conclusion: Our results demonstrate suitability of islets isolated from CP patients of tropical region for autotransplantation.

Apoptosis and oxidative injury of donor islets during isolation and purification

Objective To observe the changes of islet cell apoptosis and oxidation - antioxidation before transplantation,and to explore pathways of islet protection. Methods Fifteen human pancreases were perfused with Hanks solution containing collagenase,then digested and isolated.

Facilitating effects of berberine on rat pancreatic islets through modulating hepatic nuclear factor 4 alpha expression and glucokinase activity

AIM： To observe the effect of berberine on insulin secretion in rat pancreatic islets and to explore its possible molecular mechanism. METHODS： Pdmary rat islets were isolated from male Sprague-Dawley rats by collagenase digestion and treated with different concentrations （1, 3, 10 and 30 μmol/L） of berberine or 1 μmol/L Glibenclamide （GB） for 24 h. Glucose-stimulated insulin secretion （GSIS） assay was conducted and insulin was determined by radioimmunoassay. 3-（4,5-Dimethylthiazol-2-yl）- 2,5-diphenyltetrazolium bromide （MTT） assay was performed to evaluate cytotoxicity. The mRNA level of hepatic nuclear factor 4 alpha （HAIF4α） was determined by reverse transcription polymerase chain reaction （RT-PCR）. Indirect immunofluorescence staining and Western blot analysis were employed to detect protein expression of HNF4α in the islets. Glucokinase （GK） activity was measured by spectrophotometric method. RESULTS： Berberine enhanced GSIS rather than basal insulin secretion dose-dependently in rat islets and showed no significant cytotoxicity on islet cells at the concentration of 10 μmol/L. Both mRNA and protein expressions of HNF4α were up-regulated by berberine in a dose-dependent manner, and GK activity was also increased accordingly. However, GB demonstrated no regulatory effects on HNF4α expression or GK activity. CONCLUSION： Berberine can enhance GSIS in rat islets, and probably exerts the insulinotropic effect via a pathway involving HNF4α and GK, which is distinct from sulphonylureas （SUs）.

Influence of heme oxygenase-1 gene transfer on the viability and function of rat islets in in vitro culture

AIM. To investigate the influence of heme oxygenase-1 （HO-1） gene transfer on the viability and function of cultured rat islets in vitro. METHODS： Islets were isolated from the pancreata of Sprague-Dawley rats by intraductal collagenase digestion, and purified by discontinuous Ficoll density gradient centrifugation. Purified rat islets were transfected with adenoviral vectors containing human HO-1 gene （Ad- HO-1） or enhanced green fluorescent protein gene （Ad- EGFP）, and then cultured for seven days. Transfection was confirmed by fluorescence microscopy and Western blot. Islet viability was evaluated by acridine orange/ propidium iodide fluorescent staining. Glucose-stimulated insulin release was detected using insulin radioimmunoassay kits and was used to assess the function of islets. Stimulation index （SI） was calculated by dividing the insulin release upon high glucose stimulation by the insulin release upon low glucose stimulation. RESULTS： After seven days culture, the viability of cultured rat islets decreased significantly （92% ± 6% vs 52% ± 13%, P 〈 0.05）, and glucose-stimulated insulin release also decreased significantly （6.47 ± 0.55 mIU/ L/30IEO vs 4.57 ± 0.40 mIU/L/3OIEO., 14.93 ± 1.17 mIU/L/30IEQ vs 9.63 ± 0.71 mIU/L/30IEQ, P 〈 0.05）. Transfection of rat islets with adenoviral vectors at an 1±10 of 20 was efficient, and did not impair islet function. At 7 d post-transfection, the viability of Ad-HO-1 transfected islets was higher than that of control islets（71% ± 15% vs 52% ± 13%, P 〈 0.05）. There was no significant difference in insulin release upon low glucose stimulation （2.8 mmol/L） among Ad-HO-1 transfected group, Ad-EGFP transfected group, and control group （P 〉 0.05）, while when stimulated by high glucose （16.7 mmol/L） solution, insulin release in Ad-HO-1 transfected group was significantly higher than that in Ad-EGFP transfected group and control group, respectively （12.50 ±2.17 mIU/L/30IEQ vs 8.87 ± 0.65 mIU/L/30IEQ, 12.50 ± 2.17 mIU/L/30IEQ vs 9.63 ± 0.71 mIU/L/30IEQ, P 〈 0.05）. The SI of Ad-HO-1 transfected group was also significantly higher than that of Ad-EGFP transfected group and control group, respectively （2.21 ± 0.02 vs 2.08 ± 0.05; 2.21 ± 0.02 vs 2.11 ± 0.03, P 〈 0.05）. CONCLUSION： The viability and function of rat islets decrease over time in in vitro culture, and heine oxygenase-1 gene transfer could improve the viability and function of cultured rat islets.

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

AIM: To determine whether the elevated vascular endothelial growth factor (VEGF) expression produced by the transfected vascular endothelial cells (VECs) could stimulate angiogenesis of the graft islets and exert its effect on the graft function. METHODS: Thirty diabetic recipient rats were divided into three groups (n = 10 per group). In the control group,300 IEQ islets were transplanted in each rat under the capsule of the right kidney,which were considered as marginal grafts. In the VEC group,VEC together with the islets were transplanted in each rat. In the VEGF group,VEC transfected by pIRES2-EGFP/ VEGF165 plasmid and the islets were transplanted in each rat. Blood glucose and insulin levels were evaluated every other day after operation. Intravenous glucose tolerance test (IVGTT) was performed 10 d after the transplantation. Hematoxylin and eosin (HE) staining was used to evaluate the histological features of the graft islets. Immunohistochemical staining was used to detect insulin-6,VEGF and CD34 (MVD) expression in the graft islets. RESULTS: Blood glucose and insulin levels in the VEGF group restored to normal 3 d after transplantation. In contrast,diabetic rats receiving the same islets with or without normal VECs displayed moderate hyperglycemia and insulin,without a significant difference between these two groups. IVGTT showed that both the amplitude of blood glucose induction and the kinetics of blood glucose in the VEGF group restored to normal after transplantation. H&E and immunohistochemical staining showed the presence of a large amount of graft islets under the capsule of the kidney,which were positively stained with insulin-6 and VEGF antibodies in the VEGF group. In the cell masses,CD34-stained VECs were observed. The similar masses were also seen in the other two groups,but with a fewer positive cells stained with insulin-6 and CD34 antibodies. No VEGF-positive cells appeared in these groups. Microvessel density (MVD) was significantly higher in the VEGF group compared to the other two groups. CONCLUSION: Elevated VEGF production by trans-fected vascular endothelial cells in the site of islet transplantation stimulates angiogenesis of the islet grafts. The accelerated islet revascularization in early stage could improve the outcome of islet transplantation,and enhance the graft survival.